Light Sabers

Enemies dueling with light sabers have graced the silver screen for several decades now. Isn’t this type of weapon the most ridiculous thing you’ve ever seen?

Answer

Yes, the light sabers would pass through one another as if nothing were there! The photons of the light are bosons, which do not repel each other. The clashing of the light sabers is pure artifact and far beyond artistic license. It’s an outright lie to the public!

There are two general categories of particles in the universe: fermions and bosons. Two identical fermions (e.g., think electrons, or any other fundamental spin 1/2 particle) cannot exist in the same quantum state defined by its 4-momentum and spin. The existence of all matter, including us humans, critically depends on the inability of two identical fermions to get together in the same state, so matter occupies a volume. That is, objects can be bigger than a point!

In the case of bosons, one can not only put as many identical bosons (think photons or any integer spin fundamental particles) into the same quantum state, they also prefer to be in one, with the probability to do so enhanced by the number N of bosons already in the state. There is no repulsion experienced. So two light sabers intersecting at an angle would pass right through one another with no change in either. If the light beams were powerful enough, though, they could cut material objects made out of fermions that is, the ordinary stuff all around us whenever this material stuff intercepts the beams because sufficient energy could be absorbed to change the physical state of the material and result in vaporization.