1
00:00:06,360 --> 00:00:09,680
Speaker 1: Some of the deepest mysteries of the universe are so big,

2
00:00:10,039 --> 00:00:14,480
Speaker 1: so imposing, so important that even asking questions about what

3
00:00:14,560 --> 00:00:17,520
Speaker 1: they are and how they work it can leave us confused.

4
00:00:17,760 --> 00:00:20,320
Speaker 1: That's because we have to spend some time thinking about

5
00:00:20,400 --> 00:00:24,600
Speaker 1: what exactly we're asking and what kind of answer we want.

6
00:00:25,079 --> 00:00:27,760
Speaker 1: But we shouldn't shy away from these kinds of questions

7
00:00:27,800 --> 00:00:32,000
Speaker 1: because they are the most important questions. Understanding the nature

8
00:00:32,120 --> 00:00:35,360
Speaker 1: of our reality means understanding the context of our lives,

9
00:00:35,800 --> 00:00:38,920
Speaker 1: where we live, how we live, maybe even why we live.

10
00:00:39,400 --> 00:00:42,159
Speaker 1: And what the universe has taught us is that it

11
00:00:42,200 --> 00:00:47,240
Speaker 1: always requires persistent, careful effort to unpack the deepest mysteries.

12
00:00:47,479 --> 00:00:49,680
Speaker 1: We have been chiseling away at the rock face of

13
00:00:49,680 --> 00:00:54,520
Speaker 1: physics for thousands of years, mostly cluelessly, but occasionally a

14
00:00:54,720 --> 00:00:57,520
Speaker 1: great hunk of understanding will open up and will see

15
00:00:57,560 --> 00:01:00,640
Speaker 1: everything in a new light. So it's worth asking the

16
00:01:00,680 --> 00:01:04,840
Speaker 1: biggest questions, the ones where the question itself can be confusing,

17
00:01:05,200 --> 00:01:08,319
Speaker 1: because looking for answers might eventually help us figure it

18
00:01:08,360 --> 00:01:11,759
Speaker 1: all out, or help us realize we're asking the wrong question.

19
00:01:12,040 --> 00:01:14,440
Speaker 1: So today on the podcast, we're going to dig deep

20
00:01:14,600 --> 00:01:17,679
Speaker 1: into what we know about maybe the most basic question

21
00:01:17,959 --> 00:01:23,240
Speaker 1: about the universe. We'll be asking what is space.

22
00:01:37,520 --> 00:01:40,960
Speaker 2: Welcome to Daniel and Kelly's Extraordinary Universe. Today we are

23
00:01:41,000 --> 00:01:44,920
Speaker 2: talking about what is space? And I am Kelly Wienersmith,

24
00:01:45,000 --> 00:01:47,240
Speaker 2: and I take up space. How about you?

25
00:01:49,640 --> 00:01:52,600
Speaker 1: I'm Daniel Whitson. I'm a professor of physics, which means

26
00:01:52,600 --> 00:01:55,640
Speaker 1: I probably should understand something about space.

27
00:01:56,080 --> 00:01:57,840
Speaker 2: I'm going to start with a confession. So, like when

28
00:01:57,880 --> 00:02:00,480
Speaker 2: I was in high school and college, I did really

29
00:02:00,560 --> 00:02:02,600
Speaker 2: well in physics. I was in the honors classes, I

30
00:02:02,640 --> 00:02:04,960
Speaker 2: got a's. I really liked the stuff about circuitry. But

31
00:02:05,040 --> 00:02:07,840
Speaker 2: whenever we would talk about what is space or what

32
00:02:07,960 --> 00:02:11,760
Speaker 2: is time? I would feel very frustrated because like you

33
00:02:11,880 --> 00:02:14,079
Speaker 2: were taking this thing that I felt like I could

34
00:02:14,120 --> 00:02:16,000
Speaker 2: work with in my day to day life, and it

35
00:02:16,040 --> 00:02:20,800
Speaker 2: felt like it was being made unnecessarily complicated. And I

36
00:02:20,800 --> 00:02:23,160
Speaker 2: think I also felt a little insecure because it's like

37
00:02:23,200 --> 00:02:26,079
Speaker 2: I can't even understand what is space, and I think

38
00:02:26,080 --> 00:02:27,840
Speaker 2: it just made me frustrated and I would kind of

39
00:02:27,840 --> 00:02:30,480
Speaker 2: shut down. And as an adult, I feel different about it.

40
00:02:30,639 --> 00:02:33,160
Speaker 2: I think it's interesting. I think thinking about it creates

41
00:02:33,200 --> 00:02:35,800
Speaker 2: like testable predictions that teach us about the universe and

42
00:02:35,800 --> 00:02:38,120
Speaker 2: then we can do practical things with that knowledge. But like,

43
00:02:38,440 --> 00:02:41,400
Speaker 2: what was your journey along questions like this? And am

44
00:02:41,400 --> 00:02:44,720
Speaker 2: I the only physics student in classes who isn't like, oh,

45
00:02:44,760 --> 00:02:46,760
Speaker 2: this is fun and is like, no, I knew this,

46
00:02:46,880 --> 00:02:48,000
Speaker 2: Why are you doing this to me?

47
00:02:49,200 --> 00:02:51,840
Speaker 1: I think that's a whole spectrum of people in physics,

48
00:02:52,080 --> 00:02:53,960
Speaker 1: and I think it's a big tent, and I'm glad

49
00:02:54,080 --> 00:02:56,280
Speaker 1: there are people who are like, hey, look, this gives

50
00:02:56,320 --> 00:02:59,280
Speaker 1: us tools so that we can calculate how our cannonballs

51
00:02:59,320 --> 00:03:02,320
Speaker 1: fly over castle walls. That's really all we care about,

52
00:03:02,360 --> 00:03:04,680
Speaker 1: So let's just do that and move on. And then

53
00:03:04,720 --> 00:03:07,280
Speaker 1: there's the folks on the sort of philosophical side of

54
00:03:07,320 --> 00:03:10,680
Speaker 1: things that really want to understand why balls fly over

55
00:03:10,720 --> 00:03:14,160
Speaker 1: castle walls because they have deeper questions about like why

56
00:03:14,200 --> 00:03:16,360
Speaker 1: is there anything and how does it all work? And

57
00:03:16,360 --> 00:03:18,760
Speaker 1: the amazing thing about physics is that it not only

58
00:03:19,000 --> 00:03:22,240
Speaker 1: lets you do practical stuff bill transistors and iPhones, but

59
00:03:22,280 --> 00:03:24,000
Speaker 1: then you get to turn around and ask like, well,

60
00:03:24,040 --> 00:03:26,240
Speaker 1: why does this work at all? And what does that

61
00:03:26,320 --> 00:03:29,639
Speaker 1: tell us about the actual universe we live in? So yeah,

62
00:03:29,760 --> 00:03:33,520
Speaker 1: touches on like technological, fascinating, useful stuff all the way

63
00:03:33,560 --> 00:03:36,760
Speaker 1: to philosophical stuff, and yeah, I always found myself sort

64
00:03:36,760 --> 00:03:39,320
Speaker 1: of on the philosophical side of things, and I was

65
00:03:39,320 --> 00:03:41,080
Speaker 1: the kind of kid who was like, whoa, what is

66
00:03:41,160 --> 00:03:44,560
Speaker 1: space anyway? Man? And this is before I smoked any

67
00:03:44,600 --> 00:03:46,920
Speaker 1: banana peels. I was wondering about what would it be

68
00:03:47,040 --> 00:03:49,040
Speaker 1: like to live in space that was four dimensions or

69
00:03:49,080 --> 00:03:51,160
Speaker 1: two dimensions? And why is it that we can only

70
00:03:51,200 --> 00:03:53,839
Speaker 1: think in three dimensions? So for me, these questions were

71
00:03:53,840 --> 00:03:56,440
Speaker 1: cat in it, even though I didn't understand anything about them.

72
00:03:56,680 --> 00:03:59,280
Speaker 1: And it's only now as a professional physicist that I

73
00:03:59,360 --> 00:04:01,960
Speaker 1: understand why we don't understand anything about them.

74
00:04:03,800 --> 00:04:06,040
Speaker 2: I hope that we can get to that in the

75
00:04:06,080 --> 00:04:09,400
Speaker 2: show today so that the people like me who are

76
00:04:09,440 --> 00:04:12,200
Speaker 2: just like, well now you've just made me confused, have

77
00:04:12,280 --> 00:04:15,600
Speaker 2: a better sense of why we're asking these questions and

78
00:04:15,640 --> 00:04:19,760
Speaker 2: why they're fundamentally important and not just physicists making things complicated.

79
00:04:19,839 --> 00:04:21,200
Speaker 2: Like every once in a while, I'll be like, well,

80
00:04:21,240 --> 00:04:25,760
Speaker 2: we haven't married relativity and quantum mechanics, and so what

81
00:04:25,839 --> 00:04:29,479
Speaker 2: if when people say like space bends and time is blow, Like,

82
00:04:29,520 --> 00:04:31,520
Speaker 2: what if none of that is true because we haven't

83
00:04:31,560 --> 00:04:33,359
Speaker 2: married these things, And so then why do I have

84
00:04:33,480 --> 00:04:35,960
Speaker 2: to do this, and then I get super frustrated, and

85
00:04:36,320 --> 00:04:37,960
Speaker 2: I don't know, maybe I shouldn't be so negative. At

86
00:04:37,960 --> 00:04:40,080
Speaker 2: the beginning of our show. I'm not actually negative, like

87
00:04:40,120 --> 00:04:42,720
Speaker 2: I'm excited about it, but I'm remembering Kelly from the

88
00:04:42,760 --> 00:04:45,960
Speaker 2: past feeling very frustrated about this stuff.

89
00:04:46,080 --> 00:04:48,000
Speaker 1: Well, I think we're going to be aiming today's episode

90
00:04:48,040 --> 00:04:50,680
Speaker 1: at Kelly of the past, somebody who is curious about

91
00:04:50,720 --> 00:04:53,200
Speaker 1: how the world works but doesn't want like a wall

92
00:04:53,200 --> 00:04:56,040
Speaker 1: of confusing language where words suddenly mean things that they

93
00:04:56,080 --> 00:04:59,160
Speaker 1: didn't mean before. And let's remember that that's the whole

94
00:04:59,200 --> 00:05:01,520
Speaker 1: project of physical We take the world that we kind

95
00:05:01,560 --> 00:05:04,200
Speaker 1: of understand we've been living in any way, and we

96
00:05:04,279 --> 00:05:06,839
Speaker 1: try to systematize it. We try to say, well, you know,

97
00:05:07,000 --> 00:05:09,440
Speaker 1: at what angle will your cannon ball fly over the

98
00:05:09,440 --> 00:05:11,640
Speaker 1: council walls? And do you have to factor in the

99
00:05:11,680 --> 00:05:13,760
Speaker 1: wind resistance? And then we get to turn around and

100
00:05:13,760 --> 00:05:15,640
Speaker 1: be like, well, why does this work? What does that

101
00:05:15,720 --> 00:05:17,880
Speaker 1: tell us it? Lets us do something which I think

102
00:05:17,920 --> 00:05:20,640
Speaker 1: is really awesome. We just peel back that layer of

103
00:05:20,680 --> 00:05:22,960
Speaker 1: intuitive reality and say, hey, we thought the universe was

104
00:05:23,000 --> 00:05:25,520
Speaker 1: like this, Actually it turns out it works like that.

105
00:05:25,800 --> 00:05:28,320
Speaker 1: The universe is different from the way we thought it was,

106
00:05:28,400 --> 00:05:31,640
Speaker 1: and that's wonderful. That's the incredible experience we're going for

107
00:05:31,760 --> 00:05:33,840
Speaker 1: in physics. We want to pull the veil from our

108
00:05:33,839 --> 00:05:37,000
Speaker 1: eyes and figure out how the universe actually is. I

109
00:05:37,040 --> 00:05:39,280
Speaker 1: think what we'll discover today is that, wow, we really

110
00:05:39,320 --> 00:05:42,679
Speaker 1: just don't know that the universe works. But it's important

111
00:05:42,680 --> 00:05:44,839
Speaker 1: that everybody understand what we do know and what we

112
00:05:44,920 --> 00:05:48,360
Speaker 1: don't know about these really basic questions about the nature.

113
00:05:48,160 --> 00:05:50,560
Speaker 2: Of the universe, right And if you stop asking the questions,

114
00:05:50,600 --> 00:05:52,680
Speaker 2: then you never get to the answer. So it's important

115
00:05:52,680 --> 00:05:53,159
Speaker 2: to keep.

116
00:05:53,040 --> 00:05:55,279
Speaker 1: Going exactly and that thing. It might be helpful for

117
00:05:55,320 --> 00:05:57,920
Speaker 1: people when we're talking about something as fuzzy and difficult

118
00:05:57,920 --> 00:06:00,440
Speaker 1: to grapple with a space to think about like what

119
00:06:00,520 --> 00:06:02,880
Speaker 1: kind of question we're asking and what kind of answers

120
00:06:02,880 --> 00:06:05,400
Speaker 1: are satisfactory? You know, because when we ask a vague

121
00:06:05,440 --> 00:06:08,560
Speaker 1: question like what is space? What are we really asking

122
00:06:08,640 --> 00:06:11,320
Speaker 1: when we say that? Even so often in philosophy, I

123
00:06:11,360 --> 00:06:14,240
Speaker 1: replace a confusing word with something familiar, like replace the

124
00:06:14,240 --> 00:06:16,760
Speaker 1: confusing word with an elephant, and think, what does the

125
00:06:16,839 --> 00:06:19,039
Speaker 1: question mean if I'm talking about an elephant? You know,

126
00:06:19,080 --> 00:06:21,960
Speaker 1: So if somebody asks you, hey, what is an elephant.

127
00:06:22,320 --> 00:06:23,880
Speaker 1: You know, what kind of question is that? What kind

128
00:06:23,920 --> 00:06:26,320
Speaker 1: of answers do we expect to that kind of question?

129
00:06:26,400 --> 00:06:28,240
Speaker 2: When I was reading through our outline today, one of

130
00:06:28,240 --> 00:06:30,520
Speaker 2: the things that got me excited was thinking back to

131
00:06:30,520 --> 00:06:32,479
Speaker 2: grad school and when we would talk about behavior and

132
00:06:32,480 --> 00:06:34,520
Speaker 2: we'd be like, well, what is the behavior? And there's

133
00:06:34,600 --> 00:06:36,960
Speaker 2: like at least four different ways to think about it,

134
00:06:37,000 --> 00:06:39,520
Speaker 2: you know, like how did it evolve? What neurotransmitters make

135
00:06:39,560 --> 00:06:43,440
Speaker 2: this behavior happen? What things that happened beforehands initiate the behavior?

136
00:06:43,520 --> 00:06:45,320
Speaker 2: And so in the case of behavior, there's a lot

137
00:06:45,400 --> 00:06:48,039
Speaker 2: of different answers you could have for that question. Is

138
00:06:48,080 --> 00:06:50,440
Speaker 2: it the same for space? Are we looking for like

139
00:06:50,480 --> 00:06:53,120
Speaker 2: an equation? So yeah, like what would make a satisfying

140
00:06:53,160 --> 00:06:55,320
Speaker 2: answer for something like this? Or are there lots?

