1 00:00:00,160 --> 00:00:05,200 Speaker 1: My welcome to Stuff to Blow Your Mind, the production 2 00:00:05,240 --> 00:00:14,120 Speaker 1: of My Heart Radio. Hey you welcome to Stuff to 3 00:00:14,120 --> 00:00:17,000 Speaker 1: Blow Your Mind. My name is Robert Lamb and I'm 4 00:00:17,040 --> 00:00:20,200 Speaker 1: Joe McCormick. And for today's episode, we're going to be 5 00:00:20,280 --> 00:00:24,480 Speaker 1: chatting with Daniel Whitson, who is a particle physicist and 6 00:00:24,560 --> 00:00:28,280 Speaker 1: science communicator and one of the hosts of the podcast 7 00:00:28,440 --> 00:00:32,360 Speaker 1: Daniel and Jorge Explain the Universe. This is Daniel's third 8 00:00:32,440 --> 00:00:35,480 Speaker 1: time hopping on the show with us. The previous episodes 9 00:00:35,560 --> 00:00:40,479 Speaker 1: were in September of twenty nineteen and April of And 10 00:00:40,760 --> 00:00:42,680 Speaker 1: for this episode, we're gonna be talking about a book. 11 00:00:43,000 --> 00:00:46,320 Speaker 1: Daniel and his co host and co author Jorge cham 12 00:00:46,320 --> 00:00:50,200 Speaker 1: have a new book called Frequently Asked Questions about the Universe. 13 00:00:50,880 --> 00:00:52,760 Speaker 1: So it was a real pleasure to have Daniel on 14 00:00:52,800 --> 00:00:55,200 Speaker 1: the show for the hat trick, and I guess without 15 00:00:55,240 --> 00:01:01,040 Speaker 1: any further delay, we will go right into the interview. Daniel, 16 00:01:01,120 --> 00:01:02,920 Speaker 1: welcome back to the show. We're so glad you're here. 17 00:01:03,240 --> 00:01:05,280 Speaker 1: Thanks very much for having me back. Always fun to 18 00:01:05,280 --> 00:01:08,640 Speaker 1: talk to you guys about things that blew my mind. Awesome, 19 00:01:08,680 --> 00:01:12,400 Speaker 1: So um, the podcast Daniel and Jorge Explain the Universe 20 00:01:12,520 --> 00:01:16,000 Speaker 1: still going strong um. How how far are you into 21 00:01:16,080 --> 00:01:20,399 Speaker 1: explaining the universe in its entirely? We have explained zero 22 00:01:20,400 --> 00:01:23,759 Speaker 1: point zero zero zero zero zero zero zero zero one 23 00:01:23,800 --> 00:01:27,399 Speaker 1: percent of the universe so far. Nice. I actually I 24 00:01:27,440 --> 00:01:29,480 Speaker 1: was looking at your recent episodes and I saw did 25 00:01:29,520 --> 00:01:31,680 Speaker 1: you recently do one that was an interview with Sean 26 00:01:31,760 --> 00:01:35,840 Speaker 1: Carroll about the uh, the many worlds interpretation of quantum mechanics. 27 00:01:35,920 --> 00:01:38,920 Speaker 1: I know, I know he favors that, right. Yeah, we 28 00:01:38,959 --> 00:01:41,640 Speaker 1: actually have a series where I interview an expert on 29 00:01:41,800 --> 00:01:45,160 Speaker 1: each of the interpretations of quantum mechanics. We did one 30 00:01:45,160 --> 00:01:48,640 Speaker 1: on Copenhagen interpretation with annam Becker, We did one on 31 00:01:49,120 --> 00:01:53,320 Speaker 1: the relational interpretation of quantum mechanics with Carlo Rovelli, and 32 00:01:53,320 --> 00:01:56,320 Speaker 1: then we talked to Sean about many Worlds interpretation. And 33 00:01:56,440 --> 00:01:58,279 Speaker 1: just a couple of weeks ago we did one about 34 00:01:58,280 --> 00:02:02,440 Speaker 1: the pilot wave theory of quantum mechanics, which totally blew 35 00:02:02,480 --> 00:02:07,800 Speaker 1: my mind. Really much overlooked and unnecessarily maligned interpretation of 36 00:02:07,840 --> 00:02:11,839 Speaker 1: quantum mechanics, in my opinion, malign, like people are being 37 00:02:11,880 --> 00:02:15,760 Speaker 1: mean to it. Well, there's this famous proof by John 38 00:02:15,840 --> 00:02:19,799 Speaker 1: von Neuman like seventy years ago demonstrating that it was 39 00:02:19,880 --> 00:02:23,160 Speaker 1: essentially impossible, and because von Neuman is such a giant 40 00:02:23,200 --> 00:02:26,160 Speaker 1: of the field, everybody thought, well, that's that. Turns out 41 00:02:26,200 --> 00:02:30,200 Speaker 1: he was wrong, though, and and it took people years 42 00:02:30,240 --> 00:02:32,200 Speaker 1: to figure it out. It was Bell actually who figured 43 00:02:32,240 --> 00:02:35,240 Speaker 1: out that Noeman was wrong, and that it's possible to 44 00:02:35,320 --> 00:02:40,440 Speaker 1: have a theory of quantum mechanics with hidden variables that's deterministic, 45 00:02:40,480 --> 00:02:44,359 Speaker 1: that's not random at all um. But still to this day, 46 00:02:44,400 --> 00:02:48,720 Speaker 1: nobody really takes pilot wave theory seriously, to Bell's great restoration. 47 00:02:48,800 --> 00:02:52,079 Speaker 1: And I think it's because Neuman sort of threw shade 48 00:02:52,120 --> 00:02:54,760 Speaker 1: on it decades ago and it never really recovered. I 49 00:02:54,760 --> 00:02:57,560 Speaker 1: guess that's always dangerous when there's like a famously smart 50 00:02:57,600 --> 00:03:00,360 Speaker 1: person who has an opinion absolutely and I find that 51 00:03:00,400 --> 00:03:04,480 Speaker 1: physics Nobel Prize winners are especially guilty of this imagining 52 00:03:04,600 --> 00:03:07,480 Speaker 1: that they are experts in every corner of everything and 53 00:03:07,520 --> 00:03:12,280 Speaker 1: opining on economics or you know, social politics or whatever. 54 00:03:12,680 --> 00:03:14,520 Speaker 1: If you have Nobel Prize winner in front of your name, 55 00:03:14,560 --> 00:03:17,639 Speaker 1: you're an expert. Uh So, today we wanted to talk 56 00:03:17,680 --> 00:03:20,600 Speaker 1: about a couple of chapters that are in a book 57 00:03:20,600 --> 00:03:22,920 Speaker 1: of yours. Did that come out earlier this year? Tell 58 00:03:23,000 --> 00:03:25,120 Speaker 1: us a bit about the book. Yeah, so the book 59 00:03:25,200 --> 00:03:28,200 Speaker 1: is called Frequently Asked Questions about the Universe that I 60 00:03:28,240 --> 00:03:30,680 Speaker 1: wrote together with my co host on the podcast and 61 00:03:30,760 --> 00:03:35,080 Speaker 1: longtime collaborator Or Cham who's also famous for being the 62 00:03:35,120 --> 00:03:39,720 Speaker 1: genius behind PhD comics. And the book comes from noticing 63 00:03:39,800 --> 00:03:43,840 Speaker 1: that people who write into our podcast often ask similar 64 00:03:43,880 --> 00:03:46,400 Speaker 1: types of questions. There are a few things that seems 65 00:03:46,440 --> 00:03:50,440 Speaker 1: like everybody just wants to know about or understand or 66 00:03:50,520 --> 00:03:52,800 Speaker 1: the things that people grapple with. You know, I'm a 67 00:03:52,800 --> 00:03:56,160 Speaker 1: professional particle physicist in my day job, um, and so 68 00:03:56,200 --> 00:03:59,000 Speaker 1: I like asking questions about, you know, the deep nature 69 00:03:59,120 --> 00:04:02,440 Speaker 1: of the universe, usend, how our space and time really related. 70 00:04:02,760 --> 00:04:05,200 Speaker 1: But you don't have to be a professor of physics 71 00:04:05,200 --> 00:04:08,560 Speaker 1: to find these things interesting. And we feel like, in 72 00:04:08,560 --> 00:04:13,520 Speaker 1: a sense, you know, curiosity is democratic. Everybody wonders about 73 00:04:13,520 --> 00:04:16,279 Speaker 1: these things. So we wanted to try to attack some 74 00:04:16,360 --> 00:04:19,720 Speaker 1: of these really big questions that everybody wonders about in 75 00:04:19,720 --> 00:04:22,279 Speaker 1: an approachable way, in a way that doesn't require you 76 00:04:22,320 --> 00:04:26,680 Speaker 1: to really have any knowledge of modern physics at all. Yeah. 77 00:04:26,520 --> 00:04:29,200 Speaker 1: I've really been enjoying the chapter as I was reading. 78 00:04:29,440 --> 00:04:31,400 Speaker 1: One thing I like that you do in this book 79 00:04:31,480 --> 00:04:34,080 Speaker 1: is um is that you know, it's not like a 80 00:04:34,360 --> 00:04:37,360 Speaker 1: continuous narrative that has to you have to have read 81 00:04:37,440 --> 00:04:40,320 Speaker 1: everything that came before in order to understand. Like, the 82 00:04:40,400 --> 00:04:43,680 Speaker 1: chapters can be consumed pretty much on their own, right. Yeah, 83 00:04:43,720 --> 00:04:46,560 Speaker 1: we figured, you know, each chapter should be like one 84 00:04:46,600 --> 00:04:48,880 Speaker 1: long bathroom break. So I mean, I'm not telling you 85 00:04:48,880 --> 00:04:51,120 Speaker 1: where to read it, but if you're looking for reading 86 00:04:51,360 --> 00:04:54,400 Speaker 1: while you're busy sitting down doing something else, each chapter 87 00:04:54,560 --> 00:04:57,719 Speaker 1: you know, should entertain you while you're doing your business. 88 00:04:57,760 --> 00:04:59,840 Speaker 1: Just you know, don't get so distracted that you forget 89 00:04:59,880 --> 00:05:04,359 Speaker 1: to flush right now. Obviously this edition would lack the 90 00:05:04,440 --> 00:05:07,440 Speaker 1: wonderful illustrations that are in the print and the Kendall version. 91 00:05:07,760 --> 00:05:10,599 Speaker 1: But um, but you guys put together an audio version 92 00:05:10,600 --> 00:05:13,159 Speaker 1: as well, right, yes we did. We got to record 93 00:05:13,240 --> 00:05:15,559 Speaker 1: the audio version of the book, which is out now also, 94 00:05:16,000 --> 00:05:19,520 Speaker 1: and the chapters are read by me and by Jorge alternating, 95 00:05:19,880 --> 00:05:22,240 Speaker 1: which is a lot of fun just sort of hear 96 00:05:22,320 --> 00:05:25,440 Speaker 1: your words come to life. But yes, the audiobook does 97 00:05:25,520 --> 00:05:29,000 Speaker 1: miss some other the real genius of Jorge's drawings. Um. 98 00:05:29,320 --> 00:05:31,920 Speaker 1: Jorge and I started working together on science communication more 99 00:05:31,960 --> 00:05:33,840 Speaker 1: than ten years ago when I reached out to him 100 00:05:33,839 --> 00:05:37,480 Speaker 1: because I thought that cartoons would be a really great 101 00:05:37,640 --> 00:05:41,760 Speaker 1: medium for communicating science because they don't take themselves seriously, 102 00:05:42,000 --> 00:05:44,159 Speaker 1: you know, they're a cartoon is different from like a 103 00:05:44,320 --> 00:05:47,400 Speaker 1: figure into science paper, you know, which is very official 104 00:05:47,480 --> 00:05:50,120 Speaker 1: and formal. A cartoon like makes fun of itself and 105 00:05:50,279 --> 00:05:52,839 Speaker 1: is easy to you know, hang out with and accessible. 106 00:05:53,320 --> 00:05:55,800 Speaker 1: And Jorge was great at that kind of stuff. So 107 00:05:55,839 --> 00:05:59,640 Speaker 1: he and I started working together on explaining science using 108 00:05:59,640 --> 00:06:02,160 Speaker 1: cartoon is a long time ago. Um, And one thing 109 00:06:02,200 --> 00:06:05,960 Speaker 1: I really value about his cartoons is not just that 110 00:06:06,040 --> 00:06:09,040 Speaker 1: they are good visual explainers. He has a real visual 111 00:06:09,160 --> 00:06:12,680 Speaker 1: skill for explaining something simply on the page, but also 112 00:06:12,760 --> 00:06:14,800 Speaker 1: that there's sort of a second voice there you can hear, 113 00:06:14,839 --> 00:06:16,800 Speaker 1: like in the text is the voice of me as 114 00:06:16,839 --> 00:06:19,480 Speaker 1: a physicist, and then the cartoons you can hear sort 115 00:06:19,480 --> 00:06:22,640 Speaker 1: of his response to some of the crazy ideas UM. 116 00:06:22,760 --> 00:06:24,960 Speaker 1: And that sort of mirrors the way the podcast works. 117 00:06:24,960 --> 00:06:28,039 Speaker 1: On the podcast, I'm talking about physics and Jorges you 118 00:06:28,040 --> 00:06:29,920 Speaker 1: know something like that doesn't make any sense, or how 119 00:06:29,920 --> 00:06:32,279 Speaker 1: could that possibly be? Or what you got to explain 120 00:06:32,320 --> 00:06:34,640 Speaker 1: that again? Because so it sort of tries to capture 121 00:06:34,680 --> 00:06:37,440 Speaker 1: those two voices. Yeah, I really liked that the the 122 00:06:37,480 --> 00:06:40,400 Speaker 1: illustrations almost seem kind of riffing on the written contents 123 00:06:40,440 --> 00:06:43,680 Speaker 1: of the book. Well, so, the parts of the book 124 00:06:43,680 --> 00:06:45,440 Speaker 1: that we wanted to focus on today, I think we're 125 00:06:45,480 --> 00:06:49,680 Speaker 1: mostly centered around the idea of time and so maybe 126 00:06:49,720 --> 00:06:52,000 Speaker 1: maybe a good place to start is you have a 127 00:06:52,080 --> 00:06:54,400 Speaker 1: chapter in the book where you talk about time travel 128 00:06:54,680 --> 00:06:58,520 Speaker 1: and you make some arguments about which types of time 129 00:06:58,520 --> 00:07:02,120 Speaker 1: travel are plausible from a physics perspective and which are not. 130 00:07:02,960 --> 00:07:04,440 Speaker 1: So maybe that would be a good place to start 131 00:07:04,440 --> 00:07:06,080 Speaker 1: to give us the way of the land, like what 132 00:07:06,120 --> 00:07:08,880 Speaker 1: types of time travel are the least consistent with the 133 00:07:08,920 --> 00:07:14,280 Speaker 1: known laws of physics and which are the most consistent. Yeah. Sure, 134 00:07:14,680 --> 00:07:17,200 Speaker 1: So for those of your listeners who are busy building 135 00:07:17,240 --> 00:07:21,640 Speaker 1: their time travel devices, of this useful advice. Well, you know, 136 00:07:21,680 --> 00:07:25,080 Speaker 1: the kind of time travel that's most inconsistent with the 137 00:07:25,120 --> 00:07:27,200 Speaker 1: law of physics is the kind that most people want 138 00:07:27,280 --> 00:07:29,800 Speaker 1: to do, you know, which is I want to go 139 00:07:29,880 --> 00:07:33,360 Speaker 1: back in time and change something. I want to not 140 00:07:33,600 --> 00:07:35,760 Speaker 1: spill my coffee on my lap, or I wanted to 141 00:07:35,800 --> 00:07:38,760 Speaker 1: go you know, not um make a mistake, or I 142 00:07:38,760 --> 00:07:40,920 Speaker 1: want to go ask that person out in high school, 143 00:07:41,000 --> 00:07:43,160 Speaker 1: which I was too timid to do. And now I 144 00:07:43,200 --> 00:07:45,640 Speaker 1: realized I should have that kind of thing. It's not 145 00:07:45,720 --> 00:07:48,080 Speaker 1: just that it's ruled out by the laws of physics. 