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      Figure 1.1. Not all swans are white. This is the Australian black swan. (Courtesy Wikimedia Commons.)

      Thus, science is very different from what most people think it is. When scientists speak to each other, they are not after “truth.” They are careful not to use the words true or fact, and strictly speaking, we don’t “prove things true.” Instead, scientists are trying to test and falsify, and test again, until an idea is well corroborated (not “proven true”). What most people would call a “fact” is an “extremely well-supported explanation.” To a scientist, the highest form of a corroborated hypothesis is a theory, a group of interrelated and well-corroborated hypotheses and observations that have received widespread acceptance because they explain so much.

      Sadly, the public uses these words and concepts very differently. In everyday usage, theory means a wild speculative idea, like “theories of why JFK was assassinated.” Creationists take advantage of the confusion and exploit this meaning of the word by denigrating evolution as “just a theory.” Well, gravity is just a theory too, but the objects around you are not floating around in the air. Thanks to the germ theory of disease, we believe that bacteria and viruses are the major causes of diseases, not some sort of “ill humor” in your blood that your doctor would remove by bleeding you with leeches.

      Likewise, in the public debate about scientific topics, science deniers will put down an idea they oppose (like climate change) by saying that it’s not “proven true” or “100 percent true.” Nothing in science is “proven true,” and everything has probabilities associated with it. I can’t say that I can “prove” you would die if you jumped off a twenty-story building, but I can say that it’s likely to happen with a 99 percent probability—and most nonsuicidal people will not take that less than 1 percent chance that they won’t die.

      As Carl Sagan said, “Skeptical scrutiny is the means, in both science and religion, by which deep thoughts can be winnowed from deep nonsense.”⁶ Science is basically applied skepticism. We try to be skeptical of all ideas until they have been tested and corroborated again and again, and then we only give our provisional assent. We don’t believe in an idea; we accept it based on evidence. (Believe is a religious and cultural word, not a scientific one.) Most humans are cautious of people trying to sell them worthless junk or politicians making impractical promises or swindlers trying to con them into believing something or buying something. We all know that advertising is exaggerated or deceptive or distorted, and in many cases, it is an outright lie. We try to look for good products and avoid junk when we are shopping, and we employ the old Latin maxim caveat emptor, “let the buyer beware.” Yet many people won’t employ the same skepticism to outlandish claims about religious miracles or UFOs or Bigfoot or a wide variety of paranormal ideas that sucker people every day. Most of the ideas in this book fall within the realm of outlandish and even bizarre, but there are plenty of believers. Yet these same people are skeptical elsewhere in their lives and won’t fall for a deceptive ad on TV or the internet or a telemarketer trying to sell them something.

      Scientists are humans too, and although they try to be hard-boiled skeptics, they cannot avoid falling for the traps in thinking and sometimes embrace ideas that fit what they want to believe rather than what is. As Carl Sagan wrote, “There are many hypotheses in science which are wrong. That’s perfectly all right; they’re the aperture to finding out what’s right. Science is a self-correcting process. To be accepted, new ideas must survive the most rigorous standards of evidence and scrutiny.”⁷ For this reason, there is an important quality control mechanism built into the fabric of science: peer review. This is very different from the internet, which is a giant cesspool of garbage and bad ideas with no fact-checking, and it is very different from partisan media outlets, which have given up reporting anything “fair and balanced” but churn out nonstop propaganda.

      Scientists, on the other hand, must submit their ideas to the harsh review and scrutiny of other scientists before they can be published. Usually these reviews are anonymous, and they can be sent to any qualified scientist, including your worst critic. If your idea is rejected, you can give up, or you can try to do a better job of supporting your hypothesis and submit it again. Peer review weeds out the bad ideas in science, and after a harsh round of review before publication, and an even harsher scrutiny in the years after publication, most ideas in science that have survived many years are probably true and have passed quality control.

      Peer review is particularly important in evaluating our own ideas, since we are inclined to think our own ideas are right and cannot judge them critically. As the Nobel Prize–winning Caltech physicist Richard Feynman said, “The first principle is that you must not fool yourself and you are the easiest person to fool.”⁸ Many scientific experiments are run by the double-blind method, in which neither the subjects of the experiments nor the investigators know what is in sample A or sample B. In a double-blind experiment, the samples are coded so that no one knows what is in each sample, and only after the experiment is over do the scientists find out whether the results agree with their expectations or not. As Feynman said, “It doesn’t matter how beautiful your theory is, it doesn’t matter how smart you are. If it doesn’t agree with experiment, it’s wrong.”⁹ Ultimately, bad ideas are weeded out, and good ones survive to become the established framework of scientific theory that all scientists build upon.

      The mad scientist stereotype that prevails in nearly all media is completely wrong not just because of the clothing, behavior, and apparatuses that are shown. It’s wrong because the “mad scientist” is not testing hypotheses about nature or experimenting to find out what is really true. A cartoon on the internet shows someone interrogating a classic mad scientist. The interrogator asks, “Why did you build a death ray?” The mad scientist says, “To take over the world.” “No, I mean what hypothesis are you testing? Are you just making mad observations?” The mad scientist responds, “Look, I’m just trying to take over the world. That’s all.” The interrogator continues, “You at least are going to have some of the world as a mad control group, right?”

      As the cartoon suggests, he’s really not a scientist at all; he’s just a “mad engineer.” (Engineers may understand science, but their goal is not to discover truths about nature but to apply science to make inventions or practical devices.)

       Science, Intuition, and Common Sense

      Common sense is that which tells us the world is flat.

      —Stuart Chase, quoted in S. I. Hayakawa, Language in Thought and Action

      Common sense is the very antipodes of science.

      —Edward Bradford Titchener, Systematic Psychology: Prolegomena

      We’re living in what Carl Sagan correctly termed a demon-haunted world. We have created a Star Wars civilization but we have Paleolithic emotions, medieval institutions and godlike technology. That’s dangerous.

      —E. O. Wilson, quoted in New Scientist

      The great biologist (and defender of Darwin) Thomas Henry Huxley wrote, “Science is simply common sense at its best, that is, rigidly accurate in observation, and merciless to fallacy in logic.”¹⁰ Scientists and philosophers often claim that science is based on common sense. But at

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