Friday, April 25, 2008
Announcements:
- All assignments are due today, so if there is anything that you
still need to finish (test corrections, personal website, etc.) do so
today by midnight.
- Course
grades have been updated on Blackboard. Please review these
scores to ensure that my records agree with yours, especially Class
Participation.
- Our final exam is scheduled for 8:00 am on Friday, May 2 (in our regular classroom).
If you intend to take this exam at another time, you first need to get
a permission slip from your academic dean, and then make arrangements with me to take this exam at another time.
- The
format of the final exam will be similar to your midterm exams:
50 multiple-choice questions based on homework, class notes, and
textbook material.
- A
review session for the final exam will be held on Wednesday, April 30,
4:00 - 5:00 pm, in Phillips 247 (our regular classroom).
Assignments:
- Read chapter 18 and answer the recommended homework questions and problems.
- Submit any remaining assignments by midnight tonight: test corrections, website reviews, personal website, etc.
- Study for the final exam!
Chapter 18 - Quantum Fields
Field view of reality - All matter and radiation are made of fields. Mass comes from the energy of these fields.
Matter fields and EM fields are quantized, which means that they can only have certain total energy values.
Because
of quantization, these fields act like particles and exhibit
uncertainty and nonlocality when they interact with other systems.
Quantum
field theory explains the existence of particles such as photons,
electrons, and positrons as quantized bundles of energy.
Quantum electrodynamics (QED) - features photons and electrons
electroweak
unification is the theory that ties the electromagnetic force with the
nuclear weak force, which is felt by neutrinos.
Feynman diagrams are useful for understanding QED interactions and for aiding calculations.
Low-energy QED -> classical electrodynamics, but high-energy QED in strongly non-Newtonian (Fig. 18).
particles and antiparticles
Positron (anti-electron) was predicted by Dirac's relativistic version
of the Schroedinger equation, discovered in 1932, and confirmed again
by QED much later.
matter and antimatter, pair creation and annihilation.
Bubble tracks in a cloud chamber have been used to analyze the charge, mass, and velocity of fundamental particles.
Vacuum (empty space) existence is a strong argument for the physical reality of quantum fields.
Fundamental "particles" such as electrons and quarks are truly
point-particles that do not occupy any space but are "field centers".
neutrinos - predicted by electroweak theory
strong force
quarks
standard model - Fermilab link , chart
grand unified theory - features quarks
theory of everything - gravitons; gravity is the force that does not easily fit with the others.
String theory (hypothesis) - quantized theory of gravity
Strings (if they exist) are incredibly small. This slide show gives a sense of this scale, much like the Powers of 10 video shown earlier in the semester.
Brian Greene's book "The Elegant Universe" (also available as a NOVA special) is a good reference for nonscientists.
Epilogue - good overview of the principle themes of the book