Scientists model quantum travel to the past։ Could this technology become the basis of a time machine?

Researchers at the University of Cambridge have made significant strides in understanding the intriguing concept of time travel, thanks to the manipulation of entanglement, a key feature of quantum theory. Their groundbreaking study could have implications for gamblers, investors, and quantum experimentalists, potentially allowing them to retroactively alter past actions and improve their current outcomes.

The idea of particles traveling backward in time remains a contentious subject among physicists. While scientists have previously explored models of spacetime loops, this new study connects time travel simulations with quantum metrology, a field that employs quantum theory for precise measurements. The findings were published in the journal Physical Review Letters.

Lead author David Arvidsson-Shukur from the Hitachi Cambridge Laboratory explains the concept using a gift analogy: "Imagine that you want to send a gift to someone. You need to send it on day one to ensure it arrives on day three, but you only receive that person's wish list on day two. In this scenario, it's impossible for you to know in advance what they will want as a gift. Now imagine you can change what you send on day one with the information from the wish list received on day two. Our simulation uses quantum entanglement manipulation to show how you could retroactively change your previous actions to ensure the final outcome is the one you want."

The simulation is based on quantum entanglement, a phenomenon where quantum particles can remain connected, even when separated, allowing for complex computational tasks in quantum computing. In this scenario, researchers entangle two particles, send one for an experiment, and manipulate the other to change the first particle's past state, thereby altering the experiment's outcome.

However, the simulation has a 75% chance of failure, according to Arvidsson-Shukur. He likens this to the gift analogy, where one out of four times, the gift will be as desired, but the other times, it could be a variation of what was expected.

To overcome the probability of failure, the researchers propose sending a large number of entangled photons and using a filter to select the correct, updated information. In the analogy, this is akin to sending numerous parcels and subsequently instructing the recipient to discard the incorrect deliveries.

Lead author Arvidsson-Shukur emphasizes that their research is not about building a time travel machine but rather a deep exploration of the fundamentals of quantum mechanics. While it doesn't enable individuals to change their past, it offers insights into creating a better future by addressing past mistakes.

This research received support from several organizations, including the Sweden-America Foundation, the Lars Hierta Memorial Foundation, Girton College, and the Engineering and Physical Sciences Research Council (EPSRC), part of UK Research and Innovation (UKRI).