It's confirmed, matter is merely vacuum fluctuations.

[malawi_glenn]

I don't know that, have you aksed him?

"Maybe he means LHC" would be the correct answer from you ;-)

 

[marcus]

Yes, if it were true. Is it? I am not able to read the journal Science, and there is no preprint in the ArXiV.

One should assume that the only inputs are quark masses for u,d and QCD coupling constant at some energy. Is it? Moreover, how about the dependence with quark mass?

Arivero, I will quote some short excerpts of the articles in Science. First (not to answer your question but to give some background) here is a quote from Kronfeld's perspective piece:==quote from Science==
To make progress despite limited computing power, 20 years' worth of lattice QCD calculations were carried out omitting the extra quark-antiquark pairs. The computation of the nucleon's mass passed some technical milestones (8, 9) but was still unsatisfactory. As well as demonstrating the validity of strongly coupled QCD, we want to compute properties of hadrons ab initio, to help interpret experiments in particle and in nuclear physics. Without the quark-antiquark pairs, it is impossible to quantify the associated uncertainty.

A breakthrough came 5 years ago, with the first wide-ranging calculations incorporating the back-reaction of up, down, and strange quark pairs (10, 11). This work used a mathematical representation of quarks that is relatively fast to implement computationally (12), and these methods enjoyed several noteworthy successes, such as predicting some then-unmeasured hadron properties (13). This formulation is, however, not well suited to the nucleon, and so a principal task for lattice QCD remained unfinished.

Dürr et al. use a more transparent formulation of quarks that is well suited to the nucleon and other baryons (hadrons composed of three quarks). They compute the masses of eight baryons and four mesons (hadrons composed of one quark and one antiquark). Three of these masses are used to fix the three free parameters of QCD. The other nine agree extremely well with measured values, in most cases with total uncertainty below 4%.

For example, the nucleon mass is computed to be 936 ± 25 ± 22 MeV/c^2 compared with 939 MeV/c^2 for the neutron, where c is the speed of light and the reported errors are the statistical and systematic uncertainties, respectively. The final result comes after careful extrapolation to zero lattice spacing and to quark masses as small as those of up and down (the two lightest quarks, with masses below 6 MeV/c^2). The latter extrapolation may not be needed in the future. Last July, a Japanese collaboration announced a set of lattice-QCD calculations (14) of the nucleon and other hadron masses with quark masses as small as those of up and down.

...
...

Dürr et al. start with QCD's defining equations and present a persuasive, complete, and direct demonstration that QCD generates the mass of the nucleon and of several other hadrons. These calculations teach us that even if the quark masses vanished, the nucleon mass would not change much, a phenomenon sometimes called "mass without mass" (19, 20). It then raises the question of the origin of the tiny up and down quark masses. ... whether the responsible mechanism is the Higgs boson or something more spectacular.
==endquote==

Here is the link to Kronfeld's perspective piece given in post #1 of the thread
The Weight of the World Is Quantum Chromodynamics
http://www.sciencemag.org/cgi/content/summary/sci;322/5905/1198
"Ab initio calculations of the proton and neutron masses have now been achieved, a milestone in a 30-year effort of theoretical and computational physics."

 

[marcus]

...

http://www.sciencemag.org/cgi/content/abstract/sci;322/5905/1224
Ab Initio Determination of Light Hadron Masses
S. Dürr,1 Z. Fodor,1,2,3 J. Frison,4 C. Hoelbling,2,3,4 R. Hoffmann,2 S. D. Katz,2,3 S. Krieg,2 T. Kurth,2 L. Lellouch,4 T. Lippert,2,5 K. K. Szabo,2 G. Vulvert4

"More than 99% of the mass of the visible universe is made up of protons and neutrons. Both particles are much heavier than their quark and gluon constituents, and the Standard Model of particle physics should explain this difference. We present a full ab initio calculation of the masses of protons, neutrons, and other light hadrons, using lattice quantum chromodynamics. Pion masses down to 190 mega–electron volts are used to extrapolate to the physical point, with lattice sizes of approximately four times the inverse pion mass. Three lattice spacings are used for a continuum extrapolation. Our results completely agree with experimental observations and represent a quantitative confirmation of this aspect of the Standard Model with fully controlled uncertainties."

