Six Not-So-Easy Pieces

Summary

Six Not-So-Easy Pieces by Richard Feynman is a collection of more advanced physics lectures taken from his famous Feynman Lectures on Physics. This companion to Six Easy Pieces looks into more challenging and foundational topics of modern physics, particularly Einstein's theory of relativity, the concepts of space-time, and the importance of symmetry in understanding physical laws.

Symmetries in nature (e.g., rotational symmetry, reflection symmetry) simplify physical laws and lead to conservation principles like the conservation of momentum and angular momentum.

Time symmetry leads to conservation of energy. Spatial symmetry leads to conservation of momentum. Rotational symmetry leads to conservation of angular momentum.

Einsteins Relativity

Time Dilation: Time runs slower for an observer moving at high speeds relative to a stationary observer. Length Contraction: Objects moving at high speeds appear shorter in the direction of motion to an outside observer. Mass-Energy Equivalence: Energy and mass are equivalent, they can be converted into one another (which gives atomic bombs the immense energy). It is described by the most famous equation in physics:

$E = mc^2$

This famous equation is only a special case (for things without impulse (where $p = 0$)) of the more encompassing equation that Einstein developed, which describes the relation between energy and momentum in general.

$E = \sqrt{(mc^2)^2 + (pc)^2}$

General Relativity: The combination of space and time into a single entity—space-time—provides a unified framework for understanding the universe and is one of Einstein's greatest insights. This space time can be curved by things that have mass, which explains time dilation, length contraction, and why things fall down, beautifully. Furthermore it is experimentally verified because it can predict the paths that orbits take without the errors than Newton's theories had. Furthermore, we can even detect the bending of space and time in phenomena such as gravitational waves. Things fall because they follow geodesics. Geodesics are the shortest paths in curved space-time, and they determine the motion of objects in a gravitational field. A straight line in a curved space might not look straight to the person on the trajectory. This is beautifully explained in one of Vsauces videos too.

All in all this book offers a deeper dive into fundamental principles of physics, particularly relativity, symmetry, and space-time. While more advanced than Six Easy Pieces, the book remains engaging and thought-provoking throughout. Yet, I would still prefer to read the Feynman Lectures in full instead of this compilation.