Can effect come before cause in the quantum realm? Maybe notVink Fan/Shutterstock
First comes cause, then comes effect – or does it? This order of events has previously been upended in the quantum realm, with the possibility of both A-causes-B and B-causes-A happening simultaneously. But a new mathematical analysis suggests this quantum quirk may be hemmed in by the very structure of space-time.

For more than a decade, physicists have been grappling with the idea of indefinite causal order –instances where it is impossible to tell whether cause came…