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

B Extreme gravity waves

  1. Aug 23, 2015 #1
    --

    Hi.

    When a gravity wave pass earth then the time goes a little faster and/or slower.
    Can there be a phenomenon in the universe that create a gravity wave that is so curved,
    that when it pass earth, the time stop or go infinitely fast?

    Regards Magi

    --
     
  2. jcsd
  3. Aug 23, 2015 #2

    Dale

    Staff: Mentor

    There are pp-wave spacetimes with a lightlike singularity. I don't know much about them but they are sometimes known as a "wave of death".
     
  4. Aug 23, 2015 #3

    pervect

    User Avatar
    Staff Emeritus
    Science Advisor

    It's unclear how to interpret the original question, I'm not aware of any clear physically significant notion of what it would mean for "time to stop". Some notions of "time-stopping" might be based on time-coordinates, which depend on the observer and their coordinate choices, other notions of "time stopping" might be based on legacy ideas of "absolute time" that are not compatible with special relativity.

    A question that is closely related that should be able to be answered more directly is whether gravitational wave space-times ave the same causal structure as the flat space-time of special relativity. I beleive the answer to this is no. See for instance

    http://arxiv.org/abs/hep-th/0211195
    I'm not sure how to accurately describe "not globally hyperbolic" in lay terms, a rather imprecise translation would be "not causal". Having closed time-like curves is one way space-times can fail to be globally hyperbolic, but there are other ways.
     
  5. Aug 23, 2015 #4

    bcrowell

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    You chose the "A" (advanced) level prefix for this thread, which would imply that you want a mathematical answer pitched at the graduate level, but the question is phrased in a nonmathematical way, so I assume the first thing we need to do is to interpret your question into more rigorous mathematical language.

    One way, which is I think what DaleSpam had in mind in #2, was to interpret this as a question about a singularity. Then the answer is that singularities are a generic outcome in GR -- in some sense "most" initial conditions will lead to singularities, so the answer to your question is guaranteed to be yes.

    Another possible interpretation is that you're asking about event horizons -- an event horizon is a place where time does in some loose verbal sense "stop" as "seen" by a distant observer (scare quotes because these words don't really mean anything rigorous).

    The interpretation I had from reading your question is that you were asking about degeneracy of the metric. The most common situation that occurs is that we get some solution to the Einstein field equations, such as the Schwarzschild solution written in Schwarzschild coordinates, and it has a coordinate singularity in it, where the metric becomes degenerate. Since it's only a coordinate singularity, it can be removed by a better choice of coordinates. However, there is no guarantee that a metric degeneracy cannot actually happen physically. The standard formulation of GR doesn't work when the metric is degenerate, since, e.g., we always assume that we can raise and lower tensor indices at will. However, there are other formulations of GR, such as the Ashtekar formulation, that are equivalent to the standard one under normal conditions but do allow degeneracy of the metric. So I think the answer is that we don't know whether metric degeneracy is possible, and it's probably not even clear how to interpret such a possibility physically. E.g., if the metric signature becomes 0+++ or ++++ somewhere, then measurement processes presumably become impossible there, and it becomes problematic to associate the predictions of the theory with any type of observation.
     
    Last edited: Aug 23, 2015
  6. Aug 23, 2015 #5

    Nugatory

    User Avatar

    Staff: Mentor

    In the meantime, I edited the thread prefix down to "B" because it appeared to me that the question was looking for a more qualitative and heuristic answer.
     
  7. Aug 23, 2015 #6
    Ok.

    I rewrite it.


    When a gravity wave pass earth then the time goes a little faster and/or slower.
    Can there be a phenomenon in the universe that create a gravity wave that is so curved,
    that when it pass earth, the time almost stop (99%) or go almost infinitely fast(99%)?

    Regards Magi

    --
     
  8. Aug 23, 2015 #7

    Dale

    Staff: Mentor

    Did you read the responses? I don't think that your rewrite changes any of the responses. Maybe you should reply to whatever you found helpful or confusing.
     
  9. Aug 24, 2015 #8
    --

    What I am interested in is what happens if there is gravity waves that is so intense that the time stop or go infinitely fast,
    when it pass the earth and us.
    Can we detect the gravity wave by detecting the time stop or jumps ahead.

    And another question.
    When I am in this gravity wave when it go through me.
    Am I spread out in the whole gravity wave that instance?
    Can I use it to move to another place in the universe?

    I have other questions in this area but lets start with this and see where we end up.


    Regards

    Magnus
     
  10. Aug 24, 2015 #9
    Time is a purely local concept, so you need to specify with regards to which reference point you consider the time dilation. A single clock is never "dilated" locally in its own frame, you need at least two clocks for that.