141
00:06:55,600 --> 00:06:57,839
Speaker 1: No, You're right, what we're looking for our answers to

142
00:06:57,920 --> 00:06:59,760
Speaker 1: questions like well what can space do?

143
00:07:00,360 --> 00:07:00,520
Speaker 3: Right?

144
00:07:00,520 --> 00:07:02,800
Speaker 1: Like what is an elephant? Well, an elephant has big ears,

145
00:07:02,839 --> 00:07:04,560
Speaker 1: it does this thing? Right, you can describe it, You

146
00:07:04,600 --> 00:07:07,120
Speaker 1: can describe what it does. You can also ask like, well,

147
00:07:07,120 --> 00:07:09,360
Speaker 1: why is there space? You know the same way you

148
00:07:09,400 --> 00:07:11,080
Speaker 1: can be like why do we have elephants? You know,

149
00:07:11,200 --> 00:07:13,960
Speaker 1: there's a story there that tells us something about elephants

150
00:07:14,040 --> 00:07:17,840
Speaker 1: the relationship to other living things. Right, we can also ask, well,

151
00:07:18,160 --> 00:07:20,760
Speaker 1: what is space made out of? Is it itself the

152
00:07:20,840 --> 00:07:23,560
Speaker 1: fundamental thing in the universe where like you just got

153
00:07:23,600 --> 00:07:25,520
Speaker 1: to have it, you don't have universe without it? Or

154
00:07:25,560 --> 00:07:28,840
Speaker 1: somehow like elephants and ice cream, does it emerge from

155
00:07:29,000 --> 00:07:32,080
Speaker 1: the workings of other little bits deeper inside it that

156
00:07:32,240 --> 00:07:35,800
Speaker 1: somehow weave themselves together to make this experience we call space.

157
00:07:35,960 --> 00:07:38,360
Speaker 1: That's what I was referring to earlier, where in that scenario,

158
00:07:38,400 --> 00:07:41,600
Speaker 1: you're like pulling back a layer of reality understanding what's

159
00:07:41,640 --> 00:07:44,760
Speaker 1: going on underneath. So you discover that your experience is

160
00:07:44,760 --> 00:07:47,640
Speaker 1: not like fundamental, it's just sort of like one thing

161
00:07:47,680 --> 00:07:49,920
Speaker 1: that the universe can do. It can make elephants, it

162
00:07:49,920 --> 00:07:51,880
Speaker 1: can make ice cream, it can also not. So those

163
00:07:51,880 --> 00:07:53,600
Speaker 1: are the kind of questions I want to know the

164
00:07:53,640 --> 00:07:56,760
Speaker 1: answers to about space, like what can it do? Why

165
00:07:56,760 --> 00:07:59,880
Speaker 1: do we have it? Is it itself made us something smaller?

166
00:08:00,120 --> 00:08:02,840
Speaker 1: Or is it fundamental? Is it a requirement for the universe.

167
00:08:03,240 --> 00:08:04,680
Speaker 2: So one of the things that I was worried about

168
00:08:04,680 --> 00:08:06,960
Speaker 2: when we started talking about this question was the word

169
00:08:07,040 --> 00:08:10,920
Speaker 2: space has been used by so many other fields that

170
00:08:11,000 --> 00:08:13,560
Speaker 2: now it's not confusing from a physics perspective, it's just

171
00:08:13,680 --> 00:08:16,480
Speaker 2: confusing because humans use that word for lots of different things.

172
00:08:16,640 --> 00:08:20,000
Speaker 2: But I think I was definitely proved wrong there because

173
00:08:20,040 --> 00:08:22,880
Speaker 2: when you asked the audience to tell us what they

174
00:08:22,880 --> 00:08:26,120
Speaker 2: thought space was, nobody was like, well, space is the

175
00:08:26,360 --> 00:08:30,320
Speaker 2: literature on space, and like everyone got it. I guess

176
00:08:30,360 --> 00:08:32,080
Speaker 2: they know us well enough to know what we were

177
00:08:32,080 --> 00:08:34,800
Speaker 2: probably talking about. So let's hear what the listeners had

178
00:08:34,800 --> 00:08:35,199
Speaker 2: to say.

179
00:08:35,280 --> 00:08:37,280
Speaker 1: That's right, And if you would like to participate in

180
00:08:37,320 --> 00:08:41,000
Speaker 1: the audience participation segments of this podcast, please write to

181
00:08:41,080 --> 00:08:44,960
Speaker 1: us to questions at Danielankelly dot org. We will set

182
00:08:45,000 --> 00:08:47,920
Speaker 1: you up and you can hear your voice speculating basistly

183
00:08:48,160 --> 00:08:50,400
Speaker 1: on the podcast. Here's a bunch of people answering the

184
00:08:50,480 --> 00:08:52,240
Speaker 1: question what is space.

185
00:08:53,120 --> 00:08:54,880
Speaker 4: I don't think that space is a real thing.

186
00:08:54,960 --> 00:08:56,720
Speaker 1: I think that space is just an abstraction.

187
00:08:56,880 --> 00:09:02,319
Speaker 5: Perhaps space is a medium in which fields can exist,

188
00:09:02,679 --> 00:09:10,280
Speaker 5: that has shape and perhaps has density and can change

189
00:09:10,480 --> 00:09:17,160
Speaker 5: in its form. Space is like an invisible lattice, geometric framework.

190
00:09:17,480 --> 00:09:21,160
Speaker 1: Or other diffuse concept that is just a name we

191
00:09:21,240 --> 00:09:22,520
Speaker 1: give our experience.

192
00:09:22,760 --> 00:09:28,840
Speaker 2: The composite of all energy fields, gravitational fields, and dimensions.

193
00:09:28,360 --> 00:09:31,560
Speaker 4: The medium that we are traveling through. It's like combining

194
00:09:31,600 --> 00:09:35,000
Speaker 4: the trajectory of the Earth of some galaxy.

195
00:09:35,400 --> 00:09:41,240
Speaker 1: Universe. Space is that which matter can move within.

196
00:09:41,600 --> 00:09:45,280
Speaker 3: Space is the background fabric of the entire universe.

197
00:09:45,600 --> 00:09:48,240
Speaker 4: I think to think of space as a huge collection

198
00:09:48,320 --> 00:09:52,280
Speaker 4: of spots that can have multiple states of excitement, and

199
00:09:52,320 --> 00:09:55,679
Speaker 4: the excitement of a spot interferes with its neighbors.

200
00:09:55,240 --> 00:09:58,520
Speaker 1: The replacement or nothing.

201
00:09:58,840 --> 00:10:03,319
Speaker 4: A physical meta that we can experience and move around

202
00:10:03,840 --> 00:10:06,679
Speaker 4: and in which events occur that we can observe and

203
00:10:06,880 --> 00:10:07,680
Speaker 4: try to understand.

204
00:10:08,480 --> 00:10:14,400
Speaker 3: Space is this kind of thing in which everything happens,

205
00:10:14,760 --> 00:10:17,680
Speaker 3: but we can't see or feel it. We can only

206
00:10:17,760 --> 00:10:19,400
Speaker 3: see the evidence of it.

207
00:10:20,120 --> 00:10:22,120
Speaker 1: I think this is outdated now, but I still just

208
00:10:22,160 --> 00:10:24,560
Speaker 1: think of spice as a volume that we can put

209
00:10:24,559 --> 00:10:25,160
Speaker 1: stuff into.

210
00:10:25,679 --> 00:10:27,760
Speaker 4: I think space used to be seen as like a

211
00:10:27,800 --> 00:10:31,880
Speaker 4: substrate where everything happened on or within, But I believe

212
00:10:32,000 --> 00:10:34,920
Speaker 4: now space is kind of understood to be the thing

213
00:10:35,040 --> 00:10:36,000
Speaker 4: that is happening.

214
00:10:36,480 --> 00:10:39,440
Speaker 2: So none of the people who answered the question were

215
00:10:39,520 --> 00:10:43,160
Speaker 2: like Daniel, I hate you, or like Daniel go away,

216
00:10:43,440 --> 00:10:46,400
Speaker 2: So it seems like everybody was, you know, enjoying thinking

217
00:10:46,440 --> 00:10:48,439
Speaker 2: it through and giving you an answer, and we got

218
00:10:48,440 --> 00:10:50,920
Speaker 2: some pretty good answers. So maybe the world is not

219
00:10:51,000 --> 00:10:53,800
Speaker 2: filled with angry young versions of Kelly, which is great,

220
00:10:53,840 --> 00:10:56,320
Speaker 2: would be better. I was also like a goth chick

221
00:10:56,400 --> 00:10:58,760
Speaker 2: covered in black all the time. I've cheered up a

222
00:10:58,760 --> 00:10:59,120
Speaker 2: bit too.

223
00:10:59,280 --> 00:11:01,000
Speaker 1: I want to see when those pictures at some point.

224
00:11:01,160 --> 00:11:02,680
Speaker 2: All right, I'll share one with you, but not with

225
00:11:02,720 --> 00:11:06,000
Speaker 2: everyone else. So, yeah, what did you think of these answers?

226
00:11:06,280 --> 00:11:06,480
Speaker 4: Yeah?

227
00:11:06,520 --> 00:11:08,360
Speaker 1: I thought it was good. And I also love hearing

228
00:11:08,360 --> 00:11:09,959
Speaker 1: people grapple with a hard question.

229
00:11:10,080 --> 00:11:10,240
Speaker 3: You know.

230
00:11:10,280 --> 00:11:12,120
Speaker 1: It's the kind of thing, as you say, everybody's got

231
00:11:12,120 --> 00:11:15,040
Speaker 1: some intuition about what space is because we live in it, right,

232
00:11:15,200 --> 00:11:18,280
Speaker 1: and yet it's difficult to say, like exactly what is

233
00:11:18,320 --> 00:11:20,320
Speaker 1: it and where it comes from a lot of people

234
00:11:20,480 --> 00:11:23,800
Speaker 1: described what it can do, right, or it can hold,

235
00:11:23,960 --> 00:11:26,559
Speaker 1: you can have things in space. So I think those

236
00:11:26,600 --> 00:11:29,080
Speaker 1: are all fine ways to approach this problem. But I

237
00:11:29,120 --> 00:11:30,839
Speaker 1: hope by the end of the podcast we give people

238
00:11:30,880 --> 00:11:33,800
Speaker 1: a really comprehensive view of like what physics says about

239
00:11:33,840 --> 00:11:37,840
Speaker 1: space and all the different, confusing, contradictory things the physics

240
00:11:37,840 --> 00:11:39,480
Speaker 1: says about what space might be.

241
00:11:39,960 --> 00:11:42,200
Speaker 2: All right, So then what do you think is the

242
00:11:42,240 --> 00:11:45,240
Speaker 2: best place to start. So to me, I'm just like

243
00:11:45,400 --> 00:11:47,240
Speaker 2: I don't know space. It's like there's like stuff in

244
00:11:47,240 --> 00:11:49,319
Speaker 2: front of me. But if my table is there, it

245
00:11:49,360 --> 00:11:51,480
Speaker 2: still counts as space because my table's just like in

246
00:11:51,600 --> 00:11:55,040
Speaker 2: the space. And to be honest, that I think is

247
00:11:55,280 --> 00:11:57,880
Speaker 2: most everything I've thought about this question. So where do

248
00:11:57,960 --> 00:11:58,800
Speaker 2: we go from here?

249
00:12:00,120 --> 00:12:02,080
Speaker 1: Maybe the best place to start is to try to answer,

250
00:12:02,160 --> 00:12:04,920
Speaker 1: like what is we're asking about? You know, when we

251
00:12:04,960 --> 00:12:06,840
Speaker 1: say space, what do we even mean by it before

252
00:12:06,880 --> 00:12:08,559
Speaker 1: we talk about like where it comes from and how

253
00:12:08,600 --> 00:12:10,320
Speaker 1: it works and what the rules are and what physics

254
00:12:10,360 --> 00:12:13,360
Speaker 1: has learned, Like what is the thing we're asking about?

255
00:12:13,520 --> 00:12:16,640
Speaker 1: You know, let's at least pinpoint the elephant here. And

256
00:12:16,880 --> 00:12:19,720
Speaker 1: you know, in my mind, space is not about the

257
00:12:19,760 --> 00:12:23,559
Speaker 1: stuff in the universe, It's about what's underneath it. It's

258
00:12:23,559 --> 00:12:26,200
Speaker 1: about the underlying fabric. So like, take a chunk of

259
00:12:26,320 --> 00:12:29,959
Speaker 1: universe wherever it is, and remove everything you can remove,

260
00:12:30,360 --> 00:12:32,400
Speaker 1: so it maybe there's a peanut in the universe, toss

261
00:12:32,480 --> 00:12:35,040
Speaker 1: that out, Maybe there's a planet there, toss that out,

262
00:12:35,280 --> 00:12:37,800
Speaker 1: Maybe there's a galaxy whatever, pushed out all to the side.

263
00:12:37,880 --> 00:12:40,960
Speaker 1: Empty it as much as possible, right, because the thing

264
00:12:41,000 --> 00:12:43,679
Speaker 1: we're not talking about is like particles and matter and

265
00:12:43,720 --> 00:12:47,200
Speaker 1: photons and stuff. Let's talk about what's underneath it. That's

266
00:12:47,240 --> 00:12:49,800
Speaker 1: really what's exciting to me about this question is that

267
00:12:49,840 --> 00:12:52,800
Speaker 1: we're like digging under the carpet of the universe, right,

268
00:12:53,160 --> 00:12:55,880
Speaker 1: And so to me, space is what's left when you

269
00:12:55,960 --> 00:12:59,920
Speaker 1: remove everything that you could remove from a portion of

270
00:13:00,040 --> 00:13:00,680
Speaker 1: the universe.

271
00:13:00,920 --> 00:13:03,200
Speaker 2: So, like in my office right now, and if we

272
00:13:03,200 --> 00:13:05,560
Speaker 2: were to try to figure out what space is in

273
00:13:05,640 --> 00:13:07,680
Speaker 2: terms of my office, we'd turn it into a vacuum.

274
00:13:07,760 --> 00:13:09,400
Speaker 2: So I should leave my office if we're going to

275
00:13:09,440 --> 00:13:12,559
Speaker 2: do this experiment, like we take everything out, and now

276
00:13:12,600 --> 00:13:14,920
Speaker 2: we're asking what are we left with?

277
00:13:15,160 --> 00:13:17,320
Speaker 1: Yeah, well we'd have to take you out because you're

278
00:13:17,320 --> 00:13:20,800
Speaker 1: not space right your stuff? Yeah, so yeah, remove all

279
00:13:20,800 --> 00:13:24,120
Speaker 1: the stuff what is left? And that opens up immediately like,

280
00:13:24,160 --> 00:13:26,719
Speaker 1: well is there anything left? Does it mean anything to

281
00:13:26,800 --> 00:13:29,040
Speaker 1: have space there without stuff in it? Is space just

282
00:13:29,080 --> 00:13:31,760
Speaker 1: defined to be the place between stuff? Or is it

283
00:13:31,800 --> 00:13:36,560
Speaker 1: a thing itself? Right? Is space a kind of stuff? Right?

