Daniel and Jorge Explain the UniverseDaniel and Jorge talk about how the Universe's preference for left-handed particles may have shaped our chemistry.
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Hey or hey, I realize I've never asked you this. Are you left or right handed?
Usually gre out with my right hand.
Sure, you've tried to draw with your other hand. What's that like?
It's pretty tricky. Yeah, if you're used to doing things with one hand, it's hard to switch.
Well, what about driving? Have you ever driven on the left side of the road?
You mean, on purpose or against the law or following the laws of traffic?
Well, you know there are some places in the world where they drive on the other side.
I have driven in Australia and England. Yeah, it's pretty tricky, but any after a while you get used to it.
What would you say, is better your left side of the road driving or you're left handed drawing.
Well, I've fortunately have not had an accident on either side of the road, so the data says that I am equally good.
Well, I'm glad you're even handed.
That sounds like a left handed compliment, Daniel.
I think that's right.
I am Porhem, a cartoonist and the creator of PhD comics.
Hi, I'm Dan. I'm a particle physicist and a professor at UC Irvine, and I have tried to do math left handed.
I mean you write out math with your left hand? Is that what you mean?
Yeah? I try to write out math with my left hand or sometimes upside down. Sometimes when I'm teaching math to my kids, I have to write it so that they can see it, which requires a little bit of awkward gymnastics.
M But if you use your left hand, then maybe it's normal.
If I use my left hand, then my handwriting looks as sloppy as theirs.
I know people who aspire to be ambidextrous so they purposely use the mouse. Even though they're right handed, they user mouse but their left hand so that they're you know, are able.
To do both. I would you give my right arm to be ambidextrous.
Well, if you give your right arm, then you wouldn't be ambidexters. Sounds like you're caught in a paradox. But welcome to our podcast Daniel and Jorge Explain the Universe, a production of iHeartRadio.
In which we try to tickle the right side of your brain and the left side of your brain. We want to understand the entire universe, the top half, the bottom half, the left side, the right side, and everything in between, even the backside, the backside, the front side, the dark side, and the light side. Every side of the universe deserves to be understood, and we think it's possible. And on this podcast we ask those big questions about the nature of reality, the nature of life, why we are all here, what it all means, how long we will be here, and whether we are alone, and we try to explain all of them to you. And today I want to especially explain things to Walter Bloom, a long time listener of the pod from Switzerland, whose girlfriend, Victoria wants to wish him a happy thirty eighth birthday. Happy birthday, Walter.
Yeah, it is a big universe to explain. It is a wide universe full of many sides to it, many different ways that you can look at things, and also many different ways that things can be put together. We are almost an infinite way for that or to arrange itself.
And one of the joys of physics is figuring out how the universe works, because then we get to ask why. When we discover that we are put together out of tiny little particles, we get to wonder like, hmmm, why is the universe arranged out of these tiny little particles? Why does it have these patterns? What does that really mean? The joy physics is really that it's setting us up to ask philosophy questions.
Oh, is that the main goal of physics just to be a primer, like a trailer to philosophy, just the opening act for philosophies, That's what you're saying. Physicists are just there to warm up the crowd.
In the end, I think that almost science really is motivated by philosophy questions. You know, at the heart of almost every science question we ask there is a why question, which is in the end fundamentally philosophical.
Yeah, and we ask these questions not just because it's interesting and fascinating and we understand more about the universe. But sometimes these questions and these issues have a big impact on our daily, everyday lives, even maybe on life itself.
Yeah, we notice these patterns in the universe. The universe seems to organize itself in this way and not some other way. We notice sometimes there are symmetries in the universe, like you could rotate everything and the laws of physics wouldn't change. But also sometimes we notice that there are there are not symmetries in the universe if the universe has a strong opinion about how things should be done and the opposite way just does not happen. Time flows forwards and not backwards, and these are the things that inspire our philosophical musings to wonder what it would be like for a universe where time flowed backwards, or what it would be like for a universe in the mirror of our universe.
Yeah, And so our universe likes to put things together in a particular way, and you can trace sometimes that to the very properties of the smallest particles in the universe, the things that everything is made out of, and sometaly these properties can have a pretty big impact on what gets formed in the universe and even whether we would be here or not.
It does seem sometimes like at the smallest level, the universe follows really different rules, really strange quantum rules that don't really affect our lives, Like how a particle moves through space is totally different from how a baseball flies through space. But as you say, sometimes there is a connection. Sometimes we can even find a portal from the tiniest particle to our everyday lives.
So to be on the podcast, we'll be tackling the question does particle spin affect life on Earth? Are we trying to put a positive spin here on life on Earth?
I'm trying to put a positive spin on particles. I'm like, look, particles are relevant.
Give me money, is what you're saying.
Well, you know that's the philosophy that's underlying all of it. In the end, Yes, we're trying to make our science relevant.
Now, do you share any of your funding with philosophers?
Philosophers really need funding. I mean, how much does paper and pencil cost anyway.
Isn't that aren't those the tools of your research as well?
