String Theory – we have gone nuts trying to understand this because we are no physicists or mathematicians. We will try to summarize whatever we managed to understand about this theory over months of study. In case we make any mistake, we humbly request you to bring that to our notice (if possible with a simple and accurate explanation) so that we can fix our mistake as soon as possible.

Before we plunge into our rookie-style explanation, let us try to summarize the points that we will cover in the rest of the article.

- What is String Theory?
- What are strings?
- Problems that led to String Theory.
- Why are there extra dimensions in String Theory?
- Problems with String Theory.
- String Theory and Multiverse.

Now that we have a summary of to-be-learned stuff, let us waste time no further and start exploring each part individually. Stay with us and if you think things are getting complicated a bit, take a break, enjoy a coffee or two and come back. We ain’t going nowhere!

## So, What Is String Theory?

String Theory is a short name for Superstring Theory. Yes! The real name is Superstring Theory but some also call it the M-Theory. In truth there are different versions of String Theory. Many of these versions are consistent and M-Theory is the name given to mathematical model that unifies all these consistent Superstring theories.

Hey wait! Did we say mathematical? Of course we did! String Theory is actually a mathematical model. But why is it a mathematical model? We know that we have heard of String Theory in context of universe, in context of black holes, in context of sub-atomic or quantum physics. Well, we are not wrong! But there is a teeny tiny problem. String Theory is yet to give an experimental observation, i.e. scientists are yet to conduct an experiment that confirms at least something that this theory states. Though rapidly developing, we are still stuck with a mathematical framework only!

You will often hear people calling this theory by the name Unified Field Theory or Theory of Everything. But why? What does that mean? Possibly you already know this but let us just put it down once again – there are four primary forces of nature – Electromagnetism, Gravity, Strong Nuclear Force and Weak Nuclear Force.

There is a problem here. We do not have a single theory that can explain all these four natural forces. We do have different theories for different natural forces but merging them together gives rise to weird inconsistencies that break down laws of physics. This simply means that none of the individual theories are complete or at least, none of them manage to explain all natural forces. Apparently, String Theory seems to be very much capable of incorporating all these four natural forces within a single framework and hence the names – Unified Field Theory or Theory of Everything.

## What Are Strings?

Now we have a problem. Where is this word ‘string’ coming from? We more or less know what strings are. They make up our clothes, there are strings present in spider webs, suspension bridges have these long cables that are strings too – just bigger versions you know. So, why strings? Why not just something else? Interesting question.

In order to answer this question, we need to go back to our schools. You remember the basic atomic theory? We have learned that matter is made up of molecules that further break down into atoms, which in turn are made up of electrons, protons and neutrons and again there are smaller particles known as quarks that make up electrons and protons. We know that these sub-atomic particles are extremely small. The question here is, ‘how will you represent a particle if you are asked to show it on a piece of paper?’ Logically, you will simply make a DOT on a piece of paper and say, ‘hey look – that’s a quark!’ You will possibly make a bigger dot and call it electron and so on! So basically what we have learned in schools is that a particle is a point-like entity that has no dimensions.

Everything from quantum mechanics to Einstein’s General Theory of Relativity is based on these point-like particle entities. Unfortunately, none of them manage to give a unified theory for all four natural forces. This is where scientists felt, back in 1980s, that there has to be a radical paradigm shift in how we look into sub-atomic world. That’s when it was proposed (simply put, ‘assumed’) that sub-atomic particles are not point-like entities but rather, they are string-like entities with only and only one dimension, that is length. There is no width or height to these string-like entities.

Here is how strings are defined:

- There are no quarks. There are just strings. A quark is actually replaced by a string in the String theory. So basically the chain is: there are no quarks, there are just strings > strings make up electrons, protons and neutrons > electrons, protons and neutrons make up atoms > atoms make up molecules > molecules make up matter.
- These string-like entities or simply strings are way too small to be seen by modern-day highly sophisticated instruments.
- These strings may be present as open strings or closed-loop strings.
- Each string has a particular vibration mode (i.e. it vibrates in a particular way). The frequency of the vibration corresponds to each particle and thereby determines the mass and size of the particle. Simply put, the way a string vibrates actually determines the mass and size of a particle.
- Again, the way a string vibrates actually determines the color of particle in what we call Quantum Chromodynamics (it is a quantum field theory that we are going to skip for good).
- Even the charge (positive or negative) of a particle is determined by the way a string vibrates!
- As per String Theory, each individual string is so small in length that it always appears to be a point. However, it is not a point. It has a length of 10
^{-33}centimeters.

Okay, now that we have a fairly good working idea of what really strings are (remember that when we say working idea, we simply mean knowledge good enough to get a simple understanding of String Theory), we can move on to the next part.

