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Classic Tholenator(tm) tholed:
Tom Van Flandern writes: Unfortunately, you are right about this. "Ad hominem, insulting, argumentative, unscientific, trolling." --Tom Van Flandern How ironic. If he were truly right about that, Van Flandern, then one might expect a person interested in being correct to take the recommended action, yet you have not. Why is that? Tholen has been an embarrassment to his employer, his colleagues, and even to some of his friends. "Ad hominem, insulting, argumentative, unscientific, trolling." --Tom Van Flandern How ironic. But I've come to expect such statements from you without any supporting evidence, Van Flandern. Deeply buried in his robotic messages are a few nuggets actually worth discussing. You're erroneously presupposing that any "robotic messages" have been made, Van Flandern. I tried to dig those out and ignore the trash. Obviously not, given that you haven't ignored the EPH, Van Flandern. But it was no use - he wouldn't allow limiting the discussion and staying on topic. As if the comments you've made here are on the topic of Deep Impact, eh Van Flandern? More classic hypocrisy. Tholen seems unable to concede anything What seems to you is irrelevant, Van Flandern; the facts are relevant. and hence unable to learn and evolve his knowledge and behavior, Classic unsubstantiated and erroneous claim. the way the rest of us try to do. I know you've tried to evolve the predictions made by the EPH, Van Flandern, which happens to be one of the many problems with it. As if anticipating my remarks, I see that Tholen has now posted two single-issue messages. You have a problem with "limiting the discussion and staying on topic", Van Flandern? If so, then you're being inconsistent again. Both are reasonable points of potentially broader interest. Unlike your ad hominems above, Van Flandern. If he stuck to that mode of posting, people might actually start reading his posts again and appreciating his shared expertise. How ironic, coming from someone who hasn't stuck to that mode of posting. So I'll answer these two and any occasional future post made in that same constructive style. And ignore anything that you do not wish to address, such as the matter of outbursts. Yes, I already know I'm going to regret giving him another chance. No need to say "I told you so!" :-) "Ad hominem, insulting, argumentative, unscientific, trolling." --Tom Van Flandern How ironic. The quick rise in ultraviolet light indicates the probe hit a hard surface ... possible crystalline silicates ... large surface craters ... possible layering ... overall appearance indistinguishable from an asteroid ... no increase in water emission or other volatiles ... evolved surface with dust not coming from inside ... no new jet formed ] Newsgroups: sci.astro,alt.sci.planetary ] Subject: Palomar Observatory's 200-inch Hale Telescope Observes Comet ] Impact ] Date: 21 Jul 2005 15:57:18 -0700 ] Message-ID: .com ] ] Caltech News Release ] For Immediate Release ] July 21, 2005 ] ] Deep Impact: During and After Impact ] ] PALOMAR MOUNTAIN, Calif. - Astronomers using the Palomar ] Observatory's 200-inch Hale Telescope have been amazed by comet ] Tempel 1's behavior during and after its collision with the Deep ] Impact space probe. ] ] In the minutes just after the impact the comet was seen to increase ] its near-infrared brightness nearly fivefold. As the event ] progressed astronomers at Palomar were able to distinguish jets of ] material venting from the comet's nucleus that have persisted for ] days. Hmm. Van Flandern says no new jet formed. Yet Palomar observed something that persisted for days, something they're calling jets. Who is correct? Or are they talking about two different things but using the same name for them? It is nice you recognize the latter possibility. In a clearer statement of what was observed, we have the following: ESO Press Release 19/05, 14 July 2005, That is not a clearer statement, but rather a different statement from a different set of observers working at a different telescope, Van Flandern. "Clearer" implies a reworded statement about the same observations from the same people, but that's not the case here. http://www.hq.eso.org/outreach/press...pr-19-05.html: "From the current analysis, it appears most likely that the impactor did not create a large new zone of activity and may have failed to liberate a large quantity of pristine material from beneath the surface. The appearance of a new plume-like structure diffused away in the days following impact, with the comet taking again the appearance it had before the impact. The same jets were visible before and after impact, demonstrating that the comet activity survived widely unaffected by the spacecraft crash." That the same jets were active both before and after isn't very revealing, Van Flandern. I don't know of anybody who predicted that the impact would cause activity to stop. But it does raise the issue as to what is causing jets to occur in the first place. Debris clouds orbiting a solid nucleus can't produce jets that rotate with the nucleus. But there's more from the Caltech press release: ] This apparent dust plume has persisted for several nights, allowing ] astronomers to watch the comet's slow rotation. The night after ] impact the plume was on the far side of the comet, but was visible ] again the next evening as the comet's rotation brought it back into ] view. Two days after impact, the plume was seen again, this time ] extending about 200 km (124 miles) from the comet's center. ] According to Bidushi Bhattacharya of the California Institute of ] Technology's (Caltech) Spitzer Science Center, "This could be ] indicative of an outburst of gas and dust still taking place near the ] region of the impact." Is that the best you can do? The quick rise in ultraviolet light indicates the probe hit a hard surface ... possible crystalline silicates ... large surface craters ... possible layering ... overall appearance indistinguishable from an asteroid ... no increase in water emission or other volatiles From IAU Circular 8571, dated 2005 July 22: ] Spectral features due to water ice, ] water vapor, and carbonaceous materials (carbonates and ] hydrogenated aromatic hydrocarbons) were detected in the 5.8-7.2- ] micron region. ] The ejecta spectral signatures were ] detected from the time of impact through at least 41 hr afterwards, ] but by 121 hr after impact all spectral signatures above the pre- ] impact levels were absent. In a clearer statement of what was observed, we have the following: Harvard-Smithsonian Center for Astrophysics, Press Release No. 05-23, July 8, 2005, http://www.cfa.harvard.edu/press/pr0523.html. "Scientists report seeing only weak emission from water vapor and a host of other gases that were expected to erupt from the impact site. Short-period comets like Tempel 1 have been baked repeatedly by the sun during their passages through the inner solar system. The effects of that heat are estimated to extend more than three feet beneath the surface of the nucleus. But the Deep Impact indicates that these effects could be much deeper. And theories about the volatile layers below the surface of short-period comets will have to be revised. Post-impact measurements showed the comet was releasing only about 550 pounds of water per second - an emission rate very similar to pre-impact values, and less than seen during natural outbursts in the weeks before the impact. Related gas production rates (such as hydrogen cyanide) remained so low that only an upper limit on the total could be measured. Scientists remained hopeful that major outgassing from the impact site might still occur in the coming weeks." I'm sure the Deep Impact team will have more to say on these issues soon. Is that your first reaction to a report of water vapor emission, Van Flandern? How does a "solid rocky asteroid" produce water vapor emission? Kuhn says that scientific paradigms change by evolution rather than revolution. And Lipton says: ] In science, this is known as "shooting an arrow into a target, then ] painting a bull's eye around the arrow" something you quoted recently, Van Flandern. What is the essential difference? Oh, one is positive spin, the other is negative spin. So I expect we will now start to see the Dirty Snowball model evolve in the direction of minimizing the differences between it and EPH's Satellite Model for comets. Why would you expect the Dirty Snowball model to minimize the differences between it and a failed EPH model, Van Flandern? That's okay with me. Our goal here is progress, Then explain how a "solid rocky asteroid" can have water vapor emission, how jets can be produced and rotate with the comet, and what causes outbursts, all based on the EPH, Van Flandern. not vindication. Then what motivated your ad hominems quoted at the beginning of this response, Van Flandern? And I'd like to think we can agree on that. I would hope that we could agree on wanting the truth. But perhaps a Jack Nicholson quotation from "A Few Good Men" would be appropriate here. Why are you filling sci.astro with your antagonism and quotes from your enemies files, Classic Tholenator(tm)? -- Official Associate AFA-B Vote Rustler "Don't be too envious. Yes, I have got it all. I am rich, I have a good education, and I am rather good looking .. so where does that leave you? C." -- Charles D. "Chuckweasel" Bohne polishes his ego a bit "That's what you expect from people who think that the cyberworld isn't "RL"." -- Dr. David Tholen, Psychic Astrologer |
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In article ,
Tom Van Flandern wrote: "Paul Schlyter" writes: [Schlyter]: Does SR say anything about gravity? I thought GR did that..... Right. SR and LR are strictly about the relativity of motion. SR says nothing can propagate FTL in forward time; so if the propagation of gravitational force/acceleration does that, then gravity falsifies SR in favor of LR. And experiments show that target bodies respond to the near-instantaneous position of accelerating source masses, not their retarded positions. [Schlyter]: Anyway, in GR, the gravitational force is a pseudo-force which really does not exist - quite similar to the centrifugal force or the coreolis force. At what speed does the centrifugal force propagate? :-) This is a commonly misunderstood and mis-taught aspect of GR. GR has two physical interpretations: field GR and geometric GR. In the former (as favored by Einstein, Dirac, and Feynman, among others), gravitation is a classical force, period. In the latter (the version more commonly taught these days), gravity is just 4-space geometry. The geometric GR has one big advantage: it nicely explains why the inertial mass and the gravitational mass are the same. Btw do you know about any experimental situation we are able to realize, or any natural situation we are able to observe, where the field GR and the geometric GR produce different predictions? Do they ever produce different predictions? It is commonly said that objects just follow the curvature of spacetime, so their motion requires no force. However, IMO, saying that does nothing but confuse the hell out of students. Nature doesn't care about being easily understandable to students.... :-) And perhaps some teachers too are confused? Anyway, whether students are confused or not is a pedagogical, not a scientific, problem. In fact, Vigier and I explained why the geometric interpretation of GR may now be considered falsified: 1) Geometric GR has no cause to initiate the motion of bodies at rest in a gravitational field. (Curvature alone cannot initiate motion unless a force acts. There is no "downhill" in space.) Nothing _can_ be "at rest" in 4-dimensional space-time. In the "t" (time) dimension, everything moves at the speed of light. Even if everything is initially at rest in the "space coordinates" (x,y,z), due to the curvature of space-time things will start moving in the x,y,z coordinates as well (this is vaguely similar to the situation where a body, initially at rest in an non-rotating spherical coordinate system, away from its "equator", and then given a uniform linear motion precisely along one latitude line i.e. a motion only in longitude, soon will appear to "move" in latitude and radius as well). If we start with an initial condition where everything is at rest in x,y,z the motion predicted by geometric GR should be the same as the motion predicted by the field GR. And in the low-gravity limit they should both be the same as the motion predicted by Newtonian physics. You seem to want to consider space dimensions (x,y,z) separately from the time dimension (t) in GR. You cannot do that. In GR space-time is curved. Note that this is not the same as saying "space is curved" or "time is curved" or even "space is curved and time is curved". One cannot separate space from time in GR -- they must be treated as one integral unit. The only way to put something "at rest" in 4-dimensional space-time would be to stop time itself! And if time itself has stopped, well then everything will indeed be at rest, no matter what physical model we choose. An ordinary photograph mimics that pretty well: it will "stop time" in the picture. 2) Geometric GR requires creation -ex nihilo- for the new 3-space momentum of target bodies in a gravitational field. :-) ....well GR is certainly not a TOE (Theory Of Everything) - but we already knew that, didn't we? So leave the creation out of the discussion here and consider GR as a model of something which already exists. OK? 3) In classical physics, force is defined as the time rate of change of momentum in 3-space. Target bodies change their 3-space momentum, which means they experience a force by definition. I think we both agree that NP (Newtonian Physics) defines the concept of a force..... :-) 4) Even geometric GR must derive 3-space equations of motion to compare its predictions against observations. In doing so, GR uses *instantaneous* (not retarded) potential gradients, which is the mathematical equivalent of adopting infinite force propagation speed. If it did not do that, GR would not agree with observations or with Newtonian gravity (which necessarily has infinite force propagation speed) in the low-velocity, weak-field limit, and would therefore be a wrong theory. Aaaahhhh, your good ol' "Newtonial limit" argument.... Of course GR must mimic NP at is low-speed and low-gravity limit! And this includes the instantaneous potential gradients, creating an illusion of gravity propagating instantly. The best I can do here is to point to the sci.physics FAQ, where Steve Carlip writes about how fast the force of gravity propagates. [Schlyter]: according to GR, gravity does not propagate FTL. So says Carlip, and since, as you correctly pointed out, I'm no expert in GR, I cannot argue against that. But I do trust his expertise in GR more than yours. My senior co-author and I critiqued Carlip's arguments in our "Foundations of Physics" paper, and there has been no further response in three years. Perhaps Carlip thinks he can do better things with his time than discuss with someone who e.g. thinks that space coordinates can be dealt with separately from time in geometric GR... :-) And perhaps you feel you've won this discussion. But winning a discussion is one thing - actually being right is something different. But I understand your position. For each problem in life, we each must choose whether to learn enough to make our own judgment, or whether to trust some expert's judgment. And we each learn by trial and error how to improve our choices of experts. Why don't we revisit this in five years and see if you are still happy with your choice of expert for this "speed of gravity" issue? Sure - but if you want me to change my opinion about your ideas, you must stop talking about the instantaneous potential of the force of gravity as if it was a "proof" for gravity propagating much faster than light in GR. [tvf]: in 1990 I founded Meta Research to look into all ideas in astronomy that meet the criteria of scientific method but are ignored solely because they conflict with a mainstream paradigm. [Schlyter]: If your EPH should become an accepted mainstream model, how would Meta Research deal with it then? Would Meta Research stop promoting it then? After all, it would then no longer be in conflict with the mainstream paradigm, and would thus be outside of what Meta Research is supposed to deal with. If mainstream astronomy were not stuck on several dead-end theories, there would be no need for Meta Research to exist. [Schlyter]: I guess the major weakness with the EPH hypothesis is that we know of no feasible mechanism by which a planet could spontaneously explode. Incorrect. See http://metaresearch.org/solar%20syst...Explosions.asp. ....an interesting collection of ad hoc hypotheses.... Phase changes: they occur naturally of course. The most well-known example is of course water freezing, melting, evaporating, condensing. But did you ever see any explosions during such a phase change? Can we expect to see a piece of melting (or freezing) ice spontaneously explode, scattering itself around? No. So is it reasonable to expect a whole planet to explode just because the lava inside "freezes"? Natural fission reactors: requires a lot - a lot ! - of uranium to be able to explode a whole planet. And such a body wouldn't even be a planet. It would, by definition, be - a star! So basically you're here suggesting the existense of planet-sized stars which at some point go nova. And if this was a significant creation process for the asteroids, we should expect to find a lot of uranium on asteroid samples, much more than on Earth samples. Gravitational heat energy: occurs mainly in the contraction phase so this mechanism would mean that the contracting body would "bounce back" and disintegrate. But would a planet really have formed in such a case? [Schlyter]: So that's probably what's required to get EPH accepted as a mainstream model: find a feasible physical mechanism by which a planet can spontaneously explode. After all, ad hoc adjustments and additions to models not requiring magic is easier to accept than a model which does require some magic. Suggestion noted and requirement already met. I assure you, no model ever supported by Meta Research will require "magic". We are advocates of "deep reality physics". See "Physics has its principles" at http://metaresearch.org/cosmology/Ph...Principles.asp. No magic or miracles allowed, in contrast with several mainstream theories (e.g., the Big Bang origin, and initiating motion in GR without a force acting). FYI: it's not enough that you yourself consider the explanations feasible. You must also convince the scientific community that they are feasible to have your model accepted as a mainstream model. :-) -- ---------------------------------------------------------------- Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN e-mail: pausch at stockholm dot bostream dot se WWW: http://stjarnhimlen.se/ |
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This replies to Paul Schlyter and Dave Tholen.
