The Metaphysics of Time Travel

Reading Time: 14 minutes

The following was a college essay written by John Mancini. It has been edited and approved by Ariel Hobbs. If you have a Theology essay that you would like published that received a grade of an A- or higher, please be sure to contact us.

By John Mancini, University of Rhode Island

Back to the Future, Terminator, and most recently Avengers: Endgame all share a commonality: they all revolve around time-travel. While a marvelous plot device, which some argue has been overdone, there always remains that one individual in the theatre who, after the time-traveling action has taken place, exclaims, “Oh, come on. That is not possible.” In such movies, the audience is asked, not explicitly, to suspend their disbelief for the sake of the plot. The degree to which the audience must do so, however, varies from film to film. With that said, which time-travel-oriented movie requires the most suspension of disbelief? That is, how possible is time-travel? Now, a common error in addressing this question is in immediately referring to quantum physics to design a theoretical method of time-traveling — this is not what I am asking, however. I am not asking how time-travel can be done. I am asking: is it logically possible that one could transport himself to another particular point in time? The field of study to turn to, then, is not quantum physics but philosophy, seeing as it includes the study of logic and attempts to understand concepts seemingly incomprehensible, such as time-travel. To properly delve into the subject matter, however, we must narrow our focus within philosophy. Our philosophical focus, then, shall be upon “metaphysics,” or, according to the Stanford Encyclopedia of Philosophy, as understood from the ancients, “‘science’ that [studies] ‘being as such’” (van Inwagen and Sullivan). I am going to further refine metaphysics, however, by only citing metaphysics as concerns St. Thomas Aquinas, due to how intelligently and extensively Aquinas constructed his study. In this way, Aquinas has adequately answered virtually all questions any individual could ask regarding his metaphysics.

As for how “being” relates to time-travel, this is where the story gets interesting. Being remains quite the complex term, but the key attribute as pertaining to time-travel remains the one stating that being is active through existence and change, i.e. for time to be being it must be subject to change and relate to participation in existence. With that said, there are three main views to consider when defining how time functions: Eternalism, possibilism, and presentism. Eternalism views time like a system, composing of parts we call the past, present, and future. One way to envision this is to view time as a collection of three blocks, where — to us — each mode of time represents its own block making up the cube of time. This is why eternalism is often credited as the “block universe” theory. Consequently, in viewing time as a system with all of its modes having their own block to constitute the cube, eternalism regards the past, present, and future as all equally real, i.e. equally being. This is because, as Norris Clarke explains in The One and the Many, an explanation of Thomistic metaphysics, time as a metaphysical system would require that all of its parts exist in themselves in order to compose such an extrinsic unity (Clarke, 66-67). Eternalism, then, is a monistic view of time, where, as Joel Hunter from the Internet Encyclopedia of Philosophy writes, “Everything is one; the appearance of things coming to be and ceasing to be, of time passing or flowing, is simply phenomenal, not real” (Hunter). In this way, all events of the past, present, and future are set; we cannot change what will happen because each event has already occurred in being real. This is unintelligible for Aquinas, due to his belief that we all have free will; a set future completely diminishes one’s ability to choose his own path. This also deprives our actions of any meaning, as they have all been predetermined, and so our choices become illusory.

Possibilism, on the other hand, argues that only the past and present are equally real, while the future remains the only mode of time that is uncertain and changeable. In this way, possibilism is credited as the “growing block” theory, where the past and present have their own blocks, and the future’s block is undergoing construction. With that said, this constructing future can pan out many different ways across many different predetermined worldlines, “only one of which will become actual for [an] object” (Hunter). The problem with this ideology, as understood through Aquinas, is that we still do not properly have free will. Aquinas did not believe that the future could ensue according to different “worldlines,” he believed it ensued according to our choices. In this way, the future remains nonbeing and completely unknown because there remains nothing to know in contemplating the future. Accordingly, it is not so much that we choose worldlines, as this would imply that we could know such worldlines and pick the most preferable one. It is rather that we choose what actions to commit, thus making our own worldlines, which we can only know at the present time of creating them. Hence, to a possibilist, our actions have meaning but not to the extent that they should, as we are limited in what futures we can actualize.

