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1. The theory of everything

2. Let’s try to understand what is string theory all about?

3. String theory is a theoretical framework that tries to tackle the problems of how
and why the universe is like what it is now. In string theory, point-like particles are
replaced by one-dimensional entities called strings. String theory explains how
these infinitesimal strings travel and interact with each other. In normal classical
distance scales (larger than the string scale), a string is very similar to a normal
particle with its charge.
Refrence Link: https://byjus.com/physics/stringtheory/

4. 1-Macroscopic Level-matter
2-Molecular Level
3-Atomic Level-protons ,
neutrons, electrons
4-Subatomic Level-electrons
5-Subatomic Level-quarks
6-String Level

5.  In general relativity, gravity is a force that bends and warps space-time around supermassive bodies.
Even though gravity is one of the four fundamental forces in nature, it is very weak compared to the
other three forces (electromagnetism, weak force and strong force). So it can’t be observed or
identified on the scale of subatomic particles. However, gravity is very dominant in long-distance
scenarios. It controls the structure of the macro universe (galaxies, planets, stars, moons).
 String theory is a solution to general relativity which talks about big objects and quantum field theory
which talks about minute particles
 Reference Link: https://www.britannica.com/science/brane

6. Even though bosonic string theory was the first concrete version of string theory, it was only
concerned about bosons (a group of particles that transfer forces between fermions or matter). In
order to negotiate such limits, bosonic string theory was replaced by a class of theories called
superstring theories. These theories explain both fermions and bosons. So the whole standard
model came under the string theory hypothesis. The most striking development was the introduction
of supersymmetry. It allows each boson to have a counterpart fermion.
There are many versions of superstring theory.
 Type I
 Type IIA
 Type IIB
 Heterotic string theory (SO(32)
 Heterotic string theory (E8×E8)
 The various versions have different sets of strings. The particles that form at low energy levels show
varied symmetries.
Reference Link: https://www.britannica.com/science/brane

8.  In general, the term duality refers to a situation where two seemingly different physical systems turn out
to be equivalent in a nontrivial way.
 T Duality-
 The T-duality related the string theories to each other and the heterotic string theories to each other, indicating that they were
different manifestations of the same fundamental theory.
 S Duality-
 The duality is connected to the concept of a coupling constant, which is the value that tells the interaction strength of the string
by describing how probable it is that the string will break apart or join with other strings.
 For eg in electromagnetism the coupling constant is propotional to the square of electric charge.
Reference-https://en.wikipedia.org/wiki/String_theory

9.  String theory was developed from the idea of remodelling point particles to one-
dimensional entities called strings

 A string can be open or closed. An open string has two open ends, and a closed string
forms a closed loop. Strings have a tiny dimension, approximately the order of
planck’s length 10^-33 cm. This is the scale at which quantum gravity is believed to
become significant.
 Refrence Link: https://byjus.com/physics/stringtheory/

10.  Brane is a physical object that generalizes the notion of a point particle to higher dimensions.
 Branes are objects which can travel through space-time fabric, as per the constraints of quantum
mechanics.
 Branes possess mass and can have properties like charge.
 Brane is an entity that is extended in multiple dimensions. The brane concept arises in string and
universal theories like general relativity and quantum mechanics.
Here are some of the technical sides of
different branes.
Particle can be viewed as brane of dimension 0.
String can be viewed as dimension of brane 1.
Reference Link: https://www.britannica.com/science/brane

11.  We, as humans, can only perceive and control three dimensions (length, height and width).
 With the inception of general relativity, time is considered the fourth dimension. The only difference is
that we can control the first three spatial dimensions, but we cannot handle the time dimension.
 In general relativity, space and time are not separate; space-time is one entity.
 Gravity is considered as the byproduct of space-time geometry.
String Theory
 String theory must incorporate far more space-time dimensions than standard 3d or 4d space-time
for a solid mathematical base.
 There are twenty-six and ten dimensions in bosonic string and superstring theory, respectively.
 However, M-theory points to space-time with 11-dimensions.
Reference Link: https://www.britannica.com/science/brane

12. In 1995 Edward Witten stated that all the string theory versions
are just different limiting cases of one super theory.
It is called the M theory. It is based on eleven dimensions.
Edward formulated this conclusion, based on the findings of
Michael Duff, Chris Hull, Ashok Sen and Paul Townsend.
Refrence Link
https://byjus.com/physics/stringtheory/

