Part 4! How did String Theory get started? What has made the idea so popular over the decades? Can we ever truly have a theory of quantum gravity? What is supersymmetry, the landscape, and the AdS/CFT Correspondence? What do holograms have to do with this? How many dimensions do we live in? Why does String Theory have such a hard time making predictions? How are we supposed to judge a theory that isn’t done yet? It’s a non-stop String Theory bonanza as I discuss these questions and more in today’s Ask a Spaceman!
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EPISODE TRANSCRIPTION (AUTO-GENERATED)
What is beauty? Well, that's a really lame way to start an episode because honestly, I'm the wrong guy to ask. Seriously, you ask me a beauty about beauty and I just start thinking about cheese. So instead, we're going to talk about something else, symmetry. Sometimes you hear that people say that symmetry is beautiful, but in math and physics, symmetry is powerful.
Almost all of modern physics, which is our deep understanding of the universe, relies on symmetry. But what is symmetry? I hinted at it in the last episode, and today we're gonna keep it as super broad as possible because the symmetries that we're going to explore are going to quickly go from obvious to arcane to just plain weird. And so the definition of symmetry that I'm gonna try to work with and we're gonna explore and that we're gonna use in math and physics is that when you change something about the situation and yet it stays the same. So if you change something but it still stays the same, that is symmetry.
For example, a symmetric face. Whether you look at the right side versus the left side of the face, you change something which side of the face you're looking at, but the face still looks the same if it's symmetric. Like, you're, it's been flipped, of course, because now you're looking at the left side versus the right, but the arrangement of the eyebrows, in the size of the nostril, in the angle of the nasolabial fold, they all look the same in a symmetric face, whether you're looking at the left or the right. There's a symmetry in that face, and you might or might not also consider that particular face beautiful, but that's none of my business, and it's not important. It's symmetric.
You change something left or right, but the face stayed the same. So how is symmetry important in physics? Well, we're a few episodes deep into our deep, deep, deep dive exploration of string theory, and we've covered two of the major threads of string theory. That pun just keeps on giving. We've looked at strings as the fundamental object of most extreme importance of the universe, as in stuff is made out of strings.
It's not made out of fields. It's not made out of curved space time. It's not made out of particles. It's made out of strings. That is thread number one, and thread number two is that, oh yeah, there are a lot more dimensions in our universe than we realize, but they're all curled up on themselves, so we never notice and really only the strings care.
And today we're going to look at the third thread of string theory, which is something called supersymmetry. Supersymmetry, which is like symmetry, but more so elevated string theory in the nineteen seventies. In our narration, in our story for the past few episodes, we've been focused a lot on the nineteen sixties, almost proto string theory, where it was just some clever mathematics to try to understand the nature of the strong nuclear force. And then last episode, we looked at the extra dimensions. We skipped ahead a little bit to find that the original string theory that had 26 dimensions was reduced to 10.
Now we're going back in time. Now it's gonna be back in the nineteen seventies, and supersymmetry elevated string theory from being just a theory of bosons of the strong nuclear force of the force carriers in general to something that could potentially explain all the forces and all the particles, all the bosons and all the fermions, and it did so by finding something, well, I don't know, beautiful, but at least symmetric. And searching for symmetry is a fine and different aspects and understandings of our world. We're gonna unify quantum mechanics with special relativity to quantum field theory. We're gonna unify the physics of our terrestrial experience with the physics of the heavens and get a universal gravity.
Guess what powers the process of unification? No points awarded for correctly guessing its symmetry. Symmetry is what fuels our unification engine. Think of Newton's work. To unify the gravity of the earth with the gravity in space, there is a symmetry there.
You change where you are in the universe, but gravity still acts like gravity. He found a symmetry. He was able to exploit that to create a unification. There are symmetries between electricity and magnetism. Right?
You can have a changing electric field, and that can create a magnetic field. And you can have a changing magnetic field, and that can create an electric field. And, actually, anything that you write down in terms of electric fields, you can end up writing down in terms of magnetic fields and vice versa. There is a symmetry there. You can change something, and yet it stays the same.
