Time is difficult to explain. When looking for a dictionary explanation, time is described as "the general term for the experience of duration." But what is duration?
We have contradictory ways of speaking about time. We think of time as a quantity. It is something we waste, spend, or save. We also think of time as a medium we are passing through every day.

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The idea of time travel is a very recent idea that starts with H.G. Wells's 1895 novel, The Time Machine. After that, we find the concept in American science fiction, or in modernist literature - each twisting time in new ways, to explore the unpredictability of memory.
Stephen Hawking also played with the idea of time travel. He proposed the idea that it can't happen because it didn't happen.

The idea of time travel

The internet changed our perception of time: We're looking at the past on our video screens, and it's just as clear as something in the present, making it feel like an unending present.
Time travel is also a powerful way to imagine what the future might bring. Time travel allows us to explore the consequences of our worst tendencies.

Our perception of time

Over 50 scientific papers are published a year on the idea of time travel. Even though they will probably never solve the problem of time travel, they still love to talk about wormholes and dark matter.
Einstein, with his theory of relativity, spoke of time as a fourth dimension. After that, Hermann Minkowski said that we should talk about space and time as a union of the two, spacetime, where the future already exists, and the past still exists. Today we're comfortable talking about time as a fourth dimension.

Scientists and time travel

One of the reasons we continue to be so fascinated with time travel is that we can go back and undo our mistakes. Then we also have a curiosity about the future.
However, every time travel story is about death. The idea of time travel is ultimately about our desire to defeat death.

