Nouvelles du Vide

pp.55-56: "Vacuum energy and gravity (...)For decades nobody else seems to have worried about contributions of quantum fluctuations to the cosmological constant, although physicists learned after Dirac's hole theory that the vacuum state in quantum field theory is not empty but has interesting physical properties. As far as we know, the first one to come back to possible contributions of the vacuum energy density to the cosmological constant was Zel'dovich. He discussed this issue in two papers (Zel'dovich, 1967, 1968) during the third renaissance period of the A-term, but before the advent of spontaneously-broken gauge theories. He pointed out that, even if one assumes in a completely ad-hoc fashion that the zero-point contributions to the vacuum energy density are exactly cancelled by a bare term, there still remain higher-order effects. In particular, gravitational interactions between the particles in the vacuum fluctuations are expected on dimensional grounds to lead to a gravitational self-energy density of order Gµ6, where µ is some cut-off scale. Even for µ as low as 1 GeV, this is about 9 orders of magnitude larger than the observational bound.This strongly suggests that there is something profound that we do not seem to understand at all, certainly not in quantum field theory (nor, at least so far, in string theory). We are unable to calculate the vacuum energy density in quantum field theories, such as the Standard Model of particle physics. But we can attempt to make what appear to be reasonable order-of-magnitude estimates for the various contributions. All expectations are in dramatic conflict with the facts (see, e.g ., Straumann, 2003b). Trying to arrange the cosmological constant to be zero is unnatural in a technical sense. It is like enforcing a particle to be massless, by fine-tuning the parameters of the theory when there is no symmetry principle implying a vanishing mass. The vacuum energy density is unprotected from large quantum corrections. This problem is particularly severe in field theories with spontaneous symmetry breaking. In such models there are usually several possible vacuum states with different energy densities. Furthermore, the energy density is determined by what is called the effective potential, and this is a dynamical object. Nobody can see any reason why the vacuum of the Standard Model we ended up as the universe cooled, has—by the standards of particle physics—an almost vanishing energy density. Most likely, we shall only find a satisfactory answer once we have a theory that successfully combines the concepts and laws of GR with those of quantum theory.
For a number of years now, cosmology has been going through a fruitful and exciting period. Some of the developments are clearly of general interest, well beyond the fields of astrophysics and cosmology. Lack of space prevents us from even indicating the most important issues of current interest. "

Is string theory in trouble?

Extraits: "Second was the discovery that the value of the cosmological constant - the energy of empty space which contributes to the expansion rate of the universe - seems absurdly improbable, and nothing in fundamental physics is able to explain why. I remember when Steven Weinberg first suggested that the cosmological constant might be anthropically determined - that it has to be this way otherwise we would not be here to observe it. I was very impressed with the argument, but troubled by it. Like everybody else, I thought the cosmological constant was probably zero - meaning that all the quantum fluctuations that make up the vacuum energy cancel out, and gravity alone affects the expansion of the universe. It would be much easier to explain if they cancelled out to zero, rather than to nearly zero. The discovery that there is a non-zero cosmological constant changed everything. Still, those two things were not enough to tip the balance for me."
http://www.newscientist.com/channel/fundamentals/mg18825305.800.html

Gravitation from a Gauge like Formulation

par B.G. Sidharth
International Institute for Applicable Mathematics & Information Sciences, Hyderabad (India) & Udine (Italy)
B.M. Birla Science Centre, Adarsh Nagar, Hyderabad - 500 063 (India)
Résumé: After many fruitless decades of trying to unify electromagnetism and gravitation, it is now being realized that this can be done only in discrete spacetime, as indeed the author had demonstrated. In this context, a unified description of gravitation and electromagnetism is provided within the framework of a gauge like formulation. "These latest theories discard the differentiable spacetime of earlier approaches and rely on a lattice like approach to spacetime, wherein there is a minimum fundamental interval which replaces the point space time of earlier theories. Indeed as Hooft has remarked, “It is some what puzzling to the present author why the lattice structure of space and time had escaped attention from other investigators up till now....”
http://www.ensmp.fr/aflb/AFLB-302/aflb302m301.htm

Quelques tendances de recherche récentes en développement faisant intervenir l'énergie du vide:

Leading role of gravity in the structure of spinning particle

Résumé: The Kerr-Newman solution has g=2 as that of the Dirac electron and is considered as a model of spinning particle in general relativity. The Kerr geometry changes cardinally our representations on the role of gravity in the particle physics. We show that the Kerr gravitational field has a stringy local action and a topological peculiarity which are extended up to the Compton distances, and also a strong non-local action playing the key role in the mass-renormalization and regularization of singularities. The Kerr-Newman gravity determines the structure of spinning particle in the form of a relativistically rotating disk, a highly oblate bag of the Compton radius. Interior of this bag consists of an AdS or dS ``false vacuum'', depending on the correlation of the mass density and charge. In the same time, the local action of gravitational field may be considered as negligible for regularized particle.

