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Accelerated expansion and perceived gravity

  1. Nov 12, 2015 #1
    Since the universe is expanding at an accelerated rate and accelerating frames can perceive that motion as being the result of a gravitational field, have we ever been able to sense a gravitation field fluctuation in the Earth that occurs every 24 hrs? Would someone not be facing the direction of acceleration at some point in the day and be facing away from that direction 12 hrs later? Wouldn't this acceleration seem to add to and then subtract from our Earth's own gravitational field strength throughout the day?

    Just curious-
  2. jcsd
  3. Nov 12, 2015 #2


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    There is no "direction of acceleration". If you think so you have not understood how the expansion of the universe takes place - it is not about us moving away from a centre in an accelerated motion.

    I also suggest you read this: Cosmology's sole "rate of expansion" is declining
  4. Nov 12, 2015 #3


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    The expansion is far too small for us to sense on Earth. Many orders of magnitude too small.
    But, we can see evidence in sensitive measurements of the cosmic microwave background. We can measure a very small difference in the background radiation from one side of the sky and the other side which rotates around us every 24 hours. This is called the CMB anisotropy dipole moment, and is due to the Earth traveling with respect to the large-scale structures in our vicinity. This is due Doppler shift, which is due to velocity, not acceleration. But with higher order moments, it might be possible to see evidence of the accelerating expansion.
  5. Nov 12, 2015 #4


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    "Accelerated expansion" does not imply "accelerating frames". The term "accelerated" in "accelerated expansion" means coordinate acceleration, not proper acceleration; the proper acceleration of the objects in the universe whose motion we describe as "accelerated expansion" is zero. They are in free fall, so locally they are at rest in an inertial frame and do not see any of the effects you describe. And the Earth itself is one of those objects (i.e., it is in free fall, so locally it is in an inertial frame), so it doesn't see those effects either.
  6. Nov 12, 2015 #5
    This question seems to me to be a gross abuse of the "A" label. What do the heavy hitters think, and are the labels moderated?
  7. Nov 12, 2015 #6


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    You're right, fixed.
  8. Nov 12, 2015 #7


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    Drat, I thought I was moving to advanced!
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