Speaker 1: Hey, or hey. You know what's still amazes me that
Speaker 1: they give to introverts like us a podcast that blows
Speaker 1: my mind every week. But also, rainbows are awesome, But
Speaker 1: what about them amazes you? Everything is amazing about them.
Speaker 1: They are amazingly beautiful, But I'm amazed that they like exist,
Speaker 1: that they happen in the universe. You know that there's
Speaker 1: a science behind them, right, They're not just like magical.
Speaker 1: I get that there's science there, but I just think
Speaker 1: it's incredible that we live in the universe where this
Speaker 1: kind of thing actually happens. I mean, if you read
Speaker 1: about this in the science fiction book, you would think
Speaker 1: it's pretty farfetched. Well, it depends what what kind of
Speaker 1: science fiction you're reading. Does it also involve unicorns? Unicorns
Speaker 1: like a podcast with two introverts? Wait, who is the
Speaker 1: unicorn in this case? Because you can only have one,
Speaker 1: it's in the name unicorn. Collectively, we are one unicorn.
Speaker 1: Hi am Jorhemmack, cartoonists and the creator of PhD comics. Hi,
Speaker 1: I'm Daniel. I'm a particle physicist and a professor at
Speaker 1: U c Irvine, and I called dibbs on being the
Speaker 1: front two legs of the unicorn costume. Oh good, it's
Speaker 1: going to be the back end. Maybe you can have
Speaker 1: a guest host go. That's why we have guest hosts exactly.
Speaker 1: But anyways, welcome to our podcast, Daniel and Jorge Explain
Speaker 1: the Universe, a production of I Heart Radio, the podcasting
Speaker 1: which we talk about everything that's out there in the
Speaker 1: universe and try to explain all of it to you.
Speaker 1: We explore the complete spectrum of possible physical phenomena, including rainbows.
Speaker 1: If unicorns were real, we would talk about them as well.
Speaker 1: But we don't shy away from digging deep into the
Speaker 1: fabric of reality, understanding how it all works, and trying
Speaker 1: to explain to you what scientists are thinking about, what
Speaker 1: they are puzzling over, and what ideas they are bouncing
Speaker 1: around their unicorn brains. That's right, because it is a
Speaker 1: very colorful universe. Well have amazing sites like rainbows, and
Speaker 1: we like to follow that arc of science to see
Speaker 1: what is at the end of it if there is
Speaker 1: indeed a big part of gold or some other element,
Speaker 1: you know, because it just don't really discriminate between elements,
Speaker 1: do they We don't. But I would like to accept
Speaker 1: my grand funding in pots of gold if that was possible,
Speaker 1: you know, rather than just like dollars in a bank account. Yeah,
Speaker 1: but then then your grand funding is depending on gold
Speaker 1: currency markets. What is the exchange rate between gold and science? Anyway,
Speaker 1: I don't keep track, but he's made me think of
Speaker 1: another question, Daniel, in a multiverse, right, technically in a
Speaker 1: multiverse or maybe even in an infinite universe. Uh, unicorns
Speaker 1: probably exists, right, I mean it is possible, so therefore
Speaker 1: it must be true. It must be horses out there
Speaker 1: in the multiverse or an infinite universe with horns in
Speaker 1: their foreheads. Probably out there somewhere in the multiverse there
Speaker 1: are unicorn physicists being paid to do their science in
Speaker 1: pots of gold. Maybe even two unicorns on a podcast
Speaker 1: talking about what it would be like if humans were
Speaker 1: doing science instead of them humans were real, Like, maybe
Speaker 1: humans are the unicorns in the unicorn world. If you're
Speaker 1: already unicorns, why would you even think up humans? Right?
Speaker 1: Are do you think of something so boring and ugly
Speaker 1: compared to unicorns? Or maybe like regular horses are the
Speaker 1: unicorns for them? They're like can you imagine a horse
Speaker 1: without a horn? Or maybe it's the other direction, Maybe
Speaker 1: they're imagining two horned horses, right, Yeah, that would be
Speaker 1: like wild to them. That would be an imaginary and magic.
Speaker 1: And on this podcast, we do like to use our
Speaker 1: imagination to consider the ways that the universe might be.
Speaker 1: After all, we are trapped on this tiny little rock
Speaker 1: in a little corner of space, trying to understand the
Speaker 1: entire cosmos, which requires somehow developing a model for how
Speaker 1: it all works, and extrappling in that model out to
Speaker 1: the very far edges of the universe, far forward in
Speaker 1: time and far backwards in time. Because we want to
Speaker 1: do more than just tell stories about unicorns and rainbows.
Speaker 1: We want a mathematical story that explains what we see
Speaker 1: in the universe and tells us what has already happened
Speaker 1: and hopefully why. Yeah, because the nature of the universe
Speaker 1: doesn't just affect the cosmos out there in space and
Speaker 1: other galaxies. It affects us here and on Earth and
Speaker 1: in our everyday lives. Every time you look up after
Speaker 1: a nice rainfall and see a rainbow, that's physics kind
Speaker 1: of affecting how you see the world. And I don't
Speaker 1: want to talk more about rainbows and unicorns, but I
Speaker 1: do think rainbows are amazing. It's incredible that this physical
Speaker 1: effect happens, and it shimmers in the air, and it
Speaker 1: happens so often, and it's so beautiful. It's just like,
Speaker 1: how lucky are we to live in the universe where
Speaker 1: such beauty occurs? Makes me wonder about the whole nature
Speaker 1: of beauty. But that's a whole philosophical rainbow that we
Speaker 1: definitely don't want to walk down today. What we do
Speaker 1: want to wonder about is why the universe works this
Speaker 1: way and what it means about the history of the
Speaker 1: universe as well. He says, the way the universe works
Speaker 1: affects our daily lives because it tells us about the
Speaker 1: context of our lives. It tells us how the universe
Speaker 1: came to be and what it means that we are here. Yeah,
Speaker 1: and the history of humanity has been about making theories
Speaker 1: that hopefully explain what's going on and gives us an
Speaker 1: understanding about why things are the way they are and
Speaker 1: how we can maybe affect them or change them, or
Speaker 1: at least dream up of fantastical things. And while we've
Speaker 1: made a lot of progress and understand in the nature
Speaker 1: of the universe and its history, how it got to
Speaker 1: look the way that it is, and wondering about how
Speaker 1: it started, or at least the very first few moments
Speaker 1: of it. There are still a lot of question marks
Speaker 1: there about what happened early on, a lot of things
Speaker 1: about our theories that don't quite make sense, leaving lots
Speaker 1: of room for creative people to imagine all sorts of
Speaker 1: theoretical rainbows and unicorns to fill in the gap. I
Speaker 1: thought you didn't want to talk about rainbows anymore, Daniel,
Speaker 1: keep bringing it up. Not literal rainbows. These are figurative
Speaker 1: rain us now. But the arc of history is an
Speaker 1: interesting wine, but it's not a necessarily straight line. Sometimes
Speaker 1: we come up with theories that explain what we can
Speaker 1: see and what we can experiment with out there, but
Speaker 1: then later they turn out to be wrong, and that's
Speaker 1: okay because that's part of science and it's an evolving process.
Speaker 1: It's a really interesting distinction, for example, between math and science,
Speaker 1: Like the science that we had two hundred years ago
Speaker 1: is now evolved to the science we have today, and
Speaker 1: we expect in the future we will have even crisper
Speaker 1: ideas of how the universe works. But mathematical proofs that
Speaker 1: were developed thousands of years ago. Those are still correct,
Speaker 1: and we expect those to still be correct in a
Speaker 1: few thousand years. So it's fascinating how science and math
Speaker 1: develop sort of differently, even though science is built on math. Yeah,
Speaker 1: and so we have theories that currently describe everything we
Speaker 1: can see around those quantum mechanics and gravity or I
Speaker 1: guess special relativity. But the question is are those actually right?
