Is the answer to the universe's greatest mystery hidden in a pile of sand? Theoretical physicist Per Bak thinks it may be. He believes science's greatest challenge is to figure out how the universe's complex phenomena emerge from laws of physics, laws so simple that they all can be written down on a single piece of paper. So he studies emergent, complex phenomena -- like traffic jams and mass extinctions and avalanches -- by looking at their parts.

What interests Professor Bak is life. Economics. History. How can you start with quarks and gluons and get humans and astrophysics and earthquakes? So he studies grains of sand. And the cars that make up traffic. He looks at the parts to understand the whole. (It's known as bottom-up science, as compared to traditional top-down physics.) Say goodbye to a nice, steady, equilibrium perspective, says Professor Bak. Equilibrium equals death. Things do not rock along smoothly, change in small increments. Change is catastrophic. We must learn to adapt because we cannot predict.

Per Bak is credited with discovering a process for understanding complex systems called self-organized criticality -- self-organized because no engineer had a hand in them, critical because they balance at a critical point between order and chaos. That's where interesting things happen, he says. Like life.

It's all within the laws of physics, he assures us, claiming (as physicists are wont to do) all of the universe for his discipline. We just don't really understand what those laws are, he says. That requires a very different way of thinking. Science as such is not changing, he says -- curiosity is still the only reason for doing it, it is still empirical, requires observing and describing the reality we see. But the language of science IS changing. Contingency is a very important part of that language: what happens affects what happens affects what happens. Narrative -- what Professor Bak calls the language of history -- is what science now requires.

We are further constrained by our imaginations. The farthest afield we can go is into what Per Bak and others call the Adjacent Possible. We cannot imagine a world entirely different from our own, our brains cannot visualize what could have happened, we can only visualize what did happen and extrapolate a bit. That locks us into our history.

Based on his observations of how nature works, Dr. Bak suggests a two fold strategy for coping with the complexities humanity faces. Don't try to optimize and predict. Can't be done. Adapt. It's something nature has been doing for a long, long time.


[This Program was recorded February 1, 2000, in Santa Fe, New Mexico, U.S.]

Narrative Physics



Per Bak

    ... theoretical physicist, discoverer of self-organized criticality. Professor Bak was trained as a condensed matter physicist, and is now internationally known for his studies of self-organizing criticality and a variety of applications of power laws. Author of How Nature Works, Dr. Bak had been based at the Niels Bohr Institute in Copenhagen, Denmark. He was in transition to the Imperial College in London, England and on the faculty of the Santa Fe Institute. Sadly, Dr. Bak died in October, 2002 after a long illness.

Edited Excerpts of the Conversation:



Conversation 1


Per Bak describes self-organized criticality in terms of the dynamics of the world in which we live to Paula Gordon and Bill Russell. He discredits a smooth, gradually changing equilibrium model, offering real life instead -- the catastrophic ways in which things actually change, exemplified by earthquakes, volcanoes, Wall Street and mass extinctions.



Conversation 2


Sand piles are Professor Bak's classic metaphor for how he sees our world. He suggests why predictability is extraordinarily difficult. He summarizes "self-organized" and "criticality," with examples. It is only at the edge between chaos and order that interesting things happens, he asserts. That, he believes, is where the world sits, including life itself. He expands, explaining why he believes earth's whole ecology is, or at least could be, sitting at the critical state. He describes co-evolutionary avalanches.




Conversation 3


Professor Bak, a physicist looking for general theories, describes power laws, relationships which can only be observed at the critical state. Equilibrium equals death, he declares, with examples. Statistical physics has been misused, says Professor Bak, who describes the one path which the universe as we know it has followed. He urges talk of thermodynamics (particularly entropy) be kept out of any discussion about life, economics, or geophysics. He amplifies. Ideas about the contingency of existence are explored, with examples. Professor Bak explains why we are locked into our history, and defines the Adjacent Possible. He explains how massive contingencies affect how he approaches his science. Again using the sand pile example, he tells us what we can and cannot affect. He dismisses the idea that the world is deterministic as a complete illusion and explains why. He suggests what we can predict.



Conversation 4


Automobile traffic is another example Professor Bak employs in thinking about how complex systems and power laws work. He tells us why the best we can do in such a self-organizing system is to sit at the critical state, between order and chaos. He explains how scientists study such emergent phenomena. He tells us why this is bottom-up science, how it is that the complex comes from the simple. He describes what he believes is the greatest mystery of all. He suggest the limits of mathematics, with examples. He gives a simple explanation of emergent phenomena.




Conversation 5


Curiosity is the reason for doing science, according to Professor Bak, who expands, using examples from his own work. He tells us why science is turning to the language of history. In thinking about what a new science would look like, Professor Bak further elaborates on the idea of the Adjacent Possible. He remarks on the series of accidents that we know as evolution, confident that all of life evolved together as an ecology. He explains why he believes it is impossible to create sustainable systems. He offers what he believes is a better strategy.



Conversation 6


Dr. Bak, the physicist, claims all phenomena as the realm of physics, and describes his own explorations. He describes the trajectory he sees for science. He criticizes equilibrium economics, explaining what can and cannot be predicted. Professor Bak summarizes what he believes is the best we can do.




Related Links:

How Nature Works, by Dr. Per Bak, is published by Copernicus Books.



Meeting Per Bak was an unexpected delight. We thank Stuart Kauffman, who introduced us to Dr. Bak's ideas in At Home in the Universe and then introduced us to Per Bak himself when we were together in Santa