Part 6: These short videos were created in August 2007 by Dr. Christopher D. Impey, Professor of Astronomy at the University of Arizona, for his students. They cover a broad range of terms, concepts, and princples in astronomy and astrobiology. Dr. Impey is a University Distinguished Professor and Deputy Head of the Astonomy Department. All videos are intended solely for educational purposes and are licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License. The full list of collections follows below:
Astronomy with Chris Impey -
01. Fundamentals of Science and Astronomy
02. Ancient Astronomy and Celestial Phenomena
03. Concepts and History of Astronomy and Physics
04. Chemistry and Physics
05. Quantum Theory and Radiation
06. Optics and Quantum Theory
07. Geology and Physics
08. Solar Neighborhood and Space Exploration
09. Outer Planets and Planetary Atmospheres
10. The Solar System
11. Interplanetary Bodies
12. Formation and Nature of Planetary Systems
13. Particle Physics and the Sun
14. Stars 1
15. Stars 2
16. Stars 3
17. Galactic Mass Distribtuion and Galaxy Structure
19. Galaxies 2
20. Galaxy Interaction and Motion
21. Deep Space and High-Energy Phenomena
22. The Big Bang, Inflation, and General Cosmology
23. The Big Bang, Inflation, and General Cosmology 2
24. Chemistry and Context for Life
25. Early Earth and Life Processes
26. Life on Earth
27. Life in the Universe
28. Interstellar Travel, SETI, and the Rarity of Life
29. Prospects of Nonhuman Intelligences
Limit to Precision
Transcript: We’re used to the idea that scientists can measure quantities more and more accurately with more and more observations or better and better measuring equipment. This is not true in the world of the atom. There’s a fundamental limit to the precision with which we can measure the physical world. Werner Heisenberg put a mathematical form on the limit to precision; it’s called the Heisenberg Uncertainty Principle. In Heisenberg’s formulation, the product of the uncertainty in position and the uncertainty of momentum of any object is greater then or equal to the Planck constant. The Planck constant is a very tiny number, 10-34 in metric units. This is a tiny amount of imprecision. In the regular world we would never see this. If you used this formula to calculate the imprecision on the velocity of a fastball measured with a radar gun, you would find that our imprecision by Heisenberg’s principle is 10-34, the thirty-fourth decimal place, but if you apply the quantity and the calculation to the hydrogen atom you’ll find that our limit to precision of measurement of the velocity of an electron orbiting a hydrogen atom is almost complete. We do not know its position or its speed with any certainty whatsoever. The quantum world is uncertain. Heisenberg had a second form of his principle which said that the uncertainty in the measurement of energy times the uncertainty in the time over which that energy is measured is also greater to or equal then the Planck constant. For Heisenberg’s Uncertainty Principle may seem esoteric, but it is demonstrated in physics labs around the world everyday. There is a veil below which we have no certain knowledge of the microscopic world.
Transcript: Werner Heisenberg was a German physicist who working in the 1920s and 1930s produced much of the mathematical formulas of the quantum theory of matter and radiation. His towering achievement is the Heisenberg Uncertainty Principle which has enormous philosophical consequences because it removes the idea of determinism from physical theories of the world and says that at the microscopic level we are always uncertain in our measurements of physical quantities. Heisenberg had an interesting career. Refusing to leave Germany as the war approached, he ended up being co-opted into the German bomb making effort and was actually imprisoned by the allies for several years at the end of the Second World War. Heisenberg won the Nobel Prize in physics for his work on the quantum theory.
Transcript: Neils Bohr was a Danish physicist who won the Nobel Prize early in the last century. One of the towering figures of modern physics, he established an institute in Copenhagen that was a Mecca for physicists from all around Europe. Bohr was an architect of the modern view of the atom within the quantum theory of a nucleus surrounded by electrons that could only take fixed energy levels. Bohr believed deeply in the quantum theory and had violent arguments with Einstein who believed there must be a deeper theory of matter. Bohr was also famous for a sense of humor. When he was being interviewed after having won the Nobel Prize by a journalist from the New York Times, the journalist stopped on the threshold of his laboratory noticing a horseshoe that was pinned above the door. “Surely Professor Bohr,” he said, “you of all people, a physical scientist, winner of the Nobel Prize, are not superstitious.” Bohr looked at him and said, “I’ve heard that it works whether you believe in it or not.”
Transcript: When a hot object like a star is observed directly, two types of radiation are seen at the same time. One is the smooth continuous spectrum or thermal spectrum whose peak wavelength reflects the temperature of the object being observed. For a star like the Sun emitting yellow light, this peak wavelength is in the visible spectrum, and the surface temperature of the sun is at about 5,700 Kelvin. In addition to the smooth radiation of the thermal spectrum the hot or ionized gas also emits emission lines, sharp spectral features whose positions reflect the chemical composition of the gas. These two things combined make up the typical emission spectrum of a hot gas in any astronomical situation.
Transcript: Atoms gain energy by collisions or by absorbing photons of radiation. However atoms cannot absorb photons with any energy or wavelength. The energy states of an atom are quantized so atoms can only gain energy according to wavelengths that correspond to the energy difference between electron energy levels. This removal of waves of a certain value leaves dark features in the spectrum or absorption lines. Since atoms that are raised in energy eventually reemit photons, why do the dark absorption lines not get filled in? Usually this is because the atoms causing the absorption are being seen with the background radiating source. As the photons are reemitted they are reemitted in all directions. And so the dark absorption likes are not completely filled in, and we see a series of dark lines in the spectrum.
Transcript: Atoms produce sharp spectral features of emission or absorption corresponding to the specific energy states of the atom. Each element has its own set of energy states. Atoms that are grouped into molecules have a much larger set of possible energy states, in part because they share electrons and in part because they can vibrate and oscillate many different ways. This large set of possible energy states produces a large set of corresponding spectral transitions. Often, these blend together to produce broad bands rather than sharp narrow lines, and so we talk about the spectral bands of either emission or absorption caused by molecules.
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Limited in scope but pretty well informative. Took no time to get through on double speed haha