It's confirmed, matter is merely vacuum fluctuations.

[marcus]

"It's confirmed, matter is merely vacuum fluctuations."

This was the title of a NewSci article tht just appeared
http://www.newscientist.com/article/dn16095-its-confirmed-matter-is-merely-vacuum-fluctuations.html

Lattice QCD calculation that took a year of supercomputer time at the Jülich research center, was just reported in Science:

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.

The current issue lf Science also has a commentary by Andreas Kronfeld, a guy at Fermilab, titled
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."

If anyone wants a non-mathy non-technical explanation of what this is about, Frank Wilczek has a pretty good video talk and essay about the Origin of Mass, linked at his website. And several chapters about it in his new book The Lightness of Being.

 

[ZapperZ]

Kronfeld's review of the work was surprisingly disappointing on details and impact. Nature's daily news has a clearer description on what this all means.

http://www.nature.com/news/2008/081120/full/news.2008.1246.html

The link is open for free only for a limited time, so read it now.

Read, for example, at the end on the "collider question".

Zz.

 

[marcus]

http://www.nature.com/news/2008/081120/full/news.2008.1246.html

The link is open for free only for a limited time, so read it now.

Thanks! Will get to it immediately.

 

[Riogho]

I thought binding energy was always negative?

 

[BenTheMan]

I think the title is misleading.

Dark matter is a particle, not a vacuum fluctuation, and last I checked there's more dark matter than protons.

And either way, this isn't a new result, is it? We can all add the mass of 2 up quarks and a down quark and see that this number (15 MeV) is much less than the mass of the proton (938 MeV).

 

[humanino]

And either way, this isn't a new result, is it? We can all add the mass of 2 up quarks and a down quark and see that this number (15 MeV) is much less than the mass of the proton (938 MeV).

At some point, someone wants to stand up and say "that's it, we understand nonperturbative QCD". Even with the results presented here, we are decades from being able to say that.

 

[BenTheMan]

I think it's marcus's headline that is misleading---this is the kind of crap that science journalists pull to sell magazines. I don't blame marcus, because it looks like he cut and pasted the headline from somewhere else.

The importance isn't the fact that "vacuum fluctuations comprise most of matter", this was known long ago---like I said, anyone who has had a remedial class in particle physics could tell you the difference between valence quarks and sea quarks. The importance is that (if it's right), the authors have calculated the neutron mass from first principles (nothing about a proton).

I don't know of the status of other lattice simulations---but I think that the calculation of the neutron mass is (was) an open problem. Maybe someone more familiar with all of this can correct me.

humanino---

I didn't want to suggest that we understood non-perturbative QCD in a quantitative manner, but many qualitative results are pretty well known---specifically, that the mass of the proton comes from places other than the valence quarks. We also know lots of mass ratios that work to the 10% level, why pions are light and protons are heavy, etc.

 

[ZapperZ]

I think the title is misleading.

Dark matter is a particle, not a vacuum fluctuation, and last I checked there's more dark matter than protons.

And either way, this isn't a new result, is it? We can all add the mass of 2 up quarks and a down quark and see that this number (15 MeV) is much less than the mass of the proton (938 MeV).

Yes, but no one has been able to calculate it from First Principle using just the Standard Model alone. This theoretical calculation employed on QCD principles, and the fact that they could derive the mass of these nucleons is a tremendous success for QCD and the Standard Model. This is similar to calculating the electron gyromagnetic ratio, which is still the crowning success of QED.

Zz.

 

[marcus]

An experimental physicist at Fermilab, member of the D0 team, and author of a couple of books, put it this way at another forum:

"I haven't read these results, but if they bear up under further scrutiny, these are a big deal. I know Kronfeld...he's a serious player. I don't personally know the other guys. These results underscore an exceedingly important point. To very good approximation, there is very little mass (in the way most people think about it) in the universe. There is (nearly) only energy..."

