1 00:00:53,800 --> 00:00:58,000 This is the story of the greatest scientific discovery ever. 2 00:00:58,035 --> 00:01:01,519 The discovery that everything is made of atoms. 3 00:01:02,599 --> 00:01:07,037 The vast variety and richness of everything we see around us in the world and beyond, 4 00:01:07,072 --> 00:01:09,555 how it's built up, how it all fits together 5 00:01:09,590 --> 00:01:11,920 is all down to atoms 6 00:01:11,955 --> 00:01:14,159 and the mysterious laws they obey. 7 00:01:14,194 --> 00:01:19,353 As scientists delved deep into the atom, into the very heart of matter, 8 00:01:19,388 --> 00:01:22,489 they unravelled Nature's most shocking secrets. 9 00:01:22,524 --> 00:01:25,591 They had to abandon everything they believed in 10 00:01:25,626 --> 00:01:27,636 and create a whole new science. 11 00:01:27,671 --> 00:01:32,909 A science that today underpins the whole of physics, chemistry, biology, 12 00:01:32,944 --> 00:01:35,233 and maybe even life itself. 13 00:01:35,268 --> 00:01:40,188 But for me, the story of how humanity solved the mystery of the atom 14 00:01:40,223 --> 00:01:42,764 is both inspiring and remarkable. 15 00:01:42,799 --> 00:01:45,272 It's a story of great geniuses. 16 00:01:45,307 --> 00:01:48,826 Of men and women driven by their thirst for knowledge and glory. 17 00:01:49,905 --> 00:01:54,308 It's a story of false starts and conflicts, of ambition and revelation. 18 00:01:54,343 --> 00:01:58,581 A story that lead us through some of the most exciting and exhilarating ideas 19 00:01:58,616 --> 00:02:01,139 ever conceived of by the human race. 20 00:02:01,174 --> 00:02:03,876 And for a working physicist like me, 21 00:02:03,911 --> 00:02:06,579 it's the most important story there is. 22 00:02:28,894 --> 00:02:31,578 On 5th October, 1906, 23 00:02:31,613 --> 00:02:33,657 in a hotel room near Trieste, 24 00:02:33,692 --> 00:02:37,931 a German scientist called Ludwig Boltzmann hanged himself. 25 00:02:40,250 --> 00:02:43,450 Boltzmann had a long history of psychological problems 26 00:02:43,485 --> 00:02:46,926 and one of the key factors in his depression 27 00:02:46,961 --> 00:02:50,333 was that he'd been vilified, even ostracised, 28 00:02:50,368 --> 00:02:53,651 for believing something that today we take for granted. 29 00:02:53,686 --> 00:02:59,305 He believed that matter cannot be infinitely divisible into ever smaller pieces. 30 00:02:59,340 --> 00:03:04,923 Instead, he argued that ultimately everything is made of basic building blocks - 31 00:03:04,958 --> 00:03:06,683 atoms. 32 00:03:09,922 --> 00:03:14,362 It seems incredible now that Boltzmann's revelation was so controversial. 33 00:03:14,397 --> 00:03:16,325 But 100 years ago, 34 00:03:16,360 --> 00:03:21,279 arguing atoms were real was considered by most to be a waste of time. 35 00:03:23,838 --> 00:03:26,283 Although philosophers since the Greeks 36 00:03:26,318 --> 00:03:31,517 had speculated that the world might be made out of some kind of basic unit of matter, 37 00:03:31,552 --> 00:03:34,596 they realised that they were far too small to see 38 00:03:34,631 --> 00:03:37,440 even under the most powerful microscopes. 39 00:03:37,475 --> 00:03:42,114 Speculating about them was therefore a complete waste of time. 40 00:03:43,193 --> 00:03:46,431 But then, in the middle of the 19th century, 41 00:03:46,466 --> 00:03:49,315 whether or not the atom was real 42 00:03:49,350 --> 00:03:52,229 was suddenly a question of burning importance. 43 00:03:52,950 --> 00:03:54,670 The reason was this. 44 00:03:54,705 --> 00:03:55,830 Steam. 45 00:04:06,585 --> 00:04:09,825 By the 1850s, it was changing the world. 46 00:04:09,860 --> 00:04:12,070 It powered the mighty engines, 47 00:04:12,105 --> 00:04:16,104 the trains, the ships, the factories of the Industrial Revolution. 48 00:04:16,139 --> 00:04:19,508 So figuring out how to use it more effectively 49 00:04:19,543 --> 00:04:24,422 became a matter of crucial commercial, political and military significance. 50 00:04:24,457 --> 00:04:26,386 Not surprisingly, then, 51 00:04:26,421 --> 00:04:30,579 it became the key question of 19th-century science. 52 00:04:36,177 --> 00:04:40,138 The demand to build more powerful and efficient steam engines 53 00:04:40,173 --> 00:04:42,982 in turn created an urgent need 54 00:04:43,017 --> 00:04:46,614 to understand and predict the behaviour of water and steam 55 00:04:46,649 --> 00:04:49,174 at high temperatures and pressures. 56 00:04:53,894 --> 00:04:56,658 Ludwig Boltzmann and his scientific allies 57 00:04:56,693 --> 00:05:01,691 showed that if you imagined steam as made of millions of tiny rigid spheres, 58 00:05:01,726 --> 00:05:02,935 atoms, 59 00:05:02,970 --> 00:05:06,573 then you could create some powerful mathematical equations. 60 00:05:06,608 --> 00:05:11,208 And those equations are capable of predicting the behaviour of steam 61 00:05:11,243 --> 00:05:13,367 with incredible accuracy. 62 00:05:16,406 --> 00:05:21,409 But these same equations plunged Boltzmann and his fellow atomists into controversy. 63 00:05:21,444 --> 00:05:26,963 Their enemies argued that since the atoms referred to in their calculations were invisible, 64 00:05:26,998 --> 00:05:29,802 they were merely a mathematical convenience 65 00:05:29,837 --> 00:05:32,007 rather than real physical objects. 66 00:05:32,042 --> 00:05:36,361 To claim that imaginary entities were real seemed presumptuous, 67 00:05:36,396 --> 00:05:38,126 even blasphemous. 68 00:05:38,161 --> 00:05:41,400 Boltzmann's critics argued that it was sacrilegious 69 00:05:41,435 --> 00:05:44,163 to reduce God's miraculous creation 70 00:05:44,198 --> 00:05:48,398 down to a series of collisions between tiny inanimate spheres. 71 00:05:48,433 --> 00:05:52,996 Boltzmann was condemned as an irreligious materialist. 72 00:05:58,195 --> 00:06:00,958 The tragic irony of Boltzmann's story 73 00:06:00,993 --> 00:06:03,612 is that when he took his own life in 1906, 74 00:06:03,647 --> 00:06:06,234 he was unaware that he'd been vindicated. 75 00:06:06,268 --> 00:06:08,438 You see, a year before he died, 76 00:06:08,473 --> 00:06:10,716 a young scientist had published a paper 77 00:06:10,751 --> 00:06:15,270 which undeniably, irrefutably, proclaimed the reality of the atom. 78 00:06:15,305 --> 00:06:17,828 You might have heard of this young scientist. 79 00:06:17,863 --> 00:06:19,950 His name was Albert Einstein. 80 00:06:27,546 --> 00:06:30,865 In 1905, the year before Boltzmann's suicide, 81 00:06:30,900 --> 00:06:33,590 Albert Einstein was 26 years old. 82 00:06:33,625 --> 00:06:38,184 His brash arrogance had upset most of his professors and teachers 83 00:06:38,219 --> 00:06:40,348 and he was barely employable. 84 00:06:40,383 --> 00:06:43,262 Then he got his girlfriend pregnant. 85 00:06:43,297 --> 00:06:46,106 That was followed by a hasty marriage. 86 00:06:46,141 --> 00:06:51,581 He needed a job. Any job. Having not quite distinguished himself at university, 87 00:06:51,616 --> 00:06:55,496 he took up a job as a patents clerk here in Berne in Switzerland. 88 00:06:55,531 --> 00:06:59,377 He'd moved into this small one-bedroom apartment on Kramgasse 89 00:06:59,412 --> 00:07:02,096 with his young wife Mileva. 90 00:07:15,733 --> 00:07:18,497 Despite dire personal straits, 91 00:07:18,532 --> 00:07:21,297 the young Einstein had a burning ambition. 92 00:07:21,332 --> 00:07:24,330 He was desperate to make his mark as a physicist. 93 00:07:25,411 --> 00:07:29,409 And in 1905, during one miraculous year, 94 00:07:29,444 --> 00:07:33,374 the mark he made was truly incredible. 95 00:07:33,409 --> 00:07:38,287 Having an undemanding job meant that young Einstein had plenty of time on his hands 96 00:07:38,322 --> 00:07:40,886 both at work and here in this tiny apartment 97 00:07:40,921 --> 00:07:42,891 to think deep thoughts. 98 00:07:42,926 --> 00:07:47,084 In the space of just a few months, he was to publish several papers 99 00:07:47,119 --> 00:07:49,369 that would change science for ever. 100 00:07:49,404 --> 00:07:52,403 Now, everyone's heard of his Theory of Relativity, 101 00:07:52,438 --> 00:07:54,327 even if they don't understand it. 102 00:07:54,362 --> 00:07:58,761 His paper on the nature of light would win him the Nobel Prize a few years later. 103 00:07:58,796 --> 00:08:01,958 But ironically, it wasn't either of these two papers 104 00:08:01,993 --> 00:08:05,119 that had the most impact on the discovery of atoms. 105 00:08:05,154 --> 00:08:07,244 The one that made all the difference 106 00:08:07,279 --> 00:08:12,557 was a short paper on how tiny grains of pollen danced in water. 107 00:08:20,395 --> 00:08:24,358 Almost 80 years earlier, in 1827, 108 00:08:24,393 --> 00:08:27,052 a Scottish botanist called Robert Brown 109 00:08:27,087 --> 00:08:29,878 sprinkled pollen grains in some water 110 00:08:29,914 --> 00:08:32,671 and examined it through a microscope. 