4
votes
0answers
48 views

The difference between The Dilaton and The Radion?

I have read this question on the Dilaton, but I am a little confused with the distinction between the Dilaton and the Radion. I definitely have the feeling that these two scalar fields are different ...
2
votes
0answers
45 views

Stringy corrections to Friedmann equation

Does anyone know a reference or a paper which discusses string theory correction to Friedmann equations?
4
votes
2answers
101 views

Proof that higher genus surface admits a metric of negative Ricci scalar everywhere

In the Green, Schwarz and Witten Superstring Theory textbook, the paragraph below equation 3.3.15 says, For genus greater than one, it can be shown that the surface admits a metric of everywhere ...
0
votes
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 ...
14
votes
2answers
306 views

Newtonian gravity from the holographic principle?

Can one understand Newton's law of gravitation using the holographic principle (or does such reasoning just amount to dimensional analysis)? Following an argument similar to one given by Erik ...
1
vote
1answer
137 views

Dimension & non - locality problem in string theory

I have some questions with string theory: Why is it that there is exactly 4 large spacetime dimensions while the rest remain small? It is a nonlocal QFT. How could that fit in GR?
6
votes
2answers
357 views

The General Relativity from String Theory Point of View [duplicate]

I have a hard time understand the statement that When you only look at the classical limit or classical physics, string theory exactly agrees with general relativity Because from what I know, ...
9
votes
2answers
266 views

Conformal Compactification of spacetime

I have been reading Penrose's paper titled "Relativistic Symmetry Groups" where the concept of conformal compactification of a space-time is discussed. My other references have been this and this. In ...
3
votes
2answers
125 views

Symmetry transformation in AdS space

In AdS/CFT papers the action of the SO(D,2) symmetry is usually given at the boundary where the transformations are just the conformal transformations (Poincare, scaling and special) for D+1 ...
2
votes
1answer
186 views

Stringy corrections of Einstein's vacuum field equations

From string theory, the vacuum field equations obtain correction of the order $O[\alpha'R]^n$ such that they can be written as $$ R_{\alpha\beta} -\frac{1}{2}g_{\alpha\beta}R + O[\alpha'R] = 0 $$ ...
3
votes
1answer
107 views

Energy Functional

I am a graduate student in pure mathematics, during my study on Ricci Flow I faced some functional known as energy functional. For example Einstein-Hilbert functional is called an energy functional, ...
1
vote
1answer
87 views

Can the fuzzball conjecture be applied to microscopically explain the entropy of a region beyond the gravitational observer horizon?

In this article discussing this and related papers, it is explained among other things, how the neighborhood of an observer's worldline can be approximated by a region of Minkowsky spacetime. If I ...
2
votes
1answer
118 views

Strings on a curved spacetime

Suppose we are interested in in string on a specific metric G, is it necessary to include a Dilaton field on back ground in order to preserve the Weyl invariance? suppose the spacetime is not empty, ...
9
votes
1answer
429 views

In what limit does string theory reproduce general relativity? [duplicate]

In quantum mechanical systems which have classical counterparts, we can typically recover classical mechanics by letting $\hbar \rightarrow 0$. Is recovering Einstein's field equations (conceptually) ...
9
votes
1answer
188 views

Equation of state of cosmic strings and branes

I'm sure these are basic ideas covered in string cosmology or advanced GR, but I've done very little string theory, so I hope you will forgive some elementary questions. I'm just trying to fit some ...
5
votes
2answers
705 views

What is background independence and how important is it?

What is background independence and how important is it? In order to be a theory of everything, will the final string-theory/m-theory have to be background independent? Does the current lack of ...
4
votes
1answer
673 views

How do Einstein's field equations come out of string theory?

The classical theory of spacetime geometry that we call gravity is described at its core by the Einstein field equations, which relate the curvature of spacetime to the distribution of matter and ...
12
votes
1answer
1k views

Is String Theory formulated in flat or curved spacetime?

String Theory is formulated in 10 or 11 (or 26?) dimensions where it is assumed that all of the space dimensions except for 3 (large) space dimensions and 1 time dimension are a compact manifold with ...
1
vote
0answers
161 views

Extending General Relativity with Kahler Manifolds?

Standard general relativity is based on Riemannian manifolds. However, the simplest extension of Riemannian manifolds seems to be Kahler manifolds, which have a complex (hermitian) structure, a ...
5
votes
0answers
148 views

Implications of Unruh-inertia to theories of gravity

If it turns out to be true that the galaxy rotation curves can be explained away by Unruh modes that become greater than the Hubble scale at accelerations around $10^{-10} m/s^2$ as proposed in here, ...
3
votes
1answer
166 views

Where does this equation for a perturbed metric come from?