146 00:07:48,320 --> 00:07:51,840 Speaker 1: In my view, it's not even sort of internally self 147 00:07:51,880 --> 00:07:55,440 Speaker 1: consistent what it means um, you know, and and a 148 00:07:55,480 --> 00:07:58,240 Speaker 1: lot of people think about time travel is like I 149 00:07:58,280 --> 00:08:01,320 Speaker 1: want to go back in time, as if time was 150 00:08:01,400 --> 00:08:04,680 Speaker 1: a place, like if it's a somewhere you can go. 151 00:08:05,520 --> 00:08:08,240 Speaker 1: It's just sort of like along a different direction or something. 152 00:08:08,640 --> 00:08:10,880 Speaker 1: And it's tempting to think about it that way because 153 00:08:10,960 --> 00:08:13,840 Speaker 1: we we hear a lot about modern physics telling us 154 00:08:13,880 --> 00:08:16,920 Speaker 1: that space and time are related and time is like 155 00:08:16,960 --> 00:08:19,440 Speaker 1: a fourth dimension of space, and so it makes you 156 00:08:20,080 --> 00:08:22,600 Speaker 1: want to think about time as a direction in which 157 00:08:22,640 --> 00:08:25,960 Speaker 1: you can move and maybe you could just rewind it somehow, right, 158 00:08:26,440 --> 00:08:29,480 Speaker 1: But the problem is that time. You know, first of all, 159 00:08:29,520 --> 00:08:31,640 Speaker 1: we don't understand time like at all, and we can 160 00:08:31,680 --> 00:08:33,840 Speaker 1: dig into that in a minute if you like. Um. 161 00:08:33,880 --> 00:08:36,200 Speaker 1: But the problem is that time sort of reflects how 162 00:08:36,240 --> 00:08:39,800 Speaker 1: the universe changes. And so you know, I think about 163 00:08:39,840 --> 00:08:43,640 Speaker 1: time is like you have a timeline. That timeline is 164 00:08:43,760 --> 00:08:47,080 Speaker 1: the universe changing, Like you have the universe at one moment, 165 00:08:47,120 --> 00:08:50,240 Speaker 1: and you have the universe at another moment. The next 166 00:08:50,320 --> 00:08:54,680 Speaker 1: moment comes later in time, and things can't change without time. 167 00:08:54,760 --> 00:08:59,400 Speaker 1: Time is that change. So the self consistency problem is 168 00:08:59,440 --> 00:09:02,800 Speaker 1: that going back in time to change it changes the 169 00:09:02,960 --> 00:09:07,839 Speaker 1: timeline itself. So like, how does the timeline change If 170 00:09:07,840 --> 00:09:11,280 Speaker 1: the timeline is the change, how does the timeline itself change? 171 00:09:11,400 --> 00:09:15,199 Speaker 1: It would need like its own time, Like the timeline 172 00:09:15,240 --> 00:09:18,120 Speaker 1: is now moving through time because it was a time 173 00:09:18,120 --> 00:09:21,079 Speaker 1: before you changed in a time after you changed it. 174 00:09:21,160 --> 00:09:24,040 Speaker 1: So it needs like a second dimension of time. I mean, 175 00:09:24,080 --> 00:09:26,800 Speaker 1: it just sort of all becomes very complicated and falls 176 00:09:26,840 --> 00:09:29,160 Speaker 1: apart as soon as you start thinking about it carefully. 177 00:09:29,559 --> 00:09:32,839 Speaker 1: So going back and changing something in the past really 178 00:09:32,880 --> 00:09:35,840 Speaker 1: just makes no sense from a physics point of view. Yeah, 179 00:09:36,160 --> 00:09:40,000 Speaker 1: I love this because I have long kind of been 180 00:09:40,040 --> 00:09:42,640 Speaker 1: skeptical about the idea of time travel into the past. 181 00:09:42,720 --> 00:09:45,400 Speaker 1: And one of the reasons I had doubts about this 182 00:09:45,840 --> 00:09:48,640 Speaker 1: is that wouldn't we expect to have already encountered lots 183 00:09:48,679 --> 00:09:51,839 Speaker 1: of time travelers at some point in history? And there's 184 00:09:52,040 --> 00:09:54,640 Speaker 1: no unambiguous evidence of that. I mean, obviously some people, 185 00:09:54,720 --> 00:09:58,000 Speaker 1: you know, they're weird little things people think or time travel, 186 00:09:58,040 --> 00:10:00,840 Speaker 1: but nothing that looks really clear. So It kind of 187 00:10:00,880 --> 00:10:04,080 Speaker 1: makes me think that if if time travel into the 188 00:10:04,080 --> 00:10:07,560 Speaker 1: past ever happens in the future, it will be of 189 00:10:07,559 --> 00:10:10,720 Speaker 1: a very limited nature. Yeah, I love that as an 190 00:10:10,800 --> 00:10:14,880 Speaker 1: experimental proof, you know, like, if time travel exists any 191 00:10:14,960 --> 00:10:18,160 Speaker 1: time in the future, then you would expect to see it. Now. 192 00:10:18,200 --> 00:10:21,040 Speaker 1: I love that. It's just such a powerful argument. It 193 00:10:21,080 --> 00:10:24,200 Speaker 1: sort of reminds me of Stephen Hawking's famous invitation to 194 00:10:24,320 --> 00:10:27,600 Speaker 1: time travelers where he threw a party and then he 195 00:10:27,679 --> 00:10:31,080 Speaker 1: posted the invitation later after the party. The idea of 196 00:10:31,120 --> 00:10:33,120 Speaker 1: being the time travelers, you know, they should be able 197 00:10:33,160 --> 00:10:35,840 Speaker 1: to get there anyway, And of course nobody showed up 198 00:10:35,880 --> 00:10:40,600 Speaker 1: to his party. Well we know he might have dispensed 199 00:10:40,600 --> 00:10:47,640 Speaker 1: with them, or maybe he is a time traveler. Oh 200 00:10:47,679 --> 00:10:49,920 Speaker 1: that's a good premise for a sci fi movie like 201 00:10:49,960 --> 00:10:53,080 Speaker 1: The Time Traveler Hunters, trying to eliminate all evidence of 202 00:10:53,080 --> 00:10:57,679 Speaker 1: the time travelers. Well that that kind of plays into um, 203 00:10:58,000 --> 00:10:59,839 Speaker 1: you know, someone, what you're talking about about it being 204 00:11:00,080 --> 00:11:01,679 Speaker 1: if it if it does exist in the future, then 205 00:11:01,679 --> 00:11:03,960 Speaker 1: it must be limited in scope. And I guess you 206 00:11:03,960 --> 00:11:05,520 Speaker 1: could look at it a couple of different We could 207 00:11:05,559 --> 00:11:08,240 Speaker 1: basically just scify the hell out of it in multiple directions. 208 00:11:08,280 --> 00:11:11,520 Speaker 1: But you know, you could say, like, well, maybe travel 209 00:11:11,559 --> 00:11:13,800 Speaker 1: into the past. It has a range, and we haven't 210 00:11:13,800 --> 00:11:16,520 Speaker 1: reached the point to where time machines of the future 211 00:11:16,520 --> 00:11:19,679 Speaker 1: can reach us. Or it's just so tightly policed that 212 00:11:19,720 --> 00:11:21,560 Speaker 1: nobody can make it back. You know, we have time 213 00:11:21,600 --> 00:11:24,760 Speaker 1: cops or or something that are that are keeping people 214 00:11:24,880 --> 00:11:28,240 Speaker 1: from making too much of a show of the whole thing. 215 00:11:28,520 --> 00:11:31,040 Speaker 1: There's so many of those science fiction depictions of like 216 00:11:31,120 --> 00:11:35,240 Speaker 1: a big time bureaucracy, you know that's managing the time flow, 217 00:11:35,480 --> 00:11:38,239 Speaker 1: like you saw that in Loki and in Umbrella Academy 218 00:11:38,360 --> 00:11:42,040 Speaker 1: and and It and in um that book recently, this 219 00:11:42,120 --> 00:11:44,640 Speaker 1: is how you win the time war. And those can 220 00:11:44,679 --> 00:11:46,319 Speaker 1: be a lot of fun, but also I feel like 221 00:11:46,360 --> 00:11:49,600 Speaker 1: they're they just make no sense at all. You know, 222 00:11:50,000 --> 00:11:53,120 Speaker 1: how do you have this weird administration that's separated from 223 00:11:53,160 --> 00:11:58,120 Speaker 1: time and also weirdly frozen in like nineties bureaucracy. It's 224 00:11:58,120 --> 00:11:59,920 Speaker 1: you know, it's fun, but not not if you think 225 00:12:00,000 --> 00:12:02,760 Speaker 1: about it really at all. What also reminds me a 226 00:12:02,800 --> 00:12:05,160 Speaker 1: lot of something I was actually chatting with you about 227 00:12:05,320 --> 00:12:07,840 Speaker 1: a couple of weeks ago, when I interviewed you for 228 00:12:07,880 --> 00:12:10,520 Speaker 1: a short freelance piece for How Stuff works dot com 229 00:12:10,559 --> 00:12:14,959 Speaker 1: about UM about the zoo hypothesis. Uh you you spoke 230 00:12:15,000 --> 00:12:19,280 Speaker 1: about about that for the interview, and uh you mentioned 231 00:12:19,280 --> 00:12:21,440 Speaker 1: that one of the strong arguments against it is that 232 00:12:21,480 --> 00:12:25,200 Speaker 1: if there is actually this, um, this conspiracy of of 233 00:12:25,280 --> 00:12:29,000 Speaker 1: aliens to avoid contact with humans and and and keep 234 00:12:29,080 --> 00:12:31,120 Speaker 1: us in the dark about the uh you know, the 235 00:12:31,160 --> 00:12:36,079 Speaker 1: galactic civilizations just outside of our view, UM, the main 236 00:12:36,160 --> 00:12:40,400 Speaker 1: argument against it is that governments as we know them, 237 00:12:40,440 --> 00:12:42,880 Speaker 1: by the only model that we know the the the 238 00:12:42,960 --> 00:12:45,559 Speaker 1: human model, are not really good at keeping secrets. They're 239 00:12:45,600 --> 00:12:48,240 Speaker 1: not good at advanaging secrets. And it seems like you 240 00:12:48,240 --> 00:12:51,640 Speaker 1: could also apply that to the idea of intelligent beings 241 00:12:51,679 --> 00:12:55,719 Speaker 1: or humans and the future managing the timeline and so forth. Exactly, 242 00:12:55,800 --> 00:12:58,280 Speaker 1: you know, some version of Elon Musk and the future 243 00:12:58,360 --> 00:13:00,640 Speaker 1: is get his hands on it, and he's gonna launch 244 00:13:00,679 --> 00:13:03,720 Speaker 1: a bunch of crazy, you know, missions, and somebody's gonna 245 00:13:03,720 --> 00:13:06,520 Speaker 1: mess something up. So it's hard to imagine that people 246 00:13:06,520 --> 00:13:09,160 Speaker 1: in the future having time travel and somehow keeping a 247 00:13:09,160 --> 00:13:13,720 Speaker 1: secretor slipping into the past unnoticed and nobody ever, you know, 248 00:13:13,800 --> 00:13:16,920 Speaker 1: breaking the protocol or something. It's it just becomes totally 249 00:13:16,960 --> 00:13:20,200 Speaker 1: implausible the more you think about it. Picking up off that. 250 00:13:20,240 --> 00:13:22,640 Speaker 1: I mean, this is another one of the weird things 251 00:13:22,679 --> 00:13:26,080 Speaker 1: about time is it seems like time is actually one 252 00:13:26,160 --> 00:13:31,200 Speaker 1: of the arguments against the idea of a coherent galactic civilization, 253 00:13:31,720 --> 00:13:34,240 Speaker 1: if this makes any sense, because like you think, a 254 00:13:34,280 --> 00:13:37,360 Speaker 1: civilization in order to organize itself, has to have some 255 00:13:38,120 --> 00:13:42,560 Speaker 1: pretty close to synchronous uh, you know, thing going on, 256 00:13:42,679 --> 00:13:45,960 Speaker 1: Like things have to be happening pretty close to around 257 00:13:45,960 --> 00:13:47,880 Speaker 1: the same time for them. But does it even make 258 00:13:47,960 --> 00:13:51,360 Speaker 1: sense for I don't know, one planet in a galactic 259 00:13:51,400 --> 00:13:54,440 Speaker 1: civilization to be part of a civilization with one on 260 00:13:54,440 --> 00:13:56,360 Speaker 1: the other side of the galaxy. I mean, is there 261 00:13:56,400 --> 00:14:00,080 Speaker 1: you know, can they say, uh, is there such a thing? 