1
00:00:08,440 --> 00:00:11,520
Speaker 1: Hey, Daniel, do you ever do physics demonstrations at home

2
00:00:11,640 --> 00:00:13,480
Speaker 1: with the kids or on the kids?

3
00:00:15,480 --> 00:00:18,040
Speaker 2: We have a strict no experimenting on the kids policy

4
00:00:18,079 --> 00:00:19,560
Speaker 2: without both parents' consent.

5
00:00:20,120 --> 00:00:21,880
Speaker 1: Oh good, did you have a process?

6
00:00:22,840 --> 00:00:25,560
Speaker 2: We had to create a process after one of us

7
00:00:25,640 --> 00:00:27,880
Speaker 2: was winging it. But yeah, I love doing physics demonstrations

8
00:00:27,920 --> 00:00:29,960
Speaker 2: at home, though usually they don't work.

9
00:00:30,200 --> 00:00:32,520
Speaker 1: What do you mean do you break the laws of physics?

10
00:00:33,520 --> 00:00:36,040
Speaker 2: Well, I remember, for example, trying to show the kids

11
00:00:36,080 --> 00:00:38,360
Speaker 2: that everything falls at the same speed m.

12
00:00:39,080 --> 00:00:41,240
Speaker 1: And the laws of physics didn't cooperate.

13
00:00:42,520 --> 00:00:44,440
Speaker 2: Well, it was at the dinner table, and I used

14
00:00:44,440 --> 00:00:46,600
Speaker 2: little bits of our dinner, and we have a dog,

15
00:00:46,760 --> 00:00:49,479
Speaker 2: so only one piece actually made it to the floor.

16
00:00:49,800 --> 00:00:53,479
Speaker 1: WHOA. I guess your dog was trying to challenge the

17
00:00:53,520 --> 00:00:56,960
Speaker 1: laws of physics or just your physics demonstration.

18
00:00:57,160 --> 00:00:59,360
Speaker 2: I think I didn't appreciate the gravity of such an

19
00:00:59,400 --> 00:01:00,680
Speaker 2: experiment for my dog, but.

20
00:01:00,600 --> 00:01:02,560
Speaker 1: I'm sure your dog heavily appreciated it.

21
00:01:04,240 --> 00:01:05,520
Speaker 2: I got his massive thank you.

22
00:01:21,080 --> 00:01:21,240
Speaker 3: Hi.

23
00:01:21,240 --> 00:01:23,920
Speaker 1: I am Horhemrick, cartoonists and the author of Oliver's Great

24
00:01:23,959 --> 00:01:24,680
Speaker 1: Big Universe.

25
00:01:24,800 --> 00:01:27,679
Speaker 2: Hi. I'm Daniel. I'm a particle physicist and a professor

26
00:01:27,760 --> 00:01:30,280
Speaker 2: at UC Irvine, and I think physics can help us

27
00:01:30,360 --> 00:01:31,800
Speaker 2: understand the world around us.

28
00:01:31,880 --> 00:01:34,240
Speaker 1: Yeah, physics is a powerful tool to help us look

29
00:01:34,280 --> 00:01:36,520
Speaker 1: at the world, challenge the laws of it, and try

30
00:01:36,560 --> 00:01:38,520
Speaker 1: to figure out how it all works. Because it's a

31
00:01:38,600 --> 00:01:43,520
Speaker 1: pretty wonderful universe that's pretty amazing to discover and to appreciate.

32
00:01:43,800 --> 00:01:47,240
Speaker 2: That's right, from the tiniest little particles to big baseballs

33
00:01:47,240 --> 00:01:50,280
Speaker 2: and enormous black holes. There's lots of mysteries out there,

34
00:01:50,440 --> 00:01:53,120
Speaker 2: lots of questions to ask, lots of puzzles to solve

35
00:01:53,200 --> 00:01:56,600
Speaker 2: at all different scales. It's not just particle physics that's

36
00:01:56,640 --> 00:01:58,280
Speaker 2: revealing the truth about reality.

37
00:01:58,560 --> 00:02:01,920
Speaker 1: Yeah, they're big puzzles, like what will dogs eat pretty

38
00:02:01,960 --> 00:02:05,200
Speaker 1: much anything? Will they eat dark matter?

39
00:02:06,520 --> 00:02:09,960
Speaker 2: Well, I've seen them eat various dark matters for sure. Y.

40
00:02:10,120 --> 00:02:14,880
Speaker 1: Yeah, I know it's coming in and out both ends.

41
00:02:14,919 --> 00:02:18,880
Speaker 1: That's not good. But yeah, even dogs can be physicists

42
00:02:18,880 --> 00:02:20,680
Speaker 1: if they also are trying to figure out how the

43
00:02:20,760 --> 00:02:24,000
Speaker 1: universe works, how things fall, and what rate do they fall.

44
00:02:24,080 --> 00:02:26,799
Speaker 1: And that's something that even physicists today are looking at

45
00:02:26,840 --> 00:02:28,080
Speaker 1: and are puzzling about.

46
00:02:28,280 --> 00:02:30,000
Speaker 2: That's right, And we're hoping that our dogs will help

47
00:02:30,080 --> 00:02:31,840
Speaker 2: us figure it out and that it won't be too

48
00:02:31,960 --> 00:02:33,000
Speaker 2: rough a journey.

49
00:02:34,520 --> 00:02:37,440
Speaker 1: So welcome to our podcast, Daniel and Jorge Explain the Universe,

50
00:02:37,480 --> 00:02:39,880
Speaker 1: a production of iHeartRadio.

51
00:02:39,320 --> 00:02:42,520
Speaker 2: Where no pun is too corny, no mystery too grand,

52
00:02:42,639 --> 00:02:46,080
Speaker 2: and no puzzle too deep for us to explore. We

53
00:02:46,120 --> 00:02:48,880
Speaker 2: think that everything out there can be understood, and that

54
00:02:49,000 --> 00:02:51,799
Speaker 2: you deserve to understand it. We want to make these

55
00:02:51,840 --> 00:02:54,360
Speaker 2: ideas click together in your mind so you have that

56
00:02:54,639 --> 00:02:57,720
Speaker 2: aham moment when it all makes sense.

57
00:02:58,320 --> 00:03:00,040
Speaker 1: It's right because we are here to dis because the

58
00:03:00,040 --> 00:03:03,840
Speaker 1: fundamental loss of the universe and also the fundamental laws

59
00:03:03,880 --> 00:03:07,959
Speaker 1: of the universe testing its limits. Are there limits? I

60
00:03:07,960 --> 00:03:09,000
Speaker 1: think we just hit that limit.

61
00:03:09,120 --> 00:03:11,640
Speaker 2: If you compress too many dad jokes into a podcast,

62
00:03:11,880 --> 00:03:13,520
Speaker 2: does it collapse into a black hole?

63
00:03:13,720 --> 00:03:15,840
Speaker 1: Does it become a granddad podcast? Now?

64
00:03:16,400 --> 00:03:18,799
Speaker 2: And there are physics questions about gravity that we ask

65
00:03:18,880 --> 00:03:20,520
Speaker 2: that are not related to punts.

66
00:03:21,080 --> 00:03:24,560
Speaker 1: Yeah. Gravity is one of the biggest mysteries in the universe.

67
00:03:24,600 --> 00:03:28,480
Speaker 1: It basically holds everything together and makes all the stars

68
00:03:28,520 --> 00:03:30,880
Speaker 1: and galaxies out their work. But there are a lot

69
00:03:30,919 --> 00:03:33,360
Speaker 1: of big things about it that we still don't understand.

70
00:03:33,480 --> 00:03:35,840
Speaker 2: It's one of my favorite things in physics where something

71
00:03:36,000 --> 00:03:38,520
Speaker 2: right in front of you is a big mystery. You

72
00:03:38,520 --> 00:03:42,000
Speaker 2: don't need a ten billion dollar particle collider to ask, like, well,

73
00:03:42,040 --> 00:03:44,760
Speaker 2: why do things move? Or why am I sticking to

74
00:03:44,800 --> 00:03:47,120
Speaker 2: the Earth, or why does the Earth go around the Sun?

75
00:03:47,400 --> 00:03:49,520
Speaker 2: You just look at the world around you and ask

76
00:03:49,600 --> 00:03:53,360
Speaker 2: these basic questions. And our understanding of how this very simple,

77
00:03:53,600 --> 00:03:58,760
Speaker 2: everyday experience happens has changed over decades and centuries and millennia.

78
00:03:58,960 --> 00:04:01,320
Speaker 1: Yeah, gravity is I kind of a big deal. It's

79
00:04:01,320 --> 00:04:04,200
Speaker 1: a heavy topic. It's a massive question that physicists have

80
00:04:04,320 --> 00:04:06,520
Speaker 1: about how the universe works. And it's not just in

81
00:04:06,520 --> 00:04:09,360
Speaker 1: front of us. It's all around us, under us, low us,

82
00:04:09,480 --> 00:04:12,120
Speaker 1: behind us, on top of us, but well, hopefully not

83
00:04:12,320 --> 00:04:13,160
Speaker 1: too on top of us.

84
00:04:13,200 --> 00:04:16,599
Speaker 2: If you're listening to this podcast, Deep Deep Underground, then yes,

85
00:04:16,760 --> 00:04:18,880
Speaker 2: it's on top of you. And an important way to

86
00:04:19,000 --> 00:04:22,359
Speaker 2: make progress in these big questions is to look for patterns.

87
00:04:22,640 --> 00:04:25,320
Speaker 2: When Newton noticed that the same laws could be applied

88
00:04:25,360 --> 00:04:28,159
Speaker 2: to the motions of things in the heavens as on Earth,

89
00:04:28,440 --> 00:04:31,360
Speaker 2: he understood that his theory was more general than just

90
00:04:31,360 --> 00:04:34,360
Speaker 2: describing planets, that a single idea encompassed all of it.

91
00:04:34,440 --> 00:04:37,320
Speaker 2: So looking for clues means looking for patterns, finding apparent

92
00:04:37,360 --> 00:04:40,680
Speaker 2: coincidences and digging into them to figure out what the

93
00:04:40,800 --> 00:04:42,359
Speaker 2: underlying mechanism really is.

94
00:04:42,680 --> 00:04:45,560
Speaker 1: Yeah, and sometimes in looking for patterns, physicists notice certain

95
00:04:45,600 --> 00:04:49,120
Speaker 1: things match up in a very suspicious and interesting way,

96
00:04:49,560 --> 00:04:52,240
Speaker 1: and so it makes them wonder is this a coincidence

97
00:04:52,440 --> 00:04:55,919
Speaker 1: or does this reveal something fundamental about the universe?

98
00:04:56,080 --> 00:04:58,000
Speaker 2: Like if you just lost two hundred bucks and then

99
00:04:58,040 --> 00:05:00,160
Speaker 2: your friend is like, hey, I have an extra two

100
00:05:00,200 --> 00:05:02,640
Speaker 2: hundred bucks to spend, you might think that there's an

101
00:05:02,640 --> 00:05:04,479
Speaker 2: explanation that tells the whole story.

102
00:05:04,560 --> 00:05:06,320
Speaker 1: Yeah, obviously you need better friends.

103
00:05:08,360 --> 00:05:10,040
Speaker 2: Obviously, dinner's on your friend tonight.

104
00:05:10,520 --> 00:05:13,080
Speaker 1: Yeah, obviously you're eating scrats with the dog tonight.

105
00:05:14,240 --> 00:05:14,840
Speaker 2: Sounds like it.

106
00:05:15,040 --> 00:05:17,159
Speaker 1: So today on the podcast, we'll be tackling the question

107
00:05:22,240 --> 00:05:26,480
Speaker 1: what's the difference between inertial and gravitational mass.

108
00:05:26,720 --> 00:05:29,680
Speaker 2: It turns out there's a massive conceptual difference, but almost

109
00:05:29,720 --> 00:05:30,880
Speaker 2: no actual difference.

110
00:05:31,279 --> 00:05:32,960
Speaker 1: All right, well, it sounds like it's a detail we're

111
00:05:32,960 --> 00:05:35,119
Speaker 1: going to dig into here today. I guess the idea

112
00:05:35,120 --> 00:05:37,240
Speaker 1: is that there are different kinds of masses in physics.

113
00:05:37,400 --> 00:05:39,640
Speaker 2: There are different kinds of masses in physics, and that

114
00:05:39,680 --> 00:05:42,479
Speaker 2: comes from just having different kinds of experience. You know,

115
00:05:42,520 --> 00:05:45,159
Speaker 2: we live in the world, we describe what we see,

116
00:05:45,200 --> 00:05:47,320
Speaker 2: and the job of physics is to boil down all

117
00:05:47,360 --> 00:05:51,160
Speaker 2: of those experiences into as few concepts as possible, to say,

118
00:05:51,200 --> 00:05:55,040
Speaker 2: can we explain static electricity and lightning with one idea?

119
00:05:55,240 --> 00:05:58,160
Speaker 2: If possible, then that'd be a great success. And so

120
00:05:58,200 --> 00:06:01,159
Speaker 2: we have lots of different experiences of masks and the

121
00:06:01,160 --> 00:06:03,600
Speaker 2: goals to try to like boil it down into just

122
00:06:03,640 --> 00:06:07,760
Speaker 2: one explanation, a holistic view that explains the entire universe.

123
00:06:08,640 --> 00:06:10,800
Speaker 1: I wonder, is it kind of like having a separate

124
00:06:10,839 --> 00:06:13,039
Speaker 1: space in your stomach for dessert, Like, is some of

125
00:06:13,080 --> 00:06:15,200
Speaker 1: my mass due to dessert and some of it is

126
00:06:15,279 --> 00:06:16,320
Speaker 1: due to regular food.

127
00:06:17,240 --> 00:06:20,359
Speaker 2: Some of my mass is definitely due to dessert, for sure,

128
00:06:23,200 --> 00:06:25,520
Speaker 2: and there's always room for dessert. I'm not sure if

129
00:06:25,520 --> 00:06:28,080
Speaker 2: that's black hole creation in my stomach or what.

130
00:06:28,600 --> 00:06:30,600
Speaker 1: And if you throw white chocolate into a black hole,

131
00:06:30,640 --> 00:06:32,160
Speaker 1: what happens? Does it explode?

132
00:06:32,240 --> 00:06:34,520
Speaker 2: The black hole does something magical? It turns the white

133
00:06:34,600 --> 00:06:39,000
Speaker 2: chocolate dark, not into dark chocolate, unfortunately, but it just turns

134
00:06:39,000 --> 00:06:40,080
Speaker 2: it into more black hole.

