Quantum Physics
1995 - The M-theory
M-theory was used to explain a number of previously observed dualities (using which one string theory could be transformed into another). M-Theory requires 11-dimensions and higher dimensional objects called D-branes. M-theory is widely regarded as the theory of everything.
1997 - AdS/CFT correspondence
Proposed by Juan Maldacena in 1997, the correspondence associates the type IIB superstring theory in 10-dimensional Anti-de Sitter space (AdS) with the conformal field theory (CFT) such as supersymmetric Yang-Mills theory in 4-dimensional spacetime. The significance of AdS/CFT correspondence is the relation of quantum gravity and quantum field theory. Thus, it's also named "gauge/gravity duality".
M-Theory
This is unifying theories that try to combines the 5 different string theories into one theory. This theory was to predict that all these different theories were connected due to some underlying theory of which they were all approximations. This theory is somewhat vague in nature and has not yet been pinned down. M-theory marks the end of "string theory".
Who Invented the String Theory?
This theory contains multiple versions since it was proposed by physicists in the 1960s.
1968 - Particle theorists develop theories that support string theory
Three particle theorists independently realize that the dual theories developed in 1968 to describe the particle spectrum also describe the quantum mechanics of oscillating strings.
Basic Properties
Two actions are used to describe how strings move along space and time. It will predict how and where the string will be on the world sheet and describe it in spacetime.
1921 - Kaluza-Klein Theory
Two scientists by the name Kaluza and Klein discover that electromagnetism can be derived from gravity if there are 4 dimensions. This adds feasibility to the string theory. Kaluza and Klein made this discovery independent of eachother.
Heterotic strings
Type HO & Type HE string theory - A closed string which is a hybrid of a superstring and a bosonic string. - Right-moving vibrations resemble the Type II strings and whose left-moving vibrations resemble the bosonic strings. - Both have difference gauge group which is SO(32) for type HO, E8×E8 for type HE.
1) Polyakov
Used in 2D conformal field theory to describe the worldsheet of string in string theory
Why Bosonic String Theory Doesn't Describe Our Universe?
1. The existence of massless particles, which hadn't been observed experimentally 2. The existence of tachyons, which move faster than the speed of light 3. The fact that fermions, such as electrons, can't exist 4. The existence of 25 spatial dimensions 5. The fact that certain configurations of interacting strings gave rise to infinities
5 Theories of String Theory
1. Type I 2. Type IIA 3. Type IIB 4. Type HO 5. Type HE
Type I String Theory
- Involves both open and closed strings. - Contains a form of symmetry that's mathematically designated as a symmetry group. - Happens to be the group of rotations and reflections in 32 dimensions.
Characteristic of the Strings
1) The strings oscillate due to tension and kinetic energy acting on it. 2) The quantum mechanics of strings states these oscillations will be in vibrational modes. 3) These modes behave differently from particles. 4) The mass, spin, and charge of spring is depends on the string's dynamics.
Possible Implication of String Theory
1)Parallel universe 2)Wormholes 3)String theory and time travel 4)String theory an big bang 5)The end of the universe
Levels of Magnification
1. Macroscopic level - Matter 2. Molecular level 3. Atomic level -- Protons, neutrons, and electrons 4. Subatomic level -- Electron 5. Subatomic level Quarks 6. String level
The End of the Universe
A final version of string theory may help us ultimately determine the matter density and cosmological constant of the universe. By determining these values, cosmologists will be able to determine whether our universe will ultimately contract in upon itself, ending in a big crunch and perhaps start all over again.
1980 - Superstring
A mathematical relation between bosons and fermions. String theory and supersymmetry yield an excitation spectrum which contains equal number of Bosons and Fermions. The resulting objects are called superstrings.
1973 - Goldstone publishes paper
A scientist by the name of Goldstone published paper on String quantization. Generated interest in the field.
1943-1960 - S-Matrix Theory
A theory initiated by the German physicist Werner Heisenberg in 1943 and developed extensively in the 1950s and 1960s to describe strong interactions in terms of their scattering properties. S-matrix theory uses general properties, such as causality in quantum mechanics and the special theory of relativity. The discovery of quantum chromodynamics as the fundamental theory of strong interactions limited the use of S-matrix theory to a convenient way of deriving general results for scattering in quantum field theories. String theory, as a theory for hadrons, originated in attempts to provide a more fundamental basis for S-matrix theory.
1984 - The biggest year for String Theory
Deadly anomalies that threatened to make the theory senseless were discovered to cancel each other when the underlying symmetries in the theory belong two special groups. Finally string theory is accepted by the mainstream physics community as an actual candidate theory uniting quantum mechanics, particle physics and gravity.