111 00:08:35,751 --> 00:08:38,435 What he found was really strange. 112 00:08:38,470 --> 00:08:41,709 Instead of the pollen grains floating gently in the water, 113 00:08:41,744 --> 00:08:43,552 they danced around furiously, 114 00:08:43,587 --> 00:08:46,713 almost as though they were alive. Now, 115 00:08:46,748 --> 00:08:50,066 while this so-called "Brownian motion" was strange, 116 00:08:50,101 --> 00:08:51,950 scientists soon forgot about it. 117 00:08:51,985 --> 00:08:57,345 They found it mundane, even boring. Who cared if the pollen jiggled about in the water? 118 00:08:57,380 --> 00:09:00,868 And what had the jiggling to do with atoms anyway? 119 00:09:00,903 --> 00:09:06,422 For nearly 80 years, Brown's discovery remained a little-known scientific anomaly. 120 00:09:06,457 --> 00:09:10,660 Then Einstein changed everything. 121 00:09:10,695 --> 00:09:12,705 In one staggering insight, 122 00:09:12,740 --> 00:09:16,825 Einstein saw that Brownian motion was all about atoms. 123 00:09:16,860 --> 00:09:21,197 In fact, he realised that the jiggling of pollen grains in water 124 00:09:21,232 --> 00:09:25,536 could settle the raging debate about the reality of atoms for ever. 125 00:09:27,296 --> 00:09:29,060 His argument was simple. 126 00:09:29,095 --> 00:09:34,255 The pollen will only jiggle if they were being jostled by something else. 127 00:09:35,294 --> 00:09:40,172 So Einstein said that the water must be made of tiny atom-like particles 128 00:09:40,207 --> 00:09:42,497 which themselves are jiggling 129 00:09:42,532 --> 00:09:44,892 and continually buffeting the pollen. 130 00:09:44,927 --> 00:09:47,096 If there were no atoms, 131 00:09:47,131 --> 00:09:49,610 then the pollen would stay still. 132 00:09:49,645 --> 00:09:52,054 So Boltzmann and his contemporaries 133 00:09:52,089 --> 00:09:55,448 had been rowing furiously about this question for nothing. 134 00:09:55,483 --> 00:09:57,692 The answer was there all along. 135 00:09:57,727 --> 00:10:01,847 Einstein proved that for Brownian motion to happen, 136 00:10:01,882 --> 00:10:04,405 atoms must exist. 137 00:10:11,043 --> 00:10:14,882 Einstein's paper went way beyond just verbal arguments. 138 00:10:14,917 --> 00:10:16,647 With flawless mathematics, 139 00:10:16,682 --> 00:10:19,201 he proved that the dance of the pollen 140 00:10:19,236 --> 00:10:21,538 revealed the size of the atom. 141 00:10:21,573 --> 00:10:23,805 And it's mind-numbingly tiny. 142 00:10:23,840 --> 00:10:27,525 One tenth of a millionth of a millimetre across! 143 00:10:27,560 --> 00:10:33,237 A single human hair, itself one of the narrowest things visible to the naked eye, 144 00:10:33,272 --> 00:10:36,317 is over one million atoms wide. 145 00:10:36,352 --> 00:10:38,480 Let me put it another way. 146 00:10:38,515 --> 00:10:42,160 There are more atoms in a single glass of water 147 00:10:42,195 --> 00:10:46,633 than there are glasses of water in all the oceans of the world! 148 00:10:46,668 --> 00:10:50,192 It sort of hurts your head just to think about it. 149 00:10:53,592 --> 00:10:56,157 Einstein's paper ended the debate 150 00:10:56,192 --> 00:10:59,330 about whether the atom was real or not. 151 00:10:59,365 --> 00:11:02,469 And Boltzmann had been totally vindicated. 152 00:11:02,504 --> 00:11:05,229 The atom had to be real. 153 00:11:18,104 --> 00:11:20,784 By the early years of the 20th century, 154 00:11:20,819 --> 00:11:22,429 the atom had arrived. 155 00:11:22,464 --> 00:11:26,783 Scientists who'd argued that the atom was real were no longer heretics. 156 00:11:26,818 --> 00:11:29,219 In a dramatic sudden reversal, 157 00:11:29,254 --> 00:11:31,585 they became the new orthodoxy. 158 00:11:31,620 --> 00:11:35,064 But they were to pay a huge price for their success. 159 00:11:35,099 --> 00:11:39,619 Before they'd had a chance to congratulate each other on discovering the atom, 160 00:11:39,654 --> 00:11:41,943 it ripped the rug out from under their feet 161 00:11:41,978 --> 00:11:46,457 and sent them spiralling into a bizarre and at times terrifying new world. 162 00:11:46,492 --> 00:11:48,622 And it all kicked off here 163 00:11:48,656 --> 00:11:53,656 in what by 1910 was the world's centre for atomic physics - 164 00:11:53,691 --> 00:11:55,095 Manchester. 165 00:12:12,889 --> 00:12:16,253 Two of the most extraordinary men in the history of science 166 00:12:16,288 --> 00:12:22,167 worked here in the physics department of Manchester University between 1911 and 1916. 167 00:12:22,202 --> 00:12:24,932 They were Ernest Rutherford and Niels Bohr, 168 00:12:24,967 --> 00:12:27,846 on the face of it, two very different personalities 169 00:12:27,881 --> 00:12:30,324 and the unlikeliest of collaborators. 170 00:12:31,923 --> 00:12:34,843 Rutherford was from a remote part of New Zealand 171 00:12:34,878 --> 00:12:36,723 and grew up on a farm. 172 00:12:38,242 --> 00:12:40,087 Bohr was born in Copenhagen, 173 00:12:40,122 --> 00:12:43,781 wealthy and erudite, virtually an aristocrat. 174 00:12:43,816 --> 00:12:47,440 Rutherford was the ultimate experimentalist. 175 00:12:47,475 --> 00:12:49,084 He loved technology 176 00:12:49,119 --> 00:12:54,239 and ingenious arrangements of batteries, coils, magnets and radioactive rocks. 177 00:12:54,274 --> 00:12:58,034 But he was also blessed with a profound intuition. 178 00:12:58,069 --> 00:13:01,761 In contrast, Bohr was the ultimate theoretician. 179 00:13:01,796 --> 00:13:05,794 To him, science was about deep thought and abstract mathematics. 180 00:13:05,829 --> 00:13:09,633 Pen and paper, chalk and blackboard were his tools. 181 00:13:09,668 --> 00:13:12,312 Logic was his path to truth. 182 00:13:14,232 --> 00:13:18,711 Although their approaches to their work couldn't have been more different, 183 00:13:18,746 --> 00:13:20,876 they had one thing in common. 184 00:13:20,911 --> 00:13:25,269 They were prepared to ditch three centuries of scientific convention 185 00:13:25,304 --> 00:13:28,109 if it didn't fit what they believed to be true. 186 00:13:28,144 --> 00:13:30,592 They were genuine revolutionaries. 187 00:13:30,627 --> 00:13:35,946 Rutherford and Bohr were two of the most extraordinary minds ever produced by the human race. 188 00:13:35,981 --> 00:13:39,346 But it would take every bit of their dogged tenacity 189 00:13:39,381 --> 00:13:41,184 and inspirational brilliance 190 00:13:41,219 --> 00:13:43,344 to take on the atom. 191 00:13:50,383 --> 00:13:55,581 In 1907, Ernest Rutherford took over the physics department in Manchester. 192 00:13:55,616 --> 00:14:00,018 This was a period of momentous scientific change. 193 00:14:02,218 --> 00:14:04,904 Just over ten years earlier, in Germany, 194 00:14:04,939 --> 00:14:09,136 came the first demonstration of weird rays that see through flesh 195 00:14:09,171 --> 00:14:10,782 to reveal our bones. 196 00:14:10,817 --> 00:14:12,860 These rays were so inexplicable 197 00:14:12,895 --> 00:14:15,294 scientists didn't know what to call them. 198 00:14:15,329 --> 00:14:18,095 So they were named x-rays. 199 00:14:22,893 --> 00:14:25,512 A couple of years after that, in Cambridge, 200 00:14:25,547 --> 00:14:28,096 it was shown that powerful electric currents 201 00:14:28,131 --> 00:14:32,291 could produce strange streams of tiny glowing charged particles 202 00:14:32,326 --> 00:14:34,609 that were called electrons. 203 00:14:37,168 --> 00:14:40,133 And in 1896 in Paris, 204 00:14:40,168 --> 00:14:42,812 came the most significant discovery of all. 205 00:14:42,847 --> 00:14:48,066 One that, more than any other, would unlock the secrets of the atom. 206 00:14:48,101 --> 00:14:53,284 The metal uranium was shown to emit a strange and powerful energy 207 00:14:53,319 --> 00:14:56,569 that was named radioactivity. 208 00:14:56,604 --> 00:14:59,663 It seemed straight out of science fiction. 209 00:14:59,698 --> 00:15:02,722 Radioactive metals were warm to touch. 210 00:15:02,757 --> 00:15:04,806 They could even burn the skin. 211 00:15:04,841 --> 00:15:09,680 And the rays could pass through solid matter as if it wasn't there. 212 00:15:09,715 --> 00:15:13,576 It truly was a marvel of the modern age. 213 00:15:13,611 --> 00:15:17,438 Rutherford was obsessed with radioactivity. 214 00:15:17,473 --> 00:15:19,841 All sorts of questions plagued him. 215 00:15:19,876 --> 00:15:22,895 How was it made? Why did it come in different forms? 216 00:15:22,930 --> 00:15:25,914 How far could it travel through a vacuum or through air? 217 00:15:25,949 --> 00:15:28,798 Did it alter the materials that it encountered? 218 00:15:28,833 --> 00:15:33,953 In Manchester, together with his assistants, Hans Geiger - of Geiger counter fame - 219 00:15:33,988 --> 00:15:38,072 and Ernest Marsden, he devised a series of experiments 220 00:15:38,107 --> 00:15:41,030 that would probe the enigma of radioactivity. 221 00:15:42,551 --> 00:15:45,750 1909. Manchester University. 