Our Imperiled World: It took billions of years to make the earth habitable for humans. It won’t take that long to ruin it.
The American Scholar: Our Imperiled World - Owen Gingerich
I’m holding in my hands two ball bearings, each about two centimeters in diameter. I propose to build a model of our cosmic environment here at the United Nations Headquarters in New York. The first sphere represents the sun. On this scale Earth will be two meters away, and much too small for you to see it. Mars, even smaller, will be another meter farther from the sun. On this scale, where should we place the second sphere, representing the closest star to our own solar system? On top of the Empire State Building? At JFK? Much too close! It should be placed some distance beyond Toronto.
These stars are but two among the 200 billion in our Milky Way Galaxy. That’s some 30 stars apiece for every man, woman, and child on Earth. On the scale of our ball-bearing model, the Milky Way would go far beyond the moon! So now let’s collapse our model by 10 billion times, such that our disk-shaped, pinwheel galaxy would be the size of a two-euro coin. Now where should I place a second two-euro coin to represent the next closest major spiral galaxy? In London? Be surprised! The coins should be only about 60 centimeters apart. Collisions between stars are fantastically rare because stars are so far apart, whereas collisions between galaxies are common because the galaxies are relatively close together, though the collisions take ages to happen.
A most curious and interesting fact about the distant galaxies is that they are rushing away from each other, and the farther they are from us, the faster they are going. It’s as if an immense explosion took place, as indeed it did, and the faster fragments are the farthest away. We can calculate from the speeds and distance when that explosion happened, 13.7 billion years ago, the creation of the universe, and the creation of time itself. This means we live in a universe with a history, a universe that has been changing throughout time. It is the history of the universe, and our place within it, that I want to sketch briefly.
In the first three minutes of that fiery Big Bang, the two lightest elements were created, hydrogen and helium. Fire of sorts existed, yes, but no earth or air, and no water because there was no oxygen for H2O. The Big Bang was over before the heavier elements had a chance to form.