WEBVTT 0 00:00:00.960 --> 00:00:01.440 Andrew Dunkley: Hi there. 1 00:00:01.440 --> 00:00:03.920 Andrew Dunkley: This is Space Nuts. It's a Q and A edition. 2 00:00:04.120 --> 00:00:06.080 Uh, my name is Andrew Dunkley. Thanks for 3 00:00:06.080 --> 00:00:08.680 your company. In, uh, this episode we will 4 00:00:08.680 --> 00:00:11.680 endeavour to answer audience 5 00:00:11.680 --> 00:00:14.040 questions. Uh, Kevin wants to know about 6 00:00:14.040 --> 00:00:16.399 stopping a photon. Did that really happen? 7 00:00:17.180 --> 00:00:19.840 Ah, we've got a, uh, duo 8 00:00:20.160 --> 00:00:22.960 named Reynold and Brian wanting to ask about 9 00:00:22.960 --> 00:00:25.520 intertwining electromagnetic fields. 10 00:00:26.320 --> 00:00:29.200 Um, the speed of colliding particles in the 11 00:00:29.360 --> 00:00:32.300 Large Hadron Collider is a question we've 12 00:00:32.300 --> 00:00:35.220 received. And Mark is asking us 13 00:00:35.220 --> 00:00:38.220 about the excess number of satellites in 14 00:00:38.220 --> 00:00:40.980 space and what can be done about it. He's got 15 00:00:40.980 --> 00:00:43.500 an idea. We will see what that's all about 16 00:00:43.740 --> 00:00:46.140 on this episode of space nuts. 17 00:00:46.220 --> 00:00:48.700 Generic: 15 seconds. Guidance is internal. 18 00:00:48.940 --> 00:00:51.660 10, 9. Ignition 19 00:00:51.660 --> 00:00:52.620 sequence start. 20 00:00:52.780 --> 00:00:53.501 Professor Fred Watson: Space nuts. 21 00:00:53.573 --> 00:00:56.360 Generic: 5, 4, 3. 2. 1. 2, 3, 4, 22 00:00:56.431 --> 00:00:58.540 5, 5, 4, 3, 2, 1. 23 00:00:58.620 --> 00:00:59.820 Professor Fred Watson: Space nuts. 24 00:00:59.900 --> 00:01:01.740 Generic: Astronauts report it feels good. 25 00:01:02.920 --> 00:01:04.600 Andrew Dunkley: And he's back again for more. 26 00:01:04.980 --> 00:01:06.800 Uh, it is Professor Fred Watson Watson, 27 00:01:06.800 --> 00:01:08.440 Astronomer at large. Hello Fred Watson. 28 00:01:08.840 --> 00:01:11.720 Professor Fred Watson: Hello Andrew. Um, fancy seeing you here. Yes, 29 00:01:12.680 --> 00:01:13.400 in my study. 30 00:01:13.640 --> 00:01:16.600 Andrew Dunkley: Yes, I'm in mine as well. Although it's 31 00:01:16.600 --> 00:01:18.319 hard to see because the background's all 32 00:01:18.319 --> 00:01:20.520 blurred. I must have a setting 33 00:01:21.080 --> 00:01:23.040 that I changed in this thing and I can't 34 00:01:23.040 --> 00:01:25.600 figure it out how to undo it. But um, it 35 00:01:25.600 --> 00:01:28.040 doesn't really matter. You probably don't 36 00:01:28.040 --> 00:01:29.720 want to see all the junk at the back of my 37 00:01:29.720 --> 00:01:32.240 room anyway. It's not as good as your 38 00:01:32.240 --> 00:01:32.760 junk. 39 00:01:32.760 --> 00:01:35.500 Professor Fred Watson: Oh, it's good Chunk. My microscope, uh, there 40 00:01:35.500 --> 00:01:35.780 as well. 41 00:01:35.780 --> 00:01:36.820 Andrew Dunkley: Oh yeah, that's nice. 42 00:01:37.700 --> 00:01:39.580 Professor Fred Watson: If I see anything I need to look at closely, 43 00:01:39.580 --> 00:01:41.220 I can just turn around in my chair and have a 44 00:01:41.220 --> 00:01:41.460 look. 45 00:01:41.540 --> 00:01:43.380 Andrew Dunkley: Yeah, well, your age, that's probably. 46 00:01:46.420 --> 00:01:47.580 You walked into that one. 47 00:01:47.580 --> 00:01:48.660 Professor Fred Watson: I did deny. Yes. 48 00:01:50.110 --> 00:01:52.340 Andrew Dunkley: Um, shall we answer some questions? 49 00:01:53.690 --> 00:01:54.820 Professor Fred Watson: Uh, no, no, let's 50 00:01:57.510 --> 00:01:59.340 Andrew Dunkley: uh, let's go to our first question. It's an 51 00:01:59.340 --> 00:02:01.540 audio question and it comes from Kevin. 52 00:02:03.470 --> 00:02:06.110 Kevin: Hello, space notes. My name is Kevin. I'm 53 00:02:06.110 --> 00:02:08.670 from Las Vegas, Nevada and I finally have a 54 00:02:08.670 --> 00:02:11.030 question to ask you after listening to you 55 00:02:11.030 --> 00:02:13.950 guys from the beginning. It's regarding 56 00:02:14.030 --> 00:02:16.470 an article that I came across but didn't get 57 00:02:16.470 --> 00:02:18.830 to fully read on how we have 58 00:02:18.830 --> 00:02:21.630 officially docked a particle 59 00:02:21.630 --> 00:02:24.510 of light. Not just slowed it down but full 60 00:02:24.510 --> 00:02:27.510 on. Um, stop. My question is kind of a 61 00:02:27.510 --> 00:02:30.300 two part A, is this a 62 00:02:30.300 --> 00:02:32.580 legitimate thing? Have we stopped a, uh, 63 00:02:32.740 --> 00:02:35.380 photon from moving and B, 64 00:02:36.260 --> 00:02:38.180 if not, this can be posed as a what if 65 00:02:38.180 --> 00:02:41.100 question. But what's the consequences for 66 00:02:41.100 --> 00:02:43.380 a photon that come to a complete stop? 67 00:02:43.860 --> 00:02:46.580 Now, photons don't have rest mass. It's only 68 00:02:46.580 --> 00:02:49.420 in the mass of their energy. But does 69 00:02:49.420 --> 00:02:52.340 it Gain rest mass now that it is at a rest 70 00:02:52.820 --> 00:02:55.780 or is this one of those it enters 71 00:02:56.170 --> 00:02:58.570 and just ends up going back to the speed of 72 00:02:58.570 --> 00:03:01.290 light once whatever's holding it lets go? 73 00:03:02.120 --> 00:03:04.930 Um, Google doesn't quite give me the run 74 00:03:04.930 --> 00:03:07.650 around for a bunch of stuff so I figured I'd 75 00:03:07.650 --> 00:03:10.610 ask you guys. Love the show. Thank you for 76 00:03:10.610 --> 00:03:11.130 listening. 77 00:03:11.850 --> 00:03:12.369 Professor Fred Watson: Thank you. 78 00:03:12.369 --> 00:03:14.810 Andrew Dunkley: Kevin. Uh, I love this question. Uh, this is 79 00:03:14.810 --> 00:03:17.450 a subject that has come up uh, a few times 80 00:03:17.610 --> 00:03:20.530 over the years and it prompted me to do 81 00:03:20.530 --> 00:03:23.400 a bit of research. Uh, and I did find uh, 82 00:03:23.400 --> 00:03:26.330 an article on the Physics World website 83 00:03:26.410 --> 00:03:27.990 that uh, discusses this. 84 00:03:27.990 --> 00:03:29.670 Professor Fred Watson: Fred Watson Good. 85 00:03:32.590 --> 00:03:34.880 Uh, yes, that's right. Look, it's ah, 86 00:03:36.150 --> 00:03:38.630 it really is an interesting um, process. 