WEBVTT 00:00:01.083 --> 00:00:04.268 Every day we face issues like climate change 00:00:04.268 --> 00:00:05.708 or the safety of vaccines 00:00:05.708 --> 00:00:08.348 where we have to answer questions whose answers 00:00:08.348 --> 00:00:11.659 rely heavily on scientific information. 00:00:11.659 --> 00:00:15.033 Scientists tell us that the world is warming. 00:00:15.033 --> 00:00:17.281 Scientists tell us that vaccines are safe. 00:00:17.281 --> 00:00:19.465 But how do we know if they are right? 00:00:19.465 --> 00:00:21.569 Why should be believe the science? 00:00:21.569 --> 00:00:24.898 The fact is, many of us actually don't believe the science. 00:00:24.898 --> 00:00:27.314 Public opinion polls consistently show 00:00:27.314 --> 00:00:29.634 that significant proportions of the American people 00:00:29.634 --> 00:00:33.225 don't believe the climate is warming due to human activities, 00:00:33.225 --> 00:00:36.724 don't think that there is evolution by natural selection, 00:00:36.724 --> 00:00:40.805 and aren't persuaded by the safety of vaccines. NOTE Paragraph 00:00:40.805 --> 00:00:44.316 So why should we believe the science? 00:00:44.316 --> 00:00:47.957 Well, scientists don't like talking about science as a matter of belief. 00:00:47.957 --> 00:00:50.444 In fact, they would contract science with faith, 00:00:50.444 --> 00:00:53.068 and they would say belief is the domain of faith. 00:00:53.068 --> 00:00:57.238 And faith is a separate thing apart and distinct from science. 00:00:57.238 --> 00:00:59.790 Indeed they would say religion is based on faith 00:00:59.790 --> 00:01:04.254 or maybe the calculous of Pascal's wager. 00:01:04.254 --> 00:01:07.110 Blaise Pascal was a 17th century mathematician 00:01:07.110 --> 00:01:09.630 who tried to bring scientific reasoning to the question of 00:01:09.630 --> 00:01:11.542 whether or not he should believe in God, 00:01:11.542 --> 00:01:13.616 and his wager went like this: 00:01:13.616 --> 00:01:15.935 well, if God doesn't exist 00:01:15.935 --> 00:01:18.595 but I decide to believe in him 00:01:18.595 --> 00:01:20.538 nothing much is really lost. 00:01:20.538 --> 00:01:22.451 Maybe a few hours on Sunday. 00:01:22.451 --> 99:59:59.999 [Laughter] 99:59:59.999 --> 99:59:59.999 But if he does exist and I don't believe in him, 99:59:59.999 --> 99:59:59.999 then I'm in deep trouble. 99:59:59.999 --> 99:59:59.999 And so Pascal said, we'd better believe in God. 99:59:59.999 --> 99:59:59.999 Or as one of my college professors said, 99:59:59.999 --> 99:59:59.999 "he clutched for the handmill of faith". 99:59:59.999 --> 99:59:59.999 He made that leap of faith 99:59:59.999 --> 99:59:59.999 leaving science and rationalism behind. NOTE Paragraph 99:59:59.999 --> 99:59:59.999 Now the fact is though, for most of us 99:59:59.999 --> 99:59:59.999 most scientific claims are a leap of faith. 99:59:59.999 --> 99:59:59.999 We can't really judge scientific claims for ourselves in most cases. 99:59:59.999 --> 99:59:59.999 And indeed this is actually true for most scientists as well 99:59:59.999 --> 99:59:59.999 outside of their own specialties. 99:59:59.999 --> 99:59:59.999 So if you think about it, a geologist can't tell you 99:59:59.999 --> 99:59:59.999 wether a vaccine is safe. 99:59:59.999 --> 99:59:59.999 Most chemists are not experts in evolutionary theory. 99:59:59.999 --> 99:59:59.999 A physicist cannot tell you, despite the claims of some of them, 99:59:59.999 --> 99:59:59.999 wether or not tobacco causes cancer. 99:59:59.999 --> 99:59:59.999 So, if even scientists themselves have to make a leap of faith 99:59:59.999 --> 99:59:59.999 outside their own fields, 99:59:59.999 --> 99:59:59.999 then why do they accept the claims of other scientists? 99:59:59.999 --> 99:59:59.999 Why do they believe each other's claims? 99:59:59.999 --> 99:59:59.999 And should we believe those claims? NOTE Paragraph 99:59:59.999 --> 99:59:59.999 So what I'd like to argue is yes, we should. 