Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

It's confirmed, matter is merely vacuum fluctuations.

  1. Nov 21, 2008 #1

    marcus

    User Avatar
    Science Advisor
    Gold Member
    2015 Award
    Dearly Missed

    "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.
     
    Last edited: Nov 21, 2008
  2. jcsd
  3. Nov 21, 2008 #2

    ZapperZ

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

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

    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.
     
  4. Nov 21, 2008 #3

    marcus

    User Avatar
    Science Advisor
    Gold Member
    2015 Award
    Dearly Missed

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

    Thanks! Will get to it immediately.
     
  5. Nov 21, 2008 #4
    Re: "It's confirmed, matter is merely vacuum fluctuations."

    I thought binding energy was always negative?
     
  6. Nov 21, 2008 #5
    Re: "It's confirmed, matter is merely vacuum fluctuations."

    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).
     
  7. Nov 21, 2008 #6
    Re: "It's confirmed, matter is merely vacuum fluctuations."

    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.
     
  8. Nov 21, 2008 #7
    Re: "It's confirmed, matter is merely vacuum fluctuations."

    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.
     
  9. Nov 21, 2008 #8

    ZapperZ

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

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

    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.
     
  10. Nov 21, 2008 #9

    marcus

    User Avatar
    Science Advisor
    Gold Member
    2015 Award
    Dearly Missed

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

    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:
    http://en.wikipedia.org/wiki/Quark
     
    Last edited: Nov 21, 2008
  11. Nov 21, 2008 #10

    marcus

    User Avatar
    Science Advisor
    Gold Member
    2015 Award
    Dearly Missed

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


    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"
     
    Last edited: Nov 21, 2008
  12. Nov 21, 2008 #11

    atyy

    User Avatar
    Science Advisor

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

    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?
     
  13. Nov 21, 2008 #12

    marcus

    User Avatar
    Science Advisor
    Gold Member
    2015 Award
    Dearly Missed

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

    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. :biggrin:

    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 dont 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!
     
    Last edited: Nov 21, 2008
  14. Nov 21, 2008 #13

    atyy

    User Avatar
    Science Advisor

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

    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?
     
  15. Nov 21, 2008 #14

    ZapperZ

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

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

    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.
     
    Last edited: Nov 21, 2008
  16. Nov 21, 2008 #15

    atyy

    User Avatar
    Science Advisor

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

    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.
     
  17. Nov 21, 2008 #16
    Re: "It's confirmed, matter is merely vacuum fluctuations."

    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.
     
  18. Nov 21, 2008 #17

    atyy

    User Avatar
    Science Advisor

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

    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?
     
  19. Nov 21, 2008 #18
    Re: "It's confirmed, matter is merely vacuum fluctuations."

    Or that they put a semi-colon in the wrong place.
     
  20. Nov 21, 2008 #19
    Re: "It's confirmed, matter is merely vacuum fluctuations."

    dammit...I saw that and didn't fix it :)
     
  21. Nov 21, 2008 #20
    Re: "It's confirmed, matter is merely vacuum fluctuations."

    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.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: It's confirmed, matter is merely vacuum fluctuations.
Loading...