Is Time Travel Possible?
From summer blockbusters
to sensational science headlines
, modern culture is constantly inundated with tales of time travel. But when you boil down the physics involved, is it possible to travel through time?
To answer this question, I tracked down theoretical physicist and cosmologist Paul Davies
, author of "How to Build a Time Machine
SLIDE SHOW: What are the favored time travel methods as used in science fiction?
We are all time travelers
"The short answer is that time travel into the future is not only possible, it's been done, and we've known about it for over a century," says Davies. "The reason that the public doesn’t seem to know about it is because the amount of time travel involved is so pitifully small that it doesn't make for a 'Doctor Who' style adventure."
A phenomenon called time dilation
is the key here. Time passes more slowly the closer you approach the speed of light -- an unbreakable cosmic speed limit. As such, the hands of a clock in a speeding train would move more slowly than those in a stationary clock. The difference would not be humanly noticeable, but when the train pulled back into the station, the two clocks would be off by billionths of a second. If such a train could attain 99.999 percent light speed, only 1 year would pass onboard for every 223 years back at the train station.
But speed isn't the only factor that affects time. On a much smaller scale, mass also influences time. Time slows down the closer you are to the center of a massive object......................
A number of questions about time travel remain unanswered. Will time tourists from the future ever show up to help us out? We'll just have to wait and see. But if they come here using a wormhole time machine, we'll have to build one first. After all, you couldn't cross a bridge if only one side had been completed, right?
"Theoretically, it would take more than 100 years to create a 100-years' time difference between the two ends of a wormhole," Davies says, "so there's no way that our descendants could come back and tell us we're wrong about this."