The emphasis is his. Andreas Kronfeld is part of the Fermilab theory group. Kronfeld's comment, quoted in post #1, was:

"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."

To get an idea of Kronfeld's perspective and interests, here is his homepage:
http://theory.fnal.gov/people/kronfeld/
PhD Cornell 1985, 3 year DESY postdoc, then Fermilab 1988-present.

One concept that seems to come up in Kronfeld's work is the sea quark, the vacuum as a virtual quark ocean. Interesting sideline--here's the wiki-word on the quark sea:

Sea quarks

The quarks that contribute to the quantum numbers of the hadrons are called valence quarks (q_v). Hadrons also contain virtual quark–antiquark (qq) pairs, known as sea quarks (q_s), originating from the gluons' strong interaction field. Such sea quarks are much less stable, and they annihilate each other very quickly within the interior of the hadron. When a gluon is split, sea quarks are formed, and this process also works in reverse in that the annihilation of two sea quarks will reproduce a gluon.[57] In addition to this, sea quarks can hadronize via a certain fragmentation function; for instance, a sea quark hadronizing into a pi meson ... There is a constant quantum flux of sea quarks that are born from the vacuum, and this allows for a steady cycle of gluon splits and rebirths. This flux is colloquially known as "the sea".[59]

http://en.wikipedia.org/wiki/Quark

 

[marcus]

Yes, but no one has been able to calculate it from First Principle using just the Standard Model alone. This theoretical calculation employed on QCD principles, and the fact that they could derive the mass of these nucleons is a tremendous success for QCD and the Standard Model. This is similar to calculating the electron gyromagnetic ratio, which is still the crowning success of QED.

Zz.

This really nails it! I don't see how to say it better.
Another short headline that I like is the title of the Nature.news piece by Philip Ball that you linked to:
Nuclear masses calculated from scratch
http://www.nature.com/news/2008/081120/full/news.2008.1246.html

The phrase from scratch says what's important about this achievement.

If I have any notion of what is going on in Frank Wilczek's head, I'll bet he feels as good about this successful lattice calculation as he did about the prize in 2004.

typo: I think you meant "employed only QCD principles" rather than "employed on QCD principles"

 

[atyy]

So how standard is the standard model? If this is big news, then was it conceivable before this that the standard model is actually wrong well within its supposed domain of validity? If so, why is it usually said (at least in popular physics accounts) that the experimental discovery of the Higgs is all that's left to complete it? If not, why isn't this just considered a book-keeping calculation?

 

[marcus]

So how standard is the standard model? If this is big news, then was it conceivable before this that the standard model is actually wrong well within its supposed domain of validity? If so, why is it usually said (at least in popular physics accounts) that the experimental discovery of the Higgs is all that's left to complete it? If not, why isn't this just considered a book-keeping calculation?

Hmmm. Interesting thought. Well let's see, in science (physics especially) no theory is ever proven true. You keep testing it, hoping you can catch it in error (which will show you "new physics".)

My understanding is that experimentalists have been trying to show the SM was wrong about something for 30 years now and they have sounded rather frustrated at times that all they seem able to do is confirm it.

But surely nobody thinks the SM is the final theory! Nobody thinks it is CORRECT in some fundamental sense. If nothing else, eventually we'll have a new spacetime continuum to replace the flat Minkowski space of Special Relativity that QFT is built on. And particle physics will move over to the new continuum (which probably won't be a differential manifold---won't be smooth at small scale) and things will look different. Eventually SM will be retired, put out to pasture, or be regarded as merely an effective theory for calculating some stuff.

So why am I celebrating? you want to know. Why is this heroic year-long calculation such a triumph? Well for one thing it is a triumph computationally. The numerical analysts had to be creative and find shortcuts to speed up the computation.
For another, nobody knew it would come out right! This is yet another test of QCD and the Standard Model. It could have shown that QCD is wrong! Now what thrills me is that such a remarkable test was accomplished, whatever the outcome: win or lose.

