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#11
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Link between dark matter and baryonic matter
Dear Yousuf Khan:
On Wednesday, October 19, 2016 at 11:46:24 PM UTC-7, Yousuf Khan wrote: On 10/16/2016 1:05 PM, dlzc wrote: Dear Yousuf Khan: On Saturday, October 15, 2016 at 10:45:21 PM UTC-7, Yousuf Khan wrote: ... Maybe the issue here is not to find a new modification of Newtonian gravity, but perhaps our reliance on still using Newtonian gravity even 100 years after we found a better theory of gravity might be the problem here? I find it more likely that a nearly 100 year old assumption that luminosity is directly proportional to the amount of mass present, when it has long been known that luminosity drops off rapidly with surface temperature. If you have cooler objects, they simply don't put out as much light... especially in the visible light bands. But they do still glow in the cooler invisible light bands like IR and microwave and radio. At a *much* lower luminosity. Remember, they use luminosity, essentially watts, and calibrate to normal-mass-present. We're still using Newtonian gravity after all of these years, because it's frankly much easier to calculate with than General Relativity. Paper on this subject for a "simple" galaxy, and evaluating the possible error between Newtonian gravity-as-a-force and GR, and in that galaxy, it is a 1% (or so) error, not the necessary 300% error. That's the point I'm trying to make, they are using "simple" galaxy models, rather than full galaxy models. Even dwarf spiral galaxies need Dark Matter, however. And they have a few billion stars. This should be doable soon. GR really kicks in: - to handle light, - to handle advancement of perihelion (for close objects), - to handle gravitational radiation. But in a many-body system such as stars in a galaxy or galaxies in a universe, those simple inverse-distance squared relationships simply don't work out anymore? They do work out "well enough", for simple gravitation. But we are "blind as bats" at these scales, and have a full complement of "flatlander fallacies" that we have to divest ourselves of. So then we're basically agreeing on this. Newtonian gravity might be one of those flatlander fallacies. Remove the *serious* errors of (normal-mass / luminosity) calibration, and then see if you think a further 5 or 10% (max) correction is necessary. We're still using Newtonian gravity in this day and age because we still don't have computers strong enough to do a GR calculation for an entire galaxy. False. The amount of computer time might still be abysmally long for an interesting galaxy, but it would still be doable. After all, Nature does this math in real time... Nature has its own entire universe-sized quantum computer to work with. We can barely put two qubits together yet. But GR (like Newton), is a classical solution. GR simplifies to Newton, under the right circumstances, circumstances suitable to galaxies "in the large". I don't think GR explains "Dark Matter", better than Newton does. They both have to accept that there is more matter that our myopic vision cannot detect (except via gravity). Using even our strongest supercomputers we can do perhaps a simulation of only a few million stars in a galaxy using GR, but our galaxy contains perhaps as much as 400 billion stars, so we keep approximating with Newton. Yet, even small spirals show a need for Dark Matter. Globular clusters, essentially don't. Then we need to investigate where the globular clusters differ from dwarf galaxies. There is no significant rotation in a globular cluster, so the normal mass present, is explained by microlensing, and other methods that apply equally well to a spiral's nucleus, or a globular cluster (expected to be ancient cores of spiral galaxies). If one day we can do a full simulation of the Milky Way with all of its entire 400 billion stars, then likely we'll see surprising results coming out of GR that are inconsistent with Newton, and then we'll be finally shaken of our illusion that Newton is "still good enough". Maybe. But the speeds and curvature on something the size of a galaxy, even the Milky Way, should present minimal error in using Newton. Well, that's been our assumption all along hasn't it? Maybe our assumption is wrong? We *know* it is still a classical theory, however. Now what I wonder is, if the "perfectly mirrored, massless box, containing photons", which has rest mass, exists between a star and the gases / dust / planets that give that star a background temperature higher than the CMBR. So some Dark Matter (probably less than 1%) might still be photons in transit between intersystem objects...? Or even neutrinos. Amen. Absolutely "dark" too, just not very massive, and in order to stay in the halo (as we observe), would have to be moving damned slowly... so would have to be too numerous to be all of Dark Matter. David A. Smith |
