String theory Definition and 833 Threads

I've completed my PhD and am leaving the field to take up a career elsewhere, however I'm interested in developing my knowledge of string theory as a (potentially lifelong) side project. I have a solid understanding of GR and some extensions (my PhD was in relativistic effects in cosmology, and...

Physicist Joseph Polchinski wrote an article (https://arxiv.org/pdf/1412.5704.pdf) where he considered the possibility that all symmetries in nature may not be fundamental. He says at page 36: "From more theoretical points of view, string theory appears to allow no exact global symmetries, and...

Given that Penrose now got the Nobel prize for a theory that is almost impossible to verify experimentally in a near future (that is, for theorems that predict singularities inside black holes), does it mean that now string theory can also get a Nobel prize? (If so, Witten and Schwarz would be...

Usually, I saw that string theory (perturbative, or matrix models) are made in a fixed background. Even if you consider that the metric is quantized and etc. there is an apparent physically motivated need for making a sum over topologies (manifolds, conifolds, orbifolds, and etc), for example...

Quite a long time ago, I read about length of strings in string theory. And, if I remember correctly, expected length was in light years. I looked at Wikipedia today, and I see currently expected length of string is very small, around Plank size. Is it changed over time, or the expected length...

If string theory is correct does it mean that elementary particles like photons, electrons, and quarks don't really exist or does it mean they do but are made of cosmic strings and so therefore are not elementary?

If anybody has studied the book: A First course in String Theory - Barton Zweibach - 2nd edition This statement is present in 6th chapter of book on pg 110

Well I became interested in String theory before my high school. Now I am in ginal year of my BS in Physics. I am working on a project in string theory.

In the notes of Arutyunov, he writes down the equation of Polyakov action in what he calls a first-order formalism(equation 3.19). But here I did not understand how he got this equation. Can someone help? Moreover, can someone explain how he got the constraints in equation 3.25? And why they...

Well there was today some lecture on String theory which I got late since I was reading something else in Condensed matter physics and then I looked at a book that I have of stochastic Integration with jumps and by associativity of ideas I searched google for Stochastic String Theory and got to...

I am a second year Physics student. I am keen to know more about the space(strings) and everything around me and how they interact with each other(the true behind energy). I really think studying physics was my perfect choice I have made and being part of Physics Forums too. Working on...

All the accounts which I have read (and which are accessible to my limited knowledge of General Relativity and its mathematics) on the holographic principle says vaguely that the AdS/CFT correspondence is very enlightening, but with the caveat that, well, we don't happen to live in an AdS space...

Is there any version of string theory or cosmological inflation that allows the most fundamental laws and constants change between universes? String Theory and Cosmological Inflation are two theories or models that allow multiple universes to exist. Laws and constants of physics could change...

As I understand it, dimension is a way of describing direction, with the first three spatial dimensions being straight lines which extend infinitely in one direction, perpendicular to each other. In string theories, several additional dimensions are required, sometimes up to nine or 10, I...

I do not pretend to understand M-theory or even any of the string theories which make it up, so the answers to these questions do not need to get too much into detail. The two (related) questions: (a) Forget for a moment that this is supposed to be describing our known universe. Is there a...

I understand that strings have a size of roughly the Planck length ##l_P## of ##10^{-35}## m. If that is the case then one would expect that their mass would be roughly the Planck mass which is an enormous ##10^{19}## GeV. (Strings that have small spins, like standard model particles, are...

Randall-Sundrum model (https://en.wikipedia.org/wiki/Randall%E2%80%93Sundrum_model) is related to string theory. String theory can be background independent (https://en.wikipedia.org/wiki/Background_independence): "String theory is usually formulated with perturbation theory around a fixed...

i can't find on internet why higher spin tensors are totally simetric. know this anyone ? I think that is connected to spin matrices.

Full quantization of gravity is a big issue, but that's not what I'm asking here. I'm asking about quantum effects that involve any form of gravitation (Newtonian or GR) but that don't require a full quantization of GR or anything like that. Things like gravitational neutron interference or the...

I have been asked to draft a (informal) research proposal for a PhD thesis. I have some background in quantum information and my interests are leaning towards the AdS/CFT correspondence. I was wondering if you could suggest a few (preferably recent) theory papers at the junction of quantum...

The fundamental building blocks of the universe is thought of super strings, if proved can solve the mysteries of the universe but if proved than how? And how can it solve the mysteries of dark energy &dark matter and black holes?

I have a masters degree. I studied general relativity and quantum field theory. I was interested in applying to PhD programs for AdS/CFT. I was wondering how integrability fits in the context of AdS/CFT. As I understand, the AdS/CFT correspondence postulates a duality between gravity theories...

M-Theory is a theory of membranes which are the fundamental objects of the theory (M2 and M5 branes), however these objects are considered solitons, solutions of supergravity. How can membranes be "fundamental" if they are solitonic solutions of supergravity? Or am I missing something? And is...

So I had a topic which I would like to fact check from an informed scientific source. Basically there is an argument about whether or not an object that naturally exists in a fourth dimensional space, would by default have more than countably infinite times the energy of a 3 dimensional Object...

