On Thu, Dec 18, 2014 at 9:52 PM, Matt Mahoney via AGI <[email protected]> wrote: > On Wed, Dec 17, 2014 at 1:27 PM, Abram Demski via AGI <[email protected]> > wrote: >> My current understanding of time is "the direction of computation". > > That is actually quite precise. The entropy of a computer can only > decrease. In a state transition diagram, states can merge but not > fork. Operations like writing a bit of memory cannot be reversed > because the previous bit was erased.
That reasoning is confused. The reference to a state transition diagram is not directly related to the discussion up until that point, and I don't believe anyone was talking about a computer program that could not respond to input. Similarly, while the state of a bit of memory is typically erased by a write, it is not necessarily always the case that all methods of restoring the previous state are going to be obliterated. And furthermore, since there are programs that are capable of restoring a state of a bit, wouldn't you have to say that this particular example shows that the 'entropy' of a computer (running programs) can not be defined as a generalization? Jim Bromer On Thu, Dec 18, 2014 at 9:52 PM, Matt Mahoney via AGI <[email protected]> wrote: > On Wed, Dec 17, 2014 at 1:27 PM, Abram Demski via AGI <[email protected]> > wrote: >> My current understanding of time is "the direction of computation". > > That is actually quite precise. The entropy of a computer can only > decrease. In a state transition diagram, states can merge but not > fork. Operations like writing a bit of memory cannot be reversed > because the previous bit was erased. > > Of course, decreasing entropy would violate thermodynamics unless it > increased elsewhere. That is why computation requires energy. To be > precise, writing a bit of memory requires kT ln 2 joules where k is > Boltzmann's constant and T is the temperature. > > Quantum computing is time reversible. The energy consumption can be > arbitrarily low, but your algorithm has to be able to run backward. > > In both quantum mechanics and general relativity, the observer plays a > central role. We can be precise by what we mean by an observer. It is > anything with memory. An observation consists of writing into it. It > explains why in physics there are some things we cannot observe. For > example, we cannot observe the wave nature of matter and energy. We > can only observe particles, which give us uncertain information about > the wave. To do otherwise would violate thermodynamics. You cannot > reduce uncertainty (entropy) through observation or learning without > increasing uncertainty (heat) somewhere else. > > -- > -- Matt Mahoney, [email protected] > > > ------------------------------------------- > AGI > Archives: https://www.listbox.com/member/archive/303/=now > RSS Feed: https://www.listbox.com/member/archive/rss/303/24379807-653794b5 > Modify Your Subscription: https://www.listbox.com/member/?&; > Powered by Listbox: http://www.listbox.com ------------------------------------------- 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