87 00:03:39.510 --> 00:03:42.470 Um, but it's uh, it's, 88 00:03:43.350 --> 00:03:46.030 there's a bit of subterfuge here in the 89 00:03:46.030 --> 00:03:46.790 nomenclature 90 00:03:47.830 --> 00:03:49.510 Andrew Dunkley: because well that's a big word. 91 00:03:50.290 --> 00:03:53.230 Professor Fred Watson: Uh, there is two big words 92 00:03:53.230 --> 00:03:55.990 there. Don't know what either of them mean. 93 00:03:57.750 --> 00:04:00.710 There's a, you're almost 94 00:04:00.710 --> 00:04:02.950 playing with words here in a way because 95 00:04:03.510 --> 00:04:06.390 you do stop light. But it's not 96 00:04:06.390 --> 00:04:08.390 the individual photon 97 00:04:09.110 --> 00:04:11.830 that stops. It gets 98 00:04:11.830 --> 00:04:13.590 converted into something else, 99 00:04:14.550 --> 00:04:16.670 if I can put it that way. So you've got to 100 00:04:16.670 --> 00:04:18.870 start off with a Bose 101 00:04:19.030 --> 00:04:21.790 Einstein condensate. A 102 00:04:21.790 --> 00:04:24.510 condensate which is ultra 103 00:04:24.510 --> 00:04:27.310 cold atoms, they're a fraction of a 104 00:04:27.310 --> 00:04:29.970 degree above absolute zero. 105 00:04:30.530 --> 00:04:33.090 And the thing about one of these, they're 106 00:04:33.090 --> 00:04:35.450 usually called a bec, a Bose Einstein 107 00:04:35.450 --> 00:04:38.170 condensate. Um, it is 108 00:04:38.170 --> 00:04:41.130 basically a whole lot of atoms and usually 109 00:04:41.130 --> 00:04:43.440 it's sodium, uh, which um, 110 00:04:44.210 --> 00:04:46.770 are so cold that they behave 111 00:04:47.410 --> 00:04:50.210 like a single quantum object. So 112 00:04:50.210 --> 00:04:52.050 it's a bit like entanglement 113 00:04:53.090 --> 00:04:55.730 where you've got two quantum particles and 114 00:04:55.730 --> 00:04:58.530 they um, behave like a single particle. 115 00:04:58.610 --> 00:05:01.420 It's that. But in a, in 116 00:05:01.420 --> 00:05:04.420 a whole petri dish if you like, a lot 117 00:05:04.420 --> 00:05:07.420 of um, a lot of uh, these atoms are 118 00:05:07.420 --> 00:05:09.420 entangled effectively. So you've got this 119 00:05:09.420 --> 00:05:12.260 bec, the boson condensate. But 120 00:05:12.260 --> 00:05:14.380 then you've got to uh, 121 00:05:14.940 --> 00:05:17.820 you sort of excite it with 122 00:05:17.820 --> 00:05:20.660 a laser and then you send your 123 00:05:20.660 --> 00:05:22.780 photon in that you want to stop. 124 00:05:23.340 --> 00:05:26.140 And um, it basically 125 00:05:26.940 --> 00:05:27.900 the photon, 126 00:05:30.970 --> 00:05:32.890 it's not a photon anymore. It's now 127 00:05:32.970 --> 00:05:35.890 interacting with these super cold 128 00:05:35.890 --> 00:05:38.890 atoms, uh, in a way that 129 00:05:39.930 --> 00:05:42.170 effectively slows the transfer of energy 130 00:05:42.170 --> 00:05:45.090 down. So it's not the same photon that 131 00:05:45.090 --> 00:05:48.050 stopped. It becomes something else. It 132 00:05:48.050 --> 00:05:50.120 becomes um, uh. 133 00:05:50.810 --> 00:05:53.290 One um, document I read 134 00:05:54.020 --> 00:05:56.500 suggests it's actually 135 00:05:56.500 --> 00:05:59.060 converted into a matter 136 00:05:59.220 --> 00:06:02.210 based hologram, uh, uh, 137 00:06:02.210 --> 00:06:05.020 which is a slightly um, odd way of putting it 138 00:06:05.020 --> 00:06:07.460 but basically it tells you that 139 00:06:08.260 --> 00:06:11.140 you've changed the photon but 140 00:06:11.680 --> 00:06:14.500 uh, you can then basically, 141 00:06:14.920 --> 00:06:17.660 um, there's 142 00:06:17.660 --> 00:06:20.580 a separate laser that's exciting the BEC 143 00:06:20.900 --> 00:06:23.820 into this unusual state. If you turn that 144 00:06:23.820 --> 00:06:26.770 off, uh, the pulse doesn't 145 00:06:26.770 --> 00:06:29.650 just slow down. Sorry, the 146 00:06:29.650 --> 00:06:31.770 photon that you're trying to stop actually 147 00:06:31.770 --> 00:06:34.010 does stop when you turn this energy off. 148 00:06:34.810 --> 00:06:36.490 And what you've got is 149 00:06:37.930 --> 00:06:38.650 essentially, 150 00:06:40.940 --> 00:06:41.100 Kevin: uh, 151 00:06:41.100 --> 00:06:42.770 Professor Fred Watson: all the information, if I can put it that 152 00:06:42.770 --> 00:06:45.210 way, contained in the photon is 153 00:06:45.450 --> 00:06:48.250 transferred into this imprint in 154 00:06:48.250 --> 00:06:50.650 the bec, in the atoms of the 155 00:06:51.290 --> 00:06:54.290 Bose Einstein condensate. It 156 00:06:54.290 --> 00:06:57.210 becomes, as I said earlier, like a hologram. 157 00:06:57.590 --> 00:06:59.750 But then if you turn that, what's called the 158 00:06:59.750 --> 00:07:02.630 coupling laser back on, um, the light 159 00:07:02.950 --> 00:07:05.430 pulse is reconstructed 160 00:07:05.830 --> 00:07:08.750 and sets off again on its path. I haven't 161 00:07:08.750 --> 00:07:11.350 explained that very well, but that's 162 00:07:11.350 --> 00:07:12.550 basically what's happening. 163 00:07:12.790 --> 00:07:14.470 Andrew Dunkley: Okay, so 164 00:07:15.350 --> 00:07:17.990 Kevin's right. Uh, we 165 00:07:17.990 --> 00:07:20.150 have demonstrated that you can 166 00:07:20.630 --> 00:07:23.550 slow light down. I, uh, think when the storey 167 00:07:23.550 --> 00:07:25.030 first came out, they actually said they 168 00:07:25.030 --> 00:07:27.750 stopped it. Uh, but 169 00:07:28.550 --> 00:07:30.450 second, uh, part of his question was, 170 00:07:31.650 --> 00:07:34.330 does it reconstitute itself and get on with 171 00:07:34.330 --> 00:07:36.650 its journey? And the answer is yes, that's 172 00:07:36.650 --> 00:07:36.930 correct. 173 00:07:36.930 --> 00:07:39.850 Professor Fred Watson: Yeah. So this is. It's not, um, a 174 00:07:39.850 --> 00:07:41.610 particular, you know, it's not a specific 175 00:07:41.610 --> 00:07:43.850 piece of research. This. There's a whole lot 176 00:07:43.850 --> 00:07:46.530 of research going on. It's almost like 177 00:07:46.930 --> 00:07:49.810 becoming, um, uh, just a 178 00:07:50.290 --> 00:07:53.130 everyday tool of physicists to do this, to 179 00:07:53.130 --> 00:07:56.130 stop pulses of light, uh, and 180 00:07:56.400 --> 00:07:58.600 tinker around and see what they can learn 181 00:07:58.600 --> 00:08:00.800 from it. Making that grossly 182 00:08:00.800 --> 00:08:03.160 oversimplified. So I apologise to all my 183 00:08:03.160 --> 00:08:06.120 physicist friends. Um, but it's, um, 184 00:08:06.640 --> 00:08:09.480 almost a routine process to do this. Now. I 185 00:08:09.480 --> 00:08:11.600 think I'm right in saying that not just. 186 00:08:12.000 --> 00:08:14.000 Although I suspect it's only a few labs in 187 00:08:14.000 --> 00:08:15.360 the world that have got the equipment 188 00:08:15.360 --> 00:08:17.520 necessary, uh, to do it. Because 189 00:08:18.080 --> 00:08:20.040 it's not just your everyday microscope or 190 00:08:20.040 --> 00:08:22.720 anything like that. It's, uh, quite a 191 00:08:22.720 --> 00:08:25.040 specific piece of, uh, infrastructure, 192 00:08:25.040 --> 00:08:27.560 including the Bose Einstein condensate, which 193 