Ten billion dollar particle colliders. You can't build those out of pencil and paper.
Well you could, you just haven't tried.
The paper mache particle collider. Put that on the table next time we're discussing the future of the field.
Can you demonstrate mathematically that you cannot build a particle collider with paper mache?
That's true? The spitball collider. Yeah, let's see what we can learn by colliding spitballs at nearly the speed of light.
Yeah, it's possible, right, it is possible.
I have to do some pencil and paper calculations to see what kind of experiments we could do and what we might learn about the universe from a paper machet collider.
Yeah, all fund that here, here's five bucks. But this is an interesting question. We're trying to link life on Earth to something as small and maybe seemingly insignificant as the spin, the fundamental particle of nature. That's a pretty big leap.
It is a pretty big leap, And you might think it sounds a little bit desperate, like is Daniel just trying to be irrelevant to life? But remember that I'm actually doing this research mostly because I think it's irrelevant honestly, because it doesn't affect everyday life on Earth, which means you can't use it to build weapons.
Wait, did you just admit your research is irrelevant to all life on Earth.
It's irrelevant in the sense that it doesn't have immediate practical applications.
Wait did you admit your research has no immediate practical applications?
Oh?
Absolutely, yes, learning about particles has no immediate practical applications. I can't tell you tomorrow that it's going to improve technology or even next year. It's basic research in the sense that we might discover something crazy and new about the universe, which down the road I'm sure will benefit society, But in terms of like immediate impact and you know tomorrow's weapons systems, No, we have no relevance.
All right, Well, I guess possible deniability is important for some people. But this is an interesting question to wonder if maybe the spin of particles could have affected how life on Earth evolved, or even if life itself evolved at all on this planet.
Yeah, it's a fascinating hypothesis with a little bit of evidence to back it up.
Well, as usual, we were wondering how many people had thought about this question, had thought about maybe the properties of particles having an impact on life on Earth. So, as usual, Daniel went out there to ask people do you think particle spin can affect life on Earth?
So thank you very much to everybody who participates in this segment of the podcast. We really appreciate hearing your thoughts and I think everybody out there enjoys it as well. If you'd like to share your thoughts on the topic of the day for future episod modes, please don't be shy. Write to us two questions at Daniel and Jorge dot com.
What people had to say.
I don't really know what particle spin is, but I could surely say that it does not affect life on other planets from the Solar System.
Well, everything is spinning. Particles are spinning, the Earth is spinning, the galaxy spinning, reams are spinning. Everything is spinning. So yeah, the life is spinning.
I'm going to say yes, because it affects the.
Way matter is made up.
But I really don't know what would happen if particle spin were to be reversed. I don't know if you would even recognize the effects of that.
I think it can.
Be interpreted maybe a couple of ways outside of the necessity of spend make physics work. I would say probably not very much impact. Like I don't think. I don't think like DNA is interacting with particle spin. All right, some people said yes and people said no. There are strong opinions here. There are positive and negative spins.
On one hand, it does seem hard to imagine that the behaviors of tiny little particles could affect something like life on Earth. On the other hand, if you believe reductionism, if you believe that everything in the universe comes out of how tiny little bits are dancing around and tuing and frowing, then in principle everything about life comes down to how particles work. Well.
Yeah, I mean I guess if particles, for example, didn't feel the electromagnetic force, I mean, the whole universe would be different.
Yeah. I'm sitting here trying to imagine what a universe would be like without electromagnetism. I mean, it would be a dark universe for sure, right, there would be no light at all in that universe.
Yeah. Or I guess even if the particles had a different mass. It would also change the whole universe, right, like planets would form differently, galaxies would form differently. Who knows, and maybe life can or could have or would have formed here on Earth.
Yeah, it's a deep mystery why the parameters of the universe seem to be set up to allow life. Although you know, that's just sort of like life that we can imagine. It's possible that if you tweaked all those parameters you might have completely different chemistry. But that might allow for different kinds of biology, different kinds of life, maybe even different kinds of intelligence. So while the universe does sort of seem fine tuned for us, it might be that other fine tunings are good for other kinds of beings.
All right, Well, the question at hand is does particle spin affect life on Earth? And so I guess particle spin is something that is a property of particles. Maybe we can get a little bit into that first.
Particle spin is a really fun and super weird property of particles, and it's especially fascinating because the universe seems to have a preference for one kind of spin over another kind of spin. Fundamentally, we don't really know what particle spin is I mean, you might imagine that it's like a little ball and it's spinning. The problem is that particles are not little balls, and they don't really have surfaces, so we don't think that they are physically spinning. But they do have a proper which is very similar to the kind of things we call spin. For like the Earth is spinning and the galaxy is spinning. Particles have properties which have similar mathematical behaviors to spin of like big objects, and so we call it spin even though it's not like technically physically spinning.
Right, because quantum particles are not like little balls, as you said, they're like little dots basically, and so they have this property called spin. And if it's not related to it actually spinning, why did you call it spin or not you specifically, but you know the physicism Firth did it. Why did they call it spin?
