Grandfather paradox


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The grandfather paradox is a logical conundrum that could emerge if someone traveled back in time. The term comes from the idea that if a person travels back to a time before their grandpa had children and murders him, their own birth will be impossible. So, if time travel is conceivable, it must avoid such a contradiction somehow.

The grandfather paradox involves any modification to the past, and it appears in various forms. Physicist John Garrison describes a variant of the paradox with electrical circuits that send signals via a time machine to shut itself down and receives the signal before sending it. In philosophy, a similar conundrum is known as the “retro-suicide paradox” or “autoinfanticide” involves going back in time and murdering a younger version of yourself. The “Hitler paradox” or “Hitler’s murder dilemma” is a fairly common cliché in science fiction in which the hero travels back in time to kill Adolf Hitler before he can start World War II. Rather than physically blocking time travel, the action eliminates any justification for the travel, as well as all awareness that the reason ever existed. Furthermore, the ramifications of Hitler’s existence are so massive and all-encompassing that it seems possible that anyone born after the war was influenced in some way by its impacts, and therefore the lineage part of the paradox would directly apply in some way.

Interpretations of the grandfather paradox concept​

Some argue that the grandfather paradox should be approached from a parallel universe perspective. When a time traveler kills their grandfather, they are actually killing an alternate/parallel version of their grandfather, and the time traveler’s original universe remains unaltered; it may be argued that this is not “genuine” time travel because the traveler arrives in a different universe’s history rather than their own.

According to Tim Maudlin, a philosopher at New York University, early versions of the grandfather paradox attempted to prove that time travel was logically impossible. The latter is a regular writer on physics and philosophy. “In a way, that’s like asking why I can’t be wet and fully dry right now,” he explained. “That is, of course, logically impossible. What are you inquiring about?”

Even though we do not know whether time travel to the past is physically conceivable, we may use modal logic to prove that changing the past results in a logical contradiction. Suppose the past happened in a certain manner. In that case, the past cannot have happened in any other manner. A time traveler would not be able to change their past; they could only behave in a way that is consistent with what transpired.

Does the grandfather paradox rule out time travel?​

Consideration of the grandfather paradox has led some to believe that time travel is paradoxical by definition and so logically impossible. For example, in the textbook Logical Reasoning, philosopher Bradley Dowden argued that the potential of producing a contradiction rules out time travel to the past. However, some philosophers and scientists argue that time travel into the past does not have to be logically impossible if there is no way of modifying the past, as stated by the Novikov self-consistency principle. Dowden changed his mind after being persuaded in an exchange with philosopher Norman Swartz.

Nonetheless, the grandfather paradox cannot rule out time travel. Time travel’s logical consistency is heavily dependent on the concept of time, and physicists have many alternative methods of conceptualizing time. Assume, for example, that some physical rules are probabilistic rather than precisely determined. In that case, it opens the door to different results from a trip to the past, which may not be create such paradoxes.

“It’s actually more difficult than you think to come up with a situation with no consistent solutions,” Maudlin explained. He uses the example of a time traveler traveling back in time to shoot themself as a logically consistent time travel scenario. They intend to kill but fail due to a trembling in their fingers. The non-lethal shot hits a nerve in the traveler’s previous self, producing tremors in their hand for the rest of their lives.

Time travel can also be distinguished from the concepts of influencing the past or backward causation. Maudlin, on the other hand, does not believe in reverse causality. “I believe it goes against the nature of time itself,” he remarked. “That is not the majority opinion.”

What is time?​

People in Western cultures often think of time as a straight line. The present is a point in the middle, while the past extends in one direction and the future unfolds in the other. There might or might not be a beginning or an end. There is also the Newtonian concept of global time, which states that the same chronology applies everywhere in the universe.

Nonetheless, philosophers, physicists, and fiction writers have imagined alternate timelines with greater dimensions and traits. Hourglasses, loops, circles, cylinders, and Mobius strips have been used as visualizations. There are also other less serious fictional stories, such as “Jeremy Bearimy,” that allows for the idea of time travel.

Einstein’s theory of relativity has had a tremendous impact. Theoretically, relativity permits space and time to fold over on themselves, resulting in formations known as closed time-like curves. If these time loops exist, they would constitute a type of time travel because anyone within the loop would return to the same point in time.

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