What is String theory: Definition and 829 Discussions
In physics, string theory is a theoretical framework in which the point-like particles of particle physics are replaced by one-dimensional objects called strings. String theory describes how these strings propagate through space and interact with each other. On distance scales larger than the string scale, a string looks just like an ordinary particle, with its mass, charge, and other properties determined by the vibrational state of the string. In string theory, one of the many vibrational states of the string corresponds to the graviton, a quantum mechanical particle that carries gravitational force. Thus string theory is a theory of quantum gravity.
String theory is a broad and varied subject that attempts to address a number of deep questions of fundamental physics. String theory has contributed a number of advances to mathematical physics, which have been applied to a variety of problems in black hole physics, early universe cosmology, nuclear physics, and condensed matter physics, and it has stimulated a number of major developments in pure mathematics. Because string theory potentially provides a unified description of gravity and particle physics, it is a candidate for a theory of everything, a self-contained mathematical model that describes all fundamental forces and forms of matter. Despite much work on these problems, it is not known to what extent string theory describes the real world or how much freedom the theory allows in the choice of its details.
String theory was first studied in the late 1960s as a theory of the strong nuclear force, before being abandoned in favor of quantum chromodynamics. Subsequently, it was realized that the very properties that made string theory unsuitable as a theory of nuclear physics made it a promising candidate for a quantum theory of gravity. The earliest version of string theory, bosonic string theory, incorporated only the class of particles known as bosons. It later developed into superstring theory, which posits a connection called supersymmetry between bosons and the class of particles called fermions. Five consistent versions of superstring theory were developed before it was conjectured in the mid-1990s that they were all different limiting cases of a single theory in 11 dimensions known as M-theory. In late 1997, theorists discovered an important relationship called the AdS/CFT correspondence, which relates string theory to another type of physical theory called a quantum field theory.
One of the challenges of string theory is that the full theory does not have a satisfactory definition in all circumstances. Another issue is that the theory is thought to describe an enormous landscape of possible universes, which has complicated efforts to develop theories of particle physics based on string theory. These issues have led some in the community to criticize these approaches to physics, and to question the value of continued research on string theory unification.
Hi all!
I am ready for applying for my PhD which I want to be on String Theory and in Europe. I am finishing my master's degree in Theoretical Physics and currently I am researching Holographic Renormalization for asymptotically non-AdS space-times.
I am interested in all aspects of String...
Why string field theory doesn't explane a black singularity but its called the theory of everything?
It just explanes quantum gravity not why the universe exists or why we exist, what I am tring to say is that it should not be called the theory of everything.
... due to whatever. What has the effort provided besides showing that the universe doesn't work a certain way? Assuming it has aided in other areas of physics and mathematics. Any examples?
Thanks.
This was just posted on arxiv. It seems to be of general interest so here's a thread in case anyone wants to discuss it.
http://arxiv.org/abs/1308.1977
Holography without strings?
Donald Marolf
(Submitted on 8 Aug 2013)
A defining feature of holographic dualities is that, along with the bulk...
Laurent Freidel is working on string theory again. His earlier paper, with Krasnov and Livine, which had a remark on the subject was Holomorphic Factorization for a Quantum Tetrahedron
http://arxiv.org/abs/1307.7080
Born Reciprocity in String Theory and the Nature of Spacetime
Laurent Freidel...
From looking at the Wikipedia entry on string theory I gather that it is found that any given physical model implies two Calabi-Yau spaces.
Perhaps one space gives rise to a sector of particles with left-handed weak interactions and the other gives rise to a sector with right-handed weak...
The notion field of Quantum Field Theory is deduced from the combination of Quantum Mechanics and Special Relativity.The local characteristic of field is led from Cluster Decomposition Principle.
String Theory is also a combination between Quantum Mechanics and Relativity Theory.Then I wonder...
In another thread Ben indicated that string theory formulated as non-linear sigma model using world-sheet action is - in some sense - background independent. To discuss this I start with a generalization of the Polyakov action
##S_G[X] = \frac{1}{4\pi\alpha}\int d^2\sigma \, \sqrt{g} \, g^{ab}...
