Does dark matter come in two types?
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From: dlzc on 17 Jun 2010 22:05 Dear eric gisse: On Jun 17, 5:46 pm, eric gisse <jowr.pi.nos...(a)gmail.com> wrote: > Yousuf Khan wrote: > > On 6/16/2010 6:31 AM, eric gisse wrote: .... > > > While I didn't say that, it actually is exactly like > > > TeVeS with its' fields with no physical source as > > > opposed to dark matter which we presume has a > > > source and dark energy which we know comes > > > from vacuum energy. .... > > You /know/ Dark Energy comes from vacuum energy? How? > > Energy gravitates. If you'd like to argue that vacuum energy > doesn't gravitate and thus isn't the source of dark energy, > then you have an uphill battle to climb. Not really, since Dark Energy is defined as causing expansion, aka. "antigravitation". So all energy doesn't gravitate, you've said that QM says that vacuum energy isn't energy so it cannot act like either energy or DE, so the hill you define isn't a hill at all. And he was asking you about your assertions, so why are you placing the hill of doing your work for you, in front of him? Are you OK, or are you just looking for a fight? David A. Smith
From: eric gisse on 17 Jun 2010 22:58 dlzc wrote: > Dear eric gisse: > > On Jun 17, 5:46 pm, eric gisse <jowr.pi.nos...(a)gmail.com> wrote: >> Yousuf Khan wrote: >> > On 6/16/2010 6:31 AM, eric gisse wrote: > ... >> > > While I didn't say that, it actually is exactly like >> > > TeVeS with its' fields with no physical source as >> > > opposed to dark matter which we presume has a >> > > source and dark energy which we know comes >> > > from vacuum energy. > ... >> > You /know/ Dark Energy comes from vacuum energy? How? >> >> Energy gravitates. If you'd like to argue that vacuum energy >> doesn't gravitate and thus isn't the source of dark energy, >> then you have an uphill battle to climb. > > Not really, since Dark Energy is defined as causing expansion, aka. > "antigravitation". So all energy doesn't gravitate, you've said that > QM says that vacuum energy isn't energy so it cannot act like either > energy or DE, so the hill you define isn't a hill at all. The direction of attraction is irrelevant to whether or not the stuff has an effect. > And he was > asking you about your assertions, so why are you placing the hill of > doing your work for you, in front of him? > > Are you OK, or are you just looking for a fight? > > David A. Smith
From: Yousuf Khan on 18 Jun 2010 08:31 On 6/18/2010 6:46 AM, eric gisse wrote: > Yousuf Khan wrote: > >> On 6/16/2010 6:31 AM, eric gisse wrote: >>> Yousuf Khan wrote: >>>> TeVeS is just a special sub-case of Dark Fluid, as is DM , Quintessence, >>>> General Relativity, MOND, f(R), etc. Just because TeVeS is included in >>>> the list doesn't mean that it's exactly like TeVeS. >>> >>> While I didn't say that, it actually is exactly like TeVeS with its' >>> fields with no physical source as opposed to dark matter which we presume >>> has a source and dark energy which we know comes from vacuum energy. >> >> You /presume/ Dark Matter has a source? What is it? > > An as of yet undiscovered particle that interacts via the weak interaction > that is rather massive or hiding in a very small corner of the parameter > space of the searches in accelerators... And what in the Standard Model of Quantum Physics leads you to believe that there might be a particle like that available to discover? Weak interactions produce neutrinos and perhaps photons. No other energy balance anomalies have ever popped out of Weak interactions. >> You /know/ Dark Energy comes from vacuum energy? How? > > Energy gravitates. If you'd like to argue that vacuum energy doesn't > gravitate and thus isn't the source of dark energy, then you have an uphill > battle to climb. Yes exactly, energy gravitates. Shouldn't vacuum energy therefore produce a compression effect rather than an expansion? How do you know that space isn't just relaxing by losing energy? >>>>> Instead of dark energy (vacuum energy from QFT) and dark matter (some >>>>> yet- undiscovered particle that only interacts via the weak >>>>> interaction) you have the presence of rather arbitrary scalar and >>>>> vector fields which have literally NO physical basis. >>>> >>>> You mean even more arbitrary than that magical fairy dust supposedly >>>> circling the galaxies that outweigh all of the stars combined? >>> >>> Actually, yeah, there are even more degrees of freedom with the modified >>> gravity theories. Dark matter is described as a perfect fluid - nothing >>> more. >> >> You mean like a "Dark Fluid"? > > No, I mean a perfect fluid like the hydrodynamic kind which has density but > no pressure. Unlike