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Einstein's Fridge

How the Difference Between Hot and Cold Explains the Universe



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About The Book

This entertaining, eye-opening account of how the laws of thermodynamics are essential to understanding the world today—from refrigeration and jet engines to calorie counting and global warming—is “a lesson in how to do popular science right” (Kirkus Reviews).

Einstein’s Fridge tells the incredible epic story of the scientists who, over two centuries, harnessed the power of heat and ice and formulated a theory essential to comprehending our universe. “Although thermodynamics has been studied for hundreds of years…few nonscientists appreciate how its principles have shaped the modern world” (Scientific American). Thermodynamics—the branch of physics that deals with energy and entropy—governs everything from the behavior of living cells to the black hole at the center of our galaxy. Not only that, but thermodynamics explains why we must eat and breathe, how lights turn on, the limits of computing, and how the universe will end.

The brilliant people who decoded its laws came from every branch of the sciences; they were engineers, physicists, chemists, biologists, cosmologists, and mathematicians. From French military engineer and physicist Sadi Carnot to Lord Kelvin, James Joule, Albert Einstein, Emmy Noether, Alan Turing, and Stephen Hawking, author Paul Sen introduces us to all of the players who passed the baton of scientific progress through time and across nations. Incredibly driven and idealistic, these brave pioneers performed groundbreaking work often in the face of torment and tragedy. Their discoveries helped create the modern world and transformed every branch of science, from biology to cosmology.

“Elegantly written and engaging” (Financial Times), Einstein’s Fridge brings to life one of the most important scientific revolutions of all time and captures the thrill of discovery and the power of scientific progress to shape the course of history.


Chapter One: A Tour of Britain CHAPTER ONE A Tour of Britain
The number of steam engines has multiplied prodigiously.

—French economist and businessman Jean-Baptiste Say on visiting Britain

On September 19, 1814, Jean-Baptiste Say, a forty-seven-year-old French businessman and economist, embarked on a ten-week spying mission to Britain. Napoléon had been exiled to the Mediterranean island of Elba three months earlier, and the trade blockade between France and her northern neighbor had ended. The new government in Paris sensed an opportunity to investigate the reasons underpinning Britain’s recent economic surge, and in Jean-Baptiste Say, they found the ideal man. Say had lived for two years in Britain as a teenager, working in the offices of various British trading companies and learning fluent English. Later, he’d run a textile factory in northern France and become a published economist, thus acquiring both a practical and theoretical appreciation of commerce.

As spying missions go, Say’s was neither dangerous nor clandestine. He made no secret of his reasons for being in Britain. A gregarious Anglophile, he crisscrossed the country, obtaining access to mines, factories, and ports and, in his leisure time, to theaters and country houses. And since his last visit twenty-six years earlier, Say witnessed a nation transformed. He began his tour in Fulham, a village to the west of London where he’d spent time in his youth. He found it unrecognizable. There were new houses all around, and a meadow he’d enjoyed strolling through years before had become a shop-filled street.

For Say, Fulham’s metamorphosis was representative of what had happened over the eighteenth century to the country as a whole. Britain’s population had soared, growing from 6 million to 9 million, and her people had become the best fed, clothed, and paid in Europe. Trade had burgeoned, too—Say noted that the number of ships in the port of London had tripled to three thousand. In other parts of the country, he admired new canals and city streets illuminated by gaslighting. He took in a foundry for machine parts in Birmingham, a seven-story textile spinning factory in Manchester, coal mines near York and Newcastle, and a steam-powered mill for weaving cotton fabrics in Glasgow. Its owner, a certain Finlay, was so proud of this machinery and indeed so unperturbed at the thought of potential French competition that he showed Say how it worked himself.

Powering this economic miracle was Britain’s cotton-manufacturing industry, whose export value had shot up twenty-five-fold in the time between Say’s first visit in the 1780s and his second in the 1810s. Many in France, including those who had had Napoléon’s ear, believed that the best way to emulate this was by acquiring an empire—Britain, after all, had access to cheap raw cotton from her colonies. Say disagreed. He considered colonialism to be unprofitable in the long run and instead regarded technological innovation as the key to Britain’s success. Above all else, one piece of technology caught Say’s eye and his imagination:

“Everywhere, the number of steam engines has multiplied prodigiously. Thirty years ago, there were only two or three of them in London; now there are thousands.… Industrial activity can no longer be profitably sustained without the powerful aid they give.”

