1 00:00:08,520 --> 00:00:10,039 Speaker 1: Hey, Daniel, who do you think would win in a 2 00:00:10,080 --> 00:00:13,039 Speaker 1: fight theoretical or an experimental physicist? 3 00:00:13,200 --> 00:00:16,360 Speaker 2: That depends are we're talking arm wrestling or like integration 4 00:00:16,520 --> 00:00:20,560 Speaker 2: competitions into what mathematical race? 5 00:00:22,040 --> 00:00:24,520 Speaker 1: Then I think I would put my money into theoretical physicist. 6 00:00:24,600 --> 00:00:25,920 Speaker 1: I mean, no offense. 7 00:00:27,520 --> 00:00:29,639 Speaker 2: Maybe we have to do the experiment, or maybe you. 8 00:00:29,600 --> 00:00:32,519 Speaker 1: Should keep this theoretical. I don't know if you want 9 00:00:32,520 --> 00:00:33,240 Speaker 1: to pick a fight. 10 00:00:33,240 --> 00:00:35,599 Speaker 2: Well, maybe the two sides of the field just compliment 11 00:00:35,640 --> 00:00:36,480 Speaker 2: each other beautifully. 12 00:00:36,640 --> 00:00:38,680 Speaker 1: Is that all it takes us? Some compliments and you 13 00:00:38,720 --> 00:00:39,920 Speaker 1: guys are back as friends. 14 00:00:40,000 --> 00:00:42,200 Speaker 2: Theories are cheap, right, They don't need money for experiments, 15 00:00:42,240 --> 00:00:44,320 Speaker 2: They just need compliments in theory. 16 00:00:44,640 --> 00:01:02,760 Speaker 1: In my experience, hi am Warham, a cartoonist and the 17 00:01:02,760 --> 00:01:04,200 Speaker 1: creator of PhD comics. 18 00:01:04,319 --> 00:01:07,240 Speaker 2: Hi, I'm Daniel. I'm a particle physicist and a professor 19 00:01:07,280 --> 00:01:09,839 Speaker 2: at UC Irvine, And back in the day, I did 20 00:01:09,880 --> 00:01:11,120 Speaker 2: want to be a theorist. 21 00:01:11,440 --> 00:01:13,240 Speaker 1: Back in the day, How old were you. 22 00:01:13,319 --> 00:01:15,120 Speaker 2: When I started grad school? I wasn't sure if I 23 00:01:15,160 --> 00:01:18,600 Speaker 2: wanted to do experimental or theoretical physics, So I guess 24 00:01:18,640 --> 00:01:20,920 Speaker 2: I was in my early twenties, which by now is 25 00:01:20,959 --> 00:01:22,199 Speaker 2: pretty far back in the day. 26 00:01:22,400 --> 00:01:24,679 Speaker 1: Did you actually get a choice, like they offer you 27 00:01:24,720 --> 00:01:26,679 Speaker 1: an option of which way to go, or do you 28 00:01:26,720 --> 00:01:28,440 Speaker 1: have to, like, I don't know, test into it. 29 00:01:28,560 --> 00:01:30,759 Speaker 2: You definitely have to kind of try out and work 30 00:01:30,800 --> 00:01:33,080 Speaker 2: with the theorists if you want to be a theorist. 31 00:01:33,680 --> 00:01:36,039 Speaker 2: But you have all the options when you start grad school. 32 00:01:36,200 --> 00:01:38,640 Speaker 2: You could end up being an experimental particle physicist or 33 00:01:38,640 --> 00:01:43,000 Speaker 2: a theoretical cosmologist or whatever. All those paths are available. 34 00:01:43,040 --> 00:01:45,440 Speaker 2: You just gotta like it enough and be good at it. 35 00:01:46,200 --> 00:01:48,120 Speaker 1: So what happened? Why didn't you pick the theory? 36 00:01:48,320 --> 00:01:51,200 Speaker 2: I discovered I just didn't like writing down equations as 37 00:01:51,280 --> 00:01:53,320 Speaker 2: much as a theorist. They would sit there and like 38 00:01:53,400 --> 00:01:57,040 Speaker 2: develop several different mathematical fonts to write their equations in, 39 00:01:57,120 --> 00:01:59,440 Speaker 2: and I was like, wow, I'm just not loving this 40 00:01:59,480 --> 00:02:00,760 Speaker 2: as much as they're loving this. 41 00:02:00,960 --> 00:02:02,520 Speaker 1: It sounds like you were against the idea of it 42 00:02:02,560 --> 00:02:03,040 Speaker 1: in theory. 43 00:02:04,800 --> 00:02:07,240 Speaker 2: My experience was the experiments were more fun. 44 00:02:07,280 --> 00:02:09,680 Speaker 1: But anyways, Welcome to our podcast Daniel and Jorge Explain 45 00:02:09,760 --> 00:02:12,560 Speaker 1: the Universe, a production of iHeartRadio. 46 00:02:11,880 --> 00:02:14,560 Speaker 2: In which we try to blur the line between theory 47 00:02:14,600 --> 00:02:17,519 Speaker 2: and experiment. We want to talk about all the concepts 48 00:02:17,560 --> 00:02:20,400 Speaker 2: in theoretical physics that try to explain what's going on 49 00:02:20,520 --> 00:02:23,360 Speaker 2: in our world, but we also try to touch back 50 00:02:23,400 --> 00:02:26,880 Speaker 2: on the ground and understand what experiments are telling us 51 00:02:26,880 --> 00:02:30,680 Speaker 2: about the nature of reality, what is Nature actually saying 52 00:02:30,720 --> 00:02:33,959 Speaker 2: to us as she spins the story of the universe, 53 00:02:34,320 --> 00:02:36,440 Speaker 2: And then we try to explain all of it to you. 54 00:02:36,639 --> 00:02:39,119 Speaker 1: That's right, because it is a pretty storied universe, full 55 00:02:39,120 --> 00:02:42,000 Speaker 1: of amazing little details and facts and things to discover 56 00:02:42,120 --> 00:02:44,520 Speaker 1: out there that we are still puzzling over and which 57 00:02:44,560 --> 00:02:50,399 Speaker 1: require all kinds of scientists to figure out, theorists and experimentalists. 58 00:02:49,480 --> 00:02:51,720 Speaker 2: And in the history of physics we have made progress 59 00:02:51,760 --> 00:02:54,880 Speaker 2: in lots of different ways. Sometimes the theorists have come 60 00:02:54,960 --> 00:02:58,080 Speaker 2: up with a clever idea, a suspicion about how the 61 00:02:58,240 --> 00:03:01,919 Speaker 2: universe might work, with lots of cool directions for experimentalists. 62 00:03:02,000 --> 00:03:04,680 Speaker 2: Go out and check this thing, Measure how light bends 63 00:03:04,720 --> 00:03:07,440 Speaker 2: around the sun, see if you can find the Higgs boson. 64 00:03:07,760 --> 00:03:11,120 Speaker 2: Those can be wonderful directions to help unravel the mysteries 65 00:03:11,160 --> 00:03:14,960 Speaker 2: of the universe. But sometimes the experimentalists lead the way, 66 00:03:15,040 --> 00:03:18,040 Speaker 2: turning on particle smashers and discovering gobs and gobs of 67 00:03:18,080 --> 00:03:20,080 Speaker 2: new particles that nobody expected. 68 00:03:20,880 --> 00:03:23,000 Speaker 1: I guess my question, Daniel is why can't you be both? 69 00:03:23,160 --> 00:03:25,679 Speaker 1: Why can't you be a theoretical and an experimental physicist. 70 00:03:26,200 --> 00:03:29,680 Speaker 2: I'm doing my best. Actually i'm doing my best. But 71 00:03:29,840 --> 00:03:32,639 Speaker 2: the reality of academia these days is to get one 72 00:03:32,639 --> 00:03:35,160 Speaker 2: of these jobs, you have to be the world's expert 73 00:03:35,240 --> 00:03:38,600 Speaker 2: in some subfield. And that makes it really hard to 74 00:03:38,760 --> 00:03:41,600 Speaker 2: sort of live between two fields because you have to 75 00:03:41,640 --> 00:03:44,640 Speaker 2: be like the top person in that field that year. 76 00:03:44,840 --> 00:03:46,600 Speaker 2: And so if the theorists aren't sure, if you're a 77 00:03:46,600 --> 00:03:49,240 Speaker 2: theorist and the experimentalist aren't sure if you're an experimentalist, 78 00:03:49,520 --> 00:03:52,080 Speaker 2: nobody's going to give you that job. So you've got 79 00:03:52,120 --> 00:03:53,960 Speaker 2: to sort of get the job in one category and 80 00:03:54,000 --> 00:03:56,360 Speaker 2: then inch your way over to the other one if 81 00:03:56,360 --> 00:04:00,720 Speaker 2: you're interested. That's kind of cliquish, it's definitely very cliquiche. Absolutely, 82 00:04:01,040 --> 00:04:04,120 Speaker 2: these fields form and then they protect themselves and it 83 00:04:04,120 --> 00:04:07,400 Speaker 2: can be hard for new kinds of subfields to emerge, 84 00:04:07,440 --> 00:04:10,480 Speaker 2: Like right now we have the emergence of physicists who 85 00:04:10,480 --> 00:04:12,920 Speaker 2: are experts in machine learning, and people aren't sure is 86 00:04:12,920 --> 00:04:16,200 Speaker 2: that theoretical is it experimental? Because you're running a bunch 87 00:04:16,240 --> 00:04:19,719 Speaker 2: of calculations nobody's really sure. Everybody knows that it's valuable, 88 00:04:19,880 --> 00:04:21,800 Speaker 2: but we aren't quite sure where to put them. 89 00:04:21,880 --> 00:04:25,400 Speaker 1: That's because they're robots? Are they in disguise? 90 00:04:27,640 --> 00:04:29,680 Speaker 2: We're all just biological robots? 91 00:04:29,720 --> 00:04:29,920 Speaker 3: Man? 92 00:04:30,040 --> 00:04:30,640 Speaker 1: Oh, there you go. 93 00:04:31,760 --> 00:04:33,600 Speaker 2: Aren't you the expert in squishy robots? 94 00:04:33,760 --> 00:04:36,080 Speaker 1: I am, Yeah, Well I used to be, at least 95 00:04:36,160 --> 00:04:38,480 Speaker 1: a lifetime ago. We're a couple of lifetimes ago. 96 00:04:38,600 --> 00:04:40,760 Speaker 2: Now back in the day. Is there such a thing 97 00:04:40,800 --> 00:04:42,320 Speaker 2: as a theoretical roboticist? 98 00:04:42,560 --> 00:04:45,599 Speaker 1: Uh? Yeah, there's a lot of theory in robotics as well. 99 00:04:45,800 --> 00:04:47,559 Speaker 1: But no, as we I guess we're not as clique 100 00:04:47,560 --> 00:04:50,080 Speaker 1: as you're just a roboticist. If you're into robots, you're 101 00:04:50,120 --> 00:04:51,560 Speaker 1: just a roboticist. 102 00:04:51,040 --> 00:04:53,880 Speaker 2: New York because you just build your own friends. You're like, hey, look, 103 00:04:53,880 --> 00:04:56,159 Speaker 2: I don't need people's friends. I can build my own. 104 00:04:56,600 --> 00:04:58,320 Speaker 1: Yeah. But as you said, I guess you need both 105 00:04:58,440 --> 00:05:01,839 Speaker 1: kinds of endeavors or search. You need experimental research and 106 00:05:01,839 --> 00:05:03,960 Speaker 1: you need theoretical research in order to figure out how 107 00:05:03,960 --> 00:05:06,240 Speaker 1: things work in the universe. Because I guess you need 108 00:05:06,279 --> 00:05:07,840 Speaker 1: to come up with a theory so that you can 109 00:05:08,000 --> 00:05:10,360 Speaker 1: prove it with an experiment, and you need an experiment 110 00:05:10,360 --> 00:05:12,640 Speaker 1: to prove the theories. Otherwise there's no science. 111 00:05:13,040 --> 00:05:15,400 Speaker 2: That's sort of a theoretical way of thinking about it, 112 00:05:15,560 --> 00:05:17,760 Speaker 2: that we come up with the theories and improve them 113 00:05:17,760 --> 00:05:22,280 Speaker 2: with experiment. Remember that sometimes experiments don't just prove theories. 114 00:05:22,320 --> 00:05:25,040 Speaker 2: They blow up theories and tell us that the universe 115 00:05:25,160 --> 00:05:27,800 Speaker 2: is different from the way we understand it and operates 116 00:05:27,800 --> 00:05:30,560 Speaker 2: in some other way we don't yet understand. Like the 117 00:05:30,560 --> 00:05:33,520 Speaker 2: photoelectric effect was a demonstration that boy, we really don't 118 00:05:33,600 --> 00:05:35,640 Speaker 2: understand at light and how it works, and it took 119 00:05:35,720 --> 00:05:38,520 Speaker 2: a few years before the theorist came up with any sort 120 00:05:38,560 --> 00:05:39,640 Speaker 2: of explanation for it. 121 00:05:39,800 --> 00:05:43,520 Speaker 1: Yeah, but I guess experimenter's lunches kind of experiment blindly, right. 122 00:05:43,560 --> 00:05:46,040 Speaker 1: You usually have some sort of theory at hand when 123 00:05:46,080 --> 00:05:49,320 Speaker 1: you design your experiments, when you go out there and 124 00:05:49,440 --> 00:05:50,120 Speaker 1: turn stuff on. 125 00:05:50,279 --> 00:05:52,120 Speaker 2: It's a bit of a raging debate right now in 126 00:05:52,200 --> 00:05:55,680 Speaker 2: experimental physics whether we should be focused on searching for 127 00:05:55,720 --> 00:05:59,160 Speaker 2: the ideas that theoretical physicists are suggesting, or whether we 128 00:05:59,200 --> 00:06:03,000 Speaker 2: should be developing strategies that are more just exploratory that 129 00:06:03,160 --> 00:06:06,400 Speaker 2: leave us open to surprises. Like when you turn on 130 00:06:06,440 --> 00:06:09,279 Speaker 2: the Hubble Space telescope and look out into space. Sure, 131 00:06:09,400 --> 00:06:11,440 Speaker 2: you want to see the things that you had in 132 00:06:11,480 --> 00:06:13,640 Speaker 2: mind to look at, but you're also open to like 133 00:06:13,880 --> 00:06:17,039 Speaker 2: seeing aliens waving at you, or seeing new kinds of 134 00:06:17,080 --> 00:06:19,279 Speaker 2: stuff you didn't even expect to see. 135 00:06:19,440 --> 00:06:21,039 Speaker 1: But I guess also at the same time, we're getting 136 00:06:21,040 --> 00:06:24,200 Speaker 1: to a spot where you know, things are so complex 137 00:06:24,320 --> 00:06:27,000 Speaker 1: and so subtle and so hidden that you kind of 138 00:06:27,120 --> 00:06:29,680 Speaker 1: need to know what you're looking for in a way, right, 139 00:06:29,680 --> 00:06:31,679 Speaker 1: it's kind of hard to just like look for everything. 