Wikipedia defines the heat death of the universe as follows:
the universe has diminished to a state of no thermodynamic free energy and therefore can no longer sustain processes that consume energy (including computation and life).
I'm actually curious about why computation can't happen without thermodynamic free energy. I'm aware of Landauer's principle, but it seems to me that a closed adiabatic system could still theoretically do internal computational work using some form of computing (perhaps reversible computing).
This system would be closed off from the rest of the universe (e.g. it couldn't have classical inputs or outputs), but it seems like it could still exist and perform computation even in a perfect thermodynamic equilibrium.
Is this form of computation inherently impossible for some reason?