135
00:06:41,160 --> 00:06:42,719
Speaker 1: That's how we're going to say that black hole spits

136
00:06:42,720 --> 00:06:44,360
Speaker 1: out the white chocolate because it's so terrible.

137
00:06:46,120 --> 00:06:48,200
Speaker 2: The only thing that can survive a black hole is

138
00:06:48,200 --> 00:06:50,000
Speaker 2: a white chocolate. No, I wish that were true. That

139
00:06:50,000 --> 00:06:51,039
Speaker 2: would be fascinating.

140
00:06:51,920 --> 00:06:53,440
Speaker 1: And then I thought you were going to say, the

141
00:06:53,480 --> 00:06:55,880
Speaker 1: only thing that can survive a white chocolate is a

142
00:06:55,920 --> 00:06:56,400
Speaker 1: black hole.

143
00:06:56,720 --> 00:06:58,640
Speaker 2: No, it'd be interesting if you threw a white chocolate

144
00:06:58,640 --> 00:07:01,960
Speaker 2: into a black hole and somehow it's quantum information was preserved,

145
00:07:02,000 --> 00:07:03,880
Speaker 2: so you could come along and tell if a black

146
00:07:03,880 --> 00:07:06,599
Speaker 2: hole had had white chocolate thrown into it or not,

147
00:07:06,680 --> 00:07:09,560
Speaker 2: if it had been tainted by the disaster that is

148
00:07:09,560 --> 00:07:10,239
Speaker 2: white chocolate.

149
00:07:10,560 --> 00:07:12,119
Speaker 1: I see, you could shame it later.

150
00:07:12,360 --> 00:07:15,560
Speaker 2: Or maybe black holes are like quantum erasers, deleting the

151
00:07:15,600 --> 00:07:18,080
Speaker 2: tragedy that is white chocolate from the universe and doing

152
00:07:18,160 --> 00:07:18,760
Speaker 2: us all a favor.

153
00:07:18,880 --> 00:07:20,600
Speaker 1: Interesting. I think that's what we all need. It's like

154
00:07:20,640 --> 00:07:22,360
Speaker 1: an incognito mode for a diet.

155
00:07:24,520 --> 00:07:26,160
Speaker 2: I can eat this, but the calories don't count.

156
00:07:26,400 --> 00:07:28,760
Speaker 1: Yeah, nobody knows why did.

157
00:07:28,640 --> 00:07:31,440
Speaker 2: You turn that off? Ever, I guess you do need

158
00:07:31,480 --> 00:07:32,520
Speaker 2: some calories.

159
00:07:32,120 --> 00:07:36,000
Speaker 1: To survive, you know, it's a dietary privacy. But anyways,

160
00:07:36,440 --> 00:07:39,440
Speaker 1: we're talking about the difference between inertial and gravitational mass.

161
00:07:39,440 --> 00:07:42,520
Speaker 1: It seems that these are two separate concepts perhaps in physics,

162
00:07:42,560 --> 00:07:44,560
Speaker 1: and the question is are they the same or are

163
00:07:44,600 --> 00:07:47,360
Speaker 1: they different things? So, as usually, we were wondering how

164
00:07:47,400 --> 00:07:49,600
Speaker 1: many people out there had thought about the difference between

165
00:07:49,640 --> 00:07:51,360
Speaker 1: inertial and gravitational mass.

166
00:07:51,440 --> 00:07:54,240
Speaker 2: Thanks very much to our army of volunteers who answers

167
00:07:54,280 --> 00:07:57,480
Speaker 2: these questions for your education and listening pleasure. If you'd

168
00:07:57,520 --> 00:07:59,800
Speaker 2: like to add your voice to the choir, we'd love

169
00:07:59,840 --> 00:08:02,000
Speaker 2: to have you. Just right to us two questions at

170
00:08:02,120 --> 00:08:03,480
Speaker 2: Daniel Andandhorge dot com.

171
00:08:03,520 --> 00:08:05,280
Speaker 1: So think about it for a second. Do you think

172
00:08:05,480 --> 00:08:09,000
Speaker 1: inertial and gravitational mass are the same. Here's what people

173
00:08:09,040 --> 00:08:09,480
Speaker 1: have to say.

174
00:08:09,600 --> 00:08:13,840
Speaker 4: Inertial mass is the mass that the higes gives, and

175
00:08:13,880 --> 00:08:17,200
Speaker 4: I think it's the mass involved in like the force

176
00:08:17,280 --> 00:08:21,480
Speaker 4: to change, like an object's velocity. And then gravitational mass.

177
00:08:22,200 --> 00:08:24,440
Speaker 4: I really never knew how to defer the too.

178
00:08:24,720 --> 00:08:29,840
Speaker 5: Inertial mass is how much an object readsists moving through space,

179
00:08:30,080 --> 00:08:32,560
Speaker 5: how much force it would take to accelerate it, And

180
00:08:32,640 --> 00:08:37,520
Speaker 5: gravitational mass has more to do with in a gravitational field.

181
00:08:37,520 --> 00:08:39,520
Speaker 2: But I believe that they are equivalent.

182
00:08:39,760 --> 00:08:42,560
Speaker 6: Well, I think that inertial mass represents how hard it

183
00:08:42,600 --> 00:08:45,800
Speaker 6: is to change the motion off the given body, and

184
00:08:45,840 --> 00:08:50,160
Speaker 6: that the gravitational mass represents how much the formation I

185
00:08:50,160 --> 00:08:53,320
Speaker 6: think they is based on fabric that samebody calls us.

186
00:08:53,480 --> 00:08:57,560
Speaker 7: I think the difference between inertia and gravitational mass is

187
00:08:58,240 --> 00:09:02,280
Speaker 7: on the inertia is on the between the particles or something.

188
00:09:02,320 --> 00:09:04,000
Speaker 7: I think that started in here. We have no idea

189
00:09:03,960 --> 00:09:06,760
Speaker 7: a book, and like, I think it's like the connecting

190
00:09:06,800 --> 00:09:10,240
Speaker 7: of the quarks and stuff, and that's what creates most mass.

191
00:09:10,280 --> 00:09:13,600
Speaker 7: So most mass is just a bonding energy, so I

192
00:09:13,600 --> 00:09:14,640
Speaker 7: think that's what energies.

193
00:09:15,040 --> 00:09:17,760
Speaker 3: Inertial mass is a measure of how hard it is

194
00:09:17,920 --> 00:09:21,280
Speaker 3: for an object to change its velocity, whether in magnitude

195
00:09:21,360 --> 00:09:25,400
Speaker 3: or direction. As for gravitational mass, it's a measure of

196
00:09:25,600 --> 00:09:28,800
Speaker 3: how much an object distorted the space time around it.

197
00:09:29,120 --> 00:09:32,720
Speaker 3: I know there is a conundrum in classical mechanics around

198
00:09:32,760 --> 00:09:36,439
Speaker 3: the fact that both these values are numerically the same,

199
00:09:37,040 --> 00:09:39,960
Speaker 3: and I believe relativity has an answer for that, but

200
00:09:40,040 --> 00:09:42,760
Speaker 3: I'm not quite sure what it is. So I'm waiting

201
00:09:42,760 --> 00:09:43,600
Speaker 3: for you guys to explain.

202
00:09:43,720 --> 00:09:46,400
Speaker 1: All Right, it's some nice, yeah, pretty deep guesses here.

203
00:09:46,480 --> 00:09:47,839
Speaker 1: I like the one that says you need a whole

204
00:09:47,880 --> 00:09:50,640
Speaker 1: podcast for that done that's the answer.

205
00:09:50,920 --> 00:09:52,480
Speaker 2: Not done yet, we're still doing it.

206
00:09:52,559 --> 00:09:54,199
Speaker 1: Well, you're listening to this, we already finished.

207
00:09:54,200 --> 00:09:54,760
Speaker 2: Oh that's true.

208
00:09:54,840 --> 00:09:56,760
Speaker 1: Yeah, yeah, we're working in the future.

209
00:09:57,000 --> 00:09:59,319
Speaker 2: But yeah, these are great answers. People definitely know about

210
00:09:59,360 --> 00:10:02,840
Speaker 2: these concepts, and some people even have ideas about their relationship.

211
00:10:03,240 --> 00:10:03,440
Speaker 4: Yeah.

212
00:10:03,480 --> 00:10:06,040
Speaker 1: I saw mentions of the Higgs boson here, I saw

213
00:10:06,120 --> 00:10:09,720
Speaker 1: mentions of acceleration and energy. Sounds like this is going

214
00:10:09,760 --> 00:10:12,040
Speaker 1: to be a pretty dense podcast.

215
00:10:13,200 --> 00:10:16,840
Speaker 2: We're going to overcome some massive misunderstandings in people's brains.

216
00:10:17,000 --> 00:10:19,640
Speaker 1: Yeah, it's a pretty heavy topic, so let's dig into it. Daniel,

217
00:10:19,960 --> 00:10:25,160
Speaker 1: what is mass to a physicist? The non religious physicists, the.

218
00:10:25,160 --> 00:10:28,360
Speaker 2: Non denominational idea of mass, I mean, mass to a

219
00:10:28,400 --> 00:10:32,240
Speaker 2: physicist is just like a more mathematical and precise description

220
00:10:32,679 --> 00:10:35,680
Speaker 2: of our experience, right. Physics is not trying to describe

221
00:10:35,679 --> 00:10:38,600
Speaker 2: a universe you don't understand or that isn't familiar to you.

222
00:10:38,880 --> 00:10:42,240
Speaker 2: We're trying to describe our universe, our everyday understanding of

223
00:10:42,280 --> 00:10:44,160
Speaker 2: what it's like to be in the world, and that

224
00:10:44,240 --> 00:10:47,280
Speaker 2: means explaining our intuitive experience, you know, the way that

225
00:10:47,320 --> 00:10:49,640
Speaker 2: we live and we have this feeling that like you

226
00:10:49,679 --> 00:10:51,360
Speaker 2: can pick something up that is hard, and you pick

227
00:10:51,400 --> 00:10:53,680
Speaker 2: something else up and it's easy. Or you push on

228
00:10:53,760 --> 00:10:55,640
Speaker 2: something and it's hard to get it moving, you push

229
00:10:55,679 --> 00:10:58,360
Speaker 2: on something else and it's easier to get it moving,

230
00:10:58,400 --> 00:11:00,679
Speaker 2: and that somehow that that might relate to, like how

231
00:11:00,760 --> 00:11:03,880
Speaker 2: much stuff there is to something. You put another watermelon

232
00:11:03,880 --> 00:11:05,840
Speaker 2: in the shopping cart and it's a little bit harder

233
00:11:05,840 --> 00:11:06,559
Speaker 2: to get it rolling.

234
00:11:06,880 --> 00:11:09,560
Speaker 1: So you're saying, the intuitive definition of mass is just

235
00:11:09,559 --> 00:11:11,440
Speaker 1: how much stuff there is to something.

236
00:11:11,640 --> 00:11:14,960
Speaker 2: Yeah, I think that's the most accessible and intuitive idea

237
00:11:15,320 --> 00:11:18,040
Speaker 2: of what mass is. We think of it like the stuffiness,

238
00:11:18,160 --> 00:11:21,320
Speaker 2: you know, like this has more scoops of basic universe

239
00:11:21,360 --> 00:11:22,679
Speaker 2: stuff than something else.

240
00:11:23,120 --> 00:11:26,240
Speaker 1: Like a rock has more stuff stuffed into it. Then

241
00:11:26,400 --> 00:11:28,120
Speaker 1: let's say an air balloon.

242
00:11:28,320 --> 00:11:30,360
Speaker 2: Yeah, it certainly does. You know, there are more atoms,

243
00:11:30,400 --> 00:11:33,040
Speaker 2: it's denser. If you add up the amount of stuff

244
00:11:33,040 --> 00:11:35,080
Speaker 2: in all those atoms in a rock, then there's more

245
00:11:35,120 --> 00:11:37,640
Speaker 2: in that than in a balloon, for example. Absolutely, the

246
00:11:37,720 --> 00:11:40,400
Speaker 2: job of physics isn't to like rely on these fuzzy

247
00:11:40,440 --> 00:11:44,079
Speaker 2: concepts and just accept our intuitive understanding. It's to make

248
00:11:44,120 --> 00:11:49,199
Speaker 2: a more precise mathematical description of what's actually happening, so

249
00:11:49,280 --> 00:11:51,760
Speaker 2: we can extract from that some understanding of like what

250
00:11:51,800 --> 00:11:53,359
Speaker 2: the rules of the universe.

251
00:11:53,000 --> 00:11:55,400
Speaker 1: Are, right, because I guess there are kind of two

252
00:11:55,480 --> 00:11:57,600
Speaker 1: kinds of mass, right, Like there's a measure of how

253
00:11:57,640 --> 00:12:00,640
Speaker 1: hard something is to push to get a going, and

254
00:12:00,679 --> 00:12:02,920
Speaker 1: then also how hard it is to lift up from

255
00:12:02,920 --> 00:12:03,320
Speaker 1: the ground.

256
00:12:03,400 --> 00:12:06,640
Speaker 2: Exactly, there's two different things you can do to stuff. Right.

257
00:12:06,679 --> 00:12:09,920
Speaker 2: You can push that shopping cart filled with watermelons, and

258
00:12:10,000 --> 00:12:11,680
Speaker 2: you know, if you put more watermelons in it, it

259
00:12:11,720 --> 00:12:14,720
Speaker 2: takes a bigger push. And then there's also like actually

260
00:12:14,760 --> 00:12:18,480
Speaker 2: lifting the shopping card of watermelons over your head, and

261
00:12:18,559 --> 00:12:20,760
Speaker 2: the more watermelons that are in there, the more force

262
00:12:20,840 --> 00:12:24,440
Speaker 2: it takes. And those are actually two separate concepts, right,

263
00:12:24,520 --> 00:12:27,720
Speaker 2: they're related in that more watermelons makes it harder. But

264
00:12:27,760 --> 00:12:30,560
Speaker 2: if you're just pushing the watermelons, then you're not lifting

265
00:12:30,559 --> 00:12:33,480
Speaker 2: them against gravity, right, You're just like speeding them up.

266
00:12:34,080 --> 00:12:36,280
Speaker 2: And that's what we call inertial mass. It's just like

267
00:12:36,640 --> 00:12:39,640
Speaker 2: how hard it is to get something going even in

268
00:12:39,679 --> 00:12:42,199
Speaker 2: outer space. Right, things take a push to get moving

269
00:12:42,240 --> 00:12:43,840
Speaker 2: even when there's no gravity.

