### Why the Entropy of the Universe is Zero! Dr. James Baugh, Georgia College Mathematics Department

#### Abstract

In quantum mechanics we have a very peculiar property for composite quantum systems (for example the system of two photons). The entropy of the whole may be less than the sum of the entropies of the parts. This occurs in particular when the two subsystems are entangled. In this talk I will show (with simple examples):* How we use density operators to describe general probabilistic information in quantum theory,

* How (Shannon) entropy is defined using the density operator,

* The relationship between the density operator of a composite (product) system and its subsystems,

* What entanglement means in this format and how it equates to this peculiar entropy deficit.

I will then recast the idea of entropy in terms of entanglement and show thus that The Universe by definition has zero entropy.