Only a Theory?

By Laurie Hatton (in collaboration with her local Brights Community Cluster)

Sherlock Holmes commonly stated to Watson, “I have a theory.” The word “theory” means that something is a guess or speculative idea. Right?  Well, yes it can. However, when a scientist uses the term theory, he or she means something totally different.  A scientific theory is an idea that has a lot of evidence to back it up – no guessing involved.

NACA Physicist Studying Alpha Rays

Photo: NASA

Scientists start with a hypothesis – an educated guess based on observation.  A hypothesis can be either supported or refuted through testing or observation. Key hypotheses are tested over and over by independent researchers.

When people say, “I have a theory about that,” what they often mean is that they have a hypothesis.

A scientific theory is much more than a hypothesis.  It is a hypothesis that has been tested and shown to be true beyond any reasonable doubt.  Either that or it is an all-encompassing explanation of a set of well supported hypotheses.  Scientific theories can be shown to be false. But, by the time an idea has made it to “theory,” the evidence is so strong that this almost never happens.  Scientists may argue about the details of the supporting evidence, but rarely about the theory itself.

People used to believe that the sun, moon and stars revolved around the Earth. Evidence now shows that the Earth is a tiny speck orbiting a relatively average sized star, hurtling along on the inside edge of one of the spiral arms of the Milky Way galaxy, which is one of hundreds of billions of galaxies in the universe. These are theories.  They are supported by rigorously tested hypotheses.  In this day and age, people don’t seem to have a problem believing Earth’s puny position in the universe.

Up until very recently, most people believed that the continents had always been where they are now. It was generally considered “just a coincidence” that they looked as though they fit together like a jigsaw puzzle. It was suggested in the late 1500s that they might have once been joined, and since the 1960s, most people understand that the continents were once one, and have split and moved apart or crashed into each other over billions of years, and are in fact still moving. There is strong evidence for the theory of plate tectonics.

Evolution by natural selection is a theory.  It is supported by many lines of evidence. This evidence includes the obvious fossil record, but also genetics, comparative anatomy, and the geographic distribution of species, among many other things. Prior to Darwin’s On The Origin of the Species by Means of Natural Selection, some scientists suspected that evolution had happened.  However, they could not explain how it happened.  Darwin gave us a clear overarching explanation.

Next time you hear someone use the word theory, play Sherlock Holmes; do they really mean hypothesis?

I recently saw a bumper sticker that read, “Evolution is only a theory.  Just”  Oh, wait.  It’s on the back of my car.

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