1 00:00:08,560 --> 00:00:11,360 Speaker 1: Hey, Jorgey, where were you when you heard about the 2 00:00:11,400 --> 00:00:16,560 Speaker 1: first gravitational wave discovery? I don't know. Probably home in 3 00:00:16,600 --> 00:00:19,800 Speaker 1: my pajamas. That's like ninety nine percent of my life. 4 00:00:19,840 --> 00:00:22,400 Speaker 1: Are you telling me you don't remember? How could you 5 00:00:22,480 --> 00:00:26,079 Speaker 1: forget such a pivotal moment in science history? Well? I 6 00:00:26,079 --> 00:00:31,120 Speaker 1: remember pivotal moments in history, just not it's a physical history. 7 00:00:32,680 --> 00:00:34,760 Speaker 1: Was this a very significant moment for you? Oh? Of 8 00:00:34,800 --> 00:00:37,960 Speaker 1: course it was huge. People have been looking for gravitational 9 00:00:38,000 --> 00:00:41,600 Speaker 1: ways for decades and I was personally one of the skeptics, 10 00:00:41,920 --> 00:00:45,240 Speaker 1: so it was mind blowing when they actually saw one. 11 00:00:45,960 --> 00:00:48,919 Speaker 1: Because you've proven wrong is at the historical event here. 12 00:00:50,360 --> 00:00:52,519 Speaker 1: It certainly left an imprint on me, like a big 13 00:00:52,520 --> 00:01:10,400 Speaker 1: footstep in your brain. Hi am or Handway, cartoonists and 14 00:01:10,440 --> 00:01:13,200 Speaker 1: the creator of PhD comics. Hi. I'm Daniel. I'm a 15 00:01:13,200 --> 00:01:16,039 Speaker 1: particle physicist and a professor at UC Irvine, and I 16 00:01:16,120 --> 00:01:19,960 Speaker 1: love to be wrong about physics discoveries, but only physics discoveries. 17 00:01:20,080 --> 00:01:23,080 Speaker 1: What does your spouse think about that? I don't have 18 00:01:23,120 --> 00:01:26,240 Speaker 1: the expertise to be intelligently wrong about anything else. I'm 19 00:01:26,280 --> 00:01:29,520 Speaker 1: just wrong about other stuff. I see. There's a difference 20 00:01:29,560 --> 00:01:33,920 Speaker 1: between being intelligently wrong and regular wrong. But that doesn't 21 00:01:33,920 --> 00:01:36,120 Speaker 1: seem right when it comes to big ideas in physics. 22 00:01:36,200 --> 00:01:38,800 Speaker 1: I sometimes disagree with the mainstream and think, oh, that 23 00:01:38,840 --> 00:01:40,800 Speaker 1: will never happen, or that's not going to work, or 24 00:01:40,800 --> 00:01:42,960 Speaker 1: the universe can't be that way I saw. I'm a 25 00:01:43,000 --> 00:01:45,319 Speaker 1: bit more skeptical sometimes than others. But then when the 26 00:01:45,360 --> 00:01:49,280 Speaker 1: universe comes through and delivers an incredible result or discovery, 27 00:01:49,480 --> 00:01:52,200 Speaker 1: I'm happy that it did. We can sound like physics 28 00:01:52,320 --> 00:01:54,600 Speaker 1: is just a bunch of people throwing out a random 29 00:01:54,600 --> 00:01:59,360 Speaker 1: ideas and arguing about it until the universe reveals its Well, 30 00:01:59,400 --> 00:02:02,240 Speaker 1: you know that's not the complete process, but generating random 31 00:02:02,240 --> 00:02:04,600 Speaker 1: ideas is part of the process. The next step is 32 00:02:04,640 --> 00:02:07,040 Speaker 1: sort of a filter like does that idea make any sense? 33 00:02:07,080 --> 00:02:09,840 Speaker 1: And can it describe our universe at all? But there 34 00:02:09,919 --> 00:02:13,720 Speaker 1: is definitely a step where you're just like brainstorming random craziness. 35 00:02:13,800 --> 00:02:17,000 Speaker 1: Maybe this, maybe that, Maybe it's all just kittens all 36 00:02:17,000 --> 00:02:19,360 Speaker 1: the way down. Sounds like the cuts me out, but 37 00:02:19,480 --> 00:02:22,280 Speaker 1: welcome for our podcast, Daniel and Jorge Explain the Universe, 38 00:02:22,360 --> 00:02:25,160 Speaker 1: a production of iHeartRadio in which we do our best 39 00:02:25,240 --> 00:02:27,440 Speaker 1: not to be wrong about what we do and do 40 00:02:27,520 --> 00:02:31,000 Speaker 1: not understand about the nature of the universe. One thing 41 00:02:31,000 --> 00:02:34,880 Speaker 1: we're not skeptical about is humanity's ability to understand the 42 00:02:35,040 --> 00:02:38,200 Speaker 1: nature of the universe, to cast our brains out into 43 00:02:38,240 --> 00:02:41,880 Speaker 1: the cosmos, to wiggle it along with gravitational waves, to 44 00:02:42,000 --> 00:02:44,760 Speaker 1: send it flying into the hearts of neutron stars and 45 00:02:44,840 --> 00:02:48,440 Speaker 1: deep down into the frothing craziness of quantum mechanics. We 46 00:02:48,480 --> 00:02:51,240 Speaker 1: will keep pushing and pushing until we understand the entire 47 00:02:51,320 --> 00:02:54,600 Speaker 1: universe and explain most of it to you. Yeah, although, Daniel, 48 00:02:54,600 --> 00:02:56,560 Speaker 1: if you like being wrong so much, why don't you 49 00:02:56,600 --> 00:02:58,560 Speaker 1: do it more often? Oh, you'd be surprised. It's not 50 00:02:58,600 --> 00:03:02,920 Speaker 1: a rare event, almost a hobby. But it is an 51 00:03:02,919 --> 00:03:06,880 Speaker 1: amazing and wonderful universe. It's so big and so incredibly 52 00:03:06,960 --> 00:03:09,359 Speaker 1: vast that it kind of makes you wonder what out 53 00:03:09,360 --> 00:03:11,800 Speaker 1: there can have an impact on it. If anything, we 54 00:03:11,840 --> 00:03:15,160 Speaker 1: are definitely still understanding all the ways the universe works, 55 00:03:15,320 --> 00:03:18,079 Speaker 1: the way energy slashes through it, the way particles fly 56 00:03:18,240 --> 00:03:21,400 Speaker 1: through space, what space even is if you have to 57 00:03:21,440 --> 00:03:24,320 Speaker 1: even have space in our universe. There are so many 58 00:03:24,440 --> 00:03:27,080 Speaker 1: very basic questions that we don't have answers to about 59 00:03:27,080 --> 00:03:29,679 Speaker 1: the very nature of the cosmos. In which we reside 60 00:03:29,720 --> 00:03:32,200 Speaker 1: and what that means for human existence, what it means 61 00:03:32,240 --> 00:03:34,880 Speaker 1: to be alive in this crazy cosmos, and you know 62 00:03:35,040 --> 00:03:37,680 Speaker 1: how we should spend our lives. And so we keep 63 00:03:37,720 --> 00:03:40,840 Speaker 1: digging into the very firmament of the universe we find 64 00:03:40,840 --> 00:03:43,800 Speaker 1: ourselves in to try to understand its basic nature. What 65 00:03:44,080 --> 00:03:46,720 Speaker 1: is this place we find ourselves in. That's right, because 66 00:03:46,760 --> 00:03:48,760 Speaker 1: there are a lot of questions we can ask about 67 00:03:48,760 --> 00:03:51,280 Speaker 1: the universe, and the universe is always happy to provide 68 00:03:51,280 --> 00:03:54,960 Speaker 1: its interesting answers. The universe is strange and weird and 69 00:03:55,000 --> 00:03:58,480 Speaker 1: sometimes very unexpected, none more so than some of the 70 00:03:58,920 --> 00:04:02,240 Speaker 1: amazing discoveries we've made in the last few decades. Yeah, 71 00:04:02,280 --> 00:04:04,280 Speaker 1: and we can be surprised by the universe sort of 72 00:04:04,280 --> 00:04:07,480 Speaker 1: in two different ways. One way is to come up 73 00:04:07,480 --> 00:04:10,080 Speaker 1: with a new idea for how the universe works, a 74 00:04:10,200 --> 00:04:14,440 Speaker 1: theory of description of the mathematics underlying the universe, and 75 00:04:14,480 --> 00:04:17,160 Speaker 1: then go out and search for those things. For example, 76 00:04:17,200 --> 00:04:21,400 Speaker 1: Einstein's general relativity predicted black holes before we even saw them. 77 00:04:21,400 --> 00:04:23,760 Speaker 1: It suggested these should be a real thing. They should 78 00:04:23,760 --> 00:04:25,640 Speaker 1: be out there in the universe. They should be happening. 79 00:04:25,640 --> 00:04:27,760 Speaker 1: You should be able to find them, and people search 80 00:04:27,839 --> 00:04:31,000 Speaker 1: for them for decades and then finally eventually actually found them, 81 00:04:31,120 --> 00:04:33,880 Speaker 1: despite a large fraction in the community being skeptical that 82 00:04:33,960 --> 00:04:37,680 Speaker 1: they existed at all. So those folks were surprised because 83 00:04:37,839 --> 00:04:41,360 Speaker 1: what was predicted was actually out there. Well, we found something, 84 00:04:41,600 --> 00:04:43,160 Speaker 1: But I thought that you told me last time that 85 00:04:43,240 --> 00:04:46,159 Speaker 1: we're not one hundred percent sure they're black holes. Oh, 86 00:04:46,200 --> 00:04:48,479 Speaker 1: you're absolutely right. We're not one hundred percent sure or 87 00:04:48,520 --> 00:04:52,880 Speaker 1: basically anything we know about the universe, but specifically black holes. 88 00:04:53,000 --> 00:04:55,000 Speaker 1: We've never been close enough to one and never seen 89 00:04:55,120 --> 00:04:57,480 Speaker 1: the heart of one to be sure that there's really 90 00:04:57,480 --> 00:05:02,839 Speaker 1: a general relativistic singularity something. They're very compact and very massive, 91 00:05:03,040 --> 00:05:06,240 Speaker 1: very much distorting space and time. We don't know if 92 00:05:06,240 --> 00:05:09,120 Speaker 1: it's actually a black hole or a dark star, or 93 00:05:09,160 --> 00:05:12,640 Speaker 1: a fuzzball or something else quantum mechanical. That's like you're saying, 94 00:05:12,640 --> 00:05:14,680 Speaker 1: the only thing we can be sure about is that 95 00:05:14,720 --> 00:05:19,800 Speaker 1: we're not sure. Science is a process we hope gradually 96 00:05:19,880 --> 00:05:23,560 Speaker 1: bending towards the truth. As we refine our mental model 97 00:05:23,600 --> 00:05:25,560 Speaker 1: for what we think is happening out there in the universe, 98 00:05:25,640 --> 00:05:27,760 Speaker 1: we can come up with clever ways to test it, 99 00:05:28,000 --> 00:05:30,600 Speaker 1: and sometimes the universe says, yep, you are totally right. 100 00:05:30,720 --> 00:05:34,320 Speaker 1: Good job, and sometimes the universe says something else completely 101 00:05:34,320 --> 00:05:37,080 Speaker 1: different is going on. Yeah, and speaking of bending the 102 00:05:37,200 --> 00:05:40,800 Speaker 1: universe and our minds, another interesting discovery that was made 103 00:05:40,839 --> 00:05:44,240 Speaker 1: in the last few years that literally has made ripples 104 00:05:44,279 --> 00:05:49,840 Speaker 1: across the science landscape and the universe itself are gravitational waves. 105 00:05:50,040 --> 00:05:52,440 Speaker 1: The ripples and the fabric of space itself that are 106 00:05:52,640 --> 00:05:55,800 Speaker 1: made by super heavy objects moving really really fast. That's right, 107 00:05:55,839 --> 00:05:59,400 Speaker 1: And actually gravitational waves are made by everybody. Anything with 108 00:05:59,560 --> 00:06:03,120 Speaker 1: mass accelerating is making a gravitational wave. Hold up your 109 00:06:03,160 --> 00:06:05,440 Speaker 1: hand right now and wiggle it back and forth and boom, 110 00:06:05,800 --> 00:06:09,640 Speaker 1: you just created a gravitational wave which is rippling through 111 00:06:10,000 --> 00:06:13,320 Speaker 1: the universe. More like a wave wave. Let maybe when 112 00:06:13,360 --> 00:06:15,960 Speaker 1: you do it with your arm or what do you 113 00:06:15,960 --> 00:06:18,200 Speaker 1: call it, like a small wave in a small pond, 114 00:06:18,360 --> 00:06:22,520 Speaker 1: A ripple, A ripple. Yeah, I'm not judging anybody's waves 115 00:06:22,520 --> 00:06:24,960 Speaker 1: by their size. You know, size doesn't matter when it 116 00:06:24,960 --> 00:06:27,880 Speaker 1: comes to gravitational waves. But the point is that everything 117 00:06:27,880 --> 00:06:30,760 Speaker 1: out there that has mass and the accelerates changes the 118 00:06:30,800 --> 00:06:34,800 Speaker 1: shape of space and ripples that information their existence their 119 00:06:34,839 --> 00:06:38,520 Speaker 1: gravity throughout the universe in a way very similar to 120 00:06:38,640 --> 00:06:41,760 Speaker 1: how an electron creates an electric field, and if you 121 00:06:41,800 --> 00:06:44,760 Speaker 1: wiggle it, it creates a wiggling electric field, which is 122 00:06:44,800 --> 00:06:49,200 Speaker 1: basically a photon sending its message out there through space. 