Isn't that more to flip a bit than representing a bit, though? Another angle might be to look at the Bekenstein bound, i.e. that if you have a physical system

Isn't that more to flip a bit than representing a bit, though? Another angle might be to look at the Bekenstein bound, i.e. that if you have a physical system of mass-energy m, there's a maximal number of bits B that it can contain. Though that also would need a system-containing volume (surface area?) which would also be arbitrary.