1. Two faster-than-light questions.

Imagine a bike chain wrapped around two gears and the gears are turning together. Now imagine the distance between the two gears is half a million miles. Neglecting the amount of force required to stop it's inertia (by assuming you've got a really big lever and arm to stop it), if you were to stop one gear, would the other gear stop at exactly the same time?

Second, imagine you have a crystal with a perfect lattice structure (say, diamond), also half a million miles long but only a few inches wide. If I were to twist that crystal at one end, would the other end twist at the same time?

Is there any real-life scientific principle that suggests that FTL is possible?

2. Originally Posted by Nordstern
Two faster-than-light questions.

Imagine a bike chain wrapped around two gears and the gears are turning together. Now imagine the distance between the two gears is half a million miles. Neglecting the amount of force required to stop it's inertia (by assuming you've got a really big lever and arm to stop it), if you were to stop one gear, would the other gear stop at exactly the same time?

Second, imagine you have a crystal with a perfect lattice structure (say, diamond), also half a million miles long but only a few inches wide. If I were to twist that crystal at one end, would the other end twist at the same time?

Is there any real-life scientific principle that suggests that FTL is possible?
Ooh, fun ones!

Nope, neither the bike chain/crystal violate FTL. Short version: even twisting a "small" (i.e. normal sized) version takes a non-zero amount of time for the "twist" or "stop" to propagate.

Imagine this: You have a garden hose filled with marbles. You push a marble in one end, a marble comes out the other end. It may *appear* instantaneous, but it does take time for each marble to pass on the force. If you had a garden hose wrapped around the world, full of marbles, and pushed one in one end, it would take a noticeable amount of time for the marble to come out the other end.

Are there scientific principles that propose FTL? Well, yes and no.

Relativity flat out forbids *accelerating* something to the speed of light. Requires infinite energy or infinite time, both of which are problematic.

However, there are theories that propose ways "around" the speed of light (see: Alcubierre drive or krasnikov tube), but these also have problems (such as requiring negative energy densities.) And even if FTL is possible, it might cause shitloads of problems with causality.

3. Originally Posted by shaewyn
Originally Posted by Nordstern
Two faster-than-light questions.

Imagine a bike chain wrapped around two gears and the gears are turning together. Now imagine the distance between the two gears is half a million miles. Neglecting the amount of force required to stop it's inertia (by assuming you've got a really big lever and arm to stop it), if you were to stop one gear, would the other gear stop at exactly the same time?

Second, imagine you have a crystal with a perfect lattice structure (say, diamond), also half a million miles long but only a few inches wide. If I were to twist that crystal at one end, would the other end twist at the same time?

Is there any real-life scientific principle that suggests that FTL is possible?
Ooh, fun ones!

Nope, neither the bike chain/crystal violate FTL. Short version: even twisting a "small" (i.e. normal sized) version takes a non-zero amount of time for the "twist" or "stop" to propagate.

Imagine this: You have a garden hose filled with marbles. You push a marble in one end, a marble comes out the other end. It may *appear* instantaneous, but it does take time for each marble to pass on the force. If you had a garden hose wrapped around the world, full of marbles, and pushed one in one end, it would take a noticeable amount of time for the marble to come out the other end.

Are there scientific principles that propose FTL? Well, yes and no.

Relativity flat out forbids *accelerating* something to the speed of light. Requires infinite energy or infinite time, both of which are problematic.

However, there are theories that propose ways "around" the speed of light (see: Alcubierre drive or krasnikov tube), but these also have problems (such as requiring negative energy densities.) And even if FTL is possible, it might cause shitloads of problems with causality.
The thing to remember is that the only thing that bonds atoms into molecules is the electromagnetic force. The electromagnetic force is carried by photons (either virtual or real).

Consider that light itself is just electromagnetic waves/photons, and you can see immediately that any force applied to a solid can only propagate at light speed.

4. Beaten by good answers. Sufficed to say that it wouldn't matter if the crystal was a billion miles long or one inch long, or if it was a perfect lattice or not, nothing done to one end of the crystal will ever instantly affect the other. It's always going to be made up of particles that transmit the force at some given rate. It's a red herring to think that making it long enough will change anything about its behavior when it comes to relativity.

Though I guess if you made it small enough it would be in two places at once and have a twin that instantly rotated when the original rotated, while vibrating and not vibrating at the same time, until you looked away and then they turned into sausages.

5. I'm sure we had this force transmission argument about 10 pages ago.

6. The speed of light seems to be the solidest part of current physics (terrible experimenters with neutrinos non-withstanding). If you think you've found some delightfully clever way to get around it, the universe has a delightfully simple way to make sure it doesn't work.