They call it spin because even if it isn't actually physically spinning, it is a form of angular momentum. Right, Things in the universe can spin, and they can have momentum in the same way that things can have normal momentum.
Right.
Momentum is just like if you push an object it keeps going, or if you don't push it, it doesn't go anywhere. The same thing holds true for spin. If you spin something, it'll keep spinning, like out in space where there isn't any air to slow it down. Or if you don't push an object, it won't spin. Right, something floating in space won't spin unless you push it. That's angular momentum, and that's conserved in the universe. That's why if you push something to make it spin, it'll just keep spinning out there in space until something stops it. But it can transfer that angular momentum to something else, right, It can bump into something else and make that spin. We call particle spin spin because it's a kind of angular momentum. You can take angler momentum and convert it into particle spin and back. So when the universe does its accounting to make sure that angular momentum is conserved, particle spin is part of its balance book. You're allowed to move some angler momentum into that category. So it really is a kind of angular momentum, even if it's a weird quantum kind.
But you said that like regular objects in space can have zero angular momentum or a little bit or a lot of angular momentum. Can particles have zero or a lot of angular momentum? And also why not just call it angular momentum?
Yes, particles can have different amounts of spin. Of Photons, for example, can have spin up or down or zero. Electrons can only have spin one half or negative one half. They can't have zero spin. They're different kind of particles. So matter particles are all either spin up or spin down by one half, whereas forest particles those can be up or down or zero.
Can the same particle have zero and then I give it a spin and then it starts spinning or is it just an inherent property of that particle.
That's a really interesting philosophy question. Right. Essentially, you're saying a photon moving through the universe with zero spin, if you give it spin, is it's still the same photon. Well, to give it spin, you have to impart angular momentum on it, which means an interaction, and so philosophically it is changed. Right, It's like interacts with some particle, and you think of that as like being absorbed and re emitted. So I think philosophically you could think of it as like a new particle, or it's at least a new quantum state. But yes, photons can have zero spin, or they can have spin one, or they're can have spin minus one.
And the spin it's on ties as well, Like can you have a photon with like three point five spin?
No, you can't, And you can't have photons with like half a spin or point seventy two nine spin. It's absolutely quantized. So photons have three possible states plus one, zero or minus one, and electrons have two states plus a half or minus a half. And that's true for all fermions. All fermions are either plus a half or minus a half. They have half integer spins. That's why we call them fermions. They all observe the Fermi exclusion principle, which means they can't be in the same quantum state as each other. Bosons, which have integer spin, they can hang out in the same states, so you can have like a million photons all in the same state.
Now, you said earlier that spin is up or down, right, that's kind of the possibilities of it. But in space there is no up and there's no down. So what does it mean for a spin to be up or down?
For a particle, Well, in the same way that you can pick any axis to calculate angle momentum, you can pick any axis to project a spin. So you have a particle, you pick an axis, you say, here, there's my axis. I want to know if its spin is up or down along this axis, And you could pick any axis you like and call it up or down. Typically, what we do is we choose the axis of the particle's motion, and we ask is the particle spin in the direction of its motion or in the opposite direction of its motion?
But isn't then then the problem the motion and not the spin. Like if I throw a baseball face up, or if I toss a frisbee face up or face down, it's not that it's a whole different frisbee. It's the same frisbee. I just threw it upside down.
Yeah, And in the case of particles, you can measure their spin along any direction. You can measure it along their motion, or you can measure it perpendicular to their motion or in any direction, and you'll always get either plus a half or minus a half or particles.
Okay, So it's just some sort of like an arbitrary label you're saying, like, particles have this thing called spin, and we're gonna there's kind of two kinds of the spin. There's the upspin and there's down spin exactly.
And the universe seems to have a preference for particles whose spin is pointed away from the direction of their motion, like an electron is flying through space in the positive x direction. The universe seems to have a preference for those particles to spin the opposite direction of their motion, for their spin to be sort of like back along the negative X axis. If their motion is in the positive X axis, we call those particles left handed. If their spin is the opposite direction of their motion.
I guess it's kind of like a clock. Like a clock can move through space where it's either the face of the clock is facing words going or the face of the clock is facing away from where it's going or facing back. And so you're saying that particles tend to be the kime where the clock face is facing back.
Those kind of particles where the clock is facing backwards, where the spin is the opposite direction of motion, we call them left handed particles. In our universe, we have left and right handed versions of most particles. But one of the forces, the weak nuclear force, which is responsible for like beta decay, it will only talk to left handed particles. It does not interact at all with right handed particles. So that's what we mean when we say the universe seems to have a preference for left handed particles. The other forces, electromagnetism, the strong force, they don't care. They're happy to talk to right or left handed particles. But the weak force only talks to left handed particles.
So it's almost like the universe is not ambidextrous, Like the universe seems to prefer or at least favor left handed particles over right handed particles.
