1. faster than light? Einstein, light, and quantum mechanics

2. Einstein, light and quantum mechanics  Folklore Einstein proved that nothing can go faster than light Einstein didn’t believe in quantum mechanics  Fact Many things go or appear to go faster than light (in some circumstances) Einstein got his Nobel Prize for quantum mechanics

3. things that go faster than light  the expansion of the universe objects cannot go faster than light across space space can expand as fast as it wants space  optical illusions jets emitted by many radio galaxies and quasars jets the “lighthouse beam” from a pulsarlighthouse beam  many particles in material the limit is the speed of light in a vacuum in material, e.g. glass, water, light slows down, but particles don’t

4. Čerenkov radiation Čerenkov radiation is emitted when a particle is moving faster than the speed of light in the material it’s travelling through – analogous to sonic boom

5. Using Čerenkov radiation

6. Detecting Čerenkov radiation light in electric charge out

7. Einstein and the nature of light  Einstein said that the speed of light in a vacuum should appear the same to all observers this is based on Maxwell’s theory of electromagnetism in Maxwell’s theory light is a wave  Therefore special relativity is a consequence of the wave picture of light

8. Einstein and the nature of light  But Einstein got his Nobel prize for his explanation of the photoelectric effect “the bold, not to say the reckless, hypothesis of an electro-magnetic light corpuscle” [Millikan]  Therefore Einstein’s Nobel prize is a consequence of the particle theory of light

9. The photoelectric effect  Light striking the surface of some materials causes emission of electrons but only if frequency is high enough higher frequency → higher energy electrons greater amplitude → more electrons  but only if frequency is high enough  This is easily explained if we think of light as consisting of “photons” with energy related to their frequency theory used by Max Planck to explain radiation from hot objects  not widely believed at the time

10. Quantum doubts  Planck (who invented it) “One should not hold against him too much that in his speculations he might have occasionally overshot the goal, as for example in his hypothesis of the quanta of light.” [A reference letter for Einstein!]  Millikan (who measured it) “This hypothesis may well be called reckless…it flies in the face of the thoroughly established facts of interference” [His paper on the measurement of h] “…this work resulted, contrary to my own expectation, in the first direct experimental proof…” [Nobel lecture]

11. Einstein and light  Einstein developed the theory of relativity by taking Maxwell’s wave theory of light and developing its logical consequences  Einstein developed the theory of the photoelectric effect by taking Planck’s theory of light and developing its logical consequences  It is a measure of his genius that he was able to do both!

12. Max von Laue, physics, 1914, X-ray diffraction Robert Millikan, physics, 1923, e and h Max Planck, physics, 1918, quanta Albert Einstein, physics, 1921, photoelectric effect Walther Nernst, chemistry, 1920, thermo- chemistry