1. Lecture Four

2. Attempts to Save Ether Hypothesis

3. Status Michelson-Morley experiment shows null result.

4. Attempts to Save Ether before Special Relativity 1.Contraction Hypothesis 2.Ether-Drag Hypothesis 3.Modify Electrodynamics

5. Contraction Hypothesis Fitzgeral (1892) Lorentz Length is contracted in the direction of motion.

6. Demolished by Kennedy-Thorndike experiment (1932)

7. Ether-Drag Hypothesis contradicted with Stellar aberration (Bradley 1727) Fizeau convection coefficient (Fresnel 1817, Fizeau 1857)

8. Stellar Aberration

12. Fizeau Experiment

13. velocity of light v in a medium of refractive index n moving with a velocity v w

14. Modify Electrodynamics Emission Theories The velocity of a light wave is connected with the motion of the source rather than with an ether.

15. Modify Electrodynamics Emission Theories The velocity of light is c relative to the original source. This velocity is independent of the state of the medium transmitting the light.

16. Emission Theories are contradicted with de Sitter observations on binary stars Michelson-Morley experiment using extraterrestrial light source

17. Conclusions The speed of light is the same in all inertial systems, independent of the relative motion of source and observer. A relativity principle applicable both to mechanics and to electrodynamics.

18. Conclusions Galilean transformations must be replaced. The laws of mechanics which were consistent with Galilean transformations needs to be modified.

19. Special Relativity Einstein 1905 “On the Electrodynamics of Moving Bodies”

20. Two Postulates Principle of Relativity Principle of Constancy of Speed of Light

21. Principle of Relativity include all laws of physics no measurements to designate an inertial system as intrinsically stationary or moving

22. Principle of Relativity no experiment entirely within an inertial system can tell the motion with respect to any other.

23. Principle of Constancy of Speed of Light consistent with Michelson- Morley experiment

24. Experimental Basis

25. Program of the Theory nature of time transformation keeping velocity of light constant Lorentz transformation

26. Einstein In his early life none of his “elders” recognized his genius. Until almost thirty he had never seen a real theoretical physicists, “except in the mirror!”

27. Einstein statistical mechanics atomic nature of matter special relativity principle of equivalence light quanta hypothesis specific heat of solids

28. Einstein 1905 Quantum theory of light Brownian motion Special Relativity

29. Einstein not in the mainstream nature of time abandoned Newton’s universal time