1 00:00:08,680 --> 00:00:12,080 Speaker 1: What if your idea of how the universe works is 2 00:00:12,160 --> 00:00:15,560 Speaker 1: just wrong? I mean, you live in a world that 3 00:00:15,720 --> 00:00:18,600 Speaker 1: seems to make sense of you, that seems to follow 4 00:00:18,720 --> 00:00:22,360 Speaker 1: rules that you're familiar with. But what if that's just wrong? 5 00:00:22,760 --> 00:00:26,599 Speaker 1: Could reality what's actually out there beyond our brains and 6 00:00:26,640 --> 00:00:30,360 Speaker 1: our senses. Could it be something so strange and bizarre 7 00:00:30,480 --> 00:00:33,640 Speaker 1: that we would hardly recognize it. Could it be dramatically 8 00:00:33,680 --> 00:00:36,960 Speaker 1: different from the glimpses we get through our senses and experiments. 9 00:00:37,560 --> 00:00:40,559 Speaker 1: There's a vital clue that might just point us in 10 00:00:40,600 --> 00:00:44,760 Speaker 1: that direction, something that has puzzled physicists and philosophers for 11 00:00:44,840 --> 00:00:48,560 Speaker 1: nearly one hundred years, and that may take another hundred 12 00:00:48,640 --> 00:00:52,000 Speaker 1: years to solve. Solving it might require us to swallow 13 00:00:52,040 --> 00:00:55,560 Speaker 1: a picture of reality that is mind bending lee strange 14 00:00:55,720 --> 00:01:15,400 Speaker 1: to our little human brains. I'm Daniel, I'm a particle physicist, 15 00:01:15,520 --> 00:01:18,880 Speaker 1: and I'm drawn to the possibility that the universe might 16 00:01:18,959 --> 00:01:21,880 Speaker 1: be very different from the way we imagine it. What 17 00:01:22,160 --> 00:01:24,920 Speaker 1: is the goal of physics, anyway, if not to reveal 18 00:01:25,080 --> 00:01:29,280 Speaker 1: the true nature of reality to us. We build mathematical 19 00:01:29,360 --> 00:01:32,600 Speaker 1: stories in our minds and apply them to our experiences. 20 00:01:33,080 --> 00:01:36,560 Speaker 1: But why immediately it's because we want to predict what 21 00:01:36,680 --> 00:01:39,440 Speaker 1: will happen when we throw a stone or jump a river. 22 00:01:40,080 --> 00:01:43,279 Speaker 1: But going deeper it gives us the chance to ask 23 00:01:43,400 --> 00:01:47,919 Speaker 1: questions about how the universe works. If our mathematical story 24 00:01:48,040 --> 00:01:51,240 Speaker 1: describes the universe, then we can look at that math 25 00:01:51,320 --> 00:01:54,080 Speaker 1: and ask why the universe seems to follow that and 26 00:01:54,480 --> 00:01:58,440 Speaker 1: what it all means. And sometimes the universe out there 27 00:01:58,480 --> 00:02:01,000 Speaker 1: seems to insist on a math modical story that we 28 00:02:01,080 --> 00:02:05,280 Speaker 1: find very weird, shocking, almost And that is the goal 29 00:02:05,360 --> 00:02:07,960 Speaker 1: of physics, not just to give us the power to 30 00:02:08,040 --> 00:02:11,040 Speaker 1: throw rocks and jump rivers, but to reveal the truth. 31 00:02:11,440 --> 00:02:13,960 Speaker 1: And the most exciting moments are when the truth and 32 00:02:14,040 --> 00:02:17,959 Speaker 1: our intuition clash dramatically, when the universe says to us, know, 33 00:02:18,800 --> 00:02:22,160 Speaker 1: your ideas about the universe are just wrong. And that's 34 00:02:22,240 --> 00:02:25,840 Speaker 1: the goal of this podcast. Daniel and Jorge Explain the Universe, 35 00:02:25,919 --> 00:02:28,799 Speaker 1: a production of I Heart Radio in which we tackle 36 00:02:28,919 --> 00:02:32,639 Speaker 1: the biggest and hardest and nastiest and funnest questions of 37 00:02:32,680 --> 00:02:35,560 Speaker 1: the universe. The ones that make your brain twist, the 38 00:02:35,600 --> 00:02:38,079 Speaker 1: ones that slip away from you just as you thought 39 00:02:38,160 --> 00:02:40,800 Speaker 1: you had figured them out. The ones that might elude 40 00:02:40,880 --> 00:02:44,680 Speaker 1: humanity for centuries or forever. We don't shy away from 41 00:02:44,720 --> 00:02:47,120 Speaker 1: any questions on the podcast, but we seek to approach 42 00:02:47,160 --> 00:02:50,440 Speaker 1: them and explain our knowledge and our ignorance to you. 43 00:02:50,880 --> 00:02:53,040 Speaker 1: My friend and co host Jorge is on a break, 44 00:02:53,240 --> 00:02:55,680 Speaker 1: but I have a special treat for you today. We 45 00:02:55,760 --> 00:02:57,840 Speaker 1: are very lucky to have as a guest one of 46 00:02:57,880 --> 00:03:01,359 Speaker 1: my favorite physicists and one of my writers about physics. 47 00:03:01,639 --> 00:03:04,760 Speaker 1: Today we'll be talking to Professor Sean Carroll about some 48 00:03:04,840 --> 00:03:07,600 Speaker 1: of the problems at the heart of quantum mechanics and 49 00:03:07,680 --> 00:03:10,440 Speaker 1: a potential solution. So today on the podcast, we'll be 50 00:03:10,480 --> 00:03:19,680 Speaker 1: answering the question what is the many worlds interpretation of 51 00:03:19,800 --> 00:03:23,800 Speaker 1: quantum mechanics. So it's my great pleasure to introduce Professor 52 00:03:23,800 --> 00:03:27,400 Speaker 1: Sean Carroll. He's a theoretical physicist at cal Tech, and 53 00:03:27,440 --> 00:03:30,640 Speaker 1: he's known for his work on cosmology, general relativity, and 54 00:03:30,639 --> 00:03:33,560 Speaker 1: the foundations of quantum mechanics. He's also the author of 55 00:03:33,600 --> 00:03:37,360 Speaker 1: several widely acclaimed and widely read books, including Something People 56 00:03:37,440 --> 00:03:39,960 Speaker 1: Hidden and The Big Picture, and is the host of 57 00:03:39,960 --> 00:03:44,360 Speaker 1: the podcast Mindscape, which might actually be nearlier than this podcast. Today, 58 00:03:44,400 --> 00:03:46,280 Speaker 1: Sean is here to talk to us about the many 59 00:03:46,320 --> 00:03:49,440 Speaker 1: worlds interpretation of quantum mechanics and the measurement problem in 60 00:03:49,520 --> 00:03:52,600 Speaker 1: quantum mechanics. Sean, Welcome to the podcast. Thanks very much 61 00:03:52,600 --> 00:03:55,040 Speaker 1: for having me here. Wonderful to have you. So I 62 00:03:55,080 --> 00:03:57,320 Speaker 1: want to die right in and before we talk about 63 00:03:57,320 --> 00:03:59,839 Speaker 1: what the many worlds interpretation is, I want to get 64 00:04:00,040 --> 00:04:03,120 Speaker 1: review on what problem it solves, Like why do we 65 00:04:03,160 --> 00:04:06,000 Speaker 1: need so many interpretations of quantum mechanics. What problem is 66 00:04:06,000 --> 00:04:08,040 Speaker 1: it that they are trying to address. I think there's 67 00:04:08,040 --> 00:04:10,200 Speaker 1: actually two problems. I mean, this is the right question, 68 00:04:10,280 --> 00:04:12,880 Speaker 1: because are we just wasting our time or it's not. Honestly, 69 00:04:12,880 --> 00:04:14,880 Speaker 1: it's not a lot of time compared to other physicists 70 00:04:14,920 --> 00:04:17,280 Speaker 1: thinking about other things. The foundations of quantum mechanics is 71 00:04:17,279 --> 00:04:19,920 Speaker 1: a minority pursuit. But I think there are two problems, 72 00:04:20,000 --> 00:04:24,520 Speaker 1: and there's such looming large problems, and quantum mechanics is 73 00:04:24,600 --> 00:04:27,840 Speaker 1: so important to modern physics that I do wish we 74 00:04:27,839 --> 00:04:30,480 Speaker 1: were spending more time on them. So in Quantum Mechanics, 75 00:04:30,640 --> 00:04:32,960 Speaker 1: I'll try to give my briefest version of quantum mechanics 76 00:04:32,960 --> 00:04:37,120 Speaker 1: that we can we talk about objects in the universe, 77 00:04:37,160 --> 00:04:39,960 Speaker 1: whether it's an electron or whatever, in a different way 78 00:04:40,000 --> 00:04:42,640 Speaker 1: than we talked about them in classical mechanics and Isaac 79 00:04:42,640 --> 00:04:45,200 Speaker 1: Newton's view the universe. And Newton's view, we would have 80 00:04:45,440 --> 00:04:48,400 Speaker 1: a position a location in space for a particle, and 81 00:04:48,440 --> 00:04:50,839 Speaker 1: we would also have a velocity. And if you knew 82 00:04:50,839 --> 00:04:53,520 Speaker 1: the positions of velocities of everything in the universe, in principle, 83 00:04:53,600 --> 00:04:55,520 Speaker 1: you could predict what would happen, and you could measure 84 00:04:55,560 --> 00:04:57,640 Speaker 1: what would happen as much as you want. In quantum 85 00:04:57,640 --> 00:05:00,279 Speaker 1: mechanics we say no, no, no, that's not how we 86 00:05:00,320 --> 00:05:04,560 Speaker 1: describe reality. There's something called the wave function, which, for 87 00:05:04,640 --> 00:05:07,760 Speaker 1: a single particle like an electron, is just very wave 88 00:05:07,839 --> 00:05:10,960 Speaker 1: like basically at every point in space that has a value. 89 00:05:11,240 --> 00:05:18,280 Speaker 1: But positions and velocities are not properties of the electron anymore. 90 00:05:18,360 --> 00:05:20,440 Speaker 1: There are things we can observe about it, and the 91 00:05:20,480 --> 00:05:23,839 Speaker 1: wave function tells us the probability that we'll get different 92 00:05:23,880 --> 00:05:27,240 Speaker 1: answers if we observe like the position or the momentum. 93 00:05:27,279 --> 00:05:29,599 Speaker 1: The momentum is just the mass times the velocity. So 94 00:05:30,240 --> 00:05:34,520 Speaker 1: this raises two big questions. One is what is the 95 00:05:34,560 --> 00:05:37,560 Speaker 1: wave function? Is it supposed to be the real world? 96 00:05:38,080 --> 00:05:41,080 Speaker 1: Is it that somehow we're not measuring the real world 97 00:05:41,120 --> 00:05:43,600 Speaker 1: exactly when we do our measurements, but it really is 98 00:05:43,640 --> 00:05:46,240 Speaker 1: described by this weird thing called the wave function that 99 00:05:46,279 --> 00:05:49,360 Speaker 1: we don't have direct access to. Or is it just 100 00:05:49,600 --> 00:05:52,120 Speaker 1: part of the world, And there's other extra variables in 101 00:05:52,160 --> 00:05:55,640 Speaker 1: addition to the wave function, hidden variables we sometimes called them. 102 00:05:55,760 --> 00:05:58,000 Speaker 1: Or does the wave function have nothing to do with 103 00:05:58,120 --> 00:06:00,480 Speaker 1: the real world, That it's just a way of printdicting 104 00:06:00,520 --> 00:06:03,240 Speaker 1: the experimental outcomes, and the real world is something much 105 00:06:03,279 --> 00:06:05,719 Speaker 1: more definite than that. So all three of these options 106 00:06:05,760 --> 00:06:07,240 Speaker 1: are very much on the table. This is what I 107 00:06:07,279 --> 00:06:10,000 Speaker 1: call the reality problem, Like what is the real world? 108 00:06:10,120 --> 00:06:12,320 Speaker 1: Is that the wave function or something weirder, something else, 109 00:06:12,360 --> 00:06:15,159 Speaker 1: I should say, not necessarily weirder. The other problem with 110 00:06:15,240 --> 00:06:17,440 Speaker 1: that brief version of quantum mechanics I just gave you 111 00:06:17,960 --> 00:06:21,800 Speaker 1: is that it involves the word measure or observe. Right, 112 00:06:22,440 --> 00:06:26,440 Speaker 1: No other fundamental theory of physics uses those words at all. 113 00:06:26,560 --> 00:06:28,440 Speaker 1: They just assume you can measure whatever you want. But 114 00:06:28,480 --> 00:06:31,960 Speaker 1: in quantum mechanics it seems to be the case that 115 00:06:32,200 --> 00:06:37,120 Speaker 1: you need separate rules for describing systems when you're not 116 00:06:37,240 --> 00:06:40,520 Speaker 1: measuring them and describing them when you are measuring them. 117 00:06:40,640 --> 00:06:43,600 Speaker 1: And so this raises what we call the measurement problem. 118 00:06:43,640 --> 00:06:47,479 Speaker 1: Which is what's up with that? Which includes like, what 119 00:06:47,520 --> 00:06:49,719 Speaker 1: do you mean measure? Does that? You know what? What 120 00:06:49,760 --> 00:06:51,600 Speaker 1: does the definition of your measurement is? Doesn't need to 121 00:06:51,600 --> 00:06:53,720 Speaker 1: be a conscious creature? Could it be a robot or 122 00:06:53,720 --> 00:06:55,960 Speaker 1: a video camera? What if you just measure it badly? 123 00:06:56,040 --> 00:06:58,080 Speaker 1: Does the same thing happen? When does it happen? How 124 00:06:58,160 --> 00:07:00,720 Speaker 1: quickly does it happen? Why is there even a separate 125 00:07:00,760 --> 00:07:02,880 Speaker 1: set of rules. So a whole bunch of questions get 126 00:07:02,920 --> 00:07:06,000 Speaker 1: swept under the rug of the measurement problem in quantum mechanics. 127 00:07:06,279 --> 00:07:08,200 Speaker 1: And I think both these are big, really big problems. 128 00:07:08,200 --> 00:07:09,880 Speaker 1: If we want to think the quantum mechanics is the 129 00:07:10,040 --> 00:07:12,520 Speaker 1: right theory of how reality works, we need to know 130 00:07:12,600 --> 00:07:14,840 Speaker 1: what reality is, and we need to know why this 131 00:07:14,960 --> 00:07:17,320 Speaker 1: measurement process plays such a special role. And you make 132 00:07:17,320 --> 00:07:20,120 Speaker 1: a really interesting distinction there. You say, an electron, we 133 00:07:20,160 --> 00:07:22,800 Speaker 1: can observe these properties of it, or we can observe 134 00:07:22,840 --> 00:07:26,320 Speaker 1: these quantities, but it no longer has these properties that 135 00:07:26,360 --> 00:07:30,280 Speaker 1: its velocity's position are not like aspects of the electron. 