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Contemplating the most challenging questions in physics

Physicists from around the world took a conversational approach to tackling the deepest questions of the universe during day two of Convergence. 

By David Harris
What do you get when you bring a hundred or so theoretical physicists together to discuss the burning physics questions of the time? Some very spirited, intriguing, and entertaining conversation.
Kicking off the more formal part of the Perimeter Institute Convergence conference, 11 groups of about a dozen physicists each met around tables to ruminate on the most interesting physics questions culled from a list of submissions by attendees. The topics covered a lot of territory, from understanding the problem of the cosmological constant through to how to solve the gender imbalance and gender discrimination in physics. 
Rather than go into the technical physics discussion at the tables, I wanted to reflect on the nature of the discussion and how it fits into the Convergence conference.
It is clear that physicists are at a point of searching for some big breakthrough that will revolutionize the field. As one physicist pointed out, there have been breakthroughs in physics about every 25 years since the time of Copernicus and that means we shouldn’t be too hasty about finding the next big thing, but also that it might not be too far into the future that we do find something significant.
From the discussions, if there were one candidate for the next big thing, it would be a theory of quantum gravity. This would have far-ranging effects within physics, not just in terms of our understanding of gravity and quantum physics, but also in terms of particle physics, quantum information theory, and through to condensed matter physics. Almost every question discussed converged on the topic of quantum gravity eventually. However, there are very different opinions on how to get to such a theory and whether we are anywhere near finding it.
A curious observation I could make about the theorists gathered is that, in general, and of course with exceptions, there is not a lot of understanding of what people in other subfields do and what their latest advances are. It seems that the days of having a good overview of all the areas of interest to the community are mostly gone, enjoyed only by the very few people who actively seek it out.
Theorists also could do with a stronger grasp of the latest experimental advances and projects being developed currently. There is a real risk that theory can become divorced from experiment in certain places, with string theory being given as the most worrying example of this potentiality.
Of course, a lot of these challenging situations are a direct result of the academic reward system. Students in physics need to specialize relatively early to be able to learn enough in a subfield to obtain a PhD; postdocs need to make significant advances within their subfield to have a hope of a tenure track job; and then tenure track physicists need to produce a substantial body of world-class work in a subfield to reach the next stage of their academic careers. Diversity and breadth of thought is not particularly rewarded in this system, and many academics complain there simply isn’t time to develop a deeper understanding of a broader range of fields.
Fortunately, it seems that places like Perimeter Institute, which operates under somewhat different circumstances to most academic institutions, allows for more possibilities of cross-pollination of ideas and mixing of subfields, making the Institute a good place for a conference such as Convergence, which is aiming to directly confront the direction and methods of physics. 
There is a real challenge in breaking out of field-based thinking, and it was evident that many physicists found it difficult to think beyond their usual frameworks and paradigms to alternative forms of physics that could potentially lead to breakthroughs. This guiding principle of conservatism in thinking is often to useful effect as it prevents physics being overrun by wild speculation, but at times of great challenges in a field, new ways of thinking are sometimes called for.
Just what guiding principles will be most useful moving forward in physics? Physicists almost all operate unconsciously according to various principles, primarily because they have been acculturated with them. These include things like Occam’s razor, Leibniz’s principle of sufficient reason, and a strong aesthetic sense for what makes good physics. All of these principles have been useful invisible guiding hands in the development of physics through the 19th and 20th centuries but will they still be useful in the 21st?
Of particular interest to me is the dominance of aesthetic motivations in theoretical physics. Many of the key questions of theoretical physics arise from a discomfort with things that aren’t simple, neat, or symmetrical. The various fine-tuning problems in physics are an example of this. Perhaps there are more fundamental principles that drive this aesthetic reasoning, or perhaps it is inherent in humans’ pattern-matching and anomaly-flagging brains to seek these kinds of solutions. However, it is probably worth physicists’ whiles to take a deeper look at what philosophers have to say about these issues.
What is very clear is that these types of discussions are very useful for physicists to have and are a great way to start off a conference that is contemplating the future and direction of physics.

David Harris is a theoretical physicist turned science journalist and communicator. He is the on-site rapporteur for the Convergence conference at Perimeter Institute. 

"What is very clear is that these types of discussions are very useful for physicists to have and are a great way to start off a conference that is contemplating the future and direction of physics."