140 00:06:31,760 --> 00:06:34,039 Speaker 2: It is really hard to look for everything you really 141 00:06:34,040 --> 00:06:36,560 Speaker 2: put your finger on it, especially when your data is 142 00:06:36,680 --> 00:06:39,440 Speaker 2: very statistical. If you do like a single experiment and 143 00:06:39,480 --> 00:06:42,280 Speaker 2: you get some weird result, you might be able to say, hey, look, 144 00:06:42,320 --> 00:06:45,400 Speaker 2: there's definitely something new here. But if the data are subtle, 145 00:06:45,440 --> 00:06:48,599 Speaker 2: if the new things appear as like trends in your data, 146 00:06:49,000 --> 00:06:50,680 Speaker 2: then you're right, it can be hard to know how 147 00:06:50,720 --> 00:06:52,640 Speaker 2: to find them. So then you have to play some 148 00:06:52,680 --> 00:06:55,599 Speaker 2: clever statistical arguments and say, well, you're the kinds of 149 00:06:55,680 --> 00:06:57,599 Speaker 2: things that we could see, and here are the ways 150 00:06:57,600 --> 00:06:59,480 Speaker 2: that we could search for them. So you have to 151 00:06:59,520 --> 00:07:01,599 Speaker 2: do a little bit more work to define the kinds 152 00:07:01,600 --> 00:07:04,120 Speaker 2: of things you might be able to see. Even if 153 00:07:04,120 --> 00:07:06,960 Speaker 2: you aren't sure which specifically might pop up in your data. 154 00:07:07,120 --> 00:07:10,240 Speaker 1: Well, sometimes there are cases where both the theories and 155 00:07:10,400 --> 00:07:13,400 Speaker 1: the experimental lists are stumped. And that is the case 156 00:07:13,400 --> 00:07:16,560 Speaker 1: where non physics. There's kind of a big hole in 157 00:07:16,560 --> 00:07:19,080 Speaker 1: physics in terms of our knowledge of how things work 158 00:07:19,080 --> 00:07:19,680 Speaker 1: in the universe. 159 00:07:19,840 --> 00:07:22,400 Speaker 2: That's right, at the most fundamental level, we still don't 160 00:07:22,440 --> 00:07:26,040 Speaker 2: really understand the basic rules of physics. We have two 161 00:07:26,600 --> 00:07:30,440 Speaker 2: pillars of modern physics relativity that tells us about space, 162 00:07:30,480 --> 00:07:33,400 Speaker 2: time and gravity, and quantum mechanics that tells us about 163 00:07:33,480 --> 00:07:36,240 Speaker 2: particles and forces, and we just don't know how to 164 00:07:36,360 --> 00:07:38,840 Speaker 2: bring them together. And it's important because it has to 165 00:07:38,920 --> 00:07:41,400 Speaker 2: do with one of the most basic questions in physics, 166 00:07:41,400 --> 00:07:44,160 Speaker 2: which is what is the universe made out of? What 167 00:07:44,320 --> 00:07:47,600 Speaker 2: is the fundamental fabric of reality? After all? 168 00:07:47,880 --> 00:07:50,480 Speaker 1: Yeah? And is it soft and comfortable? Is what I 169 00:07:50,520 --> 00:07:50,920 Speaker 1: want to know. 170 00:07:51,200 --> 00:07:52,960 Speaker 2: It seems to have a little bit of spandex in it. 171 00:07:53,000 --> 00:07:55,800 Speaker 1: Here, you guys, long is a stretchy that can accommodate 172 00:07:56,120 --> 00:07:56,840 Speaker 1: all sizes. 173 00:07:56,960 --> 00:07:59,120 Speaker 2: Because my waste is not the size it was back 174 00:07:59,120 --> 00:07:59,840 Speaker 2: in the day. 175 00:08:00,080 --> 00:08:02,960 Speaker 1: You want the universe to kind of expand with you, 176 00:08:02,960 --> 00:08:05,040 Speaker 1: your mind and your waste. But yeah, there's kind of 177 00:08:05,080 --> 00:08:07,280 Speaker 1: a big hole in our understanding of the universe, and 178 00:08:07,280 --> 00:08:09,960 Speaker 1: it has to do with gravity. We're not quite sure 179 00:08:10,000 --> 00:08:13,240 Speaker 1: where gravity falls, whether it falls or it fits with 180 00:08:13,400 --> 00:08:18,080 Speaker 1: quantum mechanic skill theory, or whether it works the way 181 00:08:18,080 --> 00:08:20,440 Speaker 1: that Einstein envisioned in special relativity. 182 00:08:20,520 --> 00:08:23,280 Speaker 2: Right, that's right. Einstein's special relativity tells us about light 183 00:08:23,320 --> 00:08:26,400 Speaker 2: and how it propagates. His theory of general relativity tells 184 00:08:26,440 --> 00:08:29,720 Speaker 2: us about space time and how it bends. And these 185 00:08:29,720 --> 00:08:32,640 Speaker 2: two theories are in conflict and tell us very different 186 00:08:32,679 --> 00:08:35,240 Speaker 2: stories about the nature of the universe. But so far 187 00:08:35,400 --> 00:08:37,160 Speaker 2: we haven't been able to figure out a way to 188 00:08:37,320 --> 00:08:41,720 Speaker 2: test them without building a solar system sized particle collider 189 00:08:42,080 --> 00:08:46,360 Speaker 2: or peering inside a black hole. So experimental physicists have 190 00:08:46,440 --> 00:08:50,120 Speaker 2: not really been able to contribute to this conversation until now. 191 00:08:50,280 --> 00:08:52,520 Speaker 1: So the deal in the podcast, we'll be asking the question, 192 00:08:57,800 --> 00:09:02,080 Speaker 1: can we test quantum gravity in a tabletop experiment? And 193 00:09:02,240 --> 00:09:04,720 Speaker 1: right here the word tabletop I think of board games. 194 00:09:07,240 --> 00:09:09,960 Speaker 1: Is this what we're talking about? Like a little cardboard 195 00:09:10,080 --> 00:09:14,400 Speaker 1: unfolding thing with pieces, And then you test quantum gravity exactly. 196 00:09:14,400 --> 00:09:16,679 Speaker 2: You can download the schematics from the internet and print 197 00:09:16,679 --> 00:09:19,760 Speaker 2: out your own Nobel Prize winning experiment. Do you go? 198 00:09:19,880 --> 00:09:23,920 Speaker 1: Is it called settlers of quarks or quantum ton. 199 00:09:24,400 --> 00:09:26,400 Speaker 2: I'll leave you to do the branding of it. But 200 00:09:26,440 --> 00:09:29,680 Speaker 2: when we say tabletop experiment in physics, we basically mean 201 00:09:30,080 --> 00:09:33,640 Speaker 2: something not like the large Hadron collider or something that 202 00:09:33,679 --> 00:09:37,640 Speaker 2: doesn't require a ten billion dollar facility staffed by thousands 203 00:09:37,679 --> 00:09:39,720 Speaker 2: of people. We mean the kind of thing a single 204 00:09:39,760 --> 00:09:42,560 Speaker 2: physicist could do in their laboratory, in the basement of 205 00:09:42,600 --> 00:09:43,960 Speaker 2: your nearby university. 206 00:09:44,520 --> 00:09:46,720 Speaker 1: I see you're talking about a million dollar tabletop, not 207 00:09:46,760 --> 00:09:48,440 Speaker 1: a billion dollar tabletop. 208 00:09:48,160 --> 00:09:51,080 Speaker 2: Exactly, just like everybody has a million dollar table in 209 00:09:51,120 --> 00:09:55,520 Speaker 2: their kitchen. No, it's really like a single physicist experiment, 210 00:09:55,600 --> 00:09:58,240 Speaker 2: something you could do in a reasonable physics lab, not 211 00:09:58,360 --> 00:10:00,880 Speaker 2: something people are going to be doing on their kits table. 212 00:10:00,840 --> 00:10:02,840 Speaker 1: Well, as usually, we were wondering how many people out 213 00:10:02,840 --> 00:10:06,000 Speaker 1: there had thought about this question or perhaps have any 214 00:10:06,040 --> 00:10:07,400 Speaker 1: ideas about how to do it. 215 00:10:07,440 --> 00:10:09,920 Speaker 2: So thanks very much to everybody who participates in this 216 00:10:10,040 --> 00:10:13,000 Speaker 2: segment of the podcast. If you've been listening for years 217 00:10:13,000 --> 00:10:15,720 Speaker 2: and would like to hear your voice speculating about the 218 00:10:15,720 --> 00:10:18,400 Speaker 2: topic of the day, please write to us two questions 219 00:10:18,440 --> 00:10:21,600 Speaker 2: at Danielandjorge dot com everybody's welcome. 220 00:10:21,840 --> 00:10:23,600 Speaker 1: So think about it for a second. Do you think 221 00:10:23,840 --> 00:10:27,480 Speaker 1: we can test quantum gravity on somebody's table? Here's what 222 00:10:27,520 --> 00:10:28,320 Speaker 1: people had to say. 223 00:10:28,400 --> 00:10:31,000 Speaker 4: Well, since quantum gravity is, you know, with the gravity 224 00:10:31,040 --> 00:10:34,120 Speaker 4: of the really small, I don't see why the experiments 225 00:10:34,559 --> 00:10:36,880 Speaker 4: with it couldn't be done on a tabletop. I just 226 00:10:37,040 --> 00:10:39,640 Speaker 4: have no idea what those experiments would even begin to 227 00:10:39,679 --> 00:10:40,000 Speaker 4: look like. 228 00:10:40,040 --> 00:10:40,240 Speaker 3: Though. 229 00:10:40,559 --> 00:10:42,880 Speaker 2: If yes, then it will come to our table soon. 230 00:10:43,000 --> 00:10:45,640 Speaker 1: But till then, I don't think it is possible at all. 231 00:10:46,040 --> 00:10:48,840 Speaker 2: Uh, yeah, you probably could, but probably not today. 232 00:10:49,480 --> 00:10:52,160 Speaker 3: I do not feel like we could test quantum gravity 233 00:10:52,200 --> 00:10:55,360 Speaker 3: in a tabletop experiment because you. 234 00:10:55,760 --> 00:10:59,480 Speaker 1: Need a lot of gravity for it to work, and 235 00:10:59,679 --> 00:11:02,000 Speaker 1: I don't think the Earth has that kind of gravity. 236 00:11:02,080 --> 00:11:05,120 Speaker 1: All right, not a lot of optimism, I like the 237 00:11:05,120 --> 00:11:07,880 Speaker 1: person who said the tabletop, I don't think so. But 238 00:11:08,000 --> 00:11:11,960 Speaker 1: maybe a desktop or on the floor, or on a shelf, 239 00:11:12,400 --> 00:11:16,120 Speaker 1: maybe mountain top maybe, yeah, tabletop on a mountain. There 240 00:11:16,160 --> 00:11:17,880 Speaker 1: you go, lower gravity. 241 00:11:18,080 --> 00:11:20,320 Speaker 2: Well, we talked recently about how to measure big g 242 00:11:20,520 --> 00:11:23,160 Speaker 2: and that experiment was definitely done on a mountain side 243 00:11:23,400 --> 00:11:27,720 Speaker 2: swinging pendulums next to a big mountain in Scotland. So yeah, 244 00:11:27,800 --> 00:11:30,600 Speaker 2: you can do funny gravity experiments on tops of mountains. 245 00:11:30,760 --> 00:11:33,480 Speaker 1: And I like the person who said probably, but not today, 246 00:11:33,840 --> 00:11:36,840 Speaker 1: Like is today a bad day for that? Were they 247 00:11:36,880 --> 00:11:40,360 Speaker 1: busy that day? How about next week? Next week work? 248 00:11:40,480 --> 00:11:42,439 Speaker 2: Please fill out this doodle pole for when we will 249 00:11:42,440 --> 00:11:43,439 Speaker 2: win a Nobel prize. 250 00:11:44,200 --> 00:11:48,000 Speaker 1: There you go. Yeah, I guess people didn't feel like 251 00:11:48,200 --> 00:11:51,240 Speaker 1: it could work. But let's find out, Daniel step us 252 00:11:51,240 --> 00:11:52,960 Speaker 1: through this. What is quantum gravity? 253 00:11:53,040 --> 00:11:55,800 Speaker 2: So when we say quantum gravity, what we mean is 254 00:11:55,840 --> 00:12:00,360 Speaker 2: a theory that explains both the quantum mechanical behavior super 255 00:12:00,440 --> 00:12:04,559 Speaker 2: tiny particles, the way like electrons and photons do things 256 00:12:04,679 --> 00:12:08,439 Speaker 2: that baseballs and basketballs and mountaintops don't do. You know, 257 00:12:08,480 --> 00:12:11,599 Speaker 2: they don't move in smooth paths. They have weird quantized 258 00:12:11,720 --> 00:12:15,160 Speaker 2: energy levels. They can be in a superposition of different states, 259 00:12:15,160 --> 00:12:18,040 Speaker 2: like maybe they're here, maybe they're there. They can interact 260 00:12:18,080 --> 00:12:20,319 Speaker 2: with each other and interfere in all sorts of complicated 261 00:12:20,400 --> 00:12:22,760 Speaker 2: ways described by their wave function. And we want a 262 00:12:22,800 --> 00:12:26,040 Speaker 2: theory that explains gravity as we know it. That things 263 00:12:26,080 --> 00:12:30,040 Speaker 2: seem to move in these inertial pass through curved space time, 264 00:12:30,600 --> 00:12:33,679 Speaker 2: and that mass in space tends to bend the path 265 00:12:34,040 --> 00:12:37,240 Speaker 2: which affects the motion of other mass. So we have 266 00:12:37,320 --> 00:12:40,200 Speaker 2: these two very different theories of the universe, and so 267 00:12:40,360 --> 00:12:43,920 Speaker 2: far we can't bring them together. So quantum gravity would 268 00:12:43,960 --> 00:12:48,120 Speaker 2: be a theory that explains both these things somehow harmoniously. 269 00:12:48,480 --> 00:12:50,440 Speaker 2: But it's not a theory that we have today. 270 00:12:50,640 --> 00:12:52,319 Speaker 1: Well, I guess maybe step us through a little bit 271 00:12:52,320 --> 00:12:54,520 Speaker 1: of what we haven't been able to bring these two 272 00:12:54,559 --> 00:12:56,760 Speaker 1: things together as far as I understand it. It's kind 273 00:12:56,760 --> 00:12:58,959 Speaker 1: of due to two things, right, Like, one is that 274 00:12:59,240 --> 00:13:02,719 Speaker 1: we haven't measure the gravitational force at the level of 275 00:13:03,240 --> 00:13:07,040 Speaker 1: quantum particles, right, that's one thing. And also we don't 276 00:13:07,080 --> 00:13:11,360 Speaker 1: know what happens to general relativity when you get down 277 00:13:11,400 --> 00:13:12,560 Speaker 1: to that small level. 278 00:13:12,320 --> 00:13:14,679 Speaker 2: Too exactly, I think you put your finger on it. Really, 279 00:13:14,720 --> 00:13:17,640 Speaker 2: we don't know what the gravity is for little particles. 280 00:13:17,760 --> 00:13:20,600 Speaker 2: The gravity for a baseball or for a moon. We 281 00:13:20,679 --> 00:13:22,840 Speaker 2: think we understand and we've been able to test that. 282 00:13:22,960 --> 00:13:23,120 Speaker 3: Right. 283 00:13:23,200 --> 00:13:26,760 Speaker 2: We see moon's orbiting planets, we see planets orbiting suns. 284 00:13:26,800 --> 00:13:29,600 Speaker 2: We see how gravity works. But that's all really really 285 00:13:29,640 --> 00:13:32,200 Speaker 2: big stuff. What we don't know is what happens when 286 00:13:32,240 --> 00:13:36,120 Speaker 2: you have gravity for particles, because particles are super duper tiny, 287 00:13:36,440 --> 00:13:39,720 Speaker 2: which makes it really complicated. For two reasons. One is 288 00:13:39,720 --> 00:13:42,600 Speaker 2: that they have almost no gravity. Remember that gravity is 289 00:13:42,640 --> 00:13:45,960 Speaker 2: like the weakest force in the universe, and so the 290 00:13:46,000 --> 00:13:49,520 Speaker 2: other forces overwhelm it. You try to do experiments with electrons, 291 00:13:49,559 --> 00:13:54,000 Speaker 2: then their charge is much more powerful than their mass. Right, 292 00:13:54,000 --> 00:13:57,800 Speaker 2: the electromagnetic force is much more powerful than the gravitational 293 00:13:57,840 --> 00:14:01,040 Speaker 2: force on an electron. So it's basically possible to measure 294 00:14:01,200 --> 00:14:03,160 Speaker 2: the gravitational force on an electron. 