WEBVTT 0 00:00:00.000 --> 00:00:02.040 Andrew Dunkley: Hello again. Thanks for joining us on Space 1 00:00:02.040 --> 00:00:04.680 Nuts. This is a Q and A edition. My name is 2 00:00:04.680 --> 00:00:06.720 Andrew Dunkley. What's a Q and A edition? 3 00:00:06.720 --> 00:00:09.520 It's an edition where we get Q's and 4 00:00:09.520 --> 00:00:12.480 give you A's because you're so clever. 5 00:00:12.800 --> 00:00:14.360 Uh, something like that. Anyway, we're going 6 00:00:14.360 --> 00:00:16.160 to answer audience questions. That's what I'm 7 00:00:16.160 --> 00:00:17.600 getting at. We've got questions about 8 00:00:17.760 --> 00:00:20.000 redshift, We've got questions about dark 9 00:00:20.080 --> 00:00:20.720 photons. 10 00:00:20.720 --> 00:00:21.040 Professor Fred Watson: What? 11 00:00:21.700 --> 00:00:24.000 Andrew Dunkley: Uh, we've got questions about deep space 12 00:00:24.160 --> 00:00:26.960 astronomy and another one about the expansion 13 00:00:26.960 --> 00:00:29.120 of the universe. I think we talked about that 14 00:00:29.120 --> 00:00:31.440 last episode. Anyway, uh, we'll see if we can 15 00:00:31.440 --> 00:00:33.900 solve all of that on this episode of space 16 00:00:33.900 --> 00:00:35.660 nuts. 15 seconds. 17 00:00:35.660 --> 00:00:38.076 Professor Fred Watson: Guidance is internal. 10, 18 00:00:38.257 --> 00:00:41.020 9, ignition sequence. Star 19 00:00:41.180 --> 00:00:41.864 space nuts. 20 00:00:41.936 --> 00:00:43.304 Andrew Dunkley: 5, 4, 3, 2. 21 00:00:43.376 --> 00:00:43.664 Roger: 1. 22 00:00:43.736 --> 00:00:46.544 Professor Fred Watson: 2, 3, 4, 5, 5, 4, 3, 2, 23 00:00:46.616 --> 00:00:48.139 1. Space nuts. 24 00:00:48.220 --> 00:00:50.060 Andrew Dunkley: Astronauts report it feels good. 25 00:00:51.260 --> 00:00:54.220 And with us again to kind of 26 00:00:54.220 --> 00:00:56.740 try to maybe answer some of that is 27 00:00:56.740 --> 00:00:58.620 Professor Fred Watson Watson, astronomer at 28 00:00:58.620 --> 00:00:59.500 large. Hello, Fred Watson. 29 00:01:00.050 --> 00:01:02.890 Professor Fred Watson: Hello, Andrew. Um, kind of is probably the 30 00:01:02.890 --> 00:01:04.530 best description really, isn't it? 31 00:01:05.650 --> 00:01:08.400 Andrew Dunkley: Possibly so. Possibly so. Um, 32 00:01:08.530 --> 00:01:10.210 but you know, it's good to get questions. 33 00:01:10.210 --> 00:01:13.210 We've got a whole new batch, so, um, let's 34 00:01:13.210 --> 00:01:14.770 get stuck straight into it. 35 00:01:14.770 --> 00:01:17.760 Now. First question comes from, um. Uh, 36 00:01:18.290 --> 00:01:20.530 I love the way he always ends his questions. 37 00:01:20.530 --> 00:01:23.070 I'm not going to reveal anything, but, um, 38 00:01:23.070 --> 00:01:24.130 let's hear from Roger. 39 00:01:24.530 --> 00:01:27.510 Roger: Hey there, Space Nuts. This is Roger 40 00:01:27.510 --> 00:01:30.110 the truck driver. Tonight I'm in, 41 00:01:30.170 --> 00:01:33.070 uh, Rutland, Vermont. Got a 42 00:01:33.070 --> 00:01:35.230 question about the red shift of galaxies. 43 00:01:36.090 --> 00:01:38.910 Um, if the light that we're seeing from a far 44 00:01:38.910 --> 00:01:41.670 off galaxy is shifted to the red and it 45 00:01:41.670 --> 00:01:43.790 started out at a higher frequency, 46 00:01:44.350 --> 00:01:46.990 doesn't that mean energy's lost somewhere 47 00:01:46.990 --> 00:01:49.710 between here and there? And is that energy 48 00:01:49.790 --> 00:01:52.610 just transferred into space? And if it 49 00:01:52.610 --> 00:01:55.090 is, does that contribute to the 50 00:01:55.090 --> 00:01:57.410 expansion of space? And I'm not saying it's 51 00:01:57.410 --> 00:01:59.890 dark energy, but does it 52 00:01:59.890 --> 00:02:02.890 contribute to it or does that 53 00:02:02.890 --> 00:02:05.370 energy get dissipated in another way? 54 00:02:06.410 --> 00:02:08.730 All right. Always digging the show, guys. 55 00:02:08.730 --> 00:02:09.690 Keep on trucking. 56 00:02:11.370 --> 00:02:14.210 Andrew Dunkley: I love that. I love that. Uh, we've got 57 00:02:14.210 --> 00:02:15.890 train drivers that do that. Unfortunately, 58 00:02:15.890 --> 00:02:17.370 they do it at 3 o' clock in the morning. 59 00:02:18.730 --> 00:02:21.330 Although today he did it at 10 to 7. I was 60 00:02:21.330 --> 00:02:23.290 pretty annoyed. Pretty annoyed. 61 00:02:23.290 --> 00:02:25.250 Professor Fred Watson: This is, uh, the one going past your place? 62 00:02:25.250 --> 00:02:27.330 Andrew Dunkley: Yeah, behind our place there's a rail line. 63 00:02:27.330 --> 00:02:29.090 It doesn't get used a heck of a lot, but when 64 00:02:29.090 --> 00:02:30.040 it does, um. 65 00:02:30.490 --> 00:02:30.970 Eli: Yes? 66 00:02:31.050 --> 00:02:33.890 Andrew Dunkley: The glasses rattle. Uh, the ones on my face, 67 00:02:33.890 --> 00:02:36.250 I mean. Uh, thanks, Roger. Great question. 68 00:02:36.460 --> 00:02:39.450 Uh, so, um, yeah, the change 69 00:02:39.450 --> 00:02:42.040 in frequency with the, um, 70 00:02:43.130 --> 00:02:46.090 energy loss, um, where does the energy go and 71 00:02:46.090 --> 00:02:48.370 does it contribute to the expansion of the 72 00:02:48.370 --> 00:02:51.250 universe? And could it possibly be. 73 00:02:51.330 --> 00:02:53.090 Maybe, maybe not dark matter 74 00:02:54.130 --> 00:02:56.450 or dark energy or something? 75 00:02:56.450 --> 00:02:58.650 Professor Fred Watson: Yeah, yeah. Um, there's a lot. 76 00:02:58.650 --> 00:02:59.970 Andrew Dunkley: He packed a lot into that question. 77 00:03:00.050 --> 00:03:02.370 Professor Fred Watson: He did. And it's a great question too. Uh, 78 00:03:02.370 --> 00:03:04.290 and, you know, I mean, it's a, 79 00:03:04.690 --> 00:03:07.450 uh, project, um, Absolutely right. The 80 00:03:07.450 --> 00:03:10.050 conservation of energy. Uh, energy 81 00:03:10.130 --> 00:03:12.690 can't be created or destroyed. That's the 82 00:03:12.690 --> 00:03:15.490 fundamental rule. Its 83 00:03:15.570 --> 00:03:17.730 energy is always conserved. 84 00:03:18.890 --> 00:03:21.890 But, uh, the universe doesn't play 85 00:03:21.890 --> 00:03:23.530 by the ordinary rules. 