Sound in space and the end of the universe

  1. Hello

    I am trying to get into physics and astronomy as a hobby so please excuse the crudity of my posts, I regrettably have no physics education past high school level but nevertheless I aim to slowly but surely learn either self-taught or through some further eduction whether at college or university level.

    I have a few questions I'd like to ask of those much more learned than I:

    Say an astronaut is in space without a space suit. The astronaut starts a song on his iPod and puts his earphones in; will he hear anything? I assume there would still need to be air (or another medium for the sound to travel) between the earphone and the astronaut's ear/eardrum?

    Secondly, is it reasonable to assume that, given the magnitude of the universe, it could have already come to an end just, the light hasn't yet travelled to the Earth? I know that currently it is thought that the universe will end in some sort of big regression so therefore it's probably unlikely to already have happened (in this manner), or is it?

    Thanks!
     
  2. jcsd
  3. phinds

    phinds 9,136
    Gold Member

    Good question. There might be enough conduction by the skin to allow some sound to be heard. Probably depends on how far into the ear the buds get. Of course, in any case, the astronaut isn't going to care since he'll be busy suffocating to death.

    This is so far off base that I can only suggest that you pursue your studies some more. The universe might or might not be infinite in size but even if it is finite and unbounded, the consensus is that is is enormously larger than the observable universe. "Big crunch" theories pretty much went out long ago. The universe is expanding and is expected to continue to do so.
     
    Last edited: Jan 17, 2014
  4. Thanks for replying, I appreciate it! I do recall reading about the expansion apparently going on forever to the point where no other galaxies will be visible to observers on Earth, but is it not true that it's thought that at some point further in the future the universe will consist of nothing more than helium and hydrogen atoms? Perhaps I am not remembering something correctly.
     
  5. phinds

    phinds 9,136
    Gold Member

    That is the "big rip" scenario and has been pretty much discredited.

    It is even possible that galaxies within local clusters will not be disturbed by the expansion, and certainly galaxies themselves are not likely to be disturbed.
     
  6. phinds

    phinds 9,136
    Gold Member

    Last edited: Jan 17, 2014
  7. Ah I see, thank you. I will certainly give those links a look. So it is currently held that the universe will continue to expand forever with no real "end"?

    On the topic of expansion, IIRC it was originally demonstrated through spectroscopy by Edwin Hubble showing the fact that light from celestial objects were red shifted. This is probably quite an easy question to answer but, how is it we know the light has been red shifted? How do we know that the light isn't emitted in the way we observe it and wasn't streched?

    Perhaps I don't quite understand red shifted light. What I mean to say is, if we observe a blue star, are we to expect it to look to the naked eye more red if it's moving away from us when we observe it? Or, are these observations made over a finite period of time? So take a spectrum on day x, wait until day y and do another and if the object appears more red/spectrum has more red light, we can assume it's moving away from us?
     
  8. jbriggs444

    jbriggs444 1,845
    Science Advisor

  9. Depending on the headphones, there could be significant sound transmitted through the bones in the head.

    I think that the general consensus, or at least the majority opinion, is that the universe will not end. It is expanding and accelerating in its expansion, so there's no reason to not expect it to expand forever.

    If the universe does come to a sudden end, then I suppose the end would happen everywhere in the universe, separated by spacelike intervals, so it wouldn't be possible to see the end of the universe in your past light cone no matter where you are.
     
  10. phinds

    phinds 9,136
    Gold Member

    The redshift correlates pretty much exactly to the distance away from us. It would be an impossible coincidence if all the stars one distance from us emitted light one color of red and those twice that far away all emitted light of a different (but the same as each other) color of red.
     
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