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What is gravitoelectromagnetism? · Daniel and Kelly’s Extraordinary Universe

• 0:08
  Speaker 1: Hey, Daniel, have you guys figured out how to make
• 0:10
  Speaker 1: quantum mechanics and gravity work together?
• 0:12
  Speaker 2: Yet? Oh?
• 0:13
  Speaker 3: Hit me hard with a nasty question right off the bat.
• 0:15
  Speaker 3: Huh well, unfortunately we haven't figured it out yet.
• 0:19
  Speaker 1: Well what have you guys been working on and how
• 0:21
  Speaker 1: long have you been working on it?
• 0:22
  Speaker 4: Like decades?
• 0:24
  Speaker 3: More than one hundred years? Actually?
• 0:26
  Speaker 1: Uh? Well, and I thought I was a little bit
• 0:29
  Speaker 1: behind on my deadlines.
• 0:30
  Speaker 4: So you know how long you think it's going to take?
• 0:33
  Speaker 1: Another weekend? Another thousand years? Can I get it in
• 0:37
  Speaker 1: by monday?
• 0:40
  Speaker 3: You know? The only progress we've really made is coming
• 0:42
  Speaker 3: up with some long, confusing names for.
• 0:44
  Speaker 1: It, like Mississippi or quantum gravity.
• 0:49
  Speaker 3: No, that would be much too clear.
• 0:51
  Speaker 1: Okay, like gravito, quantum field, hydrodynamically.
• 0:56
  Speaker 3: I think you should be a physicist, Katie. You have
• 0:59
  Speaker 3: the knack for it.
• 1:00
  Speaker 1: I know how to throw a ball and look at
• 1:02
  Speaker 1: it go up and come down, So I'm already halfway there.
• 1:20
  Speaker 3: Hi. I'm Daniel. I'm a particle physicist and a professor
• 1:23
  Speaker 3: at UC Irvine, and I desperately want to know the
• 1:26
  Speaker 3: underlying rules of the universe.
• 1:28
  Speaker 1: I am Katie Golden. I am not a particle physicist.
• 1:31
  Speaker 1: I host a podcast about animals, but that doesn't mean
• 1:35
  Speaker 1: that I couldn't maybe try to smash quantum mechanics and
• 1:39
  Speaker 1: gravity together if you give me a government grant.
• 1:44
  Speaker 3: I think everybody who's not a particle physicist should introduce
• 1:47
  Speaker 3: themselves that way. Hi, I'm Sally. I'm not a particle physicist.
• 1:50
  Speaker 4: I think that makes the most sense.
• 1:54
  Speaker 3: In that case, I should start off by listing all
• 1:56
  Speaker 3: the things that I'm not every time I introduce myself
• 1:59
  Speaker 3: to somebody. I'm not an Olympic gymnast. I'm not a
• 2:01
  Speaker 3: Wall Street trader dot dot.
• 2:03
  Speaker 4: I am not a hot dog eating champion.
• 2:05
  Speaker 3: Yet we can all aspire to stuff well. Welcome to
• 2:11
  Speaker 3: the podcast Daniel and Jorge Explain the Universe, a production
• 2:14
  Speaker 3: of iHeartRadio in which we aspire to be particle physicists.
• 2:19
  Speaker 3: We all want to understand the way the universe works.
• 2:21
  Speaker 3: We all want to figure it out, to zoom down
• 2:24
  Speaker 3: to the tiniest little bits of the universe, the basic
• 2:27
  Speaker 3: building blocks and the rules that tertangle them, and zoom
• 2:30
  Speaker 3: out from that picture to understand how it all comes
• 2:32
  Speaker 3: together to make our amazing hour Bonkers are wonderful, our
• 2:36
  Speaker 3: delicious universe.
• 2:37
  Speaker 1: Yeah, like a nice stew of concepts all mingled up
• 2:43
  Speaker 1: in the stars.
• 2:43
  Speaker 4: So yeah, I mean it is interesting.
• 2:45
  Speaker 1: Because I think we've talked a little bit on the
• 2:48
  Speaker 1: times that I've been on the show about quantum mechanics.
• 2:51
  Speaker 1: We've talked about gravity, We've talked about sort of this
• 2:54
  Speaker 1: distinction between the physics involved in the really tiny and
• 2:59
  Speaker 1: the really huge, and how it's a bit of a
• 3:02
  Speaker 1: puzzle to fit those together.
• 3:04
  Speaker 3: Yeah, the basic strategy of physics has always been to
• 3:08
  Speaker 3: zoom down to the littlest bits of the universe to
• 3:10
  Speaker 3: try to understand them, and then hope that we can carefully,
• 3:14
  Speaker 3: one step at a time, zoom out and figure out
• 3:17
  Speaker 3: how those things come together to make our world. You know,
• 3:20
  Speaker 3: how electrons and protons come together to make atoms, and
• 3:23
  Speaker 3: atoms come together to make molecules, and molecules come together
• 3:27
  Speaker 3: to make proteins, and proteins come together to make steak
• 3:29
  Speaker 3: and ice cream and all the delicious things that you eat.
• 3:32
  Speaker 3: That's sort of like reductionist approach. We zoom down and
• 3:35
  Speaker 3: then one at a time step back up to understand
• 3:38
  Speaker 3: our world. Has long been the approach we wanted to
• 3:41
  Speaker 3: take to understand the universe, and that's worked for lots
• 3:43
  Speaker 3: of stuff, like the way we understand ice cream and
• 3:45
  Speaker 3: blueberries and steak and goats and all that stuff. But
• 3:48
  Speaker 3: you're right, Katie, there's one big thing that it hasn't
• 3:51
  Speaker 3: been able to explain, maybe the biggest, most important thing
• 3:54
  Speaker 3: that shapes our universe, and that's gravity. How everything seems
• 3:58
  Speaker 3: to attract itself or how things flow through space time.
• 4:01
  Speaker 3: We still don't understand how that bubbles up from the
• 4:04
  Speaker 3: tiniest little bits of.
• 4:05
  Speaker 1: The universe because gravity is sort of, I guess, like
• 4:10
  Speaker 1: a big force that we observe. So like you know,
• 4:13
  Speaker 1: you feel gravity on a planet. Maybe you and I
• 4:16
  Speaker 1: have our own gravitational pull, but it's much weaker than
• 4:19
  Speaker 1: a planet, so we're not going to notice it. But
• 4:22
  Speaker 1: is gravity something you can really measure much when you
• 4:25
  Speaker 1: get really small, like say you're looking at particles, Like
• 4:28
  Speaker 1: does a particle have its own gravity? Or can you
• 4:31
  Speaker 1: even measure gravity of say like a neutron or a
• 4:35
  Speaker 1: proton or an electron.
• 4:37
  Speaker 3: Yeah, that's exactly the puzzle. On a theoretical sense. We
• 4:40
  Speaker 3: don't know how to stitch these two things together, and
• 4:43
  Speaker 3: we'll talk about that more during this podcast. But even
• 4:46
  Speaker 3: more frustrating in experimental sense, we can't even see what
• 4:50
  Speaker 3: the universe does. Basically, the job of physics is to
• 4:53
  Speaker 3: explain what is the universe doing, what's happening out there,
• 4:56
  Speaker 3: and why does it make sense? And the first step
• 4:59
  Speaker 3: there is to see what's happening in the universe. And
• 5:01
  Speaker 3: so the first thing you want to do if you
• 5:03
  Speaker 3: want to explain the gravity of little particles, the quantum
• 5:06
  Speaker 3: mechanical understanding of gravity is to see gravity operating on
• 5:10
  Speaker 3: little particles. That's basically what you're asking. And the challenge
• 5:13
  Speaker 3: there is that gravity is so dang weak compared to
• 5:16
  Speaker 3: the other forces of electromagnetism, even the weak force and
• 5:20
  Speaker 3: definitely the strong force, Gravity is like a bajillion zillion
• 5:23
  Speaker 3: quintillion times weaker, which is why, for example, like a
• 5:27
  Speaker 3: simple fridge magnet can overpower the gravity of the Earth
• 5:31
  Speaker 3: and hold your recipe against your fridge or your pictures
• 5:34
  Speaker 3: of your kids and their cousins. It's not hard to
• 5:37
  Speaker 3: overcome the gravity of an entire planet with a tiny
• 5:40
  Speaker 3: little bit of electromagnetism. And so when you're looking at
• 5:43
  Speaker 3: a tiny particle, a proton or a neutron, its gravity
• 5:46
  Speaker 3: is basically zero. It's so hard to measure. The smallest
• 5:50
  Speaker 3: thing we've ever measured the gravity of is something like
• 5:53
  Speaker 3: on the order of a gram, you know, which means
• 5:56
  Speaker 3: it has like ten to twenty particles in it. We
• 6:00
  Speaker 3: are nowhere close to being able to see gravity operate
• 6:04
  Speaker 3: on particles so that we can then try to explain
• 6:07
  Speaker 3: how it all works.
• 6:08
  Speaker 1: That seems kind of hard because like science is mostly
• 6:12
  Speaker 1: about say, either direct observation or setting up an experiment.
