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Best model to explain expansion of universe is needed

  1. May 17, 2009 #1

    eha

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    to better understand the expansion of universe, i probably need to see a well designed animation. neither in stretching rubber nor inflating baloon models i don't understand how does Hubble constant of 74kps fit on them. actually to apply Hubble constant i can only imagine one model and that is either overlapping or free falling, but then i can't see any expansion at all. so, i have to think more to imagine how our universe is expanding with speed rate of 74kps/per megaparsec. animations would be helpful.
     
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  3. May 17, 2009 #2

    marcus

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    Eha, would you try something, please. Just now I was trying to get google calculator to show me the Hubble rate in different units of measure and it didn't work. Google was "cranky" this morning.

    To use the calculator you just put what you want evalutated in the ordinary google window and press return and it should give you the calculation (in bold letters at the top of the search page).

    Like if you put in "2*2" it should come back with "2*2 = 4"

    See if you can get a result putting in this:

    "megaparsec/(74 km/s)"

    Type it in the usual google window, without quotes, and press return. I just tried this and it would not give answer, so I am not sure what is wrong. I also tried

    "megaParsec/(74 km/s)" and

    "1 megaparsec/(74 km/s)"

    What I want it to do is give me the reciprocal of the H rate, that is, 1/H. I know it should come out 13.2 billion years. Do you get this?
     
  4. May 17, 2009 #3

    marcus

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    Anyway when you do this calculation it puts H in different units for you which some people find easier to understand. It says that the largescale distances governed by the law will each expand by a tiny fraction of their length each year.

    The tiny fraction is 1/(13.2 billion). Each distance will expand by that small fraction of itself each year.

    Percentagewise that means each distance expands 1/132 of one percent in a million years.

    Not all distances are governed by this rule. Distances between things in orbit around each other are governed by orbit laws. The diameter of the Milky Way is determined by its dynamics. Those are not the distances that grow. The distances which follow the Hubble rule are very large distances between objects which are at rest with respect to the microwave Background. (The light left over from the ancient cloud of matter in the early universe serves as a landmark so we can be at rest with respect to the original matter before it started falling into clumps and developing random motions.)

    Distances between widely separated points both of which are at rest
    increase 1/132 percent per million years.

    Now you are asking how do I match up the balloon model with the rate of 1/132 percent per million years.

    The answer is you make sure the balloon is very big and that it expands by 1/132 percent every million years!

    But that is too slow to imagine, so think of yourself as a god for whom a million years is like a second. Now you look at your ballooniverse and it expands by 1/132 percent every second.

    Well even that is still a bit too slow to imagine, so imagine you are an even better god, for whom 100 million years is only like a second for us. Then the balloon will increase by 1/132 each second.

    Concentrate on believing that all existence is concentrated on the balloon surface---there is no inside space inside the balloon and no outside surrounding space, only the surface. A 2D surface where no extra dimensions exist. And creatures living there are 2D creatures. And the 2D surface is getting bigger by 1/132 per second.

    Points that stay at the same latitude longitude on the surface are the ones which are at rest relative to background. They are not moving. But they are getting farther apart.
     
  5. May 17, 2009 #4
    Marcus I get the correct answer.

    1.3213702 x 10^10
     
  6. May 17, 2009 #5

    eha

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    so you are saying that universe is only rubber tissue part of the baloon,or surface of the baloon. okay , let me imagine then, what part of this surface is our observable universe?and how does 74kps/megaparsec speed rate work on this model? what part of the surfaces move respectively with the speed of c,2c,3c,4c,5c and 6c ?
     
  7. May 17, 2009 #6

    marcus

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    Good! thank you. I depend on google calculator as a ready convenience, and it worries me when it seems stuck, and won't work.

    So it told you years. It said 13.2 billion years.


    BTW you should know that H is gradually decreasing, now around estimated 74 but in time it will sink down to what, something like sqrt (.75) * 74.

    (Naive people think when they hear "acceleration" that H must be increasing :biggrin: but that is wrong, very much so! It is the scale factor itself, not H.)

    So let's see what this comes to. And let us see what the 13.2 billion year figure will increase to. Naturally as H decreases the reciprocal 1/H must increase!

    Again Google can help. why don't you do the calculation?

    I get that the asymptotic value for the time, when H levels out as low as it is going to get (in a billion years or so), will be
    around 15 billion years.

    So that means that the percentage increase rate, far in the future, will not be 1/132 percent per million years. It will be more like 1/152 percent every million years. Is that what you get. Ask if it is not clear how to do the calculation. Bravo, by the way.
     
    Last edited: May 17, 2009
  8. May 17, 2009 #7

    marcus

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    At present we do not know the full extent. So we cannot answer the question in a satisfactory way. We do not know what fraction of the total is represented by our observable.

    According to the standard cosmo model, the observable extends out in all directions from us to a distance (called "particle horizon" distance) of about 46 billion LY.

    However we know from the most recent WMAP report (Komatsu et al) that the whole universe extends out at least 300 billion LY! With 95% confidence, say Komatsu et al. And could even be infinite! Is much larger than observable and we don't know how much larger.
     
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