123 00:06:49,760 --> 00:06:52,799 Speaker 1: So it's amazing that we understand gravity well enough to 124 00:06:52,800 --> 00:06:55,360 Speaker 1: talk about how it wiggles and how it ripples, and 125 00:06:55,360 --> 00:06:58,400 Speaker 1: how space can bend and flex and do all sorts 126 00:06:58,440 --> 00:07:01,640 Speaker 1: of crazy things. Yeah, because if as we've talked about before, 127 00:07:02,040 --> 00:07:05,520 Speaker 1: gravity is not like a force something that attracts you 128 00:07:05,640 --> 00:07:09,039 Speaker 1: things with an actual kind of bending of space. That's 129 00:07:09,040 --> 00:07:11,200 Speaker 1: how physicists see it. And so when you have things 130 00:07:11,240 --> 00:07:14,360 Speaker 1: moving through space, they cause ripples in this bending, sort 131 00:07:14,400 --> 00:07:17,760 Speaker 1: of like moving through molasses or water right exactly. Everything 132 00:07:17,800 --> 00:07:21,000 Speaker 1: that has mass has a gravitational field, and then if 133 00:07:21,000 --> 00:07:24,120 Speaker 1: you move that mass, the gravitational field moves, but it 134 00:07:24,160 --> 00:07:27,880 Speaker 1: doesn't move instantaneously. So the gravitational field that's like one 135 00:07:28,040 --> 00:07:31,240 Speaker 1: light second away from you doesn't change immediately if you 136 00:07:31,280 --> 00:07:34,240 Speaker 1: wiggle your mass, but it does change very very close 137 00:07:34,280 --> 00:07:37,120 Speaker 1: to the mass, and then that change ripples out at 138 00:07:37,160 --> 00:07:39,640 Speaker 1: the speed of light. So as you move a mass 139 00:07:39,640 --> 00:07:42,480 Speaker 1: back and forth, that affects the gravitational field, and the 140 00:07:42,520 --> 00:07:47,200 Speaker 1: information about you having moved it propagates through the gravitational 141 00:07:47,240 --> 00:07:50,360 Speaker 1: field at the speed of light. That's basically what a 142 00:07:50,400 --> 00:07:54,320 Speaker 1: gravitational wave is. It's just the information about gravity being 143 00:07:54,400 --> 00:07:58,440 Speaker 1: updated because something has been accelerated. Yeah, I feel like 144 00:07:58,440 --> 00:08:01,680 Speaker 1: it's almost like if you had special gravitational glasses or 145 00:08:01,720 --> 00:08:04,240 Speaker 1: something that lets you see gravitation waste, you would see 146 00:08:04,240 --> 00:08:06,600 Speaker 1: them rippling all around you. Right, it'd be almost like 147 00:08:06,640 --> 00:08:09,560 Speaker 1: a super noisy environment that you're in with gravitational waves 148 00:08:09,560 --> 00:08:13,040 Speaker 1: being generated by everything and bouncing and well I don't 149 00:08:13,040 --> 00:08:15,120 Speaker 1: know if they bounce, but being rippled out in all 150 00:08:15,160 --> 00:08:18,760 Speaker 1: directions by everything. Yeah, that's a really insightful comment. Because 151 00:08:18,800 --> 00:08:23,080 Speaker 1: we don't have gravitational glasses, Like, we can't see directly 152 00:08:23,160 --> 00:08:26,160 Speaker 1: the curvature of space. That's what's really happening. When you 153 00:08:26,200 --> 00:08:29,400 Speaker 1: create a gravitational field, Really you're bending space around an 154 00:08:29,400 --> 00:08:32,079 Speaker 1: object to change the path of things. But because we 155 00:08:32,160 --> 00:08:34,080 Speaker 1: can't see that, you can't look at a chunk of 156 00:08:34,120 --> 00:08:37,079 Speaker 1: space and say how bent it is. All we can 157 00:08:37,120 --> 00:08:40,120 Speaker 1: see is the effect of it on stuff. That's why 158 00:08:40,160 --> 00:08:43,640 Speaker 1: originally we thought gravity was a force, because it looks 159 00:08:43,679 --> 00:08:46,559 Speaker 1: like there's a force because we can't see the curvature 160 00:08:46,640 --> 00:08:49,480 Speaker 1: directly that's causing it. So really gravity is what we 161 00:08:49,520 --> 00:08:51,960 Speaker 1: call an apparent force. It's like a force you have 162 00:08:52,040 --> 00:08:54,640 Speaker 1: to add to our description in order to account for 163 00:08:54,679 --> 00:08:57,280 Speaker 1: the motion that we see, because we didn't understand that 164 00:08:57,320 --> 00:08:59,800 Speaker 1: it was just due to the curvature of space, because 165 00:08:59,800 --> 00:09:02,200 Speaker 1: we can't see that directly. As you say, we don't 166 00:09:02,240 --> 00:09:04,960 Speaker 1: have gravitational glasses. Some of them are really really big 167 00:09:05,040 --> 00:09:07,480 Speaker 1: enough to register in detectors, and some of them very 168 00:09:07,559 --> 00:09:10,840 Speaker 1: very minute. Yeah, well we don't have gravitational glasses, but 169 00:09:10,920 --> 00:09:16,240 Speaker 1: we do have gravitational ears or gravitational microphones. In recent years, 170 00:09:16,240 --> 00:09:20,320 Speaker 1: we've been able to set up incredibly large and accurate 171 00:09:20,360 --> 00:09:23,559 Speaker 1: experiments that can sense these gravitational waves coming to us 172 00:09:23,640 --> 00:09:26,480 Speaker 1: from space and the rest of the universe. And it 173 00:09:26,520 --> 00:09:29,160 Speaker 1: was a huge discovery. It really did rock the world 174 00:09:29,160 --> 00:09:32,439 Speaker 1: of physics to accomplish this. You know, Einstein predicted gravitational 175 00:09:32,520 --> 00:09:36,120 Speaker 1: waves would exist, but he also predicted that there would 176 00:09:36,120 --> 00:09:39,520 Speaker 1: be undetectable, that the effect would be too small for 177 00:09:39,679 --> 00:09:42,880 Speaker 1: humanity to ever notice. So he was right that they exist, 178 00:09:42,920 --> 00:09:46,240 Speaker 1: but he was wrong that we couldn't discover them. It 179 00:09:46,280 --> 00:09:51,199 Speaker 1: was an incredible technological feat really just like amazing engineering 180 00:09:51,320 --> 00:09:54,559 Speaker 1: of an experiment to build something sensitive enough to detect 181 00:09:54,559 --> 00:09:58,920 Speaker 1: this very very slight effect of gravitational waves. Yeah, I'm 182 00:09:58,960 --> 00:10:01,920 Speaker 1: always impressed by engine years, by anything they do, anything 183 00:10:01,920 --> 00:10:05,240 Speaker 1: that works at least. Yeah, So they've detected gravitational waves 184 00:10:05,240 --> 00:10:07,800 Speaker 1: and we're learning more about them. But how much do 185 00:10:07,840 --> 00:10:11,760 Speaker 1: we know about gravitational waves? Are they everything we think 186 00:10:11,800 --> 00:10:14,800 Speaker 1: they are or are they maybe weirder than we think 187 00:10:14,840 --> 00:10:16,880 Speaker 1: they are? So today on the podcast, we'll be asking 188 00:10:16,880 --> 00:10:25,800 Speaker 1: the question do gravitational waves last forever? I love the 189 00:10:25,840 --> 00:10:29,280 Speaker 1: gravitational waves as mind bending in brain rippling as they 190 00:10:29,360 --> 00:10:34,160 Speaker 1: are continue to provide questions and ideas and new mysteries 191 00:10:34,160 --> 00:10:37,360 Speaker 1: for us to explore. Yeah, they bend spaced and time 192 00:10:37,440 --> 00:10:40,240 Speaker 1: and our minds at our brains. Well, this is an 193 00:10:40,280 --> 00:10:43,920 Speaker 1: interesting question at Daniel. Do gravitational waves kind of last 194 00:10:44,000 --> 00:10:46,320 Speaker 1: forever or at least believe a lasting imprint on the 195 00:10:46,400 --> 00:10:49,280 Speaker 1: universe forever forever? It's kind of a big word or 196 00:10:49,320 --> 00:10:53,360 Speaker 1: a long word, what's the right gadgetor it sort of 197 00:10:53,400 --> 00:10:57,160 Speaker 1: stretches your mind to imagine something lasting forever. But here, 198 00:10:57,200 --> 00:11:01,160 Speaker 1: because we've described gravitational waves as sort of ripple through space, 199 00:11:01,160 --> 00:11:04,040 Speaker 1: it's like an update of the gravitational field as it 200 00:11:04,080 --> 00:11:07,520 Speaker 1: propagates through the universe. You imagine that when the thing 201 00:11:07,600 --> 00:11:10,720 Speaker 1: that makes the gravitational wave stops wiggling, that the gravitational 202 00:11:10,760 --> 00:11:14,520 Speaker 1: waves stop also, that they sort of pass through you 203 00:11:14,640 --> 00:11:17,120 Speaker 1: and then on to the rest of the universe without 204 00:11:17,200 --> 00:11:19,920 Speaker 1: leaving any sort of permanent effect. Yeah, sort of like 205 00:11:19,920 --> 00:11:22,319 Speaker 1: if you're out in the ocean bobbing on the waves, 206 00:11:22,360 --> 00:11:24,280 Speaker 1: and the waves it's going to go through you and 207 00:11:24,320 --> 00:11:26,560 Speaker 1: they keep going on after you. Right. The question is 208 00:11:26,720 --> 00:11:30,280 Speaker 1: does the same happen to gravitational waves or do they 209 00:11:30,360 --> 00:11:33,679 Speaker 1: leave some sort of lasting mark on spacetime as they 210 00:11:33,760 --> 00:11:37,320 Speaker 1: propagate through like footprints in the sand. Well, ocean waves 211 00:11:37,400 --> 00:11:41,040 Speaker 1: usually leave a bit of a seasickness in me that 212 00:11:41,600 --> 00:11:44,240 Speaker 1: last a good bit of time, and then you deposit 213 00:11:44,320 --> 00:11:46,520 Speaker 1: something over the edge of the boat that leaves the 214 00:11:46,640 --> 00:11:49,200 Speaker 1: mark in the ocean. Yes, it's all the cycle of 215 00:11:49,240 --> 00:11:54,200 Speaker 1: life or the cycle of the universe, the beautiful circle 216 00:11:54,240 --> 00:11:57,960 Speaker 1: of the universe. I think that's part of the water cycle. Right. Well, 217 00:11:58,000 --> 00:12:00,880 Speaker 1: this is an interesting question. Do gravitation ways leave a 218 00:12:00,960 --> 00:12:03,559 Speaker 1: lasting imprint on the universe? Do they last forever or 219 00:12:03,600 --> 00:12:06,319 Speaker 1: do they fade away at some point? And so, as usual, 220 00:12:06,360 --> 00:12:08,560 Speaker 1: we were wondering how many people out there had thought 221 00:12:08,559 --> 00:12:11,040 Speaker 1: about this question, had thought about gravitational waves and what 222 00:12:11,200 --> 00:12:13,800 Speaker 1: they do. So thanks very much to everybody who volunteers 223 00:12:13,840 --> 00:12:16,320 Speaker 1: for this segment of the podcast, and you out there 224 00:12:16,320 --> 00:12:18,880 Speaker 1: who have never volunteered, who have never written in, who 225 00:12:18,960 --> 00:12:22,000 Speaker 1: haven't heard your own voice on the podcast. We want 226 00:12:22,040 --> 00:12:24,920 Speaker 1: to hear from you right to us. Two questions at 227 00:12:25,040 --> 00:12:28,640 Speaker 1: Daniel and Jorgey dot com. It's easy and fun. Think 228 00:12:28,679 --> 00:12:30,760 Speaker 1: about it for a second. Do you think gravitational waves 229 00:12:30,880 --> 00:12:34,280 Speaker 1: leave a lasting imprint on the universe. Here's what people 230 00:12:34,360 --> 00:12:37,600 Speaker 1: had to say. My guess is yes, but I don't 231 00:12:37,640 --> 00:12:41,520 Speaker 1: have a clue how this imprint would look like. It's 232 00:12:41,520 --> 00:12:46,800 Speaker 1: an interesting question. Well, if the analogy would regular wave holds, 233 00:12:47,080 --> 00:12:51,400 Speaker 1: you know, you would expect that will never truly disappear. 