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Universe Expansion

  1. Sep 13, 2015 #1

    We all know the universe is expanding and it's doing so at a rate greater than the speed of light. But what does expansion mean? Popular Science videos usually give the loaf of bread example expanding in the oven. But even the loaf of bread has limits, it can only expand so far. Do we know or speculate if the spacetime fabric can expand forever? We already know it can curve with no limits (well, except in black holes, that's when our understanding of everything goes down the toilet). The fact is, we don't know what spacetime fabric is made of, so how can we possibly know its limits of "elasticity"? At least, I don't :)

    Great to know your thoughts. Bye!
  2. jcsd
  3. Sep 13, 2015 #2


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    Speed is not a useful measure of the expansion rate. Different distances increase at different rates - the distance to objects far away increases faster than the distance to objects nearby. There are objects where the distance increases faster than the speed of light.
    Speed per distance - the Hubble constant - is a useful value to quantify expansion.
    You hit the limit of the model. The bread is expanding in space, while the universe is spacetime itself - there is no "outside" it would expand "into".

    There is no "elasticity". A cubic meter of space today follows the same laws of physics as a cubic meter of space 10 billion years ago, although it represents a much smaller fraction of the observable universe. Space can expand forever.
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