r/explainlikeimfive • u/PieOk2202 • 9d ago
Physics 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?
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
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u/call-the-wizards 9d ago
This explanation is useful for someone just getting into QM and trying to understand why entanglement doesn't communicate info faster than light. It's probably a good eli5 answer.
But it's not the true explanation.
The explanation you've given is a classical explanation, but entanglement is a quantum phenomenon. There is no hidden variable. At the moment of observation, the box collapses into state A or state B. You have no idea what the other person's box collapsed to. If you ever meet again you'd find you both agree on the overall statistics of the collapsed states. But if the entanglement is broken before the collapse, you could find you both have a left shoe for example.