The results were 18 standard deviations from what you would expect based on Bell’s theorem, a strong indication that superposition of temporal order is a fundamental property of quantum mechanics.
But the practice remains where the mess was a few decades ago: there are many gaps. For example, many photons are lost during the experiment (about 1 percent of those sent there come out the other side to be measured). It remains technically possible that the losses were dominated by a subset of photons that would recover correlations consistent with latent variables.
The team also did not separate the apparatus far enough to rule out sub-light speed effects, and there are several potential quirks inherent in uncertain causality experiments. But the work points the way to experiments that could close those gaps, and we already have a history of slamming the door on them.
Normally, the only thing we get when we cover something weird like this is the ability to understand how weird our world really is compared to our expectations. But this is one of those cases where understanding physics has many practical applications.
“(The device used in this work) may also be interesting for applications, as it has been shown to outperform causally ordered processes in various tasks such as channel discrimination, promise problems, communication complexity, noise reduction, various thermodynamic applications, quantum metrology, quantum switch distribution, entanglement generation, and distillation.” Authors write.
In other words, being confused about time can actually be beneficial.
* If I hadn’t seen it, I wouldn’t even know that this work was done great summary of it at the American Physical Society news site.
PRX Quantum2026. DOI: 10.1103/5t2y-ddmt (About DOIs).
