Unraveling the nature of the universe is a bit like solving a murder mystery. You have to look very carefully at all the clues. You have to pull really hard on any thread that looks weird it's unexplained, because any of them might be the key that solves the whole mystery. Throughout history, whenever we've seen something we didn't understand, it's often turned out to be a big screaming clue about
the next deeper layer of understanding reality. When we saw patterns in the periodic table, they were obvious but unexplained for many years until we were able to dig deeper and discover that they all came out of how electrons arranged themselves in shells around the nucleus. The similarity of the shape of the coastlines of Africa and South America a big clue that over millions of years, the continents themselves were in motion, and these two had once been joined.
So amazing realizations can come from refusing to ignore little time clues that bother you at night. So every time we see something that doesn't make sense, we should dig deeper and look for a reason. And that's especially true when there's something that we don't understand about the whole universe when we think it should has balance, but instead it's out of balance. Why is there more matter than antimatter?
Why are some forces weaker than others? Particle physics is filled with these kinds of mysteries, and today on the podcast, we'll be digging deep into one unexplained choice. The universe seems to have made billions of years ago between being righty or lefty. Life is left handed. Particles prefer to be left handed, though most humans are right handed. Today, on the podcast, we'll be asking was the Big Bang also left handed? Welcome to Daniel and Kelly's Extraordinary left Handed Universe.
Hello. I'm Kelly Wienersmith. I study parasites, and my family is fifty percent left handed and fifty percent right handed.
Hi.
I'm Daniel. I'm a particle physicist, and I'd give my right hand to be ambidextros.
Well, Okay, that doesn't really make sense the more I think about it, but I would love to be ambidextris too. How does it fall out in your family?
We have one lefty, a bunch of righty's, and my mom was ambidextris. She could write with both hands, and some things she'd liked to do with her left hand, like cutting with scissors, and other things she liked to do with her right hand, like stirring a bowl of soup.
Interesting, I don't do anything with either hand well, like pipe petting didn't go well. My writing's illegible from either hand, but you know I can type, okay?
And who in your family is left handed?
Zach? And we think ben so.
Zach's a member of the Secret Society of Left Handers.
And the Secret Society of Red headed People. Yes, he's involved in lots of secret societies, maybe in charge of everything.
I wouldn't mind having cartoonists be in charge of most stuff. I think that would be a great way to run the world. What's the name for that, you have democracy, oligarchy, cartoonocracy?
Yeah, I don't know, but I can tell you that he doesn't run the household because he might not be confident to do that. And so I don't know that we should give him too much more power. And I don't think he wants more power. So I think maybe rule by the cartoonists, this one in particular, is maybe not a great idea. What would it be like if the world were ruled by physicists, we.
Would spend a lot more money on particle colliders. Oh my gosh, Yes, we would know so much more about the universe, but.
We'd spend less money on soap.
Sorry, fair, fair, Nobody in office would be wearing a suit, that's for sure.
That's for sure. That's a world I can get behind.
Well, we seek to find balance between the physicists and the cartoonists, and the left handiers and the right handers and everything in the universe, which is why on today's podcast we're gonna be talking about symmetry and balance and imbalance in the universe.
So I'm super interested in this topic because I only had a chance to sort of like realize that it existed back when we were writing Souonish, because we wrote a little note of bene on George Church, who is trying to make organisms where every one of their molecules
is the opposite handedness as it is now. And the ultimate goal, as I understood it, was that if you had a human of opposite handedness, no pathogens or parasites could recognize our receptors and they would never be able to infect us, and so you would be free from all infection.
But you also wouldn't have a microbiome, so you couldn't digest any food, right.
So your microbiome would also have to be made opposite handed, and then all of your foods would have to be made opposite handed, and that just seems like way too much work for the trade off and all. So like, if a global supply chain problem popped up, could you never feed anyone because they need the opposite handedness bread? It was complicated, But I remember when I was doing the research thinking why is there such a trend in
handedness for molecules? Like what caused that? And then I got too busy and so I never dug in, And today we get to find out about that.
That's right, So it'll be super fascinating when there's an asymmetry in the universe, when the universe seems to have made one choice, because then you got to ask, like, why not the other choice? What does it mean? Is it random? Is there a reason? Could it have been the other way? Are there other universes out there where another choice was made? And does that explain my whole childhood? Basically?
Wow, whoa it got deep?
And so this stretches from the mathematics of handedness, to the handedness of life, to the handedness of particles, and even the handedness of the whole universe and the origin of the universe itself. So I went out there and I asked folks what they knew about this topic, if they thought the Big Bang could have been left handed, If you'd like to play for future episodes of the podcast, please don't be shy right to us two questions at Danielandkelly dot org. So think about it for a moment.
Do you think the Big Bang could have been left handed? Here's what people had to say.