Speaker 1: Do those theories actually describe the universe in all instances
Speaker 1: or do they break down at some point? And what
Speaker 1: does that mean about our understanding of the universe. One
Speaker 1: of the most frustrating things about general relativity and quantum
Speaker 1: mechanics is that they don't agree about what happens, and
Speaker 1: maybe the most interesting moment of the universe, that is
Speaker 1: the very first few moments when things are very high
Speaker 1: energy and very dense, and we need both gravity and
Speaker 1: quantum mechanics to understand what happened. Was there singularity, was
Speaker 1: there something else? What was going on at the very
Speaker 1: beginning of the universe. We're pretty sure that our current
Speaker 1: theories can't be right, and so we're on the hunt
Speaker 1: for new ideas. So today on the podcast, we'll be
Speaker 1: tackling the question what is rainbow gravity, Daniel, is this like,
Speaker 1: how much does a rainbow way like it is a
Speaker 1: rainbow heavy? Can you measure the happiness in a rainbow?
Speaker 1: How many pots of gold are generated by general relativity?
Speaker 1: Maybe we have a new theory called golden relativity. Hey,
Speaker 1: that sounds good. No, this is literally a theory of
Speaker 1: the universe that predicts that gravity could make rainbows the
Speaker 1: same way that like prisms or drops of water make
Speaker 1: rainbows in your eyeball, Like gravity itself could bend white
Speaker 1: light and turn it into rainbows. M I guess the
Speaker 1: question is would those be regular rainbows or would you
Speaker 1: need to call them like gravitational rainbows. Yeah, those would
Speaker 1: be gravitational rainbows because you definitely wouldn't see them in
Speaker 1: the atmosphere on Earth. This would be like something you
Speaker 1: see in your spaceship as you're falling towards the edge
Speaker 1: of a black hole. But this wouldn't just be like
Speaker 1: a lens flare, like a J. J. Abrahm style lens
Speaker 1: flare on your camera or your glasses or your spaceship window.
Speaker 1: This would be like real black hole rainbows, real black
Speaker 1: hole rainbows. That's right, and you don't need to ride
Speaker 1: a unicorn across the sky to see it. If this
Speaker 1: theory is actually true, these rainbows exist in the universe,
Speaker 1: and they might have existed very early on, and they
Speaker 1: could completely change the way we think about the very
Speaker 1: first moments of the cosmos. Well, you don't need to
Speaker 1: be writing a unicorn, but obviously anything better while you're
Speaker 1: writing a unicorn, surely, I mean, I wouldn't know, but
Speaker 1: ice cream is better when you're writing a unicorn, for example? Absolutely,
Speaker 1: Well depends. Can this unicorn fly just gallop along? Because
Speaker 1: it might be hard to eat it a lick and
Speaker 1: ice cream cone while you're gelping. You know, I am
Speaker 1: not an expert on the categories of unicorns. Do unicorns
Speaker 1: come with wings or is that a pegasus? Or pegasus
Speaker 1: is just a horse with wings? What do you call
Speaker 1: it if it's a unicorn with wings? I think unicorns
Speaker 1: just fly on a on a rainbow, right? Is that
Speaker 1: what happens? Like you're galloping and then like a rainbow
Speaker 1: bridge pops up, and then then you're flying. It's like
Speaker 1: the by Frost and Thor and Welcome to the Science
Speaker 1: of Unicorns, a sub episode of rainbow gravity. Well, let's
Speaker 1: get that. You're right, let's get back on topic here.
Speaker 1: We're talking about rainbow gravity or gravitational rainbow or what's
Speaker 1: the right way to call this. Is there such a
Speaker 1: thing as rainbow gravity. There is really a theory out
Speaker 1: there in the community called rainbow gravity, and that's what
Speaker 1: we're talking about today. We're gonna try to avoid talking
Speaker 1: about unicorns, but I suspect the gravitational attraction of their
Speaker 1: gorgeousness is going to pull us back in anyway. You're
Speaker 1: saying this is sequels called unicorn gravity, lying unicorn gravity,
Speaker 1: that's the title of my next paper on this topic. Well,
Speaker 1: you're gonna take one theory combined with an imaginary theory
Speaker 1: to get an X ray imaginary in some version of
Speaker 1: the mole diverse that earns me a huge pot of
Speaker 1: grand funding, which I get in delivery of gold coins. Well,
Speaker 1: I'm gonna have one up. Even put wings on that unicorn.
Speaker 1: So my theory is gonna be the rainbow unicorn pegass
Speaker 1: gravity theory. All right, Well, then I'm gonna put horns
Speaker 1: on the wings on that unicorn. Okay, this is kidding
Speaker 1: a little HP Lovecraft in here, but it is an
Speaker 1: interesting theory. This idea of rainbow gravity or gravitational rainbows?
Speaker 1: And can gravity rainbows? So, as usual, we were wondering
Speaker 1: how many people out there had thought about this or
Speaker 1: maybe dreamt it in one of their dreams. So thank
Speaker 1: you to all the people in Unicorns who volunteered to
Speaker 1: answer these questions. We greatly appreciate it and enjoy hearing
Speaker 1: your thoughts. If you would like to participate for a
Speaker 1: future your episodes, please don't be shy. Right to me
Speaker 1: two questions at Daniel and Jorge dot com. Think about
Speaker 1: it for a second. What do you think is rainbow gravity?
Speaker 1: He was what people had to say. Okay, So rainbows
Speaker 1: are created by the reflection refraction of light, and the
Speaker 1: wavelength of that light depends on what we see in
Speaker 1: terms of its color. So rainbow gravity. If I think
Speaker 1: of gravitational waves, maybe as those waves are passing through
Speaker 1: or having light passed through. Um, maybe it's the effect
Speaker 1: that the light and the different wavelengths of the light
Speaker 1: has on those gravitational waves. Maybe I don't know. Maybe
Speaker 1: like moist that split the light based on frequency, gravity
Speaker 1: split the think based off their density, and you call
Speaker 1: the outcome rainbow gravity. And well, I've definitely never heard
Speaker 1: of rainbow gravity. So my best guess is that it
Speaker 1: is something that has to do with the way gravity
Speaker 1: effects light. Um, maybe it's a property of gravitational lensing.
Speaker 1: Oh jeez, I do not know. I would imagine that
Speaker 1: it has to do with the spectrum of light and
Speaker 1: how gravity could affect light, but I'm not sure. Maybe
Speaker 1: how gravity could split light. All right, we got a
Speaker 1: nice spectrum of answers here, very colorful, powerful. Yeah that
Speaker 1: was low hanging fruit. But yeah, a lot of some
Speaker 1: people have never heard of it, and some people had
Speaker 1: some pretty good ideas, like it's maybe gravity causing lensing,
Speaker 1: which might create a rainbow effect. Yeah, exactly. This seems
Speaker 1: to be a well named theory because it inspired some
Speaker 1: good ideas and listeners. Well, I would obviously disagree, but
Speaker 1: that's never stop physicists from naming things in counterintuitive ways.
Speaker 1: Let's see how this goes, Daniel, I mean rainbow gravity,
Speaker 1: but it is gravity actually a rainbow? I don't know.
Speaker 1: It's a really fun theory that tries to solve a
Speaker 1: problem at the heart of physics, the connection between general
Speaker 1: relativity and quantum mechanics, or more specifically, the lack of
Speaker 1: the connection along the way predicts beautiful events like rain
Speaker 1: those popping out of black holes, wait out of black holes,
Speaker 1: that would be impossible, or maybe that gets it's the rainbow,
Speaker 1: so maybe it's magical. Perhaps I should have said at
Speaker 1: the edge of black holes, Well, let's dig into it.