295 00:14:03,320 --> 00:14:04,640 Speaker 1: Can I ask why that is? 296 00:14:04,679 --> 00:14:04,880 Speaker 3: Though? 297 00:14:04,960 --> 00:14:09,000 Speaker 1: Like, couldn't I shoot an electron from here to London 298 00:14:09,040 --> 00:14:11,600 Speaker 1: and see if it curves with the curvature of the Earth. 299 00:14:11,840 --> 00:14:14,640 Speaker 2: You could try that, absolutely, I think you probably shouldn't 300 00:14:14,640 --> 00:14:17,200 Speaker 2: shoot beams across the surface of the Earth without getting 301 00:14:17,200 --> 00:14:20,600 Speaker 2: signatures from everybody who might live in between. But say 302 00:14:20,600 --> 00:14:22,680 Speaker 2: you did that, the electron would be effected by all 303 00:14:22,720 --> 00:14:26,400 Speaker 2: sorts of charged particles between here and London, right, There'd 304 00:14:26,400 --> 00:14:28,640 Speaker 2: be lots of other effects on the electron which would 305 00:14:28,720 --> 00:14:31,040 Speaker 2: swamp out any gravitational effects. 306 00:14:31,320 --> 00:14:34,400 Speaker 1: But I guess maybe, like from a satellite, I'm thinking, 307 00:14:34,520 --> 00:14:35,960 Speaker 1: you know, I just shoot a whole bunch of them, 308 00:14:36,120 --> 00:14:39,400 Speaker 1: and wouldn't the effects from other things kind of even 309 00:14:39,440 --> 00:14:42,000 Speaker 1: out If you shoot a bunch of them out, Like, 310 00:14:42,000 --> 00:14:45,000 Speaker 1: don't we have like quantum drives or like electron cannons. 311 00:14:45,320 --> 00:14:47,880 Speaker 1: What happens if I just shoot them out there in space? 312 00:14:48,000 --> 00:14:49,960 Speaker 1: Do they keep going straight or do they bend? 313 00:14:50,320 --> 00:14:52,840 Speaker 2: Yeah, you could build an electron gun and put it 314 00:14:52,880 --> 00:14:55,840 Speaker 2: in space and shoot them out, but still it would 315 00:14:55,880 --> 00:14:58,640 Speaker 2: be dominated by the effects of other particles. Remember space 316 00:14:58,720 --> 00:15:02,200 Speaker 2: is not totally empty. There's cosmic microwave background photons there, 317 00:15:02,280 --> 00:15:04,760 Speaker 2: there's other charge particles from the Sun, and all of 318 00:15:04,760 --> 00:15:07,440 Speaker 2: these would dominate the fate of that electron. Really, the 319 00:15:07,480 --> 00:15:10,840 Speaker 2: problem is that the charge is more powerful than the mass. 320 00:15:11,240 --> 00:15:13,320 Speaker 2: We talked about this once, and this is either because 321 00:15:13,400 --> 00:15:16,560 Speaker 2: gravity itself is just weaker than the other forces for 322 00:15:16,640 --> 00:15:20,000 Speaker 2: reasons we don't understand, or because electrons are just packed 323 00:15:20,000 --> 00:15:22,760 Speaker 2: with a lot of charge compared to how much mass 324 00:15:22,840 --> 00:15:25,280 Speaker 2: they have. You can think about it sort of either way. 325 00:15:25,320 --> 00:15:27,320 Speaker 2: But that just means that the effect of gravity is 326 00:15:27,360 --> 00:15:30,040 Speaker 2: tiny compared to the effect of electromagnetism. So to do 327 00:15:30,080 --> 00:15:33,360 Speaker 2: that experiment, you'd need to isolate those particles from any 328 00:15:33,440 --> 00:15:35,920 Speaker 2: sort of effect. And today we'll talk about an experiment 329 00:15:35,960 --> 00:15:37,480 Speaker 2: that's going to try to do that, all. 330 00:15:37,480 --> 00:15:40,200 Speaker 1: Right, So then that's where quantum gravity comes in. It's 331 00:15:40,360 --> 00:15:42,240 Speaker 1: kind of a is it a theory or an idea 332 00:15:42,320 --> 00:15:44,680 Speaker 1: that tries to bring these two big ideas together. 333 00:15:44,880 --> 00:15:47,600 Speaker 2: It's not a theory. It's like a category of theories. 334 00:15:47,640 --> 00:15:50,760 Speaker 2: It's like a dreamt of theory. What we want is 335 00:15:50,760 --> 00:15:52,920 Speaker 2: a theory that bring these two things together. We don't 336 00:15:52,920 --> 00:15:55,480 Speaker 2: have one. We don't know what the theory of quantum 337 00:15:55,560 --> 00:15:58,520 Speaker 2: gravity is. You know, sometimes you have like ten different 338 00:15:58,600 --> 00:16:00,880 Speaker 2: theories that describe the universe. The experiment has to go 339 00:16:00,880 --> 00:16:03,200 Speaker 2: off and tell you which one is correct. Right now, 340 00:16:03,240 --> 00:16:06,200 Speaker 2: we have zero. We have zero theories that explain quantum 341 00:16:06,200 --> 00:16:09,680 Speaker 2: mechanics and gravity at the same time. So we sort 342 00:16:09,720 --> 00:16:12,520 Speaker 2: of need an experimental result to be like, hey, this 343 00:16:12,680 --> 00:16:15,240 Speaker 2: is the right direction though where hey, here's something to 344 00:16:15,280 --> 00:16:17,680 Speaker 2: grab on to, here's a clue. But there's the second 345 00:16:17,720 --> 00:16:20,400 Speaker 2: reason why these experiments are difficult that we didn't get 346 00:16:20,440 --> 00:16:22,520 Speaker 2: to yet. One is just that gravity is so weak, 347 00:16:22,720 --> 00:16:25,880 Speaker 2: and the other is that these particles do things that 348 00:16:25,920 --> 00:16:28,520 Speaker 2: we don't know how to explain with gravity, Like particles 349 00:16:28,920 --> 00:16:32,000 Speaker 2: don't have smooth paths. It's not like the electron is 350 00:16:32,160 --> 00:16:35,600 Speaker 2: always somewhere, has some velocity. You know, you want to 351 00:16:35,640 --> 00:16:38,520 Speaker 2: calculate the gravity of an electron, you have to know 352 00:16:38,680 --> 00:16:41,000 Speaker 2: where it is, so you know how far away it is, 353 00:16:41,120 --> 00:16:44,200 Speaker 2: you can calculate it's gravity. But electrons don't have specific 354 00:16:44,240 --> 00:16:47,760 Speaker 2: locations that have probabilities, so we don't know. For example, 355 00:16:47,880 --> 00:16:50,080 Speaker 2: if an electron, when it has probabilities to be in 356 00:16:50,160 --> 00:16:53,080 Speaker 2: multiple places, does it mean it has like multiple different 357 00:16:53,280 --> 00:16:57,080 Speaker 2: possible gravities. We just don't know how to do gravity 358 00:16:57,120 --> 00:16:59,640 Speaker 2: for things that have uncertainties in their locations. 359 00:17:00,120 --> 00:17:02,160 Speaker 1: You mean, we don't know how to do that if 360 00:17:02,200 --> 00:17:06,960 Speaker 1: gravity was not a quantum force, right, Like you're sort 361 00:17:06,960 --> 00:17:10,280 Speaker 1: of assuming that. I guess you want gravity to be 362 00:17:10,560 --> 00:17:12,679 Speaker 1: like a quantum force like the other forces that we 363 00:17:12,720 --> 00:17:14,120 Speaker 1: know about, right. 364 00:17:13,960 --> 00:17:15,719 Speaker 2: Yeah, that's sort of one of the basic questions when 365 00:17:15,760 --> 00:17:17,679 Speaker 2: you want to build the theory of quantum gravity, like 366 00:17:17,800 --> 00:17:21,000 Speaker 2: is it a quantum force? If so, then two electrons 367 00:17:21,040 --> 00:17:25,480 Speaker 2: interacting gravitationally wouldn't like collapse each other's wave functions. Some 368 00:17:25,600 --> 00:17:27,720 Speaker 2: bits of one wave function would interact with some bits 369 00:17:27,760 --> 00:17:29,480 Speaker 2: of another wave function, and they could do all sorts 370 00:17:29,520 --> 00:17:32,399 Speaker 2: of weird quantum interactions. But if gravity is actually a 371 00:17:32,440 --> 00:17:35,480 Speaker 2: classical force and not a quantum force, then it would 372 00:17:35,520 --> 00:17:38,360 Speaker 2: collapse the wave function sort of like when you use 373 00:17:38,400 --> 00:17:41,240 Speaker 2: a detector in a double slit experiment, it forces the 374 00:17:41,280 --> 00:17:44,040 Speaker 2: particle to pick one of the options instead of the 375 00:17:44,080 --> 00:17:47,200 Speaker 2: other one. So we just don't know, like is gravity classical, 376 00:17:47,359 --> 00:17:49,920 Speaker 2: is it quantum mechanical. We just don't even know where 377 00:17:49,960 --> 00:17:50,359 Speaker 2: to begin. 378 00:17:50,760 --> 00:17:53,119 Speaker 1: And when you say classical, you mean like basically not 379 00:17:53,359 --> 00:17:56,920 Speaker 1: quantum mechanical, like not fuzzy, not uncertain. 380 00:17:57,040 --> 00:18:00,600 Speaker 2: Yeah, exactly, we mean not quantum is sort of an 381 00:18:00,640 --> 00:18:03,919 Speaker 2: overused word. Some people say classical to me, not relativistic, 382 00:18:04,000 --> 00:18:07,960 Speaker 2: like Newtonian, but today we mean not quantum mechanical. So 383 00:18:08,160 --> 00:18:11,000 Speaker 2: we don't know if gravity, like really is just classical 384 00:18:11,040 --> 00:18:14,440 Speaker 2: the way Einstein described it, thinking about space as smooth 385 00:18:14,560 --> 00:18:17,199 Speaker 2: and continuous and everything having passed, or if it is 386 00:18:17,240 --> 00:18:19,359 Speaker 2: a quantum effect, in which case it could either be 387 00:18:19,400 --> 00:18:23,760 Speaker 2: a force like you suggested, mediated by weird gravitons, or 388 00:18:23,800 --> 00:18:27,840 Speaker 2: maybe like space itself is quantum mechanical and uncertain. If 389 00:18:27,920 --> 00:18:31,479 Speaker 2: gravity is the curvature of space, maybe space itself can 390 00:18:31,520 --> 00:18:34,040 Speaker 2: be like maybe bent here and maybe bent there in 391 00:18:34,040 --> 00:18:38,440 Speaker 2: some weird quantum mechanical way. There's so many possible directions 392 00:18:38,440 --> 00:18:41,639 Speaker 2: for quantum gravity, nobody really knows which one is going 393 00:18:41,680 --> 00:18:45,000 Speaker 2: to build a viable theory that even can do calculations. 394 00:18:45,160 --> 00:18:47,720 Speaker 1: All right, well, let's get a little bit deeper into 395 00:18:47,760 --> 00:18:50,720 Speaker 1: quantum gravity and whether or not we can test it 396 00:18:51,000 --> 00:18:54,280 Speaker 1: and test it for under a billion dollars, because I 397 00:18:54,280 --> 00:18:57,000 Speaker 1: guess the cheaper the better. We'll dig into that, but first, 398 00:18:57,040 --> 00:19:11,480 Speaker 1: let's take a quick break. All right, we're talking about 399 00:19:11,560 --> 00:19:14,840 Speaker 1: quantum gravity and whether or not that is a thing 400 00:19:15,000 --> 00:19:18,119 Speaker 1: at all, whether it will bring together quantum mechanics in 401 00:19:18,200 --> 00:19:21,360 Speaker 1: general relativity to give us one theory of the universe, 402 00:19:21,480 --> 00:19:24,000 Speaker 1: and whether or not we can even design experiments to 403 00:19:24,160 --> 00:19:25,200 Speaker 1: test such a theory. 404 00:19:25,320 --> 00:19:27,240 Speaker 2: I like your threshold of a billion dollars. 405 00:19:27,840 --> 00:19:31,160 Speaker 1: Yeah, well though these days with inflation, maybe that's more 406 00:19:31,240 --> 00:19:31,879 Speaker 1: like ten billion. 407 00:19:31,920 --> 00:19:32,080 Speaker 3: Though. 408 00:19:33,640 --> 00:19:35,879 Speaker 2: You know, if we could spend a billion dollars and 409 00:19:35,920 --> 00:19:38,840 Speaker 2: get the answer to quantum gravity, I'm pretty sure we 410 00:19:38,840 --> 00:19:40,840 Speaker 2: would do it. The truth is, the experiments might cost 411 00:19:41,080 --> 00:19:43,000 Speaker 2: a lot more than one billion dollars. 412 00:19:43,040 --> 00:19:46,480 Speaker 1: All right, well, let's dig into the cost of these experiments. 413 00:19:46,560 --> 00:19:48,680 Speaker 1: How can we test quantum gravity and figure out whether 414 00:19:48,760 --> 00:19:49,840 Speaker 1: or not it's a real thing or not. 415 00:19:50,000 --> 00:19:51,840 Speaker 2: Well, you had sort of the right idea, which is like, 416 00:19:52,240 --> 00:19:54,560 Speaker 2: let's just zoom in on a quantum particle and look 417 00:19:54,600 --> 00:19:57,400 Speaker 2: at its gravity somehow. But remember the scale of things 418 00:19:57,440 --> 00:20:00,480 Speaker 2: we're talking about here, Like these particles are super duper tiny, 419 00:20:00,800 --> 00:20:03,359 Speaker 2: and the effects we're talking about what happened on really 420 00:20:03,440 --> 00:20:07,520 Speaker 2: really short distance scales. Like gravity gets more powerful when 421 00:20:07,520 --> 00:20:10,480 Speaker 2: things get closer together. In order for gravity to be 422 00:20:10,520 --> 00:20:13,239 Speaker 2: powerful enough for us to really test it, you need 423 00:20:13,280 --> 00:20:16,199 Speaker 2: to get things together to like the Plank scale distances 424 00:20:16,480 --> 00:20:20,000 Speaker 2: we're talking about, like ten to the minus thirty five meters. 425 00:20:20,160 --> 00:20:22,600 Speaker 2: So until recently it seemed like, well, the only way 426 00:20:22,600 --> 00:20:25,480 Speaker 2: to test quantum gravity is to have like a microscope 427 00:20:25,520 --> 00:20:27,560 Speaker 2: that can see effects at the scale of ten to 428 00:20:27,600 --> 00:20:30,920 Speaker 2: the minus thirty five meters, which felt almost impossible. 429 00:20:31,080 --> 00:20:33,320 Speaker 1: Now, I guess, pain me a picture here of what 430 00:20:33,359 --> 00:20:36,159 Speaker 1: it is that you would be trying to do. Like, 431 00:20:36,200 --> 00:20:37,840 Speaker 1: for example, what if I just take a bunch of 432 00:20:37,960 --> 00:20:41,280 Speaker 1: hydrogen atoms. Like a hydrogen atom is just an electron 433 00:20:41,320 --> 00:20:45,320 Speaker 1: and a proton, so it's perfectly balanced in terms of charge. 