Backward Time Travel Is Impossible

Everyone knows that time travel is real – it happens every day. Every time an astronaut launches into orbit, he or she experiences very slight time dilation, which means that they experience time at a slower rate than people on Earth. There are also creatures that freeze themselves during the winter, experiencing a state of suspended animation. Each of these techniques could allow a being to theoretically transport themselves far into the future. Unfortunately, without the ability to return to the present, this isn’t very useful.

Have you ever wondered what it would be like to go back in time? Well if you have any imagination at all, chances are you have. After all, who wouldn’t want to go back and walk with the dinosaurs, hang out with Abraham Lincoln or invest in Microsoft? The possibilities are endless – at least they would be if backward time travel was possible.

Before we can discuss its impossibility, we must first discuss the different theories about how backward time travel could potentially work. Of course, the technological requirements remain unknown, but the theory regarding how backward time travel would affect our world can be divided into the following general categories, summarized in the following table:

Characteristic Time Travel Theory
Fixed History Flexible History Alternate History
Description There is only a single, unchangeable timeline There’s only a single timeline, but we can change it Each action in the past produces a new timeline
In Film 12 Monkeys, The Terminator Back to the Future, Looper Terminator 2: Judgment Day, Star Trek (2009)
Problems No free will Paradoxes Can’t return to original timeline

The difference between the three interpretations can be illustrated using the story of a man who travels back in time to assassinate an infant Adolf Hitler in order to prevent World War II.

If history is fixed, then the man will not be able to prevent Hitler from coming to power. In fact, his actions will actually prove necessary for this to happen. Perhaps the man fails in his attempt to murder the child, and by doing so, scars the child and plants the seed necessary for Hitler’s evil actions. Or maybe he successfully dispatches the infant, but the family later adopts another child, naming it after their lost son, and the adopted child becomes the Hitler from history. Whatever the case, the man’s actions can’t affect the future because, from the vantage of the future, they’re already a part of the past.

With a flexible history, the man may successfully kill Hitler and prevent World War II. However, by preventing such a monumental historical event, the entire future is changed. Perhaps his grandparents never immigrate to the United States, so his parents never meet and, consequently, he’s never born. And if he’s never born, then how can he go back in time and kill Hitler? Of course, if the man doesn’t exist, then World War II happens, and the man now exists. This is known as a grandfather paradox, and it is inescapable, which is one reason why the third theory seems so attractive.

Perhaps the man does travel back in time and successfully assassinates Hitler, but instead of changing the future, an entirely new future is created. This understanding of backward time travel allows the man to change the past while preventing paradoxes from occurring. However, because the man has created a new timeline – a new universe – he is now unable to return to his own. After all, if he really has changed the past, then the future he knew no longer exists, or it exists in an alternate reality.

Another reason why this view seems to make sense is the growing belief that there are an infinite number of parallel universes. In a feeble attempt to understand the implications of quantum physics, popular culture has sifted a few concepts, including the many-worlds interpretation, which implies that all possible timelines exist in alternate realities (or universes). Although this idea would seem to support the possibility of backward time travel, we’ll see that no matter which theory we subscribe to, backward time travel is impossible.

Let’s begin by addressing the first option: fixed history theory. Imagine that you have possession of a working time travel machine, so you decide to travel back in time ten minutes to give yourself a high five. Well if history is immutable, then you won’t be able to high five yourself, or even see yourself, because you don’t remember seeing yourself ten minutes ago. See, this theory only works if we assume that the term history implies grand, complex events that no living person remembers (or of which they deny memory). If we try to change something simple and knowable, then it becomes obvious that we really should be able to change the past. So we’re left with two options: either backward time travel never ends up occurring, or history is not fixed.

Before we move on, let’s stop to discuss what we mean when we say that backward time travel is impossible. This doesn’t necessarily require that the technology is never invented; it could be that it’s just never implemented. After all, in order for us to do something, we need the both the opportunity and desire to do it. Perhaps backward time travel never happens because we decide that it shouldn’t.

Anyway, what if our history is flexible and allows us to go back and change things? Well, aside from the previously mentioned grandfather paradox (and others), there’s also no record in our history of anyone back in time and messing around. This could be due to the skill and secrecy of the travelers, but it’s difficult to imagine that no one in all of time was accidentally discovered or decided to reveal their secret. Of course, if a hidden organization tightly controlled the technology, then it might be safe. However, this would require that the secret would never be revealed throughout all of history. It would also mean that no one else ever invents time travel, otherwise they would both be editing each other’s pasts, producing competing time travelers. Basically, backward time travel can’t happen with a flexible history because it produces paradoxes, and it won’t happen because anyone who invents it will be assassinated by an opposing group. This is because backward time travel is power – the power to make the world the way you want it to be – and it’s pretty likely that no one would be comfortable with anyone else holding such power.