• 6:17
  Speaker 4: So if you can't even see it happening.
• 6:20
  Speaker 1: Or figure out how to observe it in particles, how
• 6:23
  Speaker 1: can you ever figure out how it works on such
• 6:26
  Speaker 1: a small scale.
• 6:27
  Speaker 3: Yeah, great question. Well one is you don't give up.
• 6:30
  Speaker 4: Oh I was I was gonna go for Just give up, never.
• 6:37
  Speaker 3: Give up, never give it. People are doing these incredible experiments.
• 6:41
  Speaker 3: It's really an amazing accomplishment to figure out how to
• 6:45
  Speaker 3: test gravity on the smaller and smaller things. And there's
• 6:47
  Speaker 3: this history getting all the way back to like Cavendish
• 6:50
  Speaker 3: torsion experiments of lead balls a weigh a few pounds,
• 6:53
  Speaker 3: down to smaller objects and smaller objects, and very recently
• 6:56
  Speaker 3: down to stuff like smaller than a raisin, you know,
• 6:59
  Speaker 3: a few grains of sand of material, and I really
• 7:02
  Speaker 3: want to underscore that there's a special scientific skill there.
• 7:05
  Speaker 3: It's not like mathematics or genius insight into philosophy. It's
• 7:10
  Speaker 3: experimental bravura, you know. It's what Jorge might call engineering.
• 7:14
  Speaker 3: It's like figuring out how to make your experimental system
• 7:17
  Speaker 3: so quiet and so clean and so pristine that you
• 7:20
  Speaker 3: can force the universe to reveal one of its secrets.
• 7:23
  Speaker 3: It's a really special skill in science. And so those
• 7:26
  Speaker 3: folks are working hard and drilling down. But yeah, they're
• 7:28
  Speaker 3: like twenty orders of magnitude away from figuring it out,
• 7:32
  Speaker 3: so it's going to be a while. The other thing is,
• 7:34
  Speaker 3: you could, you know, try to visit a black hole.
• 7:36
  Speaker 3: Inside a black hole. We think that gravity and quant
• 7:39
  Speaker 3: mechanics are both relevant because obviously there's strong gravity, but
• 7:42
  Speaker 3: also things are squished really really small at the singularity
• 7:46
  Speaker 3: inside the black hole. Of course, that's inside the black
• 7:50
  Speaker 3: hole beyond the event horizon. So we still haven't figured
• 7:53
  Speaker 3: out how to probe that.
• 7:54
  Speaker 1: Yeah, we've talked about this. It is not in the
• 7:57
  Speaker 1: budget to go to a black just yet.
• 8:01
  Speaker 3: No, so instead you might want to make your own
• 8:03
  Speaker 3: black hole and then study the patterns of its hawking
• 8:06
  Speaker 3: radiation to try to get some clues as to what
• 8:08
  Speaker 3: might be inside of it. But nobody succeeded in making
• 8:11
  Speaker 3: a black hole yet, and if they did, it might
• 8:13
  Speaker 3: destroy the Earth, and so there are some questions there.
• 8:17
  Speaker 3: So while the experimental side is super tooper frustrating, we
• 8:21
  Speaker 3: can try to make some progress on the theoretical side, thinking
• 8:24
  Speaker 3: deeply about the universe, eating special mushrooms and having insights
• 8:29
  Speaker 3: about you know, connections and mathematical symmetries between these two ideas,
• 8:33
  Speaker 3: to look for links, to look for connections, to look
• 8:36
  Speaker 3: for ways to fit them together in our minds that
• 8:38
  Speaker 3: might give us some new clues as to how to
• 8:41
  Speaker 3: bridge these two fundamental pillars of modern physics.
• 8:44
  Speaker 1: Now, do you get university funding for mushroom tripping in
• 8:49
  Speaker 1: the sake of theoretical physics.
• 8:52
  Speaker 3: If you can convince the funding agency that it's essential
• 8:55
  Speaker 3: for your research to make progress, then ya, I'll bet you.
• 9:00
  Speaker 3: And so today on the podcast, we'll be exploring one
• 9:02
  Speaker 3: of those potential directions to bring gravity and quantum mechanics
• 9:06
  Speaker 3: together to try to fit these two genius insights about
• 9:09
  Speaker 3: the way the universe works into one mega inside and
• 9:13
  Speaker 3: today in the podcast, we're asking the question what is
• 9:21
  Speaker 3: gravito electro magnetism? Boy? Is that a mouthful? I feel
• 9:26
  Speaker 3: like this must have been named by some German person. Yeah,
• 9:28
  Speaker 3: every time they come up with a name for something,
• 9:30
  Speaker 3: they just like stick a bunch of words together into
• 9:31
  Speaker 3: one super long word instead of.
• 9:33
  Speaker 4: Coming up with a new word.
• 9:34
  Speaker 1: It's use the words you already have, but stick them
• 9:37
  Speaker 1: all together.
• 9:40
  Speaker 3: Imagine if you came up with new ice cream flavors
• 9:42
  Speaker 3: that way, cookies and cream all one word.
• 9:45
  Speaker 4: Wait it isn't already.
• 9:48
  Speaker 3: No, No, I think that's exactly how they figured it out.
• 9:51
  Speaker 1: Like, I think it's interesting that I don't think I've
• 9:54
  Speaker 1: ever seen a question before of the audience where people
• 9:57
  Speaker 1: are just like, I can't even comprehend the name of this.
• 10:00
  Speaker 3: That's right, And so this was maybe a little bit
• 10:03
  Speaker 3: unfair to drop this on the listeners, But what the heck.
• 10:05
  Speaker 3: I think it's fun to ask the guys questions about
• 10:08
  Speaker 3: things you never heard about. So thanks very much to
• 10:10
  Speaker 3: everybody who volunteers for this audience participation segment of the
• 10:14
  Speaker 3: podcast and is caught aware by by very technical physics
• 10:17
  Speaker 3: questions without an opportunity to prepare We really appreciate you
• 10:20
  Speaker 3: being gained for this. If you would like to play
• 10:22
  Speaker 3: for future episodes of the podcast, please write to me
• 10:25
  Speaker 3: two questions at Danielanthorge dot com. So before you hear
• 10:29
  Speaker 3: these answers, think about it for a minute. What do
• 10:31
  Speaker 3: you think gravito electromagnetism could be. Here's what some listeners
• 10:37
  Speaker 3: had to say as.
• 10:38
  Speaker 2: The electrochage put off by strong gravity. Maybe I don't
• 10:46
  Speaker 2: know how you combine gravity and electromagnetism, but it sounds
• 10:52
  Speaker 2: like some kind of combo of the two. So maybe
• 10:55
  Speaker 2: it's the way in which electromagnetic fields are affected by gravity.
• 11:03
  Speaker 3: Or vice versa. I'm going to guess that gravito electromagnetism is.
• 11:10
  Speaker 1: The impact that gravity has on the electromagnetic force. I
• 11:18
  Speaker 1: wonder what insane clown posse has to say about gravito electromagnetism,
• 11:24
  Speaker 1: and if they know how it works?
• 11:25
  Speaker 4: Does that call back too old?
• 11:27
  Speaker 1: Now?
• 11:27
  Speaker 4: Am I old?
• 11:30
  Speaker 3: I'm not going to comment on it. I will say
• 11:34
  Speaker 3: that I am approaching fifty and so I've embraced being
• 11:37
  Speaker 3: fifty by calling myself fifty before I even got there.
• 11:40
  Speaker 3: And my kids think it's weird that I round myself
• 11:43
  Speaker 3: with to fifty, but I love it.
• 11:45
  Speaker 4: I do that too.
• 11:46
  Speaker 1: I round up so I'm not so shocked when it happens.
• 11:49
  Speaker 3: Exactly. That's what I was thinking. And then my daughter
• 11:52
  Speaker 3: asked me. She said, well, does that mean when you
• 11:54
  Speaker 3: turn fifty one you're gonna round yourself up to one hundred?
• 11:57
  Speaker 4: Why not?
• 11:58
  Speaker 3: Yeah, I thought, you know, for the sake of consistence,
• 12:00
  Speaker 3: I guess I have to.
• 12:01
  Speaker 1: I mean, you know, then you could be the oldest
• 12:03
  Speaker 1: person on earth, even before you start getting a pension.
• 12:07
  Speaker 3: That's true. I'm just hoping to get some of those
• 12:10
  Speaker 3: compliments like wow, Daniel, you look good for it. All right,
• 12:15
  Speaker 3: But back to the topic of quantum mechanics and gravity.
• 12:18
  Speaker 3: We see people are struggling to understand what this word means.
• 12:21
  Speaker 3: But there is a sense there that it's about some
• 12:24
  Speaker 3: relationship between gravity and electromagnetism. Maybe gravity is caused by electromagnetism,
• 12:29
  Speaker 3: or maybe you get electric charges from gravity. There's some
• 12:32
  Speaker 3: fun ideas in there.
• 12:33
  Speaker 4: It does sound like a little scammy.
