5 ms·
> But the vast majority of physicists today think the collapse of the wave-function isn’t a physical process. Because if it was, then it would have to happen in
by armchairhacker 4y ago
> But the vast majority of physicists today think the collapse of the wave-function isn’t a physical process. Because if it was, then it would have to happen instantaneously everywhere.
Why can't WFC be a physical process? Yes, when a photon on the Moon is measured it immediately changes the "wave function" of a photon on Earth from 50/50 to 100/0. But the wave function was always a probability, and probabilities always allow for hidden information. To the observer, entangled or not the calculation is still 50/50. And you can't e.g. "force" 1,000 entangled photons all to be positive to create an unlikely unusual scenario.
WFC collapse or no, both observers experience their own independent 50/50 photon collapse. It doesn't matter which observer measures first or if there is no "first" at all. The WFC may or may not be instantaneous because it doesn't matter. The fact that the particles are entangled doesn't affect observer A until he's able to observe observer B and vice versa.
For all we know all of our particles could be entangled with other particles halfway across the universe, it can't affect us until the speed of light reaches us so we can observer ourselves that the other particles are entangled.
Also why Hyperion isn't blurred, despite the fact that all of the particles which affect it are too small to be measured, is because Hyperion isn't too small to be measured. The particles aren't too small to be "measured" by Hyperion when they affect Hyperion, and just because Hyperion is further away from us doesn't mean it behaves and differently. And by seeing Hyperion's chaotic orbit we still can't predict those "unmeasurable" particles.
- mtlmtlmtlmtl 4y agoWell, to be fair, Sabine does in fact conclude at the end that it must be a physical process, and the fundamental problem [to be solved] in QM is understanding that physical process.
- zarzavat 4y agoWhat is happening physically when something is measured to distinguish it from something that is not being measured?
- armchairhacker 4y ago1) entangled particles are collapsed “instantaneously”. But it’s not really instantaneous because those particles can’t reach the initial observer/measurement until the speed of light. 2) Superpositions are collapsed which apparently causes different behavior than if they’re collapsed later. e.g. the double slit experiment, where measuring the electrons before the slit causes the interference pattern to disappear. This and Bell’s theorem are very unintuitive but they don’t necessarily break the speed of light. What if electrons are shot through a very long double slit, where they may or may not be measured early on but the observers at the end don’t know this? This still doesn’t break the speed of light because once the electrons create the interference pattern which the observers can measure to determine if they are entangled, the electrons are already local to the observers. Bell’s theorem just shows there is no one “hidden state” in entangled electrons before they are measured. The entanglement seems to create the relation “chargeA = !chargeB” without setting “A” or “B”, but when A is finally resolved, it still takes the speed of light for this information to reach B.
- lawrenceyan 4y agoIt’s so efficient. I love it.
- XorNot 4y agoIt's worth noting that "instantly" is presumed, but not guaranteed. The speed of entanglement has been measured [1] with a lower bound of 1550 * c. [1] https://www.nature.com/articles/s41598-019-48387-8 https://www.nature.com/articles/s41598-019-48387-8
- bowsamic 4y agoWe don’t currently know what is special about certain situations that causes them to be “measurements”. That’s what the “Measurement problem” is
- burrows 4y agoBut are scientists able to guess with high accuracy whether an arbitrary situation will be a measurement or not?
- readams 4y agoWorth pointing out that Bell's Theorem and experiment have ruled out hidden variable explanations, leaving only instant "communication"
- armchairhacker 4y agoWhether communication is “instant” doesn’t matter because it takes the speed of light to observe. Say A and B are entangled, both observers of A and B know they are entangled, A and B don’t have a value yet, there’s only A != B. When A gets measured, it takes the speed of light for A’s measurement to reach B. If B gets measured before then it’s still a 50/50 (and then when A is revealed it will 100% be the opposite of B). It’s true that if B gets measured B’s observer will instantly know A. But this doesn’t break the speed of light because B’s observer already knew that A != B, so they don’t need any more information from A to determine it when they measure B. Like how, if B and A were predetermined (not quantum) and then separated and B was revealed, B’s observer will instantly know A.
- deleted 4y ago[deleted]
- bowsamic 4y agoIt rules out local hidden variables, non local hidden variables (eg Bohmian mechanics) is still allowed
- rstuart4133 4y agoI think the point being made is a non-local variable is just "instant communication" in a different guise. It's a variable that everyone can see, and once it's value is observed is instantly for all observers no matter how far apart.
- bowsamic 4y agoWell the idea of hidden variables is that they are totally inaccessible to current technology, so they aren't really observable. In the case of Bohmian mechanics the "hidden variable" is the configuration of all particles in the universe, which is clearly not something that can be observed by any observer. It's also not a quantity that is changed by observation which your line "once it's value is observed is instantly for all observers no matter how far apart" implies. It isn't a quantum observable: it is a normal classical kind of state. It's just that the physics for one particle depends on the configuration of all other particles, which is completely non-local.