The Believing Brain - Michael Shermer [162]
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In the 1920s, four centuries after Galileo changed the geography of knowledge of the world and its immediate environs in space, a cosmological matrix of data, theory, and presentation came together in a new pattern that completely changed the way we view the cosmos and our place in it. As bold a pattern shatterer as he was, Galileo could never have imagined just how inconceivably vast and vacuous the heavens would turn out to be. How that new pattern was discovered, delineated, doubted, debated, and ultimately determined to be correct provides us with a final example of how science works to adjudicate disputes over conflicting patterns, and how we can avoid the trap that belief-dependent realism holds for us if we do not employ the tools of science.
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Cosmologies of Belief
On a clear night away from city lights, if you have reasonably good eyesight you can just barely make out a fuzzy patch of light near the constellation Cassiopeia (the W-shaped pattern of stars), especially if you look a little to the side of it so that the photons that left the Andromeda galaxy 2.5 million years ago land on the periphery of your retina where the dim-light sensitive rods are located. On October 6, 1923, astronomer Edwin Hubble, wielding the one-hundred-inch Hooker telescope atop Mount Wilson in the San Gabriel Mountains above the Los Angeles basin—at the time the largest light-gathering instrument in the world—confirmed that this and many of the other cloudy images he had been focusing in his eyepiece were not nebulae within the Milky Way galaxy as many astronomers believed, but were, in fact, separate galaxies—“island universes” as they were romantically called—and that the universe is bigger than anyone imagined … a lot bigger.
What Hubble confirmed after centuries of debate is that our star is not merely a grain of sand among a hundred billion grains on a single beach; in fact, there are hundreds of billions of beaches, each one of which contains hundreds of billions of grains of sand. The story of how this remarkable discovery was made demonstrates how science works in practice: not only how it requires an elegant blend of data, theory, and presentation as seen in the Galileo story, but also how scientific disputes are resolved and what happens to previously accepted theories rendered obsolete by new observations. In the world of macroscience there are few targets of observation more nebulous than the cosmic nebulae that have perplexed observers for so long. The final resolution of their nature would result in a dramatic shift in our understanding of the large-scale structure of the universe … and beyond.
Lookback Time
When you look out into space the distances are so enormous that you are looking back into time; appropriately, astronomers call this lookback time. Light travels at a speed of about 186,000 miles per second, or about 671 million miles an hour. It takes light 1.3 seconds to travel from the moon to Earth, 8.3 minutes from the sun to Earth, and 4.4 years from our closest stellar neighbor Alpha Centauri to Earth. Thus, when I said that the light from the Andromeda galaxy left 2.5 million years ago, I was using a lookback time reference because it is 2.5 million light-years away. Geologists call such long time spans deep time. Lookback time, deep time … by any other name it dwarfs the imagination of creatures that live a scant four score years.
When it comes to such astronomically distant objects as galaxies, the naked eye could not help early astronomers grasp the nature of the nebula, and thus it is that humanity had to wait until modern optics could provide us with the observational tools needed to see such enormous distances. With one exception. On that clear night away from city lights, after you’ve