Time travel is fascinating

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Since H.G. Wells imagined that time was a fourth dimension-and Einstein confirmed it-the idea of time travel has captivated us. More than 50 scientific papers are published on time travel each year, and storytellers continually explore it-from Stephen King's JFK assassination novel 11/22/63 to the steamy Outlander television series to Woody Allen's comedy Midnight in Paris. What if we could travel back in time, we wonder, and change history? Assassinate Hitler or marry that high school sweetheart who dumped us? What if we could see what the future has in store?
These are some of the ideas that bestselling author James Gleick explores in his thought-provoking new book, Time Travel: A History. Speaking from his home in New York City, he recalls how Stephen Hawking once sent out invitations to a party that had already taken place; why the Chinese government has branded time travel as "incorrect" and "frivolous"; and how the idea of time travel is, ultimately, about our desire to defeat death.
Let's cut right to the chase: What is time?
Oh, no, you didn't! [Laughs.] In A.D. 400, St. Augustine said-and many people have said the same thing since, either quoting him consciously or unconsciously-"What, then, is time? If no one asks me, I know. If I wish to explain it to one that asks, I know not." I think that is actually not a quip, but quite profound.
The best way to understand time is to recognize that we actually are very sophisticated about it. Over the past century-plus, we've learned a great deal. The physicist John Archibald Wheeler said, "Time is nature's way to keep everything from happening all at once." If you look it up in a dictionary, you get stuff like, "The general term for the experience of duration." But that's just completely punting because what is duration?
I try to steer away from aphorisms and dictionary definitions, just to say two things. First, that we have a lot of contradictory ways of talking about time. We think of time as something we waste, spend, or save, as if it's a quantity. We also think of time as a medium we are passing through every day, a river carrying us along. All of these notions are aspects of a complicated subject that has no bumper sticker answer.
"Maybe Time Doesn't Even Exist" As chief time scientist at the U.S. Naval Observatory, Demetrios Matsakis has developed some interesting theories about time.
When does the idea of time travel first appear in the West? And how did it impact popular culture?
I assumed, as a person who always read sci-fi a lot when I was a kid, that time travel is an obvious idea we're born knowing and fantasizing about. And that it must always have been part of human culture, that there must be time travel Greek myths and Chinese legends. But there aren't! Time travel turns out to be a very new idea that essentially starts with H.G. Wells's 1895 novel, The Time Machine. Before that nobody thought of putting the words time and travel together. The closest you can come before that is people falling asleep, like Rip Van Winkle, or fantasies like Charles Dickens's A Christmas Carol.
The beginning of my book is an attempt to answer the question, "Why? Why not before? Why suddenly at the end of the 19th century was it possible-necessary-for people to dream up this crazy fantasy?" Even though it's H.G. Wells who does it, people pick up his ball very quickly and run with it. You find it in American science fiction that started appearing in pulp magazines in the 1920s and 1930s, or in the great new modernist literature of Marcel Proust's In Search of Lost Time, James Joyce, and Virginia Woolf.
<img src="https://natgeo.imgix.net/03-book-talk-time-travel.adapt.590.1.jpg?auto=compress,format&amp;w=728"> Physicist Stephen Hawking is one of many scientists to explore whether time travel is theoretically possible. PHOTOGRAPH BY PAUL E. ALERS, NASA
All these writers were suddenly making time their explicit subject, twisting time in new ways, inventing new narrative techniques to deal with time, to explore the vagaries of memory or the way our consciousness changes over time.
In 1991, Stephen Hawking wrote a paper called "Chronology Protection Conjecture," in which he asked: If time travel is possible, why are we not inundated with tourists from the future? He has a point, doesn't he?
Yes! He even scheduled a party and sent out an invitation inviting time travelers to come to a party that had taken place in the past. Then he observed that none of them had shown up. [Laughs.] Hawking is one of these physicists who love playing with the idea of time travel. It's irresistible because it's so much fun! When he talks about the paradoxes of time travel it's because he's reading the same science fiction stories as the rest of us.
The paradoxes started appearing in magazines aimed mostly at young people in the 1920s. Somebody wrote in and said, "Time travel is a weird idea, because what if you go back in time and you kill your grandfather? Then your grandfather never meets your grandmother and you're never born." It's an impossible loop.
Hawking, like other physicists, decided, "Time is my business. What if we take this seriously? Can we express this in physical terms?" I don't think he succeeded but what he proposed was that the reason these paradoxes can't happen is because the universe takes care of itself. It can't happen because it didn't happen. That's the simple way of saying what the chronology protection conjecture is.
How have the Internet and other new technologies changed our perception and experience of time?
We are just beginning to see what the Internet is doing to our perception of time. We are living more and more in this networked world in which everything travels at light speed. We are multitasking and experiencing new forms of simultaneity, so the Internet appears to us as a kind of hall of mirrors. It feels as though we're embedded in an ever expanding present.
Our sense of the past changes because in some ways the past becomes more vivid than ever. We're looking at the past on our video screens and it's just as vivid if the movie is about something that happened 20 years ago, as if it is a live stream. We can't always tell the difference. On the other hand, the past that's more distant-and isn't available in video form-starts to seem more remote and fuzzier. Maybe we are forgetting how to visualize the past from reading histories. We're entering a new period of time confusion, in which we suddenly find ourselves in what looks like an unending present.
In 2011, the Chinese government issued an extraordinary denunciation of the idea of time travel. What was their beef?
