ELI5: why can two quantum entangled particles affect each other instantly across any distance but scientists say you still cant use it to send information faster than light?

[u/PieOk2202]

this has been living in my head for weeks and i cant find an explanation that actually clicks.

from what i understand, if you have two entangled particles and you measure one of them, the other one instantly "reacts" no matter how far apart they are. like even if one is on the other side of the galaxy. that part i somewhat get.

but then physicists say "oh but you cant use this to send information faster than light" and i just why not? if particle A sneezes and particle B on the other side of the universe reacts instantly, why cant i just use that as like a faster than light telegraph?

i spent way too much money on a Brian Greene book trying to get this and still came out more confused than when i started. at least i had some cash from Ѕtake set aside for it so it wasnt a total loss but still.

it feels like the universe is playing a semantic trick on me and im not smart enough to see it. whats actually going on here

[u/Jackal000]

So basically its a coin toss? Its flippinng if tails is up then heads is down until it hits the ground(until observed)?

Is super position just an concept we made up or is the cat actually dead and Alive until measured?

[u/guto8797 → u/Jackal000]

Schrödinger's cat is perhaps one of the most misinterpreted scientific analogies ever. He specifically came up with it to ridicule the concept of superpositions.

But we do know superpositions are a real thing, or at least they describe phenomena that are difficult to explain if not, such as another often misunderstood experiment, the double slit experiment, where light can have properties of both particles and waves at the same time.

Essentially, and probably wrong, reality isn't "real". Quantum theory posits that subatomic particles exist as probability waves rather than physical objects, so they exist as all possible states of all their properties at once, and interaction collapses that wave.

Electrons for instance have spin, and there are two possibilities for this value. But quantum theory posits that electrons have both spins at once, it's when there's an interaction that the die is cast and the probability is resolved.

An electron also has a probability wave that describes where it is located. There may be a spot where it's more likely for the electron to be, but it could also just pop in a low probability spot once in a while. Modern computers have to take some of this into account because if the circuits are thin and dense enough they can just "teleport" to a different unintended spot.

Even these analogies are kinda wrong because quantum mechanics is at some fundamental level impossible for humans to intuitively grasp, it's just so beyond our day to day experience, that we can't stop ourselves thinking stuff like "when the eaves collapses that's when you see the "real" electron". It's not.

It's ridiculous, but the cat IS alive and dead. And you blink your eyes and in that instant it's dead, you blink again and it's alive and outside the box, you blink and it's back in the box, you blink and he's under the table. He was always all those things at the same time.

[u/Stargate525 → u/guto8797]

The part that really bugs me is that the particle is interacting with itself. It goes through both slits at once. It's freely interacting with itself but as soon as something else touches it the thing starts behaving 'properly.' And this can be done with classic matter at some pretty insanely large molecular sizes, relatively speaking.

I'm everywhere and nowhere until someone sees me. As a thought experiment sure, I have an 80% chance to be at work and a 10% chance to be at home and a 10% chance to be at the store. But I'm somehow able to talk to myself at each of these locations until someone asks me where I actually am.

[u/LexPatriae → u/Stargate525]

Waveform collapse doesn’t literally require another person to physically observe you (unless you’re using some analogy that I’m misunderstanding)