I have been a science fiction fan since I was a child. One of my favorite science fiction genres is time travel. I used to love reading books and short stories that involved the ability to travel to the past and future. As a youngster, such tales were attractive due to their adventure – and what an adventure traveling to the age of the dinosaurs, or visiting other past famous historical events would be, right? Now that I’m an old fart, any reverie I entertain about traveling to the past these days involves being able to see and talk to the people I loved who are no longer here, just one more time. Wouldn’t that be nice? It sure would.
Have you ever really thought about it? Would you be interested in time travel? Where would you go? To the past, or the future? You might as well flip a coin, as these appear to be the only choices. Well, not really. Sadly, there is actually only one choice.
I’m bummed to say it, but travel into the past does not appear to be in the cards. Why? The major reason time travel to the past is not possible is due to what is called the “causality problem” that travel to the past would pose. You see, we just happen to live in a universe where causes precede effects, not the other way around. Expose yourself to enough sunlight and you’ll get a sunburn. Drop a car battery on your foot and it will hurt like hell. A causes B. For example, try this – at this specific moment in time, bang your fist on the table. Now try to hang onto this moment. Oops. Too late. It’s gone. The act of banging your fist on the table is now in the past. It is no longer in the present and there is no getting it back.
There literally is no escaping it. The past is, in the words of Scottish comedian Billy Connolly, “Fucking over! It’s over!” Still, people like to fantasize about time travel to the past and one thing that is keeping this topic alive is the current scientific theory of the nature of time, which is accepted by most scientists today. (As you read about it, keep this fact in mind.) This theory is known as the block universe theory and it essentially states that the past, present and future are all real and all exist at the same time!
Say what? Yep, stay with me here.
Eternalism
According to the block universe theory, that past bad haircut you got is just as real right now as the monitor you’re staring at and that piece of cake you’re going to enjoy on your birthday next year. This theory is also known as the eternalism view of time, for obvious reasons. The past, present and future is just one continuous time stream laid out both before and behind us, all at the same time. All are equally real, right now.
There is, however, a current alternative view of time known as the presentism theory of time, again for obvious reasons. In the presentism theory of time, the past and future are not real; the past is done and gone, the future hasn’t happened yet, and the only thing that is real is the present moment, what we would call now.
Presentism
Please note that this theory isn’t saying that the past and future are not real, for they are real. They’re just not all real at the same time. They’re saying that the past has already happened and has receded, i.e., it’s gone; while the future, whatever it holds, will happen, but just hasn’t happened yet. We exist in the present moment, the now, a living bridge between the past and future. Of course, the now is real, too, right now.
I’ll have much more to say about these two theories in the near future (no pun intended). As you might guess, these theories have a lot of information that needs to be unpacked. For now, be aware that they are real theories and that the block universe theory is so far enjoying its moment as the reigning theory. Why in the world is this the case? Well, without getting bogged down into the details and at the risk of oversimplifying, the main reason scientists are accepting this theory is due to thousands of experiments that clearly demonstrate the fact that the laws of physics seem to work just fine, whether run forward or backward, without any need of time. This knowledge has led a number of noted scientists to declare that time itself is not real, time is an illusion.
What? I know, this is weird and difficult to accept.
Okay, a quick example might help. Imagine sitting in your family room watching a 5-minute film of a child tossing a ball into the air and catching it, over and over (you’re easily amused). You now get up and go to the kitchen for a snack. While you’re gone, your kid starts playing the film in reverse. Snacks in hand, you now return to the family room and start watching the film again. You would not know it was running in reverse! It looks the same, forward or backward. Know this: a room full of physicists armed with pocket protectors and slide rules would all tell you that the laws of physics governing that girl throwing and catching a ball work exactly the same whether run forward or in reverse. It’s very strange, but physics just doesn’t care about time.
If you think about it, we typically will only notice something odd if a film we’re watching in reverse breaks the law of causality; for instance, if we watched a vase suddenly pick itself up from a hundred pieces on the floor, reassemble, and jump back fully reformed onto the table from which it fell. We’d all be screaming, “Bullshit!” Right? That’s because we all know that the universe we live in doesn’t allow this. That’s not the way our world works! In our universe we have this thing called the 2nd law of thermodynamics, otherwise known as entropy[i], that prevents disordered things from becoming more ordered. In our world, new things, even people, grow old, wear out and break down. Entropy never reverses.
