Is Time Travel Possible?

Happy Fourth of July!

I decided to write a very patriotic post for this year’s 4th of July. It is a tradition of mine, passed down from my father, to watch the SyFy Channel’s 48-hour Twilight Zone marathon. So naturally, science fiction usually comes to mind when I think about the birth of my country.

This week’s topic will be on the possibility of time travel!

Time is a very paradoxical thing. It’s the one thing everyone knows about, but most cannot explain. Take, for instance, St. Augustine, “What then is time? If no one asks me, I know what it is. If I wish to explain it to him who asks, I do not know.” This is one reason why I wrote my thesis on the nature of time and God’s relationship to it. Time fascinates me. I remember I use to have conversations with a friend of mine in college about time travel and what that would entail. It’s partially due to these conversations that I set my mind to reading and discussing time in a philosophical context.

But, time is a tricky thing. If you ask someone what is time and what is its nature, there is a wide range of answers you’ll get. A range as far as from saying time is everything and around everything to claiming that time is nothing at all—it’s just a human measurement of change. So, before we can actually get to the topic of time travel, we’ll have to briefly discuss what time is.

Theories on the Nature of Time

There are three theories on the nature of time. The names are rather unhelpful, but they will suffice for now.

1) The A-Theory of time.

This is probably the more intuitive theory of time. The two major components of the A-Theory are that it affirms a privileged moment (the present) and the passage of time. I call the “present” a “privileged moment” because the A-Theorist believes that the present is different from any other moment in the past and future. It has a privileged existence if you will. This privilege is defined as not just what is available to us, but also that it is the only moment in time existing. The past used to exist and the future will exist, but only the present actually exists. Most people say that times passes and that there is such a thing as the present. I mean, we talk about the “now” and we reference other days based on the present. The word “tomorrow” indicates the day after today and “yesterday” indicates the day before today; they both derive meaning from the idea of the present. The A-Theory is also called presentism.

2) The B-Theory of time.

I know, helpful terms, right? This theory denies both of A-Theory’s propositions. It affirms that there is no privileged moment and time does not pass. This view is not very intuitive at first, but it does have redeeming qualities. The idea of no present seems like crazy talk. But, the B-Theorist claims that the present is merely an illusion – we have the psychological occurrence of a present moment, but it holds no ontological existence. Additionally, on this theory, the idea of the passage of time is also an illusion. Again, this is a psychological occurrence that gives the appearance of the passage of time. This is also the view most scientists hold. Einstein’s theory of relativity seems to lean this way, though it is not a consensus. This is also the view most TV shows take, such as Agents of SHIELD, The Flash, and Dr. Who. If you’ve heard time explained as a four-dimensional cube, then you’ve heard some version of this theory. One way to think about this is to view time as we view space. There is no privileged space named “here” and space does not pass, we pass through space. So, as “here” is a relative term with no ontological preference, so “now” is also. You still may not like this view, but using the spatiotemporal analogy helps understand this position. This view is also called static theory.

3) The denial time altogether.

Many think that time isn’t really anything at all. It’s just the rate at which the Earth passes around the sun and rotates on its axis. I think we lose a lot if we deny the existence of time, but if you’re going to deny time, then at least acknowledge that there would still be time floating statically in space. Time can’t be reduced to the movement of the sun and the rotation of the earth. If you deny time, then time is simply all change, not just the earth’s change. So, the change of your cells regenerating and dying, the change of your conscious mind, the change of the earth’s position to you—these are all things that would constitute the conception of time. In other words, time = change. However, if time is not a real thing, then time travel would have to be impossible. So, this view will not be considered any further.

There are many variations to the first two positions, but I have only mentioned the mainstream views of each for time’s sake. Heh! Time jokes are very timely when writing on time….Okay, I’m done. Before moving on I want to point out that I am assuming the nature of reality is not contradictory. Meaning, a contradiction is only of the mind not fully understanding something. An apple cannot both be an apple and not an apple at the same time and in the same way.

So, based on this, is time travel possible?

