Quantum sock theory
is the current best quantum mechanical explanation of how odd socks appear. PJM almost hit the nail on the head. In fact*, there is an interdimensional wormhole portal at the back of every washing machine, through which single socks can tunnel. Due to the Pauli exclusion principle, a pair of socks may not coexist in the same quantum state, therefore only one sock of a pair can get through the tunnel at a time. Meanwhile, an equivalent, but different sock is making a random journey from another washing machine.

When you open the machine, the wormhole closes, and you are left with odd socks. Not only does this explain why some of your own socks go missing, but also why you always seem to end up with some you don't recognise.

Also, because the wormhole is part of the time-space continuum, you could possibly end up with an odd sock which you have yet to own.

_{*May not actually be fact}
( K2k6 has a proper job these days, Wed 23 Jul 2008, 13:28, Reply)