0 00:00:00,000 --> 00:00:05,000 What is the difference between a theory and a law? 1 00:00:08,000 --> 00:00:11,000 Chat with a friend about an established scientific theory, 2 00:00:11,000 --> 00:00:13,000 and she might reply, 3 00:00:13,000 --> 00:00:15,000 well, that's just a theory. 4 00:00:15,000 --> 00:00:19,000 But a conversation about an established scientific law 5 00:00:19,000 --> 00:00:20,000 rarely ends with, 6 00:00:20,000 --> 00:00:22,000 well, that's just a law. 7 00:00:22,000 --> 00:00:24,000 Why is that? 8 00:00:24,000 --> 00:00:27,000 What is the difference between a theory and a law? 9 00:00:27,000 --> 00:00:29,000 And is one better? 10 00:00:29,000 --> 00:00:33,000 Scientific laws and theories have different jobs to do. 11 00:00:33,000 --> 00:00:37,000 A scientific law predicts the results of certain initial conditions. 12 00:00:37,000 --> 00:00:40,000 It might predict your unborn child's possible hair colors, 13 00:00:40,000 --> 00:00:45,000 or how far a baseball travels when launched at a certain angle. 14 00:00:45,000 --> 00:00:50,000 In contrast, a theory tries to provide the most logical explanation 15 00:00:50,000 --> 00:00:53,000 about why things happen as they do. 16 00:00:53,000 --> 00:00:56,000 A theory might invoke dominant and recessive genes 17 00:00:56,000 --> 00:01:01,000 to explain how brown-haired parents ended up with a red-headed child, 18 00:01:01,000 --> 00:01:07,000 or use gravity to shed light on the parabolic trajectory of a baseball. 19 00:01:07,000 --> 00:01:10,000 In simplest terms, a law predicts what happens, 20 00:01:10,000 --> 00:01:13,000 while a theory proposes why. 21 00:01:13,000 --> 00:01:16,000 A theory will never grow up into a law, 22 00:01:16,000 --> 00:01:20,000 though the development of one often triggers progress on the other. 23 00:01:20,000 --> 00:01:22,000 In the 17th century, 24 00:01:22,000 --> 00:01:25,000 Johannes Kepler theorized cosmic musical harmonies 25 00:01:25,000 --> 00:01:29,000 to explain the nature of planetary orbits. 26 00:01:29,000 --> 00:01:33,000 He developed three brilliant laws of planetary motion 27 00:01:33,000 --> 00:01:37,000 while he was studying decades of precise astronomical data 28 00:01:37,000 --> 00:01:40,000 in an effort to find support for his theory. 29 00:01:40,000 --> 00:01:43,000 While his three laws are still in use today, 30 00:01:43,000 --> 00:01:48,000 gravity replaced his theory of harmonics to explain the planet's motions. 31 00:01:48,000 --> 00:01:51,000 How did Kepler get part of it wrong? 32 00:01:51,000 --> 00:01:54,000 Well, we weren't handed a universal instruction manual. 33 00:01:54,000 --> 00:01:58,000 Instead, we continually propose, challenge, revise, 34 00:01:58,000 --> 00:02:03,000 or even replace our scientific ideas as a work in progress. 35 00:02:03,000 --> 00:02:05,000 Laws usually resist change, 36 00:02:05,000 --> 00:02:09,000 since they wouldn't have been adopted if they didn't fit the data, 37 00:02:09,000 --> 00:02:14,000 though we occasionally revise laws in the face of new, unexpected information. 38 00:02:14,000 --> 00:02:19,000 A theory's acceptance, however, is often gladiatorial. 39 00:02:19,000 --> 00:02:22,000 Multiple theories may compete to supply the best explanation 40 00:02:22,000 --> 00:02:25,000 of a new scientific discovery. 41 00:02:25,000 --> 00:02:28,000 Upon further research, scientists tend to favor the theory 42 00:02:28,000 --> 00:02:31,000 that can explain most of the data, 43 00:02:31,000 --> 00:02:34,000 though there may still be gaps in our understanding. 