Time can move both forwards and backwards at the quantum scale

Some quantum systems may have two arrows of time, one running forwards as usual and another moving backwards. This means that, at some extremely small scales, time may have the option of moving in both directions – a stunning feature that may have been overlooked across much of physics.

If you consider the most basic equations of quantum physics – those that deal with single particles – there is no reason why time should always run forwards. This means fundamental…