There has recently been media coverage of our group’s research result, “Multipartite quantum states over time from two fundamental assumptions.” But as often happens, in translating a research result into a popular, easy-to-digest article, a lot of exaggeration and misunderstanding can creep in. in short: No, we did not unify quantum mechanics and relativity. (I don’t know relativity very well.) Still, we believe we resolved a subtle issue within quantum theory—and we think the real fun of scientific research comes from exactly that kind of subtlety.

Contrary to the heavily simplified coverage, this work is not a direct study of “combining quantum mechanics and relativity.” Rather, it is a theory about unifying, within quantum theory itself, two mathematical languages that had been used differently for time and for space. Why do researchers want such a unification? It comes from the observation that quantum theory is a generalization of classical probability theory. In classical probability, whether two random events are separated in space or separated in time, their correlations can be described in a single unified language: a probability distribution. In standard quantum theory, however, spatial correlations and temporal correlations have been expressed in completely different languages. Whether this mismatch is fundamental, or merely an accidental byproduct of how quantum theory historically developed, has been a long-standing question. Recently, an approach called the “quantum state over time” has been developed to unify these two types of quantum correlations. Our present work concerns a unique extension of the formalism for describing quantum states over time: it takes what had been limited to two time points and extends it uniquely to multiple time points. We do think this kind of result could eventually give ideas to researchers studying things like quantum gravity. (For an example of quantum states over time being used for temporal quantum entanglement, see: link.) But after all, this is a quantum information theory paper.