99:59:59.999 --> 99:59:59.999 But not for the reason that most of us think. 99:59:59.999 --> 99:59:59.999 Most of us were taught in school that the reason we should 99:59:59.999 --> 99:59:59.999 believe in science is because of the scientific method. 99:59:59.999 --> 99:59:59.999 We were taught that scientists follow a method 99:59:59.999 --> 99:59:59.999 and that this method guarantees the truth of their claims. 99:59:59.999 --> 99:59:59.999 The method that most of us were taught in school, 99:59:59.999 --> 99:59:59.999 we can call it the text book method, 99:59:59.999 --> 99:59:59.999 is the hypo-deductive method. 99:59:59.999 --> 99:59:59.999 According to the standard model, the textbook model, 99:59:59.999 --> 99:59:59.999 scientists develop hypotheses, they deduce the 99:59:59.999 --> 99:59:59.999 consequences for those hypotheses, 99:59:59.999 --> 99:59:59.999 and then they go out into the world and they say: 99:59:59.999 --> 99:59:59.999 Are those consequences true? 99:59:59.999 --> 99:59:59.999 Can we observe them taking place in the natural world? 99:59:59.999 --> 99:59:59.999 And if they are true, then the scientists say: 99:59:59.999 --> 99:59:59.999 Great, we know the hypothesis is correct. NOTE Paragraph 99:59:59.999 --> 99:59:59.999 So there are many famous examples in the history 99:59:59.999 --> 99:59:59.999 of science of scientists doing exactly this. 99:59:59.999 --> 99:59:59.999 One of the most famous examples 99:59:59.999 --> 99:59:59.999 comes from the work of Albert Einstein. 99:59:59.999 --> 99:59:59.999 When Einstein developed the theory of general relativity 99:59:59.999 --> 99:59:59.999 one of the consequences of his theory 99:59:59.999 --> 99:59:59.999 was that space time wasn't just an empty void 99:59:59.999 --> 99:59:59.999 but that it actually had a fabric. 99:59:59.999 --> 99:59:59.999 And that that fabric was bent 99:59:59.999 --> 99:59:59.999 in the presence of massive objects like the sun. 99:59:59.999 --> 99:59:59.999 So if this theory were true then it meant that light 99:59:59.999 --> 99:59:59.999 as it passed the sun 99:59:59.999 --> 99:59:59.999 should actually be bent around it. 99:59:59.999 --> 99:59:59.999 That was a pretty startling prediction 99:59:59.999 --> 99:59:59.999 and it took a few years before scientists 99:59:59.999 --> 99:59:59.999 were able to test it. 99:59:59.999 --> 99:59:59.999 But they did test it in 1919 99:59:59.999 --> 99:59:59.999 and low and behold it turned out to be true. 99:59:59.999 --> 99:59:59.999 Starlight actually does bend as it travels around the sun. 99:59:59.999 --> 99:59:59.999 This was a huge confirmation of the theory. 99:59:59.999 --> 99:59:59.999 It was considered proof of the truth of this radical new idea 99:59:59.999 --> 99:59:59.999 and it was written up in many newspapers around the globe. NOTE Paragraph 99:59:59.999 --> 99:59:59.999 Now sometimes this theory or this model 99:59:59.999 --> 99:59:59.999 is referred to as the deductive-nomological model. 99:59:59.999 --> 99:59:59.999 Meaning those academics like to make things complicated. [Laughter] 99:59:59.999 --> 99:59:59.999 But also because in the ideal case it's about laws. 99:59:59.999 --> 99:59:59.999 So nomological means having to do with laws. 99:59:59.999 --> 99:59:59.999 And in the ideal case, the hypothesis isn't just an idea, 99:59:59.999 --> 99:59:59.999 ideally it is a law of nature. 99:59:59.999 --> 99:59:59.999 Why does it matter that it is a law of nature? 99:59:59.999 --> 99:59:59.999 Because if it is a law, it can't be broken. 99:59:59.999 --> 99:59:59.999 If it's a law then it will always be true 99:59:59.999 --> 99:59:59.999 in all times and all places 99:59:59.999 --> 99:59:59.999 no matter what the circumstances are. 99:59:59.999 --> 99:59:59.999 And all of you know at least one example of a famous law. 99:59:59.999 --> 99:59:59.999 Einstein's famous equation, E=MC2, 99:59:59.999 --> 99:59:59.999 which tells us what the relationship is 99:59:59.999 --> 99:59:59.999 between energy and mass. 99:59:59.999 --> 99:59:59.999 And that relationship is true no matter what. NOTE Paragraph 99:59:59.999 --> 99:59:59.999 It turns out though that there are several problems with this model. 