1 00:00:00,820 --> 00:00:03,580 Hi, everybody. And welcome to the first lecture in our 2 00:00:03,580 --> 00:00:07,680 course Exploring Quantum Physics. Today, I will introduce the main 3 00:00:07,680 --> 00:00:10,990 formulation of quantum theory using Schrodinger. 4 00:00:10,990 --> 00:00:14,296 And I will also tell you a little bit about a fascinating history of the 5 00:00:14,296 --> 00:00:17,280 subject. But before going to this main part, I 6 00:00:17,280 --> 00:00:21,320 would like to talk about the process of learning quantum physics. 7 00:00:21,320 --> 00:00:25,299 And about why I think, so many people find it difficult and frustrating. 8 00:00:26,460 --> 00:00:30,288 And I hope that this brief discussion will help you avoid this frustration, and 9 00:00:30,288 --> 00:00:35,10 make the process of learning quantum physics here more effective. 10 00:00:35,10 --> 00:00:37,825 Richard Feynman doesn't really need an introduction. 11 00:00:37,825 --> 00:00:41,227 He was one of the heroes and legends in physics, universally recognized as a 12 00:00:41,227 --> 00:00:43,490 genius. He was also a great speaker and 13 00:00:43,490 --> 00:00:47,28 enthusiastic popularizer of physics. In 1979, he gave a series of very 14 00:00:47,28 --> 00:00:50,928 interesting lectures on quantum physics at the University of Auckland in New 15 00:00:50,928 --> 00:00:54,429 Zealand. They're actually available on YouTube 16 00:00:54,429 --> 00:00:57,480 online and I would encourage you to listen to them. 17 00:00:57,480 --> 00:01:00,600 If you do so, you will see that Feynman spends 30 or so, minutes in the beginning 18 00:01:00,600 --> 00:01:03,624 of his first lecture to prepare the audience for what they were going to hear 19 00:01:03,624 --> 00:01:07,954 next. In one of the main messages of this 20 00:01:07,954 --> 00:01:11,266 introductory part was that no matter what Feynman was to do, the audience wouldn't 21 00:01:11,266 --> 00:01:14,610 be able to understand Quantum Mechanics anyway. 22 00:01:14,610 --> 00:01:17,976 That he talks about physics students and physics professors and their level of 23 00:01:17,976 --> 00:01:21,564 understanding of Quantum Physics. Let's listen to what Feynman had to say 24 00:01:21,564 --> 00:01:24,651 in this regard. if I'm going to explain this theory, the 25 00:01:24,651 --> 00:01:28,10 question is, are you going to understand it? 26 00:01:28,10 --> 00:01:32,951 Will you understand the theory? When I tell you first that the first time 27 00:01:32,951 --> 00:01:37,306 we really thoroughly explain it to our own physics students is when they're in 28 00:01:37,306 --> 00:01:41,691 the third year graduate, graduate physics. 29 00:01:41,691 --> 00:01:44,809 Then, you think the answer is going to be no. 30 00:01:44,809 --> 00:01:48,262 And that's correct, you will not understand. 31 00:01:48,262 --> 00:01:49,270 >> [LAUGH] . 32 00:01:49,270 --> 00:01:51,574 >> But this business about not understanding 33 00:01:51,574 --> 00:01:56,630 is a very serious one that we have between a scientist and an audience. 34 00:01:56,630 --> 00:02:01,198 And I want to be at work with you, because I want to tell you something. 35 00:02:01,198 --> 00:02:05,296 The students do not understand it either. 36 00:02:05,296 --> 00:02:05,944 >> [LAUGH]. 37 00:02:05,944 --> 00:02:09,182 >> And that's because the professor doesn't understand. 38 00:02:09,182 --> 00:02:09,705 >> [LAUGH]. 39 00:02:09,705 --> 00:02:12,197 >> This is not a joke, but very interesting. 40 00:02:12,197 --> 00:02:14,88 >> So, what Feynman seems to be saying is 41 00:02:14,88 --> 00:02:17,931 that nobody, not even professional physicists, not even himself perhaps, 42 00:02:17,931 --> 00:02:23,940 really understand quantum physics. Well, this is probably the last thing you 43 00:02:23,940 --> 00:02:28,44 want to hear before starting this course. But this is strictly not my intention to 44 00:02:28,44 --> 00:02:31,730 give you the impression that you should give up without even trying. 45 00:02:31,730 --> 00:02:34,250 On the contrary, I'd like to speculate what I think Feynmam might have meant 46 00:02:34,250 --> 00:02:36,860 there. But why I think so many people find it 47 00:02:36,860 --> 00:02:41,582 difficult to study quantum physics and other advanced physic subjects. 48 00:02:41,582 --> 00:02:45,122 And I hope that this discussion will help us further down the road when we 49 00:02:45,122 --> 00:02:49,290 encounter unusual counter intuitive quantum phenomena. 