Does dark matter come in two types?
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From: Yousuf Khan on 23 Jun 2010 12:15 On 6/19/2010 3:32 AM, eric gisse wrote: > 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. It's likely that some of the peaks are a mishmash of the initial three sources. >> 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. Quite simple really, Dark Matter should predict all of the Dark Matter remains attached to only the galaxies in the cluster, it should go nowhere else -- ever. It wouldn't matter if there were two, three or more initial clusters merging, the DM must stay firmly around their original galaxies. If two galaxies merge during this process then their combined Dark Matter should stay firmly attached to their combined bodies. It shouldn't follow intergalactic gas, and it especially better not go off on its own towards "nowhere in particular". That's what DM supposedly does in the Bullet Cluster, and that's what it should be doing in the Train Wreck. > 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. If that's the case, then the galaxies should also get their trajectories altered along with their Dark Matter. Yousuf Khan
From: Yousuf Khan on 23 Jun 2010 14:04 On 6/22/2010 2:04 AM, eric gisse wrote: > Yousuf Khan wrote: >> The universe has precipitated down to all of the physics we see below 1 >> TeV, which we now call the Standard Model, because that's all we >> encounter in normal life these days. What makes you think that anything >> that was created above 1 TeV is stable enough to survive into the >> low-energy universe we have now, when everything else has decayed down >> to the Standard Model? > > What makes you think that we see everything? (1) Because the heavier the particles are, the less stable they are. The heaviest particle we've discovered so far, the Top quark, doesn't even last long enough to form Strong force bonds before it decays into something else: it's the only quark that's seen alone, not paired up with another quark into hadrons of some kind. That's pretty much the general case as we go up the mass scale in everything we see. and, (2) TeV physics isn't really TeV physics. We're just cranking up accelerators to create bigger and bigger junk piles, so we can sort through the rubbish to find smaller and smaller pearls. Accelerators always had to have more power than the particles they were intended to find, but now we have a 7 TeV accelerator (LHC) which is entirely devoted to finding a particle, the Higgs, that may end up weighing less than 200 GeV, if it's ever found at all. That's a 35:1 signal-to-noise ratio. The particles themselves are in the realm of GeV, not TeV. It's TeV junk piles to find GeV physics. >>> 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. >> >> The only thing I've seen described as having negative energy is the >> vacuum inside Casimir Effect plates, not standard space vacuum. > > "vacuum" and "vacuum energy" not the same thing. Read what I said again, negative energy is only inside a Casimir Effect vacuum, not a standard vacuum. Until you understand the difference between those types of vacuums, the rest of what you say is drivel. >> What's >> your source for negative energy inside a regular vacuum? > > Vacuum energy. Remember how I mentioned absolute amounts of energy > gravitating instead of just the relative amounts like in Newton? How irrelevant are you trying to be? Newton's laws treat a vacuum as having absolutely zero energy. Who mentioned anything about Newton here anyways? What you have to understand is that not all vacuums throughout the universe are necessarily the same. Some volumes of vacuums may have more energy than others, even if they have the exact same amount of matter inside them (i.e. absolutely none). They are affected by their proximity to other areas of space where there is lots of matter. The matter energizes the closer vacuums, more than the further vacuums. The entire term "vacuum" only refers to the mass density of a volume of space, not its energy density. We'll have to start eventually finding a way to measure energy densities separately from mass densities, and start referring to "mass vacuums" vs. "energy vacuums" separately. >> If the open space within our solar system is considered the baseline for >> zero energy density, then it's likely that there may be even more >> emptier space within galaxies, then even emptier between galaxies, and >> so on. So by comparison with solar system vacuum, we would have negative >> energy density everywhere else. The inter-super-galactic voids would be >> the lowest energy density of all. > > Whether or not there is a baseline is irrelevant. See above. No, it's not, see above. A "mass vacuum" inside the area of our Solar system is absolutely teaming with energy from the surrounding energy outputs of the