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