Relativity: Just the Weird Stuff, Volume 1 – Time Travel

Einstein’s theory of relativity has a reputation for being complicated. Most of us outside the world of physics will never sit down and really try to figure out the details, partly because it is hard and partly because knowing that we gain a tiny amount of weight every time we move has the potential to play havoc with a person’s self-esteem (not to mention your motivation to get off the couch). However, understanding at least a little bit about some of the universe’s weirdest phenomena will really help put things in perspective. You’ll stress less about your printer not working properly if you remind yourself that in another dimension you’ve probably already smashed it.

Time Dilation

Relativity is an especially cool concept to ponder.  Take, for example, the fact that if you were standing on a very weighty object like the sun and you were able to look through a telescope through the window of a spaceship speeding past at a crazy velocity, time on the spaceship would appear to be moving in slow motion relative to what you are experiencing from your hot seat.

This effect is called Time Dilation and it isn’t just theory, it is something scientists have observed and measured in the real world. In October of 1971 physicists Hafele and Keating sent a super-accurate atomic clock on high-speed plane trip around the world, twice. Exactly as Einstein's equations predicted, the very worldly clock had lost 59 nanoseconds when it landed relative to a synchronized clock on the ground.

Time Dilation happens on a much smaller scale every time you walk from the living room to the kitchen to make a sandwich. Relative to your friends who went sandwichless a smaller amount of time will have passed for you on the order of 0.000000(something very small) nanoseconds.

Deeply Unsatisfying Time Travel

The reason for this warping of time, believe it or not, is the speed of light. Light is the fastest thing in the universe and the universe likes keeping it that way. For that reason, things get weird the closer you get to travelling at light speed (300,000 km/s or 186,000 mps).

To borrow a famous example, imagine that there was a train track that went in a straight line around the equator and that the train that rode on it was capable of travelling at 99.9999% the speed of light. Now imagine that you are a rider on that train sitting at the back of your car. At some point you are bound to get tired of looking out the window at the endlessly sickening blur of trees and people and you might decide to go to the bathroom, which is at the front of the car.

As you walk forwards on the train which is traveling at near the speed of light, your walking speed gets added to the speed of the train much like the speed of a slushy thrown from a moving car gets added to the car’s speed. If you walk briskly enough, this could mean that you break the cosmic speed limit by traveling faster than light. The universe can’t abide this and the only way to prevent it is to make time slow down for you. The closer the train travels to the speed of light, the slower time moves for those on board.

The side effect is that you are able to travel forwards through time. If you rode the light train travelling at a certain percentage of the speed of light and disembarked one year after setting out, 100 years could have passed for everyone not on the train. As cool as that is, there is no way we know of that will definitely let you travel in the opposite direction. So unless you don’t mind everyone you know dying while you ride a train, it’s probably best to save the cost of the ticket.

Come back next week for part two where we explore mass side of the equation… And maybe lay off on the cheeseburgers until then.