284
00:13:37,160 --> 00:13:39,120
Speaker 1: I Mean, I know we're getting like really banana pels

285
00:13:39,120 --> 00:13:41,600
Speaker 1: behind the gym over here, but these are the questions

286
00:13:41,640 --> 00:13:43,600
Speaker 1: we're grappling with, and to me, this is what's exciting

287
00:13:43,600 --> 00:13:46,920
Speaker 1: about physics is that these questions are really fuzzy, and yeah,

288
00:13:47,080 --> 00:13:49,040
Speaker 1: you could you know, smoke banana peels and talk about

289
00:13:49,040 --> 00:13:51,600
Speaker 1: them all afternoon and really make no progress, or for

290
00:13:51,720 --> 00:13:54,560
Speaker 1: thousands of years and make no progress. But physics gives

291
00:13:54,559 --> 00:13:57,800
Speaker 1: you a way forward. Physics gives you this method to

292
00:13:58,000 --> 00:14:01,360
Speaker 1: like understand your intuitive experience and make it make sense

293
00:14:01,559 --> 00:14:04,080
Speaker 1: by asking, like, can we build a model that describes

294
00:14:04,120 --> 00:14:05,760
Speaker 1: what he can do? And then can we look at

295
00:14:05,760 --> 00:14:07,760
Speaker 1: that model and say, like, what does that mean about

296
00:14:07,760 --> 00:14:10,160
Speaker 1: what it is? So to me, the reason I'm a

297
00:14:10,160 --> 00:14:12,920
Speaker 1: physicist and not a philosopher is that we can't actually

298
00:14:13,000 --> 00:14:16,040
Speaker 1: make some progress if we think about it like mathematically

299
00:14:16,280 --> 00:14:17,559
Speaker 1: and systematically.

300
00:14:17,880 --> 00:14:20,280
Speaker 2: Okay, so we've now gotten to like you've removed everything,

301
00:14:20,320 --> 00:14:22,520
Speaker 2: so you've got a vacuum, and now I feel like

302
00:14:22,520 --> 00:14:24,000
Speaker 2: there's a vacuum in my brain and I'm like, well,

303
00:14:24,040 --> 00:14:26,440
Speaker 2: where do you go from there? How does physics tackle

304
00:14:26,480 --> 00:14:27,000
Speaker 2: this question?

305
00:14:27,080 --> 00:14:27,280
Speaker 3: Then?

306
00:14:27,760 --> 00:14:32,120
Speaker 1: Physics thinks about space in terms of location and motion,

307
00:14:32,480 --> 00:14:35,080
Speaker 1: because what do you have left once you've emptied your office?

308
00:14:35,480 --> 00:14:39,040
Speaker 1: There's just space there, which means the possibility to put

309
00:14:39,040 --> 00:14:40,760
Speaker 1: something in it. Right, you can put a proton in it,

310
00:14:40,840 --> 00:14:43,240
Speaker 1: But The interesting thing is you can choose where to

311
00:14:43,280 --> 00:14:45,680
Speaker 1: put the proton. You can put the proton where Kelly's

312
00:14:45,720 --> 00:14:47,520
Speaker 1: desk used to be, or you could put the proton

313
00:14:47,560 --> 00:14:51,000
Speaker 1: where Kelly's head used to be. Those in principle are different, right,

314
00:14:51,040 --> 00:14:54,240
Speaker 1: And so space offers us these choices. You can be here,

315
00:14:54,520 --> 00:14:57,200
Speaker 1: you can be there. Space seems to have inherent in

316
00:14:57,240 --> 00:15:02,440
Speaker 1: it this like location, right, and and those locations can change. So, like,

317
00:15:02,800 --> 00:15:05,360
Speaker 1: very very early on, before we were doing science, the

318
00:15:05,360 --> 00:15:07,320
Speaker 1: way we think about it science, you know, the Greeks,

319
00:15:07,760 --> 00:15:11,040
Speaker 1: they were thinking about space in terms of change, like

320
00:15:11,200 --> 00:15:14,640
Speaker 1: motion and change. So the way physics begins attacking this

321
00:15:14,720 --> 00:15:17,680
Speaker 1: problem is like why are there locations? And what are

322
00:15:17,680 --> 00:15:20,040
Speaker 1: the rules about locations? Like how do things go from

323
00:15:20,080 --> 00:15:22,160
Speaker 1: here to there? And why is here different from there?

324
00:15:22,200 --> 00:15:24,200
Speaker 1: And can you tell the difference between here and there?

325
00:15:24,960 --> 00:15:27,040
Speaker 2: In my head? Right now, I've got like a three

326
00:15:27,080 --> 00:15:32,200
Speaker 2: dimensional graph, and you identify space as like a point

327
00:15:32,240 --> 00:15:36,080
Speaker 2: on that graph, and does it stay there forever? Or

328
00:15:36,120 --> 00:15:39,080
Speaker 2: does space move? Or have you just jumped to a

329
00:15:39,120 --> 00:15:40,440
Speaker 2: different point on the graph?

330
00:15:40,680 --> 00:15:44,240
Speaker 1: Yeah? Right, great questions right, like are we moving relative

331
00:15:44,360 --> 00:15:48,120
Speaker 1: to space? Can you measure our motion relative to space?

332
00:15:48,360 --> 00:15:50,800
Speaker 1: Or can we only measure our motion relative to like

333
00:15:51,160 --> 00:15:54,920
Speaker 1: other things in space. Right, that's an early basic question,

334
00:15:55,200 --> 00:15:57,760
Speaker 1: and this is the kind of thing Aristotle was thinking about.

335
00:15:57,920 --> 00:16:00,000
Speaker 1: Aristotle was like, well, you know, why do things move

336
00:16:00,080 --> 00:16:02,640
Speaker 1: move at all? Wasn't everything just like stay the same

337
00:16:02,720 --> 00:16:05,440
Speaker 1: place you put a proton? Wasn't it just stay there forever?

338
00:16:05,720 --> 00:16:07,360
Speaker 1: And of course he was working on the surface of

339
00:16:07,360 --> 00:16:10,400
Speaker 1: the Earth, and so he noticed like, hey, things fall down, right,

340
00:16:10,560 --> 00:16:12,480
Speaker 1: Why do things fall down? Why do things seem to

341
00:16:12,560 --> 00:16:15,280
Speaker 1: move through this space? And so you see that, like

342
00:16:15,400 --> 00:16:17,520
Speaker 1: very early on, the questions of space and motion were

343
00:16:17,560 --> 00:16:19,840
Speaker 1: tied together. And you know, Aristotle didn't have like a

344
00:16:19,840 --> 00:16:23,800
Speaker 1: mathematical picture of how the universe worked or how anything happened.

345
00:16:24,000 --> 00:16:25,880
Speaker 1: He was sort of like words based, you know, it

346
00:16:25,920 --> 00:16:29,360
Speaker 1: was like vibes based signs. And he just basically said, look,

347
00:16:29,480 --> 00:16:32,600
Speaker 1: things fall down because things move according to their nature.

348
00:16:32,840 --> 00:16:35,200
Speaker 1: Matter tends to fall down. That's just it's sort of

349
00:16:35,240 --> 00:16:37,960
Speaker 1: like a descriptive. It's not really explanatory. He's just like,

350
00:16:38,080 --> 00:16:40,240
Speaker 1: stuff falls down because it's in the nature of things

351
00:16:40,280 --> 00:16:44,200
Speaker 1: to fall down. Such a circular answer. I don't even

352
00:16:44,240 --> 00:16:45,760
Speaker 1: know why it was ever satisfactory.

353
00:16:46,320 --> 00:16:49,240
Speaker 2: So we were talking about the absence of stuff, and

354
00:16:49,320 --> 00:16:53,360
Speaker 2: now we're talking about the movement of stuff, and so

355
00:16:53,400 --> 00:16:56,120
Speaker 2: the connection to space is that space is standing still

356
00:16:56,160 --> 00:16:59,120
Speaker 2: while the stuff is moving, or just that this is

357
00:16:59,160 --> 00:17:01,840
Speaker 2: the first time people have thought about the relationship between

358
00:17:01,880 --> 00:17:02,920
Speaker 2: space and stuff.

359
00:17:03,120 --> 00:17:05,360
Speaker 1: Yeah, I think all of that early on people trying

360
00:17:05,359 --> 00:17:08,080
Speaker 1: to figure out what space is by understanding how things

361
00:17:08,160 --> 00:17:10,719
Speaker 1: move through space, like what does it mean to go

362
00:17:10,760 --> 00:17:12,600
Speaker 1: from here to there? What does it mean to fall down?

363
00:17:12,720 --> 00:17:15,200
Speaker 1: And why do things fall down? Anyway, and it gives

364
00:17:15,200 --> 00:17:17,960
Speaker 1: you a handle like what does speed mean? But you know,

365
00:17:18,040 --> 00:17:21,280
Speaker 1: Aristotle's view of what this meant was basically the way

366
00:17:21,320 --> 00:17:25,080
Speaker 1: people thought about it for thousands of years until around Galileo.

367
00:17:25,760 --> 00:17:28,520
Speaker 1: And Galileo was the first person to think like, well,

368
00:17:28,640 --> 00:17:30,840
Speaker 1: what do you really mean? Aristotle like, what are you

369
00:17:30,880 --> 00:17:35,040
Speaker 1: talking about things fall down? Because down seems to kind

370
00:17:35,040 --> 00:17:37,679
Speaker 1: of depend on who you are. And he had this

371
00:17:37,720 --> 00:17:41,879
Speaker 1: famous thought experiment way before Einstein was thinking about stuff.

372
00:17:41,960 --> 00:17:44,280
Speaker 1: He was like, say you're on a boat and you're

373
00:17:44,359 --> 00:17:46,360
Speaker 1: inside the boat, so you can't see the outside. You're

374
00:17:46,400 --> 00:17:49,760
Speaker 1: like below decks, and you drop a ball. What's going

375
00:17:49,800 --> 00:17:52,639
Speaker 1: to happen? Well, Aristotle says, the ball's going to fall down.

376
00:17:52,720 --> 00:17:54,840
Speaker 1: Anybody who dropped. Anything on a boat knows the ball

377
00:17:54,880 --> 00:17:58,960
Speaker 1: falls down. Cool, But now what happens if there's somebody

378
00:17:58,960 --> 00:18:02,440
Speaker 1: on the ground and they're watching your experiment somehow does

379
00:18:02,480 --> 00:18:05,479
Speaker 1: the ball fall down according to the person on the boat,

380
00:18:05,680 --> 00:18:08,200
Speaker 1: which means it's then moving with the boat, or does

381
00:18:08,240 --> 00:18:10,720
Speaker 1: the ball fall down according to the person on the ground,

382
00:18:11,080 --> 00:18:14,120
Speaker 1: in which case it would be left behind. Right, there's

383
00:18:14,119 --> 00:18:17,280
Speaker 1: actually different predictions there. If the ball falls down according

384
00:18:17,320 --> 00:18:19,680
Speaker 1: to the person on the dock, it falls like sort

385
00:18:19,720 --> 00:18:22,639
Speaker 1: of straight down, then as the boat keeps moving, the

386
00:18:22,680 --> 00:18:25,080
Speaker 1: ball gets left behind and the person on the boat

387
00:18:25,080 --> 00:18:28,399
Speaker 1: should see the ball like weirdly fall backwards. Whereas if

388
00:18:28,440 --> 00:18:30,439
Speaker 1: the ball falls down according to the person on the

389
00:18:30,520 --> 00:18:33,800
Speaker 1: boat right, then it falls down for them, but the

390
00:18:33,800 --> 00:18:36,520
Speaker 1: person on the dock sees it moving forward with the boat,

391
00:18:36,800 --> 00:18:39,240
Speaker 1: So you can't have it fall straight down for both people.

392
00:18:39,280 --> 00:18:40,760
Speaker 1: This is what Galleo realized.

393
00:18:41,200 --> 00:18:44,320
Speaker 2: Okay, so my brain is now again trying to so

394
00:18:44,400 --> 00:18:47,159
Speaker 2: it feels like we're talking about stuff, but we're not

395
00:18:47,200 --> 00:18:52,400
Speaker 2: talking about space. And so the connection is the stuff

396
00:18:52,440 --> 00:18:55,719
Speaker 2: is moving through space, and by understanding the movement of

397
00:18:55,800 --> 00:18:58,480
Speaker 2: the stuff, we can understand the space better.

398
00:18:58,960 --> 00:19:01,480
Speaker 1: Exactly because galle is experiment helps us think about what

399
00:19:01,560 --> 00:19:05,400
Speaker 1: speed means. Right, what is velocity? Are you moving relative

400
00:19:05,440 --> 00:19:08,560
Speaker 1: to space? Are you only moving relative to other things?

401
00:19:09,000 --> 00:19:12,560
Speaker 1: And Galileo's experiment and what we call Galleyan relativity is

402
00:19:12,560 --> 00:19:16,240
Speaker 1: the velocity is just relative. You're not moving relative to space.

403
00:19:16,280 --> 00:19:18,760
Speaker 1: Space is not something like grid that fills the universe

404
00:19:18,960 --> 00:19:21,959
Speaker 1: and you could just move through space relative to that grid.

405
00:19:22,160 --> 00:19:25,600
Speaker 1: You can only measure your velocity relative to other stuff because,

406
00:19:25,640 --> 00:19:28,080
Speaker 1: like you're in the boat, there's no experiment that you

407
00:19:28,119 --> 00:19:32,320
Speaker 1: can do to measure your velocity relative to the ground. Right,

408
00:19:32,359 --> 00:19:34,040
Speaker 1: you can drop the ball, but the motion of the

409
00:19:34,040 --> 00:19:36,600
Speaker 1: ball doesn't depend on your speed relative to the ground,

410
00:19:36,960 --> 00:19:39,199
Speaker 1: So it doesn't tell you how fast you're going. You

411
00:19:39,240 --> 00:19:41,639
Speaker 1: could be standing still, you could be going super fast.

412
00:19:41,720 --> 00:19:44,280
Speaker 1: You can't tell the difference. And you're asking like, well, okay,

413
00:19:44,280 --> 00:19:46,280
Speaker 1: but aren't we supposed to be talking about space? And

414
00:19:46,320 --> 00:19:48,919
Speaker 1: what this tells us is about motion through space, and

415
00:19:48,920 --> 00:19:52,920
Speaker 1: it tells us something really deep and important that velocity

416
00:19:53,000 --> 00:19:56,080
Speaker 1: is only relative to other stuff. Space is not a

417
00:19:56,160 --> 00:20:00,000
Speaker 1: thing you can have a speed relative to. So Aristotles think,

418
00:20:00,240 --> 00:20:02,800
Speaker 1: you know, the universe is filled with space, and stuff

419
00:20:02,840 --> 00:20:06,040
Speaker 1: moves through space. According to it's like natural tendency. Galleo's like,

420
00:20:06,119 --> 00:20:09,159
Speaker 1: nu uh uh, space isn't a thing. You actually can

421
00:20:09,240 --> 00:20:12,320
Speaker 1: just move relative to other stuff in space. So that's

422
00:20:12,359 --> 00:20:15,400
Speaker 1: already like a big clue about what space might be.

423
00:20:16,160 --> 00:20:19,919
Speaker 2: Okay, So is it fair to summarize by being like

424
00:20:20,000 --> 00:20:23,880
Speaker 2: Galileo would say, there is no space. There's no grid

425
00:20:24,240 --> 00:20:27,760
Speaker 2: in the world, so no space. I'm guessing other people

426
00:20:28,080 --> 00:20:30,080
Speaker 2: have come to other conclusions. Otherwise that would be a

427
00:20:30,119 --> 00:20:33,119
Speaker 2: short episode. And so let's take a break and when

428
00:20:33,160 --> 00:20:54,160
Speaker 2: we come back, we'll find out if space exists. All right,

429
00:20:54,240 --> 00:20:58,800
Speaker 2: So Galileo telling us space doesn't exist, who are we

430
00:20:58,840 --> 00:20:59,840
Speaker 2: going to talk about next.

