Answers to Why String Theory!

This Thing is Behind Everything in The Universe

Hey Explorers,

This blog is on the simplest thing in this universe, Strings.

Strings

But lets first have a look into what I wrote a couple of months earlier.

Earlier this year, when I was trying to understand few of the most basic things in the universe, I came across Quantum Field Fluctuations.

Explaining these fields, I mentioned:

This is nothing; yes, simply nothing. 

A complete nothingness; taking out everything from a space, what's left are these Quantum Field.

And it looks something like this:

Quantum Fields 

Read the blog on these Quantum Fields here: Nothing

It's quite a time, I have been reading about the fundament things present in the universe. 

Lets take a situation, you are siting under an apple tree & an apple falls on you. Now, the very first question comes to your mind is.....

Not why did it come down, because that's already answered by Sir Newton :)

But you started thinking about what's inside this apple.

Lets break it down; start from basics, a molecule, lets go on smaller scale, an atom, Now this is the limit of classical physics, So you entered the quantum scale; you see electrons, a lot of empty space and a nucleus. Lets go deeper; hadrons are now visible which are nothing but protons and neutrons. 

Go deeper, what did you see? tiny, very tiny particles moving, which signifies they have energy, these are nothing but Quarks which are held by Gluons; Quarks combines to form hadrons; protons and neutrons are the most stable hadrons.

Quarks and Strings

Now what if I ask you to go even deeper. If you answer that, you will probably get a noble prize. As scientists have been trying to find this out for decades. Breaking down quarks might take tremendous amount of energy that we can't even figure out & a very Large Hadron Collider (LHC at CERN is 27km long).

This is how LHC works

But science don't stops here, at least until we stop being curious and limit our imagination.

So we came up with three theories to study and understand these fundamental particles. These theories are:

1. Quantum Field Theory

2. Theory of Loop Quantum Gravity &

2. String Theory

The simulation you just saw above represent Quantum Fields. These fields are the most fundamental things and an outcome of The Quantum Field Theory; which is a theoretical framework that combines Classical Physics, Special Relativity and Quantum Mechanics. As per QFT the most fundamental things present in this universe are Quantum Fields. It states Quarks are created from Quark Fields and similarly every particle is associated with its respective fields. Or simply whenever a field is disturb, it creates an unique particle.

Theory of Loop Quantum Gravity (LQG) is an attempt to create a quantum theory of gravity based directly on Einstein's Geometric Formation. It basically states that the structure of space and time is composed of finite loops woven into an extremely fine fabric. The network of these loops is called Spin Network which is at the scale of Planck Length (1.6 x 10^-35 m). 

Spin Network of Loops

The most advance direct result of LQG is Loop Quantum Cosmology (LQC). LQC advances the study of early universe and predicts a quantum bridge b/w contracting & expanding cosmological branches. 

An interesting fact is one of the founder of LQG is Dr. Abhay Ashtekar, Indian Theoretical Physicist and Director of Gravitational Physics & Geometry at PennState University.

Quantum Bridge

But why there was need for String Theory, an another theory to explain universe?

Well, It was in late 1960s when the idea of Sting Theory was proposed. Scientists where trying to reconcile the inconsistencies between Quantum Mechanics and General Relativity. One of the deepest problems in modern physics that remains unsolved is the problem of Quantum Gravity. The General Theory of Relativity is formulated with the framework of classical physics, whereas the other fundamental forces are described within the framework of quantum mechanics. A quantum theory of gravity is needed in order to reconcile general relativity with the principles of quantum mechanics, but difficulties arise when we attempt to apply the usual prescription of quantum theory to the interaction due to gravity. That's when The String Theory was proposed.

But why Strings?

String Theory has been one of the most famous, controversial & misunderstood theory. It is basically a theoretical framework where every particle is replaced with 1D objects called Strings.

Scientists thought what could be the most basic thing in geometry, a point, right? 

So we assume every particle to be a point in space, and when you break this point what you get are these tiny strings.

Now every string can stretch, bend, twist and form different shape. And specific shapes gives properties to particles. Also these strings vibrates at different frequencies, which ultimately creates fundamental forces and particles.

Strings

Ok, but why its so famous among researchers?

For years, we believed Gravity is a force, until Einstein sir gave us the Theory of Relativity.

The Einstein Field Equation which relates curvature of space-time, energy and momentum proposed the idea that gravity is not any force but an effect due to curvature in Space Time Fabric. This curvature and deformation of Space-Time Fabric depends on the Theory of Geometry.