99:59:59.999 --> 99:59:59.999 The main problem is that it's wrong. 99:59:59.999 --> 99:59:59.999 It's just not true. [Laughter] 99:59:59.999 --> 99:59:59.999 And I'm going to talk about three reasons why it's wrong. 99:59:59.999 --> 99:59:59.999 So the first reason is a logical reason, 99:59:59.999 --> 99:59:59.999 it's the problem of the fallacy of affirming the consequent. 99:59:59.999 --> 99:59:59.999 So that's another fancy academic way of saying 99:59:59.999 --> 99:59:59.999 that false theories can make true predictions. 99:59:59.999 --> 99:59:59.999 So just because the prediction comes true 99:59:59.999 --> 99:59:59.999 doesn't actually logically prove that the theory is correct. 99:59:59.999 --> 99:59:59.999 And I have a good example of that too, again from the history of science. 99:59:59.999 --> 99:59:59.999 This is a picture of the Ptolemaic universe 99:59:59.999 --> 99:59:59.999 with the Earth at the center of the universe 99:59:59.999 --> 99:59:59.999 and The Sun and the planets going around it. 99:59:59.999 --> 99:59:59.999 The Ptolemaic model was believed 99:59:59.999 --> 99:59:59.999 by many very smart people for many centuries. 99:59:59.999 --> 99:59:59.999 Well why? 99:59:59.999 --> 99:59:59.999 Well the answer is because it made lots of predictions that came true. 99:59:59.999 --> 99:59:59.999 The Ptolemaic system enabled astronomers 99:59:59.999 --> 99:59:59.999 to make accurate predictions of the motions of the planet. 99:59:59.999 --> 99:59:59.999 In fact more accurate predictions at first 99:59:59.999 --> 99:59:59.999 than the Copernican theory which we now would say is true. 99:59:59.999 --> 99:59:59.999 So that's one problem with the textbook model, 99:59:59.999 --> 99:59:59.999 a second problem is a practical problem 99:59:59.999 --> 99:59:59.999 and it's the problem of auxiliary hypotheses. 99:59:59.999 --> 99:59:59.999 Auxiliary hypotheses are assumptions 99:59:59.999 --> 99:59:59.999 that scientists are making, 99:59:59.999 --> 99:59:59.999 that they may or may not even be aware that they're making. 99:59:59.999 --> 99:59:59.999 So an important example of this comes from 99:59:59.999 --> 99:59:59.999 comes from the Copernican model 99:59:59.999 --> 99:59:59.999 which ultimately replaced the Ptolemaic system. 99:59:59.999 --> 99:59:59.999 So when Nicolaus Copernicus said, 99:59:59.999 --> 99:59:59.999 actually the Earth is not the center of the universe, 99:59:59.999 --> 99:59:59.999 the sun is the center of the solar system, 99:59:59.999 --> 99:59:59.999 the Earth moves around the sun. 99:59:59.999 --> 99:59:59.999 Scientists said, well okay, Nicolaus, if that's true 99:59:59.999 --> 99:59:59.999 we ought to be able to detect the motion 99:59:59.999 --> 99:59:59.999 of the Earth around the sun. 99:59:59.999 --> 99:59:59.999 And so this slide here illustrates a concept 99:59:59.999 --> 99:59:59.999 known as stellar parallax. 99:59:59.999 --> 99:59:59.999 And astronomers said, if the Earth is moving 99:59:59.999 --> 99:59:59.999 and we look at a prominent star, let's say, Sirius. 99:59:59.999 --> 99:59:59.999 Well I know I'm in Manhattan so you guys can't see the stars, 99:59:59.999 --> 99:59:59.999 but imagine you're out in the country, imagine you chose that rural life. 99:59:59.999 --> 99:59:59.999 And we look at a star in December, we see that star 99:59:59.999 --> 99:59:59.999 against the backdrop of distant stars. 99:59:59.999 --> 99:59:59.999 If we now make the same observation six months later 99:59:59.999 --> 99:59:59.999 when the Earth has moved to this position in June, 99:59:59.999 --> 99:59:59.999 we look at that same star and we see it against a different backdrop. 99:59:59.999 --> 99:59:59.999 That difference, that angular difference, is the stellar parallax. 