434 00:20:45,359 --> 00:20:47,000 Speaker 1: And I know that if I stick up bundle I'm 435 00:20:47,000 --> 00:20:50,600 Speaker 1: in a container, they'll sort of tend to fall down 436 00:20:50,640 --> 00:20:52,879 Speaker 1: because of gravity, right, They'll sort of accumulate the pressure 437 00:20:52,920 --> 00:20:55,560 Speaker 1: of the hydrogen tank will be higher at the bottom 438 00:20:55,600 --> 00:20:58,359 Speaker 1: than at the top. That means gravity is working on 439 00:20:58,400 --> 00:21:00,560 Speaker 1: them and it is pulling them down. Can I build 440 00:21:00,600 --> 00:21:03,119 Speaker 1: some sort of model or theory that kind of models 441 00:21:03,240 --> 00:21:05,720 Speaker 1: or tells me how it's working at the quantum level. 442 00:21:05,880 --> 00:21:09,399 Speaker 2: Well, there's the theoretical difficulty, and then there's the experimental difficulty. 443 00:21:09,800 --> 00:21:13,000 Speaker 2: On the theoretical side. Like we've tried to build those theories, 444 00:21:13,040 --> 00:21:16,159 Speaker 2: they just don't work. Gravity is complicated because everything is 445 00:21:16,200 --> 00:21:19,439 Speaker 2: affected by it. It's not like electromagnetism where you can 446 00:21:19,480 --> 00:21:24,680 Speaker 2: like shoot out photons and those photons themselves don't feel electromagnetism, right, 447 00:21:24,680 --> 00:21:28,920 Speaker 2: Photons don't interact with other photons. Gravity interacts with everything 448 00:21:28,960 --> 00:21:31,440 Speaker 2: with energy. So when you try to build a quantum 449 00:21:31,480 --> 00:21:35,440 Speaker 2: theory of gravity, like including the exchange of gravitons, those 450 00:21:35,480 --> 00:21:39,159 Speaker 2: gravitons amid other gravitons which feel those gravitons, and it 451 00:21:39,200 --> 00:21:41,919 Speaker 2: gets very hairy, very quickly. We talked once about the 452 00:21:42,200 --> 00:21:45,240 Speaker 2: strong nuclear force, which has a similar property that it's 453 00:21:45,359 --> 00:21:49,160 Speaker 2: gluons amid other gluons which affect other gluons, and it's 454 00:21:49,280 --> 00:21:52,720 Speaker 2: a nightmare to do any calculations. Gravity is even more 455 00:21:52,760 --> 00:21:55,439 Speaker 2: complex than that, and that's sort of one of the 456 00:21:55,480 --> 00:21:58,200 Speaker 2: reasons why it's been so difficult to build a theory. 457 00:21:58,280 --> 00:22:00,520 Speaker 2: So anytime people build a theory of quantum gravity, it 458 00:22:00,600 --> 00:22:04,200 Speaker 2: just sort of predicts nonsense. We just can't mathematically make 459 00:22:04,280 --> 00:22:07,159 Speaker 2: it work. And then there's the experimental challenge. And what 460 00:22:07,200 --> 00:22:09,119 Speaker 2: you're talking about is like trying to build a setup 461 00:22:09,160 --> 00:22:12,600 Speaker 2: where you can see the gravitational effects on particles. But 462 00:22:12,720 --> 00:22:15,240 Speaker 2: the experiment that you describe like a bunch of hydrogen, 463 00:22:15,440 --> 00:22:17,560 Speaker 2: you know, those are classical effects. The fact that those 464 00:22:17,640 --> 00:22:20,680 Speaker 2: hydrogen atoms are quantum particles is irrelevant to the fact 465 00:22:20,720 --> 00:22:22,359 Speaker 2: that they have more pressure on the bottom of the 466 00:22:22,400 --> 00:22:24,160 Speaker 2: tank than the top of the tank. Oh, I see. 467 00:22:24,200 --> 00:22:27,199 Speaker 1: You're trying to kind of like see what happens to 468 00:22:27,240 --> 00:22:31,919 Speaker 1: gravity at the quantum distance level. Right, that's kind of 469 00:22:31,920 --> 00:22:34,760 Speaker 1: the problem, right, Like you might be able to design 470 00:22:34,960 --> 00:22:37,600 Speaker 1: a hydrogen gun something that shoots hydrogen atoms and you 471 00:22:37,640 --> 00:22:40,639 Speaker 1: can track how the gravity affects its path, maybe, but 472 00:22:40,880 --> 00:22:43,560 Speaker 1: that doesn't necessarily tell you whether or not there's like 473 00:22:43,640 --> 00:22:48,560 Speaker 1: uncertainty or whether the there's fuzziness at the you know, 474 00:22:48,920 --> 00:22:49,880 Speaker 1: really small distance. 475 00:22:50,160 --> 00:22:51,800 Speaker 2: Exactly in the same way that like every time you 476 00:22:51,880 --> 00:22:55,399 Speaker 2: toss a baseball, and principle you're tossing quantum objects right 477 00:22:55,400 --> 00:22:57,439 Speaker 2: at a baseball. That just a bunch of quantum objects, and 478 00:22:57,480 --> 00:23:01,159 Speaker 2: definitely they're feeling gravity. We're not asking like, do electrons 479 00:23:01,160 --> 00:23:03,640 Speaker 2: and protons feel gravity? We're pretty sure they do. We're 480 00:23:03,640 --> 00:23:07,280 Speaker 2: asking is how does their quantum mechanicalness interact with their 481 00:23:07,320 --> 00:23:11,400 Speaker 2: gravitational attraction, you know, when they're doing their weird quantum stuff. 482 00:23:11,600 --> 00:23:14,480 Speaker 2: How does gravity play a role with that? You know, 483 00:23:14,520 --> 00:23:16,520 Speaker 2: if you have a particle that like has a possibility 484 00:23:16,560 --> 00:23:19,960 Speaker 2: to be here and they're simultaneously, what is its gravity? 485 00:23:20,280 --> 00:23:21,879 Speaker 2: So you've got to get something to be showing as 486 00:23:21,960 --> 00:23:25,600 Speaker 2: quantum effects, which means really small distances and revealing its 487 00:23:25,640 --> 00:23:30,240 Speaker 2: gravitational interactions, which requires really really large masses, which is 488 00:23:30,280 --> 00:23:33,400 Speaker 2: why some people are excited to see inside black holes, 489 00:23:33,640 --> 00:23:36,160 Speaker 2: because that's where you have like, really really really big 490 00:23:36,200 --> 00:23:40,640 Speaker 2: masses squeeze down to quantum distances, and so what's going 491 00:23:40,640 --> 00:23:43,160 Speaker 2: on inside a black hole would really tell us about 492 00:23:43,200 --> 00:23:46,560 Speaker 2: the nature of quantum gravity and therefore the deepest nature 493 00:23:46,560 --> 00:23:49,960 Speaker 2: of space time itself. Of course, we can't see inside 494 00:23:50,040 --> 00:23:52,720 Speaker 2: black holes, so those secrets are hidden from us. 495 00:23:53,720 --> 00:23:56,760 Speaker 1: Yeah, you might want to let that one go. It 496 00:23:56,800 --> 00:23:59,359 Speaker 1: seems like we're never going to find out what's inside 497 00:23:59,400 --> 00:24:00,000 Speaker 1: of a black hole. 498 00:24:00,359 --> 00:24:04,000 Speaker 2: There's even a theory called cosmic censorship that suggests will 499 00:24:04,040 --> 00:24:06,120 Speaker 2: never be able to answer this because the answers are 500 00:24:06,160 --> 00:24:09,120 Speaker 2: always going to be hidden behind some weird horizon. It's 501 00:24:09,119 --> 00:24:10,520 Speaker 2: sort of a pessimistic approach. 502 00:24:10,880 --> 00:24:13,720 Speaker 1: WHOA, I didn't know there was a ratings board for 503 00:24:13,760 --> 00:24:14,280 Speaker 1: the universe. 504 00:24:15,280 --> 00:24:17,440 Speaker 2: And there are even some theorists that suggests this whole 505 00:24:17,600 --> 00:24:20,359 Speaker 2: enterprise is a waste of time. Like Freeman Dyson, the 506 00:24:20,359 --> 00:24:22,640 Speaker 2: guy who thought of Dyson's fears. He likes to think 507 00:24:22,640 --> 00:24:26,160 Speaker 2: that we live in a dualistic universe, that quantum mechanics 508 00:24:26,200 --> 00:24:29,040 Speaker 2: and gravity just sort of like rule in different regimes 509 00:24:29,040 --> 00:24:31,560 Speaker 2: and they never actually overlap at any place where they 510 00:24:31,640 --> 00:24:35,399 Speaker 2: come into contact is hidden from us by these event horizons. 511 00:24:35,840 --> 00:24:39,840 Speaker 1: Like maybe gravity is classical and it's not quantum. But 512 00:24:40,160 --> 00:24:42,960 Speaker 1: you're saying, or he's saying that at the quantum level, 513 00:24:43,520 --> 00:24:46,160 Speaker 1: there's things that are happening that you will never find out. 514 00:24:46,320 --> 00:24:49,000 Speaker 2: Yeah, exactly that maybe you don't have a single theory 515 00:24:49,000 --> 00:24:51,639 Speaker 2: at the universe. You like two theories and each have 516 00:24:51,720 --> 00:24:54,680 Speaker 2: their own regime and they never overlap anywhere we could 517 00:24:54,720 --> 00:24:57,159 Speaker 2: test them. But a lot of people don't really like 518 00:24:57,200 --> 00:25:00,119 Speaker 2: that theory. I really don't like that theory because I 519 00:25:00,119 --> 00:25:02,480 Speaker 2: want there to be one theory of the universe, one 520 00:25:02,520 --> 00:25:05,880 Speaker 2: thing that explains everything, and I'd love to see these 521 00:25:05,920 --> 00:25:08,600 Speaker 2: two different concepts battle it out. I want to force 522 00:25:08,640 --> 00:25:10,439 Speaker 2: the universe to show us what the answer is. 523 00:25:10,680 --> 00:25:13,359 Speaker 1: But I wonder couldn't they Couldn't he be right though, Like, 524 00:25:13,359 --> 00:25:16,400 Speaker 1: couldn't it just be the gravity, you know, bend space 525 00:25:16,880 --> 00:25:21,320 Speaker 1: and quantum fields and quantum particles exist in that bent space. 526 00:25:21,520 --> 00:25:24,160 Speaker 2: Yeah, he could be right. But if we can come 527 00:25:24,240 --> 00:25:28,280 Speaker 2: up with some experiments that force quantum mechanics and gravity 528 00:25:28,320 --> 00:25:31,359 Speaker 2: to speak at the same moment, to say, like, all right, 529 00:25:31,720 --> 00:25:34,680 Speaker 2: here's what happens when you have a particle that has 530 00:25:34,720 --> 00:25:37,879 Speaker 2: two possibilities and it has some gravity, then we'll know. 531 00:25:38,000 --> 00:25:41,320 Speaker 2: And maybe he's right. Maybe gravity really is classical. And 532 00:25:41,359 --> 00:25:44,400 Speaker 2: what happens when particles interact gravitationally is that their wave 533 00:25:44,480 --> 00:25:48,400 Speaker 2: functions collapse, because that's what happens when classical objects interact 534 00:25:48,400 --> 00:25:50,800 Speaker 2: with quantum objects. But it sure would be nice to know. 535 00:25:51,160 --> 00:25:54,480 Speaker 1: Yeah, gravity is pretty classic. So talk to us a 536 00:25:54,520 --> 00:25:57,439 Speaker 1: little bit about how we've been trying to study this 537 00:25:57,600 --> 00:25:58,960 Speaker 1: or get answers to this question. 538 00:25:59,240 --> 00:26:02,000 Speaker 2: So, other than wishing we could see inside a black hole, 539 00:26:02,440 --> 00:26:05,920 Speaker 2: the other typical tool in our toolkit is a particle collider. 540 00:26:06,320 --> 00:26:08,960 Speaker 2: You build a big particle smasher, you pour a lot 541 00:26:09,000 --> 00:26:12,320 Speaker 2: of energy into one tiny little spot. Then you can 542 00:26:12,400 --> 00:26:15,840 Speaker 2: like break open bonds. You can see how the pieces interact. 543 00:26:15,960 --> 00:26:18,960 Speaker 2: But in order to see gravitational effects, you would need 544 00:26:19,160 --> 00:26:22,919 Speaker 2: so much energy. You'd basically need like the Plank energy. 545 00:26:23,040 --> 00:26:26,000 Speaker 2: It would require building a collider that's like the size 546 00:26:26,000 --> 00:26:28,480 Speaker 2: of the galaxy in order to get enough energy into it. 547 00:26:28,600 --> 00:26:31,640 Speaker 2: Or some calculations suggest if you build a particle collider 548 00:26:31,640 --> 00:26:33,680 Speaker 2: that big, it would collapse into a black hole. 549 00:26:33,840 --> 00:26:35,600 Speaker 1: Wait, why do you need so much energy? 550 00:26:35,720 --> 00:26:38,920 Speaker 2: Because gravity is really really weak, which means it operates 551 00:26:38,920 --> 00:26:41,919 Speaker 2: on really small distance scales. In order to get to 552 00:26:42,000 --> 00:26:45,200 Speaker 2: small distance scales, you need a lot of energy. It's 553 00:26:45,200 --> 00:26:47,600 Speaker 2: sort of like the de Burgly wavelength, right, Like the 554 00:26:47,640 --> 00:26:51,119 Speaker 2: wavelength of a particle is inversely proportional to its momentum, 555 00:26:51,400 --> 00:26:54,600 Speaker 2: and so the more momentum an object has, the smaller 556 00:26:54,680 --> 00:26:56,680 Speaker 2: its wavelength. And you want to see like really really 557 00:26:56,720 --> 00:27:00,680 Speaker 2: short distance effects, you need really really high energy probes. 558 00:27:01,160 --> 00:27:04,520 Speaker 2: So you need like super duper high energy particle collisions 559 00:27:04,640 --> 00:27:07,760 Speaker 2: in order to see things happening at really short distance scales. 560 00:27:07,960 --> 00:27:10,800 Speaker 1: Why because I guess the more energy two particles have 561 00:27:10,840 --> 00:27:13,119 Speaker 1: when they smash into each other somehow, that gives you 562 00:27:13,160 --> 00:27:15,200 Speaker 1: more resolution in space. 563 00:27:15,560 --> 00:27:19,120 Speaker 2: Yeah, exactly, The more momentum the particle has, the smaller 564 00:27:19,160 --> 00:27:21,560 Speaker 2: the wavelength of their wave function. You can think of 565 00:27:21,560 --> 00:27:24,200 Speaker 2: the motion of every particle is described by a little 566 00:27:24,240 --> 00:27:26,800 Speaker 2: wave function that determines what happens to it, the same 567 00:27:26,840 --> 00:27:28,720 Speaker 2: way you can think of like light as a wave, right, 568 00:27:28,800 --> 00:27:32,440 Speaker 2: it's wiggling around, And if you're using light to see things, 569 00:27:32,560 --> 00:27:34,600 Speaker 2: you can only really see things that are the wavelength 570 00:27:34,640 --> 00:27:38,320 Speaker 2: of that light or larger. Anything smaller than that wavelength 571 00:27:38,359 --> 00:27:40,960 Speaker 2: the photon sort of can't interact with it. And so 572 00:27:41,000 --> 00:27:42,960 Speaker 2: you want to see really really small effects, you need 573 00:27:43,040 --> 00:27:46,720 Speaker 2: really really high energy photons or in our case, we 574 00:27:46,760 --> 00:27:49,440 Speaker 2: need really really high energy particle beams to see very 575 00:27:49,520 --> 00:27:52,000 Speaker 2: very short distance interactions. 