Is time travel possible?
It is one of the classic questions from metaphysics to physics to philosophy to science fictions. In our human histories, we have been providing various hypotheses and theories.
And one of the initial questions is: What is time?
Without clarifying this question, the scope of time travel would remain vague. Generally, we perceive the sense of time with the analogy of space. Space consists of three dimensions. And as we always say, the fourth one is time. Hence, we can imagine and visualize time as a spacial entity from past to present to future. That is why one word “spacetime” could signify the totality of our universe, at least in Newtonian physics.
And if we perceive such spacetime, another question is what could be the edge of it? If we see the space, where is the boundary; where does it start; and where does it end? If we sense the time, when does it start; when does it end? Is there anything like outside of such spacetime? If any, then what is it?
Kant calls the area of these questions antinomy. We can’t reflect on these speculations without contradictions and paradoxes. And he suggested this could be our epistemological limitation.
As we all know, in physics and cosmology, the Big Bang theory is one of the answers to this antinomy. Spacetime we perceive is the process of a specific explosion from the beginning of this universe. Both space and time have created and started by this particular Big Bang.
Considering the speed of light, then the farthest end of the universe is its oldest period. We see the beginning of this universe at the very end. It sounds fascinating. It doesn’t, however, provide an answer to Kant’s antinomy. The paradox remains as is. We call it Singularity.
If time is part of the Big Bang explosion, then traveling time could provide two possibilities.
One is reversing or accelerating the Big Bang explosion itself. It sounds impossible as nobody can control the Bing Bang. Another is we move around within the Big Bang explosion. As the theory of relativity explains, extreme gravity could distort the “shape” of space and time.
If we travel with the speed of light, then our time would move slower; there will be a gap between such moving time and other time scales. Physicists have proposed various hypotheses and theories in this area. To this extent, perhaps such small variants of time travel would be possible at least theoretically.
As Hawking explains, however, going back to the past is probably impossible or more challenging. One of the critical challenges is the grandfather paradox. It directly contradicts the law of causality. If you kill your grandfather, then you must also disappear.
Some physicists and philosophers propose the hypothesis of parallel universe or multiverse. Whenever we change the past, then another world branches out. Therefore, we are living in such infinite possibilities and existing universes.
At a glance, it seems this hypothesis has addressed the grandfather paradox. I’m not sure.
Still, another approach could be eternalism and presentism. For both, we need to go back to the fundamental stance to deny the existence of spacetime.
If spacetime has created and started from the Big Bang, then it seems that this stance is going back to the nothingness and emptiness before the Big Bang, or transcending this specific explosion itself. Or else, it is the eye to gaze a sort of quantum realm.
I am very speculative here. I don’t have any theoretical basis on this speculation. But then, if we don’t see any time and space, the concept of time travel itself will disappear. Even the violation of causality might not make any sense. Antinomy is no longer antinomy. It seems we are embracing the paradox of our universe.
Image by Genty