A class of theories that attempt to explain all existing particles (including force carriers) as vibrational modes of extended objects, such as the 1-dimensional fundamental string.

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Folded and/or compacted dimensions in M-theory?

I've on many occasions that there are various numbers of 'extra' dimensions above the 4th. However, I've heard that they are 'compacted' or 'folded' tightly and unimaginably small. Now, as I ...
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86 views

Some questions about flavour and R-symmetry in $2+1$ ${\cal N}=3$ theory

I have heard this fact that for ${\cal N}=3$ theories in $2+1$ with $N_f$ ${\cal N}=3$ matter fields the flavour symmetry group is $USp(N_f)$, $U(N_f)$ or $SO(2N_f)$ depending on whether the gauge ...
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174 views

Derivation of the supergravity action in 11D

The Einstein-Hilbert action of general relativity is uniquely determined by general covariance and the requirement that only second derivatives in the metric appear. Yang-Mills theory can be motivated ...
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195 views

Is there any simple proof of the no-ghost theorem?

Is there any simple proof of the no-ghost theorem in string theory?
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1answer
384 views

Would string theory change everything? [closed]

Whilst I don't know anything except the definition of String theory and I'm a beginner, I'm curious about it. What I would like to know is: does string theory change a lot in Physics? If it's not ...
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1answer
271 views

The future of supersymmetry [duplicate]

Considering the fault of any experimental evidence from LHC for supporting the supersymmetry idea until now, can we say that it is dead? Generally the people who are working on this subject say that ...
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3answers
7k views

Total number of subatomic particles in the universe. Are they finite ? assuming any of GR or QM or even ST

Total number of subatomic particles in the universe. Are they finite ? assuming any of GR or QM or even ST.
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2answers
896 views

Understanding Black hole information paradox?

I am not a physicist, I am a enthusiast trying to understand thinking behind "Holographic Principle" by Leonard Susskind. Recently I saw program on DS Through the wormhole - The riddle of the black ...
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1answer
149 views

Does string/M-theory address higher-dimensional membrane vibration modes?

A loop is a 1-sphere that can vibrate in increasingly complex ways as it is embedded in higher dimensional spaces. Does string theory assume that 1-spheres are the only possible vibrating ...
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181 views

Strings and QFT: particles moving backward in time?

New question: In string theory and QFT, do particles travel back in time? Not related to antimatter: Do they travel back and forth in time in reality or are these just interpretations of mathematical ...
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1answer
231 views

Are string theories gauge theories?

The wikipedia page for String Theory lists SO(32) and E8×E8 as group symmetries of some of the string theory types, and the page on E8 says: E8×E8 is the gauge group of one of the two types of ...
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113 views

Commonalities among string theories?

So string theory is a developing theory with presumably different variants. What is the commonality among all these variants? What makes the next modification of a current string theory another string ...
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2answers
92 views

gravitational waves

Now that scientists found the primordial gravitational waves that formed shortly after the big bang,and we all now that just after the bang the 4 fundamental forces were unified can we consider that ...
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172 views

So physicist's really do think the Universe could be a holographic Illusion?

http://www.nature.com/news/simulations-back-up-theory-that-universe-is-a-hologram-1.14328 http://guardianlv.com/2013/12/compelling-evidence-says-our-universe-is-a-hologram/ I thought the holographic ...
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1answer
72 views

Modular invariance of CFT

I am looking at the Cardy formula for entropy in CFT, and in the article 'Kerr/CFT correspondence and its Extensions' there is a sentence: In any unitary and modular invariant CFT, the asymptotic ...
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2answers
278 views

3 Questions about modern Physics [closed]

First i'd like to apologize for both my writting skills (i'm not english) and for my physics knowledge (being them very basic and/or naive). With general relativity from Einstein, gravity is no ...
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1answer
104 views

Entropy, Mass and Brane gravity

Does string theory state as vibrational entropy increases, mass increases? Related: What is a D-brane? Reference: Cambridge Relativity
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1answer
151 views

Meaning and types of singularity in case of string or any cosmological model (Mathematical description)

What is actual meaning of singularity can we use this term for conclusion in any research paper( related to cosmological models ).what r the types .
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1answer
571 views

Question on dimensions of CFT operators (ref: MAGOO, hep-th/9905111)

Right now I am having this silly difficulty from the following: BTW, Conformal dimension/scaling dimension is -ve of mass dimension ..right? In p-63 of Magoo, after 3.15 eq, they said a.) $\phi$ is ...
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1answer
20 views

Concerning Electrogravitics in an inertial frame

Listening to Feynman, He pointed out the fact that if a magnet is in an inertial frame with respect to a coil, there can be no electromotive force and hence no electricity produced. It is only when ...
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2answers
205 views

“String” infinity paradox

The smallest particles of the universe (or the smallest part of the smallest particles of the universe) must have infinity density. But if it have infinity density, you can calculate mass of one of ...
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1answer
82 views

Theoretical String Landscape Question

Could it be plausible that the same theoretical string "shape" occurs twice. As in two or more universes with the same amount of dark energy and string shape. The term "shape" I'm defining as based ...
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1answer
63 views

Can we expect the discovery of something that moves faster than light/photons?

As our knowledge on M-Theory improves in the times ahead which may unfold some warped dimension, can we expect the discovery of something that moves faster than light/photons?
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1answer
64 views

Cosmology and TOE

I have read an answer on this site regarding the change of laws over time . However a physisct told me that the laws did evolve at planck era and then stopped evolving after it , is that true even in ...
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1answer
72 views

Can we use some type of magnifying glass to magnifying gravity react on a body by theoretical physics?

