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    ztracené heslo?
    CISTICZRichard P. Feynman
    WENCA
    WENCA --- ---
    CYBERS: to je fakt krasny
    CYBERS
    CYBERS --- ---
    LITTLELI
    LITTLELI --- ---
    WENCA: to je moc pekny clanek.
    SLAPPY
    SLAPPY --- ---
    Neobycejna teorie svetla a latky je jedna z nejlepších knih, co jsem četl. A Feynmanovi záležitosti jsou vůbec super!
    WENCA
    WENCA --- ---
    CISTICZ
    CISTICZ --- ---
    WENCA: jako super, ale pod linuxem ani hovno, takze bille seres me! :)
    WENCA
    WENCA --- ---
    ty vole, to je narez! diky bille. :)
    TIBOREC
    TIBOREC --- ---
    WENCA: joo! je to ono, dokonce i s anglickejma titulkama :) ted uz jen vysetrit par hodin casu ;)
    WENCA
    WENCA --- ---
    WENCA: aha, microsoft silverlight. bad for me.
    WENCA
    WENCA --- ---
    http://research.microsoft.com/apps/tools/tuva/index.html

    to maj bejt ty dickovo prednasky od billa. me to jenom napsalo, ze muj brower je nepodporovany, ale uz jsem se nedozvedel na cem to ma fungovat. jde to nekomu z vas?
    TIBOREC
    TIBOREC --- ---
    WENCA: to jsem nikde neobjevil, ale tu informaci mam z RSS ScienceWeeku, tak treba se tam pak objevi i vyveseni tech videi.
    WENCA
    WENCA --- ---
    TIBOREC: nevite nekdo kdy se na ty prednasky budem moct podivat? hledal jsem klicovy slovo "feynman" na http://www.gatesfoundation.org/ a nic. :(
    MOYYO
    MOYYO --- ---
    jo a tadle sajta je taky dobra:
    http://rqgravity.net/MainIndex
    MOYYO
    MOYYO --- ---
    to je zlato, cisty zlato tendle paper :)
    MOYYO
    MOYYO --- ---
    a dost, prece to sem neprepastuju cely :)

    More dramatically, both G and Hilb may be replaced by a more general sort of n-category.
    This allows for a rigorous treatment of physical theories where physical processes are described by
    n-dimensional diagrams. The basic idea, however, is always the same: a physical theory is a map
    sending sending `abstract' processes to actual transformations of a specific physical system.
    MOYYO
    MOYYO --- ---
    The advantage of this viewpoint is that now the group G can be replaced by a more general
    category. Topological quantum field theory provides the most famous example of such a generalization,
    but in retrospect the theory of Feynman diagrams provides another, and so does Penrose's
    theory of `spin networks'.
    MOYYO
    MOYYO --- ---
    In particular, we can roughly distinguish two lines of thought leading towards n-categorical
    physics: one beginning with quantum mechanics, the other with general relativity. Since a major
    challenge in physics is reconciling quantum mechanics and general relativity, it is natural to hope
    that these lines of thought will eventually merge. We are not sure yet how this will happen, but
    the two lines have already been interacting throughout the 20th century.
    MOYYO
    MOYYO --- ---
    chramostak> zrovna to ctu :)

    Before we begin our chronology, to help the reader keep from getting lost in a cloud of details,
    it will be helpful to sketch the road ahead. Why did categories turn out to be useful in physics?
    The reason is ultimately very simple. A category consists of `objects' x; y; z; : : : and `morphisms'
    which go between objects, for example
    f : x -> y
    A good example is the category of Hilbert spaces, where the objects are Hilbert spaces and the
    morphisms are bounded operators. In physics we can think of an object as a `state space' for
    some physical system, and a morphism as a `process' taking states of one system to states of
    another (perhaps the same one). In short, we use objects to describe kinematics, and morphisms
    to describe dynamics.
    ...

    This escalation of dimensions can continue. In the diagrams Feynman used to describe interacting
    particles, we can continuously interpolate between this way of switching two particles.
    This requires four dimensions: one of time and three of space. To formalize this algebraically we
    need a `symmetric monoidal category', which is a special sort of 4-category.

    More general n-categories, including those for higher values of n, may also be useful in physics.
    This is especially true in string theory and spin foam models of quantum gravity. These theories
    describe strings, graphs, and their higher-dimensional generalizations propagating in spacetimes
    which may themselves have more than 4 dimensions.
    So, in abstract the idea is simple: we can use n-categories to algebraically formalize physical
    theories in which processes can be depicted geometrically using n-dimensional diagrams.

    ...
    z

    http://math.ucr.edu/home/baez/history.pdf
    Kliknutím sem můžete změnit nastavení reklam