Big Bang Theory: Inflation

General Questions
#1

I wanted to know if anybody has any plots or graphs that describe the rate of inflation of the universe versus time. I just came to the realization that if the initial inflationary period of the universe is right (as far as the initial rates of expansion, which is immensely big) and if now the universe continues to expand, and moreover its expansion acceleration increases, then there may have been a point in time when the acceleration rate must have decreased to much lower levels then went through a trough, and now it’s increasing again. I ask because the current theory is that the end of the universe will be to expand forever faster and faster until there is basically nothing left, ie. the Big Crunch won’t happen. But why, and how confident do we feel that inflation rates won’t flip to negative acceleration in the future when forces reach a different balance?

This post brought to you inspired by Turkey Day. :smiley:

#2

It is not entirely clear from current data whether we’ve had the current rate of acceleration ever since the end of inflation, or if the current “dark energy” (or whatever it is) turned on at some point in the past. I think that the best fit favors the latter possibility, but either is still plausible, given experimental errors.

Not confident at all, really. We generally assume that the dark energy will remain at a constant value forever because that’s the simplest assumption. But we know almost nothing about what’s causing it, and assuming it’s caused by something qualitatively similar to what caused inflation, well, that did end. So no, we absolutely cannot rule out the possibility that the dark energy might turn off or reverse (or, for that matter, grow without bound) at some point in the future.

#3

We don’t really know. Extrapolating current conditions leads us to the heat death end of the universe, so it’s a reasonable logical inference and seems the most likely without invoking additional changes we can’t predict; but we have no way of knowing at present.

Dark Energy is pretty much just a placeholder name meaning “some kind of effect that we don’t yet understand”.

#4

Something like this?
http://en.wikipedia.org/wiki/File:CMB_Timeline300_no_WMAP.jpg

#5

That picture is what I thought of when I read the OP, but how quantitatively accurate is it? I’m guessing it’s more of an “artist’s impression” than anything else.

It might be that there isn’t a quantitatively accurate picture, just because we don’t have good enough data.

#6

You couldn’t put a quantitatively accurate picture on a linear scale, since inflation covers so many orders of magnitude.

#7

Can you find one on a log scale, then?

#8

Bump.

Thanks for the wiki pic, but I’m really interested in unadorned x-y graph explaining this stuff.

#9

I started a similar thread a year or two ago and didn’t get much of a salient response. What I really wanted to know (and I think you’re asking the same thing) is how big did it get, and how fast. I remember reading somewhere that one theory holds that the damn thing was 20 billion light years in diameter three minutes after the big bang. For the life of me though, I can’t find a reference to that anywhere—and I’ve looked exhaustively.

#10

I think you need to be a bit more precise about exactly what you want plotted on the x and y axes.

If you look at the top of page 3 of this paper (a link I’ve posted a few times recently) you’ll see 3 different plots of various time parameters against various distance parameters in the Lambda-CDM concordance model, a model which includes cosmic inflation.

#11

Try this link http://www.physics.princeton.edu/~steinh/0411036.pdf and look at page 4. That might help.

It’s basically Paul J. Steinhardt’s article that appeared in Scientific American’s April 2011 edition.

#12

New Scientist has an article this month with a picture similar to that, with the axes labeled quantitatively. If that link doesn’t work, here’s the direct link to the article. You may need to register to see it (free, I think).

Both the time and radius dimensions are log scale. It seems to agree with Grey’s link. Comparing with the Wikipedia picture, (looking especially where the CMB last scattering surface is) they more-or-less agree if the Wikipedia picture has a linear time scale.

I think the outer surfaces of those pictures correspond to a vertical line at 50 GlYrs in the bottom image on page 3 of the article These are my own pants linked to. Not certain about that.

#13

I think that it’s a lot easier to think of it in numerical terms rather than in graphical ones. If the article linked to in post #11 is correct and I’m interpreting the graph correctly, in the first 10 to the minus-32-th of a second of the universe (the inflationary period), the universe expanded by a factor of 10^30. From then to the billionth second of the universe (i.e. up to about 31 years after the beginning of the universe), the universe expanded by a factor of 10^24. In other words, in the first 10 to the minus-32-th of a second, the universe was expanding by a factor so large that, had the inflationary period lasted for an entire second, it would have expanded by a factor of (10^30)/(10^(32)) = 10^62. After that point, the universe only expanded by a factor of 10^24 over the next 31 years.