Announcements Homework Set 1 is due now. I will accept the homework if placed in my mailbox by 5:00pm today Solution to HW Set 1 will be posted soon (Friday?) in the class D2L shell. Homework Set 2: Schaum’s Outline # 2.8, 2.9, 2.10 & 2.11 Important hints: for 2.8 switch left for right and right for left; for 2.8 and 2.9 length contraction hasn’t been introduced yet so don’t use it.

The stage is set! Michelson/Morley show that either there isn’t a luminiferous aether or something else is at work Maxwell’s Equations are incompatible with Galilean transformations and Newton’s Laws are incompatible with Lorentz transformations

Albert Einstein Assume that the Michelson-Morley experiment proves there is no luminiferous aether. Then there is no preferred reference frame. Then Maxwell’s equations mean that the speed of light is the same for all observers regardless of any motion. What are the consequences?

The basic postulates of Special Relativity 1.The laws of physics are the same for all inertial observers. That is, observers moving at a constant velocity: no acceleration (the “special” of Special Relativity). 2.The speed of light is the same for all observers and all wavelengths regardless of any relative motion between the source and the observer.

Fundamental change in coordinates Before Special Relativity there were three independent spatial coordinates (x,y,z) and one independent temporal coordinate, t. After Special Relativity, t is no longer independent so we have (x,y,z,t) and they are not necessarily independent. The rest of the Galilean transformation may be incorrect, too

First Consequence: Simultaneous events are not simultaneous for everyone Watch YouTube video on Simultaneous Events in Relativity

Colored Card Question What does the observer on the train predict the observer on the platform will see? a)The observer on the platform sees the front bolt strike before the rear bolt. b)The observer on the platform sees the rear bolt strike before the front bolt. c)The observer on the platform sees both bolts strike at the same time (simultaneously). d)Not enough information to figure this one out.

Another Colored Card Question Suppose the observer on the train had seen simultaneous lightening flashes at the front and rear of the train. What does the observer on the platform see? a)The observer on the platform sees the front bolt strike before the rear bolt. b)The observer on the platform sees the rear bolt strike before the front bolt. c)The observer on the platform sees both bolts strike simultaneously. d)Not enough information to figure this one out.

Second Consequence: Moving observers don’t agree on lengths If the two are stationary with respect to each other, the pole is a little longer than the barn. If the two have a relative velocity the length depends on the observer. How do you measure the length of a moving object?

Third Consequence: Moving observers don’t agree on time Watch YouTube Time Dilation in Relativity video

Colored Card Question Suppose the observer on the asteroid had a laser and a mirror and timed how long it took the laser to bounce off the mirror and return. What would the pilot on the spaceship observe? a)The time he observes is longer than the time the observer on the asteroid observed. i.e. the asteroid observer’s clock is slow. b)The time he observes is less than the time the observer on the asteroid observed. i.e. the asteroid observer’s clock is fast. c)The time he observes is the same as the time the observer on the asteroid observed. d)Not enough information given to figure it out.

The Camera Lies! Watch videos on “Special Relativity Visualized” website