Relativity Odds and Ends

Question 1

Why cant someone win a race before it starts in some frame?

Answer 1

Because of causality. The first event can cause the second event, and since there is enough time for light to get from one to the other, the order is the same for all inertial frames.

Question 2

What are light cones?

Answer 2

Each event has a past and a future. On a graph, the X structures are the light cones. Events E2 and E3 can be out of causal contact but visible at a later event E1.

Question 3

Why is there an apparent electric field in a particles reference frame in a wire?

Answer 3

Because in the wires frame the positive charges are lorentz contracted, whereas in the particles the negative charges are lorentz contracted - excess of negative charge.

Question 4

How do you work out how far you could go if you leave earth with an acceleration of 1g?

Answer 4

Use addition of velocities and then use time dilation to find the acceleration in the S’ frame. Integrate twice to find the distance.