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Albert’s Excellent Adventure. The Remarkable Science (and Life) of Albert Einstein 1879-1955. Two especially good Einstein books. Einstein: His Life and Universe Walter Isaacson (Simon & Schuster, 2007) Einstein 1905: The Standard of Greatness
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Albert’s Excellent Adventure The Remarkable Science (and Life) of Albert Einstein 1879-1955
Two especially good Einstein books • Einstein: His Life and Universe Walter Isaacson (Simon & Schuster, 2007) • Einstein 1905: The Standard of Greatness John S. Rigden (Harvard University Press, 2005)
Siblings Albert & Maria (“Maja”) 1884 (ages 5 and 3) 1893 (ages 14 and 12)
Worthy Scientific Predecessors Isaac Newton (1642-1727) Michael Faraday (1791-1867) J. C. Maxwell (1831-1879)
Einstein’s Major Scientific Milestones • 1905 (age 26) – “the miraculous year” – 5 papers on the photoelectric effect, molecular sizes, Brownian motion, and special relativity • 1916-17(30’s) – general theory of relativity (GR) and its application to cosmology; radiation theory • 1924-25(mid-40’s) – statistics of identical particles • 1935(age 56) – a paper (with Podolsky & Rosen) questioning whether quantum mechanics can be regarded as completely describing physical reality
1905 - The Miraculous Year • “On a Heuristic Point of View about the Creation and Conversion of Light” (March) • “A New Determination of Molecular Dimensions” (April) • “On the Movement of Small Particles Suspended in Stationary Liquids Required by the Molecular-Kinetic Theory of Heat” (May) • “On the Electrodynamics of Moving Bodies” (June) • “Does the Inertia of a Body Depend on Its Energy Content?” (September)
Facts about the Photoelectric Effect • Shining light on a clean metal surface produces an electric current (frees electrons). • Photoelectric current is proportional to light intensity. • “Stopping voltage” does not depend on light’s intensity, but does depend on its frequency. • No current at all unless frequency is “above threshold” (threshold frequency depends on the metal used). • If the light frequency is above threshold, then even at very low light intensity (→very weak current), sometimes a photoelectron is emitted as soon as the light strikes the metal.
Einstein’s Explanation of the Photoelectric Effect(March 1905) • When light of a specific frequency interacts with matter, energy is transferred only in discrete amounts. It’s as if a beam of light consists of a hail of pellets (photons), each with the same energy: E = hf • For any given metal, there is a certain minimum amount of work Wmin that an electron must do in escaping, so that a freed electron’s kinetic energy is limited to: (KE)max = hf - W
Brownian Motion and Molecular Sizes(April and May, 1905) • Brownian motion: Microscopic particles suspended in a fluid exhibit a herky-jerky motion due to impacts from the molecules of the fluid. • The results in these papers allow for a determination of Avogadro’s number (and hence the mass of atoms) from observations of Brownian motion.
On the Electrodynamics of Moving Bodies(June 1905) • The Principle of Relativity – The laws of physics are the same in all inertial reference systems or, by means of physical experiments, one inertial coordinate system cannot be distinguished from another inertial coordinate system. • The Principle of the Constancy of Light – The speed of light is the same in all inertial reference systems, independent of the speeds of either the source of the light or the detector of the light. (as summarized by Rigden, p.87)
Does the Inertia of a Body Depend upon its Energy Content?(September 1905) • “If the theory agrees with facts, then radiation transmits inertia [mass] between emitting and absorbing bodies.” (Rigden’s translation of final sentence) • This relationship is that most famous equation E = Mc2. I suggest keeping in mind a verbal description of what happens in a reaction: Energy release = (Mass decrease) x c2
Energy-release examples • Burning carbon: C + O2 →CO2 Energy release ≈ 3 x 108 joules/kg (mass loss)/(reactant mass) ≈ 3 x 10-9 = 3 ppb(!) • Fission: 235U + n → Sr + Xe + a few neutrons Energy release ≈ 8 x 1013 joules/kg (mass loss)/(reactant mass) ≈ 9 x 10-4 = 0.09%
Mission specialist Garrett Reisman aboard Atlantis (STS-132, May 2010)
Some other Successful GR Predictions • Gravitational Redshift: As light moves upward against a gravitational field, its frequency drops. • Time-delay in Radar Ranging: As Venus moves behind the Sun, there’s a delay in getting the back the echoes of a radar beam sent from Earth. • Measurable effects of gravity waves: Observed orbit damping of a binary pulsar is apparently due to energy lost as gravitational radiation.
Two Indispensable Applications of GR:One “Far Out”; One as Close as a Cell Phone • Cosmology (structure and history of the universe at large) – GR provides a sound basis for interpreting a wide variety of observations and for visualizing our “expanding universe”. • In the design of GPS software, it’s essential to allow for the gravitational redshift (the fact that clocks run slower on Earth than at satellite altitude).
Will General Relativity Be Our Final Theory of Gravity? We Don’t Know • General Relativity has not yet been tested in very strong gravitational fields. As more and more stringent tests become possible, GR will either keep passing every test, or else it will have to be modified or abandoned. • A red flag: Although special relativity has been successfully merged with quantum mechanics, there appear to be terrible mathematical difficulties in marrying GR and quantum mechanics.
