I have two questions;
First, how was the value about the size of the universe at the end of this list http://en.wikipedia.org/wiki/Orders_...nitude_(length) calculated?
Second, how can be universe infinite if it has a finite rate of expansion and it is stated that after the first Planck time it was the size of grapefruit etc., it makes no sense to me that an universe can be infinite after a finite time expanding at a finite velocity and how its shape matters in this?

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Originally Posted by Ronald Brak

"I've explained it before, but I will explain it again for the uninitiated. Now pay close attention, this is important: Asteroids have space pirates, planets have princesses. Minor planets have minor princesses that you can practice saving from minor threats such as bad hair days or Sarlac breath before you move on to saving a full blown princess from a major threat such as an evil galactic warlord or 70s hair."

First: It was calculated using cosmic inflation theory, as your link says (your link needs to include that final bracket in order to work). Check out that cosmic inflation link at the end of that list

Second: What makes you think the universe is infinite? Also, if it doesn't make sense for it to become infinite after a finite length of time then it must have been infinite to begin with. In that case something can be infinite and can also expand.

But around here I often see the universe described as finite but unbounded. This can mean it contains a finite amount of space, but has no edge. An analogy for this, using only 2 dimensions, is the surface of a sphere. That surface is 2 dimensional, finite in spacial extent, but has no edge (if you travel far enough and can beat the rate of expansion, you find yourself back where you started). Perhaps our universe can be represented by the 3 dimensional surface of a 4 dimensional sphere.

How it can be infinite from the beggining and expand?

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Originally Posted by Ronald Brak

"I've explained it before, but I will explain it again for the uninitiated. Now pay close attention, this is important: Asteroids have space pirates, planets have princesses. Minor planets have minor princesses that you can practice saving from minor threats such as bad hair days or Sarlac breath before you move on to saving a full blown princess from a major threat such as an evil galactic warlord or 70s hair."

The visible universe certainly is not infinite.

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"I'm as accurate as any psychic. And I'm a cartoon!" -- Squidward

"Arrrgh, the laws of physics be a harsh mistress!" -- Bender

I know this ofc, but we're talking abou the REAL radius of the ENTIRE universe, not just the part we see from our viewpoint at Earth.

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Originally Posted by Ronald Brak

"I've explained it before, but I will explain it again for the uninitiated. Now pay close attention, this is important: Asteroids have space pirates, planets have princesses. Minor planets have minor princesses that you can practice saving from minor threats such as bad hair days or Sarlac breath before you move on to saving a full blown princess from a major threat such as an evil galactic warlord or 70s hair."

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Everyone is entitled to his own opinion, but not his own facts.

I get a Widipedia does not have a page by that name error.

What page did you mean?

I was confused as to where you got the information that the universe was infinite.

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"I'm as accurate as any psychic. And I'm a cartoon!" -- Squidward

"Arrrgh, the laws of physics be a harsh mistress!" -- Bender

fixed URL, the closing bracket was missing, as speedfreak also noticed.

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"Ignorance more frequently begets confidence than does knowledge" -- Charles Darwin

"Ignorance convinces" -- slang's dad

We cannot know, as of yet, if the universe is finite or infinite. If the rate of expansion is accelerating as we think it is, we will probably never know. With accelerating expansion there is a threshold beyond which we can never see, a cosmological event horizon that marks the furthest distance we will ever see new events from. Currently that horizon is around 16 billion light years away from us (in terms of proper distance) and with accelerating expansion it is moving towards us, getting closer to us.

This means that we will eventually receive the light from events happening right now that are up to 16 billion light years away, but we will never see the light from events that are occurring right now at any distance further than that. As time goes on, the threshold beyond which we cannot see new events moves towards us until, in the end, we can only see the galaxies in our own supercluster.

We think the observable universe is currently 46 billion light years in radius and its growth is accelerating, but we will only ever see up to 16 billion light years of that distance. Currently, the most distant object we have observed was under 6 billion light years away when it emitted its light nearly 13 billion years ago. So over the next billions of years we will see light coming in that was emitted at distances up to 16 billion light years. We will also of course see the light from more distant objects, but that light will have been emitted in earlier times when those objects were actually closer than 16 billion light years away.

Based on this, we do not expect to ever be able to see the edge of the universe, or to see the past light of our own galaxy coming back at us after circumnavigating the universe.

Having said all that, both possibilities still remain - the universe might be finite or infinite. But if it were infinite, how could it expand? Well, the first thing to remember is that infinity is not a number, it is not a quantity, it is a mathematical limit that you cannot count up to. If you add or subtract something from infinity, you still end up with infinity and it all depends on the context in which you are considering infinity.

Are we talking infinite space and infinite mass? Or finite mass within infinite space? It is easy to get tied up in knots at this point. If the universe were infinite would there be an infinite number of galaxies too?

What we have to consider that there is always a finite amount of space between neighbouring clusters of galaxies. Whether the universe is infinite or finite, the gaps between things are always finite in extent and quantifiable. If these distances or quantities increase, how does that effect the overall picture? Remember, infinity is not a number.