dark fluid, my meaning is specific and doesn't rely on > nuance in interpretation. A Dark Fluid would therefore also be a perfect fluid. >> So it's mere trivia that the calculated vacuum energy is 120 orders of >> magnitude larger than Dark Energy? > > No, it is one of the reasons that quantum field theory is wrong or needs > modification. The only way to bring down the size of the vacuum energy is to make the Planck scale larger in some parts of the universe, such as in those voids. >> Cosmological constant - Wikipedia, the free encyclopedia >> "As noted above, the measured cosmological constant is smaller than this >> by a factor of 10-120. This discrepancy has been termed "the worst >> theoretical prediction in the history of physics!"" >> > http://en.wikipedia.org/wiki/Cosmological_constant#Cosmological_constant_problem >> > > Glad you were there to copy and paste something from Wikipedia for me. Otherwise, you'd just pointlessly ask me for a source again. Preemptive sourcing. >>>> After putting in an arbitrary Cosmological Constant. >>> >>> This may amaze you, but lots of physical parameters are arbitrary. GR >>> doesn't predict G, or even c. >> >> No, it doesn't surprise me at all that it's arbitrarily chosen. What >> does surprise me is your complaint that various modified gravity >> theories have arbitrarily chosen values, but you're perfectly willing to >> forgive this bit of arbitrariness. As well as arbitrarily forgive the >> 120 orders of magnitude mistake for the vacuum energy. > > Apples<-> oranges. > > The cosmological constant is a 1 parameter addition to the general > relativity stress that is directly constrained by observation. The 3 (or 4) > vector components and 1 scalar component in TeVeS and similar theories are > not as much, and there is even more freedom than with dark matter. > > Recall the MOND interpolative function - hard to constrain an entire > arbitrary function, now isn't it? So quite arbitrarily, you consider one arbitrary function to be okay, but multiple functions to be not okay? >> The Train Wreck is no more of a pain of a structure than the Bullet >> Cluster. It's groups of galaxies merging with other groups of galaxies. >> If Dark Matter can explain the latter, then it should explain the former. > > That's a naive point of view. > > There are 3 lensing peaks in Abell 520, indicative of previous collisions. > It is not as simple as the Bullet cluster, though it is just as supportive > for dark matter. > > You cannot argue away the fact that there are lensing peaks offset from > visible mass distributions. Who is arguing about the existence of lensing peaks? On the contrary, it's these lenses themselves that are being used as the argument against Dark Matter. The entire Train Wreck argument is about the fact that the lensing peaks don't correspond anywhere near where Dark Matter theory says they should be. The lenses are obviously caused by something else entirely. Whether Train Wreck has undergone one collision or two, or multiple, Dark Matter theory should be able to explain it, and quite obviously it does not. My feeling is that Dark Fluid will explain it. >> Much like the curve fit that now gets added to GR, the Cosmological >> Constant? > > Which is validated by acceleration in SN1a measurements, correctly predicts > the location of the CMB acoustic peaks, and has its' constancy verified > across a region approximately a Mpc across. > > Just like MOND. Except for everything I just wrote. So you like modifying equations, but just not for Newton's equations? >> General Relativity would be out of the picture if they didn't >> choose the right arbitrary value of CC. > > Clearly you forget that the cosmological constant can be added right into > the stress tensor. Clearly I couldn't care less, because it's irrelevant. Yousuf Khan
From: eric gisse on 18 Jun 2010 15:51 Yousuf Khan wrote: > On 6/18/2010 6:46 AM, eric gisse wrote: >> Yousuf Khan wrote: >> >>> On 6/16/2010 6:31 AM, eric gisse wrote: >>>> Yousuf Khan wrote: >>>>> TeVeS is just a special sub-case of Dark Fluid, as is DM , >>>>> Quintessence, General Relativity, MOND, f(R), etc. Just because TeVeS >>>>> is included in the list doesn't mean that it's exactly like TeVeS. >>>> >>>> While I didn't say that, it actually is exactly like TeVeS with its' >>>> fields with no physical source as opposed to dark matter which we >>>> presume has a source and dark energy which we know comes from vacuum >>>> energy. >>> >>> You /presume/ Dark Matter has a source? What is it? >> >> An as of yet undiscovered particle that interacts via the weak >> interaction that is rather massive or hiding in a very small corner of >> the parameter space of the