576 00:27:51,640 --> 00:27:53,920 Speaker 1: Right, Because I guess you need things with mass, right 577 00:27:53,960 --> 00:27:57,240 Speaker 1: to test the quantum gravity or gravity at the quantum level. 578 00:27:57,280 --> 00:27:59,480 Speaker 1: And so that's also true for things with mass, Like 579 00:27:59,520 --> 00:28:03,920 Speaker 1: the faster they're going, the smaller they are, is. 580 00:28:03,840 --> 00:28:06,520 Speaker 2: That what you're saying effectively, the smaller their wavelength. Is. 581 00:28:06,640 --> 00:28:08,760 Speaker 2: Another way to think about it is that you need 582 00:28:08,880 --> 00:28:12,679 Speaker 2: enough energy in those collisions to make gravity stronger, Like 583 00:28:12,760 --> 00:28:15,760 Speaker 2: you want to overcome the electromagnetic force and the strong 584 00:28:15,800 --> 00:28:19,200 Speaker 2: force and make gravity as powerful as those other forces 585 00:28:19,480 --> 00:28:21,240 Speaker 2: so that you can see its effects. You need to 586 00:28:21,280 --> 00:28:23,560 Speaker 2: pour a lot of energy into those collisions, because the 587 00:28:23,560 --> 00:28:25,639 Speaker 2: power of gravity is linked to the mass and to 588 00:28:25,720 --> 00:28:28,480 Speaker 2: the energy of these things. So you pour enough energy 589 00:28:28,480 --> 00:28:32,320 Speaker 2: into one little location, you'll get a very strong gravitational interaction. 590 00:28:32,760 --> 00:28:34,760 Speaker 2: So if we want to see the gravitational effects on 591 00:28:34,840 --> 00:28:37,200 Speaker 2: quantum particles, you need to pour a lot of energy 592 00:28:37,200 --> 00:28:38,320 Speaker 2: into one little spot. 593 00:28:39,080 --> 00:28:40,720 Speaker 1: And is that the only way to do it through 594 00:28:40,720 --> 00:28:44,000 Speaker 1: particle colliders? Isn't there some like I don't know, like 595 00:28:44,080 --> 00:28:48,600 Speaker 1: aim your beams better approach or make smaller wavelength particles. 596 00:28:48,640 --> 00:28:50,400 Speaker 1: I don't know, Like can we do this without making 597 00:28:50,400 --> 00:28:51,960 Speaker 1: a black hole in our solar system? 598 00:28:52,160 --> 00:28:54,320 Speaker 2: The short answer is no. I mean, we do our 599 00:28:54,360 --> 00:28:57,560 Speaker 2: best with particle beam aiming already. But really the limitation 600 00:28:57,680 --> 00:28:59,720 Speaker 2: is the energy of the particles, and we have them 601 00:28:59,760 --> 00:29:02,800 Speaker 2: going as fast as we can, and the wavelength of 602 00:29:02,840 --> 00:29:06,160 Speaker 2: the particle is determined by its energy. So really sort 603 00:29:06,160 --> 00:29:08,560 Speaker 2: of at the limit there. We talked recently about other 604 00:29:08,600 --> 00:29:12,520 Speaker 2: strategies for accelerating particles that might make it smaller, faster, cheaper. 605 00:29:12,800 --> 00:29:16,240 Speaker 2: So there might be a breakthrough in accelerator technology which 606 00:29:16,240 --> 00:29:18,480 Speaker 2: could leap us up like a factor of ten or 607 00:29:18,520 --> 00:29:21,080 Speaker 2: one hundred. But we are like a factor of a 608 00:29:21,200 --> 00:29:24,640 Speaker 2: trillion away from being able to test quantum gravity in 609 00:29:24,680 --> 00:29:27,480 Speaker 2: particle colliders. So really, nowhere in the near future will 610 00:29:27,480 --> 00:29:29,440 Speaker 2: particle colliders be able to answer this question? 611 00:29:29,720 --> 00:29:32,000 Speaker 1: All right, well, I think part of what we're going 612 00:29:32,040 --> 00:29:34,719 Speaker 1: to be talking about here today are experiments that have 613 00:29:35,280 --> 00:29:37,880 Speaker 1: kind of ideas about how to test this without destroying 614 00:29:37,920 --> 00:29:42,840 Speaker 1: the Solar system. And they involve diamonds and lasers and 615 00:29:42,960 --> 00:29:48,360 Speaker 1: space lasers. No tabletop lasers in space. No, no tabletop 616 00:29:48,440 --> 00:29:51,560 Speaker 1: lasers in Pasadena. Oh that take up space in Pasadena. 617 00:29:52,720 --> 00:29:53,840 Speaker 2: A table near you? 618 00:29:54,160 --> 00:29:56,520 Speaker 1: All right, Well, to dig into it, Daniel, What is 619 00:29:56,520 --> 00:29:57,840 Speaker 1: the first of these experiments? 620 00:29:57,960 --> 00:30:01,280 Speaker 2: So the first of the experiments involves diamonds, and the 621 00:30:01,360 --> 00:30:04,880 Speaker 2: goal here essentially is to create a situation where a 622 00:30:05,000 --> 00:30:08,880 Speaker 2: particle has the probability of being in two places at once, 623 00:30:09,200 --> 00:30:11,719 Speaker 2: and then you test its gravity. You see, if it's 624 00:30:11,800 --> 00:30:14,480 Speaker 2: gravity really is sort of like split between its two 625 00:30:14,520 --> 00:30:18,160 Speaker 2: possible locations, or if when you probe it with gravity, 626 00:30:18,280 --> 00:30:21,840 Speaker 2: it somehow collapses into just having one possible location. Because 627 00:30:21,880 --> 00:30:24,440 Speaker 2: remember this, quantum particles can do this weird thing. They 628 00:30:24,480 --> 00:30:27,280 Speaker 2: can be in a superposition like if there's two possibilities 629 00:30:27,320 --> 00:30:30,440 Speaker 2: for an electron, it doesn't have to choose A or B. 630 00:30:30,880 --> 00:30:35,120 Speaker 2: It can maintain both possibilities until something interacts with it classically, 631 00:30:35,200 --> 00:30:38,120 Speaker 2: which forces it to choose. That's the weird thing about 632 00:30:38,160 --> 00:30:41,080 Speaker 2: quantum mechanics and something we don't understand. So this is 633 00:30:41,160 --> 00:30:43,640 Speaker 2: very hard, of course, because particles are very small and 634 00:30:43,680 --> 00:30:46,040 Speaker 2: they're very delicate. But they've come up with a clever 635 00:30:46,080 --> 00:30:48,960 Speaker 2: way that they think might be possible, and it involves 636 00:30:49,080 --> 00:30:52,000 Speaker 2: electrons embedded in falling diamonds. 637 00:30:52,400 --> 00:30:54,680 Speaker 1: Sounds like a rap video where there's like money and 638 00:30:54,760 --> 00:30:58,200 Speaker 1: diamonds falling from the sky. Break it down for us. 639 00:30:58,280 --> 00:30:59,480 Speaker 1: How does his experiment work? 640 00:31:00,160 --> 00:31:02,800 Speaker 2: Is you take a very tiny diamond and has a 641 00:31:02,920 --> 00:31:06,480 Speaker 2: nitrogen added inside of it, like embedded inside the diamond. 642 00:31:06,600 --> 00:31:09,080 Speaker 2: And this has a cool property, which is that if 643 00:31:09,120 --> 00:31:11,680 Speaker 2: you zap it with a laser, the electrons have a 644 00:31:11,720 --> 00:31:14,520 Speaker 2: probability to absorb that photon, which case they flip their 645 00:31:14,560 --> 00:31:17,239 Speaker 2: spin to be up, or to ignore that photon and 646 00:31:17,240 --> 00:31:19,880 Speaker 2: flip their spin to be down. So you shoot a 647 00:31:19,960 --> 00:31:22,480 Speaker 2: laser at this diamond, and now it's in a quantum 648 00:31:22,560 --> 00:31:26,560 Speaker 2: superposition of two possibilities. Maybe the electron inside there on 649 00:31:26,600 --> 00:31:29,720 Speaker 2: the nitrogen is spin up, and maybe it's spin down. 650 00:31:29,880 --> 00:31:32,480 Speaker 2: So you have your particle now in a quantum superposition. 651 00:31:32,600 --> 00:31:34,080 Speaker 2: But what you need is for it to be in 652 00:31:34,080 --> 00:31:37,640 Speaker 2: a quantum superposition of two locations rather than two spins. 653 00:31:37,800 --> 00:31:40,120 Speaker 2: So then you pass it to a little magnetic field. 654 00:31:40,320 --> 00:31:43,760 Speaker 2: The magnetic field will push it left or right based 655 00:31:43,800 --> 00:31:46,320 Speaker 2: on the spin. So you have this falling diamond which 656 00:31:46,360 --> 00:31:49,000 Speaker 2: passes through a magnetic field and it either moves left 657 00:31:49,120 --> 00:31:51,880 Speaker 2: or it moves right. Now if it's in a quantum superposition, 658 00:31:52,040 --> 00:31:54,680 Speaker 2: and then it has both possibilities to move left and 659 00:31:54,800 --> 00:31:59,520 Speaker 2: to move right. So now it's location depends on this quantumness. 660 00:32:00,000 --> 00:32:03,080 Speaker 2: It's the same thing for another diamond nearby. Now you 661 00:32:03,080 --> 00:32:06,040 Speaker 2: have this pair of falling diamonds, each of which has 662 00:32:06,040 --> 00:32:09,320 Speaker 2: the possibility to be in two slightly different locations, and 663 00:32:09,360 --> 00:32:12,440 Speaker 2: you see how they interact. Do the possibilities for one 664 00:32:12,440 --> 00:32:15,360 Speaker 2: diamond interact with the possibilities for the other diamond, or 665 00:32:15,400 --> 00:32:18,280 Speaker 2: do the two diamonds like collapse each other's wave functions. 666 00:32:18,880 --> 00:32:21,240 Speaker 1: I see, So you embed a little nitrogen atom into 667 00:32:21,240 --> 00:32:25,080 Speaker 1: the diamond Ezaly with a laser, and now the nirogen 668 00:32:25,160 --> 00:32:28,680 Speaker 1: atom has quantumn certainty, which kind of extends to the 669 00:32:28,720 --> 00:32:31,360 Speaker 1: whole diamond. Is basically what you're saying, right like if 670 00:32:31,360 --> 00:32:35,160 Speaker 1: I don't know, there's quantum certainty about the electron into nitrogen, 671 00:32:35,200 --> 00:32:37,720 Speaker 1: and that means there's quantum certainty about the whole diamond 672 00:32:38,040 --> 00:32:40,640 Speaker 1: because it could be swinging right or left. And now 673 00:32:40,800 --> 00:32:43,320 Speaker 1: if you put two of them together really close, they 674 00:32:43,320 --> 00:32:46,000 Speaker 1: should interact with gravity. And so now you have the 675 00:32:46,040 --> 00:32:50,120 Speaker 1: system where you have two quantum objects interacting with gravity exactly. 676 00:32:50,120 --> 00:32:52,440 Speaker 2: And they have some really clever mathematical way to tell 677 00:32:52,480 --> 00:32:55,680 Speaker 2: if the two diamonds interacted in a quantum way or 678 00:32:55,720 --> 00:32:58,640 Speaker 2: if the two diamonds interacted in a classical way, Like 679 00:32:58,680 --> 00:33:01,760 Speaker 2: if they interacted in a quanti when you measure the 680 00:33:01,840 --> 00:33:04,720 Speaker 2: spins of those electrons after they fall far enough in 681 00:33:04,760 --> 00:33:08,040 Speaker 2: your experiment, they'll have some cool correlation to them, and 682 00:33:08,080 --> 00:33:10,600 Speaker 2: if they interact it in a classical way, then they'll 683 00:33:10,600 --> 00:33:13,160 Speaker 2: be uncorrelated, like whether they're spin up or down will 684 00:33:13,200 --> 00:33:15,640 Speaker 2: just be random, and so because of the weird rules 685 00:33:15,640 --> 00:33:18,959 Speaker 2: of quantum mechanics, you can tell whether quantum mechanics has 686 00:33:19,040 --> 00:33:22,080 Speaker 2: been at play in the gravitational interaction, Like did gravity 687 00:33:22,360 --> 00:33:24,600 Speaker 2: cancel out the quantum mechanic effects because it's really just 688 00:33:24,640 --> 00:33:28,640 Speaker 2: a classical force, or did it allow the quantum uncertainty 689 00:33:28,920 --> 00:33:32,080 Speaker 2: to be maintained, meaning that gravity would be a quantum 690 00:33:32,280 --> 00:33:34,720 Speaker 2: mechanical effect not a classical effect. 691 00:33:34,920 --> 00:33:38,600 Speaker 1: Well, I guess quantum mechanics aside. Can you measure gravity 692 00:33:38,640 --> 00:33:41,160 Speaker 1: the force of gravity by just dropping two diamonds together 693 00:33:41,280 --> 00:33:43,680 Speaker 1: and seeing if they attract each other? Is that like 694 00:33:43,760 --> 00:33:44,680 Speaker 1: a real thing you can do. 695 00:33:44,840 --> 00:33:47,200 Speaker 2: It's a real thing you can try to do. That's very, 696 00:33:47,320 --> 00:33:51,640 Speaker 2: very difficult because little diamonds have very very gentle gravity, 697 00:33:51,720 --> 00:33:53,600 Speaker 2: and so this is not something we think we can 698 00:33:53,640 --> 00:33:56,640 Speaker 2: do today. There's a group in the UK that thinks 699 00:33:56,640 --> 00:33:58,120 Speaker 2: that they can figure out how to do this, and 700 00:33:58,120 --> 00:34:01,880 Speaker 2: there's lots of complicated steps involved and they're hoping to 701 00:34:01,920 --> 00:34:04,680 Speaker 2: maybe pull this off sometime in the next ten years. 702 00:34:05,560 --> 00:34:08,560 Speaker 2: There's a lot of really complicated moving parts involvement getting 703 00:34:08,600 --> 00:34:12,000 Speaker 2: the nitrogen inside the diamond, flipping its spin with a laser, 704 00:34:12,040 --> 00:34:15,920 Speaker 2: beam getting two pairs of diamonds to fall simultaneously close 705 00:34:16,040 --> 00:34:18,600 Speaker 2: enough each other that maybe they have a gravitational interaction. 706 00:34:18,760 --> 00:34:20,759 Speaker 2: Now you don't actually have to see any sort of 707 00:34:20,800 --> 00:34:24,120 Speaker 2: like gravitational pull. You're not measuring like how far did 708 00:34:24,120 --> 00:34:27,040 Speaker 2: the diamond move because of gravity. You're just bringing them 709 00:34:27,080 --> 00:34:30,320 Speaker 2: close enough together that you think gravity is at play. 710 00:34:30,360 --> 00:34:32,960 Speaker 2: The gravity like wakes up and says, ooh, there's something 711 00:34:33,000 --> 00:34:35,279 Speaker 2: going on here. You don't have to measure the gravity. 