Latest / Daniel and Kelly’s Extraordinary Universe / What if the speed of light were slower?

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What if the speed of light were slower? · Daniel and Kelly’s Extraordinary Universe

0:08
Speaker 1: Hey, Alry, when did you move to California? It was
0:12
Speaker 1: a long time ago. So was it like before or
0:15
Speaker 1: after the last ice age? How do you think, I
0:17
Speaker 1: am Daniel? Or do you mean like the time that
0:20
Speaker 1: the temperature drop below sixty degrees here in Los Angeles?
0:23
Speaker 1: We call that the California ice Age? Well, I mean
0:26
Speaker 1: that begs the question, did you move to California for
0:29
Speaker 1: the weather? Kind of? I mean I moved here for
0:32
Speaker 1: grad school and I actually had to choose between Stanford
0:35
Speaker 1: and Berkeley. Is there much of a weather difference on
0:37
Speaker 1: the other side of the Bay. There is, Actually there's
0:40
Speaker 1: a big difference. At least on the day that I
0:42
Speaker 1: made the decision, it was much sunnier at Stanford. I see.
0:45
Speaker 1: So you're saying Berkeley is cooler. I'm saying Berkeley is
0:48
Speaker 1: ice here and more frigid. Everybody who went to Stanford
0:52
Speaker 1: is definitely hot. It's hot place. Hi am Orhamedy cartoonist
1:10
Speaker 1: and the creator of PhD comics. Hi, I'm Daniel. I'm
1:13
Speaker 1: a particle physicist and a professor at U SEE Irvine,
1:16
Speaker 1: and I will always support Berkeley over Stanford. What about
1:19
Speaker 1: Berkeley over Irvine? Don't make me go there, man, are
1:26
Speaker 1: you pro where does it art varks or bears? Like?
1:29
Speaker 1: Which one would win in a fight? Do you think
1:30
Speaker 1: a bear or an art vark? Well, bear sleep a lot,
1:34
Speaker 1: so I think you know, while there's snooze in the
1:36
Speaker 1: art bark could just like slip in there and lick
1:38
Speaker 1: their face with its long tongue. Anyway, it's an ant
1:40
Speaker 1: eater and not an art bark. Is there a difference?
1:43
Speaker 1: Is there a difference? O? Gosh? Welcome to Creature feature
1:47
Speaker 1: the podcast about art varks and or college mascots one
1:51
Speaker 1: of the two. But anyways, welcome to a podcast. Daniel
1:53
Speaker 1: and Jorge Explain the Universe, a production of I Heart
1:56
Speaker 1: Radio in which we take you on a tour of
1:57
Speaker 1: the universe, regardless of where you went to college or
2:00
Speaker 1: if you went to college. The goal of this podcast
2:03
Speaker 1: is to get everybody on board with this journey of exploration,
2:07
Speaker 1: to wonder how the universe works, how it might have been,
2:10
Speaker 1: why it is the way that it is, and can
2:12
Speaker 1: it make sense to all of us? It's right because
2:15
Speaker 1: it is a pretty mysterious universe full of interesting phenomena
2:18
Speaker 1: for us to look at and gepe that and wonder
2:20
Speaker 1: about and there we importantly ask questions about I have
2:23
Speaker 1: a question for you, which is, you know, if Berkeley
2:25
Speaker 1: is the Golden Bear and Irvine is the ant eater,
2:29
Speaker 1: what is Stanford's mascot? Is it a tree? It's Silicon Valley? Money,
2:33
Speaker 1: piles of cash, piles of bitcoins probably these days. Yeah, well,
2:42
Speaker 1: we're not gonna let this go. Are we the Stanford
2:44
Speaker 1: Berkeley thing on this episode? Oh no, Man, Berkeley over
2:47
Speaker 1: Stanford all day every day. Maybe should discuss our after
2:52
Speaker 1: grad school school. So I went to Caltech and you
2:55
Speaker 1: went to EC Irvine. After grad school, actually went to
2:57
Speaker 1: the University of Pennsylvania, which is a private school. And yeah,
3:00
Speaker 1: then I did go to UC Irvine. And I've bounced
3:03
Speaker 1: back and forth between public and private institutions, but in
3:05
Speaker 1: the end, my heart really is in public institutions because
3:09
Speaker 1: they serve the public, and you know, to get off
3:11
Speaker 1: the jokes for a moment, like, I really do believe
3:14
Speaker 1: in the mission of educating the public and providing a
3:17
Speaker 1: path of mobility for people. California public college system from
3:21
Speaker 1: the cow States all the way up to the University
3:23
Speaker 1: of California's that they do an incredible public service. And
3:25
Speaker 1: I think that this podcast is part of that. We
3:28
Speaker 1: want to reach out and educate everybody about the mysteries
3:30
Speaker 1: of the universe, not just those that have piles of
3:33
Speaker 1: cash or stacks of bitcoin. Yeah, and that's why you
3:36
Speaker 1: renounced your undergraduate institution, right, no comment. I'm just kidding.
3:43
Speaker 1: But it is a pretty amazing universe full of things
3:45
Speaker 1: to discover that are there for everyone to wonder and
3:48
Speaker 1: to look in and to have questions about. Because people
3:51
Speaker 1: have questions. People do have questions, and they write to
3:54
Speaker 1: us with their questions. And the cross section of folks
3:57
Speaker 1: who write to us is just incredible. From seven year
3:59
Speaker 1: old wondering about black holes, to night guards at hospitals
4:03
Speaker 1: who listen to our podcast while they walk the halls,
4:06
Speaker 1: to pro bono attorneys from Alabama who listened to our
4:09
Speaker 1: podcast is a break from the craziness of their lives.
4:12
Speaker 1: Everybody out there wonders about the nature of the universe
4:15
Speaker 1: and how it works, and whether it's possible for it
4:18
Speaker 1: all to make sense to them. Yeah, that is pretty
4:20
Speaker 1: incredible to think that there are so many people listening
4:23
Speaker 1: to this and kind of thinking about the same topics
4:25
Speaker 1: at the same time. Makes us all sort of feel
4:27
Speaker 1: connected in a way like we're all wondering about the
4:29
Speaker 1: universe at the same time together. Yeah, we are all
4:32
Speaker 1: wondering about the universe, and I hope that means that
4:34
Speaker 1: we're also connected to like alien scientists who I think
4:38
Speaker 1: are probably wondering about the same universe. I like to
4:41
Speaker 1: fantasize about a whole galactic community of scientists wondering about
4:44
Speaker 1: the nature of this crazy cosmos, and we're just a
4:47
Speaker 1: tiny little piece of it. Well, I feel like you
4:49
Speaker 1: just stepped it up a notch there. I was going
4:52
Speaker 1: for some sort of human grandeur, but you took it
4:54
Speaker 1: to the galactic level. That's what we do on this podcast, man,
4:57
Speaker 1: take it to the galactic level every time. I don't
5:00
Speaker 1: know if I want to mind meld with aliens necessarily, though.
5:03
Speaker 1: Do you think we've enjoyed that experience? Well, you know,
5:06
Speaker 1: that's sort of the Berkeley approach. You know, we're all
5:08
Speaker 1: one with the universe. Man, I have to take any
5:13
Speaker 1: particular substances to kind of reach that state that I
5:16
Speaker 1: can approchase maybe at Berkeley Bananappeals for sure. Yeah. But yeah,
5:19
Speaker 1: people definitely have questions, and sometimes we get those questions
5:22
Speaker 1: here on the podcast. People send them to us over
5:25
Speaker 1: email or through social media. That's right. So if you
5:28
Speaker 1: have questions about the nature of the universe, or there's
5:30
Speaker 1: something we said on the podcast that you didn't quite understand,
5:33
Speaker 1: or there's just been something bugging you that you really
5:36
Speaker 1: need to get explained, please don't be shy right to
5:38
Speaker 1: us two questions at Daniel and Jorge dot com. We
5:41
Speaker 1: answer every single question. We will answer your question. Yeah,
5:45
Speaker 1: and sometimes the questions are so interesting that Daniel picks
5:48
Speaker 1: them to answer on the podcast. Yeah. Sometimes the questions
5:51
Speaker 1: make me go off and do a bit of a
5:53
Speaker 1: dive or research to get a solid answer. And sometimes
5:55
Speaker 1: I think it's a question that other people might want
5:57
Speaker 1: to hear the answer to. And sometimes I think this
5:59
Speaker 1: is be fun to laugh with Jorge about, make fun
6:02
Speaker 1: of or to laugh about what are your plans here? Well,
6:06
Speaker 1: you know, I try to be nice to Stanford grads
6:07
Speaker 1: who you know, went to a junior college after all,
6:10
Speaker 1: that's right, ideas who are are not physicists. So today
6:15
Speaker 1: on the podcast will be tackling listener questions number twenty
6:23
Speaker 1: five and also titled Jorhan Daniel keep Fighting about Berkeley
6:27
Speaker 1: and Stanford. You see, you really you're the ones SEO
6:30
Speaker 1: seems to be bringing it up more. No, I think
6:32
Speaker 1: that's probably true. I think Berkeley folks probably feel the
6:35
Speaker 1: Berkeley Stanford rivalry more than Stanford folks, who are like, what,
6:39
Speaker 1: who cares academy chip on the shoulder? I think so
6:42
Speaker 1: probably where the public university that could. I think the
6:46
Speaker 1: more interesting question is an art park the same as
6:49
Speaker 1: an an eater? I think the question is how did
6:52
Speaker 1: you get a Stanford education? And not know the answer
6:54
Speaker 1: to that? Well, I was in the engineering department. I
6:59
Speaker 1: didn't zoology one on one, right, Yeah, don't you like
7:02
Speaker 1: look to nature for inspiration? Well? I felt like the
7:07
Speaker 1: straw was already invented, so I didn't need to copy
7:11
Speaker 1: the ant eaters trunk. Oh, I see, all right, that's
7:13
Speaker 1: true to invent something. Yeah, and well, there's not much
7:15
Speaker 1: of a market for an ant eating robot anyway, or
7:19
Speaker 1: ant eating straw. But anyways, we're here to answer questions
7:23
Speaker 1: from listeners. And this is the twenty fifth episode that
7:26
Speaker 1: we've done this, and I feel like we don't do
7:28
Speaker 1: this enough. Daniel, I really like these episodes. Oh good, well,
7:31
Speaker 1: let's do some more of them. I think these are
7:32
Speaker 1: a lot of fun also, and today we have a
7:34
Speaker 1: question inspired by one of our previous listener question episodes.