222 00:15:45,785 --> 00:15:48,274 These are the props. 223 00:15:48,309 --> 00:15:51,947 Gold leaf, beaten until it's just a few atoms thick. 224 00:15:51,982 --> 00:15:54,391 A moveable phosphorescent screen 225 00:15:54,426 --> 00:15:57,905 that flashed when struck by radioactive waves. 226 00:15:57,940 --> 00:16:01,386 And inside this box is the star attraction. 227 00:16:01,421 --> 00:16:04,224 A tiny piece of the metal radium. 228 00:16:06,143 --> 00:16:08,788 Radium is an extraordinarily powerful source 229 00:16:08,823 --> 00:16:12,787 of the kind of radioactivity that Rutherford had named alpha-rays. 230 00:16:12,822 --> 00:16:17,225 They weren't really rays. They were more like a steady stream of particles. 231 00:16:17,260 --> 00:16:23,178 Radium spat out these particles like a machine gun that never ran out of bullets. 232 00:16:23,213 --> 00:16:26,577 Rutherford set his students a simple-enough task. 233 00:16:27,939 --> 00:16:29,502 Use the radium gun. 234 00:16:29,537 --> 00:16:32,776 Shoot the alpha-radioactivity at the gold leaf 235 00:16:32,811 --> 00:16:35,061 and with the phosphorescent plate, 236 00:16:35,096 --> 00:16:38,695 count the number of particles that come out the other side. 237 00:16:38,730 --> 00:16:42,420 In practice, that meant sitting alone in the dark 238 00:16:42,455 --> 00:16:46,853 and counting tiny, almost invisible, flashes on the phosphorescent screen. 239 00:16:46,888 --> 00:16:51,491 It was deeply tedious, but Rutherford insisted that they keep at it. 240 00:16:56,290 --> 00:16:59,929 Weeks passed and the team of researchers found nothing unusual. 241 00:16:59,964 --> 00:17:03,048 The alpha particles seemed to punch through the gold 242 00:17:03,083 --> 00:17:05,052 almost as though it wasn't there. 243 00:17:05,087 --> 00:17:09,246 Very occasionally, they would swerve slightly as they went through. 244 00:17:09,281 --> 00:17:11,885 Hardly front-page news! 245 00:17:13,085 --> 00:17:17,804 Now comes what must be the most consequential off-the-cuff remark 246 00:17:17,839 --> 00:17:19,660 in the history of science. 247 00:17:19,695 --> 00:17:21,447 One that changed the world. 248 00:17:21,482 --> 00:17:26,442 The story goes that Rutherford bumped into his assistant, Geiger, in the corridor. 249 00:17:26,477 --> 00:17:29,885 Geiger reported that so far they'd seen nothing unusual. 250 00:17:29,920 --> 00:17:33,759 In response, Rutherford could have easily nodded and walked on, 251 00:17:33,794 --> 00:17:35,044 but he didn't. 252 00:17:35,079 --> 00:17:38,077 He later claimed that he said what he said at the time 253 00:17:38,112 --> 00:17:39,753 for the sheer hell of it. 254 00:17:39,788 --> 00:17:41,362 But I don't believe him. 255 00:17:41,397 --> 00:17:44,281 Rutherford had great scientific intuition 256 00:17:44,316 --> 00:17:47,835 and I think he had a hunch that something was about to happen. 257 00:17:47,870 --> 00:17:50,400 Here's what he said to Geiger. 258 00:17:50,435 --> 00:17:55,073 "Tell young Marsden to see if he can detect any alpha particles 259 00:17:55,108 --> 00:17:59,270 "on the same side of the gold leaf as the radium source." 260 00:17:59,305 --> 00:18:03,431 In other words, see if any alpha particles are bouncing back. 261 00:18:03,466 --> 00:18:06,869 Now, it's an extraordinary suggestion from Rutherford 262 00:18:06,904 --> 00:18:09,707 and one that he had no logical reason to make. 263 00:18:09,742 --> 00:18:12,474 After all, Geiger and Marsden had spent weeks 264 00:18:12,509 --> 00:18:17,067 seeing the alpha particles do nothing but stream straight through the gold leaf, 265 00:18:17,102 --> 00:18:19,146 almost as though it wasn't there. 266 00:18:19,181 --> 00:18:21,986 Why would any bounce back? 267 00:18:29,623 --> 00:18:33,462 But Geiger and Marsden were young and in awe of the big New Zealander. 268 00:18:33,497 --> 00:18:37,501 They did their master's bidding and went back into their dark lab 269 00:18:37,536 --> 00:18:39,147 and watched patiently. 270 00:18:39,182 --> 00:18:42,424 For days, they saw absolutely nothing. 271 00:18:42,459 --> 00:18:45,185 They strained their eyes to the point of myopia 272 00:18:45,220 --> 00:18:48,997 but didn't see a single alpha particle bouncing back off the gold. 273 00:18:49,032 --> 00:18:52,777 It seemed that Rutherford's suggestion really was a stupid one. 274 00:18:52,812 --> 00:18:55,777 But then the impossible happened. 275 00:19:02,774 --> 00:19:05,019 One afternoon in 1909, 276 00:19:05,054 --> 00:19:08,972 Geiger burst into Rutherford's office with some astonishing news. 277 00:19:09,007 --> 00:19:10,936 Very, very occasionally, 278 00:19:10,971 --> 00:19:15,615 an alpha particle would indeed ricochet back off the gold leaf. 279 00:19:15,650 --> 00:19:20,608 Geiger calculated that only one in 8,000 alpha particles would do this. 280 00:19:20,643 --> 00:19:22,493 It's a tiny percentage, 281 00:19:22,528 --> 00:19:25,212 but Rutherford's mind reeled with the news. 282 00:19:25,247 --> 00:19:30,086 He would later say it was like firing a shell at a piece of tissue paper 283 00:19:30,121 --> 00:19:32,210 and have it bounce back at you. 284 00:19:32,245 --> 00:19:35,764 There and then, Rutherford knew he'd struck physics gold. 285 00:19:35,799 --> 00:19:38,289 Although it would take him over a year 286 00:19:38,324 --> 00:19:41,803 to fully understand why the alpha particles would do this, 287 00:19:41,838 --> 00:19:45,281 when he did, he would show humanity for the first time 288 00:19:45,316 --> 00:19:47,086 the inside of an atom. 289 00:19:47,121 --> 00:19:50,721 People had barely got used to the idea that atoms existed. 290 00:19:50,756 --> 00:19:54,056 But now Rutherford knew that this minute world, 291 00:19:54,091 --> 00:19:57,358 one tenth of a millionth of a millimetre across, 292 00:19:57,393 --> 00:20:00,323 had its own internal structure. 293 00:20:00,358 --> 00:20:04,121 Within the atomic, there's a sub-atomic world. 294 00:20:04,156 --> 00:20:08,316 And Ernest Rutherford believed he knew what it looked like. 295 00:20:09,675 --> 00:20:13,514 Rutherford realised that the bouncing alpha particle 296 00:20:13,549 --> 00:20:16,194 revealed an atom that was totally unexpected. 297 00:20:17,192 --> 00:20:19,597 It had no familiar analogy on Earth. 298 00:20:19,632 --> 00:20:23,071 So Rutherford looked for one in the heavens. 299 00:20:23,106 --> 00:20:26,511 He pictured the atom as a tiny solar system. 300 00:20:27,591 --> 00:20:31,148 Electrons, tiny particles of negative electricity, 301 00:20:31,183 --> 00:20:34,708 orbit around a minute positively-charged object 302 00:20:34,743 --> 00:20:36,388 called the nucleus. 303 00:20:38,547 --> 00:20:44,746 Rutherford calculated that the nucleus was 10,000 times smaller than the atom itself. 304 00:20:46,145 --> 00:20:50,784 That's why only one in 8,000 alpha particles bounced back. 305 00:20:50,818 --> 00:20:54,703 They're the ones that hit the tiny nucleus by chance. 306 00:20:54,738 --> 00:20:57,901 The rest whizz by without hitting anything. 307 00:20:59,581 --> 00:21:02,264 The first astonishing consequence of this idea 308 00:21:02,299 --> 00:21:07,180 is that Rutherford's atom is almost entirely empty space. 309 00:21:09,339 --> 00:21:14,857 That's why nearly all the alpha particles race through the gold atoms as if there's nothing there. 310 00:21:14,892 --> 00:21:17,337 There really is nothing there. 311 00:21:19,975 --> 00:21:23,174 Consider the bizarre implications of Rutherford's atom 312 00:21:23,209 --> 00:21:25,419 by imagining it on a bigger scale. 313 00:21:25,454 --> 00:21:28,377 If the nucleus were the size of a football, 314 00:21:28,412 --> 00:21:32,853 then the nearest electron would be in orbit half a mile away. 315 00:21:32,888 --> 00:21:35,771 The rest of the atom would be completely empty space. 316 00:21:36,850 --> 00:21:38,535 Let me explain it another way. 317 00:21:38,570 --> 00:21:42,528 If you were to suck out all the empty space from every atom in my body, 318 00:21:42,563 --> 00:21:46,769 then I would shrink down to a size smaller than a grain of salt. 319 00:21:46,804 --> 00:21:49,052 Of course, I'd still weigh the same. 320 00:21:49,087 --> 00:21:52,486 If you did the same thing to the entire human race, 321 00:21:52,521 --> 00:21:54,531 then all six billion of us 322 00:21:54,566 --> 00:21:57,445 would fit inside a single apple! 323 00:21:58,525 --> 00:22:02,443 The atom was unlike anything we had ever encountered before. 324 00:22:02,478 --> 00:22:05,883 And it would only get stranger and stranger! 325 00:22:06,962 --> 00:22:10,361 Almost immediately, a problem surfaced, 326 00:22:10,396 --> 00:22:11,926 and it was a big one. 327 00:22:11,961 --> 00:22:15,080 According to the tried and trusted science of the time, 328 00:22:15,115 --> 00:22:17,364 the electrons should lose their energy, 329 00:22:17,399 --> 00:22:19,918 run out of speed and spiral into the nucleus 330 00:22:19,953 --> 00:22:21,718 in less than the blink of an eye. 331 00:22:22,797 --> 00:22:26,616 Rutherford's atom contradicted the known laws of science. 