136 00:07:30,320 --> 00:07:33,200 Speaker 1: You've like separated the electron from these things we can 137 00:07:33,400 --> 00:07:35,800 Speaker 1: learn about it. Yeah, and actually in doing that, I've 138 00:07:35,800 --> 00:07:40,160 Speaker 1: already cheated I've already sort of slipped into my favorite 139 00:07:40,240 --> 00:07:43,400 Speaker 1: way of thinking about quantum mechanics because there are people 140 00:07:43,480 --> 00:07:46,200 Speaker 1: who would say that the wave function is just a 141 00:07:46,200 --> 00:07:50,320 Speaker 1: way to predict the outcomes of what you measure, and 142 00:07:50,360 --> 00:07:53,400 Speaker 1: there really is something called the position, something called the velocity. 143 00:07:53,400 --> 00:07:55,600 Speaker 1: We just don't know how to predict what it's going 144 00:07:55,640 --> 00:07:58,360 Speaker 1: to be until we measure them. Whereas someone like myself 145 00:07:58,520 --> 00:08:01,400 Speaker 1: is a way function realist, my point of view is, look, 146 00:08:01,920 --> 00:08:07,320 Speaker 1: every version of quantum mechanics uses something like the wave function, Okay, 147 00:08:07,360 --> 00:08:10,080 Speaker 1: either way function or something completely equivalent to it. So 148 00:08:10,120 --> 00:08:14,120 Speaker 1: the simplest, most minimal version of quantum mechanics would only 149 00:08:14,520 --> 00:08:17,119 Speaker 1: use the wave function, right, Like, not as a route 150 00:08:17,120 --> 00:08:19,320 Speaker 1: to get to somewhere else or as part of the story, 151 00:08:19,360 --> 00:08:21,640 Speaker 1: but the whole story. Like why not imagine that the 152 00:08:21,640 --> 00:08:25,080 Speaker 1: wave function is actually what the world is. And when 153 00:08:25,160 --> 00:08:29,040 Speaker 1: that's true in that perspective, it becomes the case that 154 00:08:29,200 --> 00:08:32,760 Speaker 1: things like positions and velocities are not features of the 155 00:08:32,800 --> 00:08:37,040 Speaker 1: wave function, there possible experimental outcomes. And that's the biggest 156 00:08:37,120 --> 00:08:39,800 Speaker 1: conceptual hurdle here, because we all look at things and 157 00:08:39,840 --> 00:08:42,160 Speaker 1: we think they have positions, and we think they have velocities, 158 00:08:42,240 --> 00:08:45,360 Speaker 1: and if you're this wave function realist kind of version 159 00:08:45,360 --> 00:08:48,320 Speaker 1: of quantum mechanics, no longer is that true. So let's 160 00:08:48,360 --> 00:08:51,760 Speaker 1: move from positions velocities to something that's more binary, because 161 00:08:51,760 --> 00:08:54,160 Speaker 1: I think it's easier to think about Let's talk about 162 00:08:54,160 --> 00:08:56,640 Speaker 1: the electron and it's spin like, maybe it's spin up 163 00:08:56,679 --> 00:08:59,600 Speaker 1: or maybe it's spin down. So then what's the problem 164 00:08:59,720 --> 00:09:03,600 Speaker 1: with the orthodox the Copenhagen approach to quantum mechanics where 165 00:09:03,640 --> 00:09:05,680 Speaker 1: you say, I have a way function that describes the 166 00:09:05,679 --> 00:09:08,280 Speaker 1: probabilities of this electron being spin up or spin down, 167 00:09:08,679 --> 00:09:10,440 Speaker 1: and then when I make a measurement, when I poke 168 00:09:10,480 --> 00:09:13,640 Speaker 1: it with my finger, the universe rolls the diet and says, okay, 169 00:09:13,640 --> 00:09:15,760 Speaker 1: well you had a sixty chance of being spin up, 170 00:09:15,760 --> 00:09:17,199 Speaker 1: so you've got to spin up or nope, you've got 171 00:09:17,160 --> 00:09:19,920 Speaker 1: to spin down this time. What's the problem with taking 172 00:09:19,920 --> 00:09:22,120 Speaker 1: that approach? Well, you already said when I measure the 173 00:09:22,160 --> 00:09:24,439 Speaker 1: spin or when I poke it, I want something more 174 00:09:24,480 --> 00:09:27,360 Speaker 1: definite than that. If what I'm talking about here is 175 00:09:27,400 --> 00:09:31,200 Speaker 1: a really fundamental theory of physics, I should not be 176 00:09:31,320 --> 00:09:35,400 Speaker 1: able to rely on weasel words about poking and measuring, 177 00:09:35,679 --> 00:09:38,960 Speaker 1: or at least I should give a super duper rigorous 178 00:09:38,960 --> 00:09:43,760 Speaker 1: definition of what exactly that is and the originators of 179 00:09:43,840 --> 00:09:48,000 Speaker 1: quantum mechanics and it's conventional textbook form. The Copenhagen interpretation 180 00:09:48,320 --> 00:09:52,760 Speaker 1: resolutely refused to do this. The strategy they adopted was 181 00:09:52,800 --> 00:09:56,600 Speaker 1: to say that observers like you and me just aren't 182 00:09:56,600 --> 00:09:59,599 Speaker 1: subject to the rules of quantum mechanics. We are classical. 183 00:09:59,640 --> 00:10:02,280 Speaker 1: We are as if quantum mechanics never happened. Okay, you 184 00:10:02,360 --> 00:10:05,600 Speaker 1: and I, and this is perfectly compatible with our everyday 185 00:10:05,600 --> 00:10:08,559 Speaker 1: experience of the world. But then they say, but individual 186 00:10:08,679 --> 00:10:11,680 Speaker 1: particles or atoms obey the rules of quantum mechanics. And 187 00:10:11,720 --> 00:10:14,400 Speaker 1: you come along and say, well, but I'm made of atoms. 188 00:10:15,000 --> 00:10:17,319 Speaker 1: How could it be with my atoms obey quantum mechanics 189 00:10:17,320 --> 00:10:20,680 Speaker 1: and I obey classical mechanics. And so the real problem 190 00:10:20,720 --> 00:10:24,199 Speaker 1: with this sort of conventional textbook version of quantum mechanics 191 00:10:24,600 --> 00:10:27,200 Speaker 1: is that it's just not a deaf and physical theory. 192 00:10:27,400 --> 00:10:30,000 Speaker 1: Is it's not even something you can compare to other things. 193 00:10:30,240 --> 00:10:33,480 Speaker 1: It assumes that we're in a regime where this division 194 00:10:33,520 --> 00:10:37,160 Speaker 1: between quantum and classical is good enough to get us by. 195 00:10:37,240 --> 00:10:39,120 Speaker 1: And I think that when it comes to fundamental physics, 196 00:10:39,200 --> 00:10:41,360 Speaker 1: we need to do better than that. And for example, 197 00:10:41,600 --> 00:10:43,880 Speaker 1: if I'm poking something with my finger, you could say, well, 198 00:10:43,920 --> 00:10:46,800 Speaker 1: I'm classical, so it should collapse the wave function. But 199 00:10:46,840 --> 00:10:48,920 Speaker 1: then you can imagine the very very tip of my 200 00:10:49,000 --> 00:10:52,160 Speaker 1: finger is just a quantum particle, and that shouldn't collapse 201 00:10:52,160 --> 00:10:54,400 Speaker 1: the wave function. And so at what point is that 202 00:10:54,440 --> 00:10:57,959 Speaker 1: wave function collapsing happening? Is it two layers of quantum particles? 203 00:10:58,040 --> 00:11:00,120 Speaker 1: Is it ten? Isn't it gets to my neuron? As 204 00:11:00,160 --> 00:11:02,600 Speaker 1: you said, there's no good answer to that. Yeah, exactly right. 205 00:11:02,640 --> 00:11:04,360 Speaker 1: And you know what if you missed the particle, or 206 00:11:04,360 --> 00:11:06,320 Speaker 1: what if you like graves it. You know, all of 207 00:11:06,360 --> 00:11:09,040 Speaker 1: these questions you can ask are just you're told you're 208 00:11:09,040 --> 00:11:11,280 Speaker 1: not allowed to ask them in the conventional way of 209 00:11:11,280 --> 00:11:13,280 Speaker 1: thinking about quantum mechanics. Well, I mean I am a 210 00:11:13,320 --> 00:11:15,680 Speaker 1: professional particle physicist. I think I know how to poke 211 00:11:15,720 --> 00:11:18,000 Speaker 1: a particle when I want to, but I won't take 212 00:11:18,000 --> 00:11:21,640 Speaker 1: on ridge at your example. Um, So then what is 213 00:11:21,760 --> 00:11:24,839 Speaker 1: the solution offered by the many world interpretation? How does 214 00:11:24,840 --> 00:11:27,680 Speaker 1: that solve this problem? So many worlds came about from 215 00:11:27,679 --> 00:11:30,800 Speaker 1: a graduate student, Hugh Everett. So this is always what 216 00:11:30,840 --> 00:11:33,680 Speaker 1: you should aspire to do as a graduate student overthrow 217 00:11:33,760 --> 00:11:38,280 Speaker 1: the fundamental nature of reality. And interestingly, Everett was working 218 00:11:38,280 --> 00:11:41,520 Speaker 1: with John Wheeler, who was a very famous physicist who 219 00:11:41,559 --> 00:11:44,680 Speaker 1: was an acolyte of Neil's Bore, the grandfather of the 220 00:11:44,720 --> 00:11:49,199 Speaker 1: Copenhagen interpretation, and Wheeler gave him the following thesis problem 221 00:11:49,400 --> 00:11:54,160 Speaker 1: quantized gravity. This turns out to be very hard quantizing gravity. 222 00:11:54,240 --> 00:11:56,360 Speaker 1: We use the word quantized as a verb to turn 223 00:11:56,400 --> 00:12:00,160 Speaker 1: an existing classical theory into a quantum theory. And what 224 00:12:00,280 --> 00:12:04,360 Speaker 1: happens with gravity gravity we understand classically pretty well in 225 00:12:04,360 --> 00:12:07,400 Speaker 1: a theory called general relativity given to us by Einstein. 226 00:12:07,520 --> 00:12:09,880 Speaker 1: And the point is that the reason why it becomes 227 00:12:09,880 --> 00:12:13,679 Speaker 1: a problem for quantum mechanics is both technical, like when 228 00:12:13,679 --> 00:12:16,280 Speaker 1: you try to quantize gravity, run into infinities and other 229 00:12:16,320 --> 00:12:20,280 Speaker 1: things you don't like, But there's also conceptual problems. Everett said, Look, 230 00:12:20,840 --> 00:12:25,600 Speaker 1: in the Copenhagen view of quantum mechanics, it's crucial that 231 00:12:25,679 --> 00:12:28,600 Speaker 1: I have the quantum system I'm looking at and the 232 00:12:28,679 --> 00:12:33,280 Speaker 1: outside observer poking it. But if I'm quantizing the universe, 233 00:12:34,640 --> 00:12:37,480 Speaker 1: then I don't have an outside observer. That I have 234 00:12:37,559 --> 00:12:40,000 Speaker 1: the whole universe, and I should include all the possible 235 00:12:40,000 --> 00:12:42,920 Speaker 1: observers in there. So he started thinking about that. He said, 236 00:12:42,920 --> 00:12:46,360 Speaker 1: what happens if we just include the quantum state of 237 00:12:46,400 --> 00:12:48,960 Speaker 1: observers as well. I don't know why it took twenty 238 00:12:49,040 --> 00:12:50,559 Speaker 1: years for people to guess this, but he has a 239 00:12:50,640 --> 00:12:53,520 Speaker 1: very natural place to go. What happens if you let 240 00:12:53,520 --> 00:12:56,360 Speaker 1: the observer be part of the way function rather than 241 00:12:56,360 --> 00:12:59,880 Speaker 1: treating them differently. So consider that electron that we have 242 00:13:00,000 --> 00:13:02,640 Speaker 1: at where you could get either spin up or spin down, right, 243 00:13:02,840 --> 00:13:06,079 Speaker 1: and consider the following possibility. Since you're a particle physicist, 244 00:13:06,080 --> 00:13:09,840 Speaker 1: we're going to assume that you're pretty good and measuring 245 00:13:10,000 --> 00:13:12,120 Speaker 1: the spin of the electron. And what that means is 246 00:13:12,720 --> 00:13:16,839 Speaker 1: if the electron was absolutely spin up, we're going to 247 00:13:16,960 --> 00:13:19,000 Speaker 1: grant you that you would always measure it to be 248 00:13:19,040 --> 00:13:21,840 Speaker 1: spin up. So that means that you, as a physical system, 249 00:13:21,880 --> 00:13:25,080 Speaker 1: would evolve into a state where your brain says, I 250 00:13:25,160 --> 00:13:27,960 Speaker 1: measured its spin up, and likewise for spin down, if 251 00:13:28,000 --> 00:13:30,920 Speaker 1: the electron was a spin down, we're going to grant 252 00:13:30,960 --> 00:13:33,319 Speaker 1: you that you would say, yep, I measured that to 253 00:13:33,360 --> 00:13:35,760 Speaker 1: be spin down. Now you're saying that I can do 254 00:13:35,840 --> 00:13:38,320 Speaker 1: something which is unfamiliar to me, which is I can 255 00:13:38,360 --> 00:13:41,400 Speaker 1: be in a quantum state, I can have a superposition 256 00:13:41,800 --> 00:13:44,480 Speaker 1: of having measured one thing and the other thing. Well, 257 00:13:44,520 --> 00:13:46,760 Speaker 1: I haven't said that yet. I'm about to say that, 258 00:13:47,160 --> 00:13:49,840 Speaker 1: but it was so far saying is if the electron 259 00:13:49,880 --> 00:13:52,680 Speaker 1: was a percent spin up and you measured its spin, 260 00:13:52,840 --> 00:13:54,240 Speaker 1: you would find it to be spin up. You're not 261 00:13:54,240 --> 00:13:56,600 Speaker 1: in a superposition of anything, right, And likewise, if it's 262 00:13:56,600 --> 00:13:58,640 Speaker 1: a hundred percent spin down, you would be spin down. 263 00:13:58,720 --> 00:14:01,840 Speaker 1: Let's assume that. Let's assume we want to be getting 264 00:14:01,880 --> 00:14:06,000 Speaker 1: the right answer when the answer is definite and known already. Okay, 265 00:14:06,040 --> 00:14:08,240 Speaker 1: I mean that's the least that we can ask. I'm 266 00:14:08,280 --> 00:14:11,360 Speaker 1: a reliable measuring device so far, yeah, exactly. But then 267 00:14:11,520 --> 00:14:15,040 Speaker 1: if you are a quantum system, that's all you need 268 00:14:15,080 --> 00:14:19,040 Speaker 1: to know because quantum mechanics, in the technical jargon, it's linear. 