And so we come to alternate history theory (also known as parallel universe theory). This concept seems plausible. After all, it allows us to change history, it doesn’t produce any paradoxes and it also seems to be supported by science. However, a problem occurs when we imagine the ramifications of an infinite number of alternate realities combined with backward time travel. If there are an infinite number of universes, then all possibilities have occurred an infinite number of times. So if backward time travel is possible, then there are an infinite number of realities in which it exists. That means there’s a universe where a person from the future decided to visit you right now. But no one is visiting you from the future, so this can’t be the case.

Some would argue that the number of universes only increases (via branching) when a backward time traveler changes something, but this implies that there’s a specific number of universes, which violates the zero, one or infinity rule. It also would mean that there’s only one original universe, which means that there’s only one chance for time travel to be invented and implemented. In addition, if traveling back in time produces a new and separate future, then there really isn’t any reason to go back in time. Think about it. If you go back time to assassinate Hitler and succeed, you didn’t really kill him, you only created a new universe in which he’s dead. In this way, backward time travel is actually completely useless since we’re unable to affect anything in the present, only create a new present where things are different. It’s like trying to save your dog from cancer by getting a new dog.

And just in case you still think time travel might happen, there’s a secret society whose members have sworn an oath, passed down through generations, that should backward time travel be invented, they will go back and stop it before it starts.

The Brain: Part I

What makes us who we are?

This question seems intriguing, but it’s actually far too vague to have any real meaning. This is also the case when people ask, “what is the meaning of life?” They think they’re being insightful, but without specifying what they’re trying to discover, the answer is made indiscernible, and the question becomes useless. To illustrate this problem, try to determine the meaning of the subject in any of the following questions:

  • What is the meaning of broccoli?
  • What is the meaning of basketball?
  • What is the meaning of five dollars?
  • What is the meaning of a question that asks about the meaning of life?

As we can see, asking such poorly-phrased questions leaves far too much room for interpretation. It’s likely that they meant to ask something like, “for what reason was life created?” or “what is the purpose of  human existence?” Now let’s return to our original inquiry, improving its structure in order to allow for a meaningful answer.

What properties possessed by an individual human distinguishes them from other humans?

Even this more pointed question still retains many different avenues of response. After all, a fingerprint is unique and distinguishes each human from all others. But the question seems philosophical in nature, so it probably doesn’t aim to address the mere physical. Its phrasing also suggests that there’s more than one correct answer, though we’re probably just looking for the most interesting and insightful one. Let’s try again.

What feature of a person contains the most crucial and meaningful components that make them a unique individual?

Now we’re onto something. We all know that everyone is unique, and we can easily distinguish one person from others, so let’s start our question for a solution by examining the ways that we tell each other apart and see if one of them satisfies our inquiry.

The first and most obvious way that we recognize each other is by our appearance. It’s true that we’re covered by clothing and makeup much of the time, and it’s also true that each of us has our own fashion sense that we pretend is unique, and yet we’re still able to recognize each other in a swimsuit or bizarre costume. This is because there’s a special part of the brain responsible for facial recognition, and it helps us tell others apart. However, few would agree that our bodies or our faces make us who we are. In the 1997 action movie Face/Off, FBI agent Sean Archer and criminal mastermind Caster Troy (played by John Travolta and Nicholas Cage irrespectively) have their faces switched. While the premise and execution of this film is obviously bad, it teaches us that we aren’t defined by our appearance. There are also those who tragically suffer amputations or facial deformation, and while they may ask serious questions about their own identity and purpose, others certainly identify them as the same person.

Those who subscribe to a materialistic view would likely argue that it’s our genetics that make us who we are. According to them, since everything can be explained by natural processes, then everything about us is derived from our genes: our appearance, ideas and abilities. On top of that, each of us has our own unique genetic code, or do we? Identical twins actually share the same DNA and, while irritatingly similar, they aren’t the same person. If two people with identical genetics can be distinct, then this can’t be what defines us.

