When trying to understand the true nature of everything,
we humans have come up with many theories in the past.
Over time, we have discovered a zoo of elementary particles,
and have come to know the existence of the four fundamental forces in our universe.
Two of the most successful theories that help us answer many questions about our universe
are General Relativity and Quantum Mechanics.
Albert Einstein's theory of general relativity is an elegant description
of how the force of gravity works at large scales while Quantum Mechanics
explains the other three fundamental forces at the smallest of scales.
However, according to General Relativity, the fabric of Space-Time is smooth and continuous
whereas Quantum Mechanics describes Space-Time as being quantized.
While both theories have helped advance many areas of science and technology,
they remain incompatible and perhaps incomplete.
So, scientists have since wondered how we can unify these two theories
to get a complete picture of the reality we occupy.
Many theories on this topic have been proposed.
But perhaps the most promising one is called String Theory.
So today, we will take a look at where String Theory comes from
and why is it a candidate for the Theory of Everything.
But as always, be sure to subscribe to our channel for more content ahead.
To understand our surroundings,
we probed the skies as well as the microscopic realm of our universe.
We discovered that everything in the universe was made up of smaller parts called atoms.
At first, we believed that the atom was indivisible.
But smashing the atoms together using the large hadron collider,
we discovered the true indivisible particles known as the elementary particles.
Elementary particles are categorized into some broad categories,
Fermions, which are matter particles,
Gauge Bosons, force carrier particles, and Scalar Bosons, particles of the Higgs Field.
Fermions include Quarks and Leptons while Gauge Bosons
include gluons, photons, and the W and Z bosons.
Gluons are responsible for mediating the strong force between particles,
photons are particles of light which carry the electromagnetic force,
and the W and Z bosons carry the weak nuclear force and are involved with radioactivity.
While this categorization of Gauge Bosons is useful in predicting and
describing how electromagnetism along with strong and weak forces work,
it says nothing about the force of gravity.
In fact, the hypothetical particle called graviton is nowhere to be found
using the standard model of particle physics.
Another problem with these elementary particles is that we cannot directly observe them.
This is because the wavelength of light which we use to see
are far too large to be reflected off of such tiny objects.
And if we made the wavelengths smaller by adding more energy to them,
it would alter the particles we want to view.
This phenomenon is more commonly known as the Heisenberg uncertainty principle.
What this means is that we cannot really see elementary particles,
but we can do precise calculations assuming that these particles occupy a point in space.
So far, this method has advanced science beyond our wildest dreams.
But this story is still incomplete.
The force of gravity is where the problem arises.
According to general relativity, gravity is not a force but just a curvature of space-time.
So, when scientists try to add a new particle called graviton to the zoo
of the elementary particles, their calculations break down.
So, to get a complete picture,
we must somehow unify gravity with the other three fundamental forces of quantum mechanics.
This means we must invent a new theory that will attempt to unify
all aspects of Quantum Mechanics and General Relativity.
This is where String Theory comes in.
The idea of String Theory first started in the 1960s when scientists tried to study
the behavior of collections of Quarks bound by the gluons of the strong force called Hedrons.
Hedrons include things like Protons, Neutrons, and Mesons.
After studying the interactions between Mesons,
scientists theorized that the quarks in Mesons may be connected by strings which
were believed to be stretched out tubes of the Strong Nuclear force.
But this theory was ultimately replaced because of some problems that accompanied it.
The reason this theory did not last is because it predicted the existence of unwanted vibrational
modes, which are just particles, in the quantum fields. For example, it predicted the existence
of a massless spin-2 particle which is the hypothesized graviton in the quantum field.
But a graviton had no place in the study of Mesons and quarks.
This development led to a major shift in thinking. Scientists proposed a new
model which could solve the problem of unifying gravity with the other forces.
They thought, what if all force-carrying particles are a result of tiny oscillating strings?
In fact, what if all particles were just random oscillations of tiny strings?
This line of thinking gave rise to the modern String Theory we know today.
Initially, String Theory did not include Fermions and
also predicted faster than light particles, Tachyons.
But adding the principle of supersymmetry solved both of these problems.
Supersymmetry says that nature is symmetric and so it predicted the
existence of many unknown particles that are symmetrical to the ones we know of so far.
So, supersymmetry combined with string theory became known as Superstring Theory which
proposed that everything in the universe is a result of tiny oscillating strings.
Furthermore, Superstring Theory also decreased the number of higher dimensions
required for these strings to vibrate in from 26 to only 10.
According to Einstein’s Theory of Relativity,
Space-Time only consists of 3 spatial dimensions plus 1 dimension of time.
But Superstring Theory, or more commonly known as String Theory,
predicts 6 additional dimensions to the four dimensions of Space-Time.
It says that at every point in space-time there are these tiny vibrating strings in 10 dimensions.
We just cannot experience these extra dimensions
because they are so tiny that only Superstrings can vibrate in them.
These vibrations of the strings are what produce all the forces and matter we see in our universe.
Although Superstring Theory was very promising, it had many different versions.
But in 1995, Ed Witten brought all consistent versions of Superstring
Theory into a single framework of M-theory.
M- theory requires an additional dimension apart from the already existing 10 dimensions
of Superstring Theory giving a total of 11 dimensions for the strings to work in. This extra
11th dimension is what allows strings to stretch out into sheets like membranes and exist within a
hyperspace that is also defined by M-theory. This is where the idea of a Multiverse originates from.
With the membranes being universes,
and the hyperspace being the Multiverse that we all know today.
Now the beauty of String Theory is that it provides its own unique interpretation to the
questions related to the beginning of the universe and how gravity can fit with the other forces.
It suggests that new universes emerge when two universes or membranes collide or split.
This may be what we perceive as the Big Bang. Moreover, it offers a solution to
the problem of why the force of gravity is so weak compared to the rest of the forces.
It proposes the existence of open and closed strings.
It says that gravity may be a closed string that can escape from the membrane into hyperspace
while open strings are bounded by the membranes they occupy.
This may explain why it takes only a tiny magnet to overcome
the force of gravity produced by the entire Earth.
So, if string theory ever becomes testable, we may have just found the ultimate theory of everything!
And that is what the current String Theory is all about.
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