269 00:14:19,560 --> 00:14:22,720 Speaker 1: So what that means is if the electron is definitely 270 00:14:22,760 --> 00:14:24,600 Speaker 1: spin up, you always get spin up. If it's definitely 271 00:14:24,640 --> 00:14:27,400 Speaker 1: spin down, you always get spin down. Then when it's 272 00:14:27,480 --> 00:14:31,440 Speaker 1: in a combination, when it's in a superposition of both, 273 00:14:31,760 --> 00:14:34,320 Speaker 1: we know what you're going to evolve into the wave 274 00:14:34,400 --> 00:14:38,720 Speaker 1: function of you, plus the electron will evolve into part 275 00:14:38,720 --> 00:14:41,240 Speaker 1: of it where the electrons spin up and you measured 276 00:14:41,280 --> 00:14:44,000 Speaker 1: its spin up, and a part where the electron is 277 00:14:44,000 --> 00:14:46,840 Speaker 1: spin down and you measured it'spin down. So this is 278 00:14:47,040 --> 00:14:50,760 Speaker 1: taking advantage of the quantum mechanical feature of entanglement that 279 00:14:50,880 --> 00:14:53,880 Speaker 1: you don't separately say, well, here's the wave function for you, 280 00:14:54,000 --> 00:14:56,920 Speaker 1: here's the way function for the electron, etcetera. There's only 281 00:14:56,960 --> 00:14:59,200 Speaker 1: one way function for everything. And in fact, ever it 282 00:14:59,320 --> 00:15:02,480 Speaker 1: referred to his own theory, not as many worlds, but 283 00:15:02,560 --> 00:15:06,280 Speaker 1: as the theory of the universal wave function. And so 284 00:15:06,600 --> 00:15:09,000 Speaker 1: everyone agrees with this. By the way, everyone agrees that 285 00:15:09,040 --> 00:15:11,080 Speaker 1: if you treat you as a quantum system and you 286 00:15:11,120 --> 00:15:15,120 Speaker 1: measure that spin, you evolve into an entangled superposition, part 287 00:15:15,160 --> 00:15:17,280 Speaker 1: of which says the electron has spin up and that's 288 00:15:17,280 --> 00:15:20,400 Speaker 1: what you saw likewise for spin down. Everett's only move 289 00:15:21,200 --> 00:15:25,800 Speaker 1: is to say, and that's okay, there's nothing wrong with that. 290 00:15:26,240 --> 00:15:30,320 Speaker 1: So the immediate visceral responses that can't be right, because 291 00:15:30,320 --> 00:15:33,400 Speaker 1: I've measured electrons before and I've never felt like I 292 00:15:33,480 --> 00:15:36,880 Speaker 1: was in a superposition. And Everett says, that's fine, because 293 00:15:36,880 --> 00:15:41,840 Speaker 1: you've misidentified yourself in the wave function. You think that 294 00:15:41,880 --> 00:15:44,760 Speaker 1: you're this combination of having measured spin up and having 295 00:15:44,760 --> 00:15:47,280 Speaker 1: measured spin down. But that's not right because you're entangled 296 00:15:47,320 --> 00:15:50,120 Speaker 1: with the electron. There's two parts of the wave function, 297 00:15:50,200 --> 00:15:52,920 Speaker 1: one of which is very consistent. The electron has spin 298 00:15:53,040 --> 00:15:54,600 Speaker 1: up and you measured to be spin up. The other 299 00:15:54,640 --> 00:15:56,760 Speaker 1: part is also very consistent, the electron has been down 300 00:15:56,800 --> 00:15:59,640 Speaker 1: and you measure to be spin down. And Everett points 301 00:15:59,680 --> 00:16:03,040 Speaker 1: out that in the future evolution of the wave function, 302 00:16:03,120 --> 00:16:06,560 Speaker 1: these two parts of the wave function will never interfere 303 00:16:06,640 --> 00:16:09,720 Speaker 1: or interact with each other. Ever, again, they have no 304 00:16:09,840 --> 00:16:12,560 Speaker 1: influence on what each other are doing. If I poke, 305 00:16:12,680 --> 00:16:15,480 Speaker 1: as you say, if I change or alter what's going 306 00:16:15,560 --> 00:16:17,880 Speaker 1: on in part of the wave function where the spin 307 00:16:18,000 --> 00:16:20,400 Speaker 1: was up, let's say, the part where spin is down 308 00:16:20,600 --> 00:16:23,400 Speaker 1: doesn't know it is not influenced by that. So it 309 00:16:23,520 --> 00:16:25,960 Speaker 1: is as if these two parts of the wave function 310 00:16:26,000 --> 00:16:29,240 Speaker 1: are now describing separate worlds. And the crucial thing to 311 00:16:29,320 --> 00:16:31,320 Speaker 1: keep in mind, whether or not do you like many worlds, 312 00:16:31,720 --> 00:16:34,600 Speaker 1: is that ever didn't put in a bunch of worlds. 313 00:16:34,640 --> 00:16:37,040 Speaker 1: All he said was that we're going to take way 314 00:16:37,040 --> 00:16:40,760 Speaker 1: functions seriously and include observers in them. The world's come 315 00:16:40,800 --> 00:16:43,840 Speaker 1: along for free. Once you believe that the electron can 316 00:16:43,880 --> 00:16:46,040 Speaker 1: be in a superposition of spin up and spin down. 317 00:16:46,480 --> 00:16:48,680 Speaker 1: You've got to be able to believe that observers can 318 00:16:48,720 --> 00:16:51,280 Speaker 1: be in the superposition of I measured spin up and 319 00:16:51,320 --> 00:16:53,800 Speaker 1: I measured spin down. I see. So he avoids this 320 00:16:53,920 --> 00:16:58,160 Speaker 1: distinction between quantum observers which don't collapse the wave function, 321 00:16:58,240 --> 00:17:01,560 Speaker 1: and classical observers, which do collapse it by saying everything 322 00:17:01,600 --> 00:17:04,359 Speaker 1: is quantum, nothing ever collapses the way function, that the 323 00:17:04,400 --> 00:17:07,480 Speaker 1: wave function is the universe that just keeps going, but 324 00:17:07,640 --> 00:17:10,520 Speaker 1: you experience one outcome rather than the other because you 325 00:17:10,560 --> 00:17:13,439 Speaker 1: are no longer every part of the way function. You 326 00:17:13,520 --> 00:17:16,080 Speaker 1: are part of the way function that experienced spin up, 327 00:17:16,160 --> 00:17:17,800 Speaker 1: or you are part of the way function that experience 328 00:17:18,000 --> 00:17:21,480 Speaker 1: spin down. Is that a fair summary? That is precisely right. Actually, 329 00:17:21,480 --> 00:17:24,760 Speaker 1: that's an excellent summary. So I think that if we're 330 00:17:24,760 --> 00:17:30,120 Speaker 1: being fair, we should all agree on the pros and cons. 331 00:17:30,240 --> 00:17:33,600 Speaker 1: At this point of view. The pro is it's just 332 00:17:33,720 --> 00:17:36,880 Speaker 1: quantum mechanics already taken at face value. There's a wave 333 00:17:36,920 --> 00:17:39,879 Speaker 1: function for everything. Like you said, everything is quantum, and 334 00:17:39,920 --> 00:17:43,440 Speaker 1: it obeys one single equation, the Schrodinger equation or some 335 00:17:43,560 --> 00:17:47,080 Speaker 1: equivalent version thereof. You don't need new variables, you don't 336 00:17:47,119 --> 00:17:50,119 Speaker 1: need new dynamical laws. You don't need any extra stuff. 337 00:17:50,560 --> 00:17:54,120 Speaker 1: So at the level of writing down the theory, it's 338 00:17:54,160 --> 00:17:57,479 Speaker 1: the simplest possible version of quantum mechanics, but of course 339 00:17:57,640 --> 00:18:01,159 Speaker 1: the cons are at the level of coming to terms 340 00:18:01,200 --> 00:18:05,800 Speaker 1: with it, it's the biggest possible imaginative leap, right because 341 00:18:05,840 --> 00:18:08,400 Speaker 1: we're saying that every single time we measure the spin 342 00:18:08,400 --> 00:18:11,199 Speaker 1: of an electron, a new world is created. And you know, 343 00:18:11,400 --> 00:18:15,639 Speaker 1: you gotta give the skeptics a fair nod to say, yeah, like, 344 00:18:15,720 --> 00:18:18,719 Speaker 1: that's a lot to buy, and we proponents of it 345 00:18:18,760 --> 00:18:20,920 Speaker 1: will say, but you already bought it when you bought 346 00:18:20,960 --> 00:18:24,239 Speaker 1: quantum mechanics, like you Nigally, We're already there. We're just 347 00:18:24,400 --> 00:18:26,040 Speaker 1: putting your face in it. Well, what do you think 348 00:18:26,080 --> 00:18:28,679 Speaker 1: that moment was like for Everett when he you know, 349 00:18:28,720 --> 00:18:31,840 Speaker 1: followed this line of thinking and then had this perhaps 350 00:18:32,000 --> 00:18:35,159 Speaker 1: moment of understanding where he realizes, hold on a second, 351 00:18:35,240 --> 00:18:37,880 Speaker 1: maybe the universe has all these different layers and he's 352 00:18:37,960 --> 00:18:40,679 Speaker 1: much vaster and much more complex than we imagine. What 353 00:18:40,760 --> 00:18:42,600 Speaker 1: was that moment? Like, did he ever write about that, 354 00:18:42,640 --> 00:18:45,800 Speaker 1: you know, moment of epiphany or or realization or understanding? 355 00:18:45,960 --> 00:18:49,080 Speaker 1: As far as I know, he didn't directly write about that, no, 356 00:18:49,359 --> 00:18:52,280 Speaker 1: but he wrote a lot. In fact, you know, Wheeler, 357 00:18:52,440 --> 00:18:56,479 Speaker 1: who is his advisor, was trying to pretend Wheeler himself 358 00:18:56,480 --> 00:18:59,480 Speaker 1: was in a superposition of effort has done something radical 359 00:18:59,480 --> 00:19:02,320 Speaker 1: and interesting, and Everett is just going along with the 360 00:19:02,359 --> 00:19:06,959 Speaker 1: conventional Copenhagen interpretation. Because Wheeler didn't want to annoy his 361 00:19:07,000 --> 00:19:10,520 Speaker 1: own mentor Neil's bore, so he had Everett both visit 362 00:19:10,680 --> 00:19:14,680 Speaker 1: Copenhagen literally, and you know bores people visit Princeton where 363 00:19:14,680 --> 00:19:17,520 Speaker 1: they were living themselves. And letters went back and forth. 364 00:19:17,560 --> 00:19:20,280 Speaker 1: So there is a lot of writing about this. And 365 00:19:20,320 --> 00:19:22,560 Speaker 1: the one thing I will say is that you know, again, 366 00:19:22,680 --> 00:19:26,280 Speaker 1: as as working physicists, both of us, some physicists are 367 00:19:26,359 --> 00:19:28,479 Speaker 1: just lucky. Sometimes right you're in the right place at 368 00:19:28,480 --> 00:19:30,960 Speaker 1: the right time, you get either the right experimental data, 369 00:19:31,080 --> 00:19:33,119 Speaker 1: you get the right idea, and and good for you, 370 00:19:33,160 --> 00:19:37,760 Speaker 1: and you get credit for that, but we do inevitably 371 00:19:38,760 --> 00:19:42,040 Speaker 1: separate that out from how good you are, how smart 372 00:19:42,080 --> 00:19:43,760 Speaker 1: you are, how brilliant you are. Right like, I mean, 373 00:19:43,800 --> 00:19:46,359 Speaker 1: there's brilliant people who just never were in the right 374 00:19:46,400 --> 00:19:48,160 Speaker 1: place at the right time, and there's some people got lucky. 375 00:19:48,160 --> 00:19:50,359 Speaker 1: And if you didn't know any better, which I didn't 376 00:19:50,359 --> 00:19:53,800 Speaker 1: when I first started thinking about this. H Everett would 377 00:19:53,800 --> 00:19:56,359 Speaker 1: be the classic example of someone who got lucky, right, 378 00:19:56,400 --> 00:19:58,080 Speaker 1: someone who's just in the right place at the right time. 379 00:19:58,080 --> 00:20:00,640 Speaker 1: You only at one idea. He left physics to graduate 380 00:20:00,640 --> 00:20:03,280 Speaker 1: school and moved on to other things. But you read 381 00:20:03,440 --> 00:20:05,960 Speaker 1: what he wrote about this stuff and you realize, oh, nope, 382 00:20:06,000 --> 00:20:10,560 Speaker 1: Actually he was brilliant. He completely understood what he was doing. 383 00:20:10,560 --> 00:20:12,520 Speaker 1: And this is what I mean by being brilliant, because 384 00:20:12,800 --> 00:20:15,679 Speaker 1: very often, like someone will have an idea in theoretical physics, 385 00:20:15,720 --> 00:20:19,960 Speaker 1: and someone else, super duper smart, will understand and appreciate 386 00:20:20,000 --> 00:20:22,520 Speaker 1: the implications of that idea and spell it all out. 387 00:20:23,000 --> 00:20:26,639 Speaker 1: And Ever did both. He really appreciated exactly what he 388 00:20:26,720 --> 00:20:29,320 Speaker 1: was saying, and in these letters going back and forth 389 00:20:29,440 --> 00:20:32,840 Speaker 1: to the giants of quantum mechanics back in Europe, Everett 390 00:20:32,880 --> 00:20:35,000 Speaker 1: more than held his own and in fact, he kind 391 00:20:35,000 --> 00:20:38,800 Speaker 1: of ran rings around him. So I don't know how 392 00:20:38,920 --> 00:20:40,840 Speaker 1: he felt when he first came up with the idea, 393 00:20:41,000 --> 00:20:44,000 Speaker 1: but I do give him credit for really thinking through 394 00:20:44,200 --> 00:20:47,000 Speaker 1: the implications of that idea. Wonderful. Well, I want to 395 00:20:47,000 --> 00:20:49,600 Speaker 1: talk more about the implications of many worlds and what 396 00:20:49,640 --> 00:21:04,919 Speaker 1: it means. But first, let's take a quick brick. All right, 397 00:21:04,960 --> 00:21:08,080 Speaker 1: we're back, and we're talking about the mind blowing idea 398 00:21:08,240 --> 00:21:10,720 Speaker 1: that maybe the universe is more than just what we see, 399 00:21:10,760 --> 00:21:13,360 Speaker 1: that there are many universes out there, part of this 400 00:21:13,680 --> 00:21:17,320 Speaker 1: quantum multiverse, where the universe is constantly splitting based on 401 00:21:17,359 --> 00:21:20,119 Speaker 1: the various possibilities of what could happen every time quantum 402 00:21:20,119 --> 00:21:23,719 Speaker 1: particles interact. And I think that the question that probably 403 00:21:23,760 --> 00:21:26,320 Speaker 1: most listeners have, it's probably a question you hear a lot, 404 00:21:26,480 --> 00:21:30,040 Speaker 1: is are these other worlds real? In