In the cartoon world, if you go back in time and kill your own grandfather — and sleep with your grandmother — everything works out just fine. Minus the part where you end up becoming your own grandfather. See: Fry, Phillip J.
However, if we could actually travel to the past, the prospect of killing our own grandfather presents a classic time traveling paradox. Let’s say we go back and kill our grandfather as a child, that action would result in us never being born. However, if we were never born that means we weren’t around to travel back in time in the first place, meaning our baby grandfather lived, meaning we were born. It’s a classic example of the hypothetical problems messing around with the past poses.
Except, it might not be a paradox at all. The folks behind the great YouTube channel MinutePhysics have a logical explanation on what would really be happening in that super weird situation. (Seriously, why are you killing your baby grandfather in the first place? What a weird use of time travel. Go buy some stocks or something.)
Before explaining their answer, they first brushed aside the alternate timeline theory, the kind you know best from Back to the Future, because it leaves us with a relatively boring answer to the entire paradox. In that scenario you don’t travel to the past that existed as part of your linear timeline, but rather to a copy, meaning you aren’t changing the actual past, just a replica of it. That’s too neat and ruins all the fun of these types of thought exercises.
Instead, they focused on the actual quandary, where you problematically influence the events of your own future on the same linear path. In that case, the logical outcome of killing your baby granddad would appear to be a closed loop (you kill him-you aren’t born-you can’t kill him-repeat), but instead they say what you have are “two entangled histories happening in parallel.”
How can that be? How can two states of existence be occurring simultaneously for the same person? Because “subatomic particles regularly do multiple different things in parallel” all the time, in what is known as quantum superposition, a property that is responsible for fusion in the sun’s core and explains the double split experiment, which you might remember seeing in physics class as an example of how light can behave like both a wave and a particle.
This results in a universe where there is a “superposition of two states,” where in your grandfather is both dead and alive, therefore you exist in a state where you are able to go back and kill him, but also where you don’t exist.
As they note, this Möbius strip-looking timeline with the two concurrent states seems to lend credence to the idea we can never travel back in time (deal with it Matthew McConaughey, you never should have left Murph in the first place), but that’s not really the point of this exercise. The point is that grandfather paradox isn’t really a paradox at all. There is a logical explanation to it, we just need to be willing to find it. We shouldn’t dismiss a tough question because it seems like the answer doesn’t exist.
What other paradox would you like to see them tackle next? Travel to our comments section below and let us know.