Okay, this has to do with chirality, But I don't think kyality is at the fundamental particle level that it wouldn't be manifested there, you know, because you've got flavor, spin, charge, flavor color, but you definitely don't have chirality built into the core properties. Now, it does come up in chemistry. I know that all chemistry on Earth is a certain kiral and I can't remember if it's left right, but
it's one type. And if we get a meteor that comes that has a different type, that shows some type of organic biological life, then we would know that it's that it's alien and not something you know that came from Earth.
Let's see, in molecules, you can have handedness based on the arrangement of the atoms in the same way your hands are left handed and right handed based on the arrangement of fingers. But in a soup of particles like protons, surely there's no way their arrangement can be left handed or right handed.
Considering the Big Bang was everywhere all at once, and we ended up in a universe with both right and left handed fundamental force particles, then maybe it was both.
So I feel like the intuition here from the answers tends to be that folks think the Big Bang was probably not left handed and produced an equal amount approximately of left and right handed molecules. That totally matches my intuition as well, but is not actually the answer, right.
Yeah, it reveals something about our prejudice, what we think is natural, what makes sense, And I think it's super fascinating in science what answers people will accept without further explanation because it aligns with their intuition and they're like, oh, yeah, that makes sense, And what answers require more explanation, and for a lot of people hearing oh it was symmetric, it was a balance between left and right handed, and then like, yeah, cool, of course it was. That doesn't
require any more explanation. But if you tell them no, it's left handed, or no it was right handed, then to ask why. And I think all the possible outcomes need a why. You know, why should it be symmetric? But we have this innate preference for symmetry for balance in the universe, which I think says something about us, but I'm not sure exactly what it says.
I think I would like to have you on the next panel that judges my grants. I like the way you think about this stuff.
It all needs answers, It all needs answers exactly every question is worth asking.
But yeah, it does make me wonder what questions we should be asking that would like have amazing impacts on how we view the world, but we just don't think to ask them because our gut says they make sense.
Exactly to me. This tendency suggests that there probably are questions we should be digging into more deeply, or it's just accepting the answers because they seem right to us without really understanding what's going on, and maybe in one hundred years or maybe when the aliens come, they're going to be like, why didn't you think about that more deeply? We would be like, I don't know, it just made sense.
Set right, right, man, exactly? Yeah?
All right.
Well, I think for anyone who hasn't thought of this concept yet, or anyone who was lucky enough to not have to go through chemistry, is maybe a little confused about what we mean by this handedness thing. So let's start at the beginning. What does it mean for something to have a handedness?
Yeah, left or right handedness really is a mathematical thing. It's a geometric thing and super fascinating. So let's start in two dimensional space. Imagine that you take two arrows right, so you know they have a tip and a tail, and then stick their tails together and have their tips be ninety degrees apart. So now you have like two
arrows that are pointing perpendicular to each other. Right now, in two dimensional space, just like on a sheet, any pair of arrows you make are always going to be essentially equivalent, And by equivalent, I mean that you could line them up on top of each other, like move them and spin them and put them on top of each other. They're always going to line up perfectly. There's no way to make a pair of arrows to follow those rules where they're perpendicular to each other, where you
can't then line them up. So that's two dimensional space, right, there's no handedness. But if you label one of the arrows X and the other one y, so they're no longer two totally symmetrical identical vectors, but they have these labels on them. Now there are two ways to arrange these two arrows, Like if the X arrow is straight up in front of you, then the Y arrow can
be to its left or to its right. And because you have these labels, there's now no way to spin the left version of it to make it look like the right version. To do that, to have one lay on top of each other, so the x is align and the ys align, you'd have to flip it over essentially reflect it, make a mirror image, go from left to right. It's analogous to notions of clockwise and counterclockwise
on the surface of a clock. Also two dimensional. Now expand our universe, add a third dimension above and below the plane and add another arrow. Take your two arrows that are perpendicular to each other. You could think of them as like the X axis and the y axis, or you could think of them as like your thumb and your pointy finger right, that are perpendicularly to each other. And now add a third arrow that comes out from where the first two were joined. Now you have to
make a choice. Do you go up above the plane or down below the plane? And you might think, oh, it doesn't matter if I stick it above the plane, I can just rotate it to make it below the plane, right, But it actually does matter. If you choose the arrow that goes up above the plane, and then you rotate the whole thing so the arrow goes below the plane, you'll find that the other two don't line up to the first two. There's no way to take that set where the arrow is above the plane and rotate it
to match the arrow those below the plane. You can see this very easily with your hands. Your hands on his left handed when it's right handed. That's why we call them that. If you take your thumb and your pointy finger and you make them ninety degrees apart, then you have your middle finger stick perpendicular to your pal so it's perpendicular to the other two. Then you have like an X, Y, Z axis, but there's no way to orient them, so they line up on top of
each other. Is one is left handed and one is right handed?
All right, So I get that. But when I think of handedness, I feel like I'm thinking of my hands and the X and the Y direction and not the Z direction. Yeah, it still doesn't work in those two dimensions. Is the point that, Kelly, your hands are actually three dimensional. You're an idiot. Stop thinking about this like they're two dimensional.
