Today, energy is very much on our minds, as we search for ways to power our civilization and serve the needs of our citizens.
But what is energy? Where does it come from? And where do we stand within the great power streams that shape time and space?
Energy comes from a Greek word for activity or working. In physics, it is simply the property or the state of anything in our universe that allows it to do work. Whether it is thermal, kinetic, electro-magnetic, chemical, or gravitational.
The 19th century German scientist Hermann von Helmholtz found that all forms of energy are equivalent, that one form can be transformed into any other. The laws of physics say that in a closed system – such as our universe – energy is conserved. It may be converted, concentrated, or dissipated, but it is never lost.
James Prescott Joule built an apparatus that demonstrated this principle. It had a weight that descended into water and caused a paddle to rotate. He showed that the gravitational energy lost by the weight is equivalent to heat gained by the water from friction with the paddle.
That led to one of several basic energy yardsticks, called a joule. Its the amount needed to lift an apple weighing 100 grams one meter against the pull of Earth’s gravity.
In case you were wondering, it takes about one hundred joules to send a tweet, so tweeted a tech from Twitter.
The metabolism of an average sized person, going about their day, generates about 100 joules a second, or 100 watts, the equivalent of a 100-watt light bulb. In vigorous exercise, the power output of the body goes up by a factor of ten, one order of magnitude, to around a thousand joules per second, or a thousand watts.
In a series of leaps, by additional factors of ten, we can explore the full energy spectrum of the universe. So far, the coldest place observed in nature is the Boomerang Nebula. Here, a dying star ejected its outer layers into space at 600,000 kilometers per hour.
As the expanding clouds of gas became more diffuse, they cooled so dramatically that their molecules fell to just one degree above Absolute Zero, one degree above the total absence of heat. That is around a billion trillionths of a joule, give or take.
That makes the signal sent by the Galileo spacecraft, as it flew around Jupiter, seem positively hot. By the time it reached Earth, its radio signal was down to 10 billion billionths of a watt. Now jump all the way to 150 billionths of a watt.
That is the amount of power entering the human eye from a pair of 50-watt car headlamps a kilometer away. Moving up a full seven powers of ten, moonlight striking a human face adds up to three hundred thousandths of a watt. That is roughly equivalent to a crickets chirp. From there, it’s a mere five powers of ten to the low wattage world of everyday human technologies.
Put ten 100-watt bulbs together. At 1000 joules per second, 1000 watts, that roughly equals the energy of sunlight striking a square meter of Earth’s surface at noon on a clear day. Gather 200 bulbs. 20,000 watts is the energy output of an automobile. A diesel locomotive: 5 million watts. An advanced jet fighter: 75 million watts. An aircraft carrier: almost two hundred million watts.
The most powerful human technologies today function in the range of a billion to 10 billion watts, including large hydro-electric or nuclear power plants. At the upper end of human technologies, was the awesome first stage of a Saturn V rocket. In five separate engines, it consumed 15 tons of fuel per second to generate 190 billion watts of power. How much power can humanity marshal? And how much do we need?