Trials of Time Travel: Questions to Answer for the Possibility of Time Travel

1) The Theory of Time trial

Right off the bat, if A-Theory tickles your fancy, then time travel seems impossible. If only the present exists, then there is no past or future in which you can travel to. You might salvage time travel to the past if you held to a growing block theory of some sort. This theory claims that the present exists and the past enjoys a less than full existence, but the future does not exist at all. On this view, you could only travel to the past. However, you’d have to affirm that existence isn’t binary. Meaning, existence isn’t something that is either on or off, it can come in levels. This is because a Growing Block theorist would view the present as having ontological privilege (it’s the real time) and the past having a less-than real existence, but it’s still real; unlike the future that has not ontological status. This seems very strange; how could someone only partially exist? Some do affirm this view of existence, though it would be necessary for the growing block theory. If you hold to B-Theory, time travel might be possible.

2) The Backward Causation trial

Secondly, if time travel is possible, then you would have to affirm backwards causation. Backwards causation is exactly what it sounds like. Typically, causation is this: first there is a cause, then there is an effect. Backwards causation, however, states that the effect can come before the cause. So, if you think backwards causation isn’t possible, then you’d have to affirm that time travel is impossible, too. At least, time travel to the past. Let’s say that you take a gray DeLorean from the year 2017 to 1917. The cause is the gray DeLorean reaching 88 mph and using a flux capacitor. The effect is you arriving in 1917. On a timeline, the effect (1917) is 100 years before the cause (2017). Thus, the effect is before the cause. In addition, if you believe that you could travel to the future, then you would not be able to get back unless backwards causation is possible.

To summarize, if you hold to A-Theory, then you probably can’t time travel. Though, the growing block theory might help you out. Also, if you think backwards causation is impossible, then time travel is out, too. Except for traveling to the future. However, if you hold to both A-Theory, or the growing block theory, and the impossibility of backwards causation, then time travel is out completely. So, at this point, only the B-Theorist who believes that backwards causation is possible can also believe that time travel is possible. Unless you wanted to believe that you could only travel to the future, then backwards causation wouldn’t be necessary. In this, time travel could be viewed as spatial movements—you can go back in forth in space; therefore, you can go back and forth in time.

This discussion has revolved around the metaphysical possibility of time travel: 1) Time would need to be a real thing, 2) B-Theory would have to be affirmed, and 3) backwards causation would have to be affirmed if you want to keep time travel to the past viable. This does not mean, however, that it is actually possible. So, even if it is metaphysically and logically possible, it may still be actually impossible. For instance, it is metaphysically and logically possible that I can jump 30 feet in the air. There is nothing illogical about this. But, I can assure you that I cannot jump 30 feet in the air. So, this conversation will not conclude with explaining how time travel might actually work. I will conclude with a few quick notes on what time travel would be like if it is an actual possibility.

On the B-Theory of time, the universe is a static block of spacetime stuff. The timeline would be static, meaning that it is not flowing and changing like a river, as some have described it. Instead, time should be viewed as a road, stationary and solid. Sometimes the road is straight other times the road is curvy. It is rough in some parts and it is smooth in other parts. This will be seen more clearly in the following questions of the nature of time travel:

Questions about the Nature of Time Travel

  • Could you meet your past/future self?

Yes. Some shows will say that this would create a time vortex or some paradoxical relapse, but this seems unreasonable. If you traveled to your past to meet yourself, you would have a memory of meeting your future self. Moreover, if you traveled to meet your future self, then your future self would have a memory of meeting his future self.

  • Could you kill your ancestor so that you were never born?

No. Remember, if you assume that reality does not actually contain contradictions, then this could not be possible even if time travel was possible. If you killed your ancestor so that you never existed, then you wouldn’t exist to go back in time and kill your ancestor. If you did go to the past to kill your ancestor, you would ultimately fail at killing them. I don’t mean this in the sense that some magical force would stop you or curve the bullet so that it hit someone else. Instead, you would either never get the chance or change your mind about killing your ancestor because, in your history, your ancestor didn’t die prematurely – obviously, because you exist. You would not lack the power to kill your ancestor, you would lack the power to bring about a contradiction. You wouldn’t be able to kill your ancestor because that’s not what happened. This leads us to the next question. (However, there is another theory that might allow you to kill your ancestor so that you were never born. This is will be discussed below.)

