1
00:00:08,520 --> 00:00:10,800
Speaker 1: A, Kelly, Is it getting warm where you guys are?

2
00:00:11,080 --> 00:00:13,880
Speaker 1: Oh my gosh. Yeah, it's Virginia and the Virginia summer

3
00:00:14,000 --> 00:00:17,560
Speaker 1: is definitely here. So does that mean sunscreen for the

4
00:00:17,640 --> 00:00:20,400
Speaker 1: kids every single day? Yeah? They hate it, but I'm

5
00:00:20,440 --> 00:00:22,960
Speaker 1: a pretty big believer in that. And what about at

6
00:00:23,040 --> 00:00:25,040
Speaker 1: night time? Do you guys put sunscreen on at night?

7
00:00:25,120 --> 00:00:27,000
Speaker 1: Why would we put sunscreen on at night? What do

8
00:00:27,080 --> 00:00:29,280
Speaker 1: you know, physicists? But I don't know. Well, you know,

9
00:00:29,640 --> 00:00:32,840
Speaker 1: stars are actually just other suns, right, So it's still

10
00:00:33,000 --> 00:00:35,519
Speaker 1: sunlight even at night. So you're trying to tell me

11
00:00:35,600 --> 00:00:37,880
Speaker 1: that the stars are going to give us skin cancer. Look,

12
00:00:37,920 --> 00:00:40,720
Speaker 1: I'm not trying to make astronomy scary. I'm just looking

13
00:00:40,720 --> 00:00:43,680
Speaker 1: out for your kids. Uh huh. Well, I guess I

14
00:00:43,680 --> 00:00:46,240
Speaker 1: gotta order a gallon to star screen. Somebody out there

15
00:00:46,280 --> 00:00:48,960
Speaker 1: is going to get star cancer, oh boy. Or someone's

16
00:00:48,960 --> 00:01:06,560
Speaker 1: gonna make a lot of money off of star screen. Hi.

17
00:01:06,720 --> 00:01:09,600
Speaker 1: I'm Daniel. I'm a particle of physicist and a professor

18
00:01:09,640 --> 00:01:12,480
Speaker 1: at UC Irvine, and it was the night sky that

19
00:01:12,640 --> 00:01:15,880
Speaker 1: got me into science. I'm Kelly Weener Smith. I'm an

20
00:01:15,880 --> 00:01:19,840
Speaker 1: adjunct assistant professor at Rice University. And while I prefer parasites.

21
00:01:19,880 --> 00:01:22,280
Speaker 1: I do love looking at the night sky. What about

22
00:01:22,440 --> 00:01:25,360
Speaker 1: parasites at night? I mean, you know, the parasites are

23
00:01:25,360 --> 00:01:27,400
Speaker 1: always out there, and they're just as good at night

24
00:01:27,400 --> 00:01:31,000
Speaker 1: as they are during the day. They're always fascinating. And

25
00:01:31,000 --> 00:01:34,760
Speaker 1: then the super meta question, do parasites look at the stars?

26
00:01:34,880 --> 00:01:38,440
Speaker 1: Can you enjoy the stars with your parasites? Oh, you know,

27
00:01:38,640 --> 00:01:41,800
Speaker 1: ecto parasites can probably look at the stars. But the

28
00:01:42,000 --> 00:01:44,800
Speaker 1: endo parasites, the ones like in your guts, they probably

29
00:01:44,800 --> 00:01:48,680
Speaker 1: don't have as good of you. Exo parasites are those

30
00:01:48,760 --> 00:01:51,320
Speaker 1: like exo planets and exo moons. Are you talking about

31
00:01:51,360 --> 00:01:57,400
Speaker 1: astro parasites parasites on other planets? I said ecto E, C,

32
00:01:57,560 --> 00:02:01,720
Speaker 1: T O M. But you know there could be exo parasites. Uh,

33
00:02:01,880 --> 00:02:03,800
Speaker 1: it wouldn't surprise me to find out that, you know,

34
00:02:03,880 --> 00:02:06,920
Speaker 1: the second organism on another planet was a parasite of

35
00:02:06,960 --> 00:02:09,760
Speaker 1: the first. That would not be too surprising to be Well.

36
00:02:09,800 --> 00:02:12,720
Speaker 1: Welcome to the podcast Daniel and Hoordey explain the universe

37
00:02:12,760 --> 00:02:19,200
Speaker 1: where we have just invented the field of exo parasitology. Yes,

38
00:02:19,360 --> 00:02:24,280
Speaker 1: job security. On this podcast we do delve deep into

39
00:02:24,320 --> 00:02:27,400
Speaker 1: the mysteries of the universe, What is out there? How

40
00:02:27,440 --> 00:02:30,400
Speaker 1: does it work? What squirmy little beings are living on

41
00:02:30,440 --> 00:02:33,720
Speaker 1: the backs of other squirmy little beings on weird planets

42
00:02:33,760 --> 00:02:37,600
Speaker 1: around other stars. We don't shy away from the biggest, deepest,

43
00:02:37,720 --> 00:02:41,360
Speaker 1: squishiest questions in the universe, and sometimes we like to

44
00:02:41,400 --> 00:02:45,480
Speaker 1: ask really basic, fundamental questions about the nature of the universe.

45
00:02:45,680 --> 00:02:48,799
Speaker 1: We find ourselves in because we think that our tiny, little,

46
00:02:48,840 --> 00:02:53,520
Speaker 1: squishy human brains are weirdly, somehow capable of understanding the

47
00:02:53,560 --> 00:02:56,920
Speaker 1: deepest cosmic mysteries, of looking out into the night sky

48
00:02:57,120 --> 00:03:00,640
Speaker 1: and from that information gleaning something big and deep and

49
00:03:00,720 --> 00:03:04,200
Speaker 1: true about the nature of the cosmos. My friend and

50
00:03:04,240 --> 00:03:06,280
Speaker 1: co host Orgy can't be with us today, but we

51
00:03:06,360 --> 00:03:10,040
Speaker 1: are very happy to have our regular guest host, Kelly Smith. Kelly,

52
00:03:10,040 --> 00:03:12,240
Speaker 1: thanks again for joining us today. Thanks for having me.

53
00:03:12,280 --> 00:03:14,800
Speaker 1: I'm excited to be here again, and today's topic is

54
00:03:14,880 --> 00:03:17,600
Speaker 1: super interesting. I can't wait to talk about it. Awesome. Well,

55
00:03:17,720 --> 00:03:20,079
Speaker 1: one reason I love thinking about today's topic is because

56
00:03:20,160 --> 00:03:22,720
Speaker 1: it really was the night sky that got me into science.

57
00:03:22,760 --> 00:03:24,880
Speaker 1: That wasn't just a sound bite when I was a kid.

58
00:03:24,960 --> 00:03:27,440
Speaker 1: I was just like all those other undergrads who write

59
00:03:27,520 --> 00:03:30,080
Speaker 1: cheesy essays about staring up in the night sky and

60
00:03:30,120 --> 00:03:32,600
Speaker 1: wondering about the universe. You know, it really is a

61
00:03:32,720 --> 00:03:36,240
Speaker 1: very attractive and easy way to get into asking questions

62
00:03:36,280 --> 00:03:38,760
Speaker 1: about the universe. Were you also a star watcher as

63
00:03:38,800 --> 00:03:41,480
Speaker 1: a kid, you know, I was more looking down at

64
00:03:41,520 --> 00:03:43,720
Speaker 1: the ground, and you know, as an ecologist, all of

65
00:03:43,800 --> 00:03:46,520
Speaker 1: our essays start off with I always liked playing in

66
00:03:46,560 --> 00:03:49,000
Speaker 1: the woods, so I mostly was looking down, but I

67
00:03:49,040 --> 00:03:51,400
Speaker 1: did like looking up when it got too dark to

68
00:03:51,440 --> 00:03:54,320
Speaker 1: find salamanders and stuff. And as an adult, I really

69
00:03:54,360 --> 00:03:56,280
Speaker 1: like looking at the night sky. Well, the funny thing

70
00:03:56,320 --> 00:03:58,360
Speaker 1: about the night sky in terms of science is that

71
00:03:58,400 --> 00:04:00,760
Speaker 1: it's very attractive. It's like easy if your people to

72
00:04:01,200 --> 00:04:04,720
Speaker 1: hear about, and astronomy seems like a very accessible topic.

73
00:04:04,800 --> 00:04:06,680
Speaker 1: But when it gets down to it, you know, like

74
00:04:06,800 --> 00:04:10,160
Speaker 1: doing science of the stars is mostly like standing around

75
00:04:10,160 --> 00:04:13,040
Speaker 1: in the cold looking through a telescope. And so while

76
00:04:13,080 --> 00:04:16,120
Speaker 1: I was very excited about astronomy as a young kid,

77
00:04:16,440 --> 00:04:18,359
Speaker 1: when I got older and tried to get into it

78
00:04:18,400 --> 00:04:20,839
Speaker 1: a little bit, I found that it wasn't really actually

79
00:04:20,920 --> 00:04:23,000
Speaker 1: for me. You know, I didn't really like staying up

80
00:04:23,080 --> 00:04:25,760
Speaker 1: late at night or staring through a telescope or dealing

81
00:04:25,800 --> 00:04:28,800
Speaker 1: with optics, So sometimes the day to day grind of

82
00:04:28,880 --> 00:04:32,919
Speaker 1: science doesn't quite match with your like fantastical aspirations. And

83
00:04:32,920 --> 00:04:35,560
Speaker 1: you know, I think one thing that draws astronomy students

84
00:04:35,560 --> 00:04:38,240
Speaker 1: and ecology students together is that both of those groups

85
00:04:38,240 --> 00:04:40,480
Speaker 1: of students think that it's going to be one thing,

86
00:04:40,560 --> 00:04:42,640
Speaker 1: like playing outside a lot, and then it ends up

87
00:04:42,680 --> 00:04:45,599
Speaker 1: being a lot of math, for example, and that is

88
00:04:45,600 --> 00:04:48,359
Speaker 1: where we lose a bunch of the outside enthusiasts. Is

89
00:04:48,360 --> 00:04:50,200
Speaker 1: there a lot of math in ecology and then you're

90
00:04:50,240 --> 00:04:53,280
Speaker 1: like putting down squares and counting how many slugs or something. Well,

91
00:04:53,320 --> 00:04:56,080
Speaker 1: I mean there's counting, but then there's also trying to like,

92
00:04:56,160 --> 00:04:59,360
Speaker 1: you know, write mathematical models to describe host predator dynamics

93
00:04:59,440 --> 00:05:01,960
Speaker 1: or whatever. Actually I took ecology because I thought it

94
00:05:02,040 --> 00:05:03,760
Speaker 1: was going to be an easy a because it's like

95
00:05:03,839 --> 00:05:06,000
Speaker 1: hippies playing in the woods. But then when I found

96
00:05:06,000 --> 00:05:08,800
Speaker 1: the equations, I fell in love. So for me, that's

97
00:05:08,839 --> 00:05:11,039
Speaker 1: what hooked me, which I'm sure is what hooked some

98
00:05:11,120 --> 00:05:14,800
Speaker 1: students on astronomy as well. Yeah. Absolutely, it is amazing

99
00:05:14,839 --> 00:05:17,000
Speaker 1: to think that we can describe what's going on over

100
00:05:17,040 --> 00:05:19,039
Speaker 1: there and it's fascinating to me that we can learn

101
00:05:19,080 --> 00:05:21,560
Speaker 1: about the rest of the universe just from looking at

102
00:05:21,560 --> 00:05:23,880
Speaker 1: our local neighborhood. You know that we have an example

103
00:05:23,960 --> 00:05:26,200
Speaker 1: star right here in our solar system, and we can

104
00:05:26,240 --> 00:05:28,200
Speaker 1: study it and think about and understand it, and then

105
00:05:28,240 --> 00:05:31,320
Speaker 1: we can apply that knowledge to the stars to saying, oh,

106
00:05:31,440 --> 00:05:33,760
Speaker 1: those are just other sons. And you know, I have

107
00:05:33,880 --> 00:05:36,719
Speaker 1: to embarrass my daughter because it was only six months

108
00:05:36,760 --> 00:05:38,320
Speaker 1: ago or so. I was talking to her and I

109
00:05:38,360 --> 00:05:41,240
Speaker 1: said something like, you know, the stars, they're just other sons, right,

110
00:05:41,680 --> 00:05:44,800
Speaker 1: And she was like, what are you serious? And then

111
00:05:44,920 --> 00:05:47,160
Speaker 1: I was like, what are you serious? You didn't know

112
00:05:47,279 --> 00:05:49,799
Speaker 1: that already. She was like no, I had no idea.

113
00:05:50,279 --> 00:05:52,640
Speaker 1: And I was so embarrassed, Like, here I am, you know,

114
00:05:52,720 --> 00:05:56,000
Speaker 1: a physicist, a science communicator, and my own daughter doesn't

115
00:05:56,040 --> 00:05:58,760
Speaker 1: know this very basic thing about the universe. Yeah. I

116
00:05:58,800 --> 00:06:01,120
Speaker 1: was gonna ask if you're a little embarrassed admitting that,

117
00:06:01,240 --> 00:06:03,240
Speaker 1: and I, yeah, I guess you are. But you know,

118
00:06:03,279 --> 00:06:05,480
Speaker 1: we all have gaps things that we just assume our

119
00:06:05,560 --> 00:06:07,680
Speaker 1: kids intu it in, but they didn't, and it's you know,

120
00:06:07,760 --> 00:06:10,279
Speaker 1: surprising sometimes. Yeah, she thought that they were sort of

121
00:06:10,320 --> 00:06:12,680
Speaker 1: like other stars, but they were much closer and much

122
00:06:12,760 --> 00:06:15,600
Speaker 1: dimmer that we were surrounded by like an ocean of

123
00:06:15,839 --> 00:06:18,039
Speaker 1: not very bright suns or something. I don't think she

124
00:06:18,040 --> 00:06:20,039
Speaker 1: had actually thought about it very much, and so you're right,

125
00:06:20,080 --> 00:06:22,560
Speaker 1: it's just something we never actually came to the point

126
00:06:22,640 --> 00:06:25,520
Speaker 1: of talking about. And now we have a fun running joke,

127
00:06:25,560 --> 00:06:27,920
Speaker 1: which is, at any time something obvious comes up about

128
00:06:27,920 --> 00:06:30,359
Speaker 1: the universe, I'm like, you are aware, of course that

129
00:06:30,480 --> 00:06:35,599
Speaker 1: the Earth is round, right, She's like, Dad, it's important

130
00:06:35,680 --> 00:06:38,080
Speaker 1: you never let kids forget if they got something wrong.