• 12:37
  Speaker 1: It sounds like something where someone's trying to sell something
• 12:40
  Speaker 1: to me, because it's just so many technical sounding words
• 12:43
  Speaker 1: all smashed together. It's like, yeah, I kind of want
• 12:48
  Speaker 1: to know what it is. The only thing I can
• 12:51
  Speaker 1: think of like these listeners is just that it's like
• 12:53
  Speaker 1: kind of trying to smoosh the concepts of gravity and
• 12:56
  Speaker 1: electromagnetism together, but I kind of want to know more
• 12:59
  Speaker 1: specifically what that is and how that works.
• 13:03
  Speaker 3: Yeah, and so delay the groundwork. I think we need
• 13:05
  Speaker 3: to spell out a little bit of detail about like
• 13:08
  Speaker 3: why this problem is hard. Why is it difficult to
• 13:11
  Speaker 3: bring gravity and electromagnetism, or gravity and quantum mechanical theories
• 13:16
  Speaker 3: of forces together in general, And so we should probably
• 13:20
  Speaker 3: start with those quantum mechanical theories. And you know, we
• 13:23
  Speaker 3: talked about electromagnetism because it's one of the fundamental forces
• 13:27
  Speaker 3: that we know about in the universe. And all of
• 13:29
  Speaker 3: these fundamental forces are quantum mechanical, meaning that we have
• 13:33
  Speaker 3: a theory of quantum mechanics that describes particles and how
• 13:36
  Speaker 3: they move through space or how they exist and how
• 13:39
  Speaker 3: they have probabilities to exist. And those quantum mechanical theories,
• 13:43
  Speaker 3: those Shroninger equations and the lagrongins and the Hamiltonians, all
• 13:47
  Speaker 3: those mathematical structures are quantum mechanical and they describe the forces.
• 13:52
  Speaker 3: So we have electromagnetism, we have the weak force, and
• 13:55
  Speaker 3: we have the strong force. All these things can be
• 13:58
  Speaker 3: described using a quant maicaanical theory. It means we know
• 14:01
  Speaker 3: how to calculate what happens when one particle pushes or
• 14:04
  Speaker 3: pulls on another particle using one of these forces. Like
• 14:08
  Speaker 3: when two electrons are coming near each other, they repel
• 14:11
  Speaker 3: each other, and they use these forces to do so.
• 14:13
  Speaker 3: They use electromagnetism, And you can think about that quantum mechanically,
• 14:17
  Speaker 3: either as one electron has a big electromagnetic field and
• 14:22
  Speaker 3: that's pushing on the other electron, or if you prefer
• 14:24
  Speaker 3: the particle picture, you can imagine that the two electrons
• 14:27
  Speaker 3: are exchanging photons. They're tossing photons back and forth, and
• 14:31
  Speaker 3: that's how they're pushing on each other. But either way,
• 14:33
  Speaker 3: we have a nice quantum mechanical picture from the ground up,
• 14:36
  Speaker 3: from the littlest bits of these three fundamental forces electromagnetism,
• 14:41
  Speaker 3: the weak force, and the strong force.
• 14:43
  Speaker 1: So is gravity even weaker than the weak force?
• 14:48
  Speaker 3: Gravity is like ten to the thirty times weaker than
• 14:52
  Speaker 3: the weak force. It's almost unimaginably weak. It's so much
• 14:56
  Speaker 3: weaker than the other forces that it's a big puzzle
• 14:59
  Speaker 3: in physics. Like in physics we look for patterns and clues.
• 15:02
  Speaker 3: We expect things that are similar in nature to all
• 15:05
  Speaker 3: operate in under similar principles and have similar numbers. So
• 15:09
  Speaker 3: if you want a lump gravity in as one of
• 15:11
  Speaker 3: the forces, then you got to answer the question why
• 15:14
  Speaker 3: is it so much weaker than the other forces? Not
• 15:17
  Speaker 3: by a factor of ten, not by a factor of
• 15:19
  Speaker 3: one hundred, not by a million, but ten with thirty
• 15:23
  Speaker 3: zeros behind it. That's a big deal.
• 15:25
  Speaker 1: And so like the difference between electromagnetism, the weak force,
• 15:29
  Speaker 1: and strong force like is not nearly as big as
• 15:33
  Speaker 1: the difference between all those three and gravity.
• 15:37
  Speaker 3: Yeah, exactly. The strong force is like ten times more
• 15:40
  Speaker 3: powerful than electromagnetism, which is like one hundred times more
• 15:43
  Speaker 3: powerful than the weak force, which is like a gajillion
• 15:47
  Speaker 3: billion of jillion times more valuation.
• 15:49
  Speaker 1: To hang on, that doesn't even sound like a number, Okay,
• 15:52
  Speaker 1: but I get it. So gravity is so incredibly weak
• 15:55
  Speaker 1: it doesn't even seem like it's in the same category
• 15:59
  Speaker 1: as these other things. It's like comparing like a blue
• 16:02
  Speaker 1: whale to an ant.
• 16:03
  Speaker 3: Yeah, that's exactly right now, fundamentally, that's not a problem.
• 16:07
  Speaker 3: Like it's possible that you could have for forces in
• 16:10
  Speaker 3: the universe and one of them is just much weaker.
• 16:13
  Speaker 3: There are ways that you can do that. It's not
• 16:15
  Speaker 3: an insurmountable issue. It's strange and it would make you
• 16:18
  Speaker 3: ask like why is that and to look for explanations,
• 16:22
  Speaker 3: but mathematically it doesn't prevent us from describing it. That's
• 16:25
  Speaker 3: not the challenge with gravity. If you sit down and
• 16:28
  Speaker 3: try to describe gravity using some kinds of maths similar
• 16:32
  Speaker 3: to the way we describe electromagnetism and the weak force
• 16:34
  Speaker 3: and strong force, to come up with like a quantum
• 16:37
  Speaker 3: theory of gravity that describes it as a force. Then
• 16:40
  Speaker 3: you start to build in gravitational fields and you can
• 16:43
  Speaker 3: think about the quantized ripples in those fields as particles.
• 16:46
  Speaker 3: In this case, it would be the graviton. So when
• 16:49
  Speaker 3: two planets come near each other and pull on each other,
• 16:52
  Speaker 3: the quantum picture of gravity would have them exchanging gravitons
• 16:57
  Speaker 3: the way two electrons are like exchange photon. So you
• 17:00
  Speaker 3: can start to go down that road mathematically and things
• 17:04
  Speaker 3: seem okay. You just like dial the force way way
• 17:06
  Speaker 3: down to make it super duper weak, but then you
• 17:09
  Speaker 3: run into a lot of mathematical problems actually making that
• 17:12
  Speaker 3: theory work.
• 17:13
  Speaker 1: How do you check your math in a situation like this,
• 17:16
  Speaker 1: Like what are the kinds of mathematical problems that you
• 17:19
  Speaker 1: run into? And how do you know that they're problems?
• 17:22
  Speaker 3: Yeah? Great question. The way that you know that your
• 17:24
  Speaker 3: theory is working or not working is that you try
• 17:27
  Speaker 3: to use it and you see if it gives reasonable results.
• 17:31
  Speaker 3: Like if you ask, I want to push these two
• 17:32
  Speaker 3: particles together, I want to calculate the probability of various outcomes.
• 17:36
  Speaker 3: I want to know the particles are going to bounce
• 17:38
  Speaker 3: off each other, or if they're going to scatter off
• 17:39
  Speaker 3: at this angle or at that angle. So you try
• 17:41
  Speaker 3: to calculate things. You try to make predictions in physics.
• 17:45
  Speaker 3: For your predictions to be reasonable, there's some limits. There's
• 17:48
  Speaker 3: some restrictions, like your predictions can't have probabilities greater than one.
• 17:52
  Speaker 3: If you ask, like is my electron going to go
• 17:54
  Speaker 3: left or right? And your theory says you have one
• 17:56
  Speaker 3: hundred and seventy five percent chance of its going left,
• 17:59
  Speaker 3: And you're like, hm, well that's that seems wrong. That
• 18:02
  Speaker 3: can't r right.
• 18:03
  Speaker 1: So when my gym teacher told me to give it
• 18:05
  Speaker 1: my one hundred and ten percent. Like, that's not right,
• 18:08
  Speaker 1: that's physically impossible.
• 18:11
  Speaker 4: That's right, my all.
• 18:14
  Speaker 3: Your gym teacher is violating the fundamental rules.
• 18:17
  Speaker 4: Of physicals call them up right now.
• 18:18
  Speaker 3: Or maybe your gym teacher is a quantum gravity theorist,
• 18:21
  Speaker 3: because that's exactly what happens when we try to make
• 18:24
  Speaker 3: a quantum gravity theory. Gravitons are really tricky because they
• 18:29
  Speaker 3: don't just transmit gravity. They have energy themselves, which means
• 18:33
  Speaker 3: they also couple to gravity. They feel gravity, they emit gravity.