7:38
Speaker 1: WHOA what We're going inception? Here we are deep diving
7:42
Speaker 1: like a question within a question episode. Yeah. Well, that's
7:44
Speaker 1: the wonderful thing about questions is that the answer is
7:46
Speaker 1: just raised more questions. They make people think in a
7:49
Speaker 1: way they had them before. They make people's brains go
7:51
Speaker 1: places they hadn't gone before without needing to buy anything
7:54
Speaker 1: on Telegraph Avenue. Yeah, but that optional, I guess. I
8:01
Speaker 1: mean it might make the podcast actually more interesting to
8:03
Speaker 1: some people exactly. That's what we've been talking about bananas
8:06
Speaker 1: the whole time. But we have three pretty awesome questions
8:10
Speaker 1: here today from listeners, and they have to do with
8:13
Speaker 1: the ice age here on planet Earth, about how photons
8:17
Speaker 1: move near black holes, and also what would happen if
8:20
Speaker 1: the speed of light changed. So thanks to those listeners
8:23
Speaker 1: who sent in their questions, and also we're willing to
8:26
Speaker 1: record their audio, and don't forget if you have a question,
8:28
Speaker 1: you can also get an answer right to questions at
8:31
Speaker 1: Daniel and Jorge dot com. Al Right, the first question
8:34
Speaker 1: we have here is from Carson, who has a question
8:37
Speaker 1: about the ice age. So I listened to the podcast
8:40
Speaker 1: about the asteroid and the dinosaurs, and I was wondering,
8:46
Speaker 1: what would happen if the ice age hadn't happened. Thanks
8:49
Speaker 1: for answering all my questions. Pretty cool question, Thank you, Carson.
8:53
Speaker 1: I guess Carson has a question is kind of like
8:55
Speaker 1: what if question, Like how different would the Earth be
8:58
Speaker 1: if certain things hadn't happened. It's a really fun question,
9:01
Speaker 1: and it gets to the heart of how our entire
9:04
Speaker 1: existence depends on so many tiny little factors, just like
9:09
Speaker 1: if an asteroid hadn't hit the Earth, or if the
9:11
Speaker 1: Earth hadn't warmed or cooled, so many chaotic events which
9:15
Speaker 1: could have been different were crucial to us being here
9:18
Speaker 1: right now, and so it's really fun to imagine alternative
9:21
Speaker 1: Earth's different scenarios where things might have turned out very differently. Yeah,
9:25
Speaker 1: I think Carson just wants us to talk about dinosaurs.
9:28
Speaker 1: But you know, you can't blame them. You know what
9:30
Speaker 1: young person doesn't want to talk about dinosaurs? Or maybe
9:33
Speaker 1: Carson's thinking about where to go to college and is wondering,
9:35
Speaker 1: you know, like Berkeley Stanford. You know, well, you're really
9:40
Speaker 1: not dropping this. Well, well, Carson, I have to tell
9:43
Speaker 1: you if there is another ice age, Berkeley's going to
9:45
Speaker 1: freeze first before Stanford. Just letting you know that it
9:48
Speaker 1: is a little bit more north and on the other
9:50
Speaker 1: side of the Bay, which gets colder, and therefore it
9:52
Speaker 1: will have a larger snowpack and better water reserves that
9:55
Speaker 1: lasted through the summer. Because we're not nice to the
10:01
Speaker 1: Bay area. I'm not sure where you're going directly thinking
10:05
Speaker 1: to me, this question is really fascinating because there are
10:08
Speaker 1: a lot of connections between ice ages and the physics
10:11
Speaker 1: of the Solar system. That is, you know, how the
10:14
Speaker 1: Earth goes around the Sun, and the variations in the
10:16
Speaker 1: Earth's orbit really do have a strong impact on how
10:19
Speaker 1: much sun we get and how much ice there is
10:22
Speaker 1: on the Earth. Yeah, it's pretty interesting the connection there,
10:25
Speaker 1: and it's amazing that Carson had been thinking about the
10:28
Speaker 1: ice age. I guess we've had several ice ages throughout
10:31
Speaker 1: the ages. We have had several ice ages, and if
10:33
Speaker 1: you cast your mind back, like really deep far into
10:36
Speaker 1: the history of the Earth, it's incredible how different the
10:40
Speaker 1: Earth looked like around six fifty million years ago. We
10:43
Speaker 1: were in the depths of an ice age, so cold
10:46
Speaker 1: that they think that ice reached all the way down
10:48
Speaker 1: to the equator, like it was basically a snowball Earth. Whoa, Yeah,
10:53
Speaker 1: Like if you took a picture of it, you would
10:54
Speaker 1: just see a big white ball, kind of like when
10:57
Speaker 1: you look at you know, some of the ice planets.
10:59
Speaker 1: So if you're an alien scientists visiting Earth for an
11:01
Speaker 1: interstellar physics conference and you arrived, you know, six million
11:05
Speaker 1: years too early, you wouldn't find anybody to talk to
11:08
Speaker 1: and you think, oh, that's just a frozen wasteland, or
11:11
Speaker 1: you might think, great ski here. Hello. Yeah, I hope
11:14
Speaker 1: that one day we like unfaw some big block of
11:17
Speaker 1: ice and find an alien skiing. That would be an
11:19
Speaker 1: incredible discovery. But then, you know, wouldn't their snowboards hover? Also?
11:26
Speaker 1: I mean, if they made it all the way here
11:27
Speaker 1: for a ski vacation, I wonder what would be in
11:29
Speaker 1: that flask. But anyways, ice ages are interesting, as you said,
11:35
Speaker 1: because they are connected to kind of the physics of
11:37
Speaker 1: our planet and the physics of our planet revolving around
11:40
Speaker 1: the Sun, like it's it's heavily tied to the orbit
11:43
Speaker 1: and the tilt of the planet. Right. There are a
11:45
Speaker 1: lot of factors that affect ice ages, from climates to
11:49
Speaker 1: continental drift, all sorts of things, and scientists don't have
11:52
Speaker 1: a complete understanding of what causes these things. There are
11:55
Speaker 1: still lots of big open questions. But one thing that
11:57
Speaker 1: we do know is that changes in how the Earth
12:00
Speaker 1: orbits the Sun, for example, whether the Earth's orbit is
12:03
Speaker 1: circular or whether it's become more elliptical, and changes in
12:06
Speaker 1: the earth tilt. These things can affect how much solar
12:10
Speaker 1: radiation falls on the Earth, and that affects the temperature
12:13
Speaker 1: for sure. Wow. Well, first of all, I guess maybe
12:15
Speaker 1: this is something I hadn't thought about. Is is the
12:17
Speaker 1: Earth's orbit not constant? Isn't it like a perfect circle
12:20
Speaker 1: or slight oval? And are you saying there's some variations
12:24
Speaker 1: in that trajectory. There are definitely variations in that trajectory.
12:28
Speaker 1: And it goes from being like almost a perfect circle
12:30
Speaker 1: to being more elliptical. And it becomes elliptical by having
12:34
Speaker 1: the semi minor axis get a little shorter. So it's
12:37
Speaker 1: not like the Earth gets further from the Sun but
12:39
Speaker 1: during parts of its orbit and then gets closer to
12:42
Speaker 1: the Sun. Wait, what so what determines these changes in
12:46
Speaker 1: our orbit? So if the Earth was alone in the
12:48
Speaker 1: Solar System, it would have a very simple, stable orbit
12:50
Speaker 1: around the Sun. But it's not, and there are other
12:53
Speaker 1: things in the Solar System, like Jupiter and other gravitational bodies.
