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nLab > Latest Changes: geometrodynamics

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  1.  
    • CommentRowNumber1.
    • CommentAuthorEric
    • CommentTimeApr 20th 2010

    Created a stub with some references for geometrodynamics.

    • CommentRowNumber2.
    • CommentAuthorUrs
    • CommentTimeApr 22nd 2010

    added an Idea-section to geometrodynamics

    • CommentRowNumber3.
    • CommentAuthorEric
    • CommentTimeApr 22nd 2010

    I don't recall seeing or reading about the connection between geometrodynamics and BF theory. Aside from that, are there people who still take the idea of geometrodynamics seriously. It is very pretty, but I can imagine some no-go theorem somewhere that refutes it with some simple gedanken experiment.

    • CommentRowNumber4.
    • CommentAuthorUrs
    • CommentTimeApr 22nd 2010

    I don’t recall seeing or reading about the connection between geometrodynamics and BF theory.

    I was thinking of the work by John Baez with some of his students (I forget who exactly that was) on 3-dimensional gravity as a TFT, where matter worldlines are realized as tubes taken out of the 3d cobordsim. That kind of phenomenon. There is more along these lines in the literature, but I don’t have the time to dig out the arguments.

    • CommentRowNumber5.
    • CommentAuthorEric
    • CommentTimeApr 25th 2010

    I added a reference to Friedman and Sorkin Spin 1/2 from Gravity and some section headers with a query box in “Spin without Spin”.

    • CommentRowNumber6.
    • CommentAuthorUrs
    • CommentTimeNov 7th 2023

    moving this old query-box dicussion out of the entry:

    +– {: .query} [[Eric]: Of the four “X without X”s above, the one that is not in Wheeler’s “Classical Physics from Geometry” is “Spin without Spin”. This is described in Section 3.4 of Matter from Space. It would be great to expand on that here. =–

    +– {: .query} Bruce Bartlett: Another example of this phenomenon seems to be the fact that Maxwell’s equations in matter are the same as Maxwell’s equations in curved space without matter! This is the basis of cloaking technology, see article by Leonhardt and Philbin. You can read this equivalence both ways. Either you can conclude that there is no such thing as curved space: it’s just a piece of dielectric material causing the light rays to bend which gives the illusion of curved space. Or you can conclude even more radically that there is no such thing as matter: what we think of as a block of wood is just a radically curved region of space (Maxwell’s equations can’t tell the difference). Or you can just think of it as a formal equivalence :-) =–

    diff, v11, current

    • CommentRowNumber7.
    • CommentAuthorUrs
    • CommentTimeNov 7th 2023
    • (edited Nov 7th 2023)

    added proper pointer to:

    diff, v11, current

    • CommentRowNumber8.
    • CommentAuthorUrs
    • CommentTimeNov 7th 2023

    fixed the reference to:

    diff, v11, current

    • CommentRowNumber9.
    • CommentAuthorUrs
    • CommentTimeJun 24th 2024

1 to 9 of 9

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