No, you're not an idiot. Your hands are three dimensional. You're exactly right. And the reason that you're like, make your hands flat, you're thinking, I make my hands flat, I lay them on top of each other. They're still not the same, right, even in sort of flat hand two dimensional world. The thing is that you're right. They're not two dimensional, and if they were, you could make them line on top of each other and be exactly
the same. The reason that they can't is because they have a top and a bottom, right, they have a thickness. If you try to put your hands together, then you meet your palms together. Then they're inverted in that third dimension, so you still are working in a three dimensional world. If you squeezed your hands in a hydraulic press so they were infinitely flat, then you could make them identical and lay them on top of each other.
I don't think it's worth it for this purpose.
That's why we have thought experiments. You don't have to actually do it. You could just think of it that way. So that's what handedness is, and that's where it comes from. It comes from our hands. Right, one hand is left handed, one hand is right handed. Amazingly, these words actually make sense and the technical definition lines up with your knowledge.
Another example of how humans sort of take the way that we see and experience the world and overlay it on our science.
Yeah, exactly right. And what would aliens call this kind.
Of stuff tentaicleness.
It's fascinating because this is a basic property of geometry, right, and it's totally arbitrary. There's nothing special but left handed or right handed right. It's just how do you orient these three vectors? And it would be really weird if the universe for some reason preferred one or the other. Mathematically, they're totally equivalent, they're completely symmetrical. There's no reason for
one to be more fundamental or more basic. There's just two choices to make here, and not everything in the universe has a handedness, right, we're talking about this combination of three vectors, or your three fingers have a handedness. But take a sphere, for example. A sphere has no handedness. There's no choices to make. There a way you can tell something as handedness is put it in front of a mirror. A mirror flips the handedness. Like if you put your left hand in front of a mirror, it
looks like a right hand. If you put your right hand in front of a mirror, it looks like a left hand. Put a sphere in front of a mirror, what do you get a sphere? Right, There's no handedness to a sphere. So some things have handedness and some things don't have handedness. So that's the sort of mathematics of handedness. And you might imagine a perfect universe everything would be symmetric. There's no reason to choose one or the other. But as we already talked about in this episode,
nobody is really symmetric. Like I use my right hand right, I am right handed, it's a part of me that breaks this symmetry that for so reason prefers to use my right hand to need doe and to write doodles and to point at things and all sorts of stuff. And some people are left handed. So the symmetry is broken sort of two levels, right. One level is every individual person prefers one or the other, and the population
has way more righties than lefties. So this symmetry is already broken even from the place where you've defined it.
Fun fact, this happens in the animal kingdom too. I remember a talk, Oh my gosh, this was two decades ago, but they were looking at blind kfish and they put them in an environment with legos in the middle, and it was a circular tank, and the fish to explore the environment, they like get you know, the vibrations or the water currents, they feel them on one side of
their body to figure out where things are. And so they'd swim around, and you could tell that they had figured out like what their environment was like because they eventually slowed down and like stopped swimming. But as soon as you moved the legos in a different configuration, they'd start swimming around again. A lot, they could tell the environment had changed and they wanted to understand how it
had changed. And they specifically would swim with one side of their body facing the legos because they had a body side that they preferred to collect information on, and so like even fish exhibits something like a preference for one side over the other. Anyway, I always remembered that it was like amazing that blind cavefish were responding to changes in their environments. Animals are incredible.
We've noticed that our dog seems to have a preference, Like when we ride in the car, he will stick his head fully out the window, but only on the right side. On the left side, he will stick his nose out the window, but he won't like all the way climb up on the armrest and get his whole shoulders out the window. So he seems to prefer the
wind on the right side of the car. And that makes me wonder, like, is he more comfortable with his right paw and looking out that window requires more strength from that leg or something, or is he fundamentally a righty I mean, have we done a lot of experiments on animals to determine, you know, if they're right left handed? Like, do chimpanzees use their right or left hand?
More?
Do you know?
I don't know. I think we need to get Katie Golded on the show from Creature Feature and she'll let us know. But I do not know the answer to that. So the left side is the side that the other cars are coming from. I wonder if it just feels safer to stick your head out farther on the opposite side than like towards incoming traffic.
Oh, we'll have to do some experiments with folks in England to see if their dogs prefer the opposite side.
There you go, that's a good experiment.
We're doing the natural experiment right here on Earth, folks. So you see that pop up in your daily life and in your own experience and in your family. But it turns out to also be important in the biochemistry of life and later on more fundamentally, in physics itself.
Yes, we said chemistry, but stick with us. This is exciting, all right, So we're back. We've talked about handedness, and I remember from organic chemistry and biokam that organic molecules are left handed in right handed And actually, when we were researching studish, Zach discovered that spearment and care away, which are very different tastes, are molecules with opposite handedness. Whoa and so like those, opposite handedness results in completely
different ways that it interacts with our body. So anyway, molecules have handedness and our chirrol and why.
