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Size of observable vs UN-observable Universe, etc

  1. Apr 1, 2015 #1
    I understand that these distances are speculative, but I am given to understand that, at the end of inflation, the diameter of the OBSERVABLE Universe was approximately 10 centimeters. However, the diameter of the UN-OBSERVABLE Universe was a good deal larger, with a diameter of approximately 1,513,728,000,000 kilometers (.16 light year).

    Until the discovery that the Universal expansion is accelerating, I believe it was assumed that an ever larger portion of the UN-observable Universe would become visible to us (i.e. more and more galaxies that were previously outside our “light cone”).

    However, now that we know that the Universe is expanding at an ACCELERATING rate, I believe that this trend has been reversed, and that LESS of the observable Universe will be visible to us until, in the far future, only our own Milky Way galaxy will be visible to us.

    Can anyone tell me if my view is accurate?

    Thanks in advance for your time,

  2. jcsd
  3. Apr 1, 2015 #2


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    I think the size of the OU can be extrapolated back from the expansion rate (which has not been constant) but requires some assumptions and I don't know/remember what the general figure is. I've seen everything from "the size of an atom" to "the size of a grapefruit".

    Any figure about the size of the unobservable universe is pure speculation. It could be infinite (in which case it was always infinite). There does seem to be general agreement that it is at least many orders of magnitude larger than the observable universe.

    In the cosmologically short term, we will see a little bit more of the universe (this gets complicated). In the long term the galaxies in our local cluster will be all that is in our observable universe.

    @marcus generally gives the best answers to this kind of question, particularly the part about seeing a bit more in the short term.
  4. Apr 1, 2015 #3
    Yes, I've seen the same figures ("size of an atom to the size of a grapefruit"). The reason I chose 10 centimeters (size of a grapefruit) is because that is the figure I've most often seen in popularized versions of inflation.

    Yes, of course, the size of the UN-observable Universe must be pure speculation. The figure I quoted (1,513,728,000,000 kilometers - .16 light year) was the figure I got from a YouTube video presented by a practicing astrophysicist who used a formula to derive that figure. This would mean that the diameter of the UN-observable Universe would be orders of magnitude larger than the observable Universe, and the ratio of observable vs unobservable would remain constant until the resumption of acceleration, about 5 billion years ago. By-the-way, I'm not an "infinity" kinda guy; I find the concept of an infinite Universe to be unacceptable.

    Excellent! Then, essentially, my perception was accurate. I appreciate the feedback, and your courtesy,

  5. Apr 1, 2015 #4


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    Well, you're not alone in that but the universe doesn't care what you think, it just does what it does. There are LOTS of things in cosmology and Quantum Mechanics that people find unacceptable but they are true none-the-less. This could just be another of them but so far we don't know.
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