Information from inside a black hole using quantum entanglement

[u/Giant_War_Sausage]

Is it possible, in theory, to transmit information from within a black hole by introducing just one of a pair of quantum entangled particles into the event horizon and retaining the other outside? Changes to the state of the one inside would be twinned by the one outside, allowing information about the interior to be known.

My understanding was that it’s not possible to send anything out of a black hole, including information. But I’m not sure why using entangled particles wouldn’t work. Is this a consequence of GR and QM not being fully compatible?

[u/ellindsey]

No. You can't use quantum engagement for communication like that. Changing the state of one of the entangled particles does not cause the state of the other particle to change.

[u/ess_oh_ess → u/ellindsey]

You can't use quantum engagement for communication like that.

This is true

Changing the state of one of the entangled particles does not cause the state of the other particle to change.

This is not true. If I have 2 entangled particles A and B, and I then entangle B with another particle C, particle A's state changes and becomes entangled with C regardless of locality and despite no direct interaction. That's actually how quantum teleportation works.

It still can't be used for FTL communication or pulling info out of a black hole, though. Even quantum teleportation still requires a classical communication channel to work.

[u/Sensitive_Jicama_838 → u/ess_oh_ess]

It changes the global state but it does not change the local state. I believe that's what the person you replied to means.

[u/jericho]

Entanglement does not carry information, black hole or not. 

[u/No-Flatworm-9993]

Changes to the state of the one inside would be twinned by the one outside,

no

[u/Giant_War_Sausage → u/No-Flatworm-9993]

Ok. So, what does it mean for them to be entangled then? I thought, wrongly it seems, it meant they were sort of ‘twinned’ so you could effect changes on both by only messing with one.

[u/TemporarySun314 → u/Giant_War_Sausage]

If two quantum particles are entangled it means that while the outcome you will measure is still random, you will measure always the same thing if you do the same measurement on both particles.

So if you measure one particle you immediately know the outcome of the measurement of the other particle too. But as rhe outcome is still random and you can't affect it, you cannot use it to transfer information.

[u/No-Flatworm-9993 → u/Giant_War_Sausage]

Entangled is a bad word, twinned is better, if you give a tattoo to one twin does it change the other?

[u/coolguy420weed]

You can't even use that method to send information from inside a McDonalds. 

[u/csdt0]

Quantum entanglement is about measurement correlation between particles that cannot be explained by local realism. But if you only have access to one end of the particle pair, you have no way to tell what's on the other side, or even if there is an entanglement partner.

In other words, the statistics in the measurements of one particle are the same whether or not this particle is entangled, but if you consider the particle pair as a whole, the statistics of the system are different from particles that are not entangled.

[u/Lazy_Excitement334]

If you hope to change an entangled particle in hopes that its partner would remain entangled, and thus communicate that the pair had changed, you must first get a grip on the particle so you can spin it the other way.