Wednesday, April 4, 2012

"I do believe in time travel. Time travel to the future. Time flows like a river and it seems as if each of us is carried relentlessly along by time's current. But time is like a river in another way. It flows at different speeds in different places and that is the key to travelling into the future. This idea was first proposed by Albert Einstein over 100 years ago."



                 - Stephen Hawking

Time flies by as we get older, as Kevin talked about in our last blog post “Time flies when you’re having fun! (and getting old?)”. But what if you think time is moving too fast and you would rather go back to a day in the past? Perhaps you think time isn't going fast enough? 

Unfortunately, travelling back in time is impossible. (Sorry Back to the Future fans. Still an awesome movie.) Stephen Hawking came up with a simple experiment that could reveal if time travel is possible in the future. 

"Let's imagine I'm throwing a party, a welcome reception for future time travelers. But there's a twist. I'm not letting anyone know about it until after the party has happened. I've drawn up an invitation giving the exact coordinates in time and space. I am hoping copies of it, in one form or another, will be around for many thousands of years. Maybe one day someone living in the future will find the information on the invitation and use a wormhole time machine to come back to my party, proving that time travel will, one day, be possible. In the meantime, my time traveler guests should be arriving any moment now. Five, four, three, two, one. But as I say this, no one has arrived. What a shame. I was hoping at least a future Miss Universe was going to step through the door."

This experiment does not work because of what we call paradoxes. Another one is called the Mad Scientist paradox, also known as the Grandfather paradox. If a scientist made a wormhole where he can see himself as he was one minute ago, he should be able to use the wormhole to shoot his earlier self.  If he is now dead, who fired the shot? It doesn't make sense.

I'm not saying all time travel is impossible. You just have to travel really, really fast. 186,000 miles per second to be exact, also known as the cosmic speed limit, or the speed of light. It may be hard to believe, but travelling close to the speed of light will transport you to the future.
 
Imagine a track for a superfast train the goes around Earth. As the train gets close to travelling at the speed of light, it becomes a time machine. At this point the train would be circling the Earth about 7 times a second (Our technology is not quite there yet). Laws of physics forbid the train from actually hitting the speed of light, but in this case we will say it's just shy of that speed.  Now something spectacular happens to the passengers onboard. Time begins to move slowly onboard relative to the rest of the world. 

This is happening to protect the cosmic speed limit.  A passenger could accidently break the speed limit but running forward up the train, adding his/her speed to the speed of the train right? Not quite. Time is slowed down onboard by the laws of nature to prevent the possibility of breaking the speed limit. 

Imagine the train was leaving the station January 1st, 2050. It circled the Earth for 100 years and is finally coming to a stop on January 1st, 2150. Time is slowed down on the train so much that the passengers will have only lived one week, though they just traveled 100 years in the future!

Of course, it seems impossible to build this superfast train. However, we once thought computers were impossible. So I will believe in the possibility of building a machine that can travel at the cosmic speed limit. For myself, I would find it quite useful. No more waiting for the next Apple product release! If you could travel to the future, where would you go?

- M@

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