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Expansion rate and corollary

by Perchie
Tags: corollary, expansion, rate
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Perchie
#1
Jan30-13, 09:34 AM
P: 20
If dark matter is accelerating the expansion of the universe, then how fast did the universe start expanding at the point of the Big Bang ?

The pre-Standard Candle model of the Big Bang held that the expansion rate had always been declining and by backward interpolation, must have been very much faster at the BB.

But if the reverse is true, how did the BB even happen - if the expansion rate was slow to zero ?

I've never heard anyone ask this question, as yet.
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mfb
#2
Jan30-13, 10:41 AM
Mentor
P: 11,570
Currently, expansion is accelerating - but some billion years ago, matter dominated and acceleration was slowing down. Expansion was quicker in the early universe.

We have a calculator here, and some nice graph showing the evolution of the size of the universe which I do not find at the moment.

But if the reverse is true, how did the BB even happen - if the expansion rate was slow to zero ?
Note that "slower in the past" (if that would be true) does not mean "goes to zero". f(x)=x+x^2 has an increasing derivative (for increasing x) as well, but its derivative is not zero at x=0.
Perchie
#3
Jan30-13, 06:59 PM
P: 20
Quote Quote by mfb View Post
Currently, expansion is accelerating - but some billion years ago, matter dominated and acceleration was slowing down. Expansion was quicker in the early universe.

We have a calculator here, and some nice graph showing the evolution of the size of the universe which I do not find at the moment.
Thanks.
:)

Naty1
#4
Feb2-13, 12:51 PM
P: 5,632
Expansion rate and corollary

then how fast did the universe start expanding at the point of the Big Bang ?
faster than light....there was a huge negative pressure..... a high energy unstable scalar [Higgs type] field...which powered early expansion.
Naty1
#5
Feb2-13, 01:01 PM
P: 5,632
If dark matter is accelerating the expansion of the universe,
you mean dark energy....the cosmological constant.....
marcus
#6
Feb2-13, 05:03 PM
Astronomy
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Quote Quote by mfb View Post

We have a calculator here, and some nice graph showing the evolution of the size of the universe which I do not find at the moment.

...
Jorrie has some nice color-coded curves showing evolution of various things. If that's what you had in mind just say. I think they might be in one of the sticky threads and I'll hunt for them.

There is a much plainer graph of the scalefactor over time that is here
http://ned.ipac.caltech.edu/level5/M...s/figure14.jpg

It shows slowing down until around year 7 billion and then speeding up after that.

I didn't have room in my signature for it, but I already had a different figure from the same article in my signature
http://ned.ipac.caltech.edu/level5/M...es/figure1.jpg

so I get it by clicking on that (which is "Figure 1") and then changing the 1 to a 14.


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