50 00:02:49,290 --> 00:02:53,700 Let us look at quantum mechanics from the perspective of all major physics theories 51 00:02:53,700 --> 00:02:58,140 out there. In this slide, I attempt to present all 52 00:02:58,140 --> 00:03:01,980 these theories in a single diagram, which, of course, is an unrealistic sort 53 00:03:01,980 --> 00:03:06,322 of silly task. And so, the result I should, I cannot, I 54 00:03:06,322 --> 00:03:11,350 shouldn't be taken too seriously. What we have here are three axis, 55 00:03:11,350 --> 00:03:17,90 labeling fundamental physics constants. So, here, I have an the inverse speed of 56 00:03:17,90 --> 00:03:22,560 light. this constant G is the gravity constant, 57 00:03:22,560 --> 00:03:30,304 which appears in the Newtonion gravity. And along the horizontal axis, I have the 58 00:03:30,304 --> 00:03:33,369 Planck constant. We show, as we show, c is the most 59 00:03:33,369 --> 00:03:37,659 important fundamental constant that appears in quantum mechanics and that it 60 00:03:37,659 --> 00:03:43,793 relates the particle and wave properties. Now, the red dots in this diagram 61 00:03:43,793 --> 00:03:48,278 represent, symbolically, major fields of physics. 62 00:03:48,278 --> 00:03:52,109 For example, on this line, I have two red dots. 63 00:03:52,109 --> 00:03:57,439 So, the one which has all, agree, responds to all physical constants being 64 00:03:57,439 --> 00:04:02,870 zero is just kinematics or classical mechanics. 65 00:04:02,870 --> 00:04:09,920 Essentially, 17th century physics. So this dot here, with the finite gravity 66 00:04:09,920 --> 00:04:17,390 constant, but all other constant. 0 is the Newtonian Gravity. 67 00:04:17,390 --> 00:04:22,62 Now, moving up, the vertical axis, to the finite speed of light, brings us to a 68 00:04:22,62 --> 00:04:26,734 theory which takes into account this finite speed with which, with which 69 00:04:26,734 --> 00:04:32,676 interactions propagate. And this is the celebrated Special 70 00:04:32,676 --> 00:04:37,346 Relativity Theory of Einstein. Combining it with gravity results in 71 00:04:37,346 --> 00:04:41,476 General Relativity, another celebrated, another very famous geometric theory of 72 00:04:41,476 --> 00:04:47,624 Einstein. Finally, moving along the horizontal axis 73 00:04:47,624 --> 00:04:52,385 to find a Planck's constant, brings us to, actually, the subject of our course, 74 00:04:52,385 --> 00:04:58,4 non-relativistic quantum mechanics. So, the results of this part, which we 75 00:04:58,4 --> 00:05:01,767 are not going to discuss too much in this course, which combines the relativistic 76 00:05:01,767 --> 00:05:05,306 effects and the quantum mechanical effects. 77 00:05:05,306 --> 00:05:09,87 And this is, so called Quantum Field Theory or Quantum Electrodynamics. 78 00:05:09,87 --> 00:05:14,301 They are more complicated theory. Actually, I could have added here another 79 00:05:14,301 --> 00:05:18,550 dot which has all fundamental physics constants. 80 00:05:18,550 --> 00:05:22,640 This is this would be theory of everything. 81 00:05:22,640 --> 00:05:27,436 It doesn't really exist yet but everybody wants to get it. 82 00:05:27,436 --> 00:05:32,330 So, this has been one of the holy grails of physics for many years. 83 00:05:32,330 --> 00:05:36,740 Now going back to learning quantum physics and what does it all have to do 84 00:05:36,740 --> 00:05:41,66 with it. so let us discuss what theory governs our 85 00:05:41,66 --> 00:05:45,651 everyday lives. What is sort of our comfort zone? 86 00:05:45,651 --> 00:05:51,30 And I would claim that we are somewhere here in this area. 87 00:05:51,30 --> 00:05:55,254 Certainly, the life skills that we encounter in our everyday lives are much 88 00:05:55,254 --> 00:05:59,410 larger than atomic. The velocities are certainly much smaller 89 00:05:59,410 --> 00:06:03,478 than the speed of light. And well, we do experience gravity on a 90 00:06:03,478 --> 00:06:06,80 daily basis. So, we're somewhere here. 91 00:06:06,80 --> 00:06:11,49 And here is also where our intuition works. 