So I have posted the whitepaper on my upcoming cryptocurrency Nebula. Nebula will be distinct from all other cryptocurrencies since the POW problem for Nebula will incentivize the future development of the reversible computer (which has not been invented yet). You can find the whitepaper on the POW problem for Nebula at
https://boolesrings.org/jvanname/2017/07/22/nebula-the-cryptocurrency-that-will-produce-the-reversible-computer/ and you can find previous discussion on how cryptocurrency POW problems will incentivize reversible computation at
https://bitcointalksearch.org/topic/m.20247850.
So Landauer's principle states that every time a bit of information is erased, ln(2)*k*T energy is used where T is the temperature and k is Boltzmann constant. Landauer's principle amounts to 2.8*10^(-21) J per bit erasure at room temperature. The efficiency of conventional computation is limited by Landauer's principle, but there is no such limit of the efficiency of reversible computation. Reversible computation however has the downside that it usually takes more steps to perform a certain calculation reversibly than it takes to perform the same calculation irreversibly. Therefore, since reversible computation requires some computational overhead, computing machinery manufacturers currently do not have an incentive to research and develop new reversible devices since any gains in efficiency will be dwarfed by the increase in the number of steps required to perform such a calculation.
Nebula will be the first cryptocurrency to incorporate a kind of POW problem which I call an RCO-POW (reversible computation optimized) problem. An RCO-POW problem is a POW problem which can be solved using a reversible computing device just as easily as it can be solved using a conventional computation device. Since RCO-POW problems can be solved using reversible computers in just as many steps as they can be solved using conventional computers, it is advantageous for one to develop energy efficient reversible computing devices to solve these RCO-POW problems. After computational device manufacturers produce devices to solve RCO-POW problems, they will have the knowledge and infrastructure to produce reversible computers for many other purposes and possibly even quantum computers.
The RCO-POW for Nebula, which we shall call R5, consists of five different algorithms. Since R5 relies on several different algorithms, it will be difficult for a single entity to launch a 51% attack against Nebula. Furthermore, since R5 has multiple algorithms to choose from, a reversible device manufacturer can choose the problem which the device will be made to solve. RCO-POW problems are not ASIC resistant since reversible computing devices can be thought of as certain kinds of ASICs and because the same qualities that make an algorithm easy to compute with a reversible device also make it easy to compute using an ASIC. Therefore R5 will be minable by CPUs/GPUs at first but R5 mining will soon be dominated by ASICs.
The problem of wasted energy and wasted resources in POW mining is one of the biggest problems with cryptocurrencies today. I hope that the cryptocurrency community will consider Nebula to be a satisfactory solution to this problem. I hope that either the cryptocurrency community would flock to Nebula or incorporate an RCO-POW into some other cryptocurrency with a high market cap.
-Joseph Van Name Ph.D.
https://boolesrings.org/jvanname