If two people look at a city from different hills, their maps don't match. One sees the tower to the left of the river, the other sees it to the right. But both know: it's the same city. That's roughly how our Universe works in this new approach to quantum gravity.
The authors suggest distinguishing between two "flavors" of spacetime. The first is common to all, like the real city down in the valley. The second is unique to each observer, like a hand-drawn sketch. This personal sketch isn't made of smooth lines but of discrete points-events linked by causality (what comes before, what comes after). The paper's main conclusion: when these two descriptions interact, the relativity of location emerges — an effect where two observers can disagree about where exactly something happened. And no exotic geometry is needed for this.
This view flips the usual picture. Previously, it was thought that the relativity of location requires complex geometry in momentum space. Here, everything is built around spacetime itself, with momenta playing a secondary role. It's as if we finally realized that it's not the hill that distorts the map, but that the map itself must be flexible. Practically, this means the new approach can be applied to cosmology on any background, not just in special cases. Causality, what happened before and what after, remains clear even in such flexible models.
as written by the authors arXiv:2604.17272
In this paper we introduce a new general framework for the study of phenomenological quantum gravity theories (PQG). The key idea is the introduction of two different types of spacetime, an observer-independent spacetime (modeled by a smooth orientable manifold) and an observer-dependent one (which has an inherently discrete causal set structure). The interaction between the two allows us to prove the main result of the paper: relative locality can be obtained in general PQG models, regardless of momentum-space curvature. {We also discuss the treatment of spacetime symmetries in our model, and introduce a direct link between spacetime symmetries and relative locality effects.} Our construction is presented in a coordinate-independent way and is based on fibre bundles where spacetime, rather than momentum-space, is the base manifold. This makes causality manifest even in general models with relative locality. Furthermore, it allows for the application of this formalism to cosmology on general backgrounds, something which is not clearly possible in the canonical approach to relative locality, where momentum-space serves as the base manifold.
If spacetime were truly discrete at the microscopic level, then on the scale of a grain of sand there would be more "points-events" than there are grains of sand on all the beaches on Earth.
In Isaac Asimov's novel "The End of Eternity," observers from different eras literally see different realities, and must coordinate them to avoid destroying history.