Is there anything faster than light?

Discussion in 'Physics & Math' started by darksidZz, Apr 6, 2016.

  1. paddoboy Valued Senior Member

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    You were totally demolished in the "cosmological redshift" thread on that issue.
    What's your answer? God?...which God?

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    Spacetime can be said to be expanding, yes. Why? We do not really know...DE? CC? ZPE?
    What's your answer? God again?

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    When exactly does expansion overcome gravity? Now that's a good question.......I don't really know. Perhaps there is some mathematical solution to that, I'm not sure. The point is though that our local group of galaxies and even beyond, is gravitationally bound and overcomes the overall large scale expansion.
    And it's spacetime, that expands, not space.
    "The views of space and time which I wish to lay before you have sprung from the soil of experimental physics, and therein lies their strength. They are radical. Henceforth space by itself, and time by itself, are doomed to fade away into mere shadows, and only a kind of union of the two will preserve an independent reality."
    Herman Minkowski

    And of course as origin has said just above, the expansion of spacetime is a result of GR: GR works and works fine,eg: GP-B, and aLIGO attest to that fact.
    To deny the obvious, is well, rather strange shall we say.

    And of course as I'm fond of telling you, it is your right to sprout whatever nonsense you see fit, and it is your right to avoid any pertinent questions anyone puts to you, but irrespective of all that, academia and mainstream remain as robust as ever. You do understand you make no difference with your nonsense, right?
     
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  3. danshawen Valued Senior Member

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    Because GR subsumes SR and SR PROHIBITS VELOCITIES > c.

    If absolute space or absolute time crept back into GR, it will need to be forcibly removed. "Curvature" of space is absolute space. Space has no inertia. Space is time. The geometry of light travel time is not Euclidean, and not a static vector space.

    It's exactly the same situation that someone else here wanted to start with assuming the results of GR and then go on to extend it to an augmented theory about the luminiferous aether, rejected as a theory of anything since 1905. Whenever you do something like copying a theory into another, then either all of the base assumptions must remain intact, or else, for the sake of consistency, you must begin again from scratch.
     
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  5. paddoboy Valued Senior Member

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    It prohibits velocities >"c" for anything with mass: Spacetime has no mass.NOTE: Spacetime, not space.
    Wow!!!!, I mean WOW!!!!!!!!!

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    Pseudoscientific word salad at its best!
     
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  7. Schneibster Registered Member

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    First, I posted while I was waking up, always a mistake- I was a little slow. And as a result, second, I didn't realize you were responding to someone whose posts I can't see. I realized later that the rest of your post was directed to another individual.
    Mmmmm, I don't think that GRT says what gravity actually is; just what it does. To have a theory that says what gravity is, I think we need a quantum gravity theory.

    I would say Strassler is right. If Higgs theory is correct, then particles gain inertial mass through interacting with the global Higgs field. GRT in this view doesn't act on mass; it acts on energy, and this view is supported by the fact that it acts on photons. Gravity, then, isn't acting on the mass of particles, but on their energy, and so is the Higgs. And this is the reason that inertial mass tracks so well with gravitational mass; both are dependent upon the energy of the particle. I also wouldn't say Strassler is trashing relativity. He's just noting an obvious fact; the equivalence principle is true (and remember it's only exactly true in a limit, in which a uniform gravity field (a physical impossibility) is present) because both gravity, which gives particles gravitational mass, and the field, the Higgs field, that gives particles inertial mass both act on particles' energy. It is therefore an unfortunate legacy of our world view that causes us to equate them.

    Does that make sense?

    But you see, relativity says precisely that one of the big differences between motion according to the scalar curvature term (ordinary motion) and according to the cosmological term (universal expansion, if the cosmological constant is positive, see de Sitter space) is that motion greater than c relative to any frame is not possible for the scalar curvature term, but is possible for recession due to the cosmological term. This is what is trying to be described with this "stretching" analogy (which as DaveC points out, fails, it's better to talk about space increasing).

    We can then see the c limit as being relative to local spacetime, and we can define local spacetime precisely because spacetime is real, as it produces the real phenomenon of angular acceleration due to rotation (among other things, such as vacuum fluctuations/zero point energy/cosmological constant, and the Higgs field, not to mention gravity). And therefore it is not unreasonable to expect to be able to see things happen to spacetime like curvature; but stretching is a bad analogy. It expands. See again de Sitter space.

    You must always remember that when you talk about "relativity" you are talking about GRT, which subsumes SRT as a limit case when spacetime curvature is zero. They are the same theory; historically Einstein discovered SRT first, then went about adding gravity and accelerated frames to it, resulting in GRT. SRT therefore does not have curvature of space because the limit case in which SRT is exactly true is the limit of zero curvature.

    Be careful you don't wind up thinking you see relativity deniers everywhere! And use the ignore button a little more. DNFTT.
     
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  8. Schneibster Registered Member

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    Well, technically it can be static if it's exactly flat, but you're correct in that it would be a very unlikely state of affairs, requiring the omega due to mass to be exactly counterbalanced by just the right omega due to cosmological constant. In our universe at this time, omega overall is mostly cosmological constant, with only a bit due to mass. And the omega due to cosmological constant is increasing due to the expansion of space. It's a positive feedback. That's why the universe's expansion started accelerating when it was about half as old as it is now; the added space added more cosmological constant which added more space faster which added cosmological constant faster...
     
