1 99:59:59,999 --> 99:59:59,999 Every day we face issues like climate change 2 99:59:59,999 --> 99:59:59,999 or the safety of vaccines 3 99:59:59,999 --> 99:59:59,999 where we have to answer questions whose answers 4 99:59:59,999 --> 99:59:59,999 rely heavily on scientific information. 5 99:59:59,999 --> 99:59:59,999 Scientists tell us that the world is warming. 6 99:59:59,999 --> 99:59:59,999 Scientists tell us that vaccines are safe. 7 99:59:59,999 --> 99:59:59,999 But how do we know if they are right? 8 99:59:59,999 --> 99:59:59,999 Why should be believe the science? 9 99:59:59,999 --> 99:59:59,999 The fact is, many of us actually don't believe the science. 10 99:59:59,999 --> 99:59:59,999 Public opinion polls consistently show 11 99:59:59,999 --> 99:59:59,999 that significant proportions of the American people 12 99:59:59,999 --> 99:59:59,999 don't believe the climate is warming due to human activities, 13 99:59:59,999 --> 99:59:59,999 don't think that there is evolution by natural selection, 14 99:59:59,999 --> 99:59:59,999 and aren't persuaded by the safety of vaccines. 15 99:59:59,999 --> 99:59:59,999 So why should we believe the science? 16 99:59:59,999 --> 99:59:59,999 Well, scientists don't like talking about science as a matter of belief. 17 99:59:59,999 --> 99:59:59,999 In fact, they would contract science with faith 18 99:59:59,999 --> 99:59:59,999 and they would say belief is the domain, faith. 19 99:59:59,999 --> 99:59:59,999 And faith is a separate thing apart and distinct from science. 20 99:59:59,999 --> 99:59:59,999 Indeed they would say religion is based on faith 21 99:59:59,999 --> 99:59:59,999 or maybe the calculous of Pascal's wager. 22 99:59:59,999 --> 99:59:59,999 Blaise Pascal was a 17th century mathematician 23 99:59:59,999 --> 99:59:59,999 who tried to bring scientific reasoning to the question of 24 99:59:59,999 --> 99:59:59,999 wether or not he should believe in God 25 99:59:59,999 --> 99:59:59,999 and his wager went like this: 26 99:59:59,999 --> 99:59:59,999 Well, if God doesn't exist but I decide to believe in him 27 99:59:59,999 --> 99:59:59,999 nothing much is really lost. 28 99:59:59,999 --> 99:59:59,999 Maybe a few hours on Sunday. 29 99:59:59,999 --> 99:59:59,999 [Laughter] 30 99:59:59,999 --> 99:59:59,999 But if he does exist and I don't believe in him, 31 99:59:59,999 --> 99:59:59,999 then I'm in deep trouble. 32 99:59:59,999 --> 99:59:59,999 And so Pascal said, we'd better believe in God. 33 99:59:59,999 --> 99:59:59,999 Or as one of my college professors said, 34 99:59:59,999 --> 99:59:59,999 "he clutched for the handmill of faith". 35 99:59:59,999 --> 99:59:59,999 He made that leap of faith 36 99:59:59,999 --> 99:59:59,999 leaving science and rationalism behind. 37 99:59:59,999 --> 99:59:59,999 Now the fact is though, for most of us 38 99:59:59,999 --> 99:59:59,999 most scientific claims are a leap of faith. 39 99:59:59,999 --> 99:59:59,999 We can't really judge scientific claims for ourselves in most cases. 40 99:59:59,999 --> 99:59:59,999 And indeed this is actually true for most scientists as well 41 99:59:59,999 --> 99:59:59,999 outside of their own specialties. 42 99:59:59,999 --> 99:59:59,999 So if you think about it, a geologist can't tell you 43 99:59:59,999 --> 99:59:59,999 wether a vaccine is safe. 44 99:59:59,999 --> 99:59:59,999 Most chemists are not experts in evolutionary theory. 45 99:59:59,999 --> 99:59:59,999 A physicist cannot tell you, despite the claims of some of them, 46 99:59:59,999 --> 99:59:59,999 wether or not tobacco causes cancer. 47 99:59:59,999 --> 99:59:59,999 So, if even scientists themselves have to make a leap of faith 48 99:59:59,999 --> 99:59:59,999 outside their own fields, 49 99:59:59,999 --> 99:59:59,999 then why do they accept the claims of other scientists? 50 99:59:59,999 --> 99:59:59,999 Why do they believe each other's claims? 51 99:59:59,999 --> 99:59:59,999 And should we believe those claims? 52 99:59:59,999 --> 99:59:59,999 So what I'd like to argue is yes, we should. 53 99:59:59,999 --> 99:59:59,999 But not for the reason that most of us think. 54 99:59:59,999 --> 99:59:59,999 Most of us were taught in school that the reason we should 55 99:59:59,999 --> 99:59:59,999 believe in science is because of the scientific method. 56 99:59:59,999 --> 99:59:59,999 We were taught that scientists follow a method 57 99:59:59,999 --> 99:59:59,999 and that this method guarantees the truth of their claims. 58 99:59:59,999 --> 99:59:59,999 The method that most of us were taught in school, 59 99:59:59,999 --> 99:59:59,999 we can call it the text book method, 60 99:59:59,999 --> 99:59:59,999 is the hypo-deductive method. 61 99:59:59,999 --> 99:59:59,999 According to the standard model, the textbook model, 62 99:59:59,999 --> 99:59:59,999 scientists develop hypotheses, they deduce the 63 99:59:59,999 --> 99:59:59,999 consequences for those hypotheses, 64 99:59:59,999 --> 99:59:59,999 and then they go out into the world and they say: 65 99:59:59,999 --> 99:59:59,999 Are those consequences true? 66 99:59:59,999 --> 99:59:59,999 Can we observe them taking place in the natural world? 67 99:59:59,999 --> 99:59:59,999 And if they are true, then the scientists say: 68 99:59:59,999 --> 99:59:59,999 Great, we know the hypothesis is correct. 69 99:59:59,999 --> 99:59:59,999 So there are many famous examples in the history 70 99:59:59,999 --> 99:59:59,999 of science of scientists doing exactly this. 71 99:59:59,999 --> 99:59:59,999 One of the most famous examples 72 99:59:59,999 --> 99:59:59,999 comes from the work of Albert Einstein. 73 99:59:59,999 --> 99:59:59,999 When Einstein developed the theory of general relativity 74 99:59:59,999 --> 99:59:59,999 one of the consequences of his theory 75 99:59:59,999 --> 99:59:59,999 was that space time wasn't just an empty void 76 99:59:59,999 --> 99:59:59,999 but that it actually had a fabric. 77 99:59:59,999 --> 99:59:59,999 And that that fabric was bent 78 99:59:59,999 --> 99:59:59,999 in the presence of massive objects like the sun. 79 99:59:59,999 --> 99:59:59,999 So if this theory were true then it meant that light 80 99:59:59,999 --> 99:59:59,999 as it passed the sun 81 99:59:59,999 --> 99:59:59,999 should actually be bent around it. 82 99:59:59,999 --> 99:59:59,999 That was a pretty startling prediction 83 99:59:59,999 --> 99:59:59,999 and it took a few years before scientists 84 99:59:59,999 --> 99:59:59,999 were able to test it. 85 99:59:59,999 --> 99:59:59,999 But they did test it in 1919 86 99:59:59,999 --> 99:59:59,999 and low and behold it turned out to be true. 87 99:59:59,999 --> 99:59:59,999 Starlight actually does bend as it travels around the sun. 88 99:59:59,999 --> 99:59:59,999 This was a huge confirmation of the theory. 89 99:59:59,999 --> 99:59:59,999 It was considered proof of the truth of this radical new idea 90 99:59:59,999 --> 99:59:59,999 and it was written up in many newspapers around the globe. 91 99:59:59,999 --> 99:59:59,999 Now sometimes this theory or this model 92 99:59:59,999 --> 99:59:59,999 is referred to as the deductive-nomological model. 93 99:59:59,999 --> 99:59:59,999 Meaning those academics like to make things complicated. [Laughter] 94 99:59:59,999 --> 99:59:59,999 But also because in the ideal case it's about laws. 95 99:59:59,999 --> 99:59:59,999 So nomological means having to do with laws. 96 99:59:59,999 --> 99:59:59,999 And in the ideal case, the hypothesis isn't just an idea, 97 99:59:59,999 --> 99:59:59,999 ideally it is a law of nature. 98 99:59:59,999 --> 99:59:59,999 Why does it matter that it is a law of nature? 99 99:59:59,999 --> 99:59:59,999 Because if it is a law, it can't be broken. 100 99:59:59,999 --> 99:59:59,999 If it's a law then it will always be true 101 99:59:59,999 --> 99:59:59,999 in all times and all places 102 99:59:59,999 --> 99:59:59,999 no matter what the circumstances are. 103 99:59:59,999 --> 99:59:59,999 And all of you know at least one example of a famous law. 104 99:59:59,999 --> 99:59:59,999 Einstein's famous equation, E=MC2, 105 99:59:59,999 --> 99:59:59,999 which tells us what the relationship is 106 99:59:59,999 --> 99:59:59,999 between energy and mass. 107 99:59:59,999 --> 99:59:59,999 And that relationship is true no matter what. 108 99:59:59,999 --> 99:59:59,999 It turns out though that there are several problems with this model. 109 99:59:59,999 --> 99:59:59,999 The main problem is that it's wrong. 110 99:59:59,999 --> 99:59:59,999 It's just not true. [Laughter] 111 99:59:59,999 --> 99:59:59,999 And I'm going to talk about three reasons why it's wrong. 112 99:59:59,999 --> 99:59:59,999 So the first reason is a logical reason, 113 99:59:59,999 --> 99:59:59,999 it's the problem of the fallacy of affirming the consequent. 114 99:59:59,999 --> 99:59:59,999 So that's another fancy academic way of saying 115 99:59:59,999 --> 99:59:59,999 that false theories can make true predictions. 116 99:59:59,999 --> 99:59:59,999 So just because the prediction comes true 117 99:59:59,999 --> 99:59:59,999 doesn't actually logically prove that the theory is correct. 118 99:59:59,999 --> 99:59:59,999 And I have a good example of that too, again from the history of science. 119 99:59:59,999 --> 99:59:59,999 This is a picture of the Ptolemaic universe 120 99:59:59,999 --> 99:59:59,999 with the Earth at the center of the universe 121 99:59:59,999 --> 99:59:59,999 and The Sun and the planets going around it. 122 99:59:59,999 --> 99:59:59,999 The Ptolemaic model was believed 123 99:59:59,999 --> 99:59:59,999 by many very smart people for many centuries. 124 99:59:59,999 --> 99:59:59,999 Well why? 125 99:59:59,999 --> 99:59:59,999 Well the answer is because it made lots of predictions that came true. 126 99:59:59,999 --> 99:59:59,999 The Ptolemaic system enabled astronomers 127 99:59:59,999 --> 99:59:59,999 to make accurate predictions of the motions of the planet. 128 99:59:59,999 --> 99:59:59,999 In fact more accurate predictions at first 129 99:59:59,999 --> 99:59:59,999 than the Copernican theory which we now would say is true. 130 99:59:59,999 --> 99:59:59,999 So that's one problem with the textbook model, 131 99:59:59,999 --> 99:59:59,999 a second problem is a practical problem 132 99:59:59,999 --> 99:59:59,999 and it's the problem of auxiliary hypotheses. 133 99:59:59,999 --> 99:59:59,999 Auxiliary hypotheses are assumptions 134 99:59:59,999 --> 99:59:59,999 that scientists are making, 135 99:59:59,999 --> 99:59:59,999 that they may or may not even be aware that they're making. 136 99:59:59,999 --> 99:59:59,999 So an important example of this comes from 137 99:59:59,999 --> 99:59:59,999 comes from the Copernican model 138 99:59:59,999 --> 99:59:59,999 which ultimately replaced the Ptolemaic system. 139 99:59:59,999 --> 99:59:59,999 So when Nicolaus Copernicus said, 140 99:59:59,999 --> 99:59:59,999 actually the Earth is not the center of the universe, 141 99:59:59,999 --> 99:59:59,999 the sun is the center of the solar system, 142 99:59:59,999 --> 99:59:59,999 the Earth moves around the sun. 143 99:59:59,999 --> 99:59:59,999 Scientists said, well okay, Nicolaus, if that's true 144 99:59:59,999 --> 99:59:59,999 we ought to be able to detect the motion 145 99:59:59,999 --> 99:59:59,999 of the Earth around the sun. 146 99:59:59,999 --> 99:59:59,999 And so this slide here illustrates a concept 147 99:59:59,999 --> 99:59:59,999 known as stellar parallax. 148 99:59:59,999 --> 99:59:59,999 And astronomers said, if the Earth is moving 149 99:59:59,999 --> 99:59:59,999 and we look at a prominent star, let's say, Sirius. 150 99:59:59,999 --> 99:59:59,999 Well I know I'm in Manhattan so you guys can't see the stars, 151 99:59:59,999 --> 99:59:59,999 but imagine you're out in the country, imagine you chose that rural life. 152 99:59:59,999 --> 99:59:59,999 And we look at a star in December, we see that star 153 99:59:59,999 --> 99:59:59,999 against the backdrop of distant stars. 154 99:59:59,999 --> 99:59:59,999 If we now make the same observation six months later 155 99:59:59,999 --> 99:59:59,999 when the Earth has moved to this position in June, 156 99:59:59,999 --> 99:59:59,999 we look at that same star and we see it against a different backdrop. 