General Question

flutherother's avatar

What is the size of the Universe?

Asked by flutherother (28815points) November 15th, 2010

We used to think it was a few hundred light years across but we now know it is much larger than that but just how big is it?

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39 Answers

marinelife's avatar

“The universe is very large and possibly infinite in volume. The region visible from Earth (the observable universe) is about 92 billion light years across,[16] based on where the expansion of space has taken the most distant objects observed.” Wikipedia

JustmeAman's avatar

It is not measurable. How can one measure infinite?

flutherother's avatar

If the universe only began 14 billion years ago light can’t have travelled more than 14 billion light years in that time so how can we see further?

poisonedantidote's avatar

@flutherother The universe is expanding is how

JustmeAman's avatar

We can’t begin to see the Universe we can only see small portions of it.

marinelife's avatar

@flutherother You are not taking into account the speed at which the universe is expanding.

coffeenut's avatar

the size of a marble. that aliens play with

mrlaconic's avatar

Perhaps this Size of our World will help give an idea of how big it is.

mammal's avatar

Size is a concept that doesn’t apply to a universe which i suspect, is unspannable, untraversable and uncrossable. Or put it another way the Universe is unlikely to cram into a Concept of such as Size without leaving a remainder.

flutherother's avatar

@marinelife I don’t quite get it. Don’t we need a frame of reference here. If we choose the earth then we can see stars/ galaxies that are a maximum of 14 billion light years away. When we see this light you are saying that the source will have moved further away from us but that doesn’t make sense from our frame of reference.

Isn’t it also true that whatever size the universe is now it was the size of a speck of dust 14 billion years ago so that if we were ever able to see that far back in time we would see everything and therefore the universe cannot be infinite.

nebule's avatar

@mrlaconic that’s just awesome!!

GeorgeGee's avatar

In effect, the most distant observable objects in the universe have been traveling away from us at greater than the speed of light since the formation of the universe. While this seems to contradict the theory of relativity, the accepted explanation is that the space between us and those objects has stretched dramatically over time. Imagine drawing a line on a grid printed on a rubber sheet. You can move one square per year and we’ll call that a light year. If while you’re drawing, we dramatically stretch the rubber sheet, you can still only draw one square, but now it’s 4 times further. And the line you’ve drawn already is 4 times longer than it was.

LostInParadise's avatar

@flutherother , You are correct. The visible universe has a radius of 14 billion light years.

PhiNotPi's avatar

In the end, the Universe will either expand until it is infinately large, and everything becomes frozen from lack of heat, or stop expanding and have the big crunch (opposite of big bang).

kfmarani's avatar

My science teacher said the universe is not infinite. if it was the sky at night would be so lit up with stars to a point that its pretty much all stars.

PhiNotPi's avatar

@kfmarani there are two reasons for that. First, interstellar dust block some light. Second, due to the finite age of the universe, light from further stars has not had time to reach us. Only if the universe was infinitely old (which it isn’t) and infinitely large (which it isn’t yet, but may become), then the night sky will be completely white with light.

GeorgeGee's avatar

@kfmarani, when I was a kid, we would look at the sky sometimes and see large swaths of mostly white areas in the sky. It’s called the milky way. Since then though, we have a lot more air and light pollution which makes it impossible to see, but check out some pictures, it was a pretty awesome sight.
http://www.spacetoday.org/images/Questions/MilkyWayGalaxyNASA.jpg
http://astronomycentral.co.uk/wp-content/uploads/2010/01/Laser-Milky-Way.jpg

ETpro's avatar

@PhiNotPi Space-time is certainly is not infinitely large. You are right. But could a finite thing ever expand enough to become infinitely large?

JustmeAman's avatar

LOL This is funny how we DEFINE the Universe like we understand it by our limited existance. LOL

mattbrowne's avatar

@flutherother – Spacetime itself can expand at a rate faster than the speed of light. This means that the universe will get very dark in the future. At some point our descendants inhabiting the merged Andromeda Milky Way can only see galaxies which are part of our own super cluster (called Virgo). The light of all other clusters cannot reach them anymore. Dark energy is relentless.

If you’re interested in distances in space I’ve created an overview some time ago

flutherother's avatar

@mattbrowne Thanks for the link. In the long term the universe will become large and dark and the stars will burn out. This won’t happen for billions upon billions of years and considering that recorded history goes back only a few thousand years this is a very long time indeed. We will become extinct before then unless we can colonise space. Maybe we should start thinking about that now.

I noticed that your link gives the size of the observable universe as 93 billion light years. I hear this figure quoted and I hear 27 billion light years quoted and I wonder in this thread which figure is correct as cosmologists cite both figures.

