As usual, Lil has been enjoying a range of summer camps from the long-lived Columbia Association Nature Camp to a couple weeks doing Ballet Intensives at her dance studio, Ballet Mobile. I loved when she achieved the next level of canoe instruction, which means she doesn't need a counselor. I love the music and history from ballet that she brings up in the car when hearing a piece of music on the radio.
But when we arrived at Johns Hopkins Center for Talented Youth (CTY) last week for the ending open house, we received a book of essays as the final product for Big Questions. Since the kids were doing presentations on various philosophical elements, I didn't get a chance to read it until that night. This isn't perfect, but it's pretty awesome to see what's turning over in her mind. We had fun discussing time travel, but I didn't know she had picked it for her essay topic. It turns out her instructor, Andrew Fyfe, had also written about time travel in a collection about J. J. Abrams, discussing Lost and Star Trek.
As I did, Lil is enjoying her time at CTY each summer. Sandy Spring Friends School is a great venue for it and she can't wait to return next year for her final year as a "Young Student." Maybe she'll head overseas like I did when I was 15 for an amazing summer abroad - SANS parents!
You Can’t Change the Past
There is no scientific consensus on whether time travel into the past will be possible for us in the future. But in this paper I aim to resolve the following question: “If time travel into the past turns out to be possible one day, will that mean we can change the past?” After all, if I could travel back into the past, it seems like I could then affect and change the past.
Before I get started answering whether backwards time travel makes changing the past possible, I need to lay out the several ways time travel could work. Then I will discuss in Section §3 whether on any of these methods changing the past would be possible.
§2. Methods of Backwards Time Travel
Here is a list of the three ways in which backwards time travel might turn out to work:
Method 1. It might turn out to be true that there exist parallel universes. Parallel different universes that unfold all the ways ours didn’t. If this turns out to be true, there will be parallel universe that are only slightly different from our universe and others that differ radically. One form of what we might consider backwards time travel would be to travel to a similar one of these parallel universes but arrive in their past. For example, to leave our universe in 2020 in our time machine and arrive at a similar parallel universe in the year 1939.
Method 2. Time travel might involve alternate timeline rather than parallel universes. Suppose I leave 2050 in a time machine and travel back to the year 1939. In doing this, I may cause a new timeline to splinter off from my original history. Now there will be two ways out universe unfolded, the original way from which I departed in 2020 and the new way which includes me arriving in my time machine in 1939.
Method 3. Maybe there don’t exist parallel universes for every possible way the universe can unfold. Maybe it isn’t possible for there to be more timelines beyond and alternate to the one we already know about. There is just this one universe and just this one timeline. If that is the case and if time travel turns out to be possible, then time travel would involve traveling back into the past of our own universe and our original timeline.
These seem to be the three possible ways backwards time travel could logically work if it turns out to be scientifically possible. Now I will turn to my central question concerning whether it could ever come to be discovered possible to not just travel back into the past but change the past. I can now answer this question by examining whether changing the past would be possible on any of the three methods time travel might turn out to work if time travel turns out to be possible at all.
§3. You Can’t Change the Past
It is clearly the case that you wouldn’t be changing the past if time travel turns out to work either in the way described by Method 1 or Method 2. The problem with these two methods of backwards time travel is that you are not changing your own past. In Method 1 you are changing the present of the parallel universe you went to. In Method 2 you are creating a new timeline with that new difference. But in each case, your original universe or timeline would still exist exactly as it always was before you engaged in your “time travel” antics.
So the only chance for changing the past is Method 3. In Method 3, time travel would involve traveling back into the past of our universe and be contained in the one and singular timeline of our universe. If time travel of the sort described by Method 3 turns out to be possible, couldn’t I then travel back into the past of my universe and timeline and change how it originally went? Couldn’t I go back in time from 2020 and delete the Holocaust from the history of the universe by assassinating Hitler in 1939? Sadly, no. Even on Method 3, changing the past would still be impossible.
History has already happened, you can’t change it! After all, if you were successful in changing the past of this universe and our timeline and thereby eliminating the holocaust from the history of the universe then why did you come back from the future and kill Hitler in the first place? If you kill him there would be no Holocaust and so no reason to kill this random person! You came back from the future because the Holocaust did happen (in some universe or some timeline) and you wanted to stop it for some other universe or in some other timeline. But it makes no logical sense to eliminate it from your own universe and timeline. It must exist in your universe and timeline because that’s why you are time traveling in the first place!
So how would time travel work if it turns out to work in the way described by Method 3? Wouldn’t it have to be possible to change the past if I could travel back into the past of my own universe and timeline? So let’s imagine that backwards time travel turns out to exist and that time travel turns out to work as described by Method 3. Further imagine that you enter a time machine in 2050 on a mission to stop Wilkes from shooting Lincoln. You come into the Ford’s Theater booth with your period revolver in order to fit into the era. Wilkes is getting his pistol ready. Then Wilkes gets ready to shoot, but notices something wrong with his pistol. He cocks his head to the side just as you shoot. You miss. It turns out that you shot Lincoln this whole time. Historians got it all wrong because Wilkes fled the scene. Wilkes just didn’t want to be blamed for what happened.
As my example shows, you might be able to travel back into the past of your own universe and timeline to try and change the past by preventing the assassination of Abraham Lincoln, but whatever you do will inevitably end up being something you already did in history. If you go back to stop the assassination of Lincoln, we know you fail because we know how the history of our universe and timeline unfolded. But perhaps we have it a little wrong. Perhaps it was a time traveler with bad aim that killed Lincoln. But no time traveler can change the past even if a time traveler might already be a part of our past.