Recent astronomy news. There are 3 trillion stars in the Milky Way. The Milky way is about 8 times bigger than was thought. We still have a shaky understanding of our own galaxy as refined measurements of star speed in the arms indicates that the volume is about 8 times more than was previously believed.
This is something that also relates to SETI and various speculation about aliens. We are still finding larger than Pluto size objects in our own solar system and are trying to pin down the size of the galaxy to an order of magnitude.
This energy scale is slightly off in that the Milky Way energy production comes at a little over 3 X 10**47 joules. Note: the point at 10**41 joules. A Type III civilization with 10**47 joules for one year could accelerate one million earth size planets to half the speed of light using one years worth of energy.
I was interested in calculating what a Kardashev Type III civilization [using the equivalent of all the solar power in a galaxy] that is mind uploaded and using reversible computing yet is still using up all of its power would be doing in terms of ballpark capabilities. How many human brain equivalents ? The estimate provides some scale to what a true galactic civilization should be minimally capable.
The performance per unit power of ordinary irreversible computing (which does an irreversible storage operation with every logic-gate operation) will start to level off, at a maximum level of at most 3.5 X 10**22 irreversible bit-operations per second in a 100 W computer that disposes displaced entropy into a room-temperature (300 K) thermal reservoir. This rate is about a million times higher than the maximum rate of bit operations in a ~30-million-gate, 1 GHz processor or 100,000 times more than an average computer now.
Reversible computing on wikipedia
Probably the largest motivation for the study of hardware and software technologies aimed at actually implementing reversible computing is that they offer what is predicted to be the only potential way to improve the energy efficiency of computers beyond the fundamental von Neumann-Landauer limit of kT ln 2 energy dissipated per irreversible bit operation, where k is Boltzmann's constant of 1.38 × 10−23 J/K, and T is the temperature of the environment into which unwanted entropy will be expelled.
As of 2005, irreversible device technology has at most ~3-4 orders of magnitude of power-performance improvements remaining.
* And then, the firm kT ln 2 (VNL) limit is encountered.
But, a wide variety of proposed reversible device technologies have been analyzed by physicists.
* With theoretical power-performance up to 10-12 orders of magnitude better than today’s CMOS! [Note: The best that we are capable of theorizing as possible would expect to be the minimum capability for the galactic Kardashev 3 civilization.]
o Ultimate limits are unclear.
So instead of 3.5 X 10*20 per watt for irreversible.
A likely minimum reversible computing capability for an advanced civilization is 10**29 operations per watt. Plus that civilization definitely could have figured out more tricks to go a lot higher.
If 10**19 operations per second is a likely upper bound to simulate a human mind, then one watt could be used to simulate 10 billion human mind equivalents. This would be simulating all the minds on earth for one watt using reasonably advanced reversible computing.
A watt is one joule of energy per second.
3*10**47 joules per year for the galaxy
31, 556 ,926 seconds per year.
10*40 joules per second for the galaxy. (Note: Wikipedia has this at 10**37 watts which is also joule per second. The Wikipedia estimates are before the adjustments to the size of the Milky Way.)
10**69 reversible operations per second.
10**19 ops/second likely level of one uploaded human mind.
The Type III civilization has a lower end of 10**50 simulated human mind equivalents.
With about 10 billion people as the population equivalent of our current world of human minds. We could consider that number a human world-mind equivalent.
The Type III civilization has a lower end of 10**40 simulated human world-mind equivalents.
The human brain has about 100 billion neurons and 10**14 to 10**15 synapses.
The range between a single cell and the human brain is about 15 orders of magnitude. The Type III civilization would exceed a world-mind by going over that range almost three times.
10**15 world-minds would exceed the world-mind as much as a human mind exceeds a single cell.
10**30 world-minds would exceed the 10**15 world-minds as much as a human mind exceeds a single cell.
10**40 world-minds would exceed the 10**30 world-mind by 10 billion times.
Because all the simulated minds would be on a reversible computing basis, then in time and everything would be reversible in the advanced simulated existence. Anything could be undone and redone/altered in the high fidelity simulated environment.
Reversible computing abstracts
Carl Sagan suggested adding another dimension: the information available to the civilization. He assigned the letter A to represent 10**6 unique bits of information (less than any recorded human culture) and each successive letter to represent an order of magnitude increase, so that a level Z civilization would have 10**31 bits. In this classification, 1973 Earth is a 0.7 H civilization, with access to 10**13 bits of information. Sagan believed that no civilization has yet reached level Z, conjecturing that so much unique information would exceed that of all the intelligent species in a galactic supercluster and observing that the universe is not old enough to effectively exchange information over larger distances. The information and energy axes are independent, so that even a level Z civilization would not need to be Kardeshev Type III.