99:59:59.999 --> 99:59:59.999 So this is the prediction that the Copernican model makes, 99:59:59.999 --> 99:59:59.999 astronomers looked for the stellar parallax 99:59:59.999 --> 99:59:59.999 and they found nothing, nothing at all. 99:59:59.999 --> 99:59:59.999 And many people argued that this proved that the Copernican model was false. NOTE Paragraph 99:59:59.999 --> 99:59:59.999 So what happened? 99:59:59.999 --> 99:59:59.999 Well in hindsight we can say that astronomers were making 99:59:59.999 --> 99:59:59.999 two auxiliary hypotheses, both of which 99:59:59.999 --> 99:59:59.999 we would now say were incorrect. 99:59:59.999 --> 99:59:59.999 The first was an assumption about the size of the Earth's orbit. 99:59:59.999 --> 99:59:59.999 Astronomers were assuming that the Earth's orbit was large 99:59:59.999 --> 99:59:59.999 relative to the stars. 99:59:59.999 --> 99:59:59.999 Today we would draw the picture more like this, 99:59:59.999 --> 99:59:59.999 this comes from NASA, 99:59:59.999 --> 99:59:59.999 and you see the Earth's orbit is actually quite small. 99:59:59.999 --> 99:59:59.999 In fact, it's actually much smaller even than shown here. 99:59:59.999 --> 99:59:59.999 The stellar parallax therefore, 99:59:59.999 --> 99:59:59.999 is very small and actually very hard to detect. NOTE Paragraph 99:59:59.999 --> 99:59:59.999 And that leads to the second reason 99:59:59.999 --> 99:59:59.999 why the prediction didn't work, 99:59:59.999 --> 99:59:59.999 because scientists were also assuming 99:59:59.999 --> 99:59:59.999 that the telescopes they had were sensitive enough 99:59:59.999 --> 99:59:59.999 to detect the parallax. 99:59:59.999 --> 99:59:59.999 And that turned out not to be true. 99:59:59.999 --> 99:59:59.999 It wasn't until the 19th century that scientists were able to detect 99:59:59.999 --> 99:59:59.999 the stellar parallax. NOTE Paragraph 99:59:59.999 --> 99:59:59.999 So, there's a third problem as well. 99:59:59.999 --> 99:59:59.999 The third problem is simply a factual problem 99:59:59.999 --> 99:59:59.999 that a lot of science doesn't fit the textbook model. 99:59:59.999 --> 99:59:59.999 A lot of science isn't deductive at all, it's actually inductive. 99:59:59.999 --> 99:59:59.999 And by that we mean that scientists don't necessarily 99:59:59.999 --> 99:59:59.999 start with theories and hypotheses, often they just 99:59:59.999 --> 99:59:59.999 start with observations of stuff going on in the world. 99:59:59.999 --> 99:59:59.999 And the most famous example of that is one of the most 99:59:59.999 --> 99:59:59.999 famous scientists who ever lived, Charles Darwin. 99:59:59.999 --> 99:59:59.999 When Darwin went out as a young man on the voyage of the Beagle, 99:59:59.999 --> 99:59:59.999 he didn't have a hypothesis, he didn't have a theory. 99:59:59.999 --> 99:59:59.999 He just knew that he wanted to have a career as a scientist 99:59:59.999 --> 99:59:59.999 and he started to collect data. 99:59:59.999 --> 99:59:59.999 Mainly he knew that he hated medicine 99:59:59.999 --> 99:59:59.999 because the sight of blood made him sick so 99:59:59.999 --> 99:59:59.999 he had to have an alternative career path. 99:59:59.999 --> 99:59:59.999 So he started collecting data. 99:59:59.999 --> 99:59:59.999 And he collected many things including his famous finches. 99:59:59.999 --> 99:59:59.999 When he collected these finches he through them in a bag 99:59:59.999 --> 99:59:59.999 and he had no idea what they meant. 99:59:59.999 --> 99:59:59.999 Many years later back in London, 99:59:59.999 --> 99:59:59.999 Darwin looked at his data again and began to develop 99:59:59.999 --> 99:59:59.999 an explanation 99:59:59.999 --> 99:59:59.999 and that explanation was the theory of natural selection. NOTE Paragraph 99:59:59.999 --> 99:59:59.999 Besides inductive science, 99:59:59.999 --> 99:59:59.999 scientists also often participate in modeling. 