1 John von Neumann–Institut für Computing, Deutsches Elektronen-Synchrotron Zeuthen, D-15738 Zeuthen and Forschungszentrum Jülich, D-52425 Jülich, Germany.
2 Bergische Universität Wuppertal, Gaussstrasse 20, D-42119 Wuppertal, Germany.
3 Institute for Theoretical Physics, Eötvös University, H-1117 Budapest, Hungary.
4 Centre de Physique Théorique (UMR 6207 du CNRS et des Universités d'Aix-Marseille I, d'Aix-Marseille II et du Sud Toulon-Var, affiliée à la FRUMAM), Case 907, Campus de Luminy, F-13288, Marseille Cedex 9, France.
5 Jülich Supercomputing Centre, FZ Jülich, D-52425 Jülich, Germany.
...

Here are some excerpts from that article. This is severely abbridged and many symbols and subscripts are missing. It can give a taste of the article, and some main conclusions, but for most of the content one must look up the article.
===exerpts from Duerr et al, Science 20 November===

...The Standard Model of particle physics predicts a cosmological, quantum chromodynamics (QCD)–related smooth transition between a high-temperature phase dominated by quarks and gluons and a low-temperature phase dominated by hadrons. The very large energy densities at the high temperatures of the early universe have essentially disappeared through expansion and cooling. Nevertheless, a fraction of this energy is carried today by quarks and gluons, which are confined into protons and neutrons. According to the mass-energy equivalence E = mc^2, we experience this energy as mass. Because more than 99% of the mass of ordinary matter comes from protons and neutrons, and in turn about 95% of their mass comes from this confined energy, it is of fundamental interest to perform a controlled ab initio calculation based on QCD to determine the hadron masses.

QCD is a generalized version of quantum electrodynamics (QED), which describes the electromagnetic interactions. The Euclidean Lagrangian with gauge coupling g and a quark mass of m can be written as... , where Fµ = µA – Aµ + [Aµ,A]. In electrodynamics, the gauge potential Aµ is a real valued field, whereas in QCD it is a 3 x 3 matrix field. Consequently, the commutator in Fµ vanishes in QED but not in QCD. The fields also have an additional "color" index in QCD, which runs from 1 to 3. Different "flavors" of quarks are represented by independent fermionic fields, with possibly different masses. In the work presented here, a full calculation of the light hadron spectrum in QCD, only three input parameters are required: the light and strange quark masses and the coupling g.

The action S of QCD is defined as the four-volume integral of ... Green's functions are averages of products of fields over all field configurations, weighted by the Boltzmann factor exp(–S). A remarkable feature of QCD is asymptotic freedom, which means that for high energies (that is, for energies at least 10 to 100 times higher than that of a proton at rest), the interaction gets weaker and weaker (1, 2), enabling perturbative calculations based on a small coupling parameter. Much less is known about the other side, where the coupling gets large, and the physics describing the interactions becomes nonperturbative. To explore the predictions of QCD in this nonperturbative regime, the most systematic approach is to discretize (3) the above Lagrangian on a hypercubic space-time lattice with spacing a, to evaluate its Green's functions numerically and to extrapolate the resulting observables to the continuum (a0). A convenient way to carry out this discretization is to place the fermionic variables on the sites of the lattice, whereas the gauge fields are treated as 3 x 3 matrices connecting these sites. In this sense, lattice QCD is a classical four-dimensional statistical physics system.

Calculations have been performed using the quenched approximation, which assumes that the fermion determinant (obtained after integrating over the fields) is independent of the gauge field. Although this approach omits the most computationally demanding part of a full QCD calculation, a thorough determination of the quenched spectrum took almost 20 years. It was shown (4) that the quenched theory agreed with the experimental spectrum to approximately 10% for typical hadron masses and demonstrated that systematic differences were observed between quenched and two-flavor QCD beyond that level of precision (4, 5).

