I'm no physicist, but the layman explanation I've heard is that the concepts of Planck length and Planck time do not imply that spacetime is discretized into li

I'm no physicist, but the layman explanation I've heard is that the concepts of Planck length and Planck time do not imply that spacetime is discretized into little "voxels"; instead these quantities are just limits on the uncertainty of any possible measurement. As I understand it there are two contributing facts: a) the Heisenberg uncertainty principle states that there's a tradeoff between certainty in position vs momentum, so if you're more certain in a particle's position you're less certain of its momentum. (For photons, momentum is proportional to frequency, i.e. wavelength, and frequency is proportional to energy.) b) By mass-energy equivalence, anything with energy has mass, therefore higher frequency photons are more "massive". A single photon of sufficiently high frequency would form a black hole. Putting those two together, to measure a distances accurately, you need higher and higher frequency photons with shorter and shorter wavelengths. For example, radar creates blurry images at ~5cm wavelengths, while ordinary photographs can be razor sharp at ~500nm. The Planck length is just the wavelength at which the photon would have so much energy that it would collapse into a black hole and break our current mathematical models. That's why it's nonsensical--with current models--to talk about lengths smaller than a Planck length, but it doesn't mean that space itself is quantized. Similar argument for time. (Also, the same logic applies to other particles like electrons, protons, and even up to macroscopic items like baseballs; everything has a wavelength...)