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Senovilla's Slowing Time Theory

  1. Dec 26, 2007 #1
    I just saw this in New Scientist:

    "...we are fooled into thinking that the expansion of the universe is accelerating, because time itself is slowing down. "

    First let me say I'm an amateur so I'm just throwing out things that occur to me about this. I'm wondering if someone with more experience could shed some light on it.

    This brings to mind time dilation, speed of light, black holes, etc. Acceleration and gravitational fields also slow time. Is there any connection? Perhaps time dilation is not an effect but a cause. If you accelerate, your time slows....but what if it's the reverse and you actually accelerate because you are slowing your time? What if gravitational fields are created by slowing time instead of the reverse?
  2. jcsd
  3. Dec 27, 2007 #2
    I believe that you have touched on an important symmetry that I have been thinking about for some time now. A symmetry between cause and effect; and to play off of this symmetry idea, but thinking about space instead of time, what if instead of matter causing space to warp, it was actually the warping of space that creates the illusion of matter. I believe that a concept is not complete if the same scenario can be described by two different explanations (such as the incompleteness of the electric and magnetic force being separate). I view these redundancies as a lack of understanding in a phenomenon.
  4. Dec 29, 2007 #3
    Even if universal slowing of time is causing the illusion of acceleration of movement, doesn't Senovilla need to posit the presence of dark energy or dark matter to explain why time is slowing in the first place? Or does he think the gradual slowing of time is a natural property of time that does not require the input of energy, motion, or gravitational fields ("time-fatigue?").
  5. Dec 29, 2007 #4
    I'm bothered that I'm only seeing this reported in "pop science" outlets like new scientist, wired etc. and no where else. If there's any real discussion of this in a specific, scientific manner, or like a paper on the Arxiv or something, I've not seen it.

    As I understand the vague discussions I've seen in those pop science writeups, there actually does seem to be some interesting potential there-- the really interesting part isn't the "time is slowing down" part, but that he's found a way to explain the acceleration of dark energy in terms of brane dynamics and M-theory. If he actually has some kind of brane model that has the features he describes, this seems to me like a noteworthy step forward for M-theory because it would mean someone got a unique and testable (though probably not falsifiable) prediction out of M-theory, to an extent that as far as I'm aware no M-theory model has done before. But I don't know if he's actually implemented any such "time is slowing down and this explains dark energy acceleration" model, or if he just made some kind of offhanded "hey, wouldn't it be cool if we could..." comment to a reporter and then it got repeated by a bunch of newspapers who don't know how to evaluate how to evaluate science but do think time slowing down "sounds interesting".
  6. Dec 29, 2007 #5


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    Accelerating expansion and change of signature
    Marc Mars, José M. M. Senovilla, Raül Vera
    4 pages. To appear in the proceedings of the Spanish Relativity Meeting ERE'07
    (Submitted on 10 Dec 2007)

    "We show that some types of sudden singularities admit a natural explanation in terms of regular changes of signature on brane-worlds in AdS5. The present accelerated expansion of the Universe and its possible ending at a sudden singularity may therefore simply be an indication that our braneworld is about to change its Lorentzian signature to an Euclidean one, while remaining fully regular. An explicit example of this behaviour satisfying the weak and strong energy conditions is presented."

    Here is the article mentioned in NewSci referenced in the O.P. (to be published in Physical Review D)

    Is the accelerated expansion evidence of a forthcoming change of signature on the brane?
    Marc Mars, José M. M. Senovilla, Raül Vera
    5 pages, 1 figure. To be published in PRD
    (Submitted on 3 Oct 2007, last revised 29 Nov 2007)

    "We show that regular changes of signature on brane-worlds in AdS bulks may account for some types of the recently fashionable sudden singularities. Therefore, the possibility that the Universe seems to approach a future sudden singularity at an accelerated rate of expansion might simply be an indication that our braneworld is about to change from Lorentzian to Euclidean signature. Both the brane and the bulk remain fully regular everywhere. We present a model in which the weak and strong energy conditions hold on the brane, in contrast with the standard cosmologies leading to the analogous kinematical behaviour (that is, with a diverging Hubble factor)."

