the possible models you could create that would be consistent with the data. Just any explanation would not be acceptable. In evolution, there are some things we know could not have happened, just as we are confident that some things have happened."

"And if different scientists can have different explanations, like Karen and I did, then I guess science also has to involve judgment to some extent," Doug says.

"But I thought scientists were supposed to be totally objective," says Karen.

"Good science always attempts to be objective, but it also relies on the individual insights of scientists. And the questions they choose to ask as well as the methods they choose to use, not to mention the interpretations they may have, can be colored by their individual interests and backgrounds. But scientific explanations are reviewed by other scientists and must be consistent with the natural world and future experiments, so there are checks on subjectivity. What we read in science books is a combination of observations and inferred explanations of those observations that can change with new research."

"Still, I'm wondering," says Karen, "how can we find out which model is right?"

"Let's just open up Barbara's tube," says Doug.

"We could do that," Barbara says. "But let's assume in this analogy that opening the tube is not possible. Sometimes scientists figure out how to open up the natural world and look inside, but sometimes they can't. And not opening up the tube is a good metaphor for how science often works. Science involves coming up with explanations that are based on evidence. With time, additional evidence might require changing the explanations, so that at any time what we have is the best explanation possible for how things work. In the future, with additional data, we may change our original explanation—just like you did, Karen.

"Remember when we were talking this morning about evolution being fact or theory? That conversation is very relevant to what we have been doing with the tubes. As scientists started to notice patterns in nature, they began to speculate about some explanations for these patterns. These explanations are analogous to your initial ideas about how my tube worked. In the terms of science, these initial ideas are called hypotheses. You noticed some patterns in how the ropes were related to each other, and you used these patterns to develop a model to explain the patterns. The model you created is analogous to the beginning of a scientific theory. Except in science, theories are only formalized after many years of testing the predictions that come from the model.

"Because of our human limitations in collecting complete data, theories necessarily contain some judgments about what is important. Judgments aren't a weakness of scientific theory. They are a basic part of how science works."

"I always thought of science as a bunch of absolute facts," says Doug. "I never thought about how knowledge is developed by scientists."

"Creativity and insight are what help make science such a powerful way of understanding the natural world.

"There's another important thing that I try to teach my students with this activity," Barbara continues. "It's important for them to be able to distinguish questions that can be answered by science from those that cannot be answered by science. Here's a list of questions that I use to get them talking. I ask them if a question can be answered by science, cannot be answered by science, or has some parts that belong to science and others that do not. Then I ask the group to select a couple of questions and discuss how they would go about answering them."



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