270
00:12:43,559 --> 00:12:46,080
Speaker 1: Right, Because the two things don't necessarily have to be

271
00:12:46,200 --> 00:12:50,200
Speaker 1: the same, right, Like, you can't imagine a scenario where maybe,

272
00:12:50,240 --> 00:12:53,520
Speaker 1: for example, there's a rock on Dolli with wheels in it,

273
00:12:53,559 --> 00:12:55,360
Speaker 1: and it takes a certain amount of force to push

274
00:12:55,400 --> 00:12:57,520
Speaker 1: it from side to side, but then it maybe takes

275
00:12:57,760 --> 00:13:00,200
Speaker 1: no force to lift it up, or maybe take it's

276
00:13:00,200 --> 00:13:03,520
Speaker 1: an extra bigger force to lift it up. Right, we

277
00:13:03,559 --> 00:13:05,880
Speaker 1: could live in a universe where those two things are

278
00:13:05,880 --> 00:13:06,679
Speaker 1: not the same.

279
00:13:06,480 --> 00:13:08,560
Speaker 2: Yeah, or even just on a planet. Right, if you

280
00:13:08,559 --> 00:13:11,000
Speaker 2: have a rock on Jupiter, then it takes a large

281
00:13:11,040 --> 00:13:13,840
Speaker 2: force to counteract Jupiter's gravity, But it takes the same

282
00:13:13,840 --> 00:13:15,720
Speaker 2: force to push its side to side on Jupiter as

283
00:13:15,720 --> 00:13:16,440
Speaker 2: it does on Earth.

284
00:13:16,480 --> 00:13:18,760
Speaker 1: All right, So then the two things are different, and

285
00:13:19,240 --> 00:13:21,320
Speaker 1: so let's dig into it a little bit more. Talk

286
00:13:21,360 --> 00:13:22,320
Speaker 1: about inertial mass.

287
00:13:22,360 --> 00:13:25,080
Speaker 2: So inertial mass is just this sense that it takes

288
00:13:25,120 --> 00:13:27,360
Speaker 2: a force to get something going. And this is basic

289
00:13:27,520 --> 00:13:30,480
Speaker 2: Newtonian mechanics. Things tend to stay at the same velocity

290
00:13:30,520 --> 00:13:32,720
Speaker 2: unless you give them a push. That push is a force,

291
00:13:33,120 --> 00:13:35,960
Speaker 2: and so this is just f equals MAA. Right, you

292
00:13:36,000 --> 00:13:37,880
Speaker 2: want something to speed up, you got to push on it,

293
00:13:37,920 --> 00:13:39,680
Speaker 2: and the amount of speed up you get for that

294
00:13:39,760 --> 00:13:42,720
Speaker 2: push depends on the thing's mass. So if it has

295
00:13:42,760 --> 00:13:45,559
Speaker 2: a small mass, like if m is very very small,

296
00:13:45,960 --> 00:13:47,320
Speaker 2: and you give it a big push, you get a

297
00:13:47,320 --> 00:13:50,120
Speaker 2: big acceleration. But if it has a large mass, like

298
00:13:50,160 --> 00:13:52,520
Speaker 2: the Earth or something, and you give it a push,

299
00:13:52,600 --> 00:13:55,360
Speaker 2: then it gets a very small acceleration. F equals MA

300
00:13:55,640 --> 00:13:58,160
Speaker 2: tells you that the larger the mass, the larger the

301
00:13:58,160 --> 00:14:00,760
Speaker 2: force you need to accelerate something to speed it.

302
00:14:00,760 --> 00:14:03,439
Speaker 1: Up, right, And so in this case, mass is the ratio.

303
00:14:03,920 --> 00:14:06,440
Speaker 1: Like what happens You've divide the force you need to

304
00:14:06,520 --> 00:14:09,439
Speaker 1: push on something to get it to a certain acceleration, right.

305
00:14:09,320 --> 00:14:12,200
Speaker 2: Exactly, And this is a very familiar experience, right. Think

306
00:14:12,200 --> 00:14:15,000
Speaker 2: about like firing a rifle. When you fire a rifle,

307
00:14:15,120 --> 00:14:17,000
Speaker 2: it's pushing on the bullet to make it go fast,

308
00:14:17,080 --> 00:14:19,520
Speaker 2: But the bullet is also pushing on the rifle. Why

309
00:14:19,560 --> 00:14:22,600
Speaker 2: doesn't the rifle zoom the other way just as fast

310
00:14:22,600 --> 00:14:25,080
Speaker 2: as the bullet. Well, because the rifle has more mass

311
00:14:25,120 --> 00:14:27,000
Speaker 2: than the bullet. They have the same force applying on

312
00:14:27,040 --> 00:14:29,000
Speaker 2: both of them, but the bullet is less mass, so

313
00:14:29,000 --> 00:14:30,280
Speaker 2: it gets more acceleration.

314
00:14:31,080 --> 00:14:33,680
Speaker 1: Or maybe think about it as like an asteroid in

315
00:14:33,720 --> 00:14:37,440
Speaker 1: space that's not in a planet or anything. The more

316
00:14:37,480 --> 00:14:40,320
Speaker 1: massive the asteroid is, the harder it is to get

317
00:14:40,320 --> 00:14:42,840
Speaker 1: it moving, that's inertial mass.

318
00:14:43,000 --> 00:14:46,080
Speaker 2: That's inertial mass exactly. So things that have this property

319
00:14:46,120 --> 00:14:49,080
Speaker 2: we call it inertial mass, are harder to get moving,

320
00:14:49,120 --> 00:14:51,200
Speaker 2: They're harder to speed up and harder to slow down.

321
00:14:51,240 --> 00:14:54,120
Speaker 2: They have inertia. That's sort of what we mean by inertia,

322
00:14:54,160 --> 00:14:55,520
Speaker 2: that we have inertial mass.

323
00:14:55,600 --> 00:14:57,920
Speaker 1: All right, Now talk about gravitational mass.

324
00:14:58,040 --> 00:15:02,080
Speaker 2: So gravitational mass is what control how much gravitational force

325
00:15:02,160 --> 00:15:04,960
Speaker 2: is applied on you. And Newton also has a formula

326
00:15:05,000 --> 00:15:08,400
Speaker 2: for this. It's gmm over R squared. We have two

327
00:15:08,440 --> 00:15:10,800
Speaker 2: masses there because two things are pulling on each other,

328
00:15:11,360 --> 00:15:14,640
Speaker 2: and more mass means more gravity. Like if you added

329
00:15:14,680 --> 00:15:16,840
Speaker 2: mass to the Earth without changing its radius, if you

330
00:15:16,840 --> 00:15:19,160
Speaker 2: made it more dense so got more massive, then it

331
00:15:19,200 --> 00:15:21,400
Speaker 2: would be pulling on you harder. And so that's the

332
00:15:21,440 --> 00:15:24,560
Speaker 2: gravitational mass. It's the mass that goes into the gravitational

333
00:15:24,600 --> 00:15:25,360
Speaker 2: force formula.

334
00:15:25,440 --> 00:15:28,000
Speaker 1: All right. Guess going back to our asteroid in space scenario,

335
00:15:28,080 --> 00:15:30,600
Speaker 1: Like if you have an asteroid in space and it's

336
00:15:30,680 --> 00:15:33,280
Speaker 1: close to a big planet, the big planet is going

337
00:15:33,320 --> 00:15:36,520
Speaker 1: to pull the asteroid towards the planet, and so the

338
00:15:36,560 --> 00:15:38,720
Speaker 1: mass of the asteroid is maybe a measure of our

339
00:15:38,760 --> 00:15:40,840
Speaker 1: heart would it be to keep the asteroid from being

340
00:15:40,880 --> 00:15:43,600
Speaker 1: pulled towards the planet? Like, if you're trying to prevent

341
00:15:43,600 --> 00:15:46,440
Speaker 1: the asteroid from falling into the planet, how hard would

342
00:15:46,440 --> 00:15:50,800
Speaker 1: it be? Depends that's gravitational mass exactly. More gravitational mass

343
00:15:50,840 --> 00:15:53,920
Speaker 1: means more gravity. Imagine you're zooming next to two.

344
00:15:53,840 --> 00:15:55,840
Speaker 2: Planets and one of them has more mass than the other,

345
00:15:55,920 --> 00:15:58,800
Speaker 2: then you're going to feel it's gravity more strongly. Right,

346
00:15:58,840 --> 00:16:01,520
Speaker 2: And this is a Newtonian picture of gravity, or gravity

347
00:16:01,640 --> 00:16:03,360
Speaker 2: is a force and you can think about it sort

348
00:16:03,360 --> 00:16:07,320
Speaker 2: of like the gravitational mass is like the charge for gravity.

349
00:16:07,360 --> 00:16:10,080
Speaker 2: Two electrons will push on each other because they both

350
00:16:10,080 --> 00:16:13,840
Speaker 2: have negative charge, and if you increase that charge, then

351
00:16:13,840 --> 00:16:16,920
Speaker 2: their force would be stronger. Well, the force law for

352
00:16:17,040 --> 00:16:19,640
Speaker 2: gravity is exactly the same structure as a force law

353
00:16:19,640 --> 00:16:22,800
Speaker 2: for electromagnetism. Where you replace the charges with the masses.

354
00:16:23,040 --> 00:16:25,160
Speaker 2: You increase the mass, you get more gravity.

355
00:16:25,520 --> 00:16:29,320
Speaker 1: Right, Like a lightweight asteroid, you wouldn't a small lightweight asteroid,

356
00:16:29,320 --> 00:16:31,400
Speaker 1: you wouldn't need to push very hard to keep it

357
00:16:31,400 --> 00:16:34,600
Speaker 1: from falling into the planet. With a huge massive asteroid,

358
00:16:34,640 --> 00:16:36,480
Speaker 1: you need to be superman basically to keep it from

359
00:16:36,600 --> 00:16:39,120
Speaker 1: smashing into the planet. All right, Well, that's the basics

360
00:16:39,120 --> 00:16:42,920
Speaker 1: of Newtonian inertial and gravitational mass. Now let's get into

361
00:16:43,320 --> 00:16:45,200
Speaker 1: where it gets kind of tricky, and are these things

362
00:16:45,200 --> 00:16:48,360
Speaker 1: the same or are they different? According to Einstein, So

363
00:16:48,480 --> 00:16:50,760
Speaker 1: let's dig into those details. But first let's take a

364
00:16:50,800 --> 00:17:06,400
Speaker 1: quick break. All right, we're asking a massive question here today.

365
00:17:07,119 --> 00:17:10,240
Speaker 1: What's the difference between inertial and gravitational mass. Are they

366
00:17:10,240 --> 00:17:12,480
Speaker 1: the same? Are they different? Are they just two sides

367
00:17:12,520 --> 00:17:14,920
Speaker 1: of the same coin? Are there two coins? How many

368
00:17:14,960 --> 00:17:16,160
Speaker 1: coins are there in the universe?

369
00:17:17,359 --> 00:17:20,360
Speaker 2: An infinite number of coins, with an infinite number of sides,

370
00:17:20,640 --> 00:17:25,639
Speaker 2: with infinite mass. Maybe it's made out of photons. Who knows.

371
00:17:25,840 --> 00:17:28,520
Speaker 1: There we go, That would explain why money's so light

372
00:17:28,560 --> 00:17:30,960
Speaker 1: in my pockets. All right, so we talked about kind

373
00:17:30,960 --> 00:17:33,400
Speaker 1: of the basics of inertial and gravitational mass. I guess

374
00:17:33,440 --> 00:17:36,119
Speaker 1: from a Newtonian perspective, so like a couple of hundred

375
00:17:36,160 --> 00:17:38,600
Speaker 1: years ago that this is when you'dn figured out, is

376
00:17:38,600 --> 00:17:41,320
Speaker 1: that you have something called inertial mass and you have

377
00:17:41,359 --> 00:17:44,480
Speaker 1: something called gravitational mass. And he basically measured them to

378
00:17:44,520 --> 00:17:46,800
Speaker 1: be the same thing, right, or he thought they were

379
00:17:46,840 --> 00:17:47,320
Speaker 1: the same thing.

380
00:17:47,440 --> 00:17:50,000
Speaker 2: He actually sort of treated them as different things, right.

381
00:17:50,359 --> 00:17:52,880
Speaker 2: He wrote them down as if they were different numbers.

382
00:17:52,920 --> 00:17:55,200
Speaker 2: Like he wrote two different formulas, and the masses in

383
00:17:55,240 --> 00:17:58,680
Speaker 2: those two formulas didn't have to agree. Like in principle

384
00:17:58,760 --> 00:18:02,199
Speaker 2: in Newtonian physics, mass in f egals ma could be

385
00:18:02,280 --> 00:18:06,159
Speaker 2: different from mass in the gravitational force formula. So he

386
00:18:06,280 --> 00:18:08,280
Speaker 2: allowed for the possibility that these were different.

387
00:18:08,440 --> 00:18:10,399
Speaker 1: Wait, what do you mean. He didn't call them mass,

388
00:18:10,440 --> 00:18:12,000
Speaker 1: he didn't call them m.

389
00:18:11,800 --> 00:18:14,320
Speaker 2: Well, and Newton actually didn't write his equations down in

390
00:18:14,440 --> 00:18:17,200
Speaker 2: terms of mathematics. Back then, the style was more pros

391
00:18:17,480 --> 00:18:19,520
Speaker 2: so a lot of newton stuff is actually written out

392
00:18:19,600 --> 00:18:22,520
Speaker 2: in sentences, so the exact notation can be a little different.

393
00:18:22,800 --> 00:18:27,080
Speaker 2: But in our modern translation of Newton's formulas, technically there's

394
00:18:27,119 --> 00:18:29,280
Speaker 2: a little I in front of the inertial mass and

395
00:18:29,320 --> 00:18:31,960
Speaker 2: a little G subscript in front of the gravitational mass,

396
00:18:31,960 --> 00:18:34,399
Speaker 2: and they don't necessarily have to be the same. In

397
00:18:34,440 --> 00:18:37,000
Speaker 2: Newtonian physics, you have to go out and measure whether

398
00:18:37,040 --> 00:18:38,160
Speaker 2: these things are the same.

399
00:18:39,200 --> 00:18:41,280
Speaker 1: But did he do it? Did Newton measure it to

400
00:18:41,320 --> 00:18:43,080
Speaker 1: be the same or did he measure it to be different?