Yeah, and it's a slight preference, right, because remember the weak force is a feeble force. It is not a powerful force. Does not control the structure of our galaxies, it does not control the structure of your body. It does not control lightning. Right, It's not a very powerful force. And so it's a subtle effect. And this was actually overlooked for years and years and years. Even well after the weak force was discovered. People hadn't really checked to see if it was symmetric, if it talked to both kinds of particles. There was this moment in the middle of last century when people realized, wow, nobody's ever actually checked this to see if the weak force was symmetric, and every thought, of course, it's symmetric. Everything in the universe is symmetric, the strong forces symmetric, electromagnetism is symmetric. It would be bonkers if the weak force was not symmetric. But nobody had checked, and so very quickly a famous scientist at Columbia skip her Christmas vacation to do this experiment and discover the shocking result that the weak force is not just a little bit anti symmetric, it's completely anti symmetric. It only talks to left handed particles. It was a huge shockwave that went through the physics community about fifty years ago.
Yeah, I think we had a whole episode about this experiment that demonstrated the universe has a little bit of a left handed preference, and so this preference has pretty big implications on how the universe works and maybe even how life on Earth developed. So let's get into right and left handedness of the universe and life on Earth. But first let's take a quick break.
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All right, we're asking the question does particle spin affect life on Earth? And so we talked about what spin is. It's a property of particles. Particles can spin up or down. They can be left handed or right handed. And this handedness is something we see all throughout, not just the universe, but nature itself. Right, I mean in chemistry they talk about handedness as well of molecules.
Yeah, you can apply this principle in general to anything. You could ask if something is left handed or right handed, and basically you're asking would it look the same in the mirror? Right? If you flipped something in the mirror, would you get something the same, and you can literally do this experiment in front of yourself with your hands. Like, take your left hand, it's not the same as your right hand right, there's a different orientation of the fingers relative to the thumb. If you put your left hand in the mirror, then it looks like your right hand. Right. The mirror flips your left hand to a right handed sort of shape. But if you just take your right hand, you can't like turn it around or twist it in any way to make it look exactly like your left hand. They're different, right. We call that chirality, that one is left handed and one is right handed, that they're not the same.
Right.
I guess if you're doing the mirror experiment, you would see that maybe some parts in your body are symmetric and are are not handed right, Like if you take, for example, your eyeball, if you put it in front of the mirror, you can't tell which eyeball it is, your right one or your left one, right the one eyeball looks the same in the mirror as it does in you. Or for example, I think your nose, right, your nose is also a symmetric You can't sort of tell which one is the mirror one which is the real nose. But like your right hand, you can't tell which one it.
Is assuming a spherical eyeball. I think that's true, and my nose actually isn't symmetrics. I could tell the difference in the mirror because it leans one way instead of the other.
That can be fixed.
Right, we are in Orange County. I mean basically, everybody's getting some work done these days. In principle, an idealized human nose, you're right, is symmetric, and yeah, hands are not symmetric. Right, the real life version of your left hand looks like a right hand in the mirror.
Right, And the same can be said about molecules, right, Like, you can arrange a molecule in a way that is symmetric where it looks the same in the mirror, or it can arrange a molecule in a way that does not look the same in the mirror.
An example of a symmetric molecule is like water. Right, water is H two Oh, you have two hydrogens with an oxygen in the middle. If you flip it, like if you make the left side the right side and vice versa, it looks the same, right, it's exactly the same in the mirror, But you can build much more complicated molecules, and chemistry of life specifically is filled with complex molecules built off of these carbon chains, and those do have a chirality. They do not look the same in the mirror. There are left handed versions and right handed versions of basically every kind of molecule. So if you just say the chemical formula see H four for example, that tells you what's in it. It doesn't tell you which orientation is it is. It's a left handed or the right handed version of that object.
Right, Like H four, you can take one carbon and four hydrogen and put them in together in one way or in a way that looks like it's a mirror image. That's what you mean, right.
Actually H four is an example of a molecule that probably is symmetric. You have the carbon and then the hydrogen's arranged around it. So I think it does look symmetric in the mirror. But as they get more complicated, you know, for example, the amino acids and the building blocks of life, these are much more complicated structures. They're not all the same in the mirror.
Yeah, Like if you take carbon, a bunch of carbon and a bunch of hydrogen and some other atoms. There are two different ways you could maybe put them together. You could put them together in one way or in a way that looks like it's a mirror image, which is not the same molecule. It just looks the same in the mirror, and it actually kind of affects how it interacts with other molecules, right, Like a right handed molecule doesn't do the same things as a left handed molecule.
Yeah, Interestingly, you can't just mix them. You can't have a bunch of left handed molecules and a bunch of right handed molecules and assume that they will all act the same. Because chemistry is like these little building blocks. It's like tiny little machines made out of proteins. They have to click together in just the right way to like activate certain sites, to cleave off bits of a molecule. It's like trying to shake somebody's hand but using the wrong hand it just doesn't sort of fit together, or trying to dance where both people are leading. In order for the chemistry of life to happen, everything has to match. It means you need like all the pieces to have the right chirality, so you can't mix and match left and right handed chemistry of life.
