Black Hole/Entanglement Question

[Gaz1982]

An overlapping question here, but would Quantum Entanglement still work if one particle was sent beyond the Event Horizon whilst its entangled particle was still this side of said Event Horizon?

 

[phinds]

"Work" in what sense? Since you can't measure anything inside the EH, how would you tell?

 

[Gaz1982]

Would the particles still be entangled either side of an event horizon?

Forgive the wolly language. I am not a physicist

 

[phinds]

Would the particles still be entangled either side of an event horizon?

Forgive the wolly language. I am not a physicist

I don't know if they would, I only know that there is no way in which it can matter.

 

[Gaz1982]

Surely it matters. Even if in theory only, the relationship can be maintained either side of an event horizon.

 

[phinds]

Surely it matters. Even if in theory only, the relationship can be maintained either side of an event horizon.

And in what way would that be meaningful? Let's assume (1) that is is maintained and (2) that it is not maintained. Explain to me what the difference is between the two in ANY practical / measurable terms.

 

[Gaz1982]

I have no practical use for it. But it intrigues me that any relationship at all can be maintained across the horizon.

Unless you have other examples?

 

[PeterDonis]

it intrigues me that any relationship at all can be maintained across the horizon.

There is nothing special about the horizon in this respect; it's just a particular case of particles being entangled at spacelike separated events, which is certainly predicted by quantum mechanics, yes.

 

[phinds]

I have no practical use for it. But it intrigues me that any relationship at all can be maintained across the horizon.

Unless you have other examples?

I agree that it is a very interesting point and I'll take Peter's word for it that it happens. I have read, much to my confusion, about how inside the EH, things become time-like rather than space-like (which would refute his argument) but I don't understand that and I don't see how it is likely to apply immediately inside the EH, but then if it doesn't, the question comes up, when does it start applying? All very weird to me.

In any case, I'm an engineer and tend to look at things from a practical point of view and entanglement already has no practical value even OUTSIDE an EH since it can't be used to communicate. I DO, on the other hand, understand the value of "pure" science for its own sake and who knows what our knowledge of entanglement might lead to at some point in the future, if only in contributing to an understanding of other phenomena. Lot's of things that at some point in our understanding of them have seemed useless to us engineers have turned out to be of great practical value.

 

[WhatIsGravity]

And in what way would that be meaningful?.

This is much more a question rather than a statement... but I'm thinking that if you 'observed' the half of an entangled pair which is outside the horizon, then that would change the entropy of the black hole; assuming entanglement holds. Which would change the temperature, surface area, and gravitational 'strength' of the black hole?

 

[phinds]

This is much more a question rather than a statement... but I'm thinking that if you 'observed' the half of an entangled pair which is outside the horizon, then that would change the entropy of the black hole; assuming entanglement holds. Which would change the temperature, surface area, and gravitational 'strength' of the black hole?

Why? How?

 

[WhatIsGravity]

Again, more of a question... I'm thinking that if you measure half an entangled pair, then the other half is defined- thus less entropy. Across an event horizon, who can say if, or moreover 'why'? The 'how' would be by the thermodynamics of black holes; Bekenstein and Hawking.

 

[PeterDonis]

I have read, much to my confusion, about how inside the EH, things become time-like rather than space-like (which would refute his argument)

You are right to be confused by such statements, since taken at face value, they're simply incorrect. (If you really want to delve into why and how they're incorrect, you should probably start a separate thread on that topic.) The key point for this discussion is that, if one member of an entangled pair of particles falls into a black hole and the other stays outside, then there will certainly be portions of the two particles' worldlines that are spacelike separated.

 

[phinds]

Thanks, Peter.

 

[phinds]

Again, more of a question... I'm thinking that if you measure half an entangled pair, then the other half is defined- thus less entropy.

Ah ... that makes sense. I wasn't thinking. Thanks for that clarification.

 

[Nugatory]

Again, more of a question... I'm thinking that if you measure half an entangled pair, then the other half is defined- thus less entropy.

You have the exact same number of microstates (one!) before and after, so no change in entropy.

 

[WhatIsGravity]

You have the exact same number of microstates (one!) before and after, so no change in entropy.

There's no way to measure it, but I can't help but wonder if that holds true across an event horizon? It seems to me, humbly, that the outside and inside of an event horizon would be two completely separate systems... yet with entanglement? I've read that un-entanglement? happens faster that the speed of light; but there can be no transfer of information, thus change in entropy..hmmm?

 

[Dale]

Locally the event horizon is simply a null surface like any other. Entanglement certainly "happens" across null surfaces and cannot be used to communicate across null surfaces. There is nothing different about an EH in this respect.

 

[Gaz1982]

I agree that it is a very interesting point and I'll take Peter's word for it that it happens. I have read, much to my confusion, about how inside the EH, things become time-like rather than space-like (which would refute his argument) but I don't understand that and I don't see how it is likely to apply immediately inside the EH, but then if it doesn't, the question comes up, when does it start applying? All very weird to me.

In any case, I'm an engineer and tend to look at things from a practical point of view and entanglement already has no practical value even OUTSIDE an EH since it can't be used to communicate. I DO, on the other hand, understand the value of "pure" science for its own sake and who knows what our knowledge of entanglement might lead to at some point in the future, if only in contributing to an understanding of other phenomena. Lot's of things that at some point in our understanding of them have seemed useless to us engineers have turned out to be of great practical value.

Cool.

I'm actually really interested in how people from different backgrounds perceive physics. I would expect an engineer to look at things in a cold, practical light.

I think bringing people into physics from all different backgrounds is very useful. As I consider physics to be the best example of us "thinking like a species" instead of as individuals or different cultures.