The grandfather paradox is the self-contradictory situation that stems from time travel scenarios. In this impossible scenario, a person travels to the past to kill his grandfather. As a result, there will be no grandfather who gives birth to his parents, and eventually the very existence of the person is violated. According to the Stanford Encyclopedia of Philosophy, this contradiction is sometimes expressed as a hypothesis for violating the logical possibility of a trip to the past. However, in the context of modern physics, there are ways to avoid this contradiction.
Description of the grandfather paradox
Suppose you have a car when it allows you to travel back in time. While you are in the past, you accidentally kill your grandfather or any of your ancestors before any reproduction. This will affect a range of future events, including your birthday. So that there will be no birth; But if you were born in the future, how can you kill your grandfather in the past? Here is a contradiction. This scenario became popular in the science fiction magazines of the 1920s and 1930s, and was called the “grandfather paradox” in the 1950s.
In fact, you do not need to kill anyone; But there are several ways you can change the date so that it will be missing you in the future. Perhaps the best example is “Back to the Future.” In this film, the main character travels to the past to separate his parents before their marriage and then tries madly to bring them back together.
Is the grandfather paradox possible?
Stephen Hawking, the most brilliant contemporary physicist, spoke about the realities of time travel. He spoke in 1999 about “space-time vortices” that show how Einstein’s theory of general relativity made time travel possible by curving space-time.
From a theoretical point of view, a tool that allows time travel and the ability to kill ancestors; It is a special type of wormhole. Wormholes are one of the most striking results of general relativity, often defined as shortcuts between one point in space and another; But Hawking shows in his speech that a wormhole can return to its starting point in time. This position is called the quasi-temporal packet curve (CTC).
But if physics made it possible to travel back in time, would the grandfather paradox still be a problem? Hawking says there are two possible ways to solve the paradox in this scenario. He first refers to a model called “continuous histories” in which the whole of time (past, present, and future) is predetermined. This way you can travel to the starting point of the date on your own date. But in the “block world” model, one can go back in time but not change it. According to this view, the grandfather paradox never arises. On the other hand, in the second option, the situation becomes more complicated.
Grandfather paradox and parallel worlds
The second way to travel to the past involves theories of quantum physics. According to this theory, an event can have several possible outputs with different probabilities of occurrence. According to Stanford’s Encyclopedia of Philosophy, the definition of “multiple worlds” in quantum theory assumes multiple outputs at “parallel” time intervals. According to this view, the grandfather paradox is solved if the time traveler lives in a period in which the grandfather lived a long life to have a child, and in a parallel period of time returns to the past to kill him and never be born. The Stanford Encyclopedia also provides a strong argument for the inability to oscillate between parallel time periods. According to Hawking in 1999, this is the hypothesis of science fiction scenarios such as Back to the Future.
If the parallel worlds intersect, you can kill your grandfather without violating your existence.
Back to the Future was made in 1985. At the time, the definition of a “parallel world” of grandfather’s paradox was a philosophical conjecture. However, in 1991, a physicist named David Deutsch put forward a stronger hypothesis. Deutsch showed that although parallel time intervals could not interact with each other, this position changed in the vicinity of the closed quasi-time curve (CTC) and with the return of the wormholes on themselves. Here, based on science fiction scenarios, different time periods collide; As a result, when the CTC loops into the past, the past is actually another time period. If this theory is proven, you can kill your grandfather in his childhood without eliminating yourself. In this case, your grandfather will never exist in the parallel world, and your grandfather’s killer exists in another world.
Solve the grandfather paradox?
It may seem strange, but there is empirical evidence for Deutsch’s solution to the grandfather’s paradox. In 2014, a team from the University of Queensland explored a simpler time travel scenario that included a similar logical paradox. The researchers published their paper in the journal Nature Communicaitons that same year. The basic idea was that a subatomic particle had to go back in time to spin the key that led to its production: if the key did not spin, the particle would never form.
One of the key features of Deutsch’s theory is that multiple probabilities must be self-consistent. In the Queensland research example, for example, if the probability of a particle going back 50-50 is likely to be 50-50, the inverted key for creating a particle is also likely. In the absence of a time machine, the researchers conducted an experiment involving a pair of photons that is logically equivalent to a single photon that goes back to create itself. This experiment was successful and the results confirmed Deutsch’s theory of self-adaptation.
The grandfather paradox and the butterfly effect
Killing a grandfather as a child is the only way to not be born; But there are other possibilities. In a system that is complex enough, even the smallest change can have long-term consequences. Just like the effect of a butterfly, the fluttering of a butterfly can cause a storm thousands of miles away. Ray Bradbury, the science-fiction writer of the 1952 story The Voice of the Storm, put forward a similar hypothesis for time travel that can be read in the Internet Archive. The character of Bradbury goes back to the time of the dinosaurs, and at this time he randomly steps on a butterfly and then goes back to the present time and encounters a society that is not recognizable to him. As a result, if social change is effective enough, the time traveler has certainly prevented his birth by killing his grandfather.
But will this be the case with the implementation of the quantum method in the grandfather paradox? According to a recent study at the Los Alamos National Laboratory, the historical period is more flexible than the butterfly effect. The researchers used a quantum computer to simulate a trip to the past. During the trip, part of the information was severely damaged, which was the computational value of stepping on a butterfly in the Jurassic era; But unlike Bradbury’s story, the continuous effect of the past in the present will be very small and insignificant. Of course, this is good news for future travelers. As a result, as long as you avoid stupid things like killing one of your direct ancestors, you can go back in time easily and without any contradictory consequences.