00:00:18.880 I'm sure that throughout the 100,000 odd years of our species existence, and even before
00:00:27.520 our ancestors looked up at the night sky and wondered what stars are. Wondering therefore
00:00:37.280 how to explain what they saw in terms of things unseen.
00:00:47.200 Okay, so most people only wondered that occasionally, like today, in breaks from whatever
00:00:54.320 normally preoccupied them. But what normally preoccupied them also involved, yearning to know,
00:01:03.760 they wished they knew how to prevent their food supply from sometimes failing and how they
00:01:11.040 could rest when they were tired without risking starvation. Be warmer, cooler, safer,
00:01:20.640 in less pain. I bet those prehistoric cave artists would have loved to know how to draw better.
00:01:31.760 In every aspect of their lives, they wished for progress just as we do, but they failed almost
00:01:43.600 completely to make any. They didn't know how to. Discoveries like fire happened so rarely that from
00:01:55.680 an individual's point of view, the world never improved. Nothing new was learned. The first clue to
00:02:05.920 the origin of starlight happened as recently as 1899 radioactivity. Within 40 years, physicists discovered
00:02:17.840 the whole explanation expressed as usual in elegant symbols. But never mind the symbols. Think how
00:02:28.400 many discoveries they represent, nuclei and nuclear reactions, of course, but isotopes,
00:02:39.360 particles of electricity, antimatter, neutrinos, the conversion of mass to energy, that's
00:02:51.600 E equals MC squared, gamma rays, transmutation. That ancient dream that had always eluded
00:03:03.360 the alchemists was achieved through the same theories that explained starlight and other
00:03:10.000 ancient mysteries and new unexpected phenomena, that all that discovered in 40 years had not been
00:03:19.920 in the previous 100,000 was not for lack of thinking about stars and all those other urgent
00:03:28.240 problems they had. They even arrived at answers such as myths that dominated their lives, yet
00:03:37.760 bore almost no resemblance to the truth. The tragedy of that protracted stagnation
00:03:46.080 isn't sufficiently recognized, I think. These were people with brains of essentially the same
00:03:52.960 design that eventually did discover all those things, but that ability to make progress remained
00:04:03.840 almost unused until the event that revolutionized the human condition and changed the universe,
00:04:13.600 or so we should hope because that event was the scientific revolution ever since which our
00:04:21.360 knowledge of the physical world and of how to adapt it to our wishes has been growing relentlessly.
00:04:29.280 Now, what had changed, what were people now doing for the first time that made that difference
00:04:36.000 between stagnation and rapid open-ended discovery? How to make that difference is surely the most
00:04:45.680 important universal truth that it's possible to know and worryingly, there's no consensus about
00:04:53.920 what it is, so I'll tell you, but I'll have to backtrack a little first before the scientific
00:05:02.720 revolution. They believed that everything important, noable, was already known, enshrined in
00:05:10.000 ancient writings, institutions, and in some genuinely useful rules of thumb which were however
00:05:17.280 entrenched as dogmas along with many falsehoods, so they believed that knowledge came from authorities
00:05:25.600 that actually knew very little and therefore progress depended on learning how to reject the authority
00:05:35.680 of learned men, priests, traditions, and rulers which is why the scientific revolution had to have
00:05:44.560 a wider context, the enlightenment, a revolution in how people sought knowledge, trying not to
00:05:55.200 rely on authority, take no one's word for it, but that can't be what made the difference.
00:06:02.080 Authorities had been rejected before many times and that rarely, if ever, caused anything
00:06:07.840 like the scientific revolution. At the time, what they thought distinguished science was a radical
00:06:15.600 idea about things unseen, known as empiricism. All knowledge derives from the senses.
00:06:26.400 Well, we've seen that that can't be true. It did help by promoting observation and experiment,
00:06:35.360 but from the outset it was obvious that there was something horribly wrong with it.
00:06:39.520 Knowledge comes from the senses in what language, certainly not the language of mathematics,
00:06:45.760 which Galileo rightly said, the book of nature is written. Look at the world, you don't see
00:06:53.440 equations carved on mountainsides. If you did, it would be because people had carved them.
00:07:00.800 By the way, why don't we do that? What's wrong with us?
00:07:04.880 Empiricism is inadequate because scientific theories explain the scene in terms of the unseen.
00:07:16.080 And the unseen, you have to admit, doesn't come to us through the senses. We don't see
00:07:22.080 those nuclear reactions in stars. We don't see the origin of species. We don't see
00:07:28.560 the curvature of spacetime and other universes, but we know about those things. How?
00:07:38.000 Well, the classic empiricist answer is induction, the unseen resembles the scene.
00:07:47.600 But it doesn't. You know what the clinching evidence was that the spacetime is curved.
00:07:54.320 It was a photograph, not of spacetime, but of any clips with the dot there rather than there.
00:08:01.680 The evidence for evolution, some rocks, and some finches. And parallel universes, again,
00:08:08.960 dots there rather than there on a screen. What we see in all these cases,
00:08:14.320 bears no resemblance to the reality that we conclude is responsible. Only a long chain of theoretical
00:08:23.920 reasoning and interpretation connects them. Ah, say creationists. So you admit it's all interpretation.
00:08:31.760 No one's ever seen evolution. We see rocks. You have your interpretation. We have ours.
