Re:Time Travel: Probability and Impossibility
by roywiggins on Tuesday November 09, 2021 @01:37PM
(#29165533)
> altering a entangled particle so it's sister particle responds is possible
Altering the particle (as far as anyone knows) breaks the entanglement. The person on one end can measure their particle, but that doesn't tell them anything about whether or how the other one was altered.
Once you observe your particle, you've collapsed the wavefunction of the entangled pair. But- crucially- it's not possible to observe the wavefunction itself, so nobody else can tell whether it's collapsed. That is, if I measure my particle, I have no idea whether the particle on the other end will or has already been changed or observed, and I can't know. It just gives me a random value and collapses the state if it hasn't already.
It's only in retrospect that you can detect entanglement; the values you get upon observation of the pairs are correlated once you have both sets of values to compare. But until then you just have a bunch of white noise, and it's not possible (this is the no-communication theorem) to make any sense of that white noise.
Altering the particle (as far as anyone knows) breaks the entanglement. The person on one end can measure their particle, but that doesn't tell them anything about whether or how the other one was altered.
Once you observe your particle, you've collapsed the wavefunction of the entangled pair. But- crucially- it's not possible to observe the wavefunction itself, so nobody else can tell whether it's collapsed. That is, if I measure my particle, I have no idea whether the particle on the other end will or has already been changed or observed, and I can't know. It just gives me a random value and collapses the state if it hasn't already.
It's only in retrospect that you can detect entanglement; the values you get upon observation of the pairs are correlated once you have both sets of values to compare. But until then you just have a bunch of white noise, and it's not possible (this is the no-communication theorem) to make any sense of that white noise.