STRING THEORY: Where are we now?
Tamiaki Yoneya · 2000
This is a brief overview on the current status of string theory for non-specialists. The purpose is to give an aspect on the nature of string theory as a unified theory of all interactions including quantum gravity and to discuss future perspectives. Particular emphases are put on the mysteries why string theory contains gravity and why it resolves the ultraviolet problems. 1. History It has long been recognized that the two main theoretical frameworks of present day physics, quantum theory and relativity theory, are not easily reconcilable together microscopically. Namely, the treatments of gravity using the methods of ordinary quantum field theory almost necessarily lead to the nonrenormalizable ultraviolet infinities. String theory is an attempt towards the ultimate theory which should explain all of the particle interactions and the fundamental structure of matter and space-time, by resolving the ultraviolet difficulties and the associated problems in a natural scheme where all other particle interactions can also be taken into account in a completely unified manner. In this talk, I would like to explain why string theory is promising for this direction and what is the present status of the development of the theory. In view of the nature of this talk, it seems appropriate to start with some account of history. Please refer to the table in the next page. The year 1998 was the 30th anniversary of string theory [1]. The first clue for string theory came from the discovery [2] of simple formula for scattering amplitudes for hadrons