Four hundred years ago exactly, Galileo Galilei pointed his telescope at the moon and began, with his wonderfully open mind, writing down what he saw. Other people had done this before him. So why include Galileo in my pantheon of the greatest thinkers ever?

Two reasons:

1. He made us understand that our universe is much bigger than we could imagine.
2. He, in his human and fallible way, stood up for truth against superstition, ignorance and fear, otherwise known as… but I get ahead of myself.

I) The universe is bigger than we can imagine

It’s one of those many cases in science, and in all thought (think: Socrates, Plato, Aristotle), when a great contribution came from several people building on the work of one another. This is wonderful. We place far too much emphasis on the solitary genius.

In Galileo’s case, he built on the prior work of, among others,

1. Copernicus,
2. Tycho Brahe, and
3. Johannes Kepler,

in the process proving wrong the views of Aristotle and everybody else that the sun (and everything else) moved around the earth.

Copernicus

Copernicus was the first to realize that the earth in fact moved around the sun, which must count as one of the most revolutionary (pun intended) advances in our understanding of ourselves and our world. But Copernicus assumed (and why not?) that the orbit was a circle.

Tycho Brahe took things an important step further not so much by thinking as by measuring: the motion of Mars, in particular. He created data, in other words.

Kepler

Kepler, who was Brahe’s assistant, then looked at those data and realized that our orbit, and those of the other planets, could not be circular but had to be elliptical. (A colleague of mine wrote a good and quick summary of all this.)

And Galileo? He filled in a lot of the blanks with his telescope.

• He saw the moons of Jupiter, realizing that they were orbiting another body besides the earth and the sun, which was a shocker.
• He saw that Venus was, like earth, orbiting the sun.
• He saw that the sun was not a prefect orb.
• He saw that the Milky Way contained uncountable stars just like our own sun.

For Homo Sapiens, who was still coming to terms with the fact that the earth was round, all this was almost too much to bear. Our universe was vastly, unimaginably, bigger than the Bible had told us. How would we react to that news?

II) Those who seek and are open to truth will have enemies

This brings us to the church, or shall we say “religion” generally. The church hated Galileo and everything he said and stood for. He questioned what they thought they “knew”, which unsettled them, scared them, threatened them. But they had power. With Nietzschean ressentiment, they attacked him.

You can make anybody recant, and Galileo did. Sort of. In any case, he was declared a heretic and sentenced to house arrest for his remaining life.

In one of my all-time favorite ironies, the Catholic Church, having condemned him, decided–359 years later, in 1992, two years before I sent my first email!–that Galileo was in fact right. How? A committee had discovered this. Good job, guys.

And so, Galileo is still with us, inspiring many. As he discovered that our universe was incomprehensibly big, we are discovering, as another colleague of mine, Geoff Carr, puts it, that

the object that people call the universe, vast though it is, may be just one of an indefinite number of similar structures … that inhabit what is referred to, for want of a better term, as the multiverse.

And as Galileo had to confront the the mobs of ignorance, fear and superstition, so do we today. Here, remind yourself with this casual comment by an Arizona state senator (!), Sylvia Allen, Republican, that the earth is 6,000 years old:

Oh, and what about Aristotle? He was the one proved wrong, you recall. That’s OK, as I have argued. You can be wrong sometimes and still be a great thinker, provided you were genuinely looking for the truth.