This book describes a surprisingly simple paradigm change in physics that makes it physically understandable, solves its many mysteries, and unifies all aspects under a single new principle. The three basic fields in physics are now physically understandable, the three particles that make all atoms can now be physically described, and the four basic forces in the universe are now physically understandable. This new physics-based theory challenges a century of math-based modern physics by physically explaining physics, an achievement that leading physicists consider impossible. Dr. Lang started this new theory in 1950 at age 21, two years after graduating from Caltech in mechanical engineering. His goal was to physically understand physics. It took him five decades to develop this new theory, and another decade to transform it into papers and books. This radically new theory results from filling all space with "spatial fluid"; this fluid follows normal fluid theory, except it has no viscosity and therefore cannot form boundary layers. By intuitively introducing many new concepts, this new theory converts physics into a physically understandable science where energy and matter become surprisingly similar. To make these improvements, it was necessary to reverse all of the assumptions made by Albert Einstein, and to ignore those of his findings that conflict with daily experience. As a consequence, space is no longer empty; the speed of light is not constant; space and time cannot warp together; and mass, length, and time cannot change with speed. This new theory physically explains how and why gravitational, electromagnetic, and quantum phenomena act as they do. A new pulsing concept provides all photons and particles of matter with their frequency, mass, gravity, and quantum properties. This theory further shows why gravitational mass and inertial mass are identical, why the speed of light can be exceeded, and why our universe probably did not result from the Big Bang. This new physics theory is radically different from Relativity, quantum theory, the ether theory of the 1800s, string theories, M-Theory, the Standard Theory, Higgs theory and others. All aspects of physics are now fluid fields that superimpose into a single unified fluid field. Any new paradigm, such as this one that is based on new physical understandings, will undoubtedly lead to important new developments and achievements. The discovery of the double helix molecule in DNA is a prime example of a paradigm change that is based on a new physical understanding that led to many new developments and achievements.