In episode 15 of the Quantum Consciousness series, Justin Riddle speculates on the notion of time travel within quantum mechanics. In quantum computation, the circuits that you design to process your information must be time reversible. This leads to a curious situation where space and time are reversible within the confines of a quantum computation. While we have already discussed times where entanglement and superposition can defy classical ideas about space, it turns out that you can design experiments that show that our classical ideas of time can be violated. To this end, we explore Wheeler’s delayed-choice experiment, which is an iteration of the double-slit experiment, where the decision to measure which slit a particle went through can be made after the particle has already passed through the slits! Another experiment is delayed-choice entanglement swapping, in which the decision to entangle two photons in the future will alter the correlation between measurements we have already made in the past! These are truly mind-boggling experiments. If we assume that the brain is able to perform quantum computations (see previous episodes), then perhaps time reversibility might be used by the brain to generate a real-time experience of the present moment. Information can be processed in the future and then referred backwards in time so that the present moment is rich with a lot of detail. However, this does not violate time paradoxes because only quantum information can be transmitted to the past, and quantum information might be more like a feeling, an impression, or a suggestion, and less like hard data. Many questions to be raised in this episode as we explore the nature of time in quantum mechanics.