157 99:59:59,999 --> 99:59:59,999 That difference, that angular difference, is the stellar parallax. 158 99:59:59,999 --> 99:59:59,999 So this is the prediction that the Copernican model makes, 159 99:59:59,999 --> 99:59:59,999 astronomers looked for the stellar parallax 160 99:59:59,999 --> 99:59:59,999 and they found nothing, nothing at all. 161 99:59:59,999 --> 99:59:59,999 And many people argued that this proved that the Copernican model was false. 162 99:59:59,999 --> 99:59:59,999 So what happened? 163 99:59:59,999 --> 99:59:59,999 Well in hindsight we can say that astronomers were making 164 99:59:59,999 --> 99:59:59,999 two auxiliary hypotheses, both of which 165 99:59:59,999 --> 99:59:59,999 we would now say were incorrect. 166 99:59:59,999 --> 99:59:59,999 The first was an assumption about the size of the Earth's orbit. 167 99:59:59,999 --> 99:59:59,999 Astronomers were assuming that the Earth's orbit was large 168 99:59:59,999 --> 99:59:59,999 relative to the stars. 169 99:59:59,999 --> 99:59:59,999 Today we would draw the picture more like this, 170 99:59:59,999 --> 99:59:59,999 this comes from NASA, 171 99:59:59,999 --> 99:59:59,999 and you see the Earth's orbit is actually quite small. 172 99:59:59,999 --> 99:59:59,999 In fact, it's actually much smaller even than shown here. 173 99:59:59,999 --> 99:59:59,999 The stellar parallax therefore, 174 99:59:59,999 --> 99:59:59,999 is very small and actually very hard to detect. 175 99:59:59,999 --> 99:59:59,999 And that leads to the second reason 176 99:59:59,999 --> 99:59:59,999 why the prediction didn't work, 177 99:59:59,999 --> 99:59:59,999 because scientists were also assuming 178 99:59:59,999 --> 99:59:59,999 that the telescopes they had were sensitive enough 179 99:59:59,999 --> 99:59:59,999 to detect the parallax. 180 99:59:59,999 --> 99:59:59,999 And that turned out not to be true. 181 99:59:59,999 --> 99:59:59,999 It wasn't until the 19th century that scientists were able to detect 182 99:59:59,999 --> 99:59:59,999 the stellar parallax. 183 99:59:59,999 --> 99:59:59,999 So, there's a third problem as well. 184 99:59:59,999 --> 99:59:59,999 The third problem is simply a factual problem 185 99:59:59,999 --> 99:59:59,999 that a lot of science doesn't fit the textbook model. 186 99:59:59,999 --> 99:59:59,999 A lot of science isn't deductive at all, it's actually inductive. 187 99:59:59,999 --> 99:59:59,999 And by that we mean that scientists don't necessarily 188 99:59:59,999 --> 99:59:59,999 start with theories and hypotheses, often they just 189 99:59:59,999 --> 99:59:59,999 start with observations of stuff going on in the world. 190 99:59:59,999 --> 99:59:59,999 And the most famous example of that is one of the most 191 99:59:59,999 --> 99:59:59,999 famous scientists who ever lived, Charles Darwin. 192 99:59:59,999 --> 99:59:59,999 When Darwin went out as a young man on the voyage of the Beagle, 193 99:59:59,999 --> 99:59:59,999 he didn't have a hypothesis, he didn't have a theory. 194 99:59:59,999 --> 99:59:59,999 He just knew that he wanted to have a career as a scientist 195 99:59:59,999 --> 99:59:59,999 and he started to collect data. 196 99:59:59,999 --> 99:59:59,999 Mainly he knew that he hated medicine 197 99:59:59,999 --> 99:59:59,999 because the sight of blood made him sick so 198 99:59:59,999 --> 99:59:59,999 he had to have an alternative career path. 199 99:59:59,999 --> 99:59:59,999 So he started collecting data. 200 99:59:59,999 --> 99:59:59,999 And he collected many things including his famous finches. 201 99:59:59,999 --> 99:59:59,999 When he collected these finches he through them in a bag 202 99:59:59,999 --> 99:59:59,999 and he had no idea what they meant. 203 99:59:59,999 --> 99:59:59,999 Many years later back in London, 204 99:59:59,999 --> 99:59:59,999 Darwin looked at his data again and began to develop 205 99:59:59,999 --> 99:59:59,999 an explanation 206 99:59:59,999 --> 99:59:59,999 and that explanation was the theory of natural selection. 207 99:59:59,999 --> 99:59:59,999 Besides inductive science, 208 99:59:59,999 --> 99:59:59,999 scientists also often participate in modeling.