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Classic episode - Why is gravity so weird? · Daniel and Kelly’s Extraordinary Universe

0:07
Speaker 1: I just think it's fascinating that it's such a fundamental
0:10
Speaker 1: force in the universe, right, Like, it's basically the thing
0:14
Speaker 1: that builds galaxies and keeps planets moving right, and gives
0:20
Speaker 1: structure to the entire cosmos.
0:22
Speaker 2: That's right. On the largest scale, it's actually the most
0:25
Speaker 2: important force. It's the reason why things look the way
0:28
Speaker 2: they do. It's the reason why our planet is round,
0:31
Speaker 2: it's the reason why we're on the planet.
0:33
Speaker 1: It's pretty important, and yet we don't know a lot
0:37
Speaker 1: about it, right Like, there's some really deep and strange
0:40
Speaker 1: mysteries about it.
0:41
Speaker 2: On one hand, we have a theory which works really
0:44
Speaker 2: really well. On the other hand, we have questions about
0:46
Speaker 2: it which seems really really basic.
0:48
Speaker 1: And not only that, it's very different than all the
0:51
Speaker 1: other forces of nature.
0:53
Speaker 2: That's right, one of these things is not like the
0:55
Speaker 2: other ones.
1:15
Speaker 1: Hi, I'm Hohe, I'm a cartoonist.
1:16
Speaker 2: And I'm Daniel. I'm a particle physicist.
1:19
Speaker 1: And this is our podcast Daniel and Jorge explain the universe.
1:22
Speaker 2: In which a cartoonist and a physicists try to figure
1:25
Speaker 2: out how to make the universe understandable to anybody.
1:28
Speaker 1: Yeah, and today on the podcast we are examining a
1:32
Speaker 1: very heavy topic, gravity and specifically why is gravity so.
1:43
Speaker 2: Weak and strange. Gravity, as we said earlier, is something
1:48
Speaker 2: which controls the structure of the universe. I mean, the
1:51
Speaker 2: reason the Solar system looks the way it does is
1:53
Speaker 2: because of gravity. The reason the Earth is round is
1:56
Speaker 2: because of gravity. The reason we have galaxies is because
1:59
Speaker 2: of gravity.
2:00
Speaker 1: The reason we weigh so much, it is because of gravity. Right,
2:03
Speaker 1: it's not my belt.
2:06
Speaker 2: No, that's because of late night cake eating.
2:10
Speaker 1: But it's such a fundamental force of nature, right, Like
2:13
Speaker 1: it's present in our everyday life. We spend a lot
2:16
Speaker 1: of time thinking about gravity, right, how not to fall down,
2:20
Speaker 1: how not to drop things, how to go up buildings,
2:23
Speaker 1: how to go down buildings.
2:24
Speaker 2: Right, that's right. It seems like one of the most
2:26
Speaker 2: important forces. I mean, if you ask people, you know,
2:29
Speaker 2: to name a force or what kind of forces they
2:31
Speaker 2: experience in their life, gravity is the one that's present
2:34
Speaker 2: in their lives. Right, you're climbing upstairs, you're fighting gravity,
2:36
Speaker 2: your trip, you fall down, you're feeling gravity. You look
2:39
Speaker 2: around you. The shape of things is controlled by gravity,
2:42
Speaker 2: and that's why it's particularly strange that gravity is the
2:46
Speaker 2: weakest force of all the forces we've discovered, it's by
2:50
Speaker 2: far the weakest.
2:51
Speaker 1: Yeah, it's really strange to hear you say that, Like,
2:54
Speaker 1: how can gravity be weak? Like you know, like it's
2:57
Speaker 1: it's keeping the whole Earth together, it's making the entire
3:00
Speaker 1: higher planet swing around going a circle basically, right. Without gravity,
3:04
Speaker 1: we would just shoot off into space.
3:06
Speaker 2: That's right. It's a really strange situation. And there's other
3:09
Speaker 2: things about gravity we don't understand as well. It's really strange.
3:12
Speaker 2: It doesn't play well with the other forces. It's very,
3:15
Speaker 2: very weak. It's a total mystery to science, except that
3:18
Speaker 2: we have a theory which works beautifully right. We can
3:20
Speaker 2: calculate exactly how mercury orbits the Sun. We can send
3:24
Speaker 2: things into outer space and know with to millimeter precision
3:26
Speaker 2: exactly where they're going to land. We have a working
3:29
Speaker 2: theory that we can use, right, but we don't understand
3:32
Speaker 2: it on a conceptual level. We have these basic, deep
3:34
Speaker 2: questions about what gravity is and how the universe works
3:38
Speaker 2: because of it.
3:38
Speaker 1: So it's a weird question, and maybe one of the
3:41
Speaker 1: people hadn't thought about before. So Daniel went out as
3:44
Speaker 1: usual and asked people on the street, why do you
3:46
Speaker 1: think gravity is so weak.
3:48
Speaker 2: Here's what a random selection of folks who were willing
3:50
Speaker 2: to talk to me on a Tuesday morning had to
3:52
Speaker 2: say about gravity. I don't know. I should don't know
3:55
Speaker 2: about that, all right. I thought it was a pretty
3:58
Speaker 2: strong force, so I don't know.
4:00
Speaker 1: But yeah, because it depends on the distance, and it's
4:05
Speaker 1: a long range one, so that's why we feel it
4:08
Speaker 1: very weak most of the time. Cool, No, okay, I
4:12
Speaker 1: have no I'm sorry, it's not very fruitful.
4:14
Speaker 2: Hmmm, I have no idea, but I'd be interested in
4:18
Speaker 2: finding out why.
4:20
Speaker 1: All right, that that was pretty good. Most people weren't
4:23
Speaker 1: surprised when you said gravity's weak.
4:26
Speaker 2: I don't know. I feel like, of all the questions
4:28
Speaker 2: I've asked people, this is the one that flumms them
4:30
Speaker 2: the most. You know. People were like, what, I have
4:33
Speaker 2: no idea, or they had crazy ideas why gravity must
4:37
Speaker 2: be weak. I feel like usually we get one person
4:40
Speaker 2: who knows what the answer is or has a good
4:41
Speaker 2: clue about what's going on. This time, I feel like
4:44
Speaker 2: almost everybody was pretty clueless. I mean, one person said
4:47
Speaker 2: I always thought gravity was pretty strong, right, which kind
4:49
Speaker 2: of sums up the situation. Right, Gravity's omnipresent in our lives.
