6 Confidence

Confidence is a tricky concept, but it’s also a pragmatic one. We can never be 100% sure of anything, but we still need to get on with the business of living our lives. There are bridges and airplanes and smartphones to build, and they all rely our current scientific theories. We don’t have certainty that these theories are correct, but we do have confidence in them. Enough confidence to build a whole civilization around the technologies that they enable.

So where does this confidence come from?

The short answer is repeated testing of falsifiable hypotheses. A slightly longer answer would point out that we use these hypotheses to build scientific models of the world, each part of which must be tested, and which together let us understand the world at a deeper level. We’ll look at models again when we contrast the heliocentric and geocentric models of the solar system.

For the moment, I’d like to offer gravity as an example of the scientific method at work. We’ll start with a phenomenon that I have a lot of confidence in. Pick up a pen or pencil and let it go. It falls. I have dropped – intentionally or unintentionally – thousands of objects in my lifetime. That’s a lot of testing. Whoever I talk to or whatever I read supports that idea that objects fall when dropped. These experiences give me confidence that if I drop a pen, it will fall.

Then along comes a helium balloon or a hot air balloon or a bird or an airplane…. But that’s not the digression that I want to make at the moment. Let’s chalk all of these phenomena up to the atmosphere and continue our observations about objects that fall. This is an example of simplifying. Scientists must simplify to get anywhere…. Of course, we need to come back around later and figure out concepts like buoyancy (helium and hot air balloons) and lift (birds and airplanes).

I’d like to point out an object that creates a larger problem for our hypothesis that objects fall when you drop them – the Moon. You cannot convince me that the Moon is “lighter than air” (really less dense than air), and what air would it float in? The Moon also has a conspicuous lack of wings. So why doesn’t it fall?

The Moon presents a real problem… It appears to be a huge sphere of rock (because it is a huge sphere of rock) and yet, it also appears to float in the sky…. Unlike any other rock we might pick up and drop.

For hundred of years, I think mankind’s answer to the problem of the Moon was a bit of a punt…. Their answer was that the Moon moves in a circle around the Earth because objects in the sky move in circles around the Earth and the Moon is an object in the sky. Things near the Earth fall if you drop them (excepting birds), the Moon doesn’t.

What we really need here is a better understanding for why things drop, a better model of what we now call gravity. Along came the 1600’s, and a fellow named Newton – building on the ideas of others – proposed that objects don’t just drop, they are pulled towards the center of the Earth by a force called gravity. This force acts between all things in the Universe – it is universal – and so of course acts between the Earth and the Moon.

In this theory, the Moon doesn’t fall because it is moving too fast. It is going so fast that instead of falling and crashing into the Earth, it swings around it, like a ball swung on the end of a tether. The ball’s tendency would be, not to turn inward and hit the person swinging it, but instead to fly outward. Similarly, without gravity, the Moon would fly off into space. It is the force of gravity that keeps it tethered, orbiting the Earth roughly once a month, out at a radius of 385,000 km from the Earth’s center, sailing along at about 3,700 km/hr.

And this new understanding of gravity was amazingly important. We would not live in the world that we do without it. However, despite this leap in human understanding, if I drop a pen, it will fall. A deeper understanding of why things fall did not change our confidence, built over thousands of lifetimes, that if you drop an object it will fall.

We are not 100% certain that our current scientific understandings are 100% correct, but we have a lot of confidence that they are a good description of the phenomena that we use them to explain. That understanding will likely improve because our current understanding probably isn’t 100% correct, but the laws of nature won’t change just because we understand them better. Our current theories will continue to work for the situations in which they were developed. Rocks dropped near the surface of the Earth will continue to fall.

This is the type of confidence that scientists and engineers use to develop new technologies and to understand our world.