Extraits: "The used in QED mass renormalization is universally recognized due to an incredible exactness of its predictions. Although its origin lies in the classical theory of a pointlike electron, there are serious problems with physical interpretation and mathematical correctness of this procedure.(...) We show that the mass renormalization and regularization of the singularities in the Kerr- Newman source are realized by gravitational field in a very natural manner.(...) We show that the Kerr gravity displays in the Compton the strong local field having a stringy structure, a nontrivial topological peculiarity and has a strong non-local action playing the key role in the mass- renormalization.(...) Some of the terms may be divergent, but the total result will not be changed, since divergences will always be compensated by contribution from gravitational term. It shows that, due to the strong non-local action, gravity has to be very essential for elementary particles, on the distances which are very far from the considered usually Planck scale."
"Regularization of the zero-point radiation
(...)Twofoldedness of the Kerr geometry confirms this point of view, since the out-going radiation on the “positive” out-sheet of the metric is compensated by an in-going radiation on the “negative” in-sheet, see Fig. 1. So, physically, there is no reason for the lost of mass by radiation. It shows, that the term F31 = γ 1 ˜r has to be identified with the vacuum zero-point field. In this case the electromagnetic excitations on the Kerr background may be interpreted as a resonance of the zero-point fluctuations on the (superconducting) source of the Kerr spinning particle [13, 9]."
http://arxiv.org/abs/hep-th/0512095

On the theory of the skewon field: From electrodynamics to gravity

F.W. Hehl, Yu.N. Obukhov, G.F. Rubilar , M. Blagojevic
15 pages, 1 figure - Journal-ref: Phys.Lett. A347 (2005) 14-24
Résumé: It has been observed since the time of Cartan, Kottler, and van Dantzig, that since the spacetime metric only enters into Maxwell's equations for electromagnetism by way of the Hodge star operator, and, more to the point, the metric structure of spacetime seems to follow from the propagation of electromagnetic waves, that perhaps one should regard the spacetime metric as a corollary to the electromagnetic structure of spacetime, and formulate the laws of electromagnetism in a metric-free fashion.
http://www.physcomments.org/node/301

Emergent physics on vacuum energy and cosmological constant

par G.E. Volovik
Low Temperature Laboratory, Helsinki University of Technology, P.O.Box 2200, FIN-02015 HUT, Finland
Abstract: The phenomenon of emergent physics in condensed-matter many-body systems has become the paradigm of modern physics, and can probably also be applied to high-energy physics and cosmology. This encouraging fact comes from the universal properties of the ground state (the analog of the quantum vacuum) in fermionic many-body systems, described in terms of the momentum-space topology. In one of the two generic universality classes of fermionic quantum vacua the gauge fields, chiral fermions, Lorentz invariance, gravity, relativistic spin, and other features of the Standard Model gradually emerge at low energy. The condensed-matter experience provides us with some criteria for selecting the proper theories in particle physics and gravity, and even suggests specific solutions to different fundamental problems. In particular, it provides us with a plausible mechanism for the solution of the cosmological constant problem, which I will discuss in some detail.
http://arxiv.org/abs/cond-mat/0507454

Zero-point energy of vacuum fluctuation as a candidate for dark energy versus a new conjecture of antigravity based on the modified Einstein field equation in general relativity