Speaker 1: Um you said, it's a new theory or a potential
Speaker 1: theory that's out there in the physics community that maybe
Speaker 1: try to explain the intersection between quantum mechanics and gravity,
Speaker 1: because those two things are not quite compatible with each other, right, Yeah,
Speaker 1: all of modern physics is built on these two ideas,
Speaker 1: quantum mechanics and general relativity. But at their hearts, these
Speaker 1: two theories are incompatible. They have completely different views of
Speaker 1: the world. Even though they're in philosophical contradiction with each other,
Speaker 1: they've survived together as twin pillars of our theory of
Speaker 1: physics because they're never actually relevant at the same time.
Speaker 1: So you can use gravity talk about really big, massive things,
Speaker 1: and you can use quantum mechanics talk about really small things,
Speaker 1: and you never really need to use both at the
Speaker 1: same time. So they've sort of survived without having to
Speaker 1: talk to each other. They're like a married couple that
Speaker 1: turned into roommates. Well that's kind of said, Well, you know,
Speaker 1: if they do try to talk to each other, it's
Speaker 1: gonna be a big argument, so they just try to
Speaker 1: avoid it. Why did another physics theoretical committee was um
Speaker 1: dysfunctional and ahead of for our potential split in the future.
Speaker 1: It's not all rainbows and unicorns. Man, all right, well,
Speaker 1: maybe I can help us understand this a little bit.
Speaker 1: Where is that incompatibility? Is it just that you do
Speaker 1: is this haven't been able to make it work in
Speaker 1: the mathematical way, or is it is there something fundamental
Speaker 1: about how they view the universe that is just totally incompatible.
Speaker 1: So there's something fundamental about the way they view the
Speaker 1: universe that is just incompatible. We'll talk about exactly what
Speaker 1: that is in a minute. And all attempts so far
Speaker 1: to unify them have failed. Mathematically just do not work.
Speaker 1: So that's essentially what the struggle is. And so let's
Speaker 1: start with quantum mechanics. Quantum mechanics specifically quantum field theory,
Speaker 1: which is this description we talked about in the podcast.
Speaker 1: A lot of space being filled with quantum fields, and
Speaker 1: particles are like ripples in those fields that propagate through
Speaker 1: space and to with each other. That's very, very successful, right.
Speaker 1: It's an amazing theory. It describes all of the particle
Speaker 1: experiments that we've done. It's made very specific predictions of
Speaker 1: numbers like ten decimal places that have all been verified experimentally.
Speaker 1: It seems like a very accurate description of what happens
Speaker 1: to particles. But it assumes that space is not curved,
Speaker 1: that space is flat, that the shortest distance between two
Speaker 1: points is always what appears to us to be a
Speaker 1: straight line, and operating in flat space essentially means that
Speaker 1: we're ignoring gravity. Quantum field theory is very successful because
Speaker 1: basically gravity is irrelevant. If you have two particles and
Speaker 1: they're pushing against each other with powerful forces, you don't
Speaker 1: really care about the gravitational effects on two electrons because
Speaker 1: gravity is so weak compared to the other forces. So
Speaker 1: quantum field theory assumes that gravity is irrelevant and does
Speaker 1: a great job of describing what happens to quantum particles. Right.
Speaker 1: Quantum mechanics assumes a flat, spased universe, but general relativity
Speaker 1: kind of assumes the opposite. Yeah, general relativity tells us
Speaker 1: that the reason we have gravity is not because there's
Speaker 1: some force out there tugging on masses, but that space
Speaker 1: bends that when you put mass into a space, it
Speaker 1: curves space. And this is not curvature like relative to
Speaker 1: some external ruler. This is intrinsic curvature, which means that
Speaker 1: it changes the relative distances between points, and effectively, it
Speaker 1: makes the shortest distance between two points seem to us
Speaker 1: like a curve because we can't see this curvature directly,
Speaker 1: and so it appears to us like there's a force
Speaker 1: because things are moving along these curves. In reality, it's
Speaker 1: just the curvature of space. But general relativity assumes that
Speaker 1: everything has a specific location and velocity, and that can
Speaker 1: be perfectly well known. We call it a classical theory
Speaker 1: because it ignores the quantum mechanical nature of the world,
Speaker 1: the fact that particles, for example, can't be pinned down
Speaker 1: to have a specific location and velocity at all times.
Speaker 1: They don't have a trajectory like that. But general relativity
Speaker 1: assumes that everything does. Fortunately, because gravity is so weak,
Speaker 1: we've only tested general relativity in scenarios where you have
Speaker 1: a huge mass like a planet or a star or
Speaker 1: a black hole, where you can basically ignore quantum mechanics,
Speaker 1: so they sort of have each their own domains. They
Speaker 1: view the world very very differently. They make totally different,
Speaker 1: incompatible assumptions about the world, and they make predictions about
Speaker 1: different parts of the world, and they're both correct in
Speaker 1: their own regimes, right, Although I guess, you know, coming
Speaker 1: at this from the outside, not having been too in mercendies,
Speaker 1: they don't sound that incompatible to me. I guess it's
Speaker 1: maybe that's one of that something other people struggle with.
Speaker 1: I mean, it's sort of like one of them says
Speaker 1: that Daniel is tall, and the other one says Daniel
Speaker 1: wards glasses like those are not necessarily incompatible. Things like
Speaker 1: couldn't quantum fields exists in space that is also bending,
Speaker 1: And couldn't bending space exists in also in the universe
Speaker 1: where particles have a minimum size and are uncertain. Yeah,
Speaker 1: we think that probably it's possible to describe both because
Speaker 1: the universe exists and it seems to be self consistent.
Speaker 1: So we think it probably is possible to reconcile gravity
Speaker 1: and quantum mechanics because both things are happening in our world.
Speaker 1: We haven't been able to do that, Like light is
Speaker 1: being bent around the Sun and it's being bent around
Speaker 1: black holes. And we know light is quantized as well.
Speaker 1: Right well, let me give you an example of something
Speaker 1: that we can't do because we can't unify gravity and
Speaker 1: quantum mechanics, is that we don't know how to calculate
Speaker 1: the gravity of particles. Quantum particles, for example, don't have
Speaker 1: a specific location that have probabilities to be in different locations,
Speaker 1: Like electron could be on the other side of the
Speaker 1: room or could be right next to you. What is
Speaker 1: the gravity of that electron whose position is uncertain? General
Speaker 1: relativity doesn't allow for any uncertainty in the position. It
Speaker 1: says your gravity depends on where you are. If where
Speaker 1: you are is uncertain, then where is your gravity? Is
Speaker 1: your gravity also uncertain or is it shared between the
Speaker 1: two different locations? Does gravity collapse that wave function forcing
Speaker 1: the electron to be in one spot from where it's
Speaker 1: gravity emanates, or is have any quantum mechanical and it
Speaker 1: allows the superposition of different gravitational attractions. That's something we
Speaker 1: don't know the answer to. That's something we can't calculate
Speaker 1: right now because we don't have a theory that does
Speaker 1: gravity for quantum objects. Right, But I guess you know,
Speaker 1: particle has some uncertain to it to it in terms
Speaker 1: of where it is and where it's going. But if
Speaker 1: you step back far enough, it does have sort of
Speaker 1: a location, right. I mean, you step back far enough
Speaker 1: from a particle, you can calculate what its gravity is. Yeah,
Speaker 1: if you step back far enough or you love enough
Speaker 1: particles together, then they start to act like classical objects
Speaker 1: like a baseball. Baseball effectively has no uncertainty on where
Speaker 1: it is and it's velocity because it acts like a
Speaker 1: classical object, which is ten to twenty six quantum objects
Speaker 1: all moving together. And so general relativity assumes that that
Speaker 1: is still true the baseball description of the world when
Speaker 1: you get down to one electron. But we know that
Speaker 1: one electron doesn't move like a baseball. It doesn't have
Speaker 1: a whole path, and so we don't know how to
Speaker 1: talk about like how two electrons interact with each other gravitationally,
Speaker 1: And we can't usted either. We can't just go and
Speaker 1: look and watch two electrons pushing against each other gravitationally
Speaker 1: because the gravitational force is so weak that we could
Speaker 1: never measure that. And so it's a big question. Right.