Above all, steam power had revolutionized Britain’s mining industry. Mines, like water wells, are shafts dug into the ground and are prone to flooding. The preindustrial horse-driven pumps had struggled to lift water out of any mines that were more than a few yards deep. Moreover, it takes around two acres to feed a horse for a year, meaning there wasn’t enough grazing land in Britain to feed the number of horses widespread mining would require. But by 1820, steam technology had advanced to the point where engines could easily pump water out of shafts that were over three hundred yards deep. This lowered the cost of mining coal, which, because coal is a crucial ingredient in the manufacture of iron, made iron more abundant, too. Between 1750 and 1805, production of the metal soared ninefold from 28,000 to 250,000 tons a year.

Steam power in early nineteenth-century Britain was ubiquitous but not as innovative as Say thought. The technology had proliferated not because Britons were especially inventive, but because their country was so replete with coal that even poorly designed and wasteful engines were profitable. Take, for example, the one installed at the Caprington Colliery in southwest Scotland in 1811, which operated on a principle pioneered a century earlier by an English inventor called Thomas Newcomen. Devices such as this weren’t what we, in the twenty-first century, regard as steam engines, in which the pressure exerted by hot steam pushes a piston. Instead, they are best understood as steam-enabled vacuum engines. The relationship between the heat created in their furnaces and the mechanical work they perform is convoluted and inefficient.

A Newcomen engine

“Newcomen engines” work as follows: Heat from burning coal creates steam. This flows via an inlet valve into a large cylinder in which a piston can move up and down. Initially the piston rests at the top of the cylinder. Once this is full of steam, the inlet valve closes. Cold water is sprayed into the cylinder, cooling the steam inside, causing it to condense into water. Because water occupies much less space than steam, this creates a partial vacuum below the piston. Atmospheric air will always try to fill a void, and the only way it can do so in this arrangement is by pushing the piston down. This is the source of the engine’s power. The steam is a means to create a vacuum and the downward pressure of the atmosphere does the work.

To observe this effect, pour a small amount of water into an empty soft-drink can and warm it until it’s filled with steam. Take some safety precautions and pick up the can with tongs—it will be hot—and quickly turn it upside down as you submerge it in a bowl of ice-cold water. The steam condenses into water, thus creating a partial vacuum inside the can. Pressure from the earth’s atmosphere will then crush the can.

In the steam engine I’ve been describing, this process—filling the cylinder with steam and condensing it to water so a partial vacuum is created—repeats over and over. Thus, the piston goes up and down, powering a pump.

Newcomen engines consumed prodigious amounts of coal. They burned a bushel—84 pounds—of coal to raise between 5 to 10 million pounds of water by one foot. This quantity, the amount of water that can be raised by one foot for every bushel burned, was called the engine’s duty. By modern standards, these engines were very inefficient, wasting around 99.5 percent of the heat energy released as the coal burned.

That such wasteful engines continued to be used for over a century was due to cheap coal. At the time of Say’s visit, Britain’s mines produced 16 million tons every year, and in the new industrial towns of Leeds and Birmingham, coal often sold at less than ten shillings per ton. At these prices, poor engine design mattered little.

Then in 1769, the Scottish engineer James Watt had patented a modification to the Newcomen engine, which roughly quadrupled its duty. But the arrival of Watt’s designs, paradoxically, put a brake on British innovation for thirty years as he and his business partner Matthew Boulton used the patent system to prevent other engineers from bringing further improvements to the market. Then, as now, commercial success was not necessarily aligned with innovation.

In addition, the people of England had a love-hate relationship with science. On the one hand, over the eighteenth century, the country’s growing middle class had developed a great interest in natural philosophy, as science was termed. Encyclopedias were bestsellers. Crowds flocked to public lectures that covered topics from the behavior of magnets to recent astronomical discoveries. Clubs sprang up as informal gatherings for scientific discussion. The most famous came to be known as the Lunar Society, which counted Watt and Boulton as members. But on the other hand, some sections of the public also grew wary of science because many of its practitioners, such as Joseph Priestley, the discoverer of oxygen, publicly supported the radical politics of the French Revolution. He paid dearly for his views. In 1791, an angry mob burned down his house and laboratory.

Moreover, England’s two universities, Oxford and Cambridge, offered no courses in subjects that resemble modern-day physics and engineering. Cambridge, being Isaac Newton’s alma mater, did rigorously train students in the mathematical principles that great scientist had discovered. But basking in Newton’s legacy, professors there saw no need to extend his work and were suspicious of novel mathematical techniques being developed abroad. In 1806, when one progressive scholar, Robert Woodhouse, urged the adoption of a European style of mathematics, he was condemned as unpatriotic in the conservative Anti-Jacobin Review. The real-world applications of mathematics were also not a priority. Yes, Newton’s laws did describe aspects of the universe we inhabit such as the orbits of planets. But Cambridge professors felt the purpose of teaching the laws was to provide mental training to students drawn from the landed gentry who would go on to serve church, state, and empire. Cambridge students railed against this, but it would be decades before attitudes changed.