Guang-jiong Ni
Department of Physics, Fudan University, Shanghai, 200433, China
Department of Physics, Portland State University, Portland, OR97207, U.S.A.
Email : pdx01018@pdx.edu
Abstract: In order to clarify why the zero-point energy associated with the vacuum fluctuations cannot be a candidate for the dark energy in the universe, a comparison with the Casimir effect is analyzed in some detail. A principle of epistemology is stressed that it is meaningless to talk about an absolute (isolated) thing. A relative thing can only be observed when it is changing with respect to other things. Then a new conjecture of antigravity --the repulsive force between matter and antimatter derived from the modified Einstein field equation in general relativity-- is proposed. this is due to the particle-antiparticle symmetry based on a new understanding about the essence of special relativity. Its possible consequences in the theory of cosmology are discussed briefly, including a new explanation for the accelerating universe and gamma-ray-bursts.
http://arxiv.org/abs/physics/0506017

Quantum ether: photons and electrons from a rotor model

Michael Levin and Xiao-Gang Wen
Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
(Dated: May, 2005)
We give an example of a purely bosonic model – a rotor model on the 3D cubic lattice – whose low energy excitations behave like massless U(1) gauge bosons and massless Dirac fermions. This model can be viewed as a "quantum ether ": a medium that gives rise to both photons and electrons. It illustrates a general mechanism for the emergence of gauge bosons and fermions known as " stringnet condensation." Other, more complex, string-net condensed models can have excitations that behave like gluons, quarks and other particles in the standard model. This suggests that photons, electrons and other elementary particles may have a unified origin: string-net condensation in our vacuum.
http://132.236.180.11/abs/hep-th/0507118

MEDIA

RADIO - De récentes interviews d'Edgar Günzig sont rediffusées par la RTBF les 18, 24, 25 et 31 décembre, 1er janvier. Sujet: LE VIDE
NB: Les émissions du samedi sont réécoutables durant une semaine via le site de Memo.
La dernière émission est écoutable via le lien: http://www.rtbf.be/media/radio/alademande/prem_curieux_1700/DI_play.m3u

L'énergie du vide dans la science-fiction

En physique quantique, l'énergie du vide s'appelle:

L'ENERGIE DU POINT ZERO

Ce concept est à la base de nouvelles théories en plein essor qui pourront bientôt déboucher sur des applications surprenantes! Ce site vous propose une collection d'articles, classés par sujet, pour vous faire une première idée de la question.
Bonne lecture!

http://users.skynet.be/pointzero

Des Nouvelles du Vide - 01 janvier 2006

articles

Einstein’s impact on the physics of the twentieth century
par Domenico Giulini (+) et Norbert Straumann(++)

Is string theory in trouble?

Gravitation from a Gauge like Formulation

Quelques tendances de recherche récentes en développement faisant intervenir l'énergie du vide:

Leading role of gravity in the structure of spinning particle

On the theory of the skewon field: From electrodynamics to gravity

Emergent physics on vacuum energy and cosmological constant

Zero-point energy of vacuum fluctuation as a candidate for dark energy versus a new conjecture of antigravity based on the modified Einstein field equation in general relativity

Quantum ether: photons and electrons from a rotor model

MEDIA

L'énergie du vide dans la science-fiction

En physique quantique, l'énergie du vide s'appelle:

L'ENERGIE DU POINT ZERO

Ce concept est à la base de nouvelles théories en plein essor qui pourront bientôt déboucher sur des applications surprenantes! Ce site vous propose une collection d'articles, classés par sujet, pour vous faire une première idée de la question. Bonne lecture!

http://users.skynet.be/pointzero

Des Nouvelles du Vide - 01 janvier 2006

articles

Einstein’s impact on the physics of the twentieth century par Domenico Giulini (+) et Norbert Straumann(++)

Is string theory in trouble?

Gravitation from a Gauge like Formulation

Quelques tendances de recherche récentes en développement faisant intervenir l'énergie du vide:

Leading role of gravity in the structure of spinning particle

On the theory of the skewon field: From electrodynamics to gravity

Emergent physics on vacuum energy and cosmological constant

Zero-point energy of vacuum fluctuation as a candidate for dark energy versus a new conjecture of antigravity based on the modified Einstein field equation in general relativity

Quantum ether: photons and electrons from a rotor model

MEDIA

L'énergie du vide dans la science-fiction

Ce concept est à la base de nouvelles théories en plein essor qui pourront bientôt déboucher sur des applications surprenantes! Ce site vous propose une collection d'articles, classés par sujet, pour vous faire une première idée de la question.
Bonne lecture!

Einstein’s impact on the physics of the twentieth century
par Domenico Giulini (+) et Norbert Straumann(++)