Quantum Idea Where The Present Influences The Past Gains Some Theoretical Support

Quantum mechanics is already weird enough, but researchers suggest that we could throw in a bit of time shenanigans to solve a controversial idea that has been debated for almost a century.

The idea is known as entanglement or, as Einstein scathingly described it, “spooky action at a distance”. This is when particles in a quantum system influence each other, even over impossibly large distances. This phenomenon has been confirmed by several experiments, checking the validity of the Bell test, but the new research argues something different might be at play.

They call it “retrocausality”. The set-up of an experiment will influence the particles in the past, so what appears to be an action at a distance is, in reality, something the observer made happen by selecting a certain experiment. Two physicists have now put some math behind this hypothesis. Their work is published in Proceedings of The Royal Society A.

"There is a small group of physicists and philosophers that think this idea is worth pursuing, including Huw Price and Ken Wharton [a physics professor at San José State University]," lead author Matthew Leifer, from Chapman University, told Phys.org. "There is not, to my knowledge, a generally agreed upon interpretation of quantum theory that recovers the whole theory and exploits this idea. It is more of an idea for an interpretation at the moment, so I think that other physicists are rightly sceptical, and the onus is on us to flesh out the idea."

This is a good approach to have. Just because the idea is very out there doesn’t mean we won’t learn something by exploring it. Since it challenges some strong tenants of quantum physics, the proposed solutions might hint at some unexpected physics even if it's not related to retrocausality.

The model assumes that quantum theory is perfectly symmetric in time, so that the laws of quantum mechanics need to look the same whether you’re watching them forward or backward. The standard analogy for this is like an egg moving across a kitchen counter. If the egg suddenly dropped on the floor and broke, you’d know you were watching it forward. We don’t see eggs jumping back together, do we?

But in the quantum world, we don’t have an arrow of time, and if we assume that things must be symmetric, then retro-causality naturally arises, the researchers argue. That allows you to get rid of entanglement and a lot of constraints placed by the Bell test.

While this is early days, it will be interesting to see if this idea can be developed in ways that can be tested against the current model.