332 00:22:26,651 --> 00:22:30,284 The atom didn't care that it defied scientific convention. 333 00:22:30,319 --> 00:22:34,015 It's almost entirely empty space and it's gonna stay that way. 334 00:22:34,050 --> 00:22:37,713 I show no signs of shrinking down to the size of a grain of salt. 335 00:22:37,748 --> 00:22:40,433 And the Earth is, well, the size of the Earth. 336 00:22:40,468 --> 00:22:42,631 It's not getting smaller. 337 00:22:46,791 --> 00:22:49,516 It's worth remembering the time scale. 338 00:22:49,551 --> 00:22:53,869 In six short years from 1905 through to 1911, 339 00:22:53,904 --> 00:22:56,672 the atom had announced its existence 340 00:22:56,707 --> 00:23:00,007 with the fact that it was unimaginably small. 341 00:23:00,042 --> 00:23:03,234 Then it revealed that it was mainly empty space. 342 00:23:03,269 --> 00:23:06,426 And now it didn't obey the known laws of physics. 343 00:23:07,506 --> 00:23:11,624 Not surprisingly, all the established scientists of the day, 344 00:23:11,659 --> 00:23:13,509 including Einstein, were baffled. 345 00:23:13,544 --> 00:23:17,303 Scientific ideas they'd put their faith in all their lives 346 00:23:17,338 --> 00:23:20,262 had failed completely to explain the atom. 347 00:23:21,341 --> 00:23:24,700 The atom now required a new generation of scientists 348 00:23:24,735 --> 00:23:27,356 to follow in Rutherford's footsteps. 349 00:23:27,391 --> 00:23:29,944 Bold, brilliant and above all, young. 350 00:23:29,979 --> 00:23:33,578 It was crucial they had no loyalty or attachment 351 00:23:33,613 --> 00:23:36,297 to ideas held by previous generations. 352 00:23:51,252 --> 00:23:54,331 One of the first of this new breed was Niels Bohr. 353 00:23:55,292 --> 00:23:57,392 He sailed from Denmark in 1911 354 00:23:57,427 --> 00:23:59,491 and made his way to English soil. 355 00:24:00,611 --> 00:24:03,174 Having finished his studies in Copenhagen, 356 00:24:03,209 --> 00:24:07,413 Bohr decided to move abroad and be at the centre of the new physics. 357 00:24:07,448 --> 00:24:13,647 The trail led him to Britain, Manchester University and Ernest Rutherford. 358 00:24:19,006 --> 00:24:20,849 Bohr had a brilliant mind, 359 00:24:20,884 --> 00:24:24,962 at times hampered by a pathological obsession with detail. 360 00:24:24,997 --> 00:24:28,839 In fact, the story goes that Bohr taught himself English 361 00:24:28,874 --> 00:24:32,681 by reading Dickens' Pickwick Papers over and over again. 362 00:24:33,800 --> 00:24:37,679 Bohr was so captivated by Rutherford's picture of the atom 363 00:24:37,714 --> 00:24:40,519 that he made it his mission to solve the puzzles 364 00:24:40,554 --> 00:24:43,124 of why the atom didn't collapse 365 00:24:43,159 --> 00:24:46,398 and why there was so much empty space. 366 00:24:48,596 --> 00:24:51,516 As one of the new breed of theoretical physicists, 367 00:24:51,551 --> 00:24:53,359 he was fearless in his thinking 368 00:24:53,394 --> 00:24:57,754 and was prepared to abandon common sense and human intuition 369 00:24:57,789 --> 00:24:59,691 to find an explanation. 370 00:24:59,726 --> 00:25:01,559 So, in a leap of genius, 371 00:25:01,594 --> 00:25:05,072 he started to look for clues about the atom's structure 372 00:25:05,107 --> 00:25:07,357 not by looking at matter 373 00:25:07,392 --> 00:25:12,550 but by examining the mysterious and wonderful nature of light. 374 00:25:20,548 --> 00:25:23,067 Now, atoms and light are clearly connected. 375 00:25:23,102 --> 00:25:25,552 Most substances glow when they're heated. 376 00:25:25,587 --> 00:25:29,070 For centuries people had realised that different substances 377 00:25:29,105 --> 00:25:33,323 glow with their own distinctive colours, a bit like a signature. 378 00:25:33,358 --> 00:25:37,542 So the green of copper, the yellow of sodium and the red of lithium. 379 00:25:38,623 --> 00:25:42,941 These colours associated with different substances are called "spectra". 380 00:25:42,976 --> 00:25:44,705 And Bohr's great insight 381 00:25:44,740 --> 00:25:50,060 was to realise that spectra are telling us something about the inner structure of the atom, 382 00:25:50,095 --> 00:25:53,139 that they could explain all that empty space. 383 00:25:54,218 --> 00:25:58,382 Bohr's idea was to take Rutherford's solar system model of the atom 384 00:25:58,417 --> 00:26:03,295 and replace it with something that's almost impossible to imagine or visualise. 385 00:26:03,330 --> 00:26:08,174 So sensible ideas like empty space and particles moving around orbits fade away. 386 00:26:08,209 --> 00:26:10,180 They're replaced with something 387 00:26:10,215 --> 00:26:15,773 that is one of the most misunderstood and misused concepts in the whole of science - 388 00:26:15,808 --> 00:26:17,576 the quantum jump. 389 00:26:17,611 --> 00:26:20,411 Now, it takes most working physicists many years 390 00:26:20,446 --> 00:26:22,496 to come to terms with quantum jumps. 391 00:26:22,531 --> 00:26:25,729 Bohr himself said that if you think you've understood it, 392 00:26:25,764 --> 00:26:28,089 then you haven't thought about it enough. 393 00:26:28,124 --> 00:26:29,933 So I'm going to take a deep breath 394 00:26:29,968 --> 00:26:32,533 and in under 30 seconds try and explain to you 395 00:26:32,568 --> 00:26:36,047 one of the most complicated concepts in the whole of science 396 00:26:36,082 --> 00:26:39,726 but one that underpins the entire universe. 397 00:26:46,484 --> 00:26:49,683 Bohr described the atom not as a solar system 398 00:26:49,718 --> 00:26:52,087 but as a multi-storey building. 399 00:26:52,122 --> 00:26:54,821 The ground floor is where the nucleus lives, 400 00:26:54,856 --> 00:26:57,486 with the electrons occupying the floors above. 401 00:26:57,521 --> 00:27:01,799 Mysterious laws mean the electrons can only live ON the floors, 402 00:27:01,834 --> 00:27:03,163 never in-between. 403 00:27:03,198 --> 00:27:05,883 Other mysterious laws mean that sometimes 404 00:27:05,918 --> 00:27:09,397 they can instantaneously jump from one floor to another. 405 00:27:10,477 --> 00:27:12,921 These are what we call quantum jumps. 406 00:27:12,956 --> 00:27:17,000 Now, Bohr had absolutely no idea what these laws were. 407 00:27:17,035 --> 00:27:21,555 But thinking like this allowed him to make a startling prediction. 408 00:27:21,590 --> 00:27:25,632 When an electron jumps from a higher floor to a lower one, 409 00:27:25,667 --> 00:27:27,469 it gives off light. 410 00:27:27,504 --> 00:27:29,237 More significantly, 411 00:27:29,272 --> 00:27:35,230 the colour of the light depends on how big or small the quantum jump the electron makes. 412 00:27:35,265 --> 00:27:40,269 So an electron jumping from the third floor to the second floor 413 00:27:40,304 --> 00:27:42,313 might give off red light. 414 00:27:42,348 --> 00:27:46,146 And an electron jumping from the tenth floor to the second floor, 415 00:27:46,181 --> 00:27:47,466 blue light. 416 00:27:52,186 --> 00:27:54,349 To test his new theory, 417 00:27:54,384 --> 00:27:57,063 Bohr used it to make a prediction. 418 00:27:58,064 --> 00:28:02,502 Could it explain the mysterious signature in the spectrum of hydrogen? 419 00:28:02,537 --> 00:28:05,199 After months of calculating furiously, 420 00:28:05,234 --> 00:28:07,860 he finally came up with the result. 421 00:28:08,940 --> 00:28:11,900 And his prediction was surprisingly accurate. 422 00:28:12,943 --> 00:28:14,824 For the first time ever, 423 00:28:14,859 --> 00:28:17,578 it looked like the spectrum could be explained. 424 00:28:18,538 --> 00:28:22,097 And back in 1913, that was big news. 425 00:28:24,696 --> 00:28:30,095 But Bohr's new idea rested on a single seriously-controversial supposition. 426 00:28:30,130 --> 00:28:32,659 Why should the electrons and the atom 427 00:28:32,694 --> 00:28:35,819 behave as though they were in a multi-storey building? 428 00:28:35,854 --> 00:28:40,332 And why should they magically perform quantum jumps from one storey to another? 429 00:28:40,367 --> 00:28:43,748 There was no precedent for it anywhere else in science. 430 00:28:43,783 --> 00:28:47,131 When one physicist claimed that the jumps were nonsense, 431 00:28:47,166 --> 00:28:49,927 Bohr replied, "Yes, you're completely right! 432 00:28:49,962 --> 00:28:52,689 "But that doesn't prove the jumps don't happen, 433 00:28:52,724 --> 00:28:55,332 "only that you cannot visualise them." 434 00:28:55,367 --> 00:29:00,570 But not being able to visualise things seemed to go against the whole purpose of science. 435 00:29:00,605 --> 00:29:06,284 Older scientists in particular felt that science was supposed to be about understanding the world, 436 00:29:06,319 --> 00:29:10,660 not about making up arbitrary rules that seem to fit the data. 437 00:29:10,695 --> 00:29:15,002 Conflict between the two generations of scientists was inevitable. 