This Corona lockdown has given us something important, something that we all yearned for – TIME. All these years, we had always wanted to spend some time on what we love and what we have wanted to learn. Leaving aside the threat of this pandemic, we did get some quality time to do what we always wanted to do.

I, for two and a half years wanted to learn more about “**What is the String Theory”**, courtesy “The Big Bang Theory” episode, where one character, Sheldon explains to another character, Penny about what is the string theory, and what are the implications of the string theory. So I decided, now is the time for me to learn about String theory.

So I bought a book – “Hyperspace” written by the astrophysicist “Michio Kaku“, who have had worked on this theory. I highly recommend reading that book to get a good knowledge in this theory

I did understand some of the basic view points about what is the string theory. So I write this article, “**What is the String Theory and 1 most important and interesting requirement of string theory” **based on my understandings.

**Contents**hide

**The Fundamental forces of Nature.**

The nature is governed by four fundamental forces. From pushing a door to sending rockets to the space, every force that we experience in life can be categorized into just these four fundamental forces.

These four forces are,

- Electromagnetic Force
- The Weak Nuclear Force
- The Strong Nuclear Force
- Gravitational Force

The **Electromagnetic Force **is the force that causes the opposite poles of a magnet to attract and also for the opposite electric charges to attract. This fundamental force is also responsible for forces like Force of friction and drag force.

The **Weak Nuclear Force **is the force which exists within the subatomic particles of an atom, which allow the nuclear fission to take place. This force is the reason why particle decay occurs. It is the reason why we are able to harness Nuclear energy.

The **Strong Nuclear Force **is the strong force between subatomic particles of an atom, which is responsible for binding the fundamental particles of matter together to form large particles.

**Gravitational Force **is the force of attraction between two objects in space. It is a large range force, but is the weakest of all the four fundamental forces. The force of gravity is the reason why the sun holds the earth in its orbit.

Newton said, Gravitational force is the force that literally attracts two bodies in space. The apple fell down on the earth because, the earth attracted the apple. But sadly he was not able to provide the reason for this attraction.

However, Einstein came in and proposed that Gravity was not a force of attraction, but rather the force was a result of the bending of the space-time fabric. (Do click on the above link to get more idea about the space-time fabric). Thus he said that gravity is a manifestation of geometry of space-time continuum, rather than an attraction. See below picture to get a rough idea of gravity as a manifestation of geometry of space-time continuum.

**The Unified Field Theory**

Imagine that you are solving a puzzle with a 100 pieces. Placing the hundred pieces in the correct position and correct orientation will solve the puzzle. You are able to confirm the correct position and orientation of most of the pieces, but the problem is, you are not able to solve it fully.

Now you are left with 4 big pieces, each of which, you got by piecing 25 smaller pieces correctly. Now you have 4 bigger pieces with you but you are not able to find the correct position and orientation to make it into one fully solved puzzle.

Why do you want to solve the puzzle? Of course the end result is a beautiful picture when it is joined together.

For years, physicists have, in a similar way tried to unify the fundamental forces of nature. Why do they want to unify? Well, with unification each force can be explained with a simple common formula. They were able to find the formulae for the individual forces, very much like the puzzle pieces.

But they were never able to piece every force together. If they unify these forces and find a unified theory, they would be able to explain each of the force as a manifestation of the unified theory.

**Attempts at Unification**

Albert Einstein in his later years, was very obsessed in providing a unified theory. In fact it is the one theory that eluded him for years till his death. Einstein had already proposed that Gravity was a result of the geometry of the space-time fabric.

Similarly he had proposed his famous equation E=mc^{2 }, which says that the energy of a particle at any instant would be equal to the product of its mass and the square of velocity of light.

This matter-energy equation he found was the sole reason for his frustration. With this equation, he was not able to explain matter in the form of a geometry. How bad he tried, he was not able to provide a geometrical solution to the matter-energy equation.

Just as Einstein was failing in his attempt at unification, the next theory called **Quantum Theory ** rose up in popularity.

The theory gave an explanation that each particle contains packets of energy called **quanta. **According to this idea, when two particles came into contact, they exchanged this “Quanta”, thereby resulting in the origin of the forces as we know it.

This theory was a very successful theory with a variety of experimental results and a lot of data supporting it, until the real problem showed up.

The big problem with quantum theory was that it was not able to explain the force of gravity. Gravity as I mentioned earlier is a long range force. The gravitational force was existent between two objects in space, however long the distance between them be.

The physicists were not able to provide a reason of gravity with respect to their quantum theory.

Thus a new theory was in the proposal – The string theory.

**So, What is the String Theory?**

There was a time when even the brightest of minds on earth scorned at the idea of atoms. To them, to say that an element is made of atoms looked farfetched.

But as more theories and experiments came in, the idea of atom was quickly accepted. Atom, then came to be known as the indivisible part of an element. Now we know it is not true.

So the question arises, What is the indivisible part of an element and What is it made of? Does the atoms have three indivisible parts, namely Electron, Proton and the neutron? That was the thought almost a century back.