131
00:06:38,200 --> 00:06:40,839
Speaker 1: You know, you need to remind them of that all

132
00:06:40,880 --> 00:06:43,040
Speaker 1: the time. No, trying not to make her feel bad. Now,

133
00:06:43,040 --> 00:06:45,320
Speaker 1: it's just my opportunity to get to like insert a

134
00:06:45,320 --> 00:06:47,880
Speaker 1: little bit of science into any random conversation because now

135
00:06:47,920 --> 00:06:50,560
Speaker 1: I have an excuse because maybe this is another thing

136
00:06:50,600 --> 00:06:53,080
Speaker 1: we just never got around to talking about. That's right,

137
00:06:53,080 --> 00:06:55,080
Speaker 1: And I'm sure she doesn't find it frustrating that you

138
00:06:55,160 --> 00:06:59,159
Speaker 1: do that at all. Oh, she teasings me back. She

139
00:06:59,360 --> 00:07:02,919
Speaker 1: is quite capable of that. I'm glad. But this question

140
00:07:03,040 --> 00:07:05,720
Speaker 1: of the stars and the night sky really has lots

141
00:07:05,760 --> 00:07:08,240
Speaker 1: of fascinating layers to it. A lot of people are

142
00:07:08,279 --> 00:07:11,000
Speaker 1: surprised when they learn, for example, that the stars are

143
00:07:11,040 --> 00:07:14,040
Speaker 1: there during the daytime, like you could see them in

144
00:07:14,160 --> 00:07:17,640
Speaker 1: principle they are shooting starlight at you and it's hitting

145
00:07:17,640 --> 00:07:20,600
Speaker 1: the earth. It's just sort of like overwhelmed by the sun.

146
00:07:20,880 --> 00:07:23,120
Speaker 1: I feel like that's probably something I didn't figure out

147
00:07:23,200 --> 00:07:25,360
Speaker 1: until I was much older, Like that's another one of

148
00:07:25,360 --> 00:07:27,360
Speaker 1: those obvious things that you should have known. But I

149
00:07:27,400 --> 00:07:29,640
Speaker 1: feel like I remember, maybe like as a senior in

150
00:07:29,680 --> 00:07:33,200
Speaker 1: high school, having a like, oh, they're still there moment,

151
00:07:34,080 --> 00:07:36,760
Speaker 1: which I should be particularly embarrassed about. But as I said,

152
00:07:36,800 --> 00:07:39,560
Speaker 1: I wasn't looking up that much. I was mostly looking down. Yeah,

153
00:07:39,640 --> 00:07:42,400
Speaker 1: And there's those shame in coming to understanding of the universe.

154
00:07:42,440 --> 00:07:44,920
Speaker 1: At any age. We should just be rewarding people for

155
00:07:44,960 --> 00:07:48,120
Speaker 1: their curiosity and their enthusiasm. And one of the things

156
00:07:48,120 --> 00:07:50,120
Speaker 1: for me that I love about the night sky and

157
00:07:50,160 --> 00:07:53,080
Speaker 1: just staring at it is trying to get a mental

158
00:07:53,160 --> 00:07:58,200
Speaker 1: image or conception, grappling with the idea of how ridiculously

159
00:07:58,280 --> 00:08:00,920
Speaker 1: far away they are. Know, I like standing on the

160
00:08:00,920 --> 00:08:04,320
Speaker 1: top of a mountain and seeing eighty miles hundred miles

161
00:08:04,320 --> 00:08:06,680
Speaker 1: on a clear day even further, but looking up in

162
00:08:06,720 --> 00:08:09,360
Speaker 1: the night sky is like standing on the top of

163
00:08:09,440 --> 00:08:12,120
Speaker 1: a mountain. The side of the Earth and staring across

164
00:08:12,240 --> 00:08:16,120
Speaker 1: billions of light years, right, those photons left those stars

165
00:08:16,200 --> 00:08:19,880
Speaker 1: millions or billions of years ago, just now arriving on Earth.

166
00:08:19,920 --> 00:08:22,960
Speaker 1: It's like it's the most spectacular view in the universe.

167
00:08:23,160 --> 00:08:26,080
Speaker 1: My brain has so much trouble wrapping its head around

168
00:08:26,160 --> 00:08:28,960
Speaker 1: distances in space. Like even just knowing that it takes like,

169
00:08:29,000 --> 00:08:31,560
Speaker 1: what six months to get to Mars, that seems crazy

170
00:08:31,560 --> 00:08:33,200
Speaker 1: because you know, it's like two days of driving to

171
00:08:33,200 --> 00:08:35,120
Speaker 1: get across the US. So it feels to me like

172
00:08:35,200 --> 00:08:39,360
Speaker 1: anything should be accessible within forty eight hours. I should

173
00:08:39,360 --> 00:08:41,559
Speaker 1: be able to drive to Mars in two days, right,

174
00:08:41,640 --> 00:08:46,000
Speaker 1: stopping at gas stations and getting like space snacks. I mean,

175
00:08:46,040 --> 00:08:48,560
Speaker 1: I understand you're going to need a different vehicle, but

176
00:08:48,640 --> 00:08:51,480
Speaker 1: it seems like it should be reachable pretty quickly. And

177
00:08:51,520 --> 00:08:54,360
Speaker 1: one of the real challenges with understanding these distances in

178
00:08:54,400 --> 00:08:56,600
Speaker 1: particular is that you have two things you have to

179
00:08:56,600 --> 00:08:59,440
Speaker 1: grapple with. Not just are the stars super far away,

180
00:08:59,640 --> 00:09:03,079
Speaker 1: but they are enormous, Like the size of a star

181
00:09:03,520 --> 00:09:07,600
Speaker 1: is just flabberghastingly huge, Like the Sun for example, right,

182
00:09:07,920 --> 00:09:10,840
Speaker 1: so much bigger than the Earth. Jupiter is like a

183
00:09:10,960 --> 00:09:13,920
Speaker 1: thousand times the volume of the Earth, and the Sun

184
00:09:14,040 --> 00:09:16,760
Speaker 1: is like a million times the volume of the Earth. Right,

185
00:09:16,840 --> 00:09:20,200
Speaker 1: that's flabbergasting. It's hard to hold that many Earth's in

186
00:09:20,280 --> 00:09:22,000
Speaker 1: your head. And there are stars out there there are

187
00:09:22,080 --> 00:09:24,040
Speaker 1: much much bigger, And yet you look up at the

188
00:09:24,120 --> 00:09:27,400
Speaker 1: night sky and they are these tiny little pin pricks, right,

189
00:09:27,520 --> 00:09:29,720
Speaker 1: And so you have to have both of these things

190
00:09:29,720 --> 00:09:33,439
Speaker 1: in your head. That these objects are enormous fireballs really

191
00:09:33,480 --> 00:09:35,960
Speaker 1: just like bigger than you can even imagine, and yet

192
00:09:36,120 --> 00:09:41,400
Speaker 1: so distant that these enormous fireballs now look super duper tiny. Right,

193
00:09:41,440 --> 00:09:43,480
Speaker 1: So two things in your head you have to sort

194
00:09:43,480 --> 00:09:46,719
Speaker 1: of like divide by each other, both huge numbers. How

195
00:09:46,760 --> 00:09:48,560
Speaker 1: big is our son relative to some of the others

196
00:09:48,600 --> 00:09:50,440
Speaker 1: you said, some of the others were much much bigger.

197
00:09:50,559 --> 00:09:52,640
Speaker 1: Is our son sort of a tiny sun? Or is

198
00:09:52,640 --> 00:09:55,760
Speaker 1: always like about average? Our son is not unusual. But

199
00:09:55,840 --> 00:09:58,840
Speaker 1: there are many stars out there that are much bigger.

200
00:09:59,040 --> 00:10:01,319
Speaker 1: For example, Beetles Juice, if you put it in our

201
00:10:01,320 --> 00:10:05,160
Speaker 1: solar system, it's radius would extend out into the asteroid

202
00:10:05,240 --> 00:10:08,679
Speaker 1: belt like Mars would be inside Middle Juice. We did

203
00:10:08,720 --> 00:10:11,080
Speaker 1: an episode about the biggest stars in the universe. Some

204
00:10:11,160 --> 00:10:13,240
Speaker 1: of them are even larger. Some of them, their radii

205
00:10:13,360 --> 00:10:16,640
Speaker 1: would extend out, you know, into the outer solar system,

206
00:10:16,880 --> 00:10:22,040
Speaker 1: you know. So there are monsters out there, absolute gargantuan monsters,

207
00:10:22,040 --> 00:10:26,079
Speaker 1: balls of burning plasma. That's really hard for me to imagine.

208
00:10:26,240 --> 00:10:29,400
Speaker 1: That's right. They're huge, they're enormous, and yet they only

209
00:10:29,440 --> 00:10:32,080
Speaker 1: appear as pin pricks in our sky. And the reason,

210
00:10:32,120 --> 00:10:35,440
Speaker 1: of course is math, because as those photons shoot out

211
00:10:35,520 --> 00:10:38,400
Speaker 1: from that star, they go in all directions, and we

212
00:10:38,480 --> 00:10:41,640
Speaker 1: only see a tiny fraction of those photons. Right. If

213
00:10:41,679 --> 00:10:43,959
Speaker 1: you're standing like a meter away from a light bulb

214
00:10:44,040 --> 00:10:46,800
Speaker 1: and you have a solar panel gathering some of that light,

215
00:10:47,040 --> 00:10:49,200
Speaker 1: you're not gathering all of the light, right, You're gathering

216
00:10:49,240 --> 00:10:51,679
Speaker 1: some fraction of the photons that come off of that

217
00:10:51,760 --> 00:10:54,400
Speaker 1: light bulb. Right, it's shooting in all directions, and the

218
00:10:54,400 --> 00:10:56,880
Speaker 1: fraction that you get like the area of your solar

219
00:10:56,880 --> 00:11:00,480
Speaker 1: panel divided by the area of that sphere that's at

220
00:11:00,520 --> 00:11:02,960
Speaker 1: your distance, right, So that's the fraction of the photons

221
00:11:03,000 --> 00:11:05,480
Speaker 1: you're getting. If you take two steps away, for example,

222
00:11:05,480 --> 00:11:07,960
Speaker 1: now you're twice as far. Then the area of that

223
00:11:08,080 --> 00:11:10,720
Speaker 1: sphere that the photons are getting spread over is now

224
00:11:10,800 --> 00:11:14,400
Speaker 1: four times as big. Because the surface of a sphere

225
00:11:14,480 --> 00:11:17,679
Speaker 1: with twice the radius is four times as big. So

226
00:11:17,720 --> 00:11:20,560
Speaker 1: the same solar panels now capturing one fourth of what

227
00:11:20,600 --> 00:11:23,240
Speaker 1: it did before. So the luminosity of a star, the

228
00:11:23,280 --> 00:11:26,920
Speaker 1: brightness of its appearance, goes like one over the distance square.

229
00:11:27,360 --> 00:11:30,360
Speaker 1: And these distances we're talking about are huge, right, Other

230
00:11:30,440 --> 00:11:33,880
Speaker 1: stars are not just super bright, they're really really far away,

231
00:11:34,040 --> 00:11:36,920
Speaker 1: So one over their distance square becomes a really big number.

232
00:11:37,000 --> 00:11:39,000
Speaker 1: But if you do that over and over and over

233
00:11:39,080 --> 00:11:43,560
Speaker 1: and over again, like billions or trillions of times, shouldn't

234
00:11:43,559 --> 00:11:45,720
Speaker 1: it be much brighter out there? Yeah, it's a really

235
00:11:45,760 --> 00:11:48,400
Speaker 1: good question. So we're balancing lots of big numbers here.

236
00:11:48,440 --> 00:11:50,439
Speaker 1: We have huge stars, so they should be admitting a

237
00:11:50,480 --> 00:11:53,080
Speaker 1: lot of light, but they're really far away, so that

238
00:11:53,120 --> 00:11:55,120
Speaker 1: cuts down their light a lot. But then there's a

239
00:11:55,160 --> 00:11:58,880
Speaker 1: lot of them. Right, three have like three almost infinite numbers,

240
00:11:58,880 --> 00:12:01,520
Speaker 1: and we're wondering, like, how how do those get fit together?

241
00:12:01,760 --> 00:12:04,760
Speaker 1: You know, if the universe is in fact infinite, wouldn't

242
00:12:04,800 --> 00:12:07,560
Speaker 1: all those numbers add up to be like a crazy

243
00:12:07,559 --> 00:12:10,760
Speaker 1: amount of light. Wouldn't Kelly's kids get like star burns

244
00:12:10,840 --> 00:12:13,160
Speaker 1: if they go out at night looking at the stars. Right,

245
00:12:13,200 --> 00:12:15,160
Speaker 1: this is a question that people have asked sort of

246
00:12:15,200 --> 00:12:18,960
Speaker 1: since antiquity, like why isn't the night sky like catastrophically

247
00:12:19,080 --> 00:12:22,680
Speaker 1: blazing full of starlight? Thank goodness for star screen. And

248
00:12:22,720 --> 00:12:30,880
Speaker 1: so today on the podcast we'll be answering why is

249
00:12:31,120 --> 00:12:33,760
Speaker 1: the night sky dark? And I love this kind of

250
00:12:33,840 --> 00:12:36,400
Speaker 1: question because it's such a simple, basic question, and it's

251
00:12:36,440 --> 00:12:38,640
Speaker 1: the kind of thing that people can think about and

252
00:12:38,679 --> 00:12:40,760
Speaker 1: have been thinking about for a long time. Right, you

253
00:12:40,800 --> 00:12:43,720
Speaker 1: don't need special tools or apparatus. Is just to sit

254
00:12:43,800 --> 00:12:46,240
Speaker 1: here on the surface of this rock and to ask

255
00:12:46,280 --> 00:12:48,520
Speaker 1: this question, like, if I have an understanding of how

256
00:12:48,520 --> 00:12:50,720
Speaker 1: the universe works, my mental model is that there are

257
00:12:50,720 --> 00:12:53,240
Speaker 1: stars everywhere, then what should I expect to see in

258
00:12:53,320 --> 00:12:56,360
Speaker 1: my night sky? Right? This is a perfect example of

259
00:12:56,360 --> 00:13:00,000
Speaker 1: what physics really is at its core. Build a model

260
00:13:00,000 --> 00:13:01,800
Speaker 1: to love the universe in your head. We make a

261
00:13:01,840 --> 00:13:03,880
Speaker 1: prediction for what you should see, and then you ask,

262
00:13:04,000 --> 00:13:07,400
Speaker 1: like does that agree with how the universe actually works?

