Physicists from the University of Queensland in Australia may have achieved time travel. The team of quantum scientists created a theoretical time loop to allow photons to interact with themselves in the past. According to the team’s publication Nature Communications, this allowed them to study a measure of quantum time called a closed timelike curve (CTC):
Here we experimentally simulate the nonlinear behaviour of a qubit interacting unitarily with an older version of itself, addressing some of the fascinating effects that arise in systems traversing a closed timelike curve.
A CTC is a mathematical model that predicts all future locations of an object while simultaneously ‘predicting’ all past locations. Closed timelike curves get interesting because the allow for past events and current events to occur simultaneously.
Temporal anomalies such as closed timelike curves can occur in theoretical spaces where gravitational fields are strong enough to warp space-time, such as in black holes. When this happens, a time loop is created, allowing objects to return to previous states and/or times.
In this experiment, photons were emitted through a barium-borate crystal into a polarizing circuit. At the other end of the circuit, the photons’ quantum states and locations were recorded. Then, scientists changed the polarity of the circuit, causing the already-observed photons to change states. Thus, changing the states of the photons in a theoretical ‘past’ ended up altering their future states.
The data this experiment generated is still highly theoretical and experimental - the title of the research team’s publication is “Experimental Simulation of Closed Timelike Curves,” after all. While the photons in this experiment did change their future states based on altering the circuit that emitted them in the past, that does not necessarily imply that the photons travelled back in time.
The explanation could be due to the effects quantum entanglement or as yet unknown laws of physics. This experiment does serve as a useful simulation of the types of interactions that occur in a time loop, however, allowing physicists to get a glimpse of the theoretical properties and effects of time travel.