• 18:37
  Speaker 3: So like when you emit a photon, photons don't feel electromagnetism,
• 18:42
  Speaker 3: they don't bounce off of other photons, they don't emit
• 18:44
  Speaker 3: other photons. Right, Photons don't feel electric charges because they
• 18:49
  Speaker 3: are neutral. They don't have a charge themselves, so they
• 18:52
  Speaker 3: will like fly right through an electric field. But a
• 18:54
  Speaker 3: graviton has energy, and gravity is felt by everything with energy,
• 18:59
  Speaker 3: So graviton feel gravity, which means they emit more gravitons,
• 19:03
  Speaker 3: and those gravitons emit more gravitons, and pretty soon you
• 19:06
  Speaker 3: have an infinite number of gravitons, and you start to
• 19:08
  Speaker 3: get nonsense answers out of your theory.
• 19:11
  Speaker 1: When you say a graviton, right, I'm thinking of a
• 19:14
  Speaker 1: particle sort of like a photon. But photons we've actually measured, right,
• 19:20
  Speaker 1: We've actually been able to sort of get physical evidence
• 19:23
  Speaker 1: of their existence. Like, do we have like physical evidence
• 19:26
  Speaker 1: of the existence of gravitons as like an existing thing
• 19:32
  Speaker 1: other than just knowing that gravity exists.
• 19:35
  Speaker 3: We do not have any evidence of gravitons. We have
• 19:38
  Speaker 3: a very successful theory of gravity. It's Einstein's theory of
• 19:41
  Speaker 3: general relativity that describes how space and time bend around
• 19:45
  Speaker 3: masses and that affects how things move, and that's very,
• 19:48
  Speaker 3: very precise, but that describes gravity as not a force.
• 19:51
  Speaker 3: It's like a bending in space and time. We're going
• 19:54
  Speaker 3: to switch over and try to think about gravity as
• 19:56
  Speaker 3: a force instead of bending in space and time. Then
• 20:00
  Speaker 3: you need these gravitons, and nobody's ever seen them. The
• 20:03
  Speaker 3: reason they're so hard to see is precisely because gravity
• 20:06
  Speaker 3: is so weak, Like electromagnetism is a pretty strong force.
• 20:10
  Speaker 3: Electrons are radiating photons all the time. It's not a
• 20:12
  Speaker 3: rare thing to happen in the universe. But gravitons are
• 20:15
  Speaker 3: more rare because gravity is so weak, and they're much
• 20:18
  Speaker 3: harder to see because gravity is so weak, so the
• 20:22
  Speaker 3: impact of like one graviton would be very very hard
• 20:25
  Speaker 3: to detect. So we don't know that gravitons are real,
• 20:29
  Speaker 3: but they are a necessary part of a theory of
• 20:31
  Speaker 3: quantum gravity that tries to make gravity look like a
• 20:34
  Speaker 3: force and fitted it into this quantum mechanical framework. So far,
• 20:38
  Speaker 3: and nobody's even been able to make the math work
• 20:40
  Speaker 3: to have like a consistent theory that we could even
• 20:43
  Speaker 3: go out and test in experiments.
• 20:45
  Speaker 1: So we can't make the math work. We can't even
• 20:48
  Speaker 1: find any evidence that gravitons exist. Things are looking pretty good,
• 20:53
  Speaker 1: pretty good so far. Maybe we should take a quick break.
• 20:57
  Speaker 1: I will look around see if I've got any gravitons
• 21:00
  Speaker 1: just kind of lying around, you never know, And then
• 21:03
  Speaker 1: when we get back, maybe we can take another crack
• 21:06
  Speaker 1: at this and see if there's any anything that actually
• 21:09
  Speaker 1: where the math you carry the ones and it all works.
• 21:13
  Speaker 4: Out all right. So bad news.
• 21:28
  Speaker 1: Daniel couldn't find any gravitons, not a single one. I'm
• 21:32
  Speaker 1: also out of milk, so things aren't looking so good
• 21:36
  Speaker 1: here do you have any good news for me in
• 21:39
  Speaker 1: our effort to smoosh together quantum mechanics and general relativity.
• 21:45
  Speaker 3: I didn't figure it out in the last couple of minutes,
• 21:47
  Speaker 3: but you know, a lot of clever people have been
• 21:49
  Speaker 3: thinking about this and trying to find some connections between
• 21:53
  Speaker 3: gravity and electromagnetism, or between electromagnetism and gravity, sort of
• 21:58
  Speaker 3: going both directions, trying to make gravity look more like
• 22:01
  Speaker 3: electromagnetism and the theoretical side, or giving up on that
• 22:05
  Speaker 3: and trying to make electromagnetism look more like gravity. So
• 22:08
  Speaker 3: we don't have any experimental results to guide us, but
• 22:11
  Speaker 3: we can still think deeply about the structure of these
• 22:13
  Speaker 3: theories and try to make some theoretical progress in our minds.
• 22:18
  Speaker 3: Magic mushrooms or no.
• 22:20
  Speaker 1: All right, so we're in the mindscape. What are we
• 22:23
  Speaker 1: doing in order to solve the hurdle of the math
• 22:27
  Speaker 1: not mathing in this idea, because it sounds like we
• 22:29
  Speaker 1: were sort of trying to think of planets as like
• 22:32
  Speaker 1: scaled up particles and gravity as like a force between them,
• 22:39
  Speaker 1: as if they're giant particles, and that didn't really work. Like,
• 22:43
  Speaker 1: is there another approach that you could use or is
• 22:46
  Speaker 1: there a way to like fine tune that approach such
• 22:48
  Speaker 1: that it actually does work.
• 22:50
  Speaker 3: Yeah, So the short answer is there isn't a great approach,
• 22:53
  Speaker 3: but that doesn't mean we can't make progress. And I
• 22:56
  Speaker 3: think people should understand that. In theoretical physics, it's not
• 22:58
  Speaker 3: like you sit down one day and come up with
• 23:00
  Speaker 3: the whole theory movies. You're entering like a mathematical jungle.
• 23:05
  Speaker 3: You're not sure if there is a path through, and
• 23:08
  Speaker 3: it takes exploration. Exploration is not just something we do
• 23:11
  Speaker 3: in experimental physics or in experimental biology. We're like walking
• 23:15
  Speaker 3: through a literal jungle looking for new kinds of frogs.
• 23:18
  Speaker 3: In theoretical physics, you can also explore. You can just
• 23:20
  Speaker 3: like try stuff and say, well, I'm going to go
• 23:22
  Speaker 3: in this direction and see if it works out, kind
• 23:25
  Speaker 3: of like when you're trying a proof in tenth grade
• 23:27
  Speaker 3: geometry and you're like, well, I'm not sure this is
• 23:29
  Speaker 3: gonna get me where I need to go, but I'm
• 23:30
  Speaker 3: gonna play around with these angles. And so in theoretical physics,
• 23:34
  Speaker 3: people are trying something that has a long tradition dating
• 23:37
  Speaker 3: all the way back to like Maxwell James Clerk, Maxwell
• 23:40
  Speaker 3: in the eighteen hundreds was looking at theories of electricity
• 23:44
  Speaker 3: and theories of magnetism, and he tried something cool. He said, well,
• 23:47
  Speaker 3: let me write down the equations for electricity and write
• 23:50
  Speaker 3: down the equations for magnetism and try to smooth them
• 23:53
  Speaker 3: together and make them look as much like each other
• 23:55
  Speaker 3: as possible. And when he did that, he realized, oh,
• 23:58
  Speaker 3: my gosh, these basically have the same equations. And not
• 24:02
  Speaker 3: only that, but you can click the equations together because
• 24:04
  Speaker 3: sometimes electric field cause magnetic field and vice versa to
• 24:08
  Speaker 3: make one bigger picture. So we had this great insight,
• 24:11
  Speaker 3: which is where we got the theory of electromagnetism. So
• 24:14
  Speaker 3: now people are trying to do something similar. They're saying,
• 24:16
  Speaker 3: let's look at the equations for electromagnetism and the equations
• 24:20
  Speaker 3: for gravity and see if we can find relationships. Are
• 24:23
  Speaker 3: they like a mirror image of each other? Can we
• 24:25
  Speaker 3: somehow find patterns there and then use that to guide
• 24:28
  Speaker 3: us through this intellectual jungle to a theory that combines
• 24:32
  Speaker 3: gravity and electromagnetism into one big theory.
• 24:35
  Speaker 1: So for someone just theoretically who does not have a
• 24:39
  Speaker 1: grasp of what theoretical math would look like, and when
• 24:44
  Speaker 1: you say equations, like what that is?
• 24:46
  Speaker 4: Like are we.
• 24:47
  Speaker 1: Talking about like you have five equations that you have
• 24:50
  Speaker 1: to memorize to understand gravity? Like are there hundreds of equations?
• 24:55
  Speaker 1: And when you're trying to like smash together equations, you know,
• 25:00
  Speaker 1: is it sort of like a brilliant mind where you
• 25:02
  Speaker 1: just see floating numbers kind of going together and doing
• 25:06
  Speaker 1: things like what in terms that someone like me who
• 25:11
  Speaker 1: math is trying to calculate a tip?
• 25:14
  Speaker 4: How does that work?