263
00:13:07,400 --> 00:13:09,960
Speaker 1: And if it doesn't, then you get an important clue

264
00:13:10,240 --> 00:13:13,679
Speaker 1: about how the universe might be different from your mental model. Well,

265
00:13:13,720 --> 00:13:15,560
Speaker 1: you forgot about the part where you spend like a

266
00:13:15,559 --> 00:13:17,320
Speaker 1: decade writing to grant so that you can get the

267
00:13:17,320 --> 00:13:19,120
Speaker 1: money to try to test the model. But but yes,

268
00:13:19,280 --> 00:13:22,080
Speaker 1: essentially that's how physics works. We're trying to make science

269
00:13:22,120 --> 00:13:27,880
Speaker 1: sound glamourus here talking all the emails and the meetings.

270
00:13:28,280 --> 00:13:30,120
Speaker 1: I'm sorry, I'm sorry, didn't mean to take away all

271
00:13:30,160 --> 00:13:33,000
Speaker 1: the beauty of physics. Al Right, Well, let's tap into

272
00:13:33,040 --> 00:13:36,600
Speaker 1: the apparent beauty of physics by asking our listeners if

273
00:13:36,640 --> 00:13:39,760
Speaker 1: they know why the night sky is dark. So I

274
00:13:39,800 --> 00:13:41,559
Speaker 1: wrote to all of them, and I asked them, if

275
00:13:41,600 --> 00:13:45,199
Speaker 1: the universe is infinite, why is the night sky dark?

276
00:13:45,360 --> 00:13:46,880
Speaker 1: If this sounds like a lot of fun to you,

277
00:13:46,960 --> 00:13:50,120
Speaker 1: and you would be willing to participate for future episodes,

278
00:13:50,160 --> 00:13:53,040
Speaker 1: please don't be shy right to us, to Daniel and

279
00:13:53,280 --> 00:13:56,840
Speaker 1: Jorge dot com, and we'll send you our recent questions.

280
00:13:57,160 --> 00:13:58,959
Speaker 1: So think about it for a minute. Do you know

281
00:13:59,600 --> 00:14:02,840
Speaker 1: why in an infinite universe the night sky is not

282
00:14:03,120 --> 00:14:06,480
Speaker 1: blazingly bright? Here's what our listeners had to say. Well,

283
00:14:06,520 --> 00:14:11,360
Speaker 1: I guess that's because from the electromagnetic spectrum that's the

284
00:14:11,480 --> 00:14:13,920
Speaker 1: light emitting of all stars and everything in the universe,

285
00:14:14,120 --> 00:14:16,760
Speaker 1: we are only able to see just this tiny fraction

286
00:14:16,840 --> 00:14:20,840
Speaker 1: that's the visible the visible spectrum. So I guess that

287
00:14:20,880 --> 00:14:24,520
Speaker 1: there are photons all around the universe, but they are

288
00:14:24,520 --> 00:14:27,360
Speaker 1: in different wavelength so we are not able to see them.

289
00:14:27,480 --> 00:14:30,120
Speaker 1: That's why the night sky looks dark for us, because

290
00:14:30,120 --> 00:14:32,880
Speaker 1: we cannot perceive it. Okay, so, first of all, the

291
00:14:32,960 --> 00:14:36,840
Speaker 1: universe is not in finite. It's just insanely huge, and

292
00:14:37,080 --> 00:14:40,480
Speaker 1: it expanding faster than the spade of light. So it

293
00:14:40,560 --> 00:14:44,000
Speaker 1: may seem infinite, but it's not infinite. As for the

294
00:14:44,080 --> 00:14:47,600
Speaker 1: question itself, I can come up with two different explanations.

295
00:14:48,120 --> 00:14:51,120
Speaker 1: One is that the light coming from really distant stars

296
00:14:51,160 --> 00:14:54,720
Speaker 1: and galaxies that they get that eventually they get really

297
00:14:54,760 --> 00:14:58,280
Speaker 1: spread out. They're not concentrated enough for us to spot,

298
00:14:58,800 --> 00:15:00,800
Speaker 1: so like in our able to see them in the

299
00:15:00,920 --> 00:15:03,840
Speaker 1: night sky. The other reason that I could come up

300
00:15:03,880 --> 00:15:06,160
Speaker 1: with was that although the speed of flight is fast,

301
00:15:06,360 --> 00:15:09,240
Speaker 1: it's not fast enough compared to the size of the universe.

302
00:15:09,640 --> 00:15:13,720
Speaker 1: So I imagine this bubble of visibility around Earth that

303
00:15:13,840 --> 00:15:17,440
Speaker 1: keeps growing every second as new light reaches us from

304
00:15:17,440 --> 00:15:20,440
Speaker 1: further places. But there is still a lot of the

305
00:15:20,520 --> 00:15:22,880
Speaker 1: universe out there from which the light has simply not

306
00:15:23,080 --> 00:15:26,040
Speaker 1: had enough time to reach us. It's because all those

307
00:15:26,040 --> 00:15:28,560
Speaker 1: stars are just too spread out and they're too far

308
00:15:28,600 --> 00:15:30,720
Speaker 1: away so that they can really make a strong light.

309
00:15:30,840 --> 00:15:33,800
Speaker 1: And I also believe that inflation plays a role, right,

310
00:15:33,840 --> 00:15:37,280
Speaker 1: because I think that in a few million or billion

311
00:15:37,360 --> 00:15:40,160
Speaker 1: years there will be rarely any stars to be seen

312
00:15:40,160 --> 00:15:42,480
Speaker 1: in the night sky. So maybe that's the point. Well,

313
00:15:42,520 --> 00:15:43,960
Speaker 1: first of all, proved to me that we live in

314
00:15:43,960 --> 00:15:48,560
Speaker 1: an infinite universe. But supposing we do, it's not just

315
00:15:48,760 --> 00:15:53,560
Speaker 1: jam packed with stars all the way out, and the

316
00:15:53,760 --> 00:15:57,080
Speaker 1: intensity of light fairies with the square of your distance

317
00:15:57,120 --> 00:15:59,760
Speaker 1: from it, so the really far away stuff is extremely

318
00:16:00,040 --> 00:16:03,560
Speaker 1: him um. And I'm sure there's some kind of math

319
00:16:03,680 --> 00:16:07,200
Speaker 1: you can do that shows a curve that approaches an

320
00:16:07,200 --> 00:16:11,280
Speaker 1: awsome tote or one of the axes and the zero

321
00:16:11,320 --> 00:16:13,600
Speaker 1: pans out there. It's kind of like, um, if you

322
00:16:13,680 --> 00:16:16,600
Speaker 1: keep going, you go one ft, and then you go

323
00:16:16,720 --> 00:16:18,440
Speaker 1: half a foot, and then you go a quarter of foot,

324
00:16:18,920 --> 00:16:22,880
Speaker 1: you never quite get there two feet away. And I'm

325
00:16:22,920 --> 00:16:26,040
Speaker 1: glad it's not effinitely late, because um, it's nice to

326
00:16:26,040 --> 00:16:27,920
Speaker 1: have some darkness every once in a while. It is

327
00:16:28,040 --> 00:16:31,680
Speaker 1: not dark at all frequencies. If we shift to the

328
00:16:31,760 --> 00:16:34,880
Speaker 1: right frequency, there's usually something coming from every point in

329
00:16:34,920 --> 00:16:39,080
Speaker 1: the sky we look at, however, for the visual range

330
00:16:39,120 --> 00:16:43,000
Speaker 1: of humans, even though at any given point in the sky.

331
00:16:43,200 --> 00:16:45,840
Speaker 1: If we look deep enough in there probably is a

332
00:16:45,880 --> 00:16:49,880
Speaker 1: source of light. There are dust clouds and gas clouds

333
00:16:49,920 --> 00:16:52,720
Speaker 1: and lots of other things that obstruct the light before

334
00:16:52,760 --> 00:16:57,480
Speaker 1: it gets to us, so within human visual range it

335
00:16:57,520 --> 00:16:59,920
Speaker 1: can look very dark, but if we shift to a

336
00:17:00,000 --> 00:17:03,000
Speaker 1: different frequency, there's usually some form of light coming in.

337
00:17:03,160 --> 00:17:06,080
Speaker 1: So I know this one. The answer is dust. The

338
00:17:06,280 --> 00:17:12,159
Speaker 1: interstellar gases are just thick enough to absorbs enough of

339
00:17:12,200 --> 00:17:16,760
Speaker 1: the radiation sent by the more distant stars that we

340
00:17:16,920 --> 00:17:20,120
Speaker 1: can't with our naked eye see things all the way

341
00:17:20,119 --> 00:17:21,720
Speaker 1: back to the dawn of time. It's what we need

342
00:17:21,760 --> 00:17:25,280
Speaker 1: things like Hubble for. So those more distant and fainter

343
00:17:25,440 --> 00:17:29,480
Speaker 1: lights do get filtered out by the dust, and so

344
00:17:29,760 --> 00:17:32,560
Speaker 1: the night sky appears dark to us instead of appearing light.

345
00:17:33,640 --> 00:17:38,320
Speaker 1: Light from different stars takes time to travel from whatever

346
00:17:38,359 --> 00:17:41,359
Speaker 1: the star is to where we are, so depending on

347
00:17:41,400 --> 00:17:43,240
Speaker 1: how far the star is, the light from it might

348
00:17:43,280 --> 00:17:47,080
Speaker 1: not have reached us yet, and so the space in

349
00:17:47,119 --> 00:17:49,680
Speaker 1: the interim for the duration for which the light hasn't

350
00:17:49,720 --> 00:17:52,600
Speaker 1: gotten here yet will be dark. Well, that is debatable

351
00:17:52,760 --> 00:17:54,600
Speaker 1: if that's even true, that we live in an under

352
00:17:54,760 --> 00:17:59,240
Speaker 1: infinite universe, but I guess the question is why wouldn't

353
00:17:59,240 --> 00:18:02,320
Speaker 1: there be as star in every direction we look? And

354
00:18:02,440 --> 00:18:05,919
Speaker 1: this would be due to um that there would be

355
00:18:05,960 --> 00:18:10,720
Speaker 1: still a couple of photons arriving from any direction. I guess, um.

356
00:18:10,760 --> 00:18:16,679
Speaker 1: But the brightness dissipates um over long distances UM in

357
00:18:16,760 --> 00:18:19,240
Speaker 1: a sphere, so we are not getting a lot of

358
00:18:19,280 --> 00:18:22,399
Speaker 1: photons um. So I guess if our eyes would be

359
00:18:22,440 --> 00:18:25,680
Speaker 1: good enough, we would be able to see a totally

360
00:18:25,720 --> 00:18:29,439
Speaker 1: lit up universe at night. You know, for this set

361
00:18:29,480 --> 00:18:32,959
Speaker 1: of answers, I was particularly impressed with your audience. Now,

362
00:18:32,960 --> 00:18:35,920
Speaker 1: of course your audience is brilliant and they always give

363
00:18:35,960 --> 00:18:39,240
Speaker 1: good answers, but for this set in particular, they really

364
00:18:39,240 --> 00:18:41,320
Speaker 1: had some clever answers. And so so, first of all,

365
00:18:41,320 --> 00:18:43,320
Speaker 1: like when you ask this question to the listeners, do

366
00:18:43,359 --> 00:18:45,760
Speaker 1: they have to answer like immediately or do they get

367
00:18:45,800 --> 00:18:47,560
Speaker 1: the question, think about it for a day and then

368
00:18:47,600 --> 00:18:50,680
Speaker 1: call in. That's a good question. Well, the rules are

369
00:18:50,880 --> 00:18:54,720
Speaker 1: no preparation, no googling, and you're supposed to give immediate

370
00:18:54,760 --> 00:18:57,199
Speaker 1: off the cuff answers. Now, I can't police them, so

371
00:18:57,240 --> 00:18:59,240
Speaker 1: I don't know if they've googled or they've gone and

372
00:18:59,240 --> 00:19:01,800
Speaker 1: looked up their star on the professor from college and

373
00:19:01,840 --> 00:19:04,440
Speaker 1: then trying to give an intelligent answer. But I'm trust

374
00:19:04,520 --> 00:19:07,159
Speaker 1: in them that these are what they immediately think that

375
00:19:07,200 --> 00:19:09,480
Speaker 1: these are. They're off the cuff responses. Yeah, yeah, I

376
00:19:09,520 --> 00:19:12,840
Speaker 1: think they're not just smart, but they're trustworthy and good

377
00:19:12,840 --> 00:19:17,000
Speaker 1: looking and good looking, that's right, many many good features.

378
00:19:17,040 --> 00:19:18,560
Speaker 1: You know, you'd have to be a great person to

379
00:19:18,560 --> 00:19:20,960
Speaker 1: be listening to this podcast. I think that's called the

380
00:19:21,000 --> 00:19:25,720
Speaker 1: halo effect. If anyway, getting off topic, but yeah, there

381
00:19:25,720 --> 00:19:27,720
Speaker 1: were like some good skeptical answers. You know, we don't

382
00:19:27,720 --> 00:19:30,120
Speaker 1: know if the universe is infinite. You've clearly taught them

383
00:19:30,160 --> 00:19:32,880
Speaker 1: about what we do and don't know. And Dust came

384
00:19:32,960 --> 00:19:34,919
Speaker 1: up to be honest, Dust I hadn't thought of as

385
00:19:34,960 --> 00:19:38,119
Speaker 1: a potential explanation until reading the answers, and so I

386
00:19:38,200 --> 00:19:40,000
Speaker 1: was I was pretty impressed with this set of answers.

387
00:19:40,040 --> 00:19:41,720
Speaker 1: What did you think? Yeah, they really run the game,

388
00:19:41,720 --> 00:19:43,840
Speaker 1: and there's a lot of different things to think about.

389
00:19:43,920 --> 00:19:46,119
Speaker 1: And that's why this is a great question because it

390
00:19:46,200 --> 00:19:48,879
Speaker 1: forces you to sort of clarify your understanding for what

391
00:19:49,000 --> 00:19:51,800
Speaker 1: really is going on, what is interfering with the light

392
00:19:51,840 --> 00:19:54,680
Speaker 1: that's coming to earth, how much should be arriving. There's

393
00:19:54,680 --> 00:19:56,240
Speaker 1: a lot of good stuff here. There is a lot

394
00:19:56,280 --> 00:19:58,480
Speaker 1: of good stuff there. And so one of the listeners said,

395
00:19:58,640 --> 00:20:01,520
Speaker 1: we don't know if the universe is infinite. Is that right?

396
00:20:01,600 --> 00:20:03,560
Speaker 1: What do we know about the size of the universe?