"Paul Schlyter" writes: [tvf]: GR has two physical interpretations: field GR and geometric GR. In the former (as favored by Einstein, Dirac, and Feynman, among others), gravitation is a classical force, period. In the latter (the version more commonly taught these days), gravity is just 4-space geometry. [Schlyter]: The geometric GR has one big advantage: it nicely explains why the inertial mass and the gravitational mass are the same. Geometric GR has two giant disadvantages because it violates two principles of physics (causality and "no creation ex nihilo") as I explained in my last post, which falsifies it for many practical purposes. Moreover, the field interpretation of GR has an even bigger advantage than the one you mention as favoring geometric GR: it explains why inertial and gravitational mass are *not* always the same, as demonstrated by D. M. Greenberger and A. W. Overhauser writing about the COW [Colella-Overhauser-Werner, 1975] neutron interferometer experiment in Rev.Mod.Phys. 51:43 (1979). This was also written up by the same authors in easier-to-read language in "The role of gravity in quantum theory", Sci.Amer. 242 (May):66-76 (1980). In essence, this experiment demonstrates a violation of the weak equivalence principle that gravity is just geometry. Here are a few relevant excerpts: [BEGIN EXCERPTS] pp. 71-72: The COW experiment demonstrated that a weak gravitational field shifts the phase of a neutron wave by the precise amount predicted by the Schrödinger equation. In other words, gravity appears in the equation as any other force would. This result was fully expected. It nonetheless had distinct implications for the interpretation of the equivalence principle in quantum mechanics . pp. 74-75: Galileo observed that all bodies fall with the same acceleration in an external gravitational field. Here "external" means that the bodies themselves are too small to contribute measurably to the field. Robert H. Dicke of Princeton University has called this observation the weak equivalence principle . the geometrical weak equivalence principle, which holds classically . states that there are no physical effects at all in an external gravitational field that depend on the mass of a point particle. . the strong equivalence principle . states that as far as the locally observed laws of physics are concerned, being at rest in a gravitational field is equivalent to being at rest in an accelerated coordinate system. . It was the strong equivalence principle that the COW experiment confirmed. . Yet surprisingly, it turns out that the result of the COW experiment is incompatible with the geometrical weak equivalence principle because interference effects in quantum mechanics depend on the mass. It is only in taking the average values of the trajectory parameters that the mass drops out. pp. 76: In classical physics, the potential has a form that guarantees the mass will drop out of the problem. In quantum mechanics, however, such is not the case. For example, in the gravitational Bohr atom, where a particle of mass m is bound to a much heavier particle of mass M, the radius of the lowest quantum state is a function of the mass m. This means that m can be determined from a measurement of the particle's radius in this state. The mass disappears only for average values over states that have extremely high quantum numbers, which behave in an essentially classical manner. Since quantum mechanics contradicts the geometrical weak equivalence principle, with its requirement that the mass drop out of the problem, it was important to test the Schrödinger equation in an experiment where gravitational forces were present. The test was necessary even though the Schrödinger equation has proved to be enormously successful for non-gravitational problems. The COW experiment was this test, and it demonstrated convincingly that the Schrödinger equation works in the presence of gravitational fields. Since the phase shift depends on mass even in the case of a gravitational field, it seems in retrospect almost accidental that the mass drops out of the classical gravitational equations. Weinberg has emphasized that most of the features of the gravitational field can be derived from its mathematical symmetry properties, as is true for any other field in quantum theory. This interpretation tends to bother theorists who prefer to think of gravity as being intrinsically related to geometry. Nevertheless, since the COW experiment confirms the applicability of quantum mechanics even in the presence of gravity, including the non-geometrical mass dependence, the experiment seems to be a step in the undermining of the purely geometrical point of view. [END EXCERPTS] [Schlyter]: Btw do you know about any experimental situation we are able to realize, or any natural situation we are able to observe, where the field GR and the geometric GR produce different predictions? Do they ever produce different predictions? The COW experiment seems to be an example of just such a difference. Experiments aside, a model or physical interpretation that does not require magic or miracles (such as causality violations or creation ex nihilo) is to be preferred over one that does require them. So that is a logic-based difference between field GR and geometric GR. [tvf]: In fact, Vigier and I explained why the geometric interpretation of GR may now be considered falsified: 1) Geometric GR has no cause to initiate the motion of bodies at rest in a gravitational field. (Curvature alone cannot initiate motion unless a force acts. There is no "downhill" in space.) [Schlyter]: Nothing _can_ be "at rest" in 4-dimensional space-time. In the "t" (time) dimension, everything moves at the speed of light. Of course. But why change the subject? My remarks obviously referred to 3-space plus time, where "rest" relative to a source mass is well-defined. The causality principle applies to real space and time. Mathematical abstractions such as GR's "spacetime" (actually a variant of proper time for most applications) are of little use when one is discussing physical interpretations or experimental evidence because observations must be made in 3-space plus time, not in Minkowski 4-space. [Schlyter]: Even if everything is initially at rest in the "space coordinates" (x,y,z), due to the curvature of space-time things will start moving in the x,y,z coordinates as well But that was my point: Mathematically, one can just say "it moves" and ignore the physics. But in physics, transition from rest in 3-space to accelerated motion requires a cause (called a "force" by definition) and a source of new momentum. No exceptions are allowed in "deep reality physics" (by contrast with philosophy and mathematics) because the former does not allow magic or miracles. No such prohibition applies to mathematics because equations can often cover over our lack of fundamental understanding of what causes are actually operating and of the operation of entities too small for existing experiments to detect them. But choosing to ignore causes does not mean we accept that a cause does not exist. So think of geometric GR as a computational device that must be set aside when one's interest is in understanding the physics of gravitation. [Schlyter]: You seem to want to consider space dimensions (x,y,z) separately from the time dimension (t) in GR. You cannot do that. On the contrary. That is what field GR is all about. Moreover, the entire field of celestial mechanics, which provides the interface between GR and observations made in the real world, is based on 3-space plus time. Without these considerations, GR would be an untested theory. [Schlyter]: In GR space-time is curved. Note that this is not the same as saying "space is curved" or "time is curved" or even "space is curved and time is curved". One cannot separate space from time in GR -- they must be treated as one integral unit. Incorrect. Geometric GR treats *imaginary* time (not real time) as a fourth spatial dimension. But that is just a mathematical convenience. Contrary to what some extremist purveyors of geometric GR have claimed, no curvature of space or time is involved in "curved spacetime". The latter expression simply means that the progression of proper time (expressed in space units by multiplying it by c) is affected by motion and gravitational potential. See for example http://metaresearch.org/cosmology/gravity/spacetime.asp and the reference to MTW therein. [Schlyter]: The only way to put something "at rest" in 4-dimensional space-time would be to stop time itself! Now you have strayed way off topic. I was speaking of rest in 3-space, which is a well-defined concept. Of course, if you have only learned the geometric interpretation of GR, you may be hard-pressed to start thinking of gravity in classical physics terms again. But you can't compare with observations or physical reality until you make that transition. Specifically, the celestial mechanics vehicle for computing orbits in GR for purposes of comparing with observations is the equations of motion, as may be found on MTW p. 1095. Even without studying or understanding these equations, you can see at a glance that they are expressions for the 3-space acceleration of bodies through space as a function of coordinate time. GR's coordinate time is a form of time that (unlike proper time) is not affected by motion or gravitational potential, and is therefore of great value for expressing the relativistic dynamics of bodies in gravitational fields. So you see, coordinate time in GR is not interchangeable with space, and the GR equations of motion (because of infinite propagation speed) are no more Lorentz-invariant than Newton's equations are. But if you wanted to complain because you weren't taught that or anything else about field GR, I'd certainly support you. IMO, the understanding of gravity in relativity has regressed considerably during the half-century since Einstein's death. [tvf]: Geometric GR requires creation -ex nihilo- for the new 3-space momentum of target bodies in a gravitational field. [Schlyter]: well GR is certainly not a TOE (Theory Of Everything) - but we already knew that, didn't we? So leave the creation out of the discussion here and consider GR as a model of something which already exists. OK? The point of my remark was to show that geometric GR is falsified in physics. Gravity cannot be simply geometry because that provides no source for new momentum. It is true that we don't officially know the source of the new momentum gravity transfers to target bodies, and that is why mathematical explanations can be substituted for physical ones. But it would be illogical to use our ignorance of the specifics to argue that specific sources do not exist. And whatever they are, they constitute a force by definition: a time rate of change of momentum. [Schlyter]: I think we both agree that NP (Newtonian Physics) defines the concept of a force..... Classical physics defines force. And that definition is as applicable in GR as in all of physics. Field GR and relativistic celestial mechanics use force explicitly when calculating orbits. [Schlyter]: Of course GR must mimic NP at is low-speed and low-gravity limit! And this includes the instantaneous potential gradients, creating an illusion of gravity propagating instantly. In what sense is this "an illusion"? When a source mass accelerates, the target body responds almost instantly, as binary pulsars prove. Moreover, the Sun also emits light, which obviously travels at the speed of light. Yet the gradients of the light field are retarded, not instantaneous. What logic exists for instantaneous relativistic potential gradients in gravitational fields when a source mass accelerates, while gradients for light fields remain retarded? [Schlyter]: The best I can do here is to point to the sci.physics FAQ, where Steve Carlip writes about how fast the force of gravity propagates. We have argued in print that Carlip's argument is not viable. Our reasoning is simple to understand, and there has been no counter-argument from anyone, including the three referees of the paper (who questioned many things, but not that). [Schlyter]: Perhaps Carlip thinks he can do better things with his time than discuss with someone who e.g. thinks that space coordinates can be dealt with separately from time in geometric GR... :-) And perhaps you feel you've won this discussion. But winning a discussion is one thing - actually being right is something different. When one argument shows the fallacy in another, that is usually a step toward getting the physics right. No one in science should be counting progress in understanding as "winning". This isn't about personalities of contests. Our logical arguments stand or fall on their merits alone. [Schlyter]: if you want me to change my opinion about your ideas, you must stop talking about the instantaneous potential of the force of gravity as if it was a "proof" for gravity propagating much faster than light in GR. I do not understand. If I show that a race car was at point x1 at time t1 and reached point x2 at time t2, can't I conclude that the minimum speed at which it traveled was (x2 - x1) / (t2 - t1)? Likewise, if a source mass at x1 accelerates at time t1 and a target body at x2 changes its acceleration to match at time t2, can't I conclude that the minimum propagation speed of that force change was (x2 - x1) / (t2 - t1)? That is what binary pulsars (rapidly accelerating masses) prove. The proof of that first appeared in my 1998 Phys.Lett.A paper, available on the web at http://metaresearch.org/cosmology/speed_of_gravity.asp. See the beginning of the section "Electromagnetic analogies and gravitational radiation". It's a single-paragraph argument with a diagram and modest mathematics. It should not be difficult to truly understand the argument, and from there to understand its implications for the propagation speed of gravity. Many before you have succeeded. [Schlyter]: I guess the major weakness with the EPH hypothesis is that we know of no feasible mechanism by which a planet could spontaneously explode. [tvf]: Incorrect. See http://metaresearch.org/solar%20syst...Explosions.asp. [Schlyter]: ...an interesting collection of ad hoc hypotheses.... That is what your question asked for: a "feasible mechanism". I provided three. [Schlyter]: Phase changes: they occur naturally of course. The most well-known example is of course water freezing, melting, evaporating, condensing. But did you ever see any explosions during such a phase change? A correspondent following this discussion who prefers not to join in directly wrote: "In the early and middle years of the steam age, boiler explosions were common. Some were large scale disasters, killing dozens of people and destroying lots of property. They still happen in parts of the world where steam powered trains are used. This may not be close enough to what Paul is talking about to satisfy him, but it is a real world example of explosion resulting from phase change. And under the right conditions. . Mountains crumbling into sand piles (as water gets into the cracks, freezes, and expands) could be described as an extended series of tiny explosions. Each one is just a little "pop", but size seems to be a secondary consideration here." [Schlyter]: Can we expect to see a piece of melting (or freezing) ice spontaneously explode, scattering itself around? No. So is it reasonable to expect a whole planet to explode just because the lava inside "freezes"? "The Krakatoa volcano explosion in the 1883 is another example of a phase-change-caused explosion. Much larger in scale and natural rather than man made." I might add that ice volcanoes are one of the newer fads in planetary astronomy. And the idea of phase changes as a planet explosion mechanism has been in the peer-reviewed literature since Ramsey's work in 1950. [Schlyter]: Natural fission reactors: requires a lot - a lot ! - of uranium to be able to explode a whole planet. Geophysicists have come to accept natural fission reactors as a reality of planets because of the discovery of some operating on Earth's surface in the distant past (e.g., at Oklo, Gabon, Africa). The geophysical literature now contains many corollary speculations, such as that the excess heat flow from the gas giant planets (twice or more what they receive from the Sun) is caused by natural fission reactors in these planets operating today. (See bibliography in the web paper I cited.) [Schlyter]: Gravitational heat energy: occurs mainly in the contraction phase so this mechanism would mean that the