99:59:59.999 --> 99:59:59.999 One of the things scientists want to do in life 99:59:59.999 --> 99:59:59.999 is to explain the causes of things. 99:59:59.999 --> 99:59:59.999 And how do we do that? 99:59:59.999 --> 99:59:59.999 Well, one way you can do it is to build a model 99:59:59.999 --> 99:59:59.999 that tests an idea. 99:59:59.999 --> 99:59:59.999 So this is a picture of Henry Cadell, 99:59:59.999 --> 99:59:59.999 who was a Scottish geologist in the 19th century. 99:59:59.999 --> 99:59:59.999 You can tell he's Scottish because he's wearing 99:59:59.999 --> 99:59:59.999 a deerstalker cap and Wellington boots. 99:59:59.999 --> 99:59:59.999 (Laughter) 99:59:59.999 --> 99:59:59.999 And Cadell wanted to answer the question, 99:59:59.999 --> 99:59:59.999 how are mountains formed? 99:59:59.999 --> 99:59:59.999 And one of the things he had observed 99:59:59.999 --> 99:59:59.999 is that if you look at mountains like the Appalachians, 99:59:59.999 --> 99:59:59.999 you often find that the rocks in them 99:59:59.999 --> 99:59:59.999 are folded, 99:59:59.999 --> 99:59:59.999 and they're folded in a particular way, 99:59:59.999 --> 99:59:59.999 which suggested to him 99:59:59.999 --> 99:59:59.999 that they were actually being compressed from the side. 99:59:59.999 --> 99:59:59.999 And this idea would later play a major role 99:59:59.999 --> 99:59:59.999 in discussions of continental drift. 99:59:59.999 --> 99:59:59.999 So he built this model, this crazy contraption 99:59:59.999 --> 99:59:59.999 with levers and wood and here's his wheelbarrow, 99:59:59.999 --> 99:59:59.999 buckets, a big sledgehammer. 99:59:59.999 --> 99:59:59.999 I don't know why he's got the Wellington boots. 99:59:59.999 --> 99:59:59.999 Maybe it's going to rain. 99:59:59.999 --> 99:59:59.999 And he created this physical model in order 99:59:59.999 --> 99:59:59.999 to demonstrate that you could in fact create 99:59:59.999 --> 99:59:59.999 patterns in rocks, or at least in this case in mud, 99:59:59.999 --> 99:59:59.999 that looked a lot like mountains 99:59:59.999 --> 99:59:59.999 if you compressed them from the side. 99:59:59.999 --> 99:59:59.999 So it was an argument about the cause of mountains. 99:59:59.999 --> 99:59:59.999 Nowadays, most scientists prefer to work inside, 99:59:59.999 --> 99:59:59.999 so they don't build physical models so much 99:59:59.999 --> 99:59:59.999 as to make computer simulations. 99:59:59.999 --> 99:59:59.999 But a computer simulation is a kind of a model. 99:59:59.999 --> 99:59:59.999 It's a model that's made with mathematics, 99:59:59.999 --> 99:59:59.999 and like the physical models of the 19th century, 99:59:59.999 --> 99:59:59.999 it's very important for thinking about causes. 99:59:59.999 --> 99:59:59.999 So one of the big questions to do with climate change, 99:59:59.999 --> 99:59:59.999 we have tremendous amounts of evidence 99:59:59.999 --> 99:59:59.999 that the earth is warming up. 99:59:59.999 --> 99:59:59.999 This slide here, the black line shows 99:59:59.999 --> 99:59:59.999 the measurements that scientists have taken 99:59:59.999 --> 99:59:59.999 for the last 150 years 99:59:59.999 --> 99:59:59.999 showing that the earth's temperature 99:59:59.999 --> 99:59:59.999 has steadily increased, 99:59:59.999 --> 99:59:59.999 and you can see in particular that in the last 50 years 99:59:59.999 --> 99:59:59.999 there's been this dramatic increase 99:59:59.999 --> 99:59:59.999 of nearly one degree Centigrade, 99:59:59.999 --> 99:59:59.999 or almost two degrees Fahrenheit. 99:59:59.999 --> 99:59:59.999 So what, though, is driving that change? 99:59:59.999 --> 99:59:59.999 How can we know what's causing 99:59:59.999 --> 99:59:59.999 the observed warming? 99:59:59.999 --> 99:59:59.999 Well, scientists can model it 99:59:59.999 --> 99:59:59.999 using a computer simulation. 