431
00:21:00,400 --> 00:21:02,919
Speaker 1: I love the way you say that because I imagine

432
00:21:02,960 --> 00:21:05,199
Speaker 1: like you saying that to Galleo, and he would probably

433
00:21:05,200 --> 00:21:08,280
Speaker 1: not agree with your phrasing of it, though I agree,

434
00:21:08,440 --> 00:21:10,280
Speaker 1: you know, I think that what Galileo tells us is

435
00:21:10,280 --> 00:21:14,399
Speaker 1: that maybe space exists, but it's just the distance between objects, right, So,

436
00:21:14,520 --> 00:21:17,520
Speaker 1: like you can have space, it's just not absolute, like

437
00:21:17,520 --> 00:21:20,200
Speaker 1: it can't exist without stuff in it. The thought experiment

438
00:21:20,200 --> 00:21:22,200
Speaker 1: we did, we were like, take everything out of Kelly's office.

439
00:21:22,359 --> 00:21:24,720
Speaker 1: It would be like, well, there's nothing in there. Space

440
00:21:24,800 --> 00:21:27,040
Speaker 1: is not a thing. If there's nothing in there. If

441
00:21:27,040 --> 00:21:29,680
Speaker 1: you evacuated the whole universe, right, got all rid of

442
00:21:29,720 --> 00:21:31,840
Speaker 1: all the particles and all the energy and everything, then

443
00:21:31,840 --> 00:21:34,120
Speaker 1: there would be no space. I think that's what Galileo

444
00:21:34,160 --> 00:21:36,199
Speaker 1: would say, not the space doesn't exist, but that it

445
00:21:36,280 --> 00:21:38,879
Speaker 1: only exists between stuff, not on its own. It's not

446
00:21:38,960 --> 00:21:40,400
Speaker 1: like a thing on its own.

447
00:21:40,880 --> 00:21:42,520
Speaker 2: So like if you had a vacuum and you cleared

448
00:21:42,520 --> 00:21:46,480
Speaker 2: out everything inside the vacuum, nothing exists in there, or

449
00:21:46,520 --> 00:21:48,400
Speaker 2: like you now have a space of non existence.

450
00:21:48,880 --> 00:21:51,439
Speaker 1: Yeah, I think that's Galileo's view. But this was very

451
00:21:51,480 --> 00:21:54,800
Speaker 1: confusing to people, and folks like Newton who spent a

452
00:21:54,800 --> 00:21:57,520
Speaker 1: lot of time thinking about motion. You know, he developed

453
00:21:57,680 --> 00:22:00,600
Speaker 1: physics basically and calculus, and he thought carefully about the

454
00:22:00,640 --> 00:22:03,679
Speaker 1: mathematical flow of things, and he unified our understanding of

455
00:22:03,720 --> 00:22:07,160
Speaker 1: gravity on the ground and in the sky. He agreed

456
00:22:07,200 --> 00:22:11,240
Speaker 1: with Galileo about how velocity works, right, obviously, he wrote

457
00:22:11,240 --> 00:22:13,359
Speaker 1: down the equations. You know, he was the first guy

458
00:22:13,400 --> 00:22:15,560
Speaker 1: to really be able to predict these things. So he

459
00:22:15,640 --> 00:22:18,720
Speaker 1: agreed the velocity is relative, but he fundamentally disagreed about

460
00:22:18,720 --> 00:22:22,320
Speaker 1: the nature of space. He was like, no, space is absolute,

461
00:22:22,520 --> 00:22:25,399
Speaker 1: it exists in and of itself and you can have

462
00:22:25,480 --> 00:22:29,399
Speaker 1: a velocity relative to it. So Galileo's like, velocity is

463
00:22:29,400 --> 00:22:31,359
Speaker 1: purely relative, and Newton is like, I agree with you

464
00:22:31,400 --> 00:22:33,879
Speaker 1: about the equations and that you can only measure your

465
00:22:33,960 --> 00:22:36,639
Speaker 1: velocity relative to other stuff. But I still believe that

466
00:22:36,680 --> 00:22:38,800
Speaker 1: space is a thing underlying everything.

467
00:22:39,560 --> 00:22:41,720
Speaker 2: So does that suggest that the things that they were

468
00:22:41,920 --> 00:22:46,800
Speaker 2: measuring are not important for understanding space because they could

469
00:22:46,920 --> 00:22:49,240
Speaker 2: get the same information and come to different conclusions.

470
00:22:49,600 --> 00:22:51,800
Speaker 1: I think it suggests that Newton was a little crazy, okay,

471
00:22:54,320 --> 00:22:57,000
Speaker 1: because his conclusion is not supported. Like, the problem with

472
00:22:57,080 --> 00:23:00,320
Speaker 1: Newton's idea that maybe space is absolute is that you

473
00:23:00,440 --> 00:23:03,399
Speaker 1: still can't ever measure your velocity relative to it. So

474
00:23:03,440 --> 00:23:06,240
Speaker 1: he believed in this thing that existed that you couldn't

475
00:23:06,280 --> 00:23:10,240
Speaker 1: ever measure, you know, Galleo says, velocity is purely relative.

476
00:23:10,280 --> 00:23:13,960
Speaker 1: There's no like velocity relative to space itself, because space

477
00:23:14,000 --> 00:23:16,719
Speaker 1: itself on its own doesn't exist, right, only exists relative

478
00:23:16,720 --> 00:23:19,240
Speaker 1: to stuff. Newton is like, yeah, I agree with you

479
00:23:19,280 --> 00:23:22,399
Speaker 1: about velocity. You can only measure with between things, but

480
00:23:22,560 --> 00:23:26,840
Speaker 1: still unobservable, unknowable to us, there is this absolute space.

481
00:23:26,960 --> 00:23:29,320
Speaker 1: Even though he could think of no way to measure

482
00:23:29,480 --> 00:23:32,600
Speaker 1: speed relative to it. So Newton believed that you could be,

483
00:23:32,640 --> 00:23:35,359
Speaker 1: for example, at rest with respect to space, and it

484
00:23:35,480 --> 00:23:38,600
Speaker 1: was some like special frame of reference there. Gallet was like, no, no,

485
00:23:38,600 --> 00:23:41,320
Speaker 1: that doesn't exist, and plus you can't measure it. So

486
00:23:41,400 --> 00:23:43,080
Speaker 1: Newton is just sort of going out in a limb

487
00:23:43,080 --> 00:23:45,840
Speaker 1: thinking that it exists even if you can't measure it.

488
00:23:45,920 --> 00:23:47,800
Speaker 2: All right, Well, I think just about every scientist you

489
00:23:47,840 --> 00:23:50,080
Speaker 2: talk to has blind spots where they're like, no, it's true,

490
00:23:50,119 --> 00:23:51,679
Speaker 2: and I can't tell you why, but I'm sure that

491
00:23:51,720 --> 00:23:54,320
Speaker 2: it's true. We're all human. So we've been saying the

492
00:23:54,359 --> 00:23:57,880
Speaker 2: word relative a lot, which makes me feel like we're

493
00:23:57,880 --> 00:24:00,760
Speaker 2: gonna have to get to Einstein eventually. Is he the

494
00:24:00,800 --> 00:24:02,520
Speaker 2: next person on your list?

495
00:24:02,880 --> 00:24:05,440
Speaker 1: He's definitely the next person on the list. And Einstein

496
00:24:05,480 --> 00:24:08,200
Speaker 1: gets a lot of credit for relativity. You think of relativity,

497
00:24:08,200 --> 00:24:11,520
Speaker 1: you think of Einstein. But the truth is that Einstein's relativity,

498
00:24:11,560 --> 00:24:14,840
Speaker 1: his concepts of space really just go back to Galileo.

499
00:24:15,200 --> 00:24:18,560
Speaker 1: It's Galileyan relativity that Einstein took and just sort of

500
00:24:18,600 --> 00:24:20,840
Speaker 1: like said, hey, let's go back to this. This made

501
00:24:20,880 --> 00:24:23,040
Speaker 1: a lot of sense to me. Let's just like build

502
00:24:23,040 --> 00:24:26,280
Speaker 1: this in at the foundations because Einstein was thinking about light.

503
00:24:26,520 --> 00:24:29,280
Speaker 1: Only a few decades earlier, Maxwell had figured out that

504
00:24:29,440 --> 00:24:32,439
Speaker 1: light is a wiggle in the electromagnetic field. And the

505
00:24:32,480 --> 00:24:35,239
Speaker 1: confusing thing about it was that Maxwell's equation said that

506
00:24:35,320 --> 00:24:37,960
Speaker 1: light should travel at a specific speed, the speed of light,

507
00:24:38,280 --> 00:24:41,439
Speaker 1: and that it shouldn't depend on your velocity at all. Like,

508
00:24:41,840 --> 00:24:44,760
Speaker 1: no matter whether you're on the Earth that's going around

509
00:24:44,760 --> 00:24:47,119
Speaker 1: the Sun, or you're in a spaceship or you're just

510
00:24:47,119 --> 00:24:49,840
Speaker 1: floating in deep space, everybody should see light travel at

511
00:24:49,840 --> 00:24:52,960
Speaker 1: the same speed, said Maxwell. And Einstein was like, hey,

512
00:24:52,960 --> 00:24:56,040
Speaker 1: well that's cool. That's actually what Galileo was saying, right.

513
00:24:56,040 --> 00:24:57,960
Speaker 1: Gallea was saying that you shouldn't be able to measure

514
00:24:58,000 --> 00:25:01,160
Speaker 1: your velocity, that there's no absolute for life, the velocity

515
00:25:01,240 --> 00:25:04,520
Speaker 1: is only relative. And so what Einstein did was apply

516
00:25:04,680 --> 00:25:08,280
Speaker 1: Galleyan relativity to Maxwell's equations and say that means that

517
00:25:08,359 --> 00:25:10,879
Speaker 1: everybody measures the speed of light to be the speed

518
00:25:10,880 --> 00:25:14,040
Speaker 1: of light, regardless of what else you're doing. That's the

519
00:25:14,080 --> 00:25:18,360
Speaker 1: foundation of Einstein's idea. But really it's taking Galileo's relativity

520
00:25:18,359 --> 00:25:19,760
Speaker 1: and just being like, hey, let's take.

521
00:25:19,640 --> 00:25:22,800
Speaker 2: This seriously, okay, And so all of that. Whenever you're

522
00:25:22,800 --> 00:25:24,720
Speaker 2: talking about the history of something. I feel like I

523
00:25:24,720 --> 00:25:25,920
Speaker 2: get it in my head. I'm like, oh, that makes

524
00:25:25,960 --> 00:25:27,280
Speaker 2: sense that it's like, oh no, wait, but then that

525
00:25:27,320 --> 00:25:29,919
Speaker 2: got overturned and you're like, oh, but I just understood it, okay,

526
00:25:29,920 --> 00:25:35,800
Speaker 2: And so that so all of that we still believe in.

527
00:25:36,040 --> 00:25:38,760
Speaker 1: Right, We wait until you understand something, Klay, and then

528
00:25:38,800 --> 00:25:41,040
Speaker 1: we overturn it. That's that's the whole plan there.

529
00:25:41,400 --> 00:25:43,960
Speaker 2: You know that I've suspected that for a long time.

530
00:25:44,080 --> 00:25:47,720
Speaker 2: But the whole world is about me and my understanding

531
00:25:47,760 --> 00:25:50,000
Speaker 2: of things. So light is always moving at the same speed,

532
00:25:50,040 --> 00:25:52,560
Speaker 2: no matter who was viewing it. That is still something

533
00:25:52,600 --> 00:25:53,080
Speaker 2: we believe.

534
00:25:53,320 --> 00:25:55,679
Speaker 1: That is still something we believe. And that is the

535
00:25:55,720 --> 00:25:59,919
Speaker 1: earthquake of Einstein's relativity. The concepts came from Galileo, but

536
00:26:00,040 --> 00:26:02,320
Speaker 1: because he applied it to light and had all sorts

537
00:26:02,359 --> 00:26:06,320
Speaker 1: of consequences. Also because Einstein connected space and time and

538
00:26:06,359 --> 00:26:08,280
Speaker 1: we're going to talk about what time means in another

539
00:26:08,320 --> 00:26:11,000
Speaker 1: episode and what it even is. But the fact that

540
00:26:11,080 --> 00:26:13,680
Speaker 1: light always moves at the same speed for all observers

541
00:26:13,920 --> 00:26:16,520
Speaker 1: connects space and time in these really unique ways. And

542
00:26:16,560 --> 00:26:18,639
Speaker 1: the short version of the story is that it means

543
00:26:18,640 --> 00:26:22,000
Speaker 1: that different people have different clocks. So like clocks tike

544
00:26:22,040 --> 00:26:24,240
Speaker 1: at different speeds at different parts of the universe, and

545
00:26:24,280 --> 00:26:27,560
Speaker 1: that's a direct consequence of how light moves through space,

546
00:26:27,920 --> 00:26:30,800
Speaker 1: because everybody sees light move at the same speed no

547
00:26:30,880 --> 00:26:33,919
Speaker 1: matter what. Then you can't have clocks that all agree

548
00:26:33,960 --> 00:26:35,640
Speaker 1: all the way through the universe. And if you want

549
00:26:35,680 --> 00:26:37,280
Speaker 1: to know more about how that works, check out the

550
00:26:37,320 --> 00:26:40,560
Speaker 1: companion episode about what time is. We'll explain all of that.

551
00:26:41,080 --> 00:26:43,800
Speaker 2: Now we've talked about the movement of light through space.

552
00:26:44,320 --> 00:26:47,959
Speaker 2: What does that tell us about how we can define space?

553
00:26:48,440 --> 00:26:51,520
Speaker 1: Yeah, so Einstein's relativity means something really important about what

554
00:26:51,680 --> 00:26:55,440
Speaker 1: space is because it connects space and time, which tells

555
00:26:55,520 --> 00:26:59,080
Speaker 1: us that time is relative also not just space. Time

556
00:26:59,119 --> 00:27:01,840
Speaker 1: is relative and the same for everybody, and it has

557
00:27:01,880 --> 00:27:05,639
Speaker 1: an important meaning for what distances are between things. It

558
00:27:05,680 --> 00:27:07,879
Speaker 1: means that like I can measure the length of a ruler,

559
00:27:07,920 --> 00:27:09,880
Speaker 1: and you can measure the length of a ruler, which

560
00:27:09,920 --> 00:27:12,560
Speaker 1: is like the distance between two points in space, and

561
00:27:12,600 --> 00:27:15,920
Speaker 1: we can get different answers and we can both be correct.

