1. Modern Physics This isn’t Newton’s Physics!

2. Democritus – 400 BC First known person to advance the idea of “atoms” as building blocks of matter.

3. Dalton – 1800 First name: John Established the likelihood that elements consist of basic structural units (like Democritus’ atoms).

4. Michelson - 1879 First name: Albert Measured the speed of light (accurately) for the first time.

5. “Luminiferous Ether” It was known that light was a wave (interference, diffraction, etc), yet it was able to travel through space which apparently contained no continuous mass. It was, therefore, assumed that some undetectable mass existed in space, the luminferous ether.

6. Michelson/Morley - 1887 Michelson, in combination with Edward Morley, conducted a famous experiment that bears their names to detect the luminiferous ether. No ether was detected

7. Hertz - 1887 First name: Heinrich Discovered the Photoelectric Effect (accidentally). Shining light on certain metals caused an electrical current.

8. Thompson – 1897 First name: JJ (Joseph John) Discovered the existence of electrons as particles. Formerly known as “cathode rays”.

9. Planck - 1900 First name: Max Radiating objects (black-body) emit specific colors regardless of temperature. EM theory predicted an “ultraviolet catastrophe”. Planck noted that blending two separate (and apparently unrelated) theories resolved the problem. Concluded that light must act like particles (photons) which contained fixed (quantized) amounts of energy related to their frequency (E=hf). Referred to as the Quantum Theory.

10. Einstein - 1905 First name: Albert Published his Theory of Special Relativity Measurement of time wouldn’t be the same for all observers, but would instead be related to their relative motions. Energy and mass were interchangeable (E=mc 2 )

11. Thompson – 1905(?) “Plum-pudding” Atomic Model

12. Millikan - 1910 First name: Robert Measured the charge on the electron in the famous experiment that bears his name.

13. Rutherford – 1911 First name: Ernest Gold Foil experiment

14. Gold Foil Experiment:

15. Rutherford’s Conclusions: Most positive charge and mass is in a small, centralized region (nucleus). A consequence of this is that there must be positive particles (protons). Electrons are “outside” the nucleus. Suggested that neutral particles consisting of proton plus electron might also be found (in the nucleus).

16. Bohr - 1913 First name: Niels Followed up Rutherford’s experiment by suggesting a “planetary” model for the atom (electrons as “planets”; nucleus as “sun”). “Orbits” had specific energies. He successfully predicted the energy levels for hydrogen atoms. Demo

17. Einstein - 1915 Explained the photoelectric effect by using Planck’s Quantum Theory. Ironically, this explanation led to the widespread acceptance of Planck’s Quantum Theory, and Einstein spent much of his later life seeking to circumvent its statistical nature (“GOD doesn’t play dice”).

18. Photoelectric Effect Energy is required to release electrons from a photoemissive metal (ionization energy). If light is a wave, then increasing brightness should release electrons.

19. Photoelectric Effect (cont.) Energy is required to release electrons from a photoemissive metal (ionization energy). If light is a photon, then increasing frequency should release electrons.

20. Millikan - 1915 Verified Einstein’s explanation of the photoelectric effect Determined the value of Planck’s constant KE max ff0f0 W0W0

21. Einstein - 1916 Published his General Theory of Relativity which led to the prediction of the existence of black holes, gravity- warped space, gravity-deflected light, etc.

22. Compton - 1922 First name: Arthur Photons colliding with electrons caused the electrons to be deflected, and the process conserved both energy and momentum. Photons act as if they have mass.

23. de Broglie - 1924 First name: Louis Suggested that just as light waves could behave like particles (photons), particles could similarly behave like waves, with wavelength related to momentum. =h/mv

24. Schroedinger - 1926 First name: Erwin Developed wave equations to define particles (electrons). Solutions to the wave equations defined the characteristics of the particles. Led to the Electron Cloud Model of the atom and removed the limitations inherent in Bohr’s model of the atom.

25. Heisenberg - 1927 First name: Werner Published his Uncertainty Principle. It was impossible to determine both the momentum AND position of a particle/wave. Measuring affects the measurements.

26. Chadwick – 1932 First name: James Discovered the neutron

27. Gell-Mann and Zweig - 1964 First names: Murray and George Proposed that nucleons were composed of smaller particles (quarks)

28. Friedman and Kendall - 1968 First names: Jerome and Henry Provided the first experimental evidence for the existence of quarks.