    I don't mean to suggest anyone read the papers, just that if anyone is curious about what he might mean by "time slowing down" (in talking to the journalist) the answer would probably be in one of the equations here---changing ratios of different time measures (tau, capital T ...).

    Senovilla has some 50 papers some of which (on other topics) have been well received with 50-60 cites. But this stuff does not seem to have generated much interest so far.

    It sounds a bit elaborate and fantastic to me personally. I'm still on the lookout for simpler explanations of quickening expansion----involving just this universe and these known dimensions. There have been some proposed.
    Last edited: Dec 29, 2007
  7. Dec 29, 2007 #6
    Marcus, wow, thanks! That is really helpful.

    Hm, so some questions:

    1. So "switching to euclidean signature" (i.e., our one timelike dimension becoming spacelike?) in the paper is expressing the same thing as "time slowing down so much it stops" in the pop-sci articles, right?

    2. The papers seem to stress that their brane model for dark energy expansion is based around the near approach of a "sudden singularity" (which I take to be the point at which we "switch to a euclidean signature"?). Does this mean that if the curve of dark energy acceleration does NOT end at a sudden singularity, then Senovilla et al's hypothesis cannot apply?

    3. What is this "sudden singularity", anyway? Is it the same thing as the "big rip"?

    Probably so! It seems like this is not nearly a major enough thing to justify by itself a belief in the existence of braneworlds/extra dimensions. Nevertheless I imagine if one had already adopted the braneworld hypothesis for other reasons, then Senovilla et al's idea about slowing time would become very attractive?
  8. Jan 31, 2008 #7
    Slowing of time can expalin acclerating expansion as we look from our slower time into the past distant era of faster time. However there is no need to look for exotic phenomenon. First step is to understand what is time and what causes time, then we may progress towards understand why time may be slowing. For details on this new concept visit:

  9. Feb 10, 2008 #8
    for me this kind of things are clearly made by 'cranks' in the same fashion that we are supposed to live in a 11-dimensional Universe, i do not know what was the referee thinking when publishing such a paper.
  10. May 30, 2009 #9
    The acceleration (not slowing) of time would more sensibly and simply account for the apparent expansion of the universe. Light emitted long ago under a slower universal clock would appear to be of a longer wavelength under todays faster universal clock. This would eliminate the need for a "placeholder" such as dark matter or dark energy. It would also eliminate the need for a "big bang".
    Time being massless requires no energy to accelerate, and so the laws of thermodynamics are preserved.
  11. May 30, 2009 #10
    So it appears that in the time since this thread was made the second paper marcus links above was published, in early 2008, in Phys Rev D and Phys Lett B. There don't seem to be any further developments on this front since then.

    Looking around to see if there had been any such developments I did discover something interesting I hadn't noticed before. The three people responsible for this theory actually first published on signature change in branes in 2001. (I also find an arxiv submission from about that time in which someone cites Mars-et-al's discovery of signature change as an argument against accepting brane cosmology, on the grounds that the author could not see any physically realistic interpretation of such a thing!) It appears that what they did in 2007-2008 was actually only to take their existing ideas of signature change in branes and apply these ideas to the practical idea of explaining the "dark energy" observation.

    I hope we hear more from these people eventually, it seems like the braneworld would be a lot more compelling if string theorists could start taking some of these "ridiculous" consequences of the brane cosmology and perhaps identify, as Mars et al did, how some of these consequences could actually be useful in explaining real-world phenomena...
  12. Jul 25, 2009 #11
    This makes no sense.

    If "time itself" really is slowing down - as Senovilla suggests - then it would have no effect: objects would move slower, but any measuring device (such as a clock) would also run slower by an equal amount. Nothing would change! For example, let's say we timed a runner taking 10 seconds to run 100 metres - then time slows down and we time him again. The runner would run twice as slowly, but our clock would also be running twice as slowly, so the runner would again complete the distance in 10 measured seconds - nothing would change! So if "time itself" speeds up or slows down it has no effect. Even our thought processes would slow down by an equivalent amount - we would notice no difference.

    So if "time itself" was running faster in the past, we would notice absolutely no difference.

    Senovilla is in fact talking about the speed of light - and not "time itself".

