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Black Holes, Tides, and Curved Spacetime: Understanding Gravity

Black Holes, Tides, and Curved Spacetime: Understanding Gravity

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Black Holes, Tides, and Curved Spacetime: Understanding Gravity

Course No. 1231
Professor Benjamin Schumacher, Ph.D.
Kenyon College
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Course No. 1231
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Course Overview

The force of gravity rules the universe. It governs our everyday lives on Earth and it controls the motions of the heavens above. Yet it is one of the least understood of all the forces of nature. To endeavor to understand this fundamental force is to experience anew something as simple as getting out of bed, throwing a ball, or diving into a pool; and it gives deep insight into the central organizing principle of the cosmos.

Consider these crucial aspects of gravity:

  • Gravity governs the rising and falling of tides—not only tides in the ocean, but tides in the solid rock of Earth itself.
  • Gravity molds the sun and planets into spheres, and it holds celestial objects in their orbits.
  • Gravity ignites the nuclear fires inside each star, then fights a billion-year battle to determine its fate.
  • Gravity collects stars into galaxies and causes galaxies to collide in intricate mergers that we can model with supercomputers.

Without gravity, everything would dissolve into a gas of randomly interacting atoms. It is the only truly universal force, affecting not just matter but also light, time, and, at a basic level, all information. The study of gravity helped spark the Scientific Revolution in the 17th century, and it continues to be at the forefront of physics today, as scientists rely on gravity to investigate otherwise inaccessible phenomena such as dark matter and dark energy. An understanding of gravity—what it is, how it works, and why it is the most dominant and puzzling force in the universe—is both endlessly fascinating and accessible to any curious person, regardless of his or her science education.

Black Holes, Tides, and Curved Spacetime: Understanding Gravity plunges you into this compelling subject in 24 intensively illustrated half-hour lectures, presented by Professor Benjamin Schumacher of Kenyon College. Professor Schumacher is an award-winning teacher, a prominent theoretical physicist, and a protégé of John Archibald Wheeler, the distinguished gravity theorist who first coined the term “black hole.”

No book or other comparable product exists that presents gravity in such comprehensible detail as this course, which covers the key ideas in gravity research over the past 400 years and gives you the background to understand today’s path-breaking theories in physics. Professor Schumacher even walks you through some of the fundamental equations in the field, such as Isaac Newton’s law of universal gravitation and Albert Einstein’s equation governing the curvature of spacetime by matter, giving you a firsthand look at the power of these mathematical expressions to explain reality—plus further opportunities to explore them with the course guidebook.

It All Started with an Apple

The course opens with Newton’s famous apple, which fell from a tree and inspired a revolutionary idea. Newton realized that the force of gravity that acts on an apple near the surface of Earth also extends to the faraway moon, keeping it in its orbit around Earth; similarly, Earth and the other planets are held in orbit around the sun by its gravity, and so on with all the stars and planets throughout the cosmos.

You learn how Newton built on the earlier work of Galileo Galilei and Johannes Kepler to formulate his celebrated law of universal gravitation, which governs the analysis of practically all motion—on Earth and in the heavens. In the first half of the course, you cover the many implications of this spectacular achievement. In the second half, you see how Einstein’s general theory of relativity solved long-standing mysteries of Newton’s theory and advanced an entirely new picture of gravity as a field. The simple reasoning that led Einstein to his extraordinary conclusions is thrilling to follow in Professor Schumacher’s elegant presentation.

Equally thrilling are the surprising features of gravity that you investigate, including these:

  • Gravity is unimaginably weak—a million, trillion, trillion, trillion times weaker than the electromagnetic force that attracts electrons to protons and holds atoms together. Which raises the question: How can weak gravity dominate all other forces?
  • Galileo was the first to point out that objects with different masses fall at the same rate. Neglecting air resistance, a heavier object does not fall faster than a lighter one—a principle famously demonstrated by an astronaut on the moon with a hammer and a feather.
  • The weightless condition that astronauts experience in space is not because they are beyond the reach of gravity, which is almost as strong in low Earth orbit as it is on the ground. Space travelers experience apparent zero gravity because they are in free fall.
  • According to Einstein, gravity is not actually a force at all. It is a warping of the four-dimensional fabric of the universe, called spacetime. A falling body steered only by gravity follows the most economical path in curved spacetime, called a geodesic.
  • From Black Holes to the Expanding Universe

