Reading The Mind of God: A Look into String Theory

 This post has been a dream of mine for a long time — and if you love physics, I can proudly say this will be my best blog yet.

"If we can unify gravity and quantum mechanics and develop a Theory of Everything, we will be able to read the mind of god"- Stephen Hawking in his book: A Brief History of Time

"God doesn't play dice with the universe"- Albert Einstein on Quantum Mechanics

"I think I can safely say nobody understands Quantum Mechanics"- Richard Feynman in an interview

"String theory is rich enough to explain all the fundamental laws of nature. It seems nothing less than a miracle that, starting from some purely geometric arguments from a string, one is able to rederive the entire progress of physics for the past two millennia.”- Michio Kaku in his book: A Scientific Odyssey

Hey!  No better way to start a physics blog than some quotes from the best people to have done it. Stephen Hawking introduced Hawking radiation and the Information Paradox, Albert Einstein introduced the theory of relativity, which nearly blew the world away (if you know, you know), Richard Feynman, one of the best quantum physicists and teachers ever and Michio Kaku, a generational string theory physicist.

The greatest problem in physics is not a small thing as even the greatest of physicists have been trying for decades but nothing has come of it. This problem, why are so many people trying to solve it? Why is it such a big deal? Well, because this problem attempts to literally explain everything in the universe.

If you have read my earlier blogs, you would know that there are 4 fundamental forces of nature- Electromagnetic, Weak, Strong and Gravitation.

Gravity being the weakest and the strong nuclear force being, as the name suggests, the strongest, although in only small distances and I mean ridiculously small. 

Einstein's theory opened the door to Quantum Mechanics, but he didn't like it because it was filled with uncertainty. Nobody knew, what to do with it or how to solve it? Over the years, physicists have made great bounds and leaps, but we are still far away from a theory explaining all the laws of nature. How do we do that? We just have to introduce a theory unifying all the 4 fundamental forces and Quantum Mechanics, sound easy enough.

But it isn't. We have made a theory unifying the electromagnetic force and Quantum Mechanics named Quantum Electrodynamics (QED). We have also established a theory unifying the weak force, electromagnetic force and Quantum Mechanics named the Electroweak Theory. Not only that, we have a theory unifying the strong force and Quantum Mechanics named Quantum Chromodynamics (QCD). Finally, we have a theory unifying all these forces with Quantum Mechanics named the Standard Model of Particle Physics, and I have written a blog about it which was literally my 2nd blog.

Did you notice a pattern there? Gravity was not included in any of those, because gravity is the weakest force and its practically negligible in the Quantum world of small particles where the other forces thrive. 

Since, its negligible, when we incorporate Einstein's theory of relativity which is primarily about gravity into Quantum Mechanics, physics just breaks down. Weird things start happening, particles start having +1000 spin and -788 spin at the same time, trust me it gets weird. 

So, we need a theory to unify Gravity into the other forces and Quantum Mechanics, who's gonna do that? Enter: Superstring Theory! 

String Theory is the closest we have ever come to a unified grand field theory and its just elegant, the math is consistent and the universe is stable and it has made some great discoveries, solved paradoxes and explained the universe in a way which was not possible before. It is the greatest hope of physicists. So, let's take a look into it! 

String Theory: It's Fundamentals

String theory tries to explain everything in the universe and it starts off by explaining the structure of the universe.

 Our traditional notion is that particles like atoms can be split into smaller subatomic particles and quarks are the smallest sub atomic particles, so they make up everything in the universe. But according to string theory, what makes up everything in the universe are strings, 1 dimensional strings.

Every particle at the most fundamental or smallest level, is made up of strings. Strings! Its just strings, and how those strings vibrate decides how the particle they make up will react. Strings can also be of different types, like some strings are close ended while others are open ended and some are both. 

So, for example- if a string vibrates and oscillates a lot, its an electron and if it vibrates slowly and doesn't oscillate much, its a proton. It's like a guitar string, how it will sound like depends on with how much power you play it and how much it vibrates and what fret you press while playing it.

Supersymmetry (SUSY)

Supersymmetry is the lost child of string theory, if its found, then string theory is gonna be very happy but if its not, its a bit hard to move forward. Without supersymmetry, the math of string theory doesn’t hold together neatly — it’s like having a band without a guitar and only drums and a singer. 

From the word, you may understand the meaning, supersymmetry tries to explain to us that this universe has symmetry, its symmetrical, its not a random distribution of particles but rather an elegant arrangement of the very fabric of space-time. Going a bit on the deeper end of the physics, there are 2 types of particles- Fermions and Bosons. Fermions are particles of matter (electrons, quarks) and Bosons are force carriers (photons, gluons).

So, fermions structurally make up everything and Bosons do the work as they carry the forces. Now, SUSY says that for every fermion, there is a partner- a boson and for every boson, there is a partner- a fermion. So, they can't be alone.

But we haven't found any of these pairings until now because it would take a lot of energy to detect them and that's, to say frankly, out of our league for now. It's such a beautiful thing to know that our universe is symmetrical, not just some mumbo jumbo of particles.

