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Cosmological expansion and uncertainty

  1. Nov 12, 2015 #1
    Firstly, I assume that I'm correct in assuming that since expansion is accelerating it will increase to any arbitrarily large value at some point in the future. If this is true, there must be some point at which particle/antiparticle pairs (due to uncertainty) are carried away from one another at greater than the speed of light, analogous to the way in which hawking radiation is created at a BH's event horizon. Is there anything wrong with this thought experiment?
  2. jcsd
  3. Nov 12, 2015 #2


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    That won't happen, because that's not what the 'acceleration' means. The rate at which particles move apart is proportional to the distance between them, and that constant of proportionality - the Hubble Parameter - is actually declining over time.

    The use of the word 'acceleration' is to signify that a particular object that is currently receding at rate R m/s will in a billion years be receding at a greater rate (expressed in m/s), unless local gravitational irregularities interfere with that. It will be receding faster simply because it is farther away.

    However if a pair were able to remain permanently separated, they would end up receding from one another superluminally once they were far enough separated.
  4. Nov 14, 2015 #3
  5. Nov 15, 2015 #4


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    For a classical black hole, Hawking raditation is not observer dependent. This is untrue for the cosmological horizon. Every observer in the universe will disagree on the location of the cosmological horizon, whereas they will all agree on the location of the event horizon of a black hole
  6. Nov 17, 2015 #5
    Thanks, good catch!

    Though I don't think that is essential for the derivation [but I didn't check]. Everyone at rest agrees on the vacuum temperature, so the relative CH location is what counts.
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