Speaker 1: But you, for example, you are able to, for example,
Speaker 1: calculate the force between two electrons to like the electromagnetic
Speaker 1: force between two electrons, right, Like, you can do that,
Speaker 1: I guess the question is why can't you do it
Speaker 1: with gravity, Like why can't you juice kind of like
Speaker 1: average it out or use probability to figure out what
Speaker 1: the most probable gravity is. So we can calculate the
Speaker 1: gravitational force between two electrons if their positions are known,
Speaker 1: but because they're quantum objects, we don't know their positions.
Speaker 1: So what you're proposing, basically, is a theory of quantum
Speaker 1: gravity that says gravity is a quantum force and interacts
Speaker 1: not with the location of the objects but with their probabilities,
Speaker 1: that it actually interacts with the wave functions of these guys.
Speaker 1: So they're trying to turn gravity into a quantum field theory,
Speaker 1: which is fine and that's cool, and a lot of
Speaker 1: people are working on that. But when you do that,
Speaker 1: you run into a lot of mathematical problems. Basically, you
Speaker 1: get lots of infinities when you try to do these calculations,
Speaker 1: and we get infinities when we do all quantum field theories.
Speaker 1: Like we talked on the podcast about something called renormalization
Speaker 1: where we tuck infinities under the rug. For example, the
Speaker 1: true charge of the electron, if you look at it
Speaker 1: really really close, seems to be negative infinity, which makes
Speaker 1: no sense. But you can sort of like wrap it
Speaker 1: in a cloud of particles and renormalize it and subtract
Speaker 1: away that infinity and say that's all fine. You can't
Speaker 1: do that for gravity, because you get an infinite number
Speaker 1: of those infinities. Gravity couples to itself and it couples
Speaker 1: to everything, and so it just sort of goes crazy,
Speaker 1: and we just don't know how to do those calculations.
Speaker 1: We don't have the mathematical framework that can successfully do that.
Speaker 1: Something has to change when particles have a really really
Speaker 1: high energy in order for those infinities to go away,
Speaker 1: all right, So that it's hard from you, uh, and
Speaker 1: nobody has been able to do it. But there is
Speaker 1: maybe a new theory or a theory out there that
Speaker 1: does seem to have maybe a magical solution to this problem,
Speaker 1: gravitational rainbows or rainbow gravity, and so let's dig into
Speaker 1: the details of that. But first let's take a quick break. Alright,
Speaker 1: we're talking about rainbow gravity, which sounds great. Who doesn't
Speaker 1: want gravity to have its own, you know, spectrum of awesomeness. Yeah, exactly.
Speaker 1: It's a very colorful theory. And you know, during the break,
Speaker 1: I went off and did a little bit of research,
Speaker 1: and I discovered the answer to one of the open
Speaker 1: questions we left dangling before. Is the answer unicorns? You know,
Speaker 1: the answer actually is alcorn, and alcorn is a unicorn
Speaker 1: with wings or a pegasus with a horn. There's a
Speaker 1: name for this thing. So somebody already did that theory.
Speaker 1: I think it's my little pony universe that might have
Speaker 1: coined this phrase. What if I crossed it with a
Speaker 1: lion that and then like a griffin unicorn pegasus. I
Speaker 1: think we better trademark that and start selling plush dollars
Speaker 1: of those lion ala corn maybe griffin corn. But we
Speaker 1: are talking about rainbow gravity, which sounds great, and it's
Speaker 1: maybe a theory that tries to unify quantum mechanics and
Speaker 1: general relativity, which are the two big theories that try
Speaker 1: to explain us, which don't quite match up when you
Speaker 1: get to certain situations. Daniel, we talked about how quantum
Speaker 1: mechanics is not good at describing gravity, and we talked
Speaker 1: about how general relativity is not good at describing things
Speaker 1: at the microscopic level exactly, and most of the time
Speaker 1: they don't conflict because quantum mechanics is king of the
Speaker 1: microscopic particles and gravity is king of the big massive stuff.
Speaker 1: But there are scenarios we think when gravity and quantum
Speaker 1: mechanics are both important. One of those is inside black holes,
Speaker 1: where things are obviously very powerful gravitationally, but they're also
Speaker 1: compressed to super tiny little divots. Right, if there is
Speaker 1: a singularity at the hart of a black hole, then
Speaker 1: that's small enough to be a quantum mechanical object. So
Speaker 1: general relativity and quantum mechanics both have something to say
Speaker 1: about what happens there. We can't see inside black hole,
Speaker 1: and so we're left only just wondering about what's going
Speaker 1: on inside. But there are scenarios outside of black holes
Speaker 1: where we think both general relativity and quantum mechanics have
Speaker 1: something to say, and that's the case of very very
Speaker 1: high energy particles. Yeah, but I guess I wonder if
Speaker 1: you need to go that extreme just to kind of
Speaker 1: see where the two theories take effect, right, because I
Speaker 1: think Einstein kind of famously proved general relativity, or at
Speaker 1: least the bending of space by looking at how light
Speaker 1: bends around solar eclipse, for example. We know that light
Speaker 1: is quantized, it follows quantum mechanical rules. So isn't that
Speaker 1: an example for example of a quantized thing following gravity
Speaker 1: technically as opposed but technically everything is a quantized thing.
Speaker 1: You are a quantized thing. I am a quantized thing.
Speaker 1: We are affected by the Earth's gravity. You know, in
Speaker 1: that case, they're not relying on the quantum nature of light.