397
00:20:03,760 --> 00:20:07,160
Speaker 1: That is correct, We do not know if the universe

398
00:20:07,359 --> 00:20:09,800
Speaker 1: is infinite. You know. We know that our patch of

399
00:20:09,840 --> 00:20:11,840
Speaker 1: the universe, what we can see, what we call the

400
00:20:11,880 --> 00:20:14,959
Speaker 1: observable universe, no part of it seems to be different

401
00:20:15,000 --> 00:20:16,840
Speaker 1: from any other part of it. That it's the universe

402
00:20:16,880 --> 00:20:20,199
Speaker 1: seems to be sort of homogeneous, and so that suggests

403
00:20:20,640 --> 00:20:23,400
Speaker 1: that no part of the universe should be special, and

404
00:20:23,600 --> 00:20:27,720
Speaker 1: it implies that perhaps the universe is infinite. We don't

405
00:20:27,760 --> 00:20:29,760
Speaker 1: know that. We've tried to measure things like we can

406
00:20:29,800 --> 00:20:34,040
Speaker 1: measure the curvature of space, how much space itself is bent.

407
00:20:34,200 --> 00:20:36,560
Speaker 1: Though we talked about in a recent episode about whether

408
00:20:36,600 --> 00:20:39,320
Speaker 1: the universe is shaped like a doughnut or a sphere

409
00:20:39,520 --> 00:20:42,880
Speaker 1: or an infinitely flat plane, we can't actually tell. We've

410
00:20:42,920 --> 00:20:46,720
Speaker 1: measured the universe is curvature to be consistent with zero curvature,

411
00:20:46,800 --> 00:20:49,200
Speaker 1: like as if it was flat. But the universe could

412
00:20:49,200 --> 00:20:51,520
Speaker 1: be flat and also not be infinite. It could like

413
00:20:51,560 --> 00:20:54,040
Speaker 1: tie together at the edges sort of like the screen

414
00:20:54,119 --> 00:20:57,080
Speaker 1: and pact Man or asteroids. So there's lots of things

415
00:20:57,119 --> 00:21:00,239
Speaker 1: we don't know, but so far it's consistent with us

416
00:21:00,240 --> 00:21:04,280
Speaker 1: seeing a finite patch of an infinite universe. But absolutely

417
00:21:04,320 --> 00:21:07,280
Speaker 1: we don't know. What do you mean by homogeneous like that?

418
00:21:07,359 --> 00:21:09,560
Speaker 1: Because you know, when I think about galaxies, they sort

419
00:21:09,560 --> 00:21:12,600
Speaker 1: of seem like clumps. But I guess, just like in general,

420
00:21:12,920 --> 00:21:16,280
Speaker 1: it's everything somewhat evenly distributed. Is that what that means

421
00:21:16,320 --> 00:21:20,000
Speaker 1: by homogeneous? We don't mean literally exactly homogeneous, because there

422
00:21:20,040 --> 00:21:22,000
Speaker 1: are parts of the universe where there are galaxies in

423
00:21:22,080 --> 00:21:23,800
Speaker 1: parts where there are not. We mean that if you

424
00:21:23,880 --> 00:21:26,640
Speaker 1: zoom out far enough, like sort of on the biggest scales,

425
00:21:26,880 --> 00:21:31,119
Speaker 1: everything seems basically smooth. There's no clusters and superclusters, but

426
00:21:31,119 --> 00:21:33,760
Speaker 1: there's no real structure beyond that, and the rules of

427
00:21:33,760 --> 00:21:36,160
Speaker 1: the universe seem to be the same everywhere. There don't

428
00:21:36,200 --> 00:21:39,240
Speaker 1: seem to be any special locations. There's no center to

429
00:21:39,280 --> 00:21:41,440
Speaker 1: the universe. As far as we can tell, everyone in

430
00:21:41,440 --> 00:21:43,760
Speaker 1: the universe seems to be similar to everywhere else in

431
00:21:43,800 --> 00:21:46,440
Speaker 1: the universe. That's what we mean. And so I thought

432
00:21:46,440 --> 00:21:51,920
Speaker 1: that everything was moving away from a central point, But

433
00:21:52,040 --> 00:21:54,000
Speaker 1: is that not true? There's no like point that we

434
00:21:54,040 --> 00:21:56,520
Speaker 1: know that everything is moving away from, like expanding out.

435
00:21:56,840 --> 00:22:00,600
Speaker 1: Everything is moving away from everything else. So the expansion

436
00:22:00,760 --> 00:22:03,520
Speaker 1: is also homogeneous, like every point in the universe is

437
00:22:03,560 --> 00:22:06,399
Speaker 1: expanding just like every other point. No, no matter where

438
00:22:06,440 --> 00:22:08,720
Speaker 1: you are in the universe, it will look like everything

439
00:22:08,840 --> 00:22:12,560
Speaker 1: is moving away from you. So either you are at

440
00:22:12,600 --> 00:22:15,040
Speaker 1: the center of the universe and there's just expansion away

441
00:22:15,040 --> 00:22:18,920
Speaker 1: from that one point, or everywhere in the universe is expanding,

442
00:22:18,920 --> 00:22:21,600
Speaker 1: which is much more likely. I am probably the center

443
00:22:21,640 --> 00:22:24,399
Speaker 1: of the universe, but maybe I'm not. I can accept that. Okay,

444
00:22:24,480 --> 00:22:26,679
Speaker 1: you're the center of your kids universe, I'm sure. But

445
00:22:26,720 --> 00:22:29,359
Speaker 1: this question about why the night sky is dark is

446
00:22:29,400 --> 00:22:32,679
Speaker 1: actually a really old question and really predates any modern

447
00:22:32,760 --> 00:22:34,920
Speaker 1: understanding of sort of like the size and shape of

448
00:22:34,960 --> 00:22:37,440
Speaker 1: the universe, and it helped spark some of these questions

449
00:22:37,480 --> 00:22:40,840
Speaker 1: like is the universe infinite? Could we possibly tell? And

450
00:22:40,880 --> 00:22:42,760
Speaker 1: a long time ago people thought it was obvious that

451
00:22:42,800 --> 00:22:44,880
Speaker 1: the universe was infinite. One of my favorite things about

452
00:22:44,880 --> 00:22:48,159
Speaker 1: the history of astronomy is seeing how like conceptions of

453
00:22:48,160 --> 00:22:51,879
Speaker 1: what is obvious or natural change with time. Right, like

454
00:22:51,960 --> 00:22:55,160
Speaker 1: a long time ago, people thought the universe was obviously infinite,

455
00:22:55,240 --> 00:22:57,280
Speaker 1: it should just go on forever. And it was just

456
00:22:57,320 --> 00:22:59,879
Speaker 1: sort of sprinkled with stars. There were no galaxies at all.

457
00:22:59,880 --> 00:23:02,560
Speaker 1: They just thought, here's a star, there's a star. The

458
00:23:02,600 --> 00:23:05,640
Speaker 1: whole universe is just like a vast sea of stars.

459
00:23:06,119 --> 00:23:09,000
Speaker 1: So when did we start learning enough to start having

460
00:23:09,000 --> 00:23:11,040
Speaker 1: a good answer to these questions. Well, it was like

461
00:23:11,080 --> 00:23:13,840
Speaker 1: a hundred years ago with Hubble and lots of others

462
00:23:13,840 --> 00:23:17,080
Speaker 1: who discovered that there are galaxies and that those galaxies

463
00:23:17,119 --> 00:23:19,800
Speaker 1: are moving away from us and the universe is expanding.

464
00:23:19,960 --> 00:23:22,480
Speaker 1: And then it became later much more natural to imagine

465
00:23:22,480 --> 00:23:25,560
Speaker 1: that the universe might be finite. In age, it seemed

466
00:23:25,600 --> 00:23:28,200
Speaker 1: like obvious that the universe should have a beginning, whereas

467
00:23:28,200 --> 00:23:30,200
Speaker 1: before that people that I was obvious that the universe

468
00:23:30,240 --> 00:23:34,000
Speaker 1: had existed forever and had no beginning and went on forever. Right,

469
00:23:34,040 --> 00:23:36,920
Speaker 1: So what seems to be like obvious and natural changes

470
00:23:36,960 --> 00:23:39,960
Speaker 1: with time, which I think it's really fascinating, an important lesson,

471
00:23:40,280 --> 00:23:43,280
Speaker 1: you know, for like making assumptions about the universe. Anyway,

472
00:23:43,280 --> 00:23:45,240
Speaker 1: thank yourself. Back to like h fifty years ago, when

473
00:23:45,240 --> 00:23:49,119
Speaker 1: people thought, Okay, the universe is infinite, there are stars everywhere.

474
00:23:49,280 --> 00:23:52,040
Speaker 1: There's sort of like dotted in this vast ocean. So

475
00:23:52,119 --> 00:23:55,040
Speaker 1: pretend you're an astronomer two fifty years ago, and that's

476
00:23:55,080 --> 00:23:57,960
Speaker 1: the sort of understanding. People were asking themselves a question

477
00:23:58,040 --> 00:24:02,000
Speaker 1: like how much starlight should expect to fall on the

478
00:24:02,040 --> 00:24:05,320
Speaker 1: Earth in that situation, in an infinite universe filled with

479
00:24:05,359 --> 00:24:08,720
Speaker 1: equally spaced stars, And so, I mean, of course you

480
00:24:08,720 --> 00:24:10,320
Speaker 1: look out at the night sky and you sort of

481
00:24:10,359 --> 00:24:12,560
Speaker 1: know what you get. What did they think that the

482
00:24:12,560 --> 00:24:15,159
Speaker 1: answer was right? So obviously they knew that the night

483
00:24:15,240 --> 00:24:18,040
Speaker 1: sky was dark, right, That wasn't the mystery. The question

484
00:24:18,119 --> 00:24:20,399
Speaker 1: was like, why is the night sky dark? Because when

485
00:24:20,440 --> 00:24:23,360
Speaker 1: they sat down to do the calculation, they were quite surprised.

486
00:24:23,720 --> 00:24:27,919
Speaker 1: They couldn't explain it right. Their calculation suggested that the

487
00:24:28,040 --> 00:24:31,280
Speaker 1: night sky should be infinitely bright if there are an

488
00:24:31,320 --> 00:24:34,280
Speaker 1: infinite number of stars out there. Okay, well, I am

489
00:24:34,440 --> 00:24:36,960
Speaker 1: dying to know what explanation they came up with to

490
00:24:37,000 --> 00:24:39,640
Speaker 1: explain the discrepancy between what they thought they should see

491
00:24:39,640 --> 00:24:41,600
Speaker 1: and what they were seeing. But first, I think we

492
00:24:41,640 --> 00:24:56,560
Speaker 1: need to take a break, all right, and we're back.

493
00:24:56,680 --> 00:24:59,280
Speaker 1: So before we left, you were telling us that in

494
00:24:59,359 --> 00:25:02,840
Speaker 1: the past there was this big question about like, well,

495
00:25:03,200 --> 00:25:05,120
Speaker 1: how much light should we be seeing, and why aren't

496
00:25:05,160 --> 00:25:07,600
Speaker 1: we seeing a lot more of it? And and what

497
00:25:07,680 --> 00:25:10,080
Speaker 1: sort of answers did they come up with? Hopefully, hopefully

498
00:25:10,119 --> 00:25:13,800
Speaker 1: the answers we have now are better. Well. The interesting

499
00:25:13,840 --> 00:25:16,439
Speaker 1: thing is they were trying to figure out whether the

500
00:25:16,560 --> 00:25:19,119
Speaker 1: nice guy should be dark or not. They knew something

501
00:25:19,160 --> 00:25:21,880
Speaker 1: about how light was transmitted that they didn't really understand

502
00:25:21,880 --> 00:25:24,600
Speaker 1: it on a microscopic scale, but they knew, for example,

503
00:25:24,880 --> 00:25:27,440
Speaker 1: that as you got further away from something, it's light

504
00:25:27,520 --> 00:25:30,280
Speaker 1: dimmed by a power of one over the distance squared.

505
00:25:30,359 --> 00:25:32,480
Speaker 1: And so you know, you apply that math to for example,

506
00:25:32,560 --> 00:25:35,960
Speaker 1: like Proxima Centauri. That's the nearest star to Earth, but

507
00:25:36,040 --> 00:25:38,639
Speaker 1: it's really still very very far away. It's only a

508
00:25:38,640 --> 00:25:41,760
Speaker 1: few light years. But in terms of like distances in

509
00:25:41,760 --> 00:25:45,160
Speaker 1: our Solar system and au, for example, is the distance

510
00:25:45,200 --> 00:25:48,040
Speaker 1: between the Earth and the Sun, proximate Centauri is two

511
00:25:48,160 --> 00:25:51,720
Speaker 1: hundred and seventy thousand a U. Right, so it's two

512
00:25:52,000 --> 00:25:54,919
Speaker 1: d seventy thousand times further from the Earth than the

513
00:25:54,960 --> 00:25:57,760
Speaker 1: Sun is. So that means that proximates Centauri is light

514
00:25:57,960 --> 00:26:02,160
Speaker 1: gets reduced by one. Were tend to the eleven relative

515
00:26:02,240 --> 00:26:04,560
Speaker 1: to the Sun, right, So our distance to the Sun

516
00:26:04,680 --> 00:26:06,639
Speaker 1: means the light from the Sun is reduced by a

517
00:26:06,680 --> 00:26:09,720
Speaker 1: certain amount, but proximate centauri is one over ten to

518
00:26:09,800 --> 00:26:13,000
Speaker 1: the eleven times dimmer than the light from the Sun

519
00:26:13,119 --> 00:26:16,240
Speaker 1: because the distance between here and there is so large. Okay,

520
00:26:16,280 --> 00:26:19,000
Speaker 1: so the equation where they were trying to figure out

521
00:26:19,080 --> 00:26:21,919
Speaker 1: that like light dims at one over the distant square.

522
00:26:21,960 --> 00:26:24,400
Speaker 1: That must have been done on Earth when they were

523
00:26:24,440 --> 00:26:27,719
Speaker 1: looking out at space, where they assuming that like space

524
00:26:27,760 --> 00:26:30,440
Speaker 1: sort of had the same atmosphere and the same sort

525
00:26:30,480 --> 00:26:33,080
Speaker 1: of dynamics, or like, how did they deal with that

526
00:26:33,160 --> 00:26:36,080
Speaker 1: sort of uncertainty? Oh yeah, great question. It wasn't always

527
00:26:36,080 --> 00:26:38,960
Speaker 1: obvious to people that the rules here on Earth also

528
00:26:39,040 --> 00:26:42,200
Speaker 1: applied to space, that you could say, like things were

529
00:26:42,200 --> 00:26:45,520
Speaker 1: fundamental and physics was universal. Newton was one of the

530
00:26:45,560 --> 00:26:47,800
Speaker 1: first people to do that, to say gravity here on

531
00:26:47,880 --> 00:26:50,920
Speaker 1: Earth also applies in space and can describe the motions

532
00:26:50,960 --> 00:26:52,879
Speaker 1: of the planets. So you're right, that is kind of

533
00:26:52,880 --> 00:26:55,240
Speaker 1: a big leap. Plus, they're assuming that light can travel

534
00:26:55,359 --> 00:26:58,160
Speaker 1: through those distances, that there isn't like dust or gas

535
00:26:58,200 --> 00:27:00,280
Speaker 1: blocking it. We'll get into the details of whether or

536
00:27:00,320 --> 00:27:02,520
Speaker 1: not gas and dust can explain it in just a minute,

537
00:27:02,560 --> 00:27:04,560
Speaker 1: but first let's start with sort of the simpler vision,

538
00:27:04,600 --> 00:27:07,640
Speaker 1: like let's just imagine that light is not blocked by anything.

