Feynman's TOE and Motl's Convenient UnTruth

Feynman's Lectures contain his description of a theory of everything, written as U=0, where U is a sum of terms for all the physical laws we know (F-ma, etc.) It is, as Lubos Motl says, a sort of joke, since all the information is contained in the individual terms. As Frank Wilczek puts it in Physics Today:
It's the sum of contributions from all the laws of physics:

U = UNewton + UGauss + . . . ,

where, for instance, UNewton = (F ­- ma)^2 and UGauss = (­del · E - rho)^2.

So we can capture all the laws of physics we know, and all the laws yet to be discovered, in this one unified equation. But it's a complete cheat, of course, because there is no useful algorithm for unpacking U, other than to go back to its component parts.


Lubos latest post is a rant attacking Thomas Thiemann's latest paper(hep-th/0608210) in which he claims of Thiemann's "Master Constraint" program that
...Thiemann's biggest discovery is thus exactly equivalent to Feynman's joke.

True? Not exactly. In fact it is a distortion so drastic as to be of the form conventionally labelled a lie.

The irony is that Motl fairly faithfully describes parts of what Thiemann did well enough that one can call "bullshit" purely on the basis of LM's own text. Thiemann has a set of constraint equations labelled by some indices. He packs these equations up into a single matrix equation. This packing has several points, which I will briefly describe, but most importantly, there is a way for "unpacking" his M, unlike Feynman's function.

The most elementary point is notational simplicity - a lot of equations are summarized as one. When Maxwell wrote down his equations, there were twelve of them: four sets of three component equations. The development of vector analysis allowed those to be simplified to the four vector equations undergrads learn today. Moreover, the vector notation makes manifest the equation's independence of particular coordinates. Four-tensor or differential form notation introduces additional concision and makes manifest the euations crucial Lorentz invariance.

Thiemann's master equation is like that. The second point of the equation is to, as he puts it:
...use the associated freedom to regularise the square of the constraints:

The generalization preserves the information present in the original equations but allows additional degrees of freedom to be exploited in solving them - this is a common tactic in physics at all levels, as Lubos well knows. In addition, such reformulations often have heuristic value, making possible new approaches and ideas.

Note that I haven't made any judgement on the usefulness or even validity of the Master Constraint Program. I have rather merely pointed out that Motl has described in a completely, and unfortunately characterically, dishonest fashion.

Comments

  1. Hello CIP! There are now real equations on my blog instead of everyone else's crude latex.
    It is soooo nice to be technologically ahead!
    I hope you are still enjoying the photos.

    ReplyDelete
  2. Dear l,

    Your equations are indeed gorgeous. How did you do them.

    I do have a technical quibble with another post of yours, though. The light in The Phial of Galadrial is the light of Earendil's star, not Elendil. That light, you might recall, is from the Silmaril mounted on Earandil's ship as it sails the skies.

    The Silmarilli, remember, were crafted by Feanor to capture the light of the two trees. Melkor poisoned the trees, stole the three Silmarils, and went into the witness protection program (changing his name to Morgoth) in Middle Earth, holing up in Thangorodrim. Luthien and Beren stole one of the Silmarils from him as the bride price of Luthien to her father, Thingol of Doriath.

    They passed it to their son Dior, who passed it to his daughter, Elwing, who gave it to Earendil, her husband, who used it to guide his ship to Valinor, resulting in the sending back of major heat to bust Morgoth.

    Their children were Elrond and Elros. Elendil was a distant descendent of Elros.

    HTH

    ReplyDelete

Post a Comment

Popular posts from this blog

Organoids and Boltzmann Brains

The Worst