4:53
Speaker 2: It dominates our experience, and yet it's so weak compared
4:57
Speaker 2: to the other really powerful forces we've discovered.
4:59
Speaker 1: Well, some people a couple of answers were that it
5:02
Speaker 1: had to do with distance, Like gravity gets really weak
5:05
Speaker 1: with distance.
5:06
Speaker 2: That's right. And the problem there is that all the
5:08
Speaker 2: forces get weak with distance, like electromagnetism also falls as
5:13
Speaker 2: a distance grows. Right, So all of these forces follow
5:16
Speaker 2: this one over R squared rule or are as your
5:19
Speaker 2: distance from the things that's giving.
5:21
Speaker 1: You the force, right, maybe maybe right.
5:24
Speaker 2: Maybe, yeah, mostly we think, And so that can't be
5:28
Speaker 2: the answer, right, because all the other forces have that
5:29
Speaker 2: same feature.
5:30
Speaker 1: So when you say it's the weak is it's not
5:32
Speaker 1: that it changes over distances differently than the other forces.
5:35
Speaker 2: That's right. So maybe we should talk about what the
5:38
Speaker 2: forces are and compare them to each other so folks
5:41
Speaker 2: can get understanding of how crazy weak gravity is. Right.
5:44
Speaker 1: So, Daniel, what are the forces of nature besides a
5:48
Speaker 1: bad movie with Ben Affleck than center bullet.
5:52
Speaker 2: Well, I think comedy. Comedy is definitely a force of nature.
5:55
Speaker 2: You know, it solves big problems around the world. Now,
5:59
Speaker 2: the fundamental force are electromagnetism, right, that's the one that
6:02
Speaker 2: controls electricity and magnetism obviously, and is responsible for the
6:06
Speaker 2: cool things like light and lightning and all that cool stuff.
6:11
Speaker 2: And then there's the weak nuclear force, which is a
6:15
Speaker 2: force which is responsible for radioactive decay of a nuclei. Right.
6:18
Speaker 2: And the cool thing about electricity and magnetism and the
6:21
Speaker 2: weak nuclear force is that we actually have shown that
6:24
Speaker 2: there are two sides of the same coin. As a
6:26
Speaker 2: particle physicist, we refer to them as one force. We
6:29
Speaker 2: call it the electro week. So sort of magnetism lost
6:33
Speaker 2: out there in the name merger, right, it should be
6:35
Speaker 2: electromagnetic week. But nobody voted to keep magnetism in the
6:39
Speaker 2: sort of the name of the partners in the law firm.
6:41
Speaker 1: Nobody lobbied for weak electro.
6:44
Speaker 2: Or magneto weak force. Yeah. Yeah, again, we are suffering
6:50
Speaker 2: the fate of some anonymous committee of scientists that get
6:53
Speaker 2: to name these things. Right, Who are these people?
6:55
Speaker 1: Probably some grad student, right or some you know, like
6:59
Speaker 1: this is really weird, we'll call it this.
7:01
Speaker 2: Yeah. So we have electricity and magnetism, which is a
7:04
Speaker 2: single force. We have the weak nuclear force, which is
7:06
Speaker 2: really should be combined with electricity and magnetism. And then
7:09
Speaker 2: there's the strong nuclear force, and this is the one
7:12
Speaker 2: that holds the nucleus together. You know, the nucleus is
7:14
Speaker 2: of just a bunch of positively charged protons and neutral neutrons. Right,
7:19
Speaker 2: it says only positively charged particles in the nucleus. So
7:22
Speaker 2: you might think, what it even holds the nucleus together? Right,
7:24
Speaker 2: you have all this positively charged stuff should be repelling themselves. Well,
7:28
Speaker 2: it's the strong nuclear force, and it does so by
7:31
Speaker 2: exchanging these crazy little particles we call gluons, and that
7:34
Speaker 2: holds the nucleus together, and it's pretty strong. It's even
7:37
Speaker 2: stronger than electromagnetism.
7:39
Speaker 1: Well, let's take a step back. So in the universe
7:41
Speaker 1: there's stuff.
7:43
Speaker 2: There's like, yes, firm that there is stuff in the university. Yes,
7:47
Speaker 2: without reservation, there is stuff.
7:49
Speaker 1: I'm glad we saw that question. But I mean it's
7:52
Speaker 1: like there's stuff that has substance to it, that has
7:55
Speaker 1: mass to it, or you know that it sort of exists.
7:58
Speaker 1: And then there's also besides the at how these things
8:01
Speaker 1: interact with each other, like how they affect each other.
8:04
Speaker 2: That's right, there's the matter and then there's the forces, right,
8:07
Speaker 2: and the forces affect how they interact with each other.
8:09
Speaker 1: And that's pretty much the universe. That's like, it's matter
8:11
Speaker 1: and forces.
8:13
Speaker 2: Yeah. One way to look at the universe is that
8:15
Speaker 2: it's particles, right, or you would say matter and their forces.
8:18
Speaker 2: In modern particle physics, we think about one level deeper,
8:21
Speaker 2: which is we think of quantum fields, and quantum fields
8:24
Speaker 2: are responsible both for matter and for forces. So we
8:27
Speaker 2: can talk about that maybe in another podcast. What is
8:30
Speaker 2: a quantum field? And how can I get one? You know,
8:32
Speaker 2: for lease or rent? What can they do for me?
8:35
Speaker 2: But yeah, I think it's fair still to think about
8:37
Speaker 2: the universe in terms of particles and forces.
8:40
Speaker 1: On that note, let's take a quick break. There are
8:56
Speaker 1: only four kinds of forces.
8:58
Speaker 2: Yeah, there are four kinds of forces, so electromagnetism, weak
9:01
Speaker 2: nuclear force, strong nuclear force, and then of course gravity. Right,
9:05
Speaker 2: that's the fourth force that we've discovered.
9:07
Speaker 1: Okay.
9:07
Speaker 2: The fascinating thing is that different particles feel different forces, right, Like,
9:12
Speaker 2: some particles feel this set of forces, some particles feel
9:15
Speaker 2: those set of forces. For example, right, particles with electric
9:19
Speaker 2: charge feel electromagnetism. Right. The electron, for example, is negatively charged.
