Modern Physics for Non-Scientists Season 1, Episode 4: Let There Be Light

Time Travel, Tunneling, Tennis, and Tea

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.

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.

Speed c 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.

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.

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.

Uncommon Sense-Stretching Time

Muons and Time-Traveling Twins

Escaping Contradiction-Simultaneity Is Relative

Faster than Light-Past, Future, and Elsewhere

Relativity implies that the time order of events can be different in different reference frames.

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.

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.

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.

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.

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.

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.

Wave or Particle?

Einstein's resolution of the photoelectric effect problem suggests that light consists of particles (photons).

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.

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.

Quantum Weirdness and Schrodinger'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.

The Particle Zoo

Cosmic Connections

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.