The Science of Time Travel

Let me preface this post by saying that I absolutely, positively believe that time travel is impossible.

Having said that, I must now admit that our current laws of physics do not absolutely, positively prove that time travel is impossible, and a variety of eminent scientists over the years have tried to construct models in which time travel is allowed.

Time Travel: What if You Can't Change the Past?

What do Charlton Heston, the Battle of Shiloh, and stories about time travel have in common?

Time Travel: A Story

As promised in my previous post, here's a short story of mine about time travel.  It appeared in the December, 2009, issue of Analog.

Time Travel: What if You Could Change the Past?

Time travel shares a dubious distinction with faster-than-light travel: they are two of the most popular ideas in all of science fiction, but also two of the most implausible from a scientific point of view. And both of them have become so ingrained in the culture of science fiction that they no longer require detailed justification when introduced into a story. As I noted earlier, the very first time travel novel, The Time Machine, begins with a lengthy explanation of the workings of time travel, while in a modern story Ann and Bob would just jump into their time machine and take off for the 13th century.

Anyone writing about time travel must choose one of two very different possibilities:

1.  Allow the past to be changed
2.  Assume the past is frozen and cannot be altered

This choice produces starkly different types of stories.  Today I want to talk about the first possibility -- I'll save the second for a later post.

Time as the 4th Dimension: a Curious Fact

I'm going to devote my next few blog posts to the ever-popular subject of time travel. In fact, my future self will be writing these posts and emailing them back in time to me, so I won't have to do the actual work of writing them myself.

Before getting started, I wanted to mention a curious fact that most people don't know about (or at least I didn't).

The Golden Age of Fantasy on Television

When was the Golden Age for fantasy-themed shows on TV? Was it the 1990s, with the debut of The X-Files and Buffy the Vampire Slayer? Or possibly now, with Game of Thrones? Forget about it! There was once a brief time when fantasy shows sprouted on television like weeds in an abandoned shopping-mall parking lot.

Pluto (the Planet, not Mickey's Dog)

With the New Horizons probe reaching Pluto in just a few more days, it seems like a good time to address a couple of questions:

1.  Is Pluto a planet?

I say YES! My opinion has no basis in science -- it arises strictly from a combination of irrational prejudice and childhood nostalgia. And I think if we're going to kick Pluto out of the society of planets, there a few other pieces of debris that should also be expelled, namely Mercury, Venus, Earth, and Mars. After all, the Solar System basically consists of four enormous planets -- Jupiter, Saturn, Uranus, and Neptune -- and a bunch of rocks. My colleague David Weintraub informs me that I won't get very far with a definition of "planet" that excludes the Earth, but I think we should be more open-minded.

2.  What's the best science fiction story about Pluto?

A Sticky Universe and the Big Rip

Some research I did with Marcelo Disconzi and Tom Kephart at Vanderbilt University on viscosity in the Universe leading to a future "big rip" has recently gotten some publicity.  Here's a story in the New Statesmen.   See, I do occasionally do science.

Update:  article in the Guardian.

The Speed of Light in Science Fiction: When Less is More

A science fiction writer can often produce a more interesting story by strictly obeying the known laws of science than by blithely ignoring them.  An obvious example is the speed limit imposed by relativity, which I discussed in an earlier post.  It might seem easier for a writer to just ignore the cosmic speed limit (“jump into hyperspace, Jimmy!”), but one can often construct a more interesting story by adhering to the cosmic speed limit and following where this leads.

The most plausible way to evade the speed of light is to exploit relativity itself, specifically, the time dilation effect.  Time slows down for passengers on a spaceship approaching the speed of light.  So a trip that appears from the outside to take thousands of years might seem to the passengers to take only a few months.  Of course, when they returned back home, the space travelers would find their friends and family turned to dust, making this a not entirely satisfactory means of space travel.  The latter problem figures prominently in the conclusion of Joe Haldeman’s Forever War, in which a soldier on an interstellar combat mission is separated from his girlfriend, and only a few years pass for him, while thousands of years pass back on Earth.  (Haldeman employs a few additional tricks from relativity to ensure a happy ending).  And the ultimate time-dilation tale is Poul Anderson’s Tau Zero.  In Anderson’s novel, a colonization vessel begins to accelerate out of control.  The time dilation becomes so extreme that the crew eventually witnesses (and survives!) the end of the universe itself.

A particularly heartrending exploitation of this idea is "The Old Equations," by Jake Kerr.  (Do you know where the title of the story comes from?)  Before I spoil it for you, you can read the story at Lightspeed magazine.  Kerr's story actually pulls a clever swindle on the reader -- while it adheres slavishly to the laws of relativity, it introduces an idea that is just as implausible (in my mind) as violating the speed of light. But like a good magician, Kerr distracts your attention so that you don't even notice it.

More on the Fermi Paradox

I have a guest blog post on the Fermi paradox here.  This is more science fiction oriented than my earlier discussion -- I examine some of the unusual ideas that science fiction writers have explored (and, in many cases, invented) to explain our lack of alien contact.  Extra credit if you can spot the reference to Veggie Tales.

Article on Intelligent Life in the Universe

How common is intelligent life in the universe? And if it's common, why haven't we seen it yet? I discuss these questions in an article at The Conversation.

Computer Nostalgia: the Birth of the Internet

Yes, like Al Gore, I was there at the birth of the Internet.  OK, maybe not the birth of the Internet, but I was there when the Internet was still in diapers and not playing nicely with other children.

Quantum Immortality

I have to admit that I had never heard of quantum immortality until I read Robert Charles Wilson's short story, "Divided by Infinity." (That's the same Wilson who wrote Spin, which I recommended in a previous post). You can read "Divided by Infinity" online at this site. Take a look at it before I spoil the story for you in the rest of my post.

Quantum Mechanics in Science Fiction

Quantum mechanics is the wacky, spooky carnival funhouse of physics.  Nothing is exactly what it seems to be.  Objects no longer occupy a definite location in space, particles act like waves and waves act like particles, and the act of observing an experiment changes the experimental outcome.  So what happens when science fiction writers try to explore a theory that is so weird that it seems like science fiction itself?

I’ll Give up Fortran when they Pry it from my Cold, Dead Hands

Yes, I still program in Fortran.  And I’m proud of it.  Every so often I tell my colleagues that it’s finally time for me to pick up a new programming language.  Maybe C++.  Or Java.  Lately, Python.  But then I sit down in a quiet place and the urge passes.  You just can’t beat Fortran, and here’s why: