Written and Illustrated by Ed Witten. (Slides 41 to 48 of 48) 41.. To test, or use, duality one has to somehow get beyond the traditional limitation of small e. And thats what happened in the last three years, (this written in 1998) with broad implications for our understanding of Standard Quantum Field Theory and String Theory.
42.. For Standard Quantum Theory we get new insights about traditional problems like 'Quark Confinement'. (Slide 42 previous post) which is related by duality to more standard physics.
43.. For String Theory we have obtained the amazing insight that ... Theres only one Theory .. the six theories discovered and studied in the last 12-25 years (Type I, Type IIA, Type IIB, Hetorotic SO/32, E8xE8, 11 dimensional SUGRA) are different limiting cases of one Theory.
44.. to understand this, we have had to crack the small e barrier, since for small e the barriers are really different. (Slide 44 below)
45.. We have also obtained a rather different view of the basic ingredients of String Theory ... Strings are, in a sense only, at most, the 'First among Equals' and share the stage with objects like 'D-branes' that are related to strings by duality.
46.. A concrete application is to 'Black Holes'. For the first time we have been able to understand the 'quantum states' or 'elementary constituents' of a Black Hole'.
47.. The big question to me, looking ahead, is whether with our new understanding we are finally well placed to answer the Big Question "What is String theory?". If we really understood that I feel sure a lot of things would become clear.
48.. Slide 48 below
Ends .......