contracting body would "bounce back" and disintegrate. But would a planet really have formed in such a case? The Le Sage model (see the subject of the latest book on the nature and origin of gravitation: "Pushing Gravity") requires gravitation to be a continuous source of heat, even when a planet is in equilibrium and no longer contracting. But if something like a core collapse traps that heat, sooner or later one cannot avoid an explosive release of all the continually increasing, stored energy. [Schlyter]: it's not enough that you yourself consider the explanations feasible. You must also convince the scientific community that they are feasible to have your model accepted as a mainstream model. The history of science shows that the "mainstream" rarely accepts an alternative model unless some traumatic event forces a revolution. For example, it took the great Leonid meteor storm of 1833 over well-populated areas of the Eastern U.S., which many took to be a sign that the world would soon end, to finally convince astronomers and everyone else that rocks did fall from the sky. Yet compelling evidence for that had already been published a generation earlier. The only alternative, according to Thomas Kuhn's work, is that the mainstream model receives patch after patch until it becomes indistinguishable from the alternative model. We can already see that continuing to happen with the competition between the Dirty Snowball and the Satellite Model for comets, perhaps accelerated to several patches at once called for by the Deep Impact experiment. So those looking for comfortable lives will remain with the conservative majority for a generation or so until the majority becomes a minority. Meanwhile, those looking for answers affording a deeper understanding and for models that make genuine predictions of new phenomena, it appears that carefully selected alternative models (supported by many thoughtful people over a period of time) are usually better than mainstream models because the alternatives came into existence to solve puzzles and anomalies where the mainstream model failed and had to be patched ad hoc. and writes: [tvf]: I'll answer these two and any occasional future post made in that same constructive style. [Tholen]: And ignore anything that you do not wish to address, such as the matter of outbursts. I answered that. In the EPH's Satellite Model, comets are asteroids that have not yet lost most of their volatiles. They do not have jets or geysers or outbursts in the literal meaning of those words. The so-called "jets" are flashlight beams shining through coma dust from bright areas of the nucleus, focused by the opposition effect. This explains why they do not show any sign of bending with rotation of the nucleus. And the so-called "outbursts" are meteor impacts. We now have direct evidence of the similarity of impact events to traditional outbursts, thanks to Deep Impact. [Tholen]: Debris clouds orbiting a solid nucleus can't produce jets that rotate with the nucleus. Flashlight beams (sunlight reflecting from bright spots preferentially back toward the light source) do rotate with the nucleus. But they remain pointing at the Sun, and nucleus rotation does not curve them even far from the nucleus. A jet should curve, a flashlight beam should not. [Tholen]: How does a "solid rocky asteroid" produce water vapor emission? Chondritic meteorites are 20% by volume interstitial water. Likewise, the water in comets should be mainly interstitial to the rock matrix. [tvf]: Our goal here is progress, [Tholen]: Then explain how a "solid rocky asteroid" can have water vapor emission, how jets can be produced and rotate with the comet, and what causes outbursts, all based on the EPH, Van Flandern. Okay, I did that. Did the progress happen? -|Tom|- Tom Van Flandern - Washington, DC - see our web site on replacement astronomy research at http://metaresearch.org |
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In article ,
Tom Van Flandern wrote: "Paul Schlyter" writes: [tvf]: GR has two physical interpretations: field GR and geometric GR. In the former (as favored by Einstein, Dirac, and Feynman, among others), gravitation is a classical force, period. In the latter (the version more commonly taught these days), gravity is just 4-space geometry. [Schlyter]: The geometric GR has one big advantage: it nicely explains why the inertial mass and the gravitational mass are the same. Geometric GR has two giant disadvantages because it violates two principles of physics (causality and "no creation ex nihilo") as I explained in my last post, which falsifies it for many practical purposes. Who defined those principles? Yourself? I think you'll find it hard to merge your request for causality with some quantum mechanical effects. Such as Heisenberg's uncertainty principle, the "tunnel effect", etc. So we can conclude that your request for causality in each and every situation is contradicted by observation at the quantum mechanical level. Yes, it's counterintuitive. Yes, Einstein disliked it too, but eventually he accepted it, since what counts is observations and experiments, not human ideas. Moreover, the field interpretation of GR has an even bigger advantage than the one you mention as favoring geometric GR: it explains why inertial and gravitational mass are *not* always the same, as demonstrated by D. M. Greenberger and A. W. Overhauser writing about the COW [Colella-Overhauser-Werner, 1975] neutron interferometer experiment in Rev.Mod.Phys. 51:43 (1979). This was also written up by the same authors in easier-to-read language in "The role of gravity in quantum theory", Sci.Amer. 242 (May):66-76 (1980). Now you've entered the realm of quantum mechanics. GR is a classical physical theory which is no longer valid in the quantum mechanical realm. Perhaps you can find some other example, in the macroscopic realm where GR remains valid, where gravitational and inertial matter of some body is different from one another? No? Perhaps the initial attempts of merging QM and GR is easier with your field interpretation of GR, but that's because "field GR" appears somewhat more similar to NP (Newtonian Physical) than "geometric GR". Yet surprisingly, it turns out that the result of the COW experiment is incompatible with the geometrical weak equivalence principle because interference effects in quantum mechanics depend on the mass. It is only in taking the average values of the trajectory parameters that the mass drops out. Why is that surprising? Didn't we already know that GR is valid only outside the reaml of QM ??? Since quantum mechanics contradicts the geometrical weak equivalence principle, (yawn....) [Schlyter]: Btw do you know about any experimental situation we are able to realize, or any natural situation we are able to observe, where the field GR and the geometric GR produce different predictions? Do they ever produce different predictions? The COW experiment seems to be an example of just such a difference. The COW experiment is in the realm of QM, which we already know is outside the realm of GR. Unfortunately we have no QMGR avaialble..... Experiments aside, a model or physical interpretation that does not require magic or miracles (such as causality violations or creation ex nihilo) is to be preferred over one that does require them. So that is a logic-based difference between field GR and geometric GR. I don't see why there's more "magic" in geometry than in "action over a distance" which the "force of gravity" really is..... But this means we both agree on this: ----------------------------------------------------------------------- A collection of macroscopic bodies (i.e. bodies large enough such that QM effects become negligible) in an otherwise empty universe, which initially are at rest in space relative to one another, will start to move due to their mutual gravitation. And this is predicted both by geometric GR and by field GR, and they both predict precisely the same trajectory for each body. ----------------------------------------------------------------------- Can we agree on this ? Or do you claim that in this scenario geometric GR will yield a different prediction compared to field GR ? [tvf]: In fact, Vigier and I explained why the geometric interpretation of GR may now be considered falsified: 1) Geometric GR has no cause to initiate the motion of bodies at rest in a gravitational field. (Curvature alone cannot initiate motion unless a force acts. There is no "downhill" in space.) [Schlyter]: Nothing _can_ be "at rest" in 4-dimensional space-time. In the "t" (time) dimension, everything moves at the speed of light. Of course. But why change the subject? I didn't "change the subject" - I merely steered back the subject so that it included a very important property of GR which you had neglected. My remarks obviously referred to 3-space plus time, where "rest" relative to a source mass is well-defined. The causality principle applies to real space and time. Your causality principle is flawed. It works well in Newtonian Physics but fails in QM (the uncertainty principle, the tunnel effect, etc) as well as in GR (your flawed conclusion that geometric GR says that those bodies initially at rest in space will remain in rest just because gravity is a pseudo-force. Yor flaw is corrected by integrating space and time to space-time, instead of keeping them separate as you insist on doing, like in Newtonian Physics). Mathematical abstractions such as GR's "spacetime" (actually a variant of proper time for most applications) are of little use when one is discussing physical interpretations or experimental evidence because observations must be made in 3-space plus time, not in Minkowski 4-space. Observations made in 3-space plus time, in a known reference frame, can be integrated into 4-spacetime and be used to validate or refute the theory. But perhaps your real objection here is that the math involved is complex? That's true, but it's merely about how practical the method is - it doesn't invalidate the principle itself. The argument "That theory must be wrong because I don't understand it" is NOT valid !!!! [Schlyter]: Even if everything is initially at rest in the "space coordinates" (x,y,z), due to the curvature of space-time things will start moving in the x,y,z coordinates as well But that was my point: Mathematically, one can just say "it moves" and ignore the physics. But in physics, transition from rest in 3-space to accelerated motion requires a cause (called a "force" by definition) and a source of new momentum. You seem to have hardwired your causality principle into your brain.. :-) No exceptions are allowed in "deep reality physics" What's this "deep reality physics" ?? A new buzzword you just invented? There is only one reality: the observations we make. Behind them we build our physical model, using mathematics as the language. And it doesn't really matter whether we use "forces" or "geometry" -- they're both just different viewpoints, each having some "magic". Every model is btw based on some "magic": the fundamental assumptions which aren't proved but which are used to build the model. For some of these fundamental assumptions we can make the "magic" vanish by pointing to some other model - a model which may have its own set of "magic". But for the remaining assumptions we have no other model to point to, but merely choose our fundamental assumptions so they appear "reasonable". Forces vs geometry can be viewed as such a choice. Your brain find it impossible to accept geometry as the fundamental cause in GR - my brain find it more acceptable. So it's perhaps just a matter of personal preferences? So think of geometric GR as a computational device that must be set aside when one's interest is in understanding the physics of gravitation. Interestingly, Copernicus used the same argument for his heliocentric model of the solar system, which the church considered unacceptable: he said it was just a computational device ..... By setting aside geometric GR we also set aside our understanding why gravitational and inertial masses are the same (at the macroscopic level, outside the realm of QM - so don't bring up that COW experiment again, please). [Schlyter]: You seem to want to consider space dimensions (x,y,z) separately from the time dimension (t) in GR. You cannot do that. On the contrary. That is what field GR is all about. Moreover, the entire field of celestial mechanics, which provides the interface between GR and observations made in the real world, is based on 3-space plus time. Without these considerations, GR would be an untested theory. Classical celestial mechanics use Newtonian mechanics, with only small relativitist corrections in a few cases. This works well in the solar system and visual double stars, but fail in situations like a binary pulsar. [tvf]: Geometric GR requires creation -ex nihilo- for the new 3-space momentum of target bodies in a gravitational field. [Schlyter]: well GR is certainly not a TOE (Theory Of Everything) - but we already knew that, didn't we? So leave the creation out of the discussion here and consider GR as a model of something which already exists. OK? The point of my remark was to show that geometric GR is falsified in physics. Gravity cannot be simply geometry because that provides no source for new momentum. Does this mean you claim that geometric GR predict that a collection of bodies initially at rest in space relative to one another and subjected to no other forces than their mutual gravity, that these bodies will remain at rest? As predicted by geometric GR of course. If not, and if geometric GR predicts the motions which actually are observed, in what way are geometric GR "falsified" ? [Schlyter]: Of course GR must mimic NP at is low-speed and low-gravity limit! And this includes the instantaneous potential gradients, creating an illusion of gravity propagating instantly. In what sense is this "an illusion"? When a source mass accelerates, the target body responds almost instantly, as binary pulsars prove. If a large mass is moved with a non-gravitational force, how long time would it take for the surroundings to sense the changed gravity force? According to you it would happen instantly. According to GR it would happen with light-speed delay. And in reality? We don't know, and we won't know until we've been able to perform the experiment. If the gravitation potential changes instantly also over large distances, no matter whether the body is moved by gravitational or non-gravitational forces, then gravity does indeed propagate FTL as you claim. But if the graviation changes instantly only when the body is moved by gravitational forces, but changes with a light-time delay when the body is moved by non-gravitational forces, then the "gravity propagates faster-than-light" is an illusion - it can not be used for e.g. sending messages faster than light. You believe that the gravitation potential should change with the same speed no matter if the body is moved with a gravitational or a non-gravitational force. That's your belief - we are currently not able to test it experimentally. "But it's not logical to believe that the potential should propagate at different speeds depending on whether the body is moved with a gravitational or a non-gravitational force!" I hear you object. Perhaps -- OTOH Nature is not limited by what we humans consider "logical" ..... Moreover, the Sun also emits light, which obviously travels at the speed of light. Yet the gradients of the light field are retarded, not instantaneous. What logic exists for instantaneous relativistic potential gradients in gravitational fields when a source mass accelerates, while gradients for light fields remain retarded? In geometric GR, gravity bends spacetime while light does not. Of course the full answer is in the field equations of gemoetric GR, which neither you nor I understand..... [Schlyter]: The best I can do here is to point to the sci.physics FAQ, where Steve Carlip writes about how fast the force of gravity propagates. We have argued in print that Carlip's argument is not viable. Our reasoning is simple to understand, and there has been no counter-argument from anyone, including the three referees of the paper (who questioned many things, but not that). That's your view. What's Carlip's view? Does he explicitly agree with you that he's wrong and you're right? g [Schlyter]: Perhaps Carlip thinks he can do better things with his time than discuss with someone who e.g. thinks that space coordinates can be dealt with separately from time in geometric