Runaway pulsar has astronomers scratching their heads

[Xamonas Chegwé]

But information IS sent faster than c in quantum entanglement.

Is it? It is possible to learn something about one particle by examine its entangled twin. So, it is theoretically possible to gain information about the quantum spin status of a particle that is (for example) 2 light-days away by examining the twin particle that was sent in the opposite direction from a point 1 light-day away. Thus, it could be said that you have gained information at twice the speed of light. However, what you can't do is utilise this effect to send useful information faster than light. Even though the two particles MUST have opposite spin states to each other, until one is examined it is impossible to know the state of either - they exist as a probability function which is equally both states. So you can't tap out Morse code in left/right spin-states and have that message received across the galaxy - all you can transmit is random gibberish - the same as if you weren't testing the particles at all!

Fun stuff.

[pErvinalia]

Yeah, I know. Although, haven't they done some quantum teleportation experiments where they sent some sort of controlled information? I try to avoid reading about quantum whatsits as it does my head in. I only have a tenuous grasp on reality as it is...

[JimC]

But information IS sent faster than c in quantum entanglement.

Is it? It is possible to learn something about one particle by examine its entangled twin. So, it is theoretically possible to gain information about the quantum spin status of a particle that is (for example) 2 light-days away by examining the twin particle that was sent in the opposite direction from a point 1 light-day away. Thus, it could be said that you have gained information at twice the speed of light. However, what you can't do is utilise this effect to send useful information faster than light. Even though the two particles MUST have opposite spin states to each other, until one is examined it is impossible to know the state of either - they exist as a probability function which is equally both states. So you can't tap out Morse code in left/right spin-states and have that message received across the galaxy - all you can transmit is random gibberish - the same as if you weren't testing the particles at all!

Fun stuff.

Random gibberish, eh?

Excellent! The entire forum can be sent to Alpha Centauri in the blink of an eye!

[FBM]

Could they not (in theory) alter, say, the spin of the observed particle, thus instantly changing its entangled partner particle?

[JimC]

Could they not (in theory) alter, say, the spin of the observed particle, thus instantly changing its entangled partner particle?

I think that would end the entanglement...

[FBM]

Not sure...

Edit: Googled. Yeah, the entanglement only affects the initial states. After that, they're free.

[Xamonas Chegwé]

Yeah, I know. Although, haven't they done some quantum teleportation experiments where they sent some sort of controlled information? I try to avoid reading about quantum whatsits as it does my head in. I only have a tenuous grasp on reality as it is...

Quantum teleportation relies on the passing of information via "classical" channels (ie. below light-speed.) Sorry. No faster-than-light info transfer yet.

[Xamonas Chegwé]

Could they not (in theory) alter, say, the spin of the observed particle, thus instantly changing its entangled partner particle?

Alter it how? When you don't know which direction it is spinning in in the first place? Not until you measure it! At that point, the twin particle's spin is fixed and the entanglement ceases.

[MiM]

But information IS sent faster than c in quantum entanglement.

No it's not. At least not according to the No-communication theorem.

By the way, I wouldn't get too excited about that paper on gravity spreading faster than light, by the Zhu guy. He originally seems to have published a paper in some Chinese journal in 2011, and then he has been adding significantly on that paper, and updating it on arXiv without any traces of going through the refereed publishing process anew. And the snippet in Wikipedia: "It is shown that the gravitational force of the Sun acting on the satellite is from the present position of the Sun", shouldn't be news at all, as it has long been known, that in classical mechanics, gravity seems to come from an objects current position. If this would not be the case the planetary orbits would be instable. In general relativity this can be explained with that gravity depends not only by the location of a mass, but also by motion. A nice short description in layman terms can be found here

[FBM]

Could they not (in theory) alter, say, the spin of the observed particle, thus instantly changing its entangled partner particle?

Alter it how? When you don't know which direction it is spinning in in the first place? Not until you measure it! At that point, the twin particle's spin is fixed and the entanglement ceases.

Yes, I looked it up.

Not sure...

Edit: Googled. Yeah, the entanglement only affects the initial states. After that, they're free.

[pErvinalia]

But information IS sent faster than c in quantum entanglement.

No it's not. At least not according to the No-communication theorem.

By the way, I wouldn't get too excited about that paper on gravity spreading faster than light, by the Zhu guy. He originally seems to have published a paper in some Chinese journal in 2011, and then he has been adding significantly on that paper, and updating it on arXiv without any traces of going through the refereed publishing process anew. And the snippet in Wikipedia: "It is shown that the gravitational force of the Sun acting on the satellite is from the present position of the Sun", shouldn't be news at all, as it has long been known, that in classical mechanics, gravity seems to come from an objects current position. If this would not be the case the planetary orbits would be instable. In general relativity this can be explained with that gravity depends not only by the location of a mass, but also by motion. A nice short description in layman terms can be found here

My head hurts just clicking on that link, let alone reading it.. But isn't it just saying that there's no way to instantaneously communicate coordinated information? The decoherence of the other particle would still be instantaneous, wouldn't it?

[MiM]

Yes, the decoherence is still instantaneous, but there is no information sent. Kind of a Schrödingers cat type problem.

[pErvinalia]

But there must be, as the properties of one particle determine the properties of the other, don't they?

[MiM]

All you need to know about Higgs and mass

[MiM]

But there must be, as the properties of one particle determine the properties of the other, don't they?

Your problem is that you are thinking at the particles in a classical way. Classical thinking just leads to strangeness and error in the quantum world.

The way quantum people like to "explain" this, is by thinking of the entangled particles as parts of one single wave function. This wave function is defined in all space. Once you make a measurement on one of the particles the wave function immediately collapses into two separate wave functions for the particles. This happens everywhere in space, not only at the "location" of the particles. But nothing moves anywhere. No I don't claim to understand this myself, our brains are just not warped to understand this kind of stuff.