How to Understand Time Travel

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By Bob Strauss
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Long a staple of pulp fiction and incomprehensible sci-fi movies, over the past few decades the concept of time travel has attracted the attention of an increasing number of physicists. The surprising fact is, as we understand them today, the laws of quantum physics and general relativity don’t quite rule out time travel as a matter of principle. Here’s a quick guide to what may (or may not) be possible as we attempt to traverse the time line.

Difficulty: Easy

Instructions

Step 1

Forward time travel is perfectly kosher. According to general relativity, as a spaceship’s velocity approaches the speed of light, the people on board age more slowly relative to stationary objects, such as planets. So, if you zoomed far out into space at 99.9% light speed, turned around, and zoomed back, you’d find yourself 10 or 20 or 100 years in the future. The only problem is, there’s no way to return to your chronological starting point!
Step 2

Some elementary particles already travel backward in time. According to a popular interpretation of particle theory, a particle’s antimatter equivalent travels in the opposite direction on the timeline (for example, a positron can be interpreted as a normal electron traveling backward in time). This odd fact can’t be harnessed for macroscopic time travel, but it at least offers some hope to physicists on a theoretical level.
Step 3

You can’t “change” the past. This is where most time-travel sci-fi goes wildly awry. Even if a brilliant physicist invents a way to travel back in time, it won’t be possible for him to (for instance) prevent the assassination of Abraham Lincoln. However, there is a quantum loophole: some theorists think it’s possible to change a timeline, meaning if you prevented Lincoln’s assassination, you’d find yourself in an “alternate” future forever cut off from your previous time.
Step 4

Wormholes are our best hope. According to current theory, space at the submicroscopic level is brimming with tiny holes, which lead from one part of the universe to another. If it were somehow possible to a) inflate one of these holes to macrosopic size and b) tug it via spacecraft to near light speed (thus causing the time-dilation effect described in Step 1), a person could theoretically enter the hole and emerge elsewhere in the universe at an earlier time. That’s a huge “if,” of course, so don’t go making your reservations yet.
Step 5

Remember, we don’t understand what “time” is. Before you can travel through something, it helps to know exactly what that something consists of. Physicists, though, have had a notoriously hard time pinning down the concept of “time,” which doesn’t even exist at the quantum level. For this reason, any innovations in time travel will probably have to await a theoretical breakthrough that explains time in the first place.

Comments

josephfiero said

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on 3/28/2008 I've always been fascinated by this theory or theories that don't mathematically rule out going backwards in time. I believe from what I've researched and the research that has happened that we can so far possibly send a encoded message back through in what is perceived in our minds as "time". The only problem is that we can only send the message as far back as he machine existed. When we create the casmir vacuum effect and increase the speed of light.