But you seem to be claiming that spacetime is unlikely to be quantized because the Planck length or Planck time, i.e. the quanta of length in spacetime, would b

But you seem to be claiming that spacetime is unlikely to be quantized because the Planck length or Planck time, i.e. the quanta of length in spacetime, would be contracted in different reference frames. Therefore Planck units of length/time wouldn't be frame invariant - they'd depend upon your inertial reference frame. So claiming Planck units are frame independent violates the idea that spacetime can't be quantized (at least for the reason you stated), since the quanta would experience relativistic contraction and dilation. The explanation seems to go against your original comment. Edit: I may have given the wrong impression - when I said "Planck units" I meant quanta of space, time, area, etc. Not "natural units" where all relevant physical constants are taken to equal one. It appears the term "Planck units" refers to one of multiple sets of natural units, of which I was not aware: https://en.wikipedia.org/wiki/Natural_units#Planck_units https://en.wikipedia.org/wiki/Natural_units#Planck_units