It is theoretically possible to travel into the past by utilizing wormholes—bridges that connect disparate points in space-time. Although Einstein’s mathematics can be applied to suggest that such time travel may be possible, a more philosophical approach reveals paradoxes that may discredit the entire idea. Let us revisit the idea of “temporal paradoxes.”
Temporal paradoxes are logical contradictions that arise when the past is altered in any way. The well-known “grandfather paradox” claims that if a time traveler went back into the past and killed their grandfather, it would prevent their own conception and existence. Therefore, there would be no one in the future to have gone back in time! Also known as a “consistency paradox,” this idea can be applied to any action that alters the past. Since it is true that the past occurred in a certain way to lead to one’s existence, it is logically contradictory for the past to have occurred in any other way. Therefore, even if we were able to travel back in time using a wormhole, the traveler(s) would necessarily have to allow the past to play out as it had previously.
In “A Brief History of Time”, Stephen Hawking offers a possible resolution to this paradox. He states that everything that happens in space-time must be a consistent solution to the laws of physics, meaning that you could not go back in time unless history showed that you had already arrived in the past and had not killed your grandfather (or committed any other act that alters the present). Essentially, Hawking claims that if time travel is possible, it must be impossible to change recorded history.
This conclusion has interesting implications for the concept of human free will—the idea that individuals are able to act at their own discretion. Rephrasing the consistency paradox is helpful: if time travel actually is possible, it would be impossible for a traveler to change history since it has to repeat itself exactly. This means that if we are someday able to travel into the past, we will be restricted by a complete lack of free will. We would have to act in a way that led exactly to the future that we left. If tomorrow a future human arrived on Earth, their future actions (along with everyone else’s) are already recorded history to the civilization that they left. I may be beating a dead horse at this point, but it is rather mind-bending.
We do not have to look so far as time travel to realize that free will is an illusion. The very fact that you have arrived at this point in the article at this exact time was not decided by you. The Exponent could have published it in a different edition, or you could have received a phone call that took your attention elsewhere—either way, your existence here reading is a direct result of external forces beyond your control.