00:08:27.560 --> 00:08:30.180 I think we're all actually made in the. Was 194 00:08:30.180 --> 00:08:32.860 it in the 1980s? Um, they were predicted by 195 00:08:32.860 --> 00:08:35.860 Bose and Einstein, two physicists. Uh, 196 00:08:35.860 --> 00:08:38.060 but I don't think we actually managed to make 197 00:08:38.060 --> 00:08:40.580 one until maybe 40 years ago. I might have 198 00:08:40.580 --> 00:08:42.860 that date wrong, but that sticks in my mind. 199 00:08:43.100 --> 00:08:45.740 Andrew Dunkley: Yeah, that's fascinating. I wonder why we're 200 00:08:45.980 --> 00:08:48.980 so keen to learn how to do this with light. I 201 00:08:48.980 --> 00:08:51.500 mean, what do we gain from it? 202 00:08:51.740 --> 00:08:54.700 Professor Fred Watson: Well, um, uh, it 203 00:08:54.940 --> 00:08:57.580 teaches you about the properties of the Bose 204 00:08:57.580 --> 00:09:00.360 Einstein condensate. And 205 00:09:00.440 --> 00:09:02.720 being able to stop a photon and store its 206 00:09:02.720 --> 00:09:05.240 energy is quite an 207 00:09:05.240 --> 00:09:07.880 interesting thing. Particularly if 208 00:09:07.960 --> 00:09:10.440 you think, well, maybe we can apply this to 209 00:09:10.600 --> 00:09:13.480 quantum computing. I think that's 210 00:09:14.170 --> 00:09:16.399 uh, one of the reasons why this is a hot 211 00:09:16.399 --> 00:09:18.760 topic, uh, that it does have 212 00:09:19.000 --> 00:09:21.400 applications for quantum, 213 00:09:21.910 --> 00:09:24.440 uh, information. It also, 214 00:09:25.410 --> 00:09:28.400 um, you know, it relates to 215 00:09:28.400 --> 00:09:30.280 our understanding of physics at the most 216 00:09:30.280 --> 00:09:32.790 basic level. Uh, it's, uh. 217 00:09:32.920 --> 00:09:35.440 Yes, it's extraordinary. I think it is a very 218 00:09:35.440 --> 00:09:38.340 useful line of research and, um. 219 00:09:38.600 --> 00:09:41.600 Sounds like it, I think. Yes, I think I 220 00:09:41.600 --> 00:09:43.040 should understand it better. That's the 221 00:09:43.040 --> 00:09:43.720 bottom line. 222 00:09:44.360 --> 00:09:46.840 Andrew Dunkley: Kevin might also be interested to know the 223 00:09:46.840 --> 00:09:49.440 revival process after you switch the laser 224 00:09:49.440 --> 00:09:52.040 back on is quite slow. It's not like it 225 00:09:52.040 --> 00:09:54.620 instantly goes back to its 300 million 226 00:09:54.620 --> 00:09:57.500 metres per second. Um, light speed, 227 00:09:57.880 --> 00:10:00.860 uh, takes a little bit, and 228 00:10:00.860 --> 00:10:03.380 I'm talking a little bit of time to, to sort 229 00:10:03.380 --> 00:10:04.980 of rev its engines back up again. 230 00:10:05.860 --> 00:10:08.700 Professor Fred Watson: Yeah, so, so that's not. I mean, photons 231 00:10:08.700 --> 00:10:11.060 in a vacuum always travel at that 300 232 00:10:11.540 --> 00:10:13.900 or 300,000 kilometres per second, the way we 233 00:10:13.900 --> 00:10:16.780 usually put it, 300 million kilometres 234 00:10:16.780 --> 00:10:19.700 per second. Um, uh, but that's only 235 00:10:19.700 --> 00:10:21.300 the speed in a vacuum. The speed in 236 00:10:21.610 --> 00:10:24.530 different, um, other media is 237 00:10:24.530 --> 00:10:24.810 different. 238 00:10:26.170 --> 00:10:28.280 Andrew Dunkley: Thanks for the question, Kevin. That's um, 239 00:10:28.330 --> 00:10:29.850 that's a really interesting one. 240 00:10:30.410 --> 00:10:33.130 Our next question, Fred Watson, comes from. 241 00:10:33.340 --> 00:10:35.010 Uh, Now I'm going to assume this is two 242 00:10:35.010 --> 00:10:37.050 people. And the reason I say that is because 243 00:10:37.050 --> 00:10:39.370 the other day we read a note from Rennie in 244 00:10:39.370 --> 00:10:41.650 California about, uh, one of his grandsons 245 00:10:41.650 --> 00:10:44.570 being inspired to perhaps study astronomy in 246 00:10:44.570 --> 00:10:47.290 the future. And these two fellows 247 00:10:47.290 --> 00:10:49.690 sport the same surname as Rennie. So I'm 248 00:10:49.690 --> 00:10:52.010 going to assume these are two people, 249 00:10:52.170 --> 00:10:54.710 Reynold and who've sent this question in. 250 00:10:55.910 --> 00:10:58.830 And if I'm wrong, I'm sorry, but, uh, I just 251 00:10:58.830 --> 00:11:00.590 got that gut feeling about it. They haven't 252 00:11:00.590 --> 00:11:02.110 actually said these are from two different 253 00:11:02.110 --> 00:11:05.070 people, but, um, uh, the fabric 254 00:11:05.070 --> 00:11:07.510 of space time consists of different 255 00:11:07.590 --> 00:11:10.470 fields. An example is the Higgs field, 256 00:11:11.420 --> 00:11:14.150 uh, electromagnetic field, et cetera. 257 00:11:14.150 --> 00:11:16.430 So my question is, theoretically, could any 258 00:11:16.430 --> 00:11:19.270 of these fields intertwine and become 259 00:11:19.270 --> 00:11:21.390 a new type of field, or could the 260 00:11:21.390 --> 00:11:24.190 intertwining effect a, uh, field 261 00:11:24.270 --> 00:11:26.190 to interfere with its behaviour? 262 00:11:28.030 --> 00:11:29.550 That's getting really into the, 263 00:11:30.980 --> 00:11:33.550 um, big complexities of, 264 00:11:34.240 --> 00:11:35.470 uh, studying 265 00:11:38.430 --> 00:11:40.430 these particles. 266 00:11:41.550 --> 00:11:43.630 It's the smallest level of anything really, 267 00:11:43.630 --> 00:11:44.190 isn't it? 268 00:11:45.310 --> 00:11:47.310 Professor Fred Watson: That's correct, yes. So we're talking about 269 00:11:47.390 --> 00:11:49.860 fundamental particles which equally, uh, 270 00:11:50.510 --> 00:11:53.210 well, can be seen as, um, uh, 271 00:11:53.540 --> 00:11:55.700 as disturbances 272 00:11:56.580 --> 00:11:59.140 or eddies if you like, in, in the field, in 273 00:11:59.140 --> 00:12:01.980 the force field. Uh, so, you 274 00:12:01.980 --> 00:12:04.860 know, whatever that force field is. But I 275 00:12:04.860 --> 00:12:06.660 think there's a fairly straightforward answer 276 00:12:06.660 --> 00:12:09.260 to this question though. Uh, um. 277 00:12:09.860 --> 00:12:12.060 Exactly. As Reynolds and Brian say, the 278 00:12:12.060 --> 00:12:13.860 fabric of space time consists of different 279 00:12:13.940 --> 00:12:16.700 fields, such as the Higgs field. And the 280 00:12:16.700 --> 00:12:18.900 Higgs boson is a disturbance within the Higgs 281 00:12:18.900 --> 00:12:21.060 field. But, um, 282 00:12:21.900 --> 00:12:23.860 uh, and so the question is, theoretically, 283 00:12:23.860 --> 00:12:25.580 could any of these fields intertwine and 284 00:12:25.580 --> 00:12:28.180 become a new type of field or could the 285 00:12:28.180 --> 00:12:30.620 intertwining affect a field to interfere with 286 00:12:30.620 --> 00:12:33.580 its behaviour? And the answer is yes to the 287 00:12:33.580 --> 00:12:36.020 first part. They don't exactly 288 00:12:36.020 --> 00:12:38.660 intertwine, they superimpose. And 289 00:12:39.140 --> 00:12:41.900 you've actually, um, Reynold and Brian 290 00:12:41.900 --> 00:12:43.860 already named one because the 291 00:12:43.860 --> 00:12:46.140 electromagnetic field is actually a 292 00:12:46.140 --> 00:12:49.140 superposition of the electric field and the 293 00:12:49.140 --> 00:12:50.860 magnetic field, which are themselves 294 00:12:50.860 --> 00:12:52.880 separate. And there are other, there are 295 00:12:52.880 --> 00:12:55.200 other superpositions as well. 296 00:12:55.280 --> 00:12:58.280 Um, uh, the weak 297 00:12:58.280 --> 00:13:01.120 nuclear force intertwines with 298 00:13:01.120 --> 00:13:03.240 the electromagnetic force to become the 299 00:13:03.240 --> 00:13:05.960 electroweak force, which is something we 300 00:13:05.960 --> 00:13:08.320 think was present in the early universe. 301 00:13:09.120 --> 00:13:10.870 Uh, so, uh, 302 00:13:12.720 --> 00:13:15.720 yes, it's interesting the way that these 303 00:13:15.720 --> 00:13:17.760 superpositions happen. So they're absolutely 304 00:13:17.760 --> 00:13:20.750 right. They can entwine, uh, and, uh, 305 00:13:22.040 --> 00:13:24.090 um, at least maybe intertwines the wrong 306 00:13:24.090 --> 00:13:27.090 word. But, uh, superimpose at least so that 307 00:13:27.090 --> 00:13:29.690 you have multiple fields becoming 308 00:13:30.570 --> 00:13:32.890 something different, a new type of field. 309 00:13:32.890 --> 00:13:34.780 Exactly as they say. Okay, yeah. 310 00:13:34.780 --> 00:13:36.730 Andrew Dunkley: Ah, it's a strange world, isn't it, when you 311 00:13:36.730 --> 00:13:39.210 get down to the. It is 312 00:13:39.530 --> 00:13:42.050 tiny, tiny objects and, um, 313 00:13:42.890 --> 00:13:44.650 Professor Fred Watson: strange in the big objects as well. 314 00:13:45.130 --> 00:13:48.030 Andrew Dunkley: I suppose so. I mean, if you 315 00:13:48.030 --> 00:13:50.270 really sit back and drink a few scotches and 316 00:13:50.270 --> 00:13:53.150 start looking up and thinking about it, your 317 00:13:53.150 --> 00:13:55.670 brain just explodes. It's probably the scotch 318 00:13:55.670 --> 00:13:57.590 more so than the problems of the universe. 319 00:13:59.980 --> 00:14:01.910 Um, it is so 320 00:14:02.710 --> 00:14:04.870 out there when you're, you know, just 321 00:14:05.110 --> 00:14:08.030 contemplating existence itself is one 322 00:14:08.030 --> 00:14:10.630 of the things I find myself thinking about 323 00:14:10.710 --> 00:14:13.350 from time to time. How is existence 324 00:14:14.910 --> 00:14:16.990 not, not just why, but how. 325 00:14:18.250 --> 00:14:19.710 Uh, it's all very weird. 326 00:14:21.190 --> 00:14:22.990 Uh, and thank you to Reynold and Brian for 327 00:14:23.070 --> 00:14:25.580 sending in that question. And, um, 328 00:14:27.310 --> 00:14:29.469 we wish you well. Uh, and please send some 329 00:14:29.469 --> 00:14:29.790 more. 330 00:14:30.330 --> 00:14:32.430 Uh, this is Space Nuts, a Q and A edition 331 00:14:32.430 --> 00:14:34.750 with Andrew Dunkley and Professor Fred Watson 332 00:14:34.750 --> 00:14:35.470 Watson. 333 00:14:36.830 --> 00:14:38.710 Andrew Dunkley: Let's take a short break from the show to 334 00:14:38.710 --> 00:14:41.540 tell you about our sponsor, NordVPN. 335 00:14:41.850 --> 00:14:43.780 Uh, let's talk about your online security. 336 00:14:44.420 --> 00:14:47.060 Now, I can tell you from personal experience, 337 00:14:47.470 --> 00:14:50.020 uh, last year when Judy and I were overseas, 338 00:14:50.020 --> 00:14:52.780 we ran into, uh, a bit of a frustrating 339 00:14:52.780 --> 00:14:55.300 issue. There were certain apps we simply 340 00:14:55.300 --> 00:14:58.100 couldn't use without a VPN connection. 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So 369 00:16:13.140 --> 00:16:15.220 there's absolutely no risk if you 370 00:16:15.220 --> 00:16:16.060 Andrew Dunkley: want to give it a go. 371 00:16:16.300 --> 00:16:18.536 Andrew Dunkley: That's nordvpn.com 372 00:16:18.944 --> 00:16:21.500 spacenuts Stay safe 373 00:16:21.579 --> 00:16:23.380 online with our sponsor, 374 00:16:23.380 --> 00:16:24.860 NordVPN 375 00:16:27.500 --> 00:16:28.540 Kevin: Space Nuts. 376 00:16:28.870 --> 00:16:30.900 Andrew Dunkley: Uh, I think we've got another audio question. 377 00:16:30.900 --> 00:16:33.470 We seem to be on a bit of a, um, um, 378 00:16:33.810 --> 00:16:36.680 um, you know, particle 379 00:16:36.680 --> 00:16:39.560 type of bender at the moment with this 380 00:16:39.560 --> 00:16:41.840 episode. Uh, this, this question comes from 381 00:16:41.840 --> 00:16:42.360 Andy. 382 00:16:43.160 --> 00:16:45.480 Andy: Hi guys. Andy again, from uk, 383 00:16:45.960 --> 00:16:47.600 actually from Cheshire, just down the road 384 00:16:47.600 --> 00:16:50.319 from the beautiful Jodrell Bank. Although 385 00:16:50.319 --> 00:16:52.320 I've never forgiven them since they took out 386 00:16:52.320 --> 00:16:55.320 the planetarium. Um, just a quick question. 387 00:16:55.810 --> 00:16:58.440 Um, the lhc, um, 388 00:16:58.760 --> 00:17:00.680 we're told that it 389 00:17:01.320 --> 00:17:03.320 accelerates particles to 390 00:17:04.120 --> 00:17:06.520 very close to the speed of light, about 0.9 C 391 00:17:06.520 --> 00:17:09.080 or whatever the actual figure is. 392 00:17:09.650 --> 00:17:12.520 Um, but they also say that 393 00:17:12.520 --> 00:17:14.720 they're colliding particles at close to the 394 00:17:14.720 --> 00:17:17.440 speed of light. Now if they're colliding 395 00:17:17.440 --> 00:17:18.920 particles that they're accelerating in 396 00:17:18.920 --> 00:17:21.560 opposite directions, surely that means they 397 00:17:21.560 --> 00:17:24.040 should be the collisions. The impact 398 00:17:24.280 --> 00:17:27.229 should be at close to twice 399 00:17:27.549 --> 00:17:29.080 the speed of light. Um, 400 00:17:30.749 --> 00:17:32.949 if you just clear that one up, I'd be very 401 00:17:32.949 --> 00:17:34.749 happy. Um, I, 402 00:17:36.429 --> 00:17:38.109 I think I'm right and I think the collisions 403 00:17:38.109 --> 00:17:39.749 are happening at greater than the speed of 404 00:17:39.749 --> 00:17:42.189 light. But prove me wrong 405 00:17:42.669 --> 00:17:45.149 again, fantastic show. Speak to you soon. 406 00:17:46.109 --> 00:17:49.069 Andrew Dunkley: Thanks, Andy. Um, reminds me of all 407 00:17:49.069 --> 00:17:49.389 those, 408 00:17:52.340 --> 00:17:52.460 Andrew Dunkley: I 409 00:17:52.460 --> 00:17:53.940 Andrew Dunkley: suppose, when they're teaching you to drive 410 00:17:53.940 --> 00:17:56.780 and they're saying, um, look, you're 411 00:17:56.780 --> 00:17:58.820 driving along the highway at 100 kilometres 412 00:17:58.820 --> 00:18:00.500 an hour and a car's coming in the opposite 413 00:18:00.500 --> 00:18:02.820 direction at 100 kilometres an hour and you, 414 00:18:03.360 --> 00:18:06.140 uh, sadly, hit each other. The 415 00:18:06.140 --> 00:18:08.660 impact speed is 200 kilometres an hour. I 416 00:18:08.660 --> 00:18:09.860 guess that's what he's getting at. 417 00:18:10.100 --> 00:18:12.170 Professor Fred Watson: Exactly that, yes. Um, 418 00:18:13.660 --> 00:18:16.340 um, and it's a natural thing and it's a 419 00:18:16.340 --> 00:18:19.340 question that we often get, uh, because it's 420 00:18:19.340 --> 00:18:20.740 completely counterintuitive. 