Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Dark Energy as Gravitational Tidal forces?

Tags:
  1. Jan 18, 2014 #1
    I’ve read a bunch of post about how the universe does not exist inside, nor is, a black-hole.

    Still, for my question I would like to assume the universe exists within an event horizon (actually highly curved space-time, that locally, appears flat), and has a massive singularity at the “central” event (in the inevitable future). (With this additional specificity I’m trying, probably unsuccessfully, to get around the arguments listed in this faq: https://www.physicsforums.com/showthread.php?t=506992 [Broken])

    Considering that the radial dimension (“distance” to central-singularity) may indeed be our time dimension (as we free-fall towards the central event, we experience the passage of time), this makes me ask a few obvious questions, but I can’t seem to find the answers out there.

    Would radial (time dimension) tidal forces fit with the measured accelerated expansion of the universe, a.k.a dark energy? (In other words, is the central singularity, which would be the source of dark energy, rather than pulling the universe apart in space, is pulling it apart in time?)

    Would longitudinal (spatial) tidal forces fit with dark-matter measurements? (object’s close to each other, appear to get pulled towards each other as they fall towards the singularity which is directly between them spatially, but in the future.)

    Would spaghettification fit with/account for the “smoothness” we observe in the distribution of energy and matter in the universe?

    Would the mathematical description of the event horizon (possibly as a 3-brane), as experienced locally, fit with the mathematical models of the big bang?
     
    Last edited by a moderator: May 6, 2017
  2. jcsd
  3. Jan 19, 2014 #2

    Drakkith

    User Avatar

    Staff: Mentor

    I don't believe any of your ideas would work.

    Nearly flat spacetime seems to be the very opposite of "highly curved".

    While a singularity may exist in our future, I'm not sure it quite matches up with the singularity of a black hole. I think, but am not certain, that the singularity in a black hole also lies in the spatial dimension. By that I mean that you can move through space to get closer to it.

    I've never even heard of tidal forces in a time dimension. I'm not sure that even makes any sense since we can only travel one way through time.

    This doesn't make any sense. The singularity cannot be in between two objects in the spatial dimension. It's simply not possible. It would appear everywhere all at once.

    Not at all. Why would it?
     
  4. Jan 19, 2014 #3

    martinbn

    User Avatar
    Science Advisor

    Drakkith, you mean nearly flat space, not space-time.
     
  5. Jan 19, 2014 #4
    Hi Drakkith,

    Thanks for the great reply. Allow me to clarify what I meant; my use of the proper language is obviously poor. I hope you reply again, good stuff.

    >>"Nearly flat spacetime seems to be the very opposite of "highly curved".
    -I agree 100%. This is why I qualified with "appears" and "locally". Consider the surface of a sphere: highly curved, yet on a small enough section of the surface, it "appears" flat locally. If my original comment is NOT a correct description of the event horizon of a super-massive black hole, please correct me.

    >>While a singularity may exist in our future, I'm not sure it quite matches up with the singularity of a black hole. I think, but am not certain, that the singularity in a black hole also lies in the spatial dimension. By that I mean that you can move through space to get closer to it.
    -I see what you’re saying about the singularity existing also in a spatial dimension. Probably I misunderstand, but can you move AWAY from the singularity in the spatial dimension, once inside the event horizon? If so, then ignore the following. If not, then that spatial dimension is starting to appear as unidirectional as time, how could one even distinguish them? And, would it be accurate to say that any spatial component of the radial dimension becomes "folded-up" and inseparable from the time dimension component?

    >>I've never even heard of tidal forces in a time dimension. I'm not sure that even makes any sense since we can only travel one way through time.
    -This comment threw me off, I thought gravity bent space-time, not just space. Regarding it making sense given the unidirectional nature of time: these tidal forces would pull objects that are closer to the singularity through the radial/time dimension, into the future, "faster" than objects farther away. Example: for every minute we move into the future, distant galaxies (in the past) move only ..say.. 30 seconds into the future, (at least as we perceive it. They would perceive the opposite.) Nothing is going backwards in time here, except perhaps the "bend" in space-time, which is not really moving nor changing shape anyway.

    >>This doesn't make any sense. The singularity cannot be in between two objects in the spatial dimension. It's simply not possible. It would appear everywhere all at once.
    -Sorry, this was a poor description. When I said "between", I did not mean, DIRECTLY between. I meant it more like "the apex of an equilateral triangle is between the two other points of the triangle. If those two other points fall towards the apex, they will get closer together." Also regarding it appearing everywhere at once, it WOULD, once we reach that event. Hmm, "everywhere at once", sounds similar to descriptions of the big bang, and is perhaps not so physically impossible after all. Regardless, of how poorly I describe longitudinal tidal forces, I would like to re-ask the question about it fitting it dark-matter measurements.

    >>Speghettification: Not at all. Why would it?
    -For some reason I was thinking speghettificiation was a process that occurred before objects pass into the event horizon, where highly curved world-lines spread the object out evenly across the surface of the event horizon. But reading up on it a bit more (after seeing your answer), I see now that I was totally off base, and speghettificiation is simply due to tidal forces. (I also see now that my earlier consideration that space-time at an event horizon appears locally, to be flat, would also eliminate such an effect.)

    Great fun, thanks again!
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Dark Energy as Gravitational Tidal forces?
Loading...