9:59:59.000,9:59:59.000 Every day we face issues like climate change 9:59:59.000,9:59:59.000 or the safety of vaccines 9:59:59.000,9:59:59.000 where we have to answer questions whose answers 9:59:59.000,9:59:59.000 rely heavily on scientific information. 9:59:59.000,9:59:59.000 Scientists tell us that the world is warming. 9:59:59.000,9:59:59.000 Scientists tell us that vaccines are safe. 9:59:59.000,9:59:59.000 But how do we know if they are right? 9:59:59.000,9:59:59.000 Why should be believe the science? 9:59:59.000,9:59:59.000 The fact is, many of us actually don't believe the science. 9:59:59.000,9:59:59.000 Public opinion polls consistently show 9:59:59.000,9:59:59.000 that significant proportions of the American people 9:59:59.000,9:59:59.000 don't believe the climate is warming due to human activities, 9:59:59.000,9:59:59.000 don't think that there is evolution by natural selection, 9:59:59.000,9:59:59.000 and aren't persuaded by the safety of vaccines. 9:59:59.000,9:59:59.000 So why should we believe the science? 9:59:59.000,9:59:59.000 Well, scientists don't like talking about [br]science as a matter of belief. 9:59:59.000,9:59:59.000 In fact, they would contract science with faith 9:59:59.000,9:59:59.000 and they would say belief is the domain, faith. 9:59:59.000,9:59:59.000 And faith is a separate thing apart and distinct from science. 9:59:59.000,9:59:59.000 Indeed they would say religion is based on faith 9:59:59.000,9:59:59.000 or maybe the calculous of Pascal's wager. 9:59:59.000,9:59:59.000 Blaise Pascal was a 17th century mathematician 9:59:59.000,9:59:59.000 who tried to bring scientific reasoning to the question of 9:59:59.000,9:59:59.000 wether or not he should believe in God 9:59:59.000,9:59:59.000 and his wager went like this: 9:59:59.000,9:59:59.000 Well, if God doesn't exist but I decide to believe in him 9:59:59.000,9:59:59.000 nothing much is really lost. 9:59:59.000,9:59:59.000 Maybe a few hours on Sunday. 9:59:59.000,9:59:59.000 [Laughter] 9:59:59.000,9:59:59.000 But if he does exist and I don't believe in him, 9:59:59.000,9:59:59.000 then I'm in deep trouble. 9:59:59.000,9:59:59.000 And so Pascal said, we'd better believe in God. 9:59:59.000,9:59:59.000 Or as one of my college professors said, 9:59:59.000,9:59:59.000 "he clutched for the handmill of faith". 9:59:59.000,9:59:59.000 He made that leap of faith 9:59:59.000,9:59:59.000 leaving science and rationalism behind. 9:59:59.000,9:59:59.000 Now the fact is though, for most of us 9:59:59.000,9:59:59.000 most scientific claims are a leap of faith. 9:59:59.000,9:59:59.000 We can't really judge scientific claims for ourselves in most cases. 9:59:59.000,9:59:59.000 And indeed this is actually true for most scientists as well 9:59:59.000,9:59:59.000 outside of their own specialties. 9:59:59.000,9:59:59.000 So if you think about it, a geologist can't tell you 9:59:59.000,9:59:59.000 wether a vaccine is safe. 9:59:59.000,9:59:59.000 Most chemists are not experts in evolutionary theory. 9:59:59.000,9:59:59.000 A physicist cannot tell you, despite the claims of some of them, 9:59:59.000,9:59:59.000 wether or not tobacco causes cancer. 9:59:59.000,9:59:59.000 So, if even scientists themselves have to make a leap of faith 9:59:59.000,9:59:59.000 outside their own fields, 9:59:59.000,9:59:59.000 then why do they accept the claims of other scientists? 9:59:59.000,9:59:59.000 Why do they believe each other's claims? 9:59:59.000,9:59:59.000 And should we believe those claims? 9:59:59.000,9:59:59.000 So what I'd like to argue is yes, we should. 9:59:59.000,9:59:59.000 But not for the reason that most of us think. 