99:59:59.999 --> 99:59:59.999 So this diagram illustrates a computer simulation 99:59:59.999 --> 99:59:59.999 that has looked at all the different factors 99:59:59.999 --> 99:59:59.999 that we know can influence the earth's climate, 99:59:59.999 --> 99:59:59.999 so sulfate particles from air pollution, 99:59:59.999 --> 99:59:59.999 volcanic dust from volcanic eruptions, 99:59:59.999 --> 99:59:59.999 changes in solar radiation, 99:59:59.999 --> 99:59:59.999 and, of course, greenhouse gases. 99:59:59.999 --> 99:59:59.999 And they asked the question, 99:59:59.999 --> 99:59:59.999 what set of variables put into a model 99:59:59.999 --> 99:59:59.999 will reproduce what we actually see in real life? 99:59:59.999 --> 99:59:59.999 So here is the real life in black. 99:59:59.999 --> 99:59:59.999 Here's the model in this light grey, 99:59:59.999 --> 99:59:59.999 and the answer is 99:59:59.999 --> 99:59:59.999 a model that includes, it's the answer E on that SAT, 99:59:59.999 --> 99:59:59.999 all of the above. 99:59:59.999 --> 99:59:59.999 The only way you can reproduce 99:59:59.999 --> 99:59:59.999 the observed temperature measurements 99:59:59.999 --> 99:59:59.999 is with all of these things put together, 99:59:59.999 --> 99:59:59.999 including greenhouse gases, 99:59:59.999 --> 99:59:59.999 and in particular you can see that the increase 99:59:59.999 --> 99:59:59.999 in greenhouse gases tracks 99:59:59.999 --> 99:59:59.999 this very dramatic increase in temperature 99:59:59.999 --> 99:59:59.999 over the last 50 years. 99:59:59.999 --> 99:59:59.999 And so this is why climate scientists say 99:59:59.999 --> 99:59:59.999 it's not just that we know that climate change is happening, 99:59:59.999 --> 99:59:59.999 we know that greenhouse gases are a major part 99:59:59.999 --> 99:59:59.999 of the reason why. 99:59:59.999 --> 99:59:59.999 So now because there all these different things 99:59:59.999 --> 99:59:59.999 that scientists do, 99:59:59.999 --> 99:59:59.999 the philosopher Paul Feyerabend famously said, 99:59:59.999 --> 99:59:59.999 "The only principle in science 99:59:59.999 --> 99:59:59.999 that doesn't inhibit progress is: anything goes." 99:59:59.999 --> 99:59:59.999 Now this quotation has often been taken out of context, 99:59:59.999 --> 99:59:59.999 because Feyerabend was not actually saying 99:59:59.999 --> 99:59:59.999 that in science anything goes. 99:59:59.999 --> 99:59:59.999 What he was saying was, 99:59:59.999 --> 99:59:59.999 actually the full quotation is, 99:59:59.999 --> 99:59:59.999 "If you press me to say 99:59:59.999 --> 99:59:59.999 what is the method of science, 99:59:59.999 --> 99:59:59.999 I would have to say: anything goes." 99:59:59.999 --> 99:59:59.999 What he was trying to say 99:59:59.999 --> 99:59:59.999 is that scientists do a lot of different things. 99:59:59.999 --> 99:59:59.999 Scientists are creative. 99:59:59.999 --> 99:59:59.999 But then this pushes the question back: 99:59:59.999 --> 99:59:59.999 if scientists don't use a single method, 99:59:59.999 --> 99:59:59.999 then how do they decide 99:59:59.999 --> 99:59:59.999 what's right and what's wrong? 99:59:59.999 --> 99:59:59.999 And who judges? 99:59:59.999 --> 99:59:59.999 And the answer is, scientists judge, 99:59:59.999 --> 99:59:59.999 and they judge by judging evidence. 99:59:59.999 --> 99:59:59.999 Scientists collect evidence in many different ways, 99:59:59.999 --> 99:59:59.999 but however they collect it, 99:59:59.999 --> 99:59:59.999 they have to subject it to scrutiny. 99:59:59.999 --> 99:59:59.999 And this led to sociologist Robert Merton 99:59:59.999 --> 99:59:59.999 to focus on this question of how scientists 99:59:59.999 --> 99:59:59.999 scrutinize data and evidence, 99:59:59.999 --> 99:59:59.999 and he said they do it in a way he called 99:59:59.999 --> 99:59:59.999 "organized skepticism." 99:59:59.999 --> 99:59:59.999 And by that he meant it's organized 99:59:59.999 --> 99:59:59.999 because they do it collectively, 99:59:59.999 --> 99:59:59.999 they do it as a group, 99:59:59.999 --> 99:59:59.999 and skepticism, because they do it from a position 99:59:59.999 --> 99:59:59.999 of distrust. 