712 00:34:35,560 --> 00:34:37,560 Speaker 2: You just have to see if gravity messes up the 713 00:34:37,640 --> 00:34:39,000 Speaker 2: quantum state. I see. 714 00:34:39,040 --> 00:34:41,120 Speaker 1: But to measure the quantum state at the end, wouldn't 715 00:34:41,120 --> 00:34:44,080 Speaker 1: you be doing something like measuring that whether or not 716 00:34:44,160 --> 00:34:47,480 Speaker 1: the two diamonds were attracted to each other gravitationally or not. 717 00:34:47,840 --> 00:34:49,960 Speaker 2: No, all you need to do is measure the spins 718 00:34:50,000 --> 00:34:53,960 Speaker 2: of those electrons embedded inside the nitrogen atoms in the diamonds. 719 00:34:54,080 --> 00:34:56,399 Speaker 2: You don't have to see the gravitational effects directly. It's 720 00:34:56,440 --> 00:34:58,040 Speaker 2: sort of like in the double slit experiment when you 721 00:34:58,080 --> 00:35:01,000 Speaker 2: add a detector and that ruins the interface spearance. We're 722 00:35:01,040 --> 00:35:03,880 Speaker 2: adding gravity to a quantum interaction and seeing if it 723 00:35:03,960 --> 00:35:05,480 Speaker 2: ruins the interference or not. 724 00:35:05,960 --> 00:35:10,440 Speaker 1: M But would that necessarily tell you anything about quantum 725 00:35:10,520 --> 00:35:12,080 Speaker 1: gravity or gravitons. 726 00:35:12,120 --> 00:35:13,799 Speaker 2: It wouldn't tell you that much, but it would be 727 00:35:13,800 --> 00:35:16,520 Speaker 2: a powerful clue. It would tell you if gravity is 728 00:35:16,600 --> 00:35:20,919 Speaker 2: classical or quantum mechanical. Like, if gravity is classical, it'll 729 00:35:20,960 --> 00:35:23,560 Speaker 2: act like a detector and it'll collapse those wave functions 730 00:35:23,600 --> 00:35:27,279 Speaker 2: and destroy this interference. If gravity is quantum mechanical, it won't, 731 00:35:27,320 --> 00:35:30,120 Speaker 2: and everything quantum mechanical will stay quantum mechanical, and you 732 00:35:30,120 --> 00:35:32,800 Speaker 2: get all sorts of weird interference. So that just tells 733 00:35:32,800 --> 00:35:35,720 Speaker 2: you if gravity is classical or quantum mechanical. It doesn't 734 00:35:35,719 --> 00:35:38,200 Speaker 2: tell you like, oh, space is quantized, or oh there 735 00:35:38,239 --> 00:35:41,320 Speaker 2: are gravitons. It doesn't tell you which theory of quantum gravity, 736 00:35:41,600 --> 00:35:43,800 Speaker 2: but it is a powerful clue. It would mean, for example, 737 00:35:43,840 --> 00:35:46,680 Speaker 2: if we know gravity is quantum mechanical, the Freeman Dyson 738 00:35:46,840 --> 00:35:50,479 Speaker 2: is wrong about classical gravity and quantum mechanics being able 739 00:35:50,480 --> 00:35:51,160 Speaker 2: to play together. 740 00:35:52,640 --> 00:35:54,400 Speaker 1: Yeah, he could be wrong, in which case he might 741 00:35:54,440 --> 00:35:58,879 Speaker 1: need to stick to them making vacuum tees. All right, Well, 742 00:35:59,480 --> 00:36:02,279 Speaker 1: that's one experiment, and I guess it's in progress. I 743 00:36:02,280 --> 00:36:04,600 Speaker 1: guess they're designing it or making it. Where are they 744 00:36:04,680 --> 00:36:04,880 Speaker 1: with that? 745 00:36:05,160 --> 00:36:08,239 Speaker 2: This physicist at University College London who's leading a team 746 00:36:08,280 --> 00:36:10,960 Speaker 2: of researchers who are trying to make this work. And 747 00:36:11,080 --> 00:36:13,799 Speaker 2: there's folks in Santa Barbara as well, and they're trying 748 00:36:13,800 --> 00:36:15,080 Speaker 2: to work on this. But you know, there's a lot 749 00:36:15,160 --> 00:36:18,120 Speaker 2: of complicated steps and making this thing do its stance 750 00:36:18,160 --> 00:36:20,360 Speaker 2: and being sure you know, what they're doing is a 751 00:36:20,400 --> 00:36:24,200 Speaker 2: lot of pieces involved, lots of complicated experimental cleverness really 752 00:36:24,200 --> 00:36:26,880 Speaker 2: required just to be able to do this test. So 753 00:36:26,920 --> 00:36:28,960 Speaker 2: they're hoping sometime in the next ten years to be 754 00:36:29,000 --> 00:36:29,879 Speaker 2: able to pull this off. 755 00:36:30,000 --> 00:36:31,919 Speaker 1: All right, Well, let's get to the second of these 756 00:36:31,960 --> 00:36:35,400 Speaker 1: potential experiments to measure quantum gravity. We'll dig into that, 757 00:36:35,480 --> 00:36:50,520 Speaker 1: but first let's take another quick break. All right, we're 758 00:36:50,560 --> 00:36:54,239 Speaker 1: talking about quantum gravity and whether or not it's a thing, 759 00:36:54,480 --> 00:36:59,400 Speaker 1: whether gravity is quantum mechanical or is it pretty and 760 00:36:59,480 --> 00:37:03,920 Speaker 1: classical and doesn't care about quantum mechanics and this weirdness 761 00:37:04,440 --> 00:37:07,040 Speaker 1: of things being uncertain, And so we talked about one 762 00:37:07,080 --> 00:37:10,640 Speaker 1: possible experiment that it might look at that using falling diamonds. 763 00:37:10,800 --> 00:37:15,320 Speaker 1: And there's another interesting potential experiments happening also, right. 764 00:37:15,280 --> 00:37:17,800 Speaker 2: That's right, And this one is being developed and built 765 00:37:17,880 --> 00:37:18,480 Speaker 2: in your. 766 00:37:18,360 --> 00:37:20,600 Speaker 1: Backyard, like literally my backyard. 767 00:37:21,239 --> 00:37:22,040 Speaker 2: Look at your window. 768 00:37:22,080 --> 00:37:22,279 Speaker 3: Man. 769 00:37:22,400 --> 00:37:23,840 Speaker 2: You ever wonder what those people are told you? 770 00:37:23,920 --> 00:37:24,160 Speaker 1: What? 771 00:37:25,480 --> 00:37:27,840 Speaker 2: No, it's at cal Tech. Both the theorists and the 772 00:37:27,880 --> 00:37:31,760 Speaker 2: experimental list are at Caltech, and it's a really cool idea. 773 00:37:31,960 --> 00:37:34,840 Speaker 2: And what they're trying to do in this experiment's completely 774 00:37:34,840 --> 00:37:37,319 Speaker 2: different from the other one is try to see if 775 00:37:37,440 --> 00:37:41,319 Speaker 2: space itself is quantum mechanical. Like, if gravity is quant 776 00:37:41,400 --> 00:37:44,920 Speaker 2: mechanical and there are gravitons, then that would mean that 777 00:37:45,040 --> 00:37:48,040 Speaker 2: graviton should be like popping out of the vacuum all 778 00:37:48,080 --> 00:37:50,879 Speaker 2: the time, the same way that other quantum particles are. 779 00:37:51,160 --> 00:37:53,200 Speaker 2: Like if you go out in the middle of empty space, 780 00:37:53,239 --> 00:37:56,120 Speaker 2: there's nothing there, there's still always a little bit of 781 00:37:56,280 --> 00:37:59,200 Speaker 2: energy in the quantum fields, which means that like those 782 00:37:59,200 --> 00:38:02,080 Speaker 2: fields can turn into particles briefly and then back into 783 00:38:02,160 --> 00:38:06,160 Speaker 2: potential energy. So if space itself is quantum mechanical, if 784 00:38:06,200 --> 00:38:10,280 Speaker 2: gravity is quantum mechanical, then gravitons should also be popping 785 00:38:10,320 --> 00:38:13,160 Speaker 2: out of the vacuum. There should be like effectively tiny 786 00:38:13,360 --> 00:38:18,560 Speaker 2: little ripples in space making quantum size gravitational waves. 787 00:38:19,239 --> 00:38:21,719 Speaker 1: WHOA wait, I think you just confused me a little bit. 788 00:38:21,800 --> 00:38:24,000 Speaker 1: So I thought there were two possibilities. Either gravity is 789 00:38:24,080 --> 00:38:28,040 Speaker 1: quantum mechanical or space is quantized. Which one are you 790 00:38:28,120 --> 00:38:28,799 Speaker 1: talking about here? 791 00:38:28,840 --> 00:38:31,680 Speaker 2: Here, we're talking about gravity being quantum mechanical, that there 792 00:38:31,719 --> 00:38:35,520 Speaker 2: exist gravitons which mediate the force of gravity, which in 793 00:38:35,560 --> 00:38:38,359 Speaker 2: this theory would be a quantum force like the other 794 00:38:38,440 --> 00:38:39,640 Speaker 2: forces in the universe. 795 00:38:39,920 --> 00:38:43,120 Speaker 1: Okay, so we're not talking about quantizing space itself. 796 00:38:42,880 --> 00:38:45,360 Speaker 2: That's right. We're not talking about quantizing space and like 797 00:38:45,400 --> 00:38:48,360 Speaker 2: a space foam. But we're talking about space being filled 798 00:38:48,400 --> 00:38:51,440 Speaker 2: with a quantum force of gravity, which would have fluctuations 799 00:38:51,480 --> 00:38:54,960 Speaker 2: in it, right, And those fluctuations would be like quantum 800 00:38:54,960 --> 00:38:59,240 Speaker 2: gravitons popping in and out of the quantum gravitational field. 801 00:39:00,360 --> 00:39:02,560 Speaker 1: I see. So anything that is quantum or has a 802 00:39:02,640 --> 00:39:05,879 Speaker 1: quantum field, by its nature, by its kind of statistical 803 00:39:05,960 --> 00:39:09,840 Speaker 1: random nature, has these particles popping out of nothingness. But 804 00:39:09,880 --> 00:39:11,920 Speaker 1: doesn't it need some sort of like energy to it. 805 00:39:11,920 --> 00:39:14,680 Speaker 2: It does, But quantum fields always have energy to them. 806 00:39:14,680 --> 00:39:18,320 Speaker 2: They can never relax down to zero because the uncertainty principle, 807 00:39:18,560 --> 00:39:21,160 Speaker 2: the minimum energy level of a quantum field is always 808 00:39:21,200 --> 00:39:24,080 Speaker 2: above zero energy, which is why there's always energy in 809 00:39:24,160 --> 00:39:26,680 Speaker 2: quantum fields, which is why there's energy in all of 810 00:39:26,719 --> 00:39:28,520 Speaker 2: space because of its quantum nature. 811 00:39:28,640 --> 00:39:30,840 Speaker 1: Well, that's kind of an odd idea, Like what happens 812 00:39:30,880 --> 00:39:33,480 Speaker 1: if a graviton appears out of nothingness, well. 813 00:39:33,280 --> 00:39:36,360 Speaker 2: Mostly almost nothing, because gravitons would be super duper tiny, 814 00:39:36,520 --> 00:39:39,319 Speaker 2: gravity is super duper weak, and so it would be 815 00:39:39,480 --> 00:39:42,239 Speaker 2: basically impossible to see these things what have effects on 816 00:39:42,320 --> 00:39:45,600 Speaker 2: super tiny distance scales we typically can't probe. But a 817 00:39:45,680 --> 00:39:49,240 Speaker 2: theorist that Caltech, Catherine Zurich, came up with this idea 818 00:39:49,280 --> 00:39:52,799 Speaker 2: that maybe gravitons can all work together. Instead of just 819 00:39:52,840 --> 00:39:55,640 Speaker 2: looking for one graviton, maybe you can look for like 820 00:39:55,800 --> 00:39:58,640 Speaker 2: larger effects of graviton sort of working together to make 821 00:39:58,719 --> 00:40:03,040 Speaker 2: something else emerge from this quantum craziness. And she designed 822 00:40:03,080 --> 00:40:04,600 Speaker 2: an experiment to maybe see that. 823 00:40:05,160 --> 00:40:09,640 Speaker 1: Hmmm, interesting, Well, we actually have an interview of Daniel 824 00:40:09,760 --> 00:40:13,080 Speaker 1: talking with professor Catherine Zurich from cal Tech about her 825 00:40:13,160 --> 00:40:14,560 Speaker 1: idea for this experiment. 826 00:40:14,640 --> 00:40:16,319 Speaker 2: That's right. Kathy and I have known each other since 827 00:40:16,360 --> 00:40:18,120 Speaker 2: we were POSTOCX, and so I called her up and 828 00:40:18,160 --> 00:40:21,000 Speaker 2: asked her about her crazy idea to not build a 829 00:40:21,000 --> 00:40:22,120 Speaker 2: black hole in Pasadena. 830 00:40:22,160 --> 00:40:23,759 Speaker 1: I feel like it's a little says, you have to 831 00:40:23,760 --> 00:40:27,320 Speaker 1: throw that disclaimer in there, it's like, what are you 832 00:40:27,320 --> 00:40:31,239 Speaker 1: guys doing? I am not destroying your town if that's 833 00:40:31,239 --> 00:40:34,759 Speaker 1: what you're asking. First of all, let's get that clear. 834 00:40:35,040 --> 00:40:36,360 Speaker 2: That didn't make you feel any better. 835 00:40:37,320 --> 00:40:40,640 Speaker 1: Nobody asked I wasn't something I was concerned about before. 836 00:40:41,160 --> 00:40:41,440 Speaker 3: All right. 837 00:40:41,480 --> 00:40:44,000 Speaker 2: In that case, I'm also not testing any nuclear weapons 838 00:40:44,040 --> 00:40:44,680 Speaker 2: in Pasadena. 839 00:40:44,840 --> 00:40:47,480 Speaker 1: Oh good, thank you. What else are you not doing 840 00:40:47,480 --> 00:40:52,000 Speaker 1: in Pasadena? Let's go down the list. All right. Well, 841 00:40:52,040 --> 00:40:55,439 Speaker 1: here is Daniel's interview with Professor Catherine Zurich from cal Tech. 842 00:40:55,719 --> 00:41:00,160 Speaker 2: All right, so it's my pleasure to welcome Professor Katherin Zurchod. 843 00:41:00,440 --> 00:41:02,160 Speaker 2: Thank you very much for chatting with us. 844 00:41:02,520 --> 00:41:04,000 Speaker 3: It's my pleasure to join you. 845 00:41:04,360 --> 00:41:07,360 Speaker 2: So help me understand, first of all, how it's possible 846 00:41:07,520 --> 00:41:11,200 Speaker 2: at all to see effects of quantum gravity. We understood 847 00:41:11,239 --> 00:41:12,840 Speaker 2: for a long time that these things were just on 848 00:41:12,880 --> 00:41:15,680 Speaker 2: the plank scale. How do they sort of work together 849 00:41:15,800 --> 00:41:19,280 Speaker 2: to emerge to some signal we can see experimentally. 