Cosmic inflation

[saturno2]

In the cosmic inflation, what is the radius that
the universe, it had in the time of 1x10 E -35 sec

[Ann]

I have been thinking about your question, saturno2, and I'm not the best person to answer it. But I found a source, Size of Universe After Inflation, which quotes a question and gives us an answer. The question is this:

Wikipedia states the period of inflation was from 10⁻³⁶ sec to around 10⁻³³ sec or 10⁻³² sec after Big Bang, but it doesn't say what the size of the universe was when inflation ended. Just saw a Brian Greene show on the Multiverse and I thought I heard him say size was galactic scales when inflation ended. However I've also read size was about a basketball.

This is part of the answer that was provided by the site that I gave a link to:

... given a size of the current observable universe [93 billion light years], we can ask how big was that volume at any particular time in the past. According to this paper at the end of inflation the universe's scale factor was about 10⁻³⁰ smaller than it is today, so that would give a diameter for the currently observable universe at the end of inflation of 0.88 millimeters which is approximately the size of a grain of sand (See calculation at WolframAlpha).

It is believed that inflation needed to expand the universe by at least a factor of 60 e-foldings (which is a factor of e⁶⁰). So using WolframAlpha again we find that the diameter of the universe before inflation would have been 7.7×10⁻³⁰ meters which is only 48,000 Planck lengths.

Perhaps Brian Greene was talking about the size of the observable universe at the time when the CMB photons started traveling towards us. That happened 379,000 years after the big bang at a redshift of 1098 which means the universe was about 84.6 million light years in diameter which, per WolframAlpha, is about half the diameter of the local super cluster of galaxies or about 840 times the diameter of our galaxy.

Ann

[saturno2]

Ann
Thanks for your important explanation

[saturno2]

I found an entry in Wikipedia. At the end of inflation,
the universe was 100 million light years of diameter.
The amazing thing of the cosmic inflation is that in
less than 1 second, the universe goes from a point of
infinite density, up to large diameter of 100 million ly.
The speed of light is a slow turtle compared with
the "quasi" instantaneous speed of the cosmic inflation.

[Ann]

Where did you find that information, Saturno2?

I found another page, http://www.physicsoftheuniverse.com/top ... ation.html, where it says:

But if, as the evidence suggests, the last time the cosmic background radiation had any contact with matter was about 450,000 years after the Big Bang (by which time the universe had cooled to around 3,000°C), then this presents a paradox, because the universe at that time would already have had a diameter of around 90 million light years

So according to that page, the universe would not be as large as about a hundred million light-years until after 450,000 years after the Big Bang, which was long after the end of inflation.

Ann

[Ann]

Well, would you believe it, Saturno? Now I found another site that gives yet another answer to the question of how big the universe was after inflation. the site is https://van.physics.illinois.edu/qa/listing.php?id=1125, and the question and the answer given there are the following:

Q:
how large was the universe after inflation?
- john kester
rochester ny
A:
John -

That's a pretty interesting question. For background, we should let other readers know that you're wondering about how big the universe was shortly after the Big Bang. The universe has been expanding since the Big Bang, but there's now very strong evidence that the initial expansion had an extremely brief period of extremely rapidly increasing expansion, called inflation.

If by 'universe' you mean all the stuff that makes up the visible universe, its radius after initial inflation was (very roughly) 10 cm, the size of your fist if we understand this site correctly. That's to be compared with 14 billion light years now. If by 'universe' you mean 'everything', including the stuff beyond our current horizon, we can't answer, because we don't know if we're part of a finite universe or an infinite universe.

By the way, it seems that the universe is again in a period of inflation, although this time it's not very dramatic.

Here's a nice Website discussing these questions in more depth
http://www.pbs.org/wgbh/nova/universe/howbig.html

-Mike and Tamara

Ann

[saturno2]

Ann
To answer your question:
I read on Wikipedia " Inflation Cosmic" link
in Spanish: " at the end of inflation the universe was
100 million light years"
But now, there is not the data there,
Two possibilities:
1.- I was wrong
2.- The article was edited. I don´t know.
Well
In Wikipedia ( link in Spanish)
" Accelerated expansion of the Universe" wrote:
" Climbing from the universe of 90 light years
of radius (r), at the end of inflation"...etc.
What is the truth?

[Ann]

Quite interesting, Saturno. As you can see, different sources give different answers. However, as you can also see, I have found two sources that agree that the universe was very small right after the end of inflation. One source says that it was 0.88 millimeters, the other one that it was ten centimeters. That is a difference of a factor of a hundred.

However, what if the size of the universe right after inflation was 100 million light years? What is the difference between, let's say, 10 centimeters and 100 million light-years?

I googled "a light-year in meters" and got 9.4605284 x 10¹⁵.

We can say, therefore, that a light-year is roughly 9 (or 10) 000,000,000,000,000 meters. A hundred million light-years would be ~100,000,000,000,000,000,000,000 meters. The difference between 10 centimeters and 10 million light-years would be, I think, about a factor of 10²³. That is a lot.

I don't believe that astronomers, when they calculate the size of the universe right after inflation, will make a mistake as big as 10²³. I think it is quite possible that they may make mistake as big as 10². For that reason, I believe that the size of the universe right after inflation might have been 0.88 millimeters, or it might have been 10 centimeters. Either is possible. But personally, I don't believe it could have been 10 million light-years right after inflation.

However, as I told you before, I found a source with says that the size of the universe was about 90 million light-years about 450,000 years after Big Bang. 90 million light-years is, for all intents and purposes, the same as a 100 million light-years. So I think that the universe was about 100 million light-years in diameter after ~450,000 years. 450,000 years would be about how long it would take for the universe to become transparent to light. The cosmic microwave background radiation was emitted when the universe became transparent. I think you recognize the picture of the cosmic microwave background.

So let's say that when this radiation was first emitted, the size of the universe was ~100 million light-years and the universe was ~450,000 years old. (Or maybe it was ~300,000 years old instead, but when we are talking about the early universe, 300,000 years or 450,000 years is very, very close to the same thing.)

Ann

[charlieo3]

Here's a practical analogy from a Sky and Telescope Magazine article:
"...the universe experienced an explosive growth spurt within its first trillionth of a trillionth of a second — a fleeting moment of hyperexpansion known as inflation. During this interval, the volume that contains today's entire visible universe probably increased by a staggering 10^60 times (that's a 1 followed by 60 zeroes) or more, from extremely submicroscopic to perhaps the size of a golf ball. [italics mine] - See more at: http://www.skyandtelescope.com/astronom ... U88sh.dpuf

I also have a college textbook that refers to the size of the universe at 10^-35 as 0.1m or "about the size of a fist."

I also heard a certain famous lecturer from the SETI Institute once say, "about the size of a grapefruit."

So, take your pick.

[saturno2]

BBC / News , wrote:
" The cosmic inflation"
... " The theory ( of the inflation) holds that this
( a fraction of a second) would have taken
the child universe of something inimaginabily
small up to something less the size of a marble (game).
The <space> has been growing for 14 billion years
from then"

[saturno2]

Guth explaned to EL PAIS / Spain ( years ago) :
" At the end of that process of inflation,
all universe,... was not more than 1 cm
of diameter. And from that moment,... the
normal expansion continued until now".

[saturno2]

Ann , charlieo3
You are right.
At the end of inflation, the universe
was a very small diameter