421 00:18:22.440 --> 00:18:25.400 Uh, exactly as, um, as Andy's saying. Uh, 422 00:18:25.520 --> 00:18:28.200 and yeah, Cheshire's lovely. He's right. And 423 00:18:28.200 --> 00:18:31.090 so is Jodrell Bank. Um, uh, uh, 424 00:18:31.120 --> 00:18:33.920 as Andy's saying, you're colliding these 425 00:18:33.920 --> 00:18:36.320 things. If I remember rightly, the, uh, 426 00:18:36.320 --> 00:18:38.720 proton, uh, speed 427 00:18:39.439 --> 00:18:41.760 within the Large Hadron Collider, 428 00:18:42.320 --> 00:18:42.960 I think it's 429 00:18:42.960 --> 00:18:46.520 99.99998% 430 00:18:46.520 --> 00:18:49.320 of the speed of light. So that's how fast 431 00:18:49.320 --> 00:18:51.320 these things are going, almost the speed of 432 00:18:51.320 --> 00:18:54.160 light. And you've got two, uh, streams of 433 00:18:54.160 --> 00:18:56.920 them going in opposite directions. You bring 434 00:18:56.920 --> 00:18:58.880 them together at the various experiment 435 00:18:58.880 --> 00:19:01.480 points. Um, I've been to some of those. I've 436 00:19:01.480 --> 00:19:03.400 been in the cavity at the cavern, actually, 437 00:19:03.400 --> 00:19:05.840 where the compact muon solenoid lives. 438 00:19:06.270 --> 00:19:08.400 Uh, and that's where they collide. So 439 00:19:08.400 --> 00:19:10.080 shouldn't they collide at nearly twice the 440 00:19:10.080 --> 00:19:12.160 speed of light? And the answer is no, 441 00:19:13.040 --> 00:19:13.840 because then 442 00:19:13.840 --> 00:19:14.640 Andrew Dunkley: you ought to be no. 443 00:19:14.800 --> 00:19:17.600 Professor Fred Watson: Yeah, that only works in classical mechanics, 444 00:19:18.290 --> 00:19:20.880 uh, where, as you said, the velocities just 445 00:19:20.880 --> 00:19:23.400 add together. Uh, if these things were 446 00:19:23.400 --> 00:19:26.110 moving, you know, in the, what we call the 447 00:19:26.110 --> 00:19:29.030 classical realm, in other words, slow stuff, 448 00:19:29.190 --> 00:19:31.750 you would add the velocities together. Uh, 449 00:19:31.830 --> 00:19:33.510 but when you get to 450 00:19:33.990 --> 00:19:36.710 relativistic speeds, as we call them, speeds 451 00:19:36.710 --> 00:19:39.310 close to the speed of light, you have to 452 00:19:39.310 --> 00:19:42.150 account for two other relativistic 453 00:19:42.150 --> 00:19:44.550 factors, which are, uh, time dilation 454 00:19:44.870 --> 00:19:47.750 and length contraction. And both of those 455 00:19:47.750 --> 00:19:50.070 things are things, uh, that become very 456 00:19:50.070 --> 00:19:52.270 significant at, uh, nearly the speed of 457 00:19:52.270 --> 00:19:54.920 light. And so when you take those into 458 00:19:54.920 --> 00:19:57.520 account, you get a different formula. And 459 00:19:58.240 --> 00:19:59.760 I don't know whether listeners are going to 460 00:19:59.760 --> 00:20:02.200 turn off here, but, uh, I'm going to give you 461 00:20:02.200 --> 00:20:04.920 the formula. So in the 462 00:20:04.920 --> 00:20:07.440 classical case, if you've got two 463 00:20:07.440 --> 00:20:10.000 velocities, U and V, it's always U and V, 464 00:20:10.240 --> 00:20:12.360 not you and me, U and V. Um, 465 00:20:13.260 --> 00:20:16.160 uh, and yes, in classical case, U plus 466 00:20:16.160 --> 00:20:18.920 V is 467 00:20:18.920 --> 00:20:21.770 the closing speed, but in the relativistic 468 00:20:21.770 --> 00:20:24.450 case, the Closing speed is u 469 00:20:24.450 --> 00:20:26.570 +v divided by 470 00:20:27.210 --> 00:20:28.650 1 over u 471 00:20:29.850 --> 00:20:32.170 times v over c squared. 472 00:20:33.690 --> 00:20:36.449 So u +v divided by 1 over 473 00:20:36.449 --> 00:20:38.850 UV over c squared. That's the 474 00:20:38.850 --> 00:20:41.250 relativistic formula. And when you put the 475 00:20:41.250 --> 00:20:44.170 numbers in, uh, you realise 476 00:20:44.250 --> 00:20:47.180 that you can never, uh, exceed the speed 477 00:20:47.180 --> 00:20:48.420 of light by this. 478 00:20:50.310 --> 00:20:53.180 Um, you just get, uh, an answer 479 00:20:53.180 --> 00:20:55.500 that's even closer to the speed of light than 480 00:20:55.500 --> 00:20:58.500 your two initial, uh, colliders. 481 00:20:58.580 --> 00:21:01.310 So, um, here's an example. Uh, 482 00:21:01.310 --> 00:21:03.620 you've got two things travelling, 483 00:21:04.100 --> 00:21:07.100 hitting each other or travelling towards each 484 00:21:07.100 --> 00:21:09.620 other at 0.8 of the speed of light. 485 00:21:09.940 --> 00:21:12.500 In the classical situation, they would be 486 00:21:13.140 --> 00:21:15.580 coming together at 1.6 times the speed of 487 00:21:15.580 --> 00:21:17.880 light. That will be their relative veloc. But 488 00:21:17.880 --> 00:21:20.550 when you do the relativistic calculation, uh, 489 00:21:20.550 --> 00:21:22.240 their Closing velocity is 490 00:21:22.240 --> 00:21:25.240 0.975 times the 491 00:21:25.240 --> 00:21:26.000 speed of light. 492 00:21:26.320 --> 00:21:26.960 Andrea: Okay. 493 00:21:31.200 --> 00:21:31.760 Andrew Dunkley: Okay. 494 00:21:33.760 --> 00:21:36.760 Professor Fred Watson: I hope that makes sense. It's all 495 00:21:36.760 --> 00:21:38.840 about the weird things that happen when you 496 00:21:38.840 --> 00:21:40.320 get near the speed of light. You know, time 497 00:21:40.320 --> 00:21:42.560 dilation itself, time slowing down for, 498 00:21:43.120 --> 00:21:45.990 uh, you know, for the. For as 499 00:21:45.990 --> 00:21:47.630 a difference between the observer and the 500 00:21:47.630 --> 00:21:49.270 person moving at the speed of light and 501 00:21:49.270 --> 00:21:50.830 length contraction. These are all weird 502 00:21:50.830 --> 00:21:53.750 things. So it shouldn't be a surprise that 503 00:21:53.750 --> 00:21:55.390 they don't just. The velocities don't just 504 00:21:55.390 --> 00:21:56.910 add together, they combine in that 505 00:21:56.910 --> 00:21:59.190 relativistic sense. Sorry about the equation. 