2. Relativity: History 1879: Born in Ulm, Germany. 1901: Worked at Swiss patent office. –Unable to obtain an academic position. 1905: Published 4 famous papers. –Paper on photoelectric effect (Nobel prize). –Paper on Brownian motion. –2 papers on Special Relativity. –Only 26 years old at the time!! 1915: General Theory of Relativity published. 1933: Einstein left Nazi-occupied Germany. –Spent remainder of time at Institute of Advanced Study in Princeton, NJ. –Attempted to develop unified theory of gravity and electromagnetism (unsuccessful).

3. Thought Experiment - Gedanken The Special Theory of Relativity Einstein asked the question “What would happed if I rode a light beam?” Would see static electric and magnetic fields with no understandable source. Electromagnetic radiation requires changing E and B fields. Einstein concluded that: No one could travel at speed of light. No one could be in frame where speed of light was anything other than c. No absolute reference frame

4. Time Dilation/Length Contraction: Muon Decay Why do we observe muons created in the upper atmosphere on earth? Proper lifetime is only  = 2.2  s  travel only ~650 m at 0.99c Need relativity to explain! –Time Dilation: What lifetime do we see? –Length Contraction: What length does the muon see? –What is the corresponding length in the earth frame? Length Contraction Muon’s frame Earth’s frame Time Dilation

5. Gallilean view of purple laser pulse V=U+V’, doesn’t work if V’ is c

6. Laser pulse for blue car frame Laser pulse for red car frame

7. Co-ordinate transforms and Minkowski space Length of car In two frames

8. Minkowski http://www.theory.caltech.edu/people/patricia/st101.html

9. Relativity of Simultaneity ct x O A B C x O A B C ct’ x’ Two events simultaneous in one inertial frame are not simultaneous in any other inertial frame moving relative to the first OR Clocks synchronized in one inertial frame are not synchronized in any other inertial frame moving relative to the first

10. Handy Light Clock Consider pulse of light bouncing between two mirrors (retroreflectors) d t o = d / c

11. Now Observe Same Clock moving Thought Experiment Gedanken Experiment Consider an inertial frame of reference: Elevator moving upward at a constant velocity, v.

12. Moving Light Clock Consider path of pulse of light in moving frame of reference: Light Clock d t o = d / c ct vt