## 12 August 2010

### And the Cow Flew Over the Moon - Newton Counters Centrifugal Force

The leading Renaissance thinkers were willing to adapt their minds to the facts but weren’t sure how to fully explain them. Although it took decades for most scientists to accept Copernicus’s revolutionary claims, those scientists were not stupid. In addition to scripture and their own senses – it was obvious even to the casual observer that the sun rose and the earth was stationary – they had a fairly reasonable, scientific objection. Copernicus could accept facts as he observed them, but didn’t really have a cogent explanation of why the solar system worked as it did.

Imagine this conversation.

Copernicus’s debate opponent says, “So, Nicoli, let me grant you your silly premise for a moment. Let’s assume that we do, indeed, circle the sun. You claim that we’re spinning through space and traveling at thousands of miles per hour. Okay. What about centrifugal force? Spin a rock at the end of a string and see how many seconds it takes the ant on that rock to fly into space. Why doesn’t this happen to us? Why don’t cows slip out of the grip of milk maids and fly over the moon?”

“I don’t know,” says our hero Copernicus. “I just know what the data suggests. We are orbiting around the sun. I can’t explain it. I just know it is so.”

“So,” continues his opponent, “you have no explanation? You make no attempt to account for the simple fact of centrifugal force? You just want us to believe something that even you don’t understand?”

“Yes.”

Not much of a debate. On the one hand we have ants without opposable thumbs obviously unable to keep their grip on a rock in orbit, a phenomenon that would suggest that we should be observing panicked cows floating off into space if Copernicus was right. And on the other hand we have someone arguing that the data on the movement of planets fits better if we assume that it is the sun and the not the earth that is stationary, if we assume that we’re hurtling through space at about a thousand miles an hour. Preposterous.

It took an Enlightenment thinker – the Enlightenment thinker – to explain why. Isaac Newton solved two problems with one universal law. It is tempting to think – reasonable to suspect – that the explanation for our circling the sun would be different from the explanation of why it is not impossible to find our car in the morning, uncertain as to where it has spun off through centrifugal force. Newton sees a falling apple and realizes that it is pulled by the same force as the earth. Gravity is the universal force that explains why cows don’t fly and the earth does. Newton added laws – a theory – to observations and facts.

Newton gave the lovers of facts a set of laws that made sense of their facts.