Chapter S2: Space and Time

Introduction
         Einstein
         1905: Special Theory of Relativity -> Space and Time
         1915: General Theory of Relativity -> Space, Time, and Gravity
         This chapter is about the Special Theory of Relativity

Reference Frames

         Earth Example of motion relative to different reference frames
         Example of motion in a straight line

         This chapter deals with reference frames having constant velocity
                  (no acceleration)
         "Constant velocity reference frame" = "free float frame"
                  = "inertial reference frame"

Underlying "assumptions" of Special Relativity

         1.) The laws of physics work just as well in any reference frame as in any other
         2.) The speed of light seems to be the same, no matter what reference frame
                  you are in
         i.e. If light is produced in a different reference frame (moving at velocity = v₁),
                  you, in your frame, don't see light's velocity as c + v₁,
                  you see light's velocity as c!

                  1887, Michelson Morley Experiment
                  Binary stars example
                  Car example
                  Colliding cars are equivalent to colliding galaxies
                  (NGC 5426 & 5427 and NGC 4038 & 4039
                  and we don't see crumpled galaxies waiting to be hit!)

Clarifications
         To notice the effects of relativity, you need very fast motions

         Slow objects act in ways we are familiar with (Example)
         But light doesn't (Example)

         We assume that the light is travelling through a vacuum (not glass, etc.)

Important Ramifications:
         1.) Nothing can move faster than the speed of light
         2.) Time runs slower for moving objects
         3.) Two events that are simultaneous in one reference frame are not in another
         4.) if you look at a moving object, it looks shorter to you (and it thinks the
                  same of you)
         5.) if you look at a moving object, it seems more massive to you (and it thinks the
                  same of you)

Showing to yourself that time runs slower for moving objects
         Jackie => moving reference frame
         Preface: slow ball example, in your frame, see longer path and "faster ball"
                  then the person in the moving frame
         Ball example

         But!! when use a beam of light, something is different, the light is moving at
                  same speed in all frames
         You still see a longer path than Jackie does
         distance = velocity * time
         So, you see a longer time than Jackie does
         Light Example

         Note: test with "pi+" meson travelling at fast speed.
                  Slowed the decay time in our reference frame (which, to the pi+ meson, is moving)

         Note: in 1975 someone tested this by putting a clock on an airplane.
                  After 15 hours in flight, the on-board clock was 6 nanoseconds
                  behind the Earth clocks

Figures for some of the other ramifications

Length contraction

Velocity addition