All across the immense reaches of time and space, energy is being exchanged, transferred, released, in a great cosmic pinball game we call our universe.
How does energy stitch the cosmos together, and how do we fit within it? We now climb the power scales of the universe, from atoms, nearly frozen to stillness, to Earth's largest explosions. From stars, colliding, exploding, to distant realms so strange and violent they challenge our imaginations. Where will we find the most powerful objects in the universe?
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's simply the property or the state of anything in our universe that allows it to do work. Whether it's 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's 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. It's 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.
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