GR... :-) And perhaps you feel you've won this discussion. But winning a discussion is one thing - actually being right is something different. When one argument shows the fallacy in another, that is usually a step toward getting the physics right. No one in science should be counting progress in understanding as "winning". This isn't about personalities of contests. Our logical arguments stand or fall on their merits alone. If so, why do you talk so much about "interpretations"? Why do you consider geometry "magic" but not forces ("action at a distance")? If it really was as simple as you suggest in your latest paragraph above, wouldn't the facts themselves be enough, without any need of interpretations? [Schlyter]: if you want me to change my opinion about your ideas, you must stop talking about the instantaneous potential of the force of gravity as if it was a "proof" for gravity propagating much faster than light in GR. I do not understand. If I show that a race car was at point x1 at time t1 and reached point x2 at time t2, can't I conclude that the minimum speed at which it traveled was (x2 - x1) / (t2 - t1)? I thought we were discussing GR, not NP..... rewrite those formulae using the field equations of gemoetric GR please..... evil grin [Schlyter]: ...an interesting collection of ad hoc hypotheses.... That is what your question asked for: a "feasible mechanism". I provided three. Yep, three ad hoc hypotheses .... when others patch on ad hoc hypotheses you complain..... [Schlyter]: Phase changes: they occur naturally of course. The most well-known example is of course water freezing, melting, evaporating, condensing. But did you ever see any explosions during such a phase change? A correspondent following this discussion who prefers not to join in directly wrote: "In the early and middle years of the steam age, boiler explosions were common. Some were large scale disasters, killing dozens of people and destroying lots of property. They still happen in parts of the world where steam powered trains are used. This may not be close enough to what Paul is talking about to satisfy him, but it is a real world example of explosion resulting from phase change. And under the right conditions. . Mountains crumbling into sand piles (as water gets into the cracks, freezes, and expands) could be described as an extended series of tiny explosions. Each one is just a little "pop", but size seems to be a secondary consideration here." True, phase changes can cause local explosions, even killing humans and destroying property. But was any of these explosions able to eject stones, or very big rocks, at Earth escape velocity (11 km/s) or larger? That what's required to make your EPH hypothesis produce asteroids. [Schlyter]: Can we expect to see a piece of melting (or freezing) ice spontaneously explode, scattering itself around? No. So is it reasonable to expect a whole planet to explode just because the lava inside "freezes"? "The Krakatoa volcano explosion in the 1883 is another example of a phase-change-caused explosion. Much larger in scale and natural rather than man made." ....and all that huge explosion managed to do was to destroy a small island and put some tons of dust in the atmosphere.... again not sufficient to produce asteroids. Sorry.... I might add that ice volcanoes are one of the newer fads in planetary astronomy. And the idea of phase changes as a planet explosion mechanism has been in the peer-reviewed literature since Ramsey's work in 1950. Perhaps you should try to build your EPH on something mode solid than fad theories..... :-) [Schlyter]: Natural fission reactors: requires a lot - a lot ! - of uranium to be able to explode a whole planet. Geophysicists have come to accept natural fission reactors as a reality of planets because of the discovery of some operating on Earth's surface in the distant past (e.g., at Oklo, Gabon, Africa). The geophysical literature now contains many corollary speculations, such as that the excess heat flow from the gas giant planets (twice or more what they receive from the Sun) is caused by natural fission reactors in these planets operating today. (See bibliography in the web paper I cited.) ....and how much did these earthly natural fission reactors eject into our atmosphere? More or less than Chernobyl? Krakatoa? [Schlyter]: Gravitational heat energy: occurs mainly in the contraction phase so this mechanism would mean that the contracting body would "bounce back" and disintegrate. But would a planet really have formed in such a case? The Le Sage model (see the subject of the latest book on the nature and origin of gravitation: "Pushing Gravity") requires gravitation to be a continuous source of heat, even when a planet is in equilibrium and no longer contracting. But if something like a core collapse traps that heat, sooner or later one cannot avoid an explosive release of all the continually increasing, stored energy. How old is this Le Sage model? [Schlyter]: it's not enough that you yourself consider the explanations feasible. You must also convince the scientific community that they are feasible to have your model accepted as a mainstream model. The history of science shows that the "mainstream" rarely accepts an alternative model unless some traumatic event forces a revolution. Yep - science is radically open to marginal change and marginally open to radical change. For example, it took the great Leonid meteor storm of 1833 over well-populated areas of the Eastern U.S., Eastern US? I though it happened in France..... which many took to be a sign that the world would soon end, to finally convince astronomers and everyone else that rocks did fall from the sky. Yet compelling evidence for that had already been published a generation earlier. It's always easy to, after the fact, find "compelling evidence" for something. But before the event it's not that easy. There are "compelling evidence" for a lot of things, a lot of which will turn out to be false when investigated more thoroughly. Science has to find a balance here. What would you favor yourself: 1. Accepting a theory which later turns out to be false, because that theory had "compelling evidence" ?? 2. Rejecting a theory which has "compelling evidence", a theory which later turns out to be true, but at this point there's no hard evidence for that theory. The only alternative, according to Thomas Kuhn's work, is that the mainstream model receives patch after patch until it becomes indistinguishable from the alternative model. That can only happen if the alternative model is a big patchwork to begin with. I mean, you didn't get GR and QM by patching NP ..... We can already see that continuing to happen with the competition between the Dirty Snowball and the Satellite Model for comets, perhaps accelerated to several patches at once called for by the Deep Impact experiment. ....and why was the Deep Impact experiment even performed, if the mainstream is uninterested in new theories and merely want to live comfortable lives as you claim in the next paragraph. So those looking for comfortable lives will remain with the conservative majority for a generation or so until the majority becomes a minority. Meanwhile, those looking for answers affording a deeper understanding and for models that make genuine predictions of new phenomena, it appears that carefully selected alternative models (supported by many thoughtful people over a period of time) are usually better than mainstream models because the alternatives came into existence to solve puzzles and anomalies where the mainstream model failed and had to be patched ad hoc. Perhaps you should be a bit more specific when talking about "alternative models". An "alternative model" is anything which contradicts the "mainstream models" (yes there are competing models also within the mainstream). And you'll find a very wide spectrum among the "alternative models" - almost everything from future mainstream models to outright New Age-inspired lunacy. -- ---------------------------------------------------------------- Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN e-mail: pausch at stockholm dot bostream dot se WWW: http://stjarnhimlen.se/ |
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The message this replies to is lengthy, but I have worked on
it as time permitted over the last 10 days. I dealt with most but not all points raised. However, the subject sprawl is getting large. And coming travel will severely limit my future responses. So comment as you wish; but if anyone needs a further response on a point or two, please so indicate. "Paul Schlyter" writes: [tvf]: Geometric GR has two giant disadvantages because it violates two principles of physics (causality and "no creation ex nihilo") as I explained in my last post, which falsifies it for many practical purposes. [Schlyter]: Who defined those principles? Yourself? The particular list I posted in my "Physics has its principles" paper (web version at http://metaresearch.org/cosmology/Ph...Principles.asp) arose from a consensus of physicists attending a conference about fundamental principles held in Sutton, Ontario in October 2002. The principles of physics (by contrast with the laws of physics) arise from logic alone, and do not depend on observations or experiments. For example, one of them is "no creation ex nihilo", which is pretty self-evident provided that one understands that it means "you cannot get something from *literally* nothing", although there is no problem getting something out of the vacuum or what appears to be nothing. As is now well known, the vacuum is filled with zero-point energy, fields, radiation, and other forms of substance. Getting something from an invisible source is not a problem. Getting something from a true void requires a miracle. Miracles are not generally considered to be impossible, but are outside the realm of explanations considered by physics. (See my answer to a later question for more about why miracles are excluded by physics.) [Schlyter]: I think you'll find it hard to merge your request for causality with some quantum mechanical effects. Such as Heisenberg's uncertainty principle, the "tunnel effect", etc. I found no problem with these concepts when strict principles of physics are adhered to, as you can read for yourself in chapter 5 of my book "Dark Matter, Missing Planets and New Comets" (North Atlantic Books, Berkeley, 2nd ed. 1999). But QM is far afield of our discussion here. Let's try not to multiply discussion threads so much. I'll simply hint that all of QM starts making sense again once we do away with the constraint that "nonlocal" actions are forbidden. As you know, my published papers show how the speed of gravity is an example of faster-than-light action in forward time, which is "nonlocal" by the QM definition. [Schlyter]: So we can conclude that your request for causality in each and every situation is contradicted by observation at the quantum mechanical level. Yes, it's counterintuitive. Yes, Einstein disliked it too, but eventually he accepted it, since what counts is observations and experiments, not human ideas. Human logic is as important (and arguably more important) as observations and experiments. Our interpretations of the latter (such as the laws of physics) are fallible and subject to evolution or even contradiction. But valid logic is immutable and provides the only true certainties we have. Because we cannot regress cause and effect infinitely far back, we must ultimately rely on logic for our first principles. To base them on observation or experiment is to build models on quicksand because there are no observers of a "First Cause". [tvf]: . neutron interferometer experiment . [Schlyter]: Now you've entered the realm of quantum mechanics. GR is a classical physical theory which is no longer valid in the quantum mechanical realm. Is that the Schlyter theorem? This is the first I've heard that the laws of gravity do not apply to quantum particles such as in the neutron interferometer. Using geometric GR, how do these particles manage to escape noticing that the spacetime they are embedded in is curved? Why are their motions exempt from conforming to the geometry that macroscopic bodies must follow? In short, why does the equivalence principle hold only for macroscopic bodies and not for quantum particles, as you seem to be hypothesizing here? [Schlyter]: Perhaps the initial attempts of merging QM and GR is easier with your field interpretation of GR, but that's because "field GR" appears somewhat more similar to NP (Newtonian Physical) than "geometric GR". Field GR is the interpretation preferred by Einstein, Dirac, and Feynman. So it seems rather inappropriate to act as if it is somehow inferior or not "real GR". [Schlyter]: I don't see why there's more "magic" in geometry than in "action over a distance" which the "force of gravity" really is..... True "action at a distance" is also forbidden by logic, although there is nothing wrong with the mere appearance of action at a distance carried by entities too small to detect. As applied to understanding gravitation, that is what the Le Sage "pushing gravity" idea is all about - a description of carriers of gravitational force from a source mass to a target body that appears to simulate action at a distance. [Schlyter]: But this means we both agree on this: ----------------------------------------------------------------------- A collection of macroscopic bodies (i.e. bodies large enough such that QM effects become negligible) in an otherwise empty universe, which initially are at rest in space relative to one another, will start to move due to their mutual gravitation. And this is predicted both by geometric GR and by field GR, and they both predict precisely the same trajectory for each body. ----------------------------------------------------------------------- Can we agree on this? Or do you claim that in this scenario geometric GR will yield a different prediction compared to field GR? Geometric GR by itself describes only the potential field and contains no forces, so by itself it is unable to explain any motions of material bodies in 3-space. Both geometric GR and field GR adopt the axiom that force is the (instantaneous) gradient of the potential, in order to derive equations of motion that allow them to predict 3-space motions with respect to time. With that caveat, yes, they both predict the same 3-space motions - but definitely not by geometry alone. Geometry has no cause that can initiate motion. Only a force can do that, force being the time rate of change of momentum by definition. In short, the alleged "geometry" and "curvature" exist only in the potential field, but neither concept does anything about initiating the 3-space motion of target bodies. It takes a force to do that. [Schlyter]: Your causality principle is flawed. It works well in Newtonian Physics but fails in . GR (your flawed conclusion that geometric GR says that those bodies initially at rest in space will remain in rest just because gravity is a pseudo-force. Your flaw is corrected by integrating space and time to space-time, instead of keeping them separate as you insist on doing, like in Newtonian Physics). Newtonian physics is not involved in this discussion in any capacity. When you use the expression "Newtonian physics", it seems apparent from context that you must mean "Euclidean flat-space geometry". So I will interpret your sentence to mean that and answer it accordingly. If that is not your meaning, please explain what any of this discussion has to do with Newtonian physics. More to the point, please elaborate how the lack of a cause to initiate motion in geometric GR is corrected by considering spacetime to be curved? My whole point is that curvature alone, in the absence of a force, cannot initiate the motion of anything. If a test particle rests on the side of a hill, it will rest there forever unless a force acts on it. For example, if the hill is on Earth, gravity would act to make the test particle start rolling downhill. But in space, if there is no force of gravity but only curvature of spacetime, the initial 4-space path of the body is a straight line by definition of "at rest", and the body can never deviate from that straight line unless a force acts. [Schlyter]: Observations made in 3-space plus time, in a known reference frame, can be integrated into 4-spacetime and be used to validate or refute the theory. Let's examine this claim too. Yes, 3-space potential and motion affect time, and can be used to convert GR's coordinate time into