1984 - First superstring Revolution
Discovery of anomaly cancellation in type I string theory
1970 - String theory is born
Dual theories developed in 1968 to describe particle spectrum also describe oscillation of strings.
Why dimension is important in String Theory?
For string theory to work, it assumes that the existence of 10 dimensions (9D of space + 1 D of time) is needed. It is important because our usual space-time doesn't give the strings enough "room" to vibrate in all the ways they need to in order to fully express themselves as all the varieties of particles in the world. They're just too constrained. In other words, the strings don't just wiggle, they wiggle hyperdimensional.
Type IIB String Theory
Involves closed strings that have asymmetrical vibrational patterns depending on whether they go left or right along the closed string, while the open strings are attached to D-branes with an even number of dimensions.
Type IIA String Theory
Involves closed strings that have symmetrical vibrational patterns regardless of whether they travel left or right along the closed string, while the open strings are attached to structures called D-branes with an odd number of dimensions.
Why We Need to Understand about String Theory?
It describes how our universe work fully. We can get to know what's happening in low energy levels and describe how forces conceptualized on a gigantic level such as gravity could affect tiny objects (electron & proton).
2) Nambu-Goto
Only works on 1D flat targets and not a primary action when physicists developed quantized version of string theory. The simplest invariant of action in bosonic string theory
Parallel Universe
Some interpretations of string theory predict that our universe is not the only one. In fact, in the most extreme versions of the theory, an infinite number of other universes exist, some of which contain exact duplicates of our own universe. It is predicted by current research studying the very nature of the cosmos itself. As a matter of fact, parallel universes aren't just predicted by string theory — one view of quantum physics has suggested the theoretical existence of a certain type of parallel universe for more than half a century.
Wormholes
String theory allows for the possibility that wormholes extend not only between distant regions of our own universe, but also between distant regions of parallel universes. Perhaps universes that have different physical laws could even be connected by wormholes. However, it's not clear whether wormholes will exist within string theory at all. As a quantum gravity theory, it's possible that the general relativity solutions that give rise to potential wormholes might go away.
What is String Theory?
String theory attempts to reconcile general relativity (gravity) with quantum physics. It states that everything in our universe is made of one-dimensional tiny vibrating strings rather than point-like particles.
String Theory and big bang
String theory is being applied to cosmology, which means that it may give insights into the formation of the universe. The exact implications are still being explored, but some believe that string theory supports the current cosmological model of inflation, while others believe it allows for entirely universal creation scenarios. In string theory, there also exists a possible alternate model to our current big bang model in which two branes collided together and our universe is the result. In this model, called the ekpyrotic universe, the universe goes through cycles of creation and destruction, over and over.
String Theory and Time-Travel
String theory may allow for multiple dimensions of time (by no means the dominant view). As the understanding of string theory grows, it's possible that scientists may discover new means of traveling through the time dimension or show that such theoretical possibilities are, in fact, impossible, as most physicists believe.
1996 - Blackhole physics explained by String Theory
String theory sheds amazing light on the perplexing subject of black hole quantum mechanics.
1974 - Theory of quantum gravity
Strings with closed loops are a candidate for gravitons, which mediate the force of gravity
Superstring Theory
Superstring theory is another name for string theory. Superstring theory helped with some of the major problems of bosonic string theory. 1. Massless particles were still present in the theory, but weren't seen as a major issue 2. Tachyons vanished 3. Fermions now existed within the theory 4. nine spatial dimensions (plus one time dimension) which means 9D of space + 1 D of time.
1976 - Supergravity
Supersymmetry and the equations of general relativity added to gravity to form supergravity
Key Events in String Theory History
The development of string theory has not always been in one clear direction. In fact, a great deal of important work was completed before physicists even realized the significance of strings.
1991 - Duality revolution
The different flavors of superstring theory were found to transform into one another using duality
First String Theory
The first string theory known as bosonic string theory, This theory had consequences that made it unrealistic to use to describe our reality. The first basic physical interpretation of string theory was particles as vibrating strings. As the strings, each representing as a particle, collided with each other.
1995 - Second superstring revolution
The research this time focused on uniting the different string theories into one by adding an 11th dimension that had been proposed by Witten and Mike Duff
String Theory Controversy
The theory may be 'true' in explaining nature's riddle, yet super-micro also exists in our universe, and new particles that are predicted to exist are too heavy to be observed in the near term foreseeable future, making it difficult to tell if string theory is correct or not.
1971 - Supersymmetry
There need to be equal number of Bosons and Fermions in the non Bosonic versions of string theory.