Sun, planets, and other material within it. A mass vacuum inside an area of space between galactic superclusters may be quite deficient of energy, relatively. >>>> 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. >> >> You're the only one that has ever described Dark Matter as a perfect >> fluid. I don't necessarily disagree with that assessment, but I've never >> seen any other papers specifically describe Dark Matter as a "perfect >> fluid". So where's your sources? > > Do I SERIOUSLY need to explain this? > > No non-gravitational or even self interactions, so there will be no > viscosity or pressure. Just density If dark matter is particle based, that's > how it has to be described. > > If you must have references with people using that description: > scholar.google.com 'lambda cold dark matter perfect fluid'. ~32,000 results > and at least a few of them have the correct combination of words. > >> >> By that same token neither has Dark Fluid ever been specifically >> described as a perfect fluid, but it is considered a "fluid". > > Not by people who know what the term 'fluid' means. > >> It even >> has it in its name, so that puts it one step closer to a fluid than Dark >> Matter is. > > If the theory were called 'dark ponies' would you expect actual ponies to > show up somewhere? Read the damn paper on the subject - there is no fluid! You didn't go far enough back in the literature. If they treated Dark Fluid like a full fluid mechanics problem, such as the Generalized Chaplygin Gas model, then it would be too hard to solve. So they "simplified" it by treating it as a scalar-field equation instead. Basically it is a satisfactory fluid statics equation, if not a fluid dynamics equation. *** http://arxiv.org/pdf/astro-ph/0601274 "Alternative models exist to explain the cosmological observations, and in particular some of them try to solve the dark energy and dark matter problems by unifying both components into a single �dark fluid�. We can for example note that the Generalized Chaplygin Gas model [4] follows this idea and is presently under scrutiny. We have shown in [5] that building such a dark fluid model is very difficult, as the model has to be in agreement with many observational constraints, and especially has to explain at the same time the cosmological repulsive effects and the local binding gravitational effects in the recent Universe. As scalar field-based models for dark energy and dark matter exist in the literature [6, 7, 8, 9, 10], it seems interesting to study unifying dark fluid models based on scalar fields. This idea has been proposed in [11]. The crucial question however concerns the form of the potential of the scalar field. In this article, we will consider a complex scalar field and propose an adequate form for its potential. We will show that this scalar field can potentially explain correctly the observations of galaxy rotation curves of spiral galaxies and the presence of strong binding gravitational effects in clusters. We will also consider the cosmological behavior of the dark fluid and show that it agrees with the cosmological constraints and observations. We will finally conclude by suggesting some further directions of investigation beyond this study." *** Yousuf Khan
From: dlzc on 23 Jun 2010 18:55 On Jun 22, 11:14 pm, eric gisse <jowr.pi.nos...(a)gmail.com> wrote: > dlzcwrote: > > [...] > > >> Gravitational lensing says something is there. Do you > >> have reason to disagree? > > > Something is there. > > Baryonic matter is wholly excluded, and leptons can't > make the mass budget. > > Ruh roh. Baryonic matter is not wholly excluded. > >> > But then neither did the > >> > stars that should have been visible from those two > >> > clusters. > > >> Stars do not meaningfully participate in a cluster > >> meregr beyond their contribution to gravitation. Direct > >> hits are a bit on the rare side. > > > Right. So the "lensing dark stuff" includes most > > of the stars. Yet it is dark. > > Welcome to the conundrum. Well, it is clear that baryonic matter is not excluded, since we know the lion's share of the stars are there. > >> >> 2) Perfect fluid with zero pressure, and no observed > >> >> non-gravitational interactions. > > >> > ... despite them looking for weak interactions... > > >> Read my words carefully. "No observed non-gravitational > >> interactions". > > >> The scattering cross section of a neutrino would fit nicely > >> within cluster merger data sets. > > > But the stars don't, and we can't see them. > > Yeah, we do. Rather clearly, actually. Not in the bullet cluster. At that distance we see "lit gass clouds", not stars. Stars are beneath the imaging threshold > >> >> Yeah, that's really arbitrary. > > >> > Sure seems that way. How do we detect the charge > >> > matter impinging on our heliosheath? > > >> Radio, direct contact with