    What Senovilla appears to be suggesting, in fact, is that the speed of light is slowing down (not time slowing down) so distant objects are not as far away as we think they are (so we falsely imagine the universe is accelerating), and then - as Skypunter suggests in his post above - that would have the effect of red-shifting the light from those distant stars.
    Last edited: Jul 25, 2009
  13. Aug 8, 2009 #12
    I understand what you are saying. However, say we were in the time reference of your second race, but were watching the first race. Yes, at the instant they happened both took 10 seconds to run 100 meters, but we are actually looking at the past the further we look since the speed of light is constant, so the first runner would appear to move faster than 10m/s. You are right, we certainly wouldn't notice it, but looking further into space, ie back in time, we would see how fast time was "running." Consequentially, he is talking about time slowing, not light. The way I interpret it, Senovilla is basically saying that what we are seeing far away is in "fast forward," so time must be slowing down. However, from what I've read and from my limited understanding, this doesn't account for more "local" affects, such as the high acceleration of galaxies. I hear they are publishing a paper in late '09, so that should be interesting to read.
  14. Aug 8, 2009 #13
    Hi Mike, yes, you've pointed out the flaw in my argument! You're quite right if we're in our present-day frame of reference and we measure the time between two events in the distant speeded-up past then we will indeed see that time has slowed down. Good point.

    However ... we're not measuring time between two events to find how quickly those distant galaxies are receding - we're measuring a length: the redshifted wavelength of light from those galaxies. And that length we measure will be unaffected when we look back into that speeded-up past - all measured lengths would be unaffected by time speeding-up. The only dimension being modified is time, and that is completely independent of length.

    Considering light emitted by those galaxies, Wavelength = speed / frequency. If speed and frequency are both doubled (twice as fast), the wavelength is unaltered.

    Basically, if we could look into the past we would see everything happening twice as fast - people running around twice as fast (as you suggest) - but the scene would "look OK": no lengths would appear to be distorted, and the colours would be correct. The wavelength of light from the scene would not be redshifted.

    So if the Hubble telescope could just sit there and watch those distant galaxies receding then it would indeed see accelerating galaxies as you suggest - everything speeded-up. That is what Senovilla appears to be suggesting. However, Hubble (and therefore we humans) can't do that. Hubble just has to take an instantaneous photograph and look at the redshifting. So Senovilla's theory cannot explain the apparent accelerating universe which we detect from our Hubble evidence.

    That's what I reckon anyway. We would not detect any redshifting due purely to time speeding-up. Any redshifting would have to be caused by genuine physical acceleration. I might well be confused - it's very mind-bending stuff.

    I had a look a Senovilla's paper - not easy reading, basically saying that cosmic time is slowing down and will disappear due to it curving round and becoming Euclidean - like in the No Bounday proposal:


    His account here is clearer.

    No, considering Wavelength = speed / frequency, the frequency would be halved in the past as you suggest, but the speed of light in the past would also be halved (everything is affected if "time itself" slows down - even the speed of light!). So the measured wavelength would be unaltered.
    Last edited: Aug 9, 2009
  15. Aug 9, 2009 #14
    So if "time itself" was running faster in the past, we would notice absolutely no difference
    I suggested that time was accellerating, not slowing down. The only evidence is red shift. Otherwise it is unnoticable because it is a universal accelleration whic could have been happenning forever and could continue to happen forever.
  16. Aug 10, 2009 #15


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    If he assumes that the speed of light is still constant at all frames, we would have to assume that space is expanding in order to conteract the superluminal effects we'd otherwise see at great distances. That is, we have to go faster to see things at "normal" speed.

    With higher density of matter, we see time slowing down even more, but not really at the same rates. With these 2 variables, one can come up with a very dynamical picture of the expansion of space. I guess you can make tricks to come up to explain the speeding up of the expansion of the univer and inflation.

    You'd have not general relaitivity anymore, but a theory in 5 dimensions, with 2 times. One that is a clock, like in GR, and other, that is a mix of clock and a rule, that is, measure in the fith dimension, the distance from any point to the initial singularity, in a 5th dimension which one can embed general relativity.

    To tell you the truth, I am not sure if there would be necessary just 1 more dimension, because if it's not GR, I am not sure how many euclidean dimensions one would need to embed general relativity. Or depending on the theory, if these extra dimensions would be curved or not.