539
00:27:07,880 --> 00:27:10,879
Speaker 1: It's just a question of distance and the number of stars.

540
00:27:11,160 --> 00:27:13,720
Speaker 1: And that's sort of like simpler model. How much light

541
00:27:13,720 --> 00:27:16,040
Speaker 1: do we expect to fall on Earth? Okay, so they

542
00:27:16,160 --> 00:27:19,240
Speaker 1: had an understanding then about how light should fall off

543
00:27:19,280 --> 00:27:22,720
Speaker 1: with distance. Did they have like an estimate for how

544
00:27:22,720 --> 00:27:25,240
Speaker 1: many stars were out there? So they didn't know how

545
00:27:25,280 --> 00:27:27,560
Speaker 1: many stars were out there, but they were assuming that

546
00:27:27,600 --> 00:27:30,320
Speaker 1: the stars were uniform right there, like every chunk of

547
00:27:30,359 --> 00:27:33,639
Speaker 1: space had on average the same number of stars. And

548
00:27:33,680 --> 00:27:36,159
Speaker 1: so you can take the fact that stars get dimmer

549
00:27:36,240 --> 00:27:39,280
Speaker 1: as they get further by one over distance squared and

550
00:27:39,320 --> 00:27:41,480
Speaker 1: the fact that there are an infinite number of stars,

551
00:27:41,560 --> 00:27:43,160
Speaker 1: and you can do the math and you can ask,

552
00:27:43,200 --> 00:27:46,159
Speaker 1: like which one wins out? Does the infinity of the

553
00:27:46,240 --> 00:27:49,720
Speaker 1: number of stars win out? Or does the growing distance

554
00:27:49,760 --> 00:27:53,640
Speaker 1: to those stars suppress the light faster than like more

555
00:27:53,680 --> 00:27:56,320
Speaker 1: stars get added, And so then because the night sky

556
00:27:56,400 --> 00:27:58,560
Speaker 1: is dark, that means the distance must win. Is that

557
00:27:58,640 --> 00:28:01,520
Speaker 1: the conclusion they came to, not the conclusion they came to. Actually,

558
00:28:01,560 --> 00:28:04,160
Speaker 1: they did the math and they discovered that the number

559
00:28:04,160 --> 00:28:06,480
Speaker 1: of stars should win. It's actually not that hard to

560
00:28:06,520 --> 00:28:08,919
Speaker 1: do the math yourself. Brightness of a star goes like

561
00:28:08,960 --> 00:28:11,520
Speaker 1: one over distance squared, and at a given distance, the

562
00:28:11,560 --> 00:28:13,439
Speaker 1: area of a sphere around the Earth also goes like

563
00:28:13,520 --> 00:28:16,960
Speaker 1: distance squared. So that means that, like any shell of

564
00:28:17,160 --> 00:28:20,640
Speaker 1: universe at an arbitrary distance from the Earth, the stars

565
00:28:20,760 --> 00:28:24,000
Speaker 1: from that shell get suppressed by one over distance squared,

566
00:28:24,080 --> 00:28:26,720
Speaker 1: but the number of stars in that shell goes like

567
00:28:26,840 --> 00:28:29,960
Speaker 1: distance squared, So those two numbers both canceled. So that

568
00:28:30,040 --> 00:28:34,040
Speaker 1: means that, like any shell of universe an arbitrary distance

569
00:28:34,080 --> 00:28:37,439
Speaker 1: away from you should have a constant brightness, like every

570
00:28:37,440 --> 00:28:40,240
Speaker 1: shell should have the same amount of brightness. Because you have,

571
00:28:40,360 --> 00:28:43,560
Speaker 1: like a shell of universe, further and further away, each

572
00:28:43,640 --> 00:28:46,480
Speaker 1: star in it gets dimmer, but the number of stars

573
00:28:46,520 --> 00:28:49,560
Speaker 1: grows perfectly to match that. So that means that every

574
00:28:49,640 --> 00:28:53,560
Speaker 1: shell of universe around us should be equally bright. Further

575
00:28:53,680 --> 00:28:57,120
Speaker 1: ones have many many more stars, each of which are dimmed,

576
00:28:57,400 --> 00:28:59,640
Speaker 1: and the closer ones have fewer stars, but they're not

577
00:28:59,760 --> 00:29:04,520
Speaker 1: dim as much. Okay, but his wifind physics so frustrating.

578
00:29:04,880 --> 00:29:08,520
Speaker 1: But but but the night sky is dark? So what

579
00:29:08,520 --> 00:29:10,840
Speaker 1: what what were they missing? What? What was not in

580
00:29:10,920 --> 00:29:13,200
Speaker 1: the equation that should have been there. You're absolutely right,

581
00:29:13,200 --> 00:29:15,120
Speaker 1: the night sky is dark, and so something is wrong

582
00:29:15,160 --> 00:29:17,560
Speaker 1: with this calculation. But just to underline it for the listeners,

583
00:29:17,600 --> 00:29:19,920
Speaker 1: you know, that means that every shell of the universe

584
00:29:20,080 --> 00:29:23,160
Speaker 1: is a fixed brightness. But there's an infinite number of shells, right,

585
00:29:23,520 --> 00:29:26,440
Speaker 1: so all those shells should add up to be an

586
00:29:26,520 --> 00:29:29,920
Speaker 1: infinite amount of light. And so this is like Heinrich Olbers.

587
00:29:29,960 --> 00:29:32,640
Speaker 1: Here's a guy in the seventeen hundreds. He's doing this calculation,

588
00:29:32,800 --> 00:29:34,480
Speaker 1: and you know he gets this number. He's like, hold

589
00:29:34,520 --> 00:29:37,200
Speaker 1: on a second, something must be wrong, as you say,

590
00:29:37,320 --> 00:29:40,920
Speaker 1: because if there's an infinite number of stars, even if

591
00:29:41,200 --> 00:29:44,120
Speaker 1: distance dims them like one over distance squared, the night

592
00:29:44,200 --> 00:29:48,320
Speaker 1: sky should be infinitely bright. You know. His calculations suggests

593
00:29:48,320 --> 00:29:50,200
Speaker 1: that if you go out at night you should be

594
00:29:50,320 --> 00:29:54,280
Speaker 1: brighter than the daytime. You should get like infinitely crisped up,

595
00:29:54,560 --> 00:29:57,560
Speaker 1: you know, by all of these stars. Right. So did

596
00:29:57,600 --> 00:30:00,040
Speaker 1: he start like the Olbers Prize to be like I

597
00:30:00,320 --> 00:30:02,600
Speaker 1: try to solve this famous problem or like how many

598
00:30:02,600 --> 00:30:05,280
Speaker 1: people cared about about this problem? At the time. A

599
00:30:05,280 --> 00:30:07,880
Speaker 1: lot of people were thinking about this, and Olbers thought

600
00:30:08,120 --> 00:30:12,400
Speaker 1: that this was proof that the universe wasn't infinite, right, thought, oh, well,

601
00:30:12,520 --> 00:30:15,120
Speaker 1: something must be wrong. One of the assumptions that go

602
00:30:15,160 --> 00:30:17,880
Speaker 1: into this calculation, right, that stars go like one of

603
00:30:17,920 --> 00:30:20,680
Speaker 1: a distant squared and that the universe is infinite and

604
00:30:20,760 --> 00:30:24,320
Speaker 1: uniformly filled with stars. One of those assumptions must be wrong.

605
00:30:24,360 --> 00:30:27,040
Speaker 1: And he thought it was clear that the universe couldn't

606
00:30:27,040 --> 00:30:29,080
Speaker 1: be infinite because I would solve the problem. You can't

607
00:30:29,120 --> 00:30:32,120
Speaker 1: get infinite light on Earth if there aren't infinite stars

608
00:30:32,200 --> 00:30:34,560
Speaker 1: out there. So he was convinced that that means that

609
00:30:34,600 --> 00:30:38,440
Speaker 1: the universe is not infinite. Okay, that makes sense. But apparently,

610
00:30:38,920 --> 00:30:40,800
Speaker 1: well you've told us that that is a question that

611
00:30:40,840 --> 00:30:43,400
Speaker 1: we're still trying to figure out the answer to, so

612
00:30:43,440 --> 00:30:46,440
Speaker 1: it must be more complicated. Yet it is in fact

613
00:30:46,480 --> 00:30:50,600
Speaker 1: more complicated. It's possible to live in an infinite universe

614
00:30:50,840 --> 00:30:54,920
Speaker 1: without an infinitely bright night sky. Right. There are other

615
00:30:55,080 --> 00:30:57,880
Speaker 1: solutions out there to this problem, but first let's tackle

616
00:30:57,920 --> 00:31:00,160
Speaker 1: one of the ones that the listeners brought up that

617
00:31:00,200 --> 00:31:03,640
Speaker 1: you mentioned earlier, which is gas and dust. Another suggestion

618
00:31:03,680 --> 00:31:06,840
Speaker 1: people had, not just our listeners, but people over the centuries,

619
00:31:07,240 --> 00:31:09,760
Speaker 1: was imagining that not all the light is getting to

620
00:31:09,840 --> 00:31:12,600
Speaker 1: the Earth, that maybe some of it is getting absorbed

621
00:31:12,640 --> 00:31:15,520
Speaker 1: by gas and dust. Basically, it's being blocked before it

622
00:31:15,560 --> 00:31:17,160
Speaker 1: gets here. And so I mean, I guess when I

623
00:31:17,160 --> 00:31:19,200
Speaker 1: think about space, I don't think about there being a

624
00:31:19,200 --> 00:31:22,240
Speaker 1: lot of gas and dust. But of course the International

625
00:31:22,280 --> 00:31:24,120
Speaker 1: Space Station needs to have what is it called a

626
00:31:24,160 --> 00:31:27,040
Speaker 1: whiffle barrier because it gets hit by all of this

627
00:31:27,120 --> 00:31:28,880
Speaker 1: space dust that you want to make sure it doesn't

628
00:31:28,880 --> 00:31:31,360
Speaker 1: get into the International Space Station. So there must be

629
00:31:31,440 --> 00:31:34,440
Speaker 1: dust up there. But is there enough dust up there

630
00:31:34,520 --> 00:31:36,920
Speaker 1: when you get out past like low Earth orbit to

631
00:31:37,000 --> 00:31:40,400
Speaker 1: be blocking the light? Absolutely, most of the mass of

632
00:31:40,400 --> 00:31:43,479
Speaker 1: the galaxy is in terms of gas and dust. Right,

633
00:31:43,600 --> 00:31:46,640
Speaker 1: Stars do not make up most of the stuff in

634
00:31:46,720 --> 00:31:49,360
Speaker 1: the galaxy. Even if we're just talking about barrionic matter,

635
00:31:49,360 --> 00:31:52,200
Speaker 1: we're not even talking about dark matter. They're vast clouds

636
00:31:52,240 --> 00:31:55,280
Speaker 1: of gas out there which might in the future become stars,

637
00:31:55,360 --> 00:31:59,440
Speaker 1: and they're huge expanses of dust from old solar systems

638
00:31:59,440 --> 00:32:01,080
Speaker 1: that blew up up And so there's a lot of

639
00:32:01,120 --> 00:32:03,280
Speaker 1: gas and dust out there, and people who study the

640
00:32:03,360 --> 00:32:05,800
Speaker 1: universe have to map that gas and dust. If they're

641
00:32:05,800 --> 00:32:07,520
Speaker 1: looking at a star and they're trying to figure out

642
00:32:07,600 --> 00:32:09,720
Speaker 1: how bright it should be, they have to know how

643
00:32:09,800 --> 00:32:12,920
Speaker 1: much stuff is between us and that star. There are

644
00:32:12,920 --> 00:32:16,240
Speaker 1: people whose entire theses are like maps of dust in

645
00:32:16,280 --> 00:32:19,800
Speaker 1: the galaxy because it's so important and it's one reason,

646
00:32:19,840 --> 00:32:22,800
Speaker 1: for example, that we can't see through the galaxy. One

647
00:32:22,800 --> 00:32:25,040
Speaker 1: of the big mysteries in astronomy these days is the

648
00:32:25,080 --> 00:32:29,360
Speaker 1: Great Attractor, this weird source of gravitational attraction that seems

649
00:32:29,400 --> 00:32:31,800
Speaker 1: to be on the other side of the Milky Way,

650
00:32:32,000 --> 00:32:34,440
Speaker 1: and we can't see what's there because the Milky Way

651
00:32:34,480 --> 00:32:38,080
Speaker 1: is so gassy and dusty that is basically blocking our view.

652
00:32:38,360 --> 00:32:40,520
Speaker 1: So it's definitely something that people have to take into

653
00:32:40,560 --> 00:32:43,160
Speaker 1: account when they're figuring out how bright and individual star

654
00:32:43,240 --> 00:32:45,440
Speaker 1: should be when seen from Earth. Are the people who

655
00:32:45,440 --> 00:32:49,800
Speaker 1: study that like not invited to the parties of people

656
00:32:49,800 --> 00:32:51,800
Speaker 1: who are excited about space stuff because to me, when

657
00:32:51,800 --> 00:32:54,400
Speaker 1: I think about space dust, I think you can't travel

658
00:32:54,440 --> 00:32:56,760
Speaker 1: to another galaxy because that space dust is going to

659
00:32:56,840 --> 00:32:59,600
Speaker 1: be like bullets going through your capsule or whatever. On

660
00:32:59,640 --> 00:33:02,160
Speaker 1: the wage with other galaxies where these like not popular

661
00:33:02,200 --> 00:33:06,040
Speaker 1: people because they kill dreams. No, they're super popular because

662
00:33:06,080 --> 00:33:08,440
Speaker 1: they enable the rest of astronomy. You know, there's so

663
00:33:08,480 --> 00:33:11,160
Speaker 1: many people who need to know how much gas and

664
00:33:11,240 --> 00:33:14,680
Speaker 1: dust is there between this object I'm studying for my thesis.