Yeah, So we don't fundamentally know the answer, and you might be wondering, like, what does handedness mean for a molecule, Well, it just means that if you put it in front of a mirror, you don't get the same molecules. So a molecule is more like the three first fingers on your hand or the xyz axis than it is like a sphere. Right, They're not symmetric. They have a handedness to them, so you can't just like spin a left handed version of amino acids into a right handed version
of methane. It's like fundamentally a diff molecule. You can tell which one is left and which one is right. And as Kelly mentioned earlier, life is built out of only one of these things. Life has chosen one of these. We are all built out of left handed amino acids, the things that make up all living creatures on earth, including the microbes that infect us are all made out of one of these things and not the other one, which is really peculiar.
Yeah, wouldn't we have a lot more options for the kinds of amino acids and stuff we could make if we had both kiralities. But I guess we already could make more amino acids than are typically used by organisms, So maybe we don't need that many more amino acids.
Yeah, because the different chiralities don't work together, like these things have to fit together really precisely. I think of these little molecules as little machines, you know, that do something biochemically. This one builds that, and this one builds the other thing, and this one rotates this thing. They're all like, you know, I imagine little legos in my head because I'm not very good chemistry, and they have
to have their particular arrangement to do their job. You can't just replace it with the opposite kirality and expect it to do the same thing, especially if everybody else is the different kirality. It might work if you flipped all of it right. You took all of life from left to right, and you can make a right handed version. I think That's one of the questions Eric Church was hoping to answer, like is it really arbitrary? Could life
work if everything was right handed? It seems like it should, But it's fascinating that you can't mix them right like a left handed person can't eat right handed food, or couldn't have a baby with a right handed person, you know, like their biochemistries just don't interact. It's fascinating.
Yeah, you said Eric Church, but I think you met George Church. Oh sorry, yeah, that's all right. So is this kind of like if you have a iPhone you can't use the apps made for Android? Could it just be that life sort of started in one direction and then some piece of machinery for life came into existence that was really good, but only the right handed molecules could be used with that piece of machinery. And that's just it got the ball rolling and the left handed
ones could never compete. Sorry, Android users, And that's why we have this preference for one. It was like some early machinery used one chirality and not the other.
Yeah, so we actually don't know the answer to that question. We don't know like does it have to be this way? Is there something about left handed molecules that are better at forming life, or something fundamentally by the biochemistry of life that prefers left handedness. That would be weird, right, because there isn't really a difference, it's just reflection. Fundamentally, the universe shouldn't prefer one or the other, but it kind of seems to And you're right that once you
choose one, you're stuck. Right. It's sort of like everybody sits down at a dinner party. Are you taking the silverware that's on your left or on your right. Once somebody takes one, everybody's gonna make the same choice, or you get clashes, right, Or as you say, once you're in the Apple ecosphere, then you got to have all Apple devices where they don't work together. So we think
that once you choose one, you're stuck with it. We don't know if it was just like a random choice, like that first living thing could have been left or right, and it was just randomly left and now we're all stuck left, or if there's a reason it has to be left or more likely to be left, and just everything has followed from that.
Yeah, but it feels to me like there's no reason why you couldn't have had a branch of life that started right and that a branch of life that started left. Like you know, the same trick could have been come upon for both kyalities and then you sort of radiate out from there, and then.
There was an epic battle right versus left.
Yeah, I'm sure the right handed would win.
But this is not something we even knew until like one hundred and fifty years ago, and it was Louis Pasteur who discovered this. He was studying this byproduct of wine fermentation, tartaric acid, and he noticed that there were two types of crystals that were made. There were mirror images of each other. So he was trying to synthesize this thing, because you can synthesize these chemicals and you can make right or left, but then you discover out
in a natural world you only ever find left. So he discovered, oh, this is a difference if I make it myself in the lab versus if I like find it from nature. And he was able to pin this down using polarized light to figure out what the chemical structure of these things were. So this is something we've only known about for one hundred and fifty years and people have been trying to figure out, like what is the cause of it for much longer than that. There
are some speculative answers. I read a paper that suggested that there could be something about how magnets formed in the Earth that prefers left handed chirality, like the magnetic field of the Earth generates some preference for the left handed versions versus the right handed versions. But it's very speculative, and this is super cool. We just learned from an amazing mission that went out and sampled an asteroid Bendu
brought stuff back to Earth we could study it. In that sample, there are equal mixtures of left and right handed organic chemicals, So huge clue because life on Earth prefers the left handed ones, but the basic ingredients for left or right handed life seem to be out there in the universe.
So when you do industrial processes like Pastura was doing, you get both kinds? Do you get both kinds evenly? Because if so, it feels like the magnet's answer doesn't work.
