The Early Universe

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Distant galaxies we observe today are as they were and where they were 12+ billion years ago. How did they get so far apart so soon after the big bang?

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It's important to remember that the big bang didn't happen at a single point in space but at every point in space at the same time.

The reason things can be so far apart is because of expansion. There's no reason why space expansion has to be limted to c. As it's not something that's moving but space itself expanding.

There was also (probably) a phase in the early universe called inflation, which was an incredibly fast expansion period:

http://en.wikipedia.org/wiki/Cosmic_inflation

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"...all of the observable universe originated in a small causally-connected region..."

Inflation for Beginners" website says:

http://www.lifesci.sussex.ac.uk/home/John_Gribbin/cosmo.htm

"Inflation expands the Universe from a size much smaller than a proton to 10 cm across in only 15 x 10(exp-33) sec. This is possible because it is spacetime itself that is expanding, carrying matter along for the ride; nothing is moving through spacetime faster than light, either during inflation or ever since."

Could you please point me to a credible theory that explains "the big bang didn't happen at a single point in space but at every point in space at the same time." That would explain why a 1 billion year old universe could have been 24 billion light years accross. Our current observed expansion would not allow it. Our current observed expansion would also, if put in reverse, bring all matter back to one place. I thought the uniformity of the universe was due to all matter being together at one point. Maybe the key is figuring out what size the universe was when the rapid expansion of inflation stopped.

Edited by NowThatWeKnow
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Well lets put it another way, the single point, is everywhere. Neither of your quotes contradicts this.

And a reference:

http://www.astro.ucla.edu/~wright/nocenter.html

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I am familiar with a balloon covered with dots being used to explain Hubble expansion and I am not trying to defend "singularity". The universe is expanding so in the past it must have been smaller. The size of an atom, our solar system, the milky way or a 12 billion light year radius chunk of space that we observe today.

It sound like you are saying that distant and infant galaxy 12 billion light years away started there at the time of the big bang and is expanding from that point. I would have thought the red shift would indicate it is moving away and was closer then that in the past.

My question now is does any one have a clue how big the universe was (give or take a million light years) at any given time shortly after the big bang? Reading about inflation does not leave me with a visual of galaxies popping out all over a space billions of light years accross in a fraction of a second. Where am I going wrong?

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Dear NowThat,

You show good taste in sources (except for one point). John Gribbin is a fine science popularizer and well qualified, PhD astrophysics Cambridge 1971. My reservation is that what you cite is dated 1996.

There was a revolutionary makeover in cosmology starting in 1998. Still going on. I would urge you to stick to sources that are no more than 4 or 5 years old. Of course it is also helpful to all of us if the sources people cite are online, so we can all look and evaluate and note context.

Try Einstein-online. It is up-to-date. The link's in my signature. It is the public outreach site of a top research institution (Max Planck/Albert Einstein Institutes). It is nonmathy popularized exposition which has both good and bad aspects but at least it is since 2005. The curator has a physics PhD, much younger guy than Gribbin (who was born in 1946).

"...all of the observable universe originated in a small causally-connected region..."

Inflation for Beginners" website says:

http://www.lifesci.sussex.ac.uk/home/John_Gribbin/cosmo.htm

...

Professional cosmologists make a sharp distinction between the universe and the observable universe. They don't claim that the universe was once concentrated in a small volume. We don't know whether the volume at putative big bang time was finite or infinite. If finite, we have no idea of the size. In the most commonly used version of the standard cosmo model the volume would have been infinite. Simplifies the math.

In my experience it is only in popularizations that writers fail to make this key distinction. Can't blame them but it causes no end of confusion.

Distant galaxies we observe today are as they were and where they were 12+ billion years ago. How did they get so far apart so soon after the big bang?

When you say

"Distant galaxies we observe today are ...where they were 12+ billion years ago."

do you mean these objects are still at the same distance from our Milkyway galaxy material?

It sounds like you are equating "where they were" with how far they were.

If that is what you mean then your very first statement, in post #1, makes me wonder. It seems quite wrong! As a rule the stuff astronomers observe is now much farther away than it originally was when it emitted the light which is only now reaching us.

For example it is estimated that the matter that emitted the CMB radiation we currently receive was 42 million LY from us (from the matter that eventually became us) when the light was emitted, 13.7 billion years ago, and that same matter is now 46 billion LY from us.

The distance between source and target has expanded by a factor of 1090 which is the same factor by which the wavelengths in the radiation itself have been extended.

If I have misunderstood what you said, please clarify.

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Dear NowThat,

I would urge you to stick to sources that are no more than 4 or 5 years old.

Good point. Things are changing quickly. Hence the name "NowThat We Know" (will bite you in the @ every time).

Try Einstein-online. It is up-to-date. The link's in my signature...

We don't know whether the volume at putative big bang time was finite or infinite. If finite, we have no idea of the size...

I did go to Einstein-online and I gathered we really do not know the size of the universe in the beginning or now. Good site and I will read more later.

When you say

"Distant galaxies we observe today are ...where they were 12+ billion years ago."

do you mean these objects are still at the same distance from our Milkyway galaxy material?

Where they were 12+ billion years ago and where they are to day are very different locations as you pointed out. I am sure there current light is permanently off our radar screen because of the expansion of space

The bottom line is is we do not have the answer to my question. If we went back 6 billion years in time I wonder how we would see that same distant galaxy? Need to think on that for a bit.

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NowThat,

I'd like to invite you to try something. You mentioned a light travel time of 12 billion years.

So go to Wright calculator and put in z=3.9 and see what current distance. And what travel time.

The flat case is the simplest, usually best to press the "flat" button.

To get to Wright calculator you just google "wright calculator", or you can use this link:

http://www.astro.ucla.edu/~wright/CosmoCalc.html

The calculator embodies the equations of the standard cosmo model, so you don't have to solve equations, do integrals etc. But you still get some hands-on experience, with only minimal maths.

You also mentioned 6 billion years. What z corresponds to that? What current distance?

I have an idea of something we could do that involves going back to a perspective of 6 billion years ago. But first I want to make sure you are comfortable with the calculator and that you have no trouble discovering what redshift light would have that has been traveling 6 billion years to get to us. It's simple trial and error---try and correct--try some z and correct a bit up or down.

=====================

The current distance, the distance now when we receive the light, is output in the box he calls comoving.

The box labeled angular size distance outputs the distance to the source when it emitted the light. These two distances should be related by the factor 1+z.

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Another calculator to get acquainted with is Morgan's "cosmos calculator"

Google cosmos calculator and see what you get.

In this case you need to type the numbers .27 and .73 and 71 (which wright gives automatically you as the default )

and then type in what you want for z

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**SPOILER** over the past 6 billion years distances (largescale ones between stuff that is unbound and free to drift apart) have expanded by a factor of 1.66

and over the past 12 billion years distances expanded by a factor of 4.9-----the factor is aways 1+z

Edited by Martin
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You also mentioned 6 billion years. What z corresponds to that? What current distance?

Your spoiler gave it away but z=.66 and current distance is 7.782 Gly. That is one neat calculator, thank you very much. I plugged in many #'s and came up with a lot of great info. Our current observed universe has actually gotten quite big. I can also see where it would be much more crowded with galaxies billions of years ago. There is no reason to believe that the universe we see is all there is but it can predict the size of the known universe at different times. I went back to the big bang and came up with an expansion factor of 865. I am sure it was not designed for that.

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