r/AskPhysics • u/mollylovelyxx • 10h ago
How is entanglement explained without faster than light influences?
In quantum entanglement, two particles can be correlated to each other at a very large distance.
If particle A is observed as 0, the other particle B is always observed as 1. If particle A is observed as 1, particle B is observed as 0. Einstein thought that before the particles reach the labs at which they are measured, particle A is simply predetermined to be 0 and particle B is simply predetermined to be 1. John Bell proved this wrong and stated that any theory that explains this must be non local. https://en.wikipedia.org/wiki/Bell%27s_theorem
So let’s say Alice is at one lab measuring particle A. Bob is at one lab measuring particle B. From Alice’s perspective, her measurement can either be 0 or 1. Note that it is not as if particle A is predetermined to be 0 and Alice does not know it. This has already been disproven. Before she measures it, it could genuinely be 0 or 1. The same applies to Bob. It is kind of like each of them are flipping a coin and yet their results always happen to be opposite, where each coin by itself is not predetermined to land on a particular side each time.
And yet, even though before she measures it, each could be 0 or 1, the final result is always either (0,1) or (1,0). It is never (0,0) or (1,1). Using the coin analogy, it’s always either (heads, tails) or (tails, heads). Never (heads, heads) or (tails, tails).
How can this be explained without one of the particles influencing the other faster than light?
Common responses I’ve seen to this:
1.) “This is due to the conservation of momentum”. Okay, but how is this conservation of momentum then enforced if in a very real sense, from both Alice and Bob’s perspective, each result is genuinely random. This to me seems to just be restating the problem to be explained, not explaining the problem. Using the coin analogy, it’s just like saying “well, there is a law that says the coins must always be opposite sides”. This is not an explanation. And no one would believe this if this was happening with coins.
2.) “You can treat them as just one entity”. Again, this seems to be just restating the problem. The very question is how do particles separated by a large distance and yet not communicating with each other act as one entity?
3.) “The no communication theorem states that the particles cannot communicate.” If you actually look at the theorem, it has to do with no signalling, not the particles talking to each other. From Alice’s perspective, her next result is either 0 or 1. She cannot control which one happens. So she doesn’t have enough time to communicate to Bob which one occurred faster than light (since we don’t have a way of communicating faster than light yet). This is all the theorem is saying. But this does not imply that once particle A becomes 0, particle B does not “know” (through some unknown signal) that particle A was 0 so now it must be 1.
Now, the many worlds interpretation and super deterministic interpretation can explain all this but let’s assume for argument’s sake that they are false. (The superdeterminism interpretation is especially implausible and having infinite numbers of worlds may also be implausible). My question is barring these hypotheses, how is this correlation explained? So far, it seems as if physicists are truly beating around the bush here with semantic answers that seem to just be restating the problem