Another post inspired by my research into my Falling Felines and Fundamental Physics book!
Energy cannot be created or destroyed, but merely converted from one form to another.
Such is a typical statement of the law of conservation of energy, one of the most important unifying principles of physics. We constantly experience its effects in our day to day lives, whether we recognize it or not. When we accelerate our car, for instance, chemical energy in the fuel is converted into rotational energy in the wheels (with some lost as heat), which is in turn converted into kinetic energy — energy of motion — which carries us from place to place. When we step on the brakes to stop the car, that kinetic energy is converted into heat and some sound energy.
The conservation of energy proves the non-existence of perpetual motion machines: in order for a machine to provide unending motion, it must have an inexhaustible source of energy to power it. Or, in other words: you can’t get more energy out of a machine than you put into it.
An illustration of a perpetual failure, via volume 1 of The Harmsworth Magazine, 1899.
The conservation of energy has even led to important new discoveries. In the 1920s, physicists realized that energy (and momentum) was seemingly not conserved in the process of beta decay, in which an electron or positron is emitted from an unstable atomic nucleus. Though some physicists (looking at you, Niels Bohr) were tempted to throw out the principle of energy conservation altogether, Wolfgang Pauli suggested in 1930 that there must in fact be another particle released in the decay — chargeless, nearly massless, and hardly interacting with ordinary matter. Experimental searches confirmed the existence of the neutrino, which is a key component in the current “theory of everything,” the Standard Model of Physics.
Though the conservation of energy is of fundamental importance in physics, it is a relative newcomer in the history of the subject. Isaac Newton’s Principia was published in 1687, marking the start of quantitative theoretical physics, but conservation of energy was not established until the 1840s, over 150 years later.
Even more curious is the manner in which the three key discoveries were made. The earliest major breakthrough was made via cannon-boring, the next work was done by a doctor, and the conclusive research was done by a brewer! Hence, a simplified history of the discovery of the conservation of energy can be described as booms, blood, and beer!
In this post, I’ll summarize the early history of the subject, and talk at length about the “booms” part of the history. In the next two posts, we’ll cover “blood” and “beer.”