    But anyway, 2 more time dimensions are necessary. It is better to study Itzhak Bars 2T physics. This is cool, because, he is a very respected theorist on the mainstream, and also has very unorthodox thinking.
    Last edited: Aug 10, 2009
  17. Aug 20, 2009 #16
    But if C is slowing down it works very well.
  18. Aug 21, 2009 #17
    Even if that were the case, there IS reason to consider such ideas: Out of the box thinking, even if incorrect, might lead to other considerations which do bear fruit and might provide a different perspective on existing problems. Maybe analogous to "greenlight" brainstorming where all ideas are listed and even other people's misinterpretations might lead somewhere. You are not obligated to accept "pop science" nor standard thoeries either....Maxwell rejected conventional thinking...so did Einstein....and on and on and on....

    I think in was Richard Feynmann said something to the effect that a good physicst is one who keeps producing bad ideas but has the tenacity to keep going until a good idea finally emerges....

    Even science fiction writing over the years has been an odd predictor of many subsequent scientific developments ....Asimov to name one...
  19. Aug 21, 2009 #18


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    Slowing of time begs the question "slowing relative to what" The principle comparison we can make is to spatial distances in the unified "space-time" and so "slowing time" and "lengthening space" become equivalent. "Slowing time" doesn't "explain" anything it just recasts the same issue in a different language.

    In more detail, to say "time is slowing" one would have to essentially compare a duration between pairs of events to something nearby. All that is near-by are distance intervals. So one is talking about seeing how objects boost in the region or effectively how the speed of light is changing in the region. We now define the speed of light as a mathematical constant and not a physical one because we use time of flight for light in vacuum to define distances in terms of durations. Invoking "time slowing down" is breaking that convention i.e. invoking a varying (over time) speed of light. Re-asserting this convention gets you back to "expanding space" vs. "contracting time".

    But this also brings up an issue I have with "hyper acceleration" and "expanding universe" since one is now talking about choosing a particular way of slicing up the space-time universe into spatial cross sections. I don't believe all of these assertions about dark energy have been parsed to see if they are really manifestations of a choice of "slicing". For example if you look at deSitter space-time "right" (one extends one's own spatial axies out geodesically) you see each observer at any space-time point will see a spatial universe of the same size. But if you take the traditional hyperbolic embedding and just naively slice it along the T axis you get the "contracting and expanding" set of spatial universes. I even have a half finished paper I was typing up "The Appearance of spatially separated events in deSitter Space-Time"

    I think you get somthing similar happening in the FRW models. It is not always appropriate to talk about a global t for which one speaks of R(t) being the radius of "the spatial universe" at time t, at least not without substantial qualification about choices of frame and realtivity.
  20. Aug 21, 2009 #19
    A very interesting paper and discussion.

    Because we have so many mathematical models and only one universe to test them in, the one we occupy, its not a surprise that most models don't fit...that is, they may be mathematically consistent but fail experimental testing.

    And that always makes one think about a multiverse. If such exists then virtually all models fit somewhere in the past, present or future!

    After all, it took about 20 years for scientists of the day to finally conclude that Maxwell's equations and Lorentz tranforms were correct, Newton and Galeli transforms were not. Likely most theoretical physicsts, being human, are rather uncomfortable with ideas that conflict with what they were taught in school; hence learning rather studying is preeminent. Even one of Einsteins professors just could not bring himself to teach the "new" Maxwell's equations which was very upsetting to Einstein.

    And "What is this "sudden singularity", anyway? Is it the same thing as the "big rip"?" is something I was puzzeling over as well....things appear "continuous" in the paper, and some models do retain such properties....
    Last edited: Aug 21, 2009
  21. Aug 21, 2009 #20
    Imagine light cones (which are usually drawn at 45 degrees) becoming narrower and narrower (the same metric is when you approach singularity in the black hole)

    From birds perspective, worldlines of 2 objects can be straignt lines. But, as lightcones become narrower and narrower, observers inside conclude that they are accelerating away from each other.

    They experience tidal forces. So yes, for the internal observer it looks exactly as big rip. After it we get 'frozen' 4-dimensional euclidean space. (the word 'after' is not correct, as that part of the universe does not have time... From that SIDE of the universe... )
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