262 00:14:00,160 --> 00:14:03,400 Speaker 1: Is what's happening right now on a planet on the 263 00:14:03,440 --> 00:14:06,120 Speaker 1: other side of the galaxy? Yeah. You make a great point, 264 00:14:06,160 --> 00:14:09,960 Speaker 1: because there's a speed limit to information moving through the universe, 265 00:14:10,400 --> 00:14:12,720 Speaker 1: which puts an effective limit on like how well you 266 00:14:12,760 --> 00:14:16,280 Speaker 1: can coordinate and organize things. Actually, think about this in 267 00:14:16,360 --> 00:14:19,600 Speaker 1: cosmology all the time, because there's a like the largest 268 00:14:19,840 --> 00:14:22,920 Speaker 1: thing that can exist in the universe just from very 269 00:14:22,920 --> 00:14:25,400 Speaker 1: simple arguments like the age of the universe and the 270 00:14:25,440 --> 00:14:28,480 Speaker 1: speed of light. You can't have an object that's like 271 00:14:29,200 --> 00:14:33,600 Speaker 1: ten thousand billion light years wide, that's like coordinated, that 272 00:14:33,680 --> 00:14:36,920 Speaker 1: has like a structure that's like gravitationally bound on itself, 273 00:14:37,360 --> 00:14:39,560 Speaker 1: because there hasn't been time for like a photon to 274 00:14:39,680 --> 00:14:43,920 Speaker 1: even cross over the entire size of that object. So 275 00:14:43,960 --> 00:14:46,400 Speaker 1: there's like a limit to how big the universe can 276 00:14:46,440 --> 00:14:49,560 Speaker 1: even build like a thing, not to mention like the 277 00:14:49,600 --> 00:14:53,800 Speaker 1: close coordination required to like organize a galactic empire. And 278 00:14:53,840 --> 00:14:57,640 Speaker 1: so yeah, absolutely, um, I think that the sheer size 279 00:14:57,680 --> 00:15:01,200 Speaker 1: of space definitely limits our ability to exploit it unless 280 00:15:01,240 --> 00:15:06,080 Speaker 1: it breaks down into you know, lots of different unorganized entities, 281 00:15:06,120 --> 00:15:08,480 Speaker 1: Like maybe we send humans in an arc off to 282 00:15:08,680 --> 00:15:11,480 Speaker 1: another star and they start their own human colony and 283 00:15:11,640 --> 00:15:13,640 Speaker 1: we're not in touch and a part of them, you know, 284 00:15:13,720 --> 00:15:16,400 Speaker 1: political nation state. But at least we're humans here and 285 00:15:16,400 --> 00:15:19,120 Speaker 1: there are humans there. Yeah, I think that's a great 286 00:15:19,160 --> 00:15:28,120 Speaker 1: way to conceptualize it. So, I guess coming back to 287 00:15:28,200 --> 00:15:31,080 Speaker 1: time travel for a minute, I wanted to talk about 288 00:15:31,080 --> 00:15:35,040 Speaker 1: some of the specifics you offer about physically plausible ways 289 00:15:35,320 --> 00:15:39,280 Speaker 1: of traveling into the past. Uh. So you mentioned a 290 00:15:39,320 --> 00:15:41,560 Speaker 1: couple of things. You mentioned the idea of wormholes, and 291 00:15:41,560 --> 00:15:44,000 Speaker 1: then you also mentioned one that might be less familiar 292 00:15:44,000 --> 00:15:47,960 Speaker 1: to people. The idea of an infinitely long cylinder of 293 00:15:48,040 --> 00:15:52,960 Speaker 1: spinning dust, which could potentially, at least maybe depending on 294 00:15:53,920 --> 00:15:56,840 Speaker 1: something about whether something about relativity is true or not, 295 00:15:57,440 --> 00:16:00,280 Speaker 1: could potentially allow time travel into the past through something 296 00:16:00,320 --> 00:16:03,880 Speaker 1: called time loops. Could could you explain how this would work? Like, 297 00:16:03,960 --> 00:16:08,040 Speaker 1: what would this experience be like for the time traveler? Yeah, well, 298 00:16:08,080 --> 00:16:10,680 Speaker 1: the short answer is, we just don't know. Uh, this 299 00:16:10,760 --> 00:16:14,600 Speaker 1: is a realm where we are like on the cutting edge. Theoretically, 300 00:16:15,120 --> 00:16:18,240 Speaker 1: people are looking at the rules of how space and 301 00:16:18,320 --> 00:16:22,320 Speaker 1: time bend and twist because you know, general relativity, our 302 00:16:22,360 --> 00:16:26,360 Speaker 1: theory for space and time itself essentially tells us that 303 00:16:26,600 --> 00:16:30,800 Speaker 1: space and time bend in response to mass and then 304 00:16:30,840 --> 00:16:33,800 Speaker 1: tell masses how to move. So, for example, you have 305 00:16:33,840 --> 00:16:36,160 Speaker 1: an empty universe and you put a star in it, 306 00:16:36,160 --> 00:16:38,880 Speaker 1: it bends the space around the star, and then the 307 00:16:38,920 --> 00:16:41,360 Speaker 1: bending of that space tells things how to move, and 308 00:16:41,400 --> 00:16:44,920 Speaker 1: not just through space but also through time. So you 309 00:16:44,960 --> 00:16:48,280 Speaker 1: go near a black hole, for example, time is slowed down. 310 00:16:48,720 --> 00:16:51,120 Speaker 1: So there's definitely some deep connection there between space and 311 00:16:51,120 --> 00:16:53,880 Speaker 1: time and what people have done is trying to explore 312 00:16:53,920 --> 00:16:56,720 Speaker 1: extreme scenarios about what happens if you do this, what 313 00:16:56,840 --> 00:16:59,640 Speaker 1: happens if you do that? Is this allowed? Is that allowed? 314 00:17:00,080 --> 00:17:02,480 Speaker 1: And so it's sort of like exploring the universe, but 315 00:17:02,600 --> 00:17:06,200 Speaker 1: just inside our own heads. We can't necessarily yet go 316 00:17:06,280 --> 00:17:08,960 Speaker 1: out there and build these things in space and say, 317 00:17:09,040 --> 00:17:12,160 Speaker 1: let's see what happens experimentally, but we can do similar 318 00:17:12,280 --> 00:17:14,840 Speaker 1: like fought experiments, where we say, what would happen if 319 00:17:14,880 --> 00:17:18,119 Speaker 1: you did this, and let's just let's assume the equations 320 00:17:18,119 --> 00:17:21,080 Speaker 1: are correct and see what happens. And so there's a 321 00:17:21,080 --> 00:17:23,840 Speaker 1: couple of fund scenarios there. One, as you said, is wormholes. 322 00:17:24,440 --> 00:17:27,760 Speaker 1: These aren't really crazy because they are like connections between 323 00:17:28,080 --> 00:17:31,119 Speaker 1: different points in space. And when you think of space, 324 00:17:31,160 --> 00:17:33,760 Speaker 1: you probably think of like just sheer emptiness, you know, 325 00:17:33,800 --> 00:17:36,639 Speaker 1: the back drop the stage on which the universe happens. 326 00:17:36,680 --> 00:17:38,920 Speaker 1: But now we know that space is more complex. It 327 00:17:39,000 --> 00:17:41,840 Speaker 1: can bend and it can twist, and that might be 328 00:17:41,880 --> 00:17:43,359 Speaker 1: something that you can put in your head. You can 329 00:17:43,400 --> 00:17:46,879 Speaker 1: imagine like space bending around the sun. But because space 330 00:17:47,040 --> 00:17:49,880 Speaker 1: is like a thing with an arrangement, it could also 331 00:17:49,920 --> 00:17:54,760 Speaker 1: do other really weird things, like be connected non trivially, 332 00:17:55,160 --> 00:17:56,920 Speaker 1: so you have like a chunk of space over here. 333 00:17:57,280 --> 00:17:59,920 Speaker 1: It can be directly connected to a chunk of space 334 00:18:00,080 --> 00:18:02,840 Speaker 1: over there. What does that mean. Well, you're used to 335 00:18:02,880 --> 00:18:06,200 Speaker 1: the space around you being connected to the space right 336 00:18:06,240 --> 00:18:07,920 Speaker 1: next to it. That's what it means to be right 337 00:18:08,000 --> 00:18:10,080 Speaker 1: next to it. Right, you take a step to the left, 338 00:18:10,119 --> 00:18:12,240 Speaker 1: you move to the next sort of piece of space. 339 00:18:12,720 --> 00:18:15,879 Speaker 1: Think of it sort of like pixels on a screen. Right, Well, 340 00:18:15,920 --> 00:18:18,879 Speaker 1: a wormhole is a connection between two points in space 341 00:18:18,920 --> 00:18:22,679 Speaker 1: that are otherwise really distant. And so you take a 342 00:18:22,680 --> 00:18:25,159 Speaker 1: step from a from one pixel and now you're in 343 00:18:25,160 --> 00:18:27,840 Speaker 1: a pixel on the other side of the screen. And 344 00:18:27,880 --> 00:18:31,359 Speaker 1: so that seems weird and impossible, but remember space can 345 00:18:31,400 --> 00:18:34,800 Speaker 1: have all sorts of strange connections, and according to the 346 00:18:34,840 --> 00:18:37,960 Speaker 1: equations of general relativity, the ones that define how space 347 00:18:38,000 --> 00:18:42,600 Speaker 1: is organized, that is allowed. It is possible. And so 348 00:18:42,760 --> 00:18:44,960 Speaker 1: a couple of folks at cal Tech we're thinking about, well, 349 00:18:45,200 --> 00:18:48,160 Speaker 1: you know what about time? Is it possible for one 350 00:18:48,359 --> 00:18:50,320 Speaker 1: end of the wormhole to be in one place and 351 00:18:50,359 --> 00:18:54,600 Speaker 1: the other end to be in another time? Because, as 352 00:18:54,600 --> 00:18:57,800 Speaker 1: you were mentioning earlier, like the notion of simultaneity, like 353 00:18:58,280 --> 00:19:02,159 Speaker 1: when is now depends really on where you are. Also, 354 00:19:02,840 --> 00:19:04,680 Speaker 1: so they have this idea to take one end of 355 00:19:04,720 --> 00:19:07,480 Speaker 1: the wormhole and you accelerate it near the speed of light. 356 00:19:07,760 --> 00:19:10,320 Speaker 1: That effectively it can be sort of back in time. 357 00:19:11,080 --> 00:19:14,119 Speaker 1: And this all works theoretically, but it also sort of 358 00:19:14,160 --> 00:19:17,560 Speaker 1: contradicts other things we know, like if you go through 359 00:19:17,560 --> 00:19:20,679 Speaker 1: this wormhole and you come out in the past, you know, 360 00:19:20,880 --> 00:19:23,439 Speaker 1: doesn't that break things like causality? And you come out 361 00:19:23,440 --> 00:19:26,639 Speaker 1: in the past and kill yourself before you um do 362 00:19:26,800 --> 00:19:28,960 Speaker 1: the experiment, Then you don't do the experiment, you don't 363 00:19:28,960 --> 00:19:32,200 Speaker 1: come out in the past. So it appears to create paradoxes, 364 00:19:32,640 --> 00:19:35,879 Speaker 1: and nobody knows like how to resolve that. Does that 365 00:19:35,920 --> 00:19:38,119 Speaker 1: mean that these things are impossible? Does that mean if 366 00:19:38,160 --> 00:19:40,600 Speaker 1: you did that, the universe would like disappear in a 367 00:19:40,640 --> 00:19:43,639 Speaker 1: puff of logic. Nobody really knows what would happen. So 368 00:19:43,680 --> 00:19:46,480 Speaker 1: that's a bit of a contradiction in the theory itself 369 00:19:46,840 --> 00:19:50,040 Speaker 1: that it predicts something which seems to be disallowed by 370 00:19:50,080 --> 00:19:53,639 Speaker 1: other parts of the theory. And it's a similar idea 371 00:19:53,760 --> 00:19:58,520 Speaker 1: for these closed timelike curves. People said, if you create 372 00:19:58,600 --> 00:20:02,800 Speaker 1: these infinitely long the cylinders of spinning dust, which doesn't 373 00:20:02,800 --> 00:20:06,320 Speaker 1: sound easy to do, then it bends time in this 374 00:20:06,320 --> 00:20:09,159 Speaker 1: way that the time then as you move forward in 375 00:20:09,240 --> 00:20:13,720 Speaker 1: time you're actually moving sort of like sideways through space 376 00:20:13,760 --> 00:20:16,520 Speaker 1: time in a way that's similar to the experience of 377 00:20:16,720 --> 00:20:20,480 Speaker 1: going into a black hole. Outside a black hole, time 378 00:20:20,640 --> 00:20:24,600 Speaker 1: always moves forwards. Inside a black hole, space has bent 379 00:20:24,800 --> 00:20:27,879 Speaker 1: so much that space only moves towards the center of 380 00:20:27,920 --> 00:20:31,520 Speaker 1: the black hole. It's like one direction to space. So 381 00:20:31,600 --> 00:20:35,040 Speaker 1: if you imagine space being distorted, not quite as much 382 00:20:35,040 --> 00:20:36,880 Speaker 1: as a black hole, but sort of in a similar 383 00:20:36,920 --> 00:20:40,960 Speaker 1: direction that it sort of bends space sideways, then you 384 00:20:40,960 --> 00:20:43,359 Speaker 1: can create these paths where something can move in a 385 00:20:43,440 --> 00:20:47,439 Speaker 1: loop through time. Um, but you would be trapped on 386 00:20:47,560 --> 00:20:50,040 Speaker 1: that loop, so you wouldn't be able to like change anything. 387 00:20:50,040 --> 00:20:52,320 Speaker 1: It's like a fixed loop, sort of like Harry Potter 388 00:20:52,440 --> 00:20:55,000 Speaker 1: style loop through time, where every time you go through 389 00:20:55,040 --> 00:20:57,880 Speaker 1: it's exactly the same thing happening. And these are really 390 00:20:57,920 --> 00:21:01,000 Speaker 1: fun because nobody knows like if these are actually possible 391 00:21:01,040 --> 00:21:03,840 Speaker 1: and what would happen if you actually went through them. 392 00:21:03,840 --> 00:21:06,200 Speaker 1: So so we don't really know, for instance, like what 393 00:21:06,480 --> 00:21:11,840 Speaker 1: conceivable reason there would be for a civilization to conceivably 394 00:21:12,320 --> 00:21:15,760 Speaker 1: construct one of these, yeah, because we don't know practically 395 00:21:15,800 --> 00:21:18,600 Speaker 1: what you could achieve. And also, an infinite cylinder of 396 00:21:18,680 --> 00:21:21,920 Speaker 1: spitting dust sounds like an expensive project. You know, the 397 00:21:21,960 --> 00:21:25,560 Speaker 1: word infinite seems to raise some doubts. And when it 398 00:21:25,560 --> 00:21:29,080 Speaker 1: comes to wormholes, people know how to calculate whether a 399 00:21:29,080 --> 00:21:32,560 Speaker 1: wormhole is allowed by the theory of general relativity. Nobody 400 00:21:32,600 --> 00:21:35,360 Speaker 1: knows how to build a wormhole. You know. It's sort 401 00:21:35,359 --> 00:21:38,520 Speaker 1: of like saying, Okay, it's possible to have an apple pie, 402 00:21:38,920 --> 00:21:42,560 Speaker 1: but but we we don't have a recipe for making one. Right. 