234 00:12:51,520 --> 00:12:55,000 Speaker 1: They will just get smaller and small smaller. The question 235 00:12:55,280 --> 00:13:00,360 Speaker 1: is is there some sort of pixelation or discrete level 236 00:13:00,440 --> 00:13:05,000 Speaker 1: where they basically disappear or not? So I don't know. 237 00:13:05,280 --> 00:13:08,640 Speaker 1: I'd be curious to learn that. Well, the electromagnetic force, 238 00:13:08,920 --> 00:13:11,120 Speaker 1: I believe, leaves an imprint on the universe in the 239 00:13:11,120 --> 00:13:15,160 Speaker 1: form of the cosmic microwave background radiation. So if electromagnetism 240 00:13:15,160 --> 00:13:18,160 Speaker 1: can do that. I don't see any reason that different 241 00:13:18,200 --> 00:13:21,920 Speaker 1: fundamental force like gravity couldn't do the same thing in 242 00:13:21,920 --> 00:13:24,680 Speaker 1: this case, leaving an impression on the universe with gravitational waves. 243 00:13:25,040 --> 00:13:27,559 Speaker 1: So yeah, I definitely think it's possible. I would imagine 244 00:13:27,600 --> 00:13:32,199 Speaker 1: possibly indirectly, just with how gravity influences mass in the universe. 245 00:13:32,480 --> 00:13:35,880 Speaker 1: But I'm unsure. All Right, lots of interesting ideas here, 246 00:13:35,880 --> 00:13:38,280 Speaker 1: going all the way way back to the cosmic microwave 247 00:13:38,360 --> 00:13:41,600 Speaker 1: background radiation. Yeah, lots of really great references here also, 248 00:13:41,800 --> 00:13:45,679 Speaker 1: like the discussion of maybe a minimum level of gravitational waves, 249 00:13:45,720 --> 00:13:48,960 Speaker 1: like getting into quantum gravity. Very cool stuff. Yeah, so 250 00:13:49,040 --> 00:13:52,000 Speaker 1: let's break it down, Daniel, Well, we already talked a 251 00:13:51,720 --> 00:13:53,920 Speaker 1: lot a lot about what is a gravitation a wave? 252 00:13:54,400 --> 00:13:56,960 Speaker 1: What else can we say about what a gravitation wave is? 253 00:13:57,280 --> 00:13:59,400 Speaker 1: I think it's worth exploring how you actually see a 254 00:13:59,480 --> 00:14:02,400 Speaker 1: gravity wave. You know, how you like build a detector 255 00:14:02,679 --> 00:14:06,000 Speaker 1: that can measure a ripple in space and in time 256 00:14:06,200 --> 00:14:08,520 Speaker 1: because it's a little bit subtle. You know, what we 257 00:14:08,640 --> 00:14:13,160 Speaker 1: see when a gravitational wave passes is our lengths distorted. 258 00:14:13,400 --> 00:14:15,640 Speaker 1: If you have, for example, two big long rulers and 259 00:14:15,679 --> 00:14:18,960 Speaker 1: they're perpendicular to each other. As a gravitational wave passes, 260 00:14:19,200 --> 00:14:22,240 Speaker 1: you'll see one of those rulers get shorter and then longer, 261 00:14:22,280 --> 00:14:24,800 Speaker 1: and the other one then get shorter and then longer. 262 00:14:24,880 --> 00:14:27,400 Speaker 1: So you see this sort of like oscillation in the 263 00:14:27,680 --> 00:14:31,160 Speaker 1: lengths of those arms of your l as it passes through. 264 00:14:31,280 --> 00:14:33,360 Speaker 1: But there's a ringle there because you can only detect 265 00:14:33,400 --> 00:14:36,480 Speaker 1: it if you build your arms the right way. Yeah, 266 00:14:36,520 --> 00:14:39,120 Speaker 1: it's sort of like a distortion of space that passes 267 00:14:39,200 --> 00:14:41,000 Speaker 1: through you, sort of like in the movies when they 268 00:14:41,040 --> 00:14:44,160 Speaker 1: try to depict like sound waves or like energy waves. 269 00:14:44,240 --> 00:14:46,040 Speaker 1: Do you see sort of a ripple in the image. 270 00:14:46,080 --> 00:14:48,520 Speaker 1: That's kind of what's happening. Right, It's like space itself 271 00:14:48,760 --> 00:14:51,240 Speaker 1: kind of short and singment tracks in one direction. And 272 00:14:51,280 --> 00:14:53,880 Speaker 1: the sort of mental steps to get there. Remember, are 273 00:14:54,040 --> 00:14:56,440 Speaker 1: that we have some object out there, like a really 274 00:14:56,480 --> 00:15:00,120 Speaker 1: massive black hole that's accelerating near another black hole. That's 275 00:15:00,120 --> 00:15:02,680 Speaker 1: why it's generating the gravitational waves. And we said the 276 00:15:02,720 --> 00:15:05,920 Speaker 1: gravitational waves are basically an update in the gravitational field 277 00:15:06,040 --> 00:15:09,200 Speaker 1: or the gravitational force, right, because as the object that's 278 00:15:09,240 --> 00:15:13,480 Speaker 1: generating the gravity is moving, its gravitational field is also moving. 279 00:15:13,640 --> 00:15:16,080 Speaker 1: But remember also that we think about gravity, not as 280 00:15:16,120 --> 00:15:18,960 Speaker 1: a force or having a field to it, but as 281 00:15:19,040 --> 00:15:22,720 Speaker 1: just bending of space. And so now instead of changing 282 00:15:22,720 --> 00:15:27,280 Speaker 1: the gravitational field, you're changing the curvature of space itself. Right, 283 00:15:27,280 --> 00:15:29,560 Speaker 1: That's why we call it a ripple in the fabric 284 00:15:29,600 --> 00:15:32,960 Speaker 1: of space time, because it's curvature in space that actually 285 00:15:33,000 --> 00:15:36,400 Speaker 1: is what causes gravity. But how do you actually measure that? Right? 286 00:15:36,560 --> 00:15:40,640 Speaker 1: How do you measure changes in distance of the universe itself? Well, 287 00:15:40,640 --> 00:15:42,920 Speaker 1: if you just build like a really long stick and 288 00:15:43,040 --> 00:15:45,520 Speaker 1: you hold it out, you won't measure any gravitational waves 289 00:15:45,800 --> 00:15:49,240 Speaker 1: because that stick is held together by atoms, which prefer 290 00:15:49,400 --> 00:15:52,640 Speaker 1: various bond lengths, and so as the gravitational wave passes through, 291 00:15:52,840 --> 00:15:55,520 Speaker 1: they'll resist a change in its length. It's like sort 292 00:15:55,520 --> 00:15:59,400 Speaker 1: of too strong. Instead, the way to detect gravitational waves 293 00:15:59,560 --> 00:16:01,760 Speaker 1: is to use something like beams of light. Instead of 294 00:16:01,800 --> 00:16:04,600 Speaker 1: having like a long physical ruler, just have like two 295 00:16:04,680 --> 00:16:07,200 Speaker 1: mirrors at the ends and bounced light back and forth. 296 00:16:07,480 --> 00:16:09,640 Speaker 1: And by measuring how long it takes light to go 297 00:16:09,720 --> 00:16:12,440 Speaker 1: back and forth, then you can measure how far apart 298 00:16:12,480 --> 00:16:16,080 Speaker 1: those mirrors are. So gravitational way that's propagating through space. 299 00:16:16,240 --> 00:16:18,720 Speaker 1: We'll sort of bring those two mirrors closer together and 300 00:16:18,760 --> 00:16:22,160 Speaker 1: then further apart, and that's what you're actually measuring. Yeah, 301 00:16:22,200 --> 00:16:25,640 Speaker 1: it's like having a ruler a mine out of empty space, basically, right. 302 00:16:26,840 --> 00:16:29,960 Speaker 1: Instead of having a ruler that's a solid object, you 303 00:16:29,960 --> 00:16:32,080 Speaker 1: just look at space and how long it takes a 304 00:16:32,160 --> 00:16:35,920 Speaker 1: laser to go through a space and then back again, right, exactly. 305 00:16:35,960 --> 00:16:38,440 Speaker 1: It's the same reason that we can't measure the expansion 306 00:16:38,480 --> 00:16:42,280 Speaker 1: of space or notice the expansion of space very well locally. Right, 307 00:16:42,320 --> 00:16:44,560 Speaker 1: people talk about how space is expanding, Why am I 308 00:16:44,680 --> 00:16:47,400 Speaker 1: not expanding? Why is the Solar System not expanding? That's 309 00:16:47,440 --> 00:16:50,000 Speaker 1: because there are forces in play to hold you together. 310 00:16:50,240 --> 00:16:52,480 Speaker 1: The atoms in your body hold you together even though 311 00:16:52,520 --> 00:16:55,880 Speaker 1: space is expanding out from under you, and gravity holds 312 00:16:55,920 --> 00:16:58,640 Speaker 1: the Solar System together even though space is trying to 313 00:16:58,680 --> 00:17:01,360 Speaker 1: expand it out. And so in the same way, to 314 00:17:01,560 --> 00:17:05,160 Speaker 1: measure the ripples in space, you need something which isn't 315 00:17:05,160 --> 00:17:07,960 Speaker 1: being held at a fixed distance. So you need these 316 00:17:07,960 --> 00:17:10,440 Speaker 1: things just sort of separated at a certain known distance 317 00:17:10,480 --> 00:17:12,560 Speaker 1: and then bounce light back and forth and see if 318 00:17:12,600 --> 00:17:15,160 Speaker 1: the travel time of light changes. There's one more sort 319 00:17:15,160 --> 00:17:18,200 Speaker 1: of experimental wrinkle there, which is that the changes are 320 00:17:18,240 --> 00:17:21,080 Speaker 1: so small it's very difficult to measure, so they have 321 00:17:21,119 --> 00:17:24,240 Speaker 1: to actually send light beams both directions come back and 322 00:17:24,280 --> 00:17:26,840 Speaker 1: then measure the difference in those travel times by using 323 00:17:26,920 --> 00:17:31,880 Speaker 1: interference of those photons. So it's like really virtuoso experimental technique. 324 00:17:32,080 --> 00:17:34,680 Speaker 1: I remember visiting these labs in the late nineties when 325 00:17:34,680 --> 00:17:36,760 Speaker 1: I was thinking about going account tech for grad school, 326 00:17:36,760 --> 00:17:39,159 Speaker 1: for example, and thinking they're never going to get this 327 00:17:39,200 --> 00:17:41,480 Speaker 1: to work. Oh my god, this is impossible. But I 328 00:17:41,520 --> 00:17:44,920 Speaker 1: was very glad when ten years later I was proven wrong. Yeah, 329 00:17:44,960 --> 00:17:48,640 Speaker 1: they're amazing experiments. And so let's get into some questions 330 00:17:48,680 --> 00:17:51,440 Speaker 1: I have about this, like, for example, why doesn't light 331 00:17:51,720 --> 00:17:54,760 Speaker 1: also get stretched out over this space? And also doesn't 332 00:17:54,760 --> 00:17:57,800 Speaker 1: the Earth itself count as a fixed ruler? So let's 333 00:17:57,800 --> 00:18:01,440 Speaker 1: get the into this and also whether these gravitational waves 334 00:18:01,560 --> 00:18:04,200 Speaker 1: have a lasting impact on the universe. First, let's take 335 00:18:04,240 --> 00:18:20,160 Speaker 1: a quick break, right, we're making waves with gravitational waves. 336 00:18:20,480 --> 00:18:23,199 Speaker 1: Are there weirder than they we think they are? And 337 00:18:23,240 --> 00:18:25,840 Speaker 1: do they leave a lasting imprint on the universe? Do 338 00:18:25,920 --> 00:18:28,399 Speaker 1: they last forever? So we've talked a little bit about 339 00:18:28,400 --> 00:18:31,040 Speaker 1: what gravitational waves are and a little bit about how 340 00:18:31,080 --> 00:18:33,640 Speaker 1: we measure them. The super tricky thing because you want 341 00:18:33,680 --> 00:18:36,240 Speaker 1: to measure a house space itself, it's expanding, but here 342 00:18:36,240 --> 00:18:39,320 Speaker 1: on Earth things are kind of held together by other forces. 343 00:18:39,640 --> 00:18:41,879 Speaker 1: Like you said, you can't really measure the bending of 344 00:18:41,960 --> 00:18:44,400 Speaker 1: space with a fixed ruler, but it doesn't the Earth 345 00:18:44,440 --> 00:18:46,159 Speaker 1: also count as a fixed ruler. Like if I have 346 00:18:46,160 --> 00:18:48,680 Speaker 1: a mirror here on a mirror over there, aren't they 347 00:18:48,680 --> 00:18:51,359 Speaker 1: held together by the floor. Yeah, if you attach your 348 00:18:51,400 --> 00:18:54,320 Speaker 1: mirrors to the Earth, then it's basically just like building 349 00:18:54,440 --> 00:18:57,600 Speaker 1: a really long ruler. It'd be very difficult to measure 350 00:18:57,600 --> 00:19:01,600 Speaker 1: gravitational waves. So when they build their experiment lego, they're 351 00:19:01,560 --> 00:19:03,760 Speaker 1: trying to isolate those mirrors from anything around them. So 352 00:19:03,800 --> 00:19:06,399 Speaker 1: if the Earth moves or wiggles or shakes or anything happens, 353 00:19:06,400 --> 00:19:09,520 Speaker 1: it doesn't affect the location of the mirrors. But this 354 00:19:09,560 --> 00:19:13,280 Speaker 1: is one limitation of our experiments and why people are 355 00:19:13,320 --> 00:19:16,399 Speaker 1: hoping to build a new version that's actually out in 356 00:19:16,680 --> 00:19:20,000 Speaker 1: space that's free from all these effects of Earth's gravity 357 00:19:20,400 --> 00:19:23,440 Speaker 1: and Earth's bonds and all that kind of stuff. Yeah, 358 00:19:23,440 --> 00:19:26,800 Speaker 1: I was gonna say, like, isn't the perfect gratational detector 359 00:19:27,040 --> 00:19:30,120 Speaker 1: or something where it's floating in space, right, so one 360 00:19:30,240 --> 00:19:33,280 Speaker 1: end is not connected to the other end, Yes, exactly, 361 00:19:33,320 --> 00:19:35,239 Speaker 1: And they have a plan for that project, which they 362 00:19:35,240 --> 00:19:38,000 Speaker 1: hope is going to launch in about twenty thirty seven. 