In the eighteen hundreds, Maxwell, in his work on the theory of =
heat, hypothesized an intelligent being (a "demon") who sits at a gate betw=
een two chambers of a gas only allowing hot (higher energy) particles in th=
e left chamber and cold (lower energy) particles in the right chamber. The =
idea is that this demon, just by *knowledge* of which particles are =
hot and which are cold, can thus result in a *decrease of **entro=
py* ~ or the creation of a temperature gradient of a gas from an equili=
brium configuration. This is a violation of the second law of thermodynamic=
s which says that entropy can only increase (or remain as is), i.e. dS >=
=3D 0, and so makes a perpetual motion machine of the second kind~

One way out from this contradiction is that the entropy of the demon's b=
ody increases when it acquires the information **by more than what the gas system would decrease such that in total, the combined demon=
's + gas's system's entropy would only increase. This is not a trivial fact=
!**

The first to demonstrate this was Leo Szilard in the 1930s who showed th= at this was indeed the case!

The main goal of the talk will be to go over Szilard's seminal paper: On The Decrease of Entropy in a Thermodyna= mic System By the Intervention of Intelligent Beings.

**The talk will be divided into three (unequal) parts:**

- Quick review of thermodynamics.
- The meaning of entropy and the work value of information.
- Szilard's engine and a proof that dS >=3D 0 for a system with such a= demon.