12:57
Speaker 1: These things have very gentle tugs on Earth's orbit. We're
13:00
Speaker 1: into a whole episode soon about spin resonances and tidle
13:04
Speaker 1: locking the whole Solar systems. That an incredibly complicated Swiss watch,
13:07
Speaker 1: but it means that there are these cycles that change
13:10
Speaker 1: how the Earth tilts and also how the Earth orbits
13:12
Speaker 1: as it goes around the Sun based on these little
13:15
Speaker 1: gentle tugs from things other than the Sun. Wow, I
13:19
Speaker 1: guess there's still pretty small changes. Maybe, like if you
13:21
Speaker 1: look at the picture of it, maybe you couldn't tell
13:23
Speaker 1: the difference between the different orbits. Yeah, the orbital changes
13:26
Speaker 1: are not huge, or if you're looking from a distance
13:29
Speaker 1: you definitely could see anything. But you know, small changes
13:32
Speaker 1: in how much the Earth tilts towards the Sun or
13:35
Speaker 1: how far away it is from the Sun you really
13:37
Speaker 1: can have a strong impact on the amount of solar radiation.
13:40
Speaker 1: For example, if you look back over the last twenty
13:43
Speaker 1: or hundred thousand years, you see variations of up to
13:46
Speaker 1: twenty percent in the amount of solar radiation that hits
13:49
Speaker 1: the Earth based on these cycles. Wow. Yeah, I guess
13:52
Speaker 1: you can sort of look at the record, right, Like
13:54
Speaker 1: you can look at ice layers and rock layers and
13:56
Speaker 1: you can see that it used to be sunnier before
13:59
Speaker 1: or not. Yeah. They do these core samples where they
14:01
Speaker 1: dig down and layers of ice in Greenland or in
14:04
Speaker 1: other parts of the world, and they can see the
14:06
Speaker 1: global temperatures and there really is variation. And they do
14:09
Speaker 1: these calculations based on you know, solar system models and
14:13
Speaker 1: to understand the variations in the Earth's tilt and orbit.
14:15
Speaker 1: And there's a really nice alignment between these global temperatures
14:18
Speaker 1: and these Earth's orbital changes. Wow. And it's crazy because
14:22
Speaker 1: it's like small, even tiny, little changes can basically change
14:26
Speaker 1: the weather. Like if the Earth tilled three degrees or
14:29
Speaker 1: two degrees this way or that way a little bit more,
14:31
Speaker 1: then suddenly we have an ice age. It really is incredible.
14:35
Speaker 1: But this is just one effect. It's important to understand
14:37
Speaker 1: other things, like atmospheric effects can drown them out. For example,
14:42
Speaker 1: if we hadn't been pumping c O two into our atmosphere,
14:45
Speaker 1: scientists predicted we'd be due for like a big glaciation
14:48
Speaker 1: stage in about fifty thou years. Now that's sort of
14:51
Speaker 1: off the table because the amount of C O two
14:53
Speaker 1: that we pumped into the atmosphere, so we can override
14:56
Speaker 1: these effects with larger effects like the Greenhouse effect. Well,
14:59
Speaker 1: it's in doable. So we can actually like change the
15:02
Speaker 1: destiny of the Earth, like we could totally ruin it
15:04
Speaker 1: perhaps even yeah, exactly. And so I just don't want
15:08
Speaker 1: anybody out there to think that all of the change
15:11
Speaker 1: in the atmosphere is due to natural effects from the
15:14
Speaker 1: Earth's orbit. This is an effect, and it has contributed
15:16
Speaker 1: to glaciation into ice ages, but it's not the only effect,
15:20
Speaker 1: and it doesn't even have to be the dominant effect.
15:22
Speaker 1: And it also sort of impact as you said, how
15:24
Speaker 1: much radiation we get. Like if if our orbit but
15:27
Speaker 1: you know, flies a little bit closer to the Sun,
15:29
Speaker 1: it's going to get a little harder on Earth too. Yeah,
15:32
Speaker 1: And some of these things can be sort of dramatic,
15:34
Speaker 1: like you have different cycles based on the orbit and
15:36
Speaker 1: the tilt and all these things that are different cycles
15:38
Speaker 1: there which have different periods like twenty or forty or
15:41
Speaker 1: a hundred thousand years. Sometimes they all come together and
15:45
Speaker 1: happen all at the same time. You can get pretty
15:47
Speaker 1: dramatic shifts in temperature, like about thirteen thousand years ago
15:51
Speaker 1: when temperatures dropped dramatically in just a few decades, and
15:54
Speaker 1: then thirteen hundred years later, temperatures spiked like ten degrees
15:58
Speaker 1: celsius within just a few years. As like all of
16:01
Speaker 1: the effects swung one way and then swung the other way.
16:04
Speaker 1: These things can have really big effects on the Earth's climate.
16:07
Speaker 1: Ten degrees is huge. It seems like it's not totally unpredictable, right, Like,
16:11
Speaker 1: we have a certain model of the Solar system and
16:13
Speaker 1: our our atmosphere, and so you know, we should believe
16:16
Speaker 1: the signists when they say what's going to happen next. Yeah,
16:19
Speaker 1: this part is pretty predictable because we have good models
16:22
Speaker 1: for how the Earth's orbit is affected by the tug
16:25
Speaker 1: of Jupiter, etcetera, etcetera. The other parts, you know, climate
16:28
Speaker 1: resonances and what happens with the greenhouse gases, that's something
16:32
Speaker 1: we're working on, is not as well understood and can
16:35
Speaker 1: be more dramatic. You know, something I didn't realize was
16:38
Speaker 1: that the climate is even affected by the flow of
16:40
Speaker 1: the continents. As the continents move over the surface of
16:44
Speaker 1: the Earth, they change how water flows. Is there a
16:47
Speaker 1: water channel between these two continents or not, for example,
16:49
Speaker 1: And that affects how the atmosphere moves, and that can
16:52
Speaker 1: have significant effects on the climate as well. There's a
16:55
Speaker 1: lot going on. It's a big complicated system with a
16:58
Speaker 1: huge number of feedback cycles, you know, so if you
17:01
Speaker 1: get it a little bit wrong, then you can get
17:02
Speaker 1: it a lot wrong. But you know, climate scientists are
17:05
Speaker 1: doing a great job at modeling this stuff. Well, I
17:07
Speaker 1: guess Carson's question is what would have happened if we
17:10
Speaker 1: hadn't had the last ice age? And so let's talk
17:13
Speaker 1: maybe about how an ice age impacts the Earth. Yeah,
17:17
Speaker 1: so the most recent ice age, scientists say, lasted from
17:21
Speaker 1: about two and a half million years ago till about
17:23
Speaker 1: twelve thousand years ago, waited less than millions of years. Yeah,
17:27
Speaker 1: these ice ages can last millions of years and sometimes
17:30
Speaker 1: hundreds of millions of years. But within an ice age
17:33
Speaker 1: there are more variations, and they call these glacial periods
17:37
Speaker 1: where things can then the glaciers can retreat and come back.
17:39
Speaker 1: And so the most dramatic and the one that really
17:41
Speaker 1: affects sort of life on Earth and the way we live.
17:43
Speaker 1: It is the last glacial period, which lasted from about
17:46
Speaker 1: a hundred thousand years ago to about twelve thousand years ago.
17:50
Speaker 1: That's the most recent impact on sort of like human
17:53
Speaker 1: development and migration, because I guess the northern parts of
17:58
Speaker 1: the and southernmost parts of the Earth more covered in
18:01
Speaker 1: ice than usual, but not completely. You said that we
18:03
Speaker 1: only got completely covered millions of years ago. That's right.
18:07
Speaker 1: During this last glacial period, we had like Canada was
18:09
Speaker 1: an ice sheet, most of the northern United States with
18:12
Speaker 1: an ice sheet. There are lots of glaciers around the
18:14
Speaker 1: world at high altitudes. But you know, it's not like
18:17
Speaker 1: the whole Earth was an ice sheet. But you know
18:19
Speaker 1: it affected the humanity. Humanity, for example, mostly lived at
18:22
Speaker 1: lower latitudes during this stage until the ice retreated and
18:26
Speaker 1: then they could migrate to Eurasia and more northern latitudes.
18:30
Speaker 1: Like it was still sunny in the Equator. Yes, it
18:32
Speaker 1: was still sunny in the Equator and hotter cool It
18:34
Speaker 1: was cooler than it is today, but obviously it was
18:37
Speaker 1: hotter at the equator than it was at the pole. Still,
18:40
Speaker 1: what about Berkeley, Berkeley will always be cool man, very chill.
18:47
Speaker 1: Not as chill as you see Santa Cruz. Right, there
18:49
Speaker 1: are the chill ones. Yep, nobody can chill like bananas slugs.
