Sunday, December 03, 2006

I cannot talk about others, but I am as enthusiastic about string theory as I have ever have been

An email interview with Ashoke Sen of the Harish Chandra Research Institute, Allahabad

Is the death of string theory a mere rumour, or is there a serious symptom of terminal illness?

String theory is an attempt to understand the basic constituents of matter and remains the leading candidate for a unified description of all the constituents and the forces operating between them.

The debate is about how much one can calculate in string theory. There is a hint that string theory contains many different phases (just like a theory of water molecules have ice, water and vapour phases) and the measurable parameters depend on which particular phase of the theory we are leaving in. If this is the case then the most likely picture of the universe is that different parts of the universe can be in different phases of string theory (just as different parts of the world can be in ice, water and vapour phases) and unless we know which of the phases describe the part of the universe we are living in we cannot calculate the fundamental constants of nature with absolute uncertainty.

There is still a debate in the community whether this picture is completely correct and it may take a few years' effort to understand the story. However if it is correct then that is something we have to accept. We cannot dictate how a fundamental theory of nature should behave; all we can do is to study how it behaves.

What could be the reason for this strong reaction to string theory? Some of the scientists in the US are even saying that it has been a sheer waste of time for the last 20 years. Is this a sign of frustration on the part of some who have dealt with the theory?

As far as I know none of those who are saying that `it has been a sheer waste of time for the last 20 years are serious workers in the field.

What do you think is the state of string theory at the moment? Is is going strong, or has it reached a dead-end of sorts for the moment?

As I explained at the beginning, whether string theory can provide us with a practical method for calculating the fundamental constants of nature is under debate. However string theory has already resolved many of the conceptual problem in combining gravity with quantum theory. One of them is to give a finite quantum theory of gravity, another is resolving the apparent paradox that arose while trying to study quantum theory of black holes. String theory is also the only known theory that has the capability of including gravity as well as the other forces of nature under one umbrella.

While a lot of the effort in string theory is now directed towards the issue of studying different possible phases of string theory and trying to see what kind of information can be extracted from these, a lot of the effort is also geared towards various conceptual issues. As far as I can see there is still a lot to be done in string theory, and it has certainly not reached a dead end.

Will string theory ever fulfil the big dream of delivering on its promise of providing the elusive Theory of Everything (TOE)?

If you ask my personal opinion, I am certain that it will in the sense
that the basic underlyling theory that describes the theory of the ultimate constituents of matter will turn out to be string theory.

What is the mood in the Indian string theory community?

I cannot talk about others, but I am as enthusiastic about string theory as I have ever have been. I think we have an extremely strong candidate for the basic constituents of matter and this theory needs to be explored much more that it has been so far.

Where do you see the string theory in another 10 years' time?

I'll not try to make any predictions since most such predictions about future scientific development have turned out to be wrong.

Even if it were to fail in its ultimate purpose, do you think that string theory has certainly opened up new frontiers in the field of theoretical physics?

String theory certainly has provided new technique for studying quantum field theories. One of the recent example is the calculation of shear viscosity of quark gluon plasma which has been used to explain some experimental phenomena in the heavy ion collider.

What have been the contributions from the Indian side to the development of string theory? (I remember Sunil Mukhi telling me in 1996 that you had some original insights into the theory, and that it was recognised in the international community.)

Indian string theorists have made non-trivial contribution to the development of string theory and continue to make an impact on the subject. Among the young string theorists who are leaders in the field one can mention Atish Dabholkar, Rajesh Gopakumar, Shiraz Minwalla, Sandip Trivedi etc.

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