9:24
Speaker 2: The proton is positively charged. You bring them close together,
9:27
Speaker 2: they're gonna pull on each other, They're gonna suck each
9:29
Speaker 2: other together, right, because they have opposite charges. We all
9:32
Speaker 2: know that. But you bring a neutral particle nearby, it
9:36
Speaker 2: just totally ignores it, right, It doesn't feel it at all. Right, Right,
9:39
Speaker 2: It's like it's like somebody's walking through a crowd of
9:42
Speaker 2: people shouting, but they have headphones on, so they can't
9:44
Speaker 2: hear anything, and they're totally oblivious to it.
9:46
Speaker 1: It's kind of like how we talked about in a
9:48
Speaker 1: previous podcast. They're almost like languages or like social media platforms.
9:53
Speaker 1: Like some people are on Twitter, some people are on Facebook,
9:55
Speaker 1: but some people are not on this. And so if somebody,
9:58
Speaker 1: if you're not on Twitter and somebody sends you a tweet,
10:00
Speaker 1: you're not gonna get it. And so it's just different
10:02
Speaker 1: ways that particles interact.
10:03
Speaker 2: That's right. Gravity is the Google plus of social media,
10:07
Speaker 2: right because nobody uses the trends. It's ancient but powerless. Yeah,
10:14
Speaker 2: And so different particles feel different forces. And for example,
10:17
Speaker 2: an electron, while it feels electromagnetism because it has a
10:20
Speaker 2: negative charge, it doesn't feel the strong force at all.
10:24
Speaker 2: It will pass right by a bunch of particles that
10:26
Speaker 2: are really tugging on each other with a strong force
10:28
Speaker 2: and not be affected at all. Whereas quarks, quarks feel
10:32
Speaker 2: all the forces. They feel a strong force, which is
10:35
Speaker 2: how they get pulled together in the nucleus. Remember, protons
10:37
Speaker 2: and neutrons are made of quarks. Quarks feel electromagnetism because
10:41
Speaker 2: they have electric charge. They feel the weak force. They
10:44
Speaker 2: also feel gravity, of course, because they have masks. So
10:46
Speaker 2: quarks get their fingers in everything feel.
10:49
Speaker 1: They get the feels for everything.
10:51
Speaker 2: They feel everything that's right, They got the strong feels.
10:55
Speaker 2: They're really deeply emotional.
10:57
Speaker 1: Part of the.
11:00
Speaker 2: And the other side of the spectrum you got things
11:01
Speaker 2: like neutrinos. The trinos don't have electric charge, so they
11:04
Speaker 2: ignore all electricity and magnetism. Right, They don't interact with light.
11:08
Speaker 2: They're invisible. They pass right through anything that They ignore
11:13
Speaker 2: electromagnetic bonds, so they pass through most materials. They don't
11:16
Speaker 2: feel the strong force. The only way they interact is
11:19
Speaker 2: with the weak force, and the weak force is pretty weak,
11:22
Speaker 2: which is why neutrinos can mostly just pass through matter unaffected.
11:29
Speaker 1: So we have four fundamental forces right, And gravity is
11:32
Speaker 1: one of these forces, and so when you say that
11:33
Speaker 1: gravity is weak, you actually mean it's weak compared to
11:37
Speaker 1: these other three forces.
11:39
Speaker 2: That's right. And so the ranking is the strong force
11:42
Speaker 2: is the strongest, so that one is actually well named.
11:45
Speaker 2: Congratulations anonymous group of scientists. Yeah, we should be called
11:50
Speaker 2: the as of twenty eighteen, currently known to be the
11:52
Speaker 2: strongest force force. After that comes electromagnetism. And you know,
11:58
Speaker 2: we know that force is pretty powerful. Stick your finger
12:00
Speaker 2: in a socket, you're gonna feel the wrath of electromagnetism. Right,
12:03
Speaker 2: It's not an unfamiliar feeling, right.
12:05
Speaker 1: Try to stick your finger in anything. You feel it, right,
12:07
Speaker 1: because it's Electromagnetism is the force that keeps you from
12:11
Speaker 1: basically passing through the table or passing through your car.
12:16
Speaker 2: Right, that's right. Because electromagnetism is the basis of chemical bonds, right,
12:20
Speaker 2: And chemical bonds are really the thing that form the
12:23
Speaker 2: structure of your body. Right. You think of your body
12:25
Speaker 2: is like a bunch of particles, but it's held together
12:27
Speaker 2: by all these forces. It's like a chain link fence
12:30
Speaker 2: binding together these little particles that prevents you from passing
12:33
Speaker 2: through something else. Yeah, So we got the strong force,
12:36
Speaker 2: and then electromagnetism, and then actually the weak nuclear force. Right,
12:40
Speaker 2: this is the force that like powers neutrinos and radioactive decay.
12:43
Speaker 2: It's much weaker than electromagnetism and much weaker than the
12:48
Speaker 2: strong force.
12:49
Speaker 1: Even weaker than the weak is gravity.
12:51
Speaker 2: That's right. If you make a list like strong force, electromagnetism,
12:55
Speaker 2: in the weak force, then you should leave like one
12:57
Speaker 2: hundred blank pages and then you get to grab because
13:00
Speaker 2: when we compare these forces, we put things like an
13:03
Speaker 2: equal distance apart, and we compare the strength of the forces.
13:06
Speaker 2: Gravity is ten to the thirty six times weaker than
13:11
Speaker 2: the weak force. That's ten with thirty six zeros in
13:15
Speaker 2: front of it.
13:15
Speaker 1: But isn't that sort of a matter of units or scale?
13:19
Speaker 1: Do you know what I mean? Like, it's much weaker,
13:21
Speaker 1: but only if you compare apples to apples, right, orange oranges?
13:26
Speaker 2: That's right. But put two protons next to each other, right,
13:28
Speaker 2: h two protons have a certain amount of mass and
13:31
Speaker 2: a certain amount of electric charge, and the force of
13:34
Speaker 2: their charges is going to be much much stronger than
13:36
Speaker 2: the force from their masses. Oh I see, So yeah,
13:38
Speaker 2: if everything was much much more massive, then there would
13:41
Speaker 2: be stronger gravity. But you can compare these things apples
13:44
Speaker 2: to apples by comparing them at you know, the same
13:46
Speaker 2: distance and the same basic unit of interaction.
13:48
Speaker 1: Right, But what if you take an apple put it
13:50
Speaker 1: next to another apple?
