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Expanding Universe

  1. Jun 21, 2010 #1
    How did scientists discover that the universe is expanding? This theory doesn't make much sense to me. What could be pushing the planets and galaxies away from each other?

    I just started reading magazines about astronomy such as "Sky and Telescope" and have started reading my physics textbook for high school so I'm not very well educated in physics or information about the universe.


    Joe
     
  2. jcsd
  3. Jun 22, 2010 #2

    Lok

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    They measured the amount of redshift and blueshift (wiki these) of distant galaxies to determine their velocity and direction from ours.
     
  4. Jun 24, 2010 #3
    Hubble verified that the universe is expanding because when he measured stars far away, he found the further away they are the higher is their red-shift as they recede from our point of oberservation.

    This expansion is the ongoing expansion begun at and caused by the Big Bang. It is not so much that there is some kind of force pushing stars and galaxies away from each other in space, but the space-time continuum itself is expanding - the space/time between stars and galaxies is getting bigger and so the distance between objects keeps getting larger.
     
  5. Jun 25, 2010 #4

    Lok

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    The initial big bang did not just create matter and that's it. There was also a huge amount of photons that escaped, and although they carry no rest mass they do contribute to a systems mass, the system being our universe.

    As our big bang probably happened from an point like object, them the photons are scattered around on a spheric surface and the matter that we see is inside. As photons are faster than matter the initial photons have nothing to reflect back so they cannot be truly seen.

    That mass that is moving away is having a few relativistic effects on us, like the time space dilation at it's accelerated rate. It is not a force although you can consider it something like that.
     
  6. Jun 25, 2010 #5

    Ich

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    Lok, your explanation does not conform to mainstream cosmology.
    Based on observational evidence, standard cosmology assumes a homogeneous universe, one which is the same everywhere. That doesn't actually have to be true in a strict sense, but should be valid for the observable universe and most likely an immensely larger region.
    It is not believed that there is a sphere of photons moving away from us. It is not believed that matter moving away causes accelerated expansion.
     
  7. Jun 25, 2010 #6

    Lok

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    You are right, yet still mainstream cosmology does not have any explanation for the accelerated expansion other then a few very far off theories like the Casimir effect.

    Is it assumed that in the Big Bang ( which might even have been relatively modest in an pyrotechnical way) only matter got created? Every experimet we do at those energy levels result in more photons than matter and no theory we know ever said that light did not escape from the big bang. So yes there was light, a lot, so where is it now? CMBR is not enough.

    Space is homogeneous I never doubted that. And matter moving away decreases the overall gravitational field which has relativistic effects on space/time. Galaxies suffer from this effect, observable in differences between center and margin rotation.

    Btw I think one can find the mass of the Big Bang Black Hole or Singularity by knowing the rate of accelerated expansion and this little fact. :P
     
  8. Jun 25, 2010 #7

    Ich

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    From your statements I conclude that your understanding of cosmology is not very deep, and misguided in some aspects. That's ok, but you must not teach your understanding someone who wants his questions answered here, especially as you are obviously well aware that your views contradict the mainstream position.

    Maybe you want to open a new thread and ask what cosmology actually says to the points you raised.
     
  9. Jun 25, 2010 #8

    Lok

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    True ... got a little carried away there. Sorry

    But as you know more about this, how many things are wrong about my assumptions
     
  10. Jun 25, 2010 #9

    Ich

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    CMB is enough. There have been ~10^9 photons per baryon when both ceased interacting. This ratio stayed the same until now. See http://physicsmadeeasy.wordpress.com/physics-made-easy/cosmology-iv/" [Broken], for example.
    No. As long as there is spherical symmetry (which is obviously the case in a homogeneous universe), the influence from matter outside a given shell is exactly 0, expanding or not.
    I'd say they rather suffer from too much gravity, not a decrease.
    Which fact? Which Big Bang Black Hole? And no, you can't find this "mass", at least not with physics as we know it.
     
    Last edited by a moderator: May 4, 2017
  11. Jun 25, 2010 #10

    Lok

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    This one bothers me as i know that gravity cancels out in a hollow shell but the relativistic effects shouldn't.
     
  12. Jun 25, 2010 #11

    Ich

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    We had a similar discussion https://www.physicsforums.com/showthread.php?t=410219".
    I think it's enough to know that the result is a mathematically proven theorem in GR. If your intuition says otherwise, try to mollify it with Chalnoth's cancellation arguments. You need those anyway to understand why orbits are stable.
     
    Last edited by a moderator: Apr 25, 2017
  13. Jun 25, 2010 #12

    Lok

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    Ok, thanks, now i've got something to scrach my shell. :P
     
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