Speaker 1: Light could have just been classical electromagnetic waves and the
Speaker 1: same thing would have happened, because in that scenario, light
Speaker 1: is moving through curved space, and so light everything else
Speaker 1: would move in a curve. So you're not relying on
Speaker 1: the quantum nature of the object there. So like a
Speaker 1: quantized particle like light or an electron, it can move
Speaker 1: through bent space, but due to gravity, you know, I
Speaker 1: mean you can you have the mass to describe a
Speaker 1: single particle, single quantum particle moving through bent space. That
Speaker 1: possible or is that is not possible? That's certainly possible,
Speaker 1: But there you're not relying on the gravity of the
Speaker 1: quantum particle. You have something else something really big and
Speaker 1: massive like the Earth or the Sun or the Moon
Speaker 1: or a black hole that's doing the bending. And so
Speaker 1: we do know how to talk about quantum particles moving
Speaker 1: through bent space that we can calculate or we don't
Speaker 1: know how to calculate is the gravity of those particles
Speaker 1: and how that contributes to bent space? Right? But doesn't
Speaker 1: the bending a space depend on the gravity on the particle? Right,
Speaker 1: Like technically you're talking about space time, right, Like if
Speaker 1: I throw a baseball at the Sun, it's not going
Speaker 1: to curve the same way that a photon is going
Speaker 1: to curve. Right, So, like eat, the bend thing of
Speaker 1: space depends on the thing that's moving. So if you
Speaker 1: can calculate the bending of space for a particle, what's
Speaker 1: worth the contradiction there? Well, because there you're ignoring the
Speaker 1: gravity of the object, like you're through a baseball or
Speaker 1: a photon near the Moon. You're not taking to account
Speaker 1: the bending of space due to the baseball or due
Speaker 1: to the photon. You're just calculate the trajectory of a
Speaker 1: test particle through the bent space due to the Moon
Speaker 1: or due to the black hole. You're not taking to
Speaker 1: account the gravity of the object itself. Don't you need
Speaker 1: that to calculate how it's going to curve around how
Speaker 1: it's gonna bend around the Moon. Now, you just need
Speaker 1: to know it's inertial mass. You don't need to know
Speaker 1: the effect of it on space time itself. You just
Speaker 1: need to understand what it's inertia is and so that
Speaker 1: you're can understand how it moves through bent space. M
Speaker 1: M I see. So the real problem is not in
Speaker 1: like how to calculate how quantum particles move through bent space,
Speaker 1: but more about how quantum particles give off gravity or
Speaker 1: you know, how they attract other particles through gravity. Yes,
Speaker 1: do they bend space exactly? And and do they bend
Speaker 1: space where they are or where they might be. That's
Speaker 1: really the question, all right, So then talk to us
Speaker 1: about this new theory rainbow gravity. So the problem comes
Speaker 1: up at very very high energies. If you have particles
Speaker 1: with super duper crazy high energies, energies like the plant
Speaker 1: energy or energies that particles had at the very beginning
Speaker 1: of the universe, they have so much energy that their
Speaker 1: gravity starts to not be ignorable. Usually when you talk
Speaker 1: about like two protons bouncing against each other. You can
Speaker 1: ignore the gravitational effects, but if those two protons have
Speaker 1: enough energy, then their gravity becomes really really powerful. Because remember,
Speaker 1: gravity is the bending of space time in response not
Speaker 1: just to mass, but in response to energy. And so
Speaker 1: take for example, two particles and collide them at super
Speaker 1: duper high energy, much higher energy than we've done before,
Speaker 1: you might get, for example, a black hole, or at
Speaker 1: least you have to take into account the gravitational interaction.
Speaker 1: So we think that maybe the solution to this problem
Speaker 1: lies in understanding what happens to particles at very very
Speaker 1: high energy, and rainbow gravity says, maybe a very high energy,
Speaker 1: the rules change a little bit, and gravity for those
Speaker 1: really high energies is a little bit different. What so,
Speaker 1: as a particle gets moving faster and faster, it accumulates energy, right,
Speaker 1: that's what you're saying. And for when you have that
Speaker 1: much energy in the small package, then you kind of
Speaker 1: have to think about how that affects gravity because gravity,
Speaker 1: I mean, we always talk about gravity being a function
Speaker 1: of mass, like the more mass you have, the more
Speaker 1: gravity you have, but it's really just about how much
Speaker 1: energy you have, right, Like the bending of space is
Speaker 1: due to the energy that you have, yes, due to
Speaker 1: energy density, not literally mass. Mass is a component of
Speaker 1: the energy density, but it's not the only contribution. Right. So,
Speaker 1: now you have like a quantum particle. It's moving really fast,
Speaker 1: but it has a lot of energy in a small place.
Speaker 1: But it's quantum, so there are some uncertainties to it.
Speaker 1: And so now the question is like, can you explain
Speaker 1: gravity in that situation. Yeah, So rainbow gravity theory says,
Speaker 1: let's change the rules gravity as you move up in energy.
Speaker 1: That currently we think that all particles feel gravity the
Speaker 1: same way. If, for example, you have a big massive
Speaker 1: objects and it's bending space, and you shoot a red
Speaker 1: photon through it or a green photon through it, those
Speaker 1: things will bend around that object the same way. They'll
Speaker 1: end up at the same place. Right that all different
Speaker 1: energies of photons all get bent the same way because
Speaker 1: they all see the same curvature of space. They're like
Speaker 1: running along the same track. But wait, don't each of
Speaker 1: those photons have a different amount of energy. Yeah, but
Speaker 1: remember we're not considering the gravitational effect of the particle,
Speaker 1: just of the other object that's curving space, that's guiding
Speaker 1: these particles. We're ignoring the gravitational effect of those particles,
Speaker 1: and the rainbow gravity says, what if that's not true?
Speaker 1: What if as you move through space, how much curvature
Speaker 1: you see depends on your energy. So for example, maybe
Speaker 1: a red photon and a green photon see a different
Speaker 1: amount of curvature. That somehow, the curvature you see depends
Speaker 1: on your energy, and so as the photons wavelength or
Speaker 1: its color, or its energy, these are all equivalent changes
Speaker 1: you see different curvature. If that happens, then if you take,
Speaker 1: for example, a beam of white light and you bend
Speaker 1: it around a black hole, each different wavelength would get
Speaker 1: bent a different amount, resulting in a rainbow. So the
Speaker 1: idea of rainbow gravity is to say, maybe gravity depends
Speaker 1: on the energy of the particle in this way, so
Speaker 1: they see a different amount of curvature, which would change
Speaker 1: how things happen at very very high energies. You're saying,
Speaker 1: like many, gravity is not constant throughout all situations, like somehow,
Speaker 1: gravity is you know, depending on how fast you're going. Technically,
Speaker 1: this is called an energy dependent metric. Metric is like
Speaker 1: the curvature of space in general relativity theory, and so
Speaker 1: typically that metric is constant, doesn't depend on what your
Speaker 1: energy is. But now they say, well, let's take that
Speaker 1: metric and make it energy dependent. Let's say that if
Speaker 1: you're moving through the universe, you might see different curvature
Speaker 1: depending on the energy you have. But then isn't like
Speaker 1: mass the same as energy? Right? So are you saying
Speaker 1: that if I have or or less mass, I'm going
Speaker 1: to see space bend differently. I think that's probably true.
Speaker 1: Very very massive particles would see space meant differently than
Speaker 1: lower mass particles. Okay, so the ideas that gravity is
Speaker 1: different depending on how fast you're moving or how much
Speaker 1: energy or mass you have, which is very different than
Speaker 1: what we we how we think about it now? Right
Speaker 1: right now, general relativity says that gravity is the same everywhere. Exactly.
Speaker 1: It says that gravity is the same everywhere. And you
Speaker 1: might be wondering, like, well, how does this solve the
Speaker 1: problem of general relativity and quantum mechanics. It's not exactly
Speaker 1: a solution. It's just sort of like maybe in this
Speaker 1: direction a solution lies. It's sort of like exploratory. Remember,
Speaker 1: you know we talked about sciences and developing process We
Speaker 1: don't always have like the final answer all at once.
Speaker 1: Sometimes what we do is we say, what's in this direction,
Speaker 1: and what happens if we try this kind of thing?
Speaker 1: Does this lead to a solution? And so it's not
Speaker 1: clear yet whether this might lead to a solution, but
Speaker 1: there's a little bit of a sketch of an argument
Speaker 1: for why it might. People have this idea for how
Speaker 1: to solve the problem of like what's the gravity of
Speaker 1: an uncertain quantum particle, of saying maybe the curvature itself
Speaker 1: has uncertainty, like I think you were saying earlier, if
Speaker 1: an electron has uncertainty and it's bending space time, then
Speaker 1: maybe spacetime itself has an uncertainty, a quantum uncertainty, like
Speaker 1: maybe we live in this universe with this bent spacetime,
Speaker 1: or maybe we live in that universe with that bent spacetime.
Speaker 1: So people have done a bunch of calculations and shown
Speaker 1: that if the curvature itself has some uncertainty, it would
Speaker 1: lead to an energy dependence of that curvature, Basically that
Speaker 1: particles moving through the universe with different energies would see
Speaker 1: different aspects of this uncertainty. So this is like saying,
Speaker 1: if space itself has some uncertainty, then you might get
Speaker 1: this kind of effect for very high energy particles I see,
Speaker 1: because you sort of maybe need gravity to be not
Speaker 1: constant throughout the universe, because you know, if these particles
Speaker 1: are quantum, that means they're here and they're there. And
Speaker 1: if they're here and there, then that can't mean that
Speaker 1: they have gravity here and they have gravity there. Or
Speaker 1: but maybe if gravity is different in the two situations,
Speaker 1: then it's like maybe has half gravity here half every there,
Speaker 1: which kind of makes a full one gravity. Yeah, exactly,
Speaker 1: And we don't know, right We do not know if
Speaker 1: gravity operates that way, if it really can be probabilistic
Speaker 1: or not. This is an attempt to incorporate that quantum
Speaker 1: uncertainty into the theory of gravity. And if you do
Speaker 1: the calculations and say what happens to particles moving to
Speaker 1: space that's uncertain, how do they bend? It turns out
Speaker 1: that particles at different energies interact with that space different
Speaker 1: that that's see a different slice of that uncertainty. So
Speaker 1: particles with really high energy would bend differently than particles
Speaker 1: with low energy as they move through that uncertain space,
Speaker 1: and that gives you rainbows and again, how does that
Speaker 1: help bring together quantum mechanics and gravity. If this is
Speaker 1: true and you see it and you confirm it's actually
Speaker 1: part of our universe, for example, it gives you a
Speaker 1: very strong hint. It tells you that spacetime itself is uncertain.
Speaker 1: One possibility is that gravity is quantum mechanical, right, that
Speaker 1: spacetime has uncertainty to it, that we live in a
Speaker 1: universe where spacetime can have two different possibilities and they
Speaker 1: get collapsed when you test them. Right. The other is
Speaker 1: that gravity is not quantum mechanical, and that gravity itself
Speaker 1: collapses those wave functions that when two electrons interact gravitationally,
Speaker 1: their wave functions don't interact. They collapse each other's wave functions.
Speaker 1: And then electron has a location here in another location there,
Speaker 1: and you have very specific sort of classical gravity. So
Speaker 1: if we see rainbow gravity, that tells us that gravity
Speaker 1: can accommodate uncertain space times, and that single particles can
Speaker 1: have gravity themselves, right, just like a planet does exactly,
Speaker 1: And I have been electron over here and over there,
Speaker 1: then space time is also fifty percent bend over here
Speaker 1: and fifty bent over there, all right, Yeah, then that's
Speaker 1: how you avoid the infinities that you're talking about earlier. Yeah,
Speaker 1: because it changes how particles move at very very high energies,
Speaker 1: which is exactly where these infinities crop up. Thinking about
Speaker 1: like what happens to particles with really high energies which
Speaker 1: bend space time, which create more gravitons, and you get
Speaker 1: this infinite pile of gravitons and a runaway energy. So
Speaker 1: if you change the behavior of the articles are very
Speaker 1: very high energy, you can basically delete those infinities because
Speaker 1: you change the rules when you get near infinity, so
Speaker 1: the infinities basically go away. Cool. All right, Well that's
Speaker 1: the theory of rainbow gravity, and so let's talk about
Speaker 1: what would happen if it is true. What kinds of
Speaker 1: things would we see out there where we see rainbows
Speaker 1: around black holes? Would we see unicorns? And would that
Speaker 1: mean that unicorns are also quantized? I hope? So I
Speaker 1: don't ever want to see one and a half unicorns. Well,
Speaker 1: if nobody wants to be your back end, then you
Speaker 1: might have to be a halfy unicorn. That's a good
Speaker 1: All right, we'll get into that, but first let's take
Speaker 1: another quick break. All right, we're talking about rainbow gravity, uh,
Speaker 1: and we're talking about what it is. And it's the
Speaker 1: new theory that kind of tries to bring together quantum
Speaker 1: mechanics and general relativity by saying that maybe gravity is
Speaker 1: not the same aim everywhere, maybe it's different for different
Speaker 1: energy particles, which would sort of help explain how gravity
Speaker 1: works at the quantum level. Now this theory was true, Daniel,
Speaker 1: does that mean we would see rainbows around black holes?
Speaker 1: It does exactly mean that we would see rainbows around
Speaker 1: black holes. Because this is a theory that tries to
Speaker 1: unify quantum mechanics and gravity, which mostly ignore each other
Speaker 1: and live in different regimes. It's a hard kind of
Speaker 1: thing to test. You need special circumstances. So this doesn't
Speaker 1: mean that we should expect to see gravitational rainbows all
Speaker 1: over the place, you know, through the moon or the sun.
Speaker 1: It's only in extreme conditions because this is a very
Speaker 1: very small effect until you get two very very high
Speaker 1: energies or very very strong curvature of space, like around
Speaker 1: a black hole. So you're in a spaceship and you're
Speaker 1: falling towards a black hole, and then white light near
Speaker 1: the event horizon would be split into all of the colors,
Speaker 1: and you would see rainbows before you get squished. Meaning
Speaker 1: like I shoot a beam of light of white light
Speaker 1: at a black hole at the very edge, and as
Speaker 1: this beam of light gets very close to the black hole,
Speaker 1: the photos that are more red would get pulled one way,
Speaker 1: and the photons that are more blue would get pulled
Speaker 1: another way, and the purple ones a bit pulled a
Speaker 1: little bit differently, And so that would actually kind of
Speaker 1: prism or split the beam of white light. Yeah, prism
Speaker 1: exactly is the right analogy. That's what a prism does,
Speaker 1: is it it bends light based on its wavelength. Different
Speaker 1: wavelengths of light get bent differently as you go from
Speaker 1: air to glass and back to air, and so they
Speaker 1: spread out white light into a rainbow. And because now
Speaker 1: we're introducing an energy dependent effect or a wavelength dependent
Speaker 1: effect on gravity, than black holes are basically prisms, and
Speaker 1: they would change a beam of white light into a
Speaker 1: spread based on the colors. Yeah, their prisms and their prisons.
Speaker 1: Because I guess you know, white light, it's not like
Speaker 1: the each photon is white. Is that you have a
Speaker 1: combination of photons, some of them are white, some of
Speaker 1: them are higher and lower energy. Right, that's what what
Speaker 1: white light is. It's not like the photons are white. Yeah,
Speaker 1: there is no individual photon that has the color white. Right.
Speaker 1: White is not a single color. It's a combination of
Speaker 1: many photons of different colors. Right. And so around a
Speaker 1: black hole in the gravity, we would be so strong
Speaker 1: that it would actually start to affect each of those
Speaker 1: photons differently, which is sort of like a prism or
Speaker 1: or a lens. I guess, which makes me wonder, like,
Speaker 1: why have we seen this effect? Have we seen? I mean,
Speaker 1: now we now have pictures of black holes that we
Speaker 1: see any rainbows around it. We do not see any
Speaker 1: rainbows around black holes yet. This would be a very
Speaker 1: very slight effect. And you need to look very carefully
Speaker 1: right at the edge of a black hole. You need
Speaker 1: a well calibrated source also to know whether you're seeing
Speaker 1: any distortion. To know whether it's a story, you have
Speaker 1: to know what it looked like before it went around
Speaker 1: the black hole. And so we don't have any nice, clear,
Speaker 1: crisp examples of that. Even around black holes. This would
Speaker 1: be a very small effect. But what do you mean
Speaker 1: it would be a small effect? Like this effect is
Speaker 1: not very strong. It's very small that the way gravity
Speaker 1: varies depending on the energy. Yeah, and this theory gravity
Speaker 1: does pen on the energy, but it's basically unobservable until
Speaker 1: you get too super duper high energies. In the same
Speaker 1: way that like effects of special relativity, you can't really
Speaker 1: observe them when you're throwing a baseball around. You don't
Speaker 1: notice clocks going slow. Your baseball doesn't seem to shrink
Speaker 1: when you throw it even though it's going faster. You
Speaker 1: don't notice the effects of special relativity here on Earth
Speaker 1: because they're negligible. In the same way, this energy dependent
Speaker 1: effect of gravity is negligible except in extreme circumstances. And
Speaker 1: so you need like a very crisp, clear setup of
Speaker 1: a beam of white light right next to a black
Speaker 1: hole and basically nothing else around so that you can
Speaker 1: observe it. But there are some other ways we might
Speaker 1: be able to test this theory. Yeah. They involved gamma rays. Yeah.
Speaker 1: So gamma rays are basically just a fancy name for
Speaker 1: super high energy photons. And there are these strange phenomena
Speaker 1: that we've talked about the podcast a few times called
Speaker 1: gamma ray bursts, where something out there in the universe
Speaker 1: sends a huge spray of very high energy gamma raise
Speaker 1: all about the same time. These things can laster like
Speaker 1: seconds or minutes. We don't really understand the source of them.
Speaker 1: Check out our whole podcast episode on that topic for
Speaker 1: a deeper dive into it. But the cool thing is
Speaker 1: that it's a nice test of this theory because it
Speaker 1: sends us a big packet of photons, some of which
Speaker 1: have huge energy, like crazy high energy photons, and they
Speaker 1: all come to us about the same time, so we
Speaker 1: can sort of use them as a probe of how
Speaker 1: they've responded to the gravity of the universe that they
Speaker 1: have flown through. Right, they might like arrive at different
Speaker 1: places in our sensor or you know, like a rainbow
Speaker 1: kind of get split, or are you saying they might
Speaker 1: arrive at different times? So if for example, they whizz
Speaker 1: around a black hole, they would get bent differently. But
Speaker 1: the universe has some curvature, and as you move through it,
Speaker 1: you're slowed down by that curvature, so they would be
Speaker 1: differently time dilated as they move through the universe if
Speaker 1: they see different curvature, so they would effectively arrive at
Speaker 1: different times. If you send like a green or red
Speaker 1: and blue photon across the universe to us. Then if
Speaker 1: this is true, those photons would arrive at different times
Speaker 1: here on Earth because they would see different amounts of curvature.
Speaker 1: Curvature affects the passage of time and effectively how long
Speaker 1: it takes light to traverse from the source. So like
Speaker 1: some of the photons would get blue shifted more than others,
Speaker 1: or wretch shifted more than others. That's kind of what
Speaker 1: you're saying, because they have to arrive at the same time,
Speaker 1: don't they Because they're moving at the speed of light,
Speaker 1: these would actually arrive at different times. I mean from
Speaker 1: their point of view, they would see different distances between
Speaker 1: the source and the destination because they're seeing different amounts
Speaker 1: of curvature of the universe. Well, that's pretty interesting, But
Speaker 1: I guess couldn't we do that experiment here on Earth?
Speaker 1: Like you know, we can create gamma rays, and we
Speaker 1: can also create you know, like ultra violet or here
Speaker 1: in other can create high energy light and super low
Speaker 1: energy light. Couldn't we do some experiment where we shoot
Speaker 1: both and see what happens. Yes, but we can't create
Speaker 1: very strong gravitational curvature right, So we can create pretty
Speaker 1: high energy photons, but not that high energy, not as
Speaker 1: high energies exist out there in the universe. Also, we
Speaker 1: don't have very strong curvature. The value of this test
Speaker 1: is that the photons are super duper high energy because
Speaker 1: they come from some astrophysical source and they fly through
Speaker 1: a huge amount of curvature. So even the small effects
Speaker 1: of curvature add up over very very long distances. What
Speaker 1: do you mean, like curvature not due to any particular
Speaker 1: thing like a black hole, which is like the general
Speaker 1: curvature of space from having stuff in it, from having
Speaker 1: stuff in it. Yeah, exactly, as you fly through the galaxy,
Speaker 1: for example, there's a small gravitational well that the whole
Speaker 1: galaxy sits in. That's the curvature of our local space.
Speaker 1: But wouldn't we see that regular light because I know
Speaker 1: there's something called gravitational lensing out there, where like a
Speaker 1: planet can sort of lens and bend light to give
Speaker 1: us a better view of another galaxy or another star,
Speaker 1: or you know, a dark matter can also kind of
Speaker 1: lens light. Wouldn't we see rainbows caused by dark matter? Too?
Speaker 1: So I think that's exactly what this is suggesting to
Speaker 1: probe right. Send a bunch of really high energy photons
Speaker 1: through space, and all the matter that's in space creates
Speaker 1: some curvature, and those photons would respond to that curvature
Speaker 1: differently based on their energies. And so you would see
Speaker 1: that then on Earth, and so yes, the galaxy and
Speaker 1: all the dark matter and are all contributing to that.
Speaker 1: The vanilla version of general relativity predicts that that wouldn't happen, right,
Speaker 1: that they all get bent the same way. And you're
Speaker 1: right that that's something that is predicted. As photons fall
Speaker 1: into a gravitational well or dig themselves out of a
Speaker 1: gravitational well, they do get shifted in frequency, for example.
Speaker 1: But we think that happens equally for photons of all energy.
Speaker 1: Rainbow gravity says that happens differently. So for very very
Speaker 1: long distances, these would accumulate, do it, all the dark
Speaker 1: matter and the other stuff in the galaxy and create
Speaker 1: a small difference in the arrival time of those photons,
Speaker 1: but not in their location, like they would all arrive
Speaker 1: at the same spot. They would use maybe be colored
Speaker 1: a little bit different, or would they actually split like
Speaker 1: a rainbow. They would actually split like a rainbow, so
Speaker 1: we wouldn't see the whole thing, right, So the whole
Speaker 1: thing we get spread out across the universe, but we
Speaker 1: would get a slice of it, and in theory we
Speaker 1: might get ones of different color that we could also
Speaker 1: test their time of arrival. So we've actually done this,
Speaker 1: and we've looked at gamma ray bursts and we've i
Speaker 1: to see if we see effects for it. There's no
Speaker 1: evidence for it so far. Even these gamma ray bursts.
Speaker 1: The evidence would be pretty subtle, and we don't have
Speaker 1: that many examples of it. So the jury is still
Speaker 1: sort of out on this theory. We don't have any
Speaker 1: evidence for it, but we also can't yet rule it out.
Speaker 1: It sounds like it's not an effect that you would
Speaker 1: see in our everyday lives, like when we see galaxies
Speaker 1: being lensed by dark matter out there, even that is
Speaker 1: not strong enough to split light due to rainbow gravity. Yeah,
Speaker 1: it requires a huge amount of energy or integration over
Speaker 1: very very long distances. I guess what maybe we are
Speaker 1: just saying is that if rainbow gravity is true, it
Speaker 1: is happening even around us, all around us, you know,
Speaker 1: like if I look at my hand, or if we
Speaker 1: look at galaxies through a dark matter gravitational lens. It
Speaker 1: is happening, but maybe just at a level that we
Speaker 1: can't discern. In the same way that like time dilation
Speaker 1: is happening all the time, length contraction is happening all
Speaker 1: the time, you just can't tell because it's so negligible.