562
00:27:16,160 --> 00:27:18,240
Speaker 1: This is something in special loyaltuty that goes by the

563
00:27:18,280 --> 00:27:21,919
Speaker 1: name length traction, and basically it just means, hey, you

564
00:27:22,000 --> 00:27:24,000
Speaker 1: assume that things have a length and have a length,

565
00:27:24,080 --> 00:27:26,040
Speaker 1: and that length is their length, and it doesn't matter

566
00:27:26,080 --> 00:27:28,479
Speaker 1: how fast you're going or where you are. Turns out

567
00:27:28,520 --> 00:27:31,400
Speaker 1: that's not true. It turns out the distances between points

568
00:27:31,560 --> 00:27:35,480
Speaker 1: what we even mean by space, depends on where you're

569
00:27:35,480 --> 00:27:38,240
Speaker 1: looking at them from and how fast you're going relative

570
00:27:38,280 --> 00:27:38,720
Speaker 1: to them.

571
00:27:39,200 --> 00:27:42,439
Speaker 2: Okay, So if we want to try to understand space,

572
00:27:43,080 --> 00:27:44,879
Speaker 2: does that mean we need to try to find ways

573
00:27:44,920 --> 00:27:49,200
Speaker 2: to hold constant how fast you're moving and the distance

574
00:27:49,240 --> 00:27:51,159
Speaker 2: between things, and then we can start to get a

575
00:27:51,200 --> 00:27:52,600
Speaker 2: handle on space.

576
00:27:53,400 --> 00:27:56,320
Speaker 1: Yeah, exactly, we want to talk about space. Space is

577
00:27:56,320 --> 00:27:58,199
Speaker 1: about the distance between things. So now we have to

578
00:27:58,240 --> 00:28:00,600
Speaker 1: think about, well, how do you measure the distance between things?

579
00:28:00,600 --> 00:28:02,560
Speaker 1: And you know, you can be pretty pedantic about it.

580
00:28:02,600 --> 00:28:04,040
Speaker 1: You can be like, well, I'm gonna hold up a

581
00:28:04,119 --> 00:28:07,680
Speaker 1: ruler between two things. I'm going to measure where thing

582
00:28:07,760 --> 00:28:10,200
Speaker 1: one is and thing two are at the same time,

583
00:28:10,640 --> 00:28:12,720
Speaker 1: and I'm gonna say, well, the difference between the marks

584
00:28:12,760 --> 00:28:15,000
Speaker 1: and the ruler, that's how far apart they are. You know,

585
00:28:15,119 --> 00:28:16,920
Speaker 1: I have my left hand and my right hand. I

586
00:28:16,960 --> 00:28:19,760
Speaker 1: put them on a ruler. There's ten centimeters long ticks

587
00:28:19,800 --> 00:28:22,440
Speaker 1: between them, So I say they're ten centimeters apart right.

588
00:28:22,600 --> 00:28:24,520
Speaker 1: And the crucial thing that I've done there is I've

589
00:28:24,560 --> 00:28:26,760
Speaker 1: done it at the same time. I said, I'm gonna

590
00:28:26,760 --> 00:28:28,359
Speaker 1: look at where my left hand is right now and

591
00:28:28,440 --> 00:28:31,000
Speaker 1: where my right hand is right now, and measure their

592
00:28:31,040 --> 00:28:33,399
Speaker 1: distances at the same time, and then I'm going to

593
00:28:33,480 --> 00:28:35,960
Speaker 1: call that the distance between them. The problem is that

594
00:28:36,000 --> 00:28:39,240
Speaker 1: Einstein's relativity and this whole speed of light business changes

595
00:28:39,280 --> 00:28:41,760
Speaker 1: what we mean by at the same time because time

596
00:28:41,840 --> 00:28:44,960
Speaker 1: is not universal anymore. So I might say I'm measuring

597
00:28:44,960 --> 00:28:46,560
Speaker 1: where my left and my right hand are at the

598
00:28:46,560 --> 00:28:49,800
Speaker 1: same time. But you might think, actually, Daniel, you messed up.

599
00:28:49,960 --> 00:28:51,840
Speaker 1: You measured where your left hand was and then a

600
00:28:51,880 --> 00:28:54,640
Speaker 1: second later where your right hand was, and if you're moving,

601
00:28:54,680 --> 00:28:57,120
Speaker 1: then now the whole measurement is messed up. So connecting

602
00:28:57,160 --> 00:28:59,680
Speaker 1: space and time changes how we think our clocks work,

603
00:28:59,720 --> 00:29:03,000
Speaker 1: which also upends how we measure distances, and in the end,

604
00:29:03,040 --> 00:29:05,360
Speaker 1: that's what space is about. Right We're talked about where

605
00:29:05,360 --> 00:29:07,560
Speaker 1: a proton is and where another proton is and how

606
00:29:07,560 --> 00:29:10,520
Speaker 1: far apart they are. Now it turns out, according to Einstein,

607
00:29:10,720 --> 00:29:13,440
Speaker 1: we don't even agree about the distances. That's not even

608
00:29:13,440 --> 00:29:15,960
Speaker 1: a fundamental thing about space. That everybody looks at a

609
00:29:16,000 --> 00:29:19,000
Speaker 1: distance and agrees about what the distance is, like how

610
00:29:19,000 --> 00:29:21,120
Speaker 1: many centimeters are there between the protons?

611
00:29:21,600 --> 00:29:25,000
Speaker 2: Okay, so it sounds like we've decided that a definition

612
00:29:25,040 --> 00:29:30,480
Speaker 2: of space has to include distance. Yeah, but people measure

613
00:29:30,520 --> 00:29:34,480
Speaker 2: distances differently depending on their conditions. Is there a way

614
00:29:35,040 --> 00:29:37,800
Speaker 2: to get around that or no, there's no way to

615
00:29:37,800 --> 00:29:40,160
Speaker 2: get two people? I need ice cream?

616
00:29:40,440 --> 00:29:42,960
Speaker 1: Yeah, exactly, there's no way around that. That turns out

617
00:29:42,960 --> 00:29:45,920
Speaker 1: to just be a feature of space that we never

618
00:29:46,000 --> 00:29:49,600
Speaker 1: noticed before because mostly we had basically no velocity relative

619
00:29:49,640 --> 00:29:52,040
Speaker 1: to each other, mostly slow speeds on the surface of

620
00:29:52,040 --> 00:29:54,560
Speaker 1: the Earth, and we didn't look at very long distances.

621
00:29:54,840 --> 00:29:58,280
Speaker 1: So we have this intuition that things have a size,

622
00:29:58,400 --> 00:30:00,200
Speaker 1: and that size is just what they are, and you

623
00:30:00,240 --> 00:30:02,080
Speaker 1: should measure that size no matter who you are and

624
00:30:02,120 --> 00:30:04,320
Speaker 1: how fast you're going. That just turns out to be wrong.

625
00:30:04,840 --> 00:30:07,440
Speaker 1: Like sometimes people ask me, you know, why do things

626
00:30:07,480 --> 00:30:10,160
Speaker 1: get shorter if you see them at high speeds. You know,

627
00:30:10,200 --> 00:30:12,440
Speaker 1: you have a ruler stick flying by you at nine

628
00:30:12,480 --> 00:30:14,360
Speaker 1: tenths of the speed of light, Why do you measure

629
00:30:14,360 --> 00:30:16,440
Speaker 1: it to be less than a meter stick? If it

630
00:30:16,480 --> 00:30:18,480
Speaker 1: was a meter when you're holding it and the answer

631
00:30:18,520 --> 00:30:21,400
Speaker 1: is not that it's shrunk there. You're imposing your like intuition,

632
00:30:21,560 --> 00:30:23,959
Speaker 1: you're prejudice that things have a size and that they

633
00:30:24,000 --> 00:30:26,880
Speaker 1: have to shrink to get shorter. The answer is lengths

634
00:30:26,880 --> 00:30:29,560
Speaker 1: depends on velocity. Like, that's just the way space works.

635
00:30:29,560 --> 00:30:31,920
Speaker 1: You can't escape it, Kelly, is no way around it.

636
00:30:32,000 --> 00:30:34,680
Speaker 1: Space just is different from the way our intuition work.

637
00:30:34,760 --> 00:30:36,800
Speaker 1: And this is why it's so important to explore it

638
00:30:36,840 --> 00:30:41,080
Speaker 1: like systematically and mathematically, because it contradicts our intuition and

639
00:30:41,080 --> 00:30:43,640
Speaker 1: it leads us, we hope, at least, to some true

640
00:30:43,720 --> 00:30:45,480
Speaker 1: insights about the nature of reality.

641
00:30:45,760 --> 00:30:48,240
Speaker 2: So why can't we just say that depending on conditions,

642
00:30:48,440 --> 00:30:52,440
Speaker 2: you get different distances, but the only thing you're differing

643
00:30:52,480 --> 00:30:55,320
Speaker 2: in is how much space you're talking about. But you

644
00:30:55,360 --> 00:30:58,840
Speaker 2: can still talk about space, like why do we have

645
00:30:58,920 --> 00:31:00,840
Speaker 2: to be able to measure it to have a definition

646
00:31:01,160 --> 00:31:01,440
Speaker 2: of it?

647
00:31:01,800 --> 00:31:03,240
Speaker 1: Why do we have to measure it to have a

648
00:31:03,280 --> 00:31:06,239
Speaker 1: definition of it? Wow, awesome question. You know. I think

649
00:31:06,320 --> 00:31:08,840
Speaker 1: that's probably because the way we do science is we

650
00:31:08,880 --> 00:31:11,160
Speaker 1: measure stuff, right, Like, you have to be able to

651
00:31:11,200 --> 00:31:14,360
Speaker 1: take measurements to have data so you can talk about

652
00:31:14,360 --> 00:31:17,960
Speaker 1: what that data means. Right, Otherwise, what are you doing.

653
00:31:18,000 --> 00:31:21,960
Speaker 1: You just smoking banana peels and having conversations, which is fine.

654
00:31:22,320 --> 00:31:25,480
Speaker 2: But so distance isn't the only way to measure things.

655
00:31:26,000 --> 00:31:29,120
Speaker 2: Why is distance the measurement that we have to have

656
00:31:29,360 --> 00:31:31,240
Speaker 2: in order to understand space?

657
00:31:31,720 --> 00:31:33,880
Speaker 1: Oh yeah, I see a great question. Well, I think

658
00:31:33,920 --> 00:31:38,440
Speaker 1: because we imagine that space is about locations, right, Even

659
00:31:38,440 --> 00:31:40,440
Speaker 1: if you think about space as some three D grid,

660
00:31:40,680 --> 00:31:46,520
Speaker 1: those are all locations, and so distances are differences between locations, right,

661
00:31:47,000 --> 00:31:49,760
Speaker 1: And either those are relative, like the only thing that

662
00:31:49,840 --> 00:31:53,320
Speaker 1: exists are distances between two points, two protons or two

663
00:31:53,400 --> 00:31:56,080
Speaker 1: ends of the ruler, or there's some absolute grid, and

664
00:31:56,120 --> 00:31:59,280
Speaker 1: you can measure your distance relative to space itself. But

665
00:31:59,360 --> 00:32:02,600
Speaker 1: in the end, distance is the thing that space is describing.

666
00:32:02,840 --> 00:32:03,000
Speaker 5: Right.

667
00:32:03,040 --> 00:32:05,560
Speaker 1: If you don't have space, you can't have distance, right,

668
00:32:05,960 --> 00:32:07,800
Speaker 1: And so that's sort of like the way we get

669
00:32:07,800 --> 00:32:08,719
Speaker 1: handle on space.

670
00:32:09,200 --> 00:32:12,640
Speaker 2: This whole podcast is about Kelly understanding herself better. It's

671
00:32:12,680 --> 00:32:15,520
Speaker 2: like part Kelly Psychology, part what is space? And I

672
00:32:15,520 --> 00:32:17,680
Speaker 2: think part of why I enjoy this conversation more as

673
00:32:17,680 --> 00:32:20,320
Speaker 2: an adult is I'm way more comfortable now being like,

674
00:32:20,600 --> 00:32:23,280
Speaker 2: this is probably a really not smart question, but I

675
00:32:23,320 --> 00:32:26,280
Speaker 2: don't care. I'm asking it, and I think in its classes.

676
00:32:26,320 --> 00:32:27,960
Speaker 2: I'd just be like, no, I can't say that, because

677
00:32:27,960 --> 00:32:29,920
Speaker 2: that would be anyway. Maybe our listeners are going to

678
00:32:29,960 --> 00:32:32,520
Speaker 2: write it and be like, you shouldn't ask those questions.

679
00:32:32,560 --> 00:32:34,720
Speaker 2: They're not good questions, but anyway.

680
00:32:34,440 --> 00:32:37,440
Speaker 1: Okay, they're perfect questions. They're perfect questions.

681
00:32:37,520 --> 00:32:40,440
Speaker 2: Yes, okay, you have to have distance, but you cannot

682
00:32:40,440 --> 00:32:43,240
Speaker 2: measure distance. Where do we go from here?

683
00:32:44,360 --> 00:32:46,760
Speaker 1: You can measure distance, it's just that the distance is

684
00:32:46,800 --> 00:32:50,320
Speaker 1: not the same for everybody. Right, that's two people measuring

685
00:32:50,320 --> 00:32:53,600
Speaker 1: the same quantities can get different answers. So distance is

686
00:32:53,640 --> 00:32:57,360
Speaker 1: not universal, but it can still exist, and then things

687
00:32:57,400 --> 00:33:00,400
Speaker 1: get crazier. Everything we're talking about so far is just

688
00:33:00,480 --> 00:33:03,320
Speaker 1: Einstein's view of how things move in sort of Newton's

689
00:33:03,360 --> 00:33:07,880
Speaker 1: idea of space. But Einstein then introduced another concept. So

690
00:33:07,920 --> 00:33:11,080
Speaker 1: now we go from special relativity to general relativity. He said,

691
00:33:11,120 --> 00:33:14,600
Speaker 1: space can do even more. We can change the relative

692
00:33:14,680 --> 00:33:19,400
Speaker 1: distances between things without those things moving. This is the

693
00:33:19,440 --> 00:33:22,840
Speaker 1: idea of space itself curving. And there's a lot of

694
00:33:22,840 --> 00:33:25,360
Speaker 1: descriptions out there in popular science about what it means

695
00:33:25,360 --> 00:33:28,280
Speaker 1: for space to curve, and many of them are very misleading.

696
00:33:28,760 --> 00:33:31,040
Speaker 1: You know, there's the famous one about the rubber sheet

697
00:33:31,040 --> 00:33:33,600
Speaker 1: that most pop side folks go to. And I really

698
00:33:33,640 --> 00:33:35,960
Speaker 1: discourage you from thinking about space in terms of a

699
00:33:36,000 --> 00:33:38,000
Speaker 1: rubber sheet, because if you think about it carefully, it

700
00:33:38,080 --> 00:33:40,760
Speaker 1: leads to all sorts of misunderstandings, you know. And so

701
00:33:40,800 --> 00:33:43,040
Speaker 1: we're going to cover the rubber sheet analogy just to

702
00:33:43,080 --> 00:33:46,200
Speaker 1: talk about why it's misleading. The general picture of the

703
00:33:46,280 --> 00:33:48,600
Speaker 1: rubber sheet is like you stretch out this rubber sheet

704
00:33:48,600 --> 00:33:50,080
Speaker 1: and then you put a bowling ball in it. The

705
00:33:50,120 --> 00:33:52,800
Speaker 1: bowling ball bends the rubber sheet, and that's supposed to

706
00:33:52,800 --> 00:33:55,800
Speaker 1: represent like how space is curving. The problem with that

707
00:33:55,880 --> 00:33:58,760
Speaker 1: analogy is that it's showing you to D space the

708
00:33:58,840 --> 00:34:03,480
Speaker 1: rubber sheet in some third dimension, like it's bending outside

709
00:34:03,600 --> 00:34:05,720
Speaker 1: the universe itself. The universe is supposed to be two D,

710
00:34:05,800 --> 00:34:08,680
Speaker 1: and the rubber sheet is bending into some other dimension,

711
00:34:09,000 --> 00:34:12,120
Speaker 1: whereas in our space. The way Einstein thinks about space

712
00:34:12,160 --> 00:34:16,400
Speaker 1: bending is it's intrinsic. There's no additional dimension. We're not

713
00:34:16,440 --> 00:34:19,840
Speaker 1: bending our three D space into some fourth dimension like

714
00:34:19,840 --> 00:34:22,880
Speaker 1: a rubber sheet bending into some new dimension we can't see.