what sense? Are 405 00:21:30,040 --> 00:21:33,160 Speaker 1: they real? Like? Is this a calculational tool to help 406 00:21:33,240 --> 00:21:36,840 Speaker 1: us understand our experience or are those worlds like in 407 00:21:36,920 --> 00:21:39,160 Speaker 1: some sense really out there? Yeah? I think they're real. 408 00:21:39,359 --> 00:21:43,040 Speaker 1: You know, this gets into deep philosophical questions about what 409 00:21:43,080 --> 00:21:45,960 Speaker 1: you mean by real right away. But you know, here's 410 00:21:46,000 --> 00:21:48,600 Speaker 1: how I think about it. If we have our best 411 00:21:48,720 --> 00:21:51,879 Speaker 1: explanation for what we observe, and that explanation takes the 412 00:21:51,920 --> 00:21:55,440 Speaker 1: form of some physical theory, and that physical theory predicts 413 00:21:55,440 --> 00:21:58,280 Speaker 1: the existence of stuff we don't observe, then we take 414 00:21:58,320 --> 00:22:02,440 Speaker 1: that stuff seriously until will we have a better physical theory? Right? So, 415 00:22:02,560 --> 00:22:05,120 Speaker 1: I mean, we often discover new things in the universe 416 00:22:05,160 --> 00:22:07,840 Speaker 1: by doing this, whether it's you know, new planets or 417 00:22:08,000 --> 00:22:12,280 Speaker 1: dark matter or whatever. And so if you take Everett's 418 00:22:12,359 --> 00:22:15,679 Speaker 1: version of quantum mechanics seriously, he solves the both the 419 00:22:15,720 --> 00:22:18,000 Speaker 1: reality problem and the measurement problem. The answer to the 420 00:22:18,040 --> 00:22:21,760 Speaker 1: reality problem is the wave function directly describes reality. The 421 00:22:21,800 --> 00:22:24,360 Speaker 1: answer to the measurement problem is when a quantum mechanical 422 00:22:24,359 --> 00:22:28,840 Speaker 1: system becomes entangled with big macroscopic things, that's what counts 423 00:22:28,880 --> 00:22:31,919 Speaker 1: as a measurement. And a prediction of his resolution to 424 00:22:31,960 --> 00:22:34,400 Speaker 1: these two problems is that these other worlds are real. 425 00:22:34,600 --> 00:22:38,920 Speaker 1: So if you want to get the benefit of his solutions, 426 00:22:39,320 --> 00:22:43,399 Speaker 1: but you find the other world's distasteful, that's okay. But 427 00:22:43,440 --> 00:22:45,840 Speaker 1: then you have to come up with a better theory, 428 00:22:45,960 --> 00:22:48,520 Speaker 1: and you have to come up with a disappearing world's 429 00:22:48,600 --> 00:22:50,959 Speaker 1: theory where you get rid of the other world. And 430 00:22:51,000 --> 00:22:52,520 Speaker 1: you can do that. People have done that. I mean, 431 00:22:52,600 --> 00:22:54,760 Speaker 1: I'm saying it in a sort of facetious voice, but 432 00:22:54,840 --> 00:22:57,320 Speaker 1: it is in fact an ongoing research program to do 433 00:22:57,400 --> 00:23:00,680 Speaker 1: exactly that. And the problem is there's a couple of problems. 434 00:23:00,680 --> 00:23:04,760 Speaker 1: One is it is inevitably more complicated, right, I mean, 435 00:23:04,800 --> 00:23:08,040 Speaker 1: you're adding something to a very clean, crisp formalism to 436 00:23:08,119 --> 00:23:10,480 Speaker 1: get rid of parts of it that you find distasteful. 437 00:23:10,640 --> 00:23:14,040 Speaker 1: And number two, it's hard to make it work. Everett 438 00:23:14,080 --> 00:23:17,159 Speaker 1: is very plug and play, and especially when you go 439 00:23:17,280 --> 00:23:20,760 Speaker 1: from a quantum mechanical theory of particles to a theory 440 00:23:20,760 --> 00:23:23,480 Speaker 1: of fields and then to a theory of quantum gravity, 441 00:23:23,520 --> 00:23:26,600 Speaker 1: which was initially his initial motivation. Every Ready in quantum 442 00:23:26,600 --> 00:23:29,840 Speaker 1: mechanics is perfectly happy doing any one of those, whereas 443 00:23:29,840 --> 00:23:32,879 Speaker 1: when you try to mess with it, adding more variables 444 00:23:32,960 --> 00:23:35,400 Speaker 1: or adding more rules or whatever, you kind of find 445 00:23:35,400 --> 00:23:37,119 Speaker 1: you have to mess with it in different ways for 446 00:23:37,200 --> 00:23:40,320 Speaker 1: every version of the theory, and who knows what will 447 00:23:40,440 --> 00:23:44,040 Speaker 1: end up being. So, both from a philosophical point of view, 448 00:23:44,160 --> 00:23:46,760 Speaker 1: and I think from a physicist point of view, the 449 00:23:46,880 --> 00:23:52,000 Speaker 1: simplicity and success of the Evert interpretation speaks to not 450 00:23:52,119 --> 00:23:54,440 Speaker 1: working so hard to get rid of the other worlds. 451 00:23:54,720 --> 00:23:57,320 Speaker 1: So I think that you're responding to sort of implied 452 00:23:57,640 --> 00:24:00,520 Speaker 1: criticism in my question, which is about the nature of 453 00:24:00,560 --> 00:24:02,760 Speaker 1: what he's real, which is totally reasonable. And you know, 454 00:24:02,800 --> 00:24:05,480 Speaker 1: I think that a lot of people argue that if 455 00:24:05,560 --> 00:24:08,720 Speaker 1: you can't measure it directly, if you can't interact with it, 456 00:24:08,960 --> 00:24:11,080 Speaker 1: then it's not real physically, that it's can only be 457 00:24:11,119 --> 00:24:14,800 Speaker 1: real philosophically. And I think that your response is probably 458 00:24:15,040 --> 00:24:17,520 Speaker 1: if it's required by your theory, and your theory is 459 00:24:17,560 --> 00:24:20,800 Speaker 1: the only one you have that describes what you can observe, 460 00:24:21,240 --> 00:24:24,359 Speaker 1: then what's required by your theory but not observed is 461 00:24:24,400 --> 00:24:27,800 Speaker 1: still real. Is that fair? Yeah? I think that's exactly right. 462 00:24:28,000 --> 00:24:32,680 Speaker 1: And honestly, if all you wanted to do was to say, 463 00:24:32,760 --> 00:24:34,880 Speaker 1: I believe everything that EVERT says, but I don't believe 464 00:24:34,880 --> 00:24:37,399 Speaker 1: the other worlds are real, you know, knock yourself out. 465 00:24:37,480 --> 00:24:39,199 Speaker 1: It's a free country, right, Like, I don't know what 466 00:24:39,359 --> 00:24:41,880 Speaker 1: you get from that. I think if you face up 467 00:24:42,040 --> 00:24:45,640 Speaker 1: to that perspective, you're going to have to change the physics. 468 00:24:45,760 --> 00:24:48,080 Speaker 1: You're gonna have to change the equations to literally get 469 00:24:48,160 --> 00:24:49,840 Speaker 1: rid of those other worlds, and you're going to get 470 00:24:49,880 --> 00:24:52,040 Speaker 1: in trouble doing that. But if it's just kind of 471 00:24:52,080 --> 00:24:54,800 Speaker 1: an attitude like I don't care about the other worlds 472 00:24:54,800 --> 00:24:57,840 Speaker 1: because I'm not in them, then that's fine. Whatever. I 473 00:24:57,880 --> 00:24:59,320 Speaker 1: do think. You know, one thing just to put on 474 00:24:59,320 --> 00:25:01,359 Speaker 1: the table that maybe we'll get back to you later, 475 00:25:01,480 --> 00:25:05,320 Speaker 1: is that it's not just philosophy, you know, I really 476 00:25:05,320 --> 00:25:08,120 Speaker 1: do think that one of the reasons why we still 477 00:25:08,160 --> 00:25:12,520 Speaker 1: struggle to understand quantum gravity, for example, as a field 478 00:25:12,640 --> 00:25:16,680 Speaker 1: of theoretical physics, is exactly because we had not struggled 479 00:25:16,720 --> 00:25:19,480 Speaker 1: hard enough to understand quantum mechanics. And I think that 480 00:25:19,640 --> 00:25:22,119 Speaker 1: rather than sort of putting the heads in the sand 481 00:25:22,160 --> 00:25:24,560 Speaker 1: and denying the existence of these other worlds, if you 482 00:25:24,640 --> 00:25:28,919 Speaker 1: do take the formalism seriously, it provides new angles of 483 00:25:28,960 --> 00:25:33,280 Speaker 1: fruitful approach to longstanding problems in physics. So you know, 484 00:25:33,520 --> 00:25:37,000 Speaker 1: it's a reason to not give in to your first 485 00:25:37,040 --> 00:25:39,520 Speaker 1: impulse to be worried about all those other worlds. Well, 486 00:25:39,560 --> 00:25:41,760 Speaker 1: we were chatting with Carlo Rovelli a few weeks ago, 487 00:25:41,800 --> 00:25:44,680 Speaker 1: and he said that every interpretation of quantum mechanics has 488 00:25:44,720 --> 00:25:46,840 Speaker 1: a cost. And I think that a lot of people 489 00:25:46,880 --> 00:25:49,639 Speaker 1: would see, you know, these infinite other universes is maybe 490 00:25:49,640 --> 00:25:52,880 Speaker 1: like a cost of the many worlds interpretation. But to me, 491 00:25:52,960 --> 00:25:56,239 Speaker 1: it's exactly what I got into physics to do, is 492 00:25:56,359 --> 00:25:59,640 Speaker 1: to blow my mind and shake up my intuition about 493 00:25:59,640 --> 00:26:01,800 Speaker 1: the universe. I don't get into physics to have the 494 00:26:01,880 --> 00:26:04,200 Speaker 1: universe say, yeah, Daniel, what you thought about the universe? 495 00:26:04,320 --> 00:26:07,440 Speaker 1: That's basically it I'm hoping to peel back a layer 496 00:26:07,480 --> 00:26:10,240 Speaker 1: of reality and see something shocking, which at first is 497 00:26:10,320 --> 00:26:13,240 Speaker 1: difficult to accept because it's different from my intuition, but 498 00:26:13,320 --> 00:26:16,200 Speaker 1: that eventually, guided by mathematics, that can help some new 499 00:26:16,240 --> 00:26:18,879 Speaker 1: intuition be like, Wow, the universe is different from what 500 00:26:18,920 --> 00:26:21,280 Speaker 1: I imagined, and it works in this incredibly beautiful way. 501 00:26:21,400 --> 00:26:22,959 Speaker 1: So to me, it's not a cost, it's a it's 502 00:26:23,000 --> 00:26:26,320 Speaker 1: a feature, it's it's the goal of digging into quantum mechanics. 503 00:26:26,440 --> 00:26:28,760 Speaker 1: But my question is, you just said that we've been 504 00:26:28,800 --> 00:26:31,920 Speaker 1: hesitant to dig into the foundations of quantum mechanics. Why 505 00:26:31,920 --> 00:26:33,240 Speaker 1: do you think that is? Why do you think that 506 00:26:33,359 --> 00:26:37,360 Speaker 1: for such an important problem at the core of modern physics, 507 00:26:37,680 --> 00:26:40,160 Speaker 1: that progress has been so slow. Why haven't we taken 508 00:26:40,160 --> 00:26:42,520 Speaker 1: this question more seriously? I think it's a large number 509 00:26:42,520 --> 00:26:44,160 Speaker 1: of reasons. And this is a very very good question 510 00:26:44,200 --> 00:26:46,520 Speaker 1: also that I've talked about other people who talked about. 511 00:26:46,560 --> 00:26:50,120 Speaker 1: But it's sort of a more sociology, psychology, history question, right, 512 00:26:50,160 --> 00:26:53,600 Speaker 1: So it's a little on shakier ground here, So forgive me. 513 00:26:53,880 --> 00:26:55,719 Speaker 1: But you know, part of it is just that we 514 00:26:55,760 --> 00:26:58,960 Speaker 1: don't know how to answer it. That if there are 515 00:26:59,040 --> 00:27:03,480 Speaker 1: different compete eating versions of quantum mechanics that are well 516 00:27:03,480 --> 00:27:06,920 Speaker 1: defined physical theories. So you know, pilot wave theories and 517 00:27:07,200 --> 00:27:10,359 Speaker 1: I guess Carlo's relational quantum mechanics, etcetera. There are various 518 00:27:10,359 --> 00:27:13,600 Speaker 1: spontaneous collapse models on the market, and these are real 519 00:27:13,640 --> 00:27:16,399 Speaker 1: physical theories. The problem with Copenhagen this is not a 520 00:27:16,400 --> 00:27:19,399 Speaker 1: real physical theory. There's it just doesn't answer certain questions 521 00:27:19,400 --> 00:27:22,439 Speaker 1: about what actually happens. But once you like put on 522 00:27:22,480 --> 00:27:24,920 Speaker 1: your big boy pants and actually make a theory, then 523 00:27:24,960 --> 00:27:26,960 Speaker 1: you can make predictions with that theory and you can 524 00:27:26,960 --> 00:27:29,359 Speaker 1: try to experimentally test them. So I think that for 525 00:27:29,400 --> 00:27:31,800 Speaker 1: a long time it was just thought to be not 526 00:27:31,960 --> 00:27:34,920 Speaker 1: very fruitful to think about these ideas because we didn't 527 00:27:34,920 --> 00:27:37,480 Speaker 1: know how to get any experimental data about them. And 528 00:27:37,520 --> 00:27:40,000 Speaker 1: the other aspect is, you know, we had other things 529 00:27:40,000 --> 00:27:44,920 Speaker 1: going on. Businesses are very good at, you know, pushing 530 00:27:44,960 --> 00:27:48,000 Speaker 1: forward in directions they can make progress on. So we're 531 00:27:48,040 --> 00:27:51,400 Speaker 1: talking about the thirties, forties, fifties, right, Like, there were 532 00:27:51,440 --> 00:27:54,440 Speaker 1: particles in nuclei to understand, there were bombs do bill, 533 00:27:54,520 --> 00:27:58,320 Speaker 1: there were superconductors to construct, and quantum field theories to invent, 534 00:27:58,400 --> 00:28:00,560 Speaker 1: and normally anything you know, it goes on and on, right, 535 00:28:00,680 --> 00:28:03,840 Speaker 1: So there's plenty of work to do that you could 536 00:28:03,840 --> 00:28:07,919 Speaker 1: connect directly to experimental progress. So it was kind of 537 00:28:07,960 --> 00:28:11,720 Speaker 1: okay to push the foundations of quantum mechanics into the background. 