44 00:02:34,000 --> 00:02:38,000 Scientists also like when a new theory successfully predicts 45 00:02:38,000 --> 00:02:40,000 previously unobserved phenomena, 46 00:02:40,000 --> 00:02:44,000 like when Dmitri Mendeleev's theory about the periodic table 47 00:02:44,000 --> 00:02:48,000 predicted several undiscovered elements. 48 00:02:48,000 --> 00:02:51,000 The term scientific theory covers a broad swath. 49 00:02:51,000 --> 00:02:55,000 Some theories are new ideas with little experimental evidence 50 00:02:55,000 --> 00:03:00,000 that scientists eye with suspicion, or even ridicule. 51 00:03:00,000 --> 00:03:03,000 Other theories, like those involving the Big Bang, evolution, 52 00:03:03,000 --> 00:03:05,000 and climate change, 53 00:03:05,000 --> 00:03:08,000 have endured years of experimental confirmation 54 00:03:08,000 --> 00:03:13,000 before earning acceptance by the majority of the scientific community. 55 00:03:13,000 --> 00:03:16,000 You would need to learn more about a specific explanation 56 00:03:16,000 --> 00:03:20,000 before you'd know how well scientists perceive it. 57 00:03:20,000 --> 00:03:23,000 The word theory alone doesn't tell you. 58 00:03:23,000 --> 00:03:28,000 In full disclosure, the scientific community has bet on the wrong horse before. 59 00:03:28,000 --> 00:03:32,000 Alchemy, the geocentric model, spontaneous generation, 60 00:03:32,000 --> 00:03:36,000 and the interstellar ether are just a few of many theories 61 00:03:36,000 --> 00:03:39,000 discarded in favor of better ones. 62 00:03:39,000 --> 00:03:42,000 But even incorrect theories had their value. 63 00:03:42,000 --> 00:03:46,000 Discredited alchemy was the birthplace of modern chemistry, 64 00:03:46,000 --> 00:03:49,000 and medicine made great strides long before we understood 65 00:03:49,000 --> 00:03:53,000 the roles of bacteria and viruses. 66 00:03:53,000 --> 00:03:57,000 That said, better theories often lead to exciting new discoveries 67 00:03:57,000 --> 00:04:01,000 that were unimaginable under the old way of thinking. 68 00:04:01,000 --> 00:04:04,000 Nor should we assume all of our current scientific theories 69 00:04:04,000 --> 00:04:06,000 will stand the test of time. 70 00:04:06,000 --> 00:04:11,000 A single unexpected result is enough to challenge the status quo. 71 00:04:11,000 --> 00:04:15,000 However, vulnerability to some potentially better explanation 72 00:04:15,000 --> 00:04:18,000 doesn't weaken a current scientific theory. 73 00:04:18,000 --> 00:04:23,000 Instead, it shields science from becoming unchallenged dogma. 74 00:04:23,000 --> 00:04:26,000 A good scientific law is a finely tuned machine, 75 00:04:26,000 --> 00:04:29,000 accomplishing its task brilliantly, 76 00:04:29,000 --> 00:04:32,000 but ignorant of why it works as well as it does. 77 00:04:32,000 --> 00:04:36,000 A good scientific theory is a bruised but unbowed fighter 78 00:04:36,000 --> 00:04:42,000 who risks defeat if unable to overpower or adapt to the next challenger. 79 00:04:42,000 --> 00:04:45,000 So different, science needs both laws and theories 80 00:04:45,000 --> 00:04:48,000 to understand the whole picture. 81 00:04:48,000 --> 00:04:51,000 So next time someone comments that it's just a theory, 82 00:04:51,000 --> 00:04:54,000 challenge them to go nine rounds with the champ 83 00:04:54,000 --> 00:04:56,000 and see if they can do any better.