    While gravity is deeply puzzling, it is also a phenomenon that lends itself to simple experiments that shed light on its unique properties. Professor Schumacher performs engaging in-studio demonstrations that show how scientists study gravity. Our knowledge of gravity has advanced from Galileo’s investigation of falling objects, to Henry Cavendish’s determination of the all-important gravitational constant, to Arthur Eddington’s proof that light bends as it passes near the sun, to today’s search for the almost infinitely subtle signature of gravitational waves. The lectures bring this exciting research to life with scores of informative graphics as well as stunning animations.

    This course also brings you to one of the most incredible predictions of Einstein’s general theory of relativity: black holes. Learn how Einstein’s theory describes deformed regions of spacetime that are completely cut off from the rest of the universe. Or are they? Professor Schumacher shows how physicists Stephen Hawking and Jacob Bekenstein discovered an intriguing exception to this rule about black holes that has profound implications for the universe.

    Another outcome of Einstein’s equations holds that the universe should be expanding, as Edwin Hubble discovered it is in the 1920s. More recently, astronomers have found that this expansion is accelerating due to an as-yet-unexplained cosmic antigravity known as dark energy. You explore other mysteries, including a Holy Grail of contemporary physics: the search for a theory that encompasses both gravity, which extends its reach across the cosmos, and quantum mechanics, which governs events at the smallest possible scale.

    In Black Holes, Tides, and Curved Spacetime, Professor Schumacher takes you to the very frontier of contemporary physics to explore several revolutionary theories. It’s one of the many ways that you learn how gravity research is no less exciting today as it was when Isaac Newton sat near an apple tree and had a brilliant idea.