363 00:19:38,160 --> 00:19:42,520 Speaker 1: Three spacecraft out in space, millions of kilometers away from 364 00:19:42,520 --> 00:19:45,280 Speaker 1: each other, shooting lasers at each other to measure their 365 00:19:45,320 --> 00:19:49,000 Speaker 1: relative distances. It sounds like science fiction, but maybe one 366 00:19:49,040 --> 00:19:51,120 Speaker 1: day it will be true. Yeah, I mean, what could 367 00:19:51,119 --> 00:19:55,359 Speaker 1: go wrong? Spaceships and lasers. I mean that's the dream, 368 00:19:55,440 --> 00:20:01,000 Speaker 1: isn't it, fully operational spaceships exactly? That I need a 369 00:20:01,040 --> 00:20:05,000 Speaker 1: fully operational size experiment. Make sure the lasers are green. 370 00:20:05,280 --> 00:20:06,879 Speaker 1: I was just going to say the lasers would be 371 00:20:06,960 --> 00:20:08,960 Speaker 1: pretty faint so they wouldn't be damaging, But you know, 372 00:20:09,000 --> 00:20:11,480 Speaker 1: in order to see them millions of kilometers away, they're 373 00:20:11,520 --> 00:20:13,480 Speaker 1: actually going to have to be pretty bright. So I 374 00:20:13,480 --> 00:20:16,680 Speaker 1: hope nobody's eyeballs and gets in the path of those lasers. Yeah, 375 00:20:16,720 --> 00:20:19,680 Speaker 1: what could go wrong? Well, speaking of lasers, another question 376 00:20:19,720 --> 00:20:22,040 Speaker 1: I had was, when you're trying to measure this bending 377 00:20:22,040 --> 00:20:25,600 Speaker 1: of space using light, doesn't light also get bent by 378 00:20:26,119 --> 00:20:28,959 Speaker 1: the gravitational wave or the bending of space? Doesn't light 379 00:20:29,000 --> 00:20:30,480 Speaker 1: sort of in a way sort of speed up or 380 00:20:30,480 --> 00:20:34,840 Speaker 1: slow down? Yeah, super fascinating question and very confusing and 381 00:20:35,000 --> 00:20:37,639 Speaker 1: something that I struggle to get my mind around sometimes. 382 00:20:37,760 --> 00:20:41,360 Speaker 1: Because light is definitely affected by the curvature of space, right, 383 00:20:41,359 --> 00:20:44,440 Speaker 1: we know that light gets bent by masses. As it 384 00:20:44,440 --> 00:20:46,600 Speaker 1: goes by a huge blob of dark matter, for example, 385 00:20:46,640 --> 00:20:48,680 Speaker 1: it can get lens and that is how we see 386 00:20:48,680 --> 00:20:51,760 Speaker 1: the curvature space in the change of the direction of light. 387 00:20:51,840 --> 00:20:54,720 Speaker 1: But remember that nearby light always travels at the speed 388 00:20:54,760 --> 00:20:58,439 Speaker 1: of light, and that sort of defines what distance is. Actually. 389 00:20:58,440 --> 00:21:01,600 Speaker 1: Our definition of the meter now is like how far 390 00:21:01,720 --> 00:21:04,600 Speaker 1: light has traveled in a certain time slice. Because light 391 00:21:04,640 --> 00:21:07,200 Speaker 1: doesn't change its speed as space gets curved. It only 392 00:21:07,240 --> 00:21:09,840 Speaker 1: just changes its direction. It doesn't. Gravity also is kind 393 00:21:09,840 --> 00:21:12,639 Speaker 1: of affect time as well, right, Like if you're near 394 00:21:12,680 --> 00:21:16,080 Speaker 1: a black hole, time slows down, and you'd actually kind 395 00:21:16,080 --> 00:21:18,639 Speaker 1: of see light slowing down. You're absolutely right, there is 396 00:21:18,680 --> 00:21:22,359 Speaker 1: a gravitational time dilation effect. If you're in an area 397 00:21:22,400 --> 00:21:26,320 Speaker 1: with strong curvature, then clocks will run slower. So for example, 398 00:21:26,359 --> 00:21:28,480 Speaker 1: you're far away from a black hole and you're looking 399 00:21:28,520 --> 00:21:31,000 Speaker 1: at somebody who's holding a clock and they're near a 400 00:21:31,040 --> 00:21:35,520 Speaker 1: black hole, their time will slow down. Right. And also 401 00:21:36,040 --> 00:21:39,040 Speaker 1: if you are watching photons near a black hole, you 402 00:21:39,119 --> 00:21:41,360 Speaker 1: can see them going on all sorts of crazy speeds 403 00:21:41,400 --> 00:21:43,679 Speaker 1: because there's an ambiguity in how to even define the 404 00:21:43,760 --> 00:21:46,439 Speaker 1: velocity of things that are far away from you and 405 00:21:46,600 --> 00:21:49,240 Speaker 1: through some sort of space curvature. We talked about this 406 00:21:49,280 --> 00:21:52,040 Speaker 1: a few times on the podcast, that general relativity doesn't 407 00:21:52,040 --> 00:21:55,119 Speaker 1: even really allow you to define velocities of things that 408 00:21:55,119 --> 00:21:58,200 Speaker 1: are either very far away if the universe is expanding, 409 00:21:58,440 --> 00:22:02,040 Speaker 1: or through curved space, because there's sort of multiple ways 410 00:22:02,080 --> 00:22:05,240 Speaker 1: to bring that thing's velocity vector over to you to 411 00:22:05,320 --> 00:22:08,000 Speaker 1: measure its velocity. But here we're talking about like very 412 00:22:08,040 --> 00:22:12,080 Speaker 1: small deviations in space and very local deviations in space, 413 00:22:12,359 --> 00:22:14,439 Speaker 1: and so from our point of view, we don't expect 414 00:22:14,440 --> 00:22:17,680 Speaker 1: it to affect the speed of photons. Well, I'm sure 415 00:22:17,720 --> 00:22:19,360 Speaker 1: it all works out in the math, but I think 416 00:22:19,359 --> 00:22:22,040 Speaker 1: the point is that when you're using lasers to measure 417 00:22:22,040 --> 00:22:26,119 Speaker 1: these distances, as a gravitational wave is passing by, the 418 00:22:26,160 --> 00:22:28,159 Speaker 1: speed of light sort of remains the same, so you 419 00:22:28,160 --> 00:22:31,840 Speaker 1: can sort of measure the length of space change exactly. 420 00:22:31,840 --> 00:22:35,600 Speaker 1: And that's really what we're talking about here, is relative distances. 421 00:22:35,960 --> 00:22:38,440 Speaker 1: You know, when we talk about spatial curvature, we don't 422 00:22:38,520 --> 00:22:43,120 Speaker 1: mean curvature with respect to some external ruler, like your 423 00:22:43,160 --> 00:22:46,639 Speaker 1: mental picture is probably that misleading bowling ball in a 424 00:22:46,760 --> 00:22:50,359 Speaker 1: rubber sheet analogy where a mass is bending space into 425 00:22:50,440 --> 00:22:53,040 Speaker 1: some other dimension. Right where we have a two dimensional 426 00:22:53,119 --> 00:22:56,280 Speaker 1: universe and the mass is bending it in some third dimension. 427 00:22:56,760 --> 00:22:59,920 Speaker 1: Our bending of space that we talk about is intrinsic. 428 00:23:00,280 --> 00:23:04,040 Speaker 1: It's just a changing of relative distances between things. So 429 00:23:04,119 --> 00:23:07,040 Speaker 1: with space is curved between two points, that just means 430 00:23:07,160 --> 00:23:09,920 Speaker 1: that those two points are now closer together. And that's 431 00:23:09,920 --> 00:23:12,320 Speaker 1: exactly what we're measuring by sending a beam of light 432 00:23:12,359 --> 00:23:14,400 Speaker 1: through and saying, oh, how long does it take light 433 00:23:14,440 --> 00:23:18,040 Speaker 1: to get through or measuring that relative distance. Well, it's 434 00:23:18,040 --> 00:23:22,159 Speaker 1: super tricky, but humans and namely engineers have done it. 435 00:23:22,240 --> 00:23:25,800 Speaker 1: They've measured gravitational ways that come from these crazy events 436 00:23:25,800 --> 00:23:28,040 Speaker 1: out there in the universe, like two black holes circling 437 00:23:28,080 --> 00:23:30,000 Speaker 1: each other in a death spiral, and so you can 438 00:23:30,080 --> 00:23:33,280 Speaker 1: capture the moments right before these things are spinning super 439 00:23:33,320 --> 00:23:35,520 Speaker 1: fast and crashing into each other. And so that's the 440 00:23:35,640 --> 00:23:39,320 Speaker 1: kind of event in the universe that makes big gravitational ways, 441 00:23:39,400 --> 00:23:42,840 Speaker 1: maybe the biggest events that we know about. But then 442 00:23:42,840 --> 00:23:45,359 Speaker 1: the question is, like what happens to gravitational ways? Do 443 00:23:45,400 --> 00:23:48,800 Speaker 1: they keep rippling out there forever, or do they get 444 00:23:48,840 --> 00:23:52,000 Speaker 1: absorbed by things as they move through the universe? Right, 445 00:23:52,040 --> 00:23:55,000 Speaker 1: And your naive picture is probably thinking about like an 446 00:23:55,040 --> 00:23:58,840 Speaker 1: antenna broadcasting a radio signal just sort of propagates out 447 00:23:58,840 --> 00:24:02,040 Speaker 1: through space. Asking a radio signal that's sort of shortened time, 448 00:24:02,119 --> 00:24:05,200 Speaker 1: like a shout, like a hello, you know in your Hello, 449 00:24:05,320 --> 00:24:08,000 Speaker 1: broadcasts out through space and it passes through space and 450 00:24:08,000 --> 00:24:10,480 Speaker 1: then it fades, and once it's gone, you can't really 451 00:24:10,520 --> 00:24:13,320 Speaker 1: detect that it was there anymore. That's sort of probably 452 00:24:13,320 --> 00:24:16,600 Speaker 1: your mental image for a gravitational wave. It creates a 453 00:24:16,720 --> 00:24:19,320 Speaker 1: ripple in space as the black holes in spiral and 454 00:24:19,359 --> 00:24:22,160 Speaker 1: then collide, and then that ripple passes through the universe. 455 00:24:22,200 --> 00:24:25,680 Speaker 1: Maybe it's detected by clever humans and aliens on its path, 456 00:24:25,880 --> 00:24:29,440 Speaker 1: and then it just passes by them and leave space unchanged. 457 00:24:29,640 --> 00:24:31,439 Speaker 1: But I guess I have a question though. Don't do 458 00:24:31,520 --> 00:24:34,760 Speaker 1: gravitational waves they hit something, they just passed through, they 459 00:24:34,800 --> 00:24:37,919 Speaker 1: never get absorbed or even as I asked earlier, bounce 460 00:24:38,280 --> 00:24:41,159 Speaker 1: Now they absolutely do get absorbed, and they can do 461 00:24:41,200 --> 00:24:44,480 Speaker 1: complicated things like reflect and bounce. I think we talked 462 00:24:44,520 --> 00:24:47,840 Speaker 1: about that once when we were talking about gravitational waves 463 00:24:47,880 --> 00:24:51,240 Speaker 1: passing around black holes, they can get lensed, for example, 464 00:24:51,520 --> 00:24:54,120 Speaker 1: by black holes, and so there's all sorts of interesting 465 00:24:54,160 --> 00:24:57,280 Speaker 1: wave effects. But as you say, they can also get absorbed. 