Calabi-Yau Manifolds 

One of the most fascinating things I find about string theory are Calabi-Yau manifolds. They are pretty simple. String theory proposes that our universe is beyond the 4 dimensions we think we live in (3 space + time). 

It actually contains 11 dimensions but how does it contain so many dimensions and why can't we see them? 

I mean, we know we can't see time but if there are 11 dimensions, shouldn't we be able to see the other 10 spatial dimensions? We cannot see those other dimensions because they are super curled up with each other into small Calabi-Yau Manifolds. 

These manifolds exist at the very fundamental level and are so curled up that we cannot see them. Let me give you an example- Imagine a straw, from far away it just looks like a straight line, 1 dimensional but you go close enough and see that its 3 dimensional, its circular. Another one, imagine an ant walking on a pipe, the ant being so small can only perceive 1 dimension, it thinks that it can only go straight or back, not left or right. But the truth is that it can, because the pipe is circular but the ant does not know that. 

Simply, just like that we can only perceive 3 dimensions because the others are so curled up, they are so minute that even our most powerful microscopes cannot detect them and we are a very long way to go to actually detect them. Calabi-Yau Manifolds are curled up dimensions, which form complex 4D structures hard for our brain to imagine. These curled-up shapes are not random — their geometry actually decides how strings vibrate, and therefore what particles exist in our universe. These structures are elegant, and exist in the spaces in dimensions. 

M-Theory 

What if I told you string theory is just part of the picture and there is something even bigger? Enter: M-Theory.

M-theory is one of the leading candidates which will outcome in a Grand Unified Field Theory. It explains the universe with a different approach, not a different way. It takes up the fundamentals of string theory, dumps in its own ideas and makes it even more elegant.

Let me give you a little bit of history on this: In the 1980's, physicists introduced SUSY but were stuck at the idea as to why string theory had 5 types because of SUSY, the 5 types just had different types of strings behaving in similar patterns. In 1995, Edward Witten told the physicists of the world that all these theories were just the same theory from different angles and unified these theories into M-Theory. 

He did this by introducing ideas such as dualities. Just like wave-particle duality of quantum mechanics explains that a wave and particle are the same thing. Like how light can look like a particle or wave depending on how you observe it.

The difference in M theory is that it introduced the idea of Branes (short for membranes and not the biology ones).  Branes were fundamental multi-dimensional objects and they are pretty important. 

They could be like a point particle (0-brane), like a string (1-brane), like a sheet (2-brane), like a 3D shape (3-brane) and so on in higher dimensions (p-branes, where p is the number of spatial dimensions).

Strings could be attached to Branes and based on the shape of the brane, the particles made up will behave differently. There is also a theory that suggests that our universe is just a 3-brane floating in higher dimensional spaces.

So, branes help define properties of dimensions, can be attached to strings and literal universes can be made up of them, nice! 

The Biggest Success of String Theory

The greatest feat achieved by String theory has been solving part of the Information Paradox, introduced by Stephen Hawking. The information paradox is that black holes radiate energy known as Hawking Radiation, but this radiation looked random, so the information which fell in the black hole got lost but that is not possible according to Quantum Mechanics. 

Now, first of all, we didn't know what the singularities inside the black hole were made up of or what kind of an arrangement of particles a black hole had, but M-theory proposed that the black hole didn't have a random arrangement but rather it was made up of branes and strings curled up in specific multi-dimensional ways and its also explained the structure of a singularity as a structure of branes and strings.

Next, D-branes (a type of brane where open strings can attach) were used to make a black hole and all the different ways the branes could vibrate and arrange themselves (microstates) was calculated and the entropy (the amount of disorder in a system) value matched the Bekenstein-Hawking formula for calculating entropy of a black hole.

 This showed that black hole do have a microstructure and the information isn't lost, its encoded in brane/string microstates. This was the biggest success achieved by string theory to date, and it shows us that it has some real potential to become the Theory of Everything.

Loop Quantum Gravity: Some Competition!

Loop Quantum Gravity is a theory which tends to unify gravity and quantum mechanics but the biggest challenge with the theory is that it does not naturally incorporate the other forces. It also doesn't explain the particles as well as string theory does. Its also very hard to test experimentally. 

It proposes that space-time is made up of tiny loops of energy and it works in our familiar 4D (3 space+ 1 time) idea. These loops form structures known as Spin networks which forms space and these combine further to form Spin foam which is Space-time. 

Its math is elegant too, but a lot of phsyicists are skeptical towards it and String theory is still in the leading as QLG hasn't made any big breakthroughs. 

Fun Fact: String Theory was developed as a mistake. In 1970's, some physicists were trying to unify Strong force and Quantum Mechanics when they suddenly realised that their theory naturally contains a hypothetical particle called a Graviton, which is a boson (a force carrier) for gravity.

P.S- I'm gonna reference my other blogs so you can get a clearer understanding of the physics.

References- Newton's Laws of Motion, The Forces of Nature, The Special Theory of Relativity, The General Theory of Relativity, The Quantum World in a Nutshell!, Wondering about the Stars, What is at the Edge of our Universe?

You can visit the above blogs at this link: deeparshbhanot.blogspot.com

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Deeparsh Bhanot