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I Effects of Stretching Space Time

  1. Mar 1, 2016 #1
    Reading about gravity waves got me back to thinking about relativity. And I am left with two questions to which I don't know the answer...

    Question 1. Gravity waves ripple through the entire universe. They will not cause any macro scale effects because local changes to space-time are very small. However is there a scale at which these small space-time distortions become important?
    For example:
    Two subatomic particles which are very small, and very close to each-other.
    Their binding/opposing forces/fields are at a very delicate equilibrium
    Could the gravity waves distorting space time around them cause the equilibrium to break, and cause some interesting phenomenon to occur? (some type of nuclear decay?). If so, could something like that happening in many places at the same time lead to some macroscopic electromagnetic event?

    Question 2. When examining the photon clock thought experiment: A pair of mirrors is moving at 0.5 the speed of light away from me. The clock's mirrors are aligned as such that the photon bouncing between them is moving parallel to the direction of the clock's movement. Since the speed of light is constant, then as seen by me, it would take the photon a different amount of time to move in one direction than it would to move the other.
    Wouldn't the blue photon complete it's journey in less time then the red one?
    Since distances are defined in light-seconds/years/hours/whatever this observation would make it seem that the clock has two different sizes, depending on the direction that the photon is bouncing.

    Would this not effect the way I would observe atoms? Namely: Electrons would seem orbit "faster" in one direction as opposed to the other. Making the atom's electron shells seem egg shaped instead of spherical. Wouldn't this cause me (the "stationary" observer) to detectsome electric/magentic field originating said atom's perceived assymetry?
    Last edited: Mar 1, 2016
  2. jcsd
  3. Mar 1, 2016 #2


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    1 Yes to the general point about gravitational waves causing changes. See Feynman's sticky beads argument. Whether you can find a system finely enough balanced to react to gravitational waves while not being triggered by some other source of noise I rather doubt. LIGO is very carefully isolated and actively managed. Also, be careful of gravity on atomic scales - we don't have a theory of quantum gravity yet.

    2 It's kind of complex. You will find that any effort to measure the time for a photon to travel one way in the light clock depends on assumptions - how you synchronise clocks at the two mirrors, basically. This means that there isn't an unambiguous answer to "does it take one photon longer than the other". You could look up the one-way speed of light if you want to know more

    I'll let someone else cover relativistic quantum field theory, but since there's no assumption-free way to say that the electron takes longer going one way than the other I would expect no effects from it. That's assuming that electrons orbit in a classical sense, which they don't, so I would not necessarily expect any intuition based off an orbiting electron to work.
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