Claus Kiefer is one of the leading experts in quantum gravity and a professor at the University of Cologne.He authored a highly popular textbook called Quantum Gravity, which is a great starting point for any research in quantum gravity. We are very glad he took the time to answer some questions. He tells us about his biggest disccovery, shares many tips for students who are interested in quantum gravity and gives some insights on his current research. Enjoy!

What are you currently working on?

I''m trying to understand, within simple models, how the arrow of time could emerge from quantum cosmology. The general ideas are outlined e.g. in my essay on ; Further I''m trying to understand, within simple models, how the singularities predicted by Einstein''s theory of general relativity can be avoided in quantum gravity.

Why is this important?

While the microscopic laws, as we know them, are time symmetric, most of the observed phenomena are not, i.e. they exhibit anarrow of time. The origin of this irreversibility may be found in atheory of quantum gravity. Such a theory must be free of singularities.

What was the biggest advance/discovery in your field in the last 20 years?

On the observational side, the discovery that the exapansion of theuniverse is accelerated and the determination of cosmological parameters from the CMB spectrum and other data. On the theoretical side,there were many small advances, but no big discovery.

What was your biggest discovery?

Perhaps the understanding of the quantum-to-classical transitionin quantum gravity/cosmology and the insight how quantum gravitational effects may be calculated and eventually observed within concrete approaches.

What is your advice to a student who wants to make a career in your field?

Be aware that this is a dangerous field, where progress is slow, but if you are really interested and talented, go ahead.

If some fairy would offer to answer you one question about nature; what would it be?

Is there a consistent quantum theory of gravity?

How far do you think are we away from answering this question?

Between 10 and 100 years.

If you could give your 20 year old self one piece of advice, what would it be?

Follow your own interests and try your best (this is what I have actually done).

What math is necessary to be able to work in your field?

Besides the standard math that every physicist needs,differential geometry and some functional analysis.

Which books do you recommend to someone who wants to do research in your field?

I hope it is not too unmodest to recommend my own book Quantum Gravity

Which books did influence you the most?

Many books, among them Misner, Thorne and Wheeler, Gravitation;Weinberg, Gravitation and Cosmology; Zeh, The physical basis of the direction of time.

What was the best physics or math book you''ve ever read?

There is no "best" one, but there are ten or so excellent books that I could recommend (including the three of the last question).

What do you wish you would''ve known earlier in your career/ when you started studying physics?

I was happy with my career, but many things I had to find out myself; so a good advice about the relevance of the various fields and about good courses/literature would have helped me a bit.

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