86 00:03:24.790 --> 00:03:26.400 Uh, and, um, 87 00:03:28.810 --> 00:03:31.210 it's an interesting answer here. 88 00:03:31.550 --> 00:03:34.450 Um, and I have to say it's changed 89 00:03:34.450 --> 00:03:37.410 my view of what this, you know, what 90 00:03:37.410 --> 00:03:40.250 the answer to this problem was because, 91 00:03:40.410 --> 00:03:43.290 um, when we've been asked this before, 92 00:03:43.370 --> 00:03:45.130 we haven't been asked it for a long time. 93 00:03:46.280 --> 00:03:48.570 I just assumed that the energy, uh, 94 00:03:49.160 --> 00:03:51.800 basically was absorbed by the universe by 95 00:03:51.800 --> 00:03:54.680 space time, uh, and 96 00:03:55.000 --> 00:03:57.400 maybe contributed to the expansion. 97 00:03:57.480 --> 00:03:58.040 Although, 98 00:04:00.390 --> 00:04:02.800 uh, you can't have it both ways because it's 99 00:04:02.800 --> 00:04:05.640 the expansion that's causing the photon's 100 00:04:05.640 --> 00:04:08.350 energy to be lost. Uh, 101 00:04:08.600 --> 00:04:11.400 and just stepping back, exactly as 102 00:04:11.400 --> 00:04:13.640 Roger said, uh, you've got light going 103 00:04:13.640 --> 00:04:15.320 through the universe. It's, 104 00:04:15.670 --> 00:04:18.570 uh, its wavelength is being stretched by 105 00:04:18.570 --> 00:04:21.490 the expansion of the universe. Therefore the 106 00:04:21.490 --> 00:04:24.410 light is losing energy. Because the energy 107 00:04:24.410 --> 00:04:26.930 of a beam of light is all about the 108 00:04:26.930 --> 00:04:28.890 frequency of the light, in other words, or 109 00:04:28.890 --> 00:04:31.610 the wavelength. Putting it another way. So 110 00:04:31.770 --> 00:04:34.490 if you increase the wavelength, you lose 111 00:04:34.490 --> 00:04:37.280 energy. And that's, um, 112 00:04:37.610 --> 00:04:40.610 a given already. Uh, so what I 113 00:04:40.610 --> 00:04:42.330 used to say was, yes, it kind of goes into 114 00:04:42.330 --> 00:04:44.610 the universe. But I've done a bit more 115 00:04:44.610 --> 00:04:46.650 reading on this and I was wrong. 116 00:04:48.760 --> 00:04:51.750 Um, because when 117 00:04:51.750 --> 00:04:54.750 you apply general relativity to 118 00:04:54.750 --> 00:04:56.950 the universe as a whole, and that's the. 119 00:04:57.510 --> 00:04:59.190 As we've talked about, and we've talked about 120 00:04:59.190 --> 00:05:01.780 it at length in the last episode, it's, uh, 121 00:05:01.780 --> 00:05:04.510 the kind of fundamental rule that governs 122 00:05:04.510 --> 00:05:06.790 everything that we understand in the 123 00:05:06.790 --> 00:05:09.270 universe. Um, when you 124 00:05:09.510 --> 00:05:11.110 apply general relativity, 125 00:05:12.820 --> 00:05:12.860 Andrew Dunkley: uh, 126 00:05:12.870 --> 00:05:15.810 Professor Fred Watson: that conservation of energy 127 00:05:16.770 --> 00:05:19.730 that we expect to happen in the 128 00:05:19.730 --> 00:05:22.050 everyday world, it 129 00:05:22.290 --> 00:05:24.900 doesn't hold good. So energy, uh, 130 00:05:25.250 --> 00:05:27.690 is not conserved in an expanding 131 00:05:27.690 --> 00:05:30.690 universe. Uh, and so 132 00:05:31.250 --> 00:05:33.010 basically the energy 133 00:05:33.810 --> 00:05:36.730 simply disappears. It's 134 00:05:36.730 --> 00:05:39.450 just not there anymore because of the 135 00:05:39.450 --> 00:05:41.810 expansion of the universe. It's not causing 136 00:05:41.810 --> 00:05:43.490 the expansion of the universe. It's not 137 00:05:43.680 --> 00:05:45.800 create contributing to dark energy or dark 138 00:05:45.800 --> 00:05:48.640 matter, the energy loss, it just vanishes. 139 00:05:49.520 --> 00:05:51.520 Wow. So work that one out. 140 00:05:51.680 --> 00:05:52.400 Andrew Dunkley: I can't. 141 00:05:53.040 --> 00:05:54.240 Professor Fred Watson: No, I can't either. 142 00:05:56.470 --> 00:05:59.400 Um, I kind of really 143 00:05:59.400 --> 00:06:01.760 need to look at the equations on this. 144 00:06:02.330 --> 00:06:04.480 Andrew Dunkley: Um, don't show them to me. I mean, 145 00:06:06.400 --> 00:06:08.160 Professor Fred Watson: yeah, I'M not that keen on looking at them 146 00:06:08.160 --> 00:06:10.830 myself either. Too much else to do. But, uh, 147 00:06:11.190 --> 00:06:14.170 um, uh, but yes, that is 148 00:06:14.250 --> 00:06:16.410 the thinking on this. 149 00:06:17.030 --> 00:06:19.890 Uh, and I think the conservation 150 00:06:19.890 --> 00:06:22.430 rule does not work, uh, 151 00:06:24.890 --> 00:06:26.810 um, when it comes to 152 00:06:28.010 --> 00:06:29.850 the universe on a whole. 153 00:06:30.170 --> 00:06:30.570 Andrew Dunkley: Yeah. 154 00:06:30.570 --> 00:06:30.930 Professor Fred Watson: Wow. 155 00:06:30.930 --> 00:06:33.650 Andrew Dunkley: Gee, um, that's quite a 156 00:06:33.650 --> 00:06:35.370 revelation. Who figured that out? 157 00:06:37.160 --> 00:06:39.770 Professor Fred Watson: Uh, uh, it's on a number of 158 00:06:40.250 --> 00:06:43.130 different, uh, physics, uh, related websites. 159 00:06:43.990 --> 00:06:45.830 Andrew Dunkley: There's the reason no one knows about it 160 00:06:45.830 --> 00:06:47.830 because it's physics and 161 00:06:48.710 --> 00:06:50.070 who reads that stuff? 162 00:06:50.870 --> 00:06:53.790 Professor Fred Watson: Yeah, I think the relativistic bit of 163 00:06:53.790 --> 00:06:56.550 it, uh, comes from the fact 164 00:06:57.110 --> 00:07:00.030 that the energy of a particle, 165 00:07:00.030 --> 00:07:02.390 which is what we're talking about, it's an 166 00:07:02.390 --> 00:07:04.950 observer dependent quantity. 167 00:07:05.750 --> 00:07:08.430 And so that's why relativity plays a part in 168 00:07:08.430 --> 00:07:10.230 this because you're the observer 169 00:07:11.270 --> 00:07:13.640 and you're talking about something that's 170 00:07:13.640 --> 00:07:15.840 relative to another observer, that is the 171 00:07:15.840 --> 00:07:18.800 photon. Uh, and that's why you've got, 172 00:07:18.840 --> 00:07:21.680 uh, a relativistic 173 00:07:22.160 --> 00:07:23.120 access. Ah, to it. 174 00:07:24.000 --> 00:07:26.880 Andrew Dunkley: Wow. Okay. Um, great question, 175 00:07:26.960 --> 00:07:29.079 Roger. I'm not sure you were expecting that 176 00:07:29.079 --> 00:07:31.840 answer, but, uh, there it is. Uh, the energy 177 00:07:31.920 --> 00:07:34.240 just gone, 178 00:07:35.360 --> 00:07:38.360 goes, vanishes, ceases to 179 00:07:38.360 --> 00:07:40.320 exist. It's a dead poly. 180 00:07:41.680 --> 00:07:44.200 So anyway, um, 181 00:07:45.200 --> 00:07:47.470 no one got that joke. I was, um, 182 00:07:48.320 --> 00:07:50.480 doing a Monty Python skit for some reason. 