What is the true nature of the universe? To answer this question, humans come up with stories to describe the world. We test our stories and learn what to keep and what to throw away. But the more we learn, the more complicated and weird our stories become. Some of them so much so that it's really hard to know what they're actually about. Like String Theory. A famous, controversial and often misunderstood story about the nature of everything. Why did we come up with it? And is it correct or just an idea we should chuck out? To understand the true nature of reality, we looked at things up close and were amazed. Wondrous landscapes in the dust, zoos of bizarre creatures, complex protein robots. All of them made from structures of molecules made up of countless even smaller things, atoms. We thought they were the final layer of reality until we smashed them together really hard and discovered things that can't be divided anymore. Elementary particles. But now we had a problem. They're so small that we could no longer look at them. Think about it. What is seeing? To see something, we need light, an electromagnetic wave. This wave hits the surface of the thing and gets reflected back from it into your eye. The wave carries information from the object that your brain uses to create an image. So you can't see something without somehow interacting with it. Seeing is touching, an active process, not a passive one. This is not a problem with most things. But particles are very, very, very small. So small that the electromagnetic waves we use to see are too big to touch them. Visible light just passes over them. We can try to solve this by creating electromagnetic waves with more and much smaller wavelengths. But in quantum physics, shorter wavelengths means more energy. So when we touch a particle with a wave that has a lot of energy, it gets a kick. By looking at a particle, we change it. In quantum physics, we cannot know where a particle is and where it's going with absolute precision. This fact is so important that it has a name, the Heisenberg Uncertainty Principle, the basis of all quantum physics. So what does a particle look like then? What is its nature? We don't know. If we look really hard, we can see a blurry sphere of influence, but not the particles themselves. We just know they exist. But if that's the case, how can we do any science with them? We did what humans do and invented a new story, a mathematical fiction. The story of the point particle. We decided that we would pretend that a particle is a point in space. Any electron is a point with a certain electric charge and a certain mass, all indistinguishable from each other. This way, physicists could define them and calculate all of their interactions. This can be made precise in quantum field theory and this solved a lot of problems. All of the standard model of particle physics is built on it and it predicts lots of things very well. Some quantum properties of the electron, for example, have been tested and are accurate up to 0.000000000002%. So while particles are not really points, by treating them as if they were, we get a pretty good picture of the universe. Not only did this idea advance science, it also led to a lot of real world technology we use every day. But there's a huge problem: gravity. In quantum mechanics, all physical forces are carried by certain particles. But according to Einstein's general relativity, gravity is not a force like the others in the universe. If the universe is a play, particles are the actors, but gravity is the stage. To put it simply, gravity is a theory of geometry, the geometry of spacetime itself, of distances which we need to describe with absolute precision. But since there is no way to precisely measure things in the quantum world, our story of gravity doesn't work with our story of quantum physics. When physicists tried to add gravity to the story by inventing a new particle, their mathematics broke down. And this is a big problem. If we could marry gravity to quantum physics and the standard model, we would have the theory of everything. So very smart people came up with a new story. They asked, what is more complex than a point? A line, or a string. String theory was born. What makes String Theory so elegant is that it describes many different elementary particles as different modes of vibration of the string. Just like a violin string vibrating differently can give you a lot of different notes, a string can give you different particles. Most importantly, this includes gravity. String theory promised to unify all fundamental forces of the universe. This caused enormous excitement and hype. String theory quickly graduated to a possible theory of everything. Unfortunately, string theory comes with a lot of strings attached. Much of the maths involving a consistent string theory does not work in our universe with its three spatial and one temporal dimensions. String theory requires 10 dimensions to work out. So string theorists did calculations in model universes and then tried to get rid of the six additional dimensions and describe our own universe. But so far, nobody has succeeded and no prediction of string theory has been proven in an experiment. So string theory did not reveal the nature of our universe. One could argue that in this case, string theory really isn't useful at all. Science is all about experiments and predictions. If we can't do those, why should we bother with strings? It really is all about how we use it. Physics is based on maths. 2 + 2 makes 4. This is true no matter how you feel about it. And the maths in string theory does work out. That's why string theory is still useful. Imagine that you want to build a cruise ship, but you only have blueprints for a small rowing boat. There are plenty of differences, the engine, the materials, the scale. But both things are fundamentally the same, things that float. So by studying the rowing boat blueprints, you might still learn something about how to build a cruise ship eventually. With string theory, we can try to answer some questions about quantum gravity that have been puzzling physicists for decades, such as how black holes work or the information paradox. String theory may point us in the right direction. When used in this spirit, string theory becomes a precious tool for theoretical physicists and helps them discover new aspects of the quantum world and some beautiful mathematics. So maybe the story of string theory is not the theory of everything. But just like the story of the point particle, it may be an extremely useful story. We don't yet know what the true nature of reality is, but we'll keep coming up with stories to try and find out until one day, hopefully, we do know.
