Re: Move versus assign
Dear David, Please explain the claim : "We observe that our universe uses a reversible computation". I do not see how this follows from the observation that, on every observable scale, there is a non-invertible (thermodynamic) arrow of time. I do not see how this is possible if your claim holds. We can add to this the strong evidence that our universe is open and very close to being "flat". Kindest regards, Stephen - Original Message - From: David Barrett-Lennard To: [EMAIL PROTECTED] Sent: Sunday, November 23, 2003 9:14 PM Subject: Move versus assign We observe that our universe uses a reversible computation, yet our brains only appear to use irreversible computation. It seems important to ask why. Is it possible for SASs to live in a universe that is directly associated with an irreversible computation? If so then why are we special? Computer science seems to be centered around the concept of assignment. For example, computer memory undergoes state changes in the form of assignments to memory locations. A Turing machine uses assignment operations each time a 1 or 0 is written on the tape. Assignment involves lost information because it simply overwrites the previous value with a new value. It is fundamentally irreversible. I have been wondering whether we can get a better understanding of reversible computation by distinguishing between movement of information and assignment of information. The analogy of the Turing machine would be that we need to cut up the tape with scissors we are only allowed to move bits of tape around, rather than reassign values on the tape. This leads quickly to the view of particles that move around, rather than the idea of a particle that is stored in space (= memory) that moves as the result of assignments to space. So rather than think of a small piece of space having an attribute of what particle is in it, we should think of a particle as having an attribute of where it is in space. The latter view makes space seem rather incidental rather than thinking of particles as being embedded in space. I wonder to what extent physicists distinguish between these two views. I guess the distinction evaporates in string theory, where there is nothing but (higher dimensional) space-time. There is nothing to assign to because the information is present in the topology of space itself. Movement of information is more like a ripple on a pond. The Turing machine seems to lack a direct relevance to our universe. However, cant a Turing machine emulate a reversible computation? - David
Re: Move versus assign
On the quantum scale, the dynamics are reversible, to a very high level of accuracy. Irreversibility appears at macroscopic scales. In answer to the original question, I would conjecture that an evolutionary process is the only process capable of generating complexity. Since we need a certain amount of complexity to be conscious, it follows that the simplest universes are ensembles of possibilities, on which anthropic selection acts to generate the needed complexity. Ensemble universes can only evolve by reversible processes - otherwise possibilities are irretrievably lost over time. On Sun, Nov 23, 2003 at 10:55:10PM -0500, Stephen Paul King wrote: Dear David, Please explain the claim : We observe that our universe uses a reversible computation. I do not see how this follows from the observation that, on every observable scale, there is a non-invertible (thermodynamic) arrow of time. I do not see how this is possible if your claim holds. We can add to this the strong evidence that our universe is open and very close to being flat. Kindest regards, Stephen - Original Message - From: David Barrett-Lennard To: [EMAIL PROTECTED] Sent: Sunday, November 23, 2003 9:14 PM Subject: Move versus assign We observe that our universe uses a reversible computation, yet our brains only appear to use irreversible computation. It seems important to ask why. Is it possible for SAS's to live in a universe that is directly associated with an irreversible computation? If so then why are we special? Computer science seems to be centered around the concept of assignment. For example, computer memory undergoes state changes in the form of assignments to memory locations. A Turing machine uses assignment operations each time a 1 or 0 is written on the tape. Assignment involves lost information because it simply overwrites the previous value with a new value. It is fundamentally irreversible. I have been wondering whether we can get a better understanding of reversible computation by distinguishing between movement of information and assignment of information. The analogy of the Turing machine would be that we need to cut up the tape with scissors - we are only allowed to move bits of tape around, rather than reassign values on the tape. This leads quickly to the view of particles that move around, rather than the idea of a particle that is stored in space (= memory) that moves as the result of assignments to space. So rather than think of a small piece of space having an attribute of what particle is in it, we should think of a particle as having an attribute of where it is in space. The latter view makes space seem rather incidental - rather than thinking of particles as being embedded in space. I wonder to what extent physicists distinguish between these two views. I guess the distinction evaporates in string theory, where there is nothing but (higher dimensional) space-time. There is nothing to assign to because the information is present in the topology of space itself. Movement of information is more like a ripple on a pond. The Turing machine seems to lack a direct relevance to our universe. However, can't a Turing machine emulate a reversible computation? - David -- A/Prof Russell Standish Director High Performance Computing Support Unit, Phone 9385 6967, 8308 3119 (mobile) UNSW SYDNEY 2052 Fax 9385 6965, 0425 253119 () Australia[EMAIL PROTECTED] Room 2075, Red Centrehttp://parallel.hpc.unsw.edu.au/rks International prefix +612, Interstate prefix 02 pgp0.pgp Description: PGP signature
