0
$\begingroup$

I have done a bit of searching for an answer to this question, but I am an amateur and suspect I lack the proper "language" to describe what I'm actually looking for, so a pointer in the right direction would be much appreciated!

Let's presume that spacetime is in fact quantized (how or why we don't care), and we have a field overlayed on top of it. We emit a particle and take a measurement, and determine its precise location. Due to the quantized nature of spacetime by our assumption, we would expect that the measured position would occur only at the lattice points of spacetime itself. This seems to imply (in my mind) that a theory of quantum gravity would necessitate that the probably density of the wavefunction itself would have to be discrete as there would be forbidden values for location.

So my questions are, first, does that even make sense/matter? Is there some underlying property of a field that would allow it to take on a continuous probability distribution even if spacetime is quantized? And second, if one would expect that the probability density function would be discrete, has anyone attempted to start out with that presumption and work backwards toward a theory of quantum gravity?

$\endgroup$
1
  • $\begingroup$ I won't venture an answer, but I think your question basically makes sense. People have indeed written papers exploring this idea: here is an older one that suggests that it might make sense to think of Hilbert space (which is the space of outcomes of a quantum measurement) as discrete: sciencedirect.com/science/article/pii/S0370269305013286#! . And here is another more recent result which suggests that the opposite is true; a quantum theory must have a continuous state space: nature.com/articles/ncomms2821. $\endgroup$ – Rococo Dec 8 '20 at 3:27
1
$\begingroup$

Among other problems, a “spacetime lattice” would violate Lorentz symmetry: different observers would disagree about the distances between the lattice points, and any “natural” value would define a preferred reference frame, in opposition to the postulates of special relativity. Violations of Lorentz symmetry would have other consequences, for which there is no experimental evidence (despite searches).

Historical note: the discovery that spin is quantized was described at the time as a discovery that space is quantized, since an angular momentum vector can point in some directions but not in others.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.