Compsci bullshit

Do one-way functions exist?

If a map is non-invertible, does it really exist?

y=x^2 is one way, because x can be both sqrt(y) and -sqrt(y).

Of course there are special reversible CPUs, which can reverse the computation, due to the type of logical gates they are built from. But that is a different story.

>>3
Tom Knight's research group at MIT fabricated a small adiabatic processor in the late 1990s. The practical logic family they developed is called split-level charge recovery logic, and can be implemented using standard (CMOS) fabrication techniques. I believe the work has been continued by Michael P Frank at Florida State University. An example of the work in Tom Knight's group is the following master's thesis (which has a pretty decent section on related work through the early 1990s.) Vieri, C J: Pendulum: A Reversible Computer Architecture, Master's Thesis, MIT EECS dept, 1995.

Reversible circuits need to be adiabatic (there can't be heat exchanges between the circuit and its environment), which means that they must be in equilibrium at all times. For any process that needs to change something you can only approximate equilibrium by making the change happen as slowly as possible.

If I remember my thermodynamics correctly, you can make the energy of a reversible computation arbitrarily small, but the minimum action (energy times time) must be a small constant.

>>4
Landauer's principle need not be supported by a reversible circuit (as it does not erase bits), and therefore the energy needed can theoretically be zero (and no heat would be released). Reversible circuits also don't need to be adiabatic; practical reversible gates have been made which are no slower than non-reversible chips (taking into account that reversible chips are usually larger, and therefore have a speed of light latency increase).