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Making sense of inflation?

  1. Feb 13, 2015 #1
    Ahoy.
    Two things ought to be known prior to your reading my terrible post:
    1. This is my first post.
    2. I don't know very much about this whole business (though time and passion suggests I should)

    Considering its my first post, let's start at the beginning:
    Now, I've been reading a whole bunch about all this inflation/Big Bang business, and I've failed to grasp the fundamentals, despite finishing multiple books on the topic, and researching it for years (which suggests a retention issue, perhaps, but I digress)
    ---
    Did space expand/explode outward from a single point, and with a boundary - like a beachball? Or did it pop in at infinite places all at once - like infinite people lighting matches in an infinite room of flammable gas? (Insert other options here).

    Help, and thanks for it.
     
  2. jcsd
  3. Feb 13, 2015 #2

    Chronos

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    Classical theory suggests a point of origin, a singularity in space and time. That model is not terribly popular. It is widely believed a working theory of quantum gravity will eliminate the initial singularity predicted by GR.
     
  4. Feb 13, 2015 #3

    bapowell

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    The big bang singularity is not a point in space, but a point in time. This type of singularity is called "space-like" -- it's really a spatial cross-section at an instant in time. The size of this cross section, whether it be infinitesimal, finite, or infinite, isn't known because this would require knowledge of the global geometry and extent of the universe. As Chronos says, however, the actual singularity itself is likely avoided with a true quantum theory of gravity.
     
  5. Feb 13, 2015 #4
  6. Feb 16, 2015 #5
    The Big Bang was not an explosion but rather a rapid expansion of space simultaneously out of "nothing" (though you have to be very careful using that term in such cases) and there would be no point saying that there was something before that, because space time was created at the Big Bang, there was no "then" then. After the Big Bang comes Inflation which is mostly based on quantum mechanics and since energy-mass equivalence does not apply to the expansion of space itself, the Universe's expansion was so rapid that it would be like a coin inflating to ten million times the width of the Milky Way.
     
  7. Feb 16, 2015 #6
    I was under the impression that the Big Bang theory simply predicts the earliest known state of the universe and its subsequent expansion from that point on, not the actual "spacetime" origin of the universe as we know it.
     
  8. Feb 16, 2015 #7
    It does, but any events before that point would be ignored because they would have no observational consequences, this is called the Anthropic principle. If you take the Earth, there is no point north of the north, it does not make sense to say there is no point north of north. It is the same with time, there was no time before that. Now this point of view is not the main point of view of the Big Bang, the main purpose is what you mentioned, but this is one aspect of it.
     
  9. Feb 16, 2015 #8

    bapowell

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    I think you mean "no boundary proposal" -- the anthropic principle is something else entirely.
     
  10. Feb 16, 2015 #9

    bapowell

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    Indeed, this is what is meant by "big bang cosmology".
     
  11. Feb 17, 2015 #10
    The term I would more think one has to be very careful using here is not "nothing", but "simultaneously"...?
     
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