18:53
Speaker 1: All right, well, let's get a little bit more into
18:55
Speaker 1: the impacts of the Ice Age on Earth and the
18:57
Speaker 1: Last Ice Age on Earth and what would happen if
19:00
Speaker 1: we hadn't had that ice age. First, let's take a
19:02
Speaker 1: quick break. All right, we are answering questions from listeners,
19:18
Speaker 1: and our first question was from Carson, who asked what
19:21
Speaker 1: would have happened if we hadn't had the I guess
19:24
Speaker 1: the Last Ice Age that's probably the one that Carson
19:26
Speaker 1: is most wondering about. And you know, the Ice Age
19:29
Speaker 1: has big impacts on geology because the glaciers can like
19:33
Speaker 1: grind mountains and create valleys. It also has a big
19:37
Speaker 1: impact on the flora and fauna that developed to adapt
19:40
Speaker 1: to that climate, and specifically it had a pretty big
19:43
Speaker 1: impact on where humans ended up and how we evolved. Yeah,
19:47
Speaker 1: it's it's sort of an interesting effect that maybe when
19:50
Speaker 1: I was younger, I hadn't thought about that, Like glaciers
19:52
Speaker 1: can really kind of like smooth over a landscape. I
19:55
Speaker 1: think a lot of the like the eastern United States
19:58
Speaker 1: has you know, more rolling hills rather than dramatic mountains
20:01
Speaker 1: because the glaciers basically like you know, crunched them all down.
20:06
Speaker 1: I'm not actually sure about that. I think that smoother
20:08
Speaker 1: mountains are just older mountains. They have been worn down
20:12
Speaker 1: by wind and rain and cycles of weather. The Rockies,
20:15
Speaker 1: for example, are sharper because they're younger. It's incredible in
20:18
Speaker 1: the history of the science is really fascinating as people
20:20
Speaker 1: realized that there was this incredible, powerful, dramatic force that
20:24
Speaker 1: happened very very slowly on Earth. These moving of these
20:27
Speaker 1: glaciers can really shape valleys and distribute boulders. It was
20:31
Speaker 1: the presence of these boulders that tip people off. People
20:34
Speaker 1: in the Alps were like, how did this rock get here?
20:36
Speaker 1: It's for much more northern climates, and people were wondering,
20:39
Speaker 1: like how to explain where all the rocks were, And
20:41
Speaker 1: very slowly they put together this crazy story about sheets
20:45
Speaker 1: of ice moving over the Earth and changing its shape.
20:48
Speaker 1: It's kind of bonkers and like boulders hitching a ride
20:51
Speaker 1: or like surfing the glacier wave. Yeah, glaciers break boulders
20:56
Speaker 1: off the mountains and then can carry them for hundreds
20:59
Speaker 1: of miles and deposit them somewhere else. Wow. Yeah, and
21:02
Speaker 1: said how stone hands got a bill. I think that
21:06
Speaker 1: was graffiti from the alien skiers. Actually the alien snowboarders
21:10
Speaker 1: came to a snowboard and piles on rocks like like
21:14
Speaker 1: the tourists usually do. I think that's another divide. We
21:17
Speaker 1: don't want to get into skiers versus snowboarders. But yeah,
21:21
Speaker 1: like you said, it really affects the trajectory not just
21:24
Speaker 1: of the landscape but also life on earth. Like if
21:26
Speaker 1: most of the Earth is covered in ice, it's gonna
21:29
Speaker 1: you know, determine what kinds of animals survive and which
21:31
Speaker 1: ones don't. And you know the kind of flora and
21:34
Speaker 1: fauna that we have. You know, the fact that we
21:36
Speaker 1: have like horses and cows, and a lot of the
21:39
Speaker 1: grains we eat are basically evolved grasses. That's due to
21:42
Speaker 1: the climate that we had. If we hadn't had an
21:45
Speaker 1: ice age, for example, the whole earth might be wetter,
21:48
Speaker 1: and it might be warmer, and it might be more
21:51
Speaker 1: covered in jungles and rainforests than grassy plains. And so
21:56
Speaker 1: the kind of farming practices we developed could have been
21:59
Speaker 1: totally different. Oh. Interesting, So that's one way, one specific
22:02
Speaker 1: way the Ice Age has you know, impacted us is
22:05
Speaker 1: we would have less fewer horses and cows and grasses, grasslands,
22:10
Speaker 1: and the whole concept of agriculture could be very different.
22:12
Speaker 1: A farm could be basically a piece of forest. You know,
22:15
Speaker 1: it's hard to imagine how civilization and how agriculture might
22:18
Speaker 1: have developed in the context of basically everybody living in
22:20
Speaker 1: the Amazon. Interesting. Yeah, because it might have also affected
22:24
Speaker 1: human development, right, absolutely. There are some theories that the
22:28
Speaker 1: harsh living conditions during the Ice Age basically forced humans
22:32
Speaker 1: to develop cognition, to evolve bigger brains so we could
22:35
Speaker 1: work together and develop tools, hunt willy mammoths, this kind
22:38
Speaker 1: of stuff. It's certainly had an impact on humans, although
22:41
Speaker 1: there's always the alternative reality game. They're like, sure that
22:45
Speaker 1: might have played a role. We don't really know what
22:47
Speaker 1: would have happened to humanity in other situations. Maybe we
22:50
Speaker 1: would have been even smarter. I see. The theory is
22:52
Speaker 1: sort of like, because it was we had these long winters,
22:56
Speaker 1: it kind of forced humans to plan ahead and to
22:58
Speaker 1: think about like crop since strategizing, which kind of pushed
23:02
Speaker 1: this to be smarter and to be and to be
23:04
Speaker 1: less procrastinators exactly. But these are always just explanatory stories, right,
23:09
Speaker 1: There's aren't really testable theories. It's very easy to look
23:12
Speaker 1: at the series events and say, oh, this makes sense,
23:14
Speaker 1: and I think this is why it happened. To really know,
23:17
Speaker 1: you'd have to run alternatives. You'd have to say, well,
23:20
Speaker 1: let's see what happens if I change things? And that's
23:23
Speaker 1: sort of a fascinating question. But one will never know
23:26
Speaker 1: the answer too, because we only have this one universe
23:28
Speaker 1: and we only see what happens to this Earth one time. Yeah,
23:31
Speaker 1: we need like a control Earth for every single conceivable
23:34
Speaker 1: experiment we do. We need the multiverse for that reason,
23:37
Speaker 1: so you can see, you know, what would happen if
23:39
Speaker 1: I had gone to Stanford? Would I be a different
23:42
Speaker 1: person today? You'd definitely be much cooler. Maybe I had
23:47
Speaker 1: or richer. Apparently, maybe you would have invented TikTok Daniel.
23:51
Speaker 1: If I had, it would have been a lot more
23:52
Speaker 1: boring than it is today. It would have been physics
23:55
Speaker 1: though exactly all right, Well, I think that answers Carson's question.
24:00
Speaker 1: If we hadn't had the ice age, things would be
24:02
Speaker 1: really different. Well, first of all, it sort of depends
24:04
Speaker 1: a lot on our trajectory in space and how close
24:07
Speaker 1: we get to the Sun and how and how tilted
24:09
Speaker 1: we are. But if we hadn't had the last one,
24:11
Speaker 1: maybe we would be eating different kinds of plants and
24:14
Speaker 1: fruits and animals and and or we might be a
24:17
Speaker 1: little bit different ourselves. Yeah, we might all be roasting
24:20
Speaker 1: banana slugs over the fire, and we might all be
24:24
Speaker 1: procrastinators instead of just some of us being procrastinators. Speaking
24:28
Speaker 1: of procrastination, let's get into our next question, and this
24:31
Speaker 1: one comes from Chris, who has a question about photons
24:35
Speaker 1: moving near black holes. Hi Danueine Horree, thank you so
24:38
Speaker 1: much for your show. I look forward to it every week.
24:41
Speaker 1: All right, here's my question about photons. So let's say
24:45
Speaker 1: we are on Miller's planet, the like the one in Interstellar,
24:50
Speaker 1: and we look up at the sky and we can
24:52
Speaker 1: see a star. So the photons coming off that sun.
24:56
Speaker 1: Let's say some of the photons missed the gravity of
24:59
Speaker 1: the planet and continue on to their destination. But a
25:03
Speaker 1: few of those photons get trapped or caught into the
25:07
Speaker 1: gravity of the planet. So from the perspective of somebody
25:12
Speaker 1: that's not in the gravity of the planet. Doesn't that
25:15
Speaker 1: photon travel slower than the other photons that moved on
25:21
Speaker 1: that didn't get caught in the gravity of the planet.
25:23
Speaker 1: Kind of confusing, all right, thanks, kind of confusing for sure.
25:28
Speaker 1: That's why we're here. I think there's a good summary
25:31
Speaker 1: of general relativity right there. Kind of confusing, I guess
25:36
Speaker 1: special realtivity. Chris, it's kind of confusing. But is there
25:41
Speaker 1: really excellent question he's asking It really difficult and subtle
25:43
Speaker 1: question about what it looks like to see a photon
25:46
Speaker 1: go near a very massive object, to be sucked into
25:49
Speaker 1: the gravity well of a black hole or a very
25:52
Speaker 1: dense planet. Right, Because we've talked about on this podcast,
25:55
Speaker 1: how when you have a lot of mass, like in
25:57
Speaker 1: a black hole or just like a heavy planet, it
25:59
Speaker 1: can bends the space time around it, and it actually
26:03
Speaker 1: sort of slows down time. I think that's maybe what
26:06
Speaker 1: he's trying to connect. Yeah, it can slow down time,
26:09
Speaker 1: and also it changes the path of these particles. It
26:11
Speaker 1: changes the fundamental geometry of space the way the particles move.