438 00:29:18,960 --> 00:29:22,644 Bohr's weird new atom and his crazy quantum jumps 439 00:29:22,679 --> 00:29:26,959 were a shot across the bow of traditional classical science 440 00:29:26,994 --> 00:29:29,878 and the old school reacted angrily. 441 00:29:29,913 --> 00:29:32,003 Leading the traditionalists 442 00:29:32,038 --> 00:29:34,877 was giant of the physics world Albert Einstein. 443 00:29:34,912 --> 00:29:37,281 He hated Bohr's ideas 444 00:29:37,316 --> 00:29:39,479 and he was going to fight them. 445 00:29:39,514 --> 00:29:43,314 Anything to save the world of order and common sense 446 00:29:43,349 --> 00:29:45,794 from this assault by madness. 447 00:29:48,193 --> 00:29:52,877 Bohr, though, was undeterred and as the 1920s dawned, 448 00:29:52,912 --> 00:29:57,629 the battle lines for one of the greatest conflicts in all science were drawn. 449 00:29:58,509 --> 00:30:01,673 Einstein spent much of the early 1920s 450 00:30:01,708 --> 00:30:05,067 arguing against Niels Bohr, with mixed success. 451 00:30:05,102 --> 00:30:08,551 His celebrity status gave him power 452 00:30:08,586 --> 00:30:12,225 so when he said he loathed ideas like quantum jumping 453 00:30:12,260 --> 00:30:15,864 that seemed plucked out of thin air, people listened. 454 00:30:15,899 --> 00:30:19,668 Then in 1925, a letter landed on his desk 455 00:30:19,703 --> 00:30:22,388 that turned out to be manna from physics heaven. 456 00:30:22,423 --> 00:30:26,547 Here finally was an idea that described the atomic world 457 00:30:26,582 --> 00:30:30,301 with the tried and trusted principles of traditional science. 458 00:30:30,336 --> 00:30:32,985 Einstein was ecstatic. He told friends, 459 00:30:33,020 --> 00:30:37,498 "Finally, a veil has been lifted on how the universe works." 460 00:30:37,533 --> 00:30:41,977 The letter came with the PhD thesis of a young Frenchman. 461 00:30:42,012 --> 00:30:45,777 And behind it lay an extraordinary tale. 462 00:31:00,092 --> 00:31:03,892 During the First World War, a young French student spent his time 463 00:31:03,927 --> 00:31:07,051 at the top of the Eiffel Tower, as a radio operator. 464 00:31:07,086 --> 00:31:10,054 His name was Prince Louis de Broglie. 465 00:31:10,089 --> 00:31:14,534 He came from French aristocracy but he was devoted to physics. 466 00:31:14,569 --> 00:31:19,287 He was so wealthy he built his own laboratory off the Champs-Elysees. 467 00:31:21,167 --> 00:31:27,604 After the war, De Broglie became gripped by the mysteries and controversies surrounding the atom. 468 00:31:27,639 --> 00:31:31,164 And then his war-time experience as a radio operator 469 00:31:31,199 --> 00:31:33,768 gave him an intriguing idea. 470 00:31:33,803 --> 00:31:37,527 Perhaps radio waves could explain the atom. 471 00:31:37,562 --> 00:31:41,601 Although invisible, they behave very much like water waves. 472 00:31:43,841 --> 00:31:46,800 Like ripples spreading out across a pond, 473 00:31:46,835 --> 00:31:49,724 radio waves obeyed mathematical equations 474 00:31:49,759 --> 00:31:54,437 that were reliable and well understood and had been worked out decades earlier. 475 00:31:54,472 --> 00:31:58,555 So for his PhD thesis, De Broglie imagined a kind of radio wave 476 00:31:58,590 --> 00:32:00,796 pushing the electron around the atom. 477 00:32:00,831 --> 00:32:03,399 He called it a pilot wave. 478 00:32:03,434 --> 00:32:08,193 This pilot wave would also hold the electron tightly in its orbit, 479 00:32:08,228 --> 00:32:10,318 stopping the atom from collapsing. 480 00:32:10,353 --> 00:32:14,132 There were no strange instant quantum jumps, 481 00:32:14,167 --> 00:32:17,876 just intuitive common sense familiar waves. 482 00:32:17,911 --> 00:32:21,548 The relief felt by the traditionalists was palpable. 483 00:32:21,583 --> 00:32:24,309 "The atom is all about waves", they cried, 484 00:32:24,344 --> 00:32:26,433 and we understand what waves are. 485 00:32:26,468 --> 00:32:31,271 Einstein and the traditionalists felt that victory was within their grasp. 486 00:32:31,306 --> 00:32:38,346 They believed they had Bohr and the new atomic science with its crazy quantum jumps on the ropes. 487 00:32:38,381 --> 00:32:42,303 But Niels Bohr wasn't the kind of man to roll over and give up. 488 00:32:44,342 --> 00:32:47,382 Even though he'd explained the spectrum of hydrogen, 489 00:32:47,417 --> 00:32:49,506 with his new revolutionary theory, 490 00:32:49,541 --> 00:32:53,340 he had nothing like Einstein's worldwide recognition. 491 00:32:53,375 --> 00:32:56,185 But in his native Denmark, 492 00:32:56,220 --> 00:32:58,458 his theory was enough to make him a star. 493 00:32:59,539 --> 00:33:04,496 Flushed with success, Niels Bohr returned to Copenhagen in 1916, a conquering hero. 494 00:33:04,531 --> 00:33:07,022 His new-found celebrity status 495 00:33:07,057 --> 00:33:10,175 meant he found it very easy to raise money for research. 496 00:33:10,210 --> 00:33:13,414 In fact, it was funding from the Carlsberg brewery 497 00:33:13,449 --> 00:33:16,619 that helped build his new research institute. 498 00:33:16,654 --> 00:33:20,812 You could say it was beer that helped us understand the secrets of the atom! 499 00:33:22,252 --> 00:33:28,010 This institute became a leading centre for research in theoretical physics that survives to this day. 500 00:33:28,045 --> 00:33:32,486 I came here in the early 1990s to carry out research on nuclear halos. 501 00:33:32,521 --> 00:33:36,928 And even then, this was the place to be to do that sort of research. 502 00:33:39,087 --> 00:33:42,291 This is the main lecture room in the Niels Bohr Institute. 503 00:33:42,326 --> 00:33:46,525 It doesn't look very impressive as far as lecture halls are concerned, 504 00:33:46,560 --> 00:33:50,020 but it's full of great quirky details. 505 00:33:50,055 --> 00:33:53,448 I remember lecturing here a few years back 506 00:33:53,483 --> 00:34:00,521 and I know that Niels Bohr himself designed some of the machinery that raised and lowered blackboards. 507 00:34:00,556 --> 00:34:05,800 There's an incredible series of boards, 508 00:34:05,835 --> 00:34:08,365 one underneath the other, 509 00:34:08,400 --> 00:34:12,078 of boards filled with his formulae 510 00:34:13,238 --> 00:34:17,156 so that he wouldn't ever need to rub out any of his equations. 511 00:34:17,191 --> 00:34:19,556 It sort of goes on and on. 512 00:34:24,835 --> 00:34:29,013 Bohr's reputation for radical and unconventional ideas 513 00:34:29,048 --> 00:34:33,191 made Copenhagen a magnet for young, ambitious physicists. 514 00:34:33,226 --> 00:34:35,877 They were keen to make their mark 515 00:34:35,912 --> 00:34:39,031 and be a part of Bohr's innovative new science, 516 00:34:39,066 --> 00:34:42,150 which came to be known as quantum mechanics. 517 00:34:44,909 --> 00:34:50,348 In 1924, in defiance of Einstein and De Broglie's traditional explanation 518 00:34:50,383 --> 00:34:54,227 of the atom, the radicals revealed a new theory, 519 00:34:54,262 --> 00:34:56,591 based on Bohr's quantum jumps. 520 00:34:56,626 --> 00:35:01,384 It was to be their most ambitious and most controversial idea yet. 521 00:35:04,863 --> 00:35:10,421 It was first developed by Wolfgang Pauli, one of Bohr's rising stars. 522 00:35:10,456 --> 00:35:14,746 Pauli took Bohr's bizarre "quantum jumps" idea 523 00:35:14,781 --> 00:35:19,219 and turned it into one of the most important concepts in the whole of science. 524 00:35:19,254 --> 00:35:21,304 And I don't say that lightly. 525 00:35:21,339 --> 00:35:27,056 Pauli's idea goes by the uninspiring title of the Exclusion Principle. 526 00:35:27,091 --> 00:35:30,976 But I think a better title would be "God's best-kept secret" 527 00:35:31,011 --> 00:35:35,815 because it explains the vast variety of Creation. 528 00:35:39,253 --> 00:35:42,453 The question Pauli's idea tried to answer was this. 529 00:35:43,532 --> 00:35:46,618 Every atom is made of the same simple components. 530 00:35:46,653 --> 00:35:50,576 So why do they appear to us in so many different guises? 531 00:35:50,611 --> 00:35:55,209 In such a rich variety of colours, textures and chemical properties? 532 00:35:55,244 --> 00:35:58,253 For instance, gold and mercury. 533 00:35:58,288 --> 00:36:01,853 Two very different elements. Gold is solid, 534 00:36:01,888 --> 00:36:06,046 mercury is liquid. Gold is inert, mercury is highly toxic. 535 00:36:06,081 --> 00:36:09,885 And yet they differ by just one electron. 536 00:36:09,920 --> 00:36:12,724 Gold has 79 and mercury has 80. 537 00:36:14,043 --> 00:36:18,242 So how does one tiny electron make all that difference? 