401
00:18:43,119 --> 00:18:45,240
Speaker 2: So Newton measured it using a pendulum, and lots of

402
00:18:45,320 --> 00:18:48,040
Speaker 2: other people have done these measurements and we find that

403
00:18:48,080 --> 00:18:50,400
Speaker 2: they are the same. And it's sort of a famous

404
00:18:50,480 --> 00:18:52,919
Speaker 2: result that people learn about, you know, in elementary school,

405
00:18:53,440 --> 00:18:56,000
Speaker 2: that two things, even if they have different mass, fall

406
00:18:56,160 --> 00:18:59,399
Speaker 2: at the same speed. That's basically testing whether inertial and

407
00:18:59,400 --> 00:19:02,760
Speaker 2: gravitational mass are the same thing. Something that has more

408
00:19:02,800 --> 00:19:05,920
Speaker 2: mass takes a bigger force to get going, but if

409
00:19:05,920 --> 00:19:08,919
Speaker 2: it has more gravitational mass also, then it gets a

410
00:19:08,920 --> 00:19:11,680
Speaker 2: bigger force from the Earth. And so something that's low

411
00:19:11,720 --> 00:19:14,240
Speaker 2: mass and something that's high mass will get accelerated the

412
00:19:14,280 --> 00:19:16,639
Speaker 2: same way by the Earth. The Earth is pulling harder

413
00:19:16,680 --> 00:19:18,959
Speaker 2: on the one with more mass, which takes more effort

414
00:19:19,000 --> 00:19:21,800
Speaker 2: to get it going. So the two things perfectly balance out.

415
00:19:22,440 --> 00:19:24,440
Speaker 1: I guess we're just lucky. Newton didn't have a dog

416
00:19:25,280 --> 00:19:28,159
Speaker 1: when he ran his experiments, so it even ran this

417
00:19:28,240 --> 00:19:30,240
Speaker 1: experiment and he measured it to be the same Did

418
00:19:30,240 --> 00:19:32,320
Speaker 1: he then conclude that it was the same thing? Did

419
00:19:32,359 --> 00:19:33,760
Speaker 1: he then start calling it the same thing?

420
00:19:33,840 --> 00:19:36,199
Speaker 2: Newton's experiment was not super precise, so this is one

421
00:19:36,280 --> 00:19:39,560
Speaker 2: hundreds of years ago, and the technology for timing things

422
00:19:39,600 --> 00:19:42,640
Speaker 2: and measuring things precisely was much fuzzier. So he concluded

423
00:19:42,680 --> 00:19:44,639
Speaker 2: these things were likely the same, but he had no

424
00:19:44,800 --> 00:19:47,800
Speaker 2: proof theoretically that showed that they had to be the same,

425
00:19:48,320 --> 00:19:50,560
Speaker 2: and he only had an experimental measurement which was kind

426
00:19:50,600 --> 00:19:53,639
Speaker 2: of fuzzy. And so people continued on measuring these things,

427
00:19:53,680 --> 00:19:56,199
Speaker 2: and they've been measuring it basically ever since. People are

428
00:19:56,200 --> 00:19:58,400
Speaker 2: basically still measuring this to see if they can find

429
00:19:58,440 --> 00:19:59,400
Speaker 2: any discrepancies.

430
00:20:00,000 --> 00:20:02,560
Speaker 1: At some point, I guess in our scientific history, scientists

431
00:20:02,560 --> 00:20:05,080
Speaker 1: sort of kind of concluded they were the same, didn't they.

432
00:20:05,480 --> 00:20:07,760
Speaker 1: I mean, at least when you're in high school, you know,

433
00:20:07,800 --> 00:20:09,679
Speaker 1: they just teach you M. They don't teach you M

434
00:20:09,720 --> 00:20:11,399
Speaker 1: I and MG. They just teach you M.

435
00:20:11,480 --> 00:20:13,320
Speaker 2: There is a sort of simplified version of it in

436
00:20:13,359 --> 00:20:16,600
Speaker 2: high school. But in Newtonian physics, these are potentially different,

437
00:20:16,640 --> 00:20:18,760
Speaker 2: which is why you know, astronauts on the Moon in

438
00:20:18,800 --> 00:20:22,480
Speaker 2: the sixties did this experiment, you know, dropping a feather

439
00:20:22,600 --> 00:20:24,879
Speaker 2: and hammer at the same time, and why in the

440
00:20:25,000 --> 00:20:27,520
Speaker 2: last couple of decades people have made this even more

441
00:20:27,560 --> 00:20:30,880
Speaker 2: precise with high tech torsion balances. The narrow this down

442
00:20:30,920 --> 00:20:33,840
Speaker 2: to the one part in ten to the thirteen. But

443
00:20:33,880 --> 00:20:35,760
Speaker 2: you know, from an experimental point of view that's not

444
00:20:35,840 --> 00:20:38,520
Speaker 2: the same. That just says it's either the same or

445
00:20:38,520 --> 00:20:39,919
Speaker 2: it's very very close together.

446
00:20:40,200 --> 00:20:41,800
Speaker 1: But I guess I mean like sort of in I

447
00:20:41,800 --> 00:20:44,040
Speaker 1: guess in our society and our culture, at least how

448
00:20:44,040 --> 00:20:47,800
Speaker 1: they teach physics in high school, right in college at

449
00:20:47,880 --> 00:20:49,879
Speaker 1: least in my time, people are just sort of assume

450
00:20:49,880 --> 00:20:50,520
Speaker 1: they're the same thing.

451
00:20:50,640 --> 00:20:52,560
Speaker 2: Well, I think there's a simplification there. It's sort of

452
00:20:52,560 --> 00:20:55,680
Speaker 2: like when people tell you of the photon has no mass. Well,

453
00:20:55,720 --> 00:20:59,119
Speaker 2: we're pretty sure the photon has either no mass or

454
00:20:59,280 --> 00:21:02,280
Speaker 2: almost nos some very very small number, but we haven't

455
00:21:02,359 --> 00:21:05,080
Speaker 2: exactly measured it to be zero. We've measured it to

456
00:21:05,080 --> 00:21:07,879
Speaker 2: be close to zero within some tolerance. So it just

457
00:21:07,920 --> 00:21:10,119
Speaker 2: depends on how precise you want to be with your language.

458
00:21:10,359 --> 00:21:13,240
Speaker 2: According to these measurements, they seem like basically the same thing.

459
00:21:13,320 --> 00:21:15,760
Speaker 2: But that's not the same as saying we understand why

460
00:21:15,760 --> 00:21:19,280
Speaker 2: they have to be the same. Theoretically they're linked. It

461
00:21:19,359 --> 00:21:21,040
Speaker 2: might just be a coincidence, all right.

462
00:21:21,080 --> 00:21:24,560
Speaker 1: So then scientists have been sticking to it. They've been

463
00:21:24,640 --> 00:21:27,080
Speaker 1: trying to do this experiment to see if these two

464
00:21:27,119 --> 00:21:29,840
Speaker 1: things are the same. Would have the experiments found.

465
00:21:29,840 --> 00:21:33,960
Speaker 2: The experiments have never found any discrepancy between gravitational mass

466
00:21:34,000 --> 00:21:37,000
Speaker 2: and inertial mass. Galleo did this experiment with like things

467
00:21:37,080 --> 00:21:40,640
Speaker 2: rolling down inclined planes. There's this apocryphal story of him

468
00:21:40,680 --> 00:21:42,879
Speaker 2: dropping things off the leaning tower at Pisa, which I

469
00:21:42,880 --> 00:21:45,399
Speaker 2: don't think ever happened. There really was this test on

470
00:21:45,440 --> 00:21:47,480
Speaker 2: the Moon where they drop a hammer and a feather,

471
00:21:48,000 --> 00:21:50,280
Speaker 2: because you know, this is only truth. There's no air resistance.

472
00:21:50,320 --> 00:21:52,760
Speaker 2: Air resistance makes everything much more complicated. If the only

473
00:21:52,760 --> 00:21:55,320
Speaker 2: force involved is a force of gravity and it just

474
00:21:55,359 --> 00:21:58,000
Speaker 2: has to overcome the inertia, then those things should perfectly

475
00:21:58,040 --> 00:22:00,840
Speaker 2: balance out if the inertial mass and the pavitational mass

476
00:22:00,880 --> 00:22:04,639
Speaker 2: are the same. So nobody's ever found any violation of

477
00:22:04,680 --> 00:22:05,960
Speaker 2: these two things being the same.

478
00:22:06,240 --> 00:22:09,280
Speaker 1: Okay, So then I guess the question is are they

479
00:22:09,520 --> 00:22:12,359
Speaker 1: actually the same or are they just being measured to

480
00:22:12,400 --> 00:22:12,840
Speaker 1: be the same.

481
00:22:12,960 --> 00:22:15,960
Speaker 2: Yeah, Like, is it a coincidence or is it really

482
00:22:16,000 --> 00:22:18,920
Speaker 2: just two ways of looking at the same thing. And

483
00:22:19,000 --> 00:22:21,720
Speaker 2: those are two very different ideas about how the world

484
00:22:21,840 --> 00:22:24,159
Speaker 2: could work. It's sort of like the way the electron

485
00:22:24,280 --> 00:22:27,840
Speaker 2: charge and the proton charge balance each other out. We think, exactly,

486
00:22:28,359 --> 00:22:31,240
Speaker 2: does that mean that there's a fundamental relationship between the two,

487
00:22:31,760 --> 00:22:33,439
Speaker 2: or do we live in a world where these two

488
00:22:33,480 --> 00:22:35,600
Speaker 2: things just happen to balance, and that's why we live

489
00:22:35,600 --> 00:22:37,720
Speaker 2: in this world. Right, Even if your experience of the

490
00:22:37,720 --> 00:22:40,640
Speaker 2: world is the same and doesn't change any experiments, it's

491
00:22:40,680 --> 00:22:43,280
Speaker 2: a very different story about how the world works, about

492
00:22:43,280 --> 00:22:44,679
Speaker 2: which universe we live in.

493
00:22:45,200 --> 00:22:47,040
Speaker 1: Okay, So what do we know about this question?

494
00:22:47,119 --> 00:22:47,199
Speaker 4: So?

495
00:22:47,240 --> 00:22:50,800
Speaker 2: Newton's answer is it's a coincidence. These are two different concepts,

496
00:22:50,800 --> 00:22:53,400
Speaker 2: they appear in two different formulas, we measure them, they

497
00:22:53,400 --> 00:22:55,880
Speaker 2: happen to be equal. End of the story. Newton says,

498
00:22:56,000 --> 00:22:58,320
Speaker 2: there's no reason for these two things to be the same.

499
00:22:58,600 --> 00:23:01,600
Speaker 2: They just happen to be. So. So Newton has two

500
00:23:01,600 --> 00:23:04,640
Speaker 2: parameters and they just happen to be exactly the same value.

501
00:23:04,680 --> 00:23:06,720
Speaker 2: But that seems like too delicious a clue. When we

502
00:23:06,800 --> 00:23:09,560
Speaker 2: find coincidences like that in nature, we're like, hmm, maybe

503
00:23:09,560 --> 00:23:11,879
Speaker 2: there's a simpler version of the story. Maybe we can

504
00:23:11,920 --> 00:23:14,000
Speaker 2: explain these two sides of the coin in terms of

505
00:23:14,200 --> 00:23:17,879
Speaker 2: one coin. And that's where Einstein comes in. Einstein has

506
00:23:17,920 --> 00:23:20,840
Speaker 2: a very different explanation for why things always fall the

507
00:23:20,840 --> 00:23:22,880
Speaker 2: same way, no matter how massive they are.

508
00:23:23,160 --> 00:23:26,800
Speaker 1: Right to Einstein, gravity is not even a force, right that's.

509
00:23:26,720 --> 00:23:29,679
Speaker 2: Right, and that's the basic answer. Einstein says, there is

510
00:23:29,760 --> 00:23:32,800
Speaker 2: no gravitational force. You can never measure gravity. You can't

511
00:23:32,840 --> 00:23:36,280
Speaker 2: feel gravity. The reason things fall is because they're actually

512
00:23:36,320 --> 00:23:39,640
Speaker 2: just moving together to follow the shape of space. Einstein says,

513
00:23:39,680 --> 00:23:41,840
Speaker 2: you're kind of asking the wrong question by saying why

514
00:23:41,880 --> 00:23:44,280
Speaker 2: these two things equal. He says, there's only one thing.

515
00:23:44,440 --> 00:23:47,480
Speaker 2: There is only inertial mass. There's no such thing as

516
00:23:47,480 --> 00:23:50,159
Speaker 2: gravitational mass, because there is no such thing as a

517
00:23:50,160 --> 00:23:51,280
Speaker 2: gravitational force.

518
00:23:51,640 --> 00:23:54,840
Speaker 1: Right. According to Einstein, gravity is like the bending of

519
00:23:54,960 --> 00:23:57,639
Speaker 1: space right, space time. That's what makes something fall to

520
00:23:57,680 --> 00:24:01,360
Speaker 1: the ground or orbit around the planet or the sun.

521
00:24:01,480 --> 00:24:04,440
Speaker 2: That's right. To Einstein, gravity is sort of like an illusion.

522
00:24:04,600 --> 00:24:07,160
Speaker 2: You can never even feel it or sense it directly.

523
00:24:07,480 --> 00:24:10,120
Speaker 2: Let's make sure we unpack that a little bit, because

524
00:24:10,200 --> 00:24:12,679
Speaker 2: there are important ideas in there that we have to

525
00:24:12,760 --> 00:24:16,200
Speaker 2: mentally import to understand what's going to happen next. I mean,

526
00:24:16,240 --> 00:24:19,480
Speaker 2: what does it mean that there's no gravitational force. You

527
00:24:19,520 --> 00:24:22,800
Speaker 2: can't measure gravity. Gravity kind of looks like a force.