Physicist describe gravity as the weakest of all four fundamental interactions. Also, all other interactions are associated with particles due to which they are significant; 

Strong Force - Gluons

Weak Force - W & Z Bosons

Electromagnetic - Photons

Gravity - ??

Now, interactions of gravity is weakest, for scale if the strong nuclear force has a magnitude of universe size, the gravity interaction will be around the size of an atom, that's 6 thousand trillion trillion trillion times small or 10^39 times smaller.

4 fundamental forces 

Then what's behind gravity? 

As per String Theory there are Gravitons, mass less state of fundamental strings, that helps in the interaction of gravity. 

There are actually two types of Strings, open and closed; open strings have D Branes at its both end while closed one are a loop that eventually gives properties to particles. 

Gravitons are closed strings, Every time matter in space interact with each others they exchange Gravitons and that's what we precise as gravity interactions. The first time LIGO detected Gravitational Waves they stated that it could have 3 x 10^(37) Gravitons flowing. Such a huge number still being very weak in intensity, now you know how weak gravity is actually.

But are these Gravitons Particles or Wave?

This was answered by Fermilab, they stated that graviton is expected to show duality just like other particles that gives us other 3 fundamental forces. Read this article by Fermilab here (Fermilab on Duality of Gravitons).

Duality of Gravitons

Scientists believe that a reconcile combination of understanding of gravity, Standard Model & Quantum physics can prove The Theory of Everything. 

Strings can move in 26 dimensions on basis of probability of its being stretch, bend, twist and formations of different shapes all while vibrating with particular frequency.  

String Theory was earlier developed as bosonic string theory, incorporating only bosons. It later developed into Superstring Theory, which posits the connection called supersymmetry b/w bosons & fermions. Further five more version of string theory were developed, which were conjectured and ultimately gave rise to M-Theory that works with 11 dimensions. 

Strings curled up in various dimensions

We know 4 dimensions and time, but scientists believe that other 6 dimensions are in compactification that means they are so tightly curled up on themselves that it required advance mathematics and geometry to understand them. Additionally they can interact with each other in more than 10^500 ways, which further increases the complexity. 

There are several equations that are vital for evolution of String Theory. The whole theoretical framework involves a wide range of mathematics. However, I'll try to provide a brief overview to key equations used in String Theory. These are:

• Nambu-Goto action equation: This equation describes how a string moves through space-time .
• Einstein Field Equations: This describes the relation b/w curvature of space-time, energy and the momentum contained within it.
• Schrodinger Equation: This is a counterpart of Newton's second law of motion. Schrodinger equation gives evolution over time of a wave function, or simply how particles evolves over time.

Now, that an overview of String Theory.

While our understanding of universe is still at a very initial stage, this theory stands as a chance to develop advance theoretical models to evolve our knowledge.  

Work done in String theory itself is also at an inceptive stage. This blog just covers a very tiny part of its wide understanding. 

One question still remains un-answered. What are applications of String Theory?

String theory can help us in many things:

• Evolution of mathematics - String Theory can help us with unifying various mathematical framework; such us developing advance mathematical tools like Calabi-Yan Manifold or Conformal Field Theory. 
• Understanding behavior of Black Holes - It's believed that Black Holes are composed of highly energized stings capable of warping space-time to an extreme degree. Also prediction of Holographic Principle that solves Black Hole information Paradox which states that information that goes into black hole should be encoded on its surface rather than in its interior. 
• Fine Tuning - understanding this will give us an apparent precision of certain physical constant that are necessary for existence of fundamental particles. 
• Understanding different physical laws and properties.

A recent study shows new connection b/w Quantum Field Theory and String Theory. It states that a certain String formulated in an appropriate spacetime in d+1 dimensions, is completely equivalent to gauge Quantum Fields formulated in flat spacetime in d-1 dimensions.

You know the best part about writing these blogs, while just trying to give an overview I got to learn tonns of new concepts. 

I really appreciate every person working behind these theories, because these theories are foundations for all coming advancement in mathematics and physics.

Cheers to all theoretical physicist, scientists and everyone involved in shaping our understanding of this beautiful universe. 

This blog is very special for me, after publishing it I got a message from Sean Carroll Sir.

Carroll Sir is a world famous Theoretical Physicist with specialization in Quantum Mechanics, General Relativity & Cosmology. He has been a research professor at number of world's top universities & research institutions. Here is his message:

This message means world to me. 

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