• 25:15
  Speaker 3: Yeah, that's a great question, and we could start off
• 25:17
  Speaker 3: pretty simply. You know, people are probably familiar with Newton's
• 25:21
  Speaker 3: law of gravity. That just says that the force between
• 25:25
  Speaker 3: two objects is proportional to the two masses divided by
• 25:29
  Speaker 3: the distance between them squared, and then you multiply that
• 25:31
  Speaker 3: whole thing by a constant big G Newton's constant. So
• 25:35
  Speaker 3: Newton's equation for the force between two objects is like
• 25:39
  Speaker 3: gmm over R squared. All right, So that's Newton's theory
• 25:43
  Speaker 3: of gravity. Then we can look over at electromagnetism. We
• 25:46
  Speaker 3: can say, what's the equation for the force between two
• 25:49
  Speaker 3: particles that have charge? Like remember our question was like
• 25:52
  Speaker 3: what happens when two electrons come near each other. Can
• 25:54
  Speaker 3: we calculate that well, Kulham's law tells us that the
• 25:58
  Speaker 3: force between two parts particles goes like the charge of
• 26:02
  Speaker 3: the two particles divided by the distance squared between them,
• 26:05
  Speaker 3: all multiplied by a constant in this case K. So
• 26:09
  Speaker 3: you look at these two equations, you notice instantly, like HM,
• 26:11
  Speaker 3: these have kind of similar structures. On the top of
• 26:14
  Speaker 3: the equation is the charge of the two objects. Where
• 26:18
  Speaker 3: gravity the charge would be the mass, and for electromagnetism
• 26:21
  Speaker 3: the charge is obviously the electric charge. And both of
• 26:24
  Speaker 3: them get weaker as the distance grows by the same
• 26:27
  Speaker 3: power you get twice as far apart. Gravity and electromagnetism
• 26:32
  Speaker 3: both get four times weaker. You go ten times further away,
• 26:35
  Speaker 3: the force of gravity and electromagnetism both go down by
• 26:39
  Speaker 3: a power of one hundred. So they have very similar
• 26:41
  Speaker 3: structures there already. That's encouraging.
• 26:44
  Speaker 1: But if it was just as simple as finding sort
• 26:47
  Speaker 1: of some of these equations that seem to look kind
• 26:50
  Speaker 1: of similar and match them together, like it seems like
• 26:53
  Speaker 1: we would have already figured this out. So what is
• 26:57
  Speaker 1: the scale of the complexity, Like, why have it we've
• 27:00
  Speaker 1: been able to find just like a bunch of these
• 27:02
  Speaker 1: equations that kind of look similar and seem to have
• 27:05
  Speaker 1: the same general structure and have them work together.
• 27:08
  Speaker 3: Yeah. Well, one issue, of course, is that we know
• 27:10
  Speaker 3: that Newton's theory of gravity is not the right theory.
• 27:13
  Speaker 4: Whoops.
• 27:15
  Speaker 3: When Newton was a very clever man, and he has
• 27:17
  Speaker 3: a very nice theory which mostly works but not.
• 27:20
  Speaker 4: Quite irresponsible with apples too.
• 27:24
  Speaker 3: Einstein's theory of gravity is not just a reimagining. It's
• 27:28
  Speaker 3: not just saying, look, the story is wrong. It's not
• 27:30
  Speaker 3: a force between objects, it's a bending of space and time.
• 27:33
  Speaker 3: It also gives different predictions, like, for example, Newton says
• 27:38
  Speaker 3: that the force just depends on the mass. It doesn't
• 27:40
  Speaker 3: depend on whether the object is spinning or not. So
• 27:44
  Speaker 3: according to Newton, if you're in orbit around the Earth,
• 27:47
  Speaker 3: whether the Earth is spinning or if it stopped spinning
• 27:49
  Speaker 3: or spinning the other way makes no difference for gravity.
• 27:52
  Speaker 3: Einstein says, Nope, that's not true. If the Earth is spinning,
• 27:56
  Speaker 3: that has more energy, and since gravity is linked to
• 27:59
  Speaker 3: energy of all kinds, not just mass, that changes the
• 28:02
  Speaker 3: gravitational force on the object in a complicated way. So
• 28:07
  Speaker 3: Einstein's equations are much more complicated than Newton's. He doesn't
• 28:10
  Speaker 3: just have like one simple force equation. He's got a
• 28:13
  Speaker 3: really complicated tensor equation, where a tensor it's just like
• 28:16
  Speaker 3: a matrix. It's like an array in computer programming, you know,
• 28:19
  Speaker 3: a way to keep track of a bunch of numbers
• 28:21
  Speaker 3: all at once. So he has more complicated equations. And
• 28:24
  Speaker 3: so you can't just say, look, Newton's law and kulums
• 28:27
  Speaker 3: are similar. You got to dig deep into Einstein's rules
• 28:30
  Speaker 3: for gravity.
• 28:31
  Speaker 1: So how do we know Einstein is right and Newton
• 28:34
  Speaker 1: is wrong. It can't just be that Einstein's got cooler
• 28:37
  Speaker 1: hair or more complex equations.
• 28:40
  Speaker 3: Well, Einstein and Newton make different predictions, and famously Einstein's
• 28:44
  Speaker 3: predictions were right. Einstein predicted stuff about how light bends
• 28:48
  Speaker 3: around the Sun during an eclipse, and he predicted stuff
• 28:51
  Speaker 3: about how mercury orbits the Sun and the angle of
• 28:54
  Speaker 3: the eclipse of mercury, how that twists as mercury is
• 28:57
  Speaker 3: orbiting the Sun. All these little difference between Newton and
• 29:00
  Speaker 3: Einstein add up and a few special cases, so we
• 29:03
  Speaker 3: know that Einstein's theory was right. So then people took
• 29:06
  Speaker 3: this on. They're like Okay, well, can I take Einstein's
• 29:09
  Speaker 3: equations and try to make them look like electromagnetism. Like
• 29:13
  Speaker 3: we were able to take Newton's law and make it
• 29:15
  Speaker 3: look like Kulam's law. Can we take Einstein's gravity and
• 29:19
  Speaker 3: make it look like electromagnetism? And people have actually succeeded
• 29:23
  Speaker 3: in doing this. There are these Gravita electromagnetic equations when
• 29:28
  Speaker 3: if you write them down, you get equations that look
• 29:30
  Speaker 3: very similar to Maxwell's equations for electromagnetism. Maxwell has four equations,
• 29:35
  Speaker 3: and I won't get into the math with you. You know,
• 29:37
  Speaker 3: there's a there's like a divergence and a curl for
• 29:40
  Speaker 3: electricity and magnetism and indie gravita electromagnetic equations. There are
• 29:46
  Speaker 3: also four equations and have a very similar structure to
• 29:50
  Speaker 3: Maxwell's equations. You should look them up and write them
• 29:52
  Speaker 3: side by side. They look very very similar. It's eerie,
• 29:55
  Speaker 3: it's spooky. It's like the universe is saying, oh, look,
• 29:58
  Speaker 3: you found the pattern. It's over here in the gravity
• 30:01
  Speaker 3: world and in the electromagnetic world.
• 30:03
  Speaker 1: This does feel like a conspiracy theorist sort of aligning
• 30:07
  Speaker 1: charts and with a corkboard and yarn and trying to
• 30:10
  Speaker 1: make these connections. But yeah, I mean, I'm looking at
• 30:14
  Speaker 1: this and you know, I don't know a look of
• 30:17
  Speaker 1: complex math, but it yes, they look very similar.
• 30:20
  Speaker 4: But if we've.
• 30:21
  Speaker 1: Found this, right, it doesn't mean that we've figured out
• 30:24
  Speaker 1: how they interlock. Like we found some similarities, some equations
• 30:28
  Speaker 1: that seem to match, but the bigger picture has not
• 30:32
  Speaker 1: yet become clear.
• 30:33
  Speaker 3: Yeah, that's right, and I hear you setting me up
• 30:35
  Speaker 3: to deliver the bad news of why this is going
• 30:37
  Speaker 3: to work. But first there's a little bit more good, okay,
• 30:40
  Speaker 3: which I think is a fun insight into how this works.
• 30:43
  Speaker 3: The thing about Einstein's equations for gravity, as we were
• 30:46
  Speaker 3: saying before, is that it gives you more than just
• 30:48
  Speaker 3: like a straightforce between two objects. Spinning objects can create
• 30:53
  Speaker 3: like torque and drag in space time itself, which gives
• 30:56
  Speaker 3: all sorts of weird forces, like if you are orbiting
• 30:59
  Speaker 3: the Earth and the Earth is spinning, then there's some
• 31:02
  Speaker 3: frame dragging effects there. Check out our whole episode about
• 31:05
  Speaker 3: that if you want more details. But effectively, it gives
• 31:08
  Speaker 3: like a twist on things that are orbiting the Earth.