665
00:33:14,720 --> 00:33:17,239
Speaker 1: So I think people are very grateful that somebody has

666
00:33:17,240 --> 00:33:19,600
Speaker 1: gone out there and like devoted five years their life

667
00:33:19,600 --> 00:33:22,440
Speaker 1: to mapping dust in the galaxy. And you know, they

668
00:33:22,480 --> 00:33:25,520
Speaker 1: also get zillions of citations. I see these These sometimes

669
00:33:25,520 --> 00:33:29,120
Speaker 1: have like five thousand citations because it's such vital work

670
00:33:29,480 --> 00:33:32,080
Speaker 1: just to understand like what's out there between us and

671
00:33:32,120 --> 00:33:35,000
Speaker 1: other stuff. Well, I'm happy for them, But unfortunately this

672
00:33:35,120 --> 00:33:38,880
Speaker 1: idea that gas and dust is dimming the otherwise infinite

673
00:33:39,000 --> 00:33:42,600
Speaker 1: light from stars that can't explain why the night sky

674
00:33:42,920 --> 00:33:45,520
Speaker 1: is dark. The problem is that gas and dust also

675
00:33:45,600 --> 00:33:48,680
Speaker 1: absorbs energy. Right, so if the universe was filled with

676
00:33:48,760 --> 00:33:53,000
Speaker 1: effectively infinite light from infinite stars had infinite time to

677
00:33:53,120 --> 00:33:55,720
Speaker 1: get here, then that gas and dust would be super

678
00:33:55,800 --> 00:33:59,520
Speaker 1: duper hot. Right. If it's blocking infinite light, then it's

679
00:33:59,560 --> 00:34:02,560
Speaker 1: absorbed being infinite light and basically gets to be the

680
00:34:02,640 --> 00:34:06,240
Speaker 1: same temperature as the stars, and it should also be glowing.

681
00:34:06,400 --> 00:34:09,959
Speaker 1: So you can't explain the non infinitely bright night sky

682
00:34:10,160 --> 00:34:12,840
Speaker 1: with gas and dust, and that would make those theses

683
00:34:12,960 --> 00:34:15,040
Speaker 1: much easier if mapping it just meant you had to

684
00:34:15,080 --> 00:34:18,160
Speaker 1: look for the glowing penches exactly, and yet we know

685
00:34:18,239 --> 00:34:20,279
Speaker 1: that the night sky is not dark, and so we

686
00:34:20,360 --> 00:34:23,560
Speaker 1: have to think more deeply about what those assumptions are

687
00:34:23,760 --> 00:34:26,160
Speaker 1: and which one might be wrong. And one of my

688
00:34:26,200 --> 00:34:28,560
Speaker 1: favorite bits of history is that an early thinker on

689
00:34:28,600 --> 00:34:31,600
Speaker 1: this question is somebody you might not imagine, somebody you

690
00:34:31,719 --> 00:34:34,360
Speaker 1: all know very well but probably don't think of in

691
00:34:34,480 --> 00:34:38,440
Speaker 1: terms of astronomy, and that's Edgar Allan Poe. What's no

692
00:34:38,560 --> 00:34:40,759
Speaker 1: way he was at UVA for a little while. You

693
00:34:40,800 --> 00:34:42,360
Speaker 1: can go to the dorm room that he was in

694
00:34:42,400 --> 00:34:44,680
Speaker 1: briefly before he left. But I don't know if I

695
00:34:44,680 --> 00:34:46,760
Speaker 1: had highlight the fact that he was only here briefly

696
00:34:46,840 --> 00:34:49,480
Speaker 1: so much during the tour. But anyway, so did he

697
00:34:49,560 --> 00:34:52,239
Speaker 1: generally think about astronomy questions or is this like the

698
00:34:52,280 --> 00:34:54,840
Speaker 1: one area of astronomy that really drew him in. No,

699
00:34:54,960 --> 00:34:56,919
Speaker 1: he was really prolific, and he wrote about all sorts

700
00:34:56,920 --> 00:34:58,640
Speaker 1: of stuff. But you know, a guy who writes horror

701
00:34:58,680 --> 00:35:00,480
Speaker 1: movies spends a lot of time up it at night,

702
00:35:00,520 --> 00:35:02,080
Speaker 1: and so I think he spent a lot of time

703
00:35:02,160 --> 00:35:06,319
Speaker 1: thinking about the stars and going for long crisp walks,

704
00:35:06,360 --> 00:35:08,160
Speaker 1: you know, in the evening. So let me redo this

705
00:35:08,239 --> 00:35:11,279
Speaker 1: quote from Edgar Allan Poe. He says, we're the succession

706
00:35:11,320 --> 00:35:14,600
Speaker 1: of stars endless. Then the background of the sky would

707
00:35:14,640 --> 00:35:19,080
Speaker 1: present us a uniform luminosity like that displayed by the galaxy,

708
00:35:19,200 --> 00:35:22,279
Speaker 1: since there could be absolutely no point in all that

709
00:35:22,360 --> 00:35:26,680
Speaker 1: background at which would not exist a star. So he's saying, basically,

710
00:35:26,800 --> 00:35:28,960
Speaker 1: in any direction you look, you should be able to

711
00:35:29,000 --> 00:35:31,840
Speaker 1: see a star. If the universe is infinite, then every

712
00:35:31,960 --> 00:35:34,319
Speaker 1: line you make you should hit a star, and so

713
00:35:34,520 --> 00:35:37,120
Speaker 1: every point in the sky should basically look like a star.

714
00:35:37,239 --> 00:35:40,280
Speaker 1: Then he goes on to say, the only mode, therefore,

715
00:35:40,680 --> 00:35:44,120
Speaker 1: in which under such a state affairs, we could comprehend

716
00:35:44,160 --> 00:35:48,240
Speaker 1: the voids which our telescopes find in innumerable directions, would

717
00:35:48,239 --> 00:35:51,640
Speaker 1: be by supposing the distance of the invisible background so

718
00:35:51,680 --> 00:35:55,360
Speaker 1: immense that no ray from it has yet been able

719
00:35:55,400 --> 00:35:58,360
Speaker 1: to reach us at all. Oh, so he's saying, everything

720
00:35:58,440 --> 00:36:01,360
Speaker 1: is so far away that the light hasn't gotten here yet,

721
00:36:01,400 --> 00:36:04,800
Speaker 1: gotten here yet exactly. And that's a really vital point.

722
00:36:04,880 --> 00:36:07,880
Speaker 1: He's thinking about the time it takes light to get

723
00:36:07,920 --> 00:36:12,080
Speaker 1: here from those stars, and he's assuming that it hasn't

724
00:36:12,120 --> 00:36:15,719
Speaker 1: had an infinite amount of time, because in Olber's calculation,

725
00:36:16,000 --> 00:36:18,279
Speaker 1: he not only assumes that the universe is infinite in

726
00:36:18,360 --> 00:36:22,880
Speaker 1: size but also infinite in age, And that's necessary because

727
00:36:23,120 --> 00:36:25,640
Speaker 1: if a star is super duper far away from us,

728
00:36:26,000 --> 00:36:28,520
Speaker 1: it's light will take a long time to get here.

729
00:36:28,760 --> 00:36:31,160
Speaker 1: If the universe is infinite in age, then it will

730
00:36:31,200 --> 00:36:33,880
Speaker 1: get here, and it will already be here because that

731
00:36:34,000 --> 00:36:36,799
Speaker 1: stars existed infinitely in the past and it's had plenty

732
00:36:36,840 --> 00:36:39,000
Speaker 1: of time to get here. But if the universe is

733
00:36:39,080 --> 00:36:42,520
Speaker 1: not infinitely old, if it started a certain number of

734
00:36:42,600 --> 00:36:45,080
Speaker 1: years ago, that means that there are some stars who

735
00:36:45,080 --> 00:36:48,160
Speaker 1: are so far away that the light from them has

736
00:36:48,280 --> 00:36:50,759
Speaker 1: never reached us, that not a single photon from that

737
00:36:50,800 --> 00:36:53,840
Speaker 1: star has arrived here on Earth. It's always surprising to

738
00:36:53,840 --> 00:36:57,520
Speaker 1: me how quick physics goes from math to like existential questions.

739
00:36:58,920 --> 00:37:02,439
Speaker 1: So was Poe sort of on track with what other

740
00:37:02,640 --> 00:37:05,719
Speaker 1: physicists at the time we're thinking, or was he the

741
00:37:05,760 --> 00:37:08,120
Speaker 1: first one to sort of think about it this way?

742
00:37:08,239 --> 00:37:11,120
Speaker 1: Or should we wait until after a break and then

743
00:37:11,120 --> 00:37:14,600
Speaker 1: find out if Poe was right. Let's leave our listeners

744
00:37:14,680 --> 00:37:17,680
Speaker 1: in deep Dark Edgar Allan Poe suspense and come back

745
00:37:17,719 --> 00:37:32,520
Speaker 1: after the break. All right, I've been dying to know.

746
00:37:33,200 --> 00:37:36,600
Speaker 1: Was Edgar Allan Poe right. Edgar Allan Poe was totally correct,

747
00:37:36,680 --> 00:37:38,840
Speaker 1: and he was also sort of a vanguard of thinking

748
00:37:38,880 --> 00:37:41,480
Speaker 1: at the time. Remember that until Hubble saw that the

749
00:37:41,560 --> 00:37:45,120
Speaker 1: universe was expanding, this is the beginning of the nineteen hundreds,

750
00:37:45,200 --> 00:37:47,640
Speaker 1: people thought it was very likely that the universe was

751
00:37:47,760 --> 00:37:51,200
Speaker 1: infinitely old, that it didn't have a beginning. The natural

752
00:37:51,280 --> 00:37:54,880
Speaker 1: concept was that everything is just hanging in space. Nothing

753
00:37:55,040 --> 00:37:57,239
Speaker 1: is changing. I mean, you don't see stars blinking out,

754
00:37:57,239 --> 00:37:59,600
Speaker 1: our new ones appearing. They thought the universe was a

755
00:37:59,680 --> 00:38:02,680
Speaker 1: turn and static, and so it wasn't until we saw

756
00:38:02,840 --> 00:38:05,600
Speaker 1: that the universe was expanding and that we could sort

757
00:38:05,600 --> 00:38:08,880
Speaker 1: of wind that history backwards to some time when the

758
00:38:08,960 --> 00:38:12,279
Speaker 1: universe was infinitely dense, before which it didn't even make

759
00:38:12,320 --> 00:38:14,880
Speaker 1: any sense to talk about time. So this whole idea

760
00:38:14,920 --> 00:38:17,960
Speaker 1: of the age of the universe being finite, being about

761
00:38:17,960 --> 00:38:21,439
Speaker 1: fourteen billion years old, that's only about a hundred years old.

762
00:38:21,560 --> 00:38:24,719
Speaker 1: Before that, even mostly thought the universe was static and

763
00:38:24,920 --> 00:38:27,279
Speaker 1: infinitely old. So I was sort of ahead of his

764
00:38:27,400 --> 00:38:30,840
Speaker 1: time here imagining this as an explanation for why the

765
00:38:30,960 --> 00:38:34,040
Speaker 1: night sky was dark. He's so great. He has a

766
00:38:34,120 --> 00:38:36,879
Speaker 1: story the title of which I forget, where essentially one

767
00:38:36,960 --> 00:38:40,239
Speaker 1: guy locks or says like, oh, let's go find this

768
00:38:40,360 --> 00:38:44,440
Speaker 1: wine which is in this basement, thank you, yes, and

769
00:38:44,480 --> 00:38:47,919
Speaker 1: he locks the other guy in the basement and then

770
00:38:48,040 --> 00:38:51,239
Speaker 1: he leaves. And a collaborator and I were talking about

771
00:38:51,239 --> 00:38:53,440
Speaker 1: how that's sort of the way, sort of like how

772
00:38:53,480 --> 00:38:58,280
Speaker 1: parasitoids lock their hosts inside the goals that they make. Anyway,

773
00:38:58,320 --> 00:39:00,640
Speaker 1: you know, we we love connecting literature who are wasps

774
00:39:00,680 --> 00:39:03,600
Speaker 1: whenever we can, and that was one of our connections.

775
00:39:03,600 --> 00:39:07,160
Speaker 1: But anyway, I digress. That means that Edgar Allan Poe

776
00:39:07,320 --> 00:39:09,640
Speaker 1: is sort of like our two degrees of separation, right.

777
00:39:09,719 --> 00:39:13,040
Speaker 1: He wrote about parasitology and he wrote about cosmology, so

778
00:39:13,080 --> 00:39:15,640
Speaker 1: he connects us well, except he didn't think he was

779
00:39:15,680 --> 00:39:18,000
Speaker 1: writing about parasitology, whereas he did think he was writing

780
00:39:18,000 --> 00:39:21,160
Speaker 1: about cosmology. But sure, yes, let's go with it. He

781
00:39:21,280 --> 00:39:23,200
Speaker 1: was just so far ahead of his time he didn't

782
00:39:23,200 --> 00:39:25,959
Speaker 1: realize he was breaking new ground in every field. Okay,

783
00:39:26,000 --> 00:39:28,439
Speaker 1: so we are back to an area where my brain

784
00:39:28,520 --> 00:39:31,360
Speaker 1: sort of has trouble keeping up with the distances and

785
00:39:31,360 --> 00:39:33,880
Speaker 1: the speeds and the sizes. So okay, so the universe

786
00:39:34,280 --> 00:39:38,680
Speaker 1: is expanding, and there we're looking at like the speed

787
00:39:38,680 --> 00:39:41,279
Speaker 1: of expansion relative to the speed of light. So does

788
00:39:41,320 --> 00:39:43,440
Speaker 1: this mean that, like, at some point in the future,

789
00:39:44,040 --> 00:39:46,080
Speaker 1: the light is gonna catch up to us and the

790
00:39:46,160 --> 00:39:49,480
Speaker 1: night sky is going to be bright? Or am I

791
00:39:49,560 --> 00:39:52,400
Speaker 1: missing something fundamental? I think I'm missing something fundamental. No,

792
00:39:52,520 --> 00:39:55,279
Speaker 1: you're absolutely not. That's a great question. So let's take

793
00:39:55,280 --> 00:39:57,600
Speaker 1: it one step at a time. So first we say

794
00:39:57,719 --> 00:40:00,919
Speaker 1: the universe is not infinitely old, which means that light

795
00:40:01,000 --> 00:40:03,799
Speaker 1: from some places hasn't reached us yet. So you can

796
00:40:03,840 --> 00:40:07,080
Speaker 1: imagine maybe the universe is infinite, maybe it goes on forever,

797
00:40:07,520 --> 00:40:09,719
Speaker 1: but we can only see a part of it. The

798
00:40:09,800 --> 00:40:11,879
Speaker 1: part of it that we can see is determined by

799
00:40:11,960 --> 00:40:14,440
Speaker 1: the speed of light and the age of the universe.