Including the effects of the light sea quarks has dramatically improved the agreement between experiment and lattice QCD results. Five years ago, a collaboration of collaborations (6) produced results for many physical quantities that agreed well with experimental results. Thanks to continuous progress since then, lattice QCD calculations can now be performed with light sea quarks whose masses are very close to their physical values (7) (though in quite small volumes). Other calculations, which include these sea-quark effects in the light hadron spectrum, have also appeared in the literature (8–16). However, all of these studies have neglected one or more of the ingredients required for a full and controlled calculation. The five most important of those are, in the order that they will be addressed below:

The inclusion of the up (u), down (d), and strange (s) quarks in the fermion determinant with an exact algorithm and with an action whose universality class is QCD. For the light hadron spectrum, the effects of the heavier charm, bottom, and top quarks are included in the coupling constant and light quark masses.

A complete determination of the masses of the light ground-state, flavor nonsinglet mesons and octet and decuplet baryons. Three of these are used to fix the masses of the isospin-averaged light (m_ud) and strange (m_s) quark masses and the overall scale in physical units.
...
...
Controlled interpolations and extrapolations of the results to physical mud and ms (or eventually directly simulating at these mass values). Although interpolations to physical m_s, corresponding to M_K 495 MeV, are straightforward, the extrapolations to the physical value of mud, corresponding to M? 135 MeV, are difficult. They need computationally intensive calculations, with M? reaching down to 200 MeV or less.

Controlled extrapolations to the continuum limit, requiring that the calculations be performed at no less than three values of the lattice spacing, in order to guarantee that the scaling region is reached.

Our analysis includes all five ingredients listed above, thus providing a calculation of the light hadron spectrum with fully controlled systematics as follows.Owing to the key statement from renormalization group theory that higher-dimension, local operators in the action are irrelevant in the continuum limit, there is, in principle, an unlimited freedom in choosing a lattice action. There is no consensus regarding which action would offer the most cost-effective approach to the continuum limit and to physical mud. We use an action that improves both the gauge and fermionic sectors and heavily suppresses nonphysical, ultraviolet modes (19). We perform a series of 2 + 1 flavor calculations; that is, we include degenerate u and d sea quarks and an additional s sea quark. We fix m_s to its approximate physical value. To interpolate to the physical value, four of our simulations were repeated with a slightly different m_s. We vary m_ud in a range that extends down to M 190 MeV.

QCD does not predict hadron masses in physical units: Only dimensionless combinations (such as mass ratios) can be calculated. To set the overall physical scale, any dimensionful observable can be used. However, practical issues influence this choice. First of all, it should be a quantity that can be calculated precisely and whose experimental value is well known. Second, it should have a weak dependence on m_ud, so that its chiral behavior does not interfere with that of other observables. Because we are considering spectral quantities here, these two conditions should guide our choice of the particle whose mass will set the scale. Furthermore, the particle should not decay under the strong interaction. On the one hand, the larger the strange content of the particle, the more precise the mass determination and the weaker the dependence on m_ud. These facts support the use of the ...?baryon, the particle with the highest strange content. On the other hand, ..
... Typical effective masses are shown in Fig. 1.
...
Fig. 1. Effective masses aM = log[C(t/a)/C(t/a + 1)], where C(t/a) is the correlator at time t, for ?, ?K, ?N,...
Fig. 2. Pion mass dependence of the nucleon (N) and for all three values of the lattice spacing. ...
...
Table 1. Spectrum results in giga–electron volts.nd bands are the experimental values with their decay widths. Our results are shown by solid circles. Vertical error bars represent our combined statistical (SEM) and systematic error estimates. ?, ?K, and ? have no error bars, because they are used to set the light quark mass, the strange quark mass and the overall scale, respectively. ...
...
Thus, our study strongly suggests that QCD is the theory of the strong interaction, at low energies as well, and furthermore that lattice studies have reached the stage where all systematic errors can be fully controlled. This will prove important in the forthcoming era in which lattice calculations will play a vital role in unraveling possible new physics from processes that are interlaced with QCD effects.

References and Notes
1. D. J. Gross, F. Wilczek, Phys. Rev. Lett. 30, 1343 (1973).
2. H. D. Politzer, Phys. Rev. Lett. 30, 1346 (1973).
3. K. G. Wilson, Phys. Rev. D Part. Fields 10, 2445 (1974).
...
...
30. Computations were performed on the Blue Gene supercomputers at FZ Jülich and at IDRIS and on clusters at Wuppertal and CPT. ...
==endquote==

 

[koolmodee]

He means LHC.

I do.

 

[sanman]

How do we differentiate between the quark sea and space itself, if the quark sea exists everywhere space does?