How the repulsion between electrons occurs in String theory and in the loop quantum gravity? The electrons will also create electrostatic fields, or will it be the another mechanism?

I posted this earlier, but the thread has been closed. String theorists frame much of their studies in the context of Planck length. The theories are meant to fold together QM and general relativity. The equation for Planck length includes the gravitational constant, G. It seems to me the...

String theorists frame much of their studies in the context of Planck length. The theories are meant to fold together QM and general relativity. The equation for Planck length includes the gravitational constant, G. It seems to me the theorists are assuming the gravitational laws extend to...

Hello everyone, I am currently finishing my Masters in Theoretical Physics and looking forward to continue in a PhD. I always thought I would love String Theory, and now that i am actually doing it I see that my feeling was correct. I do not know why but trying to understand its concepts...

Earlier in the forum Urs Schreiber discussed criticism of KKLT, and claims that string theory does not allow de Sitter vacua https://www.physicsforums.com/threads/no-metastable-type-iib-de-sitter-vacua.950271/ The following recent claims to address these concerns, and claims KKLT allows de...

I've been reading a book called hyperspace by D.R Michio Kaku. In this book he talks about unifying all the fundamental forces of nature (gravity , electromagnetic force , weak and strong nuclear forces.) My question is, what if they are not unified and we are just trying in vain. I don't...

I've heard in a general way that string theory can describe the properties of the fundamental particles through standing waves or resonances of strings. Is this in fact the case, and if so, can someone provide a link to the relevant research papers?

Possibly naive question. Wikipedia describes string theory as follows: The obvious next step (since string theory hasn't succeeded in describing our universe) would be to define elementary particles as 2D surfaces or 3D volumes or 4D space-time volumes, which may have vibrational modes similar...

Is there a fundamental equation in string theory and can it be derived from a variational principle?

I just recently graduated with a mathematics degree. Lately, I've been very fascinated with quantum mechains and string theory, but when I try to do research I am a little overwhelmed by all the varying topics of advanced mathematics I have to know. Can anyone suggest mathematical topics to...

https://arxiv.org/abs/hep-th/0605250 Here is an attempt to make bohmian mechanics compatible with string theory. It posits that T duality breaks at the fundamental level, and that the is no minimal length in the theory. Does this proposal make sense?

Bohmian mechanics requires a preferred reference frame. But String theory doesn't have any preferred frames, so isn't BM incompatible with ST?? Maybe it would be compatible with other theories of quantum gravity that permit a preferred frame (LQG, CDT)...

Take the first family of fundamental fermions, u, d, e-, and ν. The u and d are more massive than the e- and the e- is more massive than the ν. The u and d interact via 4 forces, the e- interacts via 3 forces, and the ν interacts via 2 forces. The fermions that interact via the most forces are...

Hey! I will start my third year on the theoretical physics program. I have taken an introduction course in particle physics, just the basics, not much math. (quark and Feynman diagrams the forces and interaction , CRM matrix and cabibbo angle etc. ) Now I'm choosing between relativistic...

Do the the different calabi-yau space solutions of strings theory exist is isolated space-times or are they a part of a continuous whole with space folding and unfolding as you move though space?

This is related to string theory

There are several interpretations of QM which differ from being deterministic or non deterministic, with or without hidden variables and local or non-local. As I understand it ST poses the existence of vibrating strings, that is, physical objects with definite properties, moving along a world...

I'm a speculative fiction writer and playwright, a retired archirect with a master of architecture degree in theory, and a theater producer, director, and acting improvisor. I'm currently working on a TV series of 169 episodes exploring life in a contemporary parallel universe very much like...

Speaker : Ashoke Sen ( Harish- Chandra Research Institute, Allahabad, India ) Date and Time : 10 Aug 2009, 04:00 PM Venue : AG 66, TIFR, Mumbai In these lect...

Speaker : Ashoke Sen ( Harish- Chandra Research Institute, Allahabad, India ) Date and Time : 11 Aug 2009, 04:00 PM Venue : AG 66, TIFR, Mumbai In these lect...

Speaker : Ashoke Sen ( Harish- Chandra Research Institute, Allahabad, India ) Date and Time : 12 Aug 2009, 04:00 PM Venue : AG 66, TIFR, Mumbai In these lect...

are open strings like world lines? and closed strings like loops?

In asking a question about analysis textbooks there was a bit of a chat about things like S = 1 - 1 + 1 - 1 ... = 1 - (1 + -1 +1 -1 ...) or 2S = 1 or S=1/2. I will say straight away the answer to what's going on - what infinite sums are, are simply definitions and believe it or not there are a...

This 54 page review article from a September 2017 conference in Portugal is a good starting point for people wanting an overall summary of the state of BSM physics theories that is reasonably up to date, and may suggest questions about specific theories that deserve more attention in this forum...

Allegedly, string theory (in it's simplest form) predicts that cosmological constant must be negative (or zero). Can someone explain where does this result come from? A reference would also be welcome.

Take note of today's Obied-Ooguri-Spodyneiko-Vafa 18. Curious situation: After it had influenced much the development of the string theory community’s attention and almost all of its public media perception since 2003, after what must be thousands of followup publications, the argument of KKLT...