Cells often perform computations in response to environmental cues. On
general theoretical grounds (Landauer's Principle), it is expected that such
computations require cells to consume energy. I will start by giving a
general introduction to the relationship between information and
thermodynamics using simple examples using ideal gases. I will then discuss
the thermodynamics of cellular computations by consider the classic problem,
first considered by Berg and Purcell, of determining the concentration of a
chemical ligand in the surrounding media. I will show that learning about
external concentrations necessitates the breaking of detailed balance and
consumption of energy, with greater learning requiring more energy.