magnetometers. > > >> > Can we do that over lightyears, then megamarsecs, > >> > for stellarsheaths? > > >> If you had a baseline big enough and could distinguish > >> heliopause radio noise from not only the background > >> but from the parent star itself, sure. > > > I'd like to see the stellarsheath of Barnard's star, or > > V385 Carinae... http://www.space.com/scienceastronomy/puffy-star-cosmic-jellyfish-photo-100622.html > > ... how much matter is it plowing through... > > Lots, and the source of it is the star itself. Supergiants spew. Wondering if the "bow wave" can be surveyed to detemine the amount of normal matter encountered. You can see it leaves a trail, but it also has a "hot head", where the stellarsheath encounters the interstellar medium. > >> >> >> Ask particle physics if you want to know the answer. It > >> >> >> is suspected that the particle will interact only via the > >> >> >> weak interaction and gravitation. > > >> >> > It was proposed to only interact via gravitation. Since > >> >> > we keep trying to turn it into "something", we have to > >> >> > rule out the other "three forces". > > >> >> Certainly isn't interacting via E&M or the strong force. > > >> > Lots of things don't interact that way when they are heated > >> > to tens of millions of degrees, and allowed to plow on > >> > through mostly empty space. > > >> Does synchrotron radiation not count? > > > No magnetic fields, for the most part. > > Observationally false. In intergalactic space, or even interstellar space? Observationally true. Strong magnetic sources are rare. > >> Regardless, light scatters like crazy through plasma. > > > Dense plasma, sure. > > *ANY* plasma. There is an obvious cutoff but if you argue > that the density is so tenuous that it doesn't even scatter > radio waves across the 25,000 light years between us and > intergalactic space, you will have a hard time making the > argument that there's *enough* to matter. Particles (ions, free electrons) cannot interact with radio waves. Systems of particles can. A rarefied plasma will "compress" at the passing of a radio wave, but recombination is not likely. > >> That stuff would be shining like a beacon if it were what > >> you thought. I do not know how to make it more clear > >> to you that dark matter can not be ionized gas without > >> beating you to death with an E&M textbook, then a > >> plasma physics textbook for good measure. > > > I provided a link, where hydrogen and O5- plasma was > > undetectable, invisible, until we looked at X-ray absorption. > > How long can you stand in ignorance, and act proud? > > *scratches head* > > Why are you inverting the argument? I've been claiming > all along that plasma absorbs E&M. It isn't as if X-ray > telescopes are 'new' technologies. They *don't* absorb visible, infrared, or radio. So they appear Dark. > You'll note that Chanda X-ray observations were one > of the principle measurements behind the publication > of the bullet cluster. Recombination of very hot ions with their companion free electrons will do that too. > >> >> >> The arbitrary fields crowd can only shrug, or try > >> >> >> to deflect. > > >> >> > Fields of DM... > > >> >> Not even remotely close to the same thing > >> >> conceptually, mathematically, or physically. > >> >> Dark matter is 1 parameter: density. Nothing else. > > >> > Distrtibution, arbitrary. Fit to observed data. How > >> arbitrary! > > >> *rolls eyes* > > > *meaningful comment* > > >> >> [...] > > >> >> > Look at any paper that talks about DM distribution, > >> >> > or even just galactic behaviors. First thing they do > >> >> > is derive a M/L for that galaxy, concentrating at the > >> >> > center, to apply to the rest of the galaxy. They > >> >> > can't see all the matter, so they use this luminosity > >> >> > "yardstick"... > > >> >> The mass-to-light ratio is irrelevant to the argument > >> >> (plus I thought you were using mass-to-length) > >> >> because the _shape_ of the rotation curve is the > >> >> only relevant piece of information when describing > >> >> the generalities of the situation. > > >> > No. The mass is inferred form the luminosity. > > >> Not relevant. Look at the rotation curves. > > > "All normal mass" will produce an identical rotation curve. > > >> The exact value for mass is relevant for quantification > >> but not for describing the gross features of the potential. > > > Without the M/L error, we'd find that there is no > > requirement for CDM. > > Unless we look at globular clusters, gravitational > lensing, virial mass estimates, cluster mergers... All in agreement with normal matter only. > >> > The assumption is as I describe. And the "normal > >> > mass deficit", therefore the "required Dark Matter" > >> > derives form the assumption. > > >> Sure. That's quantification. Now look at the rotation > >> curves that mesh with the