That powers a unification. General relativity identifies the symmetry that all physical laws should be the same regardless of speed, regardless of acceleration. There is this equivalence in our experiences that is a symmetry there that provides a unification. That's pretty awesome. There's a bunch of symmetries that we've used over the centuries, and we've learned a lot, and it's pretty fantastic.
We're all happy and proud of ourselves and patting ourselves on the back. But can we take it one step further and see if we can uncover any useful knowledge of the universe by examining how we move through it? Go with me here. Go with me here. Pretend you you have an experiment.
Doesn't matter what the experiment is. You're just trying to understand some aspect of physics. Just doesn't matter. And you run the experiment, you get your results. And then you turn off your machine and you wait a day.
You know, you go see a movie. You have a date. You go grocery shopping. You read a book. You should you do you.
And then you come back the next day and you run the exact same experiment and you get the same result. The fact that physics, fundamental physics, stays the same day to day is a symmetry. Yes, I know there are some things that are different. Oh, the weather, the temperature is different. Oh, oh, oh, the now the moon is in a different position at the on the sky.
Okay. That's different, but there are some things that stay the same day today. The fundamental phase, gravity is exactly the same yesterday as it was today. If you have the exact same earth, exact same sub, you just wait a couple days, you have the exact same experiment. Right?
You turn on a light bulb or you you shoot a laser and then you turn it off and you wait a couple days and you turn it back on. You assuming the thing that generates the laser is the same, but you get the exact same laser because the physics of lasers doesn't change day to day. The physics of gravity doesn't change day to day. There's a symmetry there. You change something, your time, when you do it and it hasn't changed.
This symmetry leads to conservation of energy. Yeah. The fact that energy is conserved is a consequence of the symmetry of physics with respect to time. This link is provided by an incredibly powerful mathematical theorem known as Noether's theorem or Noether's theorem. It's one of the most amazing, insightful, and, dare I say, beautiful results of modern physics, and it's right there.
Where you have a symmetry, you have a unification, you have a conservation law. The conservation of energy unifies the concept of energy, of kinetic energy, potential energy, chemical, all the kinds of energy under one roof, and it can do that because of the symmetry. And you can find another symmetry if you take your experiment, and it's a experiment on fundamental physics. And then you decide you don't like where it is, so you move it to the opposite end of the table, and you get the exact same result. Congratulations.
You found another symmetry. The fundamental laws of physics don't care about where you are in the universe. This was Einstein's whole thing. He applied it to gravity and gave us general relativity. You can apply this exact same kind of symmetry, and you get conservation of momentum.
The fact that momentum is conserved, that momentum, the total amount of momentum must stay the same is a consequence through some very cool math of the fact that there's a symmetry. Same thing if you take an experiment, pick it up, and rotate it. You change the angle of your experiment, you get conservation of angular momentum. So we've got waiting, moving through time. We've got moving through space, and we've got changing the angle.
Are there any other ways to move in space and time? Yes. I mean, there's there's spin. The concept of spin is a little bit different than the concept of rotation. Like, the Earth rotates around the sun, and it doesn't matter the time of year, and we could still do the same experiment, and that's conservation of angular momentum.
But the Earth is also spinning. But we don't care about just any old spin here. We care about quantum spin. Why? Because we have to.
Because we're trying to build a theory of quantum reality, and so you need to care about quantum spin. And quantum spin is you know, I did a whole episode on it. It's a lot like spin, but it's also quantum and also not a lot like spin at all. Feel free to listen to that episode again. Spin is one of the toughest concepts in quantum mechanics to explain, and that's saying something because basically every concept in quantum mechanics is hard to explain.
And that's because there's hardly ever anything in quantum mechanics that connects to our experiences in the everyday world. It's just a bunch of really hard math that gets the job done without anybody ever understanding why, and you can't just point to some like, hey, you know, when you see this thing, quantum mechanics is like that just smaller. No. It's it's totally different. Quantum mechanic rules are just different rules.
Seriously, just watch someone start explaining quantum mechanics, including me, and they just wave their hands around every single time. You're like, well, wave particle duality and quantum spin, and then you just start moving your hands because you're like, I really can't explain this. No one can because it's just a bunch of math. But anyway, spin, quantum spin. Quantum spin is vitally important because without quantum spin, we wouldn't have Patreon.