26:14
Speaker 1: At least two really confusing and sort of paradoxical ideas,
26:18
Speaker 1: Like one thing we say in the podcast a lot
26:20
Speaker 1: and that people talk about in physics A lot is
26:22
Speaker 1: light always moves at the speed of light, no matter
26:25
Speaker 1: who's measuring it, right, We say that a lot. On
26:27
Speaker 1: the other hand, we also say that like photons can't
26:30
Speaker 1: escape a black hole, and people might be puzzling about that,
26:33
Speaker 1: like what does that mean? How fast is a photon
26:36
Speaker 1: moving when he's trying to climb out of that gravity? Well,
26:39
Speaker 1: doesn't eventually get stopped by the gravity of the black hole.
26:42
Speaker 1: Had he reconciled those two ideas, Yeah, it's kind of
26:46
Speaker 1: confusing for sure, But I think maybe the scenario is
26:49
Speaker 1: I think he was trying to paint, is that like,
26:51
Speaker 1: let's say a star shoots off to photons and one
26:54
Speaker 1: photonogy goes clear through space, no, no, nothing in its path,
26:58
Speaker 1: But the other one flies like us, to a heavy
27:00
Speaker 1: planet or close to a black hole. Like, if you
27:02
Speaker 1: were looking at these two photons, but the one that
27:05
Speaker 1: goes near the black hole, would that one go slower? Yeah?
27:07
Speaker 1: Would you see a photon moving at less than the
27:10
Speaker 1: speed of light? And your instinct, physics wise, is to
27:13
Speaker 1: say no, absolutely, that can never happen. Problem is, that's
27:16
Speaker 1: not exactly true. Because when we say photons always travel
27:20
Speaker 1: at the speed of light, there's a qualifier there. There's
27:23
Speaker 1: a caveat that we almost never mentioned that's important in
27:26
Speaker 1: this particular case. And that caveat is that it's true
27:30
Speaker 1: that photons always travel at the speed of light. But
27:33
Speaker 1: that's only true if space is flat, that is, if
27:36
Speaker 1: there's no curvature to space, and only true for nearby observers.
27:42
Speaker 1: So the full statement is that photons only travel at
27:45
Speaker 1: the speed of light as measured locally by people nearby.
27:50
Speaker 1: In flat space, space is curved and you're far away
27:53
Speaker 1: from an object, the rule that photons have to travel
27:56
Speaker 1: at the speed of light no longer holds interesting. I
28:00
Speaker 1: think what you're saying is that, like, photons have to
28:02
Speaker 1: travel the speed of light in space right like to
28:05
Speaker 1: the photon, it's always going at the same speed. But
28:08
Speaker 1: you're saying you can't sort of squish and bend space itself,
28:12
Speaker 1: which might to a someone who's looking from far away,
28:15
Speaker 1: might make it actually go faster and slower than the
28:17
Speaker 1: speed of light. Yeah, and it goes one step deeper
28:19
Speaker 1: than that. And remember that you can't talk about velocity
28:22
Speaker 1: without talking about pairs of objects. Velocity is not a
28:25
Speaker 1: property of an object. Of ball flying through space doesn't
28:28
Speaker 1: have a speed. It only has a speed relative to observers.
28:32
Speaker 1: So whenever you talk about velocity, you can't think about
28:34
Speaker 1: a ship traveling near the speed of light. You always
28:36
Speaker 1: have to say a ship traveling at whatever speed relative
28:39
Speaker 1: to Earth, for example. So in this case, we're talking
28:42
Speaker 1: about photons relative to an observer nearby versus photons relative
28:46
Speaker 1: to an observer far away. The problem is that, in
28:48
Speaker 1: general relativity, that is the theory that tells us how
28:51
Speaker 1: to think about the universe as it curves and bends
28:54
Speaker 1: in response to mass, there is no well defined definition
28:59
Speaker 1: of velocity for something that's far away. It's like you
29:02
Speaker 1: can't even really sensibly talk about the speed of a
29:05
Speaker 1: photon that is very far away from you. Wait, what
29:08
Speaker 1: what do you mean? Like? I can see it, you know,
29:11
Speaker 1: one spot from from a distance, and then I see
29:13
Speaker 1: it in another spot from a distance a short time later.
29:17
Speaker 1: I can you know, measure with the distance between those
29:19
Speaker 1: two things and divide by the time. That would give
29:21
Speaker 1: me the its speed. Yeah, that sounds straightforward, but the
29:24
Speaker 1: problem is that you were using your local inertial reference
29:27
Speaker 1: frame to measure the path of something that's moving through
29:31
Speaker 1: curved space far away. So you're assuming that space is
29:34
Speaker 1: flat between here and there, and if it isn't, if
29:37
Speaker 1: space is curved, then the reference frame of someone else
29:41
Speaker 1: nearby those photons would be very different, and your measurement
29:44
Speaker 1: and velocity and there's won't agree. For example, a distant
29:48
Speaker 1: observer will see light near a black hole travel at
29:51
Speaker 1: all sorts of crazy speeds from less than the speed
29:54
Speaker 1: of light all the way down to zero, but a
29:56
Speaker 1: local observer near the black hole and near that photon
29:59
Speaker 1: will always measure that light moving at the speed of light.
30:02
Speaker 1: But this is more than just different reference frames having
30:05
Speaker 1: different values. We have that in special relativity and we
30:08
Speaker 1: know how to translate and compare, but because space is curved,
30:13
Speaker 1: there are many different ways to compare those measurements velocities
30:17
Speaker 1: in general relativity, So to translate between two different reference
30:21
Speaker 1: frames and curved space, now why is that? What you
30:24
Speaker 1: need to do in that case is compare its velocity
30:27
Speaker 1: to your own, right, you need relative velocity, and so
30:31
Speaker 1: you're making those measurements and so really what you're doing
30:33
Speaker 1: is you're comparing two different vectors there, like your velocity
30:37
Speaker 1: and its velocity, and that's something you can do if
30:40
Speaker 1: space is flat, but it's not something that we know
30:43
Speaker 1: how to do if space is curved. And it's useful
30:46
Speaker 1: to think about an analogy like making a measurement on
30:48
Speaker 1: the surface of the Earth. Say, for example, you have
30:51
Speaker 1: two runners and they're running a race. If they're next
30:54
Speaker 1: to each other, it's very simple to see who's faster.
30:56
Speaker 1: They're literally next to each other. Now, imagine you take
30:59
Speaker 1: one of the runs and one of them is in
31:01
Speaker 1: Paris and the other one is in Cape Town, South
31:03
Speaker 1: Africa or something. So they're like on different places in
31:06
Speaker 1: the Earth. Now they're not really running in the same direction, right,
31:09
Speaker 1: because the Earth is curved. One is running in one direction,
31:11
Speaker 1: the other one is running sort of in a different direction.
31:14
Speaker 1: So how do you compare their velocities? Right? Well, one
31:17
Speaker 1: thing you can do is to say, well, I'm gonna
31:19
Speaker 1: take the velocity vector of the Cape Town runner. I'm
31:22
Speaker 1: gonna bring it over to Paris and sort of like
31:25
Speaker 1: transported over to Paris, and then I'm going to compare
31:27
Speaker 1: the two velocities. I mean, like, if I'm floating in
31:29
Speaker 1: a space station looking at these two runners from space,
31:32
Speaker 1: you just want to compare these two, right, it doesn't
31:35
Speaker 1: matter really where you are from that perspective, You've got
31:37
Speaker 1: to bring those vectors close to each other. But why
31:40
Speaker 1: do I have to do that? I guess can I?
31:41
Speaker 1: I just, for example, from space in my space station,
31:45
Speaker 1: measure the length of the track that the American runner
31:48
Speaker 1: is in, and then measure from space the length of
31:50
Speaker 1: the track that the South African runners in. And then
31:53
Speaker 1: you know, as I see that, I start the clock
31:55
Speaker 1: when they both started running, and then I measure how
31:58
Speaker 1: long it took to get to the side of the track. Yeah,
32:00
Speaker 1: you could do that. You could ignore the curvage of
32:03
Speaker 1: the Earth and just measure their velocity relative to somebody
32:05
Speaker 1: in space. That's like, again, assuming everyone is in your
32:09
Speaker 1: local inertial frame and that space is flat. But we
32:13
Speaker 1: put people in this example on a curved surface as
32:16
Speaker 1: an analogy for what happens when space is curved. But
32:19
Speaker 1: when you're running a race, we really want the velocity
32:21
Speaker 1: along the Earth, right, not the velocity through space, which
32:25
Speaker 1: you one is the answer of if I brought the
32:27
Speaker 1: Cape Town runner to Paris, who would win this race? Right?
32:31
Speaker 1: And so the curvage of the Earth makes a difference
32:33
Speaker 1: there you can't just ignore it, alright, So you're saying
32:37
Speaker 1: that that it's hard to measure or compare velocities in
32:39
Speaker 1: curve space because things kind of get kind of wonky
32:43
Speaker 1: because spacetime is being curved. That's right, And the problem
32:46
Speaker 1: is that how you compare those two vectors depends on
32:49
Speaker 1: how you bring one vector close to the other vectors.
32:52
Speaker 1: This is called parallel transport in geometry. You want to
32:55
Speaker 1: compare two vectors, you've got to bring them near each other.
