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#21
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1 centillion light years away
Sylvia Else wrote:
My objection to dark matter and dark energy is they get into epicycles. They are not observed yet they are proposed to explain problems with edge cases. Our galaxy is rotating at a rate that should cause it to come apart given the mass that we can see. This is hardly an edge case. We need to be able to explain either how the galaxy stays together despite its mass being too low, or find a way to allow its mass to be high enough without the matter getting in the way of the things we can see. Let's see if I understand the issue correctly: Sol is in orbit around the center of mass of the galaxy, isn't it? There would be enough noise in the orbit to make it only roughly eliptical but it does orbit. The galatic rotation is the average of all of the stars and other matter that can be detected in the EM bands. Something has to have enough mass for all of those orbits to occur. The galatic arms are not so much bands of higher density of stars but bands of newer brighter stars. The arms could be formed by a statistical feature of the orbits of gas clouds plus some effect that the general galactic magnetic field has on the ionized gas. The part I don't get here is if the galactic magnetic field accelerates ions that then become a part of stars that momentum should be a part of the stellar masses so star should migrate outwards. Maybe ions form shock waves when they encounter uncharged gas clouds and those shock waves are the main source of matter for the clouds. Either there's matter that's not detectable in the EM bands and therefore the majority of the matter in the galaxy and hence the universe is in a form that does not interact with EM (dark matter) or the current estimates of galatic masses are almost two orders of magnitude too low using matter that does interact. How large could a black hole or neutron star be without being visible at over a parsec? Far enough out and you'd need to see it indirectly by apparent motion of the stars behind it because of gravitational deflection. How old would a black hole need to be to be invisible? If I understand the issue correctly the problem is the age and number of such invisible large objects. There would have to be a lot more of them than stars to account for the visible mass and that would introduce far more noise in stellar galactic orbits than has been observed. Therefore the extra mass has to be wildly disbursed not in black holes. Black holes and neutron stars do not carry enough net charge to matter in that sense but their gravititional field is so strong that objects descending towards them have a lot of electromagnetic interaction. They should glow from what boils down to descent friction. The spectra of stars observed do not match this pattern therefore such objects are not the majority of stars. Such objects should glow just from the galatic background gas (?). There should b emany and none are seen. Even the oldest should be visible from introducing a lot more noise in stellar orbits - A hundred times as many massive objects would mean orders of magnitude more close enounters would mean orders of magnitude more stars with rogue orbits. None of the expected effects of a lot of black hole or neutron stars have been observed therefore there are not 20-100 times as much mass in these objects as in stars. There is a lot of gravitational mass to be accounted for anyways based on stellar orbits. Therefore the missing mass is widely dispursed. As near as I can tell that's the main starting point of the evidence and the starting point of the line of reasoning. |
#22
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1 centillion light years away
On 14/07/2010 1:29 AM, Doug Freyburger wrote:
As near as I can tell that's the main starting point of the evidence and the starting point of the line of reasoning. Seems a reasonable summary, to which I'd only add that the missing mass cannot be within any stellar systems whose orbital mechanics are known are known, because it would affect planetary orbits. Alternatively, it would have to be a kind of mass whose gravitional effects occur only at large distances (I'm highly sceptical of that, and it would require considerable rejigging of the theoretical framework, but it's not impossible). The theory of gravity may just be wrong over large distances. Sylvia. |
#23
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1 centillion light years away
Sylvia Else wrote:
On 14/07/2010 1:29 AM, Doug Freyburger wrote: As near as I can tell that's the main starting point of the evidence and the starting point of the line of reasoning. Seems a reasonable summary, to which I'd only add that the missing mass cannot be within any stellar systems whose orbital mechanics are known are known, because it would affect planetary orbits. Alternatively, it would have to be a kind of mass whose gravitional effects occur only at large distances (I'm highly sceptical of that, and it would require considerable rejigging of the theoretical framework, but it's not impossible). The theory of gravity may just be wrong over large distances. Sylvia. So for so-called nonbaryonic dark matter what is it supposed to be composed of other than neutrinos? Other leptons? Can't be electrons. And why is it not readily observed if it's supposed to be rampant all over the universe compared to ordinary matter. Isn't disperal a key requirement if it's assumed to be in such abundance? I'm not ready to buy into the fiction that it's the speculative axions or another as yet unknown "supersymmetric particle" that also lies outside the standard model. How would such an abundance of dark matter effect particle collision experiments and the standard model? Wouldn't/shouldn't we see more lepton creation? It may not be so radical to believe the theory of gravity may just be wrong over large distances. Or that maybe our presumptions on the uniformity of space-time are wrong. Something is clearly missing. Give credit to Newton for rejecting the idea of an "aether" early on: [ from http://en.wikipedia.org/wiki/Luminiferous_aether ] "Christiaan Huygens, prior to Newton, had hypothesized that light was a wave propagating through an aether, but Newton rejected this idea. The main reason for his rejection stemmed from the fact that both men could apparently only envision light to be a longitudinal wave, like sound and other mechanical waves in fluids. However, longitudinal waves by necessity have only one form for a given propagation direction, rather than two polarizations as in a transverse wave, and thus they were unable to explain the phenomenon of birefringence, where two polarizations of light are refracted differently by a crystal. Instead, Newton preferred to imagine non-spherical particles, or "corpuscles", of light with different "sides" that give rise to birefringence. A further reason why Newton rejected light as waves in a medium was because such a medium would have to extend everywhere in space, and would thereby "disturb and retard the Motions of those great Bodies" (the planets and comets) and thus "as it [light's medium] is of no use, and hinders the Operation of Nature, and makes her languish, so there is no evidence for its Existence, and therefore it ought to be rejected." Hear hear.... Dave |
#24
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1 centillion light years away
On 14/07/2010 12:45 PM, David Spain wrote:
So for so-called nonbaryonic dark matter what is it supposed to be composed of other than neutrinos? Other leptons? Can't be electrons. And why is it not readily observed if it's supposed to be rampant all over the universe compared to ordinary matter. Isn't disperal a key requirement if it's assumed to be in such abundance? I'm not ready to buy into the fiction that it's the speculative axions or another as yet unknown "supersymmetric particle" that also lies outside the standard model. It wouldn't be readily observed if its only interactions were gravitational. It would show up in unexpectedly high red shifts of distant galaxies (we'd be seeing them earlier on, when the missing mass had had less time to slow them down, but I believe this is actually opposite to what is observed), and higher than expected rotation rates of indiviual galaxies which is what we do see. However, if something interacted only gravitationally, it would be difficult to explain its exclusion for within stella systems. As for what it's composed of, that's really putting the cart before the horse. The Universe isn't required to be constructed from the elements we currently consider to exist. So you start by constructing a theory that explains observations, and then try to attach physical meanings to the terms in the theory. If, not withstanding the objection above, a theory that described observations contained a term that could only reasonably be viewed as a homogenous 'stuff' pervading the Universe, then that's where you'd be at pending further experiments and observations. Sylvia. |
#25
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1 centillion light years away
Sylvia Else ) writes:
On 14/07/2010 12:45 PM, David Spain wrote: So for so-called nonbaryonic dark matter what is it supposed to be composed of other than neutrinos? Other leptons? Can't be electrons. And why is it not readily observed if it's supposed to be rampant all over the universe compared to ordinary matter. Isn't disperal a key requirement if it's assumed to be in such abundance? I'm not ready to buy into the fiction that it's the speculative axions or another as yet unknown "supersymmetric particle" that also lies outside the standard model. It wouldn't be readily observed if its only interactions were gravitational. It would show up in unexpectedly high red shifts of distant galaxies (we'd be seeing them earlier on, when the missing mass had had less time to slow them down, but I believe this is actually opposite to what is observed), and higher than expected rotation rates of indiviual galaxies which is what we do see. However, if something interacted only gravitationally, it would be difficult to explain its exclusion for within stella systems. I