1 00:00:01,830 --> 00:00:04,268 Every day we face issues like climate change 2 00:00:04,268 --> 00:00:05,708 or the safety of vaccines 3 00:00:05,708 --> 00:00:08,348 where we have to answer questions whose answers 4 00:00:08,348 --> 00:00:11,659 rely heavily on scientific information. 5 00:00:11,659 --> 00:00:15,330 Scientists tell us that the world is warming. 6 00:00:15,330 --> 00:00:17,281 Scientists tell us that vaccines are safe. 7 00:00:17,281 --> 00:00:19,465 But how do we know if they are right? 8 00:00:19,465 --> 00:00:21,569 Why should be believe the science? 9 00:00:21,569 --> 00:00:24,898 The fact is, many of us actually don't believe the science. 10 00:00:24,898 --> 00:00:27,314 Public opinion polls consistently show 11 00:00:27,314 --> 00:00:29,634 that significant proportions of the American people 12 00:00:29,634 --> 00:00:33,225 don't believe the climate is warming due to human activities, 13 00:00:33,225 --> 00:00:36,724 don't think that there is evolution by natural selection, 14 00:00:36,724 --> 00:00:40,805 and aren't persuaded by the safety of vaccines. 15 00:00:40,805 --> 00:00:44,316 So why should we believe the science? 16 00:00:44,316 --> 00:00:47,957 Well, scientists don't like talking about science as a matter of belief. 17 00:00:47,957 --> 00:00:50,444 In fact, they would contract science with faith, 18 00:00:50,444 --> 00:00:53,680 and they would say belief is the domain of faith. 19 00:00:53,680 --> 00:00:57,238 And faith is a separate thing apart and distinct from science. 20 00:00:57,238 --> 00:00:59,790 Indeed they would say religion is based on faith 21 00:00:59,790 --> 00:01:04,254 or maybe the calculous of Pascal's wager. 22 00:01:04,254 --> 00:01:07,110 Blaise Pascal was a 17th century mathematician 23 00:01:07,110 --> 00:01:09,630 who tried to bring scientific reasoning to the question of 24 00:01:09,630 --> 00:01:11,542 whether or not he should believe in God, 25 00:01:11,542 --> 00:01:13,616 and his wager went like this: 26 00:01:13,616 --> 00:01:15,935 well, if God doesn't exist 27 00:01:15,935 --> 00:01:18,082 but I decide to believe in him 28 00:01:18,082 --> 00:01:20,538 nothing much is really lost. 29 00:01:20,538 --> 00:01:22,451 Maybe a few hours on Sunday. 30 00:01:22,451 --> 00:01:23,234 [Laughter] 31 00:01:23,234 --> 00:01:26,385 But if he does exist and I don't believe in him, 32 00:01:26,385 --> 00:01:28,522 then I'm in deep trouble. 33 00:01:28,522 --> 00:01:31,578 And so Pascal said, we'd better believe in God. 34 00:01:31,578 --> 00:01:33,610 Or as one of my college professors said, 35 00:01:33,610 --> 00:01:36,106 "He clutched for the handmill of faith." 36 00:01:36,106 --> 00:01:37,772 He made that leap of faith 37 00:01:37,772 --> 00:01:41,896 leaving science and rationalism behind. 38 00:01:41,896 --> 00:01:45,392 Now the fact is though, for most of us, 39 00:01:45,392 --> 00:01:48,176 most scientific claims are a leap of faith. 40 00:01:48,176 --> 00:01:52,941 We can't really judge scientific claims for ourselves in most cases. 41 00:01:52,941 --> 00:01:55,701 And indeed this is actually true for most scientists as well 42 00:01:55,701 --> 00:01:57,851 outside of their own specialties. 43 00:01:57,851 --> 00:02:00,491 So if you think about it, a geologist can't tell you 44 00:02:00,491 --> 00:02:02,251 whether a vaccine is safe. 45 00:02:02,251 --> 00:02:05,241 Most chemists are not experts in evolutionary theory. 46 00:02:05,241 --> 00:02:07,053 A physicist cannot tell you, 47 00:02:07,053 --> 00:02:08,973 despite the claims of some of them, 48 00:02:08,973 --> 00:02:12,317 whether or not tobacco causes cancer. 49 00:02:12,317 --> 00:02:14,487 So, if even scientists themselves 50 00:02:14,487 --> 00:02:16,223 have to make a leap of faith 51 00:02:16,223 --> 00:02:17,895 outside their own fields, 52 00:02:17,895 --> 00:02:21,983 then why do they accept the claims of other scientists? 53 00:02:21,983 --> 00:02:24,231 Why do they believe each other's claims? 54 00:02:24,231 --> 00:02:27,111 And should we believe those claims? 55 00:02:27,111 --> 00:02:30,167 So what I'd like to argue is yes, we should, 56 00:02:30,167 --> 00:02:33,047 but not for the reason that most of us think. 