466 00:24:57,560 --> 00:25:00,880 Speaker 1: Like what happens when the gravitational wave wave passes through 467 00:25:00,880 --> 00:25:03,760 Speaker 1: the Earth is that it's squeezing the Earth a little bit, 468 00:25:03,920 --> 00:25:06,360 Speaker 1: and then it's squeezing at the other direction, and that 469 00:25:06,400 --> 00:25:09,440 Speaker 1: does take some energy, and so it's depositing a little 470 00:25:09,440 --> 00:25:11,760 Speaker 1: bit of energy, is actually heating up the Earth a 471 00:25:11,840 --> 00:25:14,960 Speaker 1: little bit. It's like a little tidal squeeze. So that 472 00:25:15,040 --> 00:25:18,080 Speaker 1: helps the gravitational wave fade. Right. First of all, it's 473 00:25:18,080 --> 00:25:21,159 Speaker 1: fading because distances are increasing. It's spreading out through a 474 00:25:21,240 --> 00:25:23,239 Speaker 1: larger and larger distance, and so it goes like one 475 00:25:23,280 --> 00:25:26,560 Speaker 1: over distance squared. But also when it passes through matter, 476 00:25:26,800 --> 00:25:29,040 Speaker 1: it does deposit a little bit of its energy into 477 00:25:29,080 --> 00:25:31,880 Speaker 1: that matter. Yeah, and the universe is full of matter, right, 478 00:25:32,000 --> 00:25:36,040 Speaker 1: I mean not a huge amount, but like in the viewer, 479 00:25:36,080 --> 00:25:38,520 Speaker 1: to emit a gravitation wave in the middle of the 480 00:25:38,560 --> 00:25:40,560 Speaker 1: Milky wave, for example, it would have to go through 481 00:25:41,000 --> 00:25:43,480 Speaker 1: all of those stars in the milky wave before it 482 00:25:43,520 --> 00:25:45,200 Speaker 1: can go out to the rest of the universe. Yeah, 483 00:25:45,200 --> 00:25:47,840 Speaker 1: that's absolutely true. But now think about a simpler scenario. 484 00:25:47,880 --> 00:25:51,240 Speaker 1: Imagine you just have like two particles floating freely in space, 485 00:25:51,600 --> 00:25:54,800 Speaker 1: and they're exactly one light second apart. A gravitational wave 486 00:25:54,840 --> 00:25:57,000 Speaker 1: passes through and it sort of brings them closer together 487 00:25:57,080 --> 00:26:00,399 Speaker 1: and then further apart again when the gravitational wave is done, 488 00:26:00,680 --> 00:26:03,040 Speaker 1: because it leave them as the same distance as they 489 00:26:03,040 --> 00:26:06,520 Speaker 1: were originally, or is there some sort of permanent distortion there? 490 00:26:06,760 --> 00:26:10,480 Speaker 1: That's the question, M, Because I guess that gravitational wave 491 00:26:10,560 --> 00:26:14,800 Speaker 1: isn't just like something that stretches space. It kind of 492 00:26:14,960 --> 00:26:17,879 Speaker 1: contracts and stretches space. Right, that's kind of what a 493 00:26:17,920 --> 00:26:20,840 Speaker 1: wave is. It's like it's an upend adet M. Absolutely 494 00:26:20,840 --> 00:26:23,480 Speaker 1: it is, and gravity is really complicated stuff. It's much 495 00:26:23,520 --> 00:26:29,960 Speaker 1: more complicated than electromagnetism, for example, because it interacts with itself. Right, 496 00:26:30,000 --> 00:26:32,480 Speaker 1: you send a photon out through space, that photon flies 497 00:26:32,480 --> 00:26:35,359 Speaker 1: through space. It's a ripple in the electromagnetic field. But 498 00:26:35,440 --> 00:26:39,159 Speaker 1: photons don't talk to other photons and don't create other photons. 499 00:26:39,600 --> 00:26:41,960 Speaker 1: Like two photons, as we talked about on the podcast once, 500 00:26:42,119 --> 00:26:44,600 Speaker 1: don't directly interact with each other. They can do it 501 00:26:44,640 --> 00:26:49,119 Speaker 1: indirectly via other virtual particles. But photons themselves don't bounce 502 00:26:49,160 --> 00:26:52,800 Speaker 1: off other photons. That's not true for gravity. Everything that 503 00:26:52,840 --> 00:26:56,920 Speaker 1: has mass or energy creates gravity and influences everything else 504 00:26:56,960 --> 00:27:00,640 Speaker 1: with mass and energy. And gravitational waves have energy, which 505 00:27:00,640 --> 00:27:05,359 Speaker 1: means they create gravitational waves, and then those create gravitational waves, 506 00:27:05,400 --> 00:27:07,880 Speaker 1: and those create gravitational waves. So you have this sort 507 00:27:07,880 --> 00:27:12,000 Speaker 1: of like nonlinear effect where gravitational waves are constantly spewing 508 00:27:12,040 --> 00:27:15,399 Speaker 1: off other gravitational waves. Yeah, so it sounds like gravitational 509 00:27:15,440 --> 00:27:19,479 Speaker 1: waves do sort of leave a pretty obvious lasting impact 510 00:27:19,480 --> 00:27:22,359 Speaker 1: on things, right, Like if a gravitational wave was big 511 00:27:22,359 --> 00:27:24,000 Speaker 1: and then went through Earth, and like you said, it 512 00:27:24,160 --> 00:27:26,440 Speaker 1: squeeze Earth in one direction and then stretch it in 513 00:27:26,480 --> 00:27:30,080 Speaker 1: the other direction, and then the vice versa and in 514 00:27:31,080 --> 00:27:33,440 Speaker 1: went through, which does heat up the Earth a little bit, 515 00:27:33,680 --> 00:27:35,919 Speaker 1: which lasts for a while at least, right, Like, it 516 00:27:35,920 --> 00:27:38,600 Speaker 1: depots some energy and we keep that energy and you 517 00:27:38,600 --> 00:27:41,480 Speaker 1: can measure that energy. Yeah, that's certainly true. And there's 518 00:27:41,520 --> 00:27:44,320 Speaker 1: this other effect even for isolated stuff, you know, even 519 00:27:44,359 --> 00:27:47,840 Speaker 1: for two particles floating out in space, there's something called 520 00:27:47,840 --> 00:27:51,800 Speaker 1: the gravitational wave memory effect. It's like it changes space 521 00:27:51,880 --> 00:27:55,720 Speaker 1: as it passes through and leaves it changed. Right, those 522 00:27:55,720 --> 00:27:58,800 Speaker 1: two particles floating out in space, when they get wiggled together, 523 00:27:58,920 --> 00:28:01,560 Speaker 1: there's no energy deposit like when the Earth gets squeezed, 524 00:28:01,680 --> 00:28:04,320 Speaker 1: because there's no like bond between these two particles floating 525 00:28:04,320 --> 00:28:07,800 Speaker 1: out in space, and yet still there's a permanent effect 526 00:28:07,840 --> 00:28:10,600 Speaker 1: on those particles. This again, is called the gravitational wave 527 00:28:10,720 --> 00:28:13,760 Speaker 1: memory effect. It's like footprints in the sand. Once the 528 00:28:13,800 --> 00:28:19,280 Speaker 1: gravitational wave passes through, it changes things even after it's gone. Wait, wait, wait, 529 00:28:19,280 --> 00:28:23,120 Speaker 1: what's it called again? The gravitational wave memory effect? Okay, sorry, 530 00:28:23,119 --> 00:28:26,719 Speaker 1: I'd for gone for a second. I walked right into that. 531 00:28:28,280 --> 00:28:33,320 Speaker 1: It's called the podcaster or dementia effect. Well, I think, 532 00:28:33,359 --> 00:28:35,640 Speaker 1: I think what you're saying is that we know that 533 00:28:35,680 --> 00:28:40,040 Speaker 1: the gravitational ways leave an impact in stuff around the universe, right, 534 00:28:40,080 --> 00:28:42,840 Speaker 1: Like if it goes through stuff, it leaves a little 535 00:28:42,840 --> 00:28:44,960 Speaker 1: bit of energy because it had to squeeze it and 536 00:28:45,040 --> 00:28:47,400 Speaker 1: stretch it. But now I think maybe the question we're 537 00:28:47,440 --> 00:28:50,640 Speaker 1: really asking in this podcast is to gravitational waves leave 538 00:28:50,680 --> 00:28:54,680 Speaker 1: an imprint on like space itself, Like the space itself 539 00:28:54,760 --> 00:28:59,240 Speaker 1: gets scarred or marred or you know, imprinted by the 540 00:28:59,560 --> 00:29:02,160 Speaker 1: gravitation wave. You make it sound so negative, like it's 541 00:29:02,200 --> 00:29:06,680 Speaker 1: been vandalized by gravitational waves or something like it's been ruined, Like, man, 542 00:29:06,800 --> 00:29:10,840 Speaker 1: I'd built this space and then those crazy teenagers marred it. Well, 543 00:29:10,880 --> 00:29:14,320 Speaker 1: I mean space is so pristine and beautiful. Yeah, for 544 00:29:14,440 --> 00:29:16,520 Speaker 1: a bunch of ripples in it. You are kind of 545 00:29:16,760 --> 00:29:19,160 Speaker 1: changing the esthetics. Yeah, but you know space is also 546 00:29:19,240 --> 00:29:22,280 Speaker 1: filled with gravitation a wave. So the space we started 547 00:29:22,280 --> 00:29:25,200 Speaker 1: with has already been imprinted on by all the gravitational 548 00:29:25,240 --> 00:29:28,600 Speaker 1: waves that came before us. Okay, so then the question 549 00:29:28,600 --> 00:29:31,479 Speaker 1: we're really asking is do gravitational waves leave a lasting 550 00:29:31,480 --> 00:29:34,640 Speaker 1: imprint on space itself? And you're saying the scenario we 551 00:29:34,640 --> 00:29:38,080 Speaker 1: should be imagining is like two particles out there in space, 552 00:29:38,200 --> 00:29:41,160 Speaker 1: floating at a certain distance from each other, and they 553 00:29:41,240 --> 00:29:44,200 Speaker 1: don't interact any other way at all, Like there's no 554 00:29:44,640 --> 00:29:48,600 Speaker 1: electromagnetic forces between them, there's I mean there's gravity. Can 555 00:29:48,640 --> 00:29:51,000 Speaker 1: they have gravity between them? Well, they're far enough apart 556 00:29:51,040 --> 00:29:54,320 Speaker 1: that there is essentially no gravity. Yeah, okay, essentially no gravity, 557 00:29:54,360 --> 00:29:56,800 Speaker 1: but no weak force and a strong force. They're just 558 00:29:56,880 --> 00:29:59,920 Speaker 1: like two lonely particles out there in space. And then 559 00:30:00,400 --> 00:30:05,280 Speaker 1: gravitational waves comes through, does it change the space between 560 00:30:05,320 --> 00:30:07,480 Speaker 1: them permanently in a way that you could be like, hey, 561 00:30:07,560 --> 00:30:11,600 Speaker 1: something came through here. Yeah, really fun question. And in 562 00:30:11,640 --> 00:30:14,360 Speaker 1: the seventies, people who were playing with the equations of 563 00:30:14,440 --> 00:30:19,280 Speaker 1: general relativity and doing calculations discovered to their surprise that 564 00:30:19,400 --> 00:30:23,240 Speaker 1: it should. This is fun because it's like a theoretical surprise. 565 00:30:23,640 --> 00:30:26,840 Speaker 1: You know, we have equations for Einstein's general relativity, but 566 00:30:26,880 --> 00:30:30,080 Speaker 1: we don't always know the consequences of them. Sometimes when 567 00:30:30,080 --> 00:30:32,120 Speaker 1: you sit down and say what would happen in this scenario, 568 00:30:32,560 --> 00:30:36,080 Speaker 1: you run into something unexpected because to understand the effects 569 00:30:36,120 --> 00:30:38,200 Speaker 1: on the universe of these equations you have to do 570 00:30:38,240 --> 00:30:40,280 Speaker 1: some calculations. You have to set it up and say, 571 00:30:40,400 --> 00:30:42,480 Speaker 1: I'll let me see if I can predict this scenario. 572 00:30:42,720 --> 00:30:45,239 Speaker 1: And so this was discovered in the seventies, and then 573 00:30:45,480 --> 00:30:47,240 Speaker 1: a lot of progress has been made in the last 574 00:30:47,280 --> 00:30:50,600 Speaker 1: few decades. But all sorts of various different kinds of 575 00:30:50,720 --> 00:30:56,200 Speaker 1: memory effects. What's it call again, I forgot I have 576 00:30:56,240 --> 00:31:00,200 Speaker 1: a memorable name. Fool me once. This effect as a 577 00:31:00,320 --> 00:31:03,360 Speaker 1: name is called the effect, and so it's a thing. 578 00:31:03,360 --> 00:31:06,160 Speaker 1: It's like a theoretical thing that says that space does 579 00:31:06,240 --> 00:31:09,720 Speaker 1: get kind of altered permanently when a gravitation wave moves 580 00:31:09,760 --> 00:31:11,240 Speaker 1: through And so how does that work, How does it 581 00:31:11,280 --> 00:31:13,280 Speaker 1: effect work? How does it come up in the equations. 