Go to patreon.com/pmsutter to keep these episodes going. I greatly, greatly appreciate all the generous contributions every single month. This is my job, and I really appreciate it. And we wouldn't have it without quantum spin. I checked.
Let's let's decompose quantum spin a little bit because it's gonna play a big role. We've we've looked at the symmetries of nature, the symmetries in time and place and angle. Let's see if there's any symmetries associated with the concept of spin. Because we got all these cool unifications. Is there any other unification that we can do?
We got these unifications because we saw all these symmetries. Like, If I change something, like, when I do an experiment, where I do an experiment, I get the exact same result. There is a symmetry there. That symmetry leads to unification, leads to very powerful physics. What about spin?
Imagine a ball. Make it out of metal. Make it have an electric charge. Make it spin really fast. Shrink it down.
Do you have quantum spin? Almost, but not quite. This is what makes it so tough. An electron has spin. Also, an electron has no spatial extent.
Let me repeat that. An electron, fundamental particle, you know, excitation of the field, if that's how you wanna feel about it today, has spin. In some sense, it acts like a tiny spinning metal electrically charged ball, And yet, an electron has no spatial extent. It doesn't take up any volume. How can you have an object that doesn't have volume have spin?
Welcome to quantum mechanics, folks, where nothing makes sense and everything's on the table. And if you're confused, well, then too bad because nature doesn't care. Electrons don't have any spatial extent and that they have spin, and yet they act like little charged metal balls. And we're just gonna live with it because it's a quantum thing, and that's what we have to do. In quantum mechanics being quantum mechanics, an electron can't have any old spin at once.
Like, if you have your big metal ball, you can spin it a little bit. You can spin it medium. You can spin it a lot. You can do all sorts of things. The electron doesn't get that flexibility.
An electron isn't like you and me that can just frolic in the meadows and spin in the sunshine. No. An electron is two in exactly two choices of spin. For various mathematical reasons that make sense, but also don't make sense because that's life, we call these two choices plus one half and minus one half. In other words, the electron has a total strength of spin, a total spin amount of a half, and we just called it a half for reasons.
But it can be in one of two directions when we go to measure it. So it can be spinning this certain amount up or spinning a certain amount down, and that's basically it. That's his only choices. But once we have this spin half, it responds to magnetic fields the same way a spinning metal ball would respond to a magnetic field with that amount of of charge, and that's, you know, in in everything. So quantum spin is a lot like normal spin, except it isn't, and it's very weird.
And there's nothing I can do about the weirdness, and we all just have to live with it. If you start getting a headache about quantum spin, it's okay. Just relax, drink some water. And instead, let's instead of trying to build metaphors and trying to explain it, let's just call it a property of fundamental particles that was only discovered one hundred years ago, and we hurriedly attached some names to it before we really understood it. And frankly, we still don't fully understand it, so we're just going to keep our chins up and keep going.
Quantum spin, it's a property. All particles have quantum spin. Every single particle point at a particle, it has quantum spin, but they come in two families. There's two families of spin. There's the family Bosie with spin zero, one, two, or three, like, no spin at all, and then one whole spin, two, twice that, three times that, four times that.
And then there's the family Fermi. These guys have spins, one half, three halves, five halves. They sit in between. Like, our electron belongs to family Fermi because it has spin one half. That's how much spin it has, and that's the only amount of spin it can ever have.
It's like its mass. Like, an electron just has a certain amount of mass, and it has a certain amount of spin, and that's it. And there's no debating it, mister. Family boson are more properly called the bosons, and these are the carriers of the forces. Like, the photon carries the electromagnetic forces, the boson.
The gluon carries the strong nuclear force. It's like its grandma. It's in the same family. And the z boson is the carrier of the weak nuclear force, and that's the photon's older brother. Like, they're all related.
They all carry forces. They all have similar kinds of jobs. You know, they look different. Like, members of family look different, but you can tell they're all related. Family Fermi are more properly called the fermions, and these are the building blocks.
These are the things you're made of. Like, an electron is a fermion, and the top quark is its great ant, and the neutrino is its weirdo cousin that nobody talks to. They all look different. They all behave a little bit differently like members of family do, but you can still tell they're related. And so the universe is made of two separate families.