57 00:02:33,047 --> 00:02:35,200 Most of us were taught in school that the reason we should 58 00:02:35,200 --> 00:02:38,832 believe in science is because of the scientific method. 59 00:02:38,832 --> 00:02:41,208 We were taught that scientists follow a method 60 00:02:41,208 --> 00:02:43,824 and that this method guarantees 61 00:02:43,824 --> 00:02:46,200 the truth of their claims. 62 00:02:46,200 --> 00:02:48,720 The method that most of us were taught in school, 63 00:02:48,720 --> 00:02:51,296 we can call it the text book method, 64 00:02:51,296 --> 00:02:54,056 is the hypothetical deductive method. 65 00:02:54,056 --> 00:02:56,924 According to the standard model, the textbook model, 66 00:02:56,924 --> 00:02:59,601 scientists develop hypotheses, they deduce 67 00:02:59,601 --> 00:03:02,121 the consequences for those hypotheses, 68 00:03:02,121 --> 00:03:03,841 and then they go out into the world and they say, 69 00:03:03,841 --> 00:03:06,715 "Okay, well are those consequences true?" 70 00:03:06,715 --> 00:03:09,428 Can we observe them taking place in the natural world? 71 00:03:09,428 --> 00:03:12,228 And if they are true, then the scientists say, 72 00:03:12,228 --> 00:03:15,434 "Great, we know the hypothesis is correct." 73 00:03:15,434 --> 00:03:17,313 So there are many famous examples in the history 74 00:03:17,313 --> 00:03:20,472 of science of scientists doing exactly this. 75 00:03:20,472 --> 00:03:22,097 One of the most famous examples 76 00:03:22,097 --> 00:03:24,593 comes from the work of Albert Einstein. 77 00:03:24,593 --> 00:03:26,985 When Einstein developed the theory of general relativity, 78 00:03:26,985 --> 00:03:29,201 one of the consequences of his theory 79 00:03:29,201 --> 00:03:32,100 was that space time wasn't just an empty void 80 00:03:32,100 --> 00:03:34,209 but that it actually had a fabric. 81 00:03:34,209 --> 00:03:36,033 And that that fabric was bent 82 00:03:36,033 --> 00:03:39,057 in the presence of massive objects like the sun. 83 00:03:39,057 --> 00:03:41,929 So if this theory were true then it meant that light 84 00:03:41,929 --> 00:03:43,457 as it passed the sun 85 00:03:43,457 --> 00:03:45,785 should actually be bent around it. 86 00:03:45,785 --> 00:03:47,985 That was a pretty startling prediction 87 00:03:47,985 --> 00:03:49,873 and it took a few years before scientists 88 00:03:49,873 --> 00:03:51,281 were able to test it. 89 00:03:51,281 --> 00:03:53,521 But they did test it in 1919, 90 00:03:53,521 --> 00:03:55,971 and lo and behold it turned out to be true. 91 00:03:55,971 --> 00:03:59,379 Starlight actually does bend as it travels around the sun. 92 00:03:59,379 --> 00:04:01,763 This was a huge confirmation of the theory. 93 00:04:01,763 --> 00:04:03,418 It was considered proof of the truth 94 00:04:03,418 --> 00:04:05,066 of this radical new idea, 95 00:04:05,066 --> 00:04:06,682 and it was written up in many newspapers 96 00:04:06,682 --> 00:04:09,098 around the globe. 97 00:04:09,098 --> 00:04:11,850 Now sometimes this theory or this model 98 00:04:11,850 --> 00:04:14,874 is referred to as the deductive-nomological model. 99 00:04:14,874 --> 00:04:18,378 Meaning those academics like to make things complicated. 100 00:04:18,378 --> 00:04:23,739 But also because in the ideal case, it's about laws. 101 00:04:23,739 --> 00:04:26,371 So nomological means having to do with laws. 102 00:04:26,371 --> 00:04:29,595 And in the ideal case, the hypothesis isn't just an idea: 103 00:04:29,595 --> 00:04:31,811 ideally, it is a law of nature. 104 00:04:31,811 --> 00:04:34,148 Why does it matter that it is a law of nature? 105 00:04:34,148 --> 00:04:36,916 Because if it is a law, it can't be broken. 106 00:04:36,916 --> 00:04:38,964 If it's a law then it will always be true 107 00:04:38,964 --> 00:04:40,508 in all times and all places 108 00:04:40,508 --> 00:04:42,684 no matter what the circumstances are. 109 00:04:42,684 --> 00:04:45,893 And all of you know at least one example of a famous law: 110 00:04:45,893 --> 00:04:49,268 Einstein's famous equation, E=MC2, 111 00:04:49,268 --> 00:04:51,188 which tells us what the relationship is 112 00:04:51,188 --> 00:04:53,701 between energy and mass. 113 00:04:53,701 --> 00:04:57,381 And that relationship is true no matter what. 114 00:04:57,381 --> 00:05:01,073 Now, it turns out though that there are several problems with this model. 