believe the usual explanation is that its density is too low to produce perceptible effects (which would of course have to be gravitational--a set of rotation-curve anomalies for the planets). As an aside, there are a number of theoretical candidates for dark matter, and the DAMA group in Italy claims to have seen the signature of one kind in observations over the last few years. (They certainly have a signal from *something*.) As for what it's composed of, that's really putting the cart before the horse. The Universe isn't required to be constructed from the elements we currently consider to exist. So you start by constructing a theory that explains observations, and then try to attach physical meanings to the terms in the theory. If, not withstanding the objection above, a theory that described observations contained a term that could only reasonably be viewed as a homogenous 'stuff' pervading the Universe, then that's where you'd be at pending further experiments and observations. Which are currently in progress. --John Park |
#26
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1 centillion light years away
David Spain wrote:
Sylvia Else wrote: Seems a reasonable summary, to which I'd only add that the missing mass cannot be within any stellar systems whose orbital mechanics are known are known, because it would affect planetary orbits ... If I read the explanations correctly the dark matter would need to be dispursed close to evenly within stellar systems but not close to evenly between galaxies. That leaves a lot of middle intragalactic distance ranges where the dispursement doesn't need to be all that even. What I don't get is why it has to end up even anyway near Sol. If it interacts by gravity there should be plenty that is gravitationally bound to Sol so it should follow a density rule AU-to-AU but planetary orbits do not suggest that. So the field needs to be fairly uniform across local interstellar space. How would such uniformity come about? It should vary randomly within a galaxy and that would reduce the stability of planetary orbits. The theory of gravity may just be wrong over large distances. General relativity corrected edge cases of Newtonian gravity. Edge case correction has already happened in science. There's also the possibility that our distance estimates are orders of magnitude higher than the correct distances. So for so-called nonbaryonic dark matter what is it supposed to be composed of other than neutrinos? Other leptons? Can't be electrons. And why is it not readily observed if it's supposed to be rampant all over the universe compared to ordinary matter. Isn't disperal a key requirement if it's assumed to be in such abundance? I'm not ready to buy into the fiction that it's the speculative axions or another as yet unknown "supersymmetric particle" that also lies outside the standard model. How would such an abundance of dark matter effect particle collision experiments and the standard model? Wouldn't/shouldn't we see more lepton creation? A particle that does not interact with the electromagnetic force does not mean it will also not interact with the electro-weak or strong forces. Neutron stars should usck the stuff up like giant vacuum cleaners of space and eventually collapse into black holes for the captured mass. We should see plenty of super nova sized explosions. Could this be a source for gamma ray bursts? It may not be so radical to believe the theory of gravity may just be wrong over large distances. Or that maybe our presumptions on the uniformity of space-time are wrong. Something is clearly missing. Give credit to Newton for rejecting the idea of an "aether" early on: I'll go with the current theory of gravity being wrong as the most likely based on the very poor model of prior science history. [ from http://en.wikipedia.org/wiki/Luminiferous_aether ] "Christiaan Huygens, prior to Newton, had hypothesized that light was a wave propagating through an aether, but Newton rejected this idea. The main reason for his rejection stemmed from the fact that both men could apparently only envision light to be a longitudinal wave, like sound and other mechanical waves in fluids. However, longitudinal waves by necessity have only one form for a given propagation direction, rather than two polarizations as in a transverse wave, and thus they were unable to explain the phenomenon of birefringence, where two polarizations of light are refracted differently by a crystal. Instead, Newton preferred to imagine non-spherical particles, or "corpuscles", of light with different "sides" that give rise to birefringence. A further reason why Newton rejected light as waves in a medium was because such a medium would have to extend everywhere in space, and would thereby "disturb and retard the Motions of those great Bodies" (the planets and comets) and thus "as it [light's medium] is of no use, and hinders the Operation of Nature, and makes her languish, so there is no evidence for its Existence, and therefore it ought to be rejected." Neither imagined the wave/particle duality of QM. |
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