00:08:39.200 Yours comes from guesswork, ours from the Bible. But what creationists and empirists,
00:08:47.760 both ignore, is that in that sense, no one's ever seen a Bible either. That the eye only detects
00:08:56.400 light, which we don't perceive, brains only detect nerve impulses. And they don't perceive even
00:09:02.880 those as what they really are, namely electrical crackles. So we perceive nothing as what it really
00:09:11.120 is. Our connection to reality is never just perception. It's always, as Karl Popper put it,
00:09:20.560 theory laden. Scientific knowledge isn't derived from anything. It's like all knowledge,
00:09:27.440 it's conjectural, guesswork. Tested by observation, not derived from it.
00:09:35.360 So were testable conjectures the great innovation that opened the intellectual prison gates?
00:09:44.320 No. Contrary to what's usually said, testability is common in myths and all sorts of other
00:09:51.920 irrational modes of thinking. Any crank claiming the sun will go out next Tuesday has got a
00:09:58.480 testable prediction. Consider the ancient Greek myth explaining seasons. Hades, God of the
00:10:08.080 underworld, kidnaps Persephone the goddess of spring and negotiates a forced marriage contract,
00:10:14.640 requiring her to return regularly and let her go. And each year she is magically compelled to
00:10:22.240 return and her mother Demeter, goddess of the earth, is sad and makes it cold and barren.
00:10:32.240 That myth is testable. If winter is caused by Demeter's sadness, then it must happen everywhere on
00:10:41.120 earth simultaneously. So if the ancient Greeks had only known that Australia is at its warmest
00:10:47.520 when Demeter is at her saddest, they'd have known that their theory is false. So what was wrong
00:10:55.680 with that myth and with all pre-scientific thinking? And what then made that momentous difference?
00:11:04.320 I think there's one thing you have to care about and that implies testability,
00:11:11.600 the scientific method, the enlightenment and everything. And here's the crucial thing
00:11:16.160 that is such a thing as a defect in a story. I don't just mean a logical defect. I mean a bad
00:11:23.520 explanation. What does that mean? Well, explanation is an assertion about what's there
00:11:30.560 unseen that accounts for what's seen. Because the explanatory role of Persephone's marriage contract
00:11:39.200 could be played equally well by infinitely many other ad hoc entities. Why a marriage contract?
00:11:46.640 And not any other reason for regular annual action. Here's one. Persephone wasn't released,
00:11:55.040 she escaped and returns every spring to take revenge on Hades with her spring powers.
00:12:02.800 She calls his domain with spring air, venting heat up to the surface creating summer.
00:12:12.640 That accounts for the same phenomena as the original myth. It's equally testable. Yet what it
00:12:20.000 asserts about reality is in many ways the opposite. And that's possible because the details of
00:12:27.840 the original myth are unrelated to seasons except via the myth itself. This easy variability
00:12:38.240 is the sign of a bad explanation. Because without a functional reason to prefer one of
00:12:48.880 countless variants, advocating one of them in preference to the others is irrational.
00:12:54.800 So for the essence of what makes the difference to enable progress, seek good explanations,
00:13:02.800 the ones that can't be easily varied while still explaining the phenomena.
00:13:09.920 Now our current explanation of seasons is that the Earth's axis is tilted like that.
00:13:16.960 So each hemisphere tilts towards the sun for half the year and away for the other half.
00:13:22.320 It's better to put that up. That's a good explanation.
00:13:30.080 Hard to vary because every detail plays a functional role. For instance, we know independently
00:13:36.320 of seasons that surfaces tilted away from radiant heat are heated less and that a spinning sphere
00:13:43.920 in space points in a constant direction. And the tilt also explains the sun's
00:13:52.320 angle of elevation at different times of year and predicts that the seasons will be out of
00:13:58.560 phase in the two hemispheres. If they'd been observed in phase, the theory would have been refuted.
00:14:04.400 But now the fact that it's also a good explanation, hard to vary, makes the crucial difference. If
00:14:14.160 the ancient Greeks had found out about seasons in Australia, they could have easily varied their
00:14:21.280 myth to predict that. For instance, when Demetto's upset, she banishes heat from her vicinity
00:14:28.720 into the other hemisphere where it makes summer. So being proved wrong by observation and changing
00:14:35.360 their theory accordingly still wouldn't have got the ancient Greeks one jot closer to understanding
00:14:41.440 seasons because their explanation was bad, easy to vary. And it's only when an explanation is
00:14:48.000 good that it even matters whether it's testable. If the axis tilt theory had been refuted,
00:14:53.520 its defenders would have had nowhere to go. No easily implemented change could make that tilt
00:15:00.240 cause the same seasons in both hemispheres. The search for hard to vary explanations
00:15:08.880 is the origin of all progress. It's the basic regulating principle of the enlightenment.
00:15:16.000 So in science, two false approaches, blight progress, one's well known, untestable theories. But
00:15:23.360 the more important one is explanationless theories. Whenever you're told that some existing
00:15:29.200 statistical trend will continue but you aren't given a hard to vary account of what causes that
00:15:36.320 trend, you're being told a wizard did it. When you're told that carrots have human rights because
00:15:42.240 they share half our genes but not how gene percentages confer rights wizard. When someone
00:15:50.960 announces that the nature, nurture debate has been settled because there's evidence that a given
00:15:57.120 percentage of our political opinions are genetically inherited. But they don't explain how
00:16:04.320 genes cause opinions. They've settled nothing. They're saying that our opinions are caused by
00:16:09.600 wizards and presumably so are their own. That the truth consists of hard to vary assertions
00:16:19.600 about reality is the most important fact about the physical world. It's a fact that is itself