• 31:11
  Speaker 3: So according to Einstein's gravity, it's not just a force
• 31:14
  Speaker 3: between two objects. There are more subtle effects there. And
• 31:17
  Speaker 3: the really cool thing is that in the gravito electromagnetic equations,
• 31:21
  Speaker 3: the ones where you take Einstein's gravity and try to
• 31:24
  Speaker 3: convert them to look like electromagnetism, you can see this emerge.
• 31:28
  Speaker 3: And in those equations you have what they call a
• 31:31
  Speaker 3: gravito electric field, which is sort of like the straight
• 31:34
  Speaker 3: up Newtonian version, plus this gravito magnetic field. So basically,
• 31:40
  Speaker 3: to explain all of Einstein's gravity you break it up
• 31:43
  Speaker 3: into two pieces, this analogy to the electric field and
• 31:46
  Speaker 3: this analogy to the magnetic field. And it goes even
• 31:49
  Speaker 3: deeper than that, because it's not just notation. It's not
• 31:52
  Speaker 3: just like, hey, let's write this down in a cute
• 31:54
  Speaker 3: way that looks sort of similar. There really is a
• 31:56
  Speaker 3: conceptual connection there because an electromagnetic the way you get
• 32:01
  Speaker 3: magnetic fields is you take electric fields and you wiggle
• 32:04
  Speaker 3: them like currents of electrons give you magnetic fields. So
• 32:07
  Speaker 3: it's like velocity dependent, right. Well, the cool thing about
• 32:11
  Speaker 3: the gravitomagnetic field, this other component of these equations you
• 32:16
  Speaker 3: have to add on to be able to describe Einstein's
• 32:18
  Speaker 3: gravity with equations that look like electromagnetism is that they
• 32:22
  Speaker 3: create velocity dependent acceleration in just the same way. For example,
• 32:27
  Speaker 3: those spinning masses. When the Earth is spinning, that's an
• 32:31
  Speaker 3: acceleration because any sort of rotation is an acceleration, and
• 32:34
  Speaker 3: that gives an acceleration. On satellites, it gives a twist,
• 32:38
  Speaker 3: it gives a pull. So when you force gravity into
• 32:41
  Speaker 3: this structure that looks like electromagnetism, you learn some things
• 32:45
  Speaker 3: about gravity. It like sorts it in your mind in
• 32:48
  Speaker 3: a way that actually gives you a little bit of insight.
• 32:50
  Speaker 3: And that's a good sign. When you're bushwhacking your way
• 32:53
  Speaker 3: through the theoretical jungle trying to make connections between things.
• 32:56
  Speaker 3: You don't have to force things into categories. When they
• 32:59
  Speaker 3: sort of naturally fall into those categories and reveals something
• 33:02
  Speaker 3: deep about the nature of that force or the nature
• 33:05
  Speaker 3: of the phenomenon, it's a sign that you might be
• 33:07
  Speaker 3: on the right track. So that's the good news that
• 33:10
  Speaker 3: there really is something satisfying about making gravity look like
• 33:14
  Speaker 3: the equations of electromagnetism. It's not just like hacking it
• 33:18
  Speaker 3: up into bits and shoving it in boxes.
• 33:20
  Speaker 1: It's not just using the same colored gelpins to write
• 33:23
  Speaker 1: the equation.
• 33:25
  Speaker 3: Exactly.
• 33:26
  Speaker 1: That sounds very promising, right, that sounds like a very
• 33:29
  Speaker 1: like promising path. And the fact that there's this wiggle
• 33:32
  Speaker 1: connection where wiggling or velocity movement for gravity like creates
• 33:38
  Speaker 1: this this field is very interesting.
• 33:42
  Speaker 4: I just I feel a butt is common.
• 33:44
  Speaker 3: There is a big butt, A.
• 33:45
  Speaker 1: Man, I knew I like big butts, and I cannot lie.
• 33:52
  Speaker 3: Now that's a reference.
• 33:53
  Speaker 4: I hope everybody hopefully Stelia.
• 33:55
  Speaker 3: The other brothers can't deny. Well, the thing that the
• 33:58
  Speaker 3: other brothers can deny is that this works in difficult situations.
• 34:03
  Speaker 3: Like we said that you could take Einstein's rules and
• 34:06
  Speaker 3: you can express them in mathematical equations that look like electromagnetism.
• 34:11
  Speaker 3: But there was a butt there I left off, And
• 34:13
  Speaker 3: the butt is This only works if gravity is kind
• 34:16
  Speaker 3: of weak, like when the curvature of space time is
• 34:19
  Speaker 3: not very strong, when you're like far from any intense mass,
• 34:23
  Speaker 3: when you're far away from a black hole, for example,
• 34:25
  Speaker 3: or even from the Sun, then this works pretty well.
• 34:29
  Speaker 3: But when the curvature of space time gets more intense,
• 34:31
  Speaker 3: this breaks down. Like the equations are just too complicated,
• 34:35
  Speaker 3: too intense. We have no way to fit them into
• 34:37
  Speaker 3: these boxes to make them look like electromagnetism. In order
• 34:41
  Speaker 3: to do that, to take the complicated Tensor equations of
• 34:44
  Speaker 3: general relativity and to make them look like electromagnetism, you
• 34:47
  Speaker 3: have to make a bunch of assumptions, and one of
• 34:49
  Speaker 3: those assumptions is gravity is pretty weak. So basically what's
• 34:53
  Speaker 3: happened here is you've avoided the hard problem. You know,
• 34:56
  Speaker 3: the hard problem of making quantum gravity work was figuring
• 34:59
  Speaker 3: out what happened when gravitons amid other gravitons amid other gravitons. Basically,
• 35:03
  Speaker 3: when gravity gets very very strong and it can no
• 35:06
  Speaker 3: longer be neglected, and that's exactly the situation that gravito
• 35:10
  Speaker 3: electromagnetism doesn't know how to answer. So it's some progress
• 35:14
  Speaker 3: in the sense of like, hmm, you found some cool
• 35:16
  Speaker 3: connections between these theories, but only in the easy parts,
• 35:20
  Speaker 3: not in the hard parts at all. When you get
• 35:22
  Speaker 3: to the hard part of gravity being very strong and
• 35:24
  Speaker 3: every graviton is emitting ten other gravitons, then this breaks
• 35:28
  Speaker 3: down and it doesn't help us at all. So it's
• 35:30
  Speaker 3: like an interesting island of understanding, but it doesn't make
• 35:34
  Speaker 3: any progress on the really hard part of the problem
• 35:37
  Speaker 3: of describing gravity as a quantum theory when gravity is
• 35:40
  Speaker 3: very very strong.
• 35:41
  Speaker 1: But could it be revealing something about gravity still, like
• 35:46
  Speaker 1: maybe that there is a significant difference between a strong
• 35:51
  Speaker 1: or large amount of gravity, like the gravity of the
• 35:54
  Speaker 1: Sun versus the Earth. If there is some kind of
• 35:56
  Speaker 1: fundamental difference between like weak levels of gravity and strong
• 36:00
  Speaker 1: levels of gravity, that seems like that could itself be
• 36:05
  Speaker 1: an interesting kind of finding, even if it still doesn't
• 36:08
  Speaker 1: solve the bigger question of how to merge those concepts.
• 36:12
  Speaker 3: Yeah, exactly, And that was the point I was trying
• 36:14
  Speaker 3: to make earlier that even intermedia progress is progress. You
• 36:18
  Speaker 3: don't have to know if this is going to fundamentally
• 36:20
  Speaker 3: solve the question of quantum mechanical gravity for it to
• 36:23
  Speaker 3: be cool that you figured something out, that you've made
• 36:25
  Speaker 3: some headway, you found some island of understanding whether it
• 36:28
  Speaker 3: actually connects to the mainland and reveals all the deep
• 36:31
  Speaker 3: secrets we don't know yet. But that doesn't mean it's
• 36:33
  Speaker 3: not worth doing and not worth exploring. Right, we've made
• 36:36
  Speaker 3: it to this stage where we've been able to accomplish
• 36:38
  Speaker 3: this connection between electromagnetism and gravity. It might be that
• 36:43
  Speaker 3: hunting around and digging around and poking in various directions.
• 36:46
  Speaker 3: Lets us build from this right that we can go
• 36:48
  Speaker 3: from here to figure out how to describe strong gravity.
• 36:51
  Speaker 3: Nobody knows how to do that yet, but this is
• 36:54
  Speaker 3: like another avenue of attack. This gives us another way
• 36:56
  Speaker 3: to think about it. At least it might be a
• 36:59
  Speaker 3: total dead end or might be the wave of the future.
• 37:02
  Speaker 3: We haven't figured that out yet. It's on the forefront
• 37:04
  Speaker 3: of knowledge.
• 37:05
  Speaker 4: I mean, let's go with not being a dead end.
• 37:09
  Speaker 1: We'll take a quick break and try to keep up
• 37:13
  Speaker 1: the optimism that this is actually going towards finding a
• 37:17
  Speaker 1: fundamental answer that'll change everyone's lives. And we're probably not
• 37:22
  Speaker 1: going to figure it out in the ad break, but
• 37:24
  Speaker 1: you know, we'll think about it. So we are back.