582 00:31:13,400 --> 00:31:16,160 Speaker 1: So there's actually a few different effects. There's a nonlinear 583 00:31:16,200 --> 00:31:18,400 Speaker 1: worm and the linear one. I think the most interesting 584 00:31:18,400 --> 00:31:21,880 Speaker 1: and least confusing to understand is the nonlinear effect. And 585 00:31:22,000 --> 00:31:24,560 Speaker 1: this comes up because gravity, as I was saying before, 586 00:31:24,800 --> 00:31:29,600 Speaker 1: couples to itself, like gravity creates more gravity, whereas photons 587 00:31:29,640 --> 00:31:34,280 Speaker 1: don't create more photons. Gravitational waves generate gravitational waves as 588 00:31:34,320 --> 00:31:37,360 Speaker 1: they pass through space, and so this creates a sort 589 00:31:37,400 --> 00:31:41,000 Speaker 1: of like nonlinear effect because the energy doesn't just fly 590 00:31:41,160 --> 00:31:43,920 Speaker 1: through the universe. It's sort of like deposits itself in 591 00:31:44,000 --> 00:31:47,160 Speaker 1: space itself as it goes along. It creates these little 592 00:31:47,200 --> 00:31:51,320 Speaker 1: mini gravitational waves that change space. Wait what as it 593 00:31:51,360 --> 00:31:54,280 Speaker 1: goes through stuff or even in empty space, even in 594 00:31:54,400 --> 00:31:58,720 Speaker 1: empty space, right. Gravitational waves themselves contain energy, and so 595 00:31:58,880 --> 00:32:01,920 Speaker 1: part of their energy goes into making other gravitational ways 596 00:32:01,960 --> 00:32:04,160 Speaker 1: as it goes along. Yeah, exactly, And so that's one 597 00:32:04,200 --> 00:32:06,480 Speaker 1: of the ways that they fade. And so if you 598 00:32:06,520 --> 00:32:08,880 Speaker 1: look at like the prediction for what should happen to 599 00:32:09,200 --> 00:32:12,520 Speaker 1: two particles as a gravitational wave passes through them. A 600 00:32:12,600 --> 00:32:15,720 Speaker 1: sort of canonical prediction you're familiar with from like Lego, etc. 601 00:32:16,360 --> 00:32:18,400 Speaker 1: Is that they get further and closer and further and closer, 602 00:32:18,480 --> 00:32:20,880 Speaker 1: and then they get back to their original location. If 603 00:32:20,920 --> 00:32:23,720 Speaker 1: you conclude all these effects of like gravitational waves generating 604 00:32:23,760 --> 00:32:26,520 Speaker 1: more gravitational waves, you see that they don't come back 605 00:32:26,520 --> 00:32:29,800 Speaker 1: to where they started. That there's a lasting effect on 606 00:32:30,040 --> 00:32:33,560 Speaker 1: the distance between these two particles, which basically means space 607 00:32:33,600 --> 00:32:38,280 Speaker 1: itself has been stretched permanently. Oh. Interesting, But I guess 608 00:32:38,280 --> 00:32:40,200 Speaker 1: the picture you're painting for us here is that the 609 00:32:40,240 --> 00:32:42,880 Speaker 1: gravitation away generates more ways. But then don't those ways 610 00:32:42,920 --> 00:32:46,160 Speaker 1: also fade away eventually? Where does the permanence come from? 611 00:32:46,280 --> 00:32:49,280 Speaker 1: The permanence comes from this nonlinearity. Right, they're fading, but 612 00:32:49,320 --> 00:32:53,280 Speaker 1: they're also generating new gravitational waves and generating new gravitational waves. 613 00:32:53,320 --> 00:32:55,840 Speaker 1: But each time it's smaller, isn't it? Each time it's smaller? 614 00:32:55,880 --> 00:32:58,080 Speaker 1: But you know, it's an infinite series. An infinite series. 615 00:32:58,120 --> 00:33:00,680 Speaker 1: Sometimes they'd diver, sometimes they go to zero row. In 616 00:33:00,680 --> 00:33:03,000 Speaker 1: this case, they add up to a constant. They add 617 00:33:03,040 --> 00:33:05,720 Speaker 1: up to a non zero value. Oh, I see it's 618 00:33:05,760 --> 00:33:08,080 Speaker 1: it's sort of like a permanent echo. Like if you're 619 00:33:08,680 --> 00:33:13,000 Speaker 1: in a close room and you say hello, hello, Hello, helloooo, 620 00:33:13,880 --> 00:33:16,880 Speaker 1: that hello never kind of goes away and it stays 621 00:33:16,920 --> 00:33:20,040 Speaker 1: where the gravitation wave went through. So it's sort of 622 00:33:20,040 --> 00:33:23,719 Speaker 1: like it it leaves a permanent echo wherever it goes. Yeah, exactly, 623 00:33:23,760 --> 00:33:26,000 Speaker 1: It's just like a permanent echo. And so that's really 624 00:33:26,080 --> 00:33:29,760 Speaker 1: kind of interesting because it's suggests that gravitational radiation is 625 00:33:29,800 --> 00:33:34,480 Speaker 1: fundamentally different from other kinds of radiation, right, It's not 626 00:33:34,640 --> 00:33:38,080 Speaker 1: as capable of transmitting energy because, as you say, it 627 00:33:38,080 --> 00:33:41,840 Speaker 1: deposits some of that in space as it goes along. Interesting, 628 00:33:41,920 --> 00:33:44,880 Speaker 1: So then that's what it does do space? And where 629 00:33:44,880 --> 00:33:47,000 Speaker 1: do there are two literal lonely particles come in? How 630 00:33:47,040 --> 00:33:49,760 Speaker 1: do those two particles notice that space space is now 631 00:33:49,760 --> 00:33:54,080 Speaker 1: full of gravitational echo because they don't go back to 632 00:33:54,120 --> 00:33:57,200 Speaker 1: their original distance. If they started out one light second 633 00:33:57,200 --> 00:34:00,360 Speaker 1: apart before the gravitation the wave has passed through, then 634 00:34:00,400 --> 00:34:02,480 Speaker 1: they wiggled out and in and out and in a 635 00:34:02,480 --> 00:34:05,280 Speaker 1: little bit. But when the gravitational wave has passed, they're 636 00:34:05,280 --> 00:34:08,400 Speaker 1: now like one point zero zero one light seconds apart, 637 00:34:08,560 --> 00:34:11,279 Speaker 1: whereas they used to be one light second apart. So 638 00:34:11,400 --> 00:34:14,720 Speaker 1: you can measure this, you can say, my gravitational waves 639 00:34:14,719 --> 00:34:18,520 Speaker 1: passed by, yet my particles are still further apart than 640 00:34:18,560 --> 00:34:22,280 Speaker 1: when they started. M We mean like the premanent echo 641 00:34:22,360 --> 00:34:26,480 Speaker 1: the lingers after the wave goes through actually results in 642 00:34:26,560 --> 00:34:29,279 Speaker 1: kind of stretching space between them exactly. And that's what 643 00:34:29,400 --> 00:34:33,080 Speaker 1: gravity is, right, is the stretching or its compression of space. 644 00:34:33,640 --> 00:34:36,440 Speaker 1: And so it's like made more space. It's like deposits 645 00:34:36,480 --> 00:34:40,759 Speaker 1: some of that energy into creating new space between these 646 00:34:40,800 --> 00:34:43,920 Speaker 1: two test particles, a very very tiny amount. Remember, gravitational 647 00:34:43,920 --> 00:34:46,920 Speaker 1: wave effects are very very subtle, which is why they 648 00:34:46,960 --> 00:34:50,680 Speaker 1: are so hard to see. The original experiment, Lego had 649 00:34:50,680 --> 00:34:53,799 Speaker 1: these arms where the mirrors were like kilometers apart, and 650 00:34:53,840 --> 00:34:56,680 Speaker 1: they saw the distance between those mirrors changed by one 651 00:34:56,800 --> 00:35:00,080 Speaker 1: one thousands of the width of a proton. Right, these 652 00:35:00,120 --> 00:35:03,760 Speaker 1: are really really tiny effects, and the gravitational wave memory 653 00:35:03,760 --> 00:35:08,560 Speaker 1: effect is even smaller than the gravitational wave effect itself. 654 00:35:08,640 --> 00:35:13,320 Speaker 1: Wait wait, wait, what's the gravitational memory effect? I forgot again. 655 00:35:13,920 --> 00:35:16,480 Speaker 1: I'm just kidding. So, like if you measured how far 656 00:35:16,600 --> 00:35:20,719 Speaker 1: these two lonely particles were before out in space, and 657 00:35:20,760 --> 00:35:23,880 Speaker 1: then what gravitational wave went through, and then you measured 658 00:35:23,920 --> 00:35:25,959 Speaker 1: it again, you would measure them to be a little 659 00:35:25,960 --> 00:35:28,600 Speaker 1: bit further apart than before. Exactly if there was nothing 660 00:35:28,640 --> 00:35:32,080 Speaker 1: else influencing them, no gravity, no bonds, nothing else but 661 00:35:32,280 --> 00:35:35,520 Speaker 1: just the shape of space, then yes, they would permanently 662 00:35:35,600 --> 00:35:38,640 Speaker 1: be further apart than when they started, even long after 663 00:35:38,760 --> 00:35:41,920 Speaker 1: the gravitational wave has passed through them. And it's like 664 00:35:41,960 --> 00:35:46,080 Speaker 1: a positive stretching effect. It's not a compression effect, right, 665 00:35:46,280 --> 00:35:51,520 Speaker 1: It's a positive stretching effect. It deposits energy, creates new space. Interesting, 666 00:35:51,520 --> 00:35:53,880 Speaker 1: and this is happening all over the universe. So are 667 00:35:53,880 --> 00:35:57,600 Speaker 1: you saying gravitational waves like black holes crashing into each other, 668 00:35:58,080 --> 00:36:00,719 Speaker 1: they're part of the reason the universe is banding? Or 669 00:36:00,760 --> 00:36:03,960 Speaker 1: does it contract in some places and expands in other places? Right? 670 00:36:04,000 --> 00:36:08,680 Speaker 1: Like when the gravitational waves get generated, does it compress space? Oh, 671 00:36:08,719 --> 00:36:12,200 Speaker 1: that's a really interesting question. Whether it overall, like integrated 672 00:36:12,239 --> 00:36:16,040 Speaker 1: overall of space, contributes to the expansion of space or 673 00:36:16,040 --> 00:36:19,000 Speaker 1: whether it cancels out somewhere. I'm not one hundred percent 674 00:36:19,000 --> 00:36:20,480 Speaker 1: sure of the answer, but I think that this is 675 00:36:20,520 --> 00:36:24,160 Speaker 1: only a positive contribution to the shape of space. And again, 676 00:36:24,200 --> 00:36:27,680 Speaker 1: this is really a tiny effect almost impossible to measure 677 00:36:28,120 --> 00:36:30,680 Speaker 1: much much smaller than the expansion of space due to 678 00:36:30,760 --> 00:36:34,000 Speaker 1: dark energy, But I think it would technically contribute to 679 00:36:34,040 --> 00:36:36,319 Speaker 1: the expansion of space. Yes, that if you had like 680 00:36:36,360 --> 00:36:39,360 Speaker 1: a universe where nothing was moving, so no gravitational waves 681 00:36:39,360 --> 00:36:43,200 Speaker 1: were created, versus a universe where things were swashing around 682 00:36:43,200 --> 00:36:46,399 Speaker 1: and gravitational waves would being made, that second one would 683 00:36:46,440 --> 00:36:49,160 Speaker 1: be expanding faster than the first one. Well, I wonder 684 00:36:49,200 --> 00:36:51,759 Speaker 1: if maybe it like does that energy has to sort 685 00:36:51,760 --> 00:36:54,880 Speaker 1: of come from somewhere, right, like when the black holes 686 00:36:54,920 --> 00:36:57,120 Speaker 1: get formed when they swirl around each other. I wonder 687 00:36:57,120 --> 00:36:59,360 Speaker 1: if that has an effect to shrink the local space. 688 00:36:59,400 --> 00:37:01,480 Speaker 1: But then it's strudges everything else out. You know what. 689 00:37:01,560 --> 00:37:04,560 Speaker 1: The energy, remember, comes from the masses of the objects 690 00:37:04,600 --> 00:37:07,880 Speaker 1: that generated. When two black holes merge, you have like 691 00:37:07,960 --> 00:37:10,160 Speaker 1: one of them is fifty solar masses and other is 692 00:37:10,200 --> 00:37:12,920 Speaker 1: fifty solar masses. The black hole that they result in 693 00:37:13,200 --> 00:37:16,120 Speaker 1: is not a hundred solar masses, it's like eighty because 694 00:37:16,120 --> 00:37:20,360 Speaker 1: they've generated an incredible amount of gravitational radiation, like twenty 695 00:37:20,480 --> 00:37:23,640 Speaker 1: solar masses worth. So that's where the energy comes from. 696 00:37:23,680 --> 00:37:25,760 Speaker 1: All right, Well, let's get into how you might measure 697 00:37:25,880 --> 00:37:29,000 Speaker 1: this interesting effect and also what it all means about 698 00:37:29,000 --> 00:37:32,560 Speaker 1: our understanding of gravity and the universe. But first, let's 699 00:37:32,560 --> 00:37:48,400 Speaker 1: take another quick break. All right, we're talking about what 700 00:37:48,600 --> 00:37:50,959 Speaker 1: was it we're talking about, Daniel, We're talking about moving 701 00:37:51,000 --> 00:37:56,040 Speaker 1: you to retirement homes. We're talking about the memory effect 702 00:37:56,040 --> 00:37:59,680 Speaker 1: of gravitational waves. This idea that gravitational waves, as they 703 00:38:00,080 --> 00:38:03,000 Speaker 1: propagate through the universe, they have a lasting effect on 704 00:38:03,080 --> 00:38:08,279 Speaker 1: space itself. It's stretching space, depositing little, tiny and everlasting 705 00:38:08,360 --> 00:38:12,240 Speaker 1: echoes of gravitational energy which stretch space and make it bigger. 