183 00:07:50.640 --> 00:07:52.000 Professor Fred Watson: Yeah, you were. That's right. 184 00:07:53.360 --> 00:07:55.520 Look, I'm pursuing this in a little bit more 185 00:07:55.520 --> 00:07:58.360 detail and, uh, just trying to, you know, see 186 00:07:58.360 --> 00:08:00.800 whether we've got alternative. Alternative 187 00:08:00.960 --> 00:08:02.320 views of this. 188 00:08:02.560 --> 00:08:04.800 Andrew Dunkley: Well, generally speaking, you do get 189 00:08:04.800 --> 00:08:06.640 alternative views when it comes to this kind 190 00:08:06.640 --> 00:08:06.840 of stuff. 191 00:08:06.840 --> 00:08:09.710 Professor Fred Watson: That's right. Um, yes, 192 00:08:09.710 --> 00:08:10.070 so 193 00:08:12.310 --> 00:08:15.310 that's right. Uh, uh, 194 00:08:15.670 --> 00:08:18.310 I think the standard explanation today is 195 00:08:18.310 --> 00:08:21.270 that energy is not conserved. 196 00:08:21.670 --> 00:08:22.230 Okay. 197 00:08:23.030 --> 00:08:24.790 Andrew Dunkley: We'll leave it at that until somebody throws 198 00:08:24.790 --> 00:08:26.070 another spanner into the. 199 00:08:26.070 --> 00:08:27.550 Professor Fred Watson: Yeah, uh, we might be giving a different 200 00:08:27.550 --> 00:08:29.350 answer next week. It could be. 201 00:08:29.910 --> 00:08:31.870 Andrew Dunkley: Thanks, Roger. Great to hear from you. Toot, 202 00:08:31.870 --> 00:08:33.510 toot. Uh, we'll catch you next time. 203 00:08:33.830 --> 00:08:36.310 Our next question comes from 204 00:08:36.470 --> 00:08:39.110 Peter. He's from San Diego, California. 205 00:08:39.190 --> 00:08:40.940 While listening to another astrophysics 206 00:08:41.329 --> 00:08:43.409 podcast, I heard the term dark 207 00:08:43.809 --> 00:08:46.329 photon for the first time. Apparently this is 208 00:08:46.329 --> 00:08:48.929 a particle astrophysicists are, uh, seeking 209 00:08:49.009 --> 00:08:51.489 in order to explain dark matter and, or dark 210 00:08:51.489 --> 00:08:54.289 energy. Could you please elaborate on what a 211 00:08:54.289 --> 00:08:56.369 dark photon could be? 212 00:08:57.190 --> 00:08:59.689 Um, dad, joke for Andrew. A photon 213 00:08:59.689 --> 00:09:02.129 travels at the speed of light. Does that mean 214 00:09:02.129 --> 00:09:04.809 a dark photon travels at the speed of 215 00:09:04.809 --> 00:09:07.649 dark. I like that. 216 00:09:07.729 --> 00:09:09.740 That's good. Yeah, that's really good. Uh, 217 00:09:09.740 --> 00:09:12.089 keep up the great work, he says. Uh, thank 218 00:09:12.089 --> 00:09:12.689 you, Peter. 219 00:09:13.070 --> 00:09:13.590 Professor Fred Watson: All as well. 220 00:09:13.590 --> 00:09:15.630 Andrew Dunkley: In San Diego, California. 221 00:09:16.170 --> 00:09:18.310 Uh, have you ever heard of a dark photon, 222 00:09:18.310 --> 00:09:18.750 Fred Watson? 223 00:09:19.050 --> 00:09:21.710 Professor Fred Watson: Um, yes, I'VE probably got a few in this box 224 00:09:21.710 --> 00:09:24.710 here. The 225 00:09:24.710 --> 00:09:26.510 speed of dark. Just, just going back to that, 226 00:09:26.590 --> 00:09:29.550 that quip, uh, there was 227 00:09:29.550 --> 00:09:32.510 a storey I read, uh, probably 228 00:09:32.990 --> 00:09:35.790 a fortnight ago, uh, about 229 00:09:36.350 --> 00:09:38.510 exactly this. In that dark 230 00:09:39.310 --> 00:09:42.230 ness can move faster than the speed 231 00:09:42.230 --> 00:09:42.670 of light. 232 00:09:43.230 --> 00:09:43.630 Andrew Dunkley: No, 233 00:09:46.510 --> 00:09:49.070 Professor Fred Watson: but it's ah, an illusory darkness. It's when 234 00:09:49.070 --> 00:09:52.030 you've got um, light beams 235 00:09:52.510 --> 00:09:55.390 interfering with one another so that 236 00:09:55.390 --> 00:09:57.310 you've uh, interference 237 00:09:58.430 --> 00:10:00.750 light beams can cancel out. So if you've got 238 00:10:00.750 --> 00:10:03.110 two light waves and you add them up out of 239 00:10:03.110 --> 00:10:04.710 phase, they can cancel out and you get 240 00:10:04.710 --> 00:10:07.690 darkness. That's a well known principle 241 00:10:07.690 --> 00:10:09.770 of interferometry. I used to play with that 242 00:10:09.770 --> 00:10:12.210 when I was a student a lot. Uh, 243 00:10:12.490 --> 00:10:14.530 but there are certain circumstances that 244 00:10:14.530 --> 00:10:17.210 those patterns of darkness can actually 245 00:10:17.210 --> 00:10:19.530 exceed the speed of light 246 00:10:20.170 --> 00:10:22.170 because they're not actually real, they're 247 00:10:22.170 --> 00:10:24.650 not real entities. They're not a thing that's 248 00:10:24.650 --> 00:10:26.650 carrying any sort of information or energy. 249 00:10:26.650 --> 00:10:29.450 They're just patterns in an 250 00:10:29.450 --> 00:10:31.090 interference pattern. They're just dark 251 00:10:31.090 --> 00:10:32.930 patches in it. And I think under certain 252 00:10:32.930 --> 00:10:35.290 circumstances they could go faster than the 253 00:10:35.290 --> 00:10:38.150 speed of light. Darkness might 254 00:10:38.150 --> 00:10:41.070 be not quite as uh, you know, as twee as 255 00:10:41.070 --> 00:10:43.710 you thought it was. I guess so 256 00:10:43.710 --> 00:10:46.710 anyway, anyway, uh, that's not the 257 00:10:47.430 --> 00:10:49.950 question, uh, because dark photons are 258 00:10:49.950 --> 00:10:52.310 definitely something different and they're 259 00:10:52.390 --> 00:10:55.270 basically uh, hypothetical. 