Expansion Rate at the Big Bang: Uncovering the Role of Dark Matter

AI Thread Summary
The discussion centers on the expansion rate of the universe at the Big Bang and the influence of dark matter and dark energy. It questions how the Big Bang could occur if the expansion rate was slow or approaching zero, suggesting that early universe expansion was actually rapid due to high energy fields. Participants clarify the distinction between dark matter and dark energy, with the latter being responsible for the current acceleration of expansion. Graphs and calculators are referenced to illustrate the evolution of the universe's size over time, showing a slowdown in expansion before it began accelerating around 7 billion years ago. The conversation highlights the complexities of cosmic expansion and the role of various forces in shaping the universe's history.
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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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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.
 
mfb said:
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.
:)
 
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.
 
If dark matter is accelerating the expansion of the universe,

you mean dark energy...the cosmological constant...
 
mfb said:
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/March03/Lineweaver/Figures/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/March03/Lineweaver/Figures/figure1.jpg

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

Thread 'Matter density right after the decoupling'

https://en.wikipedia.org/wiki/Recombination_(cosmology) Was a matter density right after the decoupling low enough to consider the vacuum as the actual vacuum, and not the medium through which the light propagates with the speed lower than ##({\epsilon_0\mu_0})^{-1/2}##? I'm asking this in context of the calculation of the observable universe radius, where the time integral of the inverse of the scale factor is multiplied by the constant speed of light ##c##.
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Thread 'Hubble Constant, Dark Energy and the Expanding Universe'

Why was the Hubble constant assumed to be decreasing and slowing down (decelerating) the expansion rate of the Universe, while at the same time Dark Energy is presumably accelerating the expansion? And to thicken the plot. recent news from NASA indicates that the Hubble constant is now increasing. Can you clarify this enigma? Also., if the Hubble constant eventually decreases, why is there a lower limit to its value?
View full post »

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