A crumpled paper bag labeled 'UNIVERSE STUFF' sits on a blue background. It opens, and a stylized depiction of outer space, filled with colorful galaxies and stars, pours out.
"What is the true nature of the universe?"
Setting: abstract animated space — bright, even
Text: "UNIVERSE STUFF"
A stylized turtle walks from left to right. Its shell is open, revealing a miniature landscape with purple mountains, a small village, and a starry night sky inside.
"To answer this question, humans come up with stories to describe the world."
Setting: abstract animated space — bright, even
Three cartoon birds interact with a model of the solar system. In the background, a green chalkboard is filled with complex physics equations and diagrams.
"But the more we learn, the more complicated and weird our stories become."
Setting: abstract classroom — bright, even
The words 'STRING THEORY' appear in glowing pink letters on a dark purple background with small star-like crosses. Squiggly lines animate around the text.
"Like String Theory."
Setting: title card — glowing from text
Text: "STRING THEORY"
A stylized ghost trap-like machine appears, sucks in the words 'STRING THEORY' with a bright flash, and then sits on the dark purple background.
"And is it correct or just an idea we should chuck out?"
Setting: abstract space — internal glow from machine
The Kurzgesagt intro sequence plays, showing a planet Earth in space. The text 'KURZGESAGT - IN A NUTSHELL -' appears below it.
Setting: outer space — soft glow around the planet
Text: "KURZGESAGT", "- IN A NUTSHELL -"
A cartoon man with purple hair looks through a magnifying glass at a collection of objects. The view through the lens transitions to a microscopic, crystalline landscape.
"To understand the true nature of reality, we looked at things up close and were amazed. Wondrous landscapes in the dust,"
Setting: abstract table — bright, even
People (1):
• leaning over a table, wearing white shirt, bald with purple hair on sides hair — curious expression
The view transitions from complex protein robots to colorful molecular structures, then zooms out to show a field of stylized atoms with electrons orbiting a central nucleus.
"All of them made from structures of molecules made up of countless even smaller things, atoms."
Setting: subatomic space — glowing from atoms
Two atoms collide with a bright flash. The flash clears to reveal three fundamental shapes: a yellow sphere, a pink teardrop, and a blue cube, representing elementary particles.
"We thought they were the final layer of reality until we smashed them together really hard and discovered things that can't be divided anymore. Elementary particles."
Setting: abstract subatomic space — soft, ambient
The cartoon man from before lowers his magnifying glass, looking confused and shrugging. The view through his eye closes like an aperture.
"But now we had a problem. They're so small that we could no longer look at them."
Setting: abstract table — bright, even
People (1):
• sitting at a table, wearing white shirt, bald with purple hair on sides hair — confused, furrowed brow
A pink electromagnetic wave travels from left to right, bounces off a blue bird, and enters a stylized eye. The view then shows a cross-section of a head, with the wave traveling through the eye to the brain.
"To see something, we need light, an electromagnetic wave. This wave hits the surface of the thing and gets reflected back from it into your eye."
Setting: abstract diagrammatic space — bright, then internal glows
A split screen shows a stylized eye on the left and a blue bird on the right. A wave connects them. The screen then shows the cartoon man reaching out and petting the bird, which looks annoyed.
"So you can't see something without somehow interacting with it. Seeing is touching, an active process, not a passive one."
Setting: abstract space — bright, even
People (1):
• leaning forward, wearing white shirt, bald with purple hair on sides hair — smiling
A four-panel grid shows various objects of different scales: chromosomes, a virus, a tardigrade, and an elephant. A magnifying glass circle focuses on the center, revealing a small blue cube particle.
"This is not a problem with most things. But particles are very, very, very small."
Setting: abstract grid — bright, even
A long, slow pink wave travels across a dark purple background where several small blue and yellow particles are floating. The wave is too large and passes over and under the particles without interacting with them.
"So small that the electromagnetic waves we use to see are too big to touch them. Visible light just passes over them."
Setting: abstract subatomic space — soft, ambient
A pink wave with a much shorter, more compressed wavelength travels between two cartoon birds. The birds appear to be in pain from the high frequency.
"We can try to solve this by creating electromagnetic waves with more and much smaller wavelengths."
Setting: abstract space — glowing from wave
A high-energy wave beam shoots across a complex, circuit-like structure, hitting a particle and sending it flying. The view is through a stylized mechanical eye.
