Chapter 2: Classical Physics

The Birth of Classical Physics

portrait of Isaac Newton
Isaac NewtonThis is a 1689 portrait of Newton by Sir Godfrey Kneller. image source (public domain)

Isaac Newton has been hailed as the greatest physicist of all time,according to this survey of contemporary physicists and the title is well deserved. Not only did he formulate a concise set of mathematical laws that apply to all matter in the universe, but he also invented calculus, just because he needed it to perform some of his computations! Coincidentally, his contemporary Gottfried Leibniz independently developed another formalization of calculus around the same time, prompting them to accuse each other of plagiarism. However, Newton’s discoveries would not have been possible without the work of his predecessors. As Newton famously wrote: “If I have seen further, it is by standing on the shoulders of giants.”Newton made this quote famous, but similar sayings have been attributed to earlier scholars. For further discussion, see this Wikipedia entry. Two of the giants to which he was referring, undoubtedly, were Kepler and Galileo.

As discussed in the previous chapter, Kepler and Galileo overturned a cosmological theory that had stood largely unquestioned since its development in ancient Greece many centuries before. And those two men did much more to pave the way for Newton, besides merely upsetting the status quo. Galileo’s contributions to the science of mechanics—a branch of physics that studies the motions of material objects—were especially influential in Newton’s thinking, leading to Newton’s famous laws of motion. (In fact, Newton credited Galileo with the discovery of the first law of motion.) Newton’s theory of gravity was likewise rooted in Galileo’s discoveries, but also depended crucially on Kepler’s work, as we’ll see in this chapter.

Newton’s laws of motion and gravitation, in turn, provided a framework for subsequent research in physics, astronomy, and other sciences. The foundations laid by Kepler, Galileo, and Newton were quickly followed by a host of new discoveries. Developments in the study of electricity and magnetism culminated in the work of James Clerk Maxwell (1831 – 1879), who did for electromagnetic theory what Newton had done for mechanics: he synthesized the discoveries of his predecessors into a simple and concise set of laws that hold throughout the universe. The laws he discovered are known as Maxwell’s equations.

Newton’s laws and Maxwell’s equations together comprise the foundation of classical physics—basically, everything that was discovered by physicists prior to the 20th century, when relativity and quantum theory were developed. (We’ll get to those in chapters 6 and 7.) Newton’s laws and Maxwell’s equations correctly describe and explain nearly everything that happens with ordinary physical objects, except for objects that are extremely fast, extremely massive, or extremely tiny. When things are moving really fast, the laws of Special Relativity are more accurate than Newton’s laws of motion; for things that are very massive, the laws of General Relativity are more accurate than Newton’s theory of gravity; and for things that are very tiny, the laws of Quantum Mechanics are more accurate than either Newton’s laws or Maxwell’s equations. For everything else, though, Newton’s laws and Maxwell’s equations work just fine, and they are still used by physicists and engineers today.

In fact, the majority of practical technologies that we use every day, from cars to computers, are based on classical physics. Exceptions include satellite communications and GPS navigation systems, which rely on Einstein’s theories of relativity. And some electronic gadgets—e.g. lasers—depend on quantum theory. Apart from those exceptions, almost all commonplace technologies are fruits of classical physics. So if you enjoy the benefits of modern technology, you have Newton and Maxwell to thank!