Part 7: History of the Earth, techniques in geology, and principles of relativity.
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 - Geology and Physics
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
Inertial and Gravitational Mass
Transcript: It seems as if there are two fundamental ways of thinking about mass. One is inertial mass, the resistance an object presents to any change in its motion. Imagine trying to push a heavy object across a smooth surface. The other is gravitational mass, the force downward on an object caused by gravity. By the time of Einstein these two masses had been found to be utterly equivalent within the limits of measurement to one part in 1015 or less. To Einstein this could not be a coincidence, and so Einstein asserted that there was no way to distinguish between acceleration caused by gravity or by acceleration caused by any other force. This is the basis of his general theory of relativity.
Transcript: Einstein's general theory of relativity is based on his assertion that there's no way to distinguish between acceleration due to gravity and acceleration due to any other force. Consider the following situation: you're in a sealed and closed elevator with no way to see outside. In one situation the elevator is stationary on the Earth's surface, and you feel your normal gravity which would cause an acceleration of 9.8 meters per second per second if you dropped an object in the elevator. In the other situation the elevator is free floating in space but is being accelerated at 9.8 meters per second per second. Standing in the elevator you would feel your normal weight, yet the situations are entirely different. In an analogous situation imagine an elevator falling in free fall on the Earth's surface. You would be weightless within the elevator. Gravity is operating the same on the elevator as on your body, but there's no way to distinguish this situation from the situation of being in the elevator in free space weightless. No gravity is operating in the second situation.
Gravity and Light
Transcript: One of the most important effects of the general theory of relativity is the fact that mass or gravity can bend light or electromagnetic radiation. To see this, consider again the example of a sealed elevator. If the elevator was in free space being accelerated and you stood in the elevator and shined a flashlight across the elevator, you can see that as light traveled across the elevator it would be deflected downwards by a tiny amount caused by the motion of the elevator itself. But since we cannot distinguish this situation from the elevator stationary on the surface of the Earth with the force caused by gravity, gravity must cause the same effect, and in fact it is the case. Mass will deflect light. The effect was measured in1919 during a total eclipse of the Sun by an eclipse expedition led by the astrophysicist Arthur Eddington. The observation of a tiny deflection of light around the limb of the Sun by the mass of the Sun, an effect of barely one arcsecond, was sufficient to confirm the general theory of relativity. It helped to make Einstein famous.
Time and Space
Transcript: In the physics of Isaac Newton, time and space are linear and absolute. Einstein’s theories of relativity changed forever our notions of time and space. In Einstein's special theory of relativity the equivalence of mass and energy and the idea that the speed of light is a fundamental constant means that time and space must be supple. Time can slow down due to high speed travel near the velocity of light. Masses can increase, and physical lengths can actually contract. These effects are real and observed in physics labs every day. In the general theory of relativity we have the idea that mass curves space. We can see this because photons must have an equivalent mass, and so photons in the presence of another gravitating object must be affected by that object. Mass curves light.
Transcript: Albert Einstein was the most famous scientist of the twentieth century and perhaps of all time. The man who invented the theories of special and general relativity was an unconventional scientist who spent most of his career outside the mainstream. His Greek teacher at high school famously said, “Einstein will never amount to much.” Einstein failed his college entrance exams twice and was only able to get admission to a teachers’ college. Eventually he worked in the Berne patent office where he gestated his famous theory of relativity. Einstein won the Nobel Prize in 1905 not for his famous theories of relativity but for his explanation of the photoelectric effect. Even late in his career Einstein did not take part in the establishment process of science. He was a loner for most of his life. He became a cultural icon late in his career when he moved to the United States and worked at the Princeton Institute for Advanced Studies. He was consulted by the president, Roosevelt, over the issue of the atomic bomb. Einstein and a number of other scientists strongly petitioned that it not be used and not even be developed. Einstein died as a cultural icon perhaps the only scientist recognizable to most members of the public.
Transcript: One of the most exciting things about exploration of the solar system with spacecraft in the last few decades is the discovery that many of the objects in the solar system have their own peculiar characteristics that make them very interesting to study. It's as if some of the moons and planets have their own personalities that we can learn through their physical properties. Regardless of these distinctive features, one of the most important things to remember when studying the solar system is called comparative planetology, the idea that there are general features of the planets that can be explained by simple physical principles. For instance, it's easy to see that the inner set of planets, Mercury, Venus, Earth, and Mars, are quite different in nature from the outer planets, Jupiter, Saturn, Uranus, and Neptune. The inner planets are small, dense, and rocky. The outer planets are large, gaseous, and have low density. Comparative planetology uses physical principles to relate planets to each other and to give us ideas for expecting what we might find when we start to investigate other planetary systems around other stars.