Yeah, that's why I fisp on people when I meet them these days. It's just too confusing. But I was thinking, it's sort of like Tetris, right, Like in Tetras, you have pieces, and like every piece in Tetris is made out of four blocks, but depending on how you put them, they're symmetrical or not. Like if you have a two y two block, that's symmetric and you can slide that in anywhere. But if you have like an L shape block, then you got to wait for the right left hand or the right side L block to fit a certain spot in your Tetris pile.
And for the chemistry of life to work, it seems like you need to be either all one chirality or all the opposite chirality. And that's exactly what we see when you take organic molecules and you sort of like distill them from living objects, from plants or whatever, you see all one chirality. All of life on Earth uses left handed amino acids and right handed sugars. There's nothing alive on Earth that uses right handed amino acids or left handed sugars, that form of life just does not exist.
Right. But it's like, it's possible to make right handed amino acids, but all life on Earth seems to use only left handed amino acids. And once life got started and life starts to make amino acid, it then only makes left kind, which is the kind of uses.
If you synthesize some organic moleculeity, like try to make one of the amino acids chemically from basic building blocks, you'll end up with both kinds, left handed and right handed. But if you pull it out of life, if you distill it from a living being, you'll only get one chirality right, and you're right. We think that life is possible with the other orientation. We suspect that it is, though of course we don't have any examples. We think that probably universe is symmetric and that it would allow for life to have both kiralities, but we don't actually know.
Well, that's interesting to think about, Like maybe there's a version of humans out there, maybe in the multiverse or maybe in this universe that uses only right handed amino acids, and maybe if we met them, I mean, we could shake hands, but we could maybe like have kids together, right, or.
Even eat their food, because our bodies cannot inter with that kind of chemistry. I mean, like some of the artificial sweeteners that are in our foods are really interesting because they exploit the fact that, despite being a sugar and they do interact with your tongue in a way that you can taste them, our bodies can't actually take them apart to use energy, so we can't metabolize them even though we can taste them because they have the wrong chirality.
Interesting. Yeah, artificial sweeteners you're saying, use the wrong candidness of sugar molecules which activate our taste buds, but they can't be processing our stomachs.
Yeah, because those are different processes, right. Tasting something recognizing the sugar your tongue doesn't actually break it down and extract the energy, and so it's like, oh, yeah, that's sugar plus one for you. But then when it gets into your stomach, the little machines down there that take things apart and actually extract the energy and turn it into ATP they're like, I don't know what to do here. My locks are not fitting into these keys, So just passes right through you.
Mmm.
Interesting. This is something we've known for a while, right.
This was discovered by Louis Pasteur himself more than one hundred and fifty years ago. He synthesized a bunch of chemicals and then he also distilled them from life, and he noticed this difference. He noticed that the ones that came from life had only one chirality, and the ones that he synthesized himself had both kinds of kyality. So it's been an open puzzle for more than one hundred and fifty years of why life has this thing. They call it bio chirality.
But back then, how do we know that a molecule was right handed or left handed? Right we can of like X ray or have super electron microscopes.
The way he discovered it was that these kiralities interact with light a little bit differently. The light can have different polarizations, which is related to the spin of those photons, and that interacts slightly differently with those photons. And so that's how he detected that the chemicals that he pulled out of life were different from the chemicals that he synthesized in the laboratory. And he actually predicted before we even knew about the weak force or parody violation. He predicted that there must be some sort of cosm particle asymmetry which is generating this fundamental asymmetry in life. So like one hundred years before we discovered parity violation, he basically predicted it.
Wait one, he was thinking, maybe the reason that life on Earth is mostly left handed one type of molecule is something like something from space.
He was thinking that this asymmetry was revealing a deep asymmetry in the universe itself, right, that there must be some sort of cosmic origin to this. So Pastora wrote this is in the eighteen forties. He wrote, quote, if the foundations of life are di symmetric, then because of die symmetric cosmic forces operating at their origin. This I think is one of the links between life on the Earth and the cosmos, that is, the totality of forces in the universe. So that's Pasteur writing in the eighteen hundreds, before we understood life the quantum nature of these forces or particle spin or parody violation at all, he had the sense that maybe the handed of life came somehow from the handedness of the universe.
Whoa feels like a little bit of a stretch there further to make that connection.
It might be one of these things where people write a lot and most of their predictions are wrong, but when they do hit the jackpot, people later on dig them out and like, hey, look how forward thinking they are, you know, the way you can find almost anything you like. In the writings of Noster.
Damis, I wonder if it's sort of like saying like, maybe in a way he would saying I mean, I'm sure I know he was a scientist, but maybe in a way you're saying, like, you know, maybe God is left handed and that's why he made a human, you know, humans in a particular handedness, or like maybe God is right handed, that's why most humans are right handed.
