Science Fact of the Day August 25, 2009
Posted by spatialrift47 in SFoTD.trackback
Electric charge comes in discrete units, i.e. it is quantized. Quantum mechanics predicts that the reason for this is the existence of single magnetic charges called monopoles (as opposed to all observed magnetic fields which are dipoles). None have yet been found. It is possible that a single magnetic monopole in the entire Universe would be sufficient to quantize all electric charge.
Yeah, can you explain the whole quantization-by-monopole thing in a simple way, or is it non-reducible? Every time I try to go through the original thing by Dirac, I black out and wake up five hours later with daisies stuck between my toes.
Yeah, Dirac’s paper doesn’t really explain the quantization. The gist of the argument is: Suppose magnetic monopoles exist. Then both magnetic and electric charges would have to be quantized to ensure that angular momentum is quantized.
A longer version: Suppose I have a Universe with electric and magnetic charges. I don’t know whether or not they are quantized. So I put all the electric charge, total Qe, in a stationary ball next to a stationary ball of all the magnetic charge, total Qm. I then compute the angular momentum stored in the field, and I find that it is proportional to Qe*Qm. Quantum mechanics tells me the angular momentum must be quantized, therefore both Qe and Qm are quantized. We know that discrete electric charges exist, thus the only remaining condition is the existence of at least one discrete magnetic charge.