<i>So supposing you simply freeze a relativistic fluid in place you&#x27;ll get an amorphous solid with a characteristic length scale and characteristic time scale. Which are both Lorentz invariant.</i><p>Doesn&#x27;t that work because the fluid has no particles in that description, because it is a continuous and smooth average about some ignored micro structure? It seems to me like you would easily loose that nice description if you replaced, for example, the smooth scalar mass density with a collection of discrete particles scattered throughout space. And that seems to be what you really want if you want to quantize space, discrete things, not smooth functions. But you seem to know physics way better than I, so I am probably missing the point, have some serious misunderstanding or something like that.