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Inflation questions

  1. Sep 18, 2008 #1
    Hello all, I'm new and this is my first Science forum I've ever joined.

    I got interested in Physics about 3 years ago after reading a book called What Remains to be Discovered. It opened my eyes to a lot of things, especially Quantum Physics. But, the most difficult thing to wrap my head around was the Inflationary Universe. I had to read that part about 5 times just to understand what it was trying to say.
    Here's what I'm still trying to grasp: Inflation caused the universe to under go a ginormous period of "size" inflation in about the amount of time it takes light to cross the nucleus of an atom (or less). What "aspect" of the universe actually inflated? The rest of the universe (matter/energy) can only expand at a certain rate, so it's behind in the race (I've read that at 300,000 years after the Big Bang the "universe" is only the size of our galaxy). So, the part that inflated was Space/Time? Keep in mind I didn't take Physics 101 in school so calculations are lost on me but I can grasp Concepts fairly well.
    Thank you in advance, Darcy
  2. jcsd
  3. Sep 18, 2008 #2


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    Well from what I understand its the space inbetween the galaxys that is expanding. Hubbles equasion shows us that v=Hd. Where h is hubbles constant, d is the distance between something and v is the velocity they are moving a part (relative to each other). He found that most galaxys are moving away from us and from each other! So he concluded that since every thing was moving away from everything space its self must be expanding.
  4. Sep 19, 2008 #3
    Yes, thanks madmike, that much I knew from reading. So, in the Beginning, Inflation was the same idea? I'm thinking a conceptual picture would be like this: think of the Big Bang as a potential bubble, a seed. The bubble starts expanding but something triggers Inflation which is expanding super fast. The rest of the universe (matter and energy) is still expanding inside this bubble at roughly the speed of light until it starts to slow down. I think I'll read more threads on Inflation, I see some here.
  5. Sep 19, 2008 #4


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    What you must rember is that space is inflating. We couldn't go out side the big bang and watch it because there is no space for us to exsist in.
  6. Sep 19, 2008 #5
    Welcome Simulacrum!
    The Inflationary period is of course a unique period in the universe. Today we know of four basic interactions in the universe, gravity, electromagnetism and the strong and weak nuclear forces. However, all of these “forces” were still united into a single Superforce at 10^-34 seconds (that’s a decimal point followed by 34 zeros and a 1) after the Big Bang. As the universe inflated exponentially from smaller than a proton to the size of a grapefruit up to 10^-32 seconds, the undiluted Superforce filled every part of this new universe. Space-time in a way is the fabric of the universe. The energy released by the Superforce and the effect of dark energy “stretches” space-time and gravity “curves” it.
    Thus, both “aspects”, space-time and the energy of the Superforce inflated. It was only after inflation that photons and then matter came into play, as the Superforce separated and the universe continued to expand and cool.

    “The rest of the universe (matter/energy) can only expand at a certain rate, so it's behind in the race…” Not sure what you mean by that.
  7. Sep 22, 2008 #6
    I find this difficult to understand, and of course I'm not alone in this. I can visualise inflation/expansion, imagining it as increasing amounts of space in between galaxies. It is, however, very difficult to understand because I don't have any biosensors or a brain capable of detecting expanding space.
    I can 'understand' temperature because I know what it feels like to be cold, or to be burnt by a flame. I am a professional engineer, which is, I suppose, much less unsettling than being a professional cosmologist, but these are just the sort of questions that fascinate me in my leisure time! I am trying to understand such concepts by suppressing my 'common sense' and, instead, trying to visualise the physical manifestations of the phenomenon's effect on matter.
  8. Oct 5, 2008 #7
    c2 is the spacetime constant.

    At the instant of the big bang, all was energy. Until the balance of space and time was achieved, mass condensed out of energy as the universe inflated beyond the speed of light

  9. Oct 5, 2008 #8


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    Don't worry. Physics can be hard to understand, but when you do understand something complicated its very rewarding. Neil Bohrs once said "Anyone who thinks they can talk about quantum theory without feeling dizzy hasn't yet understood..."
  10. Oct 5, 2008 #9


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    I think that may be a misunderstanding. Now, as has already been stated, there was neither matter nor energy in the universe at this point in its history. At least, not in any form that we would recognize today. But just for a moment, let's imagine that there were some particle (or particles) of matter existing in this early universe. You can probably see that, if these particles exist, then they exist within time and space (or space-time). So, if space-time is expanding at an inflationary rate, it can be assumed that anything embedded within space-time is being carried along at that same rate. In fact, for any particle of matter to be "left behind," it would have to travel faster than light, in the same way that a boat trying to stay a stationary in a flowing river must travel faster than (or as fast as) the flow of the river.

    So, our hypothetical particles are forced to retreat from one another at speeds greatly in excess of light speed, yet stationary within their local space-time. To do otherwise -to retreat from one another at speeds of less than c- they would have to greatly exceed light speed relative to their local space-time, and it is precisely this that the theory of Special Relativity holds to be impossible.

    It is true that inflationary theory is a prediction about the inflation of space-time itself, but we must bear in mind that everything else that exists must exist within this space-time.
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