Stuff like Alcubierre operates by working with the universe to exceed the speed of light without locally exceeding it. I honestly wouldn't be surprised if there was something that stopped it working that we haven't discovered yet.

Now, how to actually do it. The speed of light gives the limit that information can propogate through space, so that information takes 1 year to propogate 1 light year. So say we wanted to travel 1 light year much quicker than that. We have to reduce the distance, and Einstein came up with a way of doing that. An Einstein-Rosen Bridge (aka a wurmhoal) is a path from one point in space-time to another that has a length independent of the normal distance. The catch? We have never seen a wormhole, naturally occurring ones should be subatomically small and if we did somehow make a large scale one we would need some seriously freaky shit to keep it open.

7. If we're making funny superluminal propositions; let us imagine a suitable large dense object comes into the solar system at high percentage of light exactly perpendicular to the main distribution, strikes the sun and carries on going taking the sun with it out of the solar system, let's say the planets will cease orbiting and carry on in whatever direction they were going. Now the question, would earth stop orbiting the instant the sun was no longer where it should be or would it just carry on for 7-8 minutes waiting for the light of the incident to arrive? Are gravitational effects bound to c? I can't see why we would keep on orbiting once it's gone, regardless.

Apologies if retarded question.

8. Gravity, like all other things, is bound by c. It'd take 8 minutes for us to notice the lack of sun.

9. Originally Posted by tulip
If we're making funny superluminal propositions; let us imagine a suitable large dense object comes into the solar system at high percentage of light exactly perpendicular to the main distribution, strikes the sun and carries on going taking the sun with it out of the solar system, let's say the planets will cease orbiting and carry on in whatever direction they were going. Now the question, would earth stop orbiting the instant the sun was no longer where it should be or would it just carry on for 7-8 minutes waiting for the light of the incident to arrive? Are gravitational effects bound to c? I can't see why we would keep on orbiting once it's gone, regardless.

Apologies if retarded question.
Yes.

It seems to be a law of the universe that there is no way of finding out about any event sooner than the time it takes light to travel from that event to you.

10. ...with the sole exception of entangled particles.

11. Originally Posted by Steph
...with the sole exception of entangled particles.
Nope. Can't transmit information that way. The 'effect' propagates ftl if you want to think about it that way, but there's no way to tell it has without normal slower than or exactly light speed interaction as well.

12. Originally Posted by Steph
...with the sole exception of entangled particles.
To be able to distinguish the "ftl" quantum effect you need some corresponding non-quantum information about the particle, which can only be transmitted slower than light, limiting the transmission of information by entanglement to less than light speed.

13. I never really understood that.
I know there is something that prevents it from being used as FTL communication but never found a clear enough explanation why that is.

14. You have two fair coins, such that when you flip one it's exactly fifty-fifty to come down heads or tails. Once you flip one, the Hammer of Thor comes down and mashes it into the ground so it can never be flipped again.

When this has happened for one coun, if you then flip the other it will always, always come down the other way up to the first one, then again get hammered in place.

Take the coins, fly one to alpha centauri. Now, if you flip one on earth and get heads, the one on ac will always, always come down tails. Zomg ftp!

BUT
How can the person on ac tell? He flips his coin and gets heads half the time, just Luke you did. His distribution is magically constrained to be the inverse of yours (heads when you get tails and vice versa), but this distribution is exactly the same (staristically) as what he would get without the ftl business. The only way to detect the ftl influence is by knowing what the guy on earth got , which he can only know via boring Einstein.

Or to put it another way:
Ac guy tosses a coin.

No ftl entanglement gubbins: he gets fifty fifty heads tails

Ftl business: half the time (depending on the result of the random coin toss on earth) he will always get heads. Half the time he will always get tails. If earth guy tells him he got heads, he can predict perfectly what he will get when he tosses the coin, but without that info he can't tell the difference with the no entanglement case.

15. Originally Posted by definatelynotKKassandra
....
Good explanation but there seems to be no explanation understandable by laymen (me, i'm very lay) of the proof that this isn't the result of the coin tosses being determined prior to the separation of the particles. I guess they call it the hidden variables explanation, and I know it's been disproven enough for the physicists, but goddamnit why can't anyone explain it to me?
I asked before in this thread, I think. Don't feel obliged to go in circles. But every time it comes up I need to flail about because the crux of this relies on the proof that the results aren't predetermined.
I even watched a nova special on it, and when it came down to this key point, they glossed over it by saying "maths said so" which made me very angry at nova.

16. Originally Posted by Frug
Beaten by good answers. Sufficed to say that it wouldn't matter if the crystal was a billion miles long or one inch long, or if it was a perfect lattice or not, nothing done to one end of the crystal will ever instantly affect the other. It's always going to be made up of particles that transmit the force at some given rate. It's a red herring to think that making it long enough will change anything about its behavior when it comes to relativity.