13.  In a guitar String ,the different notes that sound when the string is plucked are a result
of properties of string : tension , length ,thickness
 The notes coming out of the guitar are excitation modes of the string
 The particles that are observed in particle accelerators can be thought of as musical
notes , or excitations modes of strings.
 Diff excitation modes make string appear as electrons , photons and so on
 Strings have a miniscule length that is called plank length which is about 10^-33 cm
 The strings oscillate because of tension and kinetic energy
 The quantum mechanics states that these oscillations take on vibrational modes.
 The string’s mass ,spin and charge is determined by the string’s dynamics.

14.  Start with a tiny string
 It is either an open or closed string
 It can only have bosons(particles that transmit forces) or it can also have
fermions(particles that make up matter)
 If there are only bosons,theorists will have bosonic theory
 If there are fermions the will need supersymmetry(equal number of bosons and
fermions:equal amount of forces and matter)
 This supersymmetry leaves the theorist with supersting theory

15. String theory attempts to unify all four forces namely-
gravitational force, electromagnetic force , string force and
weak force
It unifies general relativity and quantum mechanics and it
works on a simple idea that all particles are made up of
vibrating strands of energy called strings.

16. Bosonic string theory
Non-positive {displaystyle
M^{2}} states
Open and closed,
oriented
tachyon, graviton, dilaton, massless
antisymmetric tensor
Open and closed,
unoriented
tachyon, graviton, dilaton
Closed, oriented
tachyon, graviton, dilaton,
antisymmetric tensor, U(1) vector
boson
Closed, unoriented tachyon, graviton, dilaton
 Bosonic string theory is the original version
of string theory, developed in the late 1960s
and named after Satyendra Nath Bose. It is so
called because it contains only bosons in the
spectrum.
Reference-
https://en.wikipedia.org/wiki/Bosonic_string_theory#
Types_of_bosonic_strings

17.  According to string theory, all particles in the universe can be divided into two types: bosons and fermions. String theory
predicts that a type of connection, called supersymmetry, exists between these two particle types.
 Under supersymmetry, a fermion must exist for every boson and a boson for every fermion. Unfortunately, experiments
have not yet detected these extra particles.
 Supersymmetry is a specific mathematical relationship between certain elements of physics equations. It was discovered
outside of string theory, although its incorporation into string theory transformed the theory into supersymmetric string
theory (or superstring theory) in the mid-1970s.
 One benefit of supersymmetry is that it vastly simplifies string theory’s equations by allowing certain terms to cancel out.
Without supersymmetry, the equations result in physical inconsistencies, such as infinite values and imaginary energy
levels.
Reference- https://www.dummies.com/article/academics-the-
arts/science/physics/string-theory-and-supersymmetry-178720A

18. SUPERSTRING
Superstring theory is an attempt to explain all of
the particles and fundamental forces of nature in one theory by modeling
them as vibrations of tiny supersymmetric strings.
'Superstring theory' is a shorthand for supersymmetric string
theory because unlike bosonic string theory, it is the version of string
theory that accounts for both fermions and bosons and
incorporates supersymmetry to model gravity.

20.  Mathematically it has been proven that string theory exists but experimentally it
is still not proven
 NASA's Chandra X-ray Observatory helped power an experiment that might
refute string theory.
 Experimentation in real life based on string theory is still pretty new, with much
to discover.
 Scientists didn't find the particles they were seeking, which means one of a few
different takeaways.
 Researchers are still trying to find evidence to make this theory valid
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21. Machine learning may help identify universal features of the string
landscape .
 This requires string theorists to express compactification data in terms
of numerical data for mining .

22. String theory is the only known mathematically consistent quantum
theory of gravity
 String theory is hard to test experimentally because it supports a vast
landscape of effective theories at low energies
Machine learning could give us new insight into the string landscape

23.  SOME YOUTUBE LINKS FOR BETTER UNDERSTANDING
 Some YOUTUBE links for enhanced learning:-
 https://youtu.be/TI6sY0kCPpk
 https://youtu.be/-gVqZ0ubeC0
 https://youtu.be/Da-2h2B4faU
 https://youtu.be/n7cOlBxtKSo
 Source Links-
 https://byjus.com/physics/stringtheory/
 https://www.britannica.com/science/brane