## Physics Questions People Ask Fermilab

**Consequences of Superstring Theory**

**Animesh writes:**

I am doing my B.Tech in electronics engineering ,with a minor in particle physics at IIT,KANPUR,INDIA.
I would like to know the following:
WHAT WILL BE THE CONSEQUENCE OF THE SUCCESS OF THE SUPER STRING THEORY? i.e,WHEN THE FUNDAMENTAL PHOMENON OF ALL THE FORCES WILL BE KNOWN,WILL PHYSICS BE
EXHAUSTED?

Thanking you,

ANIMESH D.,

IIT,KANPUR.

Hi ANIMESH,

If the superstring theory is true, we have then a very fundemental theory of physics. We could explain gravity, the standard model of electroweak interactions and QCD, the dynamics of field theory at strong coupling (when perturbation theory is not applicable), and of course supersymmetry.

But in what sense can one say that physics will be exhausted? First of all, since the theory will be a very difficult theory to test in terms of direct signatures from colliders (even with the recent ideas of large extra dimensions and a low string energy scale), people have to think really hard to find indirect ways to test string theory, which might take many years to come. Secondly, just as the discovery of quantum mechanics did not terminate studies on E&M and classical dynamics, for example in condensed matter physics, the success of string theory would only encourage people to work out other problems, which include cosmology in particular. On the way to solving these problems, people may discover new things; maybe string theory is not all there is. This is how physics has progressed in the past. For example, at the end of the 1800s many physicists thought that physics was almost at an end, because we understood E&M and classical mechanics. There were just a few little unsolved problems, like blackbody radiation, the stability of atoms, the progression of the perihelion of Mercury... These problems were only solved by the discovery of quantum mechanics and relativity. Going even farther back in time, the model of the solar system of Ptolemy, with the Earth at the center, agreed with the data at the time and was considered the right theory for 1500 years. Only with better data in the 1600s or so could people see that the theory was wrong and a new one had to be developed. My point is that I don't think physics will be exhausted, because even if superstring theory turns out to be right (as far as we can tell) at the fundamental level, there will still be many phenomena left to understand (for example cosmology and condensed matter physics).

Heather Logan and Jing Wang

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