706 00:38:12,400 --> 00:38:14,880 Speaker 1: And so you're saying, Daniel, this effect is super duper 707 00:38:14,960 --> 00:38:17,640 Speaker 1: duper small. How can we even measure this? Can we 708 00:38:17,680 --> 00:38:19,640 Speaker 1: prove that this theory is right? So it is a 709 00:38:19,680 --> 00:38:23,239 Speaker 1: theory currently. It's a consequence of general relativity, and one 710 00:38:23,280 --> 00:38:25,640 Speaker 1: we've seen in the math, but we've never actually seen 711 00:38:25,680 --> 00:38:29,680 Speaker 1: it out there in the universe. Gravitational waves we have seen. 712 00:38:29,760 --> 00:38:32,920 Speaker 1: We know those are real. But this gravitational memory effect 713 00:38:32,920 --> 00:38:35,120 Speaker 1: that we keep forgetting what it's called this part has 714 00:38:35,200 --> 00:38:38,680 Speaker 1: not yet been seen. It's a theoretical prediction. And remember 715 00:38:38,719 --> 00:38:42,239 Speaker 1: that we have great confidence in general relativity because it's 716 00:38:42,239 --> 00:38:45,240 Speaker 1: been such a virtuoso description of how the universe works 717 00:38:45,239 --> 00:38:48,400 Speaker 1: and the nature of space itself. But we also think 718 00:38:48,480 --> 00:38:51,720 Speaker 1: that it's probably flawed because it can't describe the quantum 719 00:38:51,719 --> 00:38:54,960 Speaker 1: mechanical nature or the universe. So not everything that general 720 00:38:54,960 --> 00:38:57,920 Speaker 1: relativity predicts is guaranteed to be true, which is one 721 00:38:57,920 --> 00:38:59,560 Speaker 1: reason why we want to go out and test this. 722 00:38:59,680 --> 00:39:03,120 Speaker 1: But it's also much much smaller effect than gravitational waves. 723 00:39:03,320 --> 00:39:06,719 Speaker 1: It's predicted to be like twenty to fifty times smaller 724 00:39:07,080 --> 00:39:10,399 Speaker 1: than current gravitational waves effects we have measured. We don't 725 00:39:10,400 --> 00:39:12,920 Speaker 1: think that our current experiments like LEGO are going to 726 00:39:12,960 --> 00:39:16,880 Speaker 1: be capable of seeing this very easily, right, because, like 727 00:39:16,920 --> 00:39:20,000 Speaker 1: we talked about before, Ligo is a ruler which is 728 00:39:20,040 --> 00:39:22,360 Speaker 1: sort of attached to itself. It is a solid ruler 729 00:39:22,400 --> 00:39:24,719 Speaker 1: in a way. Right. Lego does a really good job 730 00:39:24,760 --> 00:39:27,080 Speaker 1: of trying to be independent from the Earth as much 731 00:39:27,080 --> 00:39:29,479 Speaker 1: as possible, But this is something that the Earth has 732 00:39:29,520 --> 00:39:33,759 Speaker 1: that Lego just cannot escape, and that's the Earth's gravity. Right. 733 00:39:33,840 --> 00:39:36,560 Speaker 1: We have these two mirrors where light is bouncing back 734 00:39:36,600 --> 00:39:39,080 Speaker 1: and forth between them. Imagine they're getting like squeezed a 735 00:39:39,120 --> 00:39:41,640 Speaker 1: little bit closer together or a little bit further apart. 736 00:39:41,800 --> 00:39:44,359 Speaker 1: And even if the gravitational wave wants to pass through 737 00:39:44,360 --> 00:39:46,840 Speaker 1: and leave them a little bit further apart. The Earth's 738 00:39:46,840 --> 00:39:49,640 Speaker 1: gravitational field will sort of pull them back, right, It 739 00:39:49,640 --> 00:39:52,759 Speaker 1: will pull them down and prevent them from staying a 740 00:39:52,800 --> 00:39:57,040 Speaker 1: little bit further apart. These mirrors are like suspended on cables, right, 741 00:39:57,400 --> 00:40:00,440 Speaker 1: So imagine like a pendulum that's been left little bit 742 00:40:00,440 --> 00:40:03,920 Speaker 1: away from equilibrium. If there's gravity there, it'll just swing 743 00:40:04,040 --> 00:40:07,560 Speaker 1: right back to the equilibrium position. So the Earth's gravity 744 00:40:07,640 --> 00:40:13,160 Speaker 1: sort of erases this gravitational memory effect in Lego saying 745 00:40:13,160 --> 00:40:16,320 Speaker 1: the Earth remembers. But I guess that doesn't make a 746 00:40:16,360 --> 00:40:18,319 Speaker 1: lot of sense to me, Like why would the Earth 747 00:40:18,440 --> 00:40:21,120 Speaker 1: care how far apart these mirrors are. Well, I don't 748 00:40:21,120 --> 00:40:23,719 Speaker 1: think the Earth has an opinion, Like it doesn't matter 749 00:40:23,800 --> 00:40:26,080 Speaker 1: to the Earth at all. But the Earth does have gravity, 750 00:40:26,400 --> 00:40:29,160 Speaker 1: and the effect of gravity will be to pull these 751 00:40:29,200 --> 00:40:31,839 Speaker 1: things back to where they were. In what way does 752 00:40:31,880 --> 00:40:36,160 Speaker 1: Earth's gravity pull the mirrors back? Like, why would the 753 00:40:36,200 --> 00:40:39,080 Speaker 1: Earth you want to put them back in the same position? 754 00:40:39,280 --> 00:40:41,759 Speaker 1: What was special about the original position? Well, the Earth 755 00:40:41,800 --> 00:40:44,279 Speaker 1: itself has these powerful bonds, and so we don't think 756 00:40:44,280 --> 00:40:47,080 Speaker 1: the Earth itself is changed, right, So the Earth still 757 00:40:47,080 --> 00:40:49,879 Speaker 1: has the original gravity that it had before. And these 758 00:40:49,920 --> 00:40:52,960 Speaker 1: mirrors are not floating in zero gravity, right, Their original 759 00:40:53,000 --> 00:40:56,200 Speaker 1: position was determined by the gravity of the Earth. So 760 00:40:56,239 --> 00:40:58,520 Speaker 1: they're going to end up back in that same position 761 00:40:58,880 --> 00:41:01,040 Speaker 1: if you don't apply somers to them. It's sort of 762 00:41:01,040 --> 00:41:03,400 Speaker 1: like if you went and pushed on one of those mirrors, 763 00:41:03,640 --> 00:41:06,160 Speaker 1: what would happen, Well, it would swing in one direction, 764 00:41:06,239 --> 00:41:09,160 Speaker 1: but then gravity would bring it back, right, but only 765 00:41:09,160 --> 00:41:11,279 Speaker 1: if you push it against Earth's gravity, Like if you 766 00:41:11,280 --> 00:41:15,200 Speaker 1: push it perpendicutor or to the side, the gravity Earth's 767 00:41:15,280 --> 00:41:17,279 Speaker 1: pulls is the same, isn't it? Like the Earth is 768 00:41:17,320 --> 00:41:19,279 Speaker 1: just pulling them towards the center of the Earth. Yeah, 769 00:41:19,320 --> 00:41:22,120 Speaker 1: so the mirrors are all being pulled down, right, all 770 00:41:22,120 --> 00:41:24,640 Speaker 1: being pulled down towards the center of the Earth. And 771 00:41:24,680 --> 00:41:26,839 Speaker 1: so if you give them a nudge away from that 772 00:41:26,880 --> 00:41:28,840 Speaker 1: line towards the center of the Earth, they're going to 773 00:41:28,920 --> 00:41:31,080 Speaker 1: naturally trend back towards the center of the Earth. But 774 00:41:31,120 --> 00:41:32,879 Speaker 1: if I push it along a circle around the Earth, 775 00:41:33,320 --> 00:41:35,360 Speaker 1: the gravity is the same, isn't it. Well, So remember 776 00:41:35,400 --> 00:41:38,439 Speaker 1: these mirrors are suspended on a cable with a fixed length, right, 777 00:41:38,480 --> 00:41:40,960 Speaker 1: and so if you push it then it's basically moving 778 00:41:40,960 --> 00:41:43,360 Speaker 1: it up. Just like if you have a ball on 779 00:41:43,400 --> 00:41:46,399 Speaker 1: a string and you push on the ball, the ball 780 00:41:46,480 --> 00:41:49,480 Speaker 1: goes up because the string is a fixed length, and 781 00:41:49,520 --> 00:41:51,000 Speaker 1: so now the Earth is going to pull it back 782 00:41:51,040 --> 00:41:54,120 Speaker 1: down to the equilibrium position. Oh, I see what you're saying. 783 00:41:54,160 --> 00:41:57,680 Speaker 1: The way Ligo is design these things are on pendulums, 784 00:41:57,920 --> 00:42:01,200 Speaker 1: and so the Earth's gravity wouldn't let you have a 785 00:42:01,200 --> 00:42:05,359 Speaker 1: permanent change in the space between them. Yeah, that's exactly right, 786 00:42:05,400 --> 00:42:08,360 Speaker 1: And in principle you might be able to observe it 787 00:42:08,520 --> 00:42:11,440 Speaker 1: before Earth brings some sort of back to the equilibrium position. 788 00:42:11,760 --> 00:42:14,000 Speaker 1: There's like a little bit of information there. The memory 789 00:42:14,000 --> 00:42:16,399 Speaker 1: effect might last for a little while before the Earth 790 00:42:16,400 --> 00:42:19,319 Speaker 1: erases it. But legos really just not set up to 791 00:42:19,400 --> 00:42:23,080 Speaker 1: make this kind of measurement. Instead, what you need is 792 00:42:23,120 --> 00:42:25,600 Speaker 1: the same kind of detector, but where everything is in 793 00:42:25,680 --> 00:42:29,840 Speaker 1: free fall right where there is no nearby massive object 794 00:42:29,920 --> 00:42:33,640 Speaker 1: pulling on everything. Basically you need this thing out in space. 795 00:42:34,040 --> 00:42:36,160 Speaker 1: I see. So there's just more of an excuse to 796 00:42:36,239 --> 00:42:43,640 Speaker 1: have space lasers, the operational space lasers. That's really it's 797 00:42:43,680 --> 00:42:45,680 Speaker 1: just a long con. When these guys in the seventies 798 00:42:45,680 --> 00:42:47,600 Speaker 1: were coming up with these calculations, they were just like 799 00:42:47,960 --> 00:42:50,600 Speaker 1: dot dot dot space lasers? How do we get there? 800 00:42:53,040 --> 00:42:56,400 Speaker 1: That's every physicist dream, isn't it? Shoot lasers in space? 801 00:42:56,840 --> 00:42:59,960 Speaker 1: Space lasers. It's pretty cool, though, space lasers. I mean, 802 00:43:00,000 --> 00:43:03,399 Speaker 1: that's pretty awesome. You got to say, right, that's yeah great. 803 00:43:03,440 --> 00:43:07,319 Speaker 1: Reagan thought that too. We're just going to shoot them 804 00:43:07,320 --> 00:43:10,000 Speaker 1: back and forth between these quiet little detectors in space. 805 00:43:10,040 --> 00:43:12,840 Speaker 1: I promise you, we're not going to shoot our eye out. Mom. 806 00:43:12,880 --> 00:43:15,080 Speaker 1: I feel like that kid in a Christmas story. Okay, 807 00:43:15,080 --> 00:43:16,919 Speaker 1: So then the idea is that you would have these 808 00:43:17,200 --> 00:43:19,799 Speaker 1: detectors out there in space, you know, kind of an 809 00:43:19,800 --> 00:43:22,560 Speaker 1: empty space, and then you would measure the distance between 810 00:43:22,560 --> 00:43:24,919 Speaker 1: them with super duper high accuracy. And then you would 811 00:43:24,960 --> 00:43:28,160 Speaker 1: not just measure the wave as it washes by, right, 812 00:43:28,640 --> 00:43:30,799 Speaker 1: but you might be able to measure like, oh, after 813 00:43:30,840 --> 00:43:33,440 Speaker 1: the wave went through. Now we're a little bit further apart, 814 00:43:34,000 --> 00:43:42,080 Speaker 1: which proves this idea of the what gravitational wave of memory? 815 00:43:42,680 --> 00:43:45,080 Speaker 1: I'm only saying that because maybe the listeners forgot, and 816 00:43:45,120 --> 00:43:48,520 Speaker 1: I want them to be confused the memory effect of 817 00:43:48,600 --> 00:43:52,440 Speaker 1: gravitational waves. Right, that's the idea, right, that is the idea, 818 00:43:52,520 --> 00:43:54,839 Speaker 1: And so there is actually a design for this. It's 819 00:43:54,960 --> 00:43:58,880 Speaker 1: not just physicists dreaming up space lasers. It's called LISA, 820 00:43:59,000 --> 00:44:04,400 Speaker 1: the Laser Interferometer Space Antenna, and it's basically three space 821 00:44:04,440 --> 00:44:08,080 Speaker 1: graft out there in a triangle. And you know, LIGO 822 00:44:08,160 --> 00:44:11,400 Speaker 1: is a few kilometers long. They're bouncing light back and forth. 