403 00:21:43,080 --> 00:21:44,960 Speaker 1: It's a different thing to say, like I know how 404 00:21:44,960 --> 00:21:47,800 Speaker 1: to put it together than to say it's technically allowed 405 00:21:47,840 --> 00:21:50,760 Speaker 1: to exist in the universe. You know. It's like if 406 00:21:50,760 --> 00:21:53,240 Speaker 1: you say, well, the sun is allowed by the laws 407 00:21:53,240 --> 00:21:55,239 Speaker 1: of physics, but I don't know how to make it 408 00:21:55,280 --> 00:21:57,439 Speaker 1: happen if I just start from a cloud of gas, 409 00:21:57,960 --> 00:22:00,760 Speaker 1: for example, And so that's a big le. Nobody really 410 00:22:00,800 --> 00:22:04,120 Speaker 1: knows how to build a wormhole or even keep one open. Um, 411 00:22:04,160 --> 00:22:07,040 Speaker 1: if you did manage to build one, Are there any 412 00:22:07,080 --> 00:22:11,520 Speaker 1: reasons to suspect that wormholes exist naturally? Oh, great question, 413 00:22:11,760 --> 00:22:15,360 Speaker 1: Not yet, No, um. Some people wonder if there are 414 00:22:15,400 --> 00:22:19,239 Speaker 1: wormholes that connect the super massive black holes at the 415 00:22:19,280 --> 00:22:22,280 Speaker 1: hearts of all of our galaxies, But there's not like 416 00:22:22,320 --> 00:22:26,480 Speaker 1: any evidence out there anything that can't be explained without wormholes, 417 00:22:26,480 --> 00:22:30,119 Speaker 1: that you would need wormholes to explain. Um, that would 418 00:22:30,119 --> 00:22:32,720 Speaker 1: be super cool, though no, Um, I'm not aware of 419 00:22:32,760 --> 00:22:35,639 Speaker 1: any evidence like that. Well, Daniel, you also have a 420 00:22:35,720 --> 00:22:37,800 Speaker 1: chapter in the book that I really liked on the 421 00:22:37,880 --> 00:22:41,680 Speaker 1: question of will time ever stop? And I think this 422 00:22:41,760 --> 00:22:44,320 Speaker 1: is one of those great questions because it's a yes 423 00:22:44,400 --> 00:22:49,520 Speaker 1: or no question, and like many big questions in physical cosmology, 424 00:22:49,560 --> 00:22:52,080 Speaker 1: it's a binary. But no matter which answer it is, 425 00:22:52,160 --> 00:22:55,760 Speaker 1: it's mind boggling, like it is impossible to imagine time 426 00:22:55,920 --> 00:23:00,359 Speaker 1: either stopping or going on forever. Uh So, so what 427 00:23:00,640 --> 00:23:03,480 Speaker 1: are your thoughts here about whether time will ever stop? 428 00:23:04,520 --> 00:23:06,480 Speaker 1: I go, you're feeling there, And I also think it's 429 00:23:06,480 --> 00:23:10,280 Speaker 1: really fascinating to go back through history and read about 430 00:23:10,359 --> 00:23:14,840 Speaker 1: which concept felt more natural to people. Initially, it felt 431 00:23:15,040 --> 00:23:18,480 Speaker 1: to people like time should go on forever. Obviously, that 432 00:23:18,560 --> 00:23:21,040 Speaker 1: was like a hundred fifty years ago, before we knew 433 00:23:21,080 --> 00:23:24,080 Speaker 1: that the universe was expanding. People looked out in the 434 00:23:24,119 --> 00:23:25,960 Speaker 1: stars and they looked like they were just sort of 435 00:23:26,000 --> 00:23:28,240 Speaker 1: hanging out, and they thought, maybe the universe is just 436 00:23:28,280 --> 00:23:31,680 Speaker 1: sort of there, and so obviously it's been there forever, right, 437 00:23:32,119 --> 00:23:34,960 Speaker 1: And that was like this you know, de facto assumption 438 00:23:35,080 --> 00:23:39,400 Speaker 1: in science until Hubble discovered that the universe is expanding, 439 00:23:39,880 --> 00:23:42,560 Speaker 1: and that gave the universe sort of like a direction. 440 00:23:42,600 --> 00:23:45,720 Speaker 1: It's like things are changing, and as you look back 441 00:23:45,760 --> 00:23:48,920 Speaker 1: in time, that suggests, you know, something a moment when 442 00:23:48,920 --> 00:23:52,520 Speaker 1: the universe was like crazy infinitely dense. So it suggested 443 00:23:52,520 --> 00:23:55,520 Speaker 1: a beginning. And that must have been an incredible sort 444 00:23:55,520 --> 00:24:01,680 Speaker 1: of mind bending mental gymnastics to execute to go from thinking, oh, 445 00:24:01,720 --> 00:24:04,439 Speaker 1: it makes sense for the universe to be infinite in time, 446 00:24:04,800 --> 00:24:07,119 Speaker 1: to go into like, oh, the universe had a beginning 447 00:24:07,160 --> 00:24:10,560 Speaker 1: and now let's trying to figure out what that beginning was. Um. 448 00:24:10,760 --> 00:24:13,479 Speaker 1: So I think that's really interesting. And you know, I 449 00:24:13,520 --> 00:24:16,119 Speaker 1: think the thing that's really cool about this question is 450 00:24:16,160 --> 00:24:18,280 Speaker 1: not just that it's tangible because it makes you wonder 451 00:24:18,359 --> 00:24:19,960 Speaker 1: like am I going to go on forever as the 452 00:24:20,040 --> 00:24:22,800 Speaker 1: universe always going to be here? But because it really 453 00:24:22,800 --> 00:24:25,840 Speaker 1: gets at the heart of a the deepest problem in 454 00:24:25,880 --> 00:24:30,680 Speaker 1: physics right now, like the fundamental conflict we have between 455 00:24:30,720 --> 00:24:35,680 Speaker 1: two ideas in physics, which are quantum mechanics and general relativity. 456 00:24:36,240 --> 00:24:38,560 Speaker 1: You know, we have a quantum mechanical description of how 457 00:24:38,600 --> 00:24:41,000 Speaker 1: like particles bounce off each other and we you know, 458 00:24:41,240 --> 00:24:43,080 Speaker 1: have a lot of questions about how that works. But 459 00:24:43,119 --> 00:24:45,400 Speaker 1: we have a pretty good theory for you know, understanding 460 00:24:45,440 --> 00:24:49,479 Speaker 1: quantum particles, and we've been talking about general relativity, you know, 461 00:24:49,520 --> 00:24:52,320 Speaker 1: how space bends and how it affects time and what 462 00:24:52,440 --> 00:24:55,520 Speaker 1: happens in black holes and all that stuff also very successful. 463 00:24:56,080 --> 00:24:58,800 Speaker 1: The problem is that these two theories nobody knows how 464 00:24:58,840 --> 00:25:02,360 Speaker 1: to bring them together end critically. They have very different 465 00:25:02,440 --> 00:25:06,280 Speaker 1: stories to tell about what time is. They treat time 466 00:25:06,320 --> 00:25:10,320 Speaker 1: totally differently, with huge consequences for the answer to this question, 467 00:25:10,680 --> 00:25:13,639 Speaker 1: will time ever stop? And so to me, this is 468 00:25:13,840 --> 00:25:16,160 Speaker 1: a fun question because it puts its finger on right 469 00:25:16,240 --> 00:25:20,080 Speaker 1: on that conflict. Yes, so there is. There's a concept 470 00:25:20,280 --> 00:25:24,679 Speaker 1: that you introduce in this chapter about uh sort of 471 00:25:24,760 --> 00:25:28,639 Speaker 1: time as we experience it being a sort of special 472 00:25:28,920 --> 00:25:33,560 Speaker 1: case or special circumstance of a hypothetical substance you refer 473 00:25:33,640 --> 00:25:36,760 Speaker 1: to as meta time. Can you explain something like what 474 00:25:37,000 --> 00:25:39,520 Speaker 1: are you getting at here? Well, one of the basic 475 00:25:39,600 --> 00:25:45,080 Speaker 1: questions is is time fundamental or is it emergent? You know, 476 00:25:45,160 --> 00:25:47,800 Speaker 1: a deep question in modern physics is like what are 477 00:25:47,840 --> 00:25:51,040 Speaker 1: the essential ingredients to the universe? What did it start with? 478 00:25:51,680 --> 00:25:54,520 Speaker 1: And then what sort of arises out of that, out 479 00:25:54,520 --> 00:25:58,159 Speaker 1: of the complexity of the possible interactions. You know, for example, 480 00:25:58,200 --> 00:26:00,919 Speaker 1: if you're playing with legos, the fund mental ingredients are 481 00:26:00,960 --> 00:26:03,560 Speaker 1: the basic pieces, and from that you can make complicated 482 00:26:03,600 --> 00:26:07,040 Speaker 1: things dinosaurs or pirates or spaceships or whatever. But those 483 00:26:07,080 --> 00:26:09,880 Speaker 1: spaceships they're emergent, you know, they're not necessary. They don't 484 00:26:09,880 --> 00:26:11,560 Speaker 1: have to exist. You can take it apart and just 485 00:26:11,640 --> 00:26:14,240 Speaker 1: have the legos. In the same way in our universe 486 00:26:14,680 --> 00:26:18,639 Speaker 1: there are complicated things like ice cream and hurricanes, but 487 00:26:18,760 --> 00:26:21,320 Speaker 1: those don't have to exist in the universe, right, You 488 00:26:21,320 --> 00:26:24,840 Speaker 1: can imagine a universe without hurricanes or without ice cream, 489 00:26:24,920 --> 00:26:27,159 Speaker 1: as sad as that is. So then the question is 490 00:26:27,200 --> 00:26:29,919 Speaker 1: what are the basic elements of the universe. And for 491 00:26:29,960 --> 00:26:32,760 Speaker 1: a long time, you know, people like Newton thought that, well, 492 00:26:32,760 --> 00:26:35,960 Speaker 1: obviously space and time are fundamentals of the universe. They're 493 00:26:36,000 --> 00:26:39,000 Speaker 1: just like you gotta have that, right, And now people 494 00:26:39,040 --> 00:26:41,879 Speaker 1: are wondering, like, well, is that really true? Is it 495 00:26:41,920 --> 00:26:45,959 Speaker 1: possible to have a universe without space or without time? 496 00:26:46,720 --> 00:26:49,320 Speaker 1: You know, we gotta when you're really digging deep into 497 00:26:49,320 --> 00:26:51,399 Speaker 1: the nature of the universe, you gotta push hard on 498 00:26:51,440 --> 00:26:54,680 Speaker 1: the fundamental assumptions. So There are a lot of ideas 499 00:26:54,680 --> 00:26:58,080 Speaker 1: now about how space could be emergent, you know, how 500 00:26:58,119 --> 00:27:00,760 Speaker 1: it could be that the universe that self, that space 501 00:27:00,800 --> 00:27:03,480 Speaker 1: is not a natural thing, that like ice cream, you 502 00:27:03,480 --> 00:27:06,320 Speaker 1: could have a time in the universe where there wasn't 503 00:27:06,359 --> 00:27:10,480 Speaker 1: any space. That space is like just briefly, the stitching 504 00:27:10,560 --> 00:27:15,480 Speaker 1: together of these um separated pixels of space using quantum 505 00:27:15,560 --> 00:27:18,879 Speaker 1: entanglement to sort of weave together this idea of space, 506 00:27:18,920 --> 00:27:23,280 Speaker 1: these relations between different locations that we experience, and we 507 00:27:23,280 --> 00:27:26,320 Speaker 1: could talk about that for an hour um. But even 508 00:27:26,359 --> 00:27:29,719 Speaker 1: moving beyond that, now folks are wondering, like, is time 509 00:27:30,040 --> 00:27:33,520 Speaker 1: also emergent? Is it possible that time is not a 510 00:27:33,600 --> 00:27:37,159 Speaker 1: fundamental property of the universe but it just sort of 511 00:27:37,240 --> 00:27:41,280 Speaker 1: something that exists now. And it's really hard to even 512 00:27:41,320 --> 00:27:43,520 Speaker 1: think or talk about it because, like I just said, 513 00:27:43,760 --> 00:27:47,040 Speaker 1: it exists now I'm using time to talk about when 514 00:27:47,160 --> 00:27:51,040 Speaker 1: time is. It's very complicated and confusing. But there are 515 00:27:51,080 --> 00:27:54,479 Speaker 1: some theories that tell us that time might be not 516 00:27:54,600 --> 00:27:57,440 Speaker 1: an illusion, right, not in the sense that it doesn't exist, 517 00:27:57,840 --> 00:28:00,480 Speaker 1: but it might not be fundamental, that it might rise 518 00:28:00,960 --> 00:28:06,160 Speaker 1: from complex interactions of smaller, more fundamental elements of the universe, 519 00:28:06,720 --> 00:28:09,399 Speaker 1: and so that's this idea of meta time. You have 520 00:28:09,480 --> 00:28:12,119 Speaker 1: to imagine some like deeper laws of physics that control 521 00:28:12,160 --> 00:28:15,480 Speaker 1: those fundamental bits that I'm being vague about because we 522 00:28:15,520 --> 00:28:17,520 Speaker 1: have no idea what they would be or what they are, 523 00:28:17,680 --> 00:28:20,800 Speaker 1: what the rules are. And And if this seems sort 524 00:28:20,800 --> 00:28:23,520 Speaker 1: of like frustrating, it's because we're at the very beginning 525 00:28:23,720 --> 00:28:27,000 Speaker 1: of even talking about the answers, because we're just formulating 526 00:28:27,040 --> 00:28:29,399 Speaker 1: the questions. You know, sometimes it takes like a hundred 527 00:28:29,480 --> 00:28:32,440 Speaker 1: years to figure out Okay, the important question to ask 528 00:28:32,640 --> 00:28:35,520 Speaker 1: is is there always time in the universe? What does 529 00:28:35,560 --> 00:28:37,960 Speaker 1: that mean? And how do you even think about a 530 00:28:38,040 --> 00:28:40,920 Speaker 1: universe without time? Then you can start to make progress 531 00:28:41,000 --> 00:28:44,000 Speaker 1: on the crazy ideas that might explain it. Uh. This 532 00:28:44,120 --> 00:28:45,920 Speaker 1: may be kind of a tangent, but this actually makes 533 00:28:45,920 --> 00:28:47,920 Speaker 1: me wonder about a question that's come up on the 534 00:28:47,920 --> 00:28:51,360 Speaker 1: show before. Do you have a view on what the 535 00:28:51,440 --> 00:28:57,080 Speaker 1: present is, on whether something special is actually happening in 536 00:28:57,320 --> 00:29:01,440 Speaker 1: the present? Uh? Like, does only the present exists or 537 00:29:01,480 --> 00:29:05,080 Speaker 1: does all of time exist? It's a really great question. 538 00:29:05,400 --> 00:29:08,160 Speaker 1: We don't understand that at all. I don't understand it. 539 00:29:08,520 --> 00:29:10,680 Speaker 1: I don't even know if it's a question of science 540 00:29:10,840 --> 00:29:13,280 Speaker 1: or if it's a question of philosophy because it goes 541 00:29:13,320 --> 00:29:16,360 Speaker 1: into the nature of consciousness. You know, does the whole 542 00:29:16,360 --> 00:29:19,760 Speaker 1: timeline exists and we only experience part of it? Or 543 00:29:19,800 --> 00:29:22,680 Speaker 1: you know, does the only this moment exist um? Physics 544 00:29:22,680 --> 00:29:25,160 Speaker 1: doesn't have a great way to even define what the 545 00:29:25,240 --> 00:29:29,120 Speaker 1: present is um, and so it's it's pretty hard to 546 00:29:29,120 --> 00:29:31,480 Speaker 1: put your finger on it um. And I love that 547 00:29:31,520 --> 00:29:33,760 Speaker 1: because these are questions that like, we don't even really 548 00:29:33,800 --> 00:29:37,600 Speaker 1: know how to attack these questions. And what that suggests 549 00:29:38,040 --> 00:29:40,480 Speaker 1: is that there's something wrong in the way we're organizing 550 00:29:40,480 --> 00:29:43,840 Speaker 1: our thinking. You know. It's like if you're asking a 551 00:29:43,960 --> 00:29:46,880 Speaker 1: question and you're just using the wrong language, we're using 552 00:29:46,880 --> 00:29:50,560 Speaker 1: the wrong notation, then your question seems really complicated and confusing. 