115 00:05:01,073 --> 00:05:04,425 The main problem is that it's wrong. 116 00:05:04,425 --> 00:05:08,237 It's just not true. [Laughter] 117 00:05:08,237 --> 00:05:11,250 And I'm going to talk about three reasons why it's wrong. 118 00:05:11,250 --> 00:05:13,429 So the first reason is a logical reason. 119 00:05:13,429 --> 00:05:17,535 It's the problem of the fallacy of affirming the consequent. 120 00:05:17,535 --> 00:05:19,831 So that's another fancy academic way of saying 121 00:05:19,831 --> 00:05:22,851 that false theories can make true predictions. 122 00:05:22,851 --> 00:05:24,395 So just because the prediction comes true 123 00:05:24,395 --> 00:05:27,787 doesn't actually logically prove that the theory is correct. 124 00:05:27,787 --> 00:05:31,818 And I have a good example of that too, again from the history of science. 125 00:05:31,818 --> 00:05:34,393 This is a picture of the Ptolemaic universe 126 00:05:34,393 --> 00:05:36,505 with the Earth at the center of the universe 127 00:05:36,505 --> 00:05:39,081 and The Sun and the planets going around it. 128 00:05:39,081 --> 00:05:41,097 The Ptolemaic model was believed 129 00:05:41,097 --> 00:05:44,393 by many very smart people for many centuries. 130 00:05:44,393 --> 00:05:46,129 Well, why? 131 00:05:46,129 --> 00:05:49,496 Well the answer is because it made lots of predictions that came true. 132 00:05:49,496 --> 00:05:51,512 The Ptolemaic system enabled astronomers 133 00:05:51,512 --> 00:05:54,352 to make accurate predictions of the motions of the planet, 134 00:05:54,352 --> 00:05:56,811 in fact more accurate predictions at first 135 00:05:56,811 --> 00:06:01,275 than the Copernican theory which we now would say is true. 136 00:06:01,275 --> 00:06:03,867 So that's one problem with the textbook model. 137 00:06:03,867 --> 00:06:06,353 A second problem is a practical problem, 138 00:06:06,353 --> 00:06:09,518 and it's the problem of auxiliary hypotheses. 139 00:06:09,518 --> 00:06:12,357 Auxiliary hypotheses are assumptions 140 00:06:12,357 --> 00:06:14,146 that scientists are making 141 00:06:14,146 --> 00:06:17,739 that they may or may not even be aware that they're making. 142 00:06:17,739 --> 00:06:19,770 So an important example of this 143 00:06:19,770 --> 00:06:22,185 comes from the Copernican model, 144 00:06:22,185 --> 00:06:25,177 which ultimately replaced the Ptolemaic system. 145 00:06:25,177 --> 00:06:27,177 So when Nicolaus Copernicus said, 146 00:06:27,177 --> 00:06:29,737 actually the Earth is not the center of the universe, 147 00:06:29,737 --> 00:06:31,865 the sun is the center of the solar system, 148 00:06:31,865 --> 00:06:33,587 the Earth moves around the sun. 149 00:06:33,587 --> 00:06:36,825 Scientists said, well okay, Nicolaus, if that's true 150 00:06:36,825 --> 00:06:38,579 we ought to be able to detect the motion 151 00:06:38,579 --> 00:06:40,667 of the Earth around the sun. 152 00:06:40,667 --> 00:06:42,803 And so this slide here illustrates a concept 153 00:06:42,803 --> 00:06:44,731 known as stellar parallax. 154 00:06:44,731 --> 00:06:48,393 And astronomers said, if the Earth is moving 155 00:06:48,393 --> 00:06:51,763 and we look at a prominent star, let's say, Sirius 156 00:06:51,763 --> 00:06:53,747 —well I know I'm in Manhattan so you guys can't see the stars, 157 00:06:53,747 --> 00:06:57,218 but imagine you're out in the country, imagine you chose that rural life— 158 00:06:57,218 --> 00:07:00,515 and we look at a star in December, we see that star 159 00:07:00,515 --> 00:07:03,610 against the backdrop of distant stars. 160 00:07:03,610 --> 00:07:06,474 If we now make the same observation six months later 161 00:07:06,474 --> 00:07:09,986 when the Earth has moved to this position in June, 162 00:07:09,986 --> 00:07:14,275 we look at that same star and we see it against a different backdrop. 163 00:07:14,275 --> 00:07:18,667 That difference, that angular difference, is the stellar parallax. 