A rocket ship is heading toward you at ½ c A rocket ship is heading toward you at ½ c. How fast does the light from its headlamps travel toward you? a) c b) 1.5 c c) 0.5 c d) something else The speed of light is c in all frames.

You have been placed in a rocket traveling at 99 % c and cannot look out the window. List all the tests that you could do to tell that you are traveling so fast. There are no tests that you can do. All inertial frames are equivalent.

1) The speed of light is c in all frames. 2) All inertial frames are equivalent. All the strange predictions of Special Relativity come from these two postulates and can be developed by examining the geometry of spacetime diagrams.

Spacetime diagrams can help you to visualize relativity Spacetime diagrams can help you to visualize relativity. They are similar to scale diagrams and freebody diagrams.

A spacetime diagram has time vertical A spacetime diagram has time vertical. The axes are calibrated in years and light-years. t x

Which line represents an object at rest? x A B C D

Which line represents light? x A B C D

Which line represents an impossible motion? x t A B C D x

We want a line for an object moving at 3/5 c We want a line for an object moving at 3/5 c. This will be the t’ axis for the ‘moving’ frame. Which one is correct? A B C t t x x t x t’ t’ t’ x x x

A speed of 3/5 c has a slope of 5/3. t t’ x

Which is the correct x’ axis? A B C t t t x x t x t’ t’ t’ x’ x x x x’ x’

Hint: What is true about light in all frames? A B C t t t x x t x t’ t’ t’ x’ x x x x’ x’

The two axes must be symmetric about the path of light because light must have the same speed in all frames t t’ Dt’ x’ Dx’ x