Speaker 1: All right, well, let's talk about now what would happen
Speaker 1: if this was true. We don't have evidence for it
Speaker 1: either way, whether it's true or not, but what would
Speaker 1: it mean if it If it is true that rainbow
Speaker 1: gravity exists, or like gravity is not the same everywhere
Speaker 1: for everyone except unicorns, it has really interesting consequences if
Speaker 1: you run the clock of the universe backwards. Currently we
Speaker 1: see the universes expanding, and we run the clock backwards
Speaker 1: and we do the calculations in general relativity, and they
Speaker 1: predict something really weird. They predict a singularity that as
Speaker 1: the universe got denser and denser, there's a sort of
Speaker 1: runaway gravitational effect in reverse where you end up with
Speaker 1: a singularity, but with the universe is basically compressed into
Speaker 1: incredible density. So that's the prediction of general relativity, and
Speaker 1: you know, we think that's kind of bonkers. We think
Speaker 1: that those kind of infinities probably don't exist in our universe.
Speaker 1: And this, to most physicists is a sign that general
Speaker 1: relativity needs some work right where this is a problem,
Speaker 1: and so this is where we look for alternatives, and
Speaker 1: so rainbow gravity. If you modify gravity in this way,
Speaker 1: it says well, in very high energies, things actually do change.
Speaker 1: And so you put this into the calculations instead of
Speaker 1: general relativity, and now particles that different energy are affected
Speaker 1: slightly differently by that curvature, and you don't end up
Speaker 1: with a singularity. You end up with something which like
Speaker 1: smoothly gets denser and denser. But we just sort of
Speaker 1: a minimum plateau. It's like, intuitively, you can't just like
Speaker 1: squeeze all the particles down to the same place because
Speaker 1: the particles are all now bent differently by space. M M.
Speaker 1: What would that mean for black holes? Two? Does that
Speaker 1: mean there's no singularity at the center of black holes? Yes?
Speaker 1: This basically a racist singularities in the universe, both singularities
Speaker 1: in time like what might have happened before the Big
Speaker 1: Bang and singularities in space like what's inside a black hole?
Speaker 1: Doesn't mean black holes shouldn't exist. It tails us maybe
Speaker 1: that the structure of matter inside the black hole isn't
Speaker 1: a singularity, it's something else, weirder. It's controlled by rainbow gravity.
Speaker 1: It's going to be something with a non zero size
Speaker 1: to it. It'll have a fuzzy core to it, not
Speaker 1: like a single point. Yeah, a fuzzy, colorful core probably. Yeah.
Speaker 1: There are many colors of black, absolutely glossy black, matt
Speaker 1: black right at black. Yeah. So maybe this sounds amazing,
Speaker 1: and it sounds like it would solve a big problem
Speaker 1: and maybe the biggest problem in physics right now theoretically
Speaker 1: at least, But we haven't seen evidence for it experimentally,
Speaker 1: and are there any reservations about just the theory of it.
Speaker 1: Most mainstream physicists think that this is crazy, right. They
Speaker 1: think that this is a monker's idea and just wouldn't
Speaker 1: fly basically because it violates as a central principle something
Speaker 1: that we all think probably is true, which is that
Speaker 1: observers can all agree about the physical laws. Like in
Speaker 1: our universe, we think that observers all see different things happening.
Speaker 1: But one of the foundational principles of special relativity is
Speaker 1: that the universe always follows the same laws. You might
Speaker 1: tell a different story about what happened, but everybody's story
Speaker 1: follows the same laws. This breaks that because now everything
Speaker 1: is like energy dependent, and so the amount of curvature
Speaker 1: you see depends on the energy you have. It breaks
Speaker 1: this thing we call Lorentz invariants, right, because I guess
Speaker 1: if gravity the anson how much energy you have, energy
Speaker 1: can be a relative concept, right, energy depends on how
Speaker 1: fast you're moving your kinetic energy. Then that can look
Speaker 1: differently to different people, right, Like, if you're moving super
Speaker 1: duper duper duper fast to somebody outside of yourself, you
Speaker 1: would have a lot of energy, but to you yourself,
Speaker 1: you wouldn't have a lot of energy. Is that what
Speaker 1: you mean? Yeah, there's that aspect to it, but it
Speaker 1: goes a little bit deeper than that. You know. Right now,
Speaker 1: we think that space is relative in an important way,
Speaker 1: but that there are some invariants that some things hold fast,
Speaker 1: Like the speed of light is the same for all observers.
Speaker 1: But if this theory is true, then the speed of
Speaker 1: light sort of depends on the energy of the photons. Right,
Speaker 1: These photons traveling through space effectively have different speeds and
Speaker 1: that's pretty weird. There's a lot of really strong constraints
Speaker 1: on measurements of variable speed of light, energy dependent speed
Speaker 1: of light, and so it would require, you know, a
Speaker 1: real revolution in the way we think about the nature
Speaker 1: of the universe. But maybe that's what's required, right. Our
Speaker 1: current principles general relativity and quantum mechanics have completely incompatible
Speaker 1: assumptions at their foundation, and so to unify them, we
Speaker 1: are going to have to get rid of something that
Speaker 1: we hold, choose something that we cherish. Maybe it's Lorentz
Speaker 1: and variants, maybe it's not. But before this theory is accepted,
Speaker 1: it would require us to really rebuild a lot of
Speaker 1: physics from the ground up. Yeah, I get a Physicists
Speaker 1: don't like things to change. We love things to change. Actually,
Speaker 1: our dream is to find some new theory which blows
Speaker 1: everything up. But yeah, it doesn't mean a lot of work.
Speaker 1: But that also means, you know, hey, more grand funding,
Speaker 1: more piles of gold. But I guess what you mean
Speaker 1: is like, you don't like the laws of physics to
Speaker 1: be different, and depending on where you are in the universe, yes,
Speaker 1: that's true. It would be very nice if the laws
Speaker 1: of physics were the same for everybody, and you're a
Speaker 1: guest that because it would mean slop your math, or
Speaker 1: because you haven't seen any experimental proof of that. We
Speaker 1: haven't seen any experimental proof of it. And also it's
Speaker 1: kind of a nice principle if philosophically, it just sort
Speaker 1: of like makes sense to imagine that the universe runs
Speaker 1: on a certain set of laws. Those laws are the
Speaker 1: same for everybody. It doesn't have to be true, you know,
Speaker 1: the same sense, Like, we don't even know why the
Speaker 1: universe has laws and why those laws don't change with time.
Speaker 1: There's a lot of just basic assumptions at the foundation
Speaker 1: of fundamental physics that we make and seem to work,
Speaker 1: but we don't really understand why, and we might have
Speaker 1: to revisit. Cool. Well, I guess once again, it's a
Speaker 1: stay tuned. It might be true. It might be that
Speaker 1: special thing that solves a lot of problems and feels
Speaker 1: magical to everyone. What does that term people use for
Speaker 1: something like that, a unicorn? A unicorn, right, right, So
Speaker 1: the rainbow gravity theory might be at unicorn in itself,
Speaker 1: according to a physicist right here on the podcast, Yeah,
Speaker 1: it might fly in on rainbows and solve all the
Speaker 1: problems that we have, and that will let us see
Speaker 1: the full spectrum of the universe, see all of its
Speaker 1: beautiful colors, and also let us see how it changes
Speaker 1: in space and in time. So remember that science is
Speaker 1: a continual process that involves and changes. Are understanding of
Speaker 1: the universe out there, how it works, and where it
Speaker 1: came from. And as we learned more and more about
Speaker 1: the nature of the universe, we understand more and more
Speaker 1: about how it began and what it means to be here.
Speaker 1: We hope you enjoyed that. Thanks for joining us, See
Speaker 1: you next time. Thanks for listening, and remember that Daniel
Speaker 1: and Jorge explained The Universe is a production of I
Speaker 1: Heart Radio. Or more podcast from my heart Radio visit
Speaker 1: the I heart Radio app, Apple Podcasts, or wherever you
Speaker 1: listen to your favorite shows.