GR's proper time. 3-space itself remains isotropic around any source mass, and the slight radial contraction can be neglected for our purposes here as too small to matter. For example, for GPS satellites, length contraction is just a few millimeters. So what causes the satellites to orbit the Earth? Why should the fact that their on-board clocks have sped up relative to ground clocks cause them to move in a curve around Earth instead of continuing in a straight line? "Curved spacetime" means nothing more than that the clock rates have changed. It provides no explanation for deviation from simple, linear motion. [Schlyter]: What's this "deep reality physics" ?? A new buzzword you just invented? It means physics that excludes magic or miracles for the simple reason that admitting them ends the search for understanding and predictability. Anything can be explained as a miracle, and the attempt to explain it can be dismissed because "we can't know the mind of God". Whether that is true or not, deep reality physics is tasked with explaining nature without miracles until such time as it finds something that cannot be explained in any other way. No such barrier to understanding and prediction has as yet appeared. By contrast, mathematical physics and philosophy are more concerned with descriptions of nature than with fundamental understanding, so they both regularly allow miracles. The term "deep reality physics" was coined to distinguish this type of physics from the other types. This contrast is most acute in the case of quantum mechanics, which has abandoned the principles of physics and consequently concluded "there is to deep reality to nature." Those unhappy with that conclusion have no other recourse but reverting to the principles of physics. [Schlyter]: Every model is btw based on some "magic": the fundamental assumptions which aren't proved but which are used to build the model. For some of these fundamental assumptions we can make the "magic" vanish by pointing to some other model - a model which may have its own set of "magic". But for the remaining assumptions we have no other model to point to, but merely choose our fundamental assumptions so they appear "reasonable". If the "fundamental assumptions used to build the model" are the principles of physics, there is no magic involved because the opposite of each fundamental principle (such as creation from a true void) is a form of magic. [Schlyter]: Forces vs geometry can be viewed as such a choice. Your brain finds it impossible to accept geometry as the fundamental cause in GR - my brain finds it more acceptable. So it's perhaps just a matter of personal preferences? Personal preferences are like choosing a favorite color or dessert. But cause and effect have existence in the objective reality we all experience, and not just in our minds. The goal of science is to develop tests to sort out the good and bad hypotheses. The good ones aid understanding and predictability. The bad ones are forever tacking on ad hoc helper hypotheses to accommodate new, unexpected observations (such as "dark energy" to explain the universe expansion accelerating instead of slowing through the action of gravity). [Schlyter]: By setting aside geometric GR we also set aside our understanding why gravitational and inertial masses are the same See http://metaresearch.org/cosmology/gr...%20Inertia.asp for a complete and highly intuitive explanation of why these are approximately equal without gravity being geometry in any meaningful sense. [Schlyter]: Classical celestial mechanics use Newtonian mechanics, with only small relativistic corrections in a few cases. This works well in the solar system and visual double stars, but fails in situations like a binary pulsar. Modern celestial mechanics uses the GR equations of motion for all cases where relativity is relevant. Damour developed equations of motion specifically for analyzing the binary pulsar. As I said, GR would be untested without some such vehicle to predict motions in 3-space vs. time for comparison with observations made in 3-space plus time. [tvf]: Gravity cannot be simply geometry because that provides no source for new momentum. [Schlyter]: Does this mean you claim that geometric GR predicts that a collection of bodies initially at rest in space relative to one another and subjected to no other forces than their mutual gravity, that these bodies will remain at rest? As predicted by geometric GR of course. If not, and if geometric GR predicts the motions which actually are observed, in what way is geometric GR "falsified"? Geometric GR describes only the gravitational potential field, and the potential by itself cannot cause anything to move through 3-space. Nor does it predict any curvature of 3-space. So an additional axiom or assumption is needed to get changes in motion. Both physical interpretations of GR (field and geometric) use the same axiom to get 3-space motions: that force is the gradient of potential. That allows them to derive 3-space equations of motion, without which GR would predict no accelerated 3-space motions of material bodies. A ball thrown into the air would not even slow down. [Schlyter]: If the gravitation potential changes instantly also over large distances, no matter whether the body is moved by gravitational or non-gravitational forces, then gravity does indeed propagate FTL as you claim. I claim no such thing. Gravitational potential changes occur at speed c under any circumstances. There is no dispute about that. [Schlyter]: But if the gravitation changes instantly only when the body is moved by gravitational forces. This furthers the same confusion. It is only the speed of those gravitational forces that exceeds the speed of light. So there is no need to bring in non-gravitational forces to make any points about how gravitational forces behave. [Schlyter]: Why do you consider geometry "magic" but not forces ("action at a distance")? Geometry has no 3-space motion, no momentum, and therefore cannot be a source of new 3-space motion or momentum. A curve starting a ball rolling without a force acting on the ball would be magical. Action at a distance is also magical and forbidden in deep reality physics. I certainly have never advocated it. Faster-than-light force carriers operating in forward time are the opposite of action at a distance. They carry momentum from a source mass to a target body at a finite speed. There is nothing magical about that. [tvf]: If I show that a race car was at point x1 at time t1 and reached point x2 at time t2, can't I conclude that the minimum speed at which it traveled was (x2 - x1) / (t2 - t1)? [Schlyter]: I thought we were discussing GR, not NP..... rewrite those formulae using the field equations of geometric GR please..... evil grin ?? Space is Euclidean, even in geometric GR. Our coordinate axes are Euclidean straight lines by construction, relative to which light rays near masses bend. Speed is Lorentz invariant. So my example is just as valid in a discussion of GR as it would have been if we were talking about NP, which neither of us is doing here. [Schlyter]: True, phase changes can cause local explosions, even killing humans and destroying property. But was any of these explosions able to eject stones, or very big rocks, at Earth escape velocity (11 km/s) or larger? That what's required to make your EPH hypothesis produce asteroids. Getting to speeds over 11 km/s is not a problem. Our spacecraft do it whenever needed. Ejection speeds that high from impacts are impossible because rocks don't have enough strength to remain coherent in the face of that much energy absorbed in so little time. Such rocks would vaporize. However, in an EPH event, even if the shock wave travels at twice that speed, it would take five minutes to travel Earth's radius. Rocks, like rockets, are gently accelerated to escape speeds over long-enough intervals that they have no difficulty remaining intact. And any of the three explosion mechanisms is capable of producing enough energy to explode or implode a Venus-sized planet. [Schlyter]: How old is this Le Sage model? Mid-18th century. Rumors have it that Isaac Newton knew of it too. It is so simple and natural that the ancient Greeks might have thought of it. which many took to be a sign that the world would soon end, to finally convince astronomers and everyone else that rocks did fall from the sky. Yet compelling evidence for that had already been published a generation earlier. [Schlyter]: Science has to find a balance here. What would you favor yourself: 1. Accepting a theory which later turns out to be false, because that theory had "compelling evidence" ?? 2. Rejecting a theory which has "compelling evidence", a theory which later turns out to be true, but at this point there's no hard evidence for that theory. Why must all theories be either accepted or rejected? My position is that all viable, not-yet-falsified theories should be on the scientific table for discussion and making distinguishing predictions. What would you prefer? First theory that catches on is always the winner? -|Tom|- Tom Van Flandern - Washington, DC - see our web site on replacement astronomy research at http://metaresearch.org |
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The message this replies to is lengthy, but I have worked on
it as time permitted over the last 10 days. I dealt with most but not all points raised. However, the subject sprawl is getting large. And coming travel will severely limit my future responses. So comment as you wish; but if anyone needs a further response on a point or two, please so indicate. "Paul Schlyter" writes: [tvf]: Geometric GR has two giant disadvantages because it violates two principles of physics (causality and "no creation ex nihilo") as I explained in my last post, which falsifies it for many practical purposes. [Schlyter]: Who defined those principles? Yourself? The particular list I posted in my "Physics has its principles" paper (web version at http://metaresearch.org/cosmology/Ph...Principles.asp) arose from a consensus of physicists attending a conference about fundamental principles held in Sutton, Ontario in October 2002. The principles of physics (by contrast with the laws of physics) arise from logic alone, and do not depend on observations or experiments. For example, one of them is "no creation ex nihilo", which is pretty self-evident provided that one understands that it means "you cannot get something from *literally* nothing", although there is no problem getting something out of the vacuum or what appears to be nothing. As is now well known, the vacuum is filled with zero-point energy, fields, radiation, and other forms of substance. Getting something from an invisible source is not a problem. Getting something from a true void requires a miracle. Miracles are not generally considered to be impossible, but are outside the realm of explanations considered by physics. (See my answer to a later question for more about why miracles are excluded by physics.) [Schlyter]: I think you'll find it hard to merge your request for causality with some quantum mechanical effects. Such as Heisenberg's uncertainty principle, the "tunnel effect", etc. I found no problem with these concepts when strict principles of physics are adhered to, as you can read for yourself in chapter 5 of my book "Dark Matter, Missing Planets and New Comets" (North Atlantic Books, Berkeley, 2nd ed. 1999). But QM is far afield of our discussion here. Let's try not to multiply discussion threads so much. I'll simply hint that all of QM starts making sense again once we do away with the constraint that "nonlocal" actions are forbidden. As you know, my published papers show how the speed of gravity is an example of faster-than-light action in forward time, which is "nonlocal" by the QM definition. [Schlyter]: So we can conclude that your request for causality in each and every situation is contradicted by observation at the quantum mechanical level. Yes, it's counterintuitive. Yes, Einstein disliked it too, but eventually he accepted it, since what counts is observations and experiments, not human ideas. Human logic is as important (and arguably more important) as observations and experiments. Our interpretations of the latter (such as the laws of physics) are fallible and subject to evolution or even contradiction. But valid logic is immutable and provides the only true certainties we have. Because we cannot regress cause and effect infinitely far back, we must ultimately rely on logic for our first principles. To base them on observation or experiment is to build models on quicksand because there are no observers of a "First Cause". [tvf]: . neutron interferometer experiment . [Schlyter]: Now you've entered the realm of quantum mechanics. GR is a classical physical theory which is no longer valid in the quantum mechanical realm. Is that the Schlyter theorem? This is the first I've heard that the laws of gravity do not apply to quantum particles such as in the neutron interferometer. Using geometric GR, how do these particles manage to escape noticing that the spacetime they are embedded in is curved? Why are their motions exempt from conforming to the geometry that macroscopic bodies must follow? In short, why does the equivalence principle hold only for macroscopic bodies and not for quantum particles, as you seem to be hypothesizing here? [Schlyter]: Perhaps the initial attempts of merging QM and GR is easier with your field interpretation of GR, but that's because "field GR" appears somewhat more similar to NP (Newtonian Physical) than "geometric GR". Field GR is the interpretation preferred by Einstein, Dirac, and Feynman. So it seems rather inappropriate to act as if it is somehow inferior or not "real GR". [Schlyter]: I don't see why there's more "magic" in geometry than in "action over a distance" which the "force of gravity" really is..... True "action at a distance" is also forbidden by logic, although there is nothing wrong with the mere appearance of action at a distance carried by entities too small to detect. As applied to understanding gravitation, that is what the Le Sage "pushing gravity" idea is all about - a description of carriers of gravitational force from a source mass to a target body that appears to simulate action at a distance. [Schlyter]: But this means we both agree on this: ----------------------------------------------------------------------- A collection of macroscopic bodies (i.e. bodies large enough such that QM effects become negligible) in an otherwise empty universe, which initially are at rest in space relative to one another, will start to move due to their mutual gravitation. And this is predicted both by geometric GR and by field GR, and they both predict precisely the same trajectory for each body. ----------------------------------------------------------------------- Can we agree on this? Or do you claim that in this scenario geometric GR will yield a different prediction compared to field GR? Geometric GR by itself describes only the potential field and contains no forces, so by itself it is unable to explain any motions of material bodies in 3-space. Both geometric GR and field GR adopt the axiom that force is the (instantaneous) gradient of the potential, in order to derive equations of motion that allow them to predict 3-space motions with respect to time. With that caveat, yes, they both predict the same 3-space motions - but definitely not by geometry alone. Geometry has no cause that can initiate motion. Only a force can do that, force being the time rate of change of momentum by definition. In short, the alleged "geometry" and "curvature" exist only in the potential field, but neither concept does anything about initiating the 3-space motion of target bodies. It takes a force to do that. [Schlyter]: Your causality principle is flawed. It works well in Newtonian Physics but fails in . GR (your flawed conclusion that geometric GR says that those bodies initially at rest in space will remain in rest just because gravity is a pseudo-force. Your flaw is corrected by integrating space and time to space-time, instead of keeping them separate as you insist on doing, like in Newtonian Physics). Newtonian physics is not involved in this discussion in any capacity. When you use the expression "Newtonian physics", it seems apparent from context that you must mean "Euclidean flat-space geometry". So I will interpret your sentence to mean that and answer it accordingly. If that is not your meaning, please explain what any of this discussion