715
00:34:23,160 --> 00:34:26,319
Speaker 1: That's not what space curvature is. It's just changing the

716
00:34:26,400 --> 00:34:29,719
Speaker 1: relative distances between things. So, like Kelly and I have

717
00:34:29,760 --> 00:34:32,680
Speaker 1: a certain number of thousands of miles between us right now,

718
00:34:33,000 --> 00:34:35,200
Speaker 1: what if while we both sit in our chair, you

719
00:34:35,239 --> 00:34:37,880
Speaker 1: could just change that distance, so now it's a thousand miles,

720
00:34:37,920 --> 00:34:40,520
Speaker 1: or now it's ten thousand miles. We just change the

721
00:34:40,560 --> 00:34:42,600
Speaker 1: amount of space between us.

722
00:34:43,160 --> 00:34:47,080
Speaker 2: When I think about the curvature of space, I feel like,

723
00:34:47,120 --> 00:34:49,640
Speaker 2: but isn't there now space on either side of whatever

724
00:34:49,760 --> 00:34:52,480
Speaker 2: just curved? But I guess that area is supposed to

725
00:34:52,520 --> 00:34:55,360
Speaker 2: have no space, So there's places that have no space?

726
00:34:55,719 --> 00:34:56,200
Speaker 2: Is that right?

727
00:34:56,760 --> 00:34:58,520
Speaker 1: What do you mean on either side? You mean like

728
00:34:58,680 --> 00:35:01,240
Speaker 1: are we getting pushed out in to other space or something?

729
00:35:01,560 --> 00:35:03,480
Speaker 2: So I guess maybe my brain is still stuck on

730
00:35:03,480 --> 00:35:05,520
Speaker 2: the rubber sheet. So you've got the sheet, it like

731
00:35:05,760 --> 00:35:08,960
Speaker 2: goes in where the bowling ball is. But in my head,

732
00:35:08,960 --> 00:35:11,279
Speaker 2: there's space above where the bend is, Like you know,

733
00:35:11,320 --> 00:35:13,319
Speaker 2: the sheet was there and now it's down, but there's

734
00:35:13,320 --> 00:35:15,919
Speaker 2: still something where the sheet used to be, because there's

735
00:35:15,920 --> 00:35:17,600
Speaker 2: still space there. But is that not how to think

736
00:35:17,600 --> 00:35:20,440
Speaker 2: about it? Like when it bends, there's space and there's nothing,

737
00:35:20,560 --> 00:35:21,440
Speaker 2: there's like the absence.

738
00:35:21,600 --> 00:35:24,400
Speaker 1: Yeah, exactly. That's why the rubber sheet is so confusing

739
00:35:24,480 --> 00:35:26,600
Speaker 1: because as soon as you dig into it. It leads

740
00:35:26,600 --> 00:35:28,919
Speaker 1: to questions that don't have answers because the herb sheet

741
00:35:28,960 --> 00:35:30,480
Speaker 1: is just not the way it works right. The two

742
00:35:30,520 --> 00:35:33,200
Speaker 1: D examples are useful because they are easier to think

743
00:35:33,200 --> 00:35:36,120
Speaker 1: about instead. Imagine like a map, right, so you have

744
00:35:36,160 --> 00:35:39,000
Speaker 1: your favorite country, US, Argentina or whatever, and think about

745
00:35:39,080 --> 00:35:41,319
Speaker 1: a bunch of cities on that map, and they all

746
00:35:41,320 --> 00:35:43,759
Speaker 1: have distances between them, right, and old maps you could

747
00:35:43,800 --> 00:35:46,640
Speaker 1: like look up how far it was between New York

748
00:35:46,680 --> 00:35:49,440
Speaker 1: and La or between Seattle and Miami, right, and those

749
00:35:49,480 --> 00:35:52,759
Speaker 1: are distances all right. Cool, And if you took a

750
00:35:52,840 --> 00:35:55,560
Speaker 1: ruler to the map, you could like measure those things

751
00:35:55,760 --> 00:35:58,080
Speaker 1: and the map would lay flat on a table and

752
00:35:58,160 --> 00:36:01,880
Speaker 1: you could measure those distances with rule. Cool. Now, what

753
00:36:02,040 --> 00:36:04,480
Speaker 1: if I came in and I had magic fingers, and

754
00:36:04,520 --> 00:36:07,480
Speaker 1: I'm like, I'm just going to change the distance between

755
00:36:07,640 --> 00:36:10,480
Speaker 1: LA and Seattle and I'm not going to change anything else,

756
00:36:11,000 --> 00:36:12,480
Speaker 1: or I'm gonna make it longer. I'm gonna make it

757
00:36:12,520 --> 00:36:16,359
Speaker 1: shorter that distance. Now, imagine like, does that map lie

758
00:36:16,400 --> 00:36:19,240
Speaker 1: flat on the table anymore? If I play with enough cities,

759
00:36:19,360 --> 00:36:21,920
Speaker 1: then a order accommodate having more or less space, I'm

760
00:36:21,920 --> 00:36:24,080
Speaker 1: gonna end up with wrinkles in that map. There's gonna

761
00:36:24,080 --> 00:36:26,360
Speaker 1: be no way to lay that map flat on the table.

762
00:36:26,600 --> 00:36:29,319
Speaker 1: And that's essentially what's happening in space. You put a

763
00:36:29,320 --> 00:36:32,520
Speaker 1: mass in space, and space shrinks, right. It changes the

764
00:36:32,600 --> 00:36:35,880
Speaker 1: relative distances between stuff in a way that it's no

765
00:36:35,920 --> 00:36:39,680
Speaker 1: longer conceptually flat in your mind, the way that a

766
00:36:39,800 --> 00:36:41,759
Speaker 1: sheet of paper would no longer be flat if you

767
00:36:41,880 --> 00:36:45,040
Speaker 1: just like magically change the distances between two points on

768
00:36:45,120 --> 00:36:45,960
Speaker 1: that sheet of paper.

769
00:36:46,520 --> 00:36:48,800
Speaker 2: All right, So I'm thinking about the map, and you

770
00:36:48,920 --> 00:36:52,600
Speaker 2: shortened the distance between Seattle and LA. And maybe I'm

771
00:36:52,600 --> 00:36:56,440
Speaker 2: taking everything too literally, Like has San Francisco disappeared? Are

772
00:36:56,480 --> 00:37:00,360
Speaker 2: all the people in San Francisco shorter because everything has trunk?

773
00:37:00,520 --> 00:37:06,440
Speaker 2: Or are you tunneling through the map to shorten the distance,

774
00:37:07,480 --> 00:37:09,080
Speaker 2: or do we not know what space is doing? It

775
00:37:09,080 --> 00:37:10,360
Speaker 2: could be like any of those things.

776
00:37:10,680 --> 00:37:12,719
Speaker 1: We're not tunneling through San Francisco, and we're not killing

777
00:37:12,719 --> 00:37:15,640
Speaker 1: anybody in San Francisco. I hope you all are safe

778
00:37:15,640 --> 00:37:18,960
Speaker 1: out there. We're just changing the distance between Seattle and LA.

779
00:37:19,000 --> 00:37:21,000
Speaker 1: We're just saying, hey, if you turn on a flashlight

780
00:37:21,040 --> 00:37:23,239
Speaker 1: in La, how long would it take for that light

781
00:37:23,320 --> 00:37:26,400
Speaker 1: to get to Seattle? Because the speed of light is constant.

782
00:37:26,560 --> 00:37:28,840
Speaker 1: This is a good way to measure how much space

783
00:37:28,880 --> 00:37:31,600
Speaker 1: there is. So we're saying, hey, these things are now closer.

784
00:37:31,920 --> 00:37:34,440
Speaker 1: That's what it means to shrink space. And the idea

785
00:37:34,480 --> 00:37:37,040
Speaker 1: of curvature is that it's local, right, Like you could

786
00:37:37,040 --> 00:37:40,120
Speaker 1: make everything further apart and everything closer together and keep

787
00:37:40,120 --> 00:37:43,200
Speaker 1: the map flat. But if you only squeeze two different

788
00:37:43,200 --> 00:37:46,120
Speaker 1: cities to make them closer together or further apart, then

789
00:37:46,120 --> 00:37:48,719
Speaker 1: now space has weird bends in it, right, in order

790
00:37:48,760 --> 00:37:50,680
Speaker 1: to make light take a certain amount of time to

791
00:37:50,719 --> 00:37:52,359
Speaker 1: go here and a certain amount of time to go there,

792
00:37:52,480 --> 00:37:55,000
Speaker 1: and to make all the light times work out, space

793
00:37:55,080 --> 00:37:57,080
Speaker 1: has to have weird curves and it can no longer

794
00:37:57,160 --> 00:37:59,480
Speaker 1: be flat in the same way that like, if you

795
00:37:59,560 --> 00:38:03,200
Speaker 1: magically made the time from La to Seattle five times

796
00:38:03,239 --> 00:38:05,520
Speaker 1: as long, then there would have to be more space

797
00:38:05,520 --> 00:38:07,440
Speaker 1: in there. You couldn't have a flat sheet of paper.

798
00:38:07,640 --> 00:38:10,000
Speaker 1: You need to like add more space, more land, more

799
00:38:10,080 --> 00:38:11,160
Speaker 1: road for you to drive on.

800
00:38:11,560 --> 00:38:13,319
Speaker 2: We can move forward, but I have to admit I'm

801
00:38:13,360 --> 00:38:16,480
Speaker 2: having a little trouble, Like, does that mean we have

802
00:38:16,560 --> 00:38:20,319
Speaker 2: stretched out what already exists or made more? Are there

803
00:38:20,360 --> 00:38:22,759
Speaker 2: new cities in between now or did we just take

804
00:38:22,800 --> 00:38:25,080
Speaker 2: what existed and it's like taffy and wh'ere just it's

805
00:38:25,160 --> 00:38:27,480
Speaker 2: like like all the people in between are like twice

806
00:38:27,520 --> 00:38:27,960
Speaker 2: as wide.

807
00:38:29,360 --> 00:38:33,160
Speaker 1: Yeah, okay, great question, And this is something we actually

808
00:38:33,200 --> 00:38:36,080
Speaker 1: know the answer to because we've done it. Like when

809
00:38:36,120 --> 00:38:40,360
Speaker 1: gravitational waves hit the Earth, they literally do this. They

810
00:38:40,440 --> 00:38:45,160
Speaker 1: stretch space and they shrink space. Right, So this actually happens.

811
00:38:45,719 --> 00:38:48,960
Speaker 1: And what happens when a gravitational wave passes through the Earth,

812
00:38:49,000 --> 00:38:51,600
Speaker 1: this is a wave in space itself again, which just

813
00:38:51,680 --> 00:38:55,360
Speaker 1: means you're changing their relative distances. What happens in reality

814
00:38:55,680 --> 00:38:58,880
Speaker 1: is the stuff that's holding us together, the land, the

815
00:38:59,040 --> 00:39:02,400
Speaker 1: electrochemical bond, keeps us at the same distance. And so,

816
00:39:02,640 --> 00:39:05,560
Speaker 1: for example, simplify things and say you and I were

817
00:39:05,560 --> 00:39:08,120
Speaker 1: out floating in space and we were holding a rod

818
00:39:08,160 --> 00:39:11,279
Speaker 1: that was one kilometer long, each holding one end, and

819
00:39:11,320 --> 00:39:14,920
Speaker 1: then a gravitational wave comes by and it stretches space. Well,

820
00:39:14,960 --> 00:39:16,640
Speaker 1: you and I are holding the rod, and the rod

821
00:39:16,680 --> 00:39:18,440
Speaker 1: has bonds, and so it's going to keep us at

822
00:39:18,480 --> 00:39:21,759
Speaker 1: exactly one kilometer apart, even though space is stretching around us.

823
00:39:22,080 --> 00:39:23,640
Speaker 1: So if we show in a flashlight, we would still

824
00:39:23,640 --> 00:39:26,960
Speaker 1: measure one kilometer. But if we weren't holding onto the rod, right,

825
00:39:27,000 --> 00:39:29,839
Speaker 1: there was nothing keeping us at one kilometer. Then when

826
00:39:29,920 --> 00:39:33,040
Speaker 1: space wiggles around us, we would use our flashlights and

827
00:39:33,080 --> 00:39:36,000
Speaker 1: we would measure more than one kilometer distance because it

828
00:39:36,000 --> 00:39:38,520
Speaker 1: would take light longer. So your question is, like, is

829
00:39:38,520 --> 00:39:41,040
Speaker 1: it making more space or is it stretching the space

830
00:39:41,080 --> 00:39:43,640
Speaker 1: that's already there. Nobody knows the answer to that question

831
00:39:44,040 --> 00:39:46,719
Speaker 1: because we don't really know what space is. Like, what

832
00:39:46,840 --> 00:39:50,399
Speaker 1: is happening you're asking, like the underlying mechanisms of all this, Yeah,

833
00:39:50,440 --> 00:39:53,000
Speaker 1: we have no idea what's really going on there. We

834
00:39:53,120 --> 00:39:55,480
Speaker 1: just have this mathematical theory that tells us how to

835
00:39:55,480 --> 00:39:58,920
Speaker 1: do these calculations. We don't know what's underlying going on.

836
00:39:59,480 --> 00:40:02,640
Speaker 2: But the car the way we understand these things, can

837
00:40:02,680 --> 00:40:07,280
Speaker 2: it be used to like predict and understand things we've

838
00:40:07,360 --> 00:40:10,640
Speaker 2: actually seen. This isn't just smoking banana peels. We tested

839
00:40:10,680 --> 00:40:13,239
Speaker 2: these things. Our understanding is.

840
00:40:13,239 --> 00:40:16,680
Speaker 1: Useful, absolutely, And we can measure this curvature, like if

841
00:40:16,680 --> 00:40:19,600
Speaker 1: you shine light through this space, you can tell is

842
00:40:19,640 --> 00:40:22,320
Speaker 1: space curved or is it not? Like if you shine

843
00:40:22,360 --> 00:40:25,640
Speaker 1: two parallel lines through space that's not curved. They should

844
00:40:25,680 --> 00:40:29,520
Speaker 1: never touch two photon beams through flat space should never

845
00:40:29,600 --> 00:40:32,160
Speaker 1: touch if they're in parallel, but in curved space they

846
00:40:32,160 --> 00:40:35,640
Speaker 1: will either cross or they'll split apart. Right, And we

847
00:40:35,719 --> 00:40:38,680
Speaker 1: have measured this, Like the famous proof of relativity from

848
00:40:38,680 --> 00:40:42,000
Speaker 1: Einstein was seeing light bend around the moon during the eclipse, right,

849
00:40:42,320 --> 00:40:45,680
Speaker 1: that was seeing light move through curved space and bending,

850
00:40:46,360 --> 00:40:49,040
Speaker 1: And so this is definitely something we've seen. We have

851
00:40:49,239 --> 00:40:53,200
Speaker 1: very accurate models, and general relativity is amazingly precise. It

852
00:40:53,239 --> 00:40:55,720
Speaker 1: predicts all sorts of things that nobody else could predict.