800
00:40:14,480 --> 00:40:16,960
Speaker 1: So there are things out there that have sent us

801
00:40:16,960 --> 00:40:19,640
Speaker 1: photons that are on their way screaming at the speed

802
00:40:19,640 --> 00:40:22,000
Speaker 1: of light across billions of light years, but have not

803
00:40:22,080 --> 00:40:24,960
Speaker 1: yet arrived, but will in the future arrive. Right, We'll

804
00:40:25,040 --> 00:40:27,440
Speaker 1: get here at some point. While that explains why the

805
00:40:27,560 --> 00:40:30,640
Speaker 1: night sky is not infinitely bright right now, it makes

806
00:40:30,640 --> 00:40:32,759
Speaker 1: you wonder, like, does that mean it will be much

807
00:40:32,800 --> 00:40:35,560
Speaker 1: brighter in the future. Right in that sort of scenario,

808
00:40:35,680 --> 00:40:37,960
Speaker 1: you can imagine the nights guy getting brighter and brighter

809
00:40:38,000 --> 00:40:40,920
Speaker 1: every year is sort of like more stars appear in

810
00:40:41,000 --> 00:40:43,880
Speaker 1: the night sky, so that eventually it's sort of like

811
00:40:43,960 --> 00:40:47,200
Speaker 1: fills in all the gaps, right, and then you really

812
00:40:47,239 --> 00:40:51,080
Speaker 1: need Star Screen. I feel like we've got to start

813
00:40:51,120 --> 00:40:53,680
Speaker 1: this company before this episode goes out, because otherwise somebody

814
00:40:53,680 --> 00:40:55,360
Speaker 1: else is going to pick up on this idea and

815
00:40:55,400 --> 00:40:57,640
Speaker 1: we're gonna be really grumpy that they make a billion

816
00:40:57,640 --> 00:41:00,200
Speaker 1: dollars off of star Screen. I agree. I think this

817
00:41:00,239 --> 00:41:02,800
Speaker 1: is going to be the thing that makes us forget

818
00:41:02,800 --> 00:41:07,120
Speaker 1: our books and everything else. Star Screen start exactly endorsed

819
00:41:07,120 --> 00:41:09,920
Speaker 1: by astronomers. We need like seven out of a astronomers

820
00:41:09,920 --> 00:41:12,719
Speaker 1: agree or something. Yeah, that's right, that's right. Let's convince

821
00:41:12,760 --> 00:41:15,080
Speaker 1: people that are have to worry about medical doctors, they

822
00:41:15,080 --> 00:41:19,239
Speaker 1: should listen to uh any old specialist in anything, as

823
00:41:19,400 --> 00:41:21,680
Speaker 1: you might worry about that the future of the infinitely

824
00:41:21,680 --> 00:41:23,960
Speaker 1: bright night sky. And while I might want you to

825
00:41:23,960 --> 00:41:25,960
Speaker 1: believe in that, so you buy a big tub of

826
00:41:26,000 --> 00:41:28,920
Speaker 1: star screen and smear on your kids, it's not actually

827
00:41:28,960 --> 00:41:30,879
Speaker 1: something we think is going to happen. We actually think

828
00:41:30,920 --> 00:41:33,960
Speaker 1: the opposite is happening. That as time goes on, the nights,

829
00:41:34,000 --> 00:41:36,720
Speaker 1: guy gets darker and darker and that's for the reason

830
00:41:36,719 --> 00:41:40,480
Speaker 1: that you mentioned earlier, that the universe is expanding, Right,

831
00:41:40,480 --> 00:41:42,640
Speaker 1: So even in the universe that wasn't expanding, where the

832
00:41:42,640 --> 00:41:44,600
Speaker 1: stars are just sort of like hanging there, but the

833
00:41:44,680 --> 00:41:47,680
Speaker 1: universe is not infinitely old. You wouldn't expect the nights

834
00:41:47,719 --> 00:41:49,720
Speaker 1: guy to be infinitely bright, but it would be getting

835
00:41:49,760 --> 00:41:52,920
Speaker 1: brighter and brighter as time goes on, and the size

836
00:41:52,960 --> 00:41:55,319
Speaker 1: of the observable universe, the fraction of it that we

837
00:41:55,360 --> 00:41:58,600
Speaker 1: can see got larger and larger. But what's happening is

838
00:41:58,640 --> 00:42:01,200
Speaker 1: that the universe is expand ending, and so things are

839
00:42:01,320 --> 00:42:03,880
Speaker 1: rushing away from us, and they're rushing away from us

840
00:42:04,040 --> 00:42:06,759
Speaker 1: faster and faster every year. So it's this sort of

841
00:42:06,800 --> 00:42:10,000
Speaker 1: weird effect where we can see a larger portion of space,

842
00:42:10,200 --> 00:42:12,480
Speaker 1: but things are sort of moving out of that space

843
00:42:12,920 --> 00:42:17,000
Speaker 1: faster than light itself. Right, So imagine like a sphere

844
00:42:17,120 --> 00:42:20,200
Speaker 1: that's growing. That's our observable universe. We can see anything

845
00:42:20,239 --> 00:42:22,960
Speaker 1: in that sphere, but things are rushing out of that

846
00:42:23,000 --> 00:42:26,759
Speaker 1: sphere faster than the sphere itself is growing. So the

847
00:42:26,800 --> 00:42:30,160
Speaker 1: expansion of the universe, the creation of new space between

848
00:42:30,239 --> 00:42:33,880
Speaker 1: us and other galaxies, is decreasing the number of things

849
00:42:34,040 --> 00:42:37,719
Speaker 1: in the observable universe, increasing the darkness of the night sky.

850
00:42:38,200 --> 00:42:42,320
Speaker 1: So is it that as it moves away super fast,

851
00:42:42,440 --> 00:42:45,440
Speaker 1: that our square distance is increasing so much that it

852
00:42:45,480 --> 00:42:47,759
Speaker 1: dissipates before it gets to us, or the light never

853
00:42:47,800 --> 00:42:50,800
Speaker 1: gets to us period because it's moving away so quickly.

854
00:42:51,040 --> 00:42:53,319
Speaker 1: Both effects actually are happening. There's some things that we

855
00:42:53,360 --> 00:42:55,799
Speaker 1: can see now. So their photons have reached Earth, and

856
00:42:55,880 --> 00:42:57,840
Speaker 1: some of the photons they have sent in the meantime

857
00:42:58,000 --> 00:43:01,239
Speaker 1: will reach Earth. But there are some photons that are

858
00:43:01,280 --> 00:43:04,560
Speaker 1: traveling through space, and that space is expanding faster than

859
00:43:04,600 --> 00:43:08,120
Speaker 1: the speed of lights, so those photons will never reach us.

860
00:43:08,600 --> 00:43:11,080
Speaker 1: It's like if Hussain Bolt is running at you, but

861
00:43:11,200 --> 00:43:14,600
Speaker 1: somebody's laying new track between you and him faster than

862
00:43:14,640 --> 00:43:16,520
Speaker 1: he's running, He's never gonna get it to you, no

863
00:43:16,560 --> 00:43:18,880
Speaker 1: matter how fast he is. Right, you have to be

864
00:43:18,960 --> 00:43:23,279
Speaker 1: laying pretty fast. And so there are some things out

865
00:43:23,320 --> 00:43:25,360
Speaker 1: there that we will eventually see that we have not

866
00:43:25,480 --> 00:43:28,680
Speaker 1: seen yet, things that are about sixty two billion light

867
00:43:28,760 --> 00:43:31,640
Speaker 1: years away. There are some photons they admitted that will

868
00:43:31,680 --> 00:43:34,040
Speaker 1: get here and we will be able to see them,

869
00:43:34,200 --> 00:43:37,479
Speaker 1: But anything past sixty two billion light years we will

870
00:43:37,600 --> 00:43:40,560
Speaker 1: never see it because the space between us and it

871
00:43:40,719 --> 00:43:44,279
Speaker 1: is expanding so fast that all of its photons are

872
00:43:44,280 --> 00:43:47,759
Speaker 1: basically moving away from us. So they're moving locally through

873
00:43:47,800 --> 00:43:50,600
Speaker 1: space to the speed of light, but globally, because that

874
00:43:50,680 --> 00:43:53,760
Speaker 1: space is expanding between us and them, they're actually moving

875
00:43:53,880 --> 00:43:56,719
Speaker 1: away from us, which is really weird because like, photons

876
00:43:56,760 --> 00:43:59,799
Speaker 1: pointing towards us are actually getting further away from us.

877
00:44:00,080 --> 00:44:04,080
Speaker 1: For a year, nothing about physics is intuitive, or plenty

878
00:44:04,120 --> 00:44:06,120
Speaker 1: of it is, I guess, but plenty of it's not okay,

879
00:44:06,120 --> 00:44:07,880
Speaker 1: And so then that is the final answer, Like is

880
00:44:08,200 --> 00:44:11,480
Speaker 1: that an answer that we definitely know to be true

881
00:44:11,719 --> 00:44:14,040
Speaker 1: or is this sort of on the Like we revisit

882
00:44:14,120 --> 00:44:15,600
Speaker 1: this in a couple of years and people will be

883
00:44:15,640 --> 00:44:17,800
Speaker 1: talking about how cute it was that Daniel and Kelly

884
00:44:17,840 --> 00:44:20,400
Speaker 1: thought this was the answer, Like, how confident are we

885
00:44:20,480 --> 00:44:22,560
Speaker 1: that this is the truth? Oh, you're definitely trying to

886
00:44:22,640 --> 00:44:24,400
Speaker 1: trap me here. You want to sound by so in

887
00:44:24,480 --> 00:44:26,839
Speaker 1: five years you can go like, man, Daniel, you were

888
00:44:26,920 --> 00:44:30,040
Speaker 1: so overconfident. We should definitely always be taking these things

889
00:44:30,080 --> 00:44:32,239
Speaker 1: with a grain of salt, because our understanding of them

890
00:44:32,320 --> 00:44:35,160
Speaker 1: is fairly recent. Our measurement of the expansion of the

891
00:44:35,239 --> 00:44:38,440
Speaker 1: universe and its acceleration is only twenty years old, and

892
00:44:38,480 --> 00:44:40,880
Speaker 1: that's a blink of an eye in terms of cosmology

893
00:44:40,920 --> 00:44:44,200
Speaker 1: and science, right, And so while we're fairly certain that

894
00:44:44,280 --> 00:44:47,719
Speaker 1: the universe is expanding and that that expansion is accelerating,

895
00:44:47,960 --> 00:44:50,920
Speaker 1: we have no idea what's causing that. We call this

896
00:44:51,160 --> 00:44:53,359
Speaker 1: dark energy, but that's just like a name we give

897
00:44:53,400 --> 00:44:56,040
Speaker 1: it because we have no concept of what could be

898
00:44:56,120 --> 00:44:59,000
Speaker 1: causing it. Is nothing in our equations that can't explain it.

899
00:44:59,080 --> 00:45:01,840
Speaker 1: You can put a number into Einstein's theory of general

900
00:45:01,840 --> 00:45:06,000
Speaker 1: relativity to describe this happening, but that doesn't explain why

901
00:45:06,040 --> 00:45:08,959
Speaker 1: it's happening, Like what part of the universe is doing this?

902
00:45:09,280 --> 00:45:11,480
Speaker 1: Why does it have to happen? Could it stop and

903
00:45:11,520 --> 00:45:13,520
Speaker 1: turn around and do something else in the future. We

904
00:45:13,600 --> 00:45:16,920
Speaker 1: just don't know. So there's a heavy dose of like,

905
00:45:17,120 --> 00:45:19,560
Speaker 1: oh that should be added to this, But it's sort

906
00:45:19,600 --> 00:45:21,839
Speaker 1: of like our current understanding of what might be going

907
00:45:21,880 --> 00:45:24,359
Speaker 1: on with the universe. And so does this answer help

908
00:45:24,440 --> 00:45:27,600
Speaker 1: us answer the question about the universe being infinite or no?

909
00:45:27,920 --> 00:45:32,520
Speaker 1: Because you it can be infinite well expanding, because infinity

910
00:45:32,640 --> 00:45:36,359
Speaker 1: is also complicated exactly. Infinity is though complicated. Unfortunately, what

911
00:45:36,400 --> 00:45:38,680
Speaker 1: this tells us is that the question of whether the

912
00:45:38,800 --> 00:45:42,320
Speaker 1: night sky is dark can't tell us whether the universe

913
00:45:42,560 --> 00:45:46,920
Speaker 1: is infinite, because an infinite universe and a non infinite

914
00:45:47,000 --> 00:45:50,239
Speaker 1: universe both can give you dark night skies, so you

915
00:45:50,280 --> 00:45:54,799
Speaker 1: can't tell the difference. Sorry, olders, but that's not even

916
00:45:54,800 --> 00:45:57,600
Speaker 1: the full answer. There's another reason why the night sky

917
00:45:57,760 --> 00:45:59,800
Speaker 1: is dark in an expanding universe, and I think you

918
00:46:00,000 --> 00:46:03,080
Speaker 1: i'd have mentioned earlier, which is while space is expanding,

919
00:46:03,160 --> 00:46:07,040
Speaker 1: it doesn't just affect the space between us and other galaxies.

920
00:46:07,320 --> 00:46:11,680
Speaker 1: It also stretches that light. So if space is expanding,

921
00:46:11,680 --> 00:46:15,400
Speaker 1: if it's getting larger, that means like new spaces being created,

922
00:46:15,800 --> 00:46:18,520
Speaker 1: and so photons that are flying through that space, they

923
00:46:18,600 --> 00:46:22,880
Speaker 1: get stretched, their wavelengths get longer, they get red shifted.

924
00:46:23,040 --> 00:46:25,239
Speaker 1: So your photon, for example, that was emitted from the

925
00:46:25,280 --> 00:46:29,200
Speaker 1: cosmic microwave background, this super hot plasma that existed just

926
00:46:29,280 --> 00:46:32,120
Speaker 1: after the Big Bang. That plasma was really really hot,

927
00:46:32,400 --> 00:46:35,840
Speaker 1: and the light that it generated was very very high frequency,

928
00:46:35,920 --> 00:46:39,040
Speaker 1: short wavelength. But it's been flying through the universe ever

929
00:46:39,120 --> 00:46:43,799
Speaker 1: since and it's been getting stretched out to very long wavelengths.

