The indistinctness of quantum mechanics creates a band of troubles, from maliciously shifting time-of-flight computations between satellites to mudding up Newton’s elegant, all-seeing physical examples of the universe. However, when it concerns subjects as ethereal as the New Physics, integrating really harebrained concepts like negative mass and, yes, * time travel*, that very indistinctness can become a blessing to investigators. Inside the open and transcendent possibility space allowed for by the behavior of quantum particles, we can rake in all manner of poorly understood concepts and phenomena, and that might not actually be such a wreckless thing to do. By considering quantum mechanics, a few physicists believe they might have figured out one of the oldest puzzles in the history of abstract physical thinking: the grandfather paradox.

The grandfather paradox has a particular form, and a general. The specific: What if you went back in time to a point before your parents were conceived and, while there, murdered your grandfather before he had an opportunity to father your parent. Logically, this would result in your never having been born — which signifies, you could never have lived to go back in time and kill your grandfather, which means you were born and thus could go back in time and wipe out your grandfather, which means… The more large-scale form is just this: backward time travel will inevitably interfere with the future path of the thing which travelled — be it a person or a spinning electron — and that the implicit impossibleness of this makes backward time travel impossible.

It may sound strange to have high-ranking physicists congratulating themselves for working out that time travel Is not real, but actually it is physicists’ servile adherence to formal logic has caused this conversation indispensable. Weighing the most cutting-edge mathematical models for time and space, there is just no reason that the arrow of time can not be turned backward, that you can not enter a so-called “closed time-like curve” (CTC) and loop back around to the past. No reason, naturally, except that that is plainly impossible.

The insight released is that quantum superposition may provide an out, which both permits *time travel* and does away with the paradox. Look at our general situational setup, with a photon going back in time to turn off the machine which first emitted it. This photon will at all times be in a superposition of states, implying that it can have many, oftentimes directly contradictory, states simultaneously.

It’s somewhat more complicated than all that, but the math fundamentally comes down to that. The true experiment has affirmed a principle called self-consistency, which basically states that if a particle went back in time it would have a certain chance of emerging and self-interfering across time, and that that probability is frozen to that probability that it will enter the CTC and go back in time. Nature abhors a paradox, almost as much as it abhors a vacuum. All things exist in a multiplicity of states at the same time. The arrow of time is indeed probabilistic, but time can go in other directions other than backwards. The result is that anything traveling backward in time in reality has a kind of multi-dimensional probability distribution — similar to lan electron is in all places within its positional probability distribution.

In the past, physicists have traditionally used the probabilistic model to say that while backward time travel is technically possible it’s also functionally out of the question — that the probability of being capable to travel back in a CTC and self-interfere is vanishingly close to zero but, significantly, not really zero overall. Now all of that has changed.

For more information about time travel, please visit The Quantum Time Travel Institute.