observed matter, then what's > >> actually observed. > > > The normal mass curve is established from luminosity. > > The *ROTATION CURVE* is a direct function of distance > from galactic center and speed. You said "observed matter". "Observed matter" is inferred from M/L. > Identification with how much mass is there is model > dependent, but irrelevant to the argument as the curves > speak directly to the enclosed mass. Sure. But you keep pointing to rotation curves as "proof" of DM. It *only* establishes total mass on its own. > > Which is an error. You can generate the exact same > > rotation curve with all normal matter. > > I look forward to the paper that addresses all my concerns. I look forward to the paper that reviews the M/L methodology / assumptions. > >> >> If you want to argue that the assumptions of a > >> >> massive central core and relatively lighter spiral arms > >> >> are wrong, you'll have to do a LOT better than this. > > >> > Vice versa. The central area is swept clear (this we > >> know), > > >> An odd claim given the observational fact that the central > >> core of a galaxy has a higher stellar density than the > >> outer areas. > > >http://iopscience.iop.org/0004-637X/559/1/326/fulltext > > ... Introduction "showed signatures of a single rotating disk with the > > center swept clear of material" > >http://iopscience.iop.org/1538-4357/488/2/L149/975374.text.html > > ... Conclusions. The model of the Milky Way worked if "the ?0.1 pc > > region of the Galaxy, ... is swept clear of gas" > > The scale of a galaxy is confusing you. The milky way is > ~125,000 light years wide. 1 pc - the relevant distance > scale surrounding Sgr. A* - is only 3.2 light yeras. > > When I say 'central core' I mean the luminous portion that > is approximately 1/5 of the surface area of the overall > galaxy. Not the same, not even close. What you say, does not describe what observers do to establish the M/L relationship. > [...] > > >> > So it appears > >> > to require Dark Matter where none is required. The > >> > rotation curves describe the *normal* matter. We > >> > didn't have rotation curves when the M/L method was > >> > devised. > > >> LOOK AT THE ROTATION CURVES. You keep talking > >> as if they don't exist and aren't relevant. > > > The rotation curves define the amount of mass. > > Subject to the modeling assumptions used. No, as you've said, it only defines the amount of mass, but it describes the amount of mass irrespective of modelling assumptions (discounting gravitation and Doppler effects). > > The M/L mistake defines Dark Matter, the rotation > > curve, and microlensing does not. Ask yourself how > > they know how much *normal* matter is in a given > > region of a galaxy? > > Virial theorem, dynamics if a galaxy is bound to another, > gravitational lensing, Tully-Fisher relation. Pick one. *All* I have seen used is M/L. Virial cannot distinguish between normal and Dark matter. Dynamics of bound galaxies, likewise. Gravitational lensing, likewise. Tully-Fisher relation, likewise. .... they describe matter and / or typical energies. > >> >> > For examples: > >> >> >http://www.physics.smu.edu/~kehoe/ugradRes/kv_thesis.pdf > >> >> > ... page 4. > > >> >> Look at the SHAPE OF THE CURVE. That is not > >> >> what is observed. Welcome to mid-20th century > >> >> observational astronomy. > > >> >> Now catch up to the late 20th/21st century by > >> >> learning about gravitational lensing. > > >> > Works for normal mass too. > > >> Normal mass is ruled out. Welcome to late 20th/21st > >> century observational astronomy. > > > You ignored the link. Late 20th. Hydrogen and O5- > > plasma (the "missing normal matter") is invisible > > except by absorption of X-rays from more distant > > quasars. Normal matter, yet Dark. > > What's there to see? Plasma is visible, as is well known. *Not* seen in visible, infrared, microwaves, or radio. Dark for the usual observational purposes. > >> >> You find that the gravitational mass disagrees > >> >> strongly with the visible mass, and coupled with > >> >> cluster mergers we can conclude...? > > >> > That we can't see point light sources, and we can't > >> > see ionized gas (unless it quenches). > > >> Urrrrrr....? We can see point light sources quite fine - > >> we call them stars. > > > OK, then where are the stars in the bullet cluster, the > > ones that didn't get involved in the stellar collision, but > > would be where you mythical Dark Matter is? > > Stars are visible. We don't see stars. Ergo.. Ergo, the stars are there, contibuting to gravitational lensing, but cannot be imaged. Some absorptive media is in between, or the individual stars cannot be imaged. > > Point light sources, something the size of a > > star at that distance... CANNOT be imaged. > > zuh? Correct. > > It depends on dust clouds and other stars > > to be visible. > > An