Islands in flat-space cosmology

Flat-space cosmologies (FSCs) are solutions to three-dimensional theories of gravity without cosmological constants that have cosmological horizons. A detector located near the timelike singularity of the spacetime can absorb Hawking modes that are created near the horizon. Continuation of this process will eventually cause the entropy of the radiation to be larger than the entropy of the FSC, which leads to the information paradox. In this paper, we resolve this paradox for the FSC using the island proposal. To do this, we couple an auxiliary flat bath system to this spacetime in timelike singularity so that Hawking modes are allowed to enter the bath, and the entropy of radiation can be measured in its asymptotic region where gravity is also weak. We show that adding island regions that receive the partners of Hawking modes cause the entropy of radiation to follow a Page curve, which leads to resolving the information paradox. Moreover, we design a quantum teleportation protocol by which one can extract the information residing in islands.

Automated summary

This paper resolves the information paradox in flat-space cosmologies using the island proposal, coupling an auxiliary flat bath system to the spacetime near the timelike singularity to allow Hawking modes to enter the bath for measurement. By adding island regions receiving partners of Hawking modes, the entropy of radiation follows a Page curve, leading to resolution of the information paradox. Additionally, a quantum teleportation protocol is designed to extract information residing in islands.