Hi Pete, John Archibald Wheeler has been a hero of mine also. However, I don't think I've read of an account of the implications he draws of the two-slit experiment that has been written so well and so economically. Thank you for a quite brilliant posting.
Keith At 21:44 21/05/02 -0700, you wrote: > >I'm reading behind, as I didn't check in over the (Canadian long) weekend, >but I don't want to miss out on some of the great discussion that >went by... > >On Sat, 18 May 2002, Ed Weick <[EMAIL PROTECTED]> wrote: > >>Arthur, I agree that life is a crap shoot, but I do wonder about its >>context. Is the crap shoot really all there is? Here we are, suspended >>somewhere between the infitnitesimal (strings and substrings?) and the >>infinite (mulitiple universes). Can we really say there is nothing out >>there? When I was stuck in an old folks home in Jamaica a couple of >>years ago, I read Thomas Merton, the late American Trappist. He argued >>that the rational could explain a whole lot, including natural law and >>the crap shoot, but is that all there is? Particle physicists and >>cosmologists have explained much and have given us something to wonder >>about with or with out a prime super intelligent being (God). But then >>how did it all begin (or did it ever?) and how will it all end (or will >>it ever?). In what mystery are we briefly suspended? > >I don't normally bother with "Discover" magazine, as I find it rather >trivially pop (I find Sci. Am. pop these days, but Discover is moreso), >but I had to browse it this weekend, as I saw an article about one >of my favourite thinkers. John Archibald Wheeler is a physicist who >has fascinated me all my life. Wherever the ideas of physics are >being poked and prodded to see what they say about the nature of >our conscious experience, John Wheeler is there. He collaborated with >Hugh Everett in first promulgating the "many worlds" interpretation >of quantum mechanics. He did not create, but was among the first >to play with the "anthropic principle". He is also one of the most >formidable physics minds alive, having co-authored the definitive >text on general relativity, and also what has become the essential >introductory text to special relativity. He is ninety-one years >old this year. So I had to see what he is up to these days. > >In the article, he talks about an idea I've known about for a >few years, but here he gives his personal interpretation of >the implications. The idea is this: the Young's two-slit experiment >is a simple experiment which is usually first introduced to >highschool physics students. It introduces them to the dual >wave/particle nature of light, and gives them a first look at >the counterintuitive nature of quantum mechanics. A single >source of light is used to illuminate a plate with two slits >in it. The light passes through the two slits, and in the >manner of a wave, it interferes with itself to produce light and >dark interference fringes when projected onto a surface. But >if light is also discrete photon particles, it should be possible >to detect the individual photons which make up the interference >pattern, and you can. The mystery is that if you do detect the >particles, and determine which slit they passed through, then >they have to be particles which have passed through one slit, >so they can no longer interfere with themselves, so the interference >pattern disappears. Your act of observation has changed their >character. This has been known since the beginnings of QM in >the twenties. Young's experiment, of course, goes back centuries >before that, and was part of the original evidence for the wave >nature of light. But the new twist is called the delayed-choice >variant on the YTSE. In this experiment, which was first done in >labs with lasers and fast switching optical gates, it was demonstrated >that if you arranged your timing so you knew the photons had already >passed through the slits before you activated your detector to >look for the photons (so that you might catch the photons while >they were self-interfering and still know which way they had gone), >the detector still destroyed the interference pattern. This was >genrally regarded as what was to be expected - you can never >trick QM into revealing its mechanism. However, what Wheeler >observed about this, and discusses the implications of in the >article, is that you can build a YTSE apparatus using a galaxy >3/4 of the age of the universe away, with a pair of gravitationally >lensing galaxies half the age of the universe away as the slits. >Then when you choose whether or not to turn on your detector, >you determine whether the photons in your apparatus passed across >the age and length of the universe as waves billions of light years >wide which self-interfere on your imaging surface, or as particles >which travelled in a tiny thin line straight to your photon detector. > >Your choice today has determined the nature of events across most of >the age and size of the universe. So John Wheeler sits today and >contemplates the nature of consciousness, and its place in the >universe. He says (to paraphrase) "at my age, it's time to concentrate >on just the big questions"... > > -Pete Vincent __________________________________________________________ “Writers used to write because they had something to say; now they write in order to discover if they have something to say.” John D. Barrow _________________________________________________ Keith Hudson, Bath, England; e-mail: [EMAIL PROTECTED] _________________________________________________