506 00:21:59.830 --> 00:22:01.950 It's an equation I quite like, which is why I 507 00:22:01.950 --> 00:22:02.790 threw it in there. 508 00:22:04.230 --> 00:22:06.510 Andrew Dunkley: It's fair enough, too. And, uh, hopefully 509 00:22:06.510 --> 00:22:09.100 that's solved, uh, Andy's dilemma. 510 00:22:09.100 --> 00:22:12.030 Um, he thought it would be twice the 511 00:22:12.030 --> 00:22:13.950 speed of light or something to that effect if 512 00:22:13.950 --> 00:22:16.730 you got two objects at the speed of light 513 00:22:16.730 --> 00:22:19.610 impacting each other head on. But no, can't 514 00:22:19.610 --> 00:22:21.810 be done is what you're saying. 515 00:22:22.530 --> 00:22:25.490 Professor Fred Watson: Yeah, they're close. I mean, only light 516 00:22:25.490 --> 00:22:26.930 can go at the speed of light. So you're 517 00:22:26.930 --> 00:22:28.290 talking about things going at nearly the 518 00:22:28.290 --> 00:22:31.289 speed of light. Uh, they're not colliding at 519 00:22:31.289 --> 00:22:32.810 nearly twice the speed of light. They're 520 00:22:32.810 --> 00:22:35.050 colliding at even more nearly the speed of 521 00:22:35.050 --> 00:22:37.570 light than they were to start with. But it 522 00:22:37.570 --> 00:22:39.090 never exceeds the speed of light. 523 00:22:39.570 --> 00:22:42.530 Andrew Dunkley: I get it. There you go, Andy. Uh, solved. 524 00:22:45.180 --> 00:22:47.820 Professor Fred Watson: The crew of Artemis 2 now bound for the moon. 525 00:22:48.060 --> 00:22:50.620 Humanity's next great voyage begins. 526 00:22:51.260 --> 00:22:52.380 Andrew Dunkley: Space Nuts. 527 00:22:52.540 --> 00:22:55.150 Andrew Dunkley: And our final question today comes, uh, 528 00:22:55.500 --> 00:22:58.030 from. Mark. Hi, Fred Watson, Andrew, uh, 529 00:22:58.420 --> 00:23:01.420 and team. It's, uh, Mark again from Sunny, 530 00:23:01.660 --> 00:23:02.700 is it Cece. 531 00:23:04.060 --> 00:23:06.460 Professor Fred Watson: Yes, it's where Patrick Moore used to live. 532 00:23:07.580 --> 00:23:08.620 He used to visit him. 533 00:23:08.620 --> 00:23:11.580 Andrew Dunkley: I really have to use a bigger font size with 534 00:23:11.580 --> 00:23:14.300 these questions. Sunny, uh, Selsey on the 535 00:23:14.300 --> 00:23:17.250 south coast of England. Um, in more 536 00:23:17.250 --> 00:23:19.490 than one of your podcasts, you mentioned the 537 00:23:19.490 --> 00:23:22.170 growing problem of excess satellites in space 538 00:23:22.170 --> 00:23:24.210 and what to do with them. That got me 539 00:23:24.210 --> 00:23:26.770 thinking. Would it be possible to use the 540 00:23:26.770 --> 00:23:29.170 action reaction principle to place a new 541 00:23:29.170 --> 00:23:31.849 satellite in the same place as an old 542 00:23:31.849 --> 00:23:34.730 one and move the old one into a higher 543 00:23:34.730 --> 00:23:37.610 graveyard orbit? Uh, Then at a later date, 544 00:23:37.610 --> 00:23:40.130 collect them to be dismantled safely. The way 545 00:23:40.130 --> 00:23:42.250 I look at it, if they want to put more 546 00:23:42.250 --> 00:23:44.330 satellites into space, they should also pay 547 00:23:44.330 --> 00:23:47.230 to clean the space up. Uh, I know this 548 00:23:47.230 --> 00:23:50.030 sounds, uh, a, uh, bit space 549 00:23:50.190 --> 00:23:53.110 snook, a bit like space space snooker. Yes, 550 00:23:53.110 --> 00:23:55.870 it does. Uh, but would it be possible. By the 551 00:23:55.870 --> 00:23:58.830 way, I broke the TV in the Globe Pub as a 552 00:23:58.830 --> 00:24:01.230 young man playing snooker, so probably not a 553 00:24:01.230 --> 00:24:03.110 good idea to ask me to work out the 554 00:24:03.110 --> 00:24:05.590 trajectories for all of this. Keep, uh, up 555 00:24:05.590 --> 00:24:07.150 the great work. It means a lot to everyone 556 00:24:07.150 --> 00:24:09.470 listening. And those, uh, that don't, well, 557 00:24:09.710 --> 00:24:11.390 you just gotta pity them, 558 00:24:12.830 --> 00:24:14.670 says Mark. Thanks, Mark, for the question. 559 00:24:15.410 --> 00:24:17.850 Uh, I'd love to, I'd love to have been the 560 00:24:17.850 --> 00:24:18.850 night he broke the tv. 561 00:24:18.850 --> 00:24:20.410 Professor Fred Watson: That would have been spectacular. 562 00:24:20.410 --> 00:24:20.970 Generic: Yeah. 563 00:24:20.970 --> 00:24:21.450 Andy: Gosh. 564 00:24:22.650 --> 00:24:24.930 Andrew Dunkley: Now what I want to know is, was that he's 565 00:24:24.930 --> 00:24:27.810 backswing, getting ready for the, the, 566 00:24:27.810 --> 00:24:29.970 the move of the queue that hit the screen, or 567 00:24:29.970 --> 00:24:31.450 did he actually fire a ball, 568 00:24:32.790 --> 00:24:35.090 uh, across the, across the room and hit the 569 00:24:35.090 --> 00:24:38.090 tv? Uh, you're gonna have to clarify that 570 00:24:38.090 --> 00:24:40.810 one, Mark. Um, look, 571 00:24:41.110 --> 00:24:42.960 uh, in, in regard to, um, 572 00:24:43.950 --> 00:24:45.910 cleaning up your own mess, there's actually 573 00:24:45.910 --> 00:24:48.670 a. Isn't there an international law 574 00:24:48.750 --> 00:24:51.070 that requires you to deal with your own 575 00:24:51.390 --> 00:24:52.430 stuff up there? 576 00:24:52.590 --> 00:24:55.270 Professor Fred Watson: Yes, there is now. Um, I think it was added 577 00:24:55.270 --> 00:24:57.550 to the, uh, the 578 00:24:57.710 --> 00:24:59.230 approvals given by the International 579 00:24:59.390 --> 00:25:01.310 Telecommunications Union, which is a 580 00:25:01.310 --> 00:25:04.000 governing body of all this stuff, um, 581 00:25:04.110 --> 00:25:06.590 that you. I think this came in 582 00:25:06.910 --> 00:25:09.590 probably five, 10 years ago. You have to 583 00:25:09.590 --> 00:25:12.350 demonstrate, uh, before they'll give you 584 00:25:12.810 --> 00:25:15.170 permission to launch, that you've got a way 585 00:25:15.170 --> 00:25:17.930 of removing your spacecraft from 586 00:25:17.930 --> 00:25:20.850 orbit. Um, in other words, 587 00:25:20.850 --> 00:25:22.250 you've got to be able to clean up your own 588 00:25:22.250 --> 00:25:24.810 junk. Uh, now that's 589 00:25:25.210 --> 00:25:27.330 fine for new stuff, but there's a lot of 590 00:25:27.330 --> 00:25:30.050 stuff up there that didn't 591 00:25:30.050 --> 00:25:32.770 qualify for that. And no thought was given to 592 00:25:32.770 --> 00:25:35.250 the idea of trashing space that you, you 593 00:25:35.250 --> 00:25:38.030 know, your spacecraft would 594 00:25:38.420 --> 00:25:41.300 just continue in orbit, um, after 595 00:25:41.300 --> 