32:57
Speaker 1: In flat space, that's not a big deal because if
33:00
Speaker 1: move the vector from there it here doesn't change. In
33:02
Speaker 1: curved space, the vector changes as it moves through that
33:05
Speaker 1: curved space, and so there's an infinite number of different
33:07
Speaker 1: ways you can do it, and the answer you get
33:09
Speaker 1: depends on the path. So if you bring the Cape
33:12
Speaker 1: Town Guide to Paris along one path, is vector will
33:15
Speaker 1: be in one direction. If you do it along another path,
33:18
Speaker 1: IS vector will be in a different direction. And so
33:20
Speaker 1: this is all really important because it means that you
33:22
Speaker 1: can't define the difference between those two velocity vectors across
33:27
Speaker 1: curved space, and so that means that you can't talk
33:30
Speaker 1: about the relative velocity of things that are really really
33:32
Speaker 1: far apart, you can't define what happens to a photon,
33:36
Speaker 1: and that means that the rules of special relativity and
33:38
Speaker 1: no longer apply. So a photon moving around a black
33:41
Speaker 1: hole could appear to have a velocity not the speed
33:43
Speaker 1: of light, all the way down to apparently zero velocity
33:46
Speaker 1: as it tries to climb out of that gravity. Well, right,
33:48
Speaker 1: I think what you're saying is that if we were
33:50
Speaker 1: to run the experiment that Crisp wants us to run,
33:52
Speaker 1: which is like, shoot two photons and have one go
33:55
Speaker 1: into a black hole, like, we would see one of
33:57
Speaker 1: them just fly through space away and the other one
34:01
Speaker 1: we would see actually like kind of stop at the
34:03
Speaker 1: black hole, kind of like right, like it would just
34:05
Speaker 1: stop from our point of view. From our point of view,
34:08
Speaker 1: and according to our decision about how to measure that velocity,
34:12
Speaker 1: somebody else looking from another perspective might have a different
34:15
Speaker 1: definition of like, well, here's how I'm going to bring
34:17
Speaker 1: those velocity vectors together to compare them. They might get
34:20
Speaker 1: a different answer. What do you mean, Like if I'm
34:22
Speaker 1: moving maybe at a different speed, but if I just
34:24
Speaker 1: stand on the other side of the black hole, I'm
34:26
Speaker 1: probably going to see the same thing. Right, I'm going
34:27
Speaker 1: to see one photon keep flying off and the other
34:29
Speaker 1: one stop at the black hole. Right, But in order
34:32
Speaker 1: to measure the velocity of that photon, you need to
34:35
Speaker 1: talk about how to bring its velocity vector into your
34:38
Speaker 1: local space, and there's an infinite number of ways to
34:41
Speaker 1: do that, and the choice you make about how to
34:43
Speaker 1: transport that vector changes the answer. So you and I
34:46
Speaker 1: could be right next to each other looking at the
34:48
Speaker 1: same photon. But if you have a different definition of
34:51
Speaker 1: basically velocity in general relativity than I do, we could
34:54
Speaker 1: get different answers. So that's why people say it's not
34:56
Speaker 1: well defined, because there's an infinite number of arbitrar choices
35:00
Speaker 1: you can make that do affect your answer? All right, Well,
35:03
Speaker 1: then what would be the answer for Chris? So you
35:05
Speaker 1: would you see that photon move slower, the one that
35:08
Speaker 1: goes near the heavy mass. You would see it move
35:10
Speaker 1: slower exactly no matter where you are. You would see
35:13
Speaker 1: it move slower than the speed of light, almost no
35:15
Speaker 1: matter where you are. And you know, this might be
35:17
Speaker 1: confusing to people if they think, well, how can we
35:18
Speaker 1: not define the velocity of objects that are far away?
35:21
Speaker 1: Like we talk about galaxies moving really really fast away
35:25
Speaker 1: from us, and the galaxies are very far away. That's
35:28
Speaker 1: one reason we can talk about galaxies moving away from
35:30
Speaker 1: us faster than the speed of light. One way to
35:33
Speaker 1: think about it is that space is expanding between us
35:35
Speaker 1: and those galaxies. Another totally reasonable way to think about
35:38
Speaker 1: that is to attribute that velocity actually to the objects
35:41
Speaker 1: and not to the motion of space itself. Those are
35:44
Speaker 1: both arbitrary but reasonable choices. And that's why we say,
35:47
Speaker 1: like the velocity of objects isn't well defined in gr
35:51
Speaker 1: because it requires an arbitrary choice. It's kind of like
35:54
Speaker 1: how we've always said or set often on this podcast
35:57
Speaker 1: and in our books. It's like if Hussain Bold can
35:59
Speaker 1: only run so fast on land, but if there's like
36:02
Speaker 1: new land being made between us and him, he's gonna
36:04
Speaker 1: look like he's going faster than what he can actually run.
36:07
Speaker 1: Or if there's if like the continent he's on is
36:10
Speaker 1: actually moving towards us, he might appear to be moving
36:13
Speaker 1: slower exactly. And that's the standard choice and cosmology to
36:17
Speaker 1: think of the universe as expanding in a certain way
36:19
Speaker 1: and to think of motion relative to that expanding space,
36:23
Speaker 1: And that's a totally reasonable choice, and that's what we
36:25
Speaker 1: usually do when we talk about the expansion of the
36:27
Speaker 1: universe and the velocity of really distant objects. But you
36:30
Speaker 1: could make other choices. As an arbitrary choice, it is
36:33
Speaker 1: just sort of the one people typically make. You could
36:35
Speaker 1: make other choices, which is why these velocities of very
36:38
Speaker 1: distant objects technically not well defined. And that's why you
36:41
Speaker 1: can end up in situations where you say things like, oh,
36:43
Speaker 1: light is moving slower than the speed of light. It's
36:46
Speaker 1: because velocity of far away objects is not really well defined.
36:49
Speaker 1: If you're near a photon, it will always be moving
36:52
Speaker 1: at the speed of light relative to you, right right, Yeah,
36:55
Speaker 1: Like if you're falling into the black hole with the photon,
36:57
Speaker 1: the photon would just look like it's it's moving at
36:59
Speaker 1: the speed of light. But that's because also your time
37:02
Speaker 1: frame is also being slowed down right exactly it's near you,
37:05
Speaker 1: and so locally space is always flattened near you, and
37:09
Speaker 1: so if you're with the photon, it's moving through flat
37:11
Speaker 1: space at the speed of light. A distant observer, that's
37:13
Speaker 1: where the problem comes in because the definition of velocity
37:16
Speaker 1: for distant objects is bunky in general relativity, where its
37:20
Speaker 1: Chris says, kind of confusing. I think that's the real
37:22
Speaker 1: answer for Chris here to this question. It's kind not confusing.
37:26
Speaker 1: All right, Well, let's get into our last question, and
37:28
Speaker 1: this one is a little bit related. It's another question
37:31
Speaker 1: about light and it's speed, So let's get into that.
37:34
Speaker 1: But first let's take another quick break. All right, we
37:49
Speaker 1: are answering listener questions and also debating UM Berkeley versus Stanford.
37:53
Speaker 1: Apparently there's no debate, man, I mean, it's just talking
37:56
Speaker 1: about it. But I see, well, I think there's a
38:00
Speaker 1: debate about whether there is a debate. I think it's
38:04
Speaker 1: only really one side of that debate. Now we we're
38:08
Speaker 1: answering listener questions and our last question here comes from Dennis,
38:11
Speaker 1: who has a question about the speed of light. Hello
38:14
Speaker 1: Daniel Kay, First of all, I love your podcast. I
38:17
Speaker 1: was wondering what is the minimal speed of light to
38:22
Speaker 1: sort of hold a universe together? And what would happen
38:26
Speaker 1: if a light would only have a thousand kilometers per
38:30
Speaker 1: per second of speed? What was happened? Then? Okay, thank you? Alright,
38:35
Speaker 1: awesome question from Dennis here about the speed of light,
38:38
Speaker 1: and I guess this question is sort of like, because
38:41
Speaker 1: we've talked about on this podcast before and in our
38:43
Speaker 1: book also about the speed of light is a little
38:45
Speaker 1: bit arbitrary, Like you can it could have it's it's
38:48
Speaker 1: like three millions per second, but it could have been
38:50
Speaker 1: something different. It could have been three per second or
38:53
Speaker 1: three billion meters per second, and you could maybe still
38:55
Speaker 1: have like a functioning universe. Yeah, we don't really know
38:58
Speaker 1: if it could have been something else, but we don't
39:00
Speaker 1: know why it is what it is. We have no
39:03
Speaker 1: explanation for it being that number in particular, and that
39:06
Speaker 1: suggests that maybe it could have been something else. And
39:09
Speaker 1: there's lots of really interesting philosophical wrinkles there, like are
39:12
Speaker 1: there other versions of the universe out there in the
39:15
Speaker 1: multiverse with different speeds of light? Etcetera, etcetera. And it's
39:18
Speaker 1: a really great question to ask, like what speeds are allowed?
39:22
Speaker 1: Could the universe work if the speed of light was different? Yeah?
