Written and Illustrated by Ed Witten. (Slides 31 to 40 of 48) 31.. In contrast to Gravity and Gauge Invariance, we don't yet know if SuperSymmetry is true in nature. It is one of the main targets of accelerators, including the former SSC and the future LHC (to operate at CERN, in Geneva around 2005) as well as machines that operate currently.
32.. There are some indirect experimental hints that SuperSymmetry is 'near' in energy. Coupling Constants, Energy Scales. .... if it were found that would be quite a momentous discovery, and certainly a big boost for String Theory.
33.. Bad News ? ... its time to explain why the Cosmological Constant is Zero, and we haven't ! (Slide 33 below)
34.. More 'Cosmically'. We don't really understand what the theory is. (Slide 34 above) You can describe much of Physics by particles or waves, but the waves are more fundamental; only the less fundamental particle view has been generalised in String Theory ....
35.. (Slide 35 below) So 'What is String Theory?'
36.. The problem as I have just posed it has been with us for some years, but the outlook has changed a lot in the last couple of years because of a new understanding of the role of 'duality'.
37.. In its oldest form 'duality' is a symmetry between electric and magnetic fields which holds in vacuum but is spoiled in nature (apparently) by the fact that we see electrons but not magnetic monopoles. (Slide 37 below)
38.. Quantum mechanics actually seems to make duality impossible (because of the role of the vector potential) In the 1870s (possibly means 1970s ??) Olive and Montonen had a remarkable insight about how duality might work in quantum theory.
39.. But it seemed well out of reach to determine if it was really true. That was because of a basic limitation in our abilities in physics; We are generally able to compute what happens only when the charge, e, is much less than one.
40.. Duality, though, exchanges e with 1/e and it is not possible to have both e and 1/e be much less than 1.
continues in next post .......