Before moving on to presentism, it is important to acknowledge that both possibilism and eternalism maintain that the past remains as real and being as the present. Thomistic metaphysics, however, shows that this is majorly flawed. As previously explained, in order for something to be being, it must be subject to change in one way or another and offer participation in existence. Thus, notice the contradiction in possibilism and eternalism both having the belief that the past is set or unchangeable yet also being; nothing that is unchangeable can properly be understood as being. The only mode of time we can change and actively participate in is the current moment, i.e. the present. Therefore, the present remains the only mode of time that is being, which is precisely what presentism declares. In presentism, “[t]he past was, but exists no longer; the future will be, but does not exist yet” (Hunter). In speaking, then, we can claim that one thing did exist in the past but no longer exists in the present; my cat, Miracle, did exist but has since passed on from this life and does no longer. According to possibilism or eternalism, however, Miracle still exists; she is continually experiencing her birth and death in the past, becoming being and nonbeing, never quite moving on from those lived moments. Why mourn for any loved ones, then, if they continue to exist in the past? It is because they are not here now, and this is the only time that is being, thus the only time with which we shall concern ourselves. Now that we have a proper understanding of time, we can finally move on to how time-travel is possible — to a degree — as understood logically through metaphysics.

Firstly, let us address the degrees to which time-travel is not possible. Say time-traveling involved reversing the events on Earth by flying at very high speeds into space and back to Earth, similar to Einstein’s theory of relativity. Let us then assume that I engage in such a process and take off from Doc Brown’s garage at the speed of light and return to it to find all of the events of Earth reversed by one day. How would this look? Well, here we meet some unintelligibility, due to a concept known as the “grandfather paradox.” According to Bruce Sterling from Encyclopedia Britannica, this paradox revolves around the idea that an individual who travels back in time and kills his grandfather for whatever reason, “thus [ensures] that he, the time-traveler, can never be born in the first place” (Sterling). This is because in killing his grandfather, the time-traveler prevents his parents from ever being born, meaning the time-traveler was never born, himself, and so could not have traveled through time to kill his grandfather. Likewise, if I reversed the events of Earth by one day, all of the steps leading up to my time-traveling would have never occurred, and so I never would have time-traveled. Say, however, that I somehow bypassed the grandfather paradox and traveled to the past through this method. Would this still cause unintelligibility? Well, in time-traveling this way, I would have seemingly teleported into my time-traveling device in Doc Brown’s garage at the instant to which I returned. Allow me to explain: If on the day before traveling back in time I was eating lunch with my family at 11:30 a.m., and the next day traveled back to that same moment, this time in my time-traveling device in Doc Brown’s garage, then I would clearly no longer be with my family at 11:30 a.m. Hence, from 11:29 a.m. to 11:30 a.m., I would be with my family in one instant and then not with them in the next. This is not possible; by what means did I travel to Doc Brown’s garage? Now, I would like to address the objection that there could be two of me after reversing time, one in the time-traveling device and one at lunch at 11:30 a.m. This, however, cannot be, due to us running into the grandfather paradox, once again: There being two of me at 11:30 a.m. the day before my time-traveling implies that I managed to reverse the events of the coming day, i.e. my efforts of initiating time-travel, in order for there to be a me who goes back to lunch with my family. There is only one me to feel these effects, however, so the possibility that there can be two versions of myself is a nonsensical one and cannot happen, as I would subject my only self to the effects of time-travel, the effects of reversing time. In fact, if I was to actually attempt this sort of time-travel to the past, I would find that I could not travel even a nanosecond prior to my attempt. If I did, then I would reverse time to an instant where I would not yet have begun to time-travel, thus undoing my efforts, and so would end the process. What is more, is that I, in reversing the events of Earth, cause my actions of initiating time-travel to become future and thus nonbeing. With my act of time-traveling becoming nonbeing, it also becomes unknown, and so I would not even recall attempting to travel back in time at all! A more physical proof is that I would reverse my memory in traveling to the past and so would not remember time-traveling. Hence, traveling back in time through a similar process of Einstein’s relativity remains impossible and would result in a time loop, if anything, where the time-traveler would constantly relive the event of starting to reverse time, unbeknownst to him. With that said, what if I could simply transport myself to another point in time, without initiating a physical process?

Assume that instead of reversing time back to get back to lunch with my family, I merely walked through a portal and teleported into my body at 11:30 a.m. one day prior. Does this raise any issues? Well, once again, in traveling to my past, my previous present would become the future, i.e. nonbeing. From this premise, we reach the conclusion that I would not know the future, as it is nonbeing, but perhaps I would still retain my memory and with it the knowledge regarding how the coming day could transpire under specific conditions. This proposition, however, is problematic and quite possibilist in nature, as it means that there lies a worldline already set for me to follow if I so choose. This, however, we determined is not reality, as we make our own worldlines, meaning there is never one laid out for us to actually “follow.” Furthermore, if I teleported into my body from yesterday, there is no possible way I would have any recollection of my time-traveling. This is because I do not replace my body from the past, I teleport into it. In this way, I merely become the same me from the past, destroying my body present at the moment of time-traveling, and with it the memories of that present, which then become my future. Hence, I would again create a time loop and future that endlessly becomes being and nonbeing, as I would continually teleport into my body whilst not knowing that I had just time-traveled in the first place. With that said, does this mean that such a circumstance is metaphysically plausible? Could the “portal method” work as a means of creating a time loop?