850 00:41:19,520 --> 00:41:22,280 Speaker 3: So it's just like smoke. So if you ask yourself 851 00:41:22,280 --> 00:41:27,239 Speaker 3: the question how to smoke spread? So there are interactions 852 00:41:27,280 --> 00:41:30,880 Speaker 3: of molecules on very short distance scales, much shorter than 853 00:41:30,920 --> 00:41:33,279 Speaker 3: what we can observe and yet you can see the 854 00:41:33,320 --> 00:41:38,279 Speaker 3: effects of those short distance interactions simply by waiting a 855 00:41:38,360 --> 00:41:44,640 Speaker 3: while for the effects of those short range interactions to 856 00:41:44,680 --> 00:41:50,799 Speaker 3: accumulate over time. So that's a physical analogy for what 857 00:41:50,840 --> 00:41:55,320 Speaker 3: we're interested in doing. So we have these quantum fluctuations 858 00:41:55,360 --> 00:41:58,440 Speaker 3: on very short distance scales. So in this case it's 859 00:41:58,480 --> 00:42:00,479 Speaker 3: the plank length, which is about to into the minus 860 00:42:00,520 --> 00:42:06,280 Speaker 3: thirty five meters. And the idea is that if those 861 00:42:06,680 --> 00:42:13,680 Speaker 3: quantum fluctuations accumulate over long times, then we can observe them. 862 00:42:14,000 --> 00:42:17,160 Speaker 3: They're still very small, but we can observe them then 863 00:42:17,280 --> 00:42:21,320 Speaker 3: with sufficiently precise instruments. 864 00:42:21,680 --> 00:42:25,080 Speaker 2: So what makes quantum fluctuations add up to make a 865 00:42:25,120 --> 00:42:29,480 Speaker 2: microscopic effect and what makes them not because sometimes they don't. Right, 866 00:42:29,560 --> 00:42:31,400 Speaker 2: you have like a bunch of electrons in a baseball, 867 00:42:31,400 --> 00:42:34,080 Speaker 2: they have all such fluctuations those average out to nothing. 868 00:42:34,120 --> 00:42:37,479 Speaker 2: You can see what makes these guys add up over 869 00:42:37,880 --> 00:42:39,080 Speaker 2: longer distance scales. 870 00:42:39,280 --> 00:42:43,320 Speaker 3: So it's really the fact that you're losing information. Any 871 00:42:43,560 --> 00:42:48,440 Speaker 3: measurement that you make is over a finite time. So 872 00:42:48,800 --> 00:42:50,960 Speaker 3: you know, I turn on my instrument, let's say it's 873 00:42:50,960 --> 00:42:54,560 Speaker 3: in an intraferometer, and the light goes out. It comes 874 00:42:54,600 --> 00:42:56,799 Speaker 3: back and I make a measurement of it. And so 875 00:42:57,080 --> 00:42:59,840 Speaker 3: what it does, what an instrument does, is it defines 876 00:43:00,080 --> 00:43:02,920 Speaker 3: what we call a horizon. So there's a region of 877 00:43:02,920 --> 00:43:04,840 Speaker 3: the space time that I measure and there's a region 878 00:43:04,880 --> 00:43:07,160 Speaker 3: of the space time that I don't, and so that 879 00:43:07,280 --> 00:43:12,399 Speaker 3: leads to a quantum mismeasurement effect that accumulates over time. 880 00:43:12,920 --> 00:43:16,919 Speaker 3: So you're absolutely right that, you know, normal systems, where 881 00:43:16,920 --> 00:43:21,640 Speaker 3: we can confine all of our information to a particular region, 882 00:43:22,000 --> 00:43:24,960 Speaker 3: there's no information that's going to accumulate over time. But 883 00:43:25,080 --> 00:43:29,520 Speaker 3: in this case, we can't actually confine quantum fluctuations. There's 884 00:43:29,560 --> 00:43:31,760 Speaker 3: just part of the space time that we can't measure, 885 00:43:32,080 --> 00:43:36,680 Speaker 3: and so what we're doing now is quantifying how much 886 00:43:36,800 --> 00:43:41,120 Speaker 3: of that information is lost over the period of time 887 00:43:41,120 --> 00:43:42,280 Speaker 3: that I make that measurement. 888 00:43:42,680 --> 00:43:46,160 Speaker 2: Very cool, and so what kind of models of quantum 889 00:43:46,200 --> 00:43:49,279 Speaker 2: space time is as sensitive to generally any kind of 890 00:43:49,320 --> 00:43:53,360 Speaker 2: model where space time has quantum fluctuations or only specific 891 00:43:53,400 --> 00:43:55,000 Speaker 2: sort of kinds of ideas. 892 00:43:55,280 --> 00:43:59,320 Speaker 3: So what we're trying to show is that this effect 893 00:44:00,280 --> 00:44:08,200 Speaker 3: occurs very generally across the space of theoretical ideas that 894 00:44:09,080 --> 00:44:14,160 Speaker 3: people explore, you know, commonly, So what do I mean 895 00:44:14,200 --> 00:44:17,440 Speaker 3: by that exactly, So we're still trying to understand a 896 00:44:18,280 --> 00:44:21,880 Speaker 3: precisely what are the minimal sets of requirements that you need. 897 00:44:22,239 --> 00:44:26,120 Speaker 3: At minimum, we need quantum fluctuations at the plank scale, 898 00:44:26,880 --> 00:44:32,400 Speaker 3: so that has to be there, and those quantum fluctuations 899 00:44:32,400 --> 00:44:37,440 Speaker 3: have to accumulate into the infrared. And there are various 900 00:44:37,520 --> 00:44:39,719 Speaker 3: ways that we can see that. We can see it 901 00:44:39,800 --> 00:44:43,240 Speaker 3: actually coming out in a quite broad range of theories 902 00:44:43,320 --> 00:44:46,640 Speaker 3: where we can just write down some general properties of 903 00:44:46,680 --> 00:44:49,160 Speaker 3: the theory and then crank through it and we see 904 00:44:49,200 --> 00:44:53,520 Speaker 3: this effect come out. So we think it's pretty generic. 905 00:44:53,760 --> 00:44:57,719 Speaker 2: Wonderful, And so why can't existing interchometers like LEGO, which 906 00:44:57,760 --> 00:45:01,080 Speaker 2: is already very very precise, why can't it's signatures of 907 00:45:01,120 --> 00:45:02,080 Speaker 2: this quantum fluctuation. 908 00:45:02,560 --> 00:45:04,919 Speaker 3: So we actually think that LEGO is not very far 909 00:45:05,000 --> 00:45:07,400 Speaker 3: from being able to see it. But one of the 910 00:45:07,440 --> 00:45:11,360 Speaker 3: reasons why LEGO is not optimally sensitive to this signal 911 00:45:11,719 --> 00:45:17,359 Speaker 3: is because they recycle their light by which I mean 912 00:45:17,960 --> 00:45:21,120 Speaker 3: the light beam goes out and it comes back, and 913 00:45:21,160 --> 00:45:24,080 Speaker 3: they don't make a measurement of it. After one round trick, 914 00:45:24,400 --> 00:45:27,240 Speaker 3: it actually goes out and comes back many times before 915 00:45:27,239 --> 00:45:30,200 Speaker 3: they make a measurement of it. And so for the 916 00:45:30,239 --> 00:45:34,120 Speaker 3: signals that they're interested in, which come from you know, 917 00:45:34,239 --> 00:45:38,040 Speaker 3: let's say black holes merging, that's fine because there's a 918 00:45:38,080 --> 00:45:41,920 Speaker 3: classical source that generates a wave at some frequency. In 919 00:45:42,080 --> 00:45:45,719 Speaker 3: this case, we're also interested in gravitational waves, but they're 920 00:45:45,719 --> 00:45:50,840 Speaker 3: gravitational waves that come from the vacuum fluctuating, and they're uncorrelated. 921 00:45:51,160 --> 00:45:55,040 Speaker 3: If I measured the system over time scales that are 922 00:45:55,120 --> 00:45:57,759 Speaker 3: long in comparison to the light crossing time, So the 923 00:45:57,840 --> 00:46:01,760 Speaker 3: fact that ligo weights and beam goes out and comes 924 00:46:01,800 --> 00:46:04,480 Speaker 3: back many times before they measure it means that they're 925 00:46:04,480 --> 00:46:07,000 Speaker 3: actually averaging down their signal, and so they have a 926 00:46:07,040 --> 00:46:10,640 Speaker 3: reduced sensitivity to it in comparison to if they had 927 00:46:10,640 --> 00:46:14,000 Speaker 3: this same that they could measure the same space time fluctuation. 928 00:46:14,200 --> 00:46:16,239 Speaker 3: But they did it after the light just went out 929 00:46:16,320 --> 00:46:19,440 Speaker 3: and came back. Then we claim that you can actually 930 00:46:19,440 --> 00:46:20,200 Speaker 3: see this signal. 931 00:46:20,320 --> 00:46:23,640 Speaker 2: Do these space time fluctuations look different from a gravitational 932 00:46:23,760 --> 00:46:26,360 Speaker 2: way you could get from black hole collisions, for example. 933 00:46:26,360 --> 00:46:29,120 Speaker 3: Yeah, they do. So one thing that's different about this 934 00:46:29,280 --> 00:46:31,839 Speaker 3: signal in comparison to what you would get from let's 935 00:46:31,840 --> 00:46:34,760 Speaker 3: say black hole mergers is in that case, the signal 936 00:46:34,840 --> 00:46:37,520 Speaker 3: is the signal. It doesn't depend on my measuring apparatus. 937 00:46:37,800 --> 00:46:40,000 Speaker 3: If I have a gravitational way of coming in at 938 00:46:40,040 --> 00:46:43,680 Speaker 3: some frequency. It's like your radio station is broadcasting something 939 00:46:43,840 --> 00:46:46,480 Speaker 3: and it has a frequency, and that's just you know, 940 00:46:46,520 --> 00:46:49,920 Speaker 3: you tune it to some station, and that's what it is. 941 00:46:50,200 --> 00:46:54,840 Speaker 3: In this case, what you measure actually depends on your apparatus, 942 00:46:54,880 --> 00:46:58,800 Speaker 3: like your interferometer. So if I have a smaller apparatus, 943 00:46:59,760 --> 00:47:02,400 Speaker 3: my signal is going to be coming in at a 944 00:47:02,520 --> 00:47:07,799 Speaker 3: higher number radio station. Then if I have a bigger apparatus, 945 00:47:07,880 --> 00:47:10,239 Speaker 3: then it comes in at a lower frequency station. The 946 00:47:10,280 --> 00:47:14,000 Speaker 3: reason for that is because it's the quantum mismeasurement. And 947 00:47:14,000 --> 00:47:16,440 Speaker 3: of course how much you're mismeasuring the space time depends 948 00:47:16,440 --> 00:47:19,000 Speaker 3: on how big you know, the volume of space time. 949 00:47:18,840 --> 00:47:21,240 Speaker 2: You're measuring affects your horizon. 950 00:47:21,520 --> 00:47:23,719 Speaker 3: Yeah, it depends on the size of your horizon. That's 951 00:47:23,719 --> 00:47:25,680 Speaker 3: another way of saying it. It depends on the size 952 00:47:25,680 --> 00:47:28,200 Speaker 3: of your horizon, depends on how many quantum degrees of 953 00:47:28,239 --> 00:47:33,120 Speaker 3: freedom are fluctuating inside your volume, which depends on how 954 00:47:33,160 --> 00:47:35,799 Speaker 3: big your horizon is. And so as a result, you know, 955 00:47:35,920 --> 00:47:38,279 Speaker 3: you would really know about this signal. First of all, 956 00:47:38,280 --> 00:47:41,359 Speaker 3: it would have a very particular shape, but it would 957 00:47:41,360 --> 00:47:44,080 Speaker 3: depend on your measuring apparatus, So you could compare between 958 00:47:44,080 --> 00:47:46,880 Speaker 3: different instruments and then start to tell what the source 959 00:47:46,920 --> 00:47:47,520 Speaker 3: of it would be. 960 00:47:47,719 --> 00:47:50,799 Speaker 2: And can you also see things unexpected, like if there's 961 00:47:50,800 --> 00:47:53,719 Speaker 2: a general enough detector that you might see things that 962 00:47:53,960 --> 00:47:57,359 Speaker 2: aren't these quantum fluctuations, then aren't gravitational away some black 963 00:47:57,360 --> 00:47:59,960 Speaker 2: holes but something else, you know, surprise? 964 00:48:00,600 --> 00:48:03,800 Speaker 3: Yeah. Sure, So these instruments that were interested in building, 965 00:48:03,840 --> 00:48:07,640 Speaker 3: they can be sensitive to anything that's generating gravitational waves 966 00:48:07,640 --> 00:48:11,919 Speaker 3: in that same frequency range. So the signal definitely has 967 00:48:11,960 --> 00:48:14,600 Speaker 3: to be predictive enough to be able to tell apart 968 00:48:14,760 --> 00:48:18,520 Speaker 3: different sources. And our claim is that the signal has 969 00:48:18,680 --> 00:48:22,480 Speaker 3: very particular you know, frequencies that it's peaked at. It 970 00:48:22,600 --> 00:48:26,040 Speaker 3: has angular correlations, like it depends on the angle between 971 00:48:26,080 --> 00:48:29,880 Speaker 3: the arms and your interferometer. So therefore you'll be able 972 00:48:29,960 --> 00:48:33,360 Speaker 3: to tell what the source of these gravitational waves. 973 00:48:33,080 --> 00:48:35,520 Speaker 2: Are and what's the sort of timeline like best case 974 00:48:35,560 --> 00:48:38,200 Speaker 2: scenario when you guys can build this thing and discover 975 00:48:38,320 --> 00:48:39,000 Speaker 2: quantum gravity. 976 00:48:39,239 --> 00:48:45,600 Speaker 3: Yeah yeah, So we've got the first bit of funding 977 00:48:45,840 --> 00:48:50,560 Speaker 3: to come in and my colleague Lemacullor who's spearheading this 978 00:48:50,719 --> 00:48:55,080 Speaker 3: effort here at Caltech. You know, his lab is ramping 979 00:48:55,160 --> 00:49:00,080 Speaker 3: up on this. There are some technological objectives that they 980 00:49:00,080 --> 00:49:01,840 Speaker 3: have to demonstrate, and they have to do R and 981 00:49:01,960 --> 00:49:07,439 Speaker 3: D because they're proposing a novel readout scheme for these interferometer. 982 00:49:09,040 --> 00:49:13,840 Speaker 3: What we have proposed is to have a demonstrator apparatus 983 00:49:14,719 --> 00:49:19,919 Speaker 3: that would kind of scrape the signal. Okay, we're talking 984 00:49:19,960 --> 00:49:24,880 Speaker 3: about two sigma kind of sensitivity in five years, so 985 00:49:24,960 --> 00:49:28,440 Speaker 3: I think to really start to see this, you know, 986 00:49:28,600 --> 00:49:32,239 Speaker 3: like five sigma, you're just really confident you can start 987 00:49:32,239 --> 00:49:35,760 Speaker 3: to test various aspects of it. I think we're probably 988 00:49:35,800 --> 00:49:37,799 Speaker 3: talking the ten year timescale. 