has to do with Newtonian physics. More to the point, please elaborate how the lack of a cause to initiate motion in geometric GR is corrected by considering spacetime to be curved? My whole point is that curvature alone, in the absence of a force, cannot initiate the motion of anything. If a test particle rests on the side of a hill, it will rest there forever unless a force acts on it. For example, if the hill is on Earth, gravity would act to make the test particle start rolling downhill. But in space, if there is no force of gravity but only curvature of spacetime, the initial 4-space path of the body is a straight line by definition of "at rest", and the body can never deviate from that straight line unless a force acts. [Schlyter]: Observations made in 3-space plus time, in a known reference frame, can be integrated into 4-spacetime and be used to validate or refute the theory. Let's examine this claim too. Yes, 3-space potential and motion affect time, and can be used to convert GR's coordinate time into GR's proper time. 3-space itself remains isotropic around any source mass, and the slight radial contraction can be neglected for our purposes here as too small to matter. For example, for GPS satellites, length contraction is just a few millimeters. So what causes the satellites to orbit the Earth? Why should the fact that their on-board clocks have sped up relative to ground clocks cause them to move in a curve around Earth instead of continuing in a straight line? "Curved spacetime" means nothing more than that the clock rates have changed. It provides no explanation for deviation from simple, linear motion. [Schlyter]: What's this "deep reality physics" ?? A new buzzword you just invented? It means physics that excludes magic or miracles for the simple reason that admitting them ends the search for understanding and predictability. Anything can be explained as a miracle, and the attempt to explain it can be dismissed because "we can't know the mind of God". Whether that is true or not, deep reality physics is tasked with explaining nature without miracles until such time as it finds something that cannot be explained in any other way. No such barrier to understanding and prediction has as yet appeared. By contrast, mathematical physics and philosophy are more concerned with descriptions of nature than with fundamental understanding, so they both regularly allow miracles. The term "deep reality physics" was coined to distinguish this type of physics from the other types. This contrast is most acute in the case of quantum mechanics, which has abandoned the principles of physics and consequently concluded "there is to deep reality to nature." Those unhappy with that conclusion have no other recourse but reverting to the principles of physics. [Schlyter]: Every model is btw based on some "magic": the fundamental assumptions which aren't proved but which are used to build the model. For some of these fundamental assumptions we can make the "magic" vanish by pointing to some other model - a model which may have its own set of "magic". But for the remaining assumptions we have no other model to point to, but merely choose our fundamental assumptions so they appear "reasonable". If the "fundamental assumptions used to build the model" are the principles of physics, there is no magic involved because the opposite of each fundamental principle (such as creation from a true void) is a form of magic. [Schlyter]: Forces vs geometry can be viewed as such a choice. Your brain finds it impossible to accept geometry as the fundamental cause in GR - my brain finds it more acceptable. So it's perhaps just a matter of personal preferences? Personal preferences are like choosing a favorite color or dessert. But cause and effect have existence in the objective reality we all experience, and not just in our minds. The goal of science is to develop tests to sort out the good and bad hypotheses. The good ones aid understanding and predictability. The bad ones are forever tacking on ad hoc helper hypotheses to accommodate new, unexpected observations (such as "dark energy" to explain the universe expansion accelerating instead of slowing through the action of gravity). [Schlyter]: By setting aside geometric GR we also set aside our understanding why gravitational and inertial masses are the same See http://metaresearch.org/cosmology/gr...%20Inertia.asp for a complete and highly intuitive explanation of why these are approximately equal without gravity being geometry in any meaningful sense. [Schlyter]: Classical celestial mechanics use Newtonian mechanics, with only small relativistic corrections in a few cases. This works well in the solar system and visual double stars, but fails in situations like a binary pulsar. Modern celestial mechanics uses the GR equations of motion for all cases where relativity is relevant. Damour developed equations of motion specifically for analyzing the binary pulsar. As I said, GR would be untested without some such vehicle to predict motions in 3-space vs. time for comparison with observations made in 3-space plus time. [tvf]: Gravity cannot be simply geometry because that provides no source for new momentum. [Schlyter]: Does this mean you claim that geometric GR predicts that a collection of bodies initially at rest in space relative to one another and subjected to no other forces than their mutual gravity, that these bodies will remain at rest? As predicted by geometric GR of course. If not, and if geometric GR predicts the motions which actually are observed, in what way is geometric GR "falsified"? Geometric GR describes only the gravitational potential field, and the potential by itself cannot cause anything to move through 3-space. Nor does it predict any curvature of 3-space. So an additional axiom or assumption is needed to get changes in motion. Both physical interpretations of GR (field and geometric) use the same axiom to get 3-space motions: that force is the gradient of potential. That allows them to derive 3-space equations of motion, without which GR would predict no accelerated 3-space motions of material bodies. A ball thrown into the air would not even slow down. [Schlyter]: If the gravitation potential changes instantly also over large distances, no matter whether the body is moved by gravitational or non-gravitational forces, then gravity does indeed propagate FTL as you claim. I claim no such thing. Gravitational potential changes occur at speed c under any circumstances. There is no dispute about that. [Schlyter]: But if the gravitation changes instantly only when the body is moved by gravitational forces. This furthers the same confusion. It is only the speed of those gravitational forces that exceeds the speed of light. So there is no need to bring in non-gravitational forces to make any points about how gravitational forces behave. [Schlyter]: Why do you consider geometry "magic" but not forces ("action at a distance")? Geometry has no 3-space motion, no momentum, and therefore cannot be a source of new 3-space motion or momentum. A curve starting a ball rolling without a force acting on the ball would be magical. Action at a distance is also magical and forbidden in deep reality physics. I certainly have never advocated it. Faster-than-light force carriers operating in forward time are the opposite of action at a distance. They carry momentum from a source mass to a target body at a finite speed. There is nothing magical about that. [tvf]: If I show that a race car was at point x1 at time t1 and reached point x2 at time t2, can't I conclude that the minimum speed at which it traveled was (x2 - x1) / (t2 - t1)? [Schlyter]: I thought we were discussing GR, not NP..... rewrite those formulae using the field equations of geometric GR please..... evil grin ?? Space is Euclidean, even in geometric GR. Our coordinate axes are Euclidean straight lines by construction, relative to which light rays near masses bend. Speed is Lorentz invariant. So my example is just as valid in a discussion of GR as it would have been if we were talking about NP, which neither of us is doing here. [Schlyter]: True, phase changes can cause local explosions, even killing humans and destroying property. But was any of these explosions able to eject stones, or very big rocks, at Earth escape velocity (11 km/s) or larger? That what's required to make your EPH hypothesis produce asteroids. Getting to speeds over 11 km/s is not a problem. Our spacecraft do it whenever needed. Ejection speeds that high from impacts are impossible because rocks don't have enough strength to remain coherent in the face of that much energy absorbed in so little time. Such rocks would vaporize. However, in an EPH event, even if the shock wave travels at twice that speed, it would take five minutes to travel Earth's radius. Rocks, like rockets, are gently accelerated to escape speeds over long-enough intervals that they have no difficulty remaining intact. And any of the three explosion mechanisms is capable of producing enough energy to explode or implode a Venus-sized planet. [Schlyter]: How old is this Le Sage model? Mid-18th century. Rumors have it that Isaac Newton knew of it too. It is so simple and natural that the ancient Greeks might have thought of it. which many took to be a sign that the world would soon end, to finally convince astronomers and everyone else that rocks did fall from the sky. Yet compelling evidence for that had already been published a generation earlier. [Schlyter]: Science has to find a balance here. What would you favor yourself: 1. Accepting a theory which later turns out to be false, because that theory had "compelling evidence" ?? 2. Rejecting a theory which has "compelling evidence", a theory which later turns out to be true, but at this point there's no hard evidence for that theory. Why must all theories be either accepted or rejected? My position is that all viable, not-yet-falsified theories should be on the scientific table for discussion and making distinguishing predictions. What would you prefer? First theory that catches on is always the winner? -|Tom|- Tom Van Flandern - Washington, DC - see our web site on replacement astronomy research at http://metaresearch.org |
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Tom Van Flandern writes:
I see that you once again omitted significant portions of the article to which you responded, Van Flandern, particularly the parts in which you demonstrated your hypocrisy. I've restored them for the record. Unfortunately, you are right about this. "Ad hominem, insulting, argumentative, unscientific, trolling." --Tom Van Flandern How ironic. If he were truly right about that, Van Flandern, then one might expect a person interested in being correct to take the recommended action, yet you have not. Why is that? Note: no response. Tholen has been an embarrassment to his employer, his colleagues, and even to some of his friends. "Ad hominem, insulting, argumentative, unscientific, trolling." --Tom Van Flandern How ironic. But I've come to expect such statements from you without any supporting evidence, Van Flandern. Note: no response. Deeply buried in his robotic messages are a few nuggets actually worth discussing. You're erroneously presupposing that any "robotic messages" have been made, Van Flandern. Note: no response. I tried to dig those out and ignore the trash. Obviously not, given that you haven't ignored the EPH, Van Flandern. Note: no response. But it was no use - he wouldn't allow limiting the discussion and staying on topic. As if the comments you've made here are on the topic of Deep Impact, eh Van Flandern? More classic hypocrisy. Note: no response. Tholen seems unable to concede anything What seems to you is irrelevant, Van Flandern; the facts are relevant. Note: no response. and hence unable to learn and evolve his knowledge and behavior, Classic unsubstantiated and erroneous claim. Note: no response. the way the rest of us try to do. I know you've tried to evolve the predictions made by the EPH, Van Flandern, which happens to be one of the many problems with it. Note: no response. As if anticipating my remarks, I see that Tholen has now posted two single-issue messages. You have a problem with "limiting the discussion and staying on topic", Van Flandern? If so, then you're being inconsistent again. Note: no response. Both are reasonable points of potentially broader interest. Unlike your ad hominems above, Van Flandern. Note: no response. If he stuck to that mode of posting, people might actually start reading his posts again and appreciating his shared expertise. How ironic, coming from someone who hasn't stuck to that mode of posting. Note: no response. So I'll answer these two and any occasional future post made in that same constructive style. And ignore anything that you do not wish to address, such as the matter of outbursts. I answered that. Not adequately, Van Flandern. In the EPH's Satellite Model, comets are asteroids that have not yet lost most of their volatiles. Gee, an icy dirtball. Wish I had thought of that. Now, tell me how that differs from the "mainstream" hypothesis that you loathe, Van Flandern. They do not have jets or geysers or outbursts in the literal meaning of those words. What meanings do you attach to those words, Van Flandern? The so-called "jets" are flashlight beams shining through coma dust from bright areas of the nucleus, focused by the opposition effect. Inconsistent with the observations. This explains why they do not show any sign of bending with rotation of the nucleus. You're erroneously presupposing that they do not show any signs of bending with rotation of the nucleus, Van Flandern. And the so-called "outbursts" are meteor impacts. And exactly what is the frequency of meteor impacts on an object a few kilometers in size that are large enough to produce measureable increases in brightness and significant offsets in the photocenter of the comet, Van Flandern? Now, compare that to the frequency of outbursts seen on comet Tempel 1, which was monitored rather extensively over the last couple of months. We now have direct evidence of the similarity of impact events to traditional outbursts, thanks to Deep Impact. Are you suggesting that there is some extraterrestrial intelligence out there, directing meteors to collide with comets, similar to the way in which humans directed Deep Impact to collide with comet Tempel 1? How else do you get the impact rate so high? Perhaps this extraterrestrial intelligence is the same one that built the Face on Mars? Yes, I already know I'm going to regret giving him another chance. No need to say "I told you so!" :-) "Ad hominem, insulting, argumentative, unscientific, trolling." --Tom Van Flandern How ironic. Note: no response. The quick rise in ultraviolet light indicates the probe hit a hard surface ... possible crystalline silicates ... large surface craters ... possible layering ... overall appearance indistinguishable from an asteroid ... no increase in water emission or other volatiles ... evolved surface with dust not coming from inside ... no new jet formed ] Newsgroups: sci.astro,alt.sci.planetary ] Subject: Palomar Observatory's 200-inch Hale Telescope Observes Comet Impact ] Date: 21 Jul 2005 15:57:18 -0700 ] Message-ID: .com ] ] Caltech News Release ] For Immediate Release ] July 21, 2005 ] ] Deep Impact: During and After Impact ] ] PALOMAR MOUNTAIN, Calif. - Astronomers using the Palomar ] Observatory's 200-inch Hale Telescope have been amazed by comet ] Tempel 1's behavior during and after its collision with the Deep ] Impact space probe. ] ] In the minutes just after the impact the comet was seen to increase ] its near-infrared brightness nearly fivefold. As the event ] progressed astronomers at Palomar were able to distinguish jets of ] material venting from the comet's nucleus that have persisted for ] days. Hmm. Van Flandern says no new jet formed. Yet Palomar observed something that persisted for days, something they're calling jets. Who is correct? Or are they talking about two different things but using the same name for them? It is nice you recognize the latter possibility. In a clearer statement of what was observed, we have the following: ESO Press Release 19/05, 14 July 2005, That is not a clearer statement, but rather a different statement from a different set of observers working at a different telescope, Van Flandern. "Clearer" implies a reworded statement about the same observations from the same people, but that's not the case here. Note: no response. http://www.hq.eso.org/outreach/press...pr-19-05.html: "From the current analysis, it appears most likely that the impactor did not create a large new zone of activity and may have failed to liberate a large quantity of pristine material from beneath the surface. The appearance of a new plume-like structure diffused away in the days following impact, with the comet taking again the appearance it had before the impact. The same jets were visible before and after impact, demonstrating that the comet activity survived widely unaffected by the spacecraft crash." That the same jets were active both before and after isn't very revealing, Van Flandern. I don't know of anybody who predicted that the impact would cause activity to stop. But it does raise the issue as to what is causing jets to occur in the first place. Debris clouds orbiting a solid nucleus can't produce jets that rotate with the nucleus. Flashlight beams (sunlight reflecting from bright spots preferentially back toward the light source) do rotate with the nucleus. So, where are the bright spots on Tempel 1 that are producing the so-called "flashlight beams", Van Flandern? Shouldn't Deep Impact have seen those searchlights rather easily? But they remain pointing at the Sun, and nucleus rotation does not curve them even far from the nucleus. A jet should curve, a flashlight beam should not. And you've never seen a picture of a curved jet from a comet, Van Flandern? The material ejected by Deep Impact followed a curved trajectory, apparently due to the gravity of the comet. But there's more from the Caltech press release: ] This apparent dust plume has persisted for several nights, allowing ] astronomers to watch the comet's slow rotation. The night after ] impact the plume was on the far side of the comet, but was visible ] again the next evening as the comet's rotation brought it back into ] view. Two days after impact, the plume was seen again, this time ] extending about 200 km (124 miles) from the comet's center. ] According to Bidushi Bhattacharya of the California Institute of ] Technology's (Caltech) Spitzer Science Center, "This could be ] indicative of an outburst of gas and dust still taking place near the ] region of the impact." Note: no response. Is that the best you can do? The quick rise in ultraviolet light indicates the probe hit a hard surface ... possible crystalline silicates ... large surface craters ... possible layering ... overall appearance indistinguishable from an asteroid ... no increase in water emission or other volatiles From IAU Circular 8571, dated 2005 July 22: ] Spectral features due to water ice, ] water vapor, and carbonaceous materials (carbonates and ] hydrogenated aromatic hydrocarbons) were detected in the 5.8-7.2- ] micron region. The ejecta spectral signatures were ] detected from the time of impact through at least 41 hr afterwards, ] but by 121 hr after impact all spectral signatures above the pre- ] impact levels were absent. In a clearer statement of what was observed, we have the following: Harvard-Smithsonian Center for Astrophysics, Press Release No. 05-23, July 8, 2005, http://www.cfa.harvard.edu/press/pr0523.html. "Scientists report seeing only weak emission from water vapor and a host of other gases that were expected to erupt from the impact site. Short-period comets like Tempel 1 have been baked repeatedly by the sun during their passages through the inner solar system. The effects of that heat are estimated to extend more than three feet beneath the surface of the nucleus. But the Deep Impact indicates that these effects could be much deeper. And theories about the volatile layers below the surface of short-period comets will have to be revised. Post-impact measurements showed the comet was releasing only about 550 pounds of water per second - an emission rate very similar to pre-impact values, and less than seen during natural outbursts in the weeks before the impact. Related gas production rates (such as hydrogen cyanide) remained so low that only an upper limit on the total could be measured. Scientists remained hopeful that major outgassing from the impact site might still occur in the coming weeks." I'm sure the Deep Impact team will have more to say on these issues soon. Is that your first reaction to a report of water vapor emission, Van Flandern? How does a "solid rocky asteroid" produce water vapor emission? Chondritic meteorites are 20% by volume interstitial water. Interstitial water is not the same as water vapor, Van Flandern. Likewise, the water in comets should be mainly interstitial to the rock matrix. According to whom, Van Flandern? You? The EPH? Kuhn says that scientific paradigms change by evolution rather than revolution. And Lipton says: ] In science, this is known as "shooting an arrow into a target, then ] painting a bull's eye around the arrow" something you quoted recently, Van Flandern. What is the essential difference? Oh, one is positive spin, the other is negative spin. Note: no response. So I expect we will now start to see the Dirty Snowball model evolve in the direction of minimizing the differences between it and EPH's Satellite Model for comets. Why would you expect the Dirty Snowball model to minimize the differences between it and a failed EPH model, Van Flandern? Note: no response. That's okay with me. Our goal here is progress, Then explain how a "solid rocky asteroid" can have water vapor emission, how jets can be produced and rotate with the comet, and what causes outbursts, all based on the EPH, Van Flandern. Okay, I did that. Did the progress happen? Not even close, Van Flandern. not vindication. Then what motivated your ad hominems quoted at the beginning of this response, Van Flandern? Note: no response. And I'd like to think we can agree on that. I would hope that we could agree on wanting the truth. But perhaps a Jack Nicholson quotation from "A Few Good Men" would be appropriate here. Note: no response. |
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Double-A wrote:
Michael Baldwin Bruce wrote: Dickless Davie whined: [expunged] Non sequitur. Just how many 370 kg meteorites do you think hit a target smaller than 10 km in diameter over the span of a few weeks, Van Flandern? Non sequitur. ... millions But are you refering to galaxy-wide or the whole universe ? [voided] I'd much rather see Drs. Tholen and Van Flandern debating in alt.astronomy than the daily Bruce and Deco show! Double-A And now for a serious question ... From http://impact.arc.nasa.gov/news_detail.cfm?ID=162 ... ' ... However, the fraction of the new NEAs that are larger than 1 km has declined from about 25 percent of discoveries to near 10 percent. The reason we are finding fewer large NEAs is not a failure of the search systems but rather a real depletion in the population of undiscovered large NEAs. It is, thus, a measure of the success of the program. ... ' .... there, now seems to be some sense of confidence as to knowing the number of NEOs within the proscribed orbital delineation. As per ' Close Approach Tables ' ( See http://neo.jpl.nasa.gov/cgi-bin/neo_ca ), an estimate of NEO collisions with the Earth arising from the proscribed orbital delineation can be made for an extended interval of time. Bottom line ? Does collision with the Earth from this source represent a sizable proportion of disruptive collisions ? In short, could the catalogue represented by the NEO program be a non-issue; that the bulk of significant strikes are coming from elsewhere ? RL |
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In article ,
Tom Van Flandern wrote: Article: 475300 of sci.astro "Paul Schlyter" writes: [tvf]: Geometric GR has two giant disadvantages because it violates two principles of physics (causality and "no creation ex nihilo") as I explained in my last post, which falsifies it for many practical purposes. [Schlyter]: Who defined those principles? Yourself? The particular list I posted in my "Physics has its principles" paper (web version at http://metaresearch.org/cosmology/Ph...Principles.asp) arose from a consensus of physicists attending a conference about fundamental principles held in Sutton, Ontario in October 2002. The principles of physics (by contrast with the laws of physics) arise from logic alone, and do not depend on observations or experiments. For example, one of them is "no creation ex nihilo", which is pretty self-evident provided that one understands that it means "you cannot get something from *literally* nothing", although there is no problem getting something out of the vacuum or what appears to be nothing. As is now well known, the vacuum is filled with zero-point energy, fields, radiation, and other forms of substance. Getting something from an invisible source is not a problem. Getting something from a true void requires a miracle. Miracles are not generally considered to be impossible, but are outside the realm of explanations considered by physics. (See my answer to a later question for more about why miracles are excluded by physics.) It sounds like some kind of Platonian principle, where principles are more important than empirical observations of reality..... So if there would be an empirical observation which contradicted your logical ideas, and if that observation could be repeated over and over again - does that mean you'd discard the observation and concider the logic flawless? If so, you'd be in company with Aristotle, who in his Platonian tradition considered empirical observation less important than human thoughts about logic. [Schlyter]: I think you'll find it hard to merge your request for causality with some quantum mechanical effects. Such as Heisenberg's uncertainty principle, the "tunnel effect", etc. I found no problem with these concepts when strict principles of physics are adhered to, as you can read for yourself in chapter 5 of my book "Dark Matter, Missing Planets and New Comets" (North Atlantic Books, Berkeley, 2nd ed. 1999). But QM is far afield of our discussion here. Let's try not to multiply discussion threads so much. I'll simply hint that all of QM starts making sense again once we do away with the constraint that "nonlocal" actions are forbidden. As you know, my published papers show how the speed of gravity is an example of faster-than-light action in forward time, which is "nonlocal" by the QM definition. [Schlyter]: So we can conclude that your request for causality in each and every situation is contradicted by observation at the quantum mechanical level. Yes, it's counterintuitive. Yes, Einstein disliked it too, but eventually he accepted it, since what counts is observations and experiments, not human ideas. Human logic is as important (and arguably more important) as observations and experiments. Aristotle thought so too .... and we know where that led him in the field of physics ... or "natural philosophy" as it was called back then. Our interpretations of the latter (such as the laws of physics) are fallible and subject to evolution or even contradiction. But valid logic is immutable and provides the only true certainties we have. OTOH logic is, like mathematics, an ideal world of its own, in principle detached from our physical world. So what you say here applies only to that ideal world, not to our physical world, where there'll always be small discrepancies from the ideal world of logic and mathematics. The science of applying mathematics and logic to our physical world is called physics. And there the "immutability" of logic and mathematics vanishes, since we're always dependent of our interpretations of observations and experiments. We can never escape that dependency when we deal with the physical world. Remember that even if we manage to build a model which mimics the physcal world realy well, that model still isn't the physical world, but just a model of it. Because we cannot regress cause and effect infinitely far back, we must ultimately rely on logic for our first principles. To base them on observation or experiment is to build models on quicksand because there are no observers of a "First Cause". Once again you're like Aristotle: he too didn't want to base his models on observation or experiment, probably for the same reasons as you. And as we know he reached conclusions which were utterly wrong..... His model was logical, sure, but it wasn't a model which agreed with the physical world. [tvf]: . neutron interferometer experiment . [Schlyter]: Now you've entered the realm of quantum mechanics. GR is a classical physical theory which is no longer valid in the quantum mechanical realm. Is that the Schlyter theorem? :-) ...no. It is well-known that classical theories aren't accurate at the quantum level -- you need quantum theories at that level. This is the first I've heard that the laws of gravity do not apply to quantum particles such as in the neutron interferometer. Using geometric GR, how do these particles manage to escape noticing that the spacetime they are embedded in is curved? Why are their motions exempt from conforming to the geometry that macroscopic bodies must follow? In short, why does the equivalence principle hold only for macroscopic bodies and not for quantum particles, as you seem to be hypothesizing here? Your questions here can be summarized as: why are classical theories no longer valid at the quantum level? Nobody knows why is is so -- but it is an experimental fact that a lot of physical laws valid at the macroscopic level falls. Therefore I would be very cautions when interpreting observed phenomena as a refutation of GR. [Schlyter]: Perhaps the initial attempts of merging QM and GR is easier with your field interpretation of GR, but that's because "field GR" appears somewhat more similar to NP (Newtonian Physical) than "geometric GR". Field GR is the interpretation preferred by Einstein, Dirac, and Feynman. So it seems rather inappropriate to act as if it is somehow inferior or not "real GR". [Schlyter]: I don't see why there's more "magic" in geometry than in "action over a distance" which the "force of gravity" really is..... True "action at a distance" is also forbidden by logic, although there is nothing wrong with the mere appearance of action at a distance carried by entities too small to detect. As applied to understanding gravitation, that is what the Le Sage "pushing gravity" idea is all about - a description of carriers of gravitational force from a source mass to a target body that appears to simulate action at a distance. [Schlyter]: But this means we both agree on this: ----------------------------------------------------------------------- A collection of macroscopic bodies (i.e. bodies large enough such that QM effects become negligible) in an otherwise empty universe, which initially are at rest in space relative to one another, will start to move due to their mutual gravitation. And this is predicted both by geometric GR and by field GR, and they both predict precisely the same trajectory for each body. ----------------------------------------------------------------------- Can we agree on this? Or do you claim that in this scenario geometric GR will yield a different prediction compared to field GR? Geometric GR by itself describes only the potential field and contains no forces, so by itself it is unable to explain any motions of material bodies in 3-space. Both geometric GR and field GR adopt the axiom that force is the (instantaneous) gradient of the potential, in order to derive equations of motion that allow them to predict 3-space motions with respect to time. With that caveat, yes, they both predict the same 3-space motions - but definitely not by geometry alone. Geometry has no cause that can initiate motion. Only a force can do that, force being the time rate of change of momentum by definition. In short, the alleged "geometry" and "curvature" exist only in the potential field, but neither concept does anything about initiating the 3-space motion of target bodies. It takes a force to do that. Here you say three things: 1. Field GR will initiate motions of stationary objects by the force of gravity 2. Geometric GR won't initiate such motions since geometry alone cannot do that 3. Field GR and geometric GR make the same predictions about how the bodies will move. 3. is a clear contradiction to 1. and 2. --- make up your mind !!!!!!!! [Schlyter]: Your causality principle is flawed. It works well in Newtonian Physics but fails in . GR (your flawed conclusion that geometric GR says that those bodies initially at rest in space will remain in rest just because gravity is a pseudo-force. Your flaw is corrected by integrating space