39:26
Speaker 1: Pretty cool And something I think we discussed recently in
39:29
Speaker 1: an podcast episode that was a little mind blowing for
39:31
Speaker 1: me was that you told me that a light the
39:33
Speaker 1: speed of light is not actually a fundamental like unit
39:37
Speaker 1: or value of the universe. That's right, The speed of
39:39
Speaker 1: light has units to it, right, meters per second, and
39:42
Speaker 1: so the actual number is really arbitrary because it depends
39:46
Speaker 1: on the units. So when we talk about the construction
39:49
Speaker 1: of the universe and the parameters that influence the way
39:52
Speaker 1: that it is, we try to focus on numbers that
39:55
Speaker 1: don't have units to them, dimensionless numbers, numbers like the
39:59
Speaker 1: cosmological constant which affects the expansion of the universe, or
40:03
Speaker 1: the ratio of masses of the electron to the muan,
40:06
Speaker 1: for example. And the speed of light does factor in
40:08
Speaker 1: because it's part of what we call the fine structure constant,
40:11
Speaker 1: which combines a bunch of these different constants blanks constant,
40:14
Speaker 1: the speed of light, strength of the electromagnetic force. Yeah,
40:18
Speaker 1: like this like like a ratio, right, like the speed
40:20
Speaker 1: of light divided by how quickly Berkeley students think two
40:25
Speaker 1: really big numbers. But I think the idea is that
40:30
Speaker 1: generally speaking, like you know, how fast light travels through
40:33
Speaker 1: space is sort of like a fundamental property of the
40:35
Speaker 1: universe that we currently can't really explain. Like it seems arbitrary, yeah,
40:39
Speaker 1: and it might be that it bubbles up from a
40:41
Speaker 1: deeper understanding of the nature of space time. You know
40:44
Speaker 1: if space, for example, is a quantum foam of little
40:47
Speaker 1: space pixels linked together by tiny wormholes. It could be
40:50
Speaker 1: that some property of those wormholes influences how information propagates
40:55
Speaker 1: from one space pixel to the other, and that determines
40:57
Speaker 1: the speed of light. We just don't know the sketch
41:00
Speaker 1: from maybe how you could get an answer to what
41:02
Speaker 1: the speed of light is, or it could just be
41:04
Speaker 1: a totally arbitrary It could be that as universes are created,
41:07
Speaker 1: to some random process that sets these parameters, and this
41:10
Speaker 1: is the one that we got, Like you get three
41:13
Speaker 1: hund a million per second, you get second exactly. And
41:19
Speaker 1: it's fun to think about what the universe would look like.
41:21
Speaker 1: And I love the way Dennis posed this question, which
41:24
Speaker 1: is like could the universe come together with the minimum
41:27
Speaker 1: speed of light for a universe to function? Yeah, it
41:29
Speaker 1: seems like he has he has a two part question. Actually,
41:32
Speaker 1: the first part is like, could we have a universe
41:34
Speaker 1: with a slower speed of light? And what would be
41:37
Speaker 1: the slowest speed of light that a universe would still
41:40
Speaker 1: hold together? Which is sort of an interesting way to
41:42
Speaker 1: put it, like could with the universe fall apart if
41:44
Speaker 1: the speed of light was slower. Well, you know, the
41:46
Speaker 1: way I think about this is in terms of light cones,
41:49
Speaker 1: something we talked about in the podcast once, which tells
41:52
Speaker 1: you what portion of the future of the universe you
41:55
Speaker 1: can influence and which portion of the past of the
41:58
Speaker 1: universe influences you. Because we have this maximum speed of information,
42:03
Speaker 1: it means that, for example, you can't affect things in
42:06
Speaker 1: a neighboring galaxy that are happening right now. You made
42:09
Speaker 1: a decision about something you wanted to happen in Andromeda,
42:12
Speaker 1: it would take millions of years for that decision to
42:14
Speaker 1: have any effect. That your light cone fraction of the
42:18
Speaker 1: universe in the future that you can influence, and the
42:21
Speaker 1: size of that cone, the slope of that cone is
42:23
Speaker 1: determined by the speed of light. So the speed of
42:25
Speaker 1: light was much much faster than you could influence Andromeda
42:28
Speaker 1: maybe tomorrow. If the speed of light was much much slower,
42:31
Speaker 1: that might take billions of years to affect Andromeda instead
42:34
Speaker 1: of millions. And so the size of that cone, the
42:37
Speaker 1: narrowness of that cone, is determined by the speed of light. Yeah,
42:40
Speaker 1: I mean it definitely, it would change the universe. But
42:42
Speaker 1: I think his maybe question was more like, is there
42:45
Speaker 1: something in the equations of the universe that we know
42:47
Speaker 1: about right now that if I, you know, start dialing
42:50
Speaker 1: the speed of light down, would at some point equations
42:53
Speaker 1: fail or become incoherent or illogical. Or is it really
42:57
Speaker 1: the fact that, you know, the speed of light could
42:59
Speaker 1: be one centimeter per second and you could still have
43:02
Speaker 1: a functioning universe. Yeah, as far as I know, there
43:04
Speaker 1: is no minimum speed. You would have completely different kind
43:08
Speaker 1: of universe. It would feel very, very different, and it
43:11
Speaker 1: might affect the structure of matter. You know, the orbits
43:14
Speaker 1: of the electrons, for example, are affected by the speed
43:16
Speaker 1: of light, and so you might not get hydrogen, you
43:19
Speaker 1: might get weird other forms of matter. But you would
43:22
Speaker 1: still have a universe even with a much slower or
43:24
Speaker 1: much faster speed of light. I see, like if you
43:27
Speaker 1: change the rules, the atoms and the corks and all
43:29
Speaker 1: that would just played played differently, but they could still play,
43:34
Speaker 1: They could still play exactly, and they would play differently,
43:37
Speaker 1: And the consequences of that are really hard to imagine
43:39
Speaker 1: and difficult to calculate. Also, you know, we don't really
43:42
Speaker 1: even have a great theory for like how corks come
43:44
Speaker 1: together to make protons and neutrons because it involves the
43:47
Speaker 1: strong force, which is a real pain to calculate. And
43:50
Speaker 1: so if the balance of all those forces changes, then
43:53
Speaker 1: a lot of things that are difficult to calculate would
43:56
Speaker 1: be different. So the whole universe could be very different.
43:58
Speaker 1: But you know, if the universe doesn't change that much,
44:00
Speaker 1: if the speed of light goes down by fifty or something,
44:03
Speaker 1: I think you'd largely get the same universe, but it
44:06
Speaker 1: would feel different, like you could see less of the
44:09
Speaker 1: universe out there, like our little bubble. The observable universe
44:12
Speaker 1: also depends on the speed of light, right well, but
44:15
Speaker 1: I think it's also maybe deeper, perhaps than just what
44:18
Speaker 1: we can see, because the speed of light doesn't just
44:20
Speaker 1: affect light and photons. It also sort of the term
44:23
Speaker 1: is how fast some of these fundamental particles can move, right,
44:26
Speaker 1: and also kind of like the range of their effect,
44:29
Speaker 1: right Like I'm thinking some of the force particles, if
44:31
Speaker 1: they could move faster or slower than there there, it
44:35
Speaker 1: wouldn't be a strong perhaps, that's certainly true. And the
44:37
Speaker 1: speed of light I think most directly affects the strength
44:39
Speaker 1: of the electromagnetic interaction because it goes directly into the
44:43
Speaker 1: fine structure constant, which appears in the coupling of photons
44:46
Speaker 1: to electrons and photons to other charge particles. So the
44:50
Speaker 1: speed of light was different, it would change also sort
44:52
Speaker 1: of the relative strength of electromagnetism to the other forces.
44:57
Speaker 1: All right, so, um, you said it would be different.
44:59
Speaker 1: So what are some of the ways that the universe
45:01
Speaker 1: would be different if the speed of light was slower. Well,
45:04
Speaker 1: if the universe was different, if the speed of light
45:06
Speaker 1: was slower, we couldn't have as large as structure forming
45:09
Speaker 1: in the universe. Like, in order to have a structure form,
45:12
Speaker 1: you need to have information go back and forth across it.
45:15
Speaker 1: You know, for a planet, for example, to coalesce gravitationally,
45:19
Speaker 1: you need information to propagate from one side of the
45:21
Speaker 1: planet to the other for it to be like a
45:23
Speaker 1: single object. You mean, like gravity. Even the force of
45:27
Speaker 1: gravity has a speed limit, and that speed limit is
45:30
Speaker 1: the same as the speed of light. Yeah. So if
45:31
Speaker 1: we're talking about like the speed of information through the universe,
45:35
Speaker 1: then if you're cutting the speed of information down, then
45:37
Speaker 1: gravity also transmits its information more slowly. Right, you would
45:42
Speaker 1: be basically slowing down gravity too. Yeah, you would be
45:45
Speaker 1: slowing down gravity and you would be limiting gravity in
45:48
Speaker 1: the size of the thing that it can build. You know,
45:50
Speaker 1: we think that there's like a biggest structure that can
45:53
Speaker 1: exist in the universe because it takes time for gravity
45:56
Speaker 1: to pull things together, and the universe hasn't existed for
45:59
Speaker 1: that long, so you know, the universe has been around
46:02
Speaker 1: fourteen billion years. That means you can't have a structure
46:05
Speaker 1: that's like fifty billion light years wide because it just
46:08
Speaker 1: hasn't been time for like one side of it to
46:10
Speaker 1: coordinate with the other side and like come into equilibrium
46:13
Speaker 1: with it. So there's a limit there on the biggest
46:15
Speaker 1: thing you can make, and that depends on the speed
46:17
Speaker 1: of light. Right, It's like trying to bring your kids together.
