Cosmology thread

[TJSwoboda]

Okay, since the other thread turned into angels dancing on pinheads, I want to give this another crack in its own thread.

The universe: Finite but unbounded, bounded, or infinite? Will there be a big crunch or a heat death? Is the universe's expansion accelerating, or was time passing at a different rate in the images we're looking at from 45 billion light years out, when the first stars had just formed?

The Inflation Theory postulates that in the early billionths of a second after the Big Bang, this is exactly what happened: that space expanded at a rate of speed far in excess of the speed of light. Only massless particles can travel at the speed of light. Anything with mass, even a neutrino with the least possible mass we know of, can't travel at the speed of light, it must go somewhat slower. But space has no speed limit.

It's been a while since I studied it, so I don't recall how fast the inflationary expansion was, or how long it lasted. But I do recall that because of inflation, we can only "see" a 13+ billion radius of the actual universe. since much of it is much farther away, the light has not yet had time enough to get here so we can see it.

If I understand correctly, calculations with what we understand of the Inflation Theory indicate that the universe is finite but unbounded, and is about 3x10^23 the size of the observable universe, right? How popular are other hypotheses, infinite universe etc.? I know the entire universe could, theoretically, be smaller than the observable universe, but again if I'm remembering correctly it's been proven that it has to be at least 98.5% the size of what we can see, and that figure has been climbing.

I don't like the idea of infinite matter and energy, going on forever until you're statistically likely to run into another Earth, but it is favored by some cosmologists, right?

 

[TheCPE]

I believe there is some pretty good data to suggest the shape of the universe is flat. I would speculate it is bounded and that heat death is the ultimate conclusion of our universe.

It is so difficult to conceptualize things like shape and size of the universe though. The idea of a bounded universe makes sense but it also appears to suggest a barrier or defining edge of the universe.

:shrug:

 

[James Snover]

Get me drunk and here is what I would speculate:

It is currently theorized that the universe is expanding. And the farther out we look, we see the universe expanding faster. And the rate of expansion appears to be accelerating, too. So the current conclusion is:

The universe is not only expanding, but the rate of the expansion of the universe is accelerating.

I'm not so sure that is an accurate statement. I think the statement should be:

In the past, the expansion of the universe was faster than in the present. And that in the past the rate of the expansion of the universe was accelerating.

Here's why I say that: We see the universe expanding away from us at great distances. We know that the farther out we look, the farther into the past we are looking due to the lightspeed delay. So in the far distant past, we see expansion and increase in the rate of acceleration of expansion.

But the closer in we look, within our own local group of galaxies, we see very little, or no, redshift, and we conclude there no expansion at local distances.

So it seems to me that, if the principle of "redshift = expansion of the universe" apply equally throughout the universe, then as far as we can tell, the universe most likely is not expanding "now." And since we can only see a 13+ billion light year radius, and that most of that is from the far distant past, then we don't know what the universe is doing now.

Get me really drunk, and I'll say: if we observe any local blue-shift of light, we might be in trouble. And since reduced red-shift is the same as increase in blue-shift, we might be in trouble.

And then I'll drink my third beer and pass out drunk.

 

[TJSwoboda]

At first the idea of a flat universe makes little sense to me, but then I remember that it's the consensus among cosmologists. A flat universe seems to me to imply that the geometry of the universe is Euclidean, but I'm probably reading it wrong.

Edit: Posted before I saw Jim's post. Actually, that makes a lot of sense: We can see the early universe was expanding, but at present it really isn't. Would a local blue-shift mean the universe is contracting?

 

[TheCPE]

Also, the further from the center of ejection (big bang) the higher the initial expansion velocity.

I believe there is some thoughts that perhaps parts of the universe are racing away from each other and this create bubbles and effect the observable universe.

 

[TheCPE]

Would a local blue-shift mean the universe is contracting?

Yes.

The time frame of such events however would make our observation of it even if the universe were contracting highly unlikely. That we haven't observed a blue shift to me indicates we never will.

 

[TheCPE]

Get me drunk and here is what I would speculate:

It is currently theorized that the universe is expanding. And the farther out we look, we see the universe expanding faster. And the rate of expansion appears to be accelerating, too. So the current conclusion is:

The universe is not only expanding, but the rate of the expansion of the universe is accelerating.

I'm not so sure that is an accurate statement. I think the statement should be:

In the past, the expansion of the universe was faster than in the present. And that in the past the rate of the expansion of the universe was accelerating.