260 00:10:55.510 --> 00:10:58.230 They've been hypothesised by 261 00:10:58.310 --> 00:11:01.010 physicists and cosmologists as uh, 262 00:11:01.350 --> 00:11:03.350 being a uh, force carrier 263 00:11:04.350 --> 00:11:06.670 similar to the ordinary photon 264 00:11:07.150 --> 00:11:10.110 but related to dark 265 00:11:10.270 --> 00:11:13.070 matter. In other 266 00:11:13.070 --> 00:11:15.830 words, you might have. Sorry, somebody's 267 00:11:15.830 --> 00:11:17.910 trying to phone me. I'm just gonna kill that 268 00:11:17.910 --> 00:11:20.430 call. Yeah, um, 269 00:11:21.070 --> 00:11:21.790 that was me. 270 00:11:21.790 --> 00:11:23.790 Andrew Dunkley: That was me. No it wasn't. 271 00:11:26.910 --> 00:11:29.870 Professor Fred Watson: You know, they're part of the. There may be. 272 00:11:29.950 --> 00:11:32.430 When we discover finally what dark matter is, 273 00:11:33.310 --> 00:11:35.690 there may be a suite of 274 00:11:36.250 --> 00:11:39.210 dark particles which could include 275 00:11:39.210 --> 00:11:41.610 dark photons. That's the bottom line. 276 00:11:41.850 --> 00:11:42.220 Andrew Dunkley: Right? 277 00:11:42.220 --> 00:11:45.210 Professor Fred Watson: Um, and so you know we mentioned last 278 00:11:45.210 --> 00:11:48.210 week the, or in the last episode the uh, the 279 00:11:48.210 --> 00:11:50.810 Large Hadron Collider being upgraded to the 280 00:11:50.810 --> 00:11:53.580 High Luminosity Large Hadron Collider. Um, 281 00:11:53.850 --> 00:11:56.250 that's one of the things they'd be looking 282 00:11:56.250 --> 00:11:57.770 for, will be dark photons. 283 00:11:58.730 --> 00:11:59.290 Okay. 284 00:11:59.690 --> 00:12:02.030 Andrew Dunkley: You know, I tried to do 285 00:12:02.500 --> 00:12:04.950 um, an AI search for an 286 00:12:04.950 --> 00:12:06.650 explanation on it and um, 287 00:12:07.950 --> 00:12:10.060 it sort of gave me all this gobbledygook. But 288 00:12:10.060 --> 00:12:12.950 um, you know, what would a dark 289 00:12:12.950 --> 00:12:15.750 proton, a photon do? It says it would 290 00:12:15.750 --> 00:12:17.870 carry a force within the dark sector. 291 00:12:19.230 --> 00:12:21.710 We call that the government. It might allow 292 00:12:21.710 --> 00:12:23.710 dark matter particles to interact with each 293 00:12:23.710 --> 00:12:25.990 other and it could very weakly mix with 294 00:12:25.990 --> 00:12:28.670 normal photons, giving us a way to Detect it. 295 00:12:28.750 --> 00:12:31.580 And the reason they reckon that scientists 296 00:12:31.580 --> 00:12:34.300 care about this, as you said, could explain 297 00:12:34.300 --> 00:12:36.860 what dark matter is made of. So 298 00:12:36.940 --> 00:12:39.220 therefore solving some of those gaps in our 299 00:12:39.220 --> 00:12:40.860 current physics theories. 300 00:12:43.260 --> 00:12:45.340 That's why people are interested in this and 301 00:12:45.340 --> 00:12:47.340 that's why they're upgrading the Large Hadron 302 00:12:47.340 --> 00:12:50.060 Collider. And hopefully we will 303 00:12:50.620 --> 00:12:52.700 learn more in years to come. 304 00:12:54.540 --> 00:12:55.340 That's the hope. 305 00:12:55.740 --> 00:12:58.620 Professor Fred Watson: That's the hope, yeah. So we might be talking 306 00:12:58.620 --> 00:13:01.220 one day about dark photons, um, having been 307 00:13:01.220 --> 00:13:03.890 detected, which would be a coup 308 00:13:03.890 --> 00:13:05.410 for space newts. 309 00:13:05.730 --> 00:13:08.570 Andrew Dunkley: Yes, it will. Uh, but at this stage they 310 00:13:08.570 --> 00:13:11.170 are not proven. It's just a theory. So 311 00:13:11.330 --> 00:13:13.970 that's about as much as we know at this point 312 00:13:13.970 --> 00:13:16.770 in time. But, uh, very good question. Uh, 313 00:13:16.930 --> 00:13:19.290 and, uh, thank you, Peter, for sending it in. 314 00:13:19.290 --> 00:13:22.010 This is Space Nuts with Andrew Dunkley and 315 00:13:22.010 --> 00:13:23.890 Professor Fred Watson Watson. 316 00:13:26.530 --> 00:13:29.490 0G and I feel fine. Space Nuts. 317 00:13:29.720 --> 00:13:31.560 Okay, Fred Watson, we'll move straight on to 318 00:13:31.560 --> 00:13:33.720 our next question, which is, uh, another 319 00:13:33.720 --> 00:13:36.440 audio question from Eli. 320 00:13:36.760 --> 00:13:39.000 Eli: Hello, this is Eli from 321 00:13:39.800 --> 00:13:42.240 sunny Coachella Valley in 322 00:13:42.240 --> 00:13:45.240 California. I'm embarrassed to 323 00:13:45.240 --> 00:13:47.640 admit it, but I still can't get my head 324 00:13:47.640 --> 00:13:50.640 around deep space astronomy. I get that 325 00:13:50.640 --> 00:13:53.440 the light from, say, a distant galaxy is a 326 00:13:53.440 --> 00:13:56.250 billion years old, but why 327 00:13:56.250 --> 00:13:59.210 that particular point in its time? Is 328 00:13:59.210 --> 00:14:01.450 it just a matter of whatever light is hitting 329 00:14:01.450 --> 00:14:03.730 us is the time we get to see. 330 00:14:05.090 --> 00:14:06.850 But for really early light, 331 00:14:07.890 --> 00:14:10.610 the JWST, early universe stuff 332 00:14:10.610 --> 00:14:13.090 that's been travelling for 13 billion years 333 00:14:13.090 --> 00:14:15.570 and just hitting us now, 334 00:14:16.690 --> 00:14:18.610 are we looking for the light that hasn't 335 00:14:19.010 --> 00:14:21.810 passed us by or hasn't made it here yet, 336 00:14:22.170 --> 00:14:24.610 but is from that one precise 337 00:14:24.610 --> 00:14:25.850 location long ago? 338 00:14:27.450 --> 00:14:30.210 This stuff is so difficult to get my head 339 00:14:30.210 --> 00:14:33.050 around. Love the show and hope 340 00:14:33.050 --> 00:14:34.970 you guys can clear this up for me. 341 00:14:36.150 --> 00:14:38.590 Andrew Dunkley: Uh, no, we can't. We just thought we'd, um, 342 00:14:38.590 --> 00:14:41.370 put the question in there. Thanks, 343 00:14:41.370 --> 00:14:44.210 Eli. Uh, this is a deep, um, I'm, um. 344 00:14:44.370 --> 00:14:46.450 Not only in deep space astronomy terms, but 345 00:14:46.450 --> 00:14:48.090 it is a deep, deep topic. 346 00:14:48.750 --> 00:14:51.610 Um, I mean, when we look up into the sky 347 00:14:51.610 --> 00:14:53.690 at night and we see all those beautiful 348 00:14:53.830 --> 00:14:56.550 coloured dots, we are looking at history. 