Is the universe infinite or finite?

Another effect of a laser being fired in the direction of motion as it approaches an observer is the color shift. If the beam is approaching an observer and the emitting device is moving at relativistic velocities (and even non-relativistic velocities), the approaching light is blue shifted as the wavelength is compressed. It could be compressed so much you get a fatal dose of X-rays or gamma rays as the once visible wavelengths are blue shifted. In the other direction, away from the observer, the wavelengths are red shifted being stretched into long radio waves as the observer detects them. Because the velocity of light is constant all other variables adjust to compensate. Physics is fun

MrGreenJeans said:

Physics is fun

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One of my absolute favorite subjects!!

LAW!

MrGreenJeans said:

Another effect of a laser being fired in the direction of motion as it approaches an observer is the color shift. If the beam is approaching an observer and the emitting device is moving at relativistic velocities (and even non-relativistic velocities), the approaching light is blue shifted as the wavelength is compressed. It could be compressed so much you get a fatal dose of X-rays or gamma rays as the once visible wavelengths are blue shifted. In the other direction, away from the observer, the wavelengths are red shifted being stretched into long radio waves as the observer detects them. Because the velocity of light is constant all other variables adjust to compensate.

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Yup! It's the exact same effect that I'm sure everyone has experienced with sound waves for example, as a car approaches you, the perceived pitch seems to get higher, and then as it drives away it drops. This is what is known as the Doppler Effect! And I think MrGreenJeans did a good job of describing the phenomenon as it applies to light waves.

Another fun fact that actually pertains somewhat to the original subject matter of the thread, nearly every galaxy in the universe is redshifted, so they are all moving away from us!?! This is not because we are the center of the universe (although that would be an amusing notion to entertain) but rather because the universe is expanding, and everything is slowly getting further away from everything else.

MrGreenJeans said:

Physics is fun

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photonaholic said:

One of my absolute favorite subjects!!

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I agree with these statements. Hence the whole "physics major' business that's in the works right now

ninja_tux said:

I agree with these statements. Hence the whole "physics major' business that's in the works right now

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That means University of Chicago (the Enrico Fermi stomping grounds) or the Wildcats of Northwestern?

MrGreenJeans said:

That means University of Chicago (the Enrico Fermi stomping grounds) or the Wildcats of Northwestern?

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MMM I'll say that one of those may be right...but I'd rather not say explicitly. A little anonymity is always fun

ninja_tux said:

Well to be fair most of those paradoxes have solutions

I vote that we don't derail this thread further by turning this into a "faster-than-light" debate, since in my experience it becomes more an issue of semantics than anything else, and really who wants that?

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Oooooh! a faster then light debate? Isn't saying not to let one start, almost encouraging one?

Simple proof that faster then light IS possible. All models of the big bang theory pretty much require an inflation period in which space-time itself expands faster then light, allowing for mass from point a, to get to point b quicker then light. However the mass never really moves faster then light, in any frame of reference, as it is space-time that is moving. So technically mass didn't move from point a to point b at all, and no laws of physics were violated, in any way, shape or form. and the laws of physics most certainly didn't feel the need to file a formal complaint with their HR department about being violated, as they never really felt violated or something like that.

Assuming it has happened once, then space-time can in fact be moved, or expanded, or something like that. Assuming it once expanded faster then light, and the distance between mass expanded faster then light, then it could be made to do so again.

Assuming it could be made to do so, then one could in theory move away from mass faster then light. The catch is, none of this requires that it can be compressed, which would need to happen in order to approach other mass. i.e. you could expand the space between you and the earth by a distance of 1 light year, moving yourself 1 light year away from earth, but this wouldn't get you closer to any other star, it would simply create a lot of empty space between you and the earth, stranding you 1 light year away from the nearest pizza hut. I'm quite certain that is probably out of where they will deliver too. *sigh* suddenly this whole FTL stuff doesn't sound as appetizing.

Of course if space-time can be both expanded AND compressed, or even needs to be both. then essentially a "warp drive" is possible. where you create a bubble of space-time around yourself, and compress space in front of it, and expand it again behind you. thereby moving space-time itself, while you stay still. But then other problems come into play. Like those damn klingons come and try to steal your pizza hut meat lovers pan pizza.... *sigh* ok maybe a debate ISN'T a good idea.

EDIT: what can I say. I got bored and was reading this thread again

StridAst said:

Of course if space-time can be both expanded AND compressed, or even needs to be both. then essentially a "warp drive" is possible. where you create a bubble of space-time around yourself, and compress space in front of it, and expand it again behind you. thereby moving space-time itself, while you stay still. But then other problems come into play. Like those damn klingons come and try to steal your pizza hut meat lovers pan pizza.... *sigh* ok maybe a debate ISN'T a good idea.

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Sigh yes this is, more or less, the classic argument that seems to have been around forever! I've never seen any major problems with the whole "warping" space-time idea, since as stridast pointed out, it seems to have happened before during an inflation period after the big bang. But where the semantical argument comes in is that people argue that this truly isn't "faster than light" travel since it's something IN the universe moving faster than light, but rather the universe itself...Yeah it's a silly argument, but so is the whole faster than light debate IMHO haha. Not to mention that I would think a warp drive would require truly obscene amounts of energy, so it would become impractical to travel the universe since it would be too expensive to bring along our beloved pizzerias

Yeah, it might not be FTL but it does the same thing so who cares? And why do you think it would take so much energy? You're not actually moving things, in fact you actually have less distance to move things, right? Right now I think the key is finding out how to better control and learn about gravity, if we can control gravitons or whatever is responsible for gravity we can bend space-time.

