Sciency Words: Closed Timelike Curves

Hello, friends!  Welcome to Sciency Words, a special series here on Planet Pailly where we talk about those weird words scientists like to use.  Today on Sciency Words, we’re talking about:


Austrian-born logician and mathematician Kurt Gödel was one of Albert Einstein’s closest friends.  At Princeton’s Institute for Advanced Study, the two were known to take long walks together, discussing all sorts of strange and wonderful things, no doubt.

As science historian James Gleick tells the story in his book Time Travel: A History, Gödel presented Einstein with a very special gift for Einstein’s 70th birthday.  It was the kind of gift only a person like Einstein would appreciate: a series of mathematical calculations.  Specifically, these were calculations based on Einstein’s own theory of general relativity which showed that yes, time travel is possible.

Gödel’s calculations were officially published in this 1949 paper.  Now I won’t try to explain Gödel’s math because a) I don’t really understand it and b) it’s not really important for the purposes of a Sciency Words post.  What is important for our purposes is that Gödel’s 1949 paper introduced a new concept called “closed timelike curves.”

Well, technically speaking, Gödel used the term “closed time-like lines,” not “closed timelike curves.”  But as Google ngrams shows us, the hyphen quickly dropped out of “time-like,” and by the 1990’s, “curves” beat out “lines.”  So today, closed timelike curves is the most broadly accepted way to say what Gödel was trying to say.  The term is also commonly abbreviated at C.T.C.

In short, a closed timelike curve is a path through space and time that circles back to its own beginning.  As I understand it, it would take a stupendous amount of force to twist space-time around itself in this way.  You’d need the extreme gravitational force of a black hole—or perhaps something even more extreme than that—in order to make a closed timelike curve happen.

But it could happen.  As Gödel demonstrated in 1949, general relativity would allow a closed timelike curve to exist, or at least relativity does not forbid such things from existing.

So time travel is possible.  It may not be anywhere near practical, but it is at least possible.

Speaking of time travel, are you a fan of time travel adventure stories?  The kinds of stories you might see on Doctor Who or The Twilight Zone?  Then please check out my new book, The Medusa Effect: A Tomorrow News Network Novella, featuring time traveling news reporter Talie Tappler and her cyborg cameraman, Mr. Cognis.

Sciency Words: Time

Sciency Words: (proper noun) a special series here on Planet Pailly focusing on the definitions and etymologies of science or science-related terms.  Today’s Sciency Word is:


How would you define the word time?

I recently read a book called Time Travel: A History by James Gleick.  This is one of the big questions raised by that book, and it’s a question that’s kept nagging at me.  What is time?  We all know what time is, don’t we?  We use the word all the… well, all the time.

But if you had to write a dictionary definition, what would you say?  Keep in mind the first rule of dictionaries: don’t use the word your defining in the definition of that word.  Gleick offers several interesting suggestions.  Time is the experience of duration.  Time is what keeps everything from happening all at once.  Time is the thing that clocks measure.

These are fun definitions, but I don’t find them fully satisfying.  Maybe we could turn to this classic explanation of time given in Doctor Who:

People assume time is a strict progression of cause to effect, but actually, from a non-linear, non-subjective viewpoint, it’s more like a big ball of wibbly-wobbly, timey-wimey… stuff.

In my own science fiction writing, time is often described as “a living thing,” something that’s constantly shifting, constantly changing.  History keeps rewriting itself, and time travelers speak of time in almost adversarial terms.  But while that might work for the kinds of Sci-Fi stories I want to tell, I don’t think this “living thing” notion is an actual, practical way to define what time is.

The closest I’ve come to finding a satisfying definition of time is an idea that goes back to Aristotle: time is a measure of change.  The sun changes its position in the sky.  So do the moon and all the stars.  The seasons change, one into the next into the next, until the cycle repeats.  All these cyclical changes set the standard by which we measure non-cyclical changes.  That’s what time is!

Or is it?  I said this is the closest I’ve come to finding a satisfying definition, but it still feels incomplete.  Thanks to Einstein and the theory of general relativity, we now know that time itself changes relative to acceleration and/or gravity.  So how can the measure of change be changeable?  There must be more to it than that, right?

Origin Stories: Who Invented Time Travel?

Welcome to Origin Stories, a monthly series here on Planet Pailly where we take a look at the origins of popular Sci-Fi concepts.  Today on Origin Stories, we’re looking at the origins of:


If I ever have a time machine—a real, working time machine—the first thing I’d do is go back in time and meet the person who invented time travel.  We do know who that person was.  His name was H.G. Wells, and he was the author of the classic science fiction novella The Time Machine.

Wells got the inspiration for The Time Machine from an unlikely source.  As science historian James Gleick explains in his book Time Travel: A History:

At some point [Wells] sees a printed advertisement for a contraption called Hacker’s Home Bicycle: a stationary stand with rubber wheels to let a person pedal for exercise without going anywhere.  Anywhere through space, that is.  The wheels go round and time goes by.

Of course there had been time travel-like stories before.  Remember the ghosts of Christmas Past, Present, and Future.  Remember the story of Rip Van Winkle, who found himself suddenly in the future after a really long nap.  Or remember Mark Twain’s A Connecticut Yankee in King Authur’s Court, in which a man from Connecticut gets bonked on the head and wakes up to find himself in the distant past.

But H.G. Wells was the first to take the idea of time travel semi-seriously.  He was the first to try to dress up the idea with scientific and technological jargon.  And in my opinion, no other author has handled time travel so clearly and concisely as Wells did.

The protagonist of The Time Machine, a man of science referred to only as “the Time Traveler,” first explains to a group of friends that we exist in a world of not three dimensions but four.  Everything that exists in this universe has the qualities of “Length, Breadth, Thickness, and—Duration.”  The Time Traveler’s friends then raise all the objections Wells’ readers might have had, and the Time Traveler explains all those objections away in exchanges like this:

“But,” said the Medical Man, staring hard at a coal in the fire, “if Time is really only a fourth dimension of Space, why is it, and why has it always been, regarded as something different?  And why cannot we move in Time as we move about in the other dimensions of Space?”

The Time Traveler smiled.  “Are you sure we can move freely in Space?  Right and left we can go, backward and forward freely enough, and men always have done so.  I admit we move freely in two dimensions.  But how about up and down?  Gravitation limits us there.”

“Not exactly,” said the Medical Man.  “There are balloons.”

“But before the balloons, save for spasmodic jumping and the inequalities of the surface, man had no freedom of vertical movement.”

In other words, we can only move freely in the third dimension thanks to technology—hot air balloons, airplanes, rockets….  Therefore technology may also give us the power to move freely through the fourth dimension of time.

Of course H.G. Wells didn’t actually believe in time travel.  As James Gleick goes on to say, all Wells was trying to do was “gin up a plausible-sounding plot device for a piece of fantastic storytelling.”  But as it would turn out a decade or so later, Wells was not too far off from the truth.  Physicists like Albert Einstein and Hermann Minkowski were soon treating time as variable, rather than a constant.  No, Einstein and Minkowski didn’t build any bicycle-like contraptions in their basements, but the notion of time as the fourth dimension—that soon became serious science.

Time travel has always been my favorite subgenre of science fiction.  It has been ever since my Dad first introduced me to Doctor Who.  I realize time travel isn’t everyone’s cup of tea, but personally I enjoy the kinds of brain-twisting puzzles that a good time travel adventure presents.  It’s the reason I still love Doctor Who, and it’s the reason time travel features so prominently in my own writing.

So if I ever have my own time machine, the first thing I’d do is go back in time to meet H.G. Wells.  I think I owe Mr. Wells a thank you.