538 00:28:11,920 --> 00:28:14,520 Speaker 1: That's sort of like saying, you know, my debit card 539 00:28:14,560 --> 00:28:16,520 Speaker 1: still works, so I don't need to check my balance 540 00:28:16,640 --> 00:28:19,600 Speaker 1: because probably everything is fine. That's right. I mean, that 541 00:28:19,680 --> 00:28:22,960 Speaker 1: is part of it. But also, you know, it's very 542 00:28:23,000 --> 00:28:25,680 Speaker 1: common advice when you have an enormous task in front 543 00:28:25,680 --> 00:28:27,360 Speaker 1: of you to first do the parts you can do, 544 00:28:28,320 --> 00:28:30,280 Speaker 1: rather than fretting about the parts you can't do. I 545 00:28:30,280 --> 00:28:33,840 Speaker 1: think that what has changed recently is number one, technology 546 00:28:33,920 --> 00:28:36,760 Speaker 1: has grown to the point where this idea of a 547 00:28:36,880 --> 00:28:39,880 Speaker 1: division between the classical world and the quantum world as 548 00:28:39,920 --> 00:28:42,960 Speaker 1: part of the fundamental description of reality has just become 549 00:28:42,960 --> 00:28:46,720 Speaker 1: increasingly untenable. Right, we can make much larger quantum systems 550 00:28:46,720 --> 00:28:49,800 Speaker 1: than we could back in the thirties that are in superpositions, 551 00:28:49,880 --> 00:28:52,680 Speaker 1: and we need to deal with the reality of entanglement 552 00:28:52,720 --> 00:28:55,280 Speaker 1: and so forth when we build quantum computers and things 553 00:28:55,320 --> 00:28:57,480 Speaker 1: like that. And the other is that this, you know, 554 00:28:57,800 --> 00:29:01,640 Speaker 1: enormous progress we made on under standing particle physics and 555 00:29:01,680 --> 00:29:05,960 Speaker 1: field theory has slowed in the past few decades, and 556 00:29:06,160 --> 00:29:09,240 Speaker 1: we're in this weird position where we built these amazingly 557 00:29:09,320 --> 00:29:12,000 Speaker 1: successful theories that fit all the data, but we know 558 00:29:12,040 --> 00:29:14,719 Speaker 1: they're not the final answer, right because gravity is not included, 559 00:29:14,720 --> 00:29:18,160 Speaker 1: because there are these naturalness problems, etcetera, etcetera. So one 560 00:29:18,200 --> 00:29:22,000 Speaker 1: strategy is just to stubbornly bull forward using the same 561 00:29:22,000 --> 00:29:24,440 Speaker 1: tools we've used before. But another strategy is to take 562 00:29:24,480 --> 00:29:27,200 Speaker 1: a step back and say, Okay, maybe we have to 563 00:29:27,240 --> 00:29:30,520 Speaker 1: think fundamentally in a different way about these questions to 564 00:29:30,560 --> 00:29:32,840 Speaker 1: make progress on them. And thinking about the foundations of 565 00:29:32,880 --> 00:29:35,720 Speaker 1: quantum mechanics plays into that strategy. So I guess it's 566 00:29:35,720 --> 00:29:37,600 Speaker 1: time to check the balance, huh. And we've got to 567 00:29:37,640 --> 00:29:39,800 Speaker 1: figure out what's happening down there in the vision we 568 00:29:39,880 --> 00:29:43,200 Speaker 1: keep getting turned down at the A T M. So yeah, 569 00:29:43,360 --> 00:29:45,760 Speaker 1: So then digging deep into like what it means this 570 00:29:45,960 --> 00:29:50,000 Speaker 1: many world's interpretation, The many world's interpretation says essentially that 571 00:29:50,120 --> 00:29:52,520 Speaker 1: none of these universes are special or different, that these 572 00:29:52,560 --> 00:29:55,160 Speaker 1: branching aspects of the way function, and it sort of 573 00:29:55,200 --> 00:29:58,000 Speaker 1: avoids the collapse question that way. But I can't get 574 00:29:58,040 --> 00:30:01,120 Speaker 1: around what you said earlier, which is that You're redefining 575 00:30:01,160 --> 00:30:04,640 Speaker 1: what it means to be me, right, because this universe 576 00:30:04,720 --> 00:30:07,480 Speaker 1: does feel special to me. I mean, I'm in this one. 577 00:30:07,880 --> 00:30:09,680 Speaker 1: It's the only one that I can interact with. Is 578 00:30:09,760 --> 00:30:11,560 Speaker 1: that sort of a naive objection to the many worlds 579 00:30:11,600 --> 00:30:14,320 Speaker 1: interpretation to say that this one must somehow be different? 580 00:30:14,480 --> 00:30:16,240 Speaker 1: Can you swap that away by just saying, well, the 581 00:30:16,240 --> 00:30:18,720 Speaker 1: other Daniels also think that they're the only one who 582 00:30:18,760 --> 00:30:21,600 Speaker 1: interacts with the universe. Pretty much, Yes, that is exactly 583 00:30:21,600 --> 00:30:25,080 Speaker 1: how I will slipe it away. The relevant anecdote here 584 00:30:25,160 --> 00:30:27,680 Speaker 1: that Everyboden's love this anecdote, so I will just share it. 585 00:30:27,680 --> 00:30:31,760 Speaker 1: It is actually about Ludwig Wittgenstein, the philosopher. So one 586 00:30:31,800 --> 00:30:34,720 Speaker 1: day one of his former students, Elizabeth Anscombe, was also 587 00:30:34,720 --> 00:30:37,840 Speaker 1: an extremely accomplished philosopher in her own right. She comes 588 00:30:37,840 --> 00:30:42,680 Speaker 1: across Wittgenstein, you know, standing in the yard at Cambridge 589 00:30:42,760 --> 00:30:46,560 Speaker 1: like looking at the sun and Vichenstein was famously a 590 00:30:46,560 --> 00:30:48,840 Speaker 1: little idiosyncratic. So she says, what is going on? And 591 00:30:48,840 --> 00:30:51,640 Speaker 1: he says, you know, why is it? The people were 592 00:30:51,680 --> 00:30:55,360 Speaker 1: reluctant to believe that the Earth rotated, rather than believing 593 00:30:55,360 --> 00:30:58,800 Speaker 1: that the sun moved around the Earth. And Anscomb says, well, 594 00:30:58,880 --> 00:31:02,200 Speaker 1: it just looks like the Sun moves around the earth, right, 595 00:31:02,520 --> 00:31:05,760 Speaker 1: And Vickenstein says, well, what would it have looked like 596 00:31:05,800 --> 00:31:09,880 Speaker 1: if the Earth rotated? So the point being that the 597 00:31:09,960 --> 00:31:12,720 Speaker 1: question you should be asking is not start with an 598 00:31:12,800 --> 00:31:17,080 Speaker 1: impression I see the Sun moving, and then construct a 599 00:31:17,200 --> 00:31:20,520 Speaker 1: theory that fits most closely with that immediate impression. The 600 00:31:20,600 --> 00:31:24,200 Speaker 1: strategy should be construct theories and then ask what observers 601 00:31:24,240 --> 00:31:27,160 Speaker 1: within those theories would observe, and if it's consistent with 602 00:31:27,200 --> 00:31:30,240 Speaker 1: what we observe, then it works. So the point is 603 00:31:30,280 --> 00:31:33,680 Speaker 1: that in many worlds, if there's you right here and 604 00:31:33,720 --> 00:31:36,120 Speaker 1: then you go and do some experiments at CERN and 605 00:31:36,160 --> 00:31:39,280 Speaker 1: you observe some particles, the prediction is there are now many, 606 00:31:39,280 --> 00:31:43,640 Speaker 1: many branches in which the specific pattern of particles and 607 00:31:43,680 --> 00:31:46,240 Speaker 1: a collision are different in every single branch, and the 608 00:31:46,400 --> 00:31:49,400 Speaker 1: version of you has now seen different things. And all 609 00:31:49,440 --> 00:31:52,960 Speaker 1: of those versions of you exist, and they've seen different things, 610 00:31:53,040 --> 00:31:55,000 Speaker 1: and they all think that they're special because they exist, 611 00:31:55,080 --> 00:31:57,440 Speaker 1: and the other ones are kind of dubious, but there's 612 00:31:57,440 --> 00:32:00,840 Speaker 1: no pointer that says this is the real, real one. Right. 613 00:32:00,920 --> 00:32:02,680 Speaker 1: There are other version of the quantum mechanics that try 614 00:32:02,720 --> 00:32:04,560 Speaker 1: to do that to try to say like, this is 615 00:32:04,600 --> 00:32:06,600 Speaker 1: the real branch and all the other ones are fake, 616 00:32:07,000 --> 00:32:10,760 Speaker 1: but it would still be true weave without that pointer 617 00:32:10,840 --> 00:32:13,200 Speaker 1: that says this one is real, that all of the 618 00:32:13,240 --> 00:32:16,360 Speaker 1: different versions of you on the different branches would feel 619 00:32:16,360 --> 00:32:22,240 Speaker 1: equally real. So the experimental empirical prediction of this theory 620 00:32:22,520 --> 00:32:25,200 Speaker 1: is exactly what we observe in the world, and I 621 00:32:25,200 --> 00:32:27,400 Speaker 1: think that should be the criterion for saying whether or 622 00:32:27,440 --> 00:32:30,120 Speaker 1: not it's an adequate explanation. It is interesting. It does 623 00:32:30,200 --> 00:32:32,920 Speaker 1: feel somehow like a bit of sleight of hand, like 624 00:32:32,960 --> 00:32:36,920 Speaker 1: you've taken the fuzziness of defining a classical object in 625 00:32:37,040 --> 00:32:40,440 Speaker 1: terms of quantum mechanical particles and you sort of transformed 626 00:32:40,480 --> 00:32:42,160 Speaker 1: it into like, well, I'm just going to redefine what 627 00:32:42,280 --> 00:32:44,960 Speaker 1: you are. You aren't who you thought you were. You're 628 00:32:44,960 --> 00:32:47,440 Speaker 1: just an element of this quantum wave function instead of 629 00:32:47,440 --> 00:32:50,680 Speaker 1: being like the holistic version of you. It feels to 630 00:32:50,680 --> 00:32:53,120 Speaker 1: me like, you know, when you make this step you 631 00:32:53,160 --> 00:32:55,480 Speaker 1: have this interpretation of quantum mechanics, you need to say, one, 632 00:32:55,760 --> 00:32:57,960 Speaker 1: what the wave function is. It's real, it's the universe, 633 00:32:58,280 --> 00:33:01,760 Speaker 1: But also something about like the correspondence between the quantum 634 00:33:01,800 --> 00:33:04,640 Speaker 1: state of the universe and your experience of it as 635 00:33:04,680 --> 00:33:07,960 Speaker 1: an observer. Yeah, no, that's under percent true. And so again, 636 00:33:08,000 --> 00:33:10,920 Speaker 1: if we're honest about the pros and cons, the physics 637 00:33:11,720 --> 00:33:14,080 Speaker 1: of ever writing quantum mechanics is as simple as it 638 00:33:14,120 --> 00:33:20,400 Speaker 1: can be. But the philosophy requires some new moves. And 639 00:33:20,720 --> 00:33:24,000 Speaker 1: I'm a you know, on board with people who say 640 00:33:24,400 --> 00:33:27,560 Speaker 1: I just can't accept those moves, like it's too much, 641 00:33:27,680 --> 00:33:29,760 Speaker 1: or at least say it this way. You know, if 642 00:33:29,800 --> 00:33:33,080 Speaker 1: we think we don't agree on what the correct version 643 00:33:33,080 --> 00:33:35,640 Speaker 1: of quantum mechanics is, and each of us has our 644 00:33:35,720 --> 00:33:38,440 Speaker 1: credence for saying, well, it's probably this, but unlikely that 645 00:33:38,800 --> 00:33:42,320 Speaker 1: it's perfectly fair for one of the ingredients that goes 646 00:33:42,360 --> 00:33:46,160 Speaker 1: into your choice of your personal credence to say, this 647 00:33:46,440 --> 00:33:49,720 Speaker 1: redefinition of who I am is just so dramatic that 648 00:33:49,720 --> 00:33:51,600 Speaker 1: I'm going to be skeptical of it. Maybe it's true, 649 00:33:51,800 --> 00:33:54,960 Speaker 1: but I'm gonna be a little dubious until I'm forced 650 00:33:55,000 --> 00:33:57,640 Speaker 1: into it. I think that's okay, And so I think this, 651 00:33:58,120 --> 00:34:03,000 Speaker 1: I'm completely acknowledged jing that the philosophical leaps that required 652 00:34:03,000 --> 00:34:07,000 Speaker 1: by many worlds are substantial, and in other versions they're 653 00:34:07,080 --> 00:34:09,680 Speaker 1: just not there. They don't bother me as much like 654 00:34:09,880 --> 00:34:11,880 Speaker 1: you know, I think that in physics we very often 655 00:34:12,400 --> 00:34:15,960 Speaker 1: come across better understandings of the world, including of ourselves. 656 00:34:16,080 --> 00:34:17,879 Speaker 1: Right like we might have thought back in the day 657 00:34:17,920 --> 00:34:20,840 Speaker 1: that we were a spirit animating a fleshy machine that 658 00:34:20,920 --> 00:34:23,680 Speaker 1: housed us, and now we think otherwise. I think that's okay, 659 00:34:23,760 --> 00:34:27,040 Speaker 1: as long as again, as long as the model that 660 00:34:27,080 --> 00:34:30,719 Speaker 1: we're building, once we understand it turns out to be 661 00:34:30,760 --> 00:34:33,800 Speaker 1: completely compatible with the world we observe, then I'm on board. 662 00:34:33,880 --> 00:34:37,200 Speaker 1: But then let's talk about how to use many worlds interpretation, 663 00:34:37,320 --> 00:34:39,640 Speaker 1: you know, as a functioning theory of quantum mechanics, because 664 00:34:39,760 --> 00:34:42,640 Speaker 1: something that is a bit slippery for me is that 665 00:34:42,680 --> 00:34:46,080 Speaker 1: in the Copenhagen interpretation, I know what a probability means. 