528
00:24:22,880 --> 00:24:25,960
Speaker 2: It certainly feels like we can measure it. Right. Gravity

529
00:24:26,000 --> 00:24:29,040
Speaker 2: looks like a force because we can't see the curvature

530
00:24:29,080 --> 00:24:32,040
Speaker 2: of space. We think things should move in straight lines

531
00:24:32,080 --> 00:24:35,040
Speaker 2: because we don't see that space is curved. So when

532
00:24:35,040 --> 00:24:39,160
Speaker 2: we see things move differently than we expect, Newton tells us, oh,

533
00:24:39,200 --> 00:24:41,679
Speaker 2: there's a force there, But if you could see the

534
00:24:41,720 --> 00:24:44,560
Speaker 2: curvature of space, you'd understand that it's just stuff moving

535
00:24:44,600 --> 00:24:47,960
Speaker 2: along those curves. There's no force there. It's actually just

536
00:24:48,160 --> 00:24:50,840
Speaker 2: free fall motion. So when you jump off a building,

537
00:24:50,880 --> 00:24:53,320
Speaker 2: for example, and you fall towards the Earth, you're in

538
00:24:53,400 --> 00:24:56,920
Speaker 2: free fall. There are no forces acting on you. From

539
00:24:57,000 --> 00:24:59,119
Speaker 2: your point of view, the surface of the Earth is

540
00:24:59,160 --> 00:25:02,439
Speaker 2: accelerating to towards you. And if you pulled out a

541
00:25:02,440 --> 00:25:06,119
Speaker 2: gravitometer or an accelerometer like a scale, you would measure

542
00:25:06,280 --> 00:25:09,919
Speaker 2: no acceleration. You're not accelerating. There is no force on

543
00:25:09,960 --> 00:25:13,880
Speaker 2: you at all. F equals ma equals zero. Now standing

544
00:25:13,880 --> 00:25:16,159
Speaker 2: on the surface of the Earth, you do measure acceleration.

545
00:25:16,480 --> 00:25:20,399
Speaker 2: A gravitometer like a scale measures non zero acceleration. But

546
00:25:20,440 --> 00:25:23,160
Speaker 2: that's not the force of gravity on you. That's the

547
00:25:23,200 --> 00:25:27,159
Speaker 2: surface of the Earth accelerating up against the natural free

548
00:25:27,160 --> 00:25:31,600
Speaker 2: fall motion of gravity. All acceleration is against the natural

549
00:25:31,640 --> 00:25:34,760
Speaker 2: motion of gravity. So Newton says that the person on

550
00:25:34,800 --> 00:25:37,919
Speaker 2: the surface is not accelerating and the falling person is

551
00:25:37,960 --> 00:25:41,720
Speaker 2: being accelerated by the force of gravity. But Einstein says

552
00:25:41,800 --> 00:25:44,719
Speaker 2: that the surface of the Earth is accelerating and the

553
00:25:44,760 --> 00:25:48,480
Speaker 2: person falling has no acceleration. You will not sense any

554
00:25:48,560 --> 00:25:51,879
Speaker 2: gravity there because there is no force there for you

555
00:25:51,960 --> 00:25:53,800
Speaker 2: to measure with your accelerometer.

556
00:25:54,000 --> 00:25:56,760
Speaker 1: Right, But I guess you still sort of have the

557
00:25:56,800 --> 00:26:00,400
Speaker 1: concept of mass, right, because some things bend space time

558
00:26:00,480 --> 00:26:03,600
Speaker 1: more than others. Like a feather, doesn't it bend space

559
00:26:03,600 --> 00:26:05,439
Speaker 1: and time a little bit more or less than a

560
00:26:05,480 --> 00:26:06,000
Speaker 1: bowling ball?

561
00:26:06,119 --> 00:26:09,200
Speaker 2: Yes? Absolutely, But that's just the single concept of mass, right.

562
00:26:09,240 --> 00:26:12,280
Speaker 2: That's like the inertial mass of the object. It controls

563
00:26:12,320 --> 00:26:15,320
Speaker 2: how it bends space. But everything moves through bend space

564
00:26:15,440 --> 00:26:18,000
Speaker 2: the same way, regardless of its mass. But that's just

565
00:26:18,080 --> 00:26:19,960
Speaker 2: one concept in general relativity.

566
00:26:20,240 --> 00:26:22,440
Speaker 1: What do you mean it's the same concept. So now

567
00:26:22,560 --> 00:26:25,360
Speaker 1: Einstein said that the idea that they're identical doesn't matter.

568
00:26:25,359 --> 00:26:26,920
Speaker 1: Beca is they're the same thing.

569
00:26:27,040 --> 00:26:29,719
Speaker 2: He says, there essentially is only one idea here, the

570
00:26:29,760 --> 00:26:33,159
Speaker 2: mass of the object, and that controls how it bends space.

571
00:26:33,560 --> 00:26:36,000
Speaker 2: And it's the bending of space that controls essentially how

572
00:26:36,040 --> 00:26:36,960
Speaker 2: these objects move.

573
00:26:37,480 --> 00:26:39,879
Speaker 1: Right, But isn't there like a degree to which something

574
00:26:39,960 --> 00:26:41,560
Speaker 1: bends space more than other things.

575
00:26:41,600 --> 00:26:43,800
Speaker 2: Well, the bending of space actually doesn't come from mass,

576
00:26:43,840 --> 00:26:46,840
Speaker 2: it comes from energy density. Mass doesn't have a unique

577
00:26:46,840 --> 00:26:49,600
Speaker 2: property to bend space. It's really just the energy content

578
00:26:49,640 --> 00:26:52,520
Speaker 2: of something which bends space. And you can bend space

579
00:26:52,560 --> 00:26:55,200
Speaker 2: even if you don't have mass, like a box of photons,

580
00:26:55,240 --> 00:26:56,520
Speaker 2: for example, can bend space.

581
00:26:56,840 --> 00:26:58,879
Speaker 1: Right, right, I mean we've talked about this before in

582
00:26:58,920 --> 00:27:02,040
Speaker 1: the podcast, that there really is no such thing as mass.

583
00:27:02,080 --> 00:27:03,480
Speaker 1: There's really only energy. Right.

584
00:27:03,720 --> 00:27:06,760
Speaker 2: That's a strong philosophical statement. I would say mass makes

585
00:27:06,760 --> 00:27:08,560
Speaker 2: some sense, but in the end, when you look at it,

586
00:27:08,560 --> 00:27:10,760
Speaker 2: it's basically another kind of energy. Yeah.

587
00:27:10,800 --> 00:27:12,359
Speaker 1: Yeah, I mean I'm just going by what we wrote

588
00:27:12,359 --> 00:27:12,879
Speaker 1: in our book.

589
00:27:14,680 --> 00:27:17,280
Speaker 2: I don't think we said that mass doesn't exist. We've

590
00:27:17,280 --> 00:27:19,359
Speaker 2: said that mass is internal stored energy.

591
00:27:19,600 --> 00:27:22,280
Speaker 1: Yeah, so like all mass is energy, is what we said.

592
00:27:23,359 --> 00:27:26,480
Speaker 1: But there is this weird property about energy that if

593
00:27:26,520 --> 00:27:29,879
Speaker 1: you have concentrated energy bound to like a particle or something,

594
00:27:29,920 --> 00:27:32,800
Speaker 1: then that particle is hard to move. Right. That's still

595
00:27:32,840 --> 00:27:34,479
Speaker 1: what you would call inertial mass.

596
00:27:34,760 --> 00:27:38,159
Speaker 2: But now when you say something is easier or harder

597
00:27:38,200 --> 00:27:41,480
Speaker 2: to accelerate, you're adding in other forces to make that

598
00:27:41,560 --> 00:27:44,919
Speaker 2: acceleration happen. If we're just talking about gravity, like the

599
00:27:44,960 --> 00:27:47,680
Speaker 2: experiment of dropping a bowling ball or a feather, there

600
00:27:47,720 --> 00:27:50,359
Speaker 2: is no way to accelerate it because gravity isn't the

601
00:27:50,440 --> 00:27:54,159
Speaker 2: force and doesn't accelerate things. Things just move according to

602
00:27:54,240 --> 00:27:58,720
Speaker 2: the curve of space. Other forces can provide acceleration. In fact,

603
00:27:58,840 --> 00:28:02,040
Speaker 2: they are the only way to accelerate things. So they

604
00:28:02,119 --> 00:28:05,360
Speaker 2: still have this concept of inertial mass that's separate from

605
00:28:05,440 --> 00:28:09,000
Speaker 2: gravity for the other forces. But within gravity, there's just

606
00:28:09,119 --> 00:28:12,640
Speaker 2: one concept of mass, the energy that helps bend space.

607
00:28:13,119 --> 00:28:16,040
Speaker 2: That mass doesn't play a role in how things move

608
00:28:16,160 --> 00:28:19,159
Speaker 2: through that space. So there's not a separate concept of

609
00:28:19,160 --> 00:28:23,520
Speaker 2: inertial and gravitational mass in Einstein's relativity like there is

610
00:28:23,560 --> 00:28:24,840
Speaker 2: in Newtonian gravity.

611
00:28:25,000 --> 00:28:29,320
Speaker 1: Right, But then like more energy then also then bend

612
00:28:29,359 --> 00:28:30,399
Speaker 1: space more around it.

613
00:28:30,560 --> 00:28:33,520
Speaker 2: Yes, that's right, more energy density, bend space more around it.

614
00:28:33,600 --> 00:28:36,160
Speaker 1: So what do you mean by Einstein said that it's

615
00:28:36,200 --> 00:28:38,160
Speaker 1: all the same thing? Like it can all be explained

616
00:28:38,200 --> 00:28:40,000
Speaker 1: by just the concentration of energy.

617
00:28:40,200 --> 00:28:43,440
Speaker 2: In general relativity, these all flow from the same fundamental equations.

618
00:28:43,600 --> 00:28:46,760
Speaker 2: Newton has two equations that are totally separate totally distinct,

619
00:28:47,040 --> 00:28:50,560
Speaker 2: completely different descriptions. F equals ma a is one equation.

620
00:28:50,960 --> 00:28:53,080
Speaker 2: F equals gmm over r squares the other. He has

621
00:28:53,120 --> 00:28:55,160
Speaker 2: his law of inertia, and he has his law of gravity.

622
00:28:55,440 --> 00:28:58,280
Speaker 2: For Einstein, these things all just flow from the concentration

623
00:28:58,360 --> 00:29:02,240
Speaker 2: of energy density energy city bend space, and objects move

624
00:29:02,320 --> 00:29:04,880
Speaker 2: through that bend space. But these things just all flow

625
00:29:04,880 --> 00:29:07,440
Speaker 2: from the same set of equations. There's just one equation there.

626
00:29:07,440 --> 00:29:10,240
Speaker 2: There's no room to like put in another equation with

627
00:29:10,280 --> 00:29:13,480
Speaker 2: a separate value from mass. The separate equations are the

628
00:29:13,560 --> 00:29:18,120
Speaker 2: other forces. Electromagnetism can accelerate objects, and that's a concept

629
00:29:18,200 --> 00:29:22,440
Speaker 2: totally separate from gravity. It requires a concept of inertial mass.

630
00:29:22,760 --> 00:29:25,240
Speaker 2: So if you involve the other forces, there are still

631
00:29:25,320 --> 00:29:28,400
Speaker 2: two parameters there, but now there's only one for gravity

632
00:29:28,440 --> 00:29:29,320
Speaker 2: thanks to Einstein.

633
00:29:29,480 --> 00:29:31,880
Speaker 1: But I wonder if there's like a knob there, you know,

634
00:29:32,080 --> 00:29:35,000
Speaker 1: like let's say I have I don't know, ten kilo

635
00:29:35,120 --> 00:29:38,520
Speaker 1: jewels concentrated in a the size of a lemon. Now

636
00:29:39,080 --> 00:29:41,480
Speaker 1: that amount of energy concentrated in one spot, it's going

637
00:29:41,520 --> 00:29:43,360
Speaker 1: to be a little bit hard to move. That's inertial

638
00:29:43,400 --> 00:29:46,400
Speaker 1: mass of the lemon. But then also that lemon is

639
00:29:46,440 --> 00:29:49,760
Speaker 1: bending space time around it to a certain degree, wouldn't

640
00:29:49,800 --> 00:29:52,320
Speaker 1: I call that gravitational mass, Like you can imagine ten

641
00:29:52,400 --> 00:29:55,440
Speaker 1: kilo jewels of energy bending space a lot in one

642
00:29:55,520 --> 00:29:59,000
Speaker 1: universe and bending space not much at all in another universe.

643
00:29:59,080 --> 00:30:02,560
Speaker 2: So the lemon nd space and causes curvature. But from

644
00:30:02,560 --> 00:30:04,800
Speaker 2: a gravitational point of view, it has no meaning to

645
00:30:04,840 --> 00:30:08,320
Speaker 2: say it's hard to accelerate the lemon, because gravity doesn't

646
00:30:08,320 --> 00:30:11,280
Speaker 2: accelerate things. The lemon and a pebble and a bowling

647
00:30:11,320 --> 00:30:15,160
Speaker 2: ball all moved through that curved space the same way gravitationally.

648
00:30:15,600 --> 00:30:18,520
Speaker 2: If you bring in other forces like rockets, then you've

649
00:30:18,560 --> 00:30:23,400
Speaker 2: reintroduced inertial mass, but not gravitationally. There is another nub there.

650
00:30:23,520 --> 00:30:26,880
Speaker 2: That's the gravitational constant, right, which appears in Newton's formula

651
00:30:26,920 --> 00:30:31,680
Speaker 2: but also appears in general relativity. But that affects everything, right,

652
00:30:31,760 --> 00:30:34,600
Speaker 2: That affects how much mass is going to bend space.

653
00:30:34,760 --> 00:30:36,600
Speaker 2: So you crank G up and then the same amount

654
00:30:36,640 --> 00:30:39,560
Speaker 2: of mass is going to bend space more right, But

655
00:30:39,640 --> 00:30:43,200
Speaker 2: that's simultaneously automatically also going to change how things move,

656
00:30:43,280 --> 00:30:47,280
Speaker 2: because things move just following the curvature of space. So

657
00:30:47,320 --> 00:30:49,720
Speaker 2: That's the beautiful thing about GRS that it tells you

658
00:30:50,080 --> 00:30:52,640
Speaker 2: that the way things move through space doesn't depend on

659
00:30:52,800 --> 00:30:55,920
Speaker 2: their mass. It only depends on the geometry of space.

660
00:30:55,960 --> 00:30:59,360
Speaker 2: It's purely geometric. So the reason, for example, that the

661
00:30:59,400 --> 00:31:02,080
Speaker 2: feather and the hammer fall at the same rate is

662
00:31:02,120 --> 00:31:04,440
Speaker 2: because they are both just following the curvature of space,

663
00:31:04,480 --> 00:31:07,360
Speaker 2: regardless of what their mass is. So if you crank

664
00:31:07,440 --> 00:31:10,080
Speaker 2: up g you get more curvature and that changes how

665
00:31:10,080 --> 00:31:11,040
Speaker 2: everything moves.