"But in quantum physics, shorter wavelengths means more energy. So when we touch a particle with a wave that has a lot of energy, it gets a kick."
Setting: inside a particle detector — glowing from beam and circuits
The text 'HEISENBERG UNCERTAINTY PRINCIPLE' forms on a dark purple background with colorful animated shapes and symbols floating around.
"By looking at a particle, we change it. In quantum physics, we cannot know where a particle is and where it's going with absolute precision."
Setting: title card — glowing from text
Text: "HEISENBERG UNCERTAINTY PRINCIPLE"
A black duck professor with glasses and a red sweater vest looks at a floating yellow sphere particle, which then has other particles (pink drop, blue cube) appear next to it. Lines and question marks appear, analyzing them.
"So what does a particle look like then? What is its nature?"
Setting: abstract space — soft, ambient
A yellow sphere particle dissolves into a blurry, cloud-like collection of blue and white circles, representing a probability cloud or sphere of influence.
"If we look really hard, we can see a blurry sphere of influence, but not the particles themselves."
Setting: quantum space — internal glow
The duck professor stands in front of a green chalkboard filled with equations. He wipes part of it clean with a cloth.
"But if that's the case, how can we do any science with them? We did what humans do and invented a new story, a mathematical fiction."
Setting: abstract classroom — bright, even
A 3D XYZ coordinate system appears. A small blue dot at the origin is highlighted, and a pink line traces its coordinates (x,y,z) to a point in space.
"The story of the point particle. We decided that we would pretend that a particle is a point in space."
Setting: abstract mathematical space — bright, clear
Text: "(x,y,z)"
The blurry blue sphere of influence from before appears, but now a distinct pink 'X' marks the point particle within it. The sphere then interacts with another object, represented by a yellow sphere opening up.
"This way, physicists could define them and calculate all of their interactions. This can be made precise in quantum field theory and this solved a lot of problems."
Setting: quantum space — soft, internal glows
A chart appears with three columns labeled 'Quarks', 'Leptons', and 'Bosons', each containing various stylized particle shapes.
"All of the standard model of particle physics is built on it and it predicts lots of things very well."
Setting: informational graphic — bright, even
Text: "Quarks", "Leptons", "Bosons"
The number '0.000000000002%' is displayed in large, glowing blue digits on a dark purple background.
"Some quantum properties of the electron, for example, have been tested and are accurate up to 0.000000000002%."
Setting: informational graphic — glowing from text
Text: "accurate up to", "0.000000000002%"
A three-panel split screen shows applications of quantum physics: 'Quantum Solvents', 'Hadron Therapy', and 'Maglev Trains'.
"Not only did this idea advance science, it also led to a lot of real world technology we use every day."
Setting: montage of applications — varied per panel
Text: "Quantum Solvents", "Hadron Therapy", "Maglev Trains"
A black duck is sleeping under a purple tree. A red apple falls from the tree and hits the duck on the head, waking it up with an annoyed expression.
"But there's a huge problem: gravity."
Setting: under a tree — bright, even
Three columns show the 'Weak Force', 'Electromagnetic Force', and 'Strong Force'. Below each, the corresponding force-carrying particles (W/Z Boson, Photon, Gluon) are illustrated.
"In quantum mechanics, all physical forces are carried by certain particles."
Setting: informational graphic — glowing from illustrations
Text: "Weak Force", "Electromagnetic Force", "Strong Force"
On a purple stage with red curtains, a blue pyramid particle looks sad while a pink teardrop particle dances. A yellow donut particle with wings flies down from above. The stage floor is then shown to be a green grid representing spacetime.
"If the universe is a play, particles are the actors, but gravity is the stage."
Setting: a theater stage — spotlight on stage
A green grid representing spacetime is shown. A pink line labeled 'AB' is drawn between two points, but the grid begins to warp and distort, making the distance measurement unstable.
"To put it simply, gravity is a theory of geometry, the geometry of spacetime itself, of distances which we need to describe with absolute precision."
Setting: abstract geometric space — glowing from grid
A pink bird representing physicists tries to add a green geometric shape (the graviton) to a collection of other colorful particles. The collection explodes and multiplies uncontrollably.
"When physicists tried to add gravity to the story by inventing a new particle, their mathematics broke down."
Setting: outer space — bright flashes from explosion
On a green chalkboard, a hand writes 'GRAVITY + STANDARD MODEL'. The board then flashes, revealing the word 'AWESOME!' surrounded by confetti.
"If we could marry gravity to quantum physics and the standard model, we would have the theory of everything."
Setting: abstract classroom — bright, even
Text: "GRAVITY + STANDARD MODEL", "AWESOME!"
