The theory of everything is the immediate need of Physicists. They need this for several reasons, I will discuss them. Sir albert Einstein spend almost a decade of his last days to develop the theory of everything, but failed. What is the need of theory of Everything? What it has to do with string theory?
The work on string theory began almost a half century ago in 1968. It wasn’t meant to be the theory of everything but over the years it has proved to be one of the strongest candidates. We will explore several basics about the theory, it’s postulates, it’s needs, main highlights, different versions of the theory and many more.
Let’s get started….
The need for The Theory of Everything
There are 2 main theories explaining the universe at different scale and work very well in their respective domain. The general theory of relativity explains the universe at the scale of cosmos like the planets, stars, galaxies, etc. The quantum theory explains the universe on the scale of atoms. The scale in between both the theories is well explained by the classical physics. But there are many things which cannot be explained by any of the known theory. When applied to those problems we get unexpected and weird solutions that are very unlikely to be physically correct.
There are 2 most popular problems arising: the infinity and the anomalies. The Infinity arises when the values of the physical parameters like the energy, probability increase to infinity (number bigger than we can imagine). The Anomalies arise when the results violate the symmetry they are supposed to preserve. It is like your own security guard tries to hurt you.
One of the most mind hurting problem in front of physicist is to answer the questions like what is inside blackhole? What was there before the big bang? The physicists fail to answer these questions. Why? It is because our present theories break down and give weird results (like infinity) when applied to explain the behavior. This is called singularity. Singularity is when the fabric of space-time bends to infinite amount.
According to General relativity, the space is smooth like classmate paper sheet. But quantum theory says that at Plank’s Length (~10-35 m), the universe is very rough. It is the sea of virtual particles. The particles and anti-particles are being created and destroyed within fraction of second. The nature is very blurry at such scale. The present theory cannot figure out this kind of behavior.
For the above mentioned and many more such reasons we need The Theory of Everything which can be done by marrying the General relativity and the Quantum field Theory together.
Elements of string theory
Before getting into string theory we need to understand several terms that form the backbone of String Theory. Those are: -
1. Strings and branes
The string is defined as the fundamental vibrating filament of energy. It is fundamental and all the known particles are made from it. Strings are 1-dimensional in nature. The strings can be open as well as close in nature. The branes are the 2-dimensional sheets upon which the strings are overlapped.
Imagine of the door mate. The threads can roughly represent the strings and the structure upon which threads are present represent branes. The string and branes are the building block of every known fundamental particle.
2. Super symmetry
Symmetry is the fundamental property of nature. Just look at yourself and things around you, everything is symmetric. In the language of physics, if 2 properties are swapped and the result remains same, it considered symmetric in nature. The super symmetry is bit different. Super symmetry states that for every boson there is a fermion and for every fermion there is a boson. Bosons are the force carrying particles like photons, gluons, etc. While, fermions are the units of matter like the electrons, protons, etc.
The relation between physics equations get simplified if we introduce super symmetry. Without super symmetry we get imaginary results or infinities, which are a warning signal that there is something wrong. However, it is not verified experimentally. We have so far discovered 18 fundamental particles. But according to string theory there must be 36 fundamental particles.
3. Higher dimensions
We live in 4-dimensional world, 3 dimensions of space and 1 dimension of time. Dimension is basically the coordinates using which our position can be determined like the latitude, longitude and height. In simple words, left or right, backward or forward, up or down are the only 3 directions in which we can move and the 4th dimension time is also being translated by us. So, these are the 4 dimensions in which we live.
What do higher dimension mean? The higher dimension means dimensions more than 3. But we only know of 4 dimensions, where are the other dimensions? The dimensions might be curled up or so small that we cannot discover them. Before Einstein, we knew about 3 space dimensions only. The other explanation is that we might have got stuck into the 3-dimensional membrane.
Just imagine of a bee who is stuck on a membrane full of glue. The bee can only be on the membrane and cannot move away from it. The same might be true for us. Several experiments are being conducted and being planned to find the hidden dimensions.
Main Highlights of string theory
There are several main points of string theory that are given in short below. I have combined the common point from several versions of string theory and presented them below.
1. All objects are composed of strings
2. String theory can explain the domains of the general theory of relativity and the quantum field theory together.
3. All the known fundamental forces can be combined into one. The known forces are the gravitational force, the electromagnetic force, the weak nuclear force and the strong nuclear force.
4. There is a super symmetry between all the fundamental particles in nature.
5. There are higher dimensions present. Some versions of string theory predict 26 dimensions and other 11 dimensions.
Different version of string theory
There are several versions of string theory but none of them has qualified to be the theory of everything. I will discuss below 2 popular early versions of string theory.
A. Bosonic string theory
This theory states that all the particles are a result of multi-dimensional string vibrations. It was developed in 1968 and was popular up to the 1970s. But this version has many problems, it was a mathematical mess. The theory was not consistent with the known physical world. It violated many proven physical laws and theories. Moreover, it was neither consistent with the general relativity nor the quantum theory.
There were 4 main results obtained from bosonic string theory: -
* There are 25 space dimensions and 1 dimension of time. All total bosonic string theory needed 26 dimensions to work properly. We only know about 4 dimensions. (big problem)
* There exists a particle that moves faster than light. The particle was named Tachyon.
* Fermions cannot exist according to this theory. This is ridiculous because we know of many fermions to exist like electrons, protons, etc.
* There exist many massless particles. We know some massless particles like photons, gluons, etc.
Tachyons are not yet found. For tachyon to move faster than light it should have negative mass. The negative mass is also not found and there is no evidence for its existence.
This theory was most popular theory of its time. The supporters of this theory cannot verify it experimentally. Hence, it lost its importance.
B. Super string theory
In 1971, the Super String Theory begin to develop. It mainly focused on the super symmetric property. It was developed by several physicists independently and included same postulates. This indicates that there is some connection between the postulates and the nature of reality. it, unlike Bosonic String Theory, included only 11 dimensions (10 space dimensions and 1 time dimension).
The notable group of Super string developers are:
a. In 1971, Evgeny Likhtman, Yuri Golfand, Vladimir Akulov and Dmitri Volkov developed the 2D super string theory. They all were Russian physicists.
b. In 1973, Julius Wess and Bruno Zumino developed the 4D version of super string theory. They all were Europeans.
c. In 1970 and 1971, Pierr Raymond, John Schwartz and Andre Neveu developed the theory.
The different group of physicists developed the theory independently and were unaware of each other’s work because there was communication gap because of the Cold War.
Bosons and fermions have different properties and cannot be swapped easily as super symmetry suggests. Naturally also the partners are not found. The corresponding partner of boson and fermion was hypothesized as super partner. The quest for super partner began.
The 2 main problems with bosonic string theory were the Tachyons and the 26 dimensions. These problems were solved up to some extent by the super string theory. The tachyons vanished and the dimensions reduced to 10. Now the main problem was to find the rest 6 dimensions as we know only 4.
There are several things explained by the string theory. Many aspects of the theory are just theoretical and not verified practically. There is a lot of research going on and surely, we will get the theory of everything in next few decades.
In the next post (27th September, 2020), I will discuss: -
* M-Theory, the mother of all string theories
* How string theory can be tested
* How mass and energy is formed according to ST
* Recent developments in String Theory
* Parallel universe and time travel according to ST
and more…… so stay tuned.
Great. Work
ReplyDeleteAwesome Blog. Keep Going. 🙂
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