666
00:31:11,320 --> 00:31:14,320
Speaker 1: Right, But the bowling bustle has more inertial mass, right,

667
00:31:14,600 --> 00:31:16,920
Speaker 1: So why does it move at the same rate as

668
00:31:16,920 --> 00:31:17,560
Speaker 1: a feather.

669
00:31:17,440 --> 00:31:20,640
Speaker 2: Because motion through space doesn't depend on your mass.

670
00:31:21,040 --> 00:31:21,160
Speaker 3: Right.

671
00:31:21,200 --> 00:31:22,920
Speaker 2: You have to get rid of this idea of inertial

672
00:31:22,960 --> 00:31:25,320
Speaker 2: mass affecting how you're going to move. What affects how

673
00:31:25,320 --> 00:31:28,000
Speaker 2: you move is just the curvature of space, just the

674
00:31:28,080 --> 00:31:30,880
Speaker 2: geometry of space time. The way to look at it

675
00:31:30,920 --> 00:31:33,360
Speaker 2: is not that both the bowling ball and the feather

676
00:31:33,440 --> 00:31:37,080
Speaker 2: are being accelerated the same amount. That's Newtonian and requires

677
00:31:37,120 --> 00:31:41,280
Speaker 2: gravitational forces balanced by inertia. The way to look at

678
00:31:41,360 --> 00:31:43,280
Speaker 2: it is that the bowling ball and feather move the

679
00:31:43,360 --> 00:31:47,520
Speaker 2: same way through space time. Neither of them is accelerating.

680
00:31:47,560 --> 00:31:51,280
Speaker 2: They're both in free fall. What's accelerating is the surface

681
00:31:51,280 --> 00:31:53,960
Speaker 2: of the Earth rushing up to them, so of course

682
00:31:53,960 --> 00:31:55,480
Speaker 2: it reaches them at the same time.

683
00:31:55,760 --> 00:31:57,719
Speaker 1: Well, maybe it would help to understand a little bit

684
00:31:57,760 --> 00:32:01,200
Speaker 1: more how gravity causes things to move and this idea

685
00:32:01,200 --> 00:32:03,560
Speaker 1: of pseudo forces. So what do you mean, Like gravity

686
00:32:03,600 --> 00:32:04,320
Speaker 1: is a pseudo force.

687
00:32:04,440 --> 00:32:07,920
Speaker 2: So electromagnetism is a real force. It like accelerates stuff, right,

688
00:32:07,960 --> 00:32:10,239
Speaker 2: It pushes and it pulls. That's what we mean by

689
00:32:10,280 --> 00:32:13,240
Speaker 2: a force. But a pseudo force is when something appears

690
00:32:13,280 --> 00:32:16,400
Speaker 2: to move without a force being applied to it, right,

691
00:32:16,440 --> 00:32:18,600
Speaker 2: And this is not unfamiliar to you. Like if you're

692
00:32:18,600 --> 00:32:20,600
Speaker 2: in the back of a truck and there's a bowling

693
00:32:20,600 --> 00:32:23,280
Speaker 2: ball there and somebody hits the gas, Then to you

694
00:32:23,360 --> 00:32:25,160
Speaker 2: in your frame of the back of the truck, the

695
00:32:25,160 --> 00:32:27,280
Speaker 2: bowling ball is going to move. They hit the gas,

696
00:32:27,280 --> 00:32:28,520
Speaker 2: the bowling ball is going to move to the back

697
00:32:28,560 --> 00:32:30,200
Speaker 2: of the truck. They hit the brakes, the bowling ball

698
00:32:30,240 --> 00:32:31,520
Speaker 2: is going to move to the front of the truck.

699
00:32:31,640 --> 00:32:34,800
Speaker 2: So you're seeing, like this ball move even though nobody's

700
00:32:34,840 --> 00:32:37,480
Speaker 2: pushing on it, right, nobody's pulling on it, nobody's applying

701
00:32:37,480 --> 00:32:39,800
Speaker 2: any force to it, but you're seeing the ball accelerate,

702
00:32:40,200 --> 00:32:43,680
Speaker 2: so there's a pseudo force there. Something is happening to

703
00:32:43,720 --> 00:32:46,200
Speaker 2: accelerate this thing even though there's no forces on it.

704
00:32:46,640 --> 00:32:48,920
Speaker 2: And in the same way, for example, if you're out

705
00:32:48,920 --> 00:32:50,600
Speaker 2: in space and you're in a rocket ship and your

706
00:32:50,640 --> 00:32:54,320
Speaker 2: rocket ship is accelerating and you drop a ball, then

707
00:32:54,360 --> 00:32:56,200
Speaker 2: that ball is going to fall to the floor. How

708
00:32:56,240 --> 00:32:58,360
Speaker 2: you can get the appearance of gravity on a spaceship

709
00:32:58,400 --> 00:33:02,400
Speaker 2: if you're accelerating, So that's a pseudo force, right. Basically, acceleration,

710
00:33:02,560 --> 00:33:05,840
Speaker 2: any accelerating frame gives you a pseudo force. There's no

711
00:33:05,920 --> 00:33:08,680
Speaker 2: gravity on the spaceship. It's just the floor is accelerating

712
00:33:08,760 --> 00:33:11,480
Speaker 2: up to meet the ball that you've dropped it. All right,

713
00:33:11,560 --> 00:33:13,880
Speaker 2: So that's the concept of a pseudo.

714
00:33:13,560 --> 00:33:16,000
Speaker 1: Force, like in those space movies where they have like

715
00:33:16,040 --> 00:33:19,560
Speaker 1: a rotating spaceship or something, and this interpretive force makes

716
00:33:19,640 --> 00:33:21,720
Speaker 1: it feel like there's gravity around you.

717
00:33:21,960 --> 00:33:23,920
Speaker 2: Exactly, that's right, yeah, but there's.

718
00:33:23,720 --> 00:33:24,920
Speaker 1: No actual gravity happening.

719
00:33:24,920 --> 00:33:28,000
Speaker 2: There's no actual gravity there. It's just acceleration that's creating

720
00:33:28,040 --> 00:33:32,400
Speaker 2: this pseudo force. And so now Einstein says, well, curvature

721
00:33:32,600 --> 00:33:35,240
Speaker 2: of space time, which is invisible to us, we can't see.

722
00:33:35,280 --> 00:33:39,600
Speaker 2: It also causes pseudo forces. Like if you're out in

723
00:33:39,720 --> 00:33:43,360
Speaker 2: space and you drop a ball and somewhere near the Earth,

724
00:33:43,480 --> 00:33:46,840
Speaker 2: it's going to drift towards the Earth, and somebody watching

725
00:33:46,880 --> 00:33:49,440
Speaker 2: you do this experiments from sort of far away is

726
00:33:49,520 --> 00:33:51,600
Speaker 2: going to notice, hmm, there seems to be a force

727
00:33:51,680 --> 00:33:54,120
Speaker 2: on this ball, and that's what Newton would call the

728
00:33:54,120 --> 00:33:57,760
Speaker 2: gravitational force. But Einstein would say, no, there's no actual

729
00:33:57,800 --> 00:34:01,160
Speaker 2: force there. It's moving because of a pseudoforce. It's moving

730
00:34:01,200 --> 00:34:04,440
Speaker 2: because actually just following the curvature of space time. You

731
00:34:04,520 --> 00:34:07,120
Speaker 2: can't see that curvature. It's not obvious to you, but

732
00:34:07,160 --> 00:34:10,080
Speaker 2: the ball is following the curvature of space time, and

733
00:34:10,120 --> 00:34:12,040
Speaker 2: to us it looks like there's a force on it,

734
00:34:12,120 --> 00:34:15,120
Speaker 2: even though there's not. The ball is not actually accelerating.

735
00:34:15,280 --> 00:34:17,480
Speaker 1: So you're saying, like what we think of it as

736
00:34:17,520 --> 00:34:22,000
Speaker 1: gravity is really just pseudo gravity, right, kind of like

737
00:34:22,120 --> 00:34:23,960
Speaker 1: when you have like a black hole and it's bending

738
00:34:23,960 --> 00:34:27,239
Speaker 1: space time around it, it's sort of like causing acceleration

739
00:34:27,520 --> 00:34:29,799
Speaker 1: around it or something. It's bending space time so that

740
00:34:29,800 --> 00:34:32,920
Speaker 1: there's acceleration so that it feels like something is pulling

741
00:34:33,000 --> 00:34:33,359
Speaker 1: us down.

742
00:34:33,440 --> 00:34:36,280
Speaker 2: So yeah, masses definitely bend space time. But the issue

743
00:34:36,280 --> 00:34:39,319
Speaker 2: of acceleration is a little bit subtle. Like if you

744
00:34:39,400 --> 00:34:41,839
Speaker 2: are that ball that's falling towards the Earth, you don't

745
00:34:41,840 --> 00:34:44,160
Speaker 2: feel any acceleration, just like if you jump off of

746
00:34:44,200 --> 00:34:46,799
Speaker 2: a building. Before you hit the ground, you feel like

747
00:34:46,840 --> 00:34:49,640
Speaker 2: you're in free fall. You feel weightless. Right, so you

748
00:34:49,680 --> 00:34:54,239
Speaker 2: never actually experience gravity. You never feel gravity accelerating you.

749
00:34:54,600 --> 00:34:57,399
Speaker 1: Okay, but to somebody standing far away, it does look

750
00:34:57,440 --> 00:34:58,520
Speaker 1: like you're accelerating, right.

751
00:34:58,400 --> 00:35:00,520
Speaker 2: That's right, that's where the pseudo force comes. Then somebody

752
00:35:00,560 --> 00:35:02,600
Speaker 2: else in an inertial frame would say, oh, there's a

753
00:35:02,600 --> 00:35:05,239
Speaker 2: force on you. You're falling down towards the center of the Earth,

754
00:35:05,320 --> 00:35:07,759
Speaker 2: or you're falling in towards that black hole, and you're

755
00:35:07,800 --> 00:35:11,440
Speaker 2: accelerating relative to them. They're seeing that pseudo force. But

756
00:35:11,480 --> 00:35:14,720
Speaker 2: Einstein says, there's no force there. It's just things moving

757
00:35:14,800 --> 00:35:18,000
Speaker 2: according to the curvature of space time. Right.

758
00:35:18,719 --> 00:35:20,760
Speaker 1: All right, Well, let's dig a little bit more into

759
00:35:20,800 --> 00:35:24,200
Speaker 1: this detail and how it compares to inertial force, how

760
00:35:24,320 --> 00:35:27,320
Speaker 1: Einstein may be grappled with the idea of inertial mass,

761
00:35:27,920 --> 00:35:30,839
Speaker 1: and maybe where mass even comes from. So let's dig

762
00:35:30,840 --> 00:35:33,640
Speaker 1: into those details. But first, let's take another quick break.

763
00:35:46,280 --> 00:35:48,600
Speaker 1: All right, we're talking about the difference between inertial and

764
00:35:48,640 --> 00:35:51,840
Speaker 1: gravitational mass, and it's getting a bit hairy, Daniel, I

765
00:35:51,880 --> 00:35:54,640
Speaker 1: feel like, because I feel like we're once again trying

766
00:35:54,640 --> 00:36:00,239
Speaker 1: to explain really difficult general relativity special relativity topics on

767
00:36:00,280 --> 00:36:02,680
Speaker 1: an audio podcast, and so it can be a little

768
00:36:02,680 --> 00:36:05,560
Speaker 1: bit confusing. But it sounds like what you're saying is

769
00:36:05,640 --> 00:36:09,920
Speaker 1: that Einstein sort of puts the whole question kind of

770
00:36:09,960 --> 00:36:12,520
Speaker 1: in the nonsense category, like it doesn't make sense to

771
00:36:12,560 --> 00:36:16,239
Speaker 1: even compare gravitational and inertial mass because to Einstein, there

772
00:36:16,280 --> 00:36:18,880
Speaker 1: is no such thing as gravitational mass.

773
00:36:18,960 --> 00:36:21,759
Speaker 2: Yeah, exactly. And it's sort of beautiful because he still

774
00:36:21,800 --> 00:36:24,680
Speaker 2: does manage to sort of like explain what we see,

775
00:36:25,000 --> 00:36:27,359
Speaker 2: Like we see these interesting things like a big ball

776
00:36:27,400 --> 00:36:29,319
Speaker 2: and a little ball fall at the same rate, and

777
00:36:29,360 --> 00:36:31,399
Speaker 2: he can still explain that and explain it in this

778
00:36:31,800 --> 00:36:35,520
Speaker 2: gorgeous geometrical explanation, and he does so by saying that

779
00:36:35,560 --> 00:36:38,800
Speaker 2: there is no ambiguity between the inertial and gravitational masses.

780
00:36:38,840 --> 00:36:40,240
Speaker 2: There's just one mass.

781
00:36:40,440 --> 00:36:42,560
Speaker 1: Well, Nick, if I can ask a question and maybe

782
00:36:42,640 --> 00:36:47,080
Speaker 1: take us deeper into the black hole, rabbit hole here.

783
00:36:47,160 --> 00:36:49,880
Speaker 1: So we're imagining this scenario where we have a bawling

784
00:36:49,920 --> 00:36:52,640
Speaker 1: ball and a feather, and let's say they're near a

785
00:36:52,640 --> 00:36:55,239
Speaker 1: black hole. Now you're saying that to somebody standing far

786
00:36:55,280 --> 00:36:58,239
Speaker 1: away from this scenario, they're both going to accelerate and

787
00:36:58,320 --> 00:37:01,040
Speaker 1: move towards the black hole at the rate. Because that's

788
00:37:01,040 --> 00:37:02,120
Speaker 1: so gravity works.

789
00:37:01,960 --> 00:37:05,520
Speaker 2: Right, because things move through space time regardless of their mass. Right,

790
00:37:05,560 --> 00:37:08,680
Speaker 2: Your mass does not affect in general relativity how you

791
00:37:08,719 --> 00:37:09,960
Speaker 2: move through space.

792
00:37:09,719 --> 00:37:13,239
Speaker 1: Time, right, right, And even though the feather has less

793
00:37:13,239 --> 00:37:15,960
Speaker 1: inertial mass than the bowling ball, the balling ball will

794
00:37:16,000 --> 00:37:18,080
Speaker 1: we definitely for sure, right, I think it has more

795
00:37:18,120 --> 00:37:18,840
Speaker 1: inertial mass.