interesting assertion. Just so we are clear, > are you seriously claiming that a star becomes > invisible after a certain point regardless of its' > luminosity? Quasars cannot be imaged. They are too distant. Quasars can be "seen". A few quasars can be "caged" to expected container galaxies. Best we can do. > >> We can also see ionized gas VERY WELL. Open a > >> plasma physics textbook. > > > X-rays. Please quit arguing from ignorance. > > ....and? My point has been rather consistently > that plasma is absorbs E&M. It doesn't, for the usual observational wavelengths. > I've been deliberately vague at what frequency > it does because that's a function of charge density. .... and ionization level. Diamonds (pure) are only able to respond on certain wavelengths, even though they can be observed via their index of refraction. We dont see them, we see *through* them. > >> >> Plus, just for giggles, > >> >http://www.naic.edu/~rminchin/virgohi21.html > > >> > Link thrown twice. See below. > > >> >> >http://www.ifa.hawaii.edu/~barnes/ast626_05/dmdg.pdf > >> >> > ... bottom of page 2. > > >> >> > They do it, because they were taught to do it that way. > > >> >> For fucks sake. This argument is stupid no > >> >> matter how it is invoked. > > >> > No, Eric, it is not. > > >> Yeah, it is. "But that's how you were taught, you don't > >> think!!!" is a rather familiar rallying cry from a large > >> percentage of this newsgroup. > > >> [snip repetitions] > > > Snip the appropriate link, because you'd rather > > argue than think. Let's try it again: > >http://sciencemag.org/cgi/content/abstract/319/5859/55 > > Given the mass-energy budget of the universe is > something like 5% baryonic, Based on? Assuming Dark Energy, you mean. > you can quadruple the amount of baryons in the > universe and still be factor of 4 on top of that short. > > That we may not know the true amount of > matter 'out there' is neither insightful or surprising. > The point is that there _is not enough as far as > we can tell_. The point is, this normal matter is invisible via normal observational means. This is stuff sourced, in part, from galaxies. How much is still in them (or fell into them in the past, given the changing size of the Universe))? It looks like Dark Matter (under normal circumstances), and acts like Dark Matter (gravitationally). > > Ask yourself how they know how much *normal* > > matter is in a given region of a galaxy? > > Obviously you think its' a wild assed guess. No, I think it was a reasonable first approximation, when it was not possible to measure rotation rates. > Saying the assumptions used by cosmology are > all wrong is easy - anyone can, and does, do that. What *scientists* are, Eric? We are *supposed* to challenge the fundamentals, the assumptions. DM arises *entirely* from this one, M/ L. > Saying modern cosmology is 'all wrong', but what > is not nearly as easy is making a coherent and > rational argument as to why. I have been both. > I know you think ionized matter can do it. I see > your opinion is apparently validated by the > discovery of 'hidden' plasma with X-ray telescopes. > But that's simply not enough. It is enough to ask. It is not addressed in older assumptions. Nor is the temperature of central stars, vs. the cooler (on average) outer stars (high luminosity center vs. relatively low luminosity outer). Nor is perhaps swept central regions vs. massive collections of observed / observable normal matter (dust lanes, rims of spiral galaxies). They just measure a characteristic wavelength emitted from a region of space, and infer normal mass from it. Period. Brainless. Not worth further mention. Assumed valid, and published with each new paper. > Look carefully at the bullet cluster picture. See > the bow shock from the ionized normal matter? > Why doesn't your solution for dark matter interact > with that? It was left behind, along with the stars that *did* "splash". > You need to apply the known rules of physical reality > consistently, not selectively. Yes. *We* do. You are so smug with your flinging of DM as an answer, and it is not at all clear to me that it is anything except a *wrong* answer. I don't expect an answer. We cannot agree right now. No point in dragging this out, as I seem to have run you out of links, and I cannot point to a paper that someone has published, that I might be parrotting to you. David A. Smith
From: eric gisse on 23 Jun 2010 21:28 Yousuf Khan wrote: [...] >> Define what dark matter 'should' predict here. > > Quite simple really, Dark Matter should predict all of the Dark Matter > remains attached to only the galaxies in the cluster, it should go > nowhere else -- ever. Wrong. Dark matter will keep going through a shock while the baryonic matter is slowed down. That's what was seen in the bullet cluster, if you actually look at the picture. [....]
