On 30/09/2014 12:02, Matt Mahoney via AGI wrote:
It would be interesting to see whether evolution is possible in a reversible cellular automaton. Evolution requires some source of randomness to induce mutations. We could use repeated encryption as a reversible pseudo-random source.
I once made some reversible CA with self-reproducing creatures in them. * Revoworms: http://alife.co.uk/revoworms/ Mutations are a fairly trivial requirement in most alife simulations - including reversible ones. The self-reproducing creatures generally bang into each other - and that's enough to generate all kinds of variations.
(Strictly speaking, you also have to reverse charge and parity along with time to make the weak nuclear force reversible).
That's probably not true - since charge and parity are probably phenomena - that *automatically* reverse when you reverse time. I have a page about that idea here: http://finitenature.com/cpt/ It's not my idea, though - Ed Fredkin came up with it. I just think it is pretty neat.
The entropy of a closed, reversible system cannot increase. You can always find the the Kolmogorov complexity of a reversible system by running it backward and measuring the length of the original program. Of course this is not what we observe. Entropy is indeed increasing. We cannot make it decrease. Time has a direction. Heat flows one way until everything is the same temperature. Why? We can blame quantum randomness, but I don't like that explanation. Schrodinger's equation gives an exact solution when you include the observer. We only prefer probabilistic approximations like the Copenhagen interpretation because it makes the computation tractable.
You see the second law of thermodynamics emerge in a wide range of reversible systems. That's been broadly understood since Boltzman's era. The only mystery in this area is why we appear to have such a low-entropy state at the start of the universe. AFAIK, we have two main candidate theories: observarion selection effects (if the early universe was high entropy, living systems would not emerge) and Occam's razor (which suggests simple beginnings). Maybe between them they explain the mystery - or maybe there's still some mystery left.
Another problem is that Morita and Imai are describing CA with infinite memory. You can always store bits without deletion by moving all of the existing bits to the next higher address and writing to address 0. You can't do that with finite memory. But finite systems can still be reversible. Any finite state machine must eventually repeat. At that point, no more information can be lost even though memory bits are still being written.
You can still reversibly copy in these finite systems. However eventually you run out of space for more copies. -- __________ |im |yler http://timtyler.org/ [email protected] Remove lock to reply. ------------------------------------------- AGI Archives: https://www.listbox.com/member/archive/303/=now RSS Feed: https://www.listbox.com/member/archive/rss/303/21088071-f452e424 Modify Your Subscription: https://www.listbox.com/member/?member_id=21088071&id_secret=21088071-58d57657 Powered by Listbox: http://www.listbox.com