989 00:49:37,880 --> 00:49:40,359 Speaker 2: So I've read your paper. There's a lot of nice 990 00:49:40,400 --> 00:49:43,520 Speaker 2: theoretical maneuvers in there. My question to you is, do 991 00:49:43,560 --> 00:49:45,320 Speaker 2: you believe this is going to be real? Like you 992 00:49:45,440 --> 00:49:47,759 Speaker 2: turn this thing on in ten years? Nature tales you 993 00:49:47,800 --> 00:49:51,040 Speaker 2: an answer. What's your confidence that this is out there 994 00:49:51,080 --> 00:49:51,799 Speaker 2: that you're going to see it? 995 00:49:52,200 --> 00:49:55,800 Speaker 3: Yeah, so it doesn't seem to be going away. Let's 996 00:49:55,800 --> 00:49:59,040 Speaker 3: put it that way. When you see something in a calculation, 997 00:50:00,120 --> 00:50:03,440 Speaker 3: you know, you try to test it by doing a 998 00:50:03,440 --> 00:50:07,840 Speaker 3: different calculation that behaves differently. You know, it has different 999 00:50:07,880 --> 00:50:11,239 Speaker 3: theoretical systematics, and the kinds of things that you could 1000 00:50:11,320 --> 00:50:14,640 Speaker 3: mess up in the calculation are different, so on and 1001 00:50:14,640 --> 00:50:17,520 Speaker 3: so forth. And then you also check for whether it's 1002 00:50:17,560 --> 00:50:21,840 Speaker 3: in conflict with anything that you know. And through the 1003 00:50:21,920 --> 00:50:25,120 Speaker 3: process of doing this, you know, based on my experience, 1004 00:50:25,120 --> 00:50:27,920 Speaker 3: when you try to build a theory, oftentimes it'll fail 1005 00:50:28,480 --> 00:50:30,280 Speaker 3: and then you try to fix it up by adding 1006 00:50:30,320 --> 00:50:33,360 Speaker 3: other things to it. This has not been like that. 1007 00:50:35,239 --> 00:50:37,440 Speaker 3: If it seems like it's going to fail for some reason, 1008 00:50:38,200 --> 00:50:40,440 Speaker 3: it means that you should just stop and wait and 1009 00:50:40,480 --> 00:50:44,560 Speaker 3: try to understand what's there better, because it fixes itself. 1010 00:50:44,960 --> 00:50:49,160 Speaker 3: So to me, that's an indication that there's something there. 1011 00:50:49,880 --> 00:50:54,040 Speaker 3: It hangs together in a very self consistent way, and 1012 00:50:54,120 --> 00:50:57,239 Speaker 3: so from that point of view, I find it theoretically 1013 00:50:57,360 --> 00:51:01,719 Speaker 3: very attractive, very interesting. It's right now, I don't want 1014 00:51:01,760 --> 00:51:05,400 Speaker 3: to tell nature what to do. Right. Nature gets to decide. 1015 00:51:05,800 --> 00:51:07,560 Speaker 3: You know, there are some things that go in right, 1016 00:51:07,560 --> 00:51:10,719 Speaker 3: there's this fundamental fluctuations and then space time you know, 1017 00:51:10,840 --> 00:51:12,800 Speaker 3: needs to remember right, so there needs to be the 1018 00:51:12,920 --> 00:51:15,560 Speaker 3: sense in which you're losing information. And if those two 1019 00:51:15,600 --> 00:51:19,240 Speaker 3: things are there in nature, and we certainly know lots 1020 00:51:19,280 --> 00:51:24,080 Speaker 3: of analogous physical systems where that happens, then we'll see it. 1021 00:51:24,480 --> 00:51:28,319 Speaker 3: But at the end of the day, nature decides. And 1022 00:51:28,360 --> 00:51:30,440 Speaker 3: that's one of the things I really like about this 1023 00:51:30,520 --> 00:51:32,600 Speaker 3: problem is I can write these things down on paper 1024 00:51:32,680 --> 00:51:36,000 Speaker 3: and they're beautiful, and I'm understanding more things about it 1025 00:51:36,040 --> 00:51:38,520 Speaker 3: from a mathematical perspective. But at the end of the day, 1026 00:51:38,880 --> 00:51:39,960 Speaker 3: nature gets to decide. 1027 00:51:40,200 --> 00:51:42,879 Speaker 2: All right, Well, we look forward to hearing nature's side 1028 00:51:42,880 --> 00:51:45,200 Speaker 2: of the story. Thanks very much for joining us today. 1029 00:51:45,760 --> 00:51:48,280 Speaker 1: All right, pretty interesting. I'm super impressed you can talk 1030 00:51:48,320 --> 00:51:51,000 Speaker 1: to a theorist. I thought you guys spoke different languages 1031 00:51:51,040 --> 00:51:52,520 Speaker 1: and didn't like each other. 1032 00:51:52,760 --> 00:51:55,719 Speaker 2: They mostly speak in Greek symbols exactly, but sometimes I 1033 00:51:55,760 --> 00:51:58,160 Speaker 2: can translate. These days, I'm trying to move a little 1034 00:51:58,160 --> 00:52:00,560 Speaker 2: bit in the direction of theoretical physics, so it's really 1035 00:52:00,600 --> 00:52:02,560 Speaker 2: fun for me to talk to these folks. But yeah, 1036 00:52:02,600 --> 00:52:05,160 Speaker 2: they think on a whole different plane of existence. But 1037 00:52:05,200 --> 00:52:08,760 Speaker 2: what's really cool are theorists who propose experiments, who develop 1038 00:52:08,920 --> 00:52:12,720 Speaker 2: new techniques and new ideas that allow experimentalists to maybe 1039 00:52:12,760 --> 00:52:16,160 Speaker 2: force the universe to reveal something about its nature. And 1040 00:52:16,200 --> 00:52:18,240 Speaker 2: the story of this one is similar to the story 1041 00:52:18,280 --> 00:52:21,960 Speaker 2: of a very similar experiment, which is LIGO, the innerferometer 1042 00:52:22,080 --> 00:52:25,960 Speaker 2: that looked for classical gravitational waves. That was originally just 1043 00:52:26,000 --> 00:52:29,120 Speaker 2: a theoretical idea, and experimentalists were like, all right, let's 1044 00:52:29,120 --> 00:52:30,719 Speaker 2: try to build it, see if we can find it, 1045 00:52:30,760 --> 00:52:33,799 Speaker 2: and they did. This is like the quantum version of it, 1046 00:52:34,160 --> 00:52:37,600 Speaker 2: which would look for little quantum ripples in space time, 1047 00:52:37,719 --> 00:52:42,360 Speaker 2: basically little quantum gravitational waves. And the experiment itself is similar. 1048 00:52:42,440 --> 00:52:45,840 Speaker 2: It's a little innerferometer. Like shoot laser beams back and forth, 1049 00:52:46,200 --> 00:52:48,160 Speaker 2: see how they overlap, and see if you can catch 1050 00:52:48,160 --> 00:52:51,480 Speaker 2: a graviton interfering with those laser beams. 1051 00:52:51,840 --> 00:52:55,279 Speaker 1: Hmmm, because the gravit times would be sort of like 1052 00:52:55,400 --> 00:52:59,000 Speaker 1: bedding space, is that the idea? Because gravity can't interact 1053 00:52:59,000 --> 00:53:01,960 Speaker 1: with footon or candy. 1054 00:53:01,680 --> 00:53:04,400 Speaker 2: Gravity doesn't interact with photons in a sort of Newtonian 1055 00:53:04,440 --> 00:53:07,520 Speaker 2: way because photons have no mass, but gravity does bend space, 1056 00:53:07,560 --> 00:53:10,759 Speaker 2: and photons move through that bend space, and so yeah, 1057 00:53:10,800 --> 00:53:14,680 Speaker 2: you're exactly right, Like a little gravitational quantum fluctuation the 1058 00:53:14,800 --> 00:53:18,320 Speaker 2: kind she's looking for, would affect the shape of space 1059 00:53:18,400 --> 00:53:20,560 Speaker 2: for one of these beams and would sort of knock 1060 00:53:20,600 --> 00:53:23,160 Speaker 2: a photon out of the path. And that's what they're 1061 00:53:23,200 --> 00:53:23,640 Speaker 2: looking for. 1062 00:53:24,440 --> 00:53:26,480 Speaker 1: The idea is that like a graviton would pop out 1063 00:53:26,480 --> 00:53:29,520 Speaker 1: of nowhere, it pops out, it bends space around it, 1064 00:53:29,600 --> 00:53:32,040 Speaker 1: and maybe it will deflect the photon. Is that the idea. 1065 00:53:32,200 --> 00:53:34,719 Speaker 2: That's the idea. But it's not one single graviton that 1066 00:53:34,760 --> 00:53:37,520 Speaker 2: would be totally invisible. It's this effect where a lot 1067 00:53:37,560 --> 00:53:41,160 Speaker 2: of gravitons are working together. And the super duper weird 1068 00:53:41,200 --> 00:53:44,000 Speaker 2: thing is that this effect only happens when you're making 1069 00:53:44,040 --> 00:53:47,200 Speaker 2: a measurement. It's a quantum effect. It comes from not 1070 00:53:47,239 --> 00:53:50,600 Speaker 2: being able to see the whole universe. So she's imagining 1071 00:53:50,640 --> 00:53:53,399 Speaker 2: space filled with all these gravitons, and when you make 1072 00:53:53,440 --> 00:53:55,319 Speaker 2: this measurement, it can only be affected by like a 1073 00:53:55,360 --> 00:53:58,520 Speaker 2: certain bubble of the universe, a bubble of the universe 1074 00:53:58,560 --> 00:54:00,960 Speaker 2: that's like close enough to you that light can travel 1075 00:54:01,000 --> 00:54:04,480 Speaker 2: to you. Because you create this information horizon, you limit 1076 00:54:04,640 --> 00:54:07,520 Speaker 2: like the wavelengths of these gravitons, and so only some 1077 00:54:07,600 --> 00:54:09,759 Speaker 2: of them can talk to your experiment, and that's what 1078 00:54:09,880 --> 00:54:12,600 Speaker 2: creates this weird effect. And I'll be totally honest, there's 1079 00:54:12,640 --> 00:54:14,920 Speaker 2: a lot of math there that I just don't even understand. 1080 00:54:15,120 --> 00:54:17,560 Speaker 2: But she's been trying to prove to herself that this 1081 00:54:17,640 --> 00:54:20,000 Speaker 2: works or that this doesn't work, and the math just 1082 00:54:20,120 --> 00:54:22,719 Speaker 2: keeps holding together no matter how she probes it. So, 1083 00:54:22,840 --> 00:54:25,280 Speaker 2: as you heard maybe in the interview, she really believes 1084 00:54:25,320 --> 00:54:25,879 Speaker 2: this is real. 1085 00:54:26,280 --> 00:54:28,120 Speaker 1: And so the idea is that you could maybe build 1086 00:54:28,160 --> 00:54:31,440 Speaker 1: this experiment on a tabletop like it could be, you know, 1087 00:54:31,520 --> 00:54:34,320 Speaker 1: a small experiment to prove a huge thing like quantum 1088 00:54:34,360 --> 00:54:35,360 Speaker 1: gravity exactly. 1089 00:54:35,600 --> 00:54:40,319 Speaker 2: Lego classical gravitational wave experiment is like kilometers long and 1090 00:54:40,360 --> 00:54:42,879 Speaker 2: cost billions of dollars. This would be like meters long. 1091 00:54:42,920 --> 00:54:45,319 Speaker 2: You literally could build it in a lab in the 1092 00:54:45,360 --> 00:54:48,920 Speaker 2: basement at Caltech, and if it works, they could see 1093 00:54:49,080 --> 00:54:52,680 Speaker 2: quantum gravitational effects on these beams of light and they 1094 00:54:52,680 --> 00:54:55,640 Speaker 2: could prove that gravitons are out there and that they're 1095 00:54:55,719 --> 00:54:58,759 Speaker 2: dancing together to make these little tiny ripples in space time. 1096 00:54:59,200 --> 00:55:02,239 Speaker 1: Cool. Well, she's welcome to hang out in my backyard 1097 00:55:02,320 --> 00:55:06,000 Speaker 1: and do the experiment here. That could be exciting. 1098 00:55:07,800 --> 00:55:09,719 Speaker 2: I don't think she wants her experiment it sprayed by 1099 00:55:09,719 --> 00:55:11,320 Speaker 2: the hose or like doused with water. 1100 00:55:11,160 --> 00:55:15,920 Speaker 1: Balloons, yeah, or have screaming kids running all around it 1101 00:55:15,960 --> 00:55:19,080 Speaker 1: that you usually it tends to make gravitons shy. 1102 00:55:19,120 --> 00:55:21,560 Speaker 2: I tend to dampen the effects of your experiment. 1103 00:55:21,920 --> 00:55:24,760 Speaker 1: All right, well, pretty exciting. Thank you to doctor Catherine 1104 00:55:24,880 --> 00:55:28,880 Speaker 1: Zurich for talking about her research. What does this all mean, Daniel, 1105 00:55:29,160 --> 00:55:32,640 Speaker 1: Are we far or near proving the idea of quantum gravity? 1106 00:55:33,120 --> 00:55:35,600 Speaker 2: I think we're still pretty far from figuring anything out. 1107 00:55:35,680 --> 00:55:37,880 Speaker 2: The theorists are working hard and making progress all the 1108 00:55:37,920 --> 00:55:41,200 Speaker 2: time about building their theories. But now it's exciting that 1109 00:55:41,280 --> 00:55:44,759 Speaker 2: we have experimental efforts which maybe in the next five, ten, 1110 00:55:44,880 --> 00:55:47,759 Speaker 2: fifteen years could provide us with really valuable clues to 1111 00:55:47,800 --> 00:55:50,680 Speaker 2: tell us, Oh, gravity is classical or nope, gravity is 1112 00:55:50,760 --> 00:55:53,360 Speaker 2: quantum mechanical. You better figure it out. That would be 1113 00:55:53,400 --> 00:55:57,359 Speaker 2: really powerful indication for sort of which direction to go theoretically. 1114 00:55:57,760 --> 00:56:00,760 Speaker 2: And I love this dance between experimental and the radical physics. 1115 00:56:00,760 --> 00:56:03,200 Speaker 2: You know, the ideas flourish and then experiments kill them, 1116 00:56:03,440 --> 00:56:07,000 Speaker 2: or sometimes experiments discover something weird which inspires lots of 1117 00:56:07,040 --> 00:56:10,279 Speaker 2: new theoretical ideas. It's really beautiful to see the interplay 1118 00:56:10,280 --> 00:56:14,360 Speaker 2: of these two different avenues of exploration. It's like a 1119 00:56:14,480 --> 00:56:17,680 Speaker 2: theoretical tango exactly. Even the physicists don't really know how 1120 00:56:17,680 --> 00:56:19,879 Speaker 2: to flirt. And I think the tango is pretty flirtatious. 1121 00:56:20,040 --> 00:56:23,280 Speaker 1: All right, Well, it sounds like the answer is stay tuned. 1122 00:56:23,520 --> 00:56:25,719 Speaker 1: In theory, it might be ten to fifteen years, but 1123 00:56:25,880 --> 00:56:28,879 Speaker 1: in reality, who knows. It could be that we may 1124 00:56:28,920 --> 00:56:31,399 Speaker 1: never answer this question, or it could be that we'll 1125 00:56:31,440 --> 00:56:33,160 Speaker 1: answer it within our lifetimes. 1126 00:56:33,400 --> 00:56:36,560 Speaker 2: That's right, we could be flirting with understanding or confusion. 1127 00:56:36,880 --> 00:56:39,600 Speaker 1: We hope you enjoyed that. Thanks for joining us, See 1128 00:56:39,640 --> 00:56:40,160 Speaker 1: you next time. 1129 00:56:48,080 --> 00:56:50,880 Speaker 2: Thanks for listening, and remember that Daniel and Jorge Explain 1130 00:56:50,920 --> 00:56:54,200 Speaker 2: the Universe is a production of iHeart Radio. For more 1131 00:56:54,280 --> 00:56:59,080 Speaker 2: podcasts from iHeartRadio, visit the iHeartRadio app, Apple Podcasts, or 1132 00:56:59,120 --> 00:57:01,360 Speaker 2: wherever you listen into your favorite shows. 1133 00:57:06,680 --> 00:57:09,400 Speaker 3: M hm h