164 00:07:18,667 --> 00:07:21,290 So this is the prediction that the Copernican model makes. 165 00:07:21,290 --> 00:07:23,371 Astronomers looked for the stellar parallax 166 00:07:23,371 --> 00:07:29,163 and they found nothing, nothing at all. 167 00:07:29,163 --> 00:07:32,779 And many people argued that this proved that the Copernican model was false. 168 00:07:32,779 --> 00:07:34,507 So what happened? 169 00:07:34,507 --> 00:07:37,100 Well in hindsight we can say that astronomers were making 170 00:07:37,100 --> 00:07:39,427 two auxiliary hypotheses, both of which 171 00:07:39,427 --> 00:07:42,069 we would now say were incorrect. 172 00:07:42,069 --> 00:07:45,635 The first was an assumption about the size of the Earth's orbit. 173 00:07:45,635 --> 00:07:48,691 Astronomers were assuming that the Earth's orbit was large 174 00:07:48,691 --> 00:07:51,259 relative to the distance of the stars. 175 00:07:51,259 --> 00:07:53,723 Today we would draw the picture more like this, 176 00:07:53,723 --> 00:07:55,260 this comes from NASA, 177 00:07:55,260 --> 00:07:57,563 and you see the Earth's orbit is actually quite small. 178 00:07:57,563 --> 00:08:00,604 In fact, it's actually much smaller even than shown here. 179 00:08:00,604 --> 00:08:01,933 The stellar parallax therefore, 180 00:08:01,933 --> 00:08:05,637 is very small and actually very hard to detect. 181 00:08:05,637 --> 00:08:07,421 And that leads to the second reason 182 00:08:07,421 --> 00:08:09,093 why the prediction didn't work, 183 00:08:09,093 --> 00:08:11,325 because scientists were also assuming 184 00:08:11,325 --> 00:08:14,365 that the telescopes they had were sensitive enough 185 00:08:14,365 --> 00:08:16,245 to detect the parallax. 186 00:08:16,245 --> 00:08:18,412 And that turned out not to be true. 187 00:08:18,412 --> 00:08:20,376 It wasn't until the 19th century 188 00:08:20,376 --> 00:08:22,048 that scientists were able to detect 189 00:08:22,048 --> 00:08:24,156 the stellar parallax. 190 00:08:24,156 --> 00:08:26,792 So, there's a third problem as well. 191 00:08:26,792 --> 00:08:29,064 The third problem is simply a factual problem, 192 00:08:29,064 --> 00:08:31,976 that a lot of science doesn't fit the textbook model. 193 00:08:31,976 --> 00:08:34,329 A lot of science isn't deductive at all, 194 00:08:34,329 --> 00:08:36,217 it's actually inductive. 195 00:08:36,217 --> 00:08:38,513 And by that we mean that scientists don't necessarily 196 00:08:38,513 --> 00:08:41,354 start with theories and hypotheses, often they just 197 00:08:41,354 --> 00:08:44,993 start with observations of stuff going on in the world. 198 00:08:44,993 --> 00:08:47,602 And the most famous example of that is one of the most 199 00:08:47,602 --> 00:08:50,767 famous scientists who ever lived, Charles Darwin. 200 00:08:50,767 --> 00:08:53,759 When Darwin went out as a young man on the voyage of the Beagle, 201 00:08:53,759 --> 00:08:57,431 he didn't have a hypothesis, he didn't have a theory. 202 00:08:57,431 --> 00:09:00,687 He just knew that he wanted to have a career as a scientist 203 00:09:00,687 --> 00:09:02,739 and he started to collect data. 204 00:09:02,739 --> 00:09:04,699 Mainly he knew that he hated medicine 205 00:09:04,699 --> 00:09:06,987 because the sight of blood made him sick so 206 00:09:06,987 --> 00:09:09,395 he had to have an alternative career path. 207 00:09:09,395 --> 00:09:11,499 So he started collecting data. 208 00:09:11,499 --> 00:09:14,635 And he collected many things including his famous finches. 209 00:09:14,635 --> 00:09:16,915 When he collected these finches, he threw them in a bag 210 00:09:16,915 --> 00:09:19,525 and he had no idea what they meant. 211 00:09:19,525 --> 00:09:21,412 Many years later back in London, 212 00:09:21,412 --> 00:09:23,625 Darwin looked at his data again and began 213 00:09:23,625 --> 00:09:26,113 to develop an explanation, 214 00:09:26,113 --> 00:09:29,561 and that explanation was the theory of natural selection. 215 00:09:29,561 --> 00:09:31,390 Besides inductive science, 216 00:09:31,390 --> 00:09:34,576 scientists also often participate in modeling. 217 00:09:34,576 --> 00:09:36,872 One of the things scientists want to do in life 218 00:09:36,872 --> 00:09:39,063 is to explain the causes of things. 