9:59:59.000,9:59:59.000 Most of us were taught in school that the reason we should 9:59:59.000,9:59:59.000 believe in science is because of the scientific method. 9:59:59.000,9:59:59.000 We were taught that scientists follow a method 9:59:59.000,9:59:59.000 and that this method guarantees the truth of their claims. 9:59:59.000,9:59:59.000 The method that most of us were taught in school, 9:59:59.000,9:59:59.000 we can call it the text book method, 9:59:59.000,9:59:59.000 is the hypo-deductive method. 9:59:59.000,9:59:59.000 According to the standard model, the textbook model, 9:59:59.000,9:59:59.000 scientists develop hypotheses, they deduce the 9:59:59.000,9:59:59.000 consequences for those hypotheses, 9:59:59.000,9:59:59.000 and then they go out into the world and they say: 9:59:59.000,9:59:59.000 Are those consequences true? 9:59:59.000,9:59:59.000 Can we observe them taking place in the natural world? 9:59:59.000,9:59:59.000 And if they are true, then the scientists say: 9:59:59.000,9:59:59.000 Great, we know the hypothesis is correct. 9:59:59.000,9:59:59.000 So there are many famous examples in the history 9:59:59.000,9:59:59.000 of science of scientists doing exactly this. 9:59:59.000,9:59:59.000 One of the most famous examples 9:59:59.000,9:59:59.000 comes from the work of Albert Einstein. 9:59:59.000,9:59:59.000 When Einstein developed the theory of general relativity 9:59:59.000,9:59:59.000 one of the consequences of his theory 9:59:59.000,9:59:59.000 was that space time wasn't just an empty void 9:59:59.000,9:59:59.000 but that it actually had a fabric. 9:59:59.000,9:59:59.000 And that that fabric was bent 9:59:59.000,9:59:59.000 in the presence of massive objects like the sun. 9:59:59.000,9:59:59.000 So if this theory were true then it meant that light 9:59:59.000,9:59:59.000 as it passed the sun 9:59:59.000,9:59:59.000 should actually be bent around it. 9:59:59.000,9:59:59.000 That was a pretty startling prediction 9:59:59.000,9:59:59.000 and it took a few years before scientists 9:59:59.000,9:59:59.000 were able to test it. 9:59:59.000,9:59:59.000 But they did test it in 1919 9:59:59.000,9:59:59.000 and low and behold it turned out to be true. 9:59:59.000,9:59:59.000 Starlight actually does bend as it travels around the sun. 9:59:59.000,9:59:59.000 This was a huge confirmation of the theory. 9:59:59.000,9:59:59.000 It was considered proof of the truth of this radical new idea 9:59:59.000,9:59:59.000 and it was written up in many newspapers around the globe. 9:59:59.000,9:59:59.000 Now sometimes this theory or this model 9:59:59.000,9:59:59.000 is referred to as the deductive-nomological model. 9:59:59.000,9:59:59.000 Meaning those academics like to make things complicated. [br][Laughter] 9:59:59.000,9:59:59.000 But also because in the ideal case it's about laws. 9:59:59.000,9:59:59.000 So nomological means having to do with laws. 9:59:59.000,9:59:59.000 And in the ideal case, the hypothesis isn't just an idea, 9:59:59.000,9:59:59.000 ideally it is a law of nature. 9:59:59.000,9:59:59.000 Why does it matter that it is a law of nature? 9:59:59.000,9:59:59.000 Because if it is a law, it can't be broken. 9:59:59.000,9:59:59.000 If it's a law then it will always be true 9:59:59.000,9:59:59.000 in all times and all places 9:59:59.000,9:59:59.000 no matter what the circumstances are. 9:59:59.000,9:59:59.000 And all of you know at least one example of a famous law. 9:59:59.000,9:59:59.000 Einstein's famous equation, E=MC2, 9:59:59.000,9:59:59.000 which tells us what the relationship is 9:59:59.000,9:59:59.000 between energy and mass. 9:59:59.000,9:59:59.000 And that relationship is true no matter what. 9:59:59.000,9:59:59.000 It turns out though that there are [br]several problems with this model. 