• 37:40
  Speaker 1: We have not yet solved how to weave together electromagnetism
• 37:46
  Speaker 1: and general relativity or gravity, but there has been some
• 37:52
  Speaker 1: interesting progress that has been made that is perhaps instructive
• 37:56
  Speaker 1: and perhaps interesting. So we had that issue that these
• 38:02
  Speaker 1: equations when gravity is weak, they seem to kind of align,
• 38:07
  Speaker 1: like you have the equations associated with general relativity and
• 38:11
  Speaker 1: then Maxwell's equations that looked similar then when gravity got
• 38:15
  Speaker 1: strong like the sun or a black hole, that kind
• 38:19
  Speaker 1: of broke down. It no longer worked in that way.
• 38:23
  Speaker 1: So is there another sort of angle of attack that
• 38:27
  Speaker 1: is being explored.
• 38:28
  Speaker 3: Yeah, people are trying so many different things at once,
• 38:31
  Speaker 3: and you know, this is the way we make progress.
• 38:32
  Speaker 3: You push your way through the jungle. Maybe you make
• 38:34
  Speaker 3: it all the way through. Maybe you run into somebody
• 38:36
  Speaker 3: else coming from the other direction right, and you can
• 38:39
  Speaker 3: join you two efforts. And so that's what's happening is
• 38:42
  Speaker 3: a bunch of people are working on trying to make
• 38:45
  Speaker 3: gravity look like electromagnetism. So that's the gravito electromagnetic approach
• 38:50
  Speaker 3: that we just talked about. But some people are working
• 38:52
  Speaker 3: in the other direction. They're saying, let's not make gravity
• 38:55
  Speaker 3: look like electromagnetism, let's make electromagnetism look like gravity. Einstein's
• 39:01
  Speaker 3: big idea was let's not think of gravity as a force,
• 39:05
  Speaker 3: let's think of it as the curvature of space time.
• 39:08
  Speaker 3: And so people are wondering, like, can we extend that idea?
• 39:11
  Speaker 3: Can we also do that for electromagnetism. Remember that the
• 39:15
  Speaker 3: way Einstein did this is he said, look, it feels
• 39:18
  Speaker 3: like there's a force between you and the Earth. Newton's
• 39:21
  Speaker 3: description of gravity as a force is compelling because when
• 39:24
  Speaker 3: you throw a ball in the air, it falls to
• 39:26
  Speaker 3: the Earth and it looks like it's getting pulled on. Right,
• 39:28
  Speaker 3: we have this experience of gravity as a force. But
• 39:32
  Speaker 3: he said that it's not actually a force. That's something
• 39:34
  Speaker 3: of an illusion. What's happening when you toss a ball
• 39:37
  Speaker 3: is that you're releasing it into free fall. Space itself
• 39:41
  Speaker 3: is curved in the vicinity of mass, so there's a
• 39:44
  Speaker 3: natural path for objects to follow in curved space time.
• 39:47
  Speaker 3: So the ball naturally falls towards the center of the Earth.
• 39:51
  Speaker 3: So Newton's picture is there's a force pulling on the ball,
• 39:55
  Speaker 3: and then it hits the Earth and it stops it
• 39:57
  Speaker 3: because the Earth is balancing that force of gravity. Einstein's
• 40:01
  Speaker 3: picture is different. Einstein says, when the ball is in
• 40:04
  Speaker 3: the air, it's in freefall. There is no force on
• 40:07
  Speaker 3: the ball at all. It's just following the motion of
• 40:09
  Speaker 3: space and time. And then the Earth stops it because
• 40:12
  Speaker 3: the Earth itself is providing a force. It's accelerating against
• 40:15
  Speaker 3: that natural motion of space time.
• 40:17
  Speaker 1: Yeah, and I think you've told me this is actually measurable, right,
• 40:21
  Speaker 1: that there is acceleration acting when you are standing on
• 40:26
  Speaker 1: the floor.
• 40:27
  Speaker 3: Exactly, if you jump off a building instead of the ball,
• 40:30
  Speaker 3: and you take a scale with you, and as you're
• 40:32
  Speaker 3: falling through the air, hurtling towards the earth, you stand
• 40:35
  Speaker 3: on the scale, what are you going to measure? You're
• 40:37
  Speaker 3: going to measure nothing, right. You have no weight, and
• 40:40
  Speaker 3: that's because you're in freefall. There's no acceleration there. You're
• 40:43
  Speaker 3: not measuring anything. If you're standing on the surface of
• 40:45
  Speaker 3: the Earth and you stand on the scale, then you
• 40:47
  Speaker 3: measure your weight. That's where there's a force, right, So
• 40:50
  Speaker 3: there really is no force on you when you are
• 40:53
  Speaker 3: in freefall. There's a force on you when you're standing
• 40:56
  Speaker 3: on the surface of the earth. That's the Earth pushing
• 40:58
  Speaker 3: up against that natural motion. So the explanation is that
• 41:02
  Speaker 3: there is no force there. There's just a curvature of
• 41:04
  Speaker 3: space and time. And we couldn't see that curvature, and
• 41:06
  Speaker 3: that's why it looks to us like there is a force.
• 41:10
  Speaker 1: Having this as the theory about gravity, like, how do
• 41:12
  Speaker 1: you then fit the quantum forces into this framework, right,
• 41:17
  Speaker 1: because like that seems fundamentally different. Those are forces, they're
• 41:21
  Speaker 1: pulling or pushing against each other. How does that fit
• 41:24
  Speaker 1: into this kind of idea of gravity being like the
• 41:27
  Speaker 1: shape of existence, which sounds it's hard for me to
• 41:32
  Speaker 1: kind of think about that, right, like the shape of
• 41:34
  Speaker 1: the universe, the shape of the fabric of the universe,
• 41:38
  Speaker 1: and then we're just kind of falling along it.
• 41:40
  Speaker 4: And then you have these particles.
• 41:42
  Speaker 1: Have we observed anything in particles that could sort of
• 41:46
  Speaker 1: fit within that framework.
• 41:48
  Speaker 3: So we haven't observed anything yet, but there are some
• 41:51
  Speaker 3: theoretical ideas. The idea is to say, well, maybe electromagnetism
• 41:55
  Speaker 3: also isn't the force. Maybe it just looks like a
• 41:58
  Speaker 3: force and it's actually the result of a second kind
• 42:02
  Speaker 3: of curvature. So we have like first kind of curvature
• 42:05
  Speaker 3: is Einstein's curvature of space time that gives us the
• 42:08
  Speaker 3: apparent force of gravity. If space can also be curved
• 42:11
  Speaker 3: in another way, and that curvature gives us the appearance
• 42:15
  Speaker 3: of the force of electromagnetism. And in order to have
• 42:19
  Speaker 3: curvature in another way, you need more dimensions of space
• 42:23
  Speaker 3: and time. The idea is, like einstein space is three
• 42:26
  Speaker 3: plus one dimensions. You start with one dimension, which is
• 42:29
  Speaker 3: a line you draw a second dimension, which is perpendicular
• 42:32
  Speaker 3: to that. Now you have like a plane. You can
• 42:34
  Speaker 3: add a third dimension which is perpendicular to both of
• 42:37
  Speaker 3: the first two, and that gives you like three D
• 42:40
  Speaker 3: space right where each of those three lines are perpendicular
• 42:43
  Speaker 3: to each other. And that's it. There's no more room
• 42:46
  Speaker 3: to add another line perpendicular to all three.
• 42:49
  Speaker 4: Right, because space, Yeah, it doesn't work.
• 42:53
  Speaker 3: It's sort of crazy in mind bending. And I remember
• 42:55
  Speaker 3: as like an eight year old trying to imagine that's
• 42:57
  Speaker 3: fourth dimension but not being able to do it. But
• 43:00
  Speaker 3: we do think of time as sort of a fourth dimension.
• 43:03
  Speaker 3: How those three change. So Einstein space is four dimensional,
• 43:07
  Speaker 3: but we can extend it by adding another dimension of
• 43:09
  Speaker 3: space and having that curvature be in that additional dimension,
• 43:14
  Speaker 3: that fifth dimension. And you might ask, well, I can't
• 43:16
  Speaker 3: see that dimension. I can't imagine where that dimension would be.
• 43:19
  Speaker 3: How does that even work? Yeah, And this fifth dimension
• 43:22
  Speaker 3: is sort of similar to the way we think about time,
• 43:24
  Speaker 3: or like time we think about as the fourth dimension.
• 43:27
  Speaker 3: Imagine three dimensional space and then imagine that changing through time. Right,
• 43:32
  Speaker 3: save your full three dimensional space, But now you have
• 43:34
  Speaker 3: like another axis along which that three dimensional space is
• 43:38
  Speaker 3: changing so to imagine another dimension of space itself. Imagine
• 43:43
  Speaker 3: three dimensional space and then imagine a bunch of copies
• 43:45
  Speaker 3: of it. And this new dimension is not like the
• 43:48
  Speaker 3: original three. Instead of going on forever, it's like a
• 43:51
  Speaker 3: little loop. It's more like in polar coordinates, how you
• 43:54
  Speaker 3: have an angle and the angle can't go from zero
• 43:57
  Speaker 3: to infinity, just goes from zero to three hundred and
• 43:59
  Speaker 3: sixty degrees and it goes back to zero again. Right,
• 44:02
  Speaker 3: Imagine a new dimension of space that's sort of similar.
