“I am ashamed at the number of things around my house and shops that are done by … human beings. Hereafter a motor must do all the chores.” – Thomas Edison
Labor Day provides us with an opportunity to consider how much labor the use of energy saves us. After all, energy is defined as the capacity to do work. Work is labor, and the more tasks that inanimate energy can do via machines, the greater the reward for humans in productivity and leisure time.
For the vast majority of human history, our ability to do work was limited by our muscles or the muscles of animals. Only through the industrial revolution and the harnessing of massive amounts of energy are we able to enjoy the technologies and comforts of modern life.
In the past, to live a life of opulence, it took hundreds of people working to provide the kind of luxuries that we take for granted. For example, it took 498 people to prepare each meal for King Louis XIV at Versailles in 1700. Today, the typical supermarket has far more food choices than King Louis XIV imagined and he was King in the world’s richest city. Today’s energy-powered transportation and communications options would also be were also unimaginable to the world’s richest people of the past and yet today even homeless people sometimes have cell phones.
To better appreciate how the use of energy saves human labor, some researched calculated how many humans it would take to generate the energy we consume on a daily basis. According to data from 2005, Jennifer Barker found that a fit person can average a sustained output of about one-tenth of a horsepower. This means that average American would have approximately 147 energy slaves working around the clock to generate the energy necessary for modern life.
Barker uses examples to illuminate our “unimaginable opulence”:
Now think about your energy slaves as you go about your day. Every time you leave a 75 Watt light bulb burning, one of these very strong energy slaves is pedaling away as hard as he can to keep it going for you. If that 25 mpg car has a 100 horsepower motor, it’s the equivalent of 1,000 strong people.
If you add up all the power we Americans use, on average, to light and heat our homes, transport us, etc. and convert it to the human energy equivalent, it’s an unimaginable opulence by the standards of all the humans who came before us. It is as if our well-being were measured by the number of energy slaves we have learned to command.
The transition from human power to animal power to machine power has made energy the master resource. “Energy will do anything that can be done in the world,” stated Johann Wolfgang von Goethe during the Industrial Revolution. The labor-enhancing, labor-saving characteristic of energy-enabled machinery was described by Erich Zimmermann in the mid-twentieth century as follows:
The shift to machine power changed America from a rural agricultural nation to an industrial giant. It also made men’s lives easier and richer. In 1850, the average American worked seventy hours a week. Today he works forty-three. In 1850, our average American produced about 27 cents’ worth of goods in an hour. Today he produces about $1.40 worth in dollars of the same purchasing power.
“By providing energy flows of high power density, fossil fuels and electricity made it possible to embark on a large-scale industrialization,” energy polymath Vaclav Smil more recently observed, “creating a predominantly urban civilization with unprecedented levels of economic growth reflected in better health, greater social opportunities, higher disposable incomes, expanded transportation and an overwhelming flow of information.”
The benefits of modern energy contribute to days off to relax and celebrate and even permanent retirement from work. This Labor Day, we should take time to appreciate energy in its many manifestations.
 Thomas Edison, quoted in Theresa Collins and Lisa Gitelman. Thomas Edison and Modern America (New York: Bedford/St. Martin’s, 2002), p. 60.
 Matt Ridely, The Rational Optimist
 Quoted in Vaclav Smil, Energy: A Beginner’s Guide (Oxford: One World, 2006), epigraph.
 Erich Zimmermann, World Resources and Industries (New York: Harper & Brothers, 1951), p. 58.
 Vaclav Smil, Energies (Cambridge, MA: The MIT Press, 1999), p. 134.