- #1
bruce2g
- 87
- 0
Hi,
I've been reading David Albert's book "Quantum Mechanics and Experience," and it got me thinking about how one could use Stern-Gerlach sorts of measurements on entangled electron pairs (or electron-positron pairs) to transmit a statistical signal from one to the other.
Let's say you have two entangled beams, one of electrons, and the other of positrons, and their spins are negatively correlated. The two beams travel in opposite directions at the same velocity through a vacuum. Bob is receiving the electrons, and Alice gets the positrons.
To keep it simple, they're at rest with respect to each other, and each is at an equal but opposite distance, D, from the source.
(1) Bob uses a Stern-Gerlach magnet to split his electron beam by spin along the Y axis at a distance D from the source. It is always on, and it creates two beams.
(2) Alice has a Stern-Gerlach magnet oriented on the X axis at a distance D+delta from the source. She examines the next bit to be sent, and if it is a '1', she turns on her magnet and she splits her positrons by spin along the X axis for five seconds. If it's a zero, she turns off the magnet.
(3) Bob has another two magnets around his two electron beams at a distance of D+2*delta from the source, once again aligned on the Y axis, and a screen that displays the beams.
It seems to me that if Alice has not turned on her magnet, then Bob will see two spots on his detector, which is the normal outcome of a Stern-Gerlach experiment.
However, if Alice has turned on her magnet, then the state vectors of her positrons (and thus Bob's electrons) will have moved to the X axis, so Bob's second detector will split the beam again, and Bob will see four spots. If this is true, and if D is great enough (> 6 light-seconds), then a bit will have been communicated faster than the speed of light, which is indicated by whether Bob sees two spots or four spots.
This setup is different from most of the FTL ideas I've seen since an individual electron will only show a diffent spin on the Y axis half the time when Alice turns on her magnet. However, if you have enough particles for each bit, you can get the error to be arbitrarily small, so that's why I specified 5 seconds for Alice to power her magnet.
I'm studying this stuff on my own, so I've probably overlooked some simple or subtle principle that would keep it from working, but I can't figure out what it is, so I'd appreciate it if someone could point out the flaw in this setup.
I've been reading David Albert's book "Quantum Mechanics and Experience," and it got me thinking about how one could use Stern-Gerlach sorts of measurements on entangled electron pairs (or electron-positron pairs) to transmit a statistical signal from one to the other.
Let's say you have two entangled beams, one of electrons, and the other of positrons, and their spins are negatively correlated. The two beams travel in opposite directions at the same velocity through a vacuum. Bob is receiving the electrons, and Alice gets the positrons.
To keep it simple, they're at rest with respect to each other, and each is at an equal but opposite distance, D, from the source.
(1) Bob uses a Stern-Gerlach magnet to split his electron beam by spin along the Y axis at a distance D from the source. It is always on, and it creates two beams.
(2) Alice has a Stern-Gerlach magnet oriented on the X axis at a distance D+delta from the source. She examines the next bit to be sent, and if it is a '1', she turns on her magnet and she splits her positrons by spin along the X axis for five seconds. If it's a zero, she turns off the magnet.
(3) Bob has another two magnets around his two electron beams at a distance of D+2*delta from the source, once again aligned on the Y axis, and a screen that displays the beams.
It seems to me that if Alice has not turned on her magnet, then Bob will see two spots on his detector, which is the normal outcome of a Stern-Gerlach experiment.
However, if Alice has turned on her magnet, then the state vectors of her positrons (and thus Bob's electrons) will have moved to the X axis, so Bob's second detector will split the beam again, and Bob will see four spots. If this is true, and if D is great enough (> 6 light-seconds), then a bit will have been communicated faster than the speed of light, which is indicated by whether Bob sees two spots or four spots.
This setup is different from most of the FTL ideas I've seen since an individual electron will only show a diffent spin on the Y axis half the time when Alice turns on her magnet. However, if you have enough particles for each bit, you can get the error to be arbitrarily small, so that's why I specified 5 seconds for Alice to power her magnet.
I'm studying this stuff on my own, so I've probably overlooked some simple or subtle principle that would keep it from working, but I can't figure out what it is, so I'd appreciate it if someone could point out the flaw in this setup.