Outreach
A brief history of string theory
String theory is currently our best candidate for a theory which unifies gravity with the other fundamental forces (the strong nuclear, the weak nuclear and the electromagnetic forces) - it is a proposed "Theory of Everything". Strng theory was discovered in the 1960's by theorists working to understand the plethora of hadronic and mesonic particles which had been found around that time. The theory had some success, eg in explaining the way such particles fitted on to so-called "Regge trajectories", but it was soon replaced, in the 1970's, by a far more powerful theory called Quantum Chromodynamics (QCD). This early string theory had major deficiencies - it contained imaginary mass particles or "tachyons", leading to problems in the quantum theory, the closed strings (loops) contained a massless spin two particle which was not observed, and finally the theory was inconsistent unless the number of spacetime dimensions was 26. The birth of string theory as a possible "Theory of Everything" however, came when it was suggested that string theory was not a theory of hadrons and mesons, but was a fundamental theory, with the massless spin two particle identified as the graviton - the conjectured carrier of the gravitational force.
The "first string revolution" occurred in the early 1980's, when Michael Green (Queen Mary) and John Schwarz (CalTech) discovered supersymmetric strings, or superstrings. Superstrings had no tachyons and had a consistent quantum theory. Furthermore, they predicted a "gauge group" for the fundamental forces. They had natural low energy limits as supergravities, or supersymmetric quantum theories living in ten spacetime dimensions. Soon after, new "heterotic" strings were found, leading to a total of five superstring theories, labelled I, IIA, IIB, HE, HO.
A "second string revolution" occurred around 1995 due to the work of Chris Hull (Queen Mary), Paul Townsend (Cambridge) and Ed Witten (Princeton). "Duality" symmetries between the different string theories were found, which led to the proposal that the five known theories are different realisations of one underlying fundamental theory, called "M theory", whose low energy limit is eleven-dimensional supergravity. Furthermore, the fundamental objects in string theory and M theory were found to include higher dimensional surfaces called "branes" as well as strings. The study of these has led to major progress in many areas in the past ten years. One key development was that of gauge theory/gravity holographic dualities in M-Theory, which began with the Matrix Model of Banks,Fischler, Shenker, Susskind and the AdS/CFT correspondence found by Juan Maldacena.
What next? We seem to be due another string revolution. A new duality between gauge theory and string theory in twistor space was found by Ed Witten in December 2003. This has led to dramatic progress in practical calculations of scattering amplitudes, relevant to forthcoming experiments at the LHC at CERN in Geneva from 2007, as well as giving new insight into the structure of gauge theory. Linking twistor string theory to M theory has thus far proved difficult, however. Other areas of active research in current string theory include the study of time-dependent and cosmologically relevant aspects of brane dynamics, integrable structures in gauge theory and new geometries in string theory. Queen Mary researchers play leading roles and are involved actively in many of these new areas of research.
More about string theory:
Queen Mary is part of the European Union network Superstrings, which comprises more than a dozen universities across Europe.There are other European networks on related subjects; information on these can be found from the following links:
Constituents, Fundamental Forces and Symmetries of the Universe,
Physics across the energy frontier: Probing the Origin of Mass,
Supersymmetry and the Early Universe.
For more information about superstrings, visit the following websites:
Superstrings.com
J. Pierre
Beyond String Theory
Cambridge Public Page
Wikipedia
Not Even Wrong - A critical blog
The Elegant Universe site
How to be a theoretical physicist
Many more references
Some talks by members of the group:
String Theory, a high school talk given by Sanjaye Ramgoolam at Highgate School (prepared with James Bedford and Costis Papageorgakis).A Theory of Everything - powerpoint talk given by Bill Spence at Queen Mary in July 2005 to Physics teachers as part of an Astrophysics Week organised by Prof. JP Emerson in the Mathematics Department.
Gauge Theories, Gravity and Twistor Strings - powerpoint talk given by Bill Spence as a joint Physics/Mathematics Colloquium at the University of Durham in May 2005. Aimed at general graduate student level.
From Twistors to Amplitudes - pdf file of research-level talk given by Andi Brandhuber in August 2005 at CERN.
Loop Amplitudes in Yang-Mills from MHV vertices - pdf file of talk given by Gabriele Travaglini at the London Mathematical Society Twistor String Workshop, Oxford, January 2005.
General Physics Information
ASPEN Centre for PhysicsHEP Institution list - CERN
Eagle Intermedia Information Service
HEPIC
Hyperspace at UBC
Institute of Physics
ICTP - Trieste
List of HEP and NP Labs - McGill
TIPTOP - The Internet Pilot to Physics
The Particle Adventure