Is our universe a closed system?

[Jig]

It's not expanding into anything. The way in which we describe the universe as expanding is that space is being created all the time at some rate.

How can space be created? [What is your difinition of "space"]

Imagine drawing a bunch of dots on a balloon, then inflating it. As you inflate the balloon, the dots will get further apart. But the material of the balloon isn't expanding into anything: the dots aren't moving into rubber off the balloon's surface. They're just getting further apart because the rubber itself is being expanded. It's the same with the universe.

I understand your analogy, though it doesn't truely make sense. The balloon is still expanding into "something"; the air around it. There is no observable evidence that suggests "something" can expand into utter nothingness. Absolute nothingness can not be infinitely vast since existence exists, therefore, absolute nothingness is either finite or imaginary.

However, it makes since for existence to be infinitely vast. This works prefectly with the nature of existence. What is wrong with concluding the universe is expanding within the cause that caused it? Since this uncaused cause (which makes up existence) is infinitely vast, it can infinitely absorb such an expansion.

When you look in the context of General Relativity, there really is no limit to space. It can be stretched, compressed, and bent, all by the action of the mass that inhabits the space. Right now, the space in our universe is being stretched by the matter that inhabits it.

This gives no insight into what the universe is expanding into.

 

[Chalnoth]

I understand your analogy, though it doesn't truely make sense. The balloon is still expanding into "something"; the air around it.

That's only an artifact of the fact that we're observing the balloon as a two-dimensional surface in three dimensions. This isn't the case in General Relativity, where you truly only have the four dimensions of our space-time. Curvature in General Relativity is not understood by imagining our spacetime is embedded in higher dimensions.

As such, just consider the rubber itself: the dots aren't moving away from one another into any new rubber, it's the rubber itself that is stretching.

Another way to look at it is to ask the question as to what an expanding universe would look like from the outside. When people have attempted to answer this question, they have found out that it appears that from the outside, the expanding universe looks like a black hole. As such the universe inside this black hole-like object can expand as fast as it wants, but it won't ever be able to escape the event horizon.

 

[Jig]

As such, just consider the rubber itself: the dots aren't moving away from one another into any new rubber, it's the rubber itself that is stretching.

This seems illogical when dealing with "space". Though spacetime is allowed to curve [not necessarily stretch]
based on the presence and amount of stress-energy, the expansion of the mass in our universe would only dilute the amount of stress-energy space is under. If spacetime was strecthing itself as a balloon does, it would not be increasing in speed as it expands.

My model follows the nature of existence, time, space, motion, and causes. Your model appears to be allowing theoretical ideas (which lack significant evidence) to lead the way.

Another way to look at it is to ask the question as to what an expanding universe would look like from the outside. When people have attempted to answer this question, they have found out that it appears that from the outside, the expanding universe looks like a black hole. As such the universe inside this black hole-like object can expand as fast as it wants, but it won't ever be able to escape the event horizon.

This is not an answer. It is also unprovable. Though I have appreciated your comments, your reasoning doesn't agree with mine.

I would like for you to discuss my model and why you think it is illogical. It would help me see your position better.

 

[Dragar]

This gives no insight into what the universe is expanding into.

Space doesn't expand 'into' anything.

I mean, think about it. You are asking a question to which a coherent answer would be a spacial location. This makes sense when we talk about things that move around from spacial location to spacial location.

But now think about asking 'what spacial location is space moving into?'. That's a non-question. You may as well ask "What colour is Wednesday?" or "What's north of the north pole?" or 'What was before time?'

Your model appears to be allowing theoretical ideas (which lack significant evidence..

I'd hardly call general relativity lacking in significant evidence.

 

[Jig]

Space doesn't expand 'into' anything.

Your response tells me you were not paying attention to the previous posts in this debate...many of your comments have been addressed. Go back and read my other posts.

 

[Dragar]

And your response tells me you haven't understood any of Chalnoth's (very fine) explanations. Try re-reading them.

 

[Chalnoth]

This seems illogical when dealing with "space". Though spacetime is allowed to curve [not necessarily stretch]
based on the presence and amount of stress-energy, the expansion of the mass in our universe would only dilute the amount of stress-energy space is under. If spacetime was strecthing itself as a balloon does, it would not be increasing in speed as it expands.

That depends upon what kinds of energy make up the universe. This is true for photons, which dilute themselves at a rate of 1/a^4. This is true for normal matter, which dilutes itself at a rate of 1/a^3. But it wouldn't be true for some other, more exotic forms of matter. Things like certain scalar fields and vacuum energy might not even change much at all in density as the universe expands.

Precisely what is causing the accelerated expansion is currently unknown, and a very interesting problem in physics today. But one possibility is simply that even if you take all matter out of a region of space, there is still some energy density of the vacuum left behind. This is, in fact, something that we expect to occur from quantum mechanics. The problem is that the most naive ideas from quantum mechanics result in a value 10^120 times bigger than what the vacuum energy would have to be to explain our current expansion. There are some ideas from the string theory landscape that might potentially solve this problem. Anyway, it's an open question, but we have no shortage of theoretical ideas of possible types of matter that don't dilute themselves as the universe expands.

