Instantaneous communication over light-year+ distances.

[her209]

Create mass from energy and vice versa.

 

[TuxDave]

Originally posted by: silverpig

Originally posted by: Matthias99

Originally posted by: dainthomas

Originally posted by: Matthias99

You can't actually transmit information directly through quantum entanglement (at least IIRC). You *can* use it for quantum cryptography, to securely send a private key to someone -- but you need another communications channel to actually send the message through. Plus, you have to get the particles to the destination first, which currently cannot be done any faster than at the speed of light.

Why not? Doesn't changing the state of one of the particles instantaneously affect the other? This could easily be used for communication.

From what I understand, not quite. While the particles are 'entangled', looking at the state of one immediately tells you what the state of the other one is, but you can't choose the state it is in. And once you have looked at them, they are no longer 'entangled'. So no, you can't transmit information like this.

Plus, you have to get the particles there in the first place.

Pretty much.

Put a black marble and a white marble in a bag. What quantum mechanics basically says is that you really have 2 "grey" marbles in there at any time, each with equal probability of coming out black or white. You and a friend each grab a marble, don't look at it, and then walk away. You go home, and so does he. Still in your hand, the marble you carry is 1/2 black and 1/2 white with equal probability, as is his. The "instantaneous" bit about quantum entanglement works like such:

You open your hand to find a black marble. You instantly know that your friend has a white one. However, this doesn't send any information. It's not like you can tell your friend "I'll go home and if my wife has dinner ready, I'll get the white marble and make sure you have the black one to let you know." You can't signal him in any way using your marble.

:thumbsup: That is a pretty damn good explanation.

 

[Woodchuck2000]

Originally posted by: BirdDad
I think he is refering to that experiment where 2 entangled electrons are a galaxy apart.Change the spin of one and the other changes instantaniously.

I'm not quite sure where this misconception comes from but that's not what happens. If that were the case, information could be transmitted.

There's an explanation here. For a simpler explanation, Silverpig's post explains it pretty nicely (and also explains why information can't be transmitted by this method!).

 

[Stiganator]

Gravity theoretical propagates across space time in an instantaneous manner. This can be understood via the sheet marble model. As the tension in the sheet approaches infinity and the gravity well is instantaneously removed. The refractory period of the space time approaches zero. You might be worried about oscillations, but keep in mind the sheet model isn't perfect and in fact the bending exhibited is in actuality pushed in all dimensions. That aside, there is currently no way for mankind to instantaneously remove matter so testing it is defenistrated. I must say it very much sounds like you'd like an ansible. I got this friend Wiggins who might be able to help....

 

[Woodchuck2000]

Originally posted by: Stiganator
Gravity theoretical propagates across space time in an instantaneous manner.

No it doesn't. It has been experimentally verified that changes in a gravitational field propagate outwards at lightspeed.

 

[Micky2Shoes]

That experiment may have been wrong. I believe that there is still a lot of debate in the scientific community about its validity.

Also I have read of experiments that have succeeded in synchronising clocks using quantum-entangled photons, which would suggest information transfer.

 

[Stiganator]

I'm no expert I should note that. But I've had a number of discussions about this and instantaneous propagation was considered the best solution. It has been a while though, so maybe someone thought of a more elegant solution. You mentioned them testing it. How did they go about doing that, I'm curious? The test would have to be removing matter instantly, correct? I can't see how else you could test it. I say put it up there with why does windows rebooting fix windows. ITS MAGIC!

 

[fogeyman]

Originally posted by: TuxDave

Originally posted by: Einstein Element

Originally posted by: TuxDave
I honestly never read of an experiment where the effects of gravity is instantaneous. As far as I recall, if the sun vaporized into nothingness, we won't feel its effect for a couple of minutes.

thats because the light takes a couple of minutes to get here, he's talking about gravity

I'm talking about gravity too.

Just a few days back in school, we watched a video on gravity and EM and nuclear forces and the "universal equation." The video argued that gravity is limited by the speed of light. I can't quite describe exactly what the video showed us so instead, think of a pool of perfectly still water. Then place several floating objects to represent our solar system with the planets and the sun. If the "sun" (the heaviest object in the center) were to be removed, a ripple effect would be created. When the wave reached each planet, that planet would be knocked out of its orbit and take a straight path into space. The speed of that wave is limited, like everything else, to the speed of light. So it would take a couple of minutes (or some length of time longer than if gravity were instantaneous) for this wave of gravity to reach the planets.