219 00:09:39,063 --> 00:09:40,848 And how do we do that? 220 00:09:40,848 --> 00:09:43,071 Well, one way you can do it is to build a model 221 00:09:43,071 --> 00:09:44,872 that tests an idea. 222 00:09:44,872 --> 00:09:46,663 So this is a picture of Henry Cadell, 223 00:09:46,663 --> 00:09:49,119 who was a Scottish geologist in the 19th century. 224 00:09:49,119 --> 00:09:50,912 You can tell he's Scottish because he's wearing 225 00:09:50,912 --> 00:09:53,064 a deerstalker cap and Wellington boots. 226 00:09:53,064 --> 00:09:55,304 [Laughter] 227 00:09:55,304 --> 00:09:57,061 And Cadell wanted to answer the question, 228 00:09:57,061 --> 00:09:58,748 how are mountains formed? 229 00:09:58,748 --> 00:10:00,244 And one of the things he had observed 230 00:10:00,244 --> 00:10:02,908 is that if you look at mountains like the Appalachians, 231 00:10:02,908 --> 00:10:04,741 you often find that the rocks in them 232 00:10:04,741 --> 00:10:06,060 are folded, 233 00:10:06,060 --> 00:10:07,636 and they're folded in a particular way, 234 00:10:07,636 --> 00:10:09,020 which suggested to him 235 00:10:09,020 --> 00:10:11,969 that they were actually being compressed from the side. 236 00:10:11,969 --> 00:10:14,157 And this idea would later play a major role 237 00:10:14,157 --> 00:10:16,500 in discussions of continental drift. 238 00:10:16,500 --> 00:10:18,956 So he built this model, this crazy contraption 239 00:10:18,956 --> 00:10:21,268 with levers and wood and here's his wheelbarrow, 240 00:10:21,268 --> 00:10:23,044 buckets, a big sledgehammer. 241 00:10:23,044 --> 00:10:25,388 I don't know why he's got the Wellington boots. 242 00:10:25,388 --> 00:10:27,165 Maybe it's going to rain. 243 00:10:27,165 --> 00:10:30,012 And he created this physical model in order 244 00:10:30,012 --> 00:10:34,525 to demonstrate that you could in fact create 245 00:10:34,525 --> 00:10:37,139 patterns in rocks, or at least in this case in mud, 246 00:10:37,139 --> 00:10:39,275 that looked a lot like mountains 247 00:10:39,275 --> 00:10:41,107 if you compressed them from the side. 248 00:10:41,107 --> 00:10:44,475 So it was an argument about the cause of mountains. 249 00:10:44,475 --> 00:10:47,443 Nowadays, most scientists prefer to work inside, 250 00:10:47,443 --> 00:10:50,043 so they don't build physical models so much 251 00:10:50,043 --> 00:10:52,371 as to make computer simulations. 252 00:10:52,371 --> 00:10:55,099 But a computer simulation is a kind of a model. 253 00:10:55,099 --> 00:10:57,243 It's a model that's made with mathematics, 254 00:10:57,243 --> 00:10:59,876 and like the physical models of the 19th century, 255 00:10:59,876 --> 00:11:03,974 it's very important for thinking about causes. 256 00:11:03,974 --> 00:11:06,509 So one of the big questions to do with climate change, 257 00:11:06,509 --> 00:11:08,372 we have tremendous amounts of evidence 258 00:11:08,372 --> 00:11:10,412 that the earth is warming up. 259 00:11:10,412 --> 00:11:12,636 This slide here, the black line shows 260 00:11:12,636 --> 00:11:14,756 the measurements that scientists have taken 261 00:11:14,756 --> 00:11:16,899 for the last 150 years 262 00:11:16,899 --> 00:11:18,299 showing that the earth's temperature 263 00:11:18,299 --> 00:11:19,923 has steadily increased, 264 00:11:19,923 --> 00:11:22,829 and you can see in particular that in the last 50 years 265 00:11:22,829 --> 00:11:24,683 there's been this dramatic increase 266 00:11:24,683 --> 00:11:26,843 of nearly one degree Centigrade, 267 00:11:26,843 --> 00:11:29,188 or almost two degrees Fahrenheit. 268 00:11:29,188 --> 00:11:31,835 So what, though, is driving that change? 269 00:11:31,835 --> 00:11:34,052 How can we know what's causing 270 00:11:34,052 --> 00:11:35,756 the observed warming? 271 00:11:35,756 --> 00:11:37,300 Well, scientists can model it 272 00:11:37,300 --> 00:11:39,428 using a computer simulation. 