Yeah, that's another great example of asymmetry. Right, why are humans mostly right handed and not left handed? We know that it can work both ways, obviously, but why are humans mostly right handed and not mostly left handed? It seems like sort of an arbitrary choice, and it makes you wonder, like where does that come from? Is it just random or is there a fundament the reason at the heart of the universe that's creating this asymmetry. That's sort of the philosophy question, right. You always want to know the why, not just the how.
Right, right, And we all know we're just here to set things up for the greater discipline of philosophy. But I think, you know, I guess if half of the humans on Earth are right handed and half of them were left handed, it would be pretty awkward all the time trying to shake hands with people. So maybe the whole reason most people right hand is just to you know, make things more social.
Yeah, I think that's beyond my pay grade, all.
Right, Well, that it's a big question. Why does life on Earth prefer one kind of handed molecules and not the other? I guess one reason is that it could have been random, right, Like it just you know, picked left handed molecules and when with that.
Yeah, it could be basically a coin flip billions of years ago that could have gone either direction. But once you pick one side, like symmetry breaking, then you just got to go with it. Like if a bunch of people are seated at a table, you have like glasses placed between the plates. Is your glass on the left side or the right side? As soon as one person picks their glass on the right side. Then everybody's going to use the right handed glass, But they could have picked the left one and everything would have worked just fine. So we don't know if it was just like a random event billions of years ago in the primordial soup that led us to all have this one handedness, or maybe there is a reason.
Yeah, I wonder like if there was some competition in the in early life billions of years ago, like maybe a bunch of particles started assembling in the left handed way and a bunch of particles started assembling in a right handed way, and for a while, maybe there was life could potentially get early on, there could have been life with both handedness. It's just that one somehow beat out the other.
Yeah, it could be, or it could be that it's selected for either before life starts or after. Right, it might be that the processes that generate these organic molecules naturally prefer to generate them in a right handed or left handed way, like out there in space when you have these organic molecules in soups, are there equal amounts of left and right handed molecules? Or is there an asymmetry there before life even gets started? Then You can also ask afterwards, if life gets started equally often left and right handed, is there some preference for is one more likely to survive? Is there something about the universe which gives one of them a boost right?
I think you're asking, maybe God is not ambidexterrous. Maybe God this my preference for right or left handed, and could we see that in the laws of the universe. And so let's get into whether or not there is a connection between the left handedness of life and the right handedness of quantum particles. But first, let's take another quick break.
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All right, we are doing some of the pre work here for philosophers. We're warming to crowd up here with some interesting thinking about the universe and life on Earth, asking the question can particle spin or did particle spin affect life on Earth? So we've talked about how fundamental quantum particles have a spin, they have an up or down spin, and we also talked about how life on Earth has a preference for left handed molecules over right handed amino acid molecules. And so the question is are these two things related. Does the spin of sparticles affect how molecules form or do somehow the laws of physics somehow prefer left handed amino acids. Let's get into that connection.
It is a really fun question. And I was reading this very long and detailed paper about the connections between particle spin and biochirality and actually start out with a bit of a rant, a complaint about calling life left handed or right handed, because there's all sorts of ways you can define it. So they prefer to define the orientation of our chemistry as live live, and the opposite orientation as evil live backwards ev il. So this whole paper talks about normal life versus evil life.
And this is a physics paper or is this a blog post?
This is a paper published in a prestigious journal.
And somehow calling life evil or live is better than calling it the left handed or right handed.
I don't know. It's a philosophy question.
So this is all based kind of on a paper that tries to make a connection between quantum particle spin and the coreality or the handedness of life molecules. Is there a connection, Daniel between these two things.
So there is a plausible mechanism for connecting the preference of the weak force to produce left handed particles and life selecting for this kind of chirality. There's a plausible mechanism. It's very very thin, it's a very very slight preference, and it's not something we've proven, but it is possible. And it comes down to particles from space. Right Cosmic rays are these particles that hit the Earth at very very high speeds and they come from like the centers of other galaxies, or they come from our Sun, and they're just normal particles, protons, electrons, positrons. Sometimes they hit the top of the app sphere and they create a big shower of particles. Because a particle hits the atmosphere, it's sort of like a meteor hitting the atmosphere. It heats up and slows down and spreads out its energy, so you get a big shower of particles on the surface. And this is something very normal. It's something we've been experiencing as living beings on the surface of the Earth for a very very long time. Cosmic rates hit the atmosphere and create essentially radiation on the surface of the Earth that interacts with us and interacts with our organic chemistry, specifically our DNA.
Right, we sort of can't see it on our regular skies, but you can sort of see it in the northern lights, right. That's kind of what the northern lights are. Particles hitting the atmosphere.
Yeah, and particles hitting the atmosphere and in that case getting shunted up to the poles by the magnetic fields. Or the reason that we don't have more radiation here on the surface of the Earth is our atmosphere. The second reason is our magnetic field acts sort of like a shield, but some of it does get through and gets down to the surface and affects the way life operates. You know, a crucial element of evolution is mutation. You don't want just to copy the genes of the parents. You want to try something new, which requires either making a mistake when you're transcribing the DNA from the parent to the child, or having a mistake introduced from for example, a cosmic ray. I mean, passing through your DNA for example, could alter the chemistry of it in the same way that like radiation can give you cancer by changing the fundamental operation of your cells, it can also change your DNA.
