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Inflation Theory and space

  1. Jul 20, 2014 #1
    "In physical cosmology, cosmic inflation, cosmological inflation, or just inflation is the exponential expansion of space in the early universe. " -Wikipedia
    Since Inflation Theory specifically talks about 'space', does it mean that inflation didn't have any effects on the temporal dimension even though space and time are interwoven?
     
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  3. Jul 20, 2014 #2

    Drakkith

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    Correct. Both inflation and regular expansion involve only the spatial dimensions, not time. Both are the result of changing spatial geometry that leaves time unaffected.
     
  4. Jul 20, 2014 #3
    Doesn't "change," though, involve time? How can something change, or go from one thing to another, if you don't include a concept/variable of time?
     
  5. Jul 20, 2014 #4
    If we consider the Hartle-Hawking state, did inflation occur before the introduction of time?
     
  6. Jul 20, 2014 #5
    From: http://en.wikipedia.org/wiki/Inflation_(cosmology [Broken])

    By this estimate, it looks as though time was already around during the inflationary epoch. Hartle-Hawking is a speculation dating prior to the planck epoch. Inflation is thought to have occurred well past this
     
    Last edited by a moderator: May 6, 2017
  7. Jul 20, 2014 #6

    Drakkith

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    Just because it occurs over time does not mean that it affects time. The spatial geometry changes over time. Time does not change as far as I know.

    In standard cosmological models, inflation takes place around 10-36 seconds after the big bang. I believe the Hartle-Hawking state is concerned with the universe prior to the big bang.
     
  8. Jul 20, 2014 #7
    If the inflationary epoch would've been longer/shorter, the rate of expansion of space would've been affected, right?
    So is there any such 'factor' that might've affected the rate of flow of time? (I know this is a stupid question, but this just occurred to me right now)
     
  9. Jul 20, 2014 #8

    Drakkith

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    Note that inflation and expansion are both the result of the geometry of space changing. This affects the position of objects relative to one another within space. As far as I know there is no analog for time since it is only one dimensional, but I'm not an expert so I could be wrong.
     
  10. Jul 21, 2014 #9
    With 142 views on this thread already, I think you're right because nobody said otherwise.
     
  11. Jul 23, 2014 #10
    Geometry of space or spacetime?
    Is it thought that spacetime did not exit prior?
    Is it thought that spacetime expanded, not just space?
     
  12. Jul 23, 2014 #11
    in this case it amounts to the same thing, the space component of spacetime expands
     
  13. Jul 24, 2014 #12
    That's exactly what I thought initially, but later when I realized that Wikipedia (and many other sources) specifically talk about 'space' in Inflation Theory, I became doubtful...
     
  14. Jul 24, 2014 #13

    phinds

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    Since inflation (if it did indeed happen, as it very likely did) did not take place instantaneously, it obviously happened over a period of time.

    Inflation is stated variously as having occurred during the period from about 10E-35 seconds after the singularity to about 10E-33 seconds after the singularity, which is to say a duration of about 10E-33 seconds.

    I've seen the amount of the expansion stated variously as being anything from about 10E40 to about 10E50, which is a range of a FACTOR of 10E10, which implies pretty strongly that the actual amount of expansion is not well known but it was huge.

    These numbers (10E-33 seconds and 10E40 factor of expansion) are simply unimaginable in anything like human terms and so the combination of the two is even less imaginable in human terms.

    Had either the duration or the expansion been a different amount with the other staying the same then the rate would obviously have been different.
     
  15. Jul 24, 2014 #14

    Ich

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    "Expanding spacetime" simply does not make sense. It would mean that you have at one point in time a certain spacetime, and at the next instant a larger one.
    There is only one spacetime. You have at one moment in time a certain space, and at the next instant a larger one. All these spaces together build spacetime, just like infinitely many 2d planes together build 3d space.

    Caution: "moment in time" and "space" are terms with a rather complicated definition in GR. Don't imagine space as something fundamental that has expansion as one of its fundamental properties. It's a bit more subtle.
     
  16. Jul 25, 2014 #15

    I guess you quoted the wrong thing while saying this.
     
  17. Jul 25, 2014 #16
    I wasn't really talking about spacetime as a whole...I was talking about space and time independently...
    Although it's understood that inflation didn't have any effects on the temporal dimension, I can't really make sense of the example given...if it's an infinitely finite system made up of different planes, if a few more planes are to stacked to the whole wouldn't it affect the system as a whole anyway?
     
  18. Jul 25, 2014 #17

    phinds

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    I have no idea what you are talking about. What do you find incorrect about what I said?
     
  19. Jul 26, 2014 #18

    The above was your reply to this, I guess:



    But you quoted this:


     
  20. Jul 26, 2014 #19

    Ich

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    I quoted bahamagreen, not you. But you seemed to agree with him at that time.
    Sorry. Another try: Forget about one dimension and imagine spacetime as some three-dimensional (instead of four-dimensional) thing. Then imagine you slice that thing into infinitely many infinitely thin sheets. This is called a "foliation".
    Now every sheet of said foliation represents a "space". The direction orthogonal to all those sheets is "time". And "space expansion" means that every later sheet is - by some measure - larger than the former ones.
    That whole "spacetime" thing is absolutely static. "Expansion" is something that denotes a difference of sheets that are separated by a certain distance in the time direction. With this in mind, it absolutely makes no sense to think about an "expansion of the time dimension".
     
  21. Jul 26, 2014 #20
    Thank you, I get it now.
    I wasn't really talking about expansion per se...I was wondering if there's anything that affected the rate of flow of time...because initially I thought inflation affected the rate of time as well.
     
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