You're right. But I think the idea is that there could be these magnetic surfaces essentially that are made that better bind to the left handed bits, and then essentially bring them together, gather them together so that they can make more complex molecules. So you might get more complex left handed structures faster than you get complex right handed structures, even if you have the same relative abundance of the precursors.
That basically it creates a playground where the lefty bits come together to make the complex structures you need for life.
I mean that feels testable.
Yes, this is totally testable. And I read an article from Science in twenty twenty three where they do experiments and they can produce this kind of effect. That doesn't mean that it's the reason why life is left handed.
It's just like there is in some sense something that prefers left handed chemistry to right handed chemistry right, and we do see other hints of that in the universe, like there are other parts of the universe that seem to prefer left handedness over right handedness, like particle physics. Particle physics has a basic preference for left handedness over right handedness, And after we dig into it, we can
come back and make the connection. People think that maybe high speed particles from space could have influenced the left or right handedness of life, on Earth.
We talked about amino acids being left handed. Amino acids come together to form proteins. Are there other things that are important to biology that also have a handedness?
Well, I think the left handed nature of the amino acids means that the sugars they make are right handed, because that's the kind of thing that a left handed amino acid will make. So those bits are sort of complementary. So there are some parts of our life biochemistry that are right handed that the amino acids are all left handed, so we call it left handed, if that makes sense.
The amino acids are the building blocks. You expect the things that the amino acids make, like proteins and sugars, to be the opposite handedness because of how they all get put together.
Yeah, exactly, Okay, And you can actually exploit that, as you were talking about earlier with flavors. Some artificial sweeteners exploit this fact. Despite being a sugar and tasting sweet, they can go through your body without being metabolized because they have the wrong handedness. So that's kind of cool.
That is kind of cool. I feel like there's a little voice in the back of my head saying wasn't there a study about how maybe they're not so good for your body? But I'm not an expert on that. Anyway, it might be worth looking up.
And we are not making any medical recommendations here, folks.
Amen, All right, So we've discussed that amino acids are building blocks of other things, and that the left handed building blocks produce right handed other things. So let's go down another level before amino acids, or maybe multiple levels before amino acids, down to particles. I knew that amino acids were left handed. Could you predict the handedness of particles because it alternates between levels.
Oh, it's a great question. We don't know the answer to that. And we knew one hundred and fifty years ago that amino acids were left handed. But physicists were confident that the universe fundamentally at the particle level had to be balanced, that it would be crazy if the universe itself was left handed in some way, like why
would it prefer one direction over the other? That was nonsense, And people did some tests early on, like let's see if electromagnetism is symmetric, is there any preference for photons to go in one direction? Or the other and they're like no. And they did tests on another force as well, the strong force, but people were very confident that the
universe didn't prefer left or right handed. And when we talk about particles, we have to be a little bit careful what we mean by left or right handed particles because the definition we gave earlier, you have like three directions. That makes sense for building molecules. Right, you're putting these things together. You can imagine like balls and sticks, and you're making something which doesn't reflect in the mirror. But particles we don't think about is having extent. Right, they're
just like dots. So what do we mean by left or right handed when it comes to particles, Well, particles don't have an extent, but they do have two different arrows. You can have particles that can be moving in one direction, so that's the momentum of the particle. Right, imagine an electron is flying through space. You could put an arrow from where it was to where it's going. That's one arrow.
The other arrow of the particle is its spin. Electrons can be spin up or spin down, so you can think of that as another little arrow, and that arrow can either be aligned with its motion, in which case we call it a right handed electron or not aligned, so pointing away from the direction it's moving. So if your two arrows of your spin and your momentum point in the same direction, we call you a right handed particle, and if they're not aligned, we call you a left handed particle.
Does it change the way we think about this when we think about electrons as waves instead of particles.
Yeah, that's a great question, and we should always keep in our minds that electrons are not tiny little balls or even dots, but they are guided by the wave function. Right, So what happens to a particle is determined by this wave its outcome, which makes some of this stuff probabilistic. Right, Like, an electron might not have a definan spin. It might
be maybe this or maybe that right. But some processes have to produce left or right handed electrons, which means you know in advance, like this one doesn't have a probability to be left or right. It has to be left or it has to be right in order to
balance with other bits. So, for example, if you have two electrons produced opposite each other, you know their momenta point opposite to each other, and you know, their spin also have to be opposite to each other, which means they're either both right handed or they're both left handed,
and you might not know that in advance. So in that case, for example, your electron is going to be fifty percent left handed and fifty percent right handed, but they have to be the same right if they're produced the same. So yeah, the wave nature gives you a probabilistic aspect to all these particles for sure.
All right, got it?
