Does the past influence the future, or is it the other way around?
Time runs forward, right? Seems so obvious when we can remember the past but not the future, but is it necessarily the case?
Theoretical physicists have been developing a new theory that demonstrates an exact link between asymmetry, and our perception of time's direction - something Stephen Hawking dubbed "the psychological arrow of time". In a nutshell, this theory claims physical laws will remain the same if we run time backwards.
"Quantum theory has been formulated based on asymmetric concepts that reflect the fact that we can know the past and are interested in predicting the future. But the concept of probability is independent of time," said Ognyan Oreshkov of the Université libre de Bruxelles, Belgium.
Standard quantum theory (as well as classical physics and the odd philosopher) says that present choices can only influence the future and not the past, a principle called ‘causality’. However, the new theory being proposed treats both causality and the psychological arrow of time as mere constraints on the information available at different times. It suggests we should adopt measurements that not only depend on the past, but also on variables in the future too.
It is conceivable, for instance, that in some parts of the universe causality might be violated. If this principle were applied on a large scale this could mean some very weird ideas: for an example, your making tea in the present could be influenced by the event of your mug smashing in the future. Douglas Adams would be proud.
A mind-boggling theory, but one Oreshkov concedes proving remains firmly in the realms of science fiction.
"Our work shows that if we believe that time symmetry must be a property of the fundamental laws of physics, we have to consider the possibility for phenomena beyond those conceivable in standard quantum theory. Whether such phenomena exist and where we could search for them is a big open question."