From: eric gisse on 23 Jun 2010 22:14
Yousuf Khan wrote: > On 6/22/2010 2:04 AM, eric gisse wrote: >> Yousuf Khan wrote: >>> The universe has precipitated down to all of the physics we see below 1 >>> TeV, which we now call the Standard Model, because that's all we >>> encounter in normal life these days. What makes you think that anything >>> that was created above 1 TeV is stable enough to survive into the >>> low-energy universe we have now, when everything else has decayed down >>> to the Standard Model? >> >> What makes you think that we see everything? > > (1) Because the heavier the particles are, the less stable they are. A trend that may or may not continue indefinitely, you do not know. > The > heaviest particle we've discovered so far, the Top quark, doesn't even > last long enough to form Strong force bonds before it decays into > something else: it's the only quark that's seen alone, not paired up > with another quark into hadrons of some kind. That's pretty much the > general case as we go up the mass scale in everything we see. > > and, > > (2) TeV physics isn't really TeV physics. We're just cranking up > accelerators to create bigger and bigger junk piles, so we can sort > through the rubbish to find smaller and smaller pearls. Accelerators > always had to have more power than the particles they were intended to > find, but now we have a 7 TeV accelerator (LHC) which is entirely > devoted to finding a particle, the Higgs, that may end up weighing less > than 200 GeV, if it's ever found at all. That's a 35:1 signal-to-noise > ratio. The particles themselves are in the realm of GeV, not TeV. It's > TeV junk piles to find GeV physics. Woah. You clearly don't know what you are talking about with that utterance. > >>>> 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. >>> >>> The only thing I've seen described as having negative energy is the >>> vacuum inside Casimir Effect plates, not standard space vacuum. >> >> "vacuum" and "vacuum energy" not the same thing. > > Read what I said again, negative energy is only inside a Casimir Effect > vacuum, not a standard vacuum. Until you understand the difference > between those types of vacuums, the rest of what you say is drivel. Once again, reading for comprehension is important. The negative energy density is there whether or not the plates are. > >>> What's >>> your source for negative energy inside a regular vacuum? >> >> Vacuum energy. Remember how I mentioned absolute amounts of energy >> gravitating instead of just the relative amounts like in Newton? > > How irrelevant are you trying to be? Newton's laws treat a vacuum as > having absolutely zero energy. Who mentioned anything about Newton here > anyways? You, implicitly, by pretending energy density doesn't gravitate. > > What you have to understand is that not all vacuums throughout the > universe are necessarily the same. Some volumes of vacuums may have more > energy than others, even if they have the exact same amount of matter > inside them (i.e. absolutely none). They are affected by their proximity > to other areas of space where there is lots of matter. The matter > energizes the closer vacuums, more than the further vacuums. > > The entire term "vacuum" only refers to the mass density of a volume of > space, not its energy density. We'll have to start eventually finding a > way to measure energy densities separately from mass densities, and > start referring to "mass vacuums" vs. "energy vacuums" separately. Oorrrr we could go with the term 'vacuum' as it is relevant to GR which happens to mean 'no non-gravitational contributions to the stress tensor'. Obviously that doesn't touch quantum vacuum. [snip rest] |