  • Could you change anything at all?

No. B-Theory commits you to a static universe. Thus, you would not be able to change anything. If you went back to stop Kennedy’s assassination, you would ultimately fail because you have knowledge of this past event. This means that it happened. This would go for the future too. Change would be impossible on two fronts. One, the metaphysical, which is what we have been talking about. The Kennedy assassination would be in your history. That means that this happened and it happened in a static universe. So, if you went back in the past to change this, you would lack the power to bring about a contradiction. The other front is an epistemological one. How could you ever know that you changed the past? If you changed the Kennedy assassination, then your memory of history would change; therefore, removing the memory of Kennedy being assassinated because it never happened. This also might mean that you would never have gone into the past to change it in the first place because it never happened. Which means, if you never go back into the past, then Kennedy does get assassinated. So, changing the past would be impossible in a static universe, but it would also cause an epistemological contradiction. Yet, this is not to say that you couldn’t be the one who assassinates Kennedy. It might be that you were always the one who assassinates Kennedy. Maybe this is why the shooter was never found…the shooter was a time traveler!

However, this answer and the above answer assume that the Branching Theory of time does not exist. The Branching Theory of time is the idea that time and other dimensions are possible and may be caused by our world. This is very close, and compatible with the multiverse theory, thought slightly different. The Branching Theory could account for making changes in the past. Let’s say that you go back in time and stop the Kennedy assassination. This seems like it would be reasonable. You do not lack the power to stop such a thing given your knowledge of the event from history books. So, why couldn’t you stop it? In the event that you do stop the assassination, this event is no longer compatible with your history (timeline). What has happened is the timeline has branched off from your previous timeline and began another world (meaning dimension). This is the theory that the X-Men movies used when they made X-Men: Days of Future Past. In this event, you are able to bring about a change, but not a change in the way that we typically think of. The change would not be reflected in your history. Instead, the branch timeline would be different from your timeline. So, the change isn’t a change in the sense that one object contains contradictory properties at different times. Instead, the change only be two different timelines. So, you are in a way changing something, but the term “change” wouldn’t be the used in the normal fashion. Regarding the previous question concerning killing your ancestor, you would still exist because your timeline was not changed, but the new branched timeline would not contain a version of you. Though, it is not certain that you could ever return to your original timeline. Dimensional hopping is different than time traveling. This will be discussed briefly below.

Branching Theory

  • Then, does B-Theory rule out free will?

No.  B-Theory is compatible with libertarian free will, soft determinism, and determinism (or some call this predestination), but it does not necessarily entail any of these views. Saying the spacetime continuum is static says nothing about the will and the ability to act. B-Theory commits one to determinism no more than a history book commits one to determinism.

  • Perhaps time travel in TV shows is just dimensional hopping?

In my estimation, probably. In Dr. Who, The Flash, and Agents of SHIELD, they all have the ability to travel to different times and change the past and future. But, as we have seen, time travel is only possible under very strict circumstances and necessarily removes the ability to change things for that particular timeline. Thus, to keep these shows’ continuity, they might just be dimensional hopping  into different spacetimes and changing things or they are creating multiple branches of timelines off of the original. This would answer the question of how they know they changed the timeline as we saw in the question regarding change.

So, those are my thoughts on time travel! A very interesting conversation and one I hope you enjoyed! For some further reading on the metaphysics of time try these books and articles:

  • “The Unreality of Time” by JME McTaggart (1906) This is where A-Theory and B-Theory were coined.
    • This is a fairly high academic article on time.
  • Travels in Four Dimensions: The Enigmas of Space and Time by Robin Le Poidevin
    • This book is a great introduction to the time discussion on an academic level.
  • Experiencing Time by Simon Prosser
    • More of a higher academic level book.
  • Metaphysics: A Very Short Introduction by Stephen Mumford
    • A more simple read, containing one chapter on time, but other chapters on change and causation.

I hope you have enjoyed this rather long blog! Next week I will return to my 600-word guideline. Until then, think well and live an examined life.

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