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  9. DaveC426913 Valued Senior Member

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    It prohibits local velocities greater than c. Any sufficiently accurate description of SR (including wiki) will include that proviso:

    https://en.wikipedia.org/wiki/Metric_expansion_of_space

    (Fun fact : did you know that when someone quotes someone else, they can omit the Username identifier data, causing it to bypass the ignore-filter? This means that everyone can benefit from the included wisdom - without an author needing to be attached to it.)
     
    Last edited: Apr 15, 2016
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  10. Schneibster Registered Member

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    DaveC posted the Wikipedia article on Metric Expansion of Space, and it says:

    I am still quibbling back and forth with DaveC over whether spacetime is a "real thing" or not, but we definitely agree on this. As in my previous post, I will point out that SRT is the case of GRT where the term that deals with universal expansion is zero. And SRT is only exactly correct in such a case, and therefore in a universe that is not expanding.

    It's not absolute spacetime. Spacetime varies, and it can do so without running into limits on mass and energy, because it is not mass or energy. Spacetime is affected by the presence of fields; otherwise how would the field get from here to there? There's another way we can tell even though it is not mass, and is not energy, it's a real thing in and of itself, beyond rotation and consequent angular acceleration.

    Spacetime is not aether, and does not act like it: photons propagate just like any other particle does. When we talk about light as a wave, it is only a mathematical analogy; what it really is is a self-sustaining oscillation in spacetime of the virtual background, just like any field and just like a propagating wave in any field. But spacetime is not the field; it's not what's "doing the waving." And so no, the idea that spacetime either requires or is any sort of "luminiferous aether" is not sustainable; if anything is "like" "luminiferous aether," it is the disturbance in the vacuum fluctuations.

    And SRT is not "copied into" GRT, it's a limit case of GRT where the spacetime curvature is zero. GRT is rather an extension of SRT to describe what happens when the spacetime curvature is not zero. Because GRT extends SRT, an addition must be made to the finiteness and maximality of c postulate: the speed of light is finite and maximal for local motion.
     
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  11. QuarkHead Remedial Math Student Valued Senior Member

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    This is logically back-to-front. The Special Theory "works" only if one assumes that light speed is a universal speed limit - you may not argue this backwards.

    It might be worth pointing out that a point in spacetime is an "event" (in the usual sense of the word). Two such events - spacetime points - cannot be connected by any sort of "travel" in the usual sense of the word.

    However, it is possible (according to the General Theory) to define a coordinate-invariant spacetime interval \(s\) by \(ds^2 = \sum\nolimits_{jk}g_{jk}dx^j dx^k\) (where the indices on the coordinates functions are 0, 1, 2, 3) . So if you want this interval to remain invariant while spacetime is expanding, the solution is simple - allow the coefficient \(g_{jk}\) to change proportionately.

    This is elementary. It merely states that in expanding space time, the metric field is not constant, even in the absence of a gravitational source.
     
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  12. Schneibster Registered Member

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    Mmmm, one can connect two events in spacetime by the propagation of a particle if they are not at a spacelike interval. And if they are at a spacelike interval they still can be connected by entanglement. So I'm not sure this is exactly true except in SRT, and even then except for spacelike intervals.

    And a varying metric field is a gravity field, as we identify it. It doesn't matter whether the non-constant metric field is associated with a scalar curvature (second term of the left side of the EFE) or a cosmological constant (third term). It still has the same effect on the stress-energy tensor. Agreed.
     
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  13. Schneibster Registered Member

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    I should note that it is for this part I liked your post.

    I disagree. It is incorrect, but it is not word salad.

    danshawen merely lacks knowledge, a situation easily remediated once he can be convinced that what he's being told is consistent with what he already knows. His conclusions are reasonable given what he's been told; he just hasn't been told enough of it yet.
     
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  14. paddoboy Valued Senior Member

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    He's been told plenty, but ignores.
    Actually even though he has me on ignore, I have a soft spot for him and see him as the best of a bad bunch.
    [That may appear to be a back handed compliment

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  15. danshawen Valued Senior Member

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    I do not lack knowledge. I simply realized that some of the the "knowledge" imparted to me is flawed and inconsistent in the extreme. Evidently, the flaws were not noticed by anyone else and the result is a real fruit salad of strange ideas that attack the heart and soul of relativity based on nothing but a determination that we know all we need to know about dark energy and universe expansion based on a single number; the cosmological constant.

    I don't think that evidence for space stretching is nearly strong enough to throw out all of the most fundamental assumptions of relativity. If the speed of light varied even slightly at cosmological distances from us, it would vary slightly here also. What do you think the cosmologically distant red shifted galaxies see when they look in our direction? The same thing that we do. Our own sky would be illuminated by Cherenkov radiation because we ourselves are traveling FTL. It isn't. Go figure. It probably isn't happening 13 billion light yeas away from us either. If it occurred in one frame and not the other, that would be a preferred reference frame, and isn't allowed by SR. I think I have effectively attacked the idea from at least half a dozen directions now, without a single salient refutation from anyone for any of them.