Though I guess if you made it small enough it would be in two places at once and have a twin that instantly rotated when the original rotated, while vibrating and not vibrating at the same time, until you looked away and then they turned into sausages.
that's actually the explanation EvE gives for FTL comms in one of the chronicles. It's something that has been proposed IRL as a means of FTL communication. Essentially any two objects identical to the point of having the same quantum state would 'resonate' (that's a gross simplification) and anything done to one would be reproduced by the other instantly regardless of distance. This depends on the mathematical model of quantum theory actually matching up with reality, and we have no way to measure much less manipulate the quantum state of matter precisely enough to even test the idea.

note: the above is a simplification of an explanation given to me by a physicist, and the math is beyond me, it makes geophysics look like preschoolers doodling.

17. I assume you've already done this, but try reading the wiki on Bell's Theorem.

Note that it's only LOCAL hidden variables that are ruled out - there can still be some 'global' field that means QM isn't actually about God playing dice, but the idea that particles can have some hidden label on them that means which way teh dice will land when you amke a meansurement is already determined has been disproven, yes.

It's not quite 'maths says so'. It's:

Assume particles have some hidden property that means the result of a measurement on them is a) not probabilistic but predetermined b) entirely local i.e. can't be affected by people tossing coins in another galaxy
---> :maths:
----> make predictions
----> DO EXPERIMENTS, and find that these predictions are violated to <large degree of accuracy/certainty>

---> conclude initial assumption is untrue, since it leads to predicitons at odds with observation

So it's not just :maths:, but the chain of reasoning leading to the inequalities is not simple for the layman. IIRC the wiki is relatively (but not completely) comprehensible. Unfortunately it's not particularly easy to explain by analogy. Sorry.

18. Originally Posted by definatelynotKKassandra
You have two fair coins, such that when you flip one it's exactly fifty-fifty to come down heads or tails. Once you flip one, the Hammer of Thor comes down and mashes it into the ground so it can never be flipped again.

When this has happened for one coun, if you then flip the other it will always, always come down the other way up to the first one, then again get hammered in place.

Take the coins, fly one to alpha centauri. Now, if you flip one on earth and get heads, the one on ac will always, always come down tails. Zomg ftp!

BUT
How can the person on ac tell? He flips his coin and gets heads half the time, just Luke you did. His distribution is magically constrained to be the inverse of yours (heads when you get tails and vice versa), but this distribution is exactly the same (staristically) as what he would get without the ftl business. The only way to detect the ftl influence is by knowing what the guy on earth got , which he can only know via boring Einstein.

Or to put it another way:
Ac guy tosses a coin.

No ftl entanglement gubbins: he gets fifty fifty heads tails

Ftl business: half the time (depending on the result of the random coin toss on earth) he will always get heads. Half the time he will always get tails. If earth guy tells him he got heads, he can predict perfectly what he will get when he tosses the coin, but without that info he can't tell the difference with the no entanglement case.
You sure it works that way? Because that way you could predict the future perfectly. Toss 10 coins and you can tell him what will be his next coin tosses.

19. Originally Posted by Zeekar
Originally Posted by definatelynotKKassandra
You have two fair coins, such that when you flip one it's exactly fifty-fifty to come down heads or tails. Once you flip one, the Hammer of Thor comes down and mashes it into the ground so it can never be flipped again.

When this has happened for one coun, if you then flip the other it will always, always come down the other way up to the first one, then again get hammered in place.

Take the coins, fly one to alpha centauri. Now, if you flip one on earth and get heads, the one on ac will always, always come down tails. Zomg ftp!

BUT
How can the person on ac tell? He flips his coin and gets heads half the time, just Luke you did. His distribution is magically constrained to be the inverse of yours (heads when you get tails and vice versa), but this distribution is exactly the same (staristically) as what he would get without the ftl business. The only way to detect the ftl influence is by knowing what the guy on earth got , which he can only know via boring Einstein.

Or to put it another way:
Ac guy tosses a coin.

No ftl entanglement gubbins: he gets fifty fifty heads tails

Ftl business: half the time (depending on the result of the random coin toss on earth) he will always get heads. Half the time he will always get tails. If earth guy tells him he got heads, he can predict perfectly what he will get when he tosses the coin, but without that info he can't tell the difference with the no entanglement case.
You sure it works that way? Because that way you could predict the future perfectly. Toss 10 coins and you can tell him what will be his next coin tosses.
C, with the provisos about how in reality it's measurements of polaristion of pairs of photons etc etc. Remember that in reality the 'coins' are things that are intrinsically linked in their properties (entangled).

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