273 00:11:39,428 --> 00:11:42,380 So this diagram illustrates a computer simulation 274 00:11:42,380 --> 00:11:44,491 that has looked at all the different factors 275 00:11:44,491 --> 00:11:46,756 that we know can influence the earth's climate, 276 00:11:46,756 --> 00:11:49,668 so sulfate particles from air pollution, 277 00:11:49,668 --> 00:11:53,188 volcanic dust from volcanic eruptions, 278 00:11:53,188 --> 00:11:54,932 changes in solar radiation, 279 00:11:54,932 --> 00:11:57,590 and, of course, greenhouse gases. 280 00:11:57,590 --> 00:11:59,148 And they asked the question, 281 00:11:59,148 --> 00:12:02,604 what set of variables put into a model 282 00:12:02,604 --> 00:12:06,076 will reproduce what we actually see in real life? 283 00:12:06,076 --> 00:12:08,180 So here is the real life in black. 284 00:12:08,180 --> 00:12:10,290 Here's the model in this light grey, 285 00:12:10,290 --> 00:12:12,011 and the answer is 286 00:12:12,011 --> 00:12:16,287 a model that includes, it's the answer E on that SAT, 287 00:12:16,287 --> 00:12:18,548 all of the above. 288 00:12:18,548 --> 00:12:20,164 The only way you can reproduce 289 00:12:20,164 --> 00:12:21,812 the observed temperature measurements 290 00:12:21,812 --> 00:12:23,900 is with all of these things put together, 291 00:12:23,900 --> 00:12:25,979 including greenhouse gases, 292 00:12:25,979 --> 00:12:28,059 and in particular you can see that the increase 293 00:12:28,059 --> 00:12:29,964 in greenhouse gases tracks 294 00:12:29,964 --> 00:12:32,084 this very dramatic increase in temperature 295 00:12:32,084 --> 00:12:34,019 over the last 50 years. 296 00:12:34,019 --> 00:12:36,484 And so this is why climate scientists say 297 00:12:36,484 --> 00:12:39,332 it's not just that we know that climate change is happening, 298 00:12:39,332 --> 00:12:42,220 we know that greenhouse gases are a major part 299 00:12:42,220 --> 00:12:45,068 of the reason why. 300 00:12:45,068 --> 00:12:47,228 So now because there all these different things 301 00:12:47,228 --> 00:12:48,847 that scientists do, 302 00:12:48,847 --> 00:12:51,823 the philosopher Paul Feyerabend famously said, 303 00:12:51,823 --> 00:12:53,799 "The only principle in science 304 00:12:53,799 --> 00:12:57,998 that doesn't inhibit progress is: anything goes." 305 00:12:57,998 --> 00:13:00,654 Now this quotation has often been taken out of context, 306 00:13:00,654 --> 00:13:02,742 because Feyerabend was not actually saying 307 00:13:02,742 --> 00:13:04,342 that in science anything goes. 308 00:13:04,342 --> 00:13:06,126 What he was saying was, 309 00:13:06,126 --> 00:13:08,014 actually the full quotation is, 310 00:13:08,014 --> 00:13:10,023 "If you press me to say 311 00:13:10,023 --> 00:13:11,766 what is the method of science, 312 00:13:11,766 --> 00:13:15,455 I would have to say: anything goes." 313 00:13:15,455 --> 00:13:16,703 What he was trying to say 314 00:13:16,703 --> 00:13:19,037 is that scientists do a lot of different things. 315 00:13:19,037 --> 00:13:21,478 Scientists are creative. 316 00:13:21,478 --> 00:13:23,758 But then this pushes the question back: 317 00:13:23,758 --> 00:13:26,599 if scientists don't use a single method, 318 00:13:26,599 --> 00:13:28,758 then how do they decide 319 00:13:28,758 --> 00:13:30,406 what's right and what's wrong? 320 00:13:30,406 --> 00:13:32,099 And who judges? 321 00:13:32,099 --> 00:13:34,078 And the answer is, scientists judge, 322 00:13:34,078 --> 00:13:37,303 and they judge by judging evidence. 323 00:13:37,303 --> 00:13:40,302 Scientists collect evidence in many different ways, 324 00:13:40,302 --> 00:13:42,374 but however they collect it, 325 00:13:42,374 --> 00:13:44,921 they have to subject it to scrutiny. 326 00:13:44,921 --> 00:13:47,231 And this led to sociologist Robert Merton 327 00:13:47,231 --> 00:13:49,551 to focus on this question of how scientists 328 00:13:49,551 --> 00:13:51,390 scrutinize data and evidence, 329 00:13:51,390 --> 00:13:53,798 and he said they do it in a way he called 330 00:13:53,798 --> 00:13:55,967 "organized skepticism." 331 00:13:55,967 --> 00:13:57,801 And by that he meant it's organized 332 00:13:57,801 --> 00:13:59,519 because they do it collectively, 333 00:13:59,519 --> 00:14:01,238 they do it as a group, 334 00:14:01,238 --> 00:14:03,774 and skepticism, because they do it from a position 335 00:14:03,774 --> 00:14:05,318 of distrust. 