    I am about as likely to believe that stretching space is a worthy idea as I am to repudiate a belief in the veracity of the fossil record and the theory of evolution, and for the same basic reasons. Stretching of space is popular with YECs because scripture was found that seems to support it. This is simply not how science is done if you are doing it correctly.

    Your objections are well noted. As I said before, you don't need to agree with me. Most of your arguments are hard to ignore, but I will take exception to this one, if you don't mind.

    You can readily see what certain members of the forum think about my rejection of something so close to the heart of their mainstream cosmology, and I really don't care what any of them think because if they think at all, they are very bad at it.
     
    Last edited: Apr 16, 2016
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  16. Schneibster Registered Member

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    Then explain the redshifts. Because that's exactly what CC does.

    It's peculiar to refer to "relativity" and only accept half of it. And even moreso to talk about "relativity" when you only mean half of it.

    There's no need to believe that the speed of light varies in order to accept CC. Nor GRT.

    Recession of distant galaxies FTL isn't "motion" or "traveling."

    It's not "stretching of space." That's only an analogy, and not a very good one.

    That's OK, you have to think it through and figure out where you made a mistake. That takes a while.
     
  17. paddoboy Valued Senior Member

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    And they probably do not give a rat's arse as to what you think and believe, and more importantly academia and mainstream cosmology are totally oblivious to your claims: Go figure.

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  18. danshawen Valued Senior Member

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    I don't need to believe that cosmologically distant galaxies have "traveled a bit further" than they could have done at sublight speeds simply because they are extreme red shifted. They are only as far away as they appear to be.

    In the 20th century in which it was discovered, the Hubble constant was NEVER BELIEVED to be something that could be extrapolated indefinitely off the far end of the graph paper, so why is it believed to predict FTL expansion now? I am speaking from direct experience with the best known cosmology back then. Much of it has not changed very much. Some that has changed is wrong.

    It doesn't matter how big a slice of the pie chart the dark energy is. NO AMOUNT of energy from any source within or without can accelerate even the tiniest chunk of matter or minuscule measure of energy FTL.
     
  19. Schneibster Registered Member

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    So how come the farther away they are, the higher their redshift? And how come all the neutral hydrogen in the space around them isn't reacting with them in ways we don't see around here?

    The Hubble constant is a rate of change of redshift over distance; Type 1a supernova data indicates that it has changed over time, but no data indicate it needs to be "extrapolated indefinitely off the far end of the graph paper."

    That's right; "dark energy" is another analogy. It's cosmological constant, and no acceleration is required, just enough space between here and there.
     
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  20. Farsight

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    It does. It varies in the room you're in. If it didn't, your pencil wouldn't fall down. See the second paragraph below, it's from the Einstein digital papers:

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    There is a preferred reference frame of sorts, the CMB reference frame. You can use this to gauge your speed through the universe. See Wikipedia:

    "From the CMB data it is seen that the Local Group (the galaxy group that includes the Milky Way galaxy) appears to be moving at 627±22 km/s relative to the reference frame of the CMB (also called the CMB rest frame, or the frame of reference in which there is no motion through the CMB) in the direction of galactic longitude l = 276°±3°, b = 30°±3°.[84][85] This motion results in an anisotropy of the data (CMB appearing slightly warmer in the direction of movement than in the opposite direction).[86] From a theoretical point of view, the existence of a CMB rest frame breaks Lorentz invariance even in empty space far away from any galaxy.[87][88] The standard interpretation of this temperature variation is a simple velocity red shift and blue shift due to motion relative to the CMB, can explain some fraction of the observed dipole temperature distribution in the CMB[89]."

    The problem is Dan, that a lot of people have a popscience misunderstanding of relativity, and they think it's mainstream. IMHO when you gain the correct understanding of relativity by reading the Einstein digital papers, expanding space isn't strange at all.
     
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  21. Q-reeus Valued Senior Member

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    I agree with those who consider Wikipedia a generally reliable - BUT far from infallible resource. In this case, note there is a link in third line of above quoted para to:
    https://en.wikipedia.org/wiki/Lorentz_invariance
    Digging further there, the very last para under sub-heading Lorentz violating models at https://en.wikipedia.org/wiki/Lorentz_covariance#Lorentz_violating_models states:
    Which basically collapses all the earlier statements in that and initially quoted Wkipedia article claiming 'violation of Lorentz invariance' via CMBR as reference.
    One needs to be sharp and objective when borrowing thought bubbles.
     
  22. river

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    Anti-gravity
     
  23. danshawen Valued Senior Member

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    That's just the movement of galaxies of the local group due to the Great Attractor, which a new member has pointed out in another thread. It is the cause of the CMBR dipole, and like any other kind of relative motion, is relativistic.

    I don't object to the idea of universe expansion due to the cosmological constant other than the YEC idea that such expansion has meaning for space itself and is FTL.

    Lots of places are inaccessible even at light speed. It is not important to me tha a G-d be able to access them.
     
    Last edited: Apr 17, 2016

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