 

[humanino]

How do we differentiate between the quark sea and space itself, if the quark sea exists everywhere space does?

Sea quarks exist only in hadrons. They are what makes up the fluctuations of the vacuum in hadrons, as opposed to the fluctuations of the vacuum anywhere else outside hadrons (which does contain quarks, but they are not called sea quarks). As a matter of practicalities, the number of quarks in a hadron is determined by inclusive scattering of an electron (or lepton) where we do not detect the recoiling hadronic system, so in principle, we also scatter on "vacuum quarks" except that this is negligibly small. That we do measure sea quarks and not vacuum quarks in those experiments is further confirmed by other experiments, like in Drell-Yann, where the scattering occurs between quarks in a hadron. Finally, exclusive measurement where we do measure not only the scattered lepton but also the recoiling hadron, confirm the same measurements of quark densities.

 

[sanman]

But if sea quarks are different than vacuum quarks, where do the sea quarks come from?
The vacuum quarks come from the vacuum (the sink). But where do sea quarks come from?
The quark sea?

I thought the quark sea was part of the vacuum. If it's not, and is actually something separate, then what are its differentiating characteristics?

Can quarks penetrate other matter without interacting with it? Can the quark sea permeate all of space - including even deep space, and the space between hadrons?

 

[humanino]

But if sea quarks are different than vacuum quarks, where do the sea quarks come from?

In hadronic language, they form the "pion cloud" which creates the bag between the vacuum outside and the one inside. From a partonic point of view, the sea quarks come from color "bremsstrahlung" (radiation of valence quarks). In the language of color superconducting model of the QCD vacuum, the condensed quarks outside the bag would be analogous to Cooper pairs breaking chiral symmetry. The sea quarks would form the analogue of a London skin insuring the confinement by a Meissner effect.

 

[InquiringLynn]

David Mill in 'Atheist Universe maintains that indeed from quantum fluctuations the present Universe came. As the quantum fluctuations follow the law of conservation of mass-energy, Existence just is.

 

[sanman]

In hadronic language, they form the "pion cloud" which creates the bag between the vacuum outside and the one inside. From a partonic point of view, the sea quarks come from color "bremsstrahlung" (radiation of valence quarks). In the language of color superconducting model of the QCD vacuum, the condensed quarks outside the bag would be analogous to Cooper pairs breaking chiral symmetry. The sea quarks would form the analogue of a London skin insuring the confinement by a Meissner effect.

So what are the dimensions and geometry of this pion cloud? How big is it?

From an interaction-target point of view, is this pion cloud significantly bigger than the nucleus, and does it have a significantly larger cross-section than the nucleus?

I'm just wondering if this pion cloud is a better interaction target than the nucleus itself - assuming it has a significantly larger size.

 

[humanino]

From data directly (model independent), we have hints of the pion cloud in the neutron. Please take a look at figure 4 in Overview of nucleon structure : we can guess a negative pion cloud between 1 and 2 fm

Model dependent hints in the nucleon can be seen in The pion mass dependence of the nucleon form-factors of the energy momentum tensor in the chiral quark-soliton model. Please take a look at figure 6.a : attractive force occur between 0.7 and 2 fm.

 

[gillianreynol]

The apparently solid stuff is no more than fluctuations in the quantum vacuum, fiendishly complex calculations confirm.

 

[PAllen]

Absolutely. From your response, I'm understanding that it had in fact not been shown that the standard model has passed all previous experimental tests (Higgs apart), contrary to my previous impression from popular science accounts.

I would state it as: QCD had never been shown to be inconsistent with any experiment, and there were many (but mostly at high energy, where QCD is simpler). In this sense, popular accounts are correct - no failure, many successes. However, no reputable source would have stated that QCD explained everything that 'should' be within its rubric. This is, I think, the most significant low energy confirmation of QCD.

Consider GR. It has had no failure yet. However some of its major predictions (e.g. gravitational waves) have not been directly confirmed (indirectly, yes, with great accuracy, in Taylor Hulse). In 1960, one could say also that it passed all tests so far, but not so many tests could be accomplished then. Similar to standard model, everyone expects GR to fail at some point (with some good ideas about where it will fail), but each new confirmation (within its expected validity) is exciting