Physics of Time Travel

To the Future

Basic Rules for Light

• Light travels at a very fast speed usually denoted as “c”.

• You cannot add onto the speed of light.• Someone shining a flashlight standing still: The

light will go at the speed “c”.• Someone shining a flashlight running at 10

mph. The light will still go at the speed of “c”.

Time and Light

• Suppose there are two people: Ann and Bob. Ann travels on very fast trains. Ann places a mirror on the ceiling and floor of the train. As the train moves, she flashes the light on the mirror and observes that the light travels back and forth from mirror to mirror. The train is traveling at the speed of c.

What Ann Sees inside train

Time and Light

• Bob is standing outside of the train track with a special camera that slows down everything down. Bob records the train moving. Since, the train is made of glass, Bob can see everything inside of the train. Bob plays the tape and saw this:

Time and Light

Speed: cDistance: 6 m

Speed = distance/timeC = 6 / t

4 m 4 m

3 m3 m

Speed: cDistance: 10 m (Pythagoras th)

Speed = distance/timeC = 10 / t

If speed is the same, but the distance observed by Bob is larger than Ann. What does that tell you about time?

Time and Light

• Time is not the same for everyone or everything!• Ann: c = 3 / time for Ann• Bob: c = 5 / time for Bob• Time for Bob is less than the time for Ann.• Bob’s time is moving slower than Ann’s time.

Time and Light

• Suppose you have an ship that can travel very close to the speed of light. If Bob and Ann are both 20. Bob stays home and Ann travels away from earth on the ship for 1 year. When Ann comes back, she will be 21, but Bob will be 27. Ann will only have to give up one year to see what will earth be like in seven years.

Time and Light

• When Bob observes Ann, time will seem slow. But for Ann and Bob, time passes on normally. One year will always “feel” like one year. This is not a method for living longer.

• In order to do this, you need to travel near the speed of light. We don’t experience this since everything moves much much slower than the speed of light.

Video: Cosmo’s Time Dilation

• http://www.youtube.com/watch?v=6Vpu6yJPRVQ

To the Past

Grandmother’s Paradox

• It’s no impossible for something to “travel” to the future with the expense of a few years.

• However, there a lot of complications when traveling to the past.

• If you travel to the past and prevented your own birth, then how did you exist in the first place?

Alternate Universe

• Maybe the assumption that there are only one universe is wrong?

• A: Decided to travel back in time. (A world where I exist)• B: Prevented my birth• C: A world where I don’t exist.• When I go back, I will go back to branch A, where I exist.

A

B

C

Wormhole

• There maybe holes in space in which we can travel between alternate universe.

Video 2: Imagining 10th Dimension

• http://www.youtube.com/watch?v=JkxieS-6WuA