Overview

Course No. 153

With scientists perhaps on the verge of unlocking the deepest secrets of the universe and with breaking news of discovery after discovery at the frontiers of research, understanding physics has never been so important. “It doesn’t take an Einstein to understand modern physics,” says Professor Wolfson at the outset of these twenty-four lectures on what may be the most important subjects in the universe: relativity and quantum physics. Both have reputations for complexity. But the basic ideas behind them are, in fact, simple and comprehensible by anyone.

These dynamic and illuminating lectures begin with a brief overview of theories of physical reality starting with Aristotle and culminating in Newtonian or “classical” physics. After that, you’ll follow along as Professor Wolfson outlines the logic that led to Einstein’s profound theory of special relativity and the simple yet far-reaching insight on which it rests. With that insight in mind, you’ll move on to consider Einstein’s theory of general relativity and its interpretation of gravitation in terms of the curvature of space and time.

From there, you’ll embark on a dazzling exploration of how inquiry into matter at the atomic and subatomic scales led to quandaries that are resolved—or at least clarified—by quantum mechanics, a vision of physical reality so profound and so at odds with our experience that it nearly defies language. By bringing relativity and quantum mechanics into the same picture, you’ll chart the development of fascinating hypotheses about the origin, development, and possible futures of the entire universe, as well as the possibility that physics can produce a “theory of everything” to account for all aspects of the physical world. But the goal throughout these lectures remains the same: to present the key ideas of modern physics in a way that makes them clear to the interested layperson.

Course Structure

01: Time Travel, Tunneling, Tennis, and Tea

What are the two big ideas of modern physics? How can nonscientists gain a handle on these ideas and the radical changes they bring to our philosophical thinking about the physical world?

Duration: 31 min

02: Heaven and Earth, Place and Motion

Understanding motion is the key to understanding space and time. Is there a “natural” state of motion? Learn why the ancients gave different answers to this question, and how Copernicus, Kepler, and Galileo laid the foundation for a new approach.

Duration: 30 min

03: The Clockwork Universe

Isaac Newton was born in 1642, the year that Galileo died. You’ll learn how he built on the work of Galileo and Kepler, developing the three laws of motion and the concept of universal gravitation. You’ll learn why Newton’s laws suggest a universe that runs like a clock.

Duration: 31 min

04: Let There Be Light!

The study of motion is not all there is to physics. By the 18th century, scientists were delving into the relationship between the two phenomena. Today, electromagnetism is known to be responsible for the chemical interactions of atoms and molecules and all of modern electronic technology.

Duration: 30 min

05: Speed—Relative to What?

In mechanics (the branch of physics that studies motion), the principle of Galilean relativity holds—meaning that the laws of mechanics are the same for anything in uniform motion. Is the same true for the laws of electromagnetism?

Duration: 30 min

06: Earth and the Ether—A Crisis in Physics

In the 1880s, Albert Michelson and Edward Morley conducted an experiment to determine the motion of Earth relative to the ether. You’ll learn about their experiment, its shocking result, and the resulting theoretical crisis.

Duration: 30 min

07: Einstein to the Rescue

In 1905 a young Swiss patent clerk named Albert Einstein resolved the crisis that flowed from the Michelson-Morley result. When Einstein discarded the ether concept and asserted that the principle of relativity holds for all of physics, mechanics as well as electromagnetism, he was making a simple claim with almost unimaginably profound implications.

Duration: 30 min

08: Uncommon Sense—Stretching Time

Why does the simple statement of relativity—that the laws of physics are the same for all observers in uniform motion—lead directly to absurd-seeming situations that violate our commonsense notions of space and time?

Duration: 31 min

09: Muons and Time-Traveling Twins

As a dramatic example of what relativity implies, you will consider a thought experiment involving a pair of twins, one of whom goes on a journey to the stars and returns to Earth younger than her sister!

Duration: 30 min

10: Escaping Contradiction—Simultaneity Is Relative

If, as relativity implies, “moving clocks run slow,” who’s to say which clock is moving?

Duration: 30 min

11: Faster than Light? Past, Future, and Elsewhere

Relativity implies that the time order of events can be different in different reference frames. Does this wreak havoc with cause and effect? Finally, why is it that nothing can go faster than light?

Duration: 30 min

12: What about E=mc² and Is Everything Relative?

Shortly after publishing his 1905 paper on special relativity, Einstein realized that his theory required a fundamental equivalence between mass and energy, which he expressed in the equation E=mc². Among other things, this famous formula means that the energy contained in a single raisin could power a large city for an entire day.

Duration: 31 min

13: A Problem of Gravity

Historically, the path to general relativity followed Einstein’s attempt to incorporate gravity into relativity theory, which led to his understanding of gravity not as a force, but as a local manifestation of geometry in curved spacetime.

Duration: 30 min

14: Curved Spacetime

What causes spacetime to curve? Einstein’s theory of relativity offers an answer, but for decades after he published it, there were only a few, very subtle tests of its validity. How has modern astrophysics changed all that?

Duration: 30 min

15: Black Holes

General relativity is similar to Newtonian gravitation except in the case of very dense objects such as collapsed stars. Learn why they are called black holes.

Duration: 30 min

16: Into the Heart of Matter

With this lecture, you turn from relativity to explore the universe at the smallest scales. By the early 1900s, Ernest Rutherford and colleagues showed that atoms consist of a positively charged nucleus surrounded by negatively charged electrons whirling around it. But Rutherford’s model could not explain all the observed phenomena.

Duration: 31 min

17: Enter the Quantum

The “stuff” of the universe—matter and energy—is not continuously subdividable but comes in discrete “chunks.” This fundamental graininess of the universe has profound implications for the behavior of matter and energy at the smallest scales.

Duration: 30 min

18: Wave or Particle?

Einstein’s resolution of the photoelectric effect problem suggests that light consists of particles (photons). But how can this be reconciled with the understanding of light as an electromagnetic wave?

Duration: 30 min

19: Quantum Uncertainty—Farewell to Determinism

Quantization places severe limits on our ability to observe nature at the atomic scale because it implies that the act of observation disturbs that which is being observed. The result is Werner Heisenberg’s famous Uncertainty Principle. What exactly does this principle say, and what are the philosophical implications?

Duration: 31 min

20: Particle or Wave?

In 1923, Louis de Broglie proposed that, like light photons, particles of matter might also display wave properties. The wave nature of smaller particles such as electrons is quite visible and leads to many unusual phenomena, including quantum tunneling mentioned in Lecture 1.

Duration: 31 min

21: Quantum Weirdness and Schrödinger’s Cat

Wave-particle duality gives rise to strange phenomena, some of which are explored in Schrödinger’s famous “cat in the box” example. Philosophical debate on Schrödinger’s cat still rages.

Duration: 30 min

22: The Particle Zoo

Are quarks, the particles that make up protons and neutrons, the truly elementary particles? What are the three fundamental forces that physicists identify as holding particles together? Are they manifestations of a single, universal force?

Duration: 30 min

23: Cosmic Connections

Why does physicist Freeman Dyson think that intelligence may persist into the infinite future, even as the universe evolves through an unimaginable richness of new forms and structures?

Duration: 31 min

24: Toward a Theory of Everything

Why can’t we answer questions about what happened before the Big Bang, or what goes on at the center of a black hole? Can we manage the formidable task of combining quantum physics with general relativity? Physics may well be the most important subject in the universe, a theoretical realm that ranges from the infinitesimally small to the infinitely vast, its laws governing time, space, and the forces that created our world.

Duration: 32 min