336 00:14:05,318 --> 00:14:07,038 That is to say, the burden of proof 337 00:14:07,038 --> 00:14:09,701 is on the person with a novel claim. 338 00:14:09,701 --> 00:14:12,914 And in this sense, science is intrinsically conservative. 339 00:14:12,914 --> 00:14:15,406 It's quite hard to persuade the scientific community 340 00:14:15,406 --> 00:14:19,187 to say, "Yes, we know something, this is true." 341 00:14:19,187 --> 00:14:21,443 So despite the popularity of the concept 342 00:14:21,443 --> 00:14:23,092 of paradigm shifts, 343 00:14:23,092 --> 00:14:24,454 what we find is that actually, 344 00:14:24,454 --> 00:14:26,699 really major changes in scientific thinking 345 00:14:26,699 --> 00:14:31,119 are relatively rare in the history of science. 346 00:14:31,119 --> 00:14:34,642 So finally that brings us to one more idea: 347 00:14:34,642 --> 00:14:38,460 if scientists judge evidence collectively, 348 00:14:38,460 --> 00:14:40,972 this has led historians to focus on the question 349 00:14:40,972 --> 00:14:42,461 of consensus, 350 00:14:42,461 --> 00:14:44,226 and to say that at the end of the day, 351 00:14:44,226 --> 00:14:46,061 what science is, 352 00:14:46,061 --> 00:14:47,820 what scientific knowledge is, 353 00:14:47,820 --> 00:14:51,119 is the consensus of the scientific experts 354 00:14:51,119 --> 00:14:53,473 who through this process of organized scrutiny, 355 00:14:53,473 --> 00:14:55,208 collective scrutiny, 356 00:14:55,208 --> 00:14:56,970 have judged the evidence 357 00:14:56,970 --> 00:14:59,577 and come to a conclusion about it, 358 00:14:59,577 --> 00:15:02,234 either yea or nay. 359 00:15:02,234 --> 00:15:03,858 So we can think of scientific knowledge 360 00:15:03,858 --> 00:15:05,890 as a consensus of experts. 361 00:15:05,890 --> 00:15:07,482 We can also think of science as being 362 00:15:07,482 --> 00:15:09,290 a kind of a jury, 363 00:15:09,290 --> 00:15:11,714 except it's a very special kind of jury. 364 00:15:11,714 --> 00:15:13,618 It's not a jury of your peers, 365 00:15:13,618 --> 00:15:16,184 it's a jury of geeks. 366 00:15:16,184 --> 00:15:19,538 It's a jury of men and women with Ph.Ds, 367 00:15:19,538 --> 00:15:21,730 and unlike a conventional jury, 368 00:15:21,730 --> 00:15:23,540 which has only two choices, 369 00:15:23,540 --> 00:15:25,895 guilty or not guilty, 370 00:15:25,895 --> 00:15:29,466 the scientific jury actually has a number of choices. 371 00:15:29,466 --> 00:15:32,095 Scientists can say yes, something's true. 372 00:15:32,095 --> 00:15:35,078 Scientists can say no, it's false. 373 00:15:35,078 --> 00:15:37,310 Or, they can say, well it might be true 374 00:15:37,310 --> 00:15:40,324 but we need to work more and collect more evidence. 375 00:15:40,324 --> 00:15:42,012 Or, they can say it might be true, 376 00:15:42,012 --> 00:15:43,650 but we don't know how to answer the question 377 00:15:43,650 --> 00:15:45,027 and we're going to put it aside 378 00:15:45,027 --> 00:15:47,883 and maybe we'll come back to it later. 379 00:15:47,883 --> 00:15:51,915 That's what scientists call "intractable." 380 00:15:51,915 --> 00:15:54,811 But this leads us to one final problem: 381 00:15:54,811 --> 00:15:57,299 if science is what scientists say it is, 382 00:15:57,299 --> 00:16:00,085 then isn't that just an appeal to authority? 383 00:16:00,085 --> 00:16:01,352 And weren't we all taught in school 384 00:16:01,352 --> 00:16:04,459 that the appeal to authority is a logical fallacy? 385 00:16:04,459 --> 00:16:07,371 Well, here's the paradox of modern science, 386 00:16:07,371 --> 00:16:09,603 the paradox of the conclusions I think historians 387 00:16:09,603 --> 00:16:12,484 and philosophers and sociologists have come to, 388 00:16:12,484 --> 00:16:15,675 that actually science is the appeal to authority, 389 00:16:15,675 --> 00:16:19,511 but it's not the authority of the individual, 390 00:16:19,511 --> 00:16:21,920 no matter how smart that individual is, 391 00:16:21,920 --> 00:16:25,655 like Plato or Socrates or Einstein. 392 00:16:25,655 --> 00:16:28,659 It's the authority of the collective community. 393 00:16:28,659 --> 00:16:31,835 You can think of it is a kind of wisdom of the crowd, 394 00:16:31,835 --> 00:16:35,291 but a very special kind of crowd. 