To answer this question, we must first return to the point I made earlier about the portal method affirming a possibilist view of time. While this statement is not inaccurate, I believe it is more accurate to say this method is an eternalist view that becomes possibilist, in considering it plausible. In opening the portal and having all of time at my disposal, am I not declaring all time as equally real, all time as equally being? This must be the case, seeing as the ability to travel to any point in time requires that no such time remain nonbeing. As previously explained, however, this means that all past beings to ever live both exist and do not exist. Hence, we can return to a presentist view of time and proclaim that since all time but the present is nonbeing, then traveling to the past using a portal requires resurrecting or recreating the respective now. Unfortunately, this, too, proves unintelligible, as we would be creating something, i.e. a previous now, out of nothing, which cannot be done; anything that is nonbeing cannot be recreated in the same manner because nonbeing is nothing and so does not provide us with any tools for creation. In other words, to create a past moment, we would require the parts of that past, which are nonbeing, to come together to form it, the product of which would still be nothing. Hence, such a process would not yield any past time into which we can travel because we have created nothing. A similar dilemma arises for traveling to the future: We would either have to create the now-that-is-yet-to-be, thus something out of nothing, or the future is already being and already set. None of what I have just written is sufficient. Thus, to answer the above question, traveling to the past or future through a portal is unintelligible and impossible, as the past is no longer being, and the future is not yet being, voiding the conditions for a time loop to transpire. There is, however, something that the portal method implies, further discrediting it as a plausible means of time-traveling, that being that time is an absolute or fourth dimension.

The idea of time as an absolute originated with Isaac Newton. According to ExactlyWhatisTime? Newton’s “absolute time” theory maintains that time continues to move, or “flow,” regardless of human conception as a fourth dimension. It views time as “a kind of container or stage setting within which physical phenomena occur in a completely deterministic way” (ExactlyWhatisTime?). The portal method reinforces this concept by viewing time as another universe into which one can go either to relive a past moment or live in a future one. Thus, the universe of time contains all that has happened and all that will happen in a predetermined way. While we have already seen that predetermined events remain flawed in constructing a view of time, there remains yet another major discrepancy in this theory. In containing all the events of the universe, time must contain all past and future beings as well, considering beings are responsible for these events. Newton agrees with this analysis but also claims that absolute time is immaterial and “empty of all real bodies” (Clarke, 175). This is a blatant contradiction; how can something be empty and full at the same time? With that said, Clarke offers a logical alternative and solution to what exactly time is. Something to keep in mind, he points out, is that we would not conceive of time without change. Clarke explains that when we utilize such terms as “before” and “after,” we do so in a spirit of referring to changes, i.e. “I ate before I was full” (Clarke, 162). Even when making claims about how long something took, we still refer to change: When I state, “The test was 50 minutes long,” I am explaining that it took me 50 minutes to complete the test. The change, then, was in my mode of being, I was in a state of not having completed the test and changed to a state of test-completion. Time, then, is a mere measurement of change. If everything in the universe was unchanging, how would we know what happened before or after something or for how long? Moreover, if everything was unchanging, then time would seemingly cease; we would all freeze in our current moments, as would everything else, because all changing processes would suddenly stop, including our bodily ones. Hence, it is not that there is a fourth dimension of time that we can willingly draw up in a portal. It is that there are constant changes coming into existence that we put into terms of time as a method of making sense of the world. As for what conducts such changes, it cannot be time, as time is entirely mental and manmade, and so without humans would not exist. This means that any sort of time-travel, as understood absolutely, is completely implausible — there is no time through which to travel. All there is, is now, and now merely exists to allow us to change, by some force independent of time, and continue on with our lives, i.e. our existence. Let us finally address, then, the only method of time-travel that remains possible: Einstein’s theory of relativity and time dilation.