This is what the video argued and I don't know enough about the subject to give my own opinion on it. This seems to be fairly solid, in any case...

 

[Woodchuck2000]

Originally posted by: Micky2Shoes
That experiment may have been wrong. I believe that there is still a lot of debate in the scientific community about its validity.

Also I have read of experiments that have succeeded in synchronising clocks using quantum-entangled photons, which would suggest information transfer.

Seriously, trust me on this one. The consensus amongst the scientific community (other than the occasional nut-job) is that gravity propogates at c. First linky i found.

There have been no experiments using entangled photons to synchronise clocks because it is impossible to do so. Link please?

Both of these are accepted as fact by those in the know.

 

[Woodchuck2000]

Originally posted by: Stiganator
I'm no expert I should note that. But I've had a number of discussions about this and instantaneous propagation was considered the best solution. It has been a while though, so maybe someone thought of a more elegant solution. You mentioned them testing it. How did they go about doing that, I'm curious? The test would have to be removing matter instantly, correct? I can't see how else you could test it. I say put it up there with why does windows rebooting fix windows. ITS MAGIC!

Here is just one of several tests that have been carried out which have proven the theory beyond all reasonable doubt.

In what circumstances would instantaneous propogation make more sense?

 

[iwantanewcomputer]

gravity travels at the speed of light. (the effects of gravitational change) Research on theoretical gravity waves suggest they propogate at c as well.

 

[concreteDonkey]

We(humans) haven't seen a gravitron yet have we?

I thought they(scientists) were still accelerating particles into each other in a massive oval particle accelerator some place in the US?

 

[roselan]

actually, the most promising "experiment plan" I do remember involves a particle "wall".

You send your particle, if you want a zero you dont check it, so the other end will see it. If you want a 1, you check it. It shall happend just before the particle hits a "wall", so that the other end won't see at all.

Question: how to build a semi-transparent wall? (which let grey particle go thru, but now black or white ones...)

Some rubber band, old swiss clock, and empty beer cans shall do the trick however

 

[MoD TaRkIn]

Originally posted by: Woodchuck2000
Seriously, trust me on this one. The consensus amongst the scientific community (other than the occasional nut-job) is that gravity propogates at c.

Couldnt agree more. There is virtually no doubt about this. Gravity travels at c. So do EM waves, and hence magnetic effects, for the people who were doubting that!

As for gravitons, particle accelerators like CERN are not the tool for detecting them. Infact, the graviton analogy may not be quite right. Gravity really shgould be though of as more of a wave (yes I know its both by wave-particle duality). Its a bit like radio frequency waves. The power is so low that you cant really treat it as individual photons, but rather as continous waves.

However, the good news is that gravitational waves are probably a matter of months away from being detected. The 2 LIGO detectors in the US and the GEO600 detector in Germany are soon to begin a correlated data gathering session lasting 18 months. These detectors are basically super sized laser interferometers, google LISA or GEO600 for a detailed explanation of how they work. But ther are now accurate enough to detect a change in path length equivilent to about 1/25th the diamiter of a proton. This should be sufficient to detect large amplitude gravitational waves (talking black hole -neutron star collision stuff here).

 

[alpha88]

Gravity travels at c.
E-M travels at c
Strong/Weak travels at c.

See the analogy about marbles to see why Quantum Entanglement does not transfer 'useful' information instantly. (It essentially transmits random information instantly, that does not make sense unless someone informs you of the other side's outcome at speed c)

 

[Woodchuck2000]

Originally posted by: alpha88
Gravity travels at c.
E-M travels at c
Strong/Weak travels at c.

See the analogy about marbles to see why Quantum Entanglement does not transfer 'useful' information instantly. (It essentially transmits random information instantly, that does not make sense unless someone informs you of the other side's outcome at speed c)

I'd still argue that nothing is transmitted whatsoever. You simply determine something, which in turn collapses a proabability wave. It just so happens that this wave desribes two physically separated entities. While our notions of locality become compromised, nothing is transmitted between the particles.