RE: Move versus assign
Russell said... In answer to the original question, I would conjecture that an evolutionary process is the only process capable of generating complexity. Since we need a certain amount of complexity to be conscious, it follows that the simplest universes are ensembles of possibilities, on which anthropic selection acts to generate the needed complexity. Ensemble universes can only evolve by reversible processes - otherwise possibilities are irretrievably lost over time. Do you think in terms of an ensemble of Turing machines, of which only a few emulate reversible processes? So do we have an irreversible computation on a Turing machine emulating a reversible computation for the universe emulating a brain doing an irreversible computation? - David
RE: Move versus assign
Hi Stephen, The thermodynamic arrow of time only seems to be related to the boundary conditions of the universe, rather than those laws of physics which we regard as independent from the boundary conditions. The success of being able to divide and conquer physics into bc laws / non bc laws is interesting and remarkable. - David -Original Message- From: Stephen Paul King [mailto:[EMAIL PROTECTED] Sent: Monday, 24 November 2003 11:55 AM To: [EMAIL PROTECTED] Subject: Re: Move versus assign Dear David, Please explain the claim : We observe that our universe uses a reversible computation. I do not see how this follows from the observation that, on every observable scale, there is a non-invertible (thermodynamic) arrow of time. I do not see how this is possible if your claim holds. We can add to this the strong evidence that our universe is open and very close to being flat. Kindest regards, Stephen - Original Message - From: David Barrett-Lennard To: [EMAIL PROTECTED] Sent: Sunday, November 23, 2003 9:14 PM Subject: Move versus assign We observe that our universe uses a reversible computation, yet our brains only appear to use irreversible computation. It seems important to ask why. Is it possible for SASs to live in a universe that is directly associated with an irreversible computation? If so then why are we special? Computer science seems to be centered around the concept of assignment. For example, computer memory undergoes state changes in the form of assignments to memory locations. A Turing machine uses assignment operations each time a 1 or 0 is written on the tape. Assignment involves lost information because it simply overwrites the previous value with a new value. It is fundamentally irreversible. I have been wondering whether we can get a better understanding of reversible computation by distinguishing between movement of information and assignment of information. The analogy of the Turing machine would be that we need to cut up the tape with scissors we are only allowed to move bits of tape around, rather than reassign values on the tape. This leads quickly to the view of particles that move around, rather than the idea of a particle that is stored in space (= memory) that moves as the result of assignments to space. So rather than think of a small piece of space having an attribute of what particle is in it, we should think of a particle as having an attribute of where it is in space. The latter view makes space seem rather incidental rather than thinking of particles as being embedded in space. I wonder to what extent physicists distinguish between these two views. I guess the distinction evaporates in string theory, where there is nothing but (higher dimensional) space-time. There is nothing to assign to because the information is present in the topology of space itself. Movement of information is more like a ripple on a pond. The Turing machine seems to lack a direct relevance to our universe. However, cant a Turing machine emulate a reversible computation? - David
Re: Move versus assign
No - I think in terms of ensembles of descriptions. Some of those descriptions describe observers observing the descriptions. It then becomes natural to ask what sort of description an observer might see, given the description must describe the observer. Turing machines don't have much to do with it, except that the observers may or may not be Turing emulable. It doesn't actually make much difference either way. Cheers On Mon, Nov 24, 2003 at 12:49:43PM +0800, David Barrett-Lennard wrote: Russell said... In answer to the original question, I would conjecture that an evolutionary process is the only process capable of generating complexity. Since we need a certain amount of complexity to be conscious, it follows that the simplest universes are ensembles of possibilities, on which anthropic selection acts to generate the needed complexity. Ensemble universes can only evolve by reversible processes - otherwise possibilities are irretrievably lost over time. Do you think in terms of an ensemble of Turing machines, of which only a few emulate reversible processes? So do we have an irreversible computation on a Turing machine emulating a reversible computation for the universe emulating a brain doing an irreversible computation? - David -- A/Prof Russell Standish Director High Performance Computing Support Unit, Phone 9385 6967, 8308 3119 (mobile) UNSW SYDNEY 2052 Fax 9385 6965, 0425 253119 () Australia[EMAIL PROTECTED] Room 2075, Red Centrehttp://parallel.hpc.unsw.edu.au/rks International prefix +612, Interstate prefix 02 pgp0.pgp Description: PGP signature