46:19
Speaker 1: If you're really slow person, you can't like if you
46:22
Speaker 1: slow down gravity, Like gravity would be trying to pull
46:26
Speaker 1: all those distant galaxies together, but maybe by the time
46:29
Speaker 1: it acts that the galaxies are long gone. Yeah. Or say,
46:33
Speaker 1: for example, you're trying to organize a family reunion. You
46:35
Speaker 1: can get in touch with much more distant relatives if
46:37
Speaker 1: you can email them rather than having to send snail
46:40
Speaker 1: mail or send a pony. Right, if you can only
46:42
Speaker 1: send a pony and you can organize a much more
46:44
Speaker 1: local family reunion, whereas if you can email people, you
46:47
Speaker 1: can get people from Singapore and people from Australia to
46:50
Speaker 1: come to your party. And so in that way, the
46:53
Speaker 1: universe would be sort of more local if the speed
46:56
Speaker 1: of light was smaller, right, Although I do know you, Daniel,
46:58
Speaker 1: and I know that a family union it would be
47:01
Speaker 1: you would organize it with ponies so that it maybe
47:05
Speaker 1: together as well. Like I put it on the back
47:07
Speaker 1: of an anteater. What's the problem you didn't get the invitation?
47:12
Speaker 1: Should have put it on the back of the tree.
47:14
Speaker 1: Banana's slug. But it's not just that it doesn't just
47:17
Speaker 1: affect the structure of the universe, right, Like if you
47:20
Speaker 1: slow down, gravity would also affect relativity to right, Yeah,
47:24
Speaker 1: a lot of the really weird effects from relativity times
47:27
Speaker 1: slowing down and things getting contracted, all that kind of stuff.
47:31
Speaker 1: We never see those effects because they only happen when
47:34
Speaker 1: you're going at very very high speeds relative to something else.
47:37
Speaker 1: So that's why it took us a long time to
47:39
Speaker 1: even discover that it's part of reality. But if the
47:42
Speaker 1: speed of light was slower, if it was like closer
47:44
Speaker 1: to human speeds, or speeds we could achieve on Earth,
47:47
Speaker 1: then we might have noticed these things because you would
47:49
Speaker 1: be able to see them, and we might have like
47:52
Speaker 1: intuition for relativity would like make sense to us in
47:55
Speaker 1: a way that right now it doesn't. Well, I wonder though,
47:58
Speaker 1: like if you slow down gravity and lights and basically
48:02
Speaker 1: how everything can propagate in the universe, wouldn't sort of
48:05
Speaker 1: time also slow down or wouldn't it feel slower as well,
48:09
Speaker 1: to the point where you know it's almost like if
48:11
Speaker 1: you're near a black hole, you know your time is
48:13
Speaker 1: moving slower, but you don't notice it. It's a great question,
48:15
Speaker 1: and this sort of goes to the heart of why
48:17
Speaker 1: we talk about dimensionless constants instead of dimension full constants
48:21
Speaker 1: like the speed of light, because for example, you could
48:24
Speaker 1: change the speed of light, but then if you tweaked
48:26
Speaker 1: a bunch of other numbers at the same time, nothing
48:28
Speaker 1: effectively would change in the universe. I think that's what
48:31
Speaker 1: you're talking about, if you tweaked a bunch of these
48:33
Speaker 1: numbers in such a way that none of the dimension
48:35
Speaker 1: list constants change. For example, if you change the speed
48:38
Speaker 1: of light, but you also change planks constant, and you
48:41
Speaker 1: change the strength of the electromagnetic force, and you wouldn't
48:44
Speaker 1: notice anything because you have look no absolute ruler to
48:47
Speaker 1: compare it to. It's sort of like if you got
48:49
Speaker 1: bigger and your ruler got bigger, you wouldn't notice any difference, right, Yeah,
48:52
Speaker 1: I think you know what I mean. It's like if
48:54
Speaker 1: you slow down the speed of light and slow down
48:55
Speaker 1: gravity put in that also maybe affect how fast you
48:59
Speaker 1: can think. Would you technically be thinking slower? Oh? Your
49:02
Speaker 1: perception of time? Oh that's fascinating from a neurobiological point
49:06
Speaker 1: of view, that's a great question. I don't know that
49:08
Speaker 1: our thinking, though, is limited by the speed of light.
49:10
Speaker 1: I think it's more affected by whether you went to
49:13
Speaker 1: Berkeley or Stanford. No, that's a great question. I don't
49:18
Speaker 1: know the answer to that. Whether the speed of your
49:20
Speaker 1: brain is actually affected by the speed of light, and
49:23
Speaker 1: whether I like our internal sense of time is affected
49:26
Speaker 1: by the speed of light. I suspect that it isn't
49:28
Speaker 1: that they're biological processes are very very slow. But I'm
49:32
Speaker 1: really just speculating there. Well, but I mean chemical reactions
49:34
Speaker 1: in your brain depend on the electromagnetic force, right, which
49:37
Speaker 1: would be slower as well. Yeah, that's true. Those bonds
49:40
Speaker 1: would have a different strength. We'll ask Katie Golden next
49:42
Speaker 1: time she's on, since she's an expert. She went to
49:46
Speaker 1: Harvard East Coast. West Coast just got complicated, all right, Well,
49:54
Speaker 1: at least team West Coast is representing today. That's right.
49:57
Speaker 1: We should unite against the true enemy, Annual the East Coast.
50:02
Speaker 1: All right, Well, it also might have a very direct
50:05
Speaker 1: impact on our everyday lives if the speed of light
50:08
Speaker 1: was slower, as specifically as you're listening to this podcast, right, Yeah,
50:12
Speaker 1: the Internet would be slower if the speed of light
50:14
Speaker 1: was slower. We relied these days on being able to
50:17
Speaker 1: like stream HD videos from around the world, downloading gigabyte
50:22
Speaker 1: files from Australia, etcetera. But the Internet moves at the
50:25
Speaker 1: speed of light and so like the bandwidth would be
50:28
Speaker 1: the same, but the latency would be longer. Like if
50:31
Speaker 1: you wanted to pin a computer in Australia and the
50:33
Speaker 1: speed of light was a thousand kilometers per second instead
50:36
Speaker 1: of three hundred million meters per second, then you would
50:38
Speaker 1: notice the different About half of our listeners are going
50:42
Speaker 1: and that's not a universe I want to live in.
50:44
Speaker 1: Forget it. Let's not even dwell on that everybody wants
50:47
Speaker 1: to live in the universe where the speed of light
50:49
Speaker 1: is faster and they get their downloads more quickly. Yeah,
50:52
Speaker 1: we all want optical fiber at the current speed. All right, Well,
50:56
Speaker 1: I think that answers the question for Dennis. There is
50:59
Speaker 1: no minimum speed of light that would hold the universe together.
51:02
Speaker 1: We could literally be like point zero zero zero zero,
51:04
Speaker 1: there is zero one per second, and you could still
51:07
Speaker 1: have a universe. It just would be super duper different. Yes,
51:10
Speaker 1: in ways that are probably impossible to predict. So hey,
51:12
Speaker 1: let's give it a try and find out. No, I
51:15
Speaker 1: want my fast internet, Daniel, I want my family reunions tomorrow.
51:20
Speaker 1: All right, Well, thank you to all of our question askers.
51:23
Speaker 1: We hope that was interesting for all of us. I
51:25
Speaker 1: think it was interestingful. It makes you kind of think about,
51:28
Speaker 1: you know, how the universe could have been different, in
51:30
Speaker 1: the Earth could have been different, all these interesting what
51:32
Speaker 1: if questions, And sometimes the hardest question is the deepest ones,
51:35
Speaker 1: the most insightful ones are the ones that everybody asks.
51:38
Speaker 1: You don't have to be an academic physicist or a
51:40
Speaker 1: working cartoonist to think deeply about the universe and ask
51:44
Speaker 1: fascinating questions, So please engage your brain and think about
51:47
Speaker 1: the universe. And if you have a question you don't
51:49
Speaker 1: know the answer to, don't be shy to write to
51:51
Speaker 1: us two questions at Daniel and Jorge dot com. Yes,
51:54
Speaker 1: and there's your questions, even if they are a little confusing.
52:00
Speaker 1: Hope you enjoyed that. Thanks for joining us, See you
52:02
Speaker 1: next time. Thanks for listening, and remember that Daniel and
52:12
Speaker 1: Jorge explained The Universe is a production of I Heart Radio.
52:16
Speaker 1: Or more podcast from my heart Radio visit the I
52:19
Speaker 1: heart Radio app, Apple Podcasts, or wherever you listen to
52:23
Speaker 1: your favorite shows.