Can we use some type of magnifying glass to magnifying gravity react on a body by theoretical physics? If so, could someone use it to destroy the earth
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1answer
171 views

Relation between Higgs boson and force of gravitation

I don't know and I can't handle it. I am so much curious about the recent discoveries in science. European Space Agency and NASA are doing great work. Hats up to these institutions. My nights are ...
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1answer
202 views

Is the quantum state or information of a particle is all that differentiates it from another particle?

So I have learned in my QM classes that you can't tell one electron from another electron. They are indistinguishable. I also learned that the wavefunction of a particle includes the spacial part and ...
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33 views

Is it possible to define a notion of temperature in a microcanonical ensemble?

I am thinking of a mircrocanonical ensemble as a finite system for which the number of particles, volume and the total energy is fixed. Is there a more refined view of this? Can I think of ...
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33 views

Book suggestion for Theoretical Physics with easy maths [duplicate]

I am a Computer Scientist with literature interest in theoretical physics. I have already read books such as A Brief History of Time and Physics of the Impossible, and I am looking for suggestion for ...
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32 views

Particle modeling in the context of numbers

We use either integers or rationals (or even complex numbers) for modeling the data. Hence, numbers impose constraints on the description of data. Namely, integers- that there exists the smallest ...
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57 views

What is the most fundamental peice of matter? What is it that thing which can no more be sub-divided?

I know that there is theory that strings are the most fundamental particles. But if it is a string, then it can be 'cut' into pieces, and if it can be 'cut', then it can be cut at infinitely many ...
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37 views

How to deduce equations 3.6.15 in Polchinski's string theory book? [duplicate]

In polchinski's first course on string, with how to deduce
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0answers
44 views

Recommendation request for a book explaining string theory to a common idiot (me) [duplicate]

I find the idea of string theory fascinating, but I'm not a student of physics, mathematics or science in general. Are there any books which effectively break down the concepts in a way that laymen ...
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48 views

String Theory- Are strings the end? What are they made of? [duplicate]

Although I have informed myself in string theory through reading books and watching videos, I do not know or understand what superstrings are made of. History has definitely shown us that when we ...
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21 views

Within the context of string theory, is matter nothing more than a vibration on a membrane of space-time? [duplicate]

I've been reading about string theory, and as I understand it, it proposes that matter is nothing more than a vibration of a membrane of space-time. Is my understanding correct?
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27 views

Lower bound bound on the mass of scalar bosons

Is there any lower bound bound on the mass of scalar bosons in nature. I know that a massless scalar boson would lead to a fifth force which would violate the equivalence principle. But is there any ...
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52 views

Extra dimensions and the big bang [duplicate]

If there were extra compact dimensions,and at the big bang all dimensions were compact,my question is why the big bang failed to expand those presumed extra dimensions like it did with the 3 spatial ...
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52 views

What is the effect of the compact extra dimensions of the heterotic theories?

The five super-string theories are generally said to be 10-dimensional. However the Heterotic theories combine a bosonic left mover (which lives in 26 dimensions) with a super right mover (which lives ...
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179 views

Why isn't there a Heterotic string theory which tensors the fermionic state with the Type II state?

The Heterotic (HO and HE) string is found by tensoring the left movers of the bosonic string theory state and the right movers of the Type II string theory state: ...
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218 views

Does String Theory explain spin?

The state of a particle will generally change if you rotate it. The details of how the state changes under an infinitesimal rotation are contained in the angular momentum operator J. This operator can ...
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76 views

How does quantum jitter “fix” the masses of strings?

So the masses of strings should be huge because of the high energy levels. Which means, in other words, the strings are vibrating with enough energy to have large masses as point particles. But ...
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41 views

why is the modelisation of elementary particle as a two dimensional object in contradiction with General Relativity?

This is asserted by Trinh Xuan Thuan in his book "Chaos & Harmony" chapter String theory.
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154 views

Colliding bubbles in hyperspace

Assuming the following A universe is the surface from a bubble in hyperspace. Inside a bubble there is nothing, only the surface represents a universe. The size of the bubble is time. Dark matter ...
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110 views

Naive Uncertainty principle for string theory

Is it possible, in some sense, that a naive uncertainly principle for string theory could be expressed as : $$ \Delta x_i \Delta p_j \Delta \sigma ~=~ \delta_{ij} \hbar \ell_s$$ where $\ell_s$ is ...
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1answer
163 views

uncertainty principle of spin in (super)string theory

In quantum mechanics, uncertainty principle states that we can only measure the quantity of spin in one axis but not others. Then what about in superstring theory? As quantum mechanics is basically ...
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73 views

Does quantum field theory accept gravitational wave?

Does quantum field theory accept gravitational wave? As quantum field theory is flat spacetime theory, I wonder whether gravitational wave would be true. Does contemporary string theory variants ...
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1answer
136 views

How many dimensions are there in total? [duplicate]

I happened to get my hands on a string theory book where its been said that the universe's fundamental particle i.e. the string, takes about ten dimensions for specifying itself under symmetry. What ...
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6answers
456 views

pros and cons of the anthropic principle

The anthropic principle has become a very popular explanation among theoretical physicists lately. Life is unlikely, but only life can observe, so we find ourselves in an unlikely position, so to ...
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1answer
208 views

Compactification of Dimensions

As the only way String theory can respect the principles of quantum mechanics and Special theory of relativity, by formulating it in hypothetical nine dimensional space. You could use string ...
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1answer
44 views

branes-collision -> big-bang -> 2nd Universe?

If the cosmological model of the Ekpyrotic universe is correct should there not always a 2nd universe be created on the 2nd brane? Pictures and articles I found speak only of one universe. Why is ...