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    CISTICZRichard P. Feynman
    WENCA
    WENCA --- ---
    http://images.google.com/images?q=physics+source%3Alife

    Celkem pekny fotky fyziku z casopisu Life.
    MOYYO
    MOYYO --- ---
    WENCA
    WENCA --- ---
    MOYYO: dik. ty mas urcite nejaky ucebnice o QED v el. podobe, ze? :) nechces pls neco upnout? :)
    WENCA
    WENCA --- ---
    eh, zajimave. a zdroj?
    MOYYO
    MOYYO --- ---
    co se clovek vsechno nedovi..

    >>>> When an isolated electron emits a photon, the photon must be reabsorbed.
    >>>> Since the electron is isolated, the photon must be reabsorbed by the
    >>>> emitting electron - that is a definitional truism, or the electron would
    >>>> not be isolated. This is represented as a loop integral. Normally that
    >>>> is thought to diverge. Actually it does not diverge. If one does not
    >>>> piss all over basic mathematics which one should learn as a first year
    >>>> undergraduate, and does the calculation properly this loop integral is
    >>>> zero.

    >>>Why do you say so? The electron self-energy loop integral is infinite.
    >>>This is shown in every QFT textbook.

    >>Every QFT textbook bar one, afaik. The one being Scharf, Finite QED.

    >>> Or I don't understand you correctly?

    >> You understand me correctly. It was fine for Dyson, Feynman, Schwinger
    >> to do the calculations in a heuristic manner, which generated
    >> divergences. It was even fine for them to deal with the divergences in
    >> an ad hoc manner. It is not fine for succeeding generations to follow
    >> the same arguments and to fail to straighten them out. As early as the
    >> seventies it had been shown by Epstein and Glaser et al that the
    >> ultraviolet divergences were to do with elementary errors in analysis,
    >> the abuse of Wick's theorem, which effectively means the changing of
    >> orders of integration where we do not have uniform convergence. I showed
    >> the same thing in my own doctoral thesis, albeit a few years later.

    >> The fact that this kind of abuse of mathematics will produce nonsensical
    >> results has been known for about two hundred years and was well sorted
    >> out by the latter half of the C19th. This is taught to first year maths
    >> undergraduates. There was some excuse in the early days of qed, but for
    >> modern text books like Peskin and Schroeder to produce the same stuff is
    >> pure incompetence, imv. Based on this bad mathematics we have whole
    >> reams of research into absolute nonsense, from the belief in the Higgs
    >> boson, false arguments about renormalisability, the conceptual basis of
    >> field theory, through to string theory.

    >I refuse to believe that Dyson, Feynman, Schwinger, Schweber, Bjorken,
    >Drell, Peskin, Schroeder, Weinberg, ... all made an elementary
    >mistake,

    An elementary mistake in a sense, but well buried in difficult
    mathematics. The fact is that physicists had never had to pay attention
    to such issues as uniform convergence when changing the order of
    integration. They were always able to argue "this is physical so it must
    be finite". That argument does not apply to the mathematical structure
    of quantum theory. It should have been quickly recognised that it does
    not apply, and the effect of changing the order of integration should
    have been examined. It was one of the things I set out to examine in my
    own thesis, and it has been examined by others before me. I don't think
    there is any excuse for your attitude. For Dyson Feynman and Schwinger
    to do a heuristic calculation to get an answer is fine. But to fail to
    recognise even after the occurrence of divergence that the calculation
    contains a mathematically illegal operation, and fail to analyse the
    effect of that operation, that is not fine. That is plain sloppy and
    mathematically incompetent. To say that "Feynman did it, so it must be
    right" is not science and it is not the way mathematics is done. It is
    necessary to construct the theory and the integrals carefully, and to
    watch things like orders of integration. In the context of these
    calculations, which are quite elaborate, that is much more difficult.
    But there is still no excuse for not doing it. Nor is there any excuse
    for writing down, as Peskin and Schroeder do, expressions equivalent to

    1 + infinity + infinity^2 + ... = 1/(1-infinity) = 0

    The effect of that, combined with the attitude "oh you get the right
    answer so it must be right" together with hostility towards anyone who
    tries to do the maths properly, is the reason why there are very few
    mathematically competent theoretical physicists, and the reason why
    theoretical physics has been stalled for fifty years.
    WENCA
    WENCA --- ---
    http://ck12.org/ je jakasi organizace, ktera se snazi vytvorit open source webovy ucebnice, ci co. vyhledal jsem si u nich slovo "feynman" a vypadl na me moc peknej popis dickovo diagramu.
    MOYYO
    MOYYO --- ---
    zatim 0.72x, nemam ted moc casu ;)
    MELOUN
    MELOUN --- ---
    MOYYO:
    WENCA: a? kua kluci to vas mam prosit? urcite jste to uz oba procetli 2x..
    MOYYO
    MOYYO --- ---
    sem polovicni fanda... kouknul sem na ni az doma ;)
    WENCA
    WENCA --- ---
    MOYYO: Si hovno fanda, ja ani na cenu nekoukal. :D
    MOYYO
    MOYYO --- ---
    tak uz mam tez novy vytisk, jupi!
    ale teda skoro 300 za takovou tenouckou mrsku je opravdu pro fanousky..
    MOYYO
    MOYYO --- ---
    no tak presne jednicka je ten druh knizky, kvuli kterymu chci poradnej ebook reader :))
    BRUSINKA
    BRUSINKA --- ---
    MOYYO: to je dobrá vyhlídka, dostat po hlavě tíhou informací:))
    (já ne, zatim se prokousávám jedničkou-respektive byla uložená do poličkky, dokud nebude čas, teď čtu jen v tramvaji)
    MOYYO
    MOYYO --- ---
    BRUSINKA: neni lehci, ja ji cet ;-)
    GRIGORIJ
    GRIGORIJ --- ---
    SARNEGARTH: diky moc! :)
    SARNEGARTH
    SARNEGARTH --- ---
    GRIGORIJ: jinak ad text v anglictine: utfg.
    SARNEGARTH
    SARNEGARTH --- ---
    GRIGORIJ: shaft passer.
    Kliknutím sem můžete změnit nastavení reklam