92 00:06:11,49 --> 00:06:15,529 And if we say, we understand something, what we usually mean by that is that we 93 00:06:15,529 --> 00:06:22,868 can relate a phenomenon to another phenomenon that occurs here in this area. 94 00:06:22,868 --> 00:06:27,284 So, for example, if we were to say that we really understand quantum mechanical 95 00:06:27,284 --> 00:06:31,828 effect, it would often times imply that we would have found a way to relate it by 96 00:06:31,828 --> 00:06:39,265 something that we all ready know here. But the problem with all this advanced 97 00:06:39,265 --> 00:06:44,953 physics subjects, especially with quantum physics, is that such a mapping, such a 98 00:06:44,953 --> 00:06:52,202 relation is not always possible. In other words, it's not always possible 99 00:06:52,202 --> 00:06:57,142 to meaningfully project quantum mechanical phenomena on this classical 100 00:06:57,142 --> 00:07:04,240 axis. And if no classical analog exist, this is 101 00:07:04,240 --> 00:07:09,390 what we call strange. And this is what we find difficult. 102 00:07:09,390 --> 00:07:13,879 But on the other hand, if we were to imagine a fictitious civilization of tiny 103 00:07:13,879 --> 00:07:19,470 species that lived on atomic scales somewhere in this area. 104 00:07:19,470 --> 00:07:25,476 So, this guys would have had really a lot of problems understanding our classical 105 00:07:25,476 --> 00:07:29,266 work. So, the problem is not really with the 106 00:07:29,266 --> 00:07:33,292 quantum physics itself but with our centristic position on how we want to 107 00:07:33,292 --> 00:07:38,279 understand it. But now, how do[UKNOWN] quantum physics 108 00:07:38,279 --> 00:07:43,894 if we can't really regularly understand it at intuitive level. 109 00:07:43,894 --> 00:07:49,554 Fortunately, there is a way to do so. By speaking in common language of all 110 00:07:49,554 --> 00:07:54,390 physic theories, that is not rooted in and is independent of our classical 111 00:07:54,390 --> 00:08:00,797 world. And this is, of course, mathematical 112 00:08:00,797 --> 00:08:06,419 formalism that needs to be developed. And it may turn out that two seemly 113 00:08:06,419 --> 00:08:10,644 unrelated phenomena, lets say, on the classical side and on the quantum side, 114 00:08:10,644 --> 00:08:17,86 may be explained by similar differential equations or something like that. 115 00:08:17,86 --> 00:08:23,38 And by studying those, we can develop intuition about something which is 116 00:08:23,38 --> 00:08:29,469 otherwise, inaccessible to us. But after this discussion, you may ask, 117 00:08:29,469 --> 00:08:34,725 why bother studying quantum physics if it's not really relevant to our everyday 118 00:08:34,725 --> 00:08:38,711 lives? So, the modulation comes from 119 00:08:38,711 --> 00:08:42,78 experiments. And more recently, also from ecological 120 00:08:42,78 --> 00:08:46,108 advances that creates systems and devices, which operate further, on the 121 00:08:46,108 --> 00:08:50,474 right of this axis. The take home message here, is that when 122 00:08:50,474 --> 00:08:54,194 you study quantum physics or any other advanced physics subject, for this 123 00:08:54,194 --> 00:08:58,274 measure, you should actually be prepared to encounter phenomena that may appear 124 00:08:58,274 --> 00:09:03,769 bizarre at the first sight. And that you may find difficult to 125 00:09:03,769 --> 00:09:06,855 understand. When it does happen don't panic and 126 00:09:06,855 --> 00:09:10,430 certainly don't drop the course because of that, and don't assume that others 127 00:09:10,430 --> 00:09:14,778 find these things obvious. It's certainly not the case. 128 00:09:14,778 --> 00:09:19,888 so, I think the best way to understand such new concepts is first, understand 129 00:09:19,888 --> 00:09:25,554 experimental data that support them. And then, develop or understand a 130 00:09:25,554 --> 00:09:31,570 mathematical formalism and the proper theory that describes these phenomena. 131 00:09:31,570 --> 00:09:34,992 So, when you use this theory again and again, you will develop your own 132 00:09:34,992 --> 00:09:40,550 intuition and get the feeling about a deeper understanding of the subject. 133 00:09:40,550 --> 00:09:44,503 So, speaking about the mathematical side, so I should mention that of course 134 00:09:44,503 --> 00:09:50,90 quantum mechanics is a demanding subject. And it, we will have to use certain vast 135 00:09:50,90 --> 00:09:54,704 mathematical techniques. But there will be lectures with different 136 00:09:54,704 --> 00:09:57,870 sort of levels of mathematical sophistication. 137 00:09:57,870 --> 00:10:00,730 Some of them will be pretty advanced, some of them actually won't use much math 138 00:10:00,730 --> 00:10:03,390 at all. And so, I, I hope that all of you with, 139 00:10:03,390 --> 00:10:07,170 with different backgrounds in different levels of mathematical preparation will 140 00:10:07,170 --> 00:10:10,983 find something that is useful and interesting.