In Science, It’s Never ‘Just a Theory’

Apr 10, 2016

Photo credit: Zohar Lazar

By Carl Zimmer

We asked readers to share the misconception that frustrates them the most on The New York Times — Science Facebook page. People had an array of answers, a number of which we addressed earlier this week. Judging from all the likes it quickly accumulated — far more than any other submission — this was the standout in terms of mass frustration.

Misconception: It’s just a theory.

Actually: Theories are neither hunches nor guesses. They are the crown jewels of science.

One day, it’s Megyn Kelly who has a theory about why Donald J. Trump hates her.

Another day, the newly released trailer for the next Star Wars movie inspires a million theories from fans about who Rey’s parents are.

And on Twitter, someone going by the name of Mothra P.I. has a theory about how cats can assume a new state of matter:

I have a theory, that cats are actually in a liquid state some of the time, as demonstrated here… pic.twitter.com/qz8x2laXWc

In everyday conversation, we tend to use the word “theory” to mean a hunch, an idle speculation, or a crackpot notion.

That’s not what “theory” means to scientists.

“In science, the word theory isn’t applied lightly,” Kenneth R. Miller, a cell biologist at Brown University, said. “It doesn’t mean a hunch or a guess. A theory is a system of explanations that ties together a whole bunch of facts. It not only explains those facts, but predicts what you ought to find from other observations and experiments.”

Dr. Miller is one of the few scientists to have explained the nature of theories on a witness stand under oath.

He is a co-author of a high school biology textbook that puts a strong emphasis on the theory of evolution. In 2002, the board of education in Cobb County, Ga., adopted the textbook but also required science teachers to put a warning sticker inside the cover of every copy.

“Evolution is a theory, not a fact, regarding the origin of living things,” the sticker read, in part.

In 2004, several Cobb County parents filed a lawsuit against the county board of education to have the stickers removed. They called Dr. Miller, who testified for about two hours, explaining, among other things, the strength of evidence for the theory of evolution.

Once the lawyers had finished questioning Dr. Miller, he stepped down from the stand and made his way out of the courtroom. On the way, he noticed a woman looking him straight in the eye.

“She said, ‘It’s only a theory, and we’re going to win this one,’  ” Dr. Miller recalled.

They didn’t. In 2005 the judge ruled against the board of education. The board appealed the decision but later agreed to remove the stickers.


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