Apologies if this post seems a bit incoherent but it may help to understand why I call myself a failed physicist as opposed to a moderately succsessful one. OK here is some context I was brutally ejected from paradise when it was made plain that despite my showing a moderate ability to pass exams on quantum field theory and group theory that there was no way I was ever going to get a grant to pursue particle physics beyond my modest MSc, This was despite the fact that I got more marks in the quantum field theory exam than other of my contempories who had already got a full time gramt. Whatever happened to them I dont know but given that their names are not seen as being leading lights in theoretical physics then I guess their career petered out eventually and they are now (just as I am) makong modest contributions to the world of industry, finance or comerce. So what was the point anyway despite the bitterness one has to acknowledge that the 'system' is extremely ruthless and that better people than me have failed to get to the holy grail of a permanemt lectureship and so despite the scars which still sting after 30 years one has to grow up and get used to it.

Anyway those who have read my blogs and contributions to the OU fora will realise that I am deeply concerned about the way modern physics has developed. So at the risk of sticking my neck out I will tty and turm the clock back 30 years when the garden seemed rosy and the nagging feeling (of which I have no means of verifying) that something was missed back in those early years. Also I will stick my neck out (and I've had a few pints so apologies for my boldness) and state some constraints that I feel that provide some basic ground rules for any theory of physics should adhere if they are to be credible.

OK when I did my MSc back in 1978-1980 the big things were gauge theories, the establishment of the standard model of particle physics and extensions which involved either supersymmetry or attempts to incorporate the established symmetry of SU(3)xSU(2)xU(1) in terms of a higher symmetry such as SU(5).

It would be a slightly cynical view (Albeit one I hold to) to claim that as far as particle physics is oncerned that there has been no real development since then apart from finding out specific values of masses of particles such as the top quark that we didn'nt know. Anyway the undoubtable succes of the standard model of particle physics in accounting for all the phenomenon that we experience at paticle acelerators at CERN or FERMILAB cannot be disputed.

So this gives me my first boundary condition of any new theory of physics to replicate our current success that it must show in a fairly obvious way that the Lagrangian of the Standard model of particle phyiscs is a part of it. (This is not true of any theory involving Superstrings)

Secondly there has to be a link with experimental results for any quantum field theory based on a Lagrangian this is fairly routine (albeit quite technically complicated) in that for a Lagrangian based on 4 diminsional space time it is relatively straightforward to calculate a scattering matrix for a given process (this seems not to be the case for any theory of superstrings or loop gravity (any experts please correct me if I'm wrong)).

Now here is the crux of my vision, when one quantizes a classical Lagrangian such as those for the strong interaction if one wants to make consistent calculations one has to introduce ghost particles and these ghost particles at first sight have to be introduced ad hoc. Neverheless once one has done this the symmetry of the strong interaction namely an SU(3) symmetry is seen as part of a deeper symetry called BRST symmetry.

which mixes fermions and bosons together

http://en.wikipedia.org/wiki/BRST_quantization

Simulataneously as these symmetries were being discovered developments of supersymmetry which also combines fermion and bosonic symmetries together were being explored

http://en.wikipedia.org/wiki/Supersymmetry

The natural extension of these techniques to relativity led to the development of a theory of gravity called

supergravity in which the quantisation of General relativity led to the coupling of the graviton a spin 2 particle to a spin 3/2 particle equation. (NB the usual claim that superstrings are the only natural way that predicts the graviton as is sometimes claimed is false any means of turning general relativity into a quantum field theory will involve the prediction of a spin 2 particle not just superstrings).

Unfortunately (and here is the failure) attempts to treat gravity as just another quantum field theory was inconcliusive (but then despite the hype superstrings are just inconclusive) so here is my statememt of faith

Supersymmetry on it's own is clearly inadequate

on the other hand Supersymmetry combined with BRST symmetrty a symmetry which seems a fundamental

symmetry of any quantisation procedure could lead to something fundamental I don't know what nor do I have any real clues as to what it might involve.

On the other hand abandoning the most empricically successful theory we have namely Lagrangian quantum field theory in favour of something like superstrings seems misguided given the empirical success of quantum ffield theory via the standard model of particle physics. And maybe just maybe a combination of BRST symmetry and supersymmetry a priori might just work.

Chris, I haven't a clue what most of this post refers to - but I'd like to.

ReplyDeleteAny chance of recommending one book I should be able to access with MST209 and M208 behind me?

PS - hope the study is going well.

How's MS324 turning out?

See the reading list I posted on books for a High Energy Physicist. You will need some background in quantum physics though before embarking on such books.

ReplyDeleteI'm afraid there isn't just one book the best one is probably Peskin and Schroeder which has a chapter on BRST symmetries, for supersymmetry there is volume 3 of Weinberg's book. Given that supergravity has been deemed a failure then there aren't that many books on the subject. Do an On line literature search and you should be able to get something.

As for MS324 so far so good but the website hasn't opened I've done most of the initial unit