#12
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Link between dark matter and baryonic matter
On 10/20/2016 11:40 AM, dlzc wrote:
Dear Yousuf Khan: On Wednesday, October 19, 2016 at 11:46:24 PM UTC-7, Yousuf Khan wrote: On 10/16/2016 1:05 PM, dlzc wrote: I find it more likely that a nearly 100 year old assumption that luminosity is directly proportional to the amount of mass present, when it has long been known that luminosity drops off rapidly with surface temperature. If you have cooler objects, they simply don't put out as much light... especially in the visible light bands. But they do still glow in the cooler invisible light bands like IR and microwave and radio. At a *much* lower luminosity. Remember, they use luminosity, essentially watts, and calibrate to normal-mass-present. Well obviously they did that because humans naturally favor those wavelengths that we can see. We also didn't take into account the higher frequency UV, X-ray, and gamma scales. These higher frequency radiation would be higher luminosity than visible light. Paper on this subject for a "simple" galaxy, and evaluating the possible error between Newtonian gravity-as-a-force and GR, and in that galaxy, it is a 1% (or so) error, not the necessary 300% error. That's the point I'm trying to make, they are using "simple" galaxy models, rather than full galaxy models. Even dwarf spiral galaxies need Dark Matter, however. And they have a few billion stars. This should be doable soon. Yes, if we can start to model a full dwarf galaxy soon, then we're likely going to find out the real differences between a GR model and a Newtonian model. GR really kicks in: - to handle light, - to handle advancement of perihelion (for close objects), - to handle gravitational radiation. The main idea of GR is the spacetime curvature vs. the simple inverse-squared distance relationship. The spacetime curvature may not always equal the inverse-squared law, even at large distances. Maybe especially at very large distances, such as galactic size ranges. There were already attempts to model GR over larger scales, such as TeVeS. So then we're basically agreeing on this. Newtonian gravity might be one of those flatlander fallacies. Remove the *serious* errors of (normal-mass / luminosity) calibration, and then see if you think a further 5 or 10% (max) correction is necessary. I don't really think finding more mass is going to make a difference here. What I think is really going to make the difference is a new way model the curvature of spacetime with the existing mass. I think when GR is iterated over many self-dependent iterations, it will result in some surprising relationships that we hadn't expected to see. Quantum computing will make this task a lot easier. One example is in the movie Interstellar. This is where they fed GR equations into a movie graphics computer, and came up with an image of a blackhole that nobody imagined in their own heads. The computer had no preconceived notions of what it should see, it just ate the input data, ran the equations, can came up with an output image. We're still using Newtonian gravity in this day and age because we still don't have computers strong enough to do a GR calculation for an entire galaxy. False. The amount of computer time might still be abysmally long for an interesting galaxy, but it would still be doable. After all, Nature does this math in real time... Nature has its own entire universe-sized quantum computer to work with. We can barely put two qubits together yet. But GR (like Newton), is a classical solution. GR simplifies to Newton, under the right circumstances, circumstances suitable to galaxies "in the large". Classical problems can still be solved through quantum qubits. In fact, classical physics could be thought to emerge from macroscopic quantum interactions. So far, we've only been considering the macroscopic effects themselves, but no one has attempted to build up to a classical solution from a series of quantum solutions. Using even our strongest supercomputers we can do perhaps a simulation of only a few million stars in a galaxy using GR, but our galaxy contains perhaps as much as 400 billion stars, so we keep approximating with Newton. Yet, even small spirals show a need for Dark Matter. Globular clusters, essentially don't. Then we need to investigate where the globular clusters differ from dwarf galaxies. There is no significant rotation in a globular cluster, so the normal mass present, is explained by microlensing, and other methods that apply equally well to a spiral's nucleus, or a globular cluster (expected to be ancient cores of spiral galaxies). There has to be rotation in a globular cluster, stars don't just stand in place with all of that gravity between them without there being curved motion. If one day we can do a full simulation of the Milky Way with all of its entire 400 billion stars, then likely we'll see surprising results coming