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24 lectures
 |  30 minutes each
Year Released: 2013
  • 1
    The Strangest Force
    Begin your exploration of gravity with Isaac Newton and the famous story of the apple. Why was it such a breakthrough to connect a falling apple with the faraway moon? Review the essential characteristics of gravity and learn why small asteroids and large planets have such different shapes. x
  • 2
    Free Fall and Inertia
    Review three great discoveries by the “grandfather” of gravity research, Galileo Galilei. His most famous experiment may never have happened, but his principle of inertia, law of free fall, and principle of relativity are the basis for everything that comes later in the science of gravity—including key breakthroughs by Einstein. x
  • 3
    Revolution in the Heavens
    Drawing on ideas and observations of Nicolaus Copernicus and Tycho Brahe, Johannes Kepler achieved a great insight about gravity by discovering three laws of planetary motion, relating to the mathematics of orbits. The cause of planetary motion, he determined, must lie in the sun. x
  • 4
    Universal Gravitation
    See how Newton was able to finish Kepler’s revolution by formulating the law of universal gravitation, which says that every object exerts an attractive force on every other object. Also explore Newton’s related discovery of the three laws of motion, which underlie the science of mechanics. x
  • 5
    The Art of Experiment
    Learn how distances in the solar system were first determined. Then chart Henry Cavendish’s historic experiment that found the value of Newton’s gravitational constant. Cavendish’s work allows almost everything in the universe to be weighed. Then see a confirmation of the equivalence principle, which says that gravitational and inertial mass are identical. x
  • 6
    Escape Velocity, Energy, and Rotation
    Begin the first of several lectures that dig deeper into Newton’s laws than Newton himself was able to go. In this lecture, apply the key concepts of energy and angular momentum to study how gravity affects motion. As an example, use simple algebra to calculate the escape velocity from Earth. x
  • 7
    Stars in Their Courses—Orbital Mechanics
    Newton was the first to realize that objects could, in theory, be sent into orbit around Earth. Explore how this works in practice, using the ideas of energy and angular momentum to study how satellites, moons, planets, and stars move through space. x
  • 8
    What Are Tides? Earth and Beyond
    Trace the origin of tides to the simple fact that gravity varies from point to point in space. This leads not just to the rise and fall of the ocean, but to the gradual slowing of Earth’s rotation, Saturn’s spectacular ring system, volcanoes on Jupiter’s moon Io, and many other phenomena. x
  • 9
    Nudge—Perturbations of Orbits
    For the next three lectures, study the effects of gravity on the motions of more than two bodies. Here, see how even very small orbital changes—small perturbations—are significant. Such effects have revealed the presence of unknown planets, both in our own solar system and around other stars. x
  • 10
    Resonance—Surprises in the Intricate Dance
    Resonance happens whenever a small periodic force produces a large effect on a periodic motion—for example, when you push a child on a swing. Learn how resonance due to gravitational interactions between three bodies can lead to amazing phenomena with planets, asteroids, and rings of planets. x
  • 11
    The Million-Body Problem
    Consider the problem of gravitational interactions between millions of bodies, such as the countless stars in a galaxy. Amazingly, mathematics can reveal useful information even in these complicated cases. Discover how the analysis of the motions of galaxies led to the prediction of dark matter. x
  • 12
    The Billion-Year Battle
    Explore the physics of stars, which are balls of gas in a billion-year battle between the inward pull of gravity and the outward pressure produced by nuclear fusion. Follow this story to its ultimate finish—the triumph of gravity in massive stars that end their lives as black holes. x
  • 13
    From Forces to Fields
    For the rest of the course, focus on the revolutionary view of gravitation launched by Albert Einstein. Review new ideas about fields that allowed physics to extend beyond Newtonian mechanics. Then see how Einstein modified Newton’s laws and created the special theory of relativity. x
  • 14
    The Falling Laboratory
    Einstein focused on gravity in his general theory of relativity. Hear about his “happiest thought”—the realization that a man in free fall perceives gravity as zero. This simple insight resolved a mystery going all the way back to Newton and led Einstein to the startling discovery that gravity affects light and time. x
  • 15
    Spacetime in Zero Gravity
    In an influential interpretation of relativity, Einstein’s former mathematics professor Hermann Minkowski reformulated the theory in terms of four-dimensional geometry, which he called spacetime. Learn how to plot events in this coordinate system in cases where gravity is zero. x
  • 16
    Spacetime Tells Matter How to Move
    See how gravity affects Minkowski’s spacetime geometry, discovering that motion in a gravitational field follows the straightest path in curved spacetime. The curvature in spacetime is not caused by gravity; it is gravity. This startling idea is the essence of Einstein’s general theory of relativity. x
  • 17
    Matter Tells Spacetime How to Curve
    The curvature of spacetime depends upon matter—and tidal effects. In this lecture, see how ordinary tidal effects reveal a simplified form of Einstein’s greatest discovery: the equation governing the curvature of spacetime by matter. x
  • 18
    Light in Curved Spacetime
    See how Einstein’s general theory of relativity predicts the bending of light in a gravitational field, famously confirmed in 1919 by the British scientist Arthur Eddington. Learn how this phenomenon creates natural gravitational lenses—and how the bending of light reveals invisible matter in deep space. x
  • 19
    Gravitomagnetism and Gravitational Waves
    The general theory of relativity predicts new phenomena of gravity analogous to those of electromagnetism. Discover how ultra-sensitive experiments have detected the gravitomagnetism of the Earth, and follow the search for elusive gravitational waves that travel through space. x
  • 20
    Gravity’s Horizon—Anatomy of a Black Hole
    Plunge into the subject of black holes, which are massive objects that have collapsed completely under their own gravity. Learn how black holes distort spacetime and explore the supermassive black holes that lie at the hearts of galaxies. Then ask: Are there such things as micro-black holes? x
  • 21
    Which Universe Is Ours?
    Investigate what Einstein called his “greatest mistake”—his rejection of his own theory’s prediction that spacetime should be dynamic and evolving. Chart the work of a group of scientists, including Alexander Friedman, Georges Lemaître, and Edwin Hubble, who advanced the realization that our universe is expanding from an apparent big bang. x
  • 22
    Cosmic Antigravity—Inflation and Dark Energy
    Using everything you’ve learned about gravity, investigate cosmic antigravity, starting with cosmic inflation, a phenomenon that exponentially increased the size of the universe during the big bang. Then, learn why dark matter cannot be made of ordinary protons and neutrons, and explore the recent discovery that the expansion of the universe is accelerating, powered by a mysterious dark energy inherent in space itself. x
  • 23
    The Force of Creation
    Use a black hole to test the laws of thermodynamics, taking a deeper look at the capacity of gravity to pull matter together and increase entropy at the same time. Probe Stephen Hawking’s most surprising discovery, and then learn that the same force that pulls the apple down and steers the stars in their courses is also nature’s ultimate source of order and complexity. x
  • 24
    The Next Revolution
    Survey the greatest unsolved problem in theoretical physics: the search for a quantum theory of gravity. Examine string theory, loop quantum gravity, and also entropic gravity, which suggests a revolutionary link with thermodynamics. Close the course with a deepened appreciation for the connection between everyday features of gravity and the most exciting questions in contemporary physics and cosmology. x