99:59:59.999 --> 99:59:59.999 That is to say, the burden of proof 99:59:59.999 --> 99:59:59.999 is on the person with a novel claim. 99:59:59.999 --> 99:59:59.999 And in this sense, science is intrinsically conservative. 99:59:59.999 --> 99:59:59.999 It's quite hard to persuade the scientific community 99:59:59.999 --> 99:59:59.999 to say, "Yes, we know something, this is true." 99:59:59.999 --> 99:59:59.999 So despite the popularity of the concept 99:59:59.999 --> 99:59:59.999 of paradigm shifts, 99:59:59.999 --> 99:59:59.999 what we find is that actually, 99:59:59.999 --> 99:59:59.999 really major changes in scientific thinking 99:59:59.999 --> 99:59:59.999 are relatively rare in the history of science. 99:59:59.999 --> 99:59:59.999 So finally that brings us to one more idea: 99:59:59.999 --> 99:59:59.999 if scientists judge evidence collectively, 99:59:59.999 --> 99:59:59.999 this has led historians to focus on the question 99:59:59.999 --> 99:59:59.999 of consensus, 99:59:59.999 --> 99:59:59.999 and to say that at the end of the day, 99:59:59.999 --> 99:59:59.999 what science is, 99:59:59.999 --> 99:59:59.999 what scientific knowledge is, 99:59:59.999 --> 99:59:59.999 is the consensus of the scientific experts 99:59:59.999 --> 99:59:59.999 who through this process of organized scrutiny, 99:59:59.999 --> 99:59:59.999 collective scrutiny, 99:59:59.999 --> 99:59:59.999 have judged the evidence 99:59:59.999 --> 99:59:59.999 and come to a conclusion about it, 99:59:59.999 --> 99:59:59.999 either yea or nay. 99:59:59.999 --> 99:59:59.999 So we can think of scientific knowledge 99:59:59.999 --> 99:59:59.999 as a consensus of experts. 99:59:59.999 --> 99:59:59.999 We can also think of science as being 99:59:59.999 --> 99:59:59.999 a kind of a jury, 99:59:59.999 --> 99:59:59.999 except it's a very special kind of jury. 99:59:59.999 --> 99:59:59.999 It's not a jury of your peers, 99:59:59.999 --> 99:59:59.999 it's a jury of geeks. 99:59:59.999 --> 99:59:59.999 It's a jury of men and women with Ph.D's, 99:59:59.999 --> 99:59:59.999 and unlike a conventional jury, 99:59:59.999 --> 99:59:59.999 which has only two choices, 99:59:59.999 --> 99:59:59.999 guilty or not guilty, 99:59:59.999 --> 99:59:59.999 the scientific jury actually has a number of choices. 99:59:59.999 --> 99:59:59.999 Scientists can say yes, something's true. 99:59:59.999 --> 99:59:59.999 Scientists can say no, it's false. 99:59:59.999 --> 99:59:59.999 Or, they can say, well it might be true 99:59:59.999 --> 99:59:59.999 but we need to work more and collect more evidence. 99:59:59.999 --> 99:59:59.999 Or, they can say it might be true, 99:59:59.999 --> 99:59:59.999 but we don't know how to answer the question 99:59:59.999 --> 99:59:59.999 and we're going to put it aside 99:59:59.999 --> 99:59:59.999 and maybe come back to it later. 99:59:59.999 --> 99:59:59.999 That's what scientists call "intractable." 99:59:59.999 --> 99:59:59.999 But this leads us to one final problem: 99:59:59.999 --> 99:59:59.999 if science is what scientists say it is, 99:59:59.999 --> 99:59:59.999 then isn't that just an appeal to authority? 99:59:59.999 --> 99:59:59.999 And weren't we all taught in school 99:59:59.999 --> 99:59:59.999 that the appeal to authority is a logical fallacy? 99:59:59.999 --> 99:59:59.999 Well, here's the paradox of modern science, 99:59:59.999 --> 99:59:59.999 the paradox of the conclusions I think historians 99:59:59.999 --> 99:59:59.999 and philosophers and sociologists have come to, 99:59:59.999 --> 99:59:59.999 that actually science is the appeal to authority, 99:59:59.999 --> 99:59:59.999 but it's not the authority of the individual, 99:59:59.999 --> 99:59:59.999 no matter how smart that individual is, 99:59:59.999 --> 99:59:59.999 like Plato or Socrates or Einstein. 99:59:59.999 --> 99:59:59.999 It's the authority of the collective community. 99:59:59.999 --> 99:59:59.999 You can think of it is a kind of wisdom of the crowd, 99:59:59.999 --> 99:59:59.999 but a very special kind of crowd. 