Over the past several decades, the topic of time travel has been considered and discussed by physicists, philosophers, journalists, presenters, and lay people. Movies have been made that feature time travel as the main plot or as one of the essential elements of the movie plot.
Some of these movies were entertaining or pleasant, but that does not mean that these movies are accurate or that time travel is possible.
Time travel, whether backwards or forwards, including changing or turning back time, is essentially a speculative, theoretical extrapolation of existing physical theories such as the theory of special relativity. Without getting into all the details or into long philosophical considerations, I esteem that time travel is not really possible or realistically doable.
Various explanations or interpretations have been provided in books or textbooks concerning time travel.
In some good textbooks dealing with the theory of relativity, it is pointed out that experiments have been carried out and have verified the time dilation equation (for example, expriments with muons, with mu mesons, …), but it is also indicated that the phenomenon is called apparent time dilation. In a similar way the phenomenon of length contraction is called apparent length contraction.
Let’s analyze as examples one or two movies featuring time travel and related effects in their plot.
In the movie Superman I starring Christopher Reeve, Superman turns back time as an emotional reaction to the death of Lois Lane. This type of action can be realistically described as a useless, naive action going against the rules of physics.
The scene in the Superman movie seems to assume that the entire world consists of planet Earth. How about “turning around” the solar system, or around the Galaxy, or around the Local Group of galaxies, and so on.
Turning back the rotation of the Earth could very well have devastating effects on everything and everyone on the planet. Not to mention the gravitational perturbations and disturbances affecting the Moon, the planets, the entire solar system, and beyond.
I think it would have been better if the writers had told the story differently, without killing Lois Lane or having Superman “turn back time”.
Time travel has been used and abused in sci-fi movies, and in movies or tv series by DC comics and Marvel comics, as some sort of deus ex machina or ultimate solution to fix everything or to set everything straight. Regrettably, this does not add to the accuracy or credibility of these movies. It also does not make them more realistic or convincing, even when exercising or trying to apply one’s suspension of disbelief.
In the movie Interstellar, physicist Kip Thorne worked out the equations that depict the path of light waves traveling through a wormhole or around a black hole. The visual effects in the film are based on the gravitational theory and the field equations of general relativity.
“Interstellar” is based on generally accurate existing theoretical and scientific concepts like neutron stars, spinning black holes, accretion disks, and time dilation.
Wormholes are theoretical physical entities that are considered to be like tunnels or shortcuts through the geometry of spacetime, connecting different parts of the universe.
According to the story in the movie, a crew of space explorers travel on an extra-galactic journey through a wormhole. They reach on the other side another solar system with a spinning black hole for a sun.
The spaceship’s destination is Gargantua, a supermassive black hole with a mass 100 million times that of the sun, located about 10 billion light-years from Earth. Gargantua rotates at 99.8 percent of the speed of light.
The movie refers to five-dimensional reality, and five-dimensional space is described in the movie as a form of extra-dimensional “tesseract” where time appears as a spatial dimension. The movie plot mentions and uses the concepts of time travel and time dilation.
I want to note that while this movie uses mostly accurate existing theoretical notions in physics, I think that the concepts of time travel and time dilation are nevertheless debatable theoretical and speculative consequences and extrapolations of physical theories such as the theory of relativity, that time travel cannot physically happen, and that it can generally be clarified by other explanations, such as being an apparent effect. In this sense, I think the use of time travel and time dilation diminishes the preciseness and undermines the realistic, plausible character of the movie.
Considering the possibility that in the future rigorous scientific experiments are made and these experiments prove the possibility of faster-than-light speeds and travel, the effects, nature and consequences of faster-than-light speeds should be carefully studied, but I don’t think time travel will be one of those consequences.
Then perhaps new equations, new explanations or new physics rules or laws would have to be formulated. Or perhaps the speed of light would be somewhat viewed like the speed of sound as a limiting speed representing a certain type of singularity. In any case, these are just speculations or general ideas at the present time.
To conclude (again), I think time travel (to the past as well as to the future ) is not possible and will not happen.
A way of proving this could be found not only in physics or in the physical or natural sciences, but also in the objective study of the structure and the rules of (human) historical events, and the realization that there are ‘laws’, patterns and regularities which govern these events.
There will be regrettably no “quantum leap time travel machine”, and no “quantum realm time machine”, these expressions illustrating how the word “quantum” is inaccurately used as a hype word in a attempt to add a veneer of “scientificity” or plausibility to the movies using them. Nobody will be able to travel in time to kill this or that person, or to change history. The Terminator will not and cannot be sent back in time, neither to save nor to kill John and Sarah Connor. The time machine in the eponymous novel by H.G. Wells is not feasible and will not work. The DC comics character the Flash will sadly not be able to change and reverse timelines, or to travel back in time to change past events. I could go on mentioning other examples, novels, works and movies, but I think I got the idea across.
The last several decades witnessed a craze or a fad for entertaining movies involving or dealing with time travel, but I consider that time travel movies, or in general movies that rely on time travel as a plot twist, plot device or as a deus ex machina to solve everything, lack scientific accuracy, and I suggest that moviemakers increasingly stop using time travel altogether, because in the future or in the next decades these types of movies will be viewed or assessed negatively.