searches in accelerators... > > And what in the Standard Model of Quantum Physics leads you to believe > that there might be a particle like that available to discover? Weak > interactions produce neutrinos and perhaps photons. No other energy > balance anomalies have ever popped out of Weak interactions. That the abundance of matter over antimatter in the universe and that the standard model is only valid to ~1TeV and that there is evidence from accelerators that there is physics beyond the standard model tells me there's room to maneuver. > >>> You /know/ Dark Energy comes from vacuum energy? How? >> >> Energy gravitates. If you'd like to argue that vacuum energy doesn't >> gravitate and thus isn't the source of dark energy, then you have an >> uphill battle to climb. > > Yes exactly, energy gravitates. Shouldn't vacuum energy therefore > produce a compression effect rather than an expansion? How do you know > that space isn't just relaxing by losing energy? Open a textbook on the subject. GR is not Newton - sign of energy matters. Vacuum energy has negative energy density - its' effect is to repulse instead of attract. > >>>>>> Instead of dark energy (vacuum energy from QFT) and dark matter (some >>>>>> yet- undiscovered particle that only interacts via the weak >>>>>> interaction) you have the presence of rather arbitrary scalar and >>>>>> vector fields which have literally NO physical basis. >>>>> >>>>> You mean even more arbitrary than that magical fairy dust supposedly >>>>> circling the galaxies that outweigh all of the stars combined? >>>> >>>> Actually, yeah, there are even more degrees of freedom with the >>>> modified gravity theories. Dark matter is described as a perfect fluid >>>> - nothing more. >>> >>> You mean like a "Dark Fluid"? >> >> No, I mean a perfect fluid like the hydrodynamic kind which has density >> but no pressure. Unlike dark fluid, my meaning is specific and doesn't >> rely on nuance in interpretation. > > A Dark Fluid would therefore also be a perfect fluid. No. http://arxiv.org/abs/0804.1588 Not a fluid, but rather further arbitrary fields inserted into the Lagrangian ala TeVeS. > >>> So it's mere trivia that the calculated vacuum energy is 120 orders of >>> magnitude larger than Dark Energy? >> >> No, it is one of the reasons that quantum field theory is wrong or needs >> modification. > > The only way to bring down the size of the vacuum energy is to make the > Planck scale larger in some parts of the universe, such as in those voids. Oooooor we acknowledge that the 'Planck scale' does not yet have any physical meaning and adjust accordingly. > >>> Cosmological constant - Wikipedia, the free encyclopedia >>> "As noted above, the measured cosmological constant is smaller than this >>> by a factor of 10-120. This discrepancy has been termed "the worst >>> theoretical prediction in the history of physics!"" >>> >> http://en.wikipedia.org/wiki/Cosmological_constant#Cosmological_constant_problem >>> >> >> Glad you were there to copy and paste something from Wikipedia for me. > > Otherwise, you'd just pointlessly ask me for a source again. Preemptive > sourcing. > >>>>> After putting in an arbitrary Cosmological Constant. >>>> >>>> This may amaze you, but lots of physical parameters are arbitrary. GR >>>> doesn't predict G, or even c. >>> >>> No, it doesn't surprise me at all that it's arbitrarily chosen. What >>> does surprise me is your complaint that various modified gravity >>> theories have arbitrarily chosen values, but you're perfectly willing to >>> forgive this bit of arbitrariness. As well as arbitrarily forgive the >>> 120 orders of magnitude mistake for the vacuum energy. >> >> Apples<-> oranges. >> >> The cosmological constant is a 1 parameter addition to the general >> relativity stress that is directly constrained by observation. The 3 (or >> 4) vector components and 1 scalar component in TeVeS and similar theories >> are not as much, and there is even more freedom than with dark matter. >> >> Recall the MOND interpolative function - hard to constrain an entire >> arbitrary function, now isn't it? > > So quite arbitrarily, you consider one arbitrary function to be okay, > but multiple functions to be not okay? Lambda is like c - fixed by observation. I do not see what is complicated about this. It isn't like MOND where you can put literally nearly any function you want in there. I intensely dislike the arrogance of people who intend to 'replace' dark matter with something cutely named like 'dark fluid' which is just TeVeS in disguise. Throwing a half dozen arbitrary fields into the mix to 'predict' what is observed is a lofty form of curve fitting. The notion that these unphysical fields