Quantum trick sees light move forwards and back in time simultaneously

Placing a particle of light in a superposition so that it is travelling both forwards and backwards in time could prove useful for quantum computation

By Alex Wilkins

A quantum experiment that sees a particle of light travel both forwards and backwards in time, at the same time, is yet another example of the weirdness of the quantum realm. Although this experiment, which has been demonstrated by two research groups, has no immediate practical use, it could eventually have implications for quantum computers or even help develop a theory of quantum gravity.

Unlike our one-way sense of time, the laws of quantum physics are indifferent to the way things …