And so this is what we call handedness for particles. Sometimes they call it helicity. And one important caveat here is that this isn't actually something that's exact, because the momentum of a particle depends on your velocity. Like you can imagine flipping the direction of a particle by zooming past it in a spaceship. So now instead of moving one direction, it looks like it's moving the other direction
that basically flips its momentum. So we actually only talk about the handedness of particles that have no mass or very very very low mass, precisely because then you can't pass them in a spaceship. To be very technical, this handedness is actually an internal label it's not a physical thing. So the direction of the two arrows, it's like an approximate way to think about the handedness of the particles. But fundamentally it's some internal label we don't understand the
way like charge is. So now I just think about these particles as having like a little label on them. Some of them have an L and some of them have an R. And we thought for a long time, like the universe shouldn't predict either one, Like if you have some particle physics process, it should make the same number of right and left handed electrons in the early universe. You should have gotten an equal mixture, right in the
same way we talked earlier about preferring symmetry. And then it was in the nineteen sixties that people realized, hey, you know, we think that the universe is balanced. We think that there is a symmetry here, and we've checked it for a couple of things, but nobody's actually gone and done the test to see if the weak nuclear force prefers left or right handed particles equally or not.
I'm just going to point out that the biologist had figured out the importance of this one hundred years earlier. Apparently. I'm glad you guys caught up though, So go ahead.
That's right. Physics is always one hundred years behind biology. That's the way it works. So there was this exciting moment in the late fifties where people realized, oh my gosh, nobody's tested this before, and it's not actually that hard to do. So then this amazing scientist, chan hin Wu realized in the late fifties, actually this wasn't difficult to test.
This is something you could figure out. So she decided to skip her Christmas holiday, she sent her husband on along and say, I'm going to stay in the lab and figure this out. You know when you get like excited about something. And she put the experiment together. She got a bunch of cobalt atoms to spin only in one direction, and then she measured the angles that the electrons came out. And this was a great test of whether the universe preferred one direction or another because the
electrons were made purely by the weak force. And she discovered not only was it out of balance, but it was completely out of balance. It wasn't like the electrons were fifty one forty nine one direction. It was like one hundred zero, like the electrons would only go in one direction. It turns out that the weak force only makes and interacts with left handed particles. It like completely doesn't play with right handed particles at all. So all
the other forces don't care. Electromagnetism, the strong force no preference, but the weak force only plays with left handed particles. This was a really shocking discovery.
And after the break we are going to one hundred percent explain to you why that is. And we're back just kidding. We never have one hundred percent explanations for anything. What is our current state of not understanding this phenomenon, Danniel.
It's not something that we understand, it's something that we describe, something we see in the universe. We can incorporate it into the mathematics of our theory, like the standard model of particle physics that describes how particles interact and how they're created and all. This kind of stuff naturally has left and right handed particles, and the mathematics of the weak force allow it to only interact with left handed particles.
But again we don't know why that is. You know, the other forces treat the particles completely equally, and the Higgs force unifies these things, Like the Higgs force combines the left handed and right handed version of particles into one that we see and know and love and has mass.
Where does it get the right handed versions if it's combining them. So it gets the right handed versions from other forces and combines them.
Okay, yeah, so you can make right handed electrons. You just can't use the weak force to do it. You can use the electromagnetic force to make right handed electrons, no problem. Oh, but those will not interact with W bosons and z bosons and stuff like that. It's really weird. And if we didn't have the weak force, we never would have discovered that our universe for some reason, seems to be left handed at a particle level.
If you were to like rank the forces in terms of like how common they are in the universe, I actually don't know the right way to rank these, Like how important is the weak force?
Amazing question? Well, you know, the most powerful force is a strong force, and then electromagnetism, then the weak force, then gravity if it's a force at all. But the weak force, in some way is so much more complex and fascinating than any of the other forces. It's got extra particles like it has the W and the Z particles, all these particles needed to do its stuff, and it's so much more complicated, and it's responsible for the Higgs boson.
So it's pretty important and weird, and in that sense it's valuable because it gives us insight into the nature of the universe. You know, it does. It's weird stuff. If everything was simple and clean, that we wouldn't learn as much about the universe. It's the ugly messes that teach us something about how the universe is actually working.
I feel like that's a lesson for my life somehow. But go ahead.
There's just such a shocking discovery that the theorist that suggested it won the Nobel Prize, just like a couple of years later. Unfortunately, chinchin Wu, who did the experiment, she didn't get the Nobel Prize. Another example of the Nobel not treating lady scientists equally. Unfortunately, there's an imbalance for you.
Yeah, that sucks. She's still alive.
She is no longer alive, but we're gonna have a whole episode about her next year, and we're going to talk to her granddaughter, who I grew.
Up with Oh fantastic, all right, I'm looking forward to that. So the weak force produces left handed electrons, and then somehow we end up with left handed amino acids. Let's talk about the intermediate scale there. How do we think scale up between left handed electrons and left handed amino acids.
Yeah, we don't know. There's a lot of speculation because this smells like a weird coincidence, Like, how is it that the universe produces more left handed particles and right handed particles and life is made out of left handed amino acids? Is that a coincidence or is there a reason?