Intermission: Note that the statement I just made is one most people would agree with. But technically, there are two things wrong with what I just said. First, I said that the second law of thermodynamics is a law. Wrong. It isn’t a law. The second thing I said is that entropy cannot reverse. Not true. Entropy could reverse. This is just a teaser for my upcoming posts about entropy. Entropy is… interesting.
Returning to the topic of time travel, you should note that if the block universe theory is valid, then the past exists at the same time as both the present and the future and thus, it would seem that theoretically at least, there might be some way to reach it, if we could just figure it out. Certainly, it would remain a topic of conversation and continue to be an object of desire for those who wish to travel to the past. We need to be careful, however, as we may find ourselves in a situation of, “be careful what you ask for.” Why? I’m sure you have heard about or seen movies or read stories depicting the incredible trouble one can get into going back into the past and changing something that affects the future. Here’s a hint, “Don’t step on that butterfly!” (10 points if you can name the author!) I’ll put the final nail in it with this thought – go back into the past and kill your grandfather. See where that gets you. Don’t you think it’s funny that no one from the future has yet visited us? What does this tell us?
As for traveling to the future, believe it or not, that’s definitely possible, once we overcome some technical issues. For example, we need to have a space ship that can approach the speed of light, and we have to have the technology to survive such a trip. This is because, as Einstein showed us in his theory of special relativity, the faster your spaceship goes, the slower time passes inside the ship. By the way, if you want to know why clocks tick slower when moving through space, you can read this post: Is Time Dilation a Jedi Mind Trick?
Here’s how time travel to the future works: If your ship left earth and traveled near the speed of light, it might only take a minute to reach the nearest star system. But back on earth, four years would have passed! Now, the ship turns around and heads back to earth at near the speed of light and “Voila!” our astronaut would’ve experienced another minute of travel, while back on earth another 4 years would have passed! Thus, the result of a one-minute flight to the nearest star system and a one-minute flight back to earth (according to the experience of the astronaut) is that our astronaut would land on earth 8 years into the future, while he would have only aged a few minutes. Cool, heh?
Have you heard of the twin paradox? This is where one twin goes up in a very fast spaceship while the other stays on earth, then a year later the twin from space lands, only now he is younger than the twin he left behind on earth. I’m not sure why this is called a paradox, because it isn’t a paradox, but it’s sure an interesting problem to consider. The math doesn’t lie. This could happen. In fact, not long ago two real twin astronauts were separated with one going to the space station for a year while his brother remained on earth. In this actual case, however, the astronaut from the space station actually aged more than the one on earth. Doh!
Does this disprove the theory? Nope. We need to remember that the astronaut in the space station wasn’t traveling even remotely close to the speed of light, plus while on the station he was exposed to radiation and all the stresses associated with space travel. So, the jury is still out on this, although most scientists feel Einstein would once again be proven correct, if we could but test it.
These days I don’t have much interest, other than curiosity, in discussions of time travel, as such a thing is never going to happen in my lifetime. At least, that’s what I believed until I discovered neuroscientist Dr. Dean Buonomano. His book, Your Brain is a Time Machine: The neuroscience and physics of time.[ii] Dean steps carefully over and around the physics of time and looks at time in this book through the lens of neuroscience, the way our brains look at and experience time.
I will explore Buonomano’s research and his book in a future post. In the meantime, let me just state this emphatically – the way we experience time is very different from the way scientists describe time! This, by the way, is a very real conundrum and it’s a problem of which Einstein was painfully aware, too. It bugged him.
While the current scientific data paints a picture of us all living in the block universe I described above, where past, present and future all exist at once, I believe we all recognize that this is definitely not the universe any of us experience on a daily basis. Not even close! And really, if you think about it, the alternative “presentism” universe – a universe where the past is done, gone, and no longer real; where the future isn’t real yet, and only the present is real now – is a universe much more akin to the way each of us experiences time daily, don’t you think? It’s certainly more intuitive.
But the current scientific data doesn’t stop there. Nope. The data takes us one step further and tells us that in addition to time itself being an illusion, the manner in which we experience time – you know, that feeling of the passage or flow of time — that one experience we all would find so exceedingly strange if we did not feel it – is an illusion! Even Einstein believed this to be the case. I find this disturbing.
These are fairly significant illusions, don’t you think? Think about it. If time itself and our experience of the passage of time are illusions, it begs huge questions about both how and why such illusions occur. These are really important questions for us humans, because they strike at the core of who we are as a species.
[i] Put simply, Entropy is defined as a state of disorder or decline into disorder. I’m working on another post that does a deep dive into entropy, a fascinating topic.
[ii] Dean Buonomano’s book was published in April 2017
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