So reversible computing requires less energy not more right? Last I heard it is damn hard to forget information.
But what happens to the outputs you don't need? They do need to go somehere. A reversible circuit ends up having a lot of unused outputs which need to be erased if the circuit is to be reused. In essence, we have traded a heatsink for a bitsink, but they are essentially the same thing.
I don't see reversible computing as categorically different from regular computing. It's regular computing, with careful and detailed heat management.
To my understanding you just need energy to set the inputs, give it a little push and everything else runs on its own (forwards and backwards).
Counter Clock World
The most powerful -- and most feared -- organisation in the world is the Library, in charge of expunging the written records of events, which have no longer happened.
https://en.wikipedia.org/wiki/Counter-Clock_World
The novel describes a future in which time has started to move in reverse, resulting in the dead reviving in their own graves ("old-birth"), living their lives in reverse, and eventually returning to the womb where they split into an egg and a sperm during copulation between a recipient woman and a man.
The Hobart Phase
The Hobart Phase is the new order of life where people rise from the dead and are rejuvenated. Time reversal apparently began in 1986. Other than aging, Hobart Phase resurrection has changed nutritional and excretion processes and associated social taboos. People do not eat, but instead consume "Sogum" anally through a pipe, and later "plop" out food orally, which is done in private, due to its 'shameful' nature. As for smoking, cigarettes are no longer smoked, but the smoke instead blown back into them, making them grow back to normal size (this also clears and freshens the air). "Goodbye" and "hello" have reversed their order within standard greetings, and "food" is used as a drop-in replacement for the expletive "shit". It is stated that Mars colonists do not have the Hobart Phase on their world, and it is limited to Earth, and presumably its lunar colonies as well.
So, we are just pushing our 0s and 1s around, instead of permanently destroying and re-creating them. As reversible logic is as universal as, say, NAND logic - wouldn't it be possible to sort the unused output bits of any gates into two pools for 0s and 1s [1] and use these pools for any constant inputs that are needed in the logic? So that we would only have to "create" any new 0s and 1s when one of these two pools runs dry?
[1] E.g. a sorting buffer with 0s at one end and 1s at the other. Or does sorting necessarily mean we are sorting unknown bits at the cost of mixing known bits (constant gate inputs)?
The entropy of a sorted list of bit is O(log(n)) while the entropy of the unsorted bits is O(n).
I don't see how it would help anyway, but maybe I'm misunderstanding your suggestion. The state of these unwanted outputs needs to be kept around, if you know they will be 0 or 1 then the state is already implicit in the machine and the output isn't actually necessary.
"sorting is not reversible"/"you can't know [the original order]"/"sorting loses information"
These replies are have two problems in common:
1. They are wrong in the context of reversible gates, because (as I have hinted in my comment) when you sort bits using a normal reversible gate, then the original order of the bits will be encoded in the unused gate outputs. No information is lost, that's why we call these gates reversible in the first place.
2. The heart of my speculation lies in the question if a special irreversible circuit could be integrated into a reversible CPU, which moves bits into order without unnecessarily grounding charges. The more I think about it, the more I tend to think it could.
Edit: To make a clearer point on where I'm coming from here: I view reversibility not as a goal in itself, but a tool to use to get ultra low power compute capabilities. To achieve this, the unused output charges need to be recycled into the system. If you solve that problem, you have achieved the goal.
At an imaginary hand waving level imagine the complete state of a cpu as passing charged capacitors around and occasionally charging new ones or discharging some. This is not all that far off of how they work...
If you want to count to 7 reversibly there's an easy way involving hitting a 7 bit shift register, 7 times. In theory there's no reason to drain any capacitors per op or per the entire system, that same unit of charge just meanders down the line. Like a CCD sensor or old fashioned bubble memory kinda. The way chips are designed today that doesn't work, but insert a lot of kinda sorta in theory it could be done.
On the other hand if you want to count to 7 using three full binary adders you're going to run into scenarios where two bits enter an adder (say, 001+001) and one bit leaves (result of 010), so at least one capacitors worth of charge got turned to heat. And that charging and discharging is basically wasting battery power for no good reason. And its not a lot of power for one capacitor, but you toggle a flip flop a couple billion times a second and then not-much adds up over time to a pretty hot CPU.