All that is known rigorously, is that PSPACE contains P. But almost all complexity theorists believe PSPACE is strictly bigger than NP, and that NP is strictly bigger than P. (The most interesting exception might be Leslie Valiant, who has suggested that even P^#P = P. But he is a wild outlier.)
The proposition at chegg.com says nothing about P, it is about “reversible PSPACE”, i.e. PSPACE when one is restricted to reversible computation. I believe this paper contains the original proof that Reversible PSPACE = PSPACE.
Right, the point is that a Reversible PSPACE appears physically realizable, while currently existing computers could not actually run for the exponential time necessary to compute PSPACE problems because they would also require exponentially much (free) energy.
All that is known rigorously, is that PSPACE contains P. But almost all complexity theorists believe PSPACE is strictly bigger than NP, and that NP is strictly bigger than P. (The most interesting exception might be Leslie Valiant, who has suggested that even P^#P = P. But he is a wild outlier.)
The proposition at chegg.com says nothing about P, it is about “reversible PSPACE”, i.e. PSPACE when one is restricted to reversible computation. I believe this paper contains the original proof that Reversible PSPACE = PSPACE.
I can’t tell what @Douglas_Knight was thinking.
Right, the point is that a Reversible PSPACE appears physically realizable, while currently existing computers could not actually run for the exponential time necessary to compute PSPACE problems because they would also require exponentially much (free) energy.