On 7/16/07, <b class="gmail_sendername">Eliezer S. Yudkowsky</b> <<a href="mailto:firstname.lastname@example.org">email@example.com</a>> wrote:<div><span class="gmail_quote"></span><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
On the one hand, I know the theory (timeless physics) lacks definitive<br>experimental proof, as yet.<br><br>On the other hand, an irrevocable ratchet has ticked forward in my<br>brain; I am no longer capable of conceiving what a "timeful" universe
<br>would be like.<br><br>It is not so much that Barbour convinced me of his viewpoint but that<br>he rendered me incapable of seeing the universe in any other way.</blockquote><div><br>I'm getting the same puzzled expression here that I did reading Barbour. This doesn't strike me as a matter of physics.
<br><br>Definition: Time is a dimension in which there is continuity, so that slice t+1 can be derived from slice t .<br><br>When we look at a universe (which can be our own, or a subset or variant thereof) with, say, two spatial dimensions, we must represent these by mapping them onto features of our own universe. Typically, to exploit special purpose hardware, we map them onto two of our own spatial dimensions. (The process becomes notoriously more difficult as the count climbs past three.)
<br><br>With a time dimension of the universe being studied, we have two major options: A) map it onto our own time dimension, or B) onto one of our spatial dimensions. Each is convenient for different purposes.<br><br>Examples of A: speech, song, movies, animation of all kinds, imperative programming, wind tunnels, most types of simulation.
<br><br>Examples of B: writing of all kinds, sheet music, calendars, timelines (the literal ones you sometimes see in history books, horizontal line with significant dates marked to scale), comic strips, certain types of functional and logic programming, light cone diagrams, 1D cellular automata simulations of the type that lay out the successive states vertically down the screen.
<br><br>It seems self-evident to me that irrespective of the detailed laws of physics, there is no basis for claiming A or B is more true than the other, and all Barbour is doing is "discovering" B, writing an admittedly very evocative description of it, and then for some strange reason claiming A isn't true.
<br><br> With various caveats regarding things like probability and approximation, I'm not a mathematician.<br></div></div>