13:52
Speaker 2: Well, I think you can do that experiment. Nothing's going
13:54
Speaker 2: to happen because gravity is so weak. Right. You don't
13:56
Speaker 2: see two apples like pulling themselves together on the counter, right,
14:00
Speaker 2: built in apple collider. You know, the apples are not
14:03
Speaker 2: drawn to each other. Gravity is a super weak force,
14:05
Speaker 2: and you can see this yourself. Right, you can do
14:08
Speaker 2: an experiment where you counter the entire gravitational force of
14:12
Speaker 2: an enormous celestial body like the Earth. Right, take a
14:15
Speaker 2: small kitchen magnet and use it to hold up a nail,
14:19
Speaker 2: and think about what's happening there. Right, you have the
14:21
Speaker 2: nail is being pulled down by every single rock in
14:25
Speaker 2: the Earth. It's pulling with all of its gravity. But
14:27
Speaker 2: a tiny little kitchen magnet totally overcomes that.
14:31
Speaker 1: It can lift a nail even though it's pulling. It's
14:34
Speaker 1: being pulled down by the whole entire planet Earth.
14:37
Speaker 2: Right exactly. And now imagine a magnet the size of
14:39
Speaker 2: the Earth, right, I mean that would be that would
14:42
Speaker 2: be extraordinarily powerful. And so you have basically like a
14:46
Speaker 2: gravitational blob the size of the Earth. Still pretty ineffective
14:49
Speaker 2: compared to electromagnetism.
14:51
Speaker 1: Mmmm, so it's weak if you sort of compare it
14:56
Speaker 1: by object, Like you said, if you take a proton
14:59
Speaker 1: and put a nice proton, the force are going to
15:02
Speaker 1: feel from electromagnetism is so much bigger than the force
15:06
Speaker 1: of gravity. They're going to feel towards each other, the
15:08
Speaker 1: same with like two electrons or two quarks and things.
15:12
Speaker 1: So in the scale of like the particles that we know,
15:15
Speaker 1: it's a really weak.
15:16
Speaker 2: Force, that's right, exactly, And yet and yet it seems
15:20
Speaker 2: to dominate, right. That's a bit of a puzzle, Like,
15:22
Speaker 2: on one hand, it's super duper weak, and we're telling
15:25
Speaker 2: you that it hardly counts for anything. On the other hand,
15:27
Speaker 2: it's responsible for the structure of the Solar System, man
15:30
Speaker 2: for the galaxy, and it's the reason the universe looks
15:32
Speaker 2: the way it is, right, right, And so that can
15:34
Speaker 2: be confusing to people, Like how do you reconcile those
15:36
Speaker 2: two things in your head?
15:37
Speaker 1: Yeah, Like, why doesn't the Earth feel an electromagnetic force
15:40
Speaker 1: with the Sun, which it would be so much bigger
15:43
Speaker 1: than the force of gravity.
15:45
Speaker 2: Yeah, well it would be pretty shocking. And that's actually
15:48
Speaker 2: the reason is gravity is different from the other forces
15:51
Speaker 2: and that it can't be canceled out right, If there
15:53
Speaker 2: was some huge electrostatic difference between the Sun and the Earth,
15:57
Speaker 2: like a bunch of positive charges there and a bunch
15:59
Speaker 2: of negative charges, it would create such an enormous force
16:03
Speaker 2: that it would be very quickly balanced. Like that's what
16:06
Speaker 2: lightning is. Right. When there's a charge differential between clouds
16:10
Speaker 2: and the grounds, it doesn't take that much before those
16:13
Speaker 2: charges want to rearrange themselves to a lower energy configuration.
16:16
Speaker 2: They rush down to the ground, or they rush up
16:18
Speaker 2: to the clouds, or they jump from clouded cloud to
16:21
Speaker 2: balance themselves out. Because you have two kinds of charges,
16:24
Speaker 2: you have positive and you have negative, so you can
16:26
Speaker 2: find an arrangement where basically everybody's happy. It's an equilibrium, right,
16:30
Speaker 2: But that's not true for gravity.
16:32
Speaker 1: Okay, I get it. So for example, if the Earth
16:34
Speaker 1: was every particle on Earth had a positive electromagnetic charge,
16:39
Speaker 1: and every particle in the Sun had a negative electromagnetic charge,
16:43
Speaker 1: there would be a humongous pull from electromagnetism pulling the
16:48
Speaker 1: Earth into the Sun.
16:49
Speaker 2: Yeah, we'd be toast pretty quick. Yeah, very long lived experment.
16:53
Speaker 1: Yeah, it would be huge. Even the opposite, if we
16:56
Speaker 1: were all positive and the Sun was all positive, we
16:58
Speaker 1: would get shot out of the sort of system very quickly.
17:01
Speaker 2: That's right. And that's why you know, early days of
17:03
Speaker 2: the Solar system being formed, you have these gases and
17:07
Speaker 2: the gas and dust coalescing, and very rapidly things neutralize, right,
17:11
Speaker 2: because anything that feels an electrostatic force to something else
17:15
Speaker 2: is going to find the opposite charge and they're going
17:18
Speaker 2: to coalesce and they're going to make something neutral. Right.
17:20
Speaker 2: That's why most of the things around you are neutral, right,
17:22
Speaker 2: Most of the elements are neutral because any deviation from
17:26
Speaker 2: neutral results in a powerful force to neutralize it.
17:29
Speaker 1: So, thankfully the Earth is made out of both like
17:32
Speaker 1: equal amounts of positive and negative particles, right, that's right.
17:36
Speaker 1: Thankfully we're sort of balanced electromagnetically, and so even if
17:40
Speaker 1: the Sun was all positive, we would look like neutral,
17:44
Speaker 1: like a neutral ball to the Sun.
17:46
Speaker 2: Yeah, that's right. Where on large scales the Earth is neutral, right,
17:49
Speaker 2: I mean there might be some residual positive or negative
17:52
Speaker 2: charge depending on the solar wind, et cetera. But basically
17:55
Speaker 2: the Earth is neutral, and so the largest force of
17:58
Speaker 2: the Earth feels is the gravity from the Sun. Even
18:00
Speaker 2: though gravity is super duper weak, right, it doesn't take
18:03
Speaker 2: a lot to counteract gravity. But it's the only player
18:06
Speaker 2: left because everybody else is sort of pair it up
18:08
Speaker 2: and danced off for the night, and gravity's just there left,
18:11
Speaker 2: hold in the bag. And gravity can't be balanced, right.
