cfgauss

No, no, you're not understanding what I'm trying to say.

First of all, there's not really one theory about what's going on in the big picture like this, although we have several good ideas. But many theories, which have evidence, have conflicting results. Mainly, there are observations "confirming" that the universe's expansion is staying the same, slowing, and speeding up. So we don't really know for sure. IMO, we need a long, more thorough and varied investigation into this to get a good answer. Then there's inflation, which looks like a good idea, but doesn't do much yet, and not everyone buys. And there's the idea that the speed of light changes over time, although, again, not everyone buys this idea. And on and on. Quantum gravity (which is what I'm interested in) may lead us to some answers on the nature of the early universe.

However, what it seems to *me* is that the universe's expansion = the speed of gravity = the speed of light. This number changes with the age of the universe (possibly due to other things, but I won't get into that). I've actually got some cool theories on this, but don't yet (and won't for a while) have the tools to deal with them. However, there are no blatant errs in any of my ideas, AFAIK.

Answerer

Well cf, you haven't really explained why you think that the universe's expansion will never be faster than the speed of light.

eh

cfgauss,

What experiments confirm that expansion rate is staying the same? Or slowing down? Theory had most believe the universe would be slowing down, so it came as a surprise that it was in fact accelerating.

This seems like a source of confusion. The speed gravity is a measure of how fast gravitational waves travel. But apparently, gravity waves and the expanding universe are not the same thing. Flat space will always expand, and the speed of expansion is not bound by the speed of light. So all bets are off when it comes to how fast the universe will expand in the future.

cfgauss

Answerer-- I never said that. Well, that depends on what you mean by "faster."

eh--

Yes, theory does say it should be slowing down, but observations say it's slowing, speeding up, and staying the same. So, we really can't know for sure until we can get a cool theory that works, or until we get more good astronomical data.

You still aren't getting the expansion thing, though. You should think of c, the speed of light, not like a constant, but more like c(t), a function that changes with time. By definition, light always moves at c. Gravity also always moves at the speed of light and the universe always expands at the speed of light. But, yes (probably, well, possibly), the universe was, in the past, expanding faster then c(now) and gravity did propagate faster than c(now). Making more sense?

Answerer

Well, actually you did as we can all see from above. You assumes that the universe expands at the speed of light(I'm not talking about C, the present speed of light but general). Yet you failed to tell us the reasons of why you like to think that the expansion of the universe can't be faster than the speed of light?

cfgauss

It does expand at the speed of light, but the speed of light changes. I don't, however, have 8 years to explain cosmology mathematically (which, AFAIK, is the only way to convincingly explain this!), so it does "because we say so" .

Osm bsm Y.

a quick clarification on what i was saying. i understand that if something goes left at the speed of light and something else goes right at the speed of light...they are moving AWAY from each other at twice the speed of light.


i think u have something with c(t) gaussface. however, it would seem that if "speed of light = speed of gravity = *speed of expansion*", when we looked backward toward where we had just traveled we would see nothing because we are out running all light behind us... in addition, how can something traveling the speed of light rotate? wouldn't the rotation facilitate faster then light movement for the surface traveling with the velocity of the whole?

of course if c(t) is true, there are some possible (observable?) aspects of it. either light that began traveling at c(now - blahblahblah) is traveling faster then c(now) and should be crashing into/interfering with light launched at c(now), or all light throughout the universe is not only launched at c(now) but will slow down to some speed c(now + blahblahblah) as it travels, but then, of course, what causes the coordination of light to have one speed and not crash/interfere? if we try to say it is coordinated throughout the universe, it would seem a moot point...similar to the ether.

again, however, i would buy into c(t) before inflationary theory, so you get my vote there.

Osm bsm Y.

this would have to be explained a bit better for me if you don't mind sparing more time on it. i don't know what he means by false vacuum or what quantum tunneling is. =(

thanks very much for your answer though. u and DNAUnion seem to have a very good grasp of early happenings theories...or atleast a strong enough fascination with it to have searched for many explanations.

i have trouble imagining an opaque universe...i read somewhere that 99.9+% of the atom was empty "space". that light is actually stopped by the atoms fields rather then true collision. in fact, even what we think of as collision is really fields pushing against fields on a level too small to see. thus defining opacity as a property of fields formed by atoms...is there particles with fields as strong that aren't quickly pulled/formed into atoms?

in a state outside the atom, unless particles that make up atoms have been destroyed since, it would seem the same amount/sparcity of particles still exists now as did then. if there was ever a time when all light could be absorbed by particles nearby, it would have to be a very dense universe. not expanded/inflated all that far. they say 300,000 years to formation of atoms and that i could buy, but it seems that there isn't enough density to absorb light that was created before that. if fields alone stopped it, those fields would have to be strong, BUT not strong enough to cause atom formation. atleast from what i understand =(

NumberTenOx

OK, lots of things to discuss! Remember I'm not an expert, just an interested person, I'm probably wrong about a lot of what I say.

About two observers moving away from each other at the speed of light: Each would see the other moving away at exactly the speed of light. This is easier to imagine if you think of them both converging on an independent observer at 3/4 the speed of light (the only thing that can travel at the speed of light is a zero-rest-mass particle, and for it time in the universe has stopped). They will each see the observer moving at 3/4 c, and each other whizzing by at less than c. They will never see each other going faster than c.

And there is no "looking backward toward where we just traveled". We are not moving anywhere. Every observer in the universe sees themselves as (relatively) motionless, and the universe is all expanding away from them.

The question of whether the universe can "expand faster than c" is something I don't quite understand. Nothing in the universe can travel faster than c, however if enough space is being "created" between two points, then their effective separation can be faster than c. That is what - I think - inflation theory says.

Even without inflation, think of this. If the size of the universe is defined by a function: D(t), is this function constrained such that any two points in the universe can't diverge at faster than c? Remember that nothing is really "moving". Space is being stretched, space is being created, really, everywhere at once. If enough space is created between two points then they will be separating at faster than c, even though nothing is really moving.

About light and atoms. First, yes, the early universe was very dense. Second, think of a single free electron. Because it's "free", a light particle traveling nearby will interact with it, will "scatter". You can think that its field extends a long way, so its ability to scatter light is large.

But when it gets bound up by a proton to make a hydrogen atom, then its field gets bound up as well. If you move a little bit away from the atom, then you don't feel the field of the electron anymore, because it gets cancelled out by the proton's field. The electron's ability to scatter light is reduced dramatically, because the light has to get close enough to the electron to feel it's field.

The reason that it took 300,000 years for atoms to form is that before that, the electrons and protons were too hot to form atoms. They might try, but they would rip apart from the heat. Only after the universe cooled down enough could they form stable atoms

Finally, about false vacuum and quantum tunneling, really you should try reading Guth's book. The false vacuum is the state of space that inflates, it has all sorts of exotic properties, the important one being that it creates more false vacuum at an exponential rate. It's a metastable state, meaning that - like a coin on it's edge - it will stay that way - even though it would be more stable lying flat. "Quantum tunneling" is the process by which it moves to the more stable state, even though it shouldn't be able to because that means passing through a state that has a higher energy density. Quantum theory says that you can do that. The more stable state for the false vacuum is regular vacuum.

NumberTenOx

And I've heard of theories where the speed of light changes with the age/size of the universe, but I don't know of any evidence that this is true. I think there is evidence to the contrary, that as far as anyone has been able to measure it has stayed the same (remember that as we look farther and farther away, we are looking back in time as well).