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Physics

Cause and effect may not actually be muddled in the quantum realm

The direction of cause and effect was brought into question for quantum objects more than a decade ago, but new calculations may offer a way to restore it

By Karmela Padavic-Callaghan

13 September 2024

Can effect come before cause in the quantum realm? Maybe not

Vink 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…

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