So there's a theory that particles from space when they smash into the atmosphere cosmic rays, they produce a shower of particles, and the weak force is involved, which means that it makes more left handed particles than right handed particles. And then dot dot dot a bunch of stuff that's not really plausible. Maybe that makes more left handed amino acids. And you know, there are papers I've read about this and I always come away from them going like, I
don't think. So it's like a real effort to draw a line between these things, because it's hard to imagine how a left handed muon is going to somehow make more amino acids that are left handed. Like, yes, the muons come in and they smash into stuff, and there's still an important part of life today, you know, breaking amino acids and creating mutations and all sorts of stuff
is important for evolution. But we don't have a microphysical explanation for why having more left handed muons could create more left handed amino acids or encourage them to form life or whatever make them more resilient. I don't know, because the weak force is very, very weak. You know, most of the time when a muon interacts with you, it's interacts electromagnetically, so it would be a very subtle effect if it even did exist. So really still an
open question. We don't understand whether there's any connection between the fundamental left handed preference of the weak force and the left handed nature of life on Earth.
Okay, so there's an important question that one of our listeners can answer, one of our young listeners. Okay, so we know we have handedness in some cases, we don't know why we have it. We don't know the implications, as you scale, is there important symmetry in other areas that gets broken.
Yeah, so great question. This inspires us to look for violations of symmetry elsewhere in the universe. Right, and we know already that the universe isn't always in balance, like, for example, we know that there are two different kinds of matter in the universe, matter and antimatter. Antimatter is like the reflection of matter, where everything has the opposite charge. So we have electrons. We can also make positrons, which are just like electrons, but they have the opposite charge.
And you can make anti protons and anti neutrons and there's nothing really anti about them except that they're not our kind of matter. So you know, you could we think, maybe build life out of anti electrons and anti protons to make anti people or whatever. We don't really know that for sure, but the laws of physics so far suggest that that's possible. But the universe has made more of matter than antimatter.
I watched too many sci fi movies. I'm under the impression that if matter and antimatter interact, they explode or consume each other in some way, Like could both of these things exist in the same universe? Or does one have to win.
They can't exist near each other because they interact very strongly. And so for example, if you have an electron and apostles near each other, they will attract each other and they will annihilate and give you photons. And it's a very efficient conversion of energy from mass to radiation. So for example, if you have a gram of matter like a raisin and a gram of antimatter like an anti raasin, and you bring them together, you get about as much energy as a nuclear bomb just out of two grams
of matter and antimatter. So yes, you can't have matter based life and antimatter based life on the same planet, but you could have, for example, matter galaxies and antimatter galaxies. Right, they don't have to touch each other. That is floating in space saying hi. But we're pretty sure that all the galaxies in the universe are matter galaxies, not anti matter g galaxies. And we can actually test this a
little bit because galaxies shoot out particles. All the stars and the black holes are emitting radiation and they shoot out electrons for example, and if there were anti galaxies, they would shoot out anti electrons and where those meet you would see these great flashes of light where the electrons and the anti electrons were meeting, and we don't
see any of that. We don't see like huge curtains of light between galaxies, which suggests that at least as far as we can see, everything is made of matter. So that's an important asymmetry in the universe, again, one we don't understand. We think probably in the Big Bang there was an equal amount of matter and antimatter, but something preferred matter because otherwise it would have all just gone away and turned into a universe filled with light
and no matter. So there's a preference there for matter. It's just an example. We don't know that it's connected to right or left handed. We call one matter and the other antimatter. It's just an example of how the universe sometimes seems to make one choice and not the other for reasons we don't understand.
All right, Well, so first of all, I think it's important to note that I'm on team anti Raisin.
That you like the golden raisins instead, I don't like any raisins.
No raisins, no raisin. Okay, yeah, team anti Razin.
But how do you feel about grapes? You like grapes but no raisins.
I'm pro grapes really interesting.
Are you anti dried fruit in general? No?
Dried mangoes? Those are great?
Oh man, we got to convert you.
This is really really important.
Is it just because you think raises ruined oatmeal cookies? Because you'd be right about that.
Yeah, that's like ninety percent of why I have trust issues. So the Big Bang had to have resulted in a preference for one or the other, right, because otherwise it would have all just like blown up at that point when it was all compressed.