349 00:14:56.950 --> 00:14:59.110 And it's variable history because some of 350 00:14:59.110 --> 00:15:01.950 it's 4.41 light years away and 351 00:15:01.950 --> 00:15:04.950 some of it's 400,000 light 352 00:15:04.950 --> 00:15:07.510 years away, some of it's further than that. 353 00:15:07.810 --> 00:15:09.750 Um, but then you've got the cosmic 354 00:15:10.230 --> 00:15:12.870 microwave background radiation, which is kind 355 00:15:12.870 --> 00:15:14.150 of a leftover of, 356 00:15:14.930 --> 00:15:17.910 um, what happened after the 357 00:15:17.910 --> 00:15:19.670 Big Bang and that, 358 00:15:20.820 --> 00:15:23.100 that's a different kettle of fish. And I can 359 00:15:23.100 --> 00:15:25.220 understand why you've got a headache. Eli, 360 00:15:25.620 --> 00:15:26.580 over to you, Fred Watson. 361 00:15:27.860 --> 00:15:30.860 Professor Fred Watson: Thanks. Um, so I 362 00:15:30.860 --> 00:15:32.580 guess uh, you know, 363 00:15:33.860 --> 00:15:36.180 I understand Eli's issue as well. 364 00:15:36.280 --> 00:15:36.980 Um, 365 00:15:38.980 --> 00:15:40.860 you've got to be in the right place at the 366 00:15:40.860 --> 00:15:43.060 right time to see a photon from a distant 367 00:15:43.060 --> 00:15:46.060 galaxy. But I guess the way 368 00:15:46.060 --> 00:15:48.020 to envisage this is if you think 369 00:15:48.970 --> 00:15:50.890 of the universe, um, 370 00:15:51.770 --> 00:15:54.450 and you've got to perhaps think of it as if 371 00:15:54.450 --> 00:15:55.770 you were looking at it from the outside, 372 00:15:55.770 --> 00:15:58.050 which we never can. But, uh, if you can think 373 00:15:58.050 --> 00:16:00.650 of it that way, then it's full of 374 00:16:01.210 --> 00:16:03.370 objects which are radiating light. 375 00:16:04.249 --> 00:16:06.930 Even in its infancy, when the universe was 376 00:16:06.930 --> 00:16:09.370 very young, the stuff in it was basically 377 00:16:09.610 --> 00:16:12.290 shining. Um, once we got past the Dark Ages, 378 00:16:12.290 --> 00:16:14.570 where no stars were shining, uh, 379 00:16:15.330 --> 00:16:18.010 um, and those are the galaxies that we now 380 00:16:18.010 --> 00:16:20.510 see. So they constantly radiate, creating 381 00:16:20.510 --> 00:16:23.470 light. And that's just like a river of 382 00:16:23.470 --> 00:16:26.470 light that's flowing down time, 383 00:16:26.470 --> 00:16:29.190 if I can put it that way. Uh, and 384 00:16:30.150 --> 00:16:33.030 a long time in the future it 385 00:16:33.030 --> 00:16:35.190 reaches us. But it's not just 386 00:16:36.070 --> 00:16:38.590 an individual photon or something that's 387 00:16:38.590 --> 00:16:41.150 reaching us. It's this stream of stuff that 388 00:16:41.150 --> 00:16:43.790 is being radiated throughout the 389 00:16:43.790 --> 00:16:46.230 universe by these galaxies. So we, 390 00:16:46.850 --> 00:16:49.760 um. And we pick it up. We 391 00:16:49.760 --> 00:16:52.520 pick it up sometimes exactly as you've said. 392 00:16:52.520 --> 00:16:54.480 Well, up to 10 billion years after it's been 393 00:16:54.800 --> 00:16:57.760 radiated. I think 12 billion years, 394 00:16:58.130 --> 00:17:00.480 uh, are the oldest or the earliest galaxies 395 00:17:00.480 --> 00:17:02.639 that we now see. We're looking back in time 396 00:17:02.639 --> 00:17:05.440 12 billion years and seeing them as they were 397 00:17:05.840 --> 00:17:08.360 perhaps a billion and a half years after the 398 00:17:08.360 --> 00:17:11.160 Big Bang. Um, and they are shining, 399 00:17:11.160 --> 00:17:13.320 they're radiating light, uh, in the early 400 00:17:13.320 --> 00:17:16.230 universe and down the track that reaches us 401 00:17:16.390 --> 00:17:18.390 because that light's going in all directions. 402 00:17:18.390 --> 00:17:20.310 So it wouldn't matter where in the universe 403 00:17:20.310 --> 00:17:22.710 we were, we would still see them. 404 00:17:23.510 --> 00:17:25.670 Uh, we'd just see them in a, you know, in a 405 00:17:25.670 --> 00:17:27.670 different position in the sky. If we're a 406 00:17:27.670 --> 00:17:30.589 long way from where we are now. Yeah, but, 407 00:17:30.589 --> 00:17:33.350 yeah, so I guess it's, you 408 00:17:33.350 --> 00:17:35.950 know, in a way, one way of thinking about 409 00:17:35.950 --> 00:17:38.910 this is if you imagine us on planet 410 00:17:38.910 --> 00:17:41.820 Earth here and imagine us being 411 00:17:41.820 --> 00:17:44.700 surrounded by a whole series of 412 00:17:44.700 --> 00:17:47.580 shells which, uh, we're at the centre 413 00:17:47.580 --> 00:17:49.340 of. And this is a bit like the crystalline 414 00:17:49.340 --> 00:17:51.820 spheres that people used to think, uh, the 415 00:17:51.820 --> 00:17:54.100 universe was made of. Uh, but 416 00:17:54.580 --> 00:17:57.340 these shells, uh, spherical shells, 417 00:17:57.340 --> 00:17:59.700 all centred on the Earth, but each one 418 00:18:00.020 --> 00:18:02.740 clicks over to a time 419 00:18:02.820 --> 00:18:05.660 further in the past, uh, because the 420 00:18:05.660 --> 00:18:08.660 light's coming to us from the whole cosmos, 421 00:18:08.660 --> 00:18:11.220 which is full of stuff. Uh, and that's why 422 00:18:11.220 --> 00:18:13.560 we, these shells sort of being 423 00:18:13.560 --> 00:18:16.140 illuminated in a way by the objects that, uh, 424 00:18:16.400 --> 00:18:18.680 radiated them at that time. Uh, 425 00:18:20.100 --> 00:18:22.880 um, that we see them because of 426 00:18:23.120 --> 00:18:25.520 the distance that they are away from us means 427 00:18:25.520 --> 00:18:28.520 that the light has taken that long to get to 428 00:18:28.520 --> 00:18:31.040 us, whether that helps or not. In fact, I 429 00:18:31.040 --> 00:18:33.040 think I've just confused it completely. But, 430 00:18:35.080 --> 00:18:36.560 Andrew Dunkley: um, I 431 00:18:38.570 --> 00:18:41.330 just doing a little experimental search here 432 00:18:41.330 --> 00:18:41.930 for a sec. 433 00:18:44.090 --> 00:18:46.970 What I agree 434 00:18:46.970 --> 00:18:49.690 with in terms of Eli's question and getting 435 00:18:49.690 --> 00:18:52.650 your head around it is, um, if 436 00:18:52.650 --> 00:18:54.730 Betelgeuse, or however you want to pronounce 437 00:18:54.730 --> 00:18:57.570 it, went supernova right now as we 438 00:18:57.570 --> 00:18:58.170 were speaking, 439 00:19:00.410 --> 00:19:02.010 we wouldn't see it for 440 00:19:03.700 --> 00:19:05.140 640 years. 