Hawking still hopes to solve the big problem of physics, that of unifying quantum mechanics and Einstein’s theory of relativity. Doing so will produce a set of laws that will explain everything in the universe, including how it all began – a breakthrough aptly dubbed the ‘Theory of Everything’.
All ten parts are well worth your time, but parts 8 – 10 are where string theory is discussed.
A brief history of string theory
Here is a very brief outline of the development of string theory, the details of which will eventually fill many large volumes written by many people directly and indirectly involved in this rich and fascinating story.
String Theory – Superstrings
Material forms in the universe are believed to be the product of vibrations.
Michael B. Green
It was realized in the 1970’s that string theory was a theory of quantum gravity, whether we liked it or not — certain vibrating strings have the right properties to represent gravitons, carriers of the gravitational force. Already, this feature distinguished string theory from other approaches; whereas head-on assaults on quantum gravity tended to run into dead ends, here was a quantum theory that insisted on gravity!
In the 1980’s the triumph of the Standard Model became complete, and work by Michael Green and John Schwarz demonstrated that string theory was a consistent framework. Physicists who would never have though of devoting themselves to quantum gravity quickly dived into string theory. It was a heady time, when promises to compute the mass of the electron any day now were thrown back and forth. True, there were five different versions of string theory, and they all lived in ten dimensions. The trick would be to find the right way to compactify those extra dimensions down to the four we know and love, and the connection to observation would be established.
That didn’t happen, but the 1990’s were nevertheless a boom time. It was realized that those five versions of the theory were different manifestations of a single underlying structure, M-theory. Tools were developed, in certain special circumstances, to tackle a famous problem introduced by Stephen Hawking in the 1970’s — calculating the entropy of black holes. Amazingly, string theory gave precisely the right answer. More and more people became convinced that there must be something right about this theory, even if we didn’t understand it very well, and even if connection to experiments remained elusive.
Since 2000, progress has slowed.
“The Man Who Led the Second Superstring Revolution”
Ed Witten has been called “the most brilliant physicist of his generation.” Some, not content with this accolade, have compared him to Isaac Newton. Witten is a deeply original and committed theoretical physicist whose primary field of research is string theory, which proposes a “theory of everything” wherein the building blocks of the universe are curves, or “strings,” formed into loops. He has been one of the field’s foremost proponents and most prolific contributors, once telling an interviewer, “It was very clear that if I didn’t spend my life concentrating on string theory, I would simply be missing my life’s calling.”
Witten’s work has been especially distinguished in its use of advanced mathematics to achieve the kind of unified field theory of the universe that was Einstein’s dream.
An appreciation by John H. Schwarz, Harold Brown Professor of Theoretical Physics, Caltech
Edward Witten, an extraordinarily creative and dedicated scientist, has had a profound impact on the development of theoretical physics and mathematics for the past 30 years. He is far and away the most cited and influential contemporary theoretical physicist. Ever since string theory took off in the mid-1980s, Witten has been a leading figure in its development. His crucial discoveries include many of the “dualities’’ that gave rise to the “second superstring revolution’’ in the mid-1990s. String theory requires a great deal of cutting-edge mathematics. Witten is the leader in using physics insights to advance fundamental mathematics, and vice versa.
In 1987 Michael Green and I coauthored a monograph entitled “Superstring Theory’’ with Witten. We were thrilled that Witten agreed to join us, since we knew that his contributions would greatly improve the final product. This work, consisting of more than 1,000 pages packed with equations, was completed in nine months. For Green and me this required dedicating 100-hour workweeks to the project. Witten, on the other hand, was able to do his share while completing several major research projects at the same time.
Witten is both deep and fast: After thinking through the ideas, he can compose an essentially error-free 100-page manuscript, often describing breakthrough original research, on his computer in a day. His papers and lectures set a new standard for clarity of exposition. And he shows no signs of slowing down.
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