Well, either more matter was made in those early moments than anti matter, and then when they annihilated, you get the massive matter left over. So either there's some early baked in preference for matter over antimatter, or it was symmetric at the beginning and there's some process which then prefers matter to antimatter. And we have a few clues. We've discovered one or two little processes that prefer making matter to antimatter, and that was sort of fascinating and
surprising and let to more Nobel prizes. These things are called CP violation if anybody wants to dig deeper into them, But they're not enough to explain it. They're like tiny little effects. It can't explain the size to the effect that we see in the universe. So this basic question, this asymmetry in the universe, we still don't have an answer to. But just to be clear again, it's not directly connected to left handed versus right handed whether the
universe is symmetric. It's just whether the universe is symmetric in a mirror. It's just another example of how the universe doesn't have to be balanced right. It can pick one or the other, we think, and we just don't
understand why it does or whether it did. But we can think about whether the universe and the Big Bang itself was symmetric from a left versus right handed point of view, Like when we talk about making those three vectors, is there something in the universe that really prefers those fundamentally at the level of the structure of the universe self, not just the particles or the amino acids or dogs or this kind of stuff. And we can think about
this by looking at the relationships between galaxies. There's this really amazing study people did last year where they basically just looked at groups of four galaxies and decided whether they would call them left handed or right handed. So remember the example of your fingers, right, you have three fingers, so three tips, and there's also the point where they all meet, so you have sort of like four points there. So if you have four points, you can say is
this a left handed grouping or right handed grouping? So they looked at all the galaxies that they could find over a million examples in this one study, and they grouped them into clusters of four and then decided is this a left handed grouping or right handed grouping? And they figured like, hey, this is just galaxies strewn out in the universe. We're just assigning left or right handed to these clusters. It should be balanced, right, There should be no reason why you would get like more right
handed or left handed clusters. But what they found is a huge bias towards left handed clusters of galaxies when you group these things together. I know, it makes no sense, like why would you prefer one or the other, But you know, they had groups check their results. This is the kind of result you sort of hope for in science, but then you're terrified of because then you're like, what, this has got to be wrong. This has been delay my paper.
Oh my gosh, did I pick the galaxies arbitrarily? I feel like that it would have to be a hard hard to pick them.
Yeah, exactly where they tried every combination, and out of a million galaxies you get a trillion trillion combinations. They make these pyramids, right, like four galaxies make this pyramid, and you can decide whether it's a left or right handed pyramid. And the chances of this being a random
fluctuation is one in three hundred billion. So either it's a crazy fluctuation, or it suggests that there's something about the universe, something about the topology, structure, the nature of space and time itself that aligns these galaxies in a more lefty way than a right handed way. It's really a fascinating clue. And it's just like adds to the story, like life is left handed, particles are left handed, something about the structure of galaxies in the universe itself is left handed.
No wonder Zach thinks he's so great.
It turns out he's right. Science has proved him right.
There's got to be something we don't understand in between there.
All right, reviewer number two over there, So this is just like a collection of clues that all point towards something that smells suggestive. But it could just be nothing. It could just be here's a bunch of coincidences, you know, left versus right. Whatever the universe just picks randomly. And we live in a multiverse with all different kinds of universes, and some of them have right handed life and right
handed particles and left handed galaxy structures. Or maybe there's something deep in the mathematics which really prefers left handed structures and can only work this way, and just we haven't puzzled it out yet. We haven't found the connections between these different layers of leftiness, and we haven't understood what about the nature of the universe requires things to
be left handed. It's a fascinating puzzle and the kind of thing I think in one hundred years, I hope we have much more clarity on.
Are we currently at the just like scratching our head and pulling out our hair phase, or are they're like four competing hypotheses and we're just waiting for the LHC to give us the answer, Like where are we right now?
I think we're in between those two different outcomes. We have some crazy ideas, like people think maybe the thing that came before that early moment of hot density, you know, the inflation and the infloton field and sort of pre Big Bang theories and everything that's pre Big bang very speculative, and that doesn't mean worthless, right, it just means like, hey, we don't really know. We're still in the building phase.
We're trying stuff out some of those Maybe we're seated by something that prefers handedness, and people are trying to build left handed ideas into that infloton field with varying success. So we don't have solid predictions that we can use to test any of these ideas. We're just sort of like, maybe this is something, and maybe this is something we should be building into our theories of the pre Big
Bang universe. We can try to look deeper into the history of time to try to understand it, Like we hope that gravitational waves from the very very early universe
will help illuminate what was going on. You know, we can only see the early universe back to about three hundred and eighty thousand years after that first understood moment because that's the first time the universe was transparent, but there's a lot of stuff going on before the universe was transparent, when it's hot and dense and opaque, and we hope that gravitational waves will give us a window into those moments and maybe this can clue there and
the polarity of those gravitational waves to see if they prefer left handed physics to right handed physics, or maybe not right maybe they are perfectly in balance. So this possibility that we could learn something, but that's very subtle physics, and seeing gravitational waves from the very early univers is notoriously tricky. There was an experiment by step two a few years ago that thought it had seen them and had evidence for inflation. Then it turned out to just be dust.
Yeah.
Yeah, Oh, that's frustrating. It's always pigeon.
Poop or dust exactly. Science is hard, people, it's hard, it is, but the mysteries are deep and they are fascinating, and all of these clues tell us like, maybe this is a thread we should pull on that's going to unravel our whole understanding of the universe, or maybe it's just a coin toss in beginning of the universe and it means nothing, and people.
Will spend entire careers trying to figure it.
Out, and maybe one of you out there will be the one to pull back the veil and help us understand the nature of our own universe.
Please do that.
Soon, Please soon. I'd love to know the answer.
Yeah.
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