18:14
Speaker 2: You feel gravity if you have any mass, right, there's
18:17
Speaker 2: only positive masses. There's no such thing as a negative
18:20
Speaker 2: mass to give anti gravity.
18:22
Speaker 1: Wow, well, let's keep going, but first let's take a
18:26
Speaker 1: quick break. Okay, So that's how gravity is so much
18:42
Speaker 1: weaker than the other forces. So how's it different than
18:46
Speaker 1: the other three forces of nature?
18:48
Speaker 2: There's like no end to waste. The gravity is weird,
18:51
Speaker 2: you know, there's no end to like the puzzles of
18:53
Speaker 2: gravity is fascinating.
18:54
Speaker 1: Bottomless pit.
18:56
Speaker 2: That's right, it's a black hole of questions. And one
19:00
Speaker 2: of my favorites is just that we have no way
19:03
Speaker 2: to sort of fit gravity in with the way the
19:06
Speaker 2: universe works according to everything else. You know, we talked
19:08
Speaker 2: earlier about how we have particles and we have forces
19:11
Speaker 2: or quantum fields equivalently, and that's a really successful way
19:15
Speaker 2: to describe the universe. You know, we have the Large
19:17
Speaker 2: Hadron Collider to explore these things really high energies, and
19:20
Speaker 2: we've understood all sorts of things using this theory. But
19:24
Speaker 2: that theory is used as quantum mechanics. So the way
19:27
Speaker 2: we describe interactions, you know, the way we talk about
19:30
Speaker 2: two electrons repelling each other, or the way lightning is
19:34
Speaker 2: formed or anything, involves passing quantum particles back and forth.
19:38
Speaker 2: And that's just not true for gravity.
19:40
Speaker 1: What does that mean? Passing particles back and forth? Like
19:43
Speaker 1: when like if I have two magnets and they're attracted
19:46
Speaker 1: to each other, they're not. They're not It's not like
19:49
Speaker 1: an invisible telekinesis pulling on each other. They're actually swapping
19:52
Speaker 1: particles and I can't see that is that kind of
19:54
Speaker 1: what do you mean?
19:55
Speaker 2: That's exactly what I mean. That the way two things
19:58
Speaker 2: interact via some four is by exchanging particles. And so
20:02
Speaker 2: for example, electromagnetism, right, is the force behind a magnet,
20:06
Speaker 2: and the way electromagnetism works, we think at a sort
20:09
Speaker 2: of microscopic particle level is that there's a particle that
20:12
Speaker 2: transmits that force, that sends sort of the information back
20:15
Speaker 2: and forth between two things that are feeling it. And
20:18
Speaker 2: in the case of electromagnetism, that particle is the photon.
20:22
Speaker 2: The particle is also a packet of light. So each
20:25
Speaker 2: of the quantum forces that we talked about before electromagnetism,
20:29
Speaker 2: the weak force and the strong force, each of them
20:31
Speaker 2: have a particle we associate with it. And that's not
20:34
Speaker 2: just like some name tag we put on and say, hey,
20:37
Speaker 2: you get this one, you get this one. We think
20:39
Speaker 2: that that's the particle that's responsible for making the force work.
20:43
Speaker 2: So when two electrons come near each other, how do
20:45
Speaker 2: they repel each other? How does that actually happen? What
20:48
Speaker 2: we think that they send photons out right, the electric
20:51
Speaker 2: field of a moving electron, Right, an accelerating electron generates photons,
20:57
Speaker 2: and those photons interact with the others, and so basically
21:01
Speaker 2: the passing messages back and forth using these quantum particles.
21:05
Speaker 1: So gravity is weird because we don't know that there
21:09
Speaker 1: is a quantum particle being exchanged when two things get
21:12
Speaker 1: attracted gravitationally.
21:14
Speaker 2: That's right. So we have this great framework. We say, oh,
21:16
Speaker 2: maybe all forces are quantum mechanical fields interacting with each other. Right,
21:22
Speaker 2: Let's apply that to the electromagnetic field. Yeah it works.
21:24
Speaker 2: Let's apply that to the weak force. Yeah it works.
21:26
Speaker 2: Let's apply to the strong force. Ooh, cool, it works.
21:29
Speaker 2: Maybe this is something deep about the way the universe works.
21:31
Speaker 2: Let's apply it to gravity. Uh oh, it doesn't work, right,
21:36
Speaker 2: So what does that mean? What does it mean when
21:38
Speaker 2: I say it doesn't work? Well? For a theory to work,
21:41
Speaker 2: it has to provide predictions for experiments. You have to
21:44
Speaker 2: be able to say, okay, theory, what would happen in
21:47
Speaker 2: this configuration if I shot a proton and another particle,
21:51
Speaker 2: predict what would happen, and then you can go off
21:53
Speaker 2: and do the experiments and compare it. Right. Well, when
21:56
Speaker 2: you do that for gravity, you try to form a
21:57
Speaker 2: quantum theory of gravity, it doesn't work. You get nonsense answers.
22:02
Speaker 2: You get answers like infinity right, or things disappear, or
22:06
Speaker 2: it's just it doesn't mathematically function. Like, there's no way
22:09
Speaker 2: to build a theory of gravity that we've discovered so
22:12
Speaker 2: far that works, that actually explains the way these things happen.
22:17
Speaker 2: There are a few candidates out there there pretty far
22:19
Speaker 2: from being a functional theory of quantum gravity, things like
22:23
Speaker 2: loop quantum gravity or string theory. But the basic problem
22:26
Speaker 2: is that quantum mechanics and general relativity, which is our
22:30
Speaker 2: best theory of gravity, do not play well together, and
22:32
Speaker 2: we have no functioning quantum theory of gravity.
22:37
Speaker 1: So does that mean that we don't have the right
22:38
Speaker 1: theory or is that gravity is just not quantum in nature?
22:43
Speaker 2: That's exactly the question we don't know the answer to.
22:45
Speaker 2: Right in one hundred years from now, somebody will know
22:47
Speaker 2: the answer to that, I hope, and they'll look back
22:49
Speaker 2: and they'll wonder, you know, why did those guys see
22:51
Speaker 2: the clues? But we don't know. It could be that
22:54
Speaker 2: there is a quantum theory of gravity. We're just not
22:56
Speaker 2: smart enough to think it up yet, right, Like the
22:58
Speaker 2: right person hasn't been born yet to put the math together.
23:01
Speaker 2: Or maybe it requires a different kind of math that
23:03
Speaker 2: we're using. Right, there's some assumption we're making that's a mistake.