538 00:36:19,242 --> 00:36:23,401 What Pauli did was pluck another quantum rule out of thin air. 539 00:36:23,436 --> 00:36:25,797 Remember Bohr's multi-storey atom? 540 00:36:25,832 --> 00:36:28,124 The nucleus is the ground floor 541 00:36:28,159 --> 00:36:31,839 with the electrons progressively filling the floors above. 542 00:36:31,874 --> 00:36:35,483 Pauli said there's another quantum rule which states crudely 543 00:36:35,518 --> 00:36:40,197 that each floor can only accommodate a fixed number of electrons. 544 00:36:40,232 --> 00:36:43,513 So if we want to add another electron to the atom, 545 00:36:43,548 --> 00:36:46,795 it has to check for a vacancy in the top floor. 546 00:36:46,830 --> 00:36:48,680 And if that floor is full, 547 00:36:48,715 --> 00:36:52,274 another floor or shell is created above it for the electron. 548 00:36:52,309 --> 00:36:55,316 In this way, a single electron 549 00:36:55,351 --> 00:36:58,195 can radically change the shape of the atom 550 00:36:58,230 --> 00:37:01,031 and this, in turn, affects how the atom behaves 551 00:37:01,066 --> 00:37:03,927 and how it fits together with other atoms. 552 00:37:03,962 --> 00:37:06,754 So Pauli's principle really is the basis 553 00:37:06,789 --> 00:37:11,547 upon which the whole of chemistry, and ultimately biology, rests. 554 00:37:15,027 --> 00:37:20,465 Pauli's Exclusion Principle was a major breakthrough for Bohr's quantum mechanics. 555 00:37:21,504 --> 00:37:25,223 For the first time, it seemed to offer us a real understanding 556 00:37:25,258 --> 00:37:28,144 of the incredible variety in the world around us 557 00:37:28,179 --> 00:37:30,142 and possibly life itself. 558 00:37:31,582 --> 00:37:35,945 Its success blew a large hole in Einstein's defence of the old physics. 559 00:37:35,980 --> 00:37:41,858 And like quantum jumping, it was straight out of the weird rule book of atomic physics. 560 00:37:41,894 --> 00:37:47,137 Pauli didn't explain why his principle worked. He said it just did. 561 00:37:53,096 --> 00:37:55,980 Einstein and the traditionalists hated it. 562 00:37:56,015 --> 00:38:00,454 For them, this sounded like arrogant, unscientific nonsense. 563 00:38:00,489 --> 00:38:03,750 But they needed to hit back, and hit back hard. 564 00:38:03,785 --> 00:38:07,012 So far, the debates about the new atomic physics 565 00:38:07,047 --> 00:38:09,496 had been polite and gentlemanly. 566 00:38:09,531 --> 00:38:13,570 Now the two sides wheeled out their biggest guns. 567 00:38:13,605 --> 00:38:16,014 Two of the greatest names in physics. 568 00:38:16,049 --> 00:38:20,689 They were two very contrasting characters who loathed each other. 569 00:38:23,726 --> 00:38:26,093 For the new revolutionary science 570 00:38:26,128 --> 00:38:28,926 was a buttoned-up, uber-competitive German 571 00:38:28,961 --> 00:38:30,646 called Werner Heisenberg. 572 00:38:31,685 --> 00:38:35,564 For the conservatives was a debonair, Byronesque Austrian 573 00:38:35,599 --> 00:38:37,443 called Irwin Schroedinger. 574 00:38:50,360 --> 00:38:51,724 Irwin Schroedinger, 575 00:38:51,759 --> 00:38:55,324 passionate and poetic, a philosopher and a romantic. 576 00:38:55,359 --> 00:38:59,238 He wrote books on the Ancient Greeks, on philosophy, on religion, 577 00:38:59,273 --> 00:39:01,282 he was influenced by Hinduism. 578 00:39:01,317 --> 00:39:03,835 He was also a very flamboyant character, 579 00:39:03,870 --> 00:39:05,921 cool, suave, sophisticated, 580 00:39:05,956 --> 00:39:08,796 a dapper dresser and a big hit with the ladies. 581 00:39:15,352 --> 00:39:18,316 Schroedinger's promiscuity was legendary. 582 00:39:18,351 --> 00:39:21,710 He had a string of girlfriends throughout his married life, 583 00:39:21,745 --> 00:39:23,312 some much younger than him. 584 00:39:24,351 --> 00:39:28,115 In 1925, 38-year-old Schroedinger 585 00:39:28,150 --> 00:39:31,548 stayed at the Alpine resort of Arosa in Switzerland 586 00:39:31,583 --> 00:39:34,625 for a secret liaison with an old girlfriend 587 00:39:34,660 --> 00:39:37,632 whose identity remains a mystery to this day. 588 00:39:37,667 --> 00:39:43,265 But their passion proved to be the catalyst for Schroedinger's creative genius. 589 00:39:46,983 --> 00:39:51,903 Another physicist said of Schroedinger's week of sexually-inspired physics, 590 00:39:51,938 --> 00:39:54,307 "He had two tasks that week. 591 00:39:54,342 --> 00:39:58,101 "Satisfy a woman and solve the riddle of the atom. 592 00:39:58,136 --> 00:40:00,700 "Fortunately, he was up to both." 593 00:40:01,940 --> 00:40:07,819 He took De Broglie's idea of mysterious pilot waves guiding electrons around an atom 594 00:40:07,854 --> 00:40:10,102 one crucial step further. 595 00:40:10,137 --> 00:40:14,776 He argued that the electron actually was a wave of energy 596 00:40:14,811 --> 00:40:19,414 vibrating so fast it looked like a cloud around the atom, 597 00:40:19,449 --> 00:40:22,735 a cloud-like wave of pure energy. 598 00:40:23,653 --> 00:40:27,572 What's more, he came up with a powerful new equation 599 00:40:27,607 --> 00:40:30,251 which completely described this wave 600 00:40:30,286 --> 00:40:33,228 and so described the whole atom 601 00:40:33,263 --> 00:40:36,136 in terms of traditional physics. 602 00:40:36,171 --> 00:40:40,848 The equation he came up with we now call Schroedinger's wave equation. 603 00:40:41,929 --> 00:40:43,728 It's incredibly powerful. 604 00:40:43,763 --> 00:40:45,493 What's unique about it 605 00:40:45,528 --> 00:40:48,851 is that it features a new quantity called the wave function 606 00:40:48,886 --> 00:40:53,886 which Schroedinger claimed completely described the behaviour of the sub-atomic world. 607 00:41:03,842 --> 00:41:07,901 Schroedinger's equation and the picture of the atom it painted, 608 00:41:07,936 --> 00:41:11,960 created during a sexually-charged holiday in the Swiss Alps, 609 00:41:11,995 --> 00:41:15,959 once again allowed scientists to visualise the atom 610 00:41:15,994 --> 00:41:17,643 in simple terms. 611 00:41:17,678 --> 00:41:21,718 It's hard to over-estimate the relief Schroedinger's idea brought 612 00:41:21,753 --> 00:41:24,242 to the traditional physics community. 613 00:41:24,277 --> 00:41:27,115 Strange though his picture of the atom was, 614 00:41:27,150 --> 00:41:29,691 at least it was a picture 615 00:41:29,726 --> 00:41:32,198 and scientists love pictures. 616 00:41:32,233 --> 00:41:34,555 They allowed them to use their intuition. 617 00:41:40,512 --> 00:41:43,236 But there was still a deep nagging problem, 618 00:41:43,271 --> 00:41:47,554 one that the radicals felt Schroedinger just couldn't reconcile. 619 00:41:47,589 --> 00:41:54,109 His new theory still couldn't account for Bohr's strange, instantaneous quantum jumps. 620 00:41:54,144 --> 00:41:57,707 The time had come for the radicals to hit back. 621 00:42:06,304 --> 00:42:08,230 In the summer of the same year, 622 00:42:08,265 --> 00:42:11,788 one of Niels Bohr's protegees, Werner Heisenberg, 623 00:42:11,823 --> 00:42:15,621 was travelling to an obscure island off the north coast of Germany. 624 00:42:16,861 --> 00:42:21,861 He was fiercely competitive and took Schroedinger's ideas as a personal affront. 625 00:42:22,701 --> 00:42:26,619 He felt strongly that the strangeness of the instant quantum jumps 626 00:42:26,654 --> 00:42:29,658 was actually the key to understanding the atom. 627 00:42:30,777 --> 00:42:33,582 He thought the atom was so unique and unusual, 628 00:42:33,617 --> 00:42:36,696 it shouldn't be compromised through a simple analogy 629 00:42:36,731 --> 00:42:38,420 like a wave or an orbit, 630 00:42:38,455 --> 00:42:40,980 or even a multi-storey building. 631 00:42:41,015 --> 00:42:45,774 He believed it was time to give up any picture of the atom at all. 632 00:42:49,813 --> 00:42:54,791 Werner Heisenberg, one of the true geniuses of the 20th century. 633 00:42:54,826 --> 00:42:59,770 Young, athletic, a great mountain climber, an excellent pianist, 634 00:42:59,805 --> 00:43:02,015 he was also an exceptional student. 635 00:43:02,050 --> 00:43:06,129 At the age of just 20, he was well on his way to finishing his PhD 636 00:43:06,164 --> 00:43:09,566 and being courted by the great universities across Europe. 637 00:43:09,601 --> 00:43:12,211 Now, in the summer of 1925, 638 00:43:12,246 --> 00:43:15,565 he was suffering from a particularly bad bout of hay fever. 639 00:43:15,600 --> 00:43:19,004 His face was swollen up almost beyond recognition. 640 00:43:19,039 --> 00:43:22,048 He decided to escape alone, here, 641 00:43:22,083 --> 00:43:26,607 to this beautiful but isolated island of Helgeland. 642 00:43:26,642 --> 00:43:31,241 He walked along the beaches, he swam, he climbed the rocks 643 00:43:31,276 --> 00:43:33,040 and he pondered. 644 00:43:39,119 --> 00:43:41,642 Ever since he'd encountered atomic physics, 645 00:43:41,677 --> 00:43:46,556 Heisenberg felt in his bones that all human attempts to visualise the atom, 646 00:43:46,591 --> 00:43:49,835 to model it with familiar images, would always fail. 647 00:43:50,915 --> 00:43:53,874 The atom, he believed, was too capricious, 648 00:43:53,909 --> 00:43:56,833 too strange to ever be explained that simply. 