I'm reading an article which includes the following equation involving a perturbed metric: $$G_{AB} = \eta_{AB} + \overset{1}{\gamma}_{AB} + 2\overset{1}{\chi}_{(A,B)}\tag{4.1}$$ I don't understand ...
-3
votes
1answer
258 views

What if microstates increase proportional to universe volume? [closed]

I am probably a delusional crank with a lot of crazy, overly speculative conjectures. If I am not delusional, than at the very least I've been ahead of the curve, the last 40 or so years. I was a ...
1
vote
2answers
409 views

Laws of gravity for a universe that only consists of two objects?

So, we know that when two objects of normal matter get away from each other, the gravitational pull they feel from each other, decreases. I wanted to see how that would work. And in my ...
1
vote
1answer
1k views

What's next after Higgs Boson discovery? [duplicate]

Possible Duplicate: Practical matter of the Higgs-Mechanism As everybody knows that the Higgs Boson was discovered on July 4th,2012, I am so curious about it. What are the possible ...
2
votes
1answer
373 views

General Relativity - Einstein field equation and quantum field theory

Einstein field equation has many solutions. Out of them, is there any solution that is incompatible with quantum field theory? Also, what solutions of Einstein field equation would be incompatible ...
9
votes
5answers
689 views

How does the string worldsheet affect the space-time in which they live?

I don't understand much about string theory and never really got much further past the Nambu-Goto action and very basic supersymmetry (SUSY) lectures in my undergraduate courses, but the only thing ...
16
votes
0answers
513 views

A dictionary of string - standard physics correspondences

Motivated by the (for me very useful) remark ''Standard model generations in string theory are the Euler number of the Calabi Yau, and it is actually reasonably doable to get 4,6,8, or 3 ...
3
votes
1answer
200 views

Could strings be geons?

Is it possible that string theory strings are geons? This may be an overly speculative or naive question, but is there an obvious reason why not? Both strings and geons seem to have roughly the same ...
5
votes
2answers
647 views

Critics of Mannheim's Conformal Gravity Theory?

I'm looking for more articles/reactions/critiques/support for Philip Mannheim's recent conformal gravity theory. See here: http://arxiv.org/abs/1101.2186v1 Any ideas on where to start?
6
votes
0answers
46 views

What is the state-of-the-art on spacelike singularities in string theory?

What lessons do we have from string theory regarding the fate of singularities in general relativity? What happens to black hole singularities? What happens to cosmological singularities? Which ...
4
votes
1answer
712 views

What do “tachionic” neutrinos mean for QG?

Reading about the spectacular Opera claim, I`m (again ;-P) wondering if a confirmation of superliminous neutrinos could help settle some still open quantum gravity issues ...? In this post, Lumo ...
3
votes
2answers
365 views

Singularities and quantized space time

Discrete space time quanta would solve the problems of infinite densities for singularities in General Relativity and Quantum Gravity by imposing a non zero limit on the minimum radius of black holes. ...
3
votes
2answers
277 views

How is the complexification of spacetime justified?

As always the caveat is that I am a mathematician with very little knowledge of physics. I've started my quest for knowledge in this field, but am very very far from having a good grasp. General ...
10
votes
3answers
785 views

Does gravity require strings?

OK, before I ask my question, let me frame it with a few (uncontroversial?) statements: The low-field-limit plane-wave solution to Einstein's equations is helicity-2. In the early days of string ...
6
votes
2answers
1k views

Does String Theory disagree with General Relativity?

I would like to expand on what I mean by the title of this question to focus the answers. Normally whenever a theory (e.g. General Relativity) replaces another (e.g. Newtonian Gravity) there is a ...
0
votes
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 .
2
votes
2answers
676 views

Black Hole Singularity and String Theory

This question arises in a somewhat naive form because I am largely unfamiliar with String Theory. I do know that it incorporates higher space dimensions where I shall take the overall dimensionality ...
-4
votes
1answer
210 views

Why String theory introduced in cosmological models to study nature of universe? [closed]

Why String theory ? simple cosmological model is not sufficient for study of nature of universe
2
votes
0answers
217 views

Singularities in Bianchi models in general relativity ( physical science)

what are the conditions to check point type singularity in a bianchi type model ? bianchi type model are of Type I,II,III,IX,IV or u can say we use different Bianchi type models having some specific ...
8
votes
2answers
795 views

Do traversable wormholes exist as solutions to string theory?

There has been some heated debate as to whether the laws of physics allow for traversable wormholes. Some physicists claim we require exotic matter to construct wormholes, but then others counter the ...
4
votes
2answers
701 views

How could spacetime become discretised at the Planck scale?

I didn't have much luck getting a response to this question before so I have tried to reword and expand it a little: In early 2010 I attended this inaugural lecture by string theorist- Prof. ...
20
votes
1answer
991 views

How does classical GR concept of space-time emerge from string theory?

First, I'll state some background that lead me to the question. I was thinking about quantization of space-time on and off for a long time but I never really looked into it any deeper (mainly because ...
5
votes
2answers
246 views

How to check Einstein-like equations on their correspondence with the real world?

Physicists studying the grounds of physics and some mathematicians often come to a theories which are like a general-relativity, but do not coincide with it. Often these theories contradict the real ...