There is still, to this day, absolutely no empirical proof that string theory is correct, or even that it can predict anything , but I know it's mathematically elegent ,here's feynman view on it:''I don’t like that they’re not calculating anything. I don’t like that they don’t check their ideas...
One of my goals in life is to get a reasonable understanding of string theory. This is done as a hobby of mine so I will not have a professor to ask.
My question is: which route would you recommend for learning this?
My thoughts:
I understand many people think highly of "A First Course...
Hey everyone, I've been trying to get a rough idea of what types of classes I should be taking for my upper level undergrad courses, and get an early idea of what type of graduate elective courses I should be taking. I'm a double major in physics and math, and plan to go to grad school for...
Hi
As far as I understand, that teleportation using quantum entanglement is only partially instantaneous, because a classical channel has to be used to send the two qbits from Point A to B. So the speed of light is the boundary as how fast teleportation can happen one day using
this...
Hi everyone. I'm interested in computational science but have an interest in string theory as well as I'm sure a few people here do. My question is does computational science have a place in the research for string theory? Would a physicist simply give some numbers for a computational...
Probably a bit abstract,but I was thinking if 4D closed strings could form knots? I mean if a closed string in 4-dimensional spacetime can be considered an unknot and a knot polynomial be associated with every closed string. I also wondered that if the fundamental strings vibrate in the knotted...
I have a question about the paper:
C. G. . Callan, R. C. Myers and M. J. Perry, “Black Holes In String Theory,” Nucl. Phys. B
311, 673 (1989).
I have attached the relevant section.
I am having trouble using equations (2.1) and (2.4) to derive (2.5) and (2.6). When I do the calculation...
Does string theory, in principle, answer why matter comes in "chunks"?
Does string theory, in principle, answer why matter comes in "chunks" of the same amount (say the mass of an electron or muon), and why the energy in the electromagnetic field of a given frequency also comes in a "chunks"...
In covariant quantization of the string, say as in David Tong's http://arxiv.org/abs/0908.0333 (p28), time is an operator.
Is the time operator Hermitian, and does it correspond to an observable?
LQG, strink theory and Penrose's spinor theory, or maybe it's twistor theory, I don't know, all I know is that all three theories achieve mathematical miracles in their attempts to go beyond the Standard Model - how can all three theories do this but be mutually exclusive at the same time. Or...
Hi everyone,
I've always wondered what's that fuss for unifying general relativity and quantum mechanics all about. I stumbled upon things like string theory(or M theory) and even loop quantum gravity( which I think is as good as string theory despite rumors).
My...
Hi!
Reading some string theory books I always find that the introductory chapters discuss the relativistic free particle.
Then they go on about showing that the action
S=-m\int^{t_1}_{t_2} dx = -m \int^{t_1}_{t_2}d\tau\sqrt{-\frac{dx^\mu}{d \tau} \frac{dx^\nu}{d \tau} \eta_{\mu\nu}}
is...
"Foundations of physics" Special Issue: Forty Years of String Theory
http://www.springer.com/physics/history+&+philosophical+foundations+of+physics/journal/10701
If this has already been mentioned feel free to delete this post.
Articles free through march,
A Critical Look at Strings (Carlo...
I have been following Dr. Michio Kaku and his ideas on string theory. My question is, with the addition of other dimensions, what types of experiments and/or results could possibly provide evidence that this theory is correct. If we currently can't perceive these "discrete" dimensions, what...
From whst I have read, anything smaller than Plancks length, you need to account for quantum gravity.. also, it is assumed strings in string theory are Plancks length.. so how could anything be smaller than Plancks length if strings are Plancks length(or greater than)? I thought strings made...
Background-independence is the requirement that the theory be formulated based only on a bare differentiable manifold but not on any prior geometry. General relativity is the first example of such a theory. This is a radical shift as all theories before General relativity had part of their...
hello,
I find both quantum mechanics and string theory to be a bit iffy. Mabey it's just because I don't understand it but I think the best way to understand the iffy stuff is to post it on here. Mentors might see this as a debate or going against mainstream physics but how are you able to make...
There was a thread about how to describe the proton in string theory that was deleted while I was writing an answer, so I will post my answer here in a new thread.
How the proton, and processes inside the proton, are described in string theory, is an open research question, part of the area...