There is agreement that what we can observe is not the entire universe and that there are unknown regions beyond the furthest we can see or ever will see. I wonder just how extensive these regions are and if there is any way we could find out.

kfmarani's avatar

The universe is immensely large, but if it was the sky would literally be FULL of stars. So full in fact that there wouldn’t be any black.

mattbrowne's avatar

@flutherother – Yes, we should colonize space. I favor sending human embryos and androids.

I think 27 billion is incorrect. See also

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

flutherother's avatar

@mattbrowne Here is an alternative view from Wendy Freedman

Space is a very inhospitable place and our technology will have to develop dramatically to make colonisation feasible. Personally, I think the human race has an attitude problem towards life forms other than our own and that it is equally important that we recognise this before we reach out into space.

ETpro's avatar

@flutherother This morning I stumbled across a fascinating and brilliantly humorous but enlightening hour-long lecture by Physicist Lawrence Krauss. The talk, ‘A Universe From Nothing’ by Lawrence Krauss, AAI 2009, is available in video on YouTube. It gets into the answers to the question of how large the Universe is near its closing. So you will need to watch it all the way through, but it provides some great insight into the subject.

kfmarani's avatar

At the moment, the universe is finite because as more time passes by, the more of the universe we see. If it was infinite, we could keep seeing more and never stop. This suggests that the universe is growing

ETpro's avatar

@kfmarani The fact that we can see back to the wall of interference when the cosmic background radiation cooled enough to stop reflecting all light means that the part of the Universe we live in, the part created by our Big Bang, must be finite and 13.72 billion years old. We can only see back to 100,000 years after T=0 because before that, the temperatures were too high to permit light to pass through the cosmic background radiation.

But the mind boggling thing is that not only could there be other universes from other Big Bangs, but we could possibly create one here and while within it it would appear to constantly expand, from our viewpoint it would appear to collapse into a black hole.

flutherother's avatar

@ETpro Thanks for the very interesting link. Our universe appears to be expanding but in effect it is getting smaller as distant galaxies fall over the edge of the horizon of the visible. Eventually we will not be able to see anything other than the stars of our own galaxy and evidence of the Big Bang will be lost. Our universe has a radius of 13.7 billion years which will eventually reduce to the diameter of our galaxy.

ETpro's avatar

@flutherother The really fun thing is that right now, anywhere you went in our universe, if you looked out, you would find that from that point, the Universe has a radius of 13.72 billion light years. Actually, if you could see far enough in any direction, you would be looking at the back of your head.

I don’t know why people have such a fascination with the supernatural. The natural is weird enough to keep my mind exploding every time I think about it.

gm_pansa's avatar

the universe? it’s infinite!

ETpro's avatar

@gm_pansa As far as I know, there is no evidence to support that, and a good deal of evidence refuting it.

LostInParadise's avatar

On the contrary, the evidence indicates that the Universe is in fact infinite. See here

ETpro's avatar

@LostInParadise Nice link, but I see nothing there stating that the Universe is infinite. It’s dealing only with its shape, and whether it will continue to expand or collapse back into itself. For some reason, it starts with a headline asking if the Universe is infinite, but never answers that question.

Here’s a bit more depth about whay scientist do not currently think the Universe in infinitely large.

LostInParadise's avatar

The article you cite only talks about the shape at the very end and does not take a stand as to which of the 3 models is correct. A flat Universe implies that it is infinite and the current evidence supports the Universe being flat, as the article I cited indicates.

flutherother's avatar

@LostInParadise The Universe can be flat without being infinite
@ETpro Your link gives the diameter of the observable universe as 93 billion light years which is not really correct. It calculates that distant galaxies have moved much further away since emitting the light that we see today but as I said above this doesn’t make sense from our frame of reference, or any other frame of reference.

LostInParadise's avatar

Now I am really confused. I thought there were 3 models for the universe, closed like a sphere, flat or like an expanding curve. According to the link the universe can be both flat and closed. The guy did say, though, that the currently favored view is that of infinite flat universe.

ETpro's avatar

@LostInParadise The flat universe does not imply that the Universe is infinite, but that it will continue to expand presumably forever/. A beginning in a singularity, and 13.75 billion years to expand implies a finite Universe. Postulating an infinite Universe is the stuff od metaphysics, as there is o way to either porve or falsify such a postulate. Since light travels at a finite speed, we can only see things that meitted their light when they we no more than 13.72 billion light years away from us.

gm_pansa's avatar

haha… just the thought of falling off the universe makes me laugh. what if it IS flat like people once thought about the earth?

….........haha
what if everything we think we know is lies?! o.0

LostInParadise's avatar

To understand the flat universe idea, you have to realize that the plane model a 2 dimensional analog of what a flat universe in 3 dimensions would be like. There is no way of visualizing what it would look like. We would be in no more danger of falling out of a flat universe than the 2 dimensional inhabitants of a planar universe.

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