As the BEC Crew of ScienceAlert writes, “time dilation describes a difference of elapsed time between two events, as measured by observers that are either moving relative to each other, or differently, depending on their proximity to a gravitational mass” (BEC Crew). In essence, time dilation maintains that the faster we move through space, the slower we move through time. This allows for one person traveling at a high enough speed — close to the speed of light — to have time to pass at a much slower rate for him than a person who is not in motion, causing the former individual to age significantly slower. Hence, if I was to fly at the speed of light to some unknown location in the universe and back, I could age 10 years, while everyone else ages 20 years. In this way, I am 10 years farther into the future than I should be and thus time-traveled. To illustrate this, relativity is often compared to a photon clock, where a light particle bounces off one side of the clock to the other, each bounce representing one second passing. If I am traveling at the speed of light, however, this photon has a greater distance to travel from one side to the other, as once it makes contact with one side, the other will have moved farther away, thereby extending the length of one second — as compared to Earth’s conception of one second, that is. Thus, flying at the speed of light would change my conception of time by expanding the amount of Earth time that seconds, minutes, hours, etc, cover, resulting in slower aging. Now, it is implied that my aging would slow in conjunction with the photon clock’s measurements. Whether such measurements would truly result in or correlate to slower aging is up for debate, but that is not my focus. With that said, I believe there lies a key factor to keep in mind with regards to Einstein’s relativity, proving that it is something other than time-travel: Time, i.e. change, continues to move forward for both the time-traveler and everyone else on Earth. This means if I was to engage in such a process, that I would not freeze my bodily processes or uncontrollable factors about myself; I would simply slow them down. Accordingly, I would also not partake in a different now from everyone else; I would merely perceive it differently. This sort of time-travel, then, is merely measuring different processes of change to create a new conception of time. Thus, if I was to continue to measure the Earth’s rotation around the sun when flying into space, I would find that I do age 20 years, whilst seemingly only aging 10. In essence, Einstein never claims that a person partakes in a different now or travels to a new dimension; if time was to suddenly stop all at once, the time-traveler would still stop in his travels at the exact same instant as everyone on Earth. This is the reason I argue that Einstein’s time dilation is not really time-travel at all: The “time-traveler” continues to live in the same moment as everyone else. How can time dilation be time-travel, then, when the time-traveler does not truly travel through time? Such a process must rather be understood as a means of slowing down the aging process, allowing one to live more Earth years than he otherwise would have. Thus, Einstein’s theory is consistent with Thomistic metaphysics and raises no metaphysical issues, deeming his “time-travel” the only degree to which said action can be possible.

To reiterate, time-travel, as understood properly through metaphysics, is only logically plausible to a small degree. We find that the only mode of time that is subject to change, thereby being, is the present, i.e. now. Possibilism and eternalism argue that other modes of time exist just as much as the present does, but this implies that they would be subject to change — which both theories claim is not the case — and also includes the contradiction of past individuals existing and not existing. Traveling into the past with such a view of time, then, is nonsensical, as the past cannot be set and open to change at the same time. With that said, we saw that reversing the events of Earth to travel to the past would only reverse one’s efforts of engaging in time-travel, and so result in the grandfather paradox, as illustrated by the Encyclopedia Britannica. On the other hand, to accelerate time into the future is to engage in Einstein’s theory of relativity, where time moves slower for one person than all others. This leads to the recognition that time is a mere mental, rational being, entirely manmade, serving the means of measuring change. All Einstein’s theory maintains, then, is that it may be possible to slow down one’s bodily processes by changing how one measures time, which does not clash with Thomistic metaphysics, considering all partake in the one and only mode of time that is being, i.e. now. All in all, we must recognize that time is a construct — a very useful construct that allows us to make sense of this world and its changes. Such a recognition leads one to question what allows us to measure these changes or what causes them in the first place, thus setting us on a quest to unravel the mysteries of the universe.


“Absolute Time.” Exactly What Is Time?, WordPress, 2020, Accessed 13 April 2020.

Clarke, Norris. The One and the Many. University of Notre Dame Press, 2014.

Crew, BEC. “Why Time Is Relative, Explained in Under 3 Minutes.” ScienceAlert, 25 Aug. 2016, Accessed 13 April 2020.

Hunter, Joel. “Time Travel.” Internet Encyclopedia of Philosophy, 2020, Accessed 13 April 2020.

Sterling, Bruce. “Time Travel.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., 11 Sept. 2019, Accessed 13 April 2020.

Van Inwagen, Peter, and Meghan Sullivan. “Metaphysics.” Stanford Encyclopedia of Philosophy, Stanford University, 31 Oct. 2014, Accessed 13 April 2020.

Edited By: Ariel Hobbs

Leave a Reply

Your email address will not be published.

Follow Us!