00:25:44.020 its useful life was over. And 596 00:25:44.020 --> 00:25:46.420 indeed for many of them, for objects, 597 00:25:47.310 --> 00:25:50.180 uh, especially ones with solar panels which 598 00:25:50.180 --> 00:25:52.820 are big and act as a drag on the residual 599 00:25:52.820 --> 00:25:55.340 atmosphere up there. Uh, even if you're up 600 00:25:55.340 --> 00:25:57.740 at, uh, uh, four or five hundred 601 00:25:57.740 --> 00:26:00.700 kilometres, there's enough atmosphere that 602 00:26:00.700 --> 00:26:03.140 if you do nothing, your spacecraft will, 603 00:26:03.670 --> 00:26:06.180 uh, the orbit will decay. It will 604 00:26:06.500 --> 00:26:08.980 hit the atmosphere and slow down and that 605 00:26:08.980 --> 00:26:11.760 brings it down lower and then it slows down 606 00:26:11.760 --> 00:26:14.640 more. And that is how 607 00:26:15.600 --> 00:26:18.320 space is kind of almost automatically cleaned 608 00:26:18.320 --> 00:26:18.560 up. 609 00:26:19.440 --> 00:26:21.040 Andrew Dunkley: And that's what's happening to the Swift. 610 00:26:21.630 --> 00:26:23.520 Professor Fred Watson: Uh, yes, that we talked about a couple of 611 00:26:23.520 --> 00:26:25.520 episodes ago. Exactly right. That's right. 612 00:26:25.839 --> 00:26:28.400 And that one's worth saving, which is why a 613 00:26:28.400 --> 00:26:30.280 mission's been mounted to do that, to boost 614 00:26:30.280 --> 00:26:32.360 it into a higher orbit. So in a way, what 615 00:26:32.360 --> 00:26:34.240 that's doing is actually what Mark is 616 00:26:34.240 --> 00:26:37.110 suggesting. You, uh, can go, uh, 617 00:26:37.140 --> 00:26:38.940 attach another rocket to it and push it up to 618 00:26:38.940 --> 00:26:41.590 a higher orbit to safeguard it. Um, 619 00:26:42.970 --> 00:26:45.820 um, so for low Earth 620 00:26:45.820 --> 00:26:48.466 orbit, There's below about 5, 621 00:26:48.574 --> 00:26:50.460 600 kilometres. There is this natural 622 00:26:50.460 --> 00:26:53.260 sweeping up as things decay 623 00:26:53.260 --> 00:26:55.780 unless you do something about it. Many 624 00:26:55.780 --> 00:26:58.340 spacecraft have got thrusters that lets you 625 00:26:58.340 --> 00:27:01.220 lift its orbit. Um, but if you switch the 626 00:27:01.220 --> 00:27:03.180 thrusters off, that means they're going to 627 00:27:03.180 --> 00:27:04.940 come back to Earth anyway. And that might be 628 00:27:04.940 --> 00:27:06.740 enough to satisfy the international 629 00:27:06.900 --> 00:27:09.760 Telecommunications Unit, uh, going higher 630 00:27:09.760 --> 00:27:10.320 up, though. 631 00:27:10.480 --> 00:27:11.120 Andrew Dunkley: Except. 632 00:27:11.440 --> 00:27:13.960 Andrew Dunkley: Yes, one more point. Uh, when these things 633 00:27:13.960 --> 00:27:15.880 are burning up, they're putting all those 634 00:27:15.880 --> 00:27:17.360 metals into our atmosphere. 635 00:27:17.440 --> 00:27:19.160 Professor Fred Watson: Yeah, you're still getting contamination. 636 00:27:19.160 --> 00:27:21.080 That's right. We're getting aluminium oxide 637 00:27:21.080 --> 00:27:23.000 and all sorts of stuff up there that 638 00:27:23.000 --> 00:27:25.760 shouldn't be there. Uh, but, 639 00:27:25.800 --> 00:27:27.840 um, yes, for higher orbits, 640 00:27:30.400 --> 00:27:32.440 these are the ones, what you might call mid 641 00:27:32.440 --> 00:27:34.800 earth orbits above 1,000 kilometres, 642 00:27:35.400 --> 00:27:38.320 uh, they're not gonna decay so readily. And 643 00:27:38.320 --> 00:27:40.620 so they are an. And then, 644 00:27:41.440 --> 00:27:44.380 uh, the, um, geostationary 645 00:27:45.020 --> 00:27:47.460 satellites. So the geostationary orbits are 646 00:27:47.460 --> 00:27:50.060 very, very specific. Um, in fact, 647 00:27:50.220 --> 00:27:52.180 all the satellites are in the same orbit, 648 00:27:52.180 --> 00:27:54.780 more or less, um, because it's the one that 649 00:27:55.020 --> 00:27:57.660 keeps them over the equator and keeps them 650 00:27:57.660 --> 00:28:00.140 going, uh, round once in a day. 651 00:28:00.620 --> 00:28:03.060 Um, those geostationary orbits, they're at 652 00:28:03.060 --> 00:28:05.980 36,000 kilometres. They have to have 653 00:28:05.980 --> 00:28:08.900 mechanisms to push them into what's called 654 00:28:08.900 --> 00:28:11.820 exactly as, uh, Malik mentions, a grave 655 00:28:12.200 --> 00:28:15.080 orbit, which just gets them out of the way so 656 00:28:15.080 --> 00:28:16.960 that when they become defunct and you can't 657 00:28:16.960 --> 00:28:18.280 control them anymore, they're not going to 658 00:28:18.280 --> 00:28:20.880 bang into one of the active geostationary 659 00:28:20.880 --> 00:28:23.760 satellites. So it is a game of snooker up 660 00:28:23.760 --> 00:28:26.440 there, um, in a perhaps more gentle way than 661 00:28:26.600 --> 00:28:29.200 knocking one satellite into another, um, and 662 00:28:29.200 --> 00:28:31.960 replacing its position in space. 663 00:28:32.360 --> 00:28:34.040 All you do, if you do that is 664 00:28:35.080 --> 00:28:37.040 you've got another one that's going to decay 665 00:28:37.040 --> 00:28:38.790 at the same rate. If it's in low Earth orbit, 666 00:28:38.940 --> 00:28:39.180 it. 667 00:28:39.500 --> 00:28:41.420 Andrew Dunkley: Yeah, they reckon there's somewhere between 668 00:28:41.500 --> 00:28:44.220 three and four and a half thousand inactive 669 00:28:44.380 --> 00:28:46.700 or defunct satellites in orbit at the moment. 670 00:28:47.100 --> 00:28:49.900 Professor Fred Watson: That's correct, yes. Um, but 671 00:28:49.900 --> 00:28:52.900 then on top of that there's a, uh, host 672 00:28:52.900 --> 00:28:55.740 of, uh, upper stages, launch, 673 00:28:55.740 --> 00:28:58.380 you know, the launch vehicles. Lots of bits 674 00:28:58.380 --> 00:29:00.660 and pieces, bits of fairing, bits of junk, 675 00:29:00.660 --> 00:29:03.180 debris from previous collisions. It's a 676 00:29:03.340 --> 00:29:05.900 fleck of paint, flecks of Paint. That's 677 00:29:05.900 --> 00:29:06.860 right. There's even a glove. 678 00:29:08.320 --> 00:29:10.800 Andrew Dunkley: And a spanner with a spanner too. Yeah, 679 00:29:10.880 --> 00:29:13.360 there's all sorts of stuff floating around. 680 00:29:13.920 --> 00:29:15.800 Professor Fred Watson: It's all going at 8 kilometres per second. 