553 00:29:50,560 --> 00:29:52,960 Speaker 1: And if you learn a new perspective and then suddenly 554 00:29:53,040 --> 00:29:55,800 Speaker 1: would make sense. You know, I'm reminded of that Far 555 00:29:55,880 --> 00:29:59,600 Speaker 1: Side cartoon where the scientists are trying to understand dolphins 556 00:30:00,080 --> 00:30:02,920 Speaker 1: and they're writing down phonetically with the dolphins are saying, 557 00:30:02,960 --> 00:30:06,440 Speaker 1: and they're saying things like, you know, obla Espanol, and 558 00:30:06,760 --> 00:30:08,680 Speaker 1: you know, the scientists don't speak Spanish, so though to 559 00:30:08,720 --> 00:30:11,720 Speaker 1: them it's just nonsense. My boys, if they knew the language, 560 00:30:11,760 --> 00:30:13,920 Speaker 1: it would all click together. And I feel like that's 561 00:30:13,920 --> 00:30:16,280 Speaker 1: the problem we have sometimes that was just not speaking 562 00:30:16,280 --> 00:30:18,880 Speaker 1: the right language at the universe yet, and that's why 563 00:30:18,920 --> 00:30:21,120 Speaker 1: some of these questions are awkward and really hard to 564 00:30:21,120 --> 00:30:24,960 Speaker 1: grapple with. I thought you were gonna say today's physicists 565 00:30:25,000 --> 00:30:31,800 Speaker 1: are only equipped with cow tools only for spherical cows, exactly, 566 00:30:32,920 --> 00:30:35,120 Speaker 1: you know, all of this um Also, it reminds me 567 00:30:35,560 --> 00:30:38,920 Speaker 1: a bit of the Copernican principle to UM. But but 568 00:30:39,040 --> 00:30:42,360 Speaker 1: going beyond just the idea of like, you know, there 569 00:30:42,400 --> 00:30:45,520 Speaker 1: being some uh I we should not not see that 570 00:30:45,560 --> 00:30:49,160 Speaker 1: there's something privileged about about our planet or about humans. 571 00:30:49,200 --> 00:30:52,120 Speaker 1: But but could you could you even apply that based 572 00:30:52,160 --> 00:30:54,200 Speaker 1: on what you're saying to to the present moment, to 573 00:30:54,280 --> 00:30:57,560 Speaker 1: this time that in which from which we are viewing 574 00:30:57,720 --> 00:31:01,360 Speaker 1: the universe. Yeah. Probably. I think that's why a lot 575 00:31:01,400 --> 00:31:04,760 Speaker 1: of progress could be made if we ever did get 576 00:31:04,800 --> 00:31:08,120 Speaker 1: to talk to alien scientists, because I think we would 577 00:31:08,160 --> 00:31:11,480 Speaker 1: learn a lot about um, you know, the biases that 578 00:31:11,560 --> 00:31:15,400 Speaker 1: creep into our questions and our reference frame for answering 579 00:31:15,400 --> 00:31:19,840 Speaker 1: those questions because of our human experience, and alien intelligence 580 00:31:19,880 --> 00:31:22,480 Speaker 1: that might have a very different relationship with a concept 581 00:31:22,480 --> 00:31:25,280 Speaker 1: of time might have a very different treatment of it 582 00:31:25,400 --> 00:31:28,880 Speaker 1: mathematically and physically, and might make a lot more sense, 583 00:31:29,200 --> 00:31:32,920 Speaker 1: you know. Um, The problem with alien intelligence, of course 584 00:31:33,080 --> 00:31:36,760 Speaker 1: is you know, finding them, talking to them, decoding their language, 585 00:31:37,280 --> 00:31:40,880 Speaker 1: and then if they are so fundamentally different that they've 586 00:31:40,920 --> 00:31:43,840 Speaker 1: made that they avoid human biases, they might be impossible 587 00:31:43,840 --> 00:31:48,200 Speaker 1: to ever understand. And so while it's tantalizing to imagine 588 00:31:48,240 --> 00:31:50,240 Speaker 1: that like aliens are out there with the answers the 589 00:31:50,320 --> 00:31:52,920 Speaker 1: deep questions about the universe, it might also be that, 590 00:31:53,160 --> 00:31:55,760 Speaker 1: uh that we could never understand what they have to say. 591 00:31:56,400 --> 00:31:58,479 Speaker 1: I have long thought we should outsource all of our 592 00:31:58,480 --> 00:32:04,520 Speaker 1: physics research to like a seven in dimensional octopus. Um, 593 00:32:04,560 --> 00:32:06,200 Speaker 1: if you know one, I'd like to meet it because 594 00:32:06,200 --> 00:32:15,680 Speaker 1: I got questions, thank uh so. But to come back 595 00:32:15,720 --> 00:32:18,960 Speaker 1: to the idea of will time ever stop? You talk 596 00:32:19,000 --> 00:32:22,440 Speaker 1: about a couple of possibilities for what that would look like. 597 00:32:22,480 --> 00:32:24,440 Speaker 1: Say that you know the far future of our own 598 00:32:24,520 --> 00:32:27,440 Speaker 1: universe at least at least what we can reason from 599 00:32:27,440 --> 00:32:29,240 Speaker 1: what we know today, and and a couple of these 600 00:32:29,240 --> 00:32:31,960 Speaker 1: options are are the Big Crunch and the heat death 601 00:32:32,000 --> 00:32:33,400 Speaker 1: of the universe. Do you do you want to talk 602 00:32:33,400 --> 00:32:36,720 Speaker 1: about what those would mean as as best we can 603 00:32:36,720 --> 00:32:41,760 Speaker 1: guess for time itself. Yes, So remember that there are 604 00:32:41,760 --> 00:32:44,160 Speaker 1: two paths to go down if you're asking questions about 605 00:32:44,160 --> 00:32:46,280 Speaker 1: the deep future of the universe, and one is quantum 606 00:32:46,280 --> 00:32:49,400 Speaker 1: mechanical and the other one is general relativity. And quantum 607 00:32:49,400 --> 00:32:52,840 Speaker 1: mechanics is pretty straightforward about this. It says that, look, 608 00:32:53,120 --> 00:32:56,880 Speaker 1: time always existed and time will always exist. And there's 609 00:32:56,920 --> 00:33:00,360 Speaker 1: a pretty simple argument there because according to quantumy annex, 610 00:33:00,680 --> 00:33:06,200 Speaker 1: quantum information can't be destroyed, like when something happens um, 611 00:33:06,280 --> 00:33:08,840 Speaker 1: you know, the information about what used to happen is 612 00:33:08,920 --> 00:33:12,600 Speaker 1: encoded into the future, and so it suggests the time 613 00:33:12,600 --> 00:33:16,200 Speaker 1: has always existed. There's no mechanism in quantum mechanics for 614 00:33:16,320 --> 00:33:19,280 Speaker 1: time to start. It should always have existed, and you 615 00:33:19,320 --> 00:33:22,040 Speaker 1: flip it around the other direction, it should always exist. 616 00:33:22,280 --> 00:33:25,240 Speaker 1: So there should always be a universe and clocks should 617 00:33:25,240 --> 00:33:29,160 Speaker 1: always tick forwards according to quantum mechanics. But that assumes 618 00:33:29,320 --> 00:33:33,240 Speaker 1: you know that space is flat and simple, and general relativity, 619 00:33:33,400 --> 00:33:36,320 Speaker 1: the other pillar of modern physics, tells us that space 620 00:33:36,440 --> 00:33:39,880 Speaker 1: is not simple. It's not flat, it's complicated. It's expanding, 621 00:33:40,680 --> 00:33:44,480 Speaker 1: and you know, the mechanism by which space is expanding 622 00:33:44,560 --> 00:33:47,480 Speaker 1: is not something that we understand hub Will discovered a 623 00:33:47,560 --> 00:33:49,960 Speaker 1: hundreds something years ago that the universe is expanding and 624 00:33:50,000 --> 00:33:52,560 Speaker 1: things are moving away from us, And then twenty something 625 00:33:52,640 --> 00:33:55,720 Speaker 1: years ago we discovered even more mind boggling lye that 626 00:33:55,720 --> 00:33:59,600 Speaker 1: that expansion is accelerating. Right, It's not like stuff is 627 00:33:59,640 --> 00:34:04,120 Speaker 1: moving through space and gradually slowing down and maybe eventually 628 00:34:04,240 --> 00:34:07,320 Speaker 1: gonna stop and turn around and come back um and collapse, 629 00:34:07,600 --> 00:34:10,960 Speaker 1: but that it's speeding up, which means that there's some massive, 630 00:34:11,080 --> 00:34:14,960 Speaker 1: incredibly powerful force in the universe that's literally tearing it apart. 631 00:34:15,960 --> 00:34:18,680 Speaker 1: Because we don't know the mechanism for it, though, we 632 00:34:18,719 --> 00:34:21,080 Speaker 1: can't predict what it's gonna do, Like it turned on 633 00:34:21,160 --> 00:34:23,840 Speaker 1: about five billion years ago, started tearing the universe apart. 634 00:34:24,280 --> 00:34:26,960 Speaker 1: Will it do that forever? If so, you end up 635 00:34:27,000 --> 00:34:30,200 Speaker 1: with like a universe where everything is super far apart. 636 00:34:30,239 --> 00:34:33,480 Speaker 1: It's just like a bunch of black holes from collapsed galaxies, 637 00:34:33,800 --> 00:34:38,440 Speaker 1: separated by you know, unthinkably vast distances, even compared to 638 00:34:38,880 --> 00:34:42,480 Speaker 1: the distances we see between our galaxy and other galaxies today. 639 00:34:43,000 --> 00:34:45,040 Speaker 1: You know, these galaxies would be so far apart that 640 00:34:45,120 --> 00:34:47,399 Speaker 1: they could never even see each other. You know, light 641 00:34:47,640 --> 00:34:51,320 Speaker 1: would never reach one from the other. On the other hand. 642 00:34:51,480 --> 00:34:54,319 Speaker 1: Dark energy could change its direction, it could stop, it 643 00:34:54,320 --> 00:34:57,400 Speaker 1: could turn around, it could cause the universe to collapse 644 00:34:57,719 --> 00:35:01,680 Speaker 1: back down into an incredible moment of singularity at the 645 00:35:01,800 --> 00:35:04,920 Speaker 1: end of the universe UM, and then we can ask 646 00:35:05,000 --> 00:35:07,840 Speaker 1: questions like, well, what happens then, you know, does the 647 00:35:07,960 --> 00:35:13,200 Speaker 1: universe stop when you reach another singularity, another moment of 648 00:35:13,239 --> 00:35:18,360 Speaker 1: incredible density. We just don't know because general relativity describes 649 00:35:18,440 --> 00:35:21,359 Speaker 1: that process. But when you actually get to the singularity, 650 00:35:21,520 --> 00:35:24,799 Speaker 1: people think of singularities is like a feature of general relativity. 651 00:35:25,000 --> 00:35:28,280 Speaker 1: Really they're like a failure of general relativity. It can't 652 00:35:28,320 --> 00:35:30,759 Speaker 1: predict anything that happens there, doesn't know what to do. 653 00:35:31,360 --> 00:35:33,759 Speaker 1: It's like, well that's the direction you're going, but once 654 00:35:33,800 --> 00:35:35,360 Speaker 1: you get there, I can't tell you what's going to 655 00:35:35,440 --> 00:35:38,600 Speaker 1: happen next. So if that happens, we just really don't 656 00:35:38,600 --> 00:35:40,640 Speaker 1: know what the fate of the universe would be in 657 00:35:40,680 --> 00:35:43,040 Speaker 1: that scenario. But you know, it wouldn't be pleasant for 658 00:35:43,160 --> 00:35:47,120 Speaker 1: humans or for seventeen seventeen dimensional octopi. But I guess 659 00:35:47,160 --> 00:35:48,960 Speaker 1: with with the other option, with like you know, the 660 00:35:49,280 --> 00:35:52,640 Speaker 1: heat death of the universe, everything just expanding and cooling 661 00:35:52,719 --> 00:35:56,680 Speaker 1: and reaching some kind of equilibrium where UM where there's 662 00:35:56,719 --> 00:36:00,960 Speaker 1: no there's no imbalance to distribute any further. Now, I 663 00:36:00,960 --> 00:36:02,839 Speaker 1: think in the book you raised the idea that this 664 00:36:02,960 --> 00:36:05,719 Speaker 1: could in a way represent a threat to to our 665 00:36:05,760 --> 00:36:09,880 Speaker 1: concept of time, because time would maybe in itself, time 666 00:36:09,920 --> 00:36:12,160 Speaker 1: has something to do with entropy, and this would be 667 00:36:12,200 --> 00:36:16,560 Speaker 1: a state of maximum entropy. Yeah, we see the universe 668 00:36:16,760 --> 00:36:21,440 Speaker 1: proceeding through time and we see entropy increasing. And entropy 669 00:36:21,480 --> 00:36:23,719 Speaker 1: is a really tricky topic. You hear people talk about 670 00:36:23,719 --> 00:36:25,279 Speaker 1: it a lot, but it's really hard to sort of 671 00:36:25,280 --> 00:36:28,640 Speaker 1: grapple with intellectually, and people try to think about it 672 00:36:28,680 --> 00:36:31,560 Speaker 1: in terms of like amount of disorder in the universe, 673 00:36:31,800 --> 00:36:35,960 Speaker 1: but that can be pretty misleading technically. It's really relates 674 00:36:36,000 --> 00:36:39,520 Speaker 1: to the number of different ways you can arrange the 675 00:36:39,560 --> 00:36:43,359 Speaker 1: microscopic nature of the universe to be consistent with the 676 00:36:43,440 --> 00:36:47,000 Speaker 1: macroscopic nature that you observe. That's a little bit more subtle, 677 00:36:47,040 --> 00:36:50,160 Speaker 1: but it's actually a more accurate guide to what entropy is. 678 00:36:50,480 --> 00:36:52,440 Speaker 1: And what we notice is that entropy seems to be 679 00:36:52,480 --> 00:36:56,439 Speaker 1: increasing through the universe, Like there's something we've observed, and 680 00:36:56,800 --> 00:36:59,120 Speaker 1: a lot of places in physics seem to be sort 681 00:36:59,160 --> 00:37:02,319 Speaker 1: of like and bivalent about time. The laws will run 682 00:37:02,360 --> 00:37:05,520 Speaker 1: the same forward or backwards. It doesn't really matter, if 683 00:37:05,640 --> 00:37:08,239 Speaker 1: you know, without friction or air resistance. For example, you 684 00:37:08,239 --> 00:37:10,160 Speaker 1: can throw a ball up in the air and it 685 00:37:10,280 --> 00:37:12,600 Speaker 1: lands back in your hands. If you played a movie 686 00:37:12,600 --> 00:37:15,160 Speaker 1: of that backwards, it would look exactly the same again 687 00:37:15,200 --> 00:37:19,200 Speaker 1: without air resistance, because that increases entropy. Um. But entropy 688 00:37:19,320 --> 00:37:21,360 Speaker 1: is the one place where in the laws of physics 689 00:37:21,440 --> 00:37:24,279 Speaker 1: there seems to be a preference for things moving forwards. 690 00:37:24,520 --> 00:37:28,240 Speaker 1: So it's often claimed that entropy might be the reason 691 00:37:28,320 --> 00:37:31,120 Speaker 1: time moves forwards. And I think that's a bit of 692 00:37:31,120 --> 00:37:34,600 Speaker 1: a step too far. You know, we see that entropy 693 00:37:34,640 --> 00:37:38,600 Speaker 1: increases as time moves forward, so there's a connection between them. 694 00:37:38,680 --> 00:37:41,040 Speaker 1: That doesn't mean necessarily the time has to move forward. 