A cartoon man's hand draws a purple-to-pink gradient circle (a closed string) on a textured yellow surface.
"So very smart people came up with a new story. They asked, what is more complex than a point? A line, or a string."
Setting: abstract drawing surface — bright, even
People (1):
•
Three circles made of vibrating, multi-colored strings are shown. Each one vibrates in a different, complex pattern.
"String theory was born. What makes String Theory so elegant is that it describes many different elementary particles as different modes of vibration of the string."
Setting: abstract space — glowing from strings
A split screen shows a planet with musical notes on the left, and a vibrating string creating different particle shapes on the right.
"Just like a violin string vibrating differently can give you a lot of different notes, a string can give you different particles."
Setting: diagrammatic space — bright, even
Three cartoon scientists cheer in front of microphones and cameras. Confetti rains down as a chalkboard behind them displays 'THEORY OF EVERYTHING'.
"String theory promised to unify all fundamental forces of the universe. This caused enormous excitement and hype."
Setting: press conference — bright, even
People (1):
• arms raised, wearing purple shirt, white beard hair — cheering
Text: "THEORY OF EVERYTHING"
A purple bird plays a drum set with a cymbal crash, delivering a pun.
"Unfortunately, string theory comes with a lot of strings attached."
Setting: abstract space — bright, even
A progress bar fills up as a counter labeled 'DIMENSIONS' goes from 1 to 4. A simple black duck is shown, representing our 4D universe.
"Much of the maths involved in a consistent string theory does not work in our universe with its three spatial and one temporal dimensions."
Setting: abstract space — bright, even
Text: "DIMENSIONS: 4"
A grid of ten panels appears, each showing the black duck distorted in a different, complex way, representing the extra dimensions. The counter now reads 'DIMENSIONS: 10'.
"String theory requires 10 dimensions to work out."
Setting: abstract grid — bright, even
Text: "DIMENSIONS: 10"
A female scientist with pink hair works by candlelight, surrounded by papers and books. She looks tired and frustrated. A male colleague peeks in.
"So string theorists did calculations in model universes and then tried to get rid of the six additional dimensions and describe our own universe."
Setting: a study or lab at night — dim, lit by candlelight
People (1):
• slumped over desk, wearing blue shirt, pink, tied up hair — tired, leaning on hand
The scientist from the previous scene gives up, her head falling onto her desk. Her pen catches fire from the candle.
"So string theory did not reveal the nature of our universe. One could argue that in this case, string theory really isn't useful at all."
Setting: a study or lab at night — dim, lit by candlelight
People (1):
• slumped over desk, wearing blue shirt, pink, tied up hair — hidden, head on desk
A purple bird is on a swing. A blue bird approaches with scissors and cuts the swing's rope, causing the purple bird to fall.
"Science is all about experiments and predictions. If we can't do those, why should we bother with strings?"
Setting: abstract playground — bright, even
A purple bird stands at a small lectern in front of a green chalkboard. It writes '2 + 2 = 4' with a piece of chalk. A blue bird looks on skeptically.
"Physics is based on maths. 2 + 2 makes 4. This is true no matter how you feel about it."
Setting: abstract classroom — bright, even
Text: "2 + 2 = 4"
A red bird wearing a captain's hat and a purple bird examine blueprints for a rowing boat. A compass and telescope are on the table.
"That's why string theory is still useful. Imagine that you want to build a cruise ship, but you only have blueprints for a small rowing boat."
Setting: workshop — bright, even
A small purple bird rows a tiny wooden boat in the ocean, next to a massive white cruise ship. The bird looks up at the large ship.
"But both things are fundamentally the same, things that float."
Setting: at sea — daylight
A black duck in a red sweater vest pulls a yellow string, opening a green door that reveals outer space. The duck walks through the door into space.
"With string theory, we can try to answer some questions about quantum gravity that have been puzzling physicists for decades, such as how black holes work or the information paradox."
Setting: abstract room with doors — bright, with a glow from the door
A black duck wearing a green hero's tunic stands in a video game-like dungeon. A grid of glowing blue mathematical symbols appears on the floor.
"When used in this spirit, string theory becomes a precious tool for theoretical physicists and helps them discover new aspects of the quantum world and some beautiful mathematics."
Setting: video game dungeon — glowing from torches and symbols
A split screen shows a point particle's path on a 3D grid on the left, and a vibrating string on the right. In the center, a duck struggles to fit a universe back into the 'UNIVERSE STUFF' bag.
"So maybe the story of string theory is not the theory of everything. But just like the story of the point particle, it may be an extremely useful story."
Setting: abstract space — bright, even