681 00:29:15.800 --> 00:29:17.040 That's the dangerous bit. 682 00:29:17.760 --> 00:29:20.640 Andrew Dunkley: So I think that, uh, was another part to his 683 00:29:20.640 --> 00:29:23.640 question. Could you replace a satellite in 684 00:29:23.640 --> 00:29:26.320 its exact position, move the 685 00:29:26.320 --> 00:29:28.680 defunct one out and put a new one in the 686 00:29:28.680 --> 00:29:31.600 exact spot that its predecessor was? 687 00:29:31.600 --> 00:29:33.760 Professor Fred Watson: Well, you could, and, uh, indeed that's done. 688 00:29:33.760 --> 00:29:36.010 You don't move the other one out. You. Once 689 00:29:36.010 --> 00:29:38.130 its orbit's decayed, you, uh, just let it 690 00:29:38.130 --> 00:29:41.090 drop. Yeah, you've got that orbit, uh, freed 691 00:29:41.090 --> 00:29:43.610 up and you put another 692 00:29:43.610 --> 00:29:44.930 spacecraft there. That's what's happening 693 00:29:44.930 --> 00:29:46.810 with Starlink. Actually, it's exactly what's 694 00:29:46.810 --> 00:29:49.210 happening. The Starlink satellites are all at 695 00:29:49.210 --> 00:29:51.730 round about 500 kilometres. They were 696 00:29:51.730 --> 00:29:54.250 planning another shell at, uh, 1200 697 00:29:54.250 --> 00:29:57.250 kilometres. But, uh, for once, um, SpaceX 698 00:29:57.250 --> 00:29:59.410 listened to the astronomy lobby. Because 699 00:29:59.410 --> 00:30:01.830 those outer ones can be visible all night in 700 00:30:01.980 --> 00:30:04.820 some parts of the world, um, even though 701 00:30:04.820 --> 00:30:06.380 they're fainter because they're higher up, 702 00:30:06.750 --> 00:30:08.860 uh, it means that they're visible for much 703 00:30:08.860 --> 00:30:10.380 longer during twilight. 704 00:30:10.860 --> 00:30:13.620 Andrew Dunkley: Yeah, and that's a real problem, isn't 705 00:30:13.620 --> 00:30:16.300 it? There you go, Mark. Uh, everything you 706 00:30:16.300 --> 00:30:19.020 said, um, is possible. And 707 00:30:19.410 --> 00:30:22.340 uh, yes, there is a law requiring people to 708 00:30:22.340 --> 00:30:24.140 clean up their messes, but at the moment, 709 00:30:24.540 --> 00:30:26.620 letting them burn up in the atmosphere is 710 00:30:26.860 --> 00:30:29.740 okay until we all die of some 711 00:30:29.740 --> 00:30:32.620 kind of metallic poisoning. Then, um, they'll 712 00:30:32.620 --> 00:30:33.960 go, ah, yeah, we should have done, done 713 00:30:33.960 --> 00:30:34.760 something about that. 714 00:30:35.080 --> 00:30:37.400 Professor Fred Watson: Unintended consequences. Yeah. 715 00:30:37.550 --> 00:30:38.920 Andrew Dunkley: Uh, lovely to hear from you, Mark. 716 00:30:38.990 --> 00:30:41.960 Um, uh, we've been talking a lot 717 00:30:41.960 --> 00:30:44.800 about particle science today, and, uh, Andrea 718 00:30:44.800 --> 00:30:47.240 in Western Australia sent, uh, something in 719 00:30:47.640 --> 00:30:49.520 a while back and I've kind of been sitting on 720 00:30:49.520 --> 00:30:51.440 it, trying to find the appropriate moment. 721 00:30:51.440 --> 00:30:53.840 And because of the, the fact that three of 722 00:30:53.840 --> 00:30:56.200 our four questions were focused on, on 723 00:30:56.200 --> 00:30:59.040 particles, I thought it was appropriate 724 00:30:59.040 --> 00:31:00.990 to play, um, uh, 725 00:31:01.450 --> 00:31:03.530 Andrea's little voice piece today. 726 00:31:05.930 --> 00:31:08.410 Andrea: Hey, you two. The joke for the day. 727 00:31:09.690 --> 00:31:12.090 Two neutrinos walked through a bar. 728 00:31:14.890 --> 00:31:15.690 Andrew Dunkley: Thanks folks. 729 00:31:15.770 --> 00:31:17.570 Andrea: Really enjoy your show and I hope you guys 730 00:31:17.570 --> 00:31:18.490 found that really fun. 731 00:31:18.490 --> 00:31:19.050 Professor Fred Watson: We did. 732 00:31:21.110 --> 00:31:22.330 Andrew Dunkley: Uh, that's a good one. 733 00:31:22.490 --> 00:31:24.370 Professor Fred Watson: That is excellent. Yeah, perfect. 734 00:31:24.370 --> 00:31:27.170 Andrew Dunkley: Perfect timing. Well, actually, I've been 735 00:31:27.170 --> 00:31:30.030 sitting on it for months, but it, 736 00:31:30.030 --> 00:31:32.390 um, seemed appropriate. Appropriate today. 737 00:31:32.630 --> 00:31:33.830 Professor Fred Watson: Yes, that's the, um, one. 738 00:31:34.390 --> 00:31:36.830 Andrew Dunkley: Now a reminder, if you have questions for us, 739 00:31:36.830 --> 00:31:39.270 we would love to get them. Uh, you need to go 740 00:31:39.270 --> 00:31:41.310 to our website to send them in, uh, which is 741 00:31:41.310 --> 00:31:44.310 easy, spacenutspodcast.com or spacenuts 742 00:31:44.310 --> 00:31:46.630 IO. Click on the Ask me anything button at 743 00:31:46.630 --> 00:31:48.310 the top, it's labelled ama. 744 00:31:49.350 --> 00:31:51.910 And that's also the logo for the Australian 745 00:31:51.910 --> 00:31:53.830 Medical Association. But don't get confused. 746 00:31:54.460 --> 00:31:56.030 Uh, they might answer it too, though. You 747 00:31:56.030 --> 00:31:58.190 never know. Uh, but send your questions into 748 00:31:58.190 --> 00:32:01.060 us because, um, there's so much stuff that 749 00:32:01.060 --> 00:32:02.780 people want to know and if you want to know 750 00:32:02.780 --> 00:32:05.740 something, the best way to find out is to ask 751 00:32:05.740 --> 00:32:07.580 us and then we'll refer it to somebody else. 752 00:32:07.740 --> 00:32:10.740 But, uh, it is, um, uh, text and audio. 753 00:32:10.740 --> 00:32:13.220 Don't forget to tell us who you are and where 754 00:32:13.220 --> 00:32:15.260 you're from. Thank you so much, Fred Watson. 755 00:32:15.260 --> 00:32:16.220 It's been a pleasure. 756 00:32:16.619 --> 00:32:18.460 Professor Fred Watson: Always a pleasure, Andrew. Great to talk. 757 00:32:19.100 --> 00:32:20.980 Andrew Dunkley: Catch you soon. Professor Fred Watson Watson, 758 00:32:20.980 --> 00:32:23.220 astronomer at large. And, uh, thanks to Huw 759 00:32:23.220 --> 00:32:25.340 in the studio, who puts everything together 760 00:32:25.340 --> 00:32:27.940 with Blu Tack. Couldn't be with us today 761 00:32:27.940 --> 00:32:30.870 though, because he drives a proton and it 762 00:32:30.870 --> 00:32:33.750 does not do the speed of light. And so he was 763 00:32:33.750 --> 00:32:35.990 late. And from me, Andrew Dunkley. Thanks for 764 00:32:35.990 --> 00:32:37.590 your company. We'll catch you on the next 765 00:32:37.590 --> 00:32:38.950 episode of Space Nuts. 766 00:32:38.950 --> 00:32:39.590 Professor Fred Watson: Bye. Bye. 767 00:32:40.710 --> 00:32:42.910 Andrew Dunkley: You've been listening to the Space Nuts 768 00:32:42.910 --> 00:32:45.910 podcast, available at 769 00:32:45.910 --> 00:32:47.910 Apple Podcasts, Spotify, 770 00:32:48.070 --> 00:32:50.830 iHeartRadio or your favourite podcast 771 00:32:50.830 --> 00:32:52.550 player. You can also stream on 772 00:32:52.550 --> 00:32:54.230 demand@bytes.com. 773 00:32:54.550 --> 00:32:56.630 Andrew Dunkley: this has been another quality podcast 774 00:32:56.630 --> 00:32:58.710 production from bytes.com.