Yeah, and that's kind of an essential ingredient in life and evolution, right, Like if you didn't have mutations, then life would never evolve, it would never change, like that's how it started. But also like you need mutations just to evolve life because of DNA never changed. If it copied perfectly from one generation to the other, you would just still have the same organism you started with. You would never evolve or come up with better versions of the species.
Yeah, in order to explore the space of all possible organisms effectively, right, you need a population that has different abilities, and the best way to do that is to introduce random mutation. That's essentially what evolution does. So cosmic rays have played an important part in our evolution. We think it's actually key. Like, if you could build a perfect shield so we had no radiation on the surface of the Earth, then the history of life on Earth would be very very different and might not have succeeded.
Right. Well, you would still have mutations, you just wouldn't have them from radiation coming from space, right.
And we don't really know what would happen in that scenario, right, life would evolve very differently, changes the conditions of life. And so what we do know is that the conditions we have here on Earth are the ones that gave birth to us, right to this kind of life.
Right. I guess if we had less of a shielding from radiation from space, we would have had more radiation and maybe too many mutations, right, in which case we wouldn't have evolved either.
Yeah, it's a really interesting question and sort of like biophilosophy, like what is the best rate of mutation we just don't know the answer to that. People theorize and run experiments, but you know, we have a certain level of radiation and we think that that's a key part of how we evolved who we are.
All right, So then how does left or right handedness come into it?
Well, it turns out that these cosmic rays that come from space are not equally left or right handed. When we talk about the particle spin, is what happens when a particle hits the upper atmosphere is it creates this shower of particles. Typically, these particles called pions, which don't live very long. They tend to decay and they decay into muons. That decay is done by the weak force. The weak force is the thing that breaks up the pions. It turns it into a muon and also for example, a neutrino. And because the weak force is in charge of that moment, it only makes left handed muons because that's all it knows how to do. It doesn't know how to make right handed muons. It ignores right handed muons. It pretends they don't even exist. So coming from space, we're overwhelmed with left handed muons, which means that the cosmic rays all of a sudden are not symmetric. Right, so the environment we've involved in is not symmetric because of the weak force, and those left handed muons tend to interact with our dens slightly differently than right handed muons would.
Meaning that most of the mions that come down on Earth are left handed, not right handed exactly.
Those muons are left handed, and that creates a slight preference for left handed amino acids. We think that left handed muons have a slightly higher probability of ionizing left handed amino acids than right handed amino acids.
Wait, what, what Why is it that left handed muons interact mostly with left handed amino acids.
It's very subtle effect, but it's again because of the weak force. The weak force has this asymmetry and has very small effects on the chemistry of life. It can, for example, change the electric and magnetic dipole moments of some of these atoms inside these molecules, so their shape is like slightly different if they're left handed or right handed, which means that the muons passing through them are like more or less likely to interact with them because they spend like more or less time within that electric or magnetic atomic fields. It's a very subtle calculation.
Wait, are you saying that the left handed muons showering the Earth, coming down on Earth through our atmosphere are more likely to interact with a certain type of atom or a certain type of electron that you can only see on the left handed molecules.
Yeah, that's right. Left handed muons will interact with right handed or left handed amino acids, but they are more likely to interact with left handed amino acids than right handed, just by a little bit. It's not like a complete preference.
Why because a left handed amino acid is different than the right handed aminu acid, not because of any spin, it's just how the particles, the atoms are arranged. So why would the left handed muon, which is a tiny, tiny particle, care about the giant structure of a molecule.
Because when the muon is interacting with that atom, it's interacting not just with the electromagnetic force, but also with the weak force, because the muon feels the weak force, and so there is a difference between the left and right handed amino acids because of the weak force it affects the electric dipole moment and the magnetic dipole moments of these atoms, and so that affects how the left or right handed particles will interact with them.
Are you saying that like a left handed amino acid is made up of different atoms or different atoms with different spins than a right handed amino acid.
No, it's the same atoms, right, it's just flipped to be left handed, and so the arrangement is slightly different, and that gives a different pattern of the electromagnetic fields. And this is a very small effect, right, This is really a tiny effect. It's like second order. This effect is like three parts in twenty thousand. Right, Most of the time these things will be treated exactly the same, because most of the time it's the electromagnetic interaction that dominates, which is symmetric. But the weak force sometimes is a thing that mediates that interaction, and so it tends to prefer the left handed version of these amino acids. But again, just a tiny fraction of the time.
It seems to be like a totally different effect, like a left handed muon. It could have been that a left handed muon prefers to interact with a right handed molecule. Right, It's just that it just so happens that the molecules that left handed NEOs like to interact with a little bit more are the ones we call the left handed amino acids.