The particles in each family are related to each other by sharing the same kind of spin. For the nerdily inclined, we call these whole integer or half integer spins. So family Bosey is whole integer, zeros, ones, twos, threes, and family Fermi's are the particles with half integer spins. But the two families aren't related to each other. They are incredibly different.
Like, the forest carriers are radically different than the building blocks. Think about it. You've got quarks and electrons and neutrinos. They do things, and they they interact and they and they just live life to the fullest, and then the force carriers are just constantly going back and forth, going back and forth. Some are even completely massless, and they can extend out to infinity.
It's just the bosons and the fermions are just radically radically different. You can pack as many bosons into a box as you want, but you can only pack so many fermions into a box. They they operate under different rules. And so when we look out at the universe, the Bose family and the Fermi family are not related unless they are. You see that the property of spin, especially quantum spin, allows a new kind of symmetry.
I emphasize allows because it doesn't require that symmetry. It doesn't doesn't mandate it. It doesn't there's no law. There's no rule. It simply permits a new kind of symmetry.
And where we see symmetries, we see unifications. We have symmetries established for all the other ways of moving through space time, for waiting a while, for changing locations, for changing direction, and spinning, even quantum spinning counts as a way of moving through space time. And even though it's only in an esoteric hard to understand quantum mechanical sense, it still counts. Okay? The mathematics allow a new kind of symmetry.
So maybe there's a symmetry associated with spin, which would mean where we see symmetries, we see unification. It means that the two great families, the bosons and the fermions, might actually be related. They might belong to the same family. How closely are they related? We don't know.
Maybe they're first cousins. Maybe they're only distant cousins. Maybe they're siblings. This new kind of potential symmetry, since it was a surprise bonus symmetry that we didn't discover until the seventies, and the seventies was a really funky time, this kind of symmetry got a new name. It was called supersymmetry.
It's like symmetry but awesome, and it has to do with quantum spin. If the universe has supersymmetry, remember this, just because we're allowed to have it doesn't mean we have to have it. But if this supersymmetry actually exists, it means that the Bose family is related to the Fermi family and it means that there's a single overarching description. Imagine a giant family tree that connects them, like the Bose family is over here all tightly knit and the Fermi family is over here all tightly knit, but you can point like, oh, there's some great great grandma that connects these two families. That's true if we live in a supersymmetric universe.
And remember that symmetries have to look the same if you change something, like left versus right on a symmetric face. You change your point of view, but you get the same arrangement of face. Here in on Earth versus up in space, you change where you are, but gravity stays the same. Now versus tomorrow has to stay the same. With sprinkles or without sprinkles, it still has to taste the same.
This is my own theory known as sprinkle symmetry, and I'm still working on it. And in supersymmetry, each fermion gets paired up with a boson. They become reflections of each other in a weird quantum mechanical mirror. It's all just a bunch of math here, folks. I'm trying to paint a picture.
Because, like, the bosons and the fermions look totally different, but supersymmetry would say, no. No. No. No. No.
You're just not looking at them in the right way. If you look at it through a particular lens, through this supersymmetry lens, you can see how there's a connection there. How's there the symmetry there? How you're really looking at the same thing but just in different ways. What does this have to do with string theory?
Well this is the third thread. Remember in the nineteen sixties string theory was just a theory of bosons and especially just the strong nuclear force. Even with extensions to electromagnetism or the weak nuclear force, it only applied to the Bose family. It was only a description of that side of the family. But by applying supersymmetry and folding that into string theory, it allows string theory to also describe the Fermi family without having to change the language of strings.
This makes string theory potentially incredibly powerful. With one way of describing subatomic physics, which is vibrating strings in tiny curled up extra dimensions, you can potentially describe all the things in the universe in ultimate unification. You're not just talking about the force carriers and you're not just talking about the building blocks. You're talking about everything with one single framework. That seems pretty awesome.
Right? It means if you look at an electron, you're really looking at a string. If you look at a photon, you're looking at a different string. If two electrons bounce off of each other, it's two strings bouncing off of each other. The light pouring into your eyeballs right now, strings, nuclear fusion, strings, doing string things, strings, strings, strings, everything strings.
