Phy107Lect38

Phy107Lect38 - Final Exam: Sat. Dec. 18, 2:45-4:45 pm, 1300...

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Mon. Dec 13 Phy107 Lecture 38 From last time… • Quantum field theory is a relativistic quantum theory of fields and interactions. • Fermions make up matter, and bosons mediate the forces by particle exchange. • Lots of particles, lots of interactions, but can be unified to some extent. • Electroweak accepted, leaving quarks and leptons as separate particles, strong and electroweak gauge bosons, Higgs boson. • GUTs attempt to include the strong force. Final Exam : Sat. Dec. 18, 2:45-4:45 pm, 1300 Sterling Exam is cumulative, covering all material
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Mon. Dec 13 Phy107 Lecture 38 Today • What about gravity - where does it fit in? • Classical vs quantum theories of gravity • Classical unification • Extra dimensions! • String theory
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Mon. Dec 13 Phy107 Lecture 38 Gravity • Haven’t talked recently about gravity. • Gravity not particularly relevant at the scale of particle physics, because the particles are not massive enough to interact gravitationally. • But shouldn’t we be able to explain gravity in the same breath as particles and interactions? • Can’t we unify both quantum mechanics and gravity into a theory of everything?
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Mon. Dec 13 Phy107 Lecture 38 Einstein’s gravity • General Relativity is a classical theory. • Einstein was a classical guy, even though he received Nobel for photoelectric effect, general theory of relativity has nothing to do with quantum mechanics. • General relativity has to do with curved space-time, and motion of objects in that curved space time.
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Mon. Dec 13 Phy107 Lecture 38 • Connect electromagnetism and gravity in a classical relativistic theory. • Kaluza and Klein found a theory in five with one interaction (5-dimensional gravity). • When one of the dimensions was ‘compactified’, two interactions resulted: gravity and electromagnetism. • What appears to us as two distinct interactions originate from only one. Kaluza & Klein, 1920
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Mon. Dec 13 Phy107 Lecture 38 Extra dimensions? • How can there be extra dimensions? • Can imagine more physical dimensions, but we do not see them • We would be unaware of them if they were very small, e.g. very strongly curved a la GR • Example: A power cable from far away looks like a one-dimensional line. • Up close we see that it is really a 2D surface – The 2nd dimension was curved so much we do not notice it.
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Phy107 Lecture 38 Compactificaton in Kaluza-Klein • The process of ‘rolling up’ the extra dimension to leave four space-time dimensions… • …made the 5-dimensional geometrical gravitational interaction appear as two different interactions in 4D: Another unification! Electromagnetism
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Phy107Lect38 - Final Exam: Sat. Dec. 18, 2:45-4:45 pm, 1300...

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