Yeah, that's right. Or in this paper they call them the live choice. And the paper they go through this very complicated calculation and they come out with this prediction. They say, we predict that there is a difference, and it has to do with the time the particle spends traversing the electromagnetic field and how the weak force interacts with it, and so they predict this very slight effect again, really really tiny effect. But the idea is that maybe over millions and billions of years, these cosmic rays introduced more ionization effects in our kind of chirality, and not in the evil the alternative kind of biochirality, which give us a boost, which let us explore these things faster, create more mutations and sort of like adapt more rapidly to changing conditions, And that may be over billions of years, led life to have this chirality instead of the opposite chirality because we get more mutations from left handed cosmic rays.
M I see I think it's all making sense now because there are many different kinds of amino acids right Like, I think maybe what this writer is saying is that there's lots of different kinds of amino acids, but the ones that are used by life right now, he wants to call those like A, and the ones the versions that are not used by us, he wants to call those B, and so he wants he's trying to say, or she's trying to say that left handed muons. Can you can prove that maybe that left handed muons somehow like to interact more with A kinds of amino acids than B kind of amino acids. They're saying that left and right for the meons and left and right for the molecules is confusing. Let's just call them what molecules A or B, A being the ones that life prefers seems to have preferred here on Earth, and then let's stick to left and right hand for the muons we're.
In the article they call A live and be evil. But yeah, we can go with A versus B.
Yeah, it sounds a little more benign.
I mean, if we do meet like humans from another place and they have the other handedness of their biochirality. You're not gonna let me call them evil humans.
No, because how do you know you're not the evil one? Maybe left handed humans are better than right handed humans.
I think I've just realized we're the baties, aren't we.
It's right, the enemy is us. We've met the enemy and it is us.
Yes, exactly. So that's the idea, and nobody knows if this effect is big enough to actually have an impact on life at all. There's a lot of dot dot dots here. It's like almost the same as Pasteur is saying, like maybe somehow the universe prefers one kind of kirality. This is a way that the universe does seem to prefer one side of a symmetric pair, and you can draw some dots between that and how it might have influenced life. It's not conclusive to say that this is definitely why life has this kirality.
But maybe the idea here is that the kinds of amino acids that flourish here on Earth flourish because they're more likely to be affected by left handed muons, which is what the universe prefers to make. And so in a way, the universe kind of preferred to make the a kind of amino acid, or the kind that led to.
Us, at least here on Earth. You know, in our Solar system, Earth is the only planet that has an atmosphere, which creates these muon showers that come all the way down to the Earth's surface. Muons don't last very long. They last for microseconds, but because they're going so fast, they actually do penetrate down to the Earth because their clocks are time dilated due to special relativity, so they tend to die off right around the Earth's surface. If the Earth's atmosphere was thicker, for example, they wouldn't make it all the way down to the ground.
Right, But that's just our Solar system. This preference for left handed muons is universal, right, It's basically a lot of the universe. And so if there are other planets like ours with an atmosphere, and if maybe the very existence of life depends on having that kind of atmosphere in that on it, the conditions may also prefer the a kind of amino acid that we're made out of. Because the universe prefers left handed muons, and so over there also the universe will prefer the A kind of amino acid.
Yeah, that's the hypothesis, right, not yet proven, but that's the idea that maybe this is the reason that we have the A kind of amino acid and not the B kind.
So you're saying we're less likely to meet evil twin versions of us out there, We're more likely to meet people who are just like us.
Yeah, maybe particle spin will make for happy reunions with aliens.
Yes, with non awkward handshakes.
Maybe we should just fist bump the aliens when they get here, just in case.
Yeah, that always works. I'm up for that. That way, you don't have to have that awkward question when you meet an alien. Hey, are you right handed or left handed? A fist bump? All right? Well, that's an interesting idea that maybe the universe does have a preference for the kind of life that we're made out of, and that we were maybe destined to be the way we are right now.
And maybe particle physics is actually relevant to our life and your life and all life in the universe.
We hope you enjoyed that. Thanks for joining us, See you next time.
Thanks for listening, and remember that Daniel and Jorge Explain the Universe is a production of iHeartRadio. For more podcasts from iHeartRadio, visit the iHeartRadio app, Apple Podcasts, or wherever you listen to your favorite shows. When you pop a piece of cheese into your mouth, you're probably not thinking about the environmental impact. But the people in the dairy industry are. That's why they're working hard every day to find new ways to reduce waste, conserve natural resources, and drive down greenhouse gas emissions. How is us dairy tackling greenhouse gases? Many farms use anaerobic digestors to turn the methane from manure into renewable energy that can power farms, towns, and electric cars. Visit you as dairy dot COM's Last Sustainability to learn more.
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We're just days away from our twenty twenty four iHeartRadio Music Festival, preceded by Capital One.
The biggest headliners in live music will be taking over to Mobile Arena.
Las Vegas lost some special surprises of moments you are not going to want to miss.
Stream only on Hulu.
Ihar Radio Music Festival.
And listen on iHeartRadio.
The most anticipated live music events of the
Year this Friday and Saturday, starting at ten thirty pm Eastern, seven thirty Pacific,