And supersymmetry is the key to unlocking that because it provides the connection between fermions and bosons. This approach called supersymmetry was actually started by string theorists in the early nineteen seventies. Other theorists, non stringy theorists, started playing around with the idea because it's a pretty awesome idea, and it's pretty generic. Like, it's just talking about fermions and bosons. And so they were able to fold it into regular or non string physics.
So nowadays, basically, every high energy physicist, every theoretical physicist knows about supersymmetry and in some level cares about supersymmetry because it's simply a part of the way we're understanding physics, whether it's string theory or anything else, it's all based on supersymmetry. Well, at least I should say we all want supersymmetry to be true. Why? Well, be one, it's awesome because it gives a single unifying framework for both fermions and bosons. And, also, it's important because it turns string theory into super string theory.
Not making this up. Technically, every time I say string theory, I should be calling it superstring theory, but I kinda refuse to do that on stand standards of principle. So it's just gonna stay as string theory, but it also potentially solves some problems in the standard model. Our standard model of particle physics physics has the three forces of nature, electromagnetism, strong nuclear, weak nuclear. It has these families of particles like the fermions, the electrons and neutrinos and quarks and all that, and it describes all the relationships between those with quantum field theory.
There are some problems in the standard model. The biggest one, which I've mentioned already, is the hierarchy problem. Gravity is way weak. Why is it so weak? Why is it so much weaker than the next weakest force which is called weak nuclear?
I mean, come on. Gravity is weaker than the force that literally has the word weak in its name. So how weak is that? Come on, gravity. For various reasons that I won't dig into, the strength of the weak nuclear force is controlled by the mass of the Higgs boson.
Okay. I will dig into it a little bit. You remember unification? I hope so. I've only said it 87 times in this episode.
We have electromagnetism as one of the forces of nature, and we have weak nuclear force as one of the forces of nature. Each one is described by its own individual symmetry. There's a symmetry that describes electromagnetism, and there's a symmetry that describes weak nuclear force. You can combine these symmetries together to get one larger symmetry, and we find that these two forces are actually different aspects of the same thing, something we call the electroweak force. The electroweak force only shows up at very high energies, but it's there.
At low energies, like normal everyday energies, electromagnetism and weak nuclear look totally different. The Higgs boson, this other particle field that's floating around the universe, does the work of breaking that symmetry. So at high energies and high temperatures, this symmetry appears and it's manifest and it's right there and you can look at it inside of a particle collider. But once you cool things down, this symmetry goes away and electromagnetism looks very, very different than weak nuclear. The Higgs boson is the thing that does the job of breaking the symmetry at low energies between electromagnetism and the weak nuclear force.
It's like at high energies when things are really hot and intense, electromagnetism and weak nuclear are best friends. But then as things start to cool off, the Higgs comes in and starts an argument that tears them apart. Like, which is better, Star Trek or Star Wars? And immediately, like, like, they never talk to each other again. But when things are hot, like, they can put aside their differences and party together, but Higgs boson's always waiting right there to, like, poke a stick or throw a rock and get them to start fighting again.
Anyway, very rough estimates in the standard model say that the Higgs should have a huge mass, like a gigantic mass. That's because the Higgs just talks to everybody. You know, imagine the Higgs walking into a crowded room at a party, and everyone just wants to say something. The neutrinos wanna come talk to it. The electrons wanna come talk to it.
The the top quark and the bottom quark wanna, you know, talk to everyone wants to talk to Higgs, and so Higgs can't go anywhere, can't get to the cheese display, can't get to the chocolate fountain. It's like the Higgs has this huge amount of mass or we predict it in very rough estimates or naive estimates that the Higgs has this huge mass because everybody loves the Higgs, and it just can't go anywhere. In the mathematics of our standard model, we have to do some real shady, tricky finagling to bring the mass of the Higgs down to what we actually measure it to be. We have to be like, okay. Okay.
Like, the electrons come and talk to it, but then positrons actually come up behind the Higgs and push it along so it can get to the buffet table. Oh, but but but then the top quark comes over here and it starts bugging the Higgs, but then the bottom quark or the charm quark comes in and nudges it along and, like, keeps it moving towards the buffet line. And so we but we we just have to come up with all these weird finaglings to, like, bring the mass of the Higgs down, and that seems weird. And this because the Higgs boson and is responsible for splitting the weak nuclear away from the electromagnetic force, The mass of the Higgs boson determines how strong the weak nuclear force is. And if we can understand why the weak nuclear force has the strength it does, maybe we can understand why gravity has the strength it does, why they're so different.