23:06
Speaker 1: Or maybe just giving it a wrong name, like maybe
23:09
Speaker 1: it should be gravi tunis or gravitinos gravitas. Wait, that's
23:17
Speaker 1: taken exactly.
23:19
Speaker 2: That's definitely the problem. That's step number one, right. We
23:21
Speaker 2: made a mistake in step number one when we could
23:22
Speaker 2: define the particle. The other option, of course, is that
23:26
Speaker 2: maybe gravity is not a quantum force the way the
23:28
Speaker 2: other forces are. Right. The other forces we call them
23:31
Speaker 2: quantum forces because they're well described by quantum mechanics. But
23:35
Speaker 2: gravity is kind of different. I mean, the current theory
23:38
Speaker 2: we have a gravity general relativity. It doesn't like to
23:41
Speaker 2: describe gravity as a force, right, describes gravity instead as
23:44
Speaker 2: a bending of space. It says that when you have
23:47
Speaker 2: mass somewhere in space, space no longer becomes straight, becomes bent. Right,
23:52
Speaker 2: So the things move in curves and circles.
23:55
Speaker 1: And it's not like an actual just a mathematical nuance
23:58
Speaker 1: or a mathematical persons afect of What really confirms it
24:02
Speaker 1: is the idea that gravity can affect things that don't
24:05
Speaker 1: have mass. Right. That's how we know it's more than
24:07
Speaker 1: just a force between things that have mass. It actually
24:10
Speaker 1: like affects space for things that don't have mass.
24:14
Speaker 2: Right, that's exactly right. So if you shoot a photon
24:17
Speaker 2: through space that has mass nearby, the photon will not
24:21
Speaker 2: move in what we consider to be a straight line, right,
24:23
Speaker 2: it'll find a path through this bent space that involves
24:26
Speaker 2: basically curving. And this is what Einstein predicted with his theory,
24:30
Speaker 2: and they saw it, you know. And you can see
24:33
Speaker 2: in space it's called gravitational lensing. You can see photons
24:36
Speaker 2: get bent by heavy objects. And it's because, as you say,
24:39
Speaker 2: the heavy objects are bending space itself.
24:41
Speaker 1: Right, It's not like gravity is pulling the photon because
24:44
Speaker 1: the photon doesn't have any mass.
24:46
Speaker 2: Right, that's right, the photon doesn't have any mass.
24:49
Speaker 1: Yeah, So that's how it's different. Like gravity seems to
24:52
Speaker 1: affect things that don't have sort of its fundamental property,
24:56
Speaker 1: you know, like electromanicnetic forces can affect something that does
25:00
Speaker 1: not have an electric charge.
25:01
Speaker 2: That's true.
25:02
Speaker 1: Gravity can affect thing everything else, right.
25:04
Speaker 2: Yeah, that's a pretty deep insight there.
25:06
Speaker 1: Well, not bad for a cartoonist, not at all.
25:10
Speaker 2: Yeah, that's a fascinating way to think about it. I
25:13
Speaker 2: think that's totally correct. Yeah. And so if gravity is
25:17
Speaker 2: instead of being a force, if it's a way we
25:19
Speaker 2: change the shape of space itself, then maybe that's why
25:22
Speaker 2: we don't have a quantum theory of it. Right, And
25:25
Speaker 2: that's amazing and it's fantastic and it's exciting. And another
25:29
Speaker 2: reason why we have a hard time bringing these two
25:30
Speaker 2: things together is that quantum mechanics, the theory we've developed
25:34
Speaker 2: only works so far in flat space. That is, if
25:38
Speaker 2: there's really heavy stuff nearby, we don't know how to
25:41
Speaker 2: do those quantum calculations. We can basically only do quantum
25:44
Speaker 2: mechanics in places where there isn't really strong gravity.
25:47
Speaker 1: So wait, it's a quantum physics doesn't work in reality basically?
25:52
Speaker 1: Is that what you're saying, Like, it doesn't work in
25:56
Speaker 1: the space that we actually live.
25:57
Speaker 2: In, Well, it works basically everywhere except for close to
26:00
Speaker 2: black holes. Mmm, right, you need basically a black hole.
26:04
Speaker 2: I have enough gravity to break down quantum mechanics because
26:07
Speaker 2: it's when when space gets really distorted that you start
26:10
Speaker 2: to see the effects of gravity on space, and then
26:13
Speaker 2: it becomes comparable to the strength of other stuff, and
26:16
Speaker 2: that's when that's when quantum mechanics breaks down. Yeah, quantum
26:19
Speaker 2: quantum field theory works basically what we call flat space,
26:22
Speaker 2: whereas gravity bends space.
26:24
Speaker 1: Wow, so earlier when we categorize gravity as part of
26:32
Speaker 1: these four fundamental forces, maybe that's just the wrong approach.
26:35
Speaker 1: Maybe you know, do you know what I mean? Like,
26:36
Speaker 1: maybe we shouldn't be categorizing these four things as one
26:41
Speaker 1: category of quote forces.
26:44
Speaker 2: That's right. It could be that it could be that
26:45
Speaker 2: there is no quantum theory of gravity as a fundamental
26:48
Speaker 2: force because it isn't one. Yeah, and it's just a
26:50
Speaker 2: feature of space, right, Absolutely, that's one possible explanation. But
26:55
Speaker 2: then we still need a way to make quantum mechanics
26:57
Speaker 2: work in bend space, right, And we still need to
27:00
Speaker 2: understand how to make our theory of general relativity play
27:04
Speaker 2: well with quantum mechanics, because we think quantum mechanics describes
27:07
Speaker 2: the universe, right, and general relativity is not a quantized theory.
27:10
Speaker 2: It's it's continuous, right. It treats space and everything as
27:14
Speaker 2: if it's infinitely divisible. Right, it's not a quantum theory
27:18
Speaker 2: at all. In fact that it came about before quantum
27:20
Speaker 2: mechanics was even invented. Right. And so while the basic
27:23
Speaker 2: tenets of it and how it distorted space are probably correct,
27:25
Speaker 2: i mean, been verified to zillion degrees of accuracy, it
27:29
Speaker 2: doesn't feel like it can be a fundamental description of
27:32
Speaker 2: nature because it's not quantum mechanical.
27:34
Speaker 1: So like we want to call it a force because
27:36
Speaker 1: it seems to move things like all the other forces,
27:40
Speaker 1: but it's maybe it's not a force. Maybe it's just
27:42
Speaker 1: kind of like some other weird property of space.
