Small Flat Universe? How is it Possible?

[benk99nenm312]

So, I now understand based on things that I have read, and things that people on this forum have told me, that the universe if flat, must be infinite. My question is, when we look into the farthest reaches of space, we see a small, finite baby universe. How is this possible? The universe can be traced back to a point when it was 10^-33 cm small. Anything infinite begins infinite, from what I have always understood. What's going on, eh?

 

[DaveC426913]

My question is, when we look into the farthest reaches of space, we see a small, finite baby universe.

We do?

 

[benk99nenm312]

we do?

The WMAP.

(poorly stated by me)

 

[DaveC426913]

The WMAP.

(poorly stated by me)

OK, the WMAP shows that the universe was small and hot at one point. This it the prevailing theory. The prevailing theory holds that the universe is about 78G ly across.

There are theories that the universe is infinite, but they are not prevailing theories, partly because, well, the evidence seems to poke a hole in them.

 

[benk99nenm312]

The most recent evidence on the shape of the universe tells us that it is perfectly flat (to within experimental and measurable error). So, what you're saying is that the prevailing theory contradicts the newest intel?

 

[DaveC426913]

The most recent evidence on the shape of the universe tells us that it is perfectly flat (to within experimental and measurable error). So, what you're saying is that the prevailing theory contradicts the newest intel?

I think that the starting premise: "if the universe is flat, it must be infinite" is flawed, or at least misunderstood.

Flatness simply refers to the balance between expansion and contraction; it does not imply infinite extent.

 

[benk99nenm312]

I think that the starting premise: "if the universe is flat, it must be infinite" is flawed, or at least misunderstood.

Flatness simply refers to the balance between expansion and contraction; it does not imply infinite extent.

I have read and heard this. I'll look for links tomorrow.

 

[benk99nenm312]

Okay, this thread is where I found this out. https://www.physicsforums.com/showthread.php?t=317682

There was also this.
http://books.google.com/books?id=UYI...over#PPA226,M1?

But I'm not sure that last book reference would help.

 

[Parlyne]

It seems to me that you're confusing the idea of the entire universe with that of the observable universe. Since the universe has finite age and light travels at a finite speed, we can only observe structures that are close enough to us for light to have propagated to us within the time that the universe has existed. We generally expect that the universe is larger than just what we can see. I believe that the 78 Gly is the best number for the current size of the observable universe. It is unknown how much larger the whole universe is.

 

[benk99nenm312]

It seems to me that you're confusing the idea of the entire universe with that of the observable universe. Since the universe has finite age and light travels at a finite speed, we can only observe structures that are close enough to us for light to have propagated to us within the time that the universe has existed. We generally expect that the universe is larger than just what we can see. I believe that the 78 Gly is the best number for the current size of the observable universe. It is unknown how much larger the whole universe is.

So what you're sayin gis that the observable universe was once very, very small, but the entire universe's size is unknown, even at the big bang?

 

[Parlyne]

So what you're sayin gis that the observable universe was once very, very small, but the entire universe's size is unknown, even at the big bang?

Quite right.

 

[benk99nenm312]

Ahh, now it makes sense.