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Effort to get us all on the same page (balloon analogy)

  1. May 30, 2016 #541
    Perhaps this point is obvious to all, but at the time the CMB was released, I suppose every point in space sent photons in every direction. What we observe now are just the photons that happened to be headed in our direction from every point (on a sphere) that has a (current) radius of 41 B LY. That is obviously much less than all of the CMB photons. Are there any numbers to go with either our local rate of arriving photons or the total number of photons that were released?
     
  2. May 31, 2016 #542
    Please ignore what I said about counting photons. Not well thought out.
     
  3. Jan 8, 2017 #543
    If we can't say space is expanding because it doesn't constitute a real expansion of any "stuff", then couldnt we conversely point at the "stuff" for what is occurring and say that relatively, matter is compressing?
     
  4. Jan 8, 2017 #544

    Jorrie

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    The way in which the redshifts of different objects at great distances vary, makes it impossible to explain with "shrinking" or "compressing" matter. In other words, irrespective of how you "shrink the ants" on the balloon, it cannot explain observations.
     
  5. Jan 8, 2017 #545
    Thank you, but its now confusing for me that the terms aren't interchangeable whether you think of the model running and see the ballon expand or imagine the model while preserving a certain balloon size?
     
  6. Jan 8, 2017 #546

    Jorrie

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    I referred to a fixed balloon size and a shrinking ant size - it cannot fit Hubble's law.

    There is however still a possibility that dark energy density is not completely homogeneous. Cosmologist David Wiltshire is a proponent of this idea. Check
    Wager between DL Wiltshire and T Padmanabhan.
     
  7. Jan 8, 2017 #547
    from the material there:
    "The mystery of dark energy is explained purely in Einstein's theory, through a deeper understanding of those parts of general relativity, which Einstein himself recognised as being difficult: the understanding of gravitational energy, given that space itself is dynamical and may contain energy and momentum."
    - David Wiltshire

    (which makes me wonder about dark energy and how much energy space contains in terms we already know about like photons, and what about sound even, but this is by the way)

    So mechanically compression is outside the accepted model and Hubble observations, I see, thankyou.

    I suppose I was asking in terms of both the actual mechanics and also in terms of becoming familiar with the analogy.

    I see the problem of gravity leaves a gap for much speculative investigation that I wouldn't lately want to get into.
     
  8. Jan 10, 2017 #548

    Nugatory

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    The first step in closing that gap is to acquire an understanding of general relativity, so that you will at least know what is already known.
     
  9. Jan 11, 2017 #549

    Nugatory

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    This thread has been open for many hundreds of posts, and it's becoming increasingly difficult to keep it organized and useful so we are closing it.

    Followup questions should go in new threads, and as always if you want to add something specifically to this thread, ask a mentor and we can reopen as needed.
     
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