441 00:19:05.780 --> 00:19:06.340 Roger: Yeah. 442 00:19:07.220 --> 00:19:09.700 Andrew Dunkley: So for it to have gone 443 00:19:09.700 --> 00:19:12.700 supernova in the past and us to witness 444 00:19:12.700 --> 00:19:14.420 it, it has to have happened 445 00:19:15.940 --> 00:19:18.660 pretty close to 640 years ago. 446 00:19:19.220 --> 00:19:20.260 Does that make sense? 447 00:19:20.420 --> 00:19:23.260 Professor Fred Watson: Yes. Um, so you could think of that in 448 00:19:23.260 --> 00:19:25.460 another way. Um, you know, 449 00:19:26.300 --> 00:19:29.060 um, anywhere between us and 640 450 00:19:29.060 --> 00:19:31.620 light years away, there could be this pulse 451 00:19:31.620 --> 00:19:33.540 of light that's on its way to us 452 00:19:34.260 --> 00:19:37.220 from Betelgeuse. Uh, it would spread 453 00:19:37.220 --> 00:19:39.940 out in a sphere, and as that sphere 454 00:19:39.940 --> 00:19:42.140 expanded, eventually it would wash over the 455 00:19:42.140 --> 00:19:44.980 Earth and we'd see it, um, and perhaps 456 00:19:44.980 --> 00:19:46.740 see it during the day as well, because it 457 00:19:46.740 --> 00:19:49.700 might get bright enough to do that. Uh, and 458 00:19:49.700 --> 00:19:51.220 I think that's a really good way of putting 459 00:19:51.220 --> 00:19:53.820 it, Andrew, because thinking, um, about the 460 00:19:53.820 --> 00:19:55.500 galaxies, they're just streaming light out 461 00:19:55.500 --> 00:19:58.300 all the time, but something like a, uh, 462 00:19:58.380 --> 00:20:01.140 supernova explosion, which gives a big pulse 463 00:20:01.140 --> 00:20:04.140 of light, um, that's perhaps easier to get 464 00:20:04.140 --> 00:20:06.180 your head around because that's. That's just 465 00:20:06.180 --> 00:20:08.940 gotta, um. It'll 466 00:20:08.940 --> 00:20:11.500 take whatever time is 467 00:20:11.500 --> 00:20:14.420 represented by the distance away. So 640 468 00:20:14.420 --> 00:20:17.260 light years away. It'll take 640 years 469 00:20:17.260 --> 00:20:19.340 to get here for that pulse to get here. But 470 00:20:19.340 --> 00:20:22.260 then it will sweep over us and we'll see the 471 00:20:22.260 --> 00:20:24.220 light. The light fading away. 472 00:20:24.460 --> 00:20:25.770 Andrew Dunkley: Yeah. And, um, 473 00:20:27.340 --> 00:20:29.500 the reason I chose that target is because 474 00:20:29.740 --> 00:20:32.500 there's a lot of conjecture about 475 00:20:32.500 --> 00:20:35.220 its future and the possibility that it's 476 00:20:35.220 --> 00:20:36.940 reaching that critical mass point. 477 00:20:37.480 --> 00:20:37.800 Professor Fred Watson: Yes. 478 00:20:38.190 --> 00:20:39.720 Andrew Dunkley: Um, but it could have already happened. 479 00:20:39.720 --> 00:20:41.240 That's the other thing. 480 00:20:42.040 --> 00:20:45.040 Professor Fred Watson: But that's something we can have no knowledge 481 00:20:45.040 --> 00:20:47.400 of. That's the key thing, because, um, 482 00:20:47.880 --> 00:20:50.360 we are limited by the speed of light. That's 483 00:20:50.440 --> 00:20:52.320 the thing that always limits our view of the 484 00:20:52.320 --> 00:20:52.760 universe. 485 00:20:52.760 --> 00:20:55.640 Andrew Dunkley: And just to confuse Eli a little bit more, 486 00:20:56.440 --> 00:20:59.040 there are, ah, probably things in the 487 00:20:59.040 --> 00:21:01.040 universe we will never witness because the 488 00:21:01.040 --> 00:21:04.000 light is just too far away to reach us in any 489 00:21:04.000 --> 00:21:05.960 reasonable amount of time. Even 490 00:21:06.910 --> 00:21:09.830 beyond the life of the Earth itself or 491 00:21:09.830 --> 00:21:12.180 our sun. Uh, 492 00:21:13.230 --> 00:21:15.750 there are things we will never, ever know 493 00:21:15.750 --> 00:21:16.030 about. 494 00:21:16.670 --> 00:21:17.310 Professor Fred Watson: Correct. 495 00:21:18.200 --> 00:21:21.040 Andrew Dunkley: Um, and that's where it just gives you, um, 496 00:21:22.430 --> 00:21:24.830 one of those Headaches that requires, uh, you 497 00:21:24.830 --> 00:21:27.630 to take paracetamol and ibuprofen at the same 498 00:21:27.630 --> 00:21:27.950 time. 499 00:21:32.100 --> 00:21:34.720 Um, deep, deep headaches. But Eli, great 500 00:21:34.720 --> 00:21:36.440 question. I'm not sure we solved your 501 00:21:36.440 --> 00:21:39.420 problem, but, um, anyway, uh, 502 00:21:40.800 --> 00:21:42.600 I try to explain this sort of stuff to my 503 00:21:42.600 --> 00:21:45.520 grandson, uh, and, uh, my granddaughters. 504 00:21:45.520 --> 00:21:48.280 And, you know, how do you 505 00:21:48.280 --> 00:21:50.160 explain time and distance 506 00:21:51.040 --> 00:21:53.970 to a young child? And, um, 507 00:21:53.970 --> 00:21:55.360 when you're trying to get through traffic, 508 00:21:57.200 --> 00:21:58.840 Professor Fred Watson: that might not be the best time to do it. 509 00:21:58.840 --> 00:22:00.720 Andrew Dunkley: Probably not, but they're very interested. 510 00:22:01.280 --> 00:22:03.240 Very interested. Thanks, Eli. 511 00:22:03.240 --> 00:22:03.840 Great question. 512 00:22:06.540 --> 00:22:09.180 Professor Fred Watson: The crew of Artemis 2 now bound for the moon, 513 00:22:09.420 --> 00:22:11.980 humanity's next great voyage begins. 514 00:22:12.620 --> 00:22:13.820 Space nuts. 515 00:22:14.140 --> 00:22:16.190 Andrew Dunkley: Our final question comes, uh, 516 00:22:16.780 --> 00:22:19.740 from Nova Scotia. It's from Ken. 517 00:22:19.910 --> 00:22:21.940 Uh, look, this is an old chestnut. We've, 518 00:22:21.940 --> 00:22:24.660 we've probably spoken about this many times, 519 00:22:24.660 --> 00:22:27.620 but it's always good to, um, to revisit. If 520 00:22:27.620 --> 00:22:30.340 the universe is expanding, what is it 521 00:22:30.340 --> 00:22:32.700 expanding into? And also, 522 00:22:33.330 --> 00:22:35.090 is the universe spherical? 