Expert: James Gort - 9/13/2007

Question
Hello again professor Gort.
I gave it a bit more thought to the imaginary universe which you so elegantly explained to me, when you answered my last question:
“How would a photon behave in a universe where all dimensions are collapsing at the speed of light?” And in an attempt to model light waves in the same, it seems to me that such universe would naturally set the interactions of the elementary forces particles as a function of their masses (give or take a couple of Higgs fields) if a few simple rules were followed, but since my fascination is with photons only, and not other elementary force carrying particles (most definitely not the graviton), I wondered if you think it is possible to model the behavior of light waves by following two simple rules (some one may feel compelled to count them as three, I see two):
A photon in free space is always repulsed by the nearest photon to its effective field distance
A photon in free space will always collide with the nearest body (considering that all dimensions are collapsing extremely fast, there is just no other place to go) resulting in absorption.
Obviously from the first two rules one may deduct that no two photons may be absorbed at the same place and time, if two photons were forced into the same localized area of a body, one would be absorbed and the other would be deflected or both would be deflected (no need in violating the first rule), indeed it would look like a very fast game of Ping-Pong.
I thank you kindly for considering this unlikely proposition.


Answer
Hi Luis,

I think the rules also need to account for photon emission.  For instance, in thermodynamic equilibrium, every absorbed photon must be balanced by an emitted photon.  So if the second rule is always true, the absorbed photon will be re-emitted and then immediately absorbed (since the nearest body just emitted it), etc.  The end result is that there are more absorptions than emissions (at least the first absorbed photon), violating thermodynamic equilibrium. So I think you need a third rule about emissions (which is not in conflict with the second rule).

I don't have a problem with the first rule, except you might think about the mechanism of the repulsion.  Quantum electrodynamics (QED) says there's no "action at a distance", but all forces are the result of exchanges of particles.  The photon-photon repulsion must therefore be the result of the interaction with some (new?) particles, or else some other mechanism is involved.  Your theory should try and address that.

If you haven't already done so, I'd urge you to read "QED" by Richard Feynman.  It's basically the story of photon-photon and photon-electron interaction (for which he won a Nobel Prize).  That doesn't mean his theory is correct, but you might get some ideas and build your own theory from it.  What QED does, however, is predict (very accurately) the outcome of experiments.  And that's the basis to test any theory.  An "explanation" by itself is not of much value if it can't predict experiments.  So your theory should try and do that.

That's one of the problems with "string theory".  It may be mathematically elegant, but so far, it hasn't predicted anything.  So as a theory, it's pretty useless.  If you have some additional time, also get "The Trouble with Physics" and "Not Even Wrong", both of which point out what a theory should be, and the problem with string theory.

Keep having those ideas, and I'll try and help if I can.  But also read those books to get a better understanding of things than I can give in a few paragraphs.

Cheers,

Prof. James Gort