memes

It's the smallest length that our current understanding of the universe will allow. Any distance smaller is immeasurable to us. To measure small things you need to be able to hit them with a photon and get a signal back; and the smaller you want to measure the higher energy that photon has to be. The planck length is the distance where the photon you are using to measure has so much energy comparable to the size that the energy density instantly creates a black hole, that swallows whatever you are trying to observe. Thus it is impossible for us to measure smaller than that distance. Things might absolutely exist at scales smaller than that, but the universe seems to lock them away from us.