Hi Chuck and DT: I really enjoy your comments except for one thing: I wish you could also make them on my blog. It would add a great deal of interest and possibly stimulate others to comment. Nobody needs to use a real name, if that's worrisome. Thanks, Joe --- On Fri, 3/27/09, daniel turner <outwest112@yahoo.com> wrote: From: daniel turner <outwest112@yahoo.com> Subject: Re: [Utah-astronomy] Musing about light To: "Utah Astronomy" <utah-astronomy@mailman.xmission.com> Date: Friday, March 27, 2009, 6:11 PM The nature of light is where we first ran into the strange world of quantum mechanics.  The best way I've found to understand it is to consider emission and adsorption to be the realm of particles and everywhere in between light acts like waves.  Einstein and Plank first demonstrated photons and their properties a century ago, yet all of optics has to do with the wave nature of light.  I had a college physics course where we passed a laser through a pair of slits and noted the interference effects of light.  Covering up one of the slits and the interference disappeared.  Back to two slits, we cranked the light intensity down until the energy was so low that only one photon a time was in the space between the source and the screen.  Then we carefully measured the flux at the target and by moving the detector around we could see that the interference pattern was still there.  Each individual photon actually went through both slits and interfered with itself.  Modern interference studies are done with light from two widely spaced telescopes that is combined into an interference pattern.  Each photon recorded has passed through both Keck I and Keck II at the same time. DT       _______________________________________________ Utah-Astronomy mailing list Utah-Astronomy@mailman.xmission.com http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy Visit the Photo Gallery: http://www.slas.us/gallery2/main.php Visit the Wiki: http://www.utahastronomy.com