Here's why I say that: We see the universe expanding away from us at great distances. We know that the farther out we look, the farther into the past we are looking due to the lightspeed delay. So in the far distant past, we see expansion and increase in the rate of acceleration of expansion.

But the closer in we look, within our own local group of galaxies, we see very little, or no, redshift, and we conclude there no expansion at local distances.

So it seems to me that, if the principle of "redshift = expansion of the universe" apply equally throughout the universe, then as far as we can tell, the universe most likely is not expanding "now." And since we can only see a 13+ billion light year radius, and that most of that is from the far distant past, then we don't know what the universe is doing now.

Get me really drunk, and I'll say: if we observe any local blue-shift of light, we might be in trouble. And since reduced red-shift is the same as increase in blue-shift, we might be in trouble.

And then I'll drink my third beer and pass out drunk.

Interesting, and this got me thinking.

I was under the impression that as you pointed out the more distant the reference (in most cases supernova) the further back in time the explosion occurred. Then by making as many supernova observations as possible and knowing relative distance and thus relative time frames of the explosions of the stars than it would be fairly simple to determine the amount of redshift of each of these events in relation to the others. Therefore, the reason we know that expansion is accelerating is because we don't observe a linear relationship in redshift based on distance.

That is my understanding of how the conclusion of an accelerating universe was drawn.

However, your post brings up a very interesting idea: If the way you describe the observations is accurate and we are seeing faster expansion at greater distance how do you discern the difference between time contraction vs expansion?

 

[oldmodman]

A farmer was standing in his field, chewing a stalk of straw.

When a city slicker drove up and asked him for directions.

"Hey buddy! Can you tell me how to get to the edge of the Universe from here?"

And the farmer replied, "Sorry to tell you mister. You can't get there from here"

 

[James Snover]

You get a lot of time to think, herding cattle all day.

A farmer was standing in his field, chewing a stalk of straw.

When a city slicker drove up and asked him for directions.

"Hey buddy! Can you tell me how to get to the edge of the Universe from here?"

And the farmer replied, "Sorry to tell you mister. You can't get there from here"

 

[astrodudepsu]

Heat death.

Flatness doesn't mean what most people think it means.

In cosmology flatness refers to the energy density of the universe. A flat universe in that case describes a universe where the critical energy density divided by the energy density equals 1.

As a visual its not dissimilar to a pane of glass. They can be convex, concave, or flat. If the ratio of critical energy density / energy density = 1 the pane is flat. If its less than 1 or greater than 1 its convex or concave. These terms are just used as conceptual aides and doesn't imply that the universe conforms to that actual shape.

It's very hard to explain without math.

 

[James Snover]

Uhh ... I'm going to have to think about that for a bit ...

But just so I'm clear on what you're saying: the rate of expansion may be uniform from now all the way to the past at 13+ lightyears, but we may be observing it to be going faster due to time running at an increased rate of speed, way out there, way back in the past. Does that accurately summarize what you're suggesting?

However, your post brings up a very interesting idea: If the way you describe the observations is accurate and we are seeing faster expansion at greater distance how do you discern the difference between time contraction vs expansion?

 

[TheCPE]

Uhh ... I'm going to have to think about that for a bit ...

But just so I'm clear on what you're saying: the rate of expansion may be uniform from now all the way to the past at 13+ lightyears, but we may be observing it to be going faster due to time running at an increased rate of speed, way out there, way back in the past. Does that accurately summarize what you're suggesting?

Right, how do you discern between time contraction vs spacial expansion. Or is this a moot point considering it isn't space AND time but space-time.

 

[astrodudepsu]

Time dilation and Lorentz contraction are related. Two sides of the same coin.

But expansion of space time is a different animal, not related to the other two above in the current standard model.

 

[TheCPE]

But expansion of space time is a different animal, not related to the other two above in the current standard model.

But would there be any way to discern that it is spacial expansion vs atomic processes retarding, ie time slowing. The difference may be pointless though as what we observe as reality is indifferent to the distinction?

 

[James Snover]

I'm going to say no, the expansion of the universe is not an apparent effect caused by the contraction of time. If it were, we would be seeing a lot more novae/supernovae the farther out (back in time) we look. The stars would be speeding right through their life cycles. That does not seem to be the case.

Right, how do you discern between time contraction vs spacial expansion. Or is this a moot point considering it isn't space AND time but space-time.