Origins of the Universe

[michel123456]

 

Analogies are like condoms. If you're going to stretch them for use with elephants, something is likely to break.

Funny.

 

But it is not a stretch, it is more like turning it inside-out.

In your analogy you say: an ocean with no boundaries, and more water (space) is constantly being added. Here water acts as the aether (dangerously).

It is NOT a situation where the amount of water remains the same and is stretched (like a condom) "until it is a thin film of water".

[neutrinosalad]

But it is not a stretch, it is more like turning it inside-out.

In your analogy you say: an ocean with no boundaries, and more water (space) is constantly being added. Here water acts as the aether (dangerously).

It is NOT a situation where the amount of water remains the same and is stretched (like a condom) "until it is a thin film of water".

 

In my analogy, water is the matter and space is expanding between the molecules of water until it is a thin film.

 

Edit: Re-reading everything and I guess my analogy is not the same as Phi's analogy. Still, I am pretty sure what I am saying is conceptually similar to what Phi is saying.

 

Also, the "thin film of water" part is coming from this article that I read: http://www.space.com/52-the-expanding-universe-from-the-big-bang-to-today.html

 

Here is where that additional part is coming from:

 

 

The shape of the universe and whether or not it is finite or infinite in extent depends on the struggle between the rate of its expansion and the pull of gravity. The strength of the pull in question depends in part on the density of the matter in the universe.

 

If the density of the universe exceeds a specific critical value, then the universe is "closed" and "positive curved" like the surface of a sphere. This means light beams that are initially parallel will converge slowly, eventually cross and return back to their starting point, if the universe lasts long enough. If so, according to NASA, the universe is not infinite but has no end, just as the area on the surface of a sphere is not infinite but has no beginning or end to speak of. The universe will eventually stop expanding and start collapsing in on itself, the so-called "Big Crunch."

If the density of the universe is less than this critical density, then the geometry of space is "open" and "negatively curved" like the surface of a saddle. If so, the universe has no bounds, and will expand forever.

If the density of the universe exactly equals the critical density, then the geometry of the universe is "flat" with zero curvature like a sheet of paper, according to NASA. If so, the universe has no bounds and will expand forever, but the rate of expansion will gradually approach zero after an infinite amount of time. Recent measurements suggest that the universe is flat with only a 2 percent margin of error.

 

I was getting the idea of the geometry of the universe being flat mixed up with the expansion of space.

 

Which is also another thing I am wondering about. Will the universe expand forever or will it reach a critical point where it starts collapsing on itself?

Edited October 26, 2015 by Capayan

[Bill Angel]

In my analogy, water is the matter and space is expanding between the molecules of water until it is a thin film.

 

Edit: Re-reading everything and I guess my analogy is not the same as Phi's analogy. Still, I am pretty sure what I am saying is conceptually similar to what Phi is saying.

 

Also, the "thin film of water" part is coming from this article that I read: http://www.space.com/52-the-expanding-universe-from-the-big-bang-to-today.html

 

Here is where that additional part is coming from:

 

If the density of the universe exactly equals the critical density, then the geometry of the universe is "flat" with zero curvature like a sheet of paper, according to NASA. If so, the universe has no bounds and will expand forever, but the rate of expansion will gradually approach zero after an infinite amount of time. Recent measurements suggest that the universe is flat with only a 2 percent margin of error.

I was getting the idea of the geometry of the universe being flat mixed up with the expansion of space.

 

Which is also another thing I am wondering about. Will the universe expand forever or will it reach a critical point where it starts collapsing on itself?

Here is another analysis of the rate of expansion of space:

Recent observations of distant supernova have suggested that the expansion of the universe is actually accelerating or speeding up... which implies the existence of a form of matter with a strong negative pressure. This strange form of matter is also sometimes referred to as the dark energy. Unlike gravity which works to slow the expansion down, dark energy works to speed the expansion up. If dark energy in fact plays a significant role in the evolution of the universe, then in all likelihood the universe will continue to expand forever.

See http://map.gsfc.nasa.gov/universe/uni_fate.html

One scenario is that in the distant future the expansion of space (driven by this dark energy) will accelerate to reach the point where all the atoms of the universe are ripped apart.

[robinpike]

 

False premise. Remember that the universe is all there is the entire time space is expanding.

 

I hesitate to introduce the balloon analogy, but what the heck. Imagine the surface of a balloon (just the surface, not the empty inside space!). No mouthpiece, seamless latex, very tiny. As it expands (not explodes), the surface gets bigger, the way space did after the BB. If you draw some dots on the surface and then blow it up, the balloon represents space and the dots represent matter like planets and stars. Space is expanding in between the matter, everywhere at once. No center on the surface of a balloon, right?

 

So from the very small size of the universe, the space expanded - but how did the expanding space cause the very dense matter to move apart?

 

Wouldn't gravity keep the matter in one lump while the space expanded?

[Strange]

 

So from the very small size of the universe, the space expanded - but how did the expanding space cause the very dense matter to move apart?

 

Wouldn't gravity keep the matter in one lump while the space expanded?

 

Effectively, because matter was homogeneously distributed through all of space so, in a sense, there wasn't anything to stop it moving apart. If there is an even distribution of matter then there is no net force. And it requires a force to stop things being affected by expansion.

[robinpike]

 

Effectively, because matter was homogeneously distributed through all of space so, in a sense, there wasn't anything to stop it moving apart. If there is an even distribution of matter then there is no net force. And it requires a force to stop things being affected by expansion.

 

Thanks, that is the point isn't it - I was thinking of the matter as a lump with space around it - and that is not the way to think of it.

[michel123456]

 

Effectively, because matter was homogeneously distributed through all of space so, in a sense, there wasn't anything to stop it moving apart. If there is an even distribution of matter then there is no net force. And it requires a force to stop things being affected by expansion.

Doesn't that presuppose an infinite amount of matter?

[Phi for All]

Thanks, that is the point isn't it - I was thinking of the matter as a lump with space around it - and that is not the way to think of it

 

As I understand it, the matter expanded when the conditions for its extreme density were released with the expansion of spacetime. It would reach a point where it was no longer dense enough to be required to remain together. Matter was then homogeneously distributed until it cooled enough to begin separating and forming the bodies made of elements we're familiar with.

[neutrinosalad]

 

As I understand it, the matter expanded when the conditions for its extreme density were released with the expansion of spacetime. It would reach a point where it was no longer dense enough to be required to remain together. Matter was then homogeneously distributed until it cooled enough to begin separating and forming the bodies made of elements we're familiar with.

 

Does the expansion of spacetime mean that at the start of the big bang, t = 0? This is for time itself.

[Strange]

 

Does the expansion of spacetime mean that at the start of the big bang, t = 0? This is for time itself.

 

There is a convention that t=0 at the "start" of the big bang. However, there are several models where there is no start (see the current thread about "no big bang", for example).

[neutrinosalad]

 

There is a convention that t=0 at the "start" of the big bang. However, there are several models where there is no start (see the current thread about "no big bang", for example).

 

Yes, I read the article in the OP of the other thread after reading your post. I like the idea of time extending in both directions perpetually. Not sure if I am a fan of the idea that there will never be a big crunch and there never was a singularity.