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MrB398
2008-Jan-18, 03:46 PM
How large is the universe?

If the big bang model is true, then there must be an edge somewhere out there.

I searched online and read that the furthest know galaxy is 14 billion light years away, so the universe must be at least 28 billion light years accross (14 billion that way, and 14 billion the other way)

Dave Mitsky
2008-Jan-18, 04:00 PM
Not exactly. See http://en.wikipedia.org/wiki/Observable_universe for a discussion on the size of the observable universe and an explanation of comoving distance.

Dave Mitsky

alainprice
2008-Jan-18, 07:03 PM
In the 14 billion light years it took for that galaxy's light to get here, it has moved farther away than 14 billion light years.

Notice the use of the word 'observable'. The true size cannot be determined at this time with current knowledge.

01101001
2008-Jan-18, 07:25 PM
If the big bang model is true, then there must be an edge somewhere out there.

goshparticle
2008-Jan-18, 07:45 PM
We are also, not holding any special position in the universe, not really in the middle.

EndeavorRX7
2008-Jan-19, 03:29 AM
Is it possible that everything in the observable universe is "gravitating" (or moving) in the same general direction?

If two objects, one on either side of our position, appear to be moving away from us then perhaps one is moving at a slower pace while the other is faster, but yet headed towards the same destination.

alainprice
2008-Jan-19, 07:13 AM
That would be tidal in nature and pull along an axis.

It is possible for the universe to 'gravitate' in a general direction. Outwards.

Louigi Verona
2008-Jan-21, 07:08 AM
I liked the idea of a small Universe and with the more distant galaxies being the result of light that has circumnavigated the universe. I must say that this is a disturbing thought though

mfumbesi
2008-Jan-21, 11:31 AM
Interesting link on Wiki. I was always under the impression that the universe had a diameter of 14*2 Billion ly. I was ignoring the observation that beyond ~14 billion ly the "universe" is said to be expanding faster than the speed of light (sorry no references....too lazy to search). My head hurts.

alainprice
2008-Jan-21, 06:16 PM
That's exactly the problem. There are parts of the universe that are currently 'out of view'. As time goes in, they will be abservable. There is no telling when this pattern will stop.

transreality
2008-Jan-22, 03:45 AM
From the 'Cosmic Web' article in Science of 4/1/2008. Sloan Digital Sky Survey mapped 800,000 galaxies, Dark Energy Survey will map 200 million galaxies, Large Synoptic Survey telescope will map 3 billion galaxies starting in 2014. There are 100 billion bright galaxies expected to exist within the observable universe. It is expected that the whole thing will be mapped within our reasonably averaged lifetime.

EndeavorRX7
2008-Jan-22, 04:22 AM
That's amazing. Makes you really wonder.

idav
2008-Jan-23, 03:37 PM
One way I've come to understand it is that the big bang was a rapid expansion of space and time from a singularity. Space time is not 3 dimensional as we are used to observing and interacting with on a daily basis. Often people try to conceptualize the size of the universe but that is somewhat like...well to quote good ole Stephen, "What is north of the north pole?"

Click Ticker
2008-Jan-25, 05:33 PM
That's exactly the problem. There are parts of the universe that are currently 'out of view'. As time goes in, they will be abservable. There is no telling when this pattern will stop.

My understanding is that as time goes on - even less will be observable due to the expansion of space which is occurring at faster than light speed. Perhaps one of our resident experts will clarify.

alainprice
2008-Jan-27, 06:53 PM
Okay, I'll take a quick crack at this one.

edit: to answer your question simply. The light that is emitted 'today' by a galaxy seen at the edge of the observable universe might never reach us. So in a sense, you are correct.

That does not prevent us from seeing the stars that shed their light 'yesterday'. Since as we look farther out, we are looking farther back, we will only be able to see more as time goes on.

Imagine a sheet of rubber being stretched out. Now imagine a toy car in the middle that we power on and start off at 1 mph. That car will always cover ground at 1 mph. As it moves on, there will be more ground to cover. It's important to forget about distances for a quick second and focus on position. Let's say it started at the walkway mark(0.5) and is trying to get to 0 . No matter how fast the sheet stretches, it is covering ground and changing its position closer and closer to 0 .

Due to the expansion of the sheet, the car had to cover a lot more distance than would have been expected. The good news is that you can take all the time you want to get there.

When we look at galaxies very far away, we calculate that it took 14 billion years for the light to get to us. However, the apparent size of the object confirms it was closer to 2 billion light years away when the photon was created.

dgavin
2008-Jan-29, 06:48 AM
Please take this in all the humor it is intended.

Q. How Big is the Universe?

A. Really FREAKING huge!

alainprice
2008-Jan-29, 07:02 PM
Please take this in all the humor it is intended.

Q. How Big is the Universe?

A. Really FREAKING huge!

I thought it was 'THIS' big! *pretends to be holding a big fish*

Maybe we should talk about its hugeness so that people really understand the scope intended.

speedfreek
2008-Jan-30, 07:56 PM
Well, we think that the observable universe has expanded to a radius of around 46.5 billion light years during its 13.7 billion year history, but the whole universe could of course be any amount larger than that.

That figure of 46.5 billion light years is the comoving distance, which represents how far away we think the most distant object in our observable universe is right now. The usually quoted figure of 13.7 billion light years for the observable universe is the light-travel time and doesn't really represent a physical distance as such. During that 13.7 billion years the observable universe has expanded from around 40 million light years in radius when the Cosmic Microwave Background Radiation was emitted (380,000 years after the Big-Bang), to around 46.5 billion light years in radius today.

And remember, the whole universe could be any size larger. We would assume that if the universe is larger than the part of it we can see, the part we cannot see would be similar to our part. If, when galaxies formed, our observable universe was 2 billion light years in radius, then we can imagine that galaxies could have formed out to any distance. There might be a galaxy that was 4 billion light years away at the time. The expansion of the universe would mean that unobservable galaxy would now be something like 93 billion light years away and its light would now be just reaching our most distant galaxy!