and time to space-time, instead of keeping them separate as you insist on doing, like in Newtonian Physics). Newtonian physics is not involved in this discussion in any capacity. When you use the expression "Newtonian physics", it seems apparent from context that you must mean "Euclidean flat-space geometry". So I will interpret your sentence to mean that and answer it accordingly. If that is not your meaning, please explain what any of this discussion has to do with Newtonian physics. More to the point, please elaborate how the lack of a cause to initiate motion in geometric GR is corrected by considering spacetime to be curved? I never said there was a lack of a cause -- I merely said there was no force of gravity in geometrical GR (and if we exclude non- gravitational forces there won't be any forces at all in geometrical GR of couse). Which implies forces cannot be the cause, but it doesn't exclude other causes. My whole point is that curvature alone, in the absence of a force, cannot initiate the motion of anything. Not even when there is an initial motion ???? In 4D space-time nothing can ever be "at rest" (unless you stop time itself), since in the t dimension everything propagates forward at c, the speed of light. That, combined with the curvature of space-time, is the cause of those initially stationary bodies starting to move: the motion, which initially was exactly parallell to the "t" direction, will, due to the curvature of space-time, partially spill over into the "xyz" directions, making the bodies starting to move also in "xyz" space. The situation is similar to this situation on normal 3D space: consider an Euclidian space and a rectilinear orthogonal coordinate system xyz, where a body moves exactly parallell to the "x" direction. No forces act on the body, which thus has rectilinear uniform motion. In the "yz" plane the body will appear to be stationary, and will appear to remain stationary forever, or until some force starts acting on the body. Now, consider the same situation in a curvilinear coordinate system. For simplicity, let's assume a spherical coordinate system: the body moves exactly towards, say, "west" at a latitude of, say, 60 degrees - thus its motion will be in longitude only. The same situation applies as in the prevous paragraph: no forces are acting on the body, which thus has a rectilinear uniform motion. Initially the body will appear stationary in both latitude and radius vector, moving only in longitude. But due to the curvature of this coordinate system, the body will soon change not just longitude but also latitude and radius vector - even though no forces are acting on the body. It's due just to geometry! If a test particle rests on the side of a hill, it will rest there forever unless a force acts on it. For example, if the hill is on Earth, gravity would act to make the test particle start rolling downhill. But in space, if there is no force of gravity but only curvature of spacetime, the initial 4-space path of the body is a straight line by definition of "at rest", and the body can never deviate from that straight line unless a force acts. ....or unless the coordinate system curves.... [Schlyter]: Observations made in 3-space plus time, in a known reference frame, can be integrated into 4-spacetime and be used to validate or refute the theory. Let's examine this claim too. Yes, 3-space potential and motion affect time, and can be used to convert GR's coordinate time into GR's proper time. 3-space itself remains isotropic around any source mass, and the slight radial contraction can be neglected for our purposes here as too small to matter. ....if the gravitational field is sufficiently weak, as in e.g. our solar system.... For example, for GPS satellites, length contraction is just a few millimeters. So what causes the satellites to orbit the Earth? Why should the fact that their on-board clocks have sped up relative to ground clocks cause them to move in a curve around Earth instead of continuing in a straight line? "Curved spacetime" means nothing more than that the clock rates have changed. It provides no explanation for deviation from simple, linear motion. Another example: throw a ball straight upwards. It moves up, stops and moves down. Near the peak its path curves sharply. Now, throw the ball again but mostly sideways, only slightly upwards. Again the ball moves up, then down -- and its path curves much less sharply. Why are the curvatures so different? They're subjected to the same gravitational field, right? The answer lies in 4D space-time: the curvature of the two paths become the same if you also account for the time dimension. I refer you to the classic "Gravitation" by Misner-Thorne-Wheeler, page 32-33, for a fuller explanation. [Schlyter]: What's this "deep reality physics" ?? A new buzzword you just invented? It means physics that excludes magic or miracles for the simple reason that admitting them ends the search for understanding and predictability. Anything can be explained as a miracle, and the attempt to explain it can be dismissed because "we can't know the mind of God". Whether that is true or not, deep reality physics is tasked with explaining nature without miracles until such time as it finds something that cannot be explained in any other way. No such barrier to understanding and prediction has as yet appeared. By contrast, mathematical physics and philosophy are more concerned with descriptions of nature than with fundamental understanding, so they both regularly allow miracles. The term "deep reality physics" was coined to distinguish this type of physics from the other types. This contrast is most acute in the case of quantum mechanics, which has abandoned the principles of physics and consequently concluded "there is to deep reality to nature." Those unhappy with that conclusion have no other recourse but reverting to the principles of physics. If the map and the terrain disagree - which one should we consider valid? The "principles of physics" is the map here - it's what you and some other think the physical world should be. Empirical observations is the terrain. "Magic" is merely a label some people attach to something they don't understand. "God" is another such label. Suppose we could, and did, travel back in time to, say, the 1700's. We brought a pair of comm radios with us and demonstrated them to the people from those times. To them these comm radios, able to transfer messages at apparently infinite speed (at least as long as we stayed here on Earth), would have looked like magic. So your "deep reality physics" which "excludes magic" is actually a way to refuse there are phenomena we humans don't yet understand. [Schlyter]: Every model is btw based on some "magic": the fundamental assumptions which aren't proved but which are used to build the model. For some of these fundamental assumptions we can make the "magic" vanish by pointing to some other model - a model which may have its own set of "magic". But for the remaining assumptions we have no other model to point to, but merely choose our fundamental assumptions so they appear "reasonable". If the "fundamental assumptions used to build the model" are the principles of physics, there is no magic involved because the opposite of each fundamental principle (such as creation from a true void) is a form of magic. Anytime you stop asking and just accept something, you treat that as magic. And then it doesn't really matter whether it's "these first principles are valid" or "god created it" or "it spontaneously appeared from the void". [Schlyter]: Forces vs geometry can be viewed as such a choice. Your brain finds it impossible to accept geometry as the fundamental cause in GR - my brain finds it more acceptable. So it's perhaps just a matter of personal preferences? Personal preferences are like choosing a favorite color or dessert. But cause and effect have existence in the objective reality we all experience, and not just in our minds. True - and in both geometric and field GR, a colleciton of bodies initially at rest to one another will start to move due to their mutual gravitation. In field GR gravitational forces cause them to move in space, while in geometric GR the geometry cause their motion in the time dimension to "spill over" as motion in space too. You've decided that you reject the geometric model of GR. Others accept it. It's a matter of personal preference... both models provide the same prediction of the motions of the bodies. The goal of science is to develop tests to sort out the good and bad hypotheses. The good ones aid understanding and predictability. The bad ones are forever tacking on ad hoc helper hypotheses to accommodate new, unexpected observations (such as "dark energy" to explain the universe expansion accelerating instead of slowing through the action of gravity). [Schlyter]: By setting aside geometric GR we also set aside our understanding why gravitational and inertial masses are the same See http://metaresearch.org/cosmology/gr...%20Inertia.asp for a complete and highly intuitive explanation of why these are approximately equal without gravity being geometry in any meaningful sense. Your strong dislike of geometry is very apparent in that article of yours. And you even contradict yourself - there you write: # Einstein used this equivalence principle to conclude that gravity is not a force while here you wrote: # Field GR is the interpretation preferred by Einstein which I consider a claim that Einstein did consider gravity being a force after all. So make up your mind !!!!! Also your figure 1, with the comment # Consider the geodesic (orbital) path of the Earth with respect to # the Sun in Figure 1. If we choose any two points along that path # (call them A and B), note that a straight line between A and B (as # could be represented by a taut rope) is a shorter path through space # than the geodesic path. shows that you just don't understand what a geodesic in 4D spacetime is: it is NOT, repeat, NOT the shortest distance in 3D space ! If you considered the full 4D spacetime, then the orbit (curved in 3D space) from A to B would be shorter than the line (straight in 3D space) from A to B. Therefore the orbit, not the line, is the geodesic. If there was no gravitational field, 4D spacetime would become Euclidian, and the "orbit" and the line would coincide. I'm actually amazed that someone like you, who consider yourself being acquainted with GR, can make such a trivial mistake. Of course there's an alternate explanation which hopefully isn't true: you understand this very well but count on most of your readers not understanding it, and then you intentionally mislead them. [Schlyter]: Classical celestial mechanics use Newtonian mechanics, with only small relativistic corrections in a few cases. This works well in the solar system and visual double stars, but fails in situations like a binary pulsar. Modern celestial mechanics uses the GR equations of motion for all cases where relativity is relevant. Damour developed equations of motion specifically for analyzing the binary pulsar. As I said, GR would be untested without some such vehicle to predict motions in 3-space vs. time for comparison with observations made in 3-space plus time. [tvf]: Gravity cannot be simply geometry because that provides no source for new momentum. [Schlyter]: Does this mean you claim that geometric GR predicts that a collection of bodies initially at rest in space relative to one another and subjected to no other forces than their mutual gravity, that these bodies will remain at rest? As predicted by geometric GR of course. If not, and if geometric GR predicts the motions which actually are observed, in what way is geometric GR "falsified"? Geometric GR describes only the gravitational potential field, and the potential by itself cannot cause anything to move through 3-space. Thus you say that, according to geometric GR, a collection of bodies initially at rest relative to one another and subjected to no other forces, that these bodies will remain at rest. Right? Nor does it predict any curvature of 3-space. So an additional axiom or assumption is needed to get changes in motion. Both physical interpretations of GR (field and geometric) use the same axiom to get 3-space motions: that force is the gradient of potential. That allows them to derive 3-space equations of motion, without which GR would predict no accelerated 3-space motions of material bodies. A ball thrown into the air would not even slow down. Do other specialists of GR agree with you here that according to geometric GR all gravitational effects vanish? E.g. Steve Carlip, does he think so too? g [Schlyter]: If the gravitation potential changes instantly also over large distances, no matter whether the body is moved by gravitational or non-gravitational forces, then gravity does indeed propagate FTL as you claim. I claim no such thing. Gravitational potential changes occur at speed c under any circumstances. There is no dispute about that. Sorry, but the gravitational force is by definition always locally perpendicular to the gravitational equipotential surfaces. This is so from the very definition of "potential" (as the integral of force). So if the force of gravity points to the instantaneous rather than the light-time retarded position of the gravitational body, then the gravitational potential too must change instantly. It does so in Newtonian physics, and deviates from this not in the first or second order but only in higher orders in GR. [Schlyter]: But if the gravitation changes instantly only when the body is moved by gravitational forces. This furthers the same confusion. It is only the speed of those gravitational forces that exceeds the speed of light. So there is no need to bring in non-gravitational forces to make any points about how gravitational forces behave. The difference between graviational and non-gravitational forces here is that the system "knows" what effects gravitational forces will have. Non-gravitational forces are not as easy to predict - they can depend on e.g. a human decision whether to fire a rocket or not. That's why I made the distinction. [Schlyter]: Why do you consider geometry "magic" but not forces ("action at a distance")? Geometry has no 3-space motion, no momentum, and therefore cannot be a source of new 3-space motion or momentum. Why do you thin that it "cannot" have this effect? Why not instead be honest and merely say you don't understand how it could have such an effect? A curve starting a ball rolling without a force acting on the ball would be magical. Interesting -- because precisely that will happen in a rotating coordinate system with no real forces acting, only pseudo-forces like the centrifugal and coriolis forces. Are the centrifugal and coriolis forces magic? [Schlyter]: Science has to find a balance here. What would you favor yourself: 1. Accepting a theory which later turns out to be false, because that theory had "compelling evidence" ?? 2. Rejecting a theory which has "compelling evidence", a theory which later turns out to be true, but at this point there's no hard evidence for that theory. Why must all theories be either accepted or rejected? My position is that all viable, not-yet-falsified theories should be on the scientific table for discussion and making distinguishing predictions. Why do we do science at all? Just as some kind of intellectual entertainment? Then it will of course become irrelevant how correct or incorrect a theory is - it'll be more important how interesting a theory is. But then science becomes nothing more than some kind of intellectual fiction... If we are to actually do something useful with science, then we'd better choose the theory which is most correct among the theories we have available. What would you prefer? First theory that catches on is always the winner? -|Tom|- As you hopefully know, scientific conclusions are never definite. Any theory is subject to revision, or rejection, if and when new evidence appears which falsifies that theory. So if a particular theory catches on first, so what? At that particular point, that theory is the best we have available. Whether it will continue to catch on also in the long run, only the future can tell. If another theoruy is better, the first theory will eventually be replaced. -- ---------------------------------------------------------------- Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN e-mail: pausch at stockholm dot bostream dot se WWW: http://stjarnhimlen.se/ |
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