Huw Price, head of the Centre for Time at the University of Sydney, thinks Maccone is simply trading one mystery for another.

"The proposal to explain the thermodynamic arrow in terms of the [quantum] effects of observers has an obvious flaw," he says. "It doesn't explain why all observers have the same orientation in time ... Why don't some observers remember what we call the future, and accumulate information towards what we call the past?"

A standard way of explaining why observers like us remember the past is by appealing to thermodynamics – the fact that entropy is increasing. This explanation is unavailable to Maccone since his theory takes that thermodynamic fact to depend on the existence of observers. Such an explanation, for Maccone, would thus be circular.

If Price is right, then Maccone has explained one temporal asymmetry at the expense of creating another that is equally hard to explain.

What's more, Price thinks that Maccone has made a hidden asymmetrical assumption. He argues that the quantum correlations Maccone relies on must be assumed to happen only in one temporal direction and not the other. "But that's just assuming the conclusion he wants to derive."