We think it might have something to do with the Higgs. We don't know. Another possibility is the large extra dimensions that I mentioned, last episode last episode, but maybe it's this. Maybe there's something else. Supersymmetry can potentially fix this problem with the fine tuning of the Higgs mass.
Because if the Fermi family and the Bose family are really related, then we can find ways for them to talk slightly differently to the Higgs that perfectly cancels out and leads to its small mass. Like, then the Higgs comes into the room, and still everyone wants to talk to the Higgs, but through supersymmetry, they just get just do a quick, like, hi, a little thumbs up, a little wave from across the room, and Higgs can go straight to the cheese and the chocolate fountain. I'm not saying the Higgs is gonna combine chocolate and cheese on the same plate. That's that's the Higgs choice, not mine. But supersymmetry can possibly do this.
So instead of everyone swamping the Higgs, they they give Higgs some space. And so that's why supersymmetry is really interesting because it can potentially solve some problems in the standard model. It was invented by string theorists for string theorists to allow them to use strings to explain all this stuff, but it turns out it has some really potentially very powerful applications in standard model physics, maybe. You see, supersymmetry isn't a single theory. It's a collection of theories all under the same general theme.
In supersymmetry, we have to ask what is the symmetry? What what is that if we look at electron and then we look at it in some weird mirror, what is its partner? In supersymmetry, each partner each particle is paired with a, are you ready for this, a superpartner that has the exact same mass and the exact same charge, but the spin is switched from, like, one half to a half. So for example, the superpartner of the electron is a particle with the exact same mass of the electron, the exact same charge of the electron, but spin one instead of spin half. But there's nothing around that looks like an electron with spin one.
There are no bosons out there with the mass of the electron, the charge of the electron, and spin one. They just don't exist. So if the whole point of this game is to say, oh, fermions and bosons are really the same thing in this mathematical quantum mirror, you should be able to find a match for everyone because that's what mirrors do. Right? That's what symmetries do.
You have to change something, but then everything else stays the same. Like, if I change the spin, I should be able to keep everything else the same, but that doesn't happen. So what we think is going on with supersymmetry is that this is a broken symmetry, exactly the same way that the symmetry, the unification between the weak nuclear force and electromagnetism is broken at low energies, but at high energies, that's when it can come into play. That's when you know, at high energies, electromagnetism and weak nuclear are on are on the exact same footing. But at low energies, this breaks.
The mirror it's like just punching the mirror. It breaks that symmetry. So we think with supersymmetry, because there's no obvious superpartners for the particles, that this only appears at high energies. When you turn up the heat in a particle collider, the superpartner should appear. You should see in a particle collider if supersymmetry is correct.
If you have an electron and you're looking for its superpartner, you should see a particle with the mass of the electron, the charge of the electron, but with a different spin. Same for every single particle. It's like if we have these two different families, the Bose family and the Fermi family, we should be able to make pairs. But we can't with our known particles. Like, no one pairs up with a photon.
No one pairs up with a top quark. So we think that there are more particles out there in the families that we haven't found yet. There are more relatives. There are more cousins. There are more great aunts that we haven't found yet that do serve as the partners, but this only happens at high energies.
In our normal everyday world, the partners are just gone. The breaking of the supersymmetry and low energies makes these super partners very, very heavy. That's the consequence of the breaking. They make them so heavy that they're super rare, so we never see them around. It's like the members of the family, like members of your family that only show up for the funerals.
At low energies, everyday energies, they're just not around. We can't see them. Their mass is too high. But then, hey. If there's a funeral, if there's a really, you know, very powerful event, a very high energy event, yeah, yeah, they'll show up.
They'll see them. And then that's how we'll find the links between the Bose family and the Fermi family. These super partner particles have awesome slash horrible names. Every particle, for example, is paired with a sparticle. And for some reason, that word just really makes me shudder.
I can't I can't explain it. An electron has a superpartner that's called the selectron. The leptons in general have partners, superpartners called the sleptons. The top quark has a partner called the Stop quark. The neutrino has a partner called the Snutrino.
