the universe

[lugal-demon-lord-king-0]

i heard somewhere that the big bang theory doesn't account for eveything so is it possible that the universe is enternal? if not how?  

[VorpalNeko]

lugal-demon-lord-king-0

i heard somewhere that the big bang theory doesn't account for eveything ...

Of course it doesn't. Nothing does, or ever could, satisfy such a standard. It really makes me wonder why those that bring up such a "point" insist on an impossibly high standard for BBT, much higher than they do for anything else, because it looks like nothing more than a dishonest rhetorical trick.

lugal-demon-lord-king-0

so is it possible that the universe is enternal? if not how?

It's possible. In one sense, it's even plausible--general relativity has a straightforward consequence that time is a property of the universe, rather than something quasi-external through which the universe evolves. So if by eternal, you mean "exists at all times" and if GTR is at correct at least in this if not in all respects, "the universe is eternal" becomes a tautology, regardless of whether time is infinite in the past direction. If there is no time outside the universe, then of course the universe exists at all times.

More complicated is the question of whether the universe is temporally infinite (as perhaps that's what you meant by "eternal"). On that issue, no one knows, or even has any good good data on. What I can say is that there are cosmological models for both cases and neither of them are strictly ruled out by observations, although those with finite extension into the past have some advantages over those that do not.  

[lugal-demon-lord-king-0]

now i am wondering of time itself. gravity could have a particle and we know its effect. electromagnetism,nuclear forces also have a effect we kinda know about. so can time have a quasi-particle or is it something like temperature?  

[Sioga]

I have a question. What is a quasi-particle?  

[VorpalNeko]

lugal-demon-lord-king-0

now i am wondering of time itself. gravity could have a particle and we know its effect.

GTR predicts gravitational waves, and QM says waves should be quantized. So it is expected that there is a quantum of spacetime curvature: the graviton. Unfortunately, just because it's named, doesn't mean it's either proven or even has a good candidate theory behind it. Although probably almost all physicists would be very surprised if gravity didn't have a graviton, whatever the details of how it behaves turn out to be.

lugal-demon-lord-king-0

electromagnetism,nuclear forces also have a effect we kinda know about. so can time have a quasi-particle or is it something like temperature?

With quantization, see above. Without... well... spacetime could have a quasiparticle even if it is not itself quantized, e.g., in plain GTR. I'm not sure whether or not it actually does, since I don't know nearly enough about gravitational waves except in the linearized limit, which would be completely inadequate and inappropriate to answer that. All I can say is that it's an interesting issue and I wouldn't be at all surprised at any answer, including "too hard to say."  

[VorpalNeko]

White Angel Raven

I have a question. What is a quasi-particle?

Good question. As an intuitive definition, we can say "some emergent property of a system that acts similarly to a particle." There are numerous examples, but one of the more straightforward ones is would be an absence of an electron. It almost seems silly at first--at the most basic level, a material would be made of atoms, and any conduction it does is caused by a flow of either electrons or positive ions. But nevertheless, it is many cases more fruitful to track the electron 'holes' rather than the electrons themselves.

But it really is much more general than that. Another example is that of water waves in a shallow channel. Under such conditions, one can have 'solitary' waves, which are stable and don't merge together. Or, more precisely, when there is a fast wave that encroaches on a slow wave, when they meet you have some (nonlinear!) mixture of the two, but a short time later they seem to separate and go on just as they were before meeting. Or did they? Another (mathematically valid) interpretation is that they bounced off one another, with the first wave gaining speed and the back (initially faster) wave losing it. They would be examples of 'solitons'--a type of quasiparticle.

There are more examples, but most of them are much less intuitive.  

[Sioga]

so a quasiparticle is basically an atom without electrons?  

[VorpalNeko]

White Angel Raven

so a quasiparticle is basically an atom without electrons?

No. But the lack of an electron could be considered a quasiparticle in some cases. (Note: that's just a particular example of a quasiparticle; see previous post for another and keep in mind there are many more.)

I'm not sure I'm making this clear enough, so let me illustrate with something more mundane: imagine you have a hole in your wall. The wall is the thing, and the hole is a property of that thing. Now let's talk about holes and completely ignore the fact that there's a wall associated with it. Then we're treating the hole as if it was a thing in itself, even though there is a wall behind it. The hole 'itself' is then a "quasi-thing", not the wall with a hole in it.

Sometimes, doing this is turns out to produce a much more powerful and insightful description of the physics involved, which is why it is done in the first place. In semiconductors, for example, electron holes act pretty much like positively-charged particles--they move around, repel one another, etc. What really happens, of course, is that the electrons shift, filling in one hole and producing another, making it seem like the hole is moving, but keeping track of all that turns out to be quite a bit more complicated than keeping track of just the hole.

Then we get other examples like soliton waves, which are waves but keep together like particles and seem to bounce off one another like particles--see previous post.  

[Sioga]

ohh. ok. sorry, im entering ninth grade this year so im probably not as educated as you are. redface im really into this stuff and want to learn as much as i can any way i can.  

[VorpalNeko]

That's no problem at all. Just ask--I can always try to make a different explanation. I don't think the OP meant quasiparticle in the technical sense either (so I answered mostly in terms of gravitons, which would not be 'quasi'). But quasiparticles are interesting in themselves.