666 00:34:46,360 --> 00:34:48,680 Speaker 1: I'm gonna do an experiment and I'm either going to 667 00:34:48,760 --> 00:34:50,360 Speaker 1: get spin up or spin down. I can look at 668 00:34:50,400 --> 00:34:52,799 Speaker 1: the way of function. I can say, well projected, you know, 669 00:34:52,880 --> 00:34:55,360 Speaker 1: against both of these possible outcomes, and those give me 670 00:34:55,400 --> 00:34:57,560 Speaker 1: the probabilities. They just use the Born rule, and whether 671 00:34:57,640 --> 00:35:00,279 Speaker 1: or not I'm a quantum or classical observer sort of 672 00:35:00,320 --> 00:35:03,640 Speaker 1: separate from that. But in many worlds, everything happens, and 673 00:35:03,680 --> 00:35:05,840 Speaker 1: so I can no longer say like, well, the probability 674 00:35:05,840 --> 00:35:09,400 Speaker 1: of this happening is six because they both happen in 675 00:35:09,480 --> 00:35:12,920 Speaker 1: some universe. How do you define probability if everything that 676 00:35:13,000 --> 00:35:15,200 Speaker 1: can happen is going to happen. Yeah, I think this 677 00:35:15,280 --> 00:35:17,440 Speaker 1: is the right question to ask. Like I said, there 678 00:35:17,480 --> 00:35:20,799 Speaker 1: are objections to many worlds that are not very good, 679 00:35:20,800 --> 00:35:25,400 Speaker 1: objections that are just misunderstandings. But there are also puzzles 680 00:35:25,560 --> 00:35:30,600 Speaker 1: or problems or things we got to address that arise 681 00:35:30,880 --> 00:35:33,600 Speaker 1: only in many worlds that weren't there before. So you know, 682 00:35:33,600 --> 00:35:36,440 Speaker 1: I gave Everett credit for solving the reality problem and 683 00:35:36,480 --> 00:35:39,840 Speaker 1: the measurement problem, an equal number of new problems arise. 684 00:35:40,040 --> 00:35:41,880 Speaker 1: And the reason why I think that's okay is because 685 00:35:41,920 --> 00:35:45,520 Speaker 1: I can see the solutions for these problems pretty clearly, 686 00:35:45,560 --> 00:35:48,120 Speaker 1: even if we don't have them completely spelled out. One 687 00:35:48,160 --> 00:35:50,080 Speaker 1: problem is just and maybe we'll get to this if 688 00:35:50,080 --> 00:35:52,719 Speaker 1: you want to, but it's the structure problem, which is 689 00:35:53,239 --> 00:35:55,879 Speaker 1: why does the world look so classical to us if 690 00:35:55,880 --> 00:35:58,400 Speaker 1: it's really this big quantum wave function. There's a lot 691 00:35:58,400 --> 00:36:00,560 Speaker 1: of details in that. And the other one, like you said, 692 00:36:00,600 --> 00:36:03,160 Speaker 1: is the probability problem. The benefit of effort is that 693 00:36:03,200 --> 00:36:06,799 Speaker 1: the underlying equations are lean and mean and austere, so 694 00:36:06,840 --> 00:36:10,200 Speaker 1: there's no room to say, okay, the wave function evolves, 695 00:36:10,719 --> 00:36:13,680 Speaker 1: and there's a rule that says the probability forgetting a 696 00:36:13,680 --> 00:36:15,880 Speaker 1: measurement is is given by the wave function square. Like, 697 00:36:15,880 --> 00:36:18,279 Speaker 1: there's no room to add extra rules like that. So 698 00:36:18,680 --> 00:36:22,239 Speaker 1: what you need to do is derive these rules, and 699 00:36:22,360 --> 00:36:24,880 Speaker 1: there are different strategies for doing it. And to be clear, 700 00:36:25,320 --> 00:36:27,640 Speaker 1: the fact that the probability is given by the wave 701 00:36:27,640 --> 00:36:31,640 Speaker 1: functions squared rather than just by the wave function or 702 00:36:31,640 --> 00:36:33,600 Speaker 1: by the wave function cube to the logarithm or whatever, 703 00:36:33,920 --> 00:36:36,360 Speaker 1: that's not the problem. Of course. It's going to be 704 00:36:36,400 --> 00:36:38,920 Speaker 1: given by the wave function squared because the set of 705 00:36:39,000 --> 00:36:42,279 Speaker 1: numbers which are given by the wave functions squared are 706 00:36:42,560 --> 00:36:45,680 Speaker 1: the unique set of numbers that are all non negative 707 00:36:45,719 --> 00:36:47,920 Speaker 1: and they add up to one and they're conserved over time. 708 00:36:48,400 --> 00:36:50,399 Speaker 1: That's what you want out of a probability. And it's 709 00:36:50,440 --> 00:36:53,319 Speaker 1: just Pythagoras theorem, right. The hypot new squared is the 710 00:36:53,360 --> 00:36:56,040 Speaker 1: other two sides squared. That's why you take all of 711 00:36:56,080 --> 00:36:58,439 Speaker 1: the different amplitudes in the wave functions squared to add 712 00:36:58,440 --> 00:37:00,799 Speaker 1: them up and get one. So that not the tricky part. 713 00:37:00,800 --> 00:37:03,200 Speaker 1: The tricky part is, like you said, why are their 714 00:37:03,200 --> 00:37:07,040 Speaker 1: probabilities at all? Because it's a completely deterministic theory and 715 00:37:07,120 --> 00:37:09,279 Speaker 1: different people have their angles on that. I think that 716 00:37:09,360 --> 00:37:14,120 Speaker 1: I've solved it along with my collaborator Chip Saban's, because well, 717 00:37:14,160 --> 00:37:15,920 Speaker 1: we borrowed an idea from someone else. I should give 718 00:37:15,920 --> 00:37:18,680 Speaker 1: credit to who's leve Widmin. But here's the idea. When 719 00:37:18,840 --> 00:37:22,279 Speaker 1: you measure that spin. So there's some amplitude saying this 720 00:37:22,320 --> 00:37:24,640 Speaker 1: spin is up. There's some amplitude saying the spin is down. 721 00:37:25,040 --> 00:37:28,080 Speaker 1: And you measure, and like you say, with probability one, 722 00:37:28,520 --> 00:37:30,880 Speaker 1: there is now a version of you on the branch 723 00:37:30,920 --> 00:37:32,360 Speaker 1: where the spin was up, in a version of you 724 00:37:32,400 --> 00:37:33,919 Speaker 1: that is on the branch where the spin is down. 725 00:37:34,239 --> 00:37:37,439 Speaker 1: But if you be a good physicist and you do 726 00:37:37,560 --> 00:37:40,920 Speaker 1: all the details carefully, you can say, well, you know, 727 00:37:41,040 --> 00:37:44,080 Speaker 1: EVERT purportedly explains to me when these measurement occurs, it's 728 00:37:44,160 --> 00:37:48,640 Speaker 1: just an entanglement process. I can calculate when it happens. 729 00:37:49,160 --> 00:37:52,760 Speaker 1: And the answer is, it happens incredibly quickly. The time 730 00:37:52,800 --> 00:37:55,719 Speaker 1: scale for the branching to happen is shorter than the 731 00:37:55,719 --> 00:37:58,520 Speaker 1: lifetime the Higgs boson for those particle physicists out there 732 00:37:58,640 --> 00:38:01,120 Speaker 1: right like less intended mine is on the seconds, and 733 00:38:01,200 --> 00:38:05,560 Speaker 1: so your brain doesn't work that fast. You can't actually 734 00:38:05,719 --> 00:38:09,400 Speaker 1: know which branch you're on as quickly as the branching happens. 735 00:38:09,520 --> 00:38:12,520 Speaker 1: So what that means is, inevitably, when the wave function 736 00:38:12,600 --> 00:38:15,560 Speaker 1: does branch, there's a period of time when there are 737 00:38:15,560 --> 00:38:18,840 Speaker 1: two copies of you who those the world is not identical, 738 00:38:18,960 --> 00:38:22,520 Speaker 1: but those copies of you are identical, okay, And neither 739 00:38:22,600 --> 00:38:25,759 Speaker 1: one of those knows what's branches on. So even if 740 00:38:25,760 --> 00:38:28,800 Speaker 1: it knows the entire way function of the universe, there's 741 00:38:28,920 --> 00:38:32,840 Speaker 1: something about itself that neither one of those copies of 742 00:38:32,880 --> 00:38:34,960 Speaker 1: you knows, namely which branch it is on. This is 743 00:38:35,000 --> 00:38:39,880 Speaker 1: called self locating uncertainty or indexical uncertainty. And in those cases, 744 00:38:40,040 --> 00:38:41,520 Speaker 1: you know there's some fact about the world, but you 745 00:38:41,520 --> 00:38:43,279 Speaker 1: don't know it. What do you do as a good 746 00:38:43,280 --> 00:38:46,280 Speaker 1: Baysian reason or as as a good modern rational person. 747 00:38:46,760 --> 00:38:50,680 Speaker 1: You assigned credences. You assigned non negative numbers that add 748 00:38:50,760 --> 00:38:53,719 Speaker 1: up to one, right, that act like probabilities. So it's 749 00:38:53,719 --> 00:38:56,960 Speaker 1: a subjective probability. I don't know which branch I'm on, 750 00:38:57,080 --> 00:38:59,479 Speaker 1: but I'm going to sign a credence, and you might say, well, 751 00:38:59,640 --> 00:39:01,120 Speaker 1: what do I care about the wave function. I'm just 752 00:39:01,120 --> 00:39:03,319 Speaker 1: going to assign credences that are fifty fifty, right, because 753 00:39:03,320 --> 00:39:05,919 Speaker 1: there's two options, I'm gonna sign equal credence. Turns out 754 00:39:05,920 --> 00:39:09,040 Speaker 1: that doesn't work. It's inconsistent because you can then branch 755 00:39:09,080 --> 00:39:12,479 Speaker 1: the wave function again. Depending on whether this spin was upper, 756 00:39:12,480 --> 00:39:14,520 Speaker 1: spin was down, you have a different number of branches, 757 00:39:14,560 --> 00:39:16,520 Speaker 1: and now you have to assign like one third, one third, 758 00:39:16,520 --> 00:39:20,359 Speaker 1: one third. So the first guy's probability changes even though 759 00:39:20,400 --> 00:39:22,359 Speaker 1: nothing happened in his world. Is that it's kind of 760 00:39:22,400 --> 00:39:27,160 Speaker 1: inconsistent over time. Assigning the Born rule probabilities, giving the 761 00:39:27,200 --> 00:39:31,200 Speaker 1: probability the credence the subjective probability assigned by the wave 762 00:39:31,239 --> 00:39:35,160 Speaker 1: functions squared is the uniquely consistent thing you can do 763 00:39:35,520 --> 00:39:40,000 Speaker 1: in this situation. So number one, there are inevitably uncertainties, 764 00:39:40,120 --> 00:39:44,240 Speaker 1: and number two, the uniquely rational way to assigned credences 765 00:39:44,320 --> 00:39:46,839 Speaker 1: to them is the Born rule. So then the uncertainties 766 00:39:46,840 --> 00:39:51,280 Speaker 1: reflect more like our ignorance rather than some fundamental property 767 00:39:51,320 --> 00:39:54,040 Speaker 1: of the universe. That's right, and people like me would 768 00:39:54,080 --> 00:39:56,719 Speaker 1: go so far as to say, that's always what you 769 00:39:56,719 --> 00:39:59,160 Speaker 1: mean by probability. I mean, there's something that happens in 770 00:39:59,200 --> 00:40:01,600 Speaker 1: the world but we don't know, so we assign different 771 00:40:01,600 --> 00:40:04,880 Speaker 1: credences to it. It's a subjectivist Bayesian version of probability. 772 00:40:05,080 --> 00:40:08,200 Speaker 1: I see. So then does Many Worlds interpretation require basian 773 00:40:08,239 --> 00:40:12,680 Speaker 1: probability and rule out frequentist probability. It certainly comports way 774 00:40:12,719 --> 00:40:16,160 Speaker 1: more comfortably with Bayesian notions of probability. So you don't 775 00:40:16,160 --> 00:40:18,359 Speaker 1: need to be as extremist as I am and think 776 00:40:18,400 --> 00:40:21,120 Speaker 1: that all probabilities are fundamentally subjective to be an ever 777 00:40:21,200 --> 00:40:24,040 Speaker 1: ready in But it doesn't hurt. It helps you sleep 778 00:40:24,080 --> 00:40:25,919 Speaker 1: better at night. Let's put it that way. Let's take 779 00:40:26,000 --> 00:40:41,200 Speaker 1: a quick break. And so then are these sort of 780 00:40:41,200 --> 00:40:44,960 Speaker 1: like philosophical explorations the only way that we can make 781 00:40:45,040 --> 00:40:48,279 Speaker 1: progress on these questions of the quantum foundations? I mean, 782 00:40:48,480 --> 00:40:52,000 Speaker 1: if we have two interpretations of quantum mechanics, Many worlds 783 00:40:52,080 --> 00:40:55,560 Speaker 1: and relational for example, and they both are you know, 784 00:40:55,680 --> 00:40:59,640 Speaker 1: actual physical theories unlike Copenhagen, and they both describe everything 785 00:40:59,640 --> 00:41:02,800 Speaker 1: that we he as observers, then are we just forced 786 00:41:02,840 --> 00:41:06,480 Speaker 1: to make philosophical choices between them? You know, as as individuals. 787 00:41:06,680 --> 00:41:08,799 Speaker 1: Are there no experiments we can do to help us 788 00:41:08,840 --> 00:41:11,680 Speaker 1: resolve this question. Well, I think there's two answers to that. 789 00:41:11,760 --> 00:41:15,160 Speaker 1: One one is that sometimes there are experiments that help 790 00:41:15,239 --> 00:41:17,960 Speaker 1: us distinguish between them. You know, Roger penn Rose has 791 00:41:17,960 --> 00:41:21,480 Speaker 1: been pushing an idea where there are objective collapses of 792 00:41:21,520 --> 00:41:23,840 Speaker 1: the wave function, where the wave function violates the Shorteninger 793 00:41:23,880 --> 00:41:26,760 Speaker 1: equation and really does collapse. Other people. There's a famous 794 00:41:26,800 --> 00:41:30,160 Speaker 1: theory called the GRW theory Gerardi, Ramini and Webber who 795 00:41:30,200 --> 00:41:33,200 Speaker 1: have a similar theory with different equations attached to it. 796 00:41:33,520 --> 00:41:36,759 Speaker 1: And these are experimentally testable, and and tests are going on, right, 797 00:41:36,800 --> 00:41:41,400 Speaker 1: so we're actually doing them. Theories like hidden variable theories 798 00:41:41,480 --> 00:41:46,399 Speaker 1: Bomian mechanics, I think they should be experimentally distinguishable from 799 00:41:46,440 --> 00:41:48,640 Speaker 1: ever ready in quantum mechanics. But the proponents of those 800 00:41:48,680 --> 00:41:51,239 Speaker 1: theories say they're not. So I'm a little suspicious about that, 801 00:41:51,280 --> 00:41:53,800 Speaker 1: But I haven't actually, I can't put a good proposal 802 00:41:53,840 --> 00:41:56,040 Speaker 1: on the table for how to experimentally distinguish them. But 803 00:41:56,080 --> 00:41:59,959 Speaker 1: I still don't quite believe the standard lure in that case. 804 00:42:00,200 --> 00:42:03,640 Speaker 1: For things like Ravelli's relational quantum mechanics, I don't understand 805 00:42:03,640 --> 00:42:06,879 Speaker 1: it well enough to say I suspect that it will 806 00:42:07,080 --> 00:42:11,040 Speaker 1: turn out to be fundamentally equivalent to one of the 807 00:42:11,080 --> 00:42:13,759 Speaker 1: other approaches. Either it's just the way function and it's 808 00:42:13,760 --> 00:42:15,680 Speaker 1: Everett with the many worlds, or there's got to be 809 00:42:15,719 --> 00:42:18,640 Speaker 1: some hidden variables, or is epistemic. I think it's closest 810 00:42:18,719 --> 00:42:22,040 Speaker 1: to what we call an epistemic approach. Episdemic approaches. I 811 00:42:22,080 --> 00:42:24,000 Speaker 1: haven't even mentioned those yet. Those are the ones where 812 00:42:24,000 --> 00:42:28,279 Speaker 1: they really say, the way function is just not reality. Okay, 813 00:42:28,400 --> 00:42:31,480 Speaker 1: In Penrose's approach or g r W or hidden variables, 814 00:42:31,520 --> 00:42:34,320 Speaker 1: the way function is part of reality, but it's dynamics 815 00:42:34,320 --> 00:42:36,160 Speaker 1: are a little bit different than an Everett, whereas in 816 00:42:36,200 --> 00:42:39,560 Speaker 1: a truly epistemic approach, the wave function is just a 817 00:42:39,600 --> 00:42:43,279 Speaker 1: calculational tool and reality is something very, very different. And 818 00:42:43,480 --> 00:42:48,600 Speaker 1: that's fine, But then what is reality? And I'm pretty sure, 819 00:42:48,760 --> 00:42:52,319 Speaker 1: at least my strong belief from the current state of 820 00:42:52,440 --> 00:42:54,759 Speaker 1: the answers people give me when I ask them, there's 821 00:42:54,800 --> 00:42:58,360 Speaker 1: no good theory of what reality actually is in these models, 822 00:42:58,400 --> 00:43:00,359 Speaker 1: and that you know, they're like, wait till water, we'll 823 00:43:00,360 --> 00:43:02,960 Speaker 1: figure that out. And in principle, that's okay. You know 824 00:43:03,080 --> 00:43:05,880 Speaker 1: that we can't ask that every theory as answer every question. 