My model follows the nature of existence, time, space, motion, and causes. Your model appears to be allowing theoretical ideas (which lack significant evidence) to lead the way.

No, dark energy is totally and completely an experiment-driven field of research. Everybody just assumed that there was none until it was experimentally shown back in 1998 that the universe's expansion was accelerating. Since then we've been successively eliminating possible explanations for this observed acceleration by performing more and more observations. Future observations of cosmic shear are expected to dramatically narrow the possibilities.

Edit: Oh, yeah, you were probably talking about me saying that space doesn't expand into anything, and that just comes down to general relativity. Dragar's got it right.

This is not an answer. It is also unprovable. Though I have appreciated your comments, your reasoning doesn't agree with mine.

I would like for you to discuss my model and why you think it is illogical. It would help me see your position better.

Here's one way of looking at it: in order to get a universe started, you'd need so much energy that you would form a black hole. So a universe starting inside another couldn't ever expand into the surrounding space, but that doesn't mean that an observer inside the universe couldn't see the universe expanding from its point of view.

This is basically an answer to the question, "If the universe was so dense at the beginning, why didn't it just form a black hole?" Well, it did! And we're still inside it!

 

[Jig]

No, dark energy is totally and completely an experiment-driven field of research.

What are the possiblities that the observed inconsistencies, said to be that of dark matters presence, are actually due to an incomplete understanding of gravitation?

Here's one way of looking at it: in order to get a universe started, you'd need so much energy that you would form a black hole.

Where did this large amount of energy come from?

 

[Job_s_First_Son]

http://www.infidels.org/library/modern/mark_vuletic/vacuum.html

Chalnoth,
I'd like your view on the article above. Is it outdated? Do you think this guy is reaching to support his conclusion? I like the particle/anitparticle thing.

Maybe this should be for another thread as it might derail this one and this has been good. Thanks Chalnoth & Jig.

 

[Nacho]

Chalnoth: Great stuff. I've enjoyed reading.

 

[Chalnoth]

What are the possiblities that the observed inconsistencies, said to be that of dark matters presence, are actually due to an incomplete understanding of gravitation?

That has been ruled out as an explanation for dark matter, by observations of the bullet cluster. It is still being explored as an explanation for dark energy, and we should be able to distinguish between modified gravity and dark energy with future cosmic shear experiments (if it's modified gravity, the cosmic shear experiments won't agree with other measurements of dark energy). Right now, from looking at the papers suggesting modified gravity, it seems extremely unlikely to me that modified gravity is causing the observed expansion. But we'll see soon enough whether or not this is the case.

Where did this large amount of energy come from?

Quantum fluctuations. There's a foam of particles popping in and out of the vacuum all the time.

 

[Chalnoth]

http://www.infidels.org/library/modern/mark_vuletic/vacuum.html

Chalnoth,
I'd like your view on the article above. Is it outdated? Do you think this guy is reaching to support his conclusion? I like the particle/anitparticle thing.

Maybe this should be for another thread as it might derail this one and this has been good. Thanks Chalnoth & Jig.

I don't know. I haven't thought about the total energy of the universe in that way. I somewhat suspect it is out of date, though, as all of it is from before the big boom in cosmology that started in 1998. I'll have to think about it a bit. But my initial reaction is that it just doesn't make sense to talk about the total energy of the universe.

 

[Dragar]

I found a pretty good FAQ by Michael Weiss and John Baez, some time ago.

 

[Simonski]

Of course it's not a closed system, it's expandin'!

 

[sodapop112]

its expanding but theres only a limited amount of matter in the universe

 

[Chalnoth]

its expanding but theres only a limited amount of matter in the universe

That's not really clear. Matter is created and destroyed all the time. Sure, the total energy that exists as normal matter is going to be roughly constant with time, but not exactly constant.

 

[sodapop112]

how is matter destroyed? even if it gets sucked into a black hole the same amount of is there...only a lot smaller and a lot more dense

 

[YOURGODSAREHERE]

The universe has been found to be a large fish tank with mirrors and lights.

 

[Chalnoth]

how is matter destroyed? even if it gets sucked into a black hole the same amount of is there...only a lot smaller and a lot more dense

The primary method for energy to be lost occurs for all relativistic particles. The particle will race off towards distant galaxies, slowly catching up to those moving at approximately the same speed. As it does this, it loses relative kinetic energy. If a good portion of the total (mass + kinetic) energy of the particle is in kinetic energy, this is energy density that has been removed from the universe.

Another method would be for dark matter particles to annihilate with one another: if dark matter is weakling interacting enough, it may be made of equal amounts matter and anti-matter. When dark matter clumps most closely, some of these particles will annihilate, setting free highly relativistic particles from the annihilation, particles which will lose energy over time due to the expansion of the universe.

And then we have vacuum energy: if the observed acceleration of the universe is really due to a constant energy density of the vacuum, then merely the expansion of the universe will increase the total energy within a certain volume that expands along with the universe.

 

[sodapop112]

how do scientists know that anti-mater exsists