this post was submitted on 28 Mar 2025
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I thought the whole point of entangled communication is that you didn’t need to “send” anything. It automatically flips the entangled bit on the other end, all that “spooky action at a distance” bidness. Why do the need to “send” entangled photons?
You need to prep by sending the entangled particles (photons in this case). The spooky action is when you act on 1, you also act on the other. The useful bit is the uniqueness of the link. It cannot be intercepted without it being obvious and detectable.
Think of it like voodoo dolls. It works at a distance, but you need to make the voodoo doll using a bit of the target, then send/take it elsewhere to stab.
I'm pretty ignorant of physics, but isn't it only certain kinds of ways of acting on the first particle that "affect" the other, namely actions that measure a property of one particle that is correlated with the same property's value on the other? At first you don't know the value of either but you know they're correlated; but then when you measure and collapse the wave function on one and discovered a value for the property, you have automatically collapsed the wave function on the other too, yielding a predictably correlated value. If it were just any kind of action that affects the other particle, you'd be able to use it to sent information instantaneously, which you can't do. So it's not quite like how people imagine voodoo dolls: do something to the doll (make a change to it) and the person feels the effect. But perhaps someone who studies this stuff can help clarify.
That's fairly close. The only proviso is there are some ways to affect the results. You can't send actual information along the link, but you can prove they were in communication. That proof requires information from the sending end however. It's only provable once that information is sent. Basically they communicate faster than light, but can't send information faster than light. Entanglement is weird.
Thank you. That is helpful and clear.
but voodoo dolls dont really work, do they?
Quantum voodoo dolls do. It's annoyed more than a few scientists over the years.
could you give some source to that? I cant find anything relating to quantum voodoo dolls
It was a bit of a joke. Entangled particles act a little like voodoo dolls, with "spooky action at a distance".
ah, world is going so crazy you cant really know what is what anymore
Once you hit quantum mechanics, you need to throw out a lot of your instinctive knowledge, and just follow the maths. How this maps back to our perception is patchy at best. Once you add science reporters, who don't actually understand the core subject, and you get some... interesting results.
In hindsight, "quantum voodoo dolls" is a term I could easily see being used. There are a lot of poorly thought out Wats to try and describe quantum weirdness.
The "spooky action" is really just the determination of a particle's spin on one side meaning you already know the other particle will have an opposite spin. This probably violates locality because you gain knowledge about something that's non-local from a quantum perspective, even though entangled particles have to start local (there are opposing interpretations, like the de Broglie-Bohm). While in fiction this might suggest that changing the state of one particle simultaneously changes the other, in real life this just means extra information you mathematically shouldn't have, and doesn't really lead to FTL information transmission. What it does mean is that if you want secure communications you can use entangled particles to generate a secret key, determining the spin of them on either side, and you can be sure that they haven't been tampered with and that the other side of the communication will be equal and opposite. It's essentially a one-time pad.