As of now, physicists say that, as you go deeper and deeper to find the indivisible part of the element, you would find something remarkable. As we go deeper, we will finally get to see the mysterious ever pervading part. This mysterious part can be found in every particle in the universe

So what is the string theory simply?

We all love music, don’t we? For me the thing about music is, it turns magical the moment a skilled artist takes up an instrument and plays it.

Take a violin for example, a skilled musician can produce different notes and breathtaking rhythms using just the four **strings** and a bow. When we wonder how the violin strings produce such amazing music, our obvious answer ends up as **Vibrations of the string.**

With just a constant vibration and different **frequencies**, you get a plethora of amazing sounds.

The above mentioned music analogy is important to understand what is the string theory and what it says.

In the above sentences, substitute the music produced by the violin, to the particles in the universe, we get the basis of **String Theory.** When we go deeper to find the mysterious part, physicist say, you would find a vibrating string of energy.

Based on the frequency of vibration of the energy string, we would get different particles.

So what is the string theory in a simple sentence? – Every particle we see is just a band of vibrating string of energy with different frequency of vibration. You, me and everything around us are just a vibrating energy string

For people with non physics background, like you and me, we can consider string theory as an extension of quantum theory. Where the quantum theory failed, string theory was passing. String theory was able to account for the gravitational effect.

All this, the string theory achieved theoretically. As usual the physicists faced a new problem with proving string theory.

** **

**The Problem in String Theory**

The success of any theory always stands in the consistent experimental verifications. With String theory however, there are no direct ways to prove it. This is because, no known instrument is capable of probing such minutely. An average string would be 10^{-33 }centimeters long.

## What is the string theory’s interesting requirement

The interesting requirement with string theory was, the calculations required ten spatial dimensions and one time dimension to unify the laws of nature.

But we human beings only know of the three spatial dimensions, namely the x-axis, y-axis and the z-axis (length, breadth and depth).

**Why does string theory require 10+1 dimensions? **

This part of the question requires some wild imagination. Take a piece of paper and lay it on the table. Now we are going to assume that people are going to live on the surface of the paper. Living in a paper means they are two-dimensional people, just like how we draw stick figures on a piece of paper

For them, all they see is two dimensions. For a two dimensional person, there is no concept of up. All they know is left and right.

Now assume that you have a wine glass, which shatters and falls on the paper where the 2-D people live. Now they see these mysterious objects that have fallen into their land, and they come to the conclusion that all these mysterious objects somehow constitute a single object, and decide to put them together.

While putting them together, they come to a dead end, when they have two pieces not compatible with each other. They become disheartened and leave the place.

But then a scientist among them says that, they may have to orient the two pieces in a mystical direction called **Up **to join them together. However he has no proof that there is a direction called “up” other than some calculations.

Some of the people will consider him as a mental person. But then there will be you looking at them from “up” and know that the scientist is right.

Now we face a similar situation. We are not able to visually see the proof of the extra dimensions and with just a set of calculations we cannot know if these extra dimensions exist or not. In that case, what is the String theory? Is it another failed attempt at unification?

**Searching for indirect proofs for String Theory**

Since there is no direct proof for finding out if the strings exists or ten dimensions exists, physicist are looking for indirect proofs.

What is the string theory’s indirect proof?

String theory is one of the theories which gives an insight about the state of the universe before the **Big Bang**. Physicists like Michio Kaku say that, the universe before the Big Bang was a full 10 dimensional universe.

The universe after the Big Bang, split into two universes, one universe with a four dimensional universe and another into a six dimensional universe. But the six dimensional universe somehow was curled up and now it is so small that they cannot be seen through any known probe.

The **Large Hadron Collider** (LHC) at CERN located at Geneva, Switzerland is looking out for the existence of these smaller spatial dimensions.

What happens at the LHC is that, two particles will be made to hit each other from the opposite direction at a velocity near the speed of light.

Then after the collision the energy will be measured. As per the energy equation, the energy before collision should be equal to the energy after collision. There, the physicists hope that if the collision has enough energy, it may eject some of the debris energy from our dimension, thereby entering into another dimension.

When some of the energy disappear, it is the proof that energy has moved away from our four dimensions to another dimension, but the energy needs to have a certain accepted pattern to accept that the energy actually entered another dimension.

So, What is the string theory? Is it going to be the actual theory of everything or is it just another stepping stone towards a theory of everything? Only time will tell.

If you want to have deeper insights about what is the string theory, please do read the book “**Hyperspace”**, written by Michio Kaku. It is really an easy to read and understandable book.

Additional Resources

https://www.ted.com/talks/brian_greene_making_sense_of_string_theory

https://www.pbs.org/wgbh/nova/elegant/view-witten.html

https://whatis.techtarget.com/definition/superstring-theory-string-theory-Theory-of-Everything

https://www.wisegeek.com/what-is-string-theory.htm

https://www.space.com/17594-string-theory.html

https://www.newscientist.com/article/dn16950-string-theory-a-beginners-guide/

https://www.britannica.com/science/string-theory

https://www.smithsonianmag.com/science-nature/string-theory-about-unravel-180953637/

https://www.livescience.com/65033-what-is-string-theory.html

Do comment your views on this article.