Scientific Theories

Earlier today, my sister-in-law asked me about science, and evolution specifically. She described how this morning, after going to church with her husband's family, she told her sister-in-law that she had some questions about how the bible fits with evolution. She used the phrase, "Since evolution is basically a fact." Her sister-in-law responded with, "It's really more of a theory."

As soon as I heard her say, even secondhand, "It's really more of a theory," I could feel myself starting to get worked up. As you can see, I haven't rambled in a long while (as I write this, I'm hoping that my blog hasn't been garbage-collected). But this brief conversation inspired me to compose a response.

The phrase, "It's really more of a theory," (and its cousin, "It's just a theory,") is evidence of a general misunderstanding of science. So I'm going to write a basic tutorial of the scientific method and how it produces theories.

So, for starters, here is a simplified version of the scientific method:

1. Observe an event.
2. Come up with a general rule that describes what you observed. It needs to predict the behavior of similar events that you have not yet observed. Call it a hypothesis.
3. Invent a way to test the predictions of your hypothesis.
4. Apply your test to one or more thus-untested events.
5. If you disproved your hypothesis, then that really sucks. You can give up and throw it out, or you can modify it to match your new observations and jump back to step 3.
6. If you get here, then congratulations, you may now call your hypothesis a theory!

Now let's try this out: I'm going to invent a theory (you may know of a similar one, some guy named Isaac Newton came up with it back in the late 1600s):

• Observation (1): I dropped a baseball, and it fell to the floor.
• Hypothesis (2): The floor possesses something which I will call gravity, which attracts baseballs.
• Test (3): I will drop another baseball (to make sure that this gravity affects all baseballs, and not just the first one), and a bowling ball (to make sure that gravity does not affect any other objects).
• Application (4): The second baseball also fell to the floor. Great, so far so good! But the bowling ball also fell... That means my hypothesis is either incomplete, or simply wrong.
• Modification (5): The floor possesses something which I will continue to call gravity, which attracts all objects.
• Test (3): I will drop a book and an egg. I can't test all objects, but at least I can be sure it will work for these.
• Application (4): The book fell to the ground. The egg did too, and it broke. That's interesting... I wonder if it would have broken if I dropped it from a smaller height, like half an inch?
• Modification (5): My hypothesis is accurate so far, but I could modify it to describe acceleration... Maybe tomorrow.
• Theory (6): Yay! I have just invented the theory of gravity!

You may notice that my theory is incomplete (it only says that the floor attracts objects, and it does not describe how that attraction affects things; do they fall at a constant rate? Do they accelerate? Do heavier objects fall faster than lighter objects?). That's fine. It only needs to describe my observations. It's now up to others to test with other floors, other objects, etc. They can expand my theory as necessary to fit their own observations.

So what does this mean? You may be familiar with gravity yourself. Is it a theory, or is it a fact? Or is it a law?

What's a law? In science, a law is a really old and well-proven theory (usually with some mathematical formulas attached to it). It has stood the test of time. No experiment has falsified (disproved) it. As for facts, that's a more interesting (i.e. difficult) distinction. Theories can be facts, but the problem is that if any experiment disproves the theory at any time in the future, then it must not have been a fact.

Gravity is all of these. It is a theory because it predicts the behavior of as-yet unobserved events, based on previous observations. It is also a law, because the theory has not been disproved after more than three hundred years. Based on this, it is safe to call gravity a fact.

But, if you drop a cantaloupe tomorrow and it does not fall, then you have just disproved the theory of gravity. That does not falsify all of the other observations about gravity up until now, though. Somebody will need to come up with a new theory that not only explains three hundred years of experiments proving gravity, it will also need to explain why your kooky cantaloupe floats.

So how does this relate to evolution and the bible? Well, I was hoping I could just stop here and let you extrapolate from the discussion about gravity so I wouldn't have to touch that topic. I strongly believe that religion is an extremely personal choice, and should therefore be extremely private. I don't like to talk about it, and I especially don't like the idea of one person telling another what to believe. I'm already about to step beyond my comfort zone. But here we go:

Evolution (driven by natural selection) is a theory. It was first described in detail by Charles Darwin about a hundred and fifty years ago. It provides a method for predicting how species came to be in their current form. Fossil evidence adds weight by showing the intermediate species that existed in the past. Until evolution was accepted by scientists, the prevailing theory was that all species were fixed at the time of creation, part of a divine plan that laid out all life on Earth.

So how could we disprove evolution? Scientists ask themselves this kind of question every day, about all sorts of different theories. A scientist's job is to look at a theory and try to figure out new ways to disprove it. Every time somebody fails to disprove a theory, the theory becomes stronger and closer to being considered a law; for example, NASA is still performing experiments to try to disprove parts of Einstein's theory of special relativity (take a look at LISA on Wikipedia).

But really, what would it take to disprove evolution? That's a hard question. The only thing I can think of would be to find a species that exists in multiple places, which could not have been transported from one place to the other. This is difficult on Earth, mostly because people move things around, but also because Pangaea and continental drift mess up the fossil record. But, for example, if the first ship from Earth to an Earth-like planet in another star system discovered Earth plants and animals, of identical species to those that exist here on Earth, that would disprove evolution as it currently exists.

What would that mean? We would need a new theory that explains why Earth life is all related to each other, and also how planet-X had the same types of life. Panspermia would be a start, but then perhaps evolution would be back in the game.

Before closing, I want to emphasize this point: Disproving evolution is a hard... not enough emphasis... HARD task. At this point, it is at about the same order of difficulty as disproving gravity. I would even say that we are past the point where it could be disproved completely; any contrary evidence would just be used to make minor modifications, resulting in a stronger theory.

So don't ever let somebody tell you, "Evolution is just a theory."