A relativistic fluid consists of actual discrete particles, although the quantities you can calculate will be be continuous approximations (very accurate ones). So, basically it is possible to make something discrete, with some associated length scale, but which looks the &#x27;same&#x27; for all observers.<p>Even I am not entirely sure how to imagine such an object though, Lorentz boosts are difficult to wrap your head around.<p>By the way, I just realised it&#x27;s a bit unclear what &#x27;freezing it in place&#x27; means. Basically I meant that you just fix all trajectories of all particles, since there are no interactions you&#x27;ll basically end up with some random straight lines. The distribution of these lines (i.e. their direction &#x2F; position) will be the same for all observers.