Unruhs Law says that "an accelerating observers in empty space will see themselves embedded in a gas of hot photons at a temperature proportional to their acceleration."
Tell me if I have this wrong, but as I understand, this is because empty space is full of virtual particles popping into existence and immediately annihilating, so you cannot detect them until you begin to accelerate. This is because an accelerating observer has an effective horizon (a Rindler horizon) which they cannot see beyond, so if one of these particles drifts out of their view and into their hidden region, they only see one of the particles (lets say they're photons) and will be able to detect it and interpret it as heat.
How is this possible? Shouldn't a photon still annihilate with its partner regardless of which side of some arbitrary horizon it's on? And is this photon pair entangled?