Well, Look at the evidence. The ONLY point we really think the universe expanded faster then light was at the earliest stages of the universe. When all the mass and energy in the universe was collected in one quite small by comparison spot. Imagine what the energy density of the universe was at the point where and when it occurred. But then the universe DID expand instead of staying one supremely dense singularity. The mass and energy overcame any gravity warping of space-time. Nevermind the fact that the initial big bang had energy densities that make ANY black hole look light by comparison, it still expanded. insanely fast.

However, it only expanded, it didn't contract. Also while gravity bends space-time, it doesn't quite make distances between objects shrink to the best of my knowledge. So is there any evidence for true contraction of space-time? Because if you can't compress as well as expand it, then faster then light travel by expanding it, will only essentially create more space-time, but NEVER shorten any distances Sure you could still get farther away, faster then a beam of light, but you couldn't catch up to a beam already moving. This sort of FTL travel actually seems to better fit the observed laws of the universe.

incidentally, before we can control gravitons, we have to first prove they exist, and how they can do what light can not. (escape from a black hole) Even if gravitons have no mass, neither does light.

ossumguywill said:

Yeah, it might not be FTL but it does the same thing so who cares? And why do you think it would take so much energy? You're not actually moving things, in fact you actually have less distance to move things, right? Right now I think the key is finding out how to better control and learn about gravity, if we can control gravitons or whatever is responsible for gravity we can bend space-time.

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I agree it's basically the same effect as "traditional" FTL travel.

I think it would take extraordinary amounts of energy since you'd actually have to alter the very fabric of the universe...and the only things that really do that are supermassive bodies, and that's not exactly usable for a "warp drive". The only other event that has warped space-time is the big bang...when there was literally more energy available than at any other point of existence. (Yeah for entropy!)

I would argue that gravity is the least understood phenomenon in the universe; none of the theories we have can accurately explain it, and even Einstein's work with it falls apart in extreme scenarios like in the singularity of a black hole.

Before anyone can even speculate on how a "warp drive" device might work, we really need to understand gravity better, mainly by finally having a reliable theory of quantum gravity. (A unified field theory would be nice too )

EDIT: Just saw stridast's post...

StridAst said:

incidentally, before we can control gravitons, we have to first prove they exist, and how they can do what light can not. (escape from a black hole) Even if gravitons have no mass, neither does light.

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Of course proving that a SINGLE graviton exists through experimentation is not feasible, our best bet is detecting gravity waves which are thought to be made up of gravitons. (This is the goal of LIGO and VIRGO. and they use LASERs!!! See: http://en.wikipedia.org/wiki/LIGO http://en.wikipedia.org/wiki/VIRGO )

Also, so far, actual evidence for a "graviton" zero. Other then the circumstantial evidence that every other force is conveyed by a particle. However, gravity never did fit well with the other forces. I guess it just doesn't play well with others... Gravity just has never been able to be combined with the other forces into a unified field theory. There has been no progress at all combining gravity with the other forces at ANY energy level.

BAD gravity! go sit in the corner.

But if there is no graviton, then how does mass curve space-time, how is the force conveyed, and what for that matter really IS space-time. I suspect if you could answer THESE questions, you would have your answer as to the original post's question of the universes infinite status.

LOL you got that post in while I was typing mine =/ similar topic

StridAst said:

LOL you got that post in while I was typing mine =/ similar topic

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This is so strange! We cover similar things as the other person is posting...I saw your post about gravitons and edited my post to include the bit about them being experimentally impossible to prove directly... We're so cool haha

StridAst said:

But if there is no graviton, then how does mass curve space-time, how is the force conveyed, and what for that matter really IS space-time. I suspect if you could answer THESE questions, you would have your answer as to the original post's question of the universes infinite status.

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Or even stranger yet...is what Einstein described as space-time truly the nature of the universe?? There are a lot of problems with space-time and gravity after all. And if space-time isn't really how the universe is laid out, then how does it all really work? Theoretical physics is just so much fun! But there's also so much ridiculously complicated math that makes my head hurt...

Yeah, all that crap about space-time is a bunch of BS. I think the universe is layed out like cheese on a pizza The planets are the little chunks of sausage and the stars are the pepperoni! I really hope nobody takes a bite from our slice anytime soon.

Hmm. you all will NEVER guess what I have been craving today

I wonder if we (sentient beings) will ever get to the point when we can modify the laws of physics. However, if we could that would mean that we would already be experiencing that (the laws of physics are maintained in all frames of reference, even through time, right?) and we couldn't tell the difference. Maybe the laws of physics are actually tweaked just right to allow the future teleportation systems to work.... they're just not so convenient for us.
Also, I was talking to my physics teacher for a minute or two about special relativity and he told me that when you get in to the field, you might stop treating things like pi as a constant because they can be warped. I think he meant that if you measure pi on a moving object while you were standing still it would change because of dilation.