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Lack of understanding of energy, quarks, and the strong force

  1. Apr 21, 2006 #1
    Hello,
    Here I go again :tongue2:
    I don't understand a few things, let me all questions put in a paragraph so that I don't miss anything

    What is an energy? (I can't understand the definition provided by the encyclopedia) And, what's up with the vacuum energy? If no particles are there, how can energy simply exist? Does space alone produces energy? If so, how does it do that? Do forces exist without particles? This thing I don't trully understand. Energy, usually is created by interference of matter with space and electromagnetic force (I only think) So, can you play chess if you lack a chess set? And also, if forces can exist without matter, do our universe have some kind of DNA? (not DNA, word by word, but a concept)
    And here's something I just thought about a few seconds ago. My another book :tongue2: says that Before the big bang, time and space weren't created yet. Alright, so first of all, if space wasn't created yet, what gave the energy, a shape of a point particle, (like it's drawn in the book, and some magazines of SciAm)? Dimensions weren't there yet, so actually the energy had no size, no shape and yet it didn't have a place to fit, hence it didn't exist. But on the other hand, if space-time was created already... I don't know what... sorry :cry: Help, Help!

    Ok, energy's done, and let's go on with the quarks,

    My particle physics book, says that strong force is produced by quark interference, or strong nuclear force exists only between quarks. Notice the word "only". So what about protons and neutrons? What keeps them together if not a strong nuclear force? Alright, and again, if it's somehow different than I think, quarks are joint by nuclear force, and if so, wouldn't the picture of an atom look somehow different, than that shown just everywhere? Because, proton and neutron wouldn't be a point particle if quarks are, and yet wouldn't the quarks also produce a force between the neutron's and proton's quarks creating one super-particle? :biggrin: I don't know but my imagination doesn't draw a nuclei like a ball, but a rectangle :rofl: SOS SOS SOS

    I would appreciate any writings,
    Thanks
     
  2. jcsd
  3. Apr 23, 2006 #2
    anyone? :frown:
     
  4. Apr 27, 2006 #3
    Arrghh, so many questions.

    You are asking to explain the entire notion of QFT. You should do a search/study yourself in stead of asking such general questions. That's why nobody is answering.

    Here is some info on fields and virtual particles.


    The most fundamental QFT-quantity is not "a particle" but "a field". In QFT, particles arise due to fluctuations of fields.

    Virtual particles are an intermediate stage of an interaction between elementary particles in QFT. They are a tool to describe these interactions, yet their existence can be proven with experiments : see the Casimir-effect.

    The QFT-vaccuum is not empty because the lowest possible energy cannot be zero (you know, because of Heisenberg uncertainty : zero energy implies infinite spread of position). thus via E=mc², the vaccuum is filled with these socalled virtual particles. It was Dirac who came up with the idea that the vacuum was filled with virtual positron and electron pairs (the reason that they were pairs has to do with conservation laws like that of electrical charge). You can break up such a pair and make the particles real when you have enough energy coming from some interaction between two charged particles that were placed inside the vaccuum.

    Indeed, virtual particles and their fields (remember that position is not a well defined quantity in QFT ) do not exist for ever. In theory this can be proven by the fact that the socalled number-operator of such particles does NOT commute with the hamiltonian (it is not a conserved quantity). Therefore we can call these virtual particles : vacuum-fluctuations.

    Problem is that if the vaccuum has a gazzillion virtual particles (suppose each such particle is represented by one LOWEST energy quantum of a harmonic oscillator), the energy of this vaccuum (the zero-point energy) becomes infinite. This will lead to difficulties with curvature of space time and this effect also predicts a very large cosmological constant. This is however against observations. A possible way out is to renormalize this positive infinity by saying that each such virtual electron and positron has a supersymmetric counterpart with opposite energy. This leads to the situation that the positive infinity is "eliminated" (it is not really gone , though) by a negative infinity coming from the supersymmetry.

    marlon
     
  5. Apr 27, 2006 #4
    I have absolutely no notion of quantum field theory. I'd like to learn it, but after I start quantum mechanics. Before I start quantum mechanics I'd like to learn mutli-variable calculus. A long time before me. Should I trust all what QFT says? Why is it considered a theory?

    Sorry but, What is infinite spread of position?

    So virtual particles arise only from the field? Then I conclude that forces may exist without particles, but then 'where is the force?' and where are the mechanics of forces? Everything is based upon something. For example atoms are based on quarks and the like, but what a force is based on?

    So what happens with those virtual particles after they appear and what causes them to behave that way? Appear and Disappear? When they Disappear what happens with the energy?

    Has carvature of space time been ever confirmed for sure?

    I would also appreciate if you answer the rest of the questions, about Big Bang, atoms and quarks (2nd and 3rd paragraph)
     
  6. May 2, 2006 #5
    Ok, in that case i suggest you need to study QM and special relativity. After that, i suggest Zee's book "QFT in a Nutshell" to start with QFT. One does not learn QFT from an open websource.

    regards
    marlon
     
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