Hey guys,
who can tell me briefly about the 10+1 dimensions in the string theory? I am going to deliver a short presentation on string theory ,but i am not very clear about the reason that we have to introduce 11dimendion to string theory ...
I just recently seen an article that the recent findings at the LHC seem to disprove supersymmetry. I would like to know how supersymmetry and string theory are connected and what the implications would be if the LHC totally disproves supersymmetry all together?
I had an exchange with Lubos Motl about this topic, in the comments here.
Very briefly, there is a 2004 paper in which the author (Kjell Rosquist) considers the old idea that the electron is actually a spinning, charged (i.e. Kerr-Newman) micro black hole. Using a purely classical model for...
Just about few hours ago,my friend and i argued about which theory is the best theory nowadays ever existed. I claim that string theory is the only game in town as what i heard from Dr. Michio Kaku's TV shows, while my friend strongly disagree with it. He claimed that quantum theory is the best...
Consider me physics illiterate since my last class was advanced placement physics in high school (over 20 years ago). I am trying to understand what the title says, How does quantum entanglement, string theory, and the BB fit together?
Skipping to the meat of the subject, everything revolves...
I was watching a video on string theory and they claim that its all vibrating strands of energy. I thought energy was just a property of the system, not a physical entity. So do they mean something else by "energy"?
I understand that suitable compactified strings in AdS correspond to conformal field theories (w/o gravity) living on the boundary space. What I do not get is the exact relationship between non-perturbative gravitational phenomena in the bulk and the CFT.
All what I have seen are...
Could someone give me a short summary(if possible) of how discovering matter is made of vibrating energy will give explanation to all four fundamental forces?
I mean we really don't know what they are, right? We just know they can be positive or negative, north or south, but we really don't know why they exist. Will string theory give a definite answer to this? And also gravity. Will it confirm Einsteins theories?
Hi, I have a question concerning simple bosonic string theory governed by the Polyakov action. Under which assumptions/requirements is the corresponding worldsheet theory a conformal field theory? Is this always true or does it depend on the topology of the worldsheet?
Conformal symmetry of...
Hi all,
Would like to start off by letting you all know i am new to the PF and the reason for joining is due to constant ideas and thoughts flooding my brain to no end, i do not have any physics degree's but i do share an intense interest in Physics.
According to a friend of mine the only...
I have recently been reading up on the basics of string theory and my question is this. How exactly are strings "allowed" to vibrate? In particular, do they have to be in all ten dimensions of space as predicted by M-theory at once? Or can they just "reside" in several of those dimensions...
It's really difficult as a layman trying to find out who is right and wrong in this debate as far as string theory. I find it kind of hard to believe that string theory is just simply completely wrong and has no relevance whatsoever to reality. After all so many theorists and so many papers...
Hi. I am fairly new to physics. I have recently read the first half of a book by Michio Kaku called “Beyond Einstein”, and I am really struggling to get my head around the superstring theory.
The superstring theory seems illogical for the following reasons...
1. Nature demands symmetry. So...
Gerard 't Hooft just dropped this interesting paper.
http://arxiv.org/abs/1207.3612
Discreteness and Determinism in Superstrings
Gerard 't Hooft
Ideas presented in two earlier papers are applied to string theory. It had been found that a deterministic cellular automaton in one space- and one...
Now obviously String Theory has been responsible for some valuable research, and even if the theory were completely disproven (although I don't see how; my understanding is that it is still too vague in it's predictions and descriptions to be proven or disproven conclusively). But String Theory...
Can Loop Quantum Gravity and String Theory coexist? What if String theory was correct in its description of matter and 3 of the 4 forces, with the only difference from modern M theory being that there is simply no real particle called the graviton, and instead, gravity is as is described by LQG...
Hi everybody,
let's assume the Higg's boson exists. If I understand String theory correctly (and I understand very little of it), then Higg's particle - just as any other particle - can be expressed as a particular vibration state of a string.
If I understand Higg's theory correctly, then...
Each year, the annual String conference provides us with a kind of snapshot of the field as it is today. The lineup of invited speakers and the titles of their talks give an idea of the current activity and interests of string researchers.
This year Strings 2012 is in Munich and starts on...