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ABOUT A CENTURY AGO, WE THOUGHT THAT HE WAS WRONG! BUT NOW… > SPOILER: It’s not an article on atoms. It’s a warm summer evening in ancient Greece. Suddenly a crazy philosopher friend of
yours tells you something even crazier! He tells you that ALL MATTER IS MADE UP OF TINY, INDIVISIBLE PARTICLES. Of course, you don’t believe him. You know that matter is made of FOUR
ELEMENTS, earth, fire, air, and water. The theory that everything is made up of four elements was a really popular theory in ancient Greece. Later, Plato assigned four different shapes to
these four elements, such as earth (cube), fire (tetrahedron), air (octahedron), and water (icosahedron). Later, Kepler expanded the theory a little more. You can read about it here: The
idea that all matter is made up of tiny, indivisible particles, is believed to have originated with the Greek philosopher Leucippus of Miletus and his student Democritus of Abdera in the 5th
century B.C. This is probably the first theory of atoms to come into existence. That’s why the word atom actually comes from the Greek word “atomos”, which means indivisible. Later, John
Dalton popularized the term. Dalton used the term “atom” to refer to the basic particle of any chemical substance in his writings. Dalton’s proposition was that each chemical element is
composed of atoms of a single, unique type. Dalton’s theory also included that these atoms cannot be altered or destroyed by chemical means. But then in 1897 J.J. Thomson discovered the
electron and disproved one of Dalton’s theories. An atom was divided. Later, protons and neutrons were discovered. And then protons and neutrons were found to be made of quarks. The theory
of indivisible particles of one kind making up the universe was shattered. But wait, the story doesn’t quite end here. It was the 1940’s and another theory was coming into existence. John
Archibald Wheeler’s introduces the theory of S-matrix in 1937. A research program was begun by Werner Heisenberg following that theory in 1943. From these, a new revolutionary theory came
into existence, the String theory. Before we jump to string theory, let’s revise our current understanding of the universe, the Standard Model. Everything is made of particles, like
electrons, quarks, neutrinos, bosons etc. Particles can move in space and they can also interact. While interacting, they can interchange with other particles. For example, EM force
(electromagnetic force) exists because of the exchange of photons. The Gluons are responsible for the strong force. All these particles belong to the Standard Model, the most precise model
of the universe we currently have. The standard model consists of two types of particles: FERMIONS, which is responsible for creating matter. BOSONS, which is responsible for creating
interactions. You might think, “Oh yeah! So, we finally have a theory of everything, right? Did we solve physics?” Well… no. There’s one interaction this model can’t describe. Gravity! One
might say, “But, didn’t Newton already explain it long ago?” See, in classical mechanics, we don’t care about quantum particles and quantum interactions. Newtonian gravity is fine for
classical mechanics, but when we try to apply it on objects too small to be seen, we fail. To work on that “too small to see” scale, when classical mechanics failed, we came up with quantum
mechanics. And the standard model still can’t explain gravity quite well. Also, by “too small to see”, I don’t refer to microscopic objects that can be seen under a microscope. I refer to
objects that are too small to be interacted with visible light, hence there is simply no question of seeing at all. Such as electrons, quarks etc. Well, on a large scale, Einstein’s general
relativity describes gravity quite well. Objects create curvature in space-time, hence, attracting other objects. In quantum mechanics, just like other forces, we thought of a particle
responsible for gravity, the graviton. But when we include the graviton in our equations, they give absurd results with infinite values. WE CAN NOT DESCRIBE GRAVITY ON A QUANTUM SCALE WITH
THE STANDARD MODEL. So, we came up with the string theory as a new model to describe everything! In the standard model, we theorize that all matters and forces are made up of different
particles and we think of them as dimensionless points. We know that they are very different from each other and have different properties. In string theory, we assume that these properties
are just an approximation. All of the particles are made up of small strings, open or closed. These strings vibrate and based on their vibrations, they make different particles. Just like a
guitar string vibrating differently produce different sounds, these strings, based on their vibrations make different particles. If we do the calculations, we find out that some strings act
like photons and gluons and even some like gravitons. Assuming the strings have different tensions and vibrate differently, we finally have something to represent the gravitons, describing
gravity on a quantum scale. The fundamental thing about string theory is that everything is made of oscillating strings, only the vibrations of the strings determine what property they get.
The theory that everything is made up of a single fundamental thing, is once again into consideration. It’s not exactly what Leucippus said but it’s quite similar! The big brain people
(a.k.a. scientists) use the principles of our current models to understand how these strings evolve and interact. Let’s think of a scenario to understand it better. You have a screen that
can capture and log the position of electrons when thrown at it. Now, you throw an electron at it. It propagates like a wave, so you don’t know for sure where that electron will materialize
on the screen. What we can do is predicting the probability of the electron materializing on a certain spot. What we do is sum all possible trajectories and interactions of the electron to
get the possibilities. But that can be a really hard task to do. For example, the electron might just emit a photon. The electron might also absorb the photon later in its path. Or maybe it
emits 3 photons. Or maybe it emits two photons at different times and absorbs them all later. So what better do the strings do? Instead of considering the particles as zero-dimensional
points, we consider them as strings, which trace a surface while propagating. It can vibrate, split and recombine and do all kinds of stuff. Splitting and then recombining will be equivalent
to emitting a photon and then reabsorbing it. It forms a geometry while doing this. By summing up all the geometries, we automatically get the probabilities. Pretty convenient, right? Also,
another cool thing. Interactions used to be instantaneous, but since the strings trace a surface, we get non-instantaneous interactions that happen gradually. This gets rid of all the
infinities when we use gravitons in the calculations. This is why string theory is so promising. But there are a lot of problems with string theory. It works with ten or eleven dimensions
(based on which model of string theory we are using). So, where are all those dimensions? There are more unexplained things with string theory than things that are explained. I will write
another article on those shortly. I will also discuss the different models of string theory. Superstring theory will probably make your mind go wobbling like a string. Make sure to follow me
to get those updates. But string theory is the closest we have come towards the theory of everything. It’s the closest we have come to a grand unified theory that explains everything in the
quantum world. Quantum gravity is one of those. Even though it is in its early stage, it is very promising to the new age scientists. Maybe soon enough we will have a breakthrough in this
field and it will be a grand day for science again.