I don't root for the SM and I don't root against the SM. I'm happy either way. What I root for is empirical testing itself, whichever way it goes. So I'm glad that this calculation has been performed. As it happens, it is a deep historical confirmation of the SM. But if they had gotten a different mass, that would be exciting and important too. The main thing is it was hard, and nontrivial, and they did it. Go humans!

 

[atyy]

Hmmm. Interesting thought. Well let's see, in science (physics especially) no theory is ever proven true. You keep testing it, hoping you can catch it in error (which will show you "new physics".)

My understanding is that experimentalists have been trying to show the SM was wrong about something for 30 years now and they have been very frustrated that all they can do is confirm it.

But surely nobody thinks the SM is the final theory! Nobody thinks it is CORRECT in some fundamental sense.

Yes, I understand that. I guess my question is a little subjective, since it's essentially "how surprised should I be?". After all, one could reasonably be surprised that Maxwell's equations work at all since that would be the "unreasonable effectiveness of mathematics" or of induction, but then logically one shouldn't be surprised if Maxwell's equations suddenly failed tomorrow well within the classical regime. Anyway, my impression (again popular physics accounts) was that the standard model had passed all previous experimental tests, and that new experiments are needed see if it will fail. If this new calculation is a big deal, does it mean that before this even previous experiments may have already revealed new physics, and we just haven't known about it?

 

[ZapperZ]

Yes, I understand that. I guess my question is a little subjective, since it's essentially "how surprised should I be?". After all, one could reasonably be surprised that Maxwell's equations work at all since that would be the "unreasonable effectiveness of mathematics" or of induction, but then logically one shouldn't be surprised if Maxwell's equations suddenly failed tomorrow well within the classical regime. Anyway, my impression (again popular physics accounts) was that the standard model had passed all previous experimental tests, and that new experiments are needed see if it will fail. If this new calculation is a big deal, does it mean that before this even previous experiments may have already revealed new physics, and we just haven't known about it?

For a theory to come up with an ab initio calculation and derive what has been only experimentally measured, is a big deal! As an experimentalist, that's what I look for in a theory. It tells me that there's some legitimacy to it. You might as well say to Robert Laughlin "So you could show how you actually derived those fractional quantum hall effect that someone else observed experimentally. Big Deal!" Yet, they gave him a Nobel Prize for it, because the physics associated with such a derivation has such wide-ranging implication.

The same can be said here. Not only is this, by itself, an amazing ability, but if you look at the report, this is almost as much as a triumph of mathematical physics, because one needed not only a lot of computing power, but very clever mathematical technique to solve something that formidable. It also gave another argument and validity to the idea that the gluons ARE the dominant source of these hadronic mass, not the various family of the Higgs. That is a significant theoretical progress, especially with the LHC about to power up.

BTW, to use your Maxwell equations example, it's like someone actually derived Maxwell equations from First Principles. While we certainly what the "end" is like, to be able to come up with it from a lower level starting point would be damn impressive.

Zz.

 

[atyy]

For a theory to come up with an ab initio calculation and derive what has been only experimentally measured, is a big deal! As an experimentalist, that's what I look for in a theory. It tells me that there's some legitimacy to it.

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.

 

[BenTheMan]

All---

It is certainly a big deal to calculate the neutron's mass from first principles.

What is not a big deal is the realization that it is mostly made up of sea quarks. This is something I learned in a particle physics class at least two years ago, from a textbook (Halzem and Martin, "Quarks and Leptons").

I don't want to trivialize what these people have done---a true, first principles calculation of the neutron mass is interesting in it's own right. However, needlessly sensationalizing results such as these is what pisses scientists off when they read science journalism.

 

[atyy]

All---

It is certainly a big deal to calculate the neutron's mass from first principles.

What is not a big deal is the realization that it is mostly made up of sea quarks. This is something I learned in a particle physics class at least two years ago, from a textbook (Halzem and Martin, "Quarks and Leptons").