823 00:44:11,520 --> 00:44:14,799 Speaker 1: This thing is going to be millions of kilometers long. 824 00:44:15,239 --> 00:44:20,399 Speaker 1: What so these are like space space? Oh yeah, these things? 825 00:44:20,440 --> 00:44:22,600 Speaker 1: I mean, why not make them really far apart, right 826 00:44:22,640 --> 00:44:25,719 Speaker 1: if you can? Because the further apart they are, the 827 00:44:25,800 --> 00:44:29,640 Speaker 1: more sensitive you are to really small gravitational waves. Not 828 00:44:29,800 --> 00:44:32,719 Speaker 1: only could this potentially detect the memory effect, it could 829 00:44:32,760 --> 00:44:36,600 Speaker 1: also measure the gravitational background effect, like, as you say, 830 00:44:36,840 --> 00:44:39,720 Speaker 1: every time you move your arm, you're creating gravitational waves, 831 00:44:39,719 --> 00:44:42,320 Speaker 1: and everything that's out there in space orbiting is creating 832 00:44:42,360 --> 00:44:45,120 Speaker 1: gravitational waves. We could sort of measure this sort of 833 00:44:45,520 --> 00:44:49,920 Speaker 1: background gravitational wave noise of the universe and get some 834 00:44:50,000 --> 00:44:53,800 Speaker 1: information about that using LISA. Oh wow, because I was 835 00:44:53,840 --> 00:44:56,320 Speaker 1: thinking this was more like maybe the gravitation will probe 836 00:44:56,400 --> 00:45:00,560 Speaker 1: be satellites that it did some relativity experiments around the Earth. 837 00:45:00,600 --> 00:45:03,040 Speaker 1: This is like out there in space base, like out 838 00:45:03,040 --> 00:45:06,280 Speaker 1: there between the planets, right, if you're talking about millions 839 00:45:06,280 --> 00:45:09,640 Speaker 1: of kilometers or is it still around Earth's orbit. It's 840 00:45:09,680 --> 00:45:12,240 Speaker 1: going to be orbiting the Sun sort of with the Earth, 841 00:45:12,520 --> 00:45:15,239 Speaker 1: and you know, millions of kilometers sounds really long, and 842 00:45:15,280 --> 00:45:17,719 Speaker 1: it is pretty big. It's bigger than the Earth, which 843 00:45:17,760 --> 00:45:20,000 Speaker 1: is kind of awesome. But these things will sort of 844 00:45:20,040 --> 00:45:22,359 Speaker 1: stay near the Earth so that we can talk to them, 845 00:45:22,440 --> 00:45:25,479 Speaker 1: communicate them, control them. They'll be orbiting the Sun sort 846 00:45:25,480 --> 00:45:29,440 Speaker 1: of with the Earth like a fully operational space station. 847 00:45:30,920 --> 00:45:33,400 Speaker 1: Not yet fully operational. This thing is just in the 848 00:45:33,400 --> 00:45:36,759 Speaker 1: planning stages. I think the earliest targeted launch date is 849 00:45:36,800 --> 00:45:40,920 Speaker 1: twenty thirty seven, which is like comfortably far away enough 850 00:45:40,960 --> 00:45:43,080 Speaker 1: in the future that nobody has to like actually build 851 00:45:43,120 --> 00:45:47,000 Speaker 1: anything today. So nobody's actually started constructing anything. I see. 852 00:45:47,000 --> 00:45:50,360 Speaker 1: We're still in the prequels. You're like in the Clone 853 00:45:50,360 --> 00:45:53,680 Speaker 1: Wars or Revel or a Rogue one. We're still drawing 854 00:45:53,719 --> 00:45:56,040 Speaker 1: pictures of Death Star on chalkboards at this point in 855 00:45:56,040 --> 00:45:58,880 Speaker 1: the story. We're not actually building any but you know, 856 00:45:59,040 --> 00:46:01,680 Speaker 1: if we build it, we will learn so much about 857 00:46:01,800 --> 00:46:06,759 Speaker 1: gravitational waves, gravitational memory, gravitational background. Maybe also even see 858 00:46:06,760 --> 00:46:11,000 Speaker 1: gravitational waves from the Big Bang, you know, ripples in space, 859 00:46:11,360 --> 00:46:14,040 Speaker 1: that were created in the very very early moments of 860 00:46:14,080 --> 00:46:18,080 Speaker 1: the universe. Wait, what, so it'd be so accurate and 861 00:46:18,120 --> 00:46:21,759 Speaker 1: so sensitive to gravitational waves that you would measure these 862 00:46:21,840 --> 00:46:24,080 Speaker 1: ripples from the beginning of the universe like those are 863 00:46:24,080 --> 00:46:27,520 Speaker 1: still around. Those we think are still around, sort of 864 00:46:27,560 --> 00:46:30,400 Speaker 1: the same way that like the cosmic microwave background radiation 865 00:46:30,719 --> 00:46:33,720 Speaker 1: is still around. These are photons from the very early universe, 866 00:46:33,920 --> 00:46:35,680 Speaker 1: but they don't go all the way back to the 867 00:46:35,800 --> 00:46:37,880 Speaker 1: very beginning of the universe. They only go back as 868 00:46:37,960 --> 00:46:41,000 Speaker 1: far as the universe has been transparent. Before some moment 869 00:46:41,040 --> 00:46:44,000 Speaker 1: in the early universe it was opaque, so you generated photons, 870 00:46:44,040 --> 00:46:46,760 Speaker 1: they just kind of absorbed. Those photons are not around anymore. 871 00:46:46,800 --> 00:46:49,160 Speaker 1: The oldest photons we can see are back when the 872 00:46:49,239 --> 00:46:53,640 Speaker 1: universe was transparent to light. But gravitational waves can go 873 00:46:53,760 --> 00:46:57,520 Speaker 1: through almost anything, right, So the universe is basically transparent 874 00:46:57,560 --> 00:47:00,680 Speaker 1: to gravitational waves, which means that if you could detect 875 00:47:01,000 --> 00:47:03,520 Speaker 1: very very faint gravitational waves, we could see all the 876 00:47:03,560 --> 00:47:06,640 Speaker 1: way back to well before that moment when the universe 877 00:47:06,680 --> 00:47:10,319 Speaker 1: was opaque and see signals and get information about the 878 00:47:10,440 --> 00:47:14,120 Speaker 1: very very early universe. So Lisa would be really powerful 879 00:47:14,400 --> 00:47:18,120 Speaker 1: sort of astrophysical and cosmologically m Yeah, you could hear 880 00:47:18,239 --> 00:47:22,359 Speaker 1: like the Big Bang itself, like the Bang, right, that's 881 00:47:22,400 --> 00:47:25,200 Speaker 1: the idea. Yeah, we might see ripples from inflation. You know, 882 00:47:25,239 --> 00:47:27,560 Speaker 1: that would be really awesome. All right, So we're building 883 00:47:27,560 --> 00:47:30,640 Speaker 1: these awesome space telescopes and we might measure and confirm 884 00:47:30,800 --> 00:47:33,600 Speaker 1: that gravitational waves do have this memory effect that leaves 885 00:47:33,719 --> 00:47:37,200 Speaker 1: kind of a standing echo across space. What would that 886 00:47:37,239 --> 00:47:40,160 Speaker 1: mean about our understanding of the universe. It would mean 887 00:47:40,200 --> 00:47:43,880 Speaker 1: that once again, general relativity is awesome and accurate. I 888 00:47:44,000 --> 00:47:46,280 Speaker 1: might also help us solve some puzzles we have about 889 00:47:46,320 --> 00:47:49,520 Speaker 1: like black holes. Remember that one mystery about black holes 890 00:47:49,640 --> 00:47:51,960 Speaker 1: is like where does the information go when something falls 891 00:47:52,080 --> 00:47:54,879 Speaker 1: into a black hole? Because we think that like black 892 00:47:54,920 --> 00:47:57,560 Speaker 1: holes don't release any information about what's inside them. And 893 00:47:57,600 --> 00:48:00,400 Speaker 1: the other hand, we also think black holes evaporative actually 894 00:48:00,800 --> 00:48:03,640 Speaker 1: due to hawking radiation, and so that information has to 895 00:48:03,680 --> 00:48:06,880 Speaker 1: go somewhere, but we don't really understand it. It's possible 896 00:48:07,000 --> 00:48:11,680 Speaker 1: that if gravitational waves are leaving permanent imprints on space, 897 00:48:12,160 --> 00:48:14,680 Speaker 1: then maybe things falling into a black hole are like 898 00:48:14,880 --> 00:48:18,640 Speaker 1: changing the space around a black hole in some important way, 899 00:48:18,880 --> 00:48:22,440 Speaker 1: leaving their information there. As they fall into the black hole, 900 00:48:22,640 --> 00:48:27,719 Speaker 1: so that it isn't actually destroyed. M interesting, like as 901 00:48:27,800 --> 00:48:30,759 Speaker 1: it falls in it leaves a little bit of a 902 00:48:30,760 --> 00:48:33,960 Speaker 1: graffiti in space itself before it gets destroyed by the 903 00:48:33,960 --> 00:48:36,200 Speaker 1: black hole. Yeah. Or maybe it's like a space angel, 904 00:48:36,400 --> 00:48:38,520 Speaker 1: you know, think about it in a positive way. It's 905 00:48:38,520 --> 00:48:43,040 Speaker 1: like making its mark on space. Space angela. You know, 906 00:48:43,040 --> 00:48:45,880 Speaker 1: you can make snow angels or sand angels. Can you 907 00:48:45,960 --> 00:48:48,279 Speaker 1: lie down in space and like wag your arms and 908 00:48:48,320 --> 00:48:50,880 Speaker 1: make a space angel? Oh? I see, I thought you 909 00:48:50,880 --> 00:48:54,200 Speaker 1: were talking about like actual space angels. I was like, yeah, 910 00:48:54,280 --> 00:48:58,239 Speaker 1: that's an interesting idea for space epic. No, that would 911 00:48:58,239 --> 00:49:00,759 Speaker 1: be a spiritual angel. I'm talking about a physical thing, 912 00:49:00,840 --> 00:49:03,520 Speaker 1: you know. I guess in principle, if you stand around 913 00:49:03,520 --> 00:49:06,440 Speaker 1: and wave your arms, you are making gravitational waves in 914 00:49:06,440 --> 00:49:10,279 Speaker 1: the shape of a space angel. I suppose. Yeah, And 915 00:49:10,800 --> 00:49:15,320 Speaker 1: technically it is permanent, like you are distorting space forever. Yeah, 916 00:49:15,360 --> 00:49:17,759 Speaker 1: you are, So be careful, everybody. What if I walk 917 00:49:17,760 --> 00:49:22,000 Speaker 1: around in a pattern that says Kilroy was here? Am 918 00:49:22,040 --> 00:49:25,399 Speaker 1: I marring the universe? Some future alien society will build 919 00:49:25,400 --> 00:49:28,520 Speaker 1: a very very sensitive gravitational wave detector and they will 920 00:49:28,520 --> 00:49:31,000 Speaker 1: read your message and they will wonder why did these 921 00:49:31,040 --> 00:49:35,120 Speaker 1: choose to send that? What does that mean? Didn't he 922 00:49:35,200 --> 00:49:38,680 Speaker 1: have anything better to do? All right, well, I think 923 00:49:38,680 --> 00:49:42,640 Speaker 1: that answers the question. Gravitational waves do leave an imprint 924 00:49:42,680 --> 00:49:45,160 Speaker 1: on the universe, on the stuff that it passes through, 925 00:49:45,320 --> 00:49:48,880 Speaker 1: and maybe theoretically it does also leave an imprint on 926 00:49:49,000 --> 00:49:53,680 Speaker 1: space itself, something that lasts forever, that echoes throughout eternity. 927 00:49:53,719 --> 00:49:57,359 Speaker 1: Then maybe some days some alien species or maybe us 928 00:49:57,360 --> 00:50:00,879 Speaker 1: in the future can read and learn about what what happened. Yeah, 929 00:50:00,920 --> 00:50:03,360 Speaker 1: if we are still doing this podcast in fifteen or 930 00:50:03,480 --> 00:50:06,280 Speaker 1: twenty years, then maybe we'll have an episode talking about 931 00:50:06,280 --> 00:50:10,720 Speaker 1: the discovery of gravitational wave memory. Yeah, assuming we remember 932 00:50:10,840 --> 00:50:15,680 Speaker 1: this episode, which I'm guessing probably not. All right, Well, 933 00:50:15,719 --> 00:50:18,839 Speaker 1: we hope you enjoyed that. Thanks for joining us, See 934 00:50:18,880 --> 00:50:29,120 Speaker 1: you next time. Thanks for listening, and remember that Daniel 935 00:50:29,160 --> 00:50:32,560 Speaker 1: and Jorge Explain the Universe is a production of iHeartRadio. 936 00:50:32,840 --> 00:50:36,720 Speaker 1: For more podcast from my Heart Radio, visit the iHeartRadio app, 937 00:50:37,000 --> 00:50:40,480 Speaker 1: Apple Podcasts, or wherever you listen to your favorite shows.