27:45
Speaker 2: Yeah, exactly. You know, maybe we've been trying to put
27:48
Speaker 2: a round peg into a square hole all these years.
27:52
Speaker 1: A gravity peg and a quantum hole.
27:54
Speaker 2: That's right, that's right. And there are other ways that
27:57
Speaker 2: people are trying to solve this problem. Like one way
27:59
Speaker 2: is things that maybe gravity is a fundamental force, but
28:02
Speaker 2: it just works a little bit differently from the other forces.
28:05
Speaker 2: For example, people think about how the universe might have
28:08
Speaker 2: additional spatial dimensions, you know, like instead of just being
28:11
Speaker 2: able to move in three directions, maybe there's like four
28:13
Speaker 2: or five six dimensions that you can move in. And
28:16
Speaker 2: folks who are interested in that should listen to our
28:18
Speaker 2: podcast on extra dimensions.
28:20
Speaker 1: No, yeah, we did a whole episode on extra dimensions,
28:22
Speaker 1: but we didn't sort of get into this particular topic.
28:24
Speaker 1: So tell us how extra dimensions might explain why gravity
28:29
Speaker 1: is so weak.
28:30
Speaker 2: Yeah, The idea is that maybe gravity isn't so weak.
28:33
Speaker 2: Maybe gravity is just as strong as all the other forces.
28:36
Speaker 2: But if there's a whole other set of dimensions out there.
28:40
Speaker 2: There's ways directions that think can move. It might be
28:44
Speaker 2: that gravity is the only thing that feels those dimensions, right.
28:47
Speaker 2: It might be that those dimensions are invisible to electromagnetism
28:50
Speaker 2: and to the weak force into the strong force, but
28:52
Speaker 2: visible to gravity. And what that means is that gravity
28:56
Speaker 2: might be basically leaking out into those other dimensions. You know,
29:00
Speaker 2: we talked about how the farther away you get from something,
29:03
Speaker 2: the weaker the forces. So like Mercury feels the force
29:06
Speaker 2: of the Sun's gravity much more strongly than Pluto does. Right,
29:09
Speaker 2: irrelevant of whether or not you call it a planet,
29:11
Speaker 2: it doesn't feel gravity very strongly. And that's because it's
29:14
Speaker 2: further from the Sun, right. I mean that goes like
29:15
Speaker 2: one over are squared or are as the distance it's
29:19
Speaker 2: one of our squared because we have three dimensions. If
29:21
Speaker 2: we had six dimensions, it would be one over R five, right,
29:25
Speaker 2: which falls much more rapidly. So if there are additional
29:29
Speaker 2: dimensions out there, okay, and only gravity feels them, then
29:33
Speaker 2: that might be the reason why gravitational force falls so quickly.
29:37
Speaker 2: Maybe gravity's actually just as strong as everything else. When
29:40
Speaker 2: you get really really close. But then these extra dimensions exist,
29:43
Speaker 2: and most of gravity leaks out into those other dimensions.
29:47
Speaker 1: Oh, sort of like between you and me, there's not
29:50
Speaker 1: just the three dimensions between you and me. May there
29:53
Speaker 1: are other secret hidden spaces kind of between you and me?
29:57
Speaker 1: Are these other dimensions exactly?
29:59
Speaker 2: Other ways for gravity to spread out, all right?
30:02
Speaker 1: And so gravity would be like just as strong as
30:04
Speaker 1: all the other forces, but it's just fleshing its muscles
30:07
Speaker 1: in these other spaces that we can't see or feel exactly.
30:11
Speaker 2: It's like, you know, if somebody's at the center of
30:13
Speaker 2: a crowd and they let go a really stinky far right.
30:16
Speaker 2: The people next to them they smell it strongly, and
30:18
Speaker 2: the people further away they smell it much more weakly,
30:21
Speaker 2: and people outside don't smell it at all.
30:22
Speaker 1: All right, now, imagine the farts really suddenly. But let's
30:26
Speaker 1: let's let's go with it.
30:27
Speaker 2: Hey, I'm trying to make this successible. You know, this
30:29
Speaker 2: is something everybody canna.
30:30
Speaker 1: Appreciate it trying to make way I get it cut it.
30:35
Speaker 2: But if there was somewhere else for that far to go,
30:37
Speaker 2: you know, if it could move not just sideways, but
30:39
Speaker 2: also could float up right so you had a really
30:42
Speaker 2: tall room in the far floated up, then people wouldn't
30:44
Speaker 2: feel it as much because most of them far would
30:46
Speaker 2: dissipate into the upper corners of the room. And so
30:50
Speaker 2: gravity might be the same way. It might be that
30:52
Speaker 2: you know, for the first millimeters, so the first centimeters,
30:55
Speaker 2: so gravity gets very weak, very quickly. It falls off
30:59
Speaker 2: really rapidly, and that then you know, at normal distances
31:02
Speaker 2: like a meter or ten meters or whatever, you don't
31:04
Speaker 2: feel those other dimensions anymore because the other other dimensions
31:07
Speaker 2: only activate it really really short distances. This is the
31:10
Speaker 2: theory people came up with, and we don't know if
31:12
Speaker 2: it's real. You know, we've tested it so far. It
31:14
Speaker 2: seems like gravity works the same way for galactic scales
31:19
Speaker 2: and for Earth scales, and for microscopic scales. It seems
31:21
Speaker 2: to always fall off at the same rate as a
31:24
Speaker 2: function of distance. So nobody's ever seen any evidence of
31:26
Speaker 2: these extra dimensions. But it's a fascinating theory and it's
31:29
Speaker 2: a you know, it's one that would give kind of
31:31
Speaker 2: a natural explanation for why gravity would fall off so
31:34
Speaker 2: quickly and why gravity is so weak. It wouldn't explain
31:37
Speaker 2: all these other things, But.
31:38
Speaker 1: In fact people sort of try to use gravity to
31:40
Speaker 1: see if there are other dimensions.
31:42
Speaker 2: Right, Yeah, that's right. It would be a really cool clue,
31:44
Speaker 2: right if And that's a fascinating way that science has done.
31:48
Speaker 2: You know, you try to look at everything around you
31:50
Speaker 2: and see if you can fit it all into one framework,
31:53
Speaker 2: like can I use this one set of ideas to
31:55
Speaker 2: describe everything? Right? Can irge edit onto one part of concepts? Yeah,
32:00
Speaker 2: that's right. In my fart theory of you in the universe.