France, however, was very different.

Jean-Baptiste Say published his observations on Britain’s economic and industrial transformation in a book entitled De l’Angleterre et des Anglais, in 1816. His report, and those of others, convinced French engineers, businessmen, and politicians that the way to catch up with Britain economically was to exploit steam power. But they faced a problem: coal was scarce south of the Channel. French mines produced a million tons annually, and as most of these were in the remote Languedoc region, the price never dropped below twenty-eight shillings per ton, three times higher than in England’s industrial heartland. This meant that from the earliest stages of their country’s industrialization, French engineers cared about engine efficiency—how to maximize the useful work that can be extracted from burning a given amount of coal—in a way most of their British counterparts did not.

French scientific and mathematical education was also very different from that in Britain, as is exemplified by the institution where Say became professor of industrial economy three years after returning to his homeland. The National Conservatory of Arts and Crafts, as it was named, was a far cry from an elite institution such as Cambridge. Located in Paris, the Conservatory was created as part of the French revolutionary government’s commitment to public education, and it embodied that regime’s conviction that science and mathematics were weapons in a war against superstition and arbitrary aristocratic privilege. They provided rational laws to help found a rational society. Subsequently, Napoléon continued to support these subjects, seeing them as important to France’s military ambitions. Working in this context, French scientists, therefore, saw Newton’s work as a foundation on which to build. They widened its reach and made it far simpler to use. At places such as the Conservatory, it was natural to think that mathematical analysis could be applied to steam engines and, in particular, to their efficiency.

And here a young student laid the foundations of the science of thermodynamics.

About The Author

Photograph by Darin Prindle

Paul Sen first encountered thermodynamics while studying engineering at the University of Cambridge. He became a documentary filmmaker with a passion for communicating profound scientific ideas in an engaging and accessible way to a wide audience with landmark TV series such as Triumph of the Nerds and Atom. These brought a love of storytelling to the worlds of science and technology. Paul’s award-winning TV company Furnace, where he is creative director, has made BBC science series such as Everything and NothingOrder and DisorderThe Secrets of Quantum Physics, and ninety-minute films such as Gravity and Me: The Force That Shapes Our Lives and Oak Tree: Nature’s Greatest Survivor. This won the prestigious Royal Television Society Award for best science and natural history program and the Grierson Award for best science documentary in 2016. Einstein’s Fridge is born out of Paul’s conviction that the history of science is the history that matters. He also creates educational videos on science and its history at  

Product Details

  • Publisher: Scribner (March 22, 2022)
  • Length: 320 pages
  • ISBN13: 9781501181313

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Raves and Reviews

“[An] elegantly written and engaging book. . . . It’s a measure of Sen’s achievement that by combining science, history and biography he takes us on a successful tour through thermodynamics.” Financial Times

“Makes a strong case that thermodynamics is every bit as lively as those other fields—and vastly more useful for understanding what makes the universe tick. . . . Thermodynamics does not bow to other fields; other fields bow to it.” —The Wall Street Journal

"An entertaining, eye-opening account of the extraordinary team of innovators who discovered the laws of thermodynamics essential to understanding the world today—from refrigeration and jet engines to calorie counting and global warming." Next Big Idea Club

“Superb. . . . Einstein’s Fridge offers an accessible and crystal-clear portrait of this discipline’s breadth. . . . [the book] wanders widely while never losing its connection to the central theme. . . . splendid.” Physics World

“Sen performs an exquisite examination of an ostensibly simple distinction, the difference between hot and cold.” —Booklist

“Although thermodynamics has been studied for hundreds of years, filmmaker Sen writes, few nonscientists appreciate how its principles have shaped the modern world.” —Scientific American

“I am grateful for Paul Sen’s fascinating new scientific history of thermodynamics—now I can explain my son’s two favorite things: fire and ice.” —Jonny Diamond, LitHub

“A lesson in how to do popular science right.” —Kirkus Reviews

“When you combine some of the most profound concepts in physics with exceptional storytelling, this is what you get: popular science writing at its very best. Einstein’s Fridge is a hugely readable and entertaining history of thermodynamics and how it has created and shaped our world.” —Jim Al-Khalili, author of The World According to Physics

“Impressive debut. . . . Sen’s history of hot and cold is pop-science that hits the mark.” —Publishers Weekly

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