99:59:59.999 --> 99:59:59.999 Science does appeal to authority, 99:59:59.999 --> 99:59:59.999 but it's not based on any individual, 99:59:59.999 --> 99:59:59.999 no matter how smart that individual may be. 99:59:59.999 --> 99:59:59.999 It's based on the collective wisdom, 99:59:59.999 --> 99:59:59.999 the collective knowledge, the collective work, 99:59:59.999 --> 99:59:59.999 of all of the scientists who have worked 99:59:59.999 --> 99:59:59.999 on a particular problem. 99:59:59.999 --> 99:59:59.999 Scientists have a kind of culture of collective distrust, 99:59:59.999 --> 99:59:59.999 this "show me" culture, 99:59:59.999 --> 99:59:59.999 illustrated by this nice woman here 99:59:59.999 --> 99:59:59.999 showing her colleagues her evidence. 99:59:59.999 --> 99:59:59.999 Of course, these people don't really look like scientists, 99:59:59.999 --> 99:59:59.999 because they're much too happy. 99:59:59.999 --> 99:59:59.999 (Laughter) 99:59:59.999 --> 99:59:59.999 Okay, so that brings me to my final point. 99:59:59.999 --> 99:59:59.999 Most of us get up in the morning. 99:59:59.999 --> 99:59:59.999 Most of us trust our cars. 99:59:59.999 --> 99:59:59.999 Well, see, now I think, I'm in Manhattan, 99:59:59.999 --> 99:59:59.999 this is a bad analogy, 99:59:59.999 --> 99:59:59.999 but most Americans who don't live in Manhattan 99:59:59.999 --> 99:59:59.999 get up in the morning and get in their cars 99:59:59.999 --> 99:59:59.999 and turn on that ignition, and their cars work, 99:59:59.999 --> 99:59:59.999 and they work incredibly well. 99:59:59.999 --> 99:59:59.999 The modern automobile hardly ever breaks down. 99:59:59.999 --> 99:59:59.999 So why is that? Why do cars work so well? 99:59:59.999 --> 99:59:59.999 It's not because of the genius of Henry Ford 99:59:59.999 --> 99:59:59.999 or Carl Benz or even Elon Musk. 99:59:59.999 --> 99:59:59.999 It's because the modern automobile 99:59:59.999 --> 99:59:59.999 is the product of more than 100 years of work 99:59:59.999 --> 99:59:59.999 by hundreds and thousands 99:59:59.999 --> 99:59:59.999 and tens of thousands of people. 99:59:59.999 --> 99:59:59.999 The modern automobile is the product 99:59:59.999 --> 99:59:59.999 of the collected work and wisdom and experience 99:59:59.999 --> 99:59:59.999 of every man and woman who has ever worked 99:59:59.999 --> 99:59:59.999 on a car, 99:59:59.999 --> 99:59:59.999 and the reliability of the technology is the result 99:59:59.999 --> 99:59:59.999 of that accumulated effort. 99:59:59.999 --> 99:59:59.999 We benefit not just from the benefit of Benz 99:59:59.999 --> 99:59:59.999 and Ford and Musk 99:59:59.999 --> 99:59:59.999 but from the collective intelligence and hard work 99:59:59.999 --> 99:59:59.999 of all of the people who have worked 99:59:59.999 --> 99:59:59.999 on the modern car. 99:59:59.999 --> 99:59:59.999 And the same is true of science, 99:59:59.999 --> 99:59:59.999 only science is even older. 99:59:59.999 --> 99:59:59.999 Our basis for trust in science is actually the same 99:59:59.999 --> 99:59:59.999 as our basis in trust in technology, 99:59:59.999 --> 99:59:59.999 and the same as our basis for trust in anything, 99:59:59.999 --> 99:59:59.999 namely, experience. 99:59:59.999 --> 99:59:59.999 But it shouldn't be blind trust 99:59:59.999 --> 99:59:59.999 anymore than we would have blind trust in anything. 99:59:59.999 --> 99:59:59.999 Our trust in science, like science itself, 99:59:59.999 --> 99:59:59.999 should be based on evidence, 99:59:59.999 --> 99:59:59.999 and that means that scientists 99:59:59.999 --> 99:59:59.999 have to become better communicators. 99:59:59.999 --> 99:59:59.999 They have to explain to us not just what they know 99:59:59.999 --> 99:59:59.999 but how they know it, 99:59:59.999 --> 99:59:59.999 and it means that we have to become better listeners. 99:59:59.999 --> 99:59:59.999 Thank you very much. 99:59:59.999 --> 99:59:59.999 (Applause)