I am working on some very smart things to say here. Really. Meanwhile, there's 
My 11 month old daughter loves electric lights. If you visit my home, you may often find me standing near the switch and flicking it on and off while the daughter watches and squeals in delight. Today morning we were playing our switching game and I explained to her with much drama how photons are expelled from the atoms in the filament, how they travel down to her eyes, how the arrow of time and principle of least action guides the photons and the whole world, etc. She, of course, giggled watching my mouth make all the funny sounds.
When my hand reached her eyes, I gave a tickle, then traced the photons back to the light and explained to her that Time was now running backwards. The vase she broke was going to be alright, the milk she threw up will be going back in, photons were getting back into the filament.. Wait a minute. That is not how nature works. Or maybe, it does work that way? Perhaps, Time can run any way it well pleases - forwards, backwards, sideways.. I say this because at the atomic level, at the level where the atom ejects or absorbs a photon, there is no way to discern the arrow of time. All interactions are symmetric with respect to time (in other words, energy is conserved). If I had not traced my hand from the filament to my daughter's eyes and thereby had not irreversibly altered her perception of the world, there would be no arrow of time to speak of. Or atleast that's what I think. What is this arrow of time? Does it exist? Does it have a preferred direction?
There's more to this than I originally thought. Nevertheless, it is always startling to find such beguiling things lurking right under the thin surface we call 'mundane reality'.
Comments
For my son's third grade science project he wanted to explain why he thought there was no present, that time was always moving and when you think of the present it is already in the past. Deep thoughts for someone so young...your daughter will surely have many deep thoughts as well!!
Posted by: Doubting Foo | November 17, 2008 8:41 AM
You didn't notice her perplexed expression at birth, when she first saw an astoundingly ordered world, light bulbs and all? After that, anyone would believe that a trend toward disorder is inevitable.
Posted by: Mark Dow | November 17, 2008 12:15 PM
Robert Oppenheimer once said that children playing in the street could teach him a lot of new physics because they had faculties of questioning that he lost years ago. Bring it on, children!
Posted by: Ashutosh | November 17, 2008 3:09 PM