523 00:22:36.770 --> 00:22:39.010 Professor Fred Watson: So, um, yes. What's it expanding into? 524 00:22:39.010 --> 00:22:41.130 Andrew Dunkley: Well, we don't know. 525 00:22:41.130 --> 00:22:43.250 Professor Fred Watson: And yes, that's. 526 00:22:43.650 --> 00:22:45.970 Yes. Uh, it's actually, we don't know. And 527 00:22:45.970 --> 00:22:48.930 maybe, maybe, maybe. So, 528 00:22:49.000 --> 00:22:51.570 um, the universe 529 00:22:52.210 --> 00:22:55.090 is everything that we can detect. That's 530 00:22:55.090 --> 00:22:56.850 the definition of the universe. Everything we 531 00:22:56.850 --> 00:22:59.490 can measure or detect. And that means, 532 00:23:00.370 --> 00:23:02.450 and we observe the expansion, 533 00:23:03.250 --> 00:23:06.210 but we don't know whether there's an edge 534 00:23:06.210 --> 00:23:08.050 to the universe. We don't know whether it's 535 00:23:08.050 --> 00:23:10.410 infinite. We don't know anything beyond the 536 00:23:10.410 --> 00:23:13.130 horizons that we see. And um, the most 537 00:23:13.130 --> 00:23:14.850 obvious one is the cosmic microwave 538 00:23:14.850 --> 00:23:16.900 background radiation, um, 539 00:23:17.730 --> 00:23:19.570 beyond which we can't see. But the universe 540 00:23:19.570 --> 00:23:21.570 almost certainly goes on beyond that, 541 00:23:22.130 --> 00:23:24.610 probably for a very long way, maybe very big. 542 00:23:24.930 --> 00:23:27.330 But we've got no knowledge of a boundary or 543 00:23:28.190 --> 00:23:30.510 any other medium that it might be expanding 544 00:23:30.510 --> 00:23:33.230 into. So, um, 545 00:23:33.610 --> 00:23:36.430 uh, one possibility is the idea of multiple 546 00:23:36.430 --> 00:23:38.830 universes. And they might 547 00:23:38.830 --> 00:23:40.990 exist maybe 548 00:23:41.630 --> 00:23:44.080 in a higher dimensional, uh, 549 00:23:45.390 --> 00:23:48.270 arena, if I can put it that way. You know, 550 00:23:48.750 --> 00:23:51.670 if you can, um, find that 551 00:23:51.670 --> 00:23:54.670 there are extra dimensions, we know the 552 00:23:54.830 --> 00:23:56.870 three dimensions of space and one of time. 553 00:23:56.870 --> 00:23:58.550 That's what we've got now. 554 00:23:59.830 --> 00:24:02.230 But, uh, if there are hidden 555 00:24:02.630 --> 00:24:04.870 extra dimensions, maybe they provide 556 00:24:05.830 --> 00:24:08.150 a venue for the universe to expand into. 557 00:24:08.970 --> 00:24:11.750 Uh, and there are various theories 558 00:24:11.750 --> 00:24:14.750 that accept that, um, M. M theory is one of 559 00:24:14.750 --> 00:24:17.710 them, where M is probably an abbreviation 560 00:24:17.710 --> 00:24:19.990 for membrane. The idea is that the universe 561 00:24:20.470 --> 00:24:22.590 can be collapsed onto a two dimensional 562 00:24:22.590 --> 00:24:24.390 membrane, and there are lots of these 563 00:24:24.390 --> 00:24:27.300 membranes in the kind 564 00:24:27.300 --> 00:24:29.580 of higher dimensional universe. But that's 565 00:24:29.580 --> 00:24:31.420 just conjecture and we've got no 566 00:24:32.060 --> 00:24:34.420 mechanism for proving that at the moment. The 567 00:24:34.420 --> 00:24:36.700 only thing we know with certainty with 568 00:24:36.700 --> 00:24:38.740 absolute certainty is that the universe is 569 00:24:38.740 --> 00:24:39.340 expanding. 570 00:24:39.500 --> 00:24:41.940 Andrew Dunkley: Yes. Uh, at an accelerating rate. Although 571 00:24:41.940 --> 00:24:43.900 the accelerating rate's not as accelerating 572 00:24:43.900 --> 00:24:45.580 as it once was. Possibly. 573 00:24:45.740 --> 00:24:46.380 Professor Fred Watson: Possibly. 574 00:24:46.530 --> 00:24:49.100 Andrew Dunkley: Um, yeah. There's three possible 575 00:24:49.980 --> 00:24:52.900 shapes of the universe. He asks if it's 576 00:24:52.900 --> 00:24:55.860 a sphere. Um, there's, uh, the flat 577 00:24:55.860 --> 00:24:58.470 universe theory. Do we have to go there? Uh, 578 00:24:58.470 --> 00:25:00.360 there's the closed universe 579 00:25:01.160 --> 00:25:04.080 theory, which is the positive curvature, so a 580 00:25:04.080 --> 00:25:06.960 sphere. Or the open universe theory, 581 00:25:06.960 --> 00:25:09.040 which is negative curvature. Huh. So it's 582 00:25:09.040 --> 00:25:11.800 more like the shape of a saddle. From what 583 00:25:11.800 --> 00:25:13.720 I'm reading, the most popular, 584 00:25:15.170 --> 00:25:17.800 uh, likelihood is the flat universe theory. 585 00:25:18.520 --> 00:25:21.080 Professor Fred Watson: But it's only flat in a Euclidean sense. 586 00:25:21.400 --> 00:25:23.960 It doesn't mean it's shaped like a 587 00:25:23.960 --> 00:25:26.920 tabletop. Uh, it means that parallel 588 00:25:26.920 --> 00:25:29.670 lines never meet. Basically, that's what we 589 00:25:29.670 --> 00:25:31.950 mean by flat. It's the shape of the geometry. 590 00:25:32.510 --> 00:25:35.030 Andrew Dunkley: And the other thing that they suggest is 591 00:25:35.030 --> 00:25:37.870 that, um, it can be flat and still 592 00:25:37.870 --> 00:25:39.790 expanding. As you said, uh, it might be 593 00:25:39.790 --> 00:25:42.510 infinite. We've talked about that before. 594 00:25:42.590 --> 00:25:45.230 And there is likely no centre and no edge. 595 00:25:46.190 --> 00:25:48.270 Professor Fred Watson: Correct. That's what we believe 596 00:25:49.070 --> 00:25:51.710 now, um, to its shape. 597 00:25:52.110 --> 00:25:54.920 So, uh, so 598 00:25:56.120 --> 00:25:58.720 basically, I think Ken's question is, is it 599 00:25:58.720 --> 00:26:00.920 spherical? And 600 00:26:01.480 --> 00:26:03.960 we don't know the answer to that. We know 601 00:26:03.960 --> 00:26:06.560 that the volume within which we can 602 00:26:06.560 --> 00:26:08.760 detect is spherical because 603 00:26:09.720 --> 00:26:12.360 the cosmic microwave background radiation 604 00:26:12.760 --> 00:26:15.160 forms an imaginary shell, 605 00:26:16.100 --> 00:26:19.080 uh, all around our galaxy. And it's 606 00:26:19.080 --> 00:26:21.440 the same distance in every direction. So in 607 00:26:21.440 --> 00:26:24.000 that regard, it's what we call isotropic, the 608 00:26:24.000 --> 00:26:26.870 same in all directions. Uh, and 609 00:26:26.870 --> 00:26:28.790 that's really the only thing we can 610 00:26:29.670 --> 00:26:32.350 lay it down to. But there are ideas that if 611 00:26:32.350 --> 00:26:34.270 you looked at the universe on a bigger scale 612 00:26:34.270 --> 00:26:36.390 than we could see, it wouldn't be. That it 613 00:26:36.390 --> 00:26:38.870 might be different in different directions. 