9:59:59.000,9:59:59.000 The main problem is that it's wrong. 9:59:59.000,9:59:59.000 It's just not true. [Laughter] 9:59:59.000,9:59:59.000 And I'm going to talk about three reasons why it's wrong. 9:59:59.000,9:59:59.000 So the first reason is a logical reason, 9:59:59.000,9:59:59.000 it's the problem of the fallacy of affirming the consequent. 9:59:59.000,9:59:59.000 So that's another fancy academic way of saying 9:59:59.000,9:59:59.000 that false theories can make true predictions. 9:59:59.000,9:59:59.000 So just because the prediction comes true 9:59:59.000,9:59:59.000 doesn't actually logically prove that the theory is correct. 9:59:59.000,9:59:59.000 And I have a good example of that too, [br]again from the history of science. 9:59:59.000,9:59:59.000 This is a picture of the Ptolemaic universe 9:59:59.000,9:59:59.000 with the Earth at the center of the universe 9:59:59.000,9:59:59.000 and The Sun and the planets going around it. 9:59:59.000,9:59:59.000 The Ptolemaic model was believed 9:59:59.000,9:59:59.000 by many very smart people for many centuries. 9:59:59.000,9:59:59.000 Well why? 9:59:59.000,9:59:59.000 Well the answer is because it made [br]lots of predictions that came true. 9:59:59.000,9:59:59.000 The Ptolemaic system enabled astronomers 9:59:59.000,9:59:59.000 to make accurate predictions of the motions of the planet. 9:59:59.000,9:59:59.000 In fact more accurate predictions at first 9:59:59.000,9:59:59.000 than the Copernican theory which we now would say is true. 9:59:59.000,9:59:59.000 So that's one problem with the textbook model, 9:59:59.000,9:59:59.000 a second problem is a practical problem 9:59:59.000,9:59:59.000 and it's the problem of auxiliary hypotheses. 9:59:59.000,9:59:59.000 Auxiliary hypotheses are assumptions 9:59:59.000,9:59:59.000 that scientists are making, 9:59:59.000,9:59:59.000 that they may or may not even be aware that they're making. 9:59:59.000,9:59:59.000 So an important example of this comes from 9:59:59.000,9:59:59.000 comes from the Copernican model 9:59:59.000,9:59:59.000 which ultimately replaced the Ptolemaic system. 9:59:59.000,9:59:59.000 So when Nicolaus Copernicus said, 9:59:59.000,9:59:59.000 actually the Earth is not the center of the universe, 9:59:59.000,9:59:59.000 the sun is the center of the solar system, 9:59:59.000,9:59:59.000 the Earth moves around the sun. 9:59:59.000,9:59:59.000 Scientists said, well okay, Nicolaus, if that's true 9:59:59.000,9:59:59.000 we ought to be able to detect the motion 9:59:59.000,9:59:59.000 of the Earth around the sun. 9:59:59.000,9:59:59.000 And so this slide here illustrates a concept 9:59:59.000,9:59:59.000 known as stellar parallax. 9:59:59.000,9:59:59.000 And astronomers said, if the Earth is moving 9:59:59.000,9:59:59.000 and we look at a prominent star, let's say, Sirius. 9:59:59.000,9:59:59.000 Well I know I'm in Manhattan so you guys can't see the stars, 9:59:59.000,9:59:59.000 but imagine you're out in the country, [br]imagine you chose that rural life. 9:59:59.000,9:59:59.000 And we look at a star in December, we see that star 9:59:59.000,9:59:59.000 against the backdrop of distant stars. 9:59:59.000,9:59:59.000 If we now make the same observation six months later 9:59:59.000,9:59:59.000 when the Earth has moved to this position in June, 9:59:59.000,9:59:59.000 we look at that same star and we see it against a different backdrop. 