The world is full of those whose quest in life is fame and wealth. In many ways their identity is tied to their notoriety and possessions, but even pop culture recognizes that money doesn’t define who we are. In her autobiographical 2001 hit single Jenny From The Block, Jennifer Lopez pleads with audiences, “don’t be fooled by the rocks that I got,” and goes onto claim that despite her wealth and status, “[she’s] still Jenny from the block.” This implies that her identity remains static despite the fact that she, “used to have a little, now [she] has a lot.”

If it isn’t her wealth and fame, maybe Ms. Lopez’ talents and accomplishments as a dancer, singer, songwriter, author, actress, fashion designer and producer that define her. After all, each of us possess unique skills and abilities that make us special (at least that’s what our mothers told us). It’s true that our skills, abilities, achievements, vocations and interests define us to a degree. An example of the value we place on our job is the fact that the first question we ask a new acquaintance is often what do you do? Many of us derive our identity primarily from our profession. However, when we encounter failure, disability or retirement, we’re still us.

So clothes don’t make the man and neither does the body. Our genes don’t make us unique individuals. On top of that, wealth and fame don’t define us and neither do our abilities or achievements. So what could it be? Perhaps we can find the solution by examining cases of people who are no longer identified as the person they once were. Unfortunately there are millions of examples of such cases.

Dementia comes in many forms, the most common being Alzheimer’s disease. Those suffering from dementia experience a number of symptoms including memory loss, memory distortion, speech and language problems, agitation, loss of balance and fine motor skills, delusions, depression and anxiety. These symptoms are caused by changes in the brain brought on by nerve cell damage, protein deposits and other complications. In advanced cases, the person may become unrecognizable to loved ones. Visiting family members may be shocked to find their relative or friend using abusive language, exhibiting violent aggression or making inappropriate sexual comments.

Brain damage can also produce equally drastic changes in people. In her article After Brain Injury: Learning to Love a Stranger, Janet Cromer details the story of her husband, who suffered anoxic brain injury. She discusses the impact of brain injury on her husband’s memory, communication, behavior and personality. She notes that the experience is like getting to know him all over again, summarizing it this way: “Imagine feeling like you’re on a first date even though you’ve been married to this person for… 30 years?”

It’s clear that our identities are largely defined by our personalities. The things we love and hate, the ways we think and act, even our way of standing perfectly still – they all define who we are. When these things change, we change. But there’s more to us than simply what we think, do and say.

The other way that we can observe changes in identity is though memory loss. In addition to the aforementioned cases of dementia, retrograde amnesia can also impair or rewrite personal identity. While most of us have no experience with amnesia, it’s obvious that a loss of knowledge of identity is a loss of identity. After all, how can you be someone you’ve never heard of? But memories don’t just allow us to recognize our own identity, they also define us, for we are obviously and seriously affected by our experiences. Brain scans reveal that those who have been traumatized, especially at a young age, actually show clear physical changed in the brain.

Though it’s pure fiction, there are cases in which we accept that a person’s identity has changed. Hollywood provides us with many examples of instantaneous change of identity due to mind transfer. In the 1976 film Freaky Friday, a mother and daughter miraculously have their memories switched (as well as their personalities). While the story may not be the most plausible, we clearly understand that the two characters are no longer themselves. 2001’s K-PAX tells the story of an alien being called Prot who inhabits the body of a human named Robert Porter. At the end of the film, the alien abandons its human form, leaving behind a catatonic Porter. Upon his departure, Prot’s former body is no longer recognizable by his friends, one of whom remarks, “That’s not Prot.”

These examples also illustrate how important memory is to our identity. Without the transference of memory, the characters would retain the knowledge of their past, including their own identity. And this is precisely why the existence of reincarnation is largely inconsequential. If we possess only the memories of ourselves, then it doesn’t matter if our life is the continuation of another. If a person experienced reincarnation or a mind transfer, but did not retain any memory, then they would be unable to identify as anyone but their current self and would therefore possess a unique identity. So don’t do good for the sake of your reincarnated self, for the being you will be will not be you.

And so we have our answer: it is our personality and memory that make us who we are. And although there is great uncertainty about how it actually works, these features are produced and stored in the brain, which somehow projects consciousness (also known as the mind). Our minds allow us to perceive, think and imagine, and while its existence is arguable metaphysical, the mind gives rise to identity. So identity is actually stored in and generated by the brain.

Now we can rest in the knowledge that our identity is safely locked inside a squishy mass hidden behind a quarter inch of bone. Unfortunately the brain remains a very mysterious and peculiar thing. In part II we will explore some of the curiosities and limits of this mighty organ that defines us.