out of GR that are inconsistent with Newton, and then we'll be finally shaken of our illusion that Newton is "still good enough". Maybe. But the speeds and curvature on something the size of a galaxy, even the Milky Way, should present minimal error in using Newton. Well, that's been our assumption all along hasn't it? Maybe our assumption is wrong? We *know* it is still a classical theory, however. Being a classical theory doesn't make it the same as Newton's gravity, it's quite a significant departure from Newton, just as Newton was a departure from Aristotle's gravity. Now what I wonder is, if the "perfectly mirrored, massless box, containing photons", which has rest mass, exists between a star and the gases / dust / planets that give that star a background temperature higher than the CMBR. So some Dark Matter (probably less than 1%) might still be photons in transit between intersystem objects...? Or even neutrinos. Amen. Absolutely "dark" too, just not very massive, and in order to stay in the halo (as we observe), would have to be moving damned slowly... so would have to be too numerous to be all of Dark Matter. Well, let's look at it practically. The Milky Way by itself is 100,000 LY across on its disk, probably 1 million LY across on its halo. So neutrinos released now from the various stars of the galaxy will remain within the borders of the galaxy for between 100,000 to 1 million years. Enough time to remain a part of the galaxy's mass. Even photons will do the same. So there's a large amount of time that energy will remain within the borders of a galaxy, and even larger amount of time that it'll remain within the borders of a galactic cluster or supercluster. Now that we have detected gravitational waves, there's another even more humongous source of energy (converting several solar masses into energy at a time) that we know travels at only the speed of light. So lots of energy stays locked into regions just due to the slow passage of time. Yousuf Khan |
#13
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Link between dark matter and baryonic matter
Dear Yousuf Khan:
On Monday, October 24, 2016 at 11:18:24 PM UTC-7, Yousuf Khan wrote: .... Well, let's look at it practically. The Milky Way by itself is 100,000 LY across on its disk, probably 1 million LY across on its halo. So neutrinos released now from the various stars of the galaxy will remain within the borders of the galaxy for between 100,000 to 1 million years. Well, they'd ("they" = neutrinos) be *average* about half that since they are generated across the disk, and if they were generated here, they'd be very energetic. If they were created much nearer the Big Bang, and are still hanging around, say in orbit, their total energy will be very close to their rest energy. Enough time to remain a part of the galaxy's mass. Even photons will do the same. So there's a large amount of time that energy will remain within the borders of a galaxy, and even larger amount of time that it'll remain within the borders of a galactic cluster or supercluster. Now that we have detected gravitational waves, there's another even more humongous source of energy (converting several solar masses into energy at a time) that we know travels at only the speed of light. Do we *know* that, however? Have we always been able to correlate a wave detection with a visible "flash" (or loss of a periodic source) in the proper direction? Side issue... So lots of energy stays locked into regions just due to the slow passage of time. Yes. So this is true of Newton, General Relativity, and its quantum replacement. But it isn't much, if the sum of each flavor of neutrinos is only 18 eV. So is this contribution 1%, 10% or the necessary 600%? I'd say it was more along the 1% lines... |
#14
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Link between dark matter and baryonic matter
In article ,
dlzc writes: Individually, no. But in groups, with a center of momentum frame, [photons] do have rest mass. So the sum of a bunch of zeroes is non-zero? That's new physics. I have no idea what "with a center of momentum frame" is supposed to mean. Standard physics says photons have momentum and energy but zero rest mass. Photons react to gravity and (in principle, but I don't think it has been measured) create gravity, but neither of those properties requires rest mass. -- Help keep our newsgroup healthy; please don't feed the trolls. Steve Willner Phone 617-495-7123 Cambridge, MA 02138 USA |
#15
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Link between dark matter and baryonic matter
Dear Steve Willner:
On Tuesday, October 25, 2016 at 11:30:27 AM UTC-7, Steve Willner wrote: In article , dlzc writes: Individually, no. But in groups, with a center of momentum frame, [photons] do have rest mass. So the sum of a bunch of zeroes is non-zero? That's new physics. Quite old, actually. I first heard of it in "Spacetime Physics" by Taylor and Wheeler. You can read about it he http://physics.stackexchange.com/que...less-particles .... or just realize for two oppositely-directed, equal-energy photons: E^2 = (sigma( p1, p2) = 0)^2 + (mc^2)^2 If the photons have non-zero energy (E=/=0), their momenta cancel, and they *must* have rest mass. I have no idea what "with a center of momentum frame" is supposed to mean. Standard physics says photons have momentum and energy but zero rest mass. Individually, yes. As a system of particles (not all even have to be photons), no. Photons react to gravity and (in principle, but I don't think it has been measured) create gravity, .... and this is the discussion here, to what extent that photons that have not yet propagated past, say 10,000 light years from the center of a spiral galaxy, contribute to the "pull" outside that distance? but neither of those properties requires rest mass. Gravitational mass, is actually the question, and so far gravitational mass = inertial mass = rest mass. David A. Smith |
#16
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Link between dark matter and baryonic matter
Dear Yousuf Khan:
So is this contribution 1%, 10% or the necessary 600%? I'd say it was more along the 1% lines... Consider that our Sun loses about 1 part in 10^14 each year (I think), due to solar wind and "mass deficit" of fusion inside it. In even 100,000 years, that is 1 part in 10^9 exodus from the Milky Way, unless significant "greenhouse gas" effect reflects it back in. David A. Smith |
#17
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Link between dark matter and baryonic matter
On Wednesday, 19 October 2016 21:06:01 UTC+2, Steve Willner wrote:
In article , Yousuf Khan writes: We're still using Newtonian gravity in this day and age because we still don't have computers strong enough to do a GR calculation for an entire galaxy. That's not the problem. GR is mathematically identical to Newtonian gravity provided gravity is not "strong" and speeds are "low" compared to the speed of light. The magnitude of the errors can be quantified for the actual gravitational potentials and speeds in any particular calculation. In some sense I have a problem with your reply. GR is not mathematical identical to Newton's Law. If you want to use GR the full Einstein equations are extremely difficult. A typical document to study is: https://arxiv.org/abs/1203.5166 "Numerical simulations of compact object binaries" by Harald P. Pfeiffer For a different document about my own investigations read this: http://users.telenet.be/nicvroom/Num..._documents.htm In this document many articles about numerical relativity are discussed, but mainly 2 or maximum 3 objects are considered. I fully agree that in many cases with great succes Newton's Law can be used. The real problems are 1) even Newtonian gravity is too hard to calculate when the system has too many bodies, It is not so difficult (using 2D configurations) to simulate Galaxy Rotation curves with 100 objects. I doubt if that is possible using the full Einstein equations. Nicolaas Vroom. |
#18
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Link between dark matter and baryonic matter
In article ,
dlzc writes: Quite old, actually. I first heard of it in "Spacetime Physics" by Taylor and Wheeler. I don't have that book on my shelf, but I can probably get it from the library. What page are you looking at (and in what edition)? You can read about it he http://physics.stackexchange.com/que...less-particles Most of the "answers" there look wrong to me, though parts of some of them are correct. ... or just realize for two oppositely-directed, equal-energy photons: E^2 = (sigma( p1, p2) = 0)^2 + (mc^2)^2 What are the symbols supposed to represent? And where does the equation come from? If the photons have non-zero energy (E=/=0), their momenta cancel, and they *must* have rest mass. For the system you describe, momentum is zero, energy is non-zero, and rest mass is zero. Gravitational mass, is actually the question, There's no such thing as "gravitational mass" in relativity unless you want to define it redundantly as E/c^2. All energy contributes to gravitation (or bends spacetime, if you prefer). -- Help keep our newsgroup healthy; please don't feed the trolls. Steve Willner Phone 617-495-7123 Cambridge, MA 02138 USA |
#20
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Link between dark matter and baryonic matter
Dear Steve Wilner:
On Friday, October 28, 2016 at 10:03:38 AM UTC-7, Steve Willner wrote: In article , dlzc writes: Quite old, actually. I first heard of it in "Spacetime Physics" by Taylor and Wheeler. I don't have that book on my shelf, but I can probably get it from the library. What page are you looking at (and in what edition)? Second Edition, Section 8.4, Sample Problem 8-2. Quote: "A system consisting entirely of zero-mass photons can itself have nonzero mass!" David A. Smith |
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