695 00:37:41,440 --> 00:37:44,279 Speaker 1: I mean, if time moved backwards, it just means that 696 00:37:44,360 --> 00:37:48,680 Speaker 1: maybe entropy would decrease, right it um creates this connection 697 00:37:48,719 --> 00:37:52,360 Speaker 1: between entropy and time, It doesn't necessarily imply a direction. 698 00:37:53,200 --> 00:37:56,239 Speaker 1: But some people wonder what would happen when you reach 699 00:37:56,280 --> 00:37:59,560 Speaker 1: a state of maximum entropy, and maximum entropy would be 700 00:37:59,560 --> 00:38:02,880 Speaker 1: as you say, a everything progresses forward and the universe 701 00:38:02,880 --> 00:38:06,520 Speaker 1: so spreads out and it becomes maximumly even there's no 702 00:38:06,680 --> 00:38:09,520 Speaker 1: like hot spots and cold spots because that allows you 703 00:38:09,560 --> 00:38:12,640 Speaker 1: to rearrange the microscopic state as many ways as possible, 704 00:38:12,680 --> 00:38:15,799 Speaker 1: so the most freedom to rearrange the microscopic state and 705 00:38:15,840 --> 00:38:19,000 Speaker 1: so the most entropy. And in that state, it's called 706 00:38:19,000 --> 00:38:21,080 Speaker 1: the heat death of the universe because you have no 707 00:38:21,160 --> 00:38:23,400 Speaker 1: hot spots and no cold spots, so no way for 708 00:38:23,440 --> 00:38:26,640 Speaker 1: like energy to flow. Nobody like do anything. The way 709 00:38:26,640 --> 00:38:29,800 Speaker 1: that you operate as a human being is through energy flows, 710 00:38:29,880 --> 00:38:33,239 Speaker 1: and the way that computation happens is through energy transfers, 711 00:38:33,719 --> 00:38:35,640 Speaker 1: and so you can't really do anything if there's no 712 00:38:35,800 --> 00:38:38,640 Speaker 1: energy ingredients. So that's why it's referred to as the 713 00:38:38,680 --> 00:38:42,520 Speaker 1: heat death of the universe. And people who think that 714 00:38:42,719 --> 00:38:46,760 Speaker 1: time is deeply connected to entropy, wonder if one entropy 715 00:38:46,800 --> 00:38:51,160 Speaker 1: reaches its maximum point, if time then somehow stops, or 716 00:38:51,280 --> 00:38:54,440 Speaker 1: maybe time stops and then turns around and entropy starts 717 00:38:54,440 --> 00:38:58,799 Speaker 1: to decrease like a bounce in time. And nobody knows 718 00:38:58,800 --> 00:39:00,960 Speaker 1: the answer to these questions when he's gonna be around 719 00:39:01,040 --> 00:39:03,799 Speaker 1: to know the answer to the questions, even if you're 720 00:39:03,800 --> 00:39:06,919 Speaker 1: optimistic about the length of human civilization. But they're really 721 00:39:06,960 --> 00:39:08,960 Speaker 1: fun to think about because they make you think about 722 00:39:08,960 --> 00:39:11,640 Speaker 1: what time is and you know, and how it relates 723 00:39:11,680 --> 00:39:15,680 Speaker 1: to the whole universe. Well, though, on the question of 724 00:39:15,719 --> 00:39:18,720 Speaker 1: nobody being around this, this may also be a tangent. 725 00:39:18,800 --> 00:39:21,440 Speaker 1: But this makes me wonder do you have opinions on 726 00:39:21,520 --> 00:39:25,040 Speaker 1: the alleged Boltzman brain problem. I know we talked about 727 00:39:25,040 --> 00:39:27,600 Speaker 1: this on an episode a few years back, and um 728 00:39:27,960 --> 00:39:30,399 Speaker 1: so maybe kind of fuzzy on the details, but if 729 00:39:30,400 --> 00:39:33,920 Speaker 1: I recall, it has been used to argue against some 730 00:39:34,120 --> 00:39:39,440 Speaker 1: types of future eternity ees. But basically the the argument 731 00:39:39,480 --> 00:39:43,400 Speaker 1: is if the universe were to go on existing literally forever, 732 00:39:43,520 --> 00:39:47,680 Speaker 1: with certain types of properties in play, eventually people whose 733 00:39:47,840 --> 00:39:52,240 Speaker 1: brains randomly formed from fluctuations in space would outnumber people 734 00:39:52,640 --> 00:39:56,040 Speaker 1: who exist through biological evolution on Rocky Planet, and thus 735 00:39:56,080 --> 00:39:58,800 Speaker 1: we would expect to be those brains instead of these 736 00:39:58,880 --> 00:40:03,720 Speaker 1: biological brains. Is that roughly right? Yeah. Essentially, it's arguing 737 00:40:04,000 --> 00:40:08,239 Speaker 1: that if the universe reaches heat death and then goes 738 00:40:08,280 --> 00:40:11,640 Speaker 1: on forever, that most of the time in the universe 739 00:40:11,840 --> 00:40:16,000 Speaker 1: is during heat death, right, that really basically randomly sampled 740 00:40:16,000 --> 00:40:18,120 Speaker 1: moment in the universe should be when the universe is 741 00:40:18,200 --> 00:40:21,640 Speaker 1: spread out and boring and gray. So then Boltsman said, well, 742 00:40:21,680 --> 00:40:23,759 Speaker 1: what if you just had a quantum fluctuation while he 743 00:40:23,920 --> 00:40:25,360 Speaker 1: was before quantum mechanics. But what if you had a 744 00:40:25,440 --> 00:40:28,799 Speaker 1: random fluctuation, Because you know, the law of entropy is statistical, 745 00:40:28,840 --> 00:40:32,480 Speaker 1: it's not exact, allows for fluctuations. And so he said, well, 746 00:40:32,520 --> 00:40:36,200 Speaker 1: what's the chances of the whole universe then being like 747 00:40:36,239 --> 00:40:40,440 Speaker 1: a fluctuation in some vast or heat dead universe that 748 00:40:40,560 --> 00:40:44,400 Speaker 1: already has existed for unknown millions of years. So he 749 00:40:44,480 --> 00:40:48,320 Speaker 1: was trying to fluctuate an entire universe out of basically nothing. 750 00:40:48,960 --> 00:40:51,680 Speaker 1: And so as a counterpoint, people are like, well, you know, 751 00:40:51,760 --> 00:40:55,399 Speaker 1: there are smaller but more ridiculous things that you could 752 00:40:55,520 --> 00:40:57,959 Speaker 1: fluctuate out of the universe, like a galaxy or even 753 00:40:57,960 --> 00:41:01,080 Speaker 1: just like one brain. And so at the point was 754 00:41:01,120 --> 00:41:05,480 Speaker 1: made actually to criticize those kinds of cosmological models, because 755 00:41:05,560 --> 00:41:09,160 Speaker 1: if your cosmological model seems less likely than you know, 756 00:41:09,360 --> 00:41:13,080 Speaker 1: brains forming spontaneously in space and thinking that they're people, 757 00:41:13,520 --> 00:41:16,719 Speaker 1: then it seems pretty unlikely. Um, And so I don't 758 00:41:16,719 --> 00:41:19,320 Speaker 1: think anybody really takes it seriously. Is like a theory 759 00:41:19,360 --> 00:41:21,960 Speaker 1: of the universe. It's sort of just more like a 760 00:41:21,960 --> 00:41:25,560 Speaker 1: mental exercise to wonder, like, how likely is your theory 761 00:41:25,680 --> 00:41:28,359 Speaker 1: of the universe. Um, you know, is it less likely 762 00:41:28,400 --> 00:41:31,960 Speaker 1: than this absurd scenario. So there's another thing you bring 763 00:41:32,040 --> 00:41:34,799 Speaker 1: up in your chapter. Will time ever stopped? Is an 764 00:41:34,840 --> 00:41:39,239 Speaker 1: idea I was instantly captivated by, which is you point 765 00:41:39,280 --> 00:41:44,319 Speaker 1: out that technically, um, time could be stopping and restarting 766 00:41:44,360 --> 00:41:47,440 Speaker 1: all the time, frequently without us ever realizing it, because 767 00:41:47,480 --> 00:41:50,920 Speaker 1: how would we know, right, Like, our consciousness or experience 768 00:41:50,960 --> 00:41:53,160 Speaker 1: of the world is through time, So if time were 769 00:41:53,200 --> 00:41:56,960 Speaker 1: to stop, uh and then restart, that might just be 770 00:41:57,000 --> 00:42:00,439 Speaker 1: invisible to us. So you know, maybe they're just uh, 771 00:42:00,640 --> 00:42:03,360 Speaker 1: these huge gaps in our life. Though. That makes me 772 00:42:03,480 --> 00:42:07,719 Speaker 1: wonder if time we're stopping, would it be possible to 773 00:42:07,760 --> 00:42:11,560 Speaker 1: measure how long it stopped for? Oh, that's really interesting. 774 00:42:12,200 --> 00:42:15,319 Speaker 1: You know, this sort of presupposes some sort of like 775 00:42:15,840 --> 00:42:20,160 Speaker 1: meta time, some you know, other rules of the universe 776 00:42:20,200 --> 00:42:25,480 Speaker 1: that's controlling our time. And because time itself controls how 777 00:42:25,520 --> 00:42:30,600 Speaker 1: our universe changes, then strictly speaking, if time does pause, 778 00:42:30,960 --> 00:42:33,120 Speaker 1: you know, according to this meta time, and then pick 779 00:42:33,200 --> 00:42:36,640 Speaker 1: up again, nothing should change because that would require our 780 00:42:36,760 --> 00:42:41,719 Speaker 1: time to tick forward. Like, no particles can move, no galaxies, 781 00:42:41,800 --> 00:42:44,920 Speaker 1: no space can be created, you know, no expansion can happen. 782 00:42:45,000 --> 00:42:48,880 Speaker 1: Without time our time ticking forward. That means that there's 783 00:42:49,040 --> 00:42:51,560 Speaker 1: nothing in our universe that should change if time doesn't 784 00:42:51,600 --> 00:42:54,120 Speaker 1: take forward, which means that there should be no way 785 00:42:54,160 --> 00:42:56,920 Speaker 1: to tell. So it could be like a near infinite 786 00:42:56,920 --> 00:43:00,960 Speaker 1: amount of time between every tick of our universe could 787 00:43:00,960 --> 00:43:03,600 Speaker 1: be passing in sort of like the meta universe. I 788 00:43:03,680 --> 00:43:06,319 Speaker 1: think the easiest way to imagine this is in the 789 00:43:06,400 --> 00:43:09,719 Speaker 1: simulation hypothesis, the idea that the universe is like a 790 00:43:09,719 --> 00:43:14,160 Speaker 1: computer program running on some mega computer, and you know, 791 00:43:14,280 --> 00:43:18,280 Speaker 1: if the aliens or super beings running that simulation paused 792 00:43:18,320 --> 00:43:20,680 Speaker 1: the simulation to go to the bathroom and come back, 793 00:43:21,320 --> 00:43:23,839 Speaker 1: then we don't know that they've paused it. Right. It's 794 00:43:23,880 --> 00:43:26,719 Speaker 1: just like the characters in your video game. They're not like, 795 00:43:26,880 --> 00:43:29,560 Speaker 1: hey buddy, that was a long number two. You know 796 00:43:29,600 --> 00:43:31,719 Speaker 1: what you're doing? Everything okay when you come back, They 797 00:43:31,719 --> 00:43:34,320 Speaker 1: have no idea, and to them, you know, the experience 798 00:43:34,440 --> 00:43:36,839 Speaker 1: is completely smooth. So I think, no, there's no way 799 00:43:36,880 --> 00:43:39,799 Speaker 1: to know how long time has been paused for if 800 00:43:39,800 --> 00:43:43,760 Speaker 1: it does get paused. I always wondered with that hypothesis, 801 00:43:43,800 --> 00:43:47,399 Speaker 1: would we notice if the resolution on our simulation was downgraded? 802 00:43:49,760 --> 00:43:52,160 Speaker 1: You mean, if they lost their funding and had to 803 00:43:52,960 --> 00:43:57,480 Speaker 1: had to go to a more course resolution decreased render distance. Yeah, 804 00:43:57,719 --> 00:43:59,880 Speaker 1: I don't know. Sometimes it does feel like the resolution 805 00:44:00,760 --> 00:44:04,319 Speaker 1: decreases or increases, and depending on what's going on, I'm 806 00:44:04,320 --> 00:44:07,120 Speaker 1: gonna blame my failing memory for that, Like you know 807 00:44:07,160 --> 00:44:10,279 Speaker 1: what the aliens have just been like cleaning up the cash, 808 00:44:10,400 --> 00:44:12,880 Speaker 1: and that's why I can't remember, you know, what happened 809 00:44:12,960 --> 00:44:14,759 Speaker 1: last week or when I agreed to clean to the 810 00:44:14,760 --> 00:44:17,920 Speaker 1: garage or whatever. Um. But there are always that we 811 00:44:18,000 --> 00:44:20,600 Speaker 1: do think we might be able to probe the resolution 812 00:44:20,760 --> 00:44:24,080 Speaker 1: of the simulation of the universe under the assumption that 813 00:44:24,120 --> 00:44:27,960 Speaker 1: we live in that crazy scenario, because these simulations the 814 00:44:27,960 --> 00:44:29,680 Speaker 1: way we do them, at least as we tend to 815 00:44:29,719 --> 00:44:33,120 Speaker 1: like divide the universe into huge cubes and stimulate each 816 00:44:33,160 --> 00:44:37,120 Speaker 1: cube separately, assuming that like the interactions between cubes are 817 00:44:37,120 --> 00:44:40,000 Speaker 1: pretty small, which works pretty well, you know, if you're 818 00:44:40,040 --> 00:44:42,759 Speaker 1: in if you're stimulating like a single galaxy at the time, 819 00:44:42,800 --> 00:44:45,239 Speaker 1: because mostly you're dominated by what's going on inside the 820 00:44:45,239 --> 00:44:48,600 Speaker 1: galaxy and now stuff from other galaxies. But we have 821 00:44:48,680 --> 00:44:52,359 Speaker 1: these particles, these crazy high energy particles that whizz through 822 00:44:52,400 --> 00:44:56,280 Speaker 1: space at velocities nobody's ever seen before or energies nobody's 823 00:44:56,320 --> 00:44:59,279 Speaker 1: ever seen before, much much higher energy than anything like 824 00:44:59,400 --> 00:45:02,960 Speaker 1: created by our particle accelerators. And they might be like 825 00:45:03,200 --> 00:45:06,719 Speaker 1: tripping up that simulation because they skipped through several of 826 00:45:06,760 --> 00:45:10,879 Speaker 1: these simulation pixels faster than anything you should expect. And 827 00:45:10,920 --> 00:45:13,160 Speaker 1: you know, there are some things about those particles we 828 00:45:13,200 --> 00:45:15,560 Speaker 1: see out there in space that we don't understand, and 829 00:45:15,600 --> 00:45:18,640 Speaker 1: so that opens the door to like maybe you could 830 00:45:18,640 --> 00:45:23,160 Speaker 1: explain those particles as being like a glitch in the simulation. Now, 831 00:45:23,840 --> 00:45:28,319 Speaker 1: speaking of simulations and going back to time travel, does 832 00:45:28,360 --> 00:45:32,280 Speaker 1: anyone out there like make any kind of an argument 833 00:45:32,840 --> 00:45:36,680 Speaker 1: for time travel into the past by saying, well, if 834 00:45:36,719 --> 00:45:40,080 Speaker 1: we are living within a simulation, then time travel into 835 00:45:40,080 --> 00:45:43,120 Speaker 1: the past and the ability to change the past would 836 00:45:43,120 --> 00:45:46,400 Speaker 1: be possible within the confines of that simulation. Yeah. You know, 837 00:45:46,600 --> 00:45:49,000 Speaker 1: if you're living in a simulation, then the rules are 838 00:45:49,040 --> 00:45:53,120 Speaker 1: essentially arbitrary, and then yeah, you could wind time backwards. 