What is String Theory in Physics?

Humans have been trying to decipher the world we live in since ages. People have had come forward with different theories to understand our reality - be it a tortoise holding the Earth on its back, or a flat earth, or geocentric model of our solar system, etc.

But in the last 100 years we have come up with much more sophisticated theories regarding the inception and the true nature of the universe we live in. String theory is one of many such theories put forward by brilliant minds of 20th century.

Standard Model of Particle physics, Supersymmetry, etc. are some other such theories that aim to explain the very basic nature of our universe, i.e. what our universe is made of and how it works. It’s a race to become the coveted “Theory of Everything”.

However, all these theories and models are work in progress. Scientists are still coming up with many new versions of these theories, and testing their various aspects. Even String Theory has numerous versions. But in this article, we will discuss the very basic fundamentals related to String Theory, that will be true for any of its version.

Table of Contents

• What is String Theory?
• Why was String Theory needed?
• Details of String Theory
• Pros and Cons of String Theory

What is String Theory?

Since ancient times, we have been used to thinking matter as made up of particles. The more we break a thing, the smaller the particles we get. Initially we got atom, then protons, neutrons, electrons, and then quarks, and then even smaller particles.

In fact, we have a zoo of elementary particles now that can be seen represented in Standard Model of Particle physics. However, String theory does not look at the universe in this manner. As per String theory, everything in the universe is made up of infinite long strings of almost zero thickness. The way these strings vibrate gives rise to different forms of elementary particles and matter.

Note

String theory sounds a lot like the Vedic idea of universe. The whole Vedic system is based on mantras and vibrations, the most important of them being the ‘OM’ mantra. ‘O’ of ‘OM’ mantra is supposed to represent the start of the universe, and ‘M’ the end.

Why was String Theory needed?

All quantum particles have a dual nature, i.e. they may exist as a particle and as a wave. This has been proved experimentally. The photoelectric effect showcases the particle nature of such quantum particles, while Young’s double slit experiment showcases their wave nature.

As per Heisenberg’s uncertainty principal, we can never know the exact position and momentum of a quantum particle at the same time. That’s because the very act of our observing it changes its position or momentum. So, quantum experts consider these quantum particles as a probability field that may condense to a point when we observe it.

However, by considering these quantum particles as points in space-time (as we do in Standard Model) we can drastically reduce the complexity that we will otherwise encounter in dealing with them.

So far so good. But there’s a problem with Standard Model of particle physics. It cannot tell us about the nature of Gravity.

In Standard Model there’s a force carrier particle that is responsible for each of the four fundamental forces of nature.

• Electromagnetic force is carried by Photons
• Strong Nuclear force is carried by Gluons
• Weak Nuclear force is carried by W-Bosons and Z-Bosons.

However, scientists have still not discovered the hypothetical force carrier particle (Graviton) for the fundamental force of Gravity. Even when they add this particle to the Standard Model in theory and calculate, the maths break down.

Moreover, as per Einstein’s General Relativity theory, gravity is unlike other fundamental forces. It’s intertwined with space-time, i.e. the very fabric of space. It influences all the particles that are in the universe. Consider gravity as a property of space-time, which is the staging area of the play being performed by various elementary particles and other fundamental forces.

Also, in quantum world we can never measure the distance between two points with precision. And to calculate gravity we need a precise distance between two objects.

So, you can see the issues scientists are facing, when it comes to combining Gravity with Standard Model or Quantum Physics. If they can do so, this will probably be the greatest discovery in Physics yet. We will get the coveted Theory of Everything.

So, to solve these issues, some scientists decided to drop the very idea that fundamental particles are points in space. They instead considered them as lines of infinite length or closed loops. String Theory was born!

Details of String Theory

So, now you know the very basics of String theory, and why was it propounded. It’s time now to delve a bit deeper into this fascinating theory.

String theory visualizes the fundamental particles as various modes of vibrations of the strings. The same string vibrating is different ways can manifest as different elementary particles, just as the strings of a violin or guitar can give out different music when vibrating in different ways.

And the most fascinating aspect of String Theory is that it includes Gravity, i.e. it explains it too. It’s one of the biggest reasons why this theory has been so popular, and has gained so much traction among the science community for so long. Probably no other theory assimilates Gravity within it in the manner that String Theory does. Gravity is the Achilles’s heel of most other theories. It is the crowning jewel of String Theory.

So, this theory gives us hope that one day we can combine all the four fundamental forces of nature within a single theory, and get the Theory of Everything.

However, there are some issues with String Theory.

Pros and Cons of String Theory

Issue 1: Too many Dimensions

We all know that we live in a 4-dimensional world – length, breadth, height (3 space dimensions), and one time dimension (that is unidirectional, as time moves only in one direction).

However, as per various versions of String Theory, we must be living in a 10 or 11 dimensional universe. It’s the only theory in whole of physics that picks its own dimensionality.

Scientists find it vey hard to visualize and work with these added dimensions, which have not yet been observed, and are purely hypothetical. As per most experts, if these extra dimensions exist, they must be curled up in a very small space, something that is too small to be observed.

Issue 2: No Prediction or Experimental proof

Till now no String Theory theorist has been successful in eliminating the extra dimensions of String Theory and predict something useful for our 4-dimensional universe. Nor has any experiment proved any aspect of String Theory. (As compared to this, Standard Model has helped scientists find many new fundamental particles, the latest being the Higgs Boson)

So, this theory is purely theoretical as of now, even after decades of work. As per some people, we need an experimental setup of the size of the solar system to conduct any test that can verify (or negate) this theory.

As it stands now, human civilization is not in the position to test this theory experimentally. This does not make it wrong, but surely acts as a demotivating factor for anyone thinking of pursuing a career in String Theory research.

But all is not lost. String theory will remain to be relevant even in the future. That’s because maths is the universal language of our universe. And String theory is built on sound maths.

It will keep on giving us clues regarding our universe, e.g. the true nature of Quantum Gravity, a very confusing and hot topic nowadays, what happens inside Black Holes, etc.

It will continue to be an efficient tool in the hands of theoretical physicists. And maybe sometime in near future, we may find the missing piece of the jigsaw puzzle, and all things may fall in place instantaneously.