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Q & A: (F)light and time

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Most recent answer: 10/22/2007
My dad and I were debating Flight, the terminator of the suns light and time, and why it is even possible to travel opposite the direction of the earths rotation. How is it possible for us to catch up with the terminator when we fly in the same direction of the earths rotation? If we were traveling at the speed of a bullet in a plane, why would a bullet fired towards the back of the plane not stand still? IF we travel faster than the rotation of the earth in the opposite direction as it, how does or does not time travel come into play. This led us to thinking about traveling the speed of light. If we managed to acheive this speed (say in a plane) would we not be able to shine a flashlight on the front hull of the plane? the back? If a beam of light was shone from a spot in space, and we launched at the speed of light from that same point at the same time, would it seem as if we were running along side the light? ...and I am not even going to go into the time travel discussion this brought about. As you might be able to guess this discussion was very frustrating so and ’light’ you can shine on this would be great, even if it doesnt answer most of the questions. Thank you Jake
- Jake (age 18)
New Jersey

Jake- You have two main categories of question. One is about motion relative to the Earth and Sun, and the other deal with hypothetical motion at the speed of light. The types of answers will be very different for these.

If you fly in the same direction that the Earth is rotating, you are rotating around the center of the Earth even faster than the Earth's surface is. So you will cross the terminator (the day/night boundary) more often than you would if you stayed home. Try to model this with a lightbilb (Sun) and a globe.

If a plane were travelling at bullet speed relative to the Earth, and you fired a bullet backward in the plane, the bullet would indeed be at rest relative to the Earth. (So far as we know, it is entirely meaningless to ask if something is stanidng still unless you say with respect to what you are measuring the motion.) Of course, that wouldn't make it at rest relative to the plane, and would not prevent it from puncturing the fuselage. So don't try it.

Wondering about what it would be like to travel at the speed of light (relative to the Earth or the bullet or the plane or whatever) can lead to some interesting thoughts, as it did for young Einstein. However, one conclusion of those interesting thoughts is that it's absolutely impossible for any object with rest mass to travel at the speed of light past any other object with rest mass. So there's nothing we can say about that situation except that it couldn't happen in a universe whose basic rules are like the ones of this universe.

Mike W.

(published on 10/22/2007)

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