825 00:43:05,920 --> 00:43:09,360 Speaker 1: As soon as it's invented. But it's also perfectly fair 826 00:43:09,480 --> 00:43:12,560 Speaker 1: to be skeptical of those theories while those questions still 827 00:43:12,640 --> 00:43:15,200 Speaker 1: linger out there. But okay, but the other answer to 828 00:43:15,200 --> 00:43:17,160 Speaker 1: your question, sorry that it takes me so long to 829 00:43:17,200 --> 00:43:19,360 Speaker 1: get to it is the proof of the pudding is 830 00:43:19,400 --> 00:43:23,440 Speaker 1: in the tasting. And if I can make progress on 831 00:43:23,640 --> 00:43:28,239 Speaker 1: other puzzles and physics by starting from an everady in 832 00:43:28,280 --> 00:43:32,080 Speaker 1: perspective and taking it seriously, whereas my friends who are 833 00:43:32,080 --> 00:43:36,080 Speaker 1: being epistemic or hidden variably or whatever don't make that progress, 834 00:43:36,200 --> 00:43:38,920 Speaker 1: then by the rules of physics, I win, and vice versa. Right, 835 00:43:38,960 --> 00:43:42,080 Speaker 1: if the people who are fundamentally pilot wave theories or 836 00:43:42,280 --> 00:43:45,000 Speaker 1: epistemic people make progress that I don't, then they win. 837 00:43:45,080 --> 00:43:48,319 Speaker 1: That's perfectly fair. So in this situation where we're not 838 00:43:48,360 --> 00:43:50,640 Speaker 1: sure what the right answer is, then by all means, 839 00:43:50,719 --> 00:43:53,600 Speaker 1: let people do research in their favorite areas, and you know, 840 00:43:53,640 --> 00:43:57,040 Speaker 1: whoever actually discover something interesting, we'll get the credit. I 841 00:43:57,120 --> 00:43:59,480 Speaker 1: like this idea of measuring competing theories by how much 842 00:43:59,480 --> 00:44:03,120 Speaker 1: progress can make, sort of theoretically or philosophically, to show 843 00:44:03,160 --> 00:44:05,960 Speaker 1: that it's like a you know, a functioning, working, fertile 844 00:44:06,000 --> 00:44:08,799 Speaker 1: intellectual playground. But you raised this interesting question of you 845 00:44:08,840 --> 00:44:10,680 Speaker 1: know what reality is? And I want to come back 846 00:44:10,719 --> 00:44:13,760 Speaker 1: to something you mentioned earlier, which is why the universe 847 00:44:13,960 --> 00:44:15,960 Speaker 1: if it is quantum, If the universe is a wave 848 00:44:16,000 --> 00:44:18,520 Speaker 1: function and there's quantum particles and everything is governed by 849 00:44:18,560 --> 00:44:21,399 Speaker 1: the shooting equation, why doesn't feel that way to us? 850 00:44:21,880 --> 00:44:24,960 Speaker 1: You know? Why we have this emergent experience which is 851 00:44:25,000 --> 00:44:28,160 Speaker 1: so drastically not quantum. Is that something we can ever 852 00:44:28,480 --> 00:44:31,160 Speaker 1: grapple with? Or is it just like other emergent phenomenon, 853 00:44:31,160 --> 00:44:33,000 Speaker 1: like asking like why is there ice cream at some 854 00:44:33,000 --> 00:44:35,600 Speaker 1: points in the universe and not other points? I think 855 00:44:35,600 --> 00:44:38,120 Speaker 1: there's actually again two aspects of this. There's sort of 856 00:44:38,120 --> 00:44:41,400 Speaker 1: the philosophical aspect and the physical aspect. The philosophical aspect 857 00:44:41,440 --> 00:44:43,200 Speaker 1: I don't have much to say about, which is just 858 00:44:43,440 --> 00:44:49,640 Speaker 1: in a world like ours. Why is it that the 859 00:44:49,680 --> 00:44:52,600 Speaker 1: idea of a self, the idea of an agent, the 860 00:44:52,680 --> 00:44:56,040 Speaker 1: idea of a conscious creature is attached to just one 861 00:44:56,080 --> 00:44:58,360 Speaker 1: branch of the wave function at a time. I already 862 00:44:58,360 --> 00:45:01,040 Speaker 1: mentioned the fact that you know, fundum mentally, the different 863 00:45:01,040 --> 00:45:03,760 Speaker 1: branches don't interact with each other. So if you tried 864 00:45:03,880 --> 00:45:07,560 Speaker 1: to say, well, I'm going to treat reality to me 865 00:45:07,920 --> 00:45:10,560 Speaker 1: as two of the branches, not any of the others. 866 00:45:10,560 --> 00:45:12,720 Speaker 1: We know the other's gonna take to these two well, 867 00:45:12,760 --> 00:45:15,040 Speaker 1: I think that someone would say, yeah, but you have 868 00:45:15,160 --> 00:45:17,600 Speaker 1: two things that have literally no impact on each other. 869 00:45:17,680 --> 00:45:20,359 Speaker 1: The analogy I use in my book is, what if 870 00:45:20,360 --> 00:45:22,600 Speaker 1: there were a ghost world? What if there's a world 871 00:45:23,160 --> 00:45:24,960 Speaker 1: that was sort of, you know, the same shape as 872 00:45:25,000 --> 00:45:27,239 Speaker 1: the Earth and the same physical location as the Earth 873 00:45:27,239 --> 00:45:28,960 Speaker 1: and space, and there were people on it, and they 874 00:45:28,960 --> 00:45:32,319 Speaker 1: talked to each other, but there's zero interaction through any 875 00:45:32,320 --> 00:45:34,800 Speaker 1: force of nature or any other kind of influence between 876 00:45:34,920 --> 00:45:36,960 Speaker 1: us and the people on ghost world. It just doesn't 877 00:45:36,960 --> 00:45:39,640 Speaker 1: make sense to call them part of the same reality, right, 878 00:45:39,680 --> 00:45:42,160 Speaker 1: I mean, they're two worlds for a long times and 879 00:45:42,160 --> 00:45:44,840 Speaker 1: purposes certainly. So that's the sort of philosophical move I 880 00:45:44,840 --> 00:45:47,480 Speaker 1: think that we don't have, at least I'm not aware 881 00:45:47,560 --> 00:45:50,200 Speaker 1: of a once and for all definition of what a 882 00:45:50,239 --> 00:45:52,759 Speaker 1: world is and how you should divide up reality in 883 00:45:52,760 --> 00:45:55,120 Speaker 1: that way. But that's the rough idea. You know, a 884 00:45:55,200 --> 00:45:57,640 Speaker 1: set of things that interact with each other is a world. 885 00:45:57,920 --> 00:46:01,320 Speaker 1: But the other interesting question is, you know I started 886 00:46:01,320 --> 00:46:03,719 Speaker 1: that by saying, in a world like ours, with laws 887 00:46:03,719 --> 00:46:06,840 Speaker 1: of physics like ours, but Okay, what are the features 888 00:46:06,840 --> 00:46:12,440 Speaker 1: of our laws of physics that allow for each individual 889 00:46:12,520 --> 00:46:15,640 Speaker 1: branch of the wave function to be mostly classical? You 890 00:46:15,640 --> 00:46:19,120 Speaker 1: were pretty good at predicting the positions of planets in 891 00:46:19,160 --> 00:46:22,759 Speaker 1: the sky and eclipses and so forth using Newtonian mechanics 892 00:46:22,800 --> 00:46:25,440 Speaker 1: long before quantum mechanics came on the scene, right, So 893 00:46:25,880 --> 00:46:29,840 Speaker 1: why is classical mechanics a good limit of quantum mechanics, 894 00:46:29,960 --> 00:46:32,400 Speaker 1: especially given that you're saying there's all these other worlds 895 00:46:32,440 --> 00:46:35,640 Speaker 1: out there, right, And that's a trickier question, And I 896 00:46:35,680 --> 00:46:39,319 Speaker 1: think that we're just beginning to make progress on it. 897 00:46:39,400 --> 00:46:42,000 Speaker 1: And the answer has things to do with ideas like 898 00:46:42,160 --> 00:46:46,520 Speaker 1: entanglement and decoherence and locality, But fundamentally, you know, that's 899 00:46:46,520 --> 00:46:48,680 Speaker 1: still a research level problem. Well, I hope that we 900 00:46:48,719 --> 00:46:50,600 Speaker 1: make some progress on it in the future. Now, I 901 00:46:50,600 --> 00:46:52,520 Speaker 1: want to take a slight turn and ask you a 902 00:46:52,520 --> 00:46:55,120 Speaker 1: little bit more of a personal question. You mentioned earlier 903 00:46:55,160 --> 00:46:57,480 Speaker 1: that not only are you, you know, talking out there 904 00:46:57,480 --> 00:46:59,680 Speaker 1: in the public about science, which are actually at practicing 905 00:46:59,680 --> 00:47:02,720 Speaker 1: physics this And you know, in my experience, most people 906 00:47:02,760 --> 00:47:05,920 Speaker 1: take one of two paths. They're either a practicing scientist 907 00:47:06,480 --> 00:47:08,879 Speaker 1: or they are a science communicator. You know, I don't 908 00:47:08,960 --> 00:47:11,160 Speaker 1: know that for example, Bill Nye or Neil de grass 909 00:47:11,160 --> 00:47:14,719 Speaker 1: Tyson is still publishing papers. But you have kept your 910 00:47:14,719 --> 00:47:17,319 Speaker 1: feet in both worlds. Has it been a challenge for 911 00:47:17,360 --> 00:47:21,080 Speaker 1: you to remain part of the scientific community and maintain 912 00:47:21,120 --> 00:47:24,439 Speaker 1: that credibility while also being a public intellectual. Yeah, there's 913 00:47:24,480 --> 00:47:27,640 Speaker 1: sort of two aspects to the challenge. One is, it's 914 00:47:27,640 --> 00:47:30,759 Speaker 1: a lot of work all these things to to write 915 00:47:30,760 --> 00:47:33,759 Speaker 1: papers and to advise grad students while also having a 916 00:47:33,800 --> 00:47:36,160 Speaker 1: podcast and writing books and so forth. But you know what, 917 00:47:36,239 --> 00:47:38,759 Speaker 1: look to be honest, it's not that much work, and 918 00:47:38,800 --> 00:47:42,960 Speaker 1: I can compartmentalize it pretty easily, and it's fun for me, 919 00:47:43,080 --> 00:47:44,839 Speaker 1: Like I get to do these things that all are 920 00:47:44,880 --> 00:47:48,800 Speaker 1: individually very fun, and my personality is such that I'd 921 00:47:48,840 --> 00:47:51,279 Speaker 1: like being able to switch gears and do different things 922 00:47:51,360 --> 00:47:53,399 Speaker 1: at different times. I would get frustrated if I did 923 00:47:53,440 --> 00:47:56,560 Speaker 1: the same exact kind of thing every day, So this 924 00:47:56,640 --> 00:47:58,760 Speaker 1: is a good way to do that. The other aspect 925 00:47:58,760 --> 00:48:01,600 Speaker 1: of the challenge is, like you said the word credibility, 926 00:48:01,640 --> 00:48:04,680 Speaker 1: like what about how other people think of you? And yeah, 927 00:48:04,719 --> 00:48:08,879 Speaker 1: that's absolutely a challenge because of course two things Number one, 928 00:48:09,320 --> 00:48:14,480 Speaker 1: public outreach and communication is itself undervalued and or devalued, 929 00:48:14,600 --> 00:48:16,920 Speaker 1: depending on who you're talking to, Like, it's considered to 930 00:48:16,960 --> 00:48:20,719 Speaker 1: be a waste of good brain CPU cycles that you 931 00:48:20,760 --> 00:48:23,600 Speaker 1: could be using doing research, right, and doing research is 932 00:48:23,640 --> 00:48:27,280 Speaker 1: what really matters. And number two, like you also imply, 933 00:48:27,680 --> 00:48:30,680 Speaker 1: there's this idea that even if you think that outreach 934 00:48:30,760 --> 00:48:35,200 Speaker 1: and communication are valuable, it's very difficult to imagine being 935 00:48:35,280 --> 00:48:39,000 Speaker 1: productive in both spheres of both doing research and doing 936 00:48:39,000 --> 00:48:42,680 Speaker 1: those kinds of things. There are famous counter examples Carl Sagan, 937 00:48:42,760 --> 00:48:46,120 Speaker 1: Stephen Hawking, etcetera. Stephen Weinberg right, who recently passed away, 938 00:48:46,160 --> 00:48:49,480 Speaker 1: but they're so rare that people almost don't take them seriously. 