796
00:37:18,840 --> 00:37:22,319
Speaker 2: But even just saying the phrase inertial mass implies F

797
00:37:22,360 --> 00:37:25,399
Speaker 2: equals MA. That's the formula that apears in so puts

798
00:37:25,400 --> 00:37:27,880
Speaker 2: you in a Newtonian point of view, right, So, like

799
00:37:28,520 --> 00:37:31,440
Speaker 2: the phrase inertial mass doesn't really belong in a conversation

800
00:37:31,560 --> 00:37:33,600
Speaker 2: about general relativity. There's just mass.

801
00:37:33,840 --> 00:37:36,200
Speaker 1: Well, like if I were to strap a rocket to

802
00:37:36,280 --> 00:37:38,319
Speaker 1: my bowling ball and a strap a little rocket to

803
00:37:38,320 --> 00:37:41,319
Speaker 1: my feather, I would need to expend more energy in

804
00:37:41,440 --> 00:37:44,799
Speaker 1: that rocket to move the bowling ball than the feather.

805
00:37:44,920 --> 00:37:47,320
Speaker 2: If you want to add in other forces electricity or

806
00:37:47,400 --> 00:37:50,120
Speaker 2: rockets or whatever, then you bring back inertial mass. But

807
00:37:50,200 --> 00:37:53,239
Speaker 2: for Einstein's gravity, there's just one mass, the one that

808
00:37:53,320 --> 00:37:56,200
Speaker 2: bends space time. Think about your big ball and your

809
00:37:56,200 --> 00:37:58,799
Speaker 2: little ball on the surface of the Earth, right, what's

810
00:37:58,800 --> 00:38:01,719
Speaker 2: happening there, Well, both of them want to be sort

811
00:38:01,719 --> 00:38:03,759
Speaker 2: of falling towards the center of the Earth to follow

812
00:38:03,800 --> 00:38:05,960
Speaker 2: the natural motion of the Earth. Both of them are

813
00:38:06,080 --> 00:38:09,840
Speaker 2: not because the Earth is pushing back up on them, right,

814
00:38:10,280 --> 00:38:12,600
Speaker 2: And so really what's happening there is like their Earth

815
00:38:12,719 --> 00:38:15,840
Speaker 2: is accelerating them up at the same rate so that

816
00:38:15,840 --> 00:38:17,879
Speaker 2: they don't fall towards the center of the Earth.

817
00:38:18,719 --> 00:38:20,239
Speaker 1: I guess maybe if we can go back to the

818
00:38:20,239 --> 00:38:22,040
Speaker 1: feather and the bowling ball, Like, if I have the

819
00:38:22,040 --> 00:38:24,279
Speaker 1: feather in the bowling ball in space, nothing around it,

820
00:38:24,280 --> 00:38:27,160
Speaker 1: no black hole, no planet Earth, and I wanted to

821
00:38:27,200 --> 00:38:30,680
Speaker 1: move them one meter, I would need more energy to

822
00:38:30,680 --> 00:38:32,879
Speaker 1: move the bowling ball than the feather, right, I don't

823
00:38:32,920 --> 00:38:33,680
Speaker 1: need a bigger force.

824
00:38:33,920 --> 00:38:36,080
Speaker 2: Yeah, if you're out in deep space and there's no

825
00:38:36,120 --> 00:38:38,960
Speaker 2: gravity in your by so space is totally flat, then

826
00:38:39,040 --> 00:38:40,759
Speaker 2: these things just sit there if you don't apply force

827
00:38:40,800 --> 00:38:43,120
Speaker 2: to them, And if you do apply force to them,

828
00:38:43,160 --> 00:38:45,080
Speaker 2: then they will accelerate. That You can sort of use

829
00:38:45,160 --> 00:38:48,560
Speaker 2: Newtonian mechanics in this context because there is no curvature

830
00:38:48,600 --> 00:38:50,600
Speaker 2: to space. And if you want to apply other forces,

831
00:38:50,680 --> 00:38:54,080
Speaker 2: ones that generate real acceleration, then you bring in inertial mass. Again,

832
00:38:54,239 --> 00:38:57,640
Speaker 2: but that concept doesn't exist in gravity anymore.

833
00:38:57,320 --> 00:38:59,759
Speaker 1: Right, and so in this case there is something calling

834
00:38:59,800 --> 00:39:02,320
Speaker 1: our like it takes a bigger force to move the

835
00:39:02,360 --> 00:39:03,480
Speaker 1: bowling ball on space.

836
00:39:03,320 --> 00:39:05,279
Speaker 2: Takes a bigger force to move the bulling ball. Yes,

837
00:39:05,360 --> 00:39:07,400
Speaker 2: Newton would say, that's inertial mass.

838
00:39:07,680 --> 00:39:10,319
Speaker 1: That's inertial mass. Okay, Now let's put the feather and

839
00:39:10,360 --> 00:39:12,480
Speaker 1: the bowling ball near a black hole and I let

840
00:39:12,520 --> 00:39:16,279
Speaker 1: go of them. You're saying, because of Einstein and the

841
00:39:16,320 --> 00:39:18,799
Speaker 1: way the black hole is bending space time around it,

842
00:39:19,200 --> 00:39:21,200
Speaker 1: the feather and the bowling ball are going to fall

843
00:39:21,239 --> 00:39:23,640
Speaker 1: towards a black hole at the same rate, because that's

844
00:39:23,680 --> 00:39:25,480
Speaker 1: how space time is bent around.

845
00:39:25,320 --> 00:39:28,640
Speaker 2: That's right, they both follow space time regardless of their mass.

846
00:39:28,880 --> 00:39:32,720
Speaker 1: Right. But now let's say I put little rocket. It's

847
00:39:32,719 --> 00:39:34,960
Speaker 1: in the feather and in the bowling ball, and I'm

848
00:39:35,000 --> 00:39:38,520
Speaker 1: trying to prevent these things from falling into the black hole.

849
00:39:38,680 --> 00:39:42,800
Speaker 1: To an outside observer far away from this catastrophic scenario.

850
00:39:42,960 --> 00:39:46,080
Speaker 1: Don't I need to push the bowling ball harder or

851
00:39:46,120 --> 00:39:48,520
Speaker 1: expand more energy in my rocket to keep the boiling

852
00:39:48,520 --> 00:39:50,600
Speaker 1: ball from falling into the black hole than the feather?

853
00:39:50,800 --> 00:39:52,799
Speaker 2: Yes, in general relativity, if you don't want to follow

854
00:39:52,840 --> 00:39:55,359
Speaker 2: the curvature of space time, then you need a force, right,

855
00:39:55,360 --> 00:39:59,359
Speaker 2: That's what forces are. Essentially, anytime you're accelerating, is accelerating

856
00:39:59,360 --> 00:40:03,279
Speaker 2: to avoid just following the curvature of space time. And so, yeah,

857
00:40:03,360 --> 00:40:06,080
Speaker 2: you need a force to push on these things. And yeah,

858
00:40:06,080 --> 00:40:07,759
Speaker 2: I think you need a bigger force to push on

859
00:40:07,800 --> 00:40:08,920
Speaker 2: the bowling ball than the feather.

860
00:40:09,040 --> 00:40:12,280
Speaker 1: Okay, so you're saying that my rocket on my bowling

861
00:40:12,280 --> 00:40:14,160
Speaker 1: ball needs to push harder than the rocket on the

862
00:40:14,160 --> 00:40:16,880
Speaker 1: feather to keep it from falling into the black hole. Right,

863
00:40:17,000 --> 00:40:20,120
Speaker 1: so's just more of something there that needs to happen

864
00:40:20,160 --> 00:40:22,879
Speaker 1: in order to keep them from falling into the black hole. Now,

865
00:40:22,960 --> 00:40:25,400
Speaker 1: is that more of that something or is that something

866
00:40:25,400 --> 00:40:27,640
Speaker 1: that there's more for the bowling ball? Is that still

867
00:40:27,680 --> 00:40:31,480
Speaker 1: inertial mass or is that a different amount related to

868
00:40:31,800 --> 00:40:34,279
Speaker 1: how much the black hole is bending space time?

869
00:40:34,440 --> 00:40:38,080
Speaker 2: Yeah, here we're talking about real acceleration opposing the natural

870
00:40:38,160 --> 00:40:41,200
Speaker 2: motion according to the curvature of space, and that has

871
00:40:41,280 --> 00:40:44,000
Speaker 2: to come from something other than gravity, which means a

872
00:40:44,040 --> 00:40:47,279
Speaker 2: real force, and that brings in inertial mass. Again, yes,

873
00:40:47,680 --> 00:40:51,600
Speaker 2: but again, there's no inertial mass in gravitational motion. The

874
00:40:51,680 --> 00:40:53,920
Speaker 2: reason the bowling ball and the feather fall towards the

875
00:40:53,920 --> 00:40:56,720
Speaker 2: black hole at the same rate without rockets.

876
00:40:56,520 --> 00:40:58,240
Speaker 1: So it's the same as inertial mass.

877
00:40:58,239 --> 00:41:00,239
Speaker 2: Then yeah, when you bring in the other forces, there

878
00:41:00,280 --> 00:41:03,200
Speaker 2: will be inertial mass again, but within gravity itself there

879
00:41:03,239 --> 00:41:05,719
Speaker 2: isn't one anymore. Like the reason that you do not

880
00:41:05,880 --> 00:41:07,680
Speaker 2: fall towards the center of the Earth is because the

881
00:41:07,680 --> 00:41:09,920
Speaker 2: surface of the Earth is pushing you up exactly the

882
00:41:10,000 --> 00:41:12,760
Speaker 2: same way that rocket is accelerating the bowling ball away

883
00:41:12,760 --> 00:41:15,000
Speaker 2: from the black hole. The surface of the Earth is

884
00:41:15,040 --> 00:41:17,760
Speaker 2: pushing you up away from gravity. And if you drop

885
00:41:17,800 --> 00:41:21,080
Speaker 2: a ball. Newton says, oh, that ball is accelerating towards

886
00:41:21,120 --> 00:41:23,440
Speaker 2: the center of the Earth. Einstein says, no, when you

887
00:41:23,520 --> 00:41:26,799
Speaker 2: drop the ball is when it stops accelerating. You are

888
00:41:26,840 --> 00:41:29,840
Speaker 2: accelerating up away from the center of the Earth, like

889
00:41:29,880 --> 00:41:31,960
Speaker 2: the bowling ball and the rocket, to avoid falling in

890
00:41:32,200 --> 00:41:34,280
Speaker 2: and the ball is now in free falls now flowing

891
00:41:34,360 --> 00:41:38,000
Speaker 2: naturally with gravity, it's stopped accelerating. That's why everything falls

892
00:41:38,040 --> 00:41:40,080
Speaker 2: at the same rate, because it's really the Earth that's

893
00:41:40,200 --> 00:41:42,720
Speaker 2: rushing up to meet it, rather than like the bowling

894
00:41:42,760 --> 00:41:44,960
Speaker 2: ball or the feather that are falling. They're just like

895
00:41:45,000 --> 00:41:47,759
Speaker 2: hanging out, not accelerating with respect to space.

896
00:41:47,880 --> 00:41:50,120
Speaker 1: Right, And so in that sense, it's the same thing,

897
00:41:50,200 --> 00:41:53,600
Speaker 1: like inertial mass is the same as gravitational mass. But

898
00:41:54,080 --> 00:41:57,239
Speaker 1: I guess my question now leading up to this is,

899
00:41:57,320 --> 00:41:59,760
Speaker 1: let's say we lived in a universe in which gravity

900
00:41:59,800 --> 00:42:04,080
Speaker 1: were differently, Like the amount of space time bending that

901
00:42:04,120 --> 00:42:06,640
Speaker 1: a black hole does is different in my universe and

902
00:42:06,680 --> 00:42:09,200
Speaker 1: in your universe. Like in my universe, the black hole,

903
00:42:10,160 --> 00:42:12,600
Speaker 1: if you constantly constant dam much energy into a spot,

904
00:42:12,760 --> 00:42:15,719
Speaker 1: doesn't bend space time very much, like almost not at all.

905
00:42:15,760 --> 00:42:16,880
Speaker 2: You're changing the value of G.

906
00:42:17,160 --> 00:42:18,319
Speaker 1: Yeah, changing the value of G.

907
00:42:18,600 --> 00:42:21,160
Speaker 2: Okay, you're making it the value of J, the whorege value.

908
00:42:21,239 --> 00:42:24,520
Speaker 1: Okay, yeah, it's the J constant that's right, for which

909
00:42:24,520 --> 00:42:26,080
Speaker 1: I'll get I'm sure i'll get an oval price. But

910
00:42:26,160 --> 00:42:29,000
Speaker 1: in your universe G is huge. So like the black

911
00:42:29,000 --> 00:42:32,280
Speaker 1: hole bends spacelime a lot, and so space in your universe,

912
00:42:32,600 --> 00:42:35,960
Speaker 1: space is rushing towards the black hole a lot, super fast,

913
00:42:35,960 --> 00:42:37,800
Speaker 1: a lot, And whereas in my universe, let's say it,

914
00:42:37,800 --> 00:42:41,200
Speaker 1: it means even zero. So now wouldn't in my universe

915
00:42:41,320 --> 00:42:43,640
Speaker 1: I would need less to spend less energy in my

916
00:42:43,719 --> 00:42:46,279
Speaker 1: rockets to keep the balling well from falling into the

917
00:42:46,280 --> 00:42:48,000
Speaker 1: black hole, whereas in your universe I would need a

918
00:42:48,040 --> 00:42:50,080
Speaker 1: lot of energy to keep the bowling ball from falling

919
00:42:50,080 --> 00:42:50,759
Speaker 1: into the black hole.

920
00:42:50,880 --> 00:42:54,120
Speaker 2: Yes, the force you need does depend on the gravitational constant,

921
00:42:54,120 --> 00:42:58,040
Speaker 2: because you're pitting gravity against non gravitational forces, which do

922
00:42:58,160 --> 00:43:01,359
Speaker 2: have a concept of inertial map. And when you fight

923
00:43:01,400 --> 00:43:04,840
Speaker 2: against the curvature with other forces than the relative strength

924
00:43:04,880 --> 00:43:06,960
Speaker 2: of curvature and those forces matters.

925
00:43:07,120 --> 00:43:09,200
Speaker 1: I guess maybe where I'm going with this is that

926
00:43:09,320 --> 00:43:11,080
Speaker 1: you're sort of making it sound like there is no

927
00:43:11,160 --> 00:43:14,600
Speaker 1: coincidence anymore with Einstein's relativity. But I wonder, and again

928
00:43:14,640 --> 00:43:16,840
Speaker 1: I'm not an expert. I'm just kind of intuitively following

929
00:43:16,960 --> 00:43:19,640
Speaker 1: my sense of intuition here. I wonder if it's still

930
00:43:19,680 --> 00:43:23,000
Speaker 1: sort of a coincidence. You just move the coincidence somewhere else, I.