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Benjamin Schumacher

About Your Professor

Benjamin Schumacher, Ph.D.
Kenyon College
Dr. Benjamin Schumacher is Professor of Physics at Kenyon College, where he has taught for 20 years. He received his Ph.D. in Theoretical Physics from The University of Texas at Austin in 1990. Professor Schumacher is the author of numerous scientific papers and two books, including Physics in Spacetime: An Introduction to Special Relativity. As one of the founders of quantum information theory, he introduced the term qubit,...
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Rated 4.7 out of 5 by 41 reviewers.
Rated 5 out of 5 by Gravity - an eye opener We tend to take gravity for granted ... the apple falls from the tree. How can this require 24 lectures? However, Professor Schumacher takes this basic premise, using an historical perspective, and takes the viewer on a journey of discovery into what gravity really is, and isn't. He is a great teacher, always engaging the audience, and able to put complex concepts into a framework that can be understood by the non-astrophysicist even though they are not intuitive. And, as indicated in the title, concepts including tides and black holes are integrated into this grand concept of gravity. Professor Schumacher does a wonderful job in laying out what turns out to be a very interesting, yet complex, topic. February 20, 2014
Rated 5 out of 5 by Opens up a difficult subject to the layperson This course offers a good historical, largely qualitative introduction to students interested in the study of gravity. The mathematics in the course are not so rigorous as to alienate viewers with a modest background in Algebra, but probably won't satisfy the student seeking a more quantitative exploration of gravity. My background is in accounting and economics and I had no trouble following the equations. In a number of places, professor Schumacher obviously employs metaphor as substitute for mathematics, which, again, may or may not appeal to one, depending on his or her background. As far as content goes, although much of the material on gravity and black holes is covered in earlier Great Courses, in my opinion, there is enough new material and fresh takes on the topics here to warrant the purchase. One thing deserves special mention. The professor did a superb job of anticipating and addressing questions which occurred to me during the lectures. One such question involved how black holes are believed to have formed at the center of galaxies. As this particular lecture wound to a close, I felt certain that he would not answer the question, but, in the end, he did. This occurred several times during each lecture and I can't applaud professor Schumacher enough for it. If one is new to the subject, perhaps professor Filippenko's excellent course on Astronomy and/or professor Carroll's equally excellent series, "Dark Matter, Dark Energy," might help to lay the groundwork for this course. January 17, 2014
Rated 5 out of 5 by Black Holes, Tides, and Curved Spacetime: Understa This is a nice and useful course. It is impactful, emphasizing the fundamental effect of gravity driving the universe. October 16, 2016
Rated 5 out of 5 by Incredibly interesting If you are wondering how someone can fill 24 lectures talking about gravity, don't worry -- it could have been twice as long. Even the first half of the course, which addresses Newtonian mechanics, is fascinating and exciting. For me, one of the most important aspects of a lecture course is that the presenter has a pleasant voice and no annoying mannerisms. Schumacher scores there. Neither does he try to score points with his personality or wardrobe. (He wears the same crumpled clothes throughout the 12 hours.) Another great thing I like about him is that he actually presents some math. Science, especially theoretical physics, is nearly all maths, so it is absurd that most science presenters refuse to show any maths at all. Schumacher does the right thing -- he presents equations and explains what they mean. We can all handle that, if the explanation is clear enough, and, for most part, it is. The visuals are good, and this guy really knows his stuff. If the course has any weakness, I would say . . . I forget. Oh yes, like many people, he describes past events in the present tense. "Einstein realizes" instead of "Einstein realized". But as that is the strongest criticism I can come up with, you can be sure this is a great course. Definitely the best course I have bought. August 27, 2016
  • 2016-10-22 T09:35:58.065-05:00
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