• 44:05
  Speaker 3: It has a maximum length, it's a circle instead of
• 44:08
  Speaker 3: an infinite line. Take three D space and sort of
• 44:11
  Speaker 3: move it around this circle. That's how we imagine a
• 44:14
  Speaker 3: universe with four spatial dimensions, the first three that are normal,
• 44:18
  Speaker 3: and then this weird rolled up dimension.
• 44:20
  Speaker 1: Is it like when your Windows computer crashes and you're
• 44:24
  Speaker 1: dragging like your cursor or a window around, and then
• 44:27
  Speaker 1: there's a bunch of little copies of that that all
• 44:30
  Speaker 1: get stacked up and messed up.
• 44:32
  Speaker 4: Is that what we're talking about here exactly?
• 44:37
  Speaker 3: Or like when you win solitaire and the cards all
• 44:39
  Speaker 3: stack on top of each other. It's difficult to imagine
• 44:42
  Speaker 3: because we're used to three D space and we think
• 44:44
  Speaker 3: in three dimensions, and so squeezing that fourth dimension into
• 44:47
  Speaker 3: your brain is really a challenge. But mathematically it allows
• 44:51
  Speaker 3: something very cool. It allows you to have another kind
• 44:54
  Speaker 3: of curvature. A curvature in this new dimension might be
• 44:58
  Speaker 3: able to explain what we see as the force of electromagnetism.
• 45:03
  Speaker 3: So in this case, not just the curvature, but the
• 45:05
  Speaker 3: whole dimension would be basically invisible to us. This is
• 45:09
  Speaker 3: an ancient idea in physics. It goes all the way
• 45:11
  Speaker 3: back to nineteen nineteen. The guy Theodor Cluza came up
• 45:15
  Speaker 3: with this, just after Einstein came up with his idea
• 45:17
  Speaker 3: of relativity, and then a few years later a guy
• 45:20
  Speaker 3: named Oscar Klein turned it into a quantum theory in
• 45:23
  Speaker 3: nineteen twenty six. And try to calculate the size of
• 45:26
  Speaker 3: this new fifth dimension and figured out how to be
• 45:29
  Speaker 3: like twenty times the plank length, which means it's like
• 45:32
  Speaker 3: super duper tiny. It's like ten to the minus thirty
• 45:36
  Speaker 3: five meters long. So this seemed really exciting.
• 45:39
  Speaker 1: I have so many questions just about that, like what
• 45:41
  Speaker 1: do you mean calculating the size of a dimension right?
• 45:46
  Speaker 3: Like, remember that this new dimension is not infinite, we
• 45:50
  Speaker 3: think that you can go as far as you want
• 45:51
  Speaker 3: in X or and y, R and z. But this
• 45:53
  Speaker 3: new dimension is a loop, which means it has a length.
• 45:57
  Speaker 3: Now there's a maximum distance in this dimension. It's unlike
• 46:01
  Speaker 3: the other ones in a really weird way, and that
• 46:04
  Speaker 3: means that you can calculate, like, well, how big could
• 46:06
  Speaker 3: it be? What is the radius of curvature? What is
• 46:08
  Speaker 3: the length around this dimension? So it's very different in
• 46:12
  Speaker 3: a really counterintuitive way. And then Einstein got to work
• 46:15
  Speaker 3: on it, and he was like, all right, this is exciting.
• 46:18
  Speaker 4: I trust him more than I trust me to think
• 46:19
  Speaker 4: about it.
• 46:21
  Speaker 3: He thought, maybe this is exciting. Maybe I can make
• 46:24
  Speaker 3: this work. Maybe I can explain all of electromagnetism using
• 46:27
  Speaker 3: curvature in this new fifth dimension. And yeah, he died
• 46:30
  Speaker 3: before he found and people had been working on it
• 46:33
  Speaker 3: for a long time and nobody's been able to crack it.
• 46:36
  Speaker 3: There are some versions of this theory which sort of work,
• 46:39
  Speaker 3: but they all predict that we would have seen a
• 46:41
  Speaker 3: bunch of new particles. They predict that electrons would like
• 46:44
  Speaker 3: vibrate in this other dimension, and they would vibrate in
• 46:47
  Speaker 3: different ways, so you would see like different versions of
• 46:50
  Speaker 3: the electron the way like a string can vibrate, but
• 46:53
  Speaker 3: it can vibrate like one mode or two modes, or
• 46:56
  Speaker 3: three modes or four modes. Electrons could vibrate in this
• 46:59
  Speaker 3: other demands in various ways, and you would see like
• 47:02
  Speaker 3: heavier and heavier versions of the electron, where the heavy
• 47:05
  Speaker 3: ones are like vibrating in this new dimension with more energy,
• 47:08
  Speaker 3: which gives them effectively more mass. But we haven't seen
• 47:12
  Speaker 3: any heavy electrons, or any heavy muons, or any heavy
• 47:14
  Speaker 3: versions of these other particles at all. People thought for
• 47:17
  Speaker 3: a while, oh, maybe the muon is a heavy version
• 47:20
  Speaker 3: of the electron, and that's actually like, you know, something
• 47:22
  Speaker 3: vibrating in this new dimension. But that doesn't quite work
• 47:25
  Speaker 3: out because the electron and the muon feel the weak
• 47:28
  Speaker 3: force a little bit differently. So the bottom line is
• 47:31
  Speaker 3: it's an exciting direction theoretically to try to make electromagnetism
• 47:35
  Speaker 3: work in this clusive cline theory, but it's made predictions
• 47:39
  Speaker 3: that haven't been born out in the data, and so
• 47:42
  Speaker 3: it's not so promising.
• 47:44
  Speaker 1: Well, we need to make a time machine go back
• 47:47
  Speaker 1: in time, and then ask Einstein, first of all, how
• 47:51
  Speaker 1: to make a time machine so that in the future
• 47:54
  Speaker 1: we can go back in time and talk to them
• 47:57
  Speaker 1: and then present them with all of this information.
• 48:00
  Speaker 4: Or maybe, uh, there will be a.
• 48:02
  Speaker 1: New kind of Einstein, or collectively instead of one super genius,
• 48:08
  Speaker 1: just a bunch of very smart people working together figuring
• 48:13
  Speaker 1: this out exactly.
• 48:14
  Speaker 3: But it's promising. It's exciting that people are trying to
• 48:17
  Speaker 3: push their way through the theoretical jungle. You know, until
• 48:20
  Speaker 3: we figure out how to make a black hole here
• 48:22
  Speaker 3: on Earth, or we've come up with some clever quantum
• 48:25
  Speaker 3: gravity experiment that lets us see particles feeling gravity and
• 48:29
  Speaker 3: understand whether they're like bending space time probabilistically, or whether
• 48:33
  Speaker 3: gravity collapses their wave functions, or what's going on, we
• 48:36
  Speaker 3: can only make progress theoretically. That means trying to find
• 48:40
  Speaker 3: mathematical relationships between these theories, either making electromagnetism look more
• 48:45
  Speaker 3: like gravity or make gravity look more like electromagnetism. So far,
• 48:49
  Speaker 3: both paths have been sort of stuck in the jungle.
• 48:52
  Speaker 3: But maybe one day people will find a connection between
• 48:54
  Speaker 3: them and will all be illuminated.
• 48:57
  Speaker 1: That is beautiful, but you do also keep breezing past
• 49:00
  Speaker 1: this plan to make up a black hole on Earth.
• 49:03
  Speaker 4: That's feel sangerous.
• 49:04
  Speaker 3: To me, it is very dangerous, but also potentially we
• 49:08
  Speaker 3: could learn a lot about the universe, so you know,
• 49:10
  Speaker 3: may be worth a risk.
• 49:11
  Speaker 4: Yeah, ultimate knowledge right before oblivion. Sign me up.
• 49:18
  Speaker 3: Sounds good. We'll stay tuned for more hints about potential
• 49:21
  Speaker 3: ultimate knowledge about the universe, just before you get sucked
• 49:25
  Speaker 3: into oblivion. Thanks so very much Katie for joining me
• 49:28
  Speaker 3: on this journey of theoretical understanding, and thanks to everybody
• 49:31
  Speaker 3: for tuning in. Tune in next time for more science
• 49:39
  Speaker 3: and curiosity. Come find us on social media where we
• 49:42
  Speaker 3: answer questions and post videos. We're on Twitter, Discord, Instant,
• 49:46
  Speaker 3: and now TikTok. Thanks for listening, and remember that Daniel
• 49:50
  Speaker 3: and Jorge Explain the Universe is a production of iHeartRadio.
• 49:53
  Speaker 3: For more podcasts from iHeartRadio, visit the iHeartRadio app, Apple Podcasts,
• 49:59
  Speaker 3: or wherever you like listen to your favorite shows.