839 00:45:53,640 --> 00:45:55,279 Speaker 1: I think this goes to the heart of, like I 840 00:45:55,280 --> 00:45:59,000 Speaker 1: think a basic confusion about time travel because people imagine, 841 00:45:59,040 --> 00:46:01,520 Speaker 1: like you get in a time machine and you and 842 00:46:01,560 --> 00:46:04,120 Speaker 1: the time machine does something to you, and then you 843 00:46:04,239 --> 00:46:06,319 Speaker 1: end up back in the past. I don't really see 844 00:46:06,360 --> 00:46:09,120 Speaker 1: how that could possibly work. What you really want in 845 00:46:09,200 --> 00:46:12,680 Speaker 1: time travel is for the whole universe to travel back 846 00:46:12,680 --> 00:46:15,080 Speaker 1: in the past and for you to not. So you 847 00:46:15,160 --> 00:46:16,960 Speaker 1: gotta like get in the time machine, and it's got 848 00:46:16,960 --> 00:46:20,640 Speaker 1: to like rewind the clocks of the rest of the universe, right. 849 00:46:20,680 --> 00:46:23,240 Speaker 1: You don't want to be like, Okay, it's still today, 850 00:46:23,360 --> 00:46:25,360 Speaker 1: but now I'm ten years younger. I mean maybe some 851 00:46:25,440 --> 00:46:28,040 Speaker 1: people want that. That's a whole different thing to look for. 852 00:46:28,520 --> 00:46:31,000 Speaker 1: If you want to like unspill your coffee, but you 853 00:46:31,040 --> 00:46:33,680 Speaker 1: still want like the ideas, you want to remember having 854 00:46:33,719 --> 00:46:36,120 Speaker 1: spilled it on yourself, so you cannot just repeat it. 855 00:46:36,320 --> 00:46:38,000 Speaker 1: Then you need to rewind the whole rest of the 856 00:46:38,120 --> 00:46:41,759 Speaker 1: universe somehow. It seems like a much bigger job that. Yeah, 857 00:46:41,800 --> 00:46:43,920 Speaker 1: that's a great point. Yeah, that so the time machine 858 00:46:43,960 --> 00:46:46,360 Speaker 1: would have to change the universe, not you. Yeah, I 859 00:46:46,480 --> 00:46:48,520 Speaker 1: never thought of it that way. Yeah. And a lot 860 00:46:48,560 --> 00:46:50,640 Speaker 1: of our listeners right in when we talk about time 861 00:46:50,640 --> 00:46:53,200 Speaker 1: travel and raise a similar point and a criticism of 862 00:46:53,239 --> 00:46:56,560 Speaker 1: science fiction levels, which is that you know, if you 863 00:46:56,640 --> 00:46:59,040 Speaker 1: do go back in time somehow, how do you know 864 00:46:59,080 --> 00:47:02,000 Speaker 1: where you're going to be? You know, because the Earth 865 00:47:02,160 --> 00:47:05,440 Speaker 1: and the sun and the milky way they're all moving, Um, 866 00:47:05,480 --> 00:47:07,480 Speaker 1: so how do you know where you're going to end up? 867 00:47:07,640 --> 00:47:10,719 Speaker 1: And it's a fun question. Um though, I think if 868 00:47:10,719 --> 00:47:13,360 Speaker 1: you're gonna pose it like, okay, you can travel through time, 869 00:47:13,440 --> 00:47:16,640 Speaker 1: then ostensibly probably you can travel travel through space time, 870 00:47:16,719 --> 00:47:19,800 Speaker 1: so you can appear wherever you want. But the problem 871 00:47:19,880 --> 00:47:22,960 Speaker 1: is like, actually, I'm not even really necessarily well defined, 872 00:47:23,040 --> 00:47:26,120 Speaker 1: because what does it mean to be here at a 873 00:47:26,160 --> 00:47:28,040 Speaker 1: point in space, or there at a point in space, 874 00:47:28,120 --> 00:47:30,719 Speaker 1: or now this point in space? Now where is that 875 00:47:30,760 --> 00:47:34,200 Speaker 1: point in the future because there is no like marker 876 00:47:34,320 --> 00:47:37,239 Speaker 1: to space. Space is all relative. It's not absolutely you 877 00:47:37,239 --> 00:47:39,600 Speaker 1: can't like grasp this point of space and give it 878 00:47:39,600 --> 00:47:41,960 Speaker 1: a name and say where does this bit go? There's 879 00:47:41,960 --> 00:47:45,319 Speaker 1: only stuff moving through space relative to each other. So 880 00:47:45,560 --> 00:47:47,719 Speaker 1: it turns out that's not even really well defined. Like 881 00:47:49,000 --> 00:47:51,719 Speaker 1: where was the Earth, you know, a million years ago 882 00:47:51,960 --> 00:47:55,319 Speaker 1: in our space? Doesn't actually have a meaning? That is 883 00:47:55,320 --> 00:47:58,399 Speaker 1: when I had thought of before that always seemed an 884 00:47:58,400 --> 00:48:09,920 Speaker 1: insurmountable problem. But this actually reminds me of another thing 885 00:48:09,920 --> 00:48:14,520 Speaker 1: I wanted to talk about briefly, which is relating time 886 00:48:14,719 --> 00:48:17,680 Speaker 1: to the history of the universe and the Big Bang, 887 00:48:18,640 --> 00:48:21,480 Speaker 1: a thing people often ask and I know, there are 888 00:48:22,040 --> 00:48:26,279 Speaker 1: theories to address this is is what happened before the 889 00:48:26,320 --> 00:48:30,000 Speaker 1: Big Bang. But if you have an understanding that, you know, 890 00:48:30,040 --> 00:48:32,520 Speaker 1: you have a singularity at the origin of the Big Bang, 891 00:48:32,600 --> 00:48:35,560 Speaker 1: that was the beginning of time itself as we know it. 892 00:48:36,120 --> 00:48:39,040 Speaker 1: What are physicists talking about exactly when they try to 893 00:48:39,160 --> 00:48:43,600 Speaker 1: envision causes leading to the first instant of the Big Bang? 894 00:48:44,160 --> 00:48:47,879 Speaker 1: Mostly they're trying to avoid that singularity because that singularity 895 00:48:47,960 --> 00:48:50,719 Speaker 1: is a problem. You know, we don't see things like 896 00:48:50,760 --> 00:48:54,239 Speaker 1: singularities in the universe. We don't see infinities, we don't 897 00:48:54,239 --> 00:48:56,840 Speaker 1: see things with infinite density, we don't see things of 898 00:48:56,880 --> 00:48:59,960 Speaker 1: infinite size. I mean, maybe the universe is itself infinite. 899 00:49:00,400 --> 00:49:03,839 Speaker 1: There's nothing that's like infinitely smooth or perfectly circular. These 900 00:49:03,840 --> 00:49:07,240 Speaker 1: are sort of abstractions in our mind. And so most 901 00:49:07,239 --> 00:49:09,879 Speaker 1: physicists who are working on the very early universe are 902 00:49:09,920 --> 00:49:13,000 Speaker 1: trying to avoid that singularity because, as I said earlier, 903 00:49:13,080 --> 00:49:15,799 Speaker 1: general relativity breaks down. That's what it means like, if 904 00:49:15,840 --> 00:49:18,440 Speaker 1: your theory predicts something infinite, it doesn't know how to 905 00:49:18,440 --> 00:49:22,080 Speaker 1: do any calculations beyond that. So instead of having like 906 00:49:22,239 --> 00:49:24,920 Speaker 1: a moment of singularity, which is sort of like the 907 00:49:25,000 --> 00:49:30,080 Speaker 1: naive general relativistic prediction of increasing density. Instead, they're going 908 00:49:30,120 --> 00:49:32,520 Speaker 1: back and saying, well, maybe the Big Bang was just 909 00:49:32,560 --> 00:49:36,960 Speaker 1: like a rapid expansion of space from a previously dense 910 00:49:37,560 --> 00:49:40,440 Speaker 1: kind of universe that we don't understand at all. So 911 00:49:40,480 --> 00:49:43,520 Speaker 1: the basic sketches like you have some kind of weird state. 912 00:49:43,760 --> 00:49:47,279 Speaker 1: The universe is filled with like inflotons, some particle we 913 00:49:47,320 --> 00:49:49,719 Speaker 1: don't know if it existed, but maybe it did. And 914 00:49:49,719 --> 00:49:53,520 Speaker 1: then those inflotons they are causing the rapid expansion of 915 00:49:53,560 --> 00:49:57,480 Speaker 1: space and decay then into normal matter. So that's so 916 00:49:57,560 --> 00:50:00,160 Speaker 1: now the Big Bang is that moment when the in 917 00:50:00,200 --> 00:50:04,120 Speaker 1: photons are expanding and then decay into like our universe. 918 00:50:04,160 --> 00:50:06,600 Speaker 1: That's how our universe is sort of created out of 919 00:50:06,640 --> 00:50:10,040 Speaker 1: these in photons, and that avoids this moment of singularity. 920 00:50:10,080 --> 00:50:12,680 Speaker 1: It's never like a moment when the universe is infinitely dense. 921 00:50:13,239 --> 00:50:16,160 Speaker 1: But you know, again, this is very speculative stuff. We 922 00:50:16,280 --> 00:50:19,840 Speaker 1: think inflation happened, this crazy expansion in the very beginning 923 00:50:20,520 --> 00:50:23,360 Speaker 1: um and this is like a way to avoid having 924 00:50:23,440 --> 00:50:27,080 Speaker 1: to put before that this dot, this singularity that breaks 925 00:50:27,120 --> 00:50:29,759 Speaker 1: all of the mathematics, instead of replacing it with like 926 00:50:29,880 --> 00:50:32,560 Speaker 1: some other weird kind of substance. We don't even really 927 00:50:32,600 --> 00:50:35,200 Speaker 1: know what it's like or what it's about. Um, we're 928 00:50:35,239 --> 00:50:38,200 Speaker 1: just really beginning to know how to ask questions about it. 929 00:50:38,880 --> 00:50:42,040 Speaker 1: And you know, that suggests a really interesting question, which 930 00:50:42,080 --> 00:50:44,840 Speaker 1: is like, if there is something before the Big Bang, 931 00:50:44,960 --> 00:50:47,600 Speaker 1: what was it? And was there something before that? It 932 00:50:47,680 --> 00:50:50,640 Speaker 1: seems like, in one hand, super frustrating because you're just 933 00:50:50,719 --> 00:50:53,640 Speaker 1: kicking the can down the road, Like, alright, so the 934 00:50:53,719 --> 00:50:56,319 Speaker 1: early universe was this expansion, and before that came something 935 00:50:56,320 --> 00:50:58,520 Speaker 1: which caused the expansion, and before that came something which 936 00:50:58,560 --> 00:51:01,520 Speaker 1: caused that, which caused the expansion. But is there in 937 00:51:01,560 --> 00:51:05,560 Speaker 1: the end something original which caused it. We don't know. 938 00:51:05,680 --> 00:51:08,680 Speaker 1: And there's two possibilities. One is that we just keep 939 00:51:08,719 --> 00:51:11,400 Speaker 1: digging forever and dig further and further and further and 940 00:51:11,440 --> 00:51:14,839 Speaker 1: further back and never get to anything which seems like 941 00:51:15,120 --> 00:51:17,960 Speaker 1: could have caused itself. Or it could be that we 942 00:51:18,000 --> 00:51:20,520 Speaker 1: get to some state where we're like, this makes sense 943 00:51:20,560 --> 00:51:23,000 Speaker 1: to have to be a beginning. It's like it's sort 944 00:51:23,000 --> 00:51:26,200 Speaker 1: of the only way things could have happened to me. 945 00:51:26,440 --> 00:51:28,440 Speaker 1: It's it's hard to grapple with these ideas, so it's 946 00:51:28,480 --> 00:51:30,600 Speaker 1: easier to think about it sort of in a parallel way, 947 00:51:30,600 --> 00:51:33,600 Speaker 1: which is like, what is the smallest thing in the universe. 948 00:51:34,080 --> 00:51:37,160 Speaker 1: We don't know if as we tear apart, particles will 949 00:51:37,239 --> 00:51:39,320 Speaker 1: keep finding things that are smaller and smaller and smaller 950 00:51:39,320 --> 00:51:41,719 Speaker 1: and smaller, or if eventually we'll get to one where, like, 951 00:51:41,760 --> 00:51:44,319 Speaker 1: you know, what, this one it makes sense to be 952 00:51:44,360 --> 00:51:47,279 Speaker 1: a fundamental ingredient to the universe. We can just start 953 00:51:47,280 --> 00:51:49,480 Speaker 1: from here and build up. You know, maybe it's like 954 00:51:49,520 --> 00:51:52,240 Speaker 1: the smallest fundamental thing. It's at the plank length or something. 