It's like we're trying to find these links between the Bose family and the Fermi family. They're not obvious. They're not there. They weren't just right there, which means this symmetry is broken at low energies. It only appears at high energies.
So at high energies, some of these extra particles should part start to appear, and then we can draw the links. Okay. There's an electron in the Fermi family. We can connect it to a selectron in the Bosie family. There's a top quark in the Fermi family.
We compare it to the stop quark in the Bosie family, and it goes in the opposite direction. For the members of the Bose family like the photon, they have a partner in the Fermi family. For the photon, it's called the photino, and for the gluon, it's called the gluino. My all time favorites for the pairing of the superpartners, the particles, the up quark. Its superpartner particle is called the sub quark, and that there's a joke in there somewhere.
Feel free to write it for me and put it on social media. And, yeah, nothing beats the w boson. The superpartner of the w boson is the we know boson. Moving on. Wow.
Okay. These superpartner particles don't exist in our everyday world because the symmetry that connects them to the particles of our everyday world is broken at low energies. We can only see it at high energies. So we need to run big giant particle collider experiments to make these particles show up. How heavy are these particles?
Well, different supersymmetric models give different answers. But no matter what, supersymmetry is a big deal because, a, it solves some problems in the standard model like the hierarchy problem, and, b, it makes string theory even better than we thought. Once string supersymmetry is added to string theory, you get three things. One, the fermions are included as strings. So just strings explain all the features of our universe, which is pretty cool.
Two, remember a few episodes ago where I talked about how the early string theories in the nineteen sixties had these things called tachyons? They predicted the existence of these massless particles that traveled faster than the speed of light, which is impossible. Well, for various complicated mathematical reasons that we will not dig into and you will thank me very much, once you introduce supersymmetry, the tachyons disappear. And, also, for various complicated mathematical reasons, the number of dimensions that you need for string theory to work drops from 26 to 10. So even though string theory failed to explain the strong nuclear force and was thought to be a dud, folks continued working on it and found some surprising features.
And remember that string theory is touted as being a theory of everything, able to unify all the forces of nature particles of nature, all the building blocks in a single description. But keep in mind, in the early 1970s when this supersymmetry thing was really getting going, all this work that I've talked about, everything that I've talked about so far in the past few episodes, the strings, the higher dimensions, supersymmetry, the whole lot was done before it was realized that string theory could also explain gravity. At the time, string theory was just being used to explain three forces in nature and the particles and the building blocks, the fermions. We didn't know yet that string theory could also explain gravity. I'm not kidding.
One of the biggest parts of string theory, like, the key thing in string theory wasn't even realized until the mid-nineteen seventies, which is exactly where we'll pick up next time. Thank you so much for listening. I'd like to thank my top Patreon contributors this month because you really are helping me keep this show on the air. Matthew k, Justin z, Justin g, Kevin o, Duncan m, Corey d, Barbara k, Nudadoo, Chris c, Robert m, Nate h, Andrew f, Chris l, John, Cameron l, Nalia, and Aaron s. You can go to patreon.com/pmsudder to learn how you can contribute.
And, of course, all the people that asked string theory questions over the years, including, but probably not limited to, John c on email, Zachary h on email, at edit verm on Twitter, Matthew y on email, Christopher l on Facebook, Firm w on YouTube, Sayan p on YouTube, Niha s on Facebook, Zachary h on email, Joyce s on email, Mauricio m on email, at Schreinik Schra on Twitter. Panos t on YouTube, Dhruv r on YouTube, Maria a on email, Terb on email, Oi Snowy on YouTube, Evan t on Patreon, Dan m on Patreon. Someone unknown on my website, John t on Facebook, at t w blanchard on Twitter, Ari on email, Chris m on email, at unplugged wire on Twitter, Giacomo s on Facebook, and Gully Foyle on YouTube. Wow. Lots of curious people.
I love it. If you're curious about something about the way the universe works, shoot me an email at askaspaceman@gmail.com. Follow me. I'm at paulmat center on social media. Go to askaspaceman.com.
Keep up reviewing on iTunes. I really appreciate it. Keep telling people we are making our way. We are about at the halfway point in our journey to finally evaluate string theory and decide if it's worth keeping alive. And I will see you next time for more complete knowledge of time and space.