We’re all too familiar with the inexorable march of time, but why exactly it flows in one direction remains a mystery of physics. A few years ago Australian physicist Joan Vaccaro proposed a new quantum theory of time, and now a team is planning to test the hypothesis by searching for time dilation in a nuclear reactor.

The “arrow of time” points from the past towards the future, but physics has a hard time explaining why it favors one direction over the other. The most widely accepted explanation for this asymmetry is covered by the second law of thermodynamics, which states that time tends to flow in the direction of increased entropy, which is essentially the measure of disorder in a system.

But according to Vaccaro’s quantum theory of time, entropy is more of a symptom of the flow of time, rather than the root cause. She uses the analogy of a tree blowing in the wind – while the leaves (entropy) may appear to be shaking the tree, they aren’t responsible for the motion themselves, but are the result of another force (wind). In this new theory, the "wind" is created by time reversal symmetry violations (T violations).

Vaccaro points out that physics regards space and time as being interconnected, as spacetime. But nature seems to treat the two differently. From experience we know, for instance, that objects are localized in space – a particular book or tree or person can only be found in one specific spot. Yet that’s not the case for time – that same book or tree or person can be found in a range of times. Because spacetime is one thing, theoretically objects localized in space should be localized in time as well, popping in and out of existence.

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