## Problems That Led To String Theory

Now the question is, how the hell did String Theory come to life anyway? What was the problem? Here comes our crazy scientist who had life-long problem with his hair – Mr. Albert Einstein. He first came up with Special Theory of Relativity where he proved that moving through space alters how time passes. This means, space and time are tied up together. This stunning discovery came in 1905. Ten years later in 1915, he again came up with another theory – the General Theory of Relativity. This time he added gravity to his space-time brew and proved that curves and warps in the space-time plane is what gives rise to gravity! That was remarkable. He proved that space, time and gravity are all interlinked.

However, Einstein was not satisfied with this. He wanted something bigger – he wanted to unify all the forces that are naturally present in universe. This quest is what he called the unified theory. Unfortunately he failed to achieve his quest and the grand dream.

On the other hand, since 1920s a different framework was gaining quite a momentum. It was none other than Quantum Mechanics. This framework dealt with the atomic and subatomic world. But there was a small problem. The framework dealt with particles so small that gravity became really irrelevant while studying how these particles interacted. So, while making calculations, this framework simply ignored or rather did not take account of the relativistic effects. But, Einstein’s General Theory of Relativity clearly proved that space, time and gravity are linked. So, ignoring gravity was not a wise thing to do.

Then a lot happened in between that we are going to skip and focus on a big picture. We are going to look at the space. In particular we will look into black holes. Since General Theory or Relativity and Quantum Mechanics were not unified, they individually failed to explain a lot of things and when these individual frameworks were brought together, they gave birth to enormous problems and inconsistencies where the laws of physics as we know today, simply broke apart.

One such classical problem was that of black hole. We know that black holes have enormous gravity. They are so dense with so powerful gravitational force that even light fails to get out once it enters the event horizon! So, people needed to work with gravity. But there was a problem. Black holes have something known as singularity – an infinitesimally small point where all the mass is concentrated, which is why such enormous gravity is created. Now, since singularity is infinitesimally small, it is very logical to apply Quantum Mechanics.

So, now there was a problem. Should scientists make use of General Theory of Relativity to explain black holes or should they use Quantum Mechanics for the purpose. You see, a black hole is in space, it has enormous gravity and it even impacts time. So, logically General Theory of Relativity should be the approach. But what about singularity? It is infinitesimally small and hence Quantum Mechanics is the best candidate for explaining black holes.

So, the most logical step was to combine the two schools! When that was done, weird things happened. What type weird things? Well, we will explain the weirdness using this: 2+3 = 66. Is that even possible? Not at least with the our senses and known laws. Simply put, laws of physics broke down. There are only two ways this can happen:

- Everything we know is absolutely wrong and requires a radical overhaul.
- Accept the fact that General Theory of Relativity and Quantum Mechanics – no matter how elegant and powerful they are, are incomplete.

This is why a proper unified model is required that can not only explain everything in the atomic and sub-atomic world but also explain everything on the grand scale of the universe. This is where the String Theory came in.

**You May Also Like: Holographic Principle – Is Our Universe a Hologram**

### So, what does String Theory really do?

What it does is it unifies the two schools – the General Theory of Relativity and Quantum Mechanics in a single unified framework where laws of physics do not break down and everything from sub-atomic interactions to events of universe to black holes to the birth of our very universe is explained at any given time and space.

That’s amazing but for starters, it is important to say that String Theory states that there are 10 dimensions. We know that our universe has 3 dimensions. String Theory says there are 7 more. So in total there are 10 dimensions.

So, where the hell are these 7 dimensions? This is a big problem for rookies like you, me and the average Joe sweating at the coffee shop counter and serving coffee to the whims of others.

When we say spatial dimensions, we mean length, width and depth. Well, they are big and we can actually see and realize them. But the extra 7? To explain that, String Theory says that these 7 additional dimensions are so small and squeezed that we have failed to detect them so far!

Let us take an example of a long pipe. One obvious dimension here is the length of the pipe. There is another one too! The circular cross section. Now start shrinking this cross section, i.e. make it smaller and smaller and smaller while keeping the length of the pipe same. Eventually if you manage to make it so small that you cannot use your naked eyes to see the cross section, what will you or a bystander be looking at? You will essentially see something that is just long and lying on the ground. You cannot figure out any other dimension but just the length but still, there is another dimension which is so small that you cannot see it.

This is precisely what String Theory says. The 7 dimensions are undetectable and hence they cannot manifest and hence, cannot be experienced.

## The Big Question: Why Do We Need Extra Dimensions In String Theory?

A simple question but an incredibly difficult one to answer without making things what we call a ‘scientific mess’. So, here is a warning. We are going to exclude those scientific rants at bay for the sake of simplicity. Remember that we are explaining String Theory in simple English!