I don't want to trivialize what these people have done---a true, first principles calculation of the neutron mass is interesting in it's own right. However, needlessly sensationalizing results such as these is what pisses scientists off when they read science journalism.

How much different a number would this new calculation have had to get (from what they actually got) to show that current theory is wrong?

 

[WarPhalange]

Or that they put a semi-colon in the wrong place.

 

[BenTheMan]

dammit...I saw that and didn't fix it :)

 

[BenTheMan]

How much different a number would this new calculation have had to get (from what they actually got) to show that current theory is wrong?

I would say that if they got a number that was TOO different, the result wouldn't have even been reported.

The impressive thing isn't that they got the right number. The impressive thing IS that they were able to do the calculation at all---this is the significant advance, not proving that "most mass is vacuum fluctuations". Like I said, I KNEW this result, and I don't even work in the field of lattice. Everybody (i.e. physicists who've had more than a remedial course in particle physics) know that it's the sea quarks, and not the valence quarks, that make up most of the mass of the proton. The up quark weighs 5 MeV, and the down quark weighs about 8 MeV. The proton is made of two up quarks and a down quark. The total mass of the three quarks (called "valence quarks") is about 20 MeV, but the proton weighs about 940 MeV. The rest of the mass of the proton comes from the "sea quarks", which are popping in and out of existence inside the proton. These virtual particle pairs make up the rest of the mass of the proton.

New Scientist has an history of irresponsible reporting when it comes to things like this (i.e. misleading headlines and overstating results). In fact, most science journalism is absolute ****. I can understand the reason why, to some extent---it's a combination of the fact that most of the reporters are absolutely clueless about physics, and most physicists are very excited about their work.

 

[gel]

So only a small fraction of the mass of a neutron comes from the quark masses. But one thing that I don't understand, is that there's no such thing as a free quark mass, as they are always bound.
There's mass terms in the Lagrangian, but I thought these were just bare masses which are chosen to match some experimentally observed quantities. Eg, bare electron mass in QED is chosen to match the observed physical mass.
So what are the masses of quarks chosen to match? and aren't the bare masses renormalized away (effectively infinite)?
I must be wrong because apparently the bare mass is a few MeV. Is this a fundamental difference between QED and QCD?

 

[BenTheMan]

Is this a fundamental difference between QED and QCD?

Yes, the coupling! QCD is strongly coupled. In QED, the further you pull an electron and a positron away from each other, the less they interact. In QCD, the converse is true. The stuff interacts more strongly as you pull things apart. This is observed in high energy particle collisions as the process of hadronization.

The question about the quark masses is a good one, and I can't answer it from the top of my head. The light quarks are particularly tricky---until recently, there was room for the up quark to be massless.

My guess is that the quark content of the pions is approximately known, and the quark content of the other hadrons is approximately known too. Then it's just a matter of finding a best fit to make all the numbers work out. Again, this is just a guess.

 

[gel]

thanks for your reply.
So, I take it that the physical mass of hadrons and mesons don't diverge (as you let the lattice become finer) if you hold the bare quark mass constant, allowing you to define a bare mass.
Unlike for an electron where the bare mass would be infinite in the limit.

 

[BenTheMan]

Well, the mass parameters in the SM actually come from the coupling to the higgs. So the quark masses (i.e. their yukawa couplings) SHOULD diverge. Then you'd have to define a bare coupling to the higgs, etc etc.

I'm not sure how it works on a lattice---again, I'm not working in that field.

 

[Haelfix]

One of the holy grails for the lattice QCD people isn't merely the masses of the proton and the neutron (thats just step 1 so to speak), its calculating the full Regge slopes and behaviour of the hadronic spectrum and to do so with confidence. I have no doubt they'll get it oneday, but it very well could be another 20 years or so for the algorithms and computers to advance sufficiently.

