We all know that time only ever moves forward in our world - no matter how many times we've wanted it to, that glass of spilt milk never un-spills itself, and we're definitely not getting any younger. There are a lot of hypotheses for why this is the case, but it's long been assumed that this one-way direction of time is a fundamental part of nature.

But new research by Joan Vaccaro from Griffith University in Australia suggests that this might not actually be the case, and there might be something deeper causing time to push forward. In fact, there might actually be a subtle difference between the two arrows of time - forwards and backwards - that's constantly driving us to the future and not the past.

Let's step back for a second, because this is some pretty mind-bending physics. The time conundrum stems from the fact that, while time only moves forward on the IRL scale, when you look at individual atoms and molecules, it doesn't much matter to them whether time is moving forwards or backwards - they seem to behave the same way regardless of the direction time's arrow is pointing.

That's not the case with space - you can't just move things around in space and expect them to be unchanged - so scientists have long assumed that there's some fundamental reason for why the Universe continues to unfold in a forwards direction in time, but not in space. This is known as the 'asymmetry' between time and space. 

The best example of this asymmetry is the fact that the equations of motion and conservation laws operate differently over time and space.

"In the connection between time and space, space is easier to understand because it's simply there. But time is forever forcing us towards the future," said Vaccaro. 

Her new proposal suggests that the two directions of time - forwards and backwards - might not actually be identical after all. 

"Experiments on subatomic particles over the past 50 years ago show that nature doesn't treat both directions of time equally," said Vaccaro. "In particular, subatomic particles called K and B mesons behave slightly differently depending on the direction of time." 

K and B mesons are super tiny subatomic particles, which means they're not easy to study without the help of some pretty sophisticated equipment. But the evidence that they behave differently depending on which way the arrow of time is facing suggests that it could be this difference, rather than some elemental part of nature, that's determining which way we move through time.

"While we are indeed moving forward in time, there is also always some movement backwards, a kind of jiggling effect, and it is this movement I want to measure using these K and B mesons," explained Vaccaro.

To investigate, she reworked the equations of quantum mechanics, assuming that time wasn't identical in both directions, and the results showed that these calculations could accurately describe our Universe.

"When this subtle behaviour is included in a model of the Universe, what we see is the Universe changing from being fixed at one moment in time to continuously evolving," said Vaccaro"In other words, the subtle behaviour appears to be responsible for making the Universe move forwards in time."

If confirmed, this would mean that we'd have to seriously rethink our understanding of the evolution of time, and the equations that it influences. But it could also lead to new insights into some of the stranger aspects of time.

"Understanding how time evolution comes about in this way opens up a whole new view on the fundamental nature of time itself," Vaccaro explained. "It may even help us to better understand bizarre ideas such as travelling back in time."

Vaccaro's calculations have been published in the journal Proceedings of the Royal Society A: Mathematical, Physical and Engineering Science.