3 ms·
It is instantly but you can not use it to transmit information. Say you have a pair of entangled spins in a superposition of the two anti-parallel states first
by danbruc 10y ago
It is instantly but you can not use it to transmit information.
Say you have a pair of entangled spins in a superposition of the two anti-parallel states first spin up and second spin down or first spin down and second spin up with equal probability for both states, i.e. each spin is up or down with a probability of 50 % but the two spins always have opposing orientations.
If you measure one of the spins, then there is no time, no matter how far the spins are separated, in which you could measure the second spin to have the same orientation as the one you just measured because the result of the measurement somehow had not yet enough time to reached the second spin, supposedly because this state change is limited to travel at the speed of light.
It is as if the spins had secretly picked on of the two possible outcomes when they were created but you just do not know which one until you perform a measurement. But this is not the case, this is what is called a local hidden variable theory and is ruled out by Bell test experiments. The spins have no definite orientation until you measure the first one but after the first measurement both spins instantaneously have a definit orientation no matter how far separated.
- platz 10y agoa side note, there isn't a universal "spin orientation detector" that reveals a spin orientation on the unit circle. You have to choose how to align the magnets so that the spin measured is either "up" or "down"; you could align the magnets any way you like, but they are fixed along an axis for the duration of the observation
- tedsanders 10y agoThere is no proof or strong evidence that this occurs instantly. Some interpretations of quantum mechanics still satisfy locality. https://en.m.wikipedia.org/wiki/Interpretations_of_quantum_mechanics https://en.m.wikipedia.org/wiki/Interpretations_of_quantum_m...
- danbruc 10y agoOne has to be careful what one means here. I meant it in the following specific sense and we have good experimental evidence for this. [...] there is no time, no matter how far the spins are separated, in which you could measure the second spin to have the same orientation as the one you just measured [...] If an interpretation makes use of non-locality to explain this fact is a different matter, but experimentally it looks exactly like measurements instantaneously affecting entangled partners.
- deleted 10y ago[deleted]