What do you think is the cause of entanglement?
If two electrons are produced in an entangled state, then if one measures the spin on one , the spin on the other will always be found to be opposite
It seems (to me) that there can only be two possible logical reasons for this --
1) They are entangled from their creation, with each having definite ,but opposite "spins" (Einstein's hidden variables idea)
2) They can constantly communicate ,instantaneously ,over any distance
What's your thinking ?
- nebLv 78 months agoFavourite answer
1) Bell’s theorem, and subsequent experimental results, have eliminated 1) as a possibility. It has proved that there is NO local reality theory that can explain the results of the experiment. Einstein’s ‘hidden variables’ belief is an example of a local reality theory. A local reality theory is a theory where causality is restricted to less than or equal to light speeds and spin values are presumed to have an existence prior to measurement.
2) this is the difficult part of the question. Faster than light communication could explain the results of Bell’s experiment. One doesn’t need to assume local realism, but propose that state information is transferred between particles faster than light. However, that is a gruesome violation of Lorentz invariance. Physicist are loathe to give that up.
The prevailing opinion is that quantum mechanics is simply a non-local theory. There is no accepted mechanism to explain that non-locality (which includes all state reduction, e.g. wave function collapse).
Note that from a non-local standpoint, entanglement doesn’t enable something to be transferred faster than light. There is something called the no-communication theorem that shows that no information can be transferred from the measurement of the first entangled particle to the measurement of the second particle. Measuring the second particle can provide no information about whether or not the first particle actually had a measurement done so obviously no information can be transferred. That’s why we can’t use entanglement for FTL communication.
- WhoLv 78 months ago
who says there are 2 electrons?
maybe there is only 1 (so there would be no "entanglement" - just 2 parts of the same particle)
(it would sure cure its wave/particle duality)
(richard feynman once proposed a theory that there is only 1 electron that gets around a bit
there was nothing in his theory that contradicts ohysics)
- 8 months ago
Number 1 is wrong. The particles don't have definite but unknown opposite spins until they are measured. Hidden variables were ruled out by Bell's Inequality and the Alain Aspect experiment.
Number 2 is wrong. If they communicate instantaneously, what frame of reference is that with respect to? Simultaneous in one frame is NOT simultaneous in another. This is proven by special relativity.
Also, that communication signal would carry no energy or momentum, could not be intercepted or blocked (not even by a black hole in between).
So what is another possibility? Nobody knows. Entanglement seems impossible, but yet it happens. Richard Feynman said "No one understands Quantum Mechanics."
- DixonLv 78 months ago
I'm no kind of expert but I imagine entangled spin detection as winnowing down which universe a measurement was made in (so they just have to be opposite) and until that winnowing happens the wave function occupies all possible universes. So that is some kind of multiverse theory.
People get all excited about entanglement of spin but really all QM is entanglement. When a photon hits screen, every other location where the photon might have been instantly 'knows' not to contain a photon. On the face of it that doesn't seem too remarkable because that is what happens with particles anyway. But the fact that the cumulative detections (can) show wave interference basically implies the wave is in all locations but the detected particle randomly appears in only one. This basic initial conundrum of QM isn't really made any different by spin entangled particles other than it is more obvious.
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- ANDYLv 58 months ago
This was, and still is, a difficult situation to understand. All particles have something called a "spin" (angular speed with a space orientation). Two particles seem to comunicate with the other, even at distances of light years (protons, electrons...etc). Many experiments have been carried out and no sure results were obtained. However, it seemed that 100% of the spins are always "opposites" (not sometimes 2/3 against 1/3 as was thought to be) meaning for every two particles entangled one will have an up spin while the other "must" have the down spin.
- cosmoLv 78 months ago
We know how to take two electrons that are not entangled, and cause them to become entangled. So (1) is out. Number (2) is "spooky action at a distance" and this is one of the great mysteries of quantum mechanics. It suggests that quantum entanglement is in some sense more "fundamental" than is spacetime.
- Anonymous8 months ago
I wouldn't worry about it too much. How about you go for a walk instead? Or maybe get a girlfriend?