Fisica 3 (2013/14)

Alessandro De AngelisUniv. Udine, INFN/INAF Trieste & LIP/IST Lisboa

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Informazioni sul corso• http://www.fisica.uniud.it/~deangeli/corsi.html

• Scopo: Discutere argomenti speciali di elettromagnetismo, con un cenno alla visione moderna. Formulazione covariante delle equazioni di Maxwell, radiazioni da particelle accelerate, propagazione e quantizzazione della radiazione elettromagnetica

• Insegnante: Alessandro De Angelis. Ricevimento: martedi’ 16:30-18:00 (o scrivetemi all’indirizzo alessandro.deangelis@uniud.it )

• Capitano del corso: ??

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Introducing myself…• Professor of physics at the University of Udine and at IST Lisboa, I am Chairman of the

MAGIC gamma-ray telescope in La Palma (Canary Islands), and member of the collaboration managing the Fermi gamma-ray satellite

• Main interests: HE particle astrophysics (in particular with gamma rays) and fundamental physics with accelerators

• Graduated in Padova (bubble chamber physics), post-doc (calibration and commissioning of a calorimeter) and then research associate and staff member at CERN (1993-1999)– Responsible of the software for physics analysis of the DELPHI experiment at LEP. Wrote the first

HEP paper using artificial Neural Networks

• Comeback to Italy in 1999, moving to gamma-ray astroparticle physics (simulation, software, physics analysis)– Fermi satellite (then called GLAST), from NASA

– MAGIC telescope, in Canary Islands. Scientific coordinator from 2005 to 2007

• Author or co-author of more than 600 scientific publications

• Courses lectured during the recent years: Electricity and Magnetism, Quantum Physics, Quantum ChromoDynamics, Astroparticle Physics, Particle Physics

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Course material• No textbook is required, as a photocopy of the material corresponding to the

lectures will be provided by the teacher to the responsible of the class or sites to download will be provided. Useful references follow:

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Evaluation

• Homework: Students will be divided in groups of 2. During the semester sets of 2 exercises will be assigned to each group; the solutions will be discussed in the class ~1 week later (please prepare your solutions in a projectable format, ppt or pdf, and give them to the course coordinator). No evaluation, but mandatory if you want to face the final test.

• Final test: 2 hours, free answer questions and problems (similar to the homeworks). No books allowed (just one a4 page).

Chance to do the final test on January 7th for the students who will do the homework

• Marks: Final test. Possibility of an oral examination if requested by the student.

• After the final test of Jan 7, oral examination including problems during normal examination seasons (Feb/Jul/Sep/Feb).

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Clouds• At the end of the XIX Century, physics appeared to be at an apex

• William Thomson a.k.a. Lord Kelvin (1824-1907) in an address to the British Association for the Advancement of Science in 1900, said

“There is nothing new to be discovered in physics now. All that remains is more and more precise measurement.”

• But later

“The beauty and clearness of the dynamical theory, which asserts heat and light to be modes of motion, is at present obscured by two clouds. The first came into existence with the undulatory theory of light, and was dealt with by Fresnel and Dr Thomas Young; it involved the question, How could the Earth move through an elastic solid, such as essentially is the luminiferous ether?”

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A cloud shielding light• Studies on electromagnetism mainly by Cavendish, Coulomb,

Ampere, Faraday lead to the famous book “A treatise on electricity and magnetism” by J.C. Maxwell, published in final form in 1873

• The electric and magnetic fields can be calculated from a set of 4 equations, which in vacuo are

• The dynamical effect on a charge is F = q (E + v x B)

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Light• Maxwell’s equation imply a wave propagation in-vacuo of

the E, B fields:

(and the same for B), with the speed of the wave given by (e0m0)-1/2

• Quoting Maxwell, “We can scarcely avoid the conclusion that light consists in the transverse undulations of the same medium which is the cause of electric and magnetic phenomena”

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A complete theory; is it consistent?

• Only Einstein realized, 30 years later, that Maxwell’s equations were inconsistent with mechanics

• The argument is subtle, and related to the exchange of reference frames

=> Maxwell’s equations were defining a privileged reference frame

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The other cloud is related to quantization

• The spectra of light emitted by hot gases were discrete

• Nothing in the physics known at that time could explain such a behavior