853
00:40:55,800 --> 00:40:58,560
Speaker 1: So it tells us what space does because not only

854
00:40:58,600 --> 00:41:01,680
Speaker 1: is space curved and light moves through it in curved ways,

855
00:41:01,680 --> 00:41:04,000
Speaker 1: but like other stuff moves through it in curved ways.

856
00:41:04,160 --> 00:41:07,279
Speaker 1: You have the Earth moving around the Sun because the

857
00:41:07,320 --> 00:41:10,360
Speaker 1: Sun has curved space around it. So it's not just

858
00:41:10,400 --> 00:41:14,440
Speaker 1: smoking banana peels. It works really really really well. But

859
00:41:14,600 --> 00:41:16,600
Speaker 1: you know, then we can ask like, well, all right,

860
00:41:16,680 --> 00:41:19,080
Speaker 1: so general relativity tells us that, like if you have

861
00:41:19,280 --> 00:41:22,800
Speaker 1: mass in space, it curves it, and that not only

862
00:41:22,920 --> 00:41:26,399
Speaker 1: our distance is relative, but like distances between stuff can

863
00:41:26,480 --> 00:41:29,680
Speaker 1: change even without that stuff moving. So like what does

864
00:41:29,719 --> 00:41:31,919
Speaker 1: that mean about what space is? Right?

865
00:41:32,600 --> 00:41:35,759
Speaker 2: And let's dig into that question after we go all

866
00:41:35,800 --> 00:41:56,440
Speaker 2: grab some more banana peels. Okay, so you just finished

867
00:41:56,440 --> 00:41:59,440
Speaker 2: saying that the distance between two objects can change even

868
00:41:59,440 --> 00:42:01,600
Speaker 2: if both of the objects like perceive that they have

869
00:42:01,640 --> 00:42:03,960
Speaker 2: stayed still. But what does that tell us about space?

870
00:42:04,880 --> 00:42:07,760
Speaker 1: So we can measure our velocity relative to other stuff,

871
00:42:08,000 --> 00:42:10,920
Speaker 1: and we can tell that space can sometimes expand and

872
00:42:10,960 --> 00:42:13,640
Speaker 1: shrink between it, and we have these amazing calculations from

873
00:42:13,719 --> 00:42:16,760
Speaker 1: general relativity, what does that tell us about what space

874
00:42:16,880 --> 00:42:19,480
Speaker 1: actually is? You know? Well, back to the conversation with

875
00:42:19,680 --> 00:42:24,480
Speaker 1: Galileo and with Newton. Einstein agrees that velocity is relative, right,

876
00:42:24,480 --> 00:42:27,040
Speaker 1: you can only measure your velocity relative to other stuff.

877
00:42:27,320 --> 00:42:29,440
Speaker 1: And it seems like he's saying that space is a

878
00:42:29,480 --> 00:42:32,400
Speaker 1: thing because space can do stuff like it can wiggle,

879
00:42:32,800 --> 00:42:35,640
Speaker 1: it can bend, it can expand. So we went from

880
00:42:35,640 --> 00:42:38,720
Speaker 1: like Galleo saying, now space is just the distance between stuff,

881
00:42:38,880 --> 00:42:41,560
Speaker 1: to Newton saying, no, space is a thing, even though

882
00:42:41,600 --> 00:42:44,439
Speaker 1: you can't measure your velocity to it, to Einstein being like, well,

883
00:42:44,440 --> 00:42:46,799
Speaker 1: space has interesting properties, so it's pretty hard to say

884
00:42:46,800 --> 00:42:51,000
Speaker 1: it's not a thing. Right. The weirdest part about Einstein's space, though,

885
00:42:51,280 --> 00:42:54,759
Speaker 1: is that you still can't measure your velocity relative to it, like,

886
00:42:54,840 --> 00:42:57,040
Speaker 1: even if you think it's out there and it has

887
00:42:57,160 --> 00:43:01,040
Speaker 1: curvature and has these properties, you can't measure your speed

888
00:43:01,160 --> 00:43:05,880
Speaker 1: relative to just space. It's something Matt Strassler calls emotional,

889
00:43:06,239 --> 00:43:09,720
Speaker 1: like there's no way to measure your speed relative to space.

890
00:43:10,040 --> 00:43:12,520
Speaker 1: So in one hand, Einstein agrees with Galleo like you

891
00:43:12,640 --> 00:43:15,440
Speaker 1: have velocities relative, but he also agrees with Newton like

892
00:43:15,520 --> 00:43:19,000
Speaker 1: space is a thing. But then back to Galleo, He's like, actually,

893
00:43:19,000 --> 00:43:20,920
Speaker 1: but you can't measure your speed relative to it, So

894
00:43:21,000 --> 00:43:22,040
Speaker 1: like what is it?

895
00:43:22,200 --> 00:43:22,399
Speaker 4: Man?

896
00:43:22,880 --> 00:43:27,759
Speaker 2: Yeah, so is this something that like when we understand

897
00:43:28,040 --> 00:43:31,840
Speaker 2: dark matter and dark energy, it could help us understand space.

898
00:43:31,920 --> 00:43:35,120
Speaker 2: Are those like just completely different problems.

899
00:43:35,520 --> 00:43:38,160
Speaker 1: They could be completely different problems or they could be connected.

900
00:43:38,200 --> 00:43:40,839
Speaker 1: You never know what thread of investigation is it really

901
00:43:40,840 --> 00:43:42,680
Speaker 1: going to help you, like figure out what's going on

902
00:43:42,760 --> 00:43:44,439
Speaker 1: and where the next breakthrough is going to come from.

903
00:43:44,640 --> 00:43:46,680
Speaker 1: What we do know is that general relativity is a

904
00:43:46,719 --> 00:43:49,440
Speaker 1: great description of space and motion, but we don't know

905
00:43:49,480 --> 00:43:52,160
Speaker 1: what's going on underneath it. Like people often ask me,

906
00:43:52,640 --> 00:43:55,399
Speaker 1: you put mass in space and space bends. Why does

907
00:43:55,400 --> 00:43:57,920
Speaker 1: it bend? What is the mechanism for bending it? What

908
00:43:58,040 --> 00:44:00,600
Speaker 1: is doing the bending? And we don't know the answer

909
00:44:00,640 --> 00:44:03,480
Speaker 1: to those questions. Remember, general relativity is a description of

910
00:44:03,480 --> 00:44:05,120
Speaker 1: what we've seen, and we can look at it and

911
00:44:05,120 --> 00:44:07,319
Speaker 1: be like, well, what does that mean about space? And

912
00:44:07,360 --> 00:44:09,520
Speaker 1: it's not a final answer. And part of the reason

913
00:44:09,560 --> 00:44:11,600
Speaker 1: we know it's not a final answer is that we

914
00:44:11,640 --> 00:44:15,200
Speaker 1: have this completely separate idea about how the universe works

915
00:44:15,239 --> 00:44:17,880
Speaker 1: and how space is that comes from the other branch

916
00:44:17,920 --> 00:44:20,040
Speaker 1: of physics that we've been developing over the last one

917
00:44:20,080 --> 00:44:23,919
Speaker 1: hundred years, which is quantum mechanics, and quantum mechanics tells

918
00:44:23,960 --> 00:44:26,759
Speaker 1: us a completely different story about space, what it is

919
00:44:26,800 --> 00:44:27,640
Speaker 1: and how it works.

920
00:44:28,160 --> 00:44:32,400
Speaker 2: So quantum mechanics would not agree that space bends in

921
00:44:32,440 --> 00:44:33,720
Speaker 2: the way that we've been talking about.

922
00:44:33,960 --> 00:44:36,879
Speaker 1: Quantum mechanics has no answer to the question of what

923
00:44:37,000 --> 00:44:40,520
Speaker 1: is bending light around the moon. Quantum mechanics can't explain

924
00:44:40,680 --> 00:44:44,800
Speaker 1: space bending. Quantum mechanics can explain gravity at all. Quantum

925
00:44:44,800 --> 00:44:47,919
Speaker 1: mechanics can explain electromagnetism, it can explain the weak force,

926
00:44:47,960 --> 00:44:50,160
Speaker 1: it can explain particles that it can explain all the

927
00:44:50,160 --> 00:44:53,359
Speaker 1: strange experiments we saw right one hundred years ago and

928
00:44:53,400 --> 00:44:56,400
Speaker 1: the experiments we do at the particle collider, and it's

929
00:44:56,440 --> 00:45:00,560
Speaker 1: an extraordinarily accurate description of everything basically particle related. But

930
00:45:00,600 --> 00:45:03,640
Speaker 1: it's built on a different assumption about space. It thinks

931
00:45:03,680 --> 00:45:06,160
Speaker 1: of space the way Newton did, just like the backdrop

932
00:45:06,239 --> 00:45:08,880
Speaker 1: on which things play out in the universe. You know,

933
00:45:08,920 --> 00:45:11,960
Speaker 1: general relativity is what we call background free. It's like

934
00:45:12,200 --> 00:45:15,360
Speaker 1: space itself is just the distances between stuff, and quantum

935
00:45:15,360 --> 00:45:17,839
Speaker 1: mechanics is like, no, there's a background there, Just lay

936
00:45:17,880 --> 00:45:21,040
Speaker 1: space out, roll it out like AstroTurf, and then particles

937
00:45:21,040 --> 00:45:23,840
Speaker 1: do their dance in that space. And so it starts

938
00:45:23,840 --> 00:45:26,759
Speaker 1: from a very different place, and it can't explain how

939
00:45:26,800 --> 00:45:29,520
Speaker 1: space bends. In fact, the space bends too much, quantum

940
00:45:29,520 --> 00:45:32,120
Speaker 1: mechanics breaks down. We don't know how to do calculations

941
00:45:32,360 --> 00:45:36,279
Speaker 1: for quantum mechanics if space is super bendy. And it

942
00:45:36,360 --> 00:45:40,080
Speaker 1: also tells us something very different about empty space. Like

943
00:45:40,120 --> 00:45:42,879
Speaker 1: the exercise we started out with where we said, take

944
00:45:42,920 --> 00:45:46,000
Speaker 1: your office, remove Kelly, remove all of her books, remove

945
00:45:46,040 --> 00:45:48,880
Speaker 1: all of her weird samples of parasites and other gross

946
00:45:48,880 --> 00:45:51,680
Speaker 1: stuff I can see in the background, and all the air.

947
00:45:52,080 --> 00:45:55,280
Speaker 1: What's left. Well, Einstein says there's nothing there, but quantum

948
00:45:55,280 --> 00:45:59,000
Speaker 1: mechanics says that's not possible because quantum mechanics says, space

949
00:45:59,280 --> 00:46:02,759
Speaker 1: in itself is filled with fields, Like what is it

950
00:46:02,800 --> 00:46:05,440
Speaker 1: that light is moving through? Anyway? It's moving through the

951
00:46:05,480 --> 00:46:08,520
Speaker 1: electromagnetic field. Well, you can't take that out of space.

952
00:46:08,760 --> 00:46:12,120
Speaker 1: Quantum mechanics says, you can't like rip the field itself out.

953
00:46:12,400 --> 00:46:14,479
Speaker 1: You can say, I'm going to take all the photons out,

954
00:46:14,880 --> 00:46:18,359
Speaker 1: but the field itself is like the capacity for light

955
00:46:18,440 --> 00:46:20,960
Speaker 1: to move through it. It's like a parking lot with

956
00:46:21,000 --> 00:46:23,680
Speaker 1: no cars in it, right, the field itself is always there.

957
00:46:24,040 --> 00:46:27,400
Speaker 1: And quantum mechanics says that we have the electromagnetic field

958
00:46:27,480 --> 00:46:29,960
Speaker 1: and the electron field and the muon fil in all

959
00:46:30,000 --> 00:46:33,040
Speaker 1: sorts of fields that they're a part of space itself.

960
00:46:33,440 --> 00:46:36,600
Speaker 1: And not only that, but these fields can never be

961
00:46:36,960 --> 00:46:39,319
Speaker 1: totally zero. You can never pull all the energy out

962
00:46:39,360 --> 00:46:42,359
Speaker 1: of them. They have a minimum quantum fuzziness, which means

963
00:46:42,360 --> 00:46:45,960
Speaker 1: that there's always energy in space. So quantum mechanics view

964
00:46:45,960 --> 00:46:47,799
Speaker 1: of space is really different. It's like you have this

965
00:46:47,880 --> 00:46:50,400
Speaker 1: absolute background on which you put these fields, and these

966
00:46:50,400 --> 00:46:53,040
Speaker 1: fields are always buzzing even if you do your best

967
00:46:53,120 --> 00:46:55,480
Speaker 1: job of pulling everything out of that space.

968
00:46:56,040 --> 00:47:01,040
Speaker 2: So are these the two main theories for space? So

969
00:47:01,080 --> 00:47:04,440
Speaker 2: there's no other like theories that physicists take seriously. I'm

970
00:47:04,440 --> 00:47:06,440
Speaker 2: sure there's plenty of people who have additional theories, but

971
00:47:06,600 --> 00:47:08,200
Speaker 2: there's no theories people take seriously.

972
00:47:08,400 --> 00:47:10,800
Speaker 1: Yeah, we have narrated down to at least two ideas

973
00:47:10,800 --> 00:47:14,600
Speaker 1: about space, both of which we're pretty sure are wrong. Hey, no,

974
00:47:14,680 --> 00:47:15,360
Speaker 1: that's progress.

975
00:47:15,440 --> 00:47:18,200
Speaker 2: That is No, that is progress. So does anybody have

976
00:47:18,440 --> 00:47:23,480
Speaker 2: any promising experiments designed to follow up on this next

977
00:47:23,719 --> 00:47:25,560
Speaker 2: or what comes next? We're at a stalemate.

978
00:47:25,600 --> 00:47:28,280
Speaker 1: It seems we are at a stalemate. And one issue

979
00:47:28,520 --> 00:47:30,880
Speaker 1: is that we don't know whether the quantum mechanics version

980
00:47:30,880 --> 00:47:33,920
Speaker 1: of space or the general relativity version of space is

981
00:47:33,960 --> 00:47:37,680
Speaker 1: correct because almost every experiment we can think of only

982
00:47:37,680 --> 00:47:40,279
Speaker 1: involves one of them. Like we can do experiments to

983
00:47:40,320 --> 00:47:44,040
Speaker 1: test general relativity, like photons bending around moons, but then

984
00:47:44,120 --> 00:47:46,960
Speaker 1: quantum effects are irrelevant because quantum effects get averaged out

985
00:47:46,960 --> 00:47:49,040
Speaker 1: when you have something as big as a moon, Or

986
00:47:49,080 --> 00:47:51,160
Speaker 1: we can think of quantum mechanical experiments we have like

987
00:47:51,200 --> 00:47:54,440
Speaker 1: one particle bouncing off another particle, but then gravity is

988
00:47:54,440 --> 00:47:57,120
Speaker 1: irrelevant because the gravity of a particle is basically zero

989
00:47:57,160 --> 00:47:59,719
Speaker 1: because gravity is super duper weak. So the only place

990
00:47:59,719 --> 00:48:02,080
Speaker 1: you could do a test to say, like, well, whose

991
00:48:02,160 --> 00:48:05,000
Speaker 1: idea of space is correct? Quantum mechanics or gravity are

992
00:48:05,040 --> 00:48:08,760
Speaker 1: experiments that are particle sized but have the masses of moons.