are 'better' than dark matter/dark energy which at least have tentative guesses at their sources is a laff riot. Inflation annoys me the same way, but not as hard because it works. > >>> The Train Wreck is no more of a pain of a structure than the Bullet >>> Cluster. It's groups of galaxies merging with other groups of galaxies. >>> If Dark Matter can explain the latter, then it should explain the >>> former. >> >> That's a naive point of view. >> >> There are 3 lensing peaks in Abell 520, indicative of previous >> collisions. It is not as simple as the Bullet cluster, though it is just >> as supportive for dark matter. >> >> You cannot argue away the fact that there are lensing peaks offset from >> visible mass distributions. > > Who is arguing about the existence of lensing peaks? On the contrary, > it's these lenses themselves that are being used as the argument against > Dark Matter. The entire Train Wreck argument is about the fact that the > lensing peaks don't correspond anywhere near where Dark Matter theory > says they should be. The lenses are obviously caused by something else > entirely. Whether Train Wreck has undergone one collision or two, or > multiple, Dark Matter theory should be able to explain it, and quite > obviously it does not. > > My feeling is that Dark Fluid will explain it. > >>> Much like the curve fit that now gets added to GR, the Cosmological >>> Constant? >> >> Which is validated by acceleration in SN1a measurements, correctly >> predicts the location of the CMB acoustic peaks, and has its' constancy >> verified across a region approximately a Mpc across. >> >> Just like MOND. Except for everything I just wrote. > > So you like modifying equations, but just not for Newton's equations? > >>> General Relativity would be out of the picture if they didn't >>> choose the right arbitrary value of CC. >> >> Clearly you forget that the cosmological constant can be added right into >> the stress tensor. > > Clearly I couldn't care less, because it's irrelevant. > > Yousuf Khan
From: eric gisse on 18 Jun 2010 17:32
Yousuf Khan wrote: [...] Clicking 'send now' instead of 'send later' did the expected. >> There are 3 lensing peaks in Abell 520, indicative of previous I wonder what I was looking at when I wrote this. http://arxiv.org/abs/0809.3139 There are 5 peaks. >> collisions. It is not as simple as the Bullet cluster, though it is just >> as supportive for dark matter. >> >> You cannot argue away the fact that there are lensing peaks offset from >> visible mass distributions. > > Who is arguing about the existence of lensing peaks? On the contrary, > it's these lenses themselves that are being used as the argument against > Dark Matter. The entire Train Wreck argument is about the fact that the > lensing peaks don't correspond anywhere near where Dark Matter theory > says they should be. ....for what value of 'should' ? http://arxiv.org/abs/0809.3139 Define what dark matter 'should' predict here. The only apparent problem is that the center has dark matter, which to me seems resolvable if you allow for dynamic friction from gravitation. This is not a collision of two massive bodies like the bullet cluster, there were apparently 3 here. Multibody collisions like that can suck the energy out of one of the members. > The lenses are obviously caused by something else > entirely. Whether Train Wreck has undergone one collision or two, or > multiple, Dark Matter theory should be able to explain it, and quite > obviously it does not. You use the word 'obviously' twice, even though in neither case is what you think obvious actually obvious. > > My feeling is that Dark Fluid will explain it. > >>> Much like the curve fit that now gets added to GR, the Cosmological >>> Constant? >> >> Which is validated by acceleration in SN1a measurements, correctly >> predicts the location of the CMB acoustic peaks, and has its' constancy >> verified across a region approximately a Mpc across. >> >> Just like MOND. Except for everything I just wrote. > > So you like modifying equations, but just not for Newton's equations? MOND gets the above wildly wrong even with the abundantly large freedom allowed by the arbitrary interpolative function. A 1 parameter 'curve fit' is not a curve fit. > >>> General Relativity would be out of the picture if they didn't >>> choose the right arbitrary value of CC. >> >> Clearly you forget that the cosmological constant can be added right into >> the stress tensor. > > Clearly I couldn't care less, because it's irrelevant. > > Yousuf Khan Not if the argument is that GR can't predict what is observed. There is no mandate from on high that the cosmological constant be separate from the stress tensor. |