931
00:43:23,000 --> 00:43:25,239
Speaker 2: Think, to me, the way to answer that question is

932
00:43:25,360 --> 00:43:27,240
Speaker 2: just to think about the bowling ball and the feather

933
00:43:27,760 --> 00:43:30,759
Speaker 2: without the other forces, because it's the fact that the

934
00:43:30,800 --> 00:43:33,959
Speaker 2: bowling ball and the feather fall at the same rate that,

935
00:43:34,000 --> 00:43:37,680
Speaker 2: in Newton's view, means these two things have to be equal, right,

936
00:43:37,719 --> 00:43:41,520
Speaker 2: That's where the coincidence comes from. And Einstein says that

937
00:43:41,520 --> 00:43:43,560
Speaker 2: the bowling ball and the feather have to follow the

938
00:43:43,560 --> 00:43:45,440
Speaker 2: same rate because they're just following me the curvature of

939
00:43:45,480 --> 00:43:48,000
Speaker 2: space time. Even if you crank up G. If you

940
00:43:48,040 --> 00:43:50,439
Speaker 2: crank up G to the new Joorge value, so now

941
00:43:50,480 --> 00:43:53,040
Speaker 2: everything is crazy curved, then the bowling ball and the

942
00:43:53,040 --> 00:43:54,880
Speaker 2: feather are going to fall into the black hole at

943
00:43:54,920 --> 00:43:57,120
Speaker 2: the same rate. They'll fall faster than in a universe

944
00:43:57,160 --> 00:43:59,400
Speaker 2: without crazy G, but they will both fall into the

945
00:43:59,400 --> 00:44:02,120
Speaker 2: black hole the same rate. If you relax G downs

946
00:44:02,160 --> 00:44:04,840
Speaker 2: so that space is curved less by mass, it's harder

947
00:44:04,840 --> 00:44:07,000
Speaker 2: to make black holes or whatever, then the bowling ball

948
00:44:07,080 --> 00:44:09,080
Speaker 2: and the feather are going to fall in more slowly,

949
00:44:09,239 --> 00:44:10,879
Speaker 2: but they're still going to fall at the same rate.

950
00:44:10,960 --> 00:44:12,040
Speaker 2: Doesn't that answer the question?

951
00:44:12,400 --> 00:44:14,719
Speaker 1: Okay, so you're saying that in your universe with the

952
00:44:14,760 --> 00:44:17,719
Speaker 1: big G, the feather and the bowling bell would fall

953
00:44:17,760 --> 00:44:20,320
Speaker 1: really fast towards a black hole, whereas in my universe

954
00:44:20,360 --> 00:44:22,200
Speaker 1: with the little G they would fall slowly.

955
00:44:22,480 --> 00:44:22,919
Speaker 2: Mm hmm.

956
00:44:23,520 --> 00:44:27,000
Speaker 1: Okay, But in both universes, if there is no black hole,

957
00:44:27,320 --> 00:44:30,040
Speaker 1: they would Both the feather and the bowling ball would

958
00:44:30,080 --> 00:44:32,879
Speaker 1: have different inertial masses to each other, but they would

959
00:44:32,960 --> 00:44:34,839
Speaker 1: The bowling ball in my universe would have the same

960
00:44:34,880 --> 00:44:37,040
Speaker 1: inertial mass as the bowling ball in your universe.

961
00:44:37,239 --> 00:44:39,960
Speaker 2: Yes, for the real forces, you still have inertial mass.

962
00:44:39,960 --> 00:44:43,600
Speaker 2: But the coincidence within gravity is explained by Einstein since

963
00:44:43,640 --> 00:44:46,839
Speaker 2: gravity now only has one mass instead of two.

964
00:44:47,239 --> 00:44:49,719
Speaker 1: You see what I mean, Like there's inertial mas. I'm

965
00:44:49,719 --> 00:44:51,920
Speaker 1: wondering if that inertial mass, which is the same in

966
00:44:51,960 --> 00:44:56,400
Speaker 1: my universe in your universe, is different than the gravitational mass,

967
00:44:56,760 --> 00:44:59,040
Speaker 1: which is different in my universe and your universe because

968
00:44:59,040 --> 00:45:01,360
Speaker 1: we have different gs, or I wonder if maybe the

969
00:45:01,480 --> 00:45:05,359
Speaker 1: answer Maybe what's confusing me is that in both universes,

970
00:45:05,480 --> 00:45:08,840
Speaker 1: the one with big G and litogy, we would in

971
00:45:08,880 --> 00:45:11,879
Speaker 1: both cases we would still be wondering about the same thing.

972
00:45:12,080 --> 00:45:15,480
Speaker 1: Like I wonder if both universes it would they would

973
00:45:15,480 --> 00:45:19,320
Speaker 1: seem like coincidences that inertial gravity and gravitational gravity in

974
00:45:19,360 --> 00:45:20,720
Speaker 1: a Newtonian sense, are the same.

975
00:45:20,880 --> 00:45:22,440
Speaker 2: I think in both the big G universe and the

976
00:45:22,480 --> 00:45:24,799
Speaker 2: little G universe, you'd have a big Newton and a

977
00:45:24,800 --> 00:45:28,200
Speaker 2: little Newton, which would have developed their own laws of

978
00:45:28,280 --> 00:45:31,440
Speaker 2: Newtonian physics, which would seem like there was a coincidence

979
00:45:31,480 --> 00:45:34,319
Speaker 2: between them because they have these two different concepts, one

980
00:45:34,360 --> 00:45:38,799
Speaker 2: of gravitational force from some gravitational mass that explains the

981
00:45:38,840 --> 00:45:42,520
Speaker 2: apparent force of gravity. But then Big Einstein and Little

982
00:45:42,560 --> 00:45:45,640
Speaker 2: Einstein would have come along and explain that there is

983
00:45:45,680 --> 00:45:48,719
Speaker 2: no force operating there, that there really is just the

984
00:45:48,760 --> 00:45:52,359
Speaker 2: one mass. And if Big Einstein and Little Einstein could

985
00:45:52,360 --> 00:45:55,040
Speaker 2: talk to each other and compare notes, if both the

986
00:45:55,160 --> 00:45:58,480
Speaker 2: universes are relativistic, then they would see that both universes

987
00:45:58,480 --> 00:46:00,920
Speaker 2: are following their laws of physics. I think it's interesting

988
00:46:00,920 --> 00:46:03,800
Speaker 2: that in one universe you have like a stronger reaction

989
00:46:03,960 --> 00:46:06,960
Speaker 2: to energy density in terms of the curvature space than

990
00:46:07,000 --> 00:46:09,399
Speaker 2: in the other, which will definitely change how things move.

991
00:46:09,719 --> 00:46:12,680
Speaker 2: But in that universe things always agree, right, Like the

992
00:46:12,680 --> 00:46:15,200
Speaker 2: two objects moving through the same space time move the

993
00:46:15,200 --> 00:46:17,760
Speaker 2: same way regardless of their mass is the key.

994
00:46:17,960 --> 00:46:20,480
Speaker 1: Okay, it sounds sort of like the main idea is

995
00:46:20,520 --> 00:46:22,879
Speaker 1: that sometimes so we think it is a coincidence, it's

996
00:46:22,920 --> 00:46:24,960
Speaker 1: really just a different way of looking at how the

997
00:46:25,040 --> 00:46:25,720
Speaker 1: universe works.

998
00:46:25,920 --> 00:46:28,520
Speaker 2: Yeah, exactly, that you can bring two different ideas together

999
00:46:28,600 --> 00:46:31,879
Speaker 2: and click them into one larger idea. Where you thought

1000
00:46:31,960 --> 00:46:34,799
Speaker 2: you had the freedom to twiddle two knobs to whatever

1001
00:46:34,880 --> 00:46:37,719
Speaker 2: values you want, but turns out they're connected in some way.

1002
00:46:37,840 --> 00:46:40,360
Speaker 2: There's a relationship between the knobs twidt the one you

1003
00:46:40,440 --> 00:46:43,400
Speaker 2: have to twiddle the other. So really there's just one knob.

1004
00:46:43,280 --> 00:46:45,880
Speaker 1: Or at least it's one knob, and maybe I don't know,

1005
00:46:46,040 --> 00:46:48,480
Speaker 1: there could still be other knobs in the universe, but

1006
00:46:48,719 --> 00:46:50,839
Speaker 1: like the ones that affect how things move and how

1007
00:46:50,840 --> 00:46:55,000
Speaker 1: things get attracted to larger objects through gravity. You're saying,

1008
00:46:55,040 --> 00:46:58,200
Speaker 1: in this universe they're sort of connected. It's like one knob,

1009
00:46:58,320 --> 00:46:59,000
Speaker 1: mm hmm.

1010
00:46:59,000 --> 00:47:01,600
Speaker 2: Exactly in our unit. First, at least you're right that

1011
00:47:01,640 --> 00:47:04,040
Speaker 2: there are other knobs for the other forces, and those

1012
00:47:04,120 --> 00:47:07,120
Speaker 2: still have the concept of inertial mass. But within gravity,

1013
00:47:07,440 --> 00:47:11,160
Speaker 2: the apparent coincidence between those two knobs gravitational and inertial

1014
00:47:11,200 --> 00:47:14,440
Speaker 2: mass is explained because there is no inertial mass in gravity,

1015
00:47:14,640 --> 00:47:17,720
Speaker 2: because it doesn't accelerate anything because it's not a force.

1016
00:47:17,920 --> 00:47:20,000
Speaker 1: So then to answer the question of the podcast, there

1017
00:47:20,040 --> 00:47:22,960
Speaker 1: is no difference between inertial or gravitational mass, or is

1018
00:47:23,000 --> 00:47:24,960
Speaker 1: the answer that this question doesn't make sense?

1019
00:47:25,080 --> 00:47:27,520
Speaker 2: The answer is that there is still inertial mass for

1020
00:47:27,600 --> 00:47:31,240
Speaker 2: other forces, but within gravity, there's just one concept of mass.

1021
00:47:31,320 --> 00:47:34,600
Speaker 2: There's no separation between gravitational and inertial mass. There is

1022
00:47:34,800 --> 00:47:38,960
Speaker 2: just mass, and we can still understand why things fall

1023
00:47:39,040 --> 00:47:41,480
Speaker 2: at the same rate even in that context. Right, we

1024
00:47:41,520 --> 00:47:44,719
Speaker 2: don't have to worry about this miraculous balance between inertia

1025
00:47:44,719 --> 00:47:47,319
Speaker 2: and gravity because they are just two sides of the

1026
00:47:47,320 --> 00:47:49,920
Speaker 2: same coin. Inertia and gravity are wrapped up by Einstein

1027
00:47:49,960 --> 00:47:53,200
Speaker 2: into one idea that controls how things move through space.

1028
00:47:53,360 --> 00:47:55,520
Speaker 1: All right, Well, it was a heavy topic, but I

1029
00:47:55,560 --> 00:47:58,680
Speaker 1: think we made it through to the other side, or

1030
00:47:58,680 --> 00:48:00,799
Speaker 1: at least we did not fall to a black hole

1031
00:48:01,239 --> 00:48:04,680
Speaker 1: well discussing it, although maybe we should just add more

1032
00:48:04,800 --> 00:48:07,919
Speaker 1: dad jokes and puns so that we, you know, reach

1033
00:48:08,000 --> 00:48:08,760
Speaker 1: the event horizon.

1034
00:48:09,000 --> 00:48:11,200
Speaker 2: Yeah, and to me, thinking about these examples really helps

1035
00:48:11,239 --> 00:48:14,759
Speaker 2: you get more intuition for thinking about gravity as just

1036
00:48:14,880 --> 00:48:17,640
Speaker 2: a geometric thing. Doesn't matter what your mass is, you

1037
00:48:17,719 --> 00:48:21,160
Speaker 2: move through space the same way mends on your velocity, certainly, right,

1038
00:48:21,200 --> 00:48:23,279
Speaker 2: And like a photon flying near a black hole is

1039
00:48:23,280 --> 00:48:26,040
Speaker 2: going to have a different trajectory than a grapefruit traveling

1040
00:48:26,040 --> 00:48:28,960
Speaker 2: at five meters per second. Your velocity definitely matters, but

1041
00:48:29,040 --> 00:48:31,799
Speaker 2: not your mass, which is just a very different way

1042
00:48:31,800 --> 00:48:33,759
Speaker 2: of thinking about the universe. And I love how the

1043
00:48:33,840 --> 00:48:36,960
Speaker 2: story of physics is explaining everything we see in all

1044
00:48:36,960 --> 00:48:40,239
Speaker 2: of our experiences with different stories, stories that update through

1045
00:48:40,280 --> 00:48:42,160
Speaker 2: time to give us a different picture of how the

1046
00:48:42,239 --> 00:48:43,240
Speaker 2: universe works.

1047
00:48:43,480 --> 00:48:45,919
Speaker 1: Yeah, although your dog had been there, may it would

1048
00:48:45,960 --> 00:48:48,799
Speaker 1: have eaten the grip and we'd still be back at uh,

1049
00:48:49,040 --> 00:48:50,400
Speaker 1: not understanding any of this.

1050
00:48:50,880 --> 00:48:52,440
Speaker 2: My dog will eat almost anything.

1051
00:48:52,800 --> 00:48:54,799
Speaker 1: All right. Well, we hope you enjoyed that. Thanks for

1052
00:48:54,840 --> 00:48:56,919
Speaker 1: joining us, See you next time.

1053
00:49:01,480 --> 00:49:04,360
Speaker 2: For more science and curiosity, come find us on social

1054
00:49:04,400 --> 00:49:09,320
Speaker 2: media where we answer questions and post videos. We're on Twitter, Discborg, Insta,

1055
00:49:09,440 --> 00:49:12,880
Speaker 2: and now TikTok. Thanks for listening, and remember that Daniel

1056
00:49:12,920 --> 00:49:16,640
Speaker 2: and Jorge Explain the Universe is a production iHeartRadio. For

1057
00:49:16,840 --> 00:49:21,799
Speaker 2: more podcasts from iHeartRadio, visit the iHeartRadio app, Apple Podcasts,

1058
00:49:21,920 --> 00:49:24,280
Speaker 2: or wherever you listen to your favorite shows.