9:59:59.000,9:59:59.000 That difference, that angular difference, is the stellar parallax. 9:59:59.000,9:59:59.000 So this is the prediction that the Copernican model makes, 9:59:59.000,9:59:59.000 astronomers looked for the stellar parallax 9:59:59.000,9:59:59.000 and they found nothing, nothing at all. 9:59:59.000,9:59:59.000 And many people argued that this proved [br]that the Copernican model was false. 9:59:59.000,9:59:59.000 So what happened? 9:59:59.000,9:59:59.000 Well in hindsight we can say that astronomers were making 9:59:59.000,9:59:59.000 two auxiliary hypotheses, both of which 9:59:59.000,9:59:59.000 we would now say were incorrect. 9:59:59.000,9:59:59.000 The first was an assumption about the size of the Earth's orbit. 9:59:59.000,9:59:59.000 Astronomers were assuming that the Earth's orbit was large 9:59:59.000,9:59:59.000 relative to the stars. 9:59:59.000,9:59:59.000 Today we would draw the picture more like this, 9:59:59.000,9:59:59.000 this comes from NASA, 9:59:59.000,9:59:59.000 and you see the Earth's orbit is actually quite small. 9:59:59.000,9:59:59.000 In fact, it's actually much smaller even than shown here. 9:59:59.000,9:59:59.000 The stellar parallax therefore, 9:59:59.000,9:59:59.000 is very small and actually very hard to detect. 9:59:59.000,9:59:59.000 And that leads to the second reason 9:59:59.000,9:59:59.000 why the prediction didn't work, 9:59:59.000,9:59:59.000 because scientists were also assuming 9:59:59.000,9:59:59.000 that the telescopes they had were sensitive enough 9:59:59.000,9:59:59.000 to detect the parallax. 9:59:59.000,9:59:59.000 And that turned out not to be true. 9:59:59.000,9:59:59.000 It wasn't until the 19th century that scientists were able to detect 9:59:59.000,9:59:59.000 the stellar parallax. 9:59:59.000,9:59:59.000 So, there's a third problem as well. 9:59:59.000,9:59:59.000 The third problem is simply a factual problem 9:59:59.000,9:59:59.000 that a lot of science doesn't fit the textbook model. 9:59:59.000,9:59:59.000 A lot of science isn't deductive at all, it's actually inductive. 9:59:59.000,9:59:59.000 And by that we mean that scientists don't necessarily 9:59:59.000,9:59:59.000 start with theories and hypotheses, often they just 9:59:59.000,9:59:59.000 start with observations of stuff going on in the world. 9:59:59.000,9:59:59.000 And the most famous example of that is one of the most 9:59:59.000,9:59:59.000 famous scientists who ever lived, Charles Darwin. 9:59:59.000,9:59:59.000 When Darwin went out as a young [br]man on the voyage of the Beagle, 9:59:59.000,9:59:59.000 he didn't have a hypothesis, he didn't have a theory. 9:59:59.000,9:59:59.000 He just knew that he wanted to have a career as a scientist 9:59:59.000,9:59:59.000 and he started to collect data. 9:59:59.000,9:59:59.000 Mainly he knew that he hated medicine 9:59:59.000,9:59:59.000 because the sight of blood made him sick so 9:59:59.000,9:59:59.000 he had to have an alternative career path. 9:59:59.000,9:59:59.000 So he started collecting data. 9:59:59.000,9:59:59.000 And he collected many things including his famous finches. 9:59:59.000,9:59:59.000 When he collected these finches he through them in a bag 9:59:59.000,9:59:59.000 and he had no idea what they meant. 9:59:59.000,9:59:59.000 Many years later back in London, 9:59:59.000,9:59:59.000 Darwin looked at his data again and began to develop 9:59:59.000,9:59:59.000 an explanation 9:59:59.000,9:59:59.000 and that explanation was the theory of natural selection. 9:59:59.000,9:59:59.000 Besides inductive science, 9:59:59.000,9:59:59.000 scientists also often participate in modeling.