In Quantum Mechanics, particles are points. No matter from which direction you take to look at a point, you will always see the exact same thing. It is nothing but a perfect spacial symmetry. But when a point is replaced by a string, which has a length, things change totally. Something that has a length will always point to some direction, right?

In Quantum Mechanics we deal with force where it is said that the effect of a force always points to the direction towards which the force is being applied. Fine now, think of the point. For a point, which has absolutely no direction, the effect of a force is always in direction of a force. Now replace the same point with a string from String Theory. Now the effect of the force will depend on two things:

- The direction of the force.
- The direction of the string towards which it is pointing.

Here is another problem. If a string is kept still, i.e. it is not moved around, it will not be still in absolute sense. It will keep vibrating at a speed which is almost the same as light’s speed. This means that a typical string has to always follow the General Theory of Relativity. On top of that, a string also invariably needs to obey every single law of physics such as angular momentum (referred to as spin), momentum, conservation of energy etc. This is necessary because we really cannot afford to build a theory that breaks laws of physics.

Again, since a string is fundamental by nature, it has to always maintain its properties even while moving through spacetime continnum. That means, it has to retain its charge, its spin, its length and its mass. Things get even more complicated because String Theory dictates that strings can actually change shape – they can split or merge when they bump into each other and when that happens, they need to not only retain their fundamental properties, they also need to follow all laws of physics.

So, gradually it became evident that within our known 3 dimensional space, strings are bound by way too many rules that do not allow them to move in our 3 dimensions. That was an ugly bump for String Theory.

In order for the theory to work, the strings had to move around else, the whole framework breaks. To overcome this problem, physicists proposed: ‘Well, there are 10 dimensions!”

Okay. That was crazy! But the physicists countered the problem of rejection of the idea of additional dimensions by stating one simple fact – ‘there are no other theories in existence which says exactly how many dimensions our space is supposed to have’. Spot on! That’s true! So voila! We have 7 more dimensions in String Theory in which the strings can move around while retaining their fundamental properties while still obeying the known laws of physics.

### But, why don’t we see these new dimensions?

That’s because they are way too small to be detected. String Theory says that these 7 dimensions curl up together in a complicated way, making a 7D structure which pretty much looks like a knot! Interestingly, these 7 dimensional knots are just as big as the strings themselves, making them way too small to be detected by even the most sophisticated tools we have today. Also, these 7D knots are present in every single point in space. Despite their presence in every point in space, we don’t feel bumpy in space or we just don’t see them simply because they are infinitesimally small (as in Quantum Mechanics we don’t feel what’s really happening in the atomic and subatomic levels because they are just too small for us to feel anything). The strings in String Theory move around inside the curled up seven dimensional knots and interact to do wonderful things in accordance with both Quantum Mechanics and General Theory of Relativity. This means that the vibration modes of the strings can now conform to the four forces of nature. Isn’t that amazing?

## What Are The Problems With String Theory?

Honestly, we ourselves are not aware of how many problems are there with String Theory because we are rookies. But, one thing that we know for sure is that the most important problem String Theory faces today is that of an experimental validation. This theory has so far not produced a single prediction that can be tested and verified via an experiment in a laboratory. Thus, it is still just a mathematical framework.

Yet another problem that comes to our non-scientific minds is that we will possibly not have any instrument ready in next 100 years at least that will allow us to test predictions that are made by String Theory.

## String Theory and Multiverse

The mathematics of String Theory has given us something really interesting. It says that while the fundamental particles are now replaced by strings, there is also something known as branes (basically membranes) of energy and that these branes are on a higher dimension known as ‘bulk’. A brane can actually hold an entire universe which is finite but without any boundaries. So, it is likely that we (including our universe) are located on one brane while there are other branes in the higher dimension or the ‘bulk’ which hold separate universes. This means there are multiple universes or as we prefer calling it, there is multiverse!

Many mathematicians have come up with the idea that the brane that holds our universe was initially empty, i.e. there was no matter and no energy. It was a completely empty brane. It just happened that this once empty brane collided with another brane that had a whole universe. This collision allowed this once empty brane of ours to capture some matter and energy that made up our universe. The collision, the mathematicians say, was so powerful and so energetic that it was the much touted Big Bang that formed our universe.

But hey, it doesn’t necessarily mean that a universe on another brane will be identical to that of ours. It also doesn’t mean that there cannot be two identical universes. That’s pretty interesting right? However, most likely all universes that are present on their individual branes are very likely different. One universe may not have gravity at all, another universe many not have anything other than neutrons and protons and electrons just flying around happily for eternity. Anything can happen in multiverse, right?

Well, that concludes our article on String Theory. Did we manage to explain it in simple English? We think we did manage to explain things. If we made a mistake, drop a comment.