939 00:48:49,600 --> 00:48:52,800 Speaker 1: And especially like there's the feeling that you should first 940 00:48:53,000 --> 00:48:58,040 Speaker 1: become a super successful researcher and then you'd be allowed 941 00:48:58,200 --> 00:49:00,000 Speaker 1: to do a little bit of writing books and things 942 00:49:00,080 --> 00:49:02,719 Speaker 1: like that. I mean, Stephen Hawking invented black hole radiation 943 00:49:02,800 --> 00:49:04,960 Speaker 1: long before he wrote A Brief History of Time and 944 00:49:05,000 --> 00:49:07,359 Speaker 1: so forth. And Carl Sagan, on the other hand, never 945 00:49:07,400 --> 00:49:09,640 Speaker 1: got elected to the National Academy of Sciences because people 946 00:49:09,760 --> 00:49:12,160 Speaker 1: thought that he spent too much time doing outreach work. 947 00:49:12,320 --> 00:49:14,680 Speaker 1: So that's a challenge. But you know, I'm too old 948 00:49:14,680 --> 00:49:17,799 Speaker 1: to worry about that these these days. Um, it has 949 00:49:17,880 --> 00:49:21,960 Speaker 1: impacted my career in very tangible, definite ways, but I'm 950 00:49:22,000 --> 00:49:24,080 Speaker 1: still having fun doing what I want to do. So 951 00:49:24,160 --> 00:49:26,480 Speaker 1: there you go. Well, that's great to hear my experience 952 00:49:26,600 --> 00:49:28,759 Speaker 1: a little bit of that. Also, when I talked to 953 00:49:28,840 --> 00:49:32,439 Speaker 1: people in my you know, card carrying particle physics world, 954 00:49:32,440 --> 00:49:34,480 Speaker 1: and they asked me, oh, are you still doing research 955 00:49:34,560 --> 00:49:36,880 Speaker 1: now that you're doing outreach, it's have to remind them 956 00:49:37,000 --> 00:49:39,480 Speaker 1: it's possible to do more than the one thing. So 957 00:49:39,520 --> 00:49:41,399 Speaker 1: it's interesting. Let me just put it this way because 958 00:49:41,400 --> 00:49:44,640 Speaker 1: I like this analogy. Physicists are not so narrow minded 959 00:49:45,120 --> 00:49:47,960 Speaker 1: that they won't allow their colleagues to do anything else. 960 00:49:48,440 --> 00:49:51,200 Speaker 1: Like if you were a ski jumper or a professional 961 00:49:51,280 --> 00:49:54,520 Speaker 1: unicyclist or whatever, or not professional but amateur unicyclist in 962 00:49:54,560 --> 00:49:57,080 Speaker 1: your spare time, other physicists would think, oh, that's cookie 963 00:49:57,080 --> 00:49:59,319 Speaker 1: and fun. Good for you, and you're probably also still 964 00:49:59,320 --> 00:50:03,720 Speaker 1: doing research. But there's something about writing books and giving 965 00:50:03,760 --> 00:50:07,640 Speaker 1: talks and making videos and so forth that is different 966 00:50:07,840 --> 00:50:11,560 Speaker 1: than writing unicycle or being a ski jumper, because that's 967 00:50:11,560 --> 00:50:14,240 Speaker 1: the kind of thing that people think, well, you should 968 00:50:14,320 --> 00:50:17,440 Speaker 1: be using that effort doing research, right, Like your unicycling 969 00:50:17,560 --> 00:50:19,319 Speaker 1: is just a different kind of thing, so we don't 970 00:50:19,320 --> 00:50:22,000 Speaker 1: think that takes away from your research. An enormous number 971 00:50:22,040 --> 00:50:25,400 Speaker 1: of professional physicists are rock climbers and mountain climbers, right, 972 00:50:25,440 --> 00:50:29,719 Speaker 1: You probably know many yourself, for example. That's fine. But 973 00:50:29,800 --> 00:50:32,200 Speaker 1: if instead of going rock climbing, you write a book, 974 00:50:32,440 --> 00:50:35,520 Speaker 1: that's actually counts against you and that it's just a 975 00:50:35,600 --> 00:50:37,800 Speaker 1: weird thing in my mind, but it's a very definite 976 00:50:37,840 --> 00:50:41,040 Speaker 1: syndrome that is strange. And you know this is it's 977 00:50:41,080 --> 00:50:44,840 Speaker 1: interesting to explore these career paths, and I wonder is 978 00:50:44,880 --> 00:50:47,799 Speaker 1: this sort of the path you envisioned for yourself. Like 979 00:50:48,040 --> 00:50:50,680 Speaker 1: if you could go back in time and describe your 980 00:50:50,719 --> 00:50:54,920 Speaker 1: life now to fresh faced assistant professor Sean Carroll one 981 00:50:55,000 --> 00:50:57,680 Speaker 1: year into your gig at University of Chicago, how do 982 00:50:57,719 --> 00:51:01,440 Speaker 1: you think that Sean would re act? Well, the specific 983 00:51:01,680 --> 00:51:04,360 Speaker 1: twists and turns of my career were not what I 984 00:51:04,360 --> 00:51:07,640 Speaker 1: predicted or wanted, but the ending point is pretty close. 985 00:51:07,760 --> 00:51:10,919 Speaker 1: You know, I always wanted to be a broader intellectual 986 00:51:11,040 --> 00:51:14,640 Speaker 1: contributor than just a narrow research physicist that you know, 987 00:51:14,760 --> 00:51:16,480 Speaker 1: since I was a kid, I wanted that, and that 988 00:51:16,600 --> 00:51:19,279 Speaker 1: was always the plan. In some sense, and I was 989 00:51:19,480 --> 00:51:24,240 Speaker 1: charmingly naive about how happy academia would be to receive 990 00:51:24,520 --> 00:51:26,600 Speaker 1: such a plan. But there was always the plan, And 991 00:51:26,680 --> 00:51:28,560 Speaker 1: I do believe that the right way to do that 992 00:51:28,719 --> 00:51:30,920 Speaker 1: is to first become an expert at something. Right Like, 993 00:51:30,960 --> 00:51:33,560 Speaker 1: you don't start out as an expert in everything you know. 994 00:51:33,600 --> 00:51:35,920 Speaker 1: You better get good at your research and your PhD 995 00:51:36,000 --> 00:51:38,920 Speaker 1: project and then sort of branch out after that. But 996 00:51:39,080 --> 00:51:41,680 Speaker 1: you can't predict all of the ins and outs. But 997 00:51:42,160 --> 00:51:44,359 Speaker 1: maybe I would have done things differently if I had 998 00:51:44,719 --> 00:51:47,200 Speaker 1: crystal ball and could predict the future. A few tweaks 999 00:51:47,239 --> 00:51:49,759 Speaker 1: here and there would have helped. But you know, I 1000 00:51:49,760 --> 00:51:52,160 Speaker 1: think I can still hold my head high about the 1001 00:51:52,239 --> 00:51:54,360 Speaker 1: choices that I made along the way. Well, what advice 1002 00:51:54,360 --> 00:51:57,400 Speaker 1: would you give to young folks now who are excited 1003 00:51:57,400 --> 00:52:01,040 Speaker 1: about science communication? In my experience, so I followed a 1004 00:52:01,080 --> 00:52:04,480 Speaker 1: fairly narrow path and got tenure as an experimental particle 1005 00:52:04,480 --> 00:52:07,160 Speaker 1: physicists before trying to branch out to outreach other types 1006 00:52:07,200 --> 00:52:09,640 Speaker 1: of things. But I see graduate students in my own 1007 00:52:09,680 --> 00:52:12,480 Speaker 1: group doing outreach, and I wonder, you know, if I 1008 00:52:12,480 --> 00:52:15,759 Speaker 1: should advise them. Look, the field is not friendly to 1009 00:52:15,920 --> 00:52:18,400 Speaker 1: this kind of breath at this age. Wait till you 1010 00:52:18,400 --> 00:52:20,360 Speaker 1: get tenure, or if I'm telling them not to be 1011 00:52:20,400 --> 00:52:23,520 Speaker 1: their authentic intellectual selves, and I should encourage them and 1012 00:52:23,560 --> 00:52:26,000 Speaker 1: the field with it to grow and accept this kind 1013 00:52:26,000 --> 00:52:28,160 Speaker 1: of activity. What would be your advice or what is 1014 00:52:28,200 --> 00:52:30,560 Speaker 1: your advice to your students when they try to emulate 1015 00:52:30,600 --> 00:52:33,200 Speaker 1: the full breadth of your activities. It's enormously good and 1016 00:52:33,280 --> 00:52:36,160 Speaker 1: important question, and the answer is not obvious. But I 1017 00:52:36,160 --> 00:52:38,840 Speaker 1: can always fall back on the maxim that I should 1018 00:52:38,840 --> 00:52:41,720 Speaker 1: tell the truth. So I can tell the truth about 1019 00:52:42,080 --> 00:52:46,879 Speaker 1: factual statements about the world without necessarily coloring them by 1020 00:52:46,920 --> 00:52:50,359 Speaker 1: normative statements. So rather than saying don't do that until 1021 00:52:50,400 --> 00:52:53,279 Speaker 1: you get tenure, I can say, look, it's great that 1022 00:52:53,680 --> 00:52:55,759 Speaker 1: you like doing a lot of different things outreach and 1023 00:52:55,800 --> 00:52:58,640 Speaker 1: so forth. I have one recent student of mine who 1024 00:52:58,719 --> 00:53:00,880 Speaker 1: is actually super duper six US full hot property in 1025 00:53:00,920 --> 00:53:04,360 Speaker 1: the job market, wrote a musical and performed it, you know, 1026 00:53:04,400 --> 00:53:06,799 Speaker 1: at cal Tech while he was in graduate school. So 1027 00:53:07,320 --> 00:53:09,920 Speaker 1: he did okay. But the point is that it's hard 1028 00:53:10,160 --> 00:53:14,120 Speaker 1: to become a professional academic, right The numbers game is bad. 1029 00:53:14,239 --> 00:53:16,360 Speaker 1: I'm at cal Tech, and I tell my students that 1030 00:53:16,400 --> 00:53:18,040 Speaker 1: if you're at a place like cal Tech or Harvard 1031 00:53:18,080 --> 00:53:21,160 Speaker 1: or whatever, and you get a PhD, maybe one in 1032 00:53:21,239 --> 00:53:25,400 Speaker 1: four of you will eventually be tenured professors in that field. 1033 00:53:25,440 --> 00:53:27,760 Speaker 1: I don't know the exact numbers, and it will depend 1034 00:53:27,760 --> 00:53:29,839 Speaker 1: a lot on sub fields and where you get your 1035 00:53:29,840 --> 00:53:32,960 Speaker 1: PhD and so forth, but the numbers are against you, certainly. 1036 00:53:33,120 --> 00:53:35,280 Speaker 1: And the thing you can say with a good amount 1037 00:53:35,320 --> 00:53:40,800 Speaker 1: of confidence is that all else being fixed, doing outreachy 1038 00:53:40,920 --> 00:53:44,400 Speaker 1: things will lower the percentage chance that you will someday 1039 00:53:44,440 --> 00:53:47,920 Speaker 1: become tenured academic. Now you might still decide to do it, 1040 00:53:48,000 --> 00:53:49,480 Speaker 1: and that's great, but I want you to go in 1041 00:53:49,600 --> 00:53:52,279 Speaker 1: with your eyes open, right Like I sometimes get in 1042 00:53:52,320 --> 00:53:56,040 Speaker 1: trouble by being a little bit too candid with my students, 1043 00:53:56,040 --> 00:53:58,319 Speaker 1: because a lot of my colleagues are like now they're 1044 00:53:58,560 --> 00:54:00,920 Speaker 1: they're young and impressionable. We have to like juice them 1045 00:54:01,000 --> 00:54:02,960 Speaker 1: up about physics. And I'm like, well, yeah, but a 1046 00:54:03,000 --> 00:54:04,960 Speaker 1: lot of them are not going to end up being physicists. 1047 00:54:05,000 --> 00:54:07,399 Speaker 1: And I think that I love the idea of going 1048 00:54:07,440 --> 00:54:09,840 Speaker 1: to grad school. I love the idea of getting a PhD. 1049 00:54:09,880 --> 00:54:12,560 Speaker 1: And I think it's intrinsically worthwhile thing. And I'm not 1050 00:54:12,560 --> 00:54:15,799 Speaker 1: going to discourage anyone from doing that because it's a 1051 00:54:15,840 --> 00:54:17,960 Speaker 1: matter of intellectual growth and so forth. I think the 1052 00:54:18,000 --> 00:54:20,760 Speaker 1: current system where you then have to do somewhere between 1053 00:54:20,800 --> 00:54:24,160 Speaker 1: five and ten years of post doc afterward is not ideal. 1054 00:54:24,640 --> 00:54:26,880 Speaker 1: But you know, if you want to get a PhD, 1055 00:54:26,920 --> 00:54:28,280 Speaker 1: then I think that's the best thing in the world. 1056 00:54:28,280 --> 00:54:31,600 Speaker 1: And then you should know what the chances are and 1057 00:54:31,640 --> 00:54:34,279 Speaker 1: what the different aspects are that affect your chances along 1058 00:54:34,320 --> 00:54:36,359 Speaker 1: the way, and then you make your own decisions. Well, 1059 00:54:36,400 --> 00:54:38,320 Speaker 1: I agree with that, and I hope that other folks 1060 00:54:38,360 --> 00:54:40,960 Speaker 1: out there can see that it's possible to be an 1061 00:54:40,960 --> 00:54:44,759 Speaker 1: academic and to do scientific communication and outreach, and that 1062 00:54:45,000 --> 00:54:48,040 Speaker 1: encourages the community to accept that into broaden our concept 1063 00:54:48,120 --> 00:54:50,439 Speaker 1: of what a healthy physicist is. You're allowed to also 1064 00:54:50,480 --> 00:54:53,359 Speaker 1: be a unicycler or to talk about science to your 1065 00:54:53,400 --> 00:54:55,600 Speaker 1: friends and neighbors on the internet. All right, we've taken 1066 00:54:55,680 --> 00:54:57,520 Speaker 1: enough of your time. Thanks very much for joining us 1067 00:54:57,560 --> 00:54:59,680 Speaker 1: and for telling us about your vision of quantum mechanics. 1068 00:54:59,680 --> 00:55:02,600 Speaker 1: And it's then do us all the crazy mind blowing 1069 00:55:02,680 --> 00:55:05,640 Speaker 1: ideas involved in the many world's interpretation. It's been a pleasure. 1070 00:55:05,719 --> 00:55:07,680 Speaker 1: It's very fortunate that we had to think about these things. 1071 00:55:07,880 --> 00:55:10,200 Speaker 1: So thanks for having me on. All right, Thanks very much, 1072 00:55:18,000 --> 00:55:20,840 Speaker 1: thanks for listening, and remember that Daniel and Jorge explained. 1073 00:55:20,880 --> 00:55:23,800 Speaker 1: The Universe is a production of I Heart Radio or 1074 00:55:23,880 --> 00:55:26,799 Speaker 1: more podcast from my heart Radio. Visit the I Heart 1075 00:55:26,880 --> 00:55:30,480 Speaker 1: Radio Apple Apple Podcasts, or wherever you listen to your 1076 00:55:30,520 --> 00:55:36,880 Speaker 1: favorite shows. Ye