THE WORLD YEAR IN PHYSICS 2005

1
THE WORLD YEAR IN PHYSICS 2005

• Einsteins 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
• --gtNIU can use feedback for desirability of
  future teacher summer camps or workshops (give
  to P.Sievert or A.Windelborn)

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Einsteins 1905 Papers

• David Hedin
• Department of Physics
• Northern Illinois University
• March 4, 2005
• A brief overview plus
• some personal perspective

3
Einsteins 1905 Papers

• March-quantization of the radiation field
  (explained photoelectric effect - Nobel Prize
  1921)
• April and May - Brownian motion
• June and September - special relativity
• Ill discuss first and third, Larry Lurio will
  talk about Brownian motion

4
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 (g )

light
electron
Electron energy linearly related to frequency of
light
Energy of Electron
metal
Similar to how digital cameras work
Frequency of Light
5
P.E. Effect - continued

• DH 1974 (age19). Photoelectric effect
  trivial/easy to understand
• AE revolutionary
• DH 2005. 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
electron
photon in
photon out
6
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

7
More on Special Relativity

• Using Lorentz transformation, Einstein redid a
  Newtonian calculation of Energy giving
• - Total Energy g mc2
• g 1/ (1 - v2 / c2
  )1/2
• Total Energy mc2 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)

8
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

ee -gt e e scattering
electron
electron
Z,g
electron
electron
9
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. Martins 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