Skulls in the Stars

Part 2 of a trilogy of posts describing the history of the discovery of conservation of energy, inspired by my research on “Falling Felines and Fundamental Physics.” Part 1 can be read here.

In 1798, Count Rumford presented the first significant challenge to the caloric theory of heat, arguing that the seemingly endless amount of heat that could be generated by boring cannons was inconsistent with the idea that heat is a fluid that lies latent in all materials — and can therefore be exhausted.  Rumford subscribed to the alternative, and it turns out correct, theory: that heat is the observable effect of random motion of particles.

But Rumford did not significantly shift the scientific consensus. In the view of most researchers, the evidence still strongly favored the caloric theory, and Rumford’s results were viewed by some as actually bolstering that theory.

It would be a number of years before the next true milestone in the idea of conservation of energy, and it would also come from an unlikely source: a physician, serving as a doctor on a ship sailing to the Dutch East Indies.  Julius Robert Mayer would introduce the first formal statement of what we now know as the conservation of energy — by making an amazingly astute observation about blood.  His discovery, however, would cost him dearly in the long run.

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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.”

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The first of what will hopefully be a small series of posts inspired by research on my Falling Felines and Fundamental Physics book, which will be sent to the publisher this week!  Made some small updates for clarity to the post since publishing.

In 1851, French physicist Léon Foucault achieved the seemingly impossible: he discovered a way to bring the motions of the cosmos into the lecture hall for anyone to see and understand.

The invention I’m talking about is now known as Foucault’s pendulum: a free-swinging pendulum that changes its direction of swing over the course of the day, and is a direct demonstration of the rotation of the Earth.

Though people of Foucault’s era certainly were aware of the rotation of the Earth, Foucault’s pendulum allowed anyone to see this motion, in real time.  Soon after Foucault’s discovery, his experiment was set up all over the world. People flocked to lecture halls with pendulums installed; after an hour-long presentation by a physicist, the audience could observe for themselves that the direction of swing had changed, directly in accordance with prediction.

Illustration of an 1861 Foucault pendulum demonstration at the London Polytechnic Institute. Image from The World of Wonders (1883).

Lots of people are aware of the connection between Foucault’s pendulum and the rotation of the Earth. Far fewer, however, are aware that the totality of Foucault’s pendulum experiments, done all around the world, demonstrate something just as profound: that the Earth is a sphere!

Explaining how this latter demonstration works takes a bit of effort, but the payoff is a profound understanding of a deep role that geometry plays in physics. In this blog post, I thought I would discuss everything about Foucault’s pendulum: its history, how it shows rotation, and how it shows the roundness of the Earth.

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