649 00:43:57,753 --> 00:44:00,972 So he decided to abandon all pictures of it 650 00:44:01,007 --> 00:44:04,191 and describe it using pure mathematics alone. 651 00:44:05,671 --> 00:44:11,229 But as he pondered, he realised the atom didn't just defy visualisation, 652 00:44:11,264 --> 00:44:14,989 it even defied traditional mathematics. 653 00:44:22,307 --> 00:44:24,751 It was while he was here on Helgeland 654 00:44:24,786 --> 00:44:28,111 that Heisenberg had an incredible revelation. 655 00:44:28,146 --> 00:44:32,384 He realised that in order to describe certain properties of atoms, 656 00:44:32,419 --> 00:44:34,982 He had to use a strange new type of mathematics. 657 00:44:36,022 --> 00:44:42,021 It seems that certain properties like where an electron is at a given time and how fast it's moving, 658 00:44:42,056 --> 00:44:46,419 when multiplied together, the order in which you multiply them matters. 659 00:44:46,454 --> 00:44:47,944 Let me try and explain. 660 00:44:47,979 --> 00:44:52,378 If we multiply two numbers together, it doesn't matter which order we do it in. 661 00:44:52,413 --> 00:44:55,977 So three times four is clearly the same as four times three. 662 00:44:56,012 --> 00:44:58,061 But when it came to atoms, 663 00:44:58,096 --> 00:45:04,214 Heisenberg realised that the order in which he multiplied quantities together gave a different answer. 664 00:45:04,249 --> 00:45:06,578 This quickly led him to other discoveries 665 00:45:06,613 --> 00:45:09,872 and he was convinced that he'd cracked a code in the atom, 666 00:45:09,907 --> 00:45:13,132 that he'd somehow found the hidden mathematics within. 667 00:45:13,167 --> 00:45:15,769 He was so excited. He was also very scared. 668 00:45:15,804 --> 00:45:18,371 That night, he climbed to the top of a rock 669 00:45:18,406 --> 00:45:20,334 and sat there waiting till dawn. 670 00:45:20,369 --> 00:45:22,929 He called it his "Night of Helgeland". 671 00:45:23,968 --> 00:45:28,128 Back at university in Goettingen, he told his colleague Max Born about it 672 00:45:28,163 --> 00:45:31,687 and they then worked together intensely for several months 673 00:45:31,721 --> 00:45:35,463 developing a whole new theory of the atom. 674 00:45:35,498 --> 00:45:39,205 A theory that today we call matrix mechanics. 675 00:45:44,523 --> 00:45:48,162 Matrix mechanics uses complex arrays of numbers, 676 00:45:48,197 --> 00:45:50,258 rather like a spreadsheet. 677 00:45:50,293 --> 00:45:52,285 By manipulating these arrays, 678 00:45:52,320 --> 00:45:56,400 Heisenberg and his mentor the brilliant physicist Max Born 679 00:45:56,435 --> 00:45:59,279 could accurately predict atomic behaviour. 680 00:46:00,318 --> 00:46:02,758 But for Einstein and the traditionalists, 681 00:46:02,793 --> 00:46:05,643 this was pure scientific heresy. 682 00:46:05,678 --> 00:46:09,596 An atom can't actually be a matrix of numbers. 683 00:46:09,631 --> 00:46:12,556 Surely we're made of atoms, not numbers? 684 00:46:17,195 --> 00:46:19,598 Back in Copenhagen, 685 00:46:19,633 --> 00:46:22,638 Bohr and Pauli were thrilled with matrix mechanics. 686 00:46:22,673 --> 00:46:26,151 So what if we couldn't imagine the atom as a physical object? 687 00:46:26,186 --> 00:46:29,195 They exalted in the purity of the mathematics 688 00:46:29,230 --> 00:46:34,794 and launched into vicious attacks against Schroedinger's vulgar sensual waves. 689 00:46:34,829 --> 00:46:40,187 Heisenberg wrote, "The more I reflect on the physical portion of Schroedinger's equation, 690 00:46:40,222 --> 00:46:42,245 "the more disgusting I find it. 691 00:46:42,280 --> 00:46:44,232 "In fact, it's just bullshit." 692 00:46:44,267 --> 00:46:47,350 But Schroedinger was equally scathing of Heisenberg, 693 00:46:47,385 --> 00:46:51,864 saying he was repelled by his methods and found his mathematics monstrous. 694 00:47:00,142 --> 00:47:06,059 In Munich in 1926, their enmity began to reach boiling point. 695 00:47:06,094 --> 00:47:09,504 Schroedinger was to give a lecture on his wave equation. 696 00:47:09,539 --> 00:47:14,258 Heisenberg scraped together the money to travel to Munich for the lecture. 697 00:47:14,293 --> 00:47:17,257 To finally come face to face with his rival. 698 00:47:21,096 --> 00:47:24,976 What was at stake was more than just Heisenberg's reputation. 699 00:47:25,011 --> 00:47:28,094 He believed Schroedinger's simplistic approach 700 00:47:28,129 --> 00:47:31,459 wasn't just misguided, but totally wrong. 701 00:47:31,494 --> 00:47:36,133 And his intention was nothing less than to destroy Schroedinger's theory. 702 00:47:40,571 --> 00:47:44,009 Schroedinger delivers his lecture on the new wave mechanics 703 00:47:44,044 --> 00:47:47,066 to a packed audience. Standing room only. 704 00:47:47,101 --> 00:47:50,089 He writes down his new wave equation. 705 00:48:01,844 --> 00:48:07,403 To Schroedinger, this describes a real physical picture of the atom. 706 00:48:07,438 --> 00:48:11,682 with electrons as waves surrounding the atomic nucleus. 707 00:48:11,717 --> 00:48:14,800 24-year-old Werner Heisenberg is in the audience. 708 00:48:14,835 --> 00:48:16,725 He can hardly contain himself. 709 00:48:16,760 --> 00:48:22,320 At the end of the lecture he stands up and delivers a monologue attacking Schroedinger's approach. 710 00:48:22,355 --> 00:48:25,519 For Heisenberg it's impossible to ever have a picture 711 00:48:25,554 --> 00:48:27,483 of what the atom is really like. 712 00:48:27,518 --> 00:48:29,802 The audience is on Schroedinger's side. 713 00:48:29,837 --> 00:48:33,375 They much prefer his simple physical interpretation 714 00:48:33,410 --> 00:48:36,880 to Heisenberg's abstract, complicated mathematics. 715 00:48:36,915 --> 00:48:40,393 Heisenberg is booed. He's told to sit down and be quiet. 716 00:48:40,428 --> 00:48:43,392 He leaves the lecture sad and depressed. 717 00:48:47,831 --> 00:48:52,990 Heisenberg returned to Copenhagen with his confidence severely dented. 718 00:48:53,025 --> 00:48:58,829 There at the institute, he and Bohr reached their darkest moment. 719 00:48:58,864 --> 00:49:03,152 Almost all of the scientific community was against them. 720 00:49:03,187 --> 00:49:08,986 They felt isolated, desperate. Their backs were against the wall. 721 00:49:10,825 --> 00:49:16,344 Despite this, they stubbornly refused to give up their controversial theory. 722 00:49:18,944 --> 00:49:22,303 This attic room was Heisenberg's study back in 1926. 723 00:49:23,382 --> 00:49:26,145 Bohr would come up here night after night 724 00:49:26,180 --> 00:49:30,460 where he and Heisenberg would argue about the meaning of quantum mechanics. 725 00:49:30,495 --> 00:49:32,984 They would argue so passionately, 726 00:49:33,019 --> 00:49:36,703 that on one occasion Heisenberg was reduced to tears. 727 00:49:36,738 --> 00:49:40,857 And then, as Heisenberg stared out of his attic window in despair 728 00:49:40,892 --> 00:49:42,301 at the park below, 729 00:49:42,336 --> 00:49:45,141 an extraordinary thought occurred to him. 730 00:49:45,176 --> 00:49:49,094 It struck him why an atom can't be visualised, 731 00:49:49,129 --> 00:49:52,139 why it can't be understood intuitively. 732 00:49:52,174 --> 00:49:56,013 It's not just because it's tiny, tricky and difficult. 733 00:49:56,048 --> 00:49:59,291 It's because it's inherently unknowable. 734 00:50:00,371 --> 00:50:06,129 He realised that there was a fundamental limit to how much we can know about the sub-atomic world. 735 00:50:06,164 --> 00:50:11,009 For instance, if we know where an electron is at a particular moment in time, 736 00:50:11,044 --> 00:50:13,572 then we cannot know how fast it's moving. 737 00:50:13,607 --> 00:50:17,886 But if we knew its speed, we wouldn't know its position. 738 00:50:17,921 --> 00:50:22,130 This ambiguity isn't a shortcoming in the theory itself. 739 00:50:22,165 --> 00:50:26,163 Nor is it due to the clumsiness of the way we carry out our measurements, 740 00:50:26,198 --> 00:50:30,284 but a fundamental truth about the way Nature behaves 741 00:50:30,319 --> 00:50:32,328 at the sub-atomic scale. 742 00:50:32,363 --> 00:50:36,927 It became known as Heisenberg's Uncertainty Principle. 743 00:50:36,962 --> 00:50:43,159 And it's probably the most profound, incredible, yet unsettling concepts 744 00:50:43,194 --> 00:50:45,000 in the whole of science. 745 00:50:50,517 --> 00:50:55,836 What Heisenberg had uncovered through his abstract matrix mechanics 746 00:50:55,871 --> 00:50:59,636 was a deep and shocking truth about the atomic world. 747 00:50:59,671 --> 00:51:03,319 Atoms are wilfully obscure. 748 00:51:03,354 --> 00:51:08,791 We can never fully know an atom's position and speed simultaneously. 