Quantum thermodynamics and quantum entanglement entropies in an expanding universe

We investigate an asymptotically spatially flat Robertson-Walker space-time from two different perspectives. First, using von Neumann entropy, we evaluate the entanglement generation due to the encoded information in space-time. Then, we work out the entropy of particle creation based on the quantum thermodynamics of the scalar field on the underlying space-time. We show that the general behavior of both entropies are the same. Therefore, the entanglement can be applied to the customary quantum thermodynamics of the universe. Also, using these entropies, we can recover some information about the parameters of space-time.