Most popular Temporal Paradoxes

A temporal paradox, time paradox, or time travel paradox is an apparent contradiction, or logical contradiction associated with the idea of time and time travel.

Causal Loop#

The causal loop is a paradox in which a future event causes the past event which leads to the future event. For example a billiard ball moves to a time travel machine and travels to its past and strikes the past self towards the time machine. The billard ball will keep traveling to its past and striking its past self. This is a classic example of a Causal loop.

Predestination Paradox#

This is when actions of the time travel become part of the history and ultimately causes the event he/she is trying to prevent to take place. Destination is predetermined and we can’t change it even if we try. If someone’s lover dies in a car accident, they travel back in time to reach their lover as soon as possible on the accident spot only to find out that they were the one who caused it. This is often associated with self-healing hypothesis - events altered by a time traveler will cause another chain of events which will cause the present to remain the same (time self heals itself).

Grandfather Paradox#

This is a famous paradox where a time traveller goes to the past and kills his grandfather in his childhood, which causes one of his parents to not be born and intern the traveller not being born. But if the traveller was never born, he can’t travel back in time to kill his grandfather. If his grandfather is not killed then the traveller will be born. We can’t predict the outcome of this.

Bootstrap Paradox#

The inventor of time machine travels back in time and gives his past self the time machine. Now, his past self already has the knowledge of time machine and he just refers that instead of inventing it. The time machine’s origin can not be determined as it was just handed over to the person who may or may not have invented it in future.

Fermi Paradox#

Fermi Paradox is the apparent contradiction for lack of evidence of alien life existence. This has been used for time traveling - If time travel were possible, where are all the visitors from the future? There are many possible answers to this. The time travellers can’t travel to arbitrary times. They disguise themselves to avoid detection.

Let’s Kill Hitler Paradox#

If someone travels to the past and kills hitler, it will cause a major change in the chain of future events, which means the future will be completely different than when the traveler hadn’t yet traveled. This also signifies that the traveler after the chain of events will not have any reason to travel in the past to kill hitler in the first place.

Newcomb’s Paradox (free will)#

If people could travel to the past, with their knowledge, decision made by other people (free will) will already be known to the traveler which contradits the existence of free will. The traveler can go in the past and win all the lotteries.