THE WORLD YEAR IN PHYSICS 2005 Einstein’s 1905 papers - D. Hedin Outreach activities - P. Sievert -grant from APS to expand school visits -possible grant to lower cost of science camp -Physics Olympics April 16 New Physics - S. Martin Nanoscience - M. van Veenendaal Solar Eclipses - M. Fortner Brownian Motion - L. Lurio Accelerator Physics - B. Erdelyi Teaching Development - A.Windelborn -->NIU can use feedback for desirability of future “teacher” summer camps or workshops (give to P.Sievert or A.Windelborn)
Einstein’s 1905 Papers David Hedin Department of Physics Northern Illinois University March 4, 2005 A brief overview plus some personal perspective
Einstein’s 1905 Papers March-quantization of the radiation field (explained photoelectric effect - Nobel Prize 1921) April and May - Brownian motion June and September - special relativity I’ll discuss first and third, Larry Lurio will talk about Brownian motion
Quantizing the Radiation Field Explained the photoelectric effect by postulating that light came in “quanta” with Energy = frequency quanta of light now understood as particles call photons ( ) metal light electron Frequency of Light Energy of Electron Electron energy linearly related to frequency of light Similar to how digital cameras work
P.E. Effect - continued DH: 1974 (age=19). Photoelectric effect trivial/easy to understand AE: “revolutionary” DH: Einstein was right. Started our understanding of physics in terms of particles light now realized to be a collection of particles (photons) each carrying energy and momentum. Accepted ~1925 following Compton effect (scattering of photon off an electron) atom electron photon in photon out electron
Special Relativity Einstein postulated that the speed of light (c) would be measured to be the same by observers in different, moving frames required replacing Galilean tranformation equations with Lorentz equations (converts (x,y,z,t) to (x’,y’,z’,t’). Time was now a variable Found that kinematics were different at higher velocities. Definitions of Newton for energy and momentum needed to be replaced DH 1974 (age 19) - complicated, non-intuitive, clearly very important physics DH 2005 (after 29 years of working at “high velocities” on Fermilab and Brookhaven experiments) - simple and intuitive - still important but would have been developed even without Einstein as velocities of particles in experiments approached c
More on Special Relativity Using Lorentz transformation, Einstein redid a “Newtonian” calculation of Energy giving - Total Energy = mc 2 = 1/ (1 - v 2 / c 2 ) 1/2 Total Energy = mc 2 + kinetic energy showed that the mass of a particle is a type of energy and one can convert mass into kinetic energy (heat) and vice-versa Allows high mass particles to be produced at accelerators like Fermilab Causes energy to be released by nuclear reactions in the Sun, nuclear reactors, etc massless particles (like photons) have only kinetic energy with E = pc (p = momentum)
Particles and Forces Einstein started the process of our current understanding of forces being due to how particles interact Electromagnetic force is due to the emission, absorption, or exchange of a photon Other forces due to the exchange of other particles - the weak nuclear force involves the W and Z electron Z, e+e -> e + e scattering
Particles and Forces Over the past 110 years, 16 particles (and their antiparticles) have been discovered. The lighter ones could be discovered by “tabletop” experiments As the mass increases, higher energy accelerators were needed plus more sensitive and more complex detectors The top quark was discovered in 1995 at Fermilab. About 190 times the mass of the proton. NIU is a member of one of the two collaborations which made this discovery More particles exist (S. Martin’s talk) - graviton (to explain gravity) - Higgs (predicted by electro-weak theory) - something “new” - current theory becomes unphysical - astronomers have detected “dark matter” New accelerators are being built or proposed -- just have to see what is found next