After reviewing the discussion of a single magnetic particle (or spin) in a heat bath, Professor Susskind continues with the development of the one-dimensional Ising model. This model does not exhibit phase transitions. He then moves on to the multi-dimensional Ising model. For any number of dimensions above one, the Ising model exhibits phase transitions at specific temperatures. This is due to the fact that, in multiple dimensions, each point in the lattice is affected by more than two neighboring lattice elements.