930
00:46:43,880 --> 00:46:46,960
Speaker 1: So does that mean that the night sky could be

931
00:46:47,000 --> 00:46:51,239
Speaker 1: bright but just at a wavelength that we don't see. So, yeah,

932
00:46:51,280 --> 00:46:53,759
Speaker 1: what does that mean. It means the night sky actually

933
00:46:54,120 --> 00:46:57,560
Speaker 1: is kind of bright, but just in wavelengths we cannot see.

934
00:46:57,680 --> 00:47:00,560
Speaker 1: So some of the starlight that's been emitted has been

935
00:47:00,640 --> 00:47:04,160
Speaker 1: red shifted outside of the visible spectrum. Like, there are

936
00:47:04,239 --> 00:47:07,600
Speaker 1: stars out there that are shining that are bright, but

937
00:47:07,719 --> 00:47:11,680
Speaker 1: your eyeballs cannot see them in optical telescopes cannot see

938
00:47:11,719 --> 00:47:14,960
Speaker 1: them because their wavelengths have been shifted into the infrared.

939
00:47:15,120 --> 00:47:18,439
Speaker 1: So the night sky is actually brighter than you see, right,

940
00:47:18,520 --> 00:47:21,440
Speaker 1: because there are all these invisible stars out there that

941
00:47:21,520 --> 00:47:24,239
Speaker 1: are shining at us in the infrared that our eyeballs

942
00:47:24,320 --> 00:47:27,759
Speaker 1: cannot see. Don't some species see in the infrared? So like,

943
00:47:27,760 --> 00:47:29,920
Speaker 1: are there some species out there for which the night

944
00:47:29,960 --> 00:47:33,759
Speaker 1: sky is bright? That's a great question. I should ask

945
00:47:33,800 --> 00:47:37,640
Speaker 1: my biology friend about that, because I don't know not

946
00:47:37,760 --> 00:47:41,160
Speaker 1: this one. But we did an episode recently about eyeballs

947
00:47:41,200 --> 00:47:43,920
Speaker 1: and how they work, and we do know that different

948
00:47:43,920 --> 00:47:46,839
Speaker 1: species are sensitive to different wavelengths of light. But you know,

949
00:47:47,080 --> 00:47:49,840
Speaker 1: we are very ingenious as a species, and we're capable

950
00:47:49,880 --> 00:47:53,040
Speaker 1: of building other kinds of eyeballs, and so we can

951
00:47:53,040 --> 00:47:55,799
Speaker 1: build telescopes that can see in the infrared and can

952
00:47:55,840 --> 00:47:58,239
Speaker 1: look up at the night sky in the very very

953
00:47:58,280 --> 00:48:01,040
Speaker 1: long wavelengths. And something that's really fun to realize as

954
00:48:01,080 --> 00:48:03,279
Speaker 1: we think about this question is that if you look

955
00:48:03,520 --> 00:48:07,480
Speaker 1: deep enough into long enough wavelengths, the sky actually is

956
00:48:07,680 --> 00:48:12,560
Speaker 1: very very bright cosmic micro background radiation that's everywhere, that's

957
00:48:12,600 --> 00:48:15,960
Speaker 1: in every direction. No matter what direction you look at

958
00:48:16,000 --> 00:48:18,359
Speaker 1: in the sky, you will see some of it. So

959
00:48:18,400 --> 00:48:21,920
Speaker 1: if your eyeballs could see the cosmic microwave background radiation

960
00:48:22,239 --> 00:48:25,640
Speaker 1: is light from the very very early universe plasma plasma

961
00:48:25,680 --> 00:48:29,280
Speaker 1: that filled the whole universe, then the night sky would

962
00:48:29,320 --> 00:48:31,440
Speaker 1: be bright, all right, So we gotta find a star

963
00:48:31,520 --> 00:48:34,120
Speaker 1: screen angle to like, we gotta make sure everybody knows

964
00:48:34,160 --> 00:48:36,040
Speaker 1: this and then explain to them that the star screen

965
00:48:36,080 --> 00:48:38,960
Speaker 1: protects against these other parts of the spectrum, and that's

966
00:48:38,960 --> 00:48:41,160
Speaker 1: where the millions are going to come from. Right, and

967
00:48:41,239 --> 00:48:43,319
Speaker 1: not to confuse the listeners, the nice guy is not

968
00:48:43,560 --> 00:48:48,280
Speaker 1: infinitely bright in the cosmic microwave background radiation. Right. Ober's paradox,

969
00:48:48,360 --> 00:48:50,600
Speaker 1: this question of why we weren't seeing light in every

970
00:48:50,600 --> 00:48:54,360
Speaker 1: directions really suggested that the nice guy should be infinitely bright.

971
00:48:54,719 --> 00:48:58,560
Speaker 1: The cosmic microwave background is almost uniformly bright because it

972
00:48:58,600 --> 00:49:01,279
Speaker 1: comes not from like little lots of stars, the way

973
00:49:01,360 --> 00:49:04,319
Speaker 1: optical visible light does, but because it came from this

974
00:49:04,480 --> 00:49:07,680
Speaker 1: plasma which filled the whole universe back before the universe

975
00:49:08,080 --> 00:49:11,600
Speaker 1: was itself transparent. And so we can still see those photons,

976
00:49:11,640 --> 00:49:13,920
Speaker 1: and we see them in every direction because that plasma

977
00:49:14,239 --> 00:49:17,360
Speaker 1: used to be filling all of space in every direction.

978
00:49:17,440 --> 00:49:19,880
Speaker 1: So if you were a little creature like a parasite

979
00:49:19,920 --> 00:49:21,480
Speaker 1: that looked up by the night sky, you could only

980
00:49:21,520 --> 00:49:24,040
Speaker 1: see the microwave, then at night the sky would be

981
00:49:24,160 --> 00:49:27,560
Speaker 1: uniformly bright. Wouldn't be infinitely bright, right, but it would

982
00:49:27,560 --> 00:49:30,640
Speaker 1: be uniform It would look very different from our night sky.

983
00:49:30,680 --> 00:49:33,319
Speaker 1: It's important to know how the parasites see things. So

984
00:49:33,440 --> 00:49:37,399
Speaker 1: I've had like three four, maybe five existential crises during

985
00:49:37,440 --> 00:49:40,080
Speaker 1: the span of our talk here. So what what does

986
00:49:40,120 --> 00:49:42,960
Speaker 1: this all mean then? So what it means is that

987
00:49:43,120 --> 00:49:46,040
Speaker 1: while we can think about the size of the universe

988
00:49:46,080 --> 00:49:47,920
Speaker 1: and what it might be made out of, and we

989
00:49:47,920 --> 00:49:49,680
Speaker 1: can play these games trying to figure out how the

990
00:49:49,719 --> 00:49:53,200
Speaker 1: universe actually looks, we can't actually tell what's out there

991
00:49:53,239 --> 00:49:56,640
Speaker 1: past our observable universe. You know, this felt like maybe

992
00:49:56,640 --> 00:49:59,560
Speaker 1: a trick, like maybe a way to figure out what

993
00:49:59,600 --> 00:50:02,560
Speaker 1: was in the deep dark ancient depths of the universe,

994
00:50:02,800 --> 00:50:05,640
Speaker 1: because it should be contributing to our night sky. Really,

995
00:50:05,680 --> 00:50:08,000
Speaker 1: what this tells us is that we're forever in a bubble.

996
00:50:08,320 --> 00:50:10,759
Speaker 1: We can't ever see what's past that bubble, so we'll

997
00:50:10,760 --> 00:50:14,279
Speaker 1: never really know what's out past the observable universe. And

998
00:50:14,320 --> 00:50:17,000
Speaker 1: even worse than that, our bubble is sort of shrinking,

999
00:50:17,239 --> 00:50:19,919
Speaker 1: while like physically in terms of length, it's getting larger

1000
00:50:20,000 --> 00:50:23,640
Speaker 1: and larger spaces expanding faster than that bubble is expanding.

1001
00:50:23,960 --> 00:50:26,040
Speaker 1: So it's sort of like our bubble of the universe

1002
00:50:26,120 --> 00:50:28,799
Speaker 1: is shrinking and shrinking, and as time goes on it

1003
00:50:28,800 --> 00:50:32,040
Speaker 1: gets smaller and smaller. It's like a fraction of the universe.

1004
00:50:32,160 --> 00:50:34,560
Speaker 1: So our children in the far far future will see

1005
00:50:34,560 --> 00:50:37,480
Speaker 1: an even smaller fraction of the universe than we are

1006
00:50:37,560 --> 00:50:40,080
Speaker 1: seeing today. So if we want to answer those questions,

1007
00:50:40,120 --> 00:50:42,680
Speaker 1: we better get on it. Like sat, well, I'm feeling

1008
00:50:42,719 --> 00:50:44,480
Speaker 1: slightly depressed now, but I guess I'm going to go

1009
00:50:44,560 --> 00:50:46,120
Speaker 1: ahead and hope that this is one of those like

1010
00:50:46,160 --> 00:50:48,319
Speaker 1: a hundred years from now, they'll be like Daniel, didn't

1011
00:50:48,360 --> 00:50:50,360
Speaker 1: think we could ever study everything, but now we know

1012
00:50:50,480 --> 00:50:53,400
Speaker 1: how to study everything. So I suppose in this particular area,

1013
00:50:53,440 --> 00:50:56,799
Speaker 1: I'm hoping that you're wrong, but you're probably not, and

1014
00:50:56,960 --> 00:50:59,160
Speaker 1: I agree we should be. We should be studying as

1015
00:50:59,239 --> 00:51:01,759
Speaker 1: much of this stuff we can. Now. Well, our great

1016
00:51:01,760 --> 00:51:04,600
Speaker 1: grandchildren will be sitting in their mansions paid for by

1017
00:51:04,640 --> 00:51:07,880
Speaker 1: the Star Screen Empire, and they'll be laughing all the

1018
00:51:07,920 --> 00:51:10,040
Speaker 1: way to the bank. That's they'll be thanking us, and

1019
00:51:10,080 --> 00:51:14,319
Speaker 1: it'll be great. So we still don't know if the

1020
00:51:14,360 --> 00:51:18,160
Speaker 1: full universe is infinite or if it's finite and wraps

1021
00:51:18,200 --> 00:51:21,200
Speaker 1: around on itself forever. It's a question people are still

1022
00:51:21,239 --> 00:51:24,200
Speaker 1: thinking about. People will still be thinking about. Maybe someday

1023
00:51:24,239 --> 00:51:26,680
Speaker 1: in the future people will find a way to probe

1024
00:51:26,680 --> 00:51:29,560
Speaker 1: this question, to sort of like extend our minds past

1025
00:51:29,600 --> 00:51:32,440
Speaker 1: the edge of the observable universe. Currently it feels like

1026
00:51:32,480 --> 00:51:35,640
Speaker 1: that's impossible according to the current laws of physics. But hey,

1027
00:51:35,800 --> 00:51:39,080
Speaker 1: let's hope future Daniel proves today Daniel wrong, and that's

1028
00:51:39,120 --> 00:51:45,520
Speaker 1: how you'll get your Nobel Prize. That's my plan, a

1029
00:51:45,560 --> 00:51:48,120
Speaker 1: good plan. I wish you luck. In case the Star

1030
00:51:48,239 --> 00:51:50,560
Speaker 1: Screen doesn't work out, you can, you know, make all

1031
00:51:50,600 --> 00:51:52,880
Speaker 1: the money that the Nobel Prize winners make. But I

1032
00:51:52,920 --> 00:51:55,719
Speaker 1: think The larger lesson aside from this particular question of

1033
00:51:55,719 --> 00:51:57,960
Speaker 1: why isn't the night sky dark, is that the larger

1034
00:51:58,080 --> 00:52:01,600
Speaker 1: strategy physics is employing a building a model in your head,

1035
00:52:01,880 --> 00:52:05,320
Speaker 1: thinking about the consequences of it, and then asking yourself like, well,

1036
00:52:05,360 --> 00:52:08,040
Speaker 1: why doesn't that work? What does that mean that the

1037
00:52:08,120 --> 00:52:11,759
Speaker 1: ideas I have don't describe the universe I'm seeing? That's

1038
00:52:11,840 --> 00:52:14,400
Speaker 1: generally the best way to win a Nobel prize is

1039
00:52:14,400 --> 00:52:17,160
Speaker 1: to try to find some discrepancy there, to discover some

1040
00:52:17,320 --> 00:52:20,360
Speaker 1: thread to pull on to unravel some deep mystery of

1041
00:52:20,400 --> 00:52:23,520
Speaker 1: the universe. It definitely is beautiful the way these models

1042
00:52:23,520 --> 00:52:26,759
Speaker 1: that you create in physics can have these amazing existential

1043
00:52:26,800 --> 00:52:29,480
Speaker 1: implications the more you think about them, and that in

1044
00:52:29,520 --> 00:52:31,960
Speaker 1: our minds we can imagine what would happen in an

1045
00:52:31,960 --> 00:52:35,920
Speaker 1: infinitely old universe with an infinite number of stars beaming

1046
00:52:35,960 --> 00:52:38,680
Speaker 1: an infinite number of photons to us. Somehow the math

1047
00:52:39,000 --> 00:52:42,040
Speaker 1: all hangs together. It's incredible. Well, thanks everyone for going

1048
00:52:42,120 --> 00:52:45,120
Speaker 1: on that journey with us to answer the question why

1049
00:52:45,480 --> 00:52:48,400
Speaker 1: is the night sky dark? After all? Why don't you

1050
00:52:48,440 --> 00:52:50,640
Speaker 1: need to buy a big tub of star scream to

1051
00:52:50,680 --> 00:52:53,600
Speaker 1: protect your children from star cancer? Don't tell them that

1052
00:52:55,760 --> 00:52:59,000
Speaker 1: in the end we believe in honesty and advertising. So

1053
00:52:59,040 --> 00:53:01,279
Speaker 1: thanks everyone for join us, and thanks again Kelly for

1054
00:53:01,360 --> 00:53:04,480
Speaker 1: coming along, asking great questions and contributing a lot of laughs.

1055
00:53:04,719 --> 00:53:06,720
Speaker 1: Thank you for having me a head fun as always.

1056
00:53:06,719 --> 00:53:09,560
Speaker 1: Thanks everybody until next time. Alright, tune in next time.

1057
00:53:17,480 --> 00:53:20,320
Speaker 1: Thanks for listening, and remember that Daniel and Jorge explained.

1058
00:53:20,360 --> 00:53:23,200
Speaker 1: The Universe is a production of I Heart Radio. For

1059
00:53:23,360 --> 00:53:26,279
Speaker 1: more podcast For my heart Radio, visit the i heart

1060
00:53:26,360 --> 00:53:29,960
Speaker 1: Radio app, Apple Podcasts, or wherever you listen to your

1061
00:53:30,040 --> 00:53:30,760
Speaker 1: favorite shows.