    I believe what you are asking about is just how much gravitational time dilation a passing GW front(s) can realistically induce in the relationship between a local clock, and a reference clock somewhere far away. Would that be right ?
     
  11. Aug 24, 2015 #10

    Nugatory

    User Avatar

    Staff: Mentor

    No.
    Maybe in principle, but in practice that approach is completely unworkable. If you google for "gravitational wave detection" you'll find some stuff about how gravitational wave detectors work.

    That will depend on the wavelength of the wave. All the gravitational waves that we expect to detect in the general vicinity of the earth will have wavelengths that are long compared with most human bodies, so yes, your entire body will be "in" the wave.... Not that you'd feel it or anything.
    No, of course not. All that happens is that there is a tiny change in the gravitational force you feel for just a moment. And it really is tiny - much smaller than the change you feel from one moment to the next because the moon is moving so pulling you in a slightly different direction from one moment to the next.
     
  12. Aug 24, 2015 #11
    The gravity wave is created from a exploding star or something, and the gravity wave then spreading out in all directions like a ballon surface when it is filled with air.
    The gravity wave(ballon surface) pass through us.
    If time goes infinitely fast when we are inside the gravity wave then the universe outside the wave stop.
    The people outside the wave see us inside moving all over in the wave that is spread in the universe like a spherical shell, expanding with the speed of light.

    Can we play with this idea ?

    I will tell you where I am going with this idea if people here can follow my thought.


    Regards
     
  13. Aug 24, 2015 #12

    Dale

    Staff: Mentor

    an exploding star doesn't produce gravitational waves at all due to the spherical symmetry. You need a quadrupole source at the least.
     
  14. Aug 24, 2015 #13
    The gravity wave is created from an exploding supernova ( http://arxiv.org/abs/1005.0779 ) in the universe, and the gravity wave then spreading out in all directions like a ballon surface when it is filled with air.
    The gravity wave(ballon surface) pass through us.
    If time goes infinitely fast when we are inside the gravity wave then the universe outside the wave stop.
    The people outside the wave see us inside moving all over in the wave that is spread in the universe like a spherical shell, expanding with the speed of light.

    Can we play with this idea ?

    I will tell you where I am going with this idea if people here can follow my thought.


    Are someone following me here?

    Magnus
     
    Last edited: Aug 24, 2015
  15. Aug 24, 2015 #14

    ChrisVer

    User Avatar
    Gold Member

  16. Aug 24, 2015 #15

    Nugatory

    User Avatar

    Staff: Mentor

    Nothing of the sort happens. Time does not go infinitely fast when we are inside the wave (and we're only inside it for a fraction of a second) and the universe outside the wave does not stop.

    You may not play with this idea here - the Physics Forums rules prohibit personal speculation not supported by real science.
     
  17. Aug 24, 2015 #16

    pervect

    User Avatar
    Staff Emeritus
    Science Advisor

    If we were doing the skit from "Dave Berry does Japan", (if you search for "No, I want to take a plane Dave Berry" without the quotes, it should return a google books hit on pg 37), I'd be the travel agent saying "Perhaps you would prefer to take a train", and magi would be the American tourist (Beth) saying, "No, I want to take a plane!". The underlying issue in the skit is that there's only one airport per island in Japan, making the tourist's request for a plane ticket between different cities on the same island nonsensical. The American tourist has a backgroud where most cities have an airport, the situation on the island is quite different than what the tourist is used to. The physical issues here are more complex than the somewhat silly skit, perhaps there COULD be some interpretation of the question that makes sense. But it's not obvious at this point what that interpretation is, so we have a similar communication issue.
     
  18. Aug 24, 2015 #17

    Nugatory

    User Avatar

    Staff: Mentor

    Now, that is some serious Google-fu!
     
  19. Aug 24, 2015 #18
    --

    I try again.

    1. Does the time slow down or run faster for a moment, when the gravity wave pass earth ?
    2. Can there be something in the universe that create a gravity wave, that is so extreme, that time almost stop or almost go infinitely fast,
    when the gravity wave pass earth ?
    3. Can somebody here imagine what would happen if there was a gravity wave that stop time or make the time go infinitely fast,
    when the gravity wave pass earth ?



    Regards MagI
     
  20. Aug 24, 2015 #19

    ChrisVer

    User Avatar
    Gold Member

    Is it a bot? :wideeyed:
     
  21. Aug 24, 2015 #20

    berkeman

    User Avatar

    Staff: Mentor

    Thread closed for Moderation...
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Extreme gravity waves
  1. Gravity waves (Replies: 23)

  2. Gravity waves (Replies: 4)

  3. Gravity Wave (Replies: 1)

  4. Gravity Waves (Replies: 36)

Loading...