955 00:51:52,640 --> 00:51:54,239 Speaker 1: We don't know if we'll ever get there, or if 956 00:51:54,280 --> 00:51:56,360 Speaker 1: it will be self evident, or if there will be 957 00:51:56,400 --> 00:51:59,160 Speaker 1: always people who say, like, I don't know, I want 958 00:51:59,160 --> 00:52:01,600 Speaker 1: to dig deeper. In the same way, it might be 959 00:52:01,640 --> 00:52:04,399 Speaker 1: that we're doomed to keep digging deeper and deeper back 960 00:52:04,440 --> 00:52:07,200 Speaker 1: into the history of the universe, never finding out if 961 00:52:07,239 --> 00:52:10,279 Speaker 1: there was an original cause. All right, so I think 962 00:52:10,320 --> 00:52:12,200 Speaker 1: we're probably getting close to the end of our time. 963 00:52:12,239 --> 00:52:14,200 Speaker 1: But I got to come back to time travel before 964 00:52:14,200 --> 00:52:16,560 Speaker 1: we do, because I'm wondering, what what do you think 965 00:52:16,960 --> 00:52:20,719 Speaker 1: You mentioned Stephen Hawking's party where the the invitations were 966 00:52:20,719 --> 00:52:23,359 Speaker 1: sent out after it happened, But what what is your 967 00:52:23,400 --> 00:52:25,640 Speaker 1: personal favorite way to hunt for a time traveler. What 968 00:52:25,640 --> 00:52:28,000 Speaker 1: would you do if you wanted to find evidence of 969 00:52:28,040 --> 00:52:31,480 Speaker 1: people from the future. Wow, I know I have never 970 00:52:31,520 --> 00:52:35,680 Speaker 1: given that any thought about evidence for people from the future. UM. 971 00:52:35,840 --> 00:52:38,799 Speaker 1: I try to think about what people would want to do, 972 00:52:39,040 --> 00:52:41,960 Speaker 1: Like if I were a time traveler, why would I 973 00:52:42,000 --> 00:52:45,680 Speaker 1: come to one? Uh? You know the obvious answers are 974 00:52:45,719 --> 00:52:48,560 Speaker 1: like change history. Uh, in which case, you know, I 975 00:52:48,600 --> 00:52:51,120 Speaker 1: guess you can blame those time travelers for you know, 976 00:52:51,440 --> 00:52:53,479 Speaker 1: the reason things have gone the way they are. Maybe 977 00:52:53,520 --> 00:52:57,000 Speaker 1: there because time travelers have come back and tweaked election 978 00:52:57,040 --> 00:53:00,719 Speaker 1: results or you know, or something like that. Um. So 979 00:53:00,800 --> 00:53:02,960 Speaker 1: I guess the best way to find time travelers with 980 00:53:03,120 --> 00:53:07,080 Speaker 1: then to be present at critical hinge moments in history 981 00:53:07,560 --> 00:53:11,640 Speaker 1: and look around for suspicious behavior. I suppose I don't 982 00:53:11,640 --> 00:53:14,279 Speaker 1: really know. That's a great question. Yeah. I was thinking 983 00:53:14,320 --> 00:53:18,399 Speaker 1: about all this in terms of of ancient aliens as well, 984 00:53:18,480 --> 00:53:20,799 Speaker 1: because both you have you have people of course who 985 00:53:20,800 --> 00:53:23,719 Speaker 1: obsess about the idea of of aliens having visited during 986 00:53:23,760 --> 00:53:26,440 Speaker 1: ancient times and so forth, and and you also have, 987 00:53:26,560 --> 00:53:29,640 Speaker 1: I guess a more recent phenomenon of people looking back 988 00:53:29,680 --> 00:53:33,040 Speaker 1: at old pictures and paintings and you know, playing this 989 00:53:33,080 --> 00:53:36,920 Speaker 1: game of basically misinterpreting um things and paintings and photos 990 00:53:36,920 --> 00:53:39,000 Speaker 1: of like looking back in an old picture and saying, oh, well, 991 00:53:39,000 --> 00:53:41,839 Speaker 1: that person, their their style of dress does not look 992 00:53:41,920 --> 00:53:45,440 Speaker 1: archaic enough. They must be traveler. Yeah. Or this painting 993 00:53:45,760 --> 00:53:48,799 Speaker 1: she's holding something that looks like an iPhone. Obviously this 994 00:53:48,880 --> 00:53:54,239 Speaker 1: is a Renaissance painting of a time travel No. I 995 00:53:54,280 --> 00:53:56,200 Speaker 1: think that just says a lot about us, you know, 996 00:53:56,239 --> 00:53:58,319 Speaker 1: and who we are, you know, the same way that 997 00:53:58,400 --> 00:54:03,400 Speaker 1: like photos of UFO, those seemed to be constantly greeny. 998 00:54:03,440 --> 00:54:07,480 Speaker 1: As you know, imaging technology improves, it's always on the 999 00:54:07,600 --> 00:54:09,920 Speaker 1: edge of the our ability to capture it. So I 1000 00:54:09,920 --> 00:54:13,280 Speaker 1: think it says something about our desire to discover weird 1001 00:54:13,360 --> 00:54:16,520 Speaker 1: things and reveal the truth, which I'm totally sympathetic to. 1002 00:54:16,640 --> 00:54:18,759 Speaker 1: I also want to peel back a layer of the 1003 00:54:18,880 --> 00:54:21,720 Speaker 1: universe and wake up to its true nature. I remember 1004 00:54:22,160 --> 00:54:24,840 Speaker 1: Carl Sagan, and I forget which which book this was, 1005 00:54:24,920 --> 00:54:26,440 Speaker 1: but it was in one of the books where he 1006 00:54:26,719 --> 00:54:29,240 Speaker 1: talks a little bit about the idea of ancient aliens, 1007 00:54:29,560 --> 00:54:34,400 Speaker 1: and I remember him him basically outlining the sort of 1008 00:54:34,960 --> 00:54:38,200 Speaker 1: ancient account, the sort of myth that one might look 1009 00:54:38,239 --> 00:54:42,600 Speaker 1: to as as the sort of ancient astronaut account that 1010 00:54:42,640 --> 00:54:45,799 Speaker 1: could exist. I have such things were possible, And I 1011 00:54:45,840 --> 00:54:47,840 Speaker 1: wonder if anyone has ever taken a similar approach to 1012 00:54:47,840 --> 00:54:50,280 Speaker 1: the concept of time travel, like like basically like boiling 1013 00:54:50,280 --> 00:54:53,239 Speaker 1: it down, saying, Okay, if there is actually evidence, say 1014 00:54:53,400 --> 00:54:58,200 Speaker 1: in you know, the historical record, all of people having 1015 00:54:58,239 --> 00:55:00,360 Speaker 1: traveled back in time, you know, well, what ex exactly 1016 00:55:00,360 --> 00:55:02,399 Speaker 1: what would be looking for? What exactly what they would 1017 00:55:02,400 --> 00:55:06,279 Speaker 1: they have been doing? Um and uh and and how 1018 00:55:06,320 --> 00:55:08,319 Speaker 1: would and I guess it would come down to, like 1019 00:55:08,640 --> 00:55:10,360 Speaker 1: you'd have to imagine, like how truthful are they going 1020 00:55:10,400 --> 00:55:12,759 Speaker 1: to be? Are they just gonna lie about themselves being 1021 00:55:12,800 --> 00:55:15,680 Speaker 1: time travels, Because that's then you can basically point to 1022 00:55:15,760 --> 00:55:19,920 Speaker 1: any pivotal individual or any person in a pivotal period 1023 00:55:19,920 --> 00:55:23,640 Speaker 1: of time, right, yeah, And would they even be humans? Right? 1024 00:55:23,719 --> 00:55:26,719 Speaker 1: Like we fantasized about going back to see the dinosaurs. 1025 00:55:27,239 --> 00:55:29,840 Speaker 1: So if now we're putting ourselves back in the past 1026 00:55:29,840 --> 00:55:32,400 Speaker 1: and imagining time travelers, we might have to imagine some 1027 00:55:32,520 --> 00:55:37,359 Speaker 1: like post human apocalyptic, newly intelligent species of you know, 1028 00:55:37,400 --> 00:55:40,640 Speaker 1: who knows what, penguins or or something coming back in 1029 00:55:40,719 --> 00:55:44,880 Speaker 1: time to investigate humans, you know, to understand what happened 1030 00:55:44,920 --> 00:55:49,480 Speaker 1: before the apocalypse or whatever. Um, but I thot machines machine. 1031 00:55:50,080 --> 00:55:53,680 Speaker 1: Most of the most of our space exploration is uncrewed probes. 1032 00:55:53,719 --> 00:55:55,680 Speaker 1: Now you would have to imagine that the same would 1033 00:55:55,719 --> 00:55:59,360 Speaker 1: hold true for time. Yeah, it's probably true, or you know, 1034 00:55:59,400 --> 00:56:01,200 Speaker 1: after the mission needs have killed us all and they 1035 00:56:01,239 --> 00:56:04,399 Speaker 1: just have myths about those weird meat creatures that used 1036 00:56:04,440 --> 00:56:08,279 Speaker 1: to uh roam the earth or something. Um. That's fun, 1037 00:56:08,320 --> 00:56:11,080 Speaker 1: but it's fundamentally is limited by our imagination. It's the 1038 00:56:11,160 --> 00:56:14,600 Speaker 1: same problem with trying to look for aliens. We look 1039 00:56:14,680 --> 00:56:17,560 Speaker 1: for aliens in the way we expect to see them, 1040 00:56:17,640 --> 00:56:21,439 Speaker 1: although we're pretty sure that if aliens exist, they're not 1041 00:56:21,560 --> 00:56:24,080 Speaker 1: anything that we expected. So we need to like push 1042 00:56:24,160 --> 00:56:26,840 Speaker 1: really hard on all the boundaries of our imagination to 1043 00:56:26,960 --> 00:56:29,800 Speaker 1: make sure we're looking for aliens as broadly as possible 1044 00:56:29,800 --> 00:56:32,160 Speaker 1: so we don't miss them. We don't just like come by, 1045 00:56:32,239 --> 00:56:34,719 Speaker 1: we're like, oh, that's not aliens. So it's the same 1046 00:56:34,719 --> 00:56:37,719 Speaker 1: problem with imagining future time travelers, like who these these 1047 00:56:37,719 --> 00:56:41,040 Speaker 1: people or things or entities are are well beyond I 1048 00:56:41,080 --> 00:56:45,680 Speaker 1: think even our most creative science fiction UM writers. Well, so, 1049 00:56:45,840 --> 00:56:48,080 Speaker 1: like you said, like what's interesting, what would be interesting 1050 00:56:48,080 --> 00:56:52,239 Speaker 1: about to someone from the future, and we instantly think, too, oh, well, 1051 00:56:52,280 --> 00:56:56,080 Speaker 1: the you know, the coronavirus or something going on in 1052 00:56:56,320 --> 00:57:00,400 Speaker 1: you know, geopolitics, or even in the environment. But it 1053 00:57:00,640 --> 00:57:02,680 Speaker 1: could be something entirely different. It could be you know, 1054 00:57:02,719 --> 00:57:06,359 Speaker 1: the very beginning of something um that doesn't matter at 1055 00:57:06,360 --> 00:57:12,439 Speaker 1: all today, right, but but matters, say in exactly which 1056 00:57:12,520 --> 00:57:15,520 Speaker 1: we could never possibly imagine. I mean, think about people 1057 00:57:15,560 --> 00:57:18,080 Speaker 1: a thousand years ago trying to anticipate was important to 1058 00:57:18,160 --> 00:57:20,880 Speaker 1: us today. We couldn't even do that from twenty years ago, 1059 00:57:21,040 --> 00:57:24,040 Speaker 1: not to mention a thousand Okay, last question, Daniel, what's 1060 00:57:24,040 --> 00:57:26,800 Speaker 1: your favorite time travel movie? Oh? My favorite time travel 1061 00:57:26,880 --> 00:57:30,400 Speaker 1: movie has to be Primer, So I think that most 1062 00:57:30,440 --> 00:57:33,680 Speaker 1: clearly sets out rules, rules that make sense, and then 1063 00:57:33,800 --> 00:57:40,040 Speaker 1: follows those really carefully with lots of fascinating and unexpected results. 1064 00:57:40,400 --> 00:57:43,320 Speaker 1: Good answer, good answer, Yeah, that's a good one. I 1065 00:57:43,360 --> 00:57:47,000 Speaker 1: often gravitate towards the ones that have really goofy time 1066 00:57:47,040 --> 00:57:49,440 Speaker 1: travel rules. But they but if they still stick to 1067 00:57:49,480 --> 00:57:55,360 Speaker 1: those rules, then I tend to forgive them. They're always 1068 00:57:55,400 --> 00:57:57,400 Speaker 1: boundary cases, though they're always cased to were like, I'm 1069 00:57:57,400 --> 00:57:59,640 Speaker 1: not sure what would happen in this scenario or that scenario. 1070 00:58:00,160 --> 00:58:02,960 Speaker 1: So I like Prime Room because it has really clear 1071 00:58:03,160 --> 00:58:06,120 Speaker 1: Chris Brules and those it has cost. You can't just 1072 00:58:06,160 --> 00:58:09,040 Speaker 1: like pop back in time. You have to like spend 1073 00:58:09,080 --> 00:58:13,240 Speaker 1: time going backwards um, which has really interesting consequences. So 1074 00:58:13,280 --> 00:58:17,080 Speaker 1: I found it to be really creative totally. All right, well, 1075 00:58:17,080 --> 00:58:19,000 Speaker 1: thanks so much for joining us today, Daniel. This has 1076 00:58:19,040 --> 00:58:21,440 Speaker 1: been a lot of fun. Thank you very much. Always 1077 00:58:21,440 --> 00:58:25,960 Speaker 1: a pleasure to talk to you guys. All right, well, 1078 00:58:25,960 --> 00:58:29,000 Speaker 1: thanks well once more to Daniel Watson for jumping on 1079 00:58:29,040 --> 00:58:33,200 Speaker 1: the old podcast machine and letting us uh pokemon prod 1080 00:58:33,320 --> 00:58:36,600 Speaker 1: um with various questions about time travel and wormholes and 1081 00:58:36,640 --> 00:58:39,280 Speaker 1: what have you. Yeah, if you want to learn more, 1082 00:58:39,320 --> 00:58:42,480 Speaker 1: so if you're not subscribed to Daniel and Jorge Explain 1083 00:58:42,560 --> 00:58:45,120 Speaker 1: the Universe, you can find that wherever you get your podcast, 1084 00:58:45,200 --> 00:58:48,680 Speaker 1: but you can also go to www dot Daniel and 1085 00:58:48,800 --> 00:58:52,200 Speaker 1: Jorge dot com. And you can also find the website 1086 00:58:52,280 --> 00:58:55,240 Speaker 1: for their new book. Again. The book is called Frequently 1087 00:58:55,280 --> 00:58:58,320 Speaker 1: Asked Questions about the Universe, and the website for that 1088 00:58:58,480 --> 00:59:02,240 Speaker 1: is www dot you Diverse f a Q dot com. 1089 00:59:02,280 --> 00:59:03,960 Speaker 1: And if you'd like to check out other episodes of 1090 00:59:04,000 --> 00:59:06,000 Speaker 1: Stuff to Blow your Mind, well you can find our 1091 00:59:06,000 --> 00:59:08,440 Speaker 1: show wherever you get your podcasts. Just look for the 1092 00:59:08,480 --> 00:59:11,880 Speaker 1: Stuff to Blow Your Mind podcast feed. We run multiple 1093 00:59:11,920 --> 00:59:15,840 Speaker 1: episodes per week, with core episodes dealing with science and 1094 00:59:15,960 --> 00:59:20,439 Speaker 1: culture on Tuesdays and Thursdays. On Monday's we do listener mail, 1095 00:59:20,480 --> 00:59:24,120 Speaker 1: on Wednesday's we do a short form artifact titled the Artifact, 1096 00:59:24,400 --> 00:59:27,120 Speaker 1: and on Friday's we do something called Weird House Cinema, 1097 00:59:27,160 --> 00:59:30,160 Speaker 1: which is our time to set aside most serious matters 1098 00:59:30,400 --> 00:59:33,439 Speaker 1: and just discuss a strange film. So, of course, thanks 1099 00:59:33,440 --> 00:59:36,080 Speaker 1: again to Daniel for joining us today, and as always 1100 00:59:36,120 --> 00:59:39,200 Speaker 1: a big thank you to our excellent audio producer Seth 1101 00:59:39,280 --> 00:59:41,880 Speaker 1: Nicholas Johnson. If you would like to get in touch 1102 00:59:41,960 --> 00:59:44,680 Speaker 1: with us with feedback on this episode or any other, 1103 00:59:44,800 --> 00:59:46,960 Speaker 1: to suggest a topic for the future, or just to 1104 00:59:47,040 --> 00:59:50,160 Speaker 1: say hi, you can email us at contact at stuff 1105 00:59:50,240 --> 01:00:00,280 Speaker 1: to Blow your Mind dot com. Stuff to All Your 1106 01:00:00,280 --> 01:00:03,200 Speaker 1: Mind is production of I Heart Radio. For more podcasts 1107 01:00:03,240 --> 01:00:05,320 Speaker 1: for My Heart Radio, visit the I Heart Radio app, 1108 01:00:05,480 --> 01:00:17,000 Speaker 1: Apple Podcasts, or wherever you listening to your favorite shows.