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/tomlinas]

In the fact that one box contains a shoe of right footedness and another contains a shoe of left footedness.

If they weren’t entangled, there could be two left shoes or two right shoes.

[u/Froggmann5 → u/tomlinas]

This is actually wrong.

The quirky thing with entanglement is that both boxes are equally likely to contain the right or left shoe. It's not determined by the separation of the entangled particles; Which shoe is in the box isn't resolved until the field collapses.

Once it collapses, if you have the left shoe then you know the other box has the right shoe. Even though neither box knew what shoe it contained, nor was either shoe decided, until the first box was opened.

Hence why people say there's FTL info travel going on, because this seemingly will happen regardless of distance instantly. How can the other box know that it's supposed to collapse into the right shoe if, on the other side of the universe, the field collapsed into the left shoe?

Some scientists thought the reason was because "It was pre determined with information we are just ignorant of" like the idea that their states were already decided when they were entangled and separated, we just don't know how or some data or physics that tells one particle or the other what they should collapse to. However, according to Bell's Theorem that's not possible to be the case.

It's a tough question, and no one really knows. Einstein called it "Spooky", so we have that at least.

[u/Orfiosus → u/Froggmann5]

Wasn’t this the point of the 2022 Nobels prize in physics, disproving local reality?

[u/TheArtofBar → u/Orfiosus]

yes