## Thursday, June 18, 2009

### How Does Time Travel Really Work, Sean Carroll?

Caltech's Sean Carroll took time off from his work to answer a few questions about time travel that we have seen in the movies. If nothing else, this news article gets a chuckle or two. For example:

"Superman" (1978 version)

How time travel is achieved: Superman zips into space and flies faster than the speed of light, round and round, reversing the planet's spin and reversing time.

Carroll says: "It would cause earthquakes and kill millions. And really, if you can do this, then why, if you're Superman, don't you do this all the time? He should be held to a higher standard."

:)

Zz.

Just to defend the Man of Steel, the director's cut shows that Kal-El is NOT reversing the spin of the Earth. Instead, he's flying around the earth faster than the speed of light, causing himself to go back in time. The planet only seems to be spinning backwards because we're seeing it in his reference frame. While this has it's own host of problems, earthquakes aren't among them.

Now if you'll excuse me, I'm due back in my mother's basement.

ZapperZ said...

If all it takes is for him to go faster than light to go back in time, then he could fly around ANYTHING in any direction. Why did he chose to fly in the opposite direction? He could even just go fly to Alpha Centauri and back.

Zz.

True, he could fly to Alpha Centauri and back, but, even assuming that he has a speed of 10c, that's going to be a five month trip. Besides, he'll want to stay close to Earth to watch what's going on and see exactly far back he has traveled.

As for why he chose to fly in the opposite direction of earth's rotation, that's only at the start of the trip. Once he goes superluminal, he sees the planet rotating in the same direction. This clearly give him a better view of the surface. Of course, it's still not perfect and he overshoots where he wanted to be, so he has to stop at the end and use a little sub-luminal travel to time dilate back to exactly where he wanted to be. Of course, since he's now travelling forward in time, he would want to travel in the same direction as the Earth's rotation to get the best view.