# Glean some information from inside a black hole

What information would this tell us?

• I fly my spaceship to a distant star that is now a black hold.
• I park my craft a safe distance away.
• I send a probe almost exactly halfway between me and the singularity.
• At this point, the probe is 1 meter closer to the singularity than to me.
• The probe entangles two particles. One heads into the singularity, one heads towards me.

When I measure the spin on the particle that comes to me, what do I see? The other particle has already been ‘observed’ as it reached the singularity. (likely it was destroyed and spaghettified before). Perhaps I will see the same spin each time on my side? Wouldn’t that tell me something about the black hole’s singularity? Or couldn’t I learn something somehow about the interior of the black hole using entanglement?

In principle, when you put a classically spinning particle into a black hole, this would chance the black hole’s angular momentum, and you could in principle measure this change in the angular momentum by investigating the properties of the BH’s gravitational field. You’re asking, “well, what happens if we put in a black hole whose angular momentum is in a quantum superposition?” In principle, this would cause the black hole’s to become entangled with the particle outside the hole. But we don’t yet have a self-consistent theory to describe quantum mechanical states of black holes; we’d need a full-on quantum theory of gravity for that.

So the unsatisfying answer is “we simply don’t know how to describe this experiment.” These types of gedanken-experiments are the kind of thing that people who are working on quantum gravity think about, but they certainly haven’t reached any definitive conclusions yet.

I think the simplest answer is that your not going to learn anything more about the black hole than you would do classically.

Entangled particles can’t actually be used to transmit information that way.

Plus, the process of dropping a particle into a black hole is probably going to be enough to break the entanglement.

Doesn’t it just entangle the black hole with the remaining particle?

I see no reason for that. The entanglement transcends light speed and works at some fundamental level of the universe we can’t explain yet. There’s no reason to believe it wouldn’t work inside and outside the schwartzchild radius. Then again, I won’t debate Chronos…