32:09
Speaker 2: The best possible way I think to unravel this is
32:11
Speaker 2: to actually go visit a black hole, because quantum mechanics
32:14
Speaker 2: and general relativity tell you very different things about what's
32:17
Speaker 2: happening inside a black hole. Right, As we said before,
32:20
Speaker 2: general relativity tells you it's an infinite tesimal dot of
32:23
Speaker 2: almost infinite density. Quantum mechanics says, you know, the universe
32:27
Speaker 2: is quantized first of all, so you can't have infinite
32:29
Speaker 2: testimal dots. And also there's sort of a minimum size
32:33
Speaker 2: to stuff, right, and you can't have all that stuff
32:35
Speaker 2: compressed in such a tiny little area. And so if
32:38
Speaker 2: you could see inside a black hole, you would learn
32:40
Speaker 2: a lot about gravity.
32:42
Speaker 1: So what would be the plan. You would go into
32:43
Speaker 1: a black hole. You would observe and discover how the
32:46
Speaker 1: universe works, and then and then you'd be stuck there.
32:49
Speaker 2: That's right. They would have to send you a Nobel
32:51
Speaker 2: Prize into the black hole after that, which is assume
32:53
Speaker 2: you'd figure it out and pause the Nobel Prize into
32:57
Speaker 2: space into the black hole. Anybod who's listening, please do
33:01
Speaker 2: not go into a black hole. Please please do not
33:03
Speaker 2: go into a black hole. But you know, we don't
33:05
Speaker 2: need to visit black holes. We could try to create
33:07
Speaker 2: them here on Earth.
33:08
Speaker 1: That sounds like a great idea.
33:10
Speaker 2: Yeah, doesn't that sound like a great idea? I mean
33:12
Speaker 2: I'm excited make it. So, Yeah, let's create a black
33:17
Speaker 2: hole and study it. Right, if gravity gets really really
33:20
Speaker 2: powerful when you get to really short distances because of
33:23
Speaker 2: this extra dimension theory, then it might be that if
33:25
Speaker 2: you shoot two protons together really really hard and they
33:28
Speaker 2: get really really close to each other, that you can
33:29
Speaker 2: create a super duper mini extra cute, little fuzzy black hole. Right,
33:34
Speaker 2: I'm trying to make it sound like a cozy thing.
33:36
Speaker 1: Yeah, you're trying to sell it, right.
33:42
Speaker 2: And so before we turned on the large Hadron collide.
33:46
Speaker 2: About ten years ago, people thought maybe by smashing these
33:48
Speaker 2: protons together we could actually create black holes and we
33:51
Speaker 2: could study them. We can reveal the deep secrets of gravity.
33:54
Speaker 1: Right, hmmm, So then the idea would be to try
33:58
Speaker 1: to make them at the Large Headron Collider and just
34:00
Speaker 1: can of see what happens, Like, does it tell us
34:02
Speaker 1: something about gravity or quantum physics at the same.
34:05
Speaker 2: Time, Yeah, exactly. By seeing how often they're made and
34:09
Speaker 2: how strong they are and what they turned into, whether
34:11
Speaker 2: they decay, we could understand something about the way black
34:14
Speaker 2: holes work, and that would have been really powerful. But
34:17
Speaker 2: unfortunately or fortunately, depending on how you feel above black holes.
34:21
Speaker 2: We haven't made any black holes at the Large Hadron
34:23
Speaker 2: Collider that we've discovered.
34:25
Speaker 1: But maybe isn't it true that maybe you've made them
34:27
Speaker 1: but they evaporate.
34:28
Speaker 2: Yes, these black holes would be very short lived, but
34:31
Speaker 2: you know, everything we make at the Large Hadron Collider
34:33
Speaker 2: is really short lived. These things last for like ten
34:34
Speaker 2: to the negative thirty seconds or ten to the negative
34:36
Speaker 2: twenty three seconds. We're pretty good at seeing short lived
34:39
Speaker 2: stuff because it usually blows up into other things, and
34:42
Speaker 2: a black hole would have a really unusual signature in
34:45
Speaker 2: our detector, it would be pretty clear to see if
34:47
Speaker 2: we had made them.
34:48
Speaker 1: Okay, but short of going into a black hole or
34:51
Speaker 1: detecting farts in extra dimensions, we may not know in
34:56
Speaker 1: the near future what what makes gravity so different?
34:59
Speaker 2: That's right, take some work. I mean. The other direction,
35:02
Speaker 2: is theoretical, is to build up a theory of quantum
35:04
Speaker 2: gravity sort of from the bottom up.
35:06
Speaker 1: Like start from the beauty of math and physics, and
35:09
Speaker 1: then try to build it up to our level exactly.
35:13
Speaker 2: And that's that's a wonderful way to do, is to say, like,
35:15
Speaker 2: maybe the universe works in this way its most basic
35:18
Speaker 2: fundamental nature, and build it up from there and see
35:21
Speaker 2: if you can describe the universe that we see around us. Wow.
35:25
Speaker 1: All right, well, that's pretty shocking to think gravity is
35:29
Speaker 1: such a place, such a big role in our lives,
35:32
Speaker 1: and yet it's like the weakling in the universe, right.
35:36
Speaker 1: It's like, imagine if if gravity was stronger, life would
35:40
Speaker 1: be a lot more chaotic, right and crazy?
35:42
Speaker 2: Yeah, exactly. We would be closer to the Sun and
35:44
Speaker 2: everything would feel more intense. It's fascinating to me that
35:47
Speaker 2: gravity has been a mystery to physics for hundreds of years.
35:50
Speaker 2: I mean it was the focus of Isaac Newton's studies,
35:53
Speaker 2: you know, like hundreds of years ago, people working on gravity.
35:56
Speaker 2: And still today, even though we've made so much progress
35:59
Speaker 2: in terms of gravity, we still have so much, so
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Speaker 2: many basic questions about it that we don't know the
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Speaker 2: answers to, not even the really beginning of how to
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Speaker 2: answer them to meet. That's fascinating. Gravity such a rich
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Speaker 2: source of mystery for physics and for everybody.
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Speaker 1: Wow, all right, cool, I think it's maybe time to
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Speaker 1: push down this question. Thanks for joining us.
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Speaker 2: If you still have a question after listening to all
36:28
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36:32
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