614 00:26:39.820 --> 00:26:42.070 Um, and that, in fact, has been 615 00:26:42.390 --> 00:26:44.950 hypothesised as one of the sources of dark 616 00:26:44.950 --> 00:26:47.270 energy, that we're just seeing a local bit of 617 00:26:47.270 --> 00:26:49.400 the universe that's expanding, whose, uh, 618 00:26:49.750 --> 00:26:51.790 expansion is increasing, whereas somewhere 619 00:26:51.790 --> 00:26:54.750 else it might be slowing down 620 00:26:54.750 --> 00:26:56.800 the expansion of the universe. Um, 621 00:26:58.990 --> 00:27:00.190 Andrew Dunkley: yeah, sorry, go on. 622 00:27:00.350 --> 00:27:02.910 Professor Fred Watson: No, that would be a universe that's not 623 00:27:02.910 --> 00:27:04.550 isotropic. It's not the same in all 624 00:27:04.550 --> 00:27:06.810 directions, but we assume it's isotropic. So, 625 00:27:06.810 --> 00:27:09.190 uh, that's all we can do in our assumptions 626 00:27:09.190 --> 00:27:10.030 in cosmology. 627 00:27:10.190 --> 00:27:13.150 Andrew Dunkley: We just can't see beyond 628 00:27:13.310 --> 00:27:15.310 what we can see. Which sounds stupid, but 629 00:27:15.470 --> 00:27:18.190 that's the way the universe is. Um, 630 00:27:18.430 --> 00:27:20.630 we've got the known universe and then the 631 00:27:20.630 --> 00:27:20.990 rest of the. 632 00:27:21.940 --> 00:27:24.140 Professor Fred Watson: That's right, basically. And the rest might 633 00:27:24.140 --> 00:27:25.700 be a lot bigger than the known universe. 634 00:27:25.940 --> 00:27:27.440 Andrew Dunkley: Yeah, but we just don't know. Um, 635 00:27:29.060 --> 00:27:30.940 the only thing I thought of is, like, you 636 00:27:30.940 --> 00:27:32.820 look at Earth's atmosphere and as you go out, 637 00:27:32.820 --> 00:27:35.460 it fins. And so there's no defined 638 00:27:35.540 --> 00:27:38.260 line between space and 639 00:27:38.660 --> 00:27:41.180 the Earth proper. Could the 640 00:27:41.180 --> 00:27:43.060 universe be of the same ilk? 641 00:27:44.180 --> 00:27:47.060 Professor Fred Watson: Yes, but that would imply that space time 642 00:27:47.060 --> 00:27:49.700 just sort of keeps. Just keeps on going. It 643 00:27:49.700 --> 00:27:50.700 just might be empty. 644 00:27:51.400 --> 00:27:53.420 Uh, yeah, 645 00:27:53.880 --> 00:27:56.060 uh, we don't know. 646 00:27:56.220 --> 00:27:57.100 Andrew Dunkley: We don't know. 647 00:27:57.500 --> 00:27:59.500 Professor Fred Watson: Why are you asking us? We don't know. 648 00:28:02.580 --> 00:28:05.500 Andrew Dunkley: Uh, um, thank you, Ken. Uh, very 649 00:28:05.500 --> 00:28:07.460 thought provoking question and thanks for 650 00:28:07.460 --> 00:28:08.060 sending it in. 651 00:28:08.060 --> 00:28:10.100 If you have questions for us, please send 652 00:28:10.100 --> 00:28:11.980 them to us via our website, 653 00:28:12.060 --> 00:28:14.700 spacenutspodcast.com spacenuts 654 00:28:14.700 --> 00:28:16.980 IO there's a little button at the top called 655 00:28:16.980 --> 00:28:19.900 AMA M and that's what you click on to 656 00:28:20.200 --> 00:28:22.080 send us text and audio questions. If you've 657 00:28:22.080 --> 00:28:23.880 got a device with a microphone, you're all 658 00:28:23.880 --> 00:28:26.720 set. Uh, most smartphones and smart devices 659 00:28:26.720 --> 00:28:29.080 have that and you can send it to us 660 00:28:29.560 --> 00:28:31.520 in audio form. Don't forget to tell us who 661 00:28:31.520 --> 00:28:32.880 you are and where you're from. Or you can 662 00:28:32.880 --> 00:28:34.480 send us a text question. Just fill in the 663 00:28:34.480 --> 00:28:37.280 blanks. And while you're there, have a look 664 00:28:37.280 --> 00:28:39.080 around, visit the shop, get something from 665 00:28:39.400 --> 00:28:42.360 yourself. Um, you know, whatever you like. 666 00:28:42.920 --> 00:28:44.480 And we're done. Fred Watson, thank you so 667 00:28:44.480 --> 00:28:45.660 much. That was a tough one. 668 00:28:47.010 --> 00:28:50.010 Professor Fred Watson: Yeah, well, we, you know, uh, Space 669 00:28:50.010 --> 00:28:52.290 Nuts always probes the limits of knowledge. 670 00:28:52.290 --> 00:28:54.010 We. It does. Ah, that's what we. 671 00:28:54.010 --> 00:28:56.570 Andrew Dunkley: Unfortunately, I have such limited knowledge, 672 00:28:56.570 --> 00:28:58.650 I'm not very helpful. But I'm glad you're 673 00:28:58.650 --> 00:28:58.930 here. 674 00:28:59.250 --> 00:29:01.929 Professor Fred Watson: No, you are very helpful and, um, so are our 675 00:29:01.929 --> 00:29:04.170 listeners because they keep on probing, which 676 00:29:04.170 --> 00:29:04.450 is great. 677 00:29:04.450 --> 00:29:06.570 Andrew Dunkley: They do indeed. All right, Fred Watson, 678 00:29:06.570 --> 00:29:07.890 thanks very much. We'll catch you on the next 679 00:29:07.890 --> 00:29:08.370 episode. 680 00:29:08.690 --> 00:29:10.170 Professor Fred Watson: Sounds great. Thanks, Andrew. 681 00:29:10.170 --> 00:29:11.770 Andrew Dunkley: Professor Fred Watson Watson, astronomer at 682 00:29:11.770 --> 00:29:13.850 large. And thanks to Huw in the studio, who 683 00:29:13.850 --> 00:29:15.530 couldn't be with us today because he's been 684 00:29:15.530 --> 00:29:17.560 expanding at an accelerating rate. So he was. 685 00:29:17.710 --> 00:29:19.910 Enter the gym. And from me, Andrew Dunkley. 686 00:29:19.910 --> 00:29:21.550 Thanks for your company. We'll see you on the 687 00:29:21.550 --> 00:29:23.070 next episode of Space Nuts. 688 00:29:23.070 --> 00:29:23.710 Professor Fred Watson: Bye. Bye. 689 00:29:24.330 --> 00:29:27.110 Andrew Dunkley: Uh, you'll be listening to the Space Nuts 690 00:29:27.110 --> 00:29:30.070 podcast, available at 691 00:29:30.070 --> 00:29:32.030 Apple Podcasts, Spotify, 692 00:29:32.190 --> 00:29:34.950 iHeartRadio or your favourite podcast 693 00:29:34.950 --> 00:29:36.670 player. You can also stream on 694 00:29:36.670 --> 00:29:38.990 demand@bytes.comm this 695 00:29:38.990 --> 00:29:41.390 Professor Fred Watson: has been another quality podcast production 696 00:29:41.390 --> 00:29:42.910 from bytes.um.com.