749 00:51:08,826 --> 00:51:13,272 The atomic world just refuses to allow that to happen. 750 00:51:13,307 --> 00:51:16,110 It was completely mind-boggling. 751 00:51:16,145 --> 00:51:18,515 But once they accepted it, 752 00:51:18,550 --> 00:51:24,192 Heisenberg and Bohr found the boost of confidence to be even more bold. 753 00:51:24,227 --> 00:51:30,986 They realised uncertainty forced them to put paradox right at the very heart of the atom. 754 00:51:34,585 --> 00:51:39,623 Atoms are not just unimaginable. They're self-contradictory. 755 00:51:39,658 --> 00:51:42,623 They behave both like particles and waves. 756 00:51:42,657 --> 00:51:44,667 And it gets weirder. 757 00:51:44,702 --> 00:51:48,581 When you're not looking at an atom, it behaves like a spread-out wave. 758 00:51:48,616 --> 00:51:50,620 But when you look to see where it is, 759 00:51:50,655 --> 00:51:52,219 it behaves like a particle. 760 00:51:52,254 --> 00:51:53,905 This is insane! 761 00:51:53,940 --> 00:51:56,585 First, atoms couldn't be visualised at all, 762 00:51:56,620 --> 00:52:01,778 now they change completely in character depending on whether or not you're looking at them. 763 00:52:03,616 --> 00:52:07,260 The Uncertainty Principle had changed everything. 764 00:52:07,295 --> 00:52:11,534 It revealed a shocking contradiction at the heart of Nature. 765 00:52:12,614 --> 00:52:15,339 Everything we see is made of atoms. 766 00:52:15,374 --> 00:52:19,138 And yet atoms themselves are unknowable. 767 00:52:19,173 --> 00:52:22,331 They can only be understood through mathematics. 768 00:52:23,451 --> 00:52:30,089 For the first time for Bohr and Heisenberg everything about the atom fell into place. 769 00:52:31,728 --> 00:52:34,892 By the autumn of 1927, 770 00:52:34,927 --> 00:52:37,651 full of confidence and smarting for a fight, 771 00:52:37,686 --> 00:52:41,806 they knew they were finally ready to take on the conservatives. 772 00:52:51,003 --> 00:52:53,088 For this physics showdown, 773 00:52:53,123 --> 00:52:56,168 they chose the Solvay Conference in Brussels. 774 00:52:56,203 --> 00:53:00,920 All the world's leading atomic physicists would attend. 775 00:53:00,955 --> 00:53:03,644 If Bohr and Heisenberg were successful, 776 00:53:03,679 --> 00:53:07,278 they would lead a total scientific revolution. 777 00:53:07,313 --> 00:53:10,855 This is amazing. I'm looking at original footage 778 00:53:10,890 --> 00:53:14,361 of the Solvay delegates coming out of these doors. 779 00:53:14,396 --> 00:53:19,035 There's Bohr talking to Schroedinger and there's Heisenberg behind them. 780 00:53:20,994 --> 00:53:24,040 There's Pauli, strange-looking guy. 781 00:53:24,075 --> 00:53:27,719 There's Einstein coming down with a big smile on his face. 782 00:53:27,754 --> 00:53:32,672 For the week of the conference, all that the delegates could think and talk about 783 00:53:32,707 --> 00:53:34,995 was Bohr's quantum mechanics. 784 00:53:35,030 --> 00:53:38,071 With uncertainty now a central plank, 785 00:53:38,106 --> 00:53:41,035 it was a truly formidable theory. 786 00:53:41,070 --> 00:53:45,308 And over the week, the final showdown played out 787 00:53:45,342 --> 00:53:49,546 between Bohr and his arch-rival, Albert Einstein. 788 00:53:49,581 --> 00:53:51,751 Einstein hated quantum mechanics. 789 00:53:51,786 --> 00:53:54,666 Every morning he'd come to Bohr with an argument 790 00:53:54,701 --> 00:53:57,070 he felt picked a hole in the new theory. 791 00:53:57,105 --> 00:54:00,709 Bohr would go away, very disturbed, and think very hard about it, 792 00:54:00,744 --> 00:54:05,742 and later he'd come back with a counter-argument that dismissed Einstein's criticism. 793 00:54:05,777 --> 00:54:09,261 This happened day after day until by the end of the conference, 794 00:54:09,296 --> 00:54:12,358 Bohr had brushed aside all of Einstein's criticisms 795 00:54:12,393 --> 00:54:15,420 and Bohr was regarded as having been victorious. 796 00:54:19,379 --> 00:54:22,223 And with that, his vision of the atom, 797 00:54:22,258 --> 00:54:26,036 which became known as the Copenhagen Interpretation, 798 00:54:26,071 --> 00:54:29,816 was suddenly at the very heart of atomic physics. 799 00:54:31,135 --> 00:54:34,853 At the end of the conference, they all gathered for the team photo. 800 00:54:34,888 --> 00:54:39,652 Never before or since have so many great names of physics 801 00:54:39,687 --> 00:54:41,658 been together in one place. 802 00:54:41,693 --> 00:54:46,110 At the front, the elder statesman of physics, Hendrik Lorentz, 803 00:54:46,145 --> 00:54:50,178 flanked on either side by Madame Curie and Albert Einstein. 804 00:54:50,213 --> 00:54:54,209 Einstein's looking rather glum because he's lost the argument. 805 00:54:55,289 --> 00:55:00,606 Louis de Broglie has also failed to convince the delegates of his views. 806 00:55:00,641 --> 00:55:03,331 Victory goes to Niels Bohr. 807 00:55:03,366 --> 00:55:05,770 He's feeling very pleased with himself. 808 00:55:05,805 --> 00:55:09,484 Next to him, one of the unsung heroes of quantum mechanics, 809 00:55:09,519 --> 00:55:13,163 the German Max Born who developed so much of the mathematics. 810 00:55:13,198 --> 00:55:16,442 And behind them, the two young disciples of Bohr, 811 00:55:16,477 --> 00:55:18,647 Heisenberg and Pauli. 812 00:55:18,682 --> 00:55:22,042 Pauli is looking rather smugly across as Schroedinger, 813 00:55:22,077 --> 00:55:24,081 a bit like the cat who's got the milk. 814 00:55:25,121 --> 00:55:28,000 This was the moment in physics when it all changed. 815 00:55:28,998 --> 00:55:31,682 The old guard was replaced by the new. 816 00:55:31,717 --> 00:55:37,317 Chance and probability became interwoven into the fabric of Nature itself 817 00:55:37,352 --> 00:55:41,356 and we could no longer describe atoms in terms of simple pictures 818 00:55:41,391 --> 00:55:44,992 but only using pure abstract mathematics. 819 00:55:45,027 --> 00:55:48,593 The Copenhagen view had been victorious. 820 00:55:53,633 --> 00:55:58,350 Although Einstein went to his grave never believing quantum mechanics, 821 00:55:58,385 --> 00:56:02,514 Solvay 1927 was the turning point 822 00:56:02,549 --> 00:56:05,728 at which the rest of the science establishment 823 00:56:05,763 --> 00:56:09,454 came to embrace the Copenhagen Interpretation. 824 00:56:09,489 --> 00:56:13,146 And that interpretation is still accepted today. 825 00:56:14,466 --> 00:56:17,390 All the physics that I use in my research, 826 00:56:17,425 --> 00:56:20,704 certainly the quantum mechanics that I teach my students 827 00:56:20,739 --> 00:56:23,188 and that fills the text books on my shelves 828 00:56:23,223 --> 00:56:30,342 is based on ideas that were hammered out and crystallised here at the Solvay Conference in October 1927. 829 00:56:31,542 --> 00:56:36,659 In a sense, everything I know about the way the world around me is made up 830 00:56:36,694 --> 00:56:38,539 started here. 831 00:56:42,578 --> 00:56:45,381 The quantum mechanical description of the atom 832 00:56:45,416 --> 00:56:49,181 is one of the crowning glories of human creativity. 833 00:56:49,216 --> 00:56:54,814 Over the last 80 years, it has been proven right, time after time 834 00:56:54,849 --> 00:56:58,091 and its authority has never been in doubt. 835 00:56:58,126 --> 00:57:01,334 It's a monumental scientific achievement. 836 00:57:03,253 --> 00:57:06,897 Between 1905 and 1927, 837 00:57:06,932 --> 00:57:09,335 science changed our view of the world. 838 00:57:09,370 --> 00:57:12,335 It also changed our view of science itself. 839 00:57:12,370 --> 00:57:16,588 As scientists probed the tiniest building blocks of matter, 840 00:57:16,623 --> 00:57:20,807 they created the most successful and powerful theory ever - 841 00:57:20,842 --> 00:57:22,532 quantum mechanics. 842 00:57:22,567 --> 00:57:26,806 It allows us to describe what everything in the universe is made of, 843 00:57:26,841 --> 00:57:29,486 how it interacts and how it all fits together. 844 00:57:29,521 --> 00:57:32,045 But it comes at a huge price. 845 00:57:33,164 --> 00:57:35,009 At its most fundamental level, 846 00:57:35,044 --> 00:57:38,763 we have to accept that Nature is ruled by chance and probability. 847 00:57:38,798 --> 00:57:41,206 Heisenberg's Uncertainty Principle 848 00:57:41,241 --> 00:57:46,561 dictates that there are certain limits on the sorts of questions we can ask the atomic world. 849 00:57:46,596 --> 00:57:50,120 Most crucially, while we now know so much more 850 00:57:50,155 --> 00:57:52,523 about what an atom is and how it behaves, 851 00:57:52,558 --> 00:57:57,041 we have to give up any possibility of imagining what it looks like. 852 00:57:57,076 --> 00:58:03,515 Our human nature has forced us to ask questions of everything we see around us in the world. 853 00:58:03,550 --> 00:58:08,113 What we've discovered has been beyond our wildest imagination.