Beyond Electricity and magnetism: Making space and time play nice with matter and forcesProf. Stephen Sekula4/28/2010Supplementary Material for PHY1308 (General Physics – Electricity and Magnetism)ABSTRACTI present a few special topics in the modern application of E+M. I then explain the twin revolutions that happened in ~1905 due to our understanding of light from Maxwell's Equations. I then discuss modern efforts to see if these twins can learn to play nice with one another.Magnetoplasma Dynamic DriveNASA Concept Art for Variable Specific Impulse Magnetoplasma Rocket (VASIMR).BioelectricityAmpullae of LorenziniThreshold of sensation: 5nV/cmElectric eels (and other animals) have special cells called “electrocytes”. They are pancake shaped, with opposite charges on opposite sides, each generating 0.15V. Thousands of these act together to create high-voltage and low-voltage electrical dischargesLive frog levitating in a 10 Tesla magnetic field.Twin Revolutions(ca 1900)the dawn of a centuryThermodynamics described heat and its relationship to work and energyMechanics described the universe as a perfect clockwork machine whose outcomes could be exactly predicted at all scales.Electromagnetism explained all electrical and magnetic phenomena, predicted new ones, and explained light as a wave.annoying little problems●There were just some “annoying little problems” left to explain away:●Maxwell's Equations claimed no medium was needed for light to propagate, yet all other waves required a medium. –if light is a wave, it needs a medium - “the aether” - to progagate. We just had to find it!–extremely sensitive experiments failed to discover any such medium.annoying little problems●There were just some “annoying little problems” left to explain away:●Maxwell's Equations also had a problem with “motion”–“The Galilean transformation” related experiments conducted by moving observers and those conducted by stationary observed.–Applying the transformation to Maxwell's Equations led to conflicting predictions about what a moving and stationary observer each predict is going on in the other person's frame of reference.The problem of the aether and the problem of motion led most physicists to conclude that the newly uncovered “Maxwell's Equations” were wrong. After all, how could classical physics uncovered over 200 years be wrong?annoying little problems●There were just some “annoying little problems” left to explain away:●Thermodynamics: a body that absorbed radiation and released it as heat – a blackbody – was predicted to emit high frequency/short wavelength light with increasingly higher and higher probability–“the ultraviolet catastrophe”The ultraviolet catastropheMax Planckca 18781858-1947German physicistMade central contributions to the study of heat (thermodynamics). Turned his attention to the problem of blackbody radiation in 1894, motivated simply by wanting to understand this phenomenon.By 1901, he had reluctantly published an explanation based on two principles: statistics and electromagnetic energy quantization – the idea that a light wave cannot have any energy that it wants.Stephen J. Sekula - SMU 17“An act of desperation”“ . . . a theoretical interpretation [of the blackbody spectrum] had to be found at any cost, no matter how high.” (Max Planck, in a letter to R.W. Wood)Stephen J. Sekula - SMU 18Electromagnetic energy quantizationE = h fElectromagnetic ENERGYA new constant - “Planck's Constant”The frequency of electromagnetic radiation (light)h=6.626×10−34 J⋅s1905Albert EinsteinAlbert Einstein(1879-1955)Fascinated by magnetism as a very early age (his father ran a company that manufactured direct current electrical equipment). Showed early talent for engineering and mathematics.Attended the Swiss Federal Institute of Technology (ETH) in Zurich in 1896 for a teaching diploma; he had shown outstanding performance in mathematics and physics on an earlier entrance exam.Albert EinsteinAlbert Einstein(1879-1955)Met his first wife, Mileva, at ETH (she was the only woman in a class of 6 that entered the teaching diploma course in 1896). They were married in 1903. She failed the exam for her teaching diploma, while Einstein passed the exam.After two frustrating years searching for a teaching post, Albert got a job at the Swiss Patent office (helped by his friends) in 1900. He worked on patent review for electromagnetic devices.Albert EinsteinAlbert Einstein(1879-1955)Einstein continued to work toward a Ph.D., which was awarded in 1905. That same year, he published four groundbreaking papers. These papers concerned:●the atomic theory of matter●how motion affects measurement (relativity)●the nature of light●the equivalence of matter and energyAlbert EinsteinAlbert Einstein(1879-1955)Einstein's most seminal work was published in 1919:●the general theory of relativity●beautifully united space and time into a single, four-dimensional system (“spacetime”)●gravity is explained by geometry●matter and energy tell spacetime how to warp (bend)●spacetime's warping tells matter and energy how to moveRelativity and quantum physicsStephen J. Sekula - SMU 25Einstein's Legacy●Light can be treated as BOTH a particle and a wave (quantum theory of radiation)●depends on the wavelength and how it compares to the dimensions of the target (e.g. atoms)●What's so special about light? (quantum theory of matter)●if light can be BOTH a particle and a wave, is matter also actually a wave too?●matter (electrons, protons, etc.) was confirmed to have wave properties (confirmed in 1927 at Bell Laboratories)●No definite state, only definite possibilities●if all things – radiation and matter – are waves, they they do not possess definite properties (e.g. an electron cannot be said, with absolute certainty, to be in one place and not another)●Probability, describing DEFINITE POSSIBILITIES, rules.Stephen J. Sekula - SMU 26Einstein's Legacy●Space and time are not fixed (relativity)●different observers AGREE on events, but not where or when they happen●All observers measure the same speed for light, REGARDLESS of their state of motion●Energy and mass are the same thing (relativity)●light is pure kinetic energy (no mass)●nothing can travel faster than light in vacuum●mass can be turned into pure energy, and pure energy into massStephen J. Sekula - SMU 27Stephen J. Sekula - SMU 28Stephen
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