(FYI, we’re talking about this post)
Thanks for being the devil’s advocate. Nobody ever stands up for that guy!
You ask an important question about the difference between a scientific theory, a scientific fact, and a scientific law, and in doing so you may have inadvertently caught a mistake in Cosmos. We’ll get to that, but first, let’s untangle these confusing terms.
A scientific theory begins life as a hypothesis. And a hypothesis is born when an observation comes together with a possible explanation in the womb of the mind. That hypothesis is fed further observations, and if all remains correct, one day it grows up into a theory. The more a theory can explain, the stronger it is. It can be modified or proven wrong by future observations. What is special about a theory is that it ultimately allows us to predict what will happen and also explain why it is happening.
A scientific law is fairly similar to a theory, except that it doesn’t explain the why. Let’s take the Law of Gravity as an example. It has been incredibly well supported by observation,and it has been revised over time to adapt to new observations (like spacetime), but nothing about the Law of Gravity explains why gravity does its gravitational things. We usually capitalize them because it makes them look more important.
A scientific fact, the way I interpret it (its philosophical definition has been debated many times), is an observation that no one has been able to disprove and that we expect two people would observe in exactly the same way regardless of when or where or how they observed it. For instance, it is a scientific fact that the jellyfish green fluorescent protein emits light at a wavelength of 509 nm when it is excited by 395 nm light. This is just a thing that happens. It is an observation that can then be applied to a more general theory of fluorescence. Got it? Good.
So what is evolution? It’s a scientific theory. It is a thing that we can see happening (yes, I mean actually observe it happening) and it also allows us to explain why it is happening. The theory of evolution encompasses all the chemistry of DNA, the random action of mutations, and the mathematics of selection. It’s a what and a why.
What about gravity? Why did Neil call it a “theory”? Here’s the mistake in Cosmos that I think you’ve identified. He shouldn’t have called gravity a theory. It’s a law. We know a lot about the what of gravity, from how mass interacts at a distance to curvatures in the fabric of spacetime, but we don’t know why gravity gravities. So you’re right that gravity is a law. Neil was wrong, at least on this week’s show.
By this time you’re all probably thinking “Joe, this is a load of semantic bulls**t!!" You are absolutely right. It is a load of semantic bulls**t. It’s actually the very definition of semantics, the study of meaning. I’d forgive some of you for thinking this is all a worthless waste of verbal and cognitive energy, because what’s wrong with just saying something is or isn’t?
Well, that all depends on what your definition of “is” is.