993
00:48:09,080 --> 00:48:12,080
Speaker 1: And so now we're talking about black holes, and so

994
00:48:12,160 --> 00:48:14,719
Speaker 1: the answer to like what space really is and how

995
00:48:14,760 --> 00:48:17,680
Speaker 1: does it all work? Is hiding behind the event horizons

996
00:48:17,680 --> 00:48:20,759
Speaker 1: of black holes, like what's in there? General relativity says

997
00:48:20,800 --> 00:48:24,560
Speaker 1: it's a singularity. Quantum mechanics says that's nonsense. They can't

998
00:48:24,600 --> 00:48:27,919
Speaker 1: both be right. They could both be wrong. So, yeah,

999
00:48:27,960 --> 00:48:30,560
Speaker 1: the answer to your question is build a spaceship, fly

1000
00:48:30,640 --> 00:48:33,239
Speaker 1: into a black hole, get the answer, but never be

1001
00:48:33,280 --> 00:48:35,360
Speaker 1: able to tell anybody about it because you're chopped forever.

1002
00:48:35,800 --> 00:48:38,399
Speaker 2: Is there any reason to hope that we'll be able

1003
00:48:38,480 --> 00:48:41,160
Speaker 2: to get the answer? Someday? Will our children be having

1004
00:48:41,239 --> 00:48:42,239
Speaker 2: the same conversation?

1005
00:48:43,800 --> 00:48:45,560
Speaker 1: I think we probably will figure it out. There are

1006
00:48:45,600 --> 00:48:48,520
Speaker 1: other ways to explore this, like the hearts of neutron

1007
00:48:48,640 --> 00:48:52,000
Speaker 1: stars are not quite dense enough to become black holes,

1008
00:48:52,040 --> 00:48:54,760
Speaker 1: but they are dense enough, or gravity and some quantum

1009
00:48:54,760 --> 00:48:58,239
Speaker 1: mechanical effects are both important, So by studying the insides

1010
00:48:58,280 --> 00:49:00,760
Speaker 1: of neutron stars we might be able to get a clue.

1011
00:49:01,000 --> 00:49:02,920
Speaker 1: But there's also just a lot of like thinking that

1012
00:49:02,960 --> 00:49:05,360
Speaker 1: we need to do. You know, it's not like we

1013
00:49:05,440 --> 00:49:07,839
Speaker 1: have a great theory that predicts what's going to happen

1014
00:49:07,920 --> 00:49:09,719
Speaker 1: that we need to go test. So we have some

1015
00:49:09,719 --> 00:49:11,359
Speaker 1: more thinking to do about like how to bring these

1016
00:49:11,400 --> 00:49:13,480
Speaker 1: things together, and there are definitely people working on it,

1017
00:49:13,520 --> 00:49:15,640
Speaker 1: you know. String theory is one effort to try to

1018
00:49:15,680 --> 00:49:19,680
Speaker 1: describe things that incorporates gravity and quantum mechanics. This other

1019
00:49:19,760 --> 00:49:23,279
Speaker 1: approaches loop quantum gravity. One of my favorite ideas is

1020
00:49:23,320 --> 00:49:27,240
Speaker 1: that space itself is made of chunks, right, like little

1021
00:49:27,239 --> 00:49:30,280
Speaker 1: pixels of space, and that what's happening when space increases

1022
00:49:30,320 --> 00:49:32,399
Speaker 1: is that you're like adding more pixels, and that when

1023
00:49:32,440 --> 00:49:36,239
Speaker 1: space shrinks is that you're decreasing these pixels. The cool

1024
00:49:36,280 --> 00:49:37,920
Speaker 1: thing about this is that it gives you a way

1025
00:49:37,960 --> 00:49:41,840
Speaker 1: to think about a universe without space. Like imagine a

1026
00:49:41,880 --> 00:49:44,280
Speaker 1: whole bunch of pixels in the beginning of the universe,

1027
00:49:44,480 --> 00:49:46,600
Speaker 1: and these pixels are not tied together in any way.

1028
00:49:46,880 --> 00:49:49,800
Speaker 1: It's like a pile of beads before you do your project.

1029
00:49:50,080 --> 00:49:52,800
Speaker 1: Then somebody comes along and they weave all these beads

1030
00:49:52,880 --> 00:49:55,760
Speaker 1: together into a sheet, right, or like a three D grid.

1031
00:49:56,200 --> 00:49:58,440
Speaker 1: That's what space is there's a bunch of these pixels

1032
00:49:58,880 --> 00:50:03,200
Speaker 1: woven together with maybe quantum forces or something into this

1033
00:50:03,320 --> 00:50:05,799
Speaker 1: three D grid that we live in and experience. But

1034
00:50:05,880 --> 00:50:08,480
Speaker 1: you could also imagine that there was a time before

1035
00:50:08,520 --> 00:50:12,000
Speaker 1: that happened, when space was like disorganized, where you couldn't

1036
00:50:12,040 --> 00:50:13,960
Speaker 1: let go from one to the other because they weren't

1037
00:50:14,000 --> 00:50:17,120
Speaker 1: connected the way they are now. So thinking about the

1038
00:50:17,200 --> 00:50:19,120
Speaker 1: nature of space and thinking about how to bring these

1039
00:50:19,120 --> 00:50:21,680
Speaker 1: ideas together is maybe a fruitful way to make progress

1040
00:50:21,680 --> 00:50:23,719
Speaker 1: because it forces you to think, like, well, what does

1041
00:50:23,760 --> 00:50:25,839
Speaker 1: this mean, and what else could it be? And could

1042
00:50:25,880 --> 00:50:28,720
Speaker 1: you have a universe without space? All this kind of stuff.

1043
00:50:29,840 --> 00:50:32,160
Speaker 2: So for the pixel theory, like when you get more

1044
00:50:32,200 --> 00:50:34,279
Speaker 2: pixels or lose pixels, where do they come from? And

1045
00:50:34,280 --> 00:50:34,879
Speaker 2: where do they go?

1046
00:50:35,560 --> 00:50:38,520
Speaker 1: Yeah? Great question, And that question assumes that they have

1047
00:50:38,560 --> 00:50:41,719
Speaker 1: to come from somewhere, right you imagining like things like

1048
00:50:41,880 --> 00:50:44,040
Speaker 1: energy in the universe are concerned. Right, you can't just

1049
00:50:44,120 --> 00:50:47,640
Speaker 1: like pop new pixels out of nothing. But you know,

1050
00:50:47,680 --> 00:50:49,760
Speaker 1: we don't actually know that. We don't know that energy

1051
00:50:49,800 --> 00:50:52,360
Speaker 1: has to be conserved in the universe. We know that,

1052
00:50:52,400 --> 00:50:56,080
Speaker 1: for example, when the universe expands, photons get red shifted,

1053
00:50:56,200 --> 00:50:59,160
Speaker 1: they get stretched to longer wavelengths. That means they lose energy.

1054
00:50:59,239 --> 00:51:02,960
Speaker 1: Where's that energy go? Nowhere? It doesn't have to go anywhere,

1055
00:51:03,000 --> 00:51:06,040
Speaker 1: because maybe energy itself is not conserved in the universe.

1056
00:51:06,360 --> 00:51:09,120
Speaker 1: So these are great questions because it might be that

1057
00:51:09,160 --> 00:51:12,319
Speaker 1: they are the wrong questions, and the contradictions that come

1058
00:51:12,400 --> 00:51:14,719
Speaker 1: up when we ask them lead us to asking the

1059
00:51:14,760 --> 00:51:17,280
Speaker 1: right questions, which we don't know what those questions are yet.

1060
00:51:17,440 --> 00:51:19,360
Speaker 1: But it's sort of like, you know, knowing the answer

1061
00:51:19,360 --> 00:51:21,279
Speaker 1: is forty two and then going back and realizing, hmm,

1062
00:51:21,360 --> 00:51:24,000
Speaker 1: maybe we asked the wrong question, or maybe we're thinking

1063
00:51:24,040 --> 00:51:26,200
Speaker 1: about this whole thing wrong, you know. I think the

1064
00:51:26,239 --> 00:51:29,520
Speaker 1: takeaway message for listeners is like, what is space? Well,

1065
00:51:29,560 --> 00:51:33,080
Speaker 1: we don't know. We have two really nice descriptions of

1066
00:51:33,080 --> 00:51:36,279
Speaker 1: what space might be, both of which work in different scenarios,

1067
00:51:36,719 --> 00:51:38,680
Speaker 1: but both of which raise a lot of questions and

1068
00:51:38,719 --> 00:51:41,040
Speaker 1: they don't agree with each other, and so we really

1069
00:51:41,080 --> 00:51:44,120
Speaker 1: just don't know what space is. Even though we've made

1070
00:51:44,120 --> 00:51:46,279
Speaker 1: a lot of progress and we can build iPhones and

1071
00:51:46,360 --> 00:51:48,520
Speaker 1: launch rockets to Mars and all sorts of stuff. We

1072
00:51:48,600 --> 00:51:51,399
Speaker 1: can move through space, we can manipulate space, doesn't mean

1073
00:51:51,440 --> 00:51:53,560
Speaker 1: we yet know what it is, and it might be

1074
00:51:53,600 --> 00:51:56,480
Speaker 1: a century or a thousand years before we really figure

1075
00:51:56,520 --> 00:51:56,879
Speaker 1: it out.

1076
00:51:57,920 --> 00:51:59,600
Speaker 2: Well, that's exciting. I'm going to try to convince my

1077
00:51:59,640 --> 00:52:02,480
Speaker 2: daughter to become a physicist. She's been wearing her Sern

1078
00:52:02,520 --> 00:52:05,440
Speaker 2: outfits in her Stern hard hat since visiting CERN, so

1079
00:52:06,080 --> 00:52:07,160
Speaker 2: maybe she's on the path.

1080
00:52:07,320 --> 00:52:09,279
Speaker 1: I think about space the way I think about like

1081
00:52:09,400 --> 00:52:12,040
Speaker 1: a photon. People are often told, like a photon is

1082
00:52:12,080 --> 00:52:14,480
Speaker 1: a particle. No, it's a wave. Or sometimes it's a particle,

1083
00:52:14,520 --> 00:52:16,640
Speaker 1: sometimes it's a wave. The way I think about it

1084
00:52:16,719 --> 00:52:18,720
Speaker 1: is like a photon. It's neither a particle or a wave.

1085
00:52:18,880 --> 00:52:21,279
Speaker 1: Sometimes it's particle like, sometimes it's a wave like. It's

1086
00:52:21,280 --> 00:52:23,879
Speaker 1: something else we haven't yet figured out. And the same

1087
00:52:23,960 --> 00:52:27,160
Speaker 1: is true of space. We can describe space sometimes using

1088
00:52:27,200 --> 00:52:30,600
Speaker 1: general relativity, we can describe it sometimes using quantum mechanics.

1089
00:52:30,880 --> 00:52:33,600
Speaker 1: But space is probably something else. We've never even imagined,

1090
00:52:33,680 --> 00:52:37,400
Speaker 1: something beyond yet our current thinking that maybe one of

1091
00:52:37,400 --> 00:52:38,960
Speaker 1: our listeners is smart enough to.

1092
00:52:38,960 --> 00:52:40,520
Speaker 2: Figure out that would be awesome.

1093
00:52:40,840 --> 00:52:42,759
Speaker 1: All right, Well, thanks for going on this journey with

1094
00:52:43,000 --> 00:52:46,600
Speaker 1: us into the philosophical underpinnings of physics. I hope I've

1095
00:52:46,600 --> 00:52:48,640
Speaker 1: convinced you that physics is a way to think about

1096
00:52:48,640 --> 00:52:51,520
Speaker 1: these big, deep questions without getting lost in the meaning

1097
00:52:51,560 --> 00:52:54,040
Speaker 1: of the words, because it lets us be mathematical to

1098
00:52:54,080 --> 00:52:57,080
Speaker 1: try to be precise, and then to ask philosophical questions

1099
00:52:57,160 --> 00:52:59,719
Speaker 1: about those mathematical models, be like, what does it mean

1100
00:52:59,719 --> 00:53:01,759
Speaker 1: that I can calculate this, but I can't measure that?

1101
00:53:02,040 --> 00:53:03,840
Speaker 1: What does it tell us about the nature of the universe?

1102
00:53:04,239 --> 00:53:06,799
Speaker 1: Even when those answers are or we really.

1103
00:53:06,560 --> 00:53:09,279
Speaker 2: Just have no clue, my brain today hurt in a

1104
00:53:09,320 --> 00:53:12,560
Speaker 2: good way. I really enjoyed thinking about this today. It

1105
00:53:12,600 --> 00:53:15,200
Speaker 2: was nice to have us someone to ask silly questions

1106
00:53:15,239 --> 00:53:16,120
Speaker 2: to well.

1107
00:53:16,160 --> 00:53:18,920
Speaker 1: Thank you for all the silly and wonderful questions, and

1108
00:53:19,000 --> 00:53:21,439
Speaker 1: thanks everybody else out there for thinking about the nature

1109
00:53:21,440 --> 00:53:23,480
Speaker 1: of the universe. If you have questions about how things work,

1110
00:53:23,560 --> 00:53:25,800
Speaker 1: don't be shy. Write to us if you have questions

1111
00:53:25,840 --> 00:53:27,359
Speaker 1: at Daniel and Kelly dot org.

1112
00:53:34,840 --> 00:53:38,680
Speaker 2: Daniel and Kelly's Extraordinary Universe is produced by iHeartRadio. We

1113
00:53:38,719 --> 00:53:40,000
Speaker 2: would love to hear from you.

1114
00:53:40,160 --> 00:53:43,080
Speaker 1: We really would. We want to know what questions you

1115
00:53:43,280 --> 00:53:45,920
Speaker 1: have about this extraordinary Universe.

1116
00:53:46,040 --> 00:53:49,000
Speaker 2: You want to know your thoughts on recent shows, suggestions

1117
00:53:49,000 --> 00:53:52,040
Speaker 2: for future shows. If you contact us, we will get

1118
00:53:52,040 --> 00:53:52,440
Speaker 2: back to you.

1119
00:53:52,680 --> 00:53:56,200
Speaker 1: We really mean it. We answer every message, Email us

1120
00:53:56,239 --> 00:53:58,680
Speaker 1: at Questions at danieland Kelly.

1121
00:53:58,520 --> 00:54:00,520
Speaker 2: Dot org, or you can find us on some social media.

1122
00:54:00,640 --> 00:54:04,440
Speaker 2: We have accounts on x, Instagram, Blue Sky and on

1123
00:54:04,520 --> 00:54:06,480
Speaker 2: all of those platforms. You can find us at D

1124
00:54:06,920 --> 00:54:08,400
Speaker 2: and K Universe.

1125
00:54:08,560 --> 00:54:10,080
Speaker 1: Don't be shy write to us