 

[sanman]

Yes, the coupling! QCD is strongly coupled. In QED, the further you pull an electron and a positron away from each other, the less they interact. In QCD, the converse is true. The stuff interacts more strongly as you pull things apart. This is observed in high energy particle collisions as the process of hadronization.

The question about the quark masses is a good one, and I can't answer it from the top of my head. The light quarks are particularly tricky---until recently, there was room for the up quark to be massless.

My guess is that the quark content of the pions is approximately known, and the quark content of the other hadrons is approximately known too. Then it's just a matter of finding a best fit to make all the numbers work out. Again, this is just a guess.

So in theory, will 2 free quarks on opposite sides of the universe have the most interaction?

I guess what I'm really asking is - how far out does this field of interaction go? Is there a distance threshold limit?
Does the interaction only increase with separation distance upto a certain distance, after which the interaction drops off?

 

[malawi_glenn]

after a certain separation distance hadronization will occur and you'll not have free quarks anymore.

 

[arivero]

Nuclear masses calculated from scratch
http://www.nature.com/news/2008/081120/full/news.2008.1246.html

The phrase from scratch says what's important about this achievement.

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?

 

[sanman]

ripples in the quark sea

after a certain separation distance hadronization will occur and you'll not have free quarks anymore.

And what causes this hadronization to occur? The quark sea?
Does the quark sea always have some surplus of particles to offer up?
Otherwise, if the quark sea donates members of its ubquitous quark-antiquark pairs to bind to the free quark as part of hadronization, then shouldn't this leave corresponding unpaired anti-quark partners remaining, which will in turn require further donations for their hadronization?

If our universe has much more matter than anti-matter, then how could the quark sea be expected to provide enough quark donations for hadronization purposes if we were to create a sufficiently large number of free quarks?

Gee, it makes it sound like there is some corresponding anti-universe which is being affected by our particle collider experiments.
Everytime we do a collider experiment to produce some free quarks, the people in the anti-universe must be simultaneously doing collider experiments to produce some free anti-quarks.

Will we never be free of these meddlers? ;)

 

[humanino]

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?

The lattice cannot provide absolute scales, even in principle. As usual, the light quark mass (u&d) are fixed by the pion, the strange by the kaon and the charm by the cascade. All other masses shown in the spectra result from those ratios.

The lattice can provide genuine insight into how QCD works. There are perspective for instance to have the quenched approximation under control, and they shed light onto why constituent quark models are so successful.

 

[arivero]

The lattice cannot provide absolute scales, even in principle. As usual, the light quark mass (u&d) are fixed by the pion, the strange by the kaon and the charm by the cascade. All other masses shown in the spectra result from those ratios.
.

Are you sure that giving the masses of pion, kaon and "cascade", the article calculates the mass of proton?

 

[humanino]

Are you sure that giving the masses of pion, kaon and "cascade", the article calculates the mass of proton?

Nucleon, lambda, hyperon and their radial excitations, as well as omega (including rho and kaon*). It made it to Science.

 

[koolmodee]

So then what is the big deal with the 'god' particle, the Higgs particle? Especially popular press keeps drumming in people's heads that the Higgs particle gives matter its mass. The main purpose CERN was built, was to find the Higgs particle, they say.

 

[malawi_glenn]

So then what is the big deal with the 'god' particle, the Higgs particle? Especially popular press keeps drumming in people's heads that the Higgs particle gives matter its mass. The main purpose CERN was built, was to find the Higgs particle, they say.

Higgs give mass to the elementary particles themselves. The mass of the quarks and the leptons.

But most of the (baryonic) mass is QCD-mass: quark-gluon sea in hadrons.

You also have the "problem" with the Dark Matter, which is thought not to be baryonic.

That CERN was built for finding the higgs boson is rediculos, CERN was built in the 1950's, decayes before Higgs particle was invented in theories..

 

[BenTheMan]

That CERN was built for finding the higgs boson is rediculos, CERN was built in the 1950's, decayes before Higgs particle was invented in theories..

He means LHC.