Professor Edward Witten is one of the most renowned and talented physicists of modern times. Currently, he works at the Institute for Advanced Study in Princeton, researching mathematical physics. He has been awarded numerous prizes and honors – like the Fields Medal and Fundamental Physics Prize, to name a few. His contributions to string theory and quantum gravity are ground-breaking. One of his most impactful works is M-theory: a unification of all the five different types of superstring theories. He also helped in the interpretation of the AdS/CFT correspondence. He has even proved theorems in general relativity and worked on topology. His work has taken him closer than most people to understanding the fundamental secrets of the universe – which is why I mailed him requesting to answer some general questions on physics and the nature of reality. I am infinitely grateful to him that he agreed.

- What/who inspired you to pursue physics?

**Since I was very young, I was fascinated by astronomy and math and later by physics. I grew up during the years of the “space race,” when everyone (at least in the U.S.) was excited about space.**

2. Do you believe that the holographic theory is so far the best explanation of the information paradox?

**Holographic duality between gauge theory and gravity is the best we have now for a nonperturbative description of quantum gravity. I would say it has helped us to understand some aspects of the black hole information paradox, but we are far from a full understanding.**

Adding to Professor Witten’s reply, holographic duality demonstrates how holography could explain and link two very different kinds of theories in physics. Juan Maldacena first proposed the idea, technically known as AdS/CFT Correspondence (essentially a correspondence between anti-de Sitter spaces used in theories of quantum gravity, and conformal field theories, used in quantum field theories). It has significantly improved our understanding of modern physics, and may even take us a long way toward a theory of everything. However, as Professor Witten points out, questions remain, and perhaps always will.

3. Do you believe that gravity could be an entropic force and not a fundamental force? How is gravity viewed from the perspective of string theory? How do you propose to explain that while all other fundamental forces (electromagnetic, strong nuclear, and weak nuclear) can be explained by the exchange of bosons, gravity cannot (we haven’t found the graviton yet!)?

**I imagine that in some sense we do not understand yet. Spacetime, gravity, and everything we see are in some sense “emergent” from a much deeper structure. Holographic duality is actually our best insight at present, albeit partial, about how that could happen.**

Adding to Professor Witten’s reply, I would like to say that the holographic theory – which basically says that the three-dimensional reality is an illusion, and is actually sort of projected from a two-dimensional surface – indeed seems appealing, mainly because it cannot be disproven and explains a lot of phenomena. The idea of an emergent reality has been pointed out by notable scientists, including Professor Witten himself.

4. Although a naive question, how do you think the approaches taken by string theory and loop quantum gravity compare?

**I do consider this question a little naive so I will not comment directly.**

I would also like to add that, contrary to common misconception, quantum gravity is not exactly a unifying theory. All it does is explain the gravitational field in a quantum-mechanically acceptable manner. String theory has also attracted widespread attention and misconceptions. Both these theories are widely believed to be candidates for unified theories. This means that these theories try to unify all the known forces and explain them all in a single framework. String theory, for instance, proposes that point-particles are actually one-dimensional strings. The properties of the particles are described by the vibrational state of the strings. However, problems remain with both string theory and quantum gravity. String theory, for instance, needs at least ten dimensions to work (and the number is greater for some other versions of string theory) and supersymmetric partners of the known particles. Scientists are presently trying to find indirect evidence of these “extra” dimensions and/or the “superparticles.”

5. Just like Gödel proved that mathematics is inexhaustible in some sense and all theorems cannot be proved, do you think a complete description of the physical reality, i.e., a true unified field theory, is also impossible? Don’t you think it is beyond our reach to understand the universe at a fundamental level since we ourselves are a part of it and have certain limitations?

**I guess the only way to find out what are the limitations on what we can understand is to do our best and see how far we can get.**

6. It is a common misconception that all there is to physics is a unified field theory. What direction do you think research in physics would take, if/after we find a theory of everything?

**The Schrödinger equation for electrons and atomic nuclei (supplemented by equations describing the interaction of matter with light) is actually an entirely adequate framework for much research in physics. So, much physics research would be only modestly affected by the emergence of a deeper theory. (The reason that I say it would be only modestly affected rather than saying it would be unaffected is that in finding a deeper theory, one might arrive at new ideas that would have an influence in other areas of physics.)**

7. Although not strictly related to physics, what would you like to say about the study of nonlinear dynamics or chaos theory, from a physics perspective?

**I am not sure why you say that these are not directly related to physics. Physics is all about dynamics, generally nonlinear, and most physical systems are chaotic. But more to the point, it turns out that black hole dynamics is chaotic and this has led to some of the interesting insights about quantum chaos in recent years.**

I would also like to add that chaos theory, studied as a branch of mathematics, has a remarkably wide range of applications, as Professor Witten says. From physics to biology, we see chaos everywhere. Chaos theory is the study of complex, unpredictable phenomena. It has been discovered that there is an underlying universality in the rules of chaos, and a new geometry of complex patterns – fractal geometry – may offer us new perspectives to interpret the complex nature around us.

8. I was deeply inspired by Schrödinger’s book – “What is life?” Science is still far from explaining consciousness at a fundamental level. I believe physics and nonlinear dynamics hold the key to a deeper understanding of complex systems (with lots of interacting parts) and in turn consciousness. What do you think?

**Like most physicists, I think that life and consciousness are “emergent phenomena”, in other words, they are part of the possible behavior one can get when many particles are interacting via simple physical laws. Maybe in the next century, advances in neuroscience and computer science will somewhat remove the mystery that surrounds consciousness.**

Adding to Professor Witten’s reply, I would like to point out that many notable physicists, like Erwin Schrödinger, believed that life and consciousness can be explained by the physical sciences. Life can be an accident of combination, perhaps. While we can’t predict the behavior of the individual constituents of the system, we can predict, to a reasonable extent, the behavior of the entire system as a whole. This means there is a possibility we may recreate the patterns that give rise to consciousness! At least, it is highly probable that consciousness can be explained by the physical sciences.

9. Your outstanding work has perhaps taken you very close to understanding the nature of reality. In general, do you think nature is random and tries out all possible paths, or is it something deeper?

**Nature seems to be based on very deep ideas and principles, of which we currently understand only a little.**

10. Finally, the Young Scientists Journal is an international peer-reviewed science journal run by young students from around the world. We aim to communicate science to a broad audience and provide research experience and opportunities to young students. Any small piece of advice you would like to give us and all the aspiring scientists out there?

**Let me wish all success and good fortune to you and all your readers.**

Professor Witten’s answers have been extremely insightful, and I, once again, humbly thank him for his time. Today, it might seem tempting to believe that nature is entirely random. Of course, determinism is not supported by modern science. However, to quote Professor Witten once more: “Nature seems to be based on very deep ideas and principles, of which we currently understand only a little.”

# Figure References

Quanta Magazine. https://d2r55xnwy6nx47.cloudfront.net/uploads/2017/11/EdWitten_2880x1780_03.jpg

### About the Author

Arpan Dey, 16, is a high-school student from India who is deeply interested in physics, mathematics and the metaphysics of science. He has been working as an editor for the Young Scientists Journal and is involved in many STEM-related activities. He also enjoys reading, writing short stories (mainly sci-fi and detective) and listening to instrumental music. He is also an aviation enthusiast.