They thought it was corrupting and decadent. It's a reminder that time travel is neither a simple nor innocent idea. It's very powerful. It enables us to imagine alternative universes, and this is another line that science fiction writers have explored. What if someone was able to go back in time and kill Hitler?
<img src="https://natgeo.imgix.net/02-book-talk-time-travel.adapt.352.1.jpg?auto=compress,format&amp;w=728"> H.G. Wells introduced the idea of time travel with his novel The Time Machine. PHOTOGRAPH BY ULLSTEIN BILD, GETTY
Time travel is also a powerful way of allowing us to imagine what the future might bring. A lot of futurists nowadays tend to be dystopian. Time travel gives us ways of exploring how the worst tendencies of our current societies could grow even worse. That's what George Orwell did in 1984. I imagine the Chinese government doesn't particularly want the equivalent of 1984 to be published in Beijing. [Laughs.]
More than 50 scientific papers a year are now published on the idea of time travel. Why are scientists drawn to the subject?
Scientists live in the same science fictional universe as all the rest of us. Time travel is a sexy and romantic idea that appeals to the physicist as much as it appeals to every teenager. I don't think scientists are ever going to solve the problem of time travel for us but they still love to talk about wormholes and dark matter.
There's a fascinating coincidence in the early history that when H.G. Wells needed to set the stage for his time machine hurtling into the future, he decided not to just jump right into his story but set the scene with a framing device-his time traveler lecturing a group of friends on the science of time-in order to justify the possibility of a time machine. His lecture introduces the idea that time is nothing more than a fourth dimension, that traveling through time is analogous to traveling through space. Since we have machines that can take us into any of the three special dimensions, including balloons and elevators, why shouldn't we have a machine able to travel through the fourth dimension?
A decade later, Einstein burst onto the scene with his theory of relativity in which time is a fourth dimension, just like space. Soon after that, Hermann Minkowski pronounced that, henceforth, we were not going to talk about space and time as separate quantities but as a union of the two, spacetime, a four-dimensional continuum in which the future already exists and the past still exists.
I'm not claiming that Einstein read H.G. Wells 10 years before. But there was something in the air that both scientists and imaginative writers were empowered to visualize time in a new way. Today, that's the way we visualize it. We're comfortable talking about time as a fourth dimension.
You quote Ursula K. Le Guin, who writes, "Story is our only boat for sailing on the river of time." Talk about storytelling and its relationship to time.
One of the things that has happened, along with our heightened awareness of time and its possibilities, is that people who invent narratives have learned very clever new techniques. Literal time travel is only one of them. You don't actually need to send your hero into the future or into the past to write a story that plays with time in clever new ways. Narrative is also how everybody, not just writers, constructs a vision of our own relationship with time. We imagine the future. We remember the past. When we do that, we're making up stories.
<img src="https://natgeo.imgix.net/04-book-talk-time-travel.adapt.590.1.jpg?auto=compress,format&amp;w=728"> In Groundhog Day, Bill Murray's character uses time travel to indulge his vices and, eventually, fix his mistakes. PHOTOGRAPH BY COLUMBIA PICTURES, GETTY
Psychologists are learning something that great storytellers have known for some time, which is that memory is not like computer retrieval. It's an active process. Every time we remember something we are remembering it a little bit differently. We're retelling the story to ourselves.
If time travel is impossible, why do we continue to be so fascinated with the idea?
One of the reasons is we want to go back and undo our mistakes. When you ask yourself, "If I had a time machine, what would I do?" sometimes the answer is, "I would go back to this particular day and do that thing over." I think one of the great time travel movies is Groundhog Day, the Bill Murray movie where he wakes up every morning and has to live the same day over and over again. He gradually realizes that perhaps fate is telling him he needs to do it over, right. Regret is the time traveler's energy bar. But that's not the only motivation for time travel. We also have curiosity about the future and interest in our parents and our children. A lot of time travel fiction is a way of asking questions about what our parents were like, or what our children will be like.
At some point during the four years I worked on this book, I also realized that, in one way or another, every time travel story is about death. Death is either explicitly there in the foreground or lurking in the background because time is a bastard, right? Time is brutal. What does time do to us? It kills us. Time travel is our way of flirting with immortality. It's the closest we're going to come to it.
This interview was edited for length and clarity.
Simon Worrall curates Book Talk. Follow him on Twitter or at simonworrallauthor.com.
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Since H.G. Wells imagined that time was a fourth dimension-and Einstein confirmed it-the idea of time travel has captivated us. More than 50 scientific papers are published on time travel each year, and storytellers continually explore it-from Stephen King's JFK assassination novel 11/22/63 to the steamy Outlander television series to Woody Allen's comedy Midnight in Paris.

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Our Obsession With Time Travel Explained | Science | National Geographic

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Our perception of time

Scientists and time travel

Time travel is fascinating

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Our Obsession With Time Travel Explained | Science | National Geographic

Time

The idea of time travel

Our perception of time

Scientists and time travel

Time travel is fascinating

IDEAS ABOUT

MORE LIKE THIS

Time Travel: Theories, Paradoxes & Possibilities

From the vault: Time travel: five ways that we could do it

5 Bizarre Paradoxes Of Time Travel Explained

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A PRO!

Bite-sized knowledge
to upgrade
your career