395 00:16:35,291 --> 00:16:37,651 Science does appeal to authority, 396 00:16:37,651 --> 00:16:40,191 but it's not based on any individual, 397 00:16:40,191 --> 00:16:42,547 no matter how smart that individual may be. 398 00:16:42,547 --> 00:16:44,528 It's based on the collective wisdom, 399 00:16:44,528 --> 00:16:47,037 the collective knowledge, the collective work, 400 00:16:47,037 --> 00:16:48,768 of all of the scientists who have worked 401 00:16:48,768 --> 00:16:51,595 on a particular problem. 402 00:16:51,595 --> 00:16:54,571 Scientists have a kind of culture of collective distrust, 403 00:16:54,571 --> 00:16:56,331 this "show me" culture, 404 00:16:56,331 --> 00:16:58,331 illustrated by this nice woman here 405 00:16:58,331 --> 00:17:01,283 showing her colleagues her evidence. 406 00:17:01,283 --> 00:17:03,510 Of course, these people don't really look like scientists, 407 00:17:03,510 --> 00:17:05,746 because they're much too happy. 408 00:17:05,746 --> 00:17:09,618 [Laughter] 409 00:17:09,618 --> 00:17:13,066 Okay, so that brings me to my final point. 410 00:17:13,066 --> 00:17:16,338 Most of us get up in the morning. 411 00:17:16,338 --> 00:17:17,978 Most of us trust our cars. 412 00:17:17,978 --> 00:17:19,450 Well, see, now I'm thinking, I'm in Manhattan, 413 00:17:19,450 --> 00:17:20,828 this is a bad analogy, 414 00:17:20,828 --> 00:17:23,542 but most Americans who don't live in Manhattan 415 00:17:23,542 --> 00:17:25,086 get up in the morning and get in their cars 416 00:17:25,086 --> 00:17:27,689 and turn on that ignition, and their cars work, 417 00:17:27,689 --> 00:17:29,600 and they work incredibly well. 418 00:17:29,600 --> 00:17:32,475 The modern automobile hardly ever breaks down. 419 00:17:32,475 --> 00:17:35,358 So why is that? Why do cars work so well? 420 00:17:35,358 --> 00:17:37,452 It's not because of the genius of Henry Ford 421 00:17:37,452 --> 00:17:41,113 or Carl Benz or even Elon Musk. 422 00:17:41,113 --> 00:17:42,905 It's because the modern automobile 423 00:17:42,905 --> 00:17:47,939 is the product of more than 100 years of work 424 00:17:47,939 --> 00:17:49,669 by hundreds and thousands 425 00:17:49,669 --> 00:17:51,135 and tens of thousands of people. 426 00:17:51,135 --> 00:17:53,226 The modern automobile is the product 427 00:17:53,226 --> 00:17:55,615 of the collected work and wisdom and experience 428 00:17:55,615 --> 00:17:58,212 of every man and woman who has ever worked 429 00:17:58,212 --> 00:17:59,950 on a car, 430 00:17:59,950 --> 00:18:02,635 and the reliability of the technology is the result 431 00:18:02,635 --> 00:18:05,438 of that accumulated effort. 432 00:18:05,438 --> 00:18:08,155 We benefit not just from the genius of Benz 433 00:18:08,155 --> 00:18:09,551 and Ford and Musk 434 00:18:09,551 --> 00:18:12,139 but from the collective intelligence and hard work 435 00:18:12,139 --> 00:18:14,060 of all of the people who have worked 436 00:18:14,060 --> 00:18:16,039 on the modern car. 437 00:18:16,039 --> 00:18:18,180 And the same is true of science, 438 00:18:18,180 --> 00:18:20,744 only science is even older. 439 00:18:20,744 --> 00:18:23,528 Our basis for trust in science is actually the same 440 00:18:23,528 --> 00:18:26,162 as our basis in trust in technology, 441 00:18:26,162 --> 00:18:29,929 and the same as our basis for trust in anything, 442 00:18:29,929 --> 00:18:32,447 namely, experience. 443 00:18:32,447 --> 00:18:34,251 But it shouldn't be blind trust 444 00:18:34,251 --> 00:18:37,301 any more than we would have blind trust in anything. 445 00:18:37,301 --> 00:18:39,612 Our trust in science, like science itself, 446 00:18:39,612 --> 00:18:41,655 should be based on evidence, 447 00:18:41,655 --> 00:18:43,197 and that means that scientists 448 00:18:43,197 --> 00:18:45,135 have to become better communicators. 449 00:18:45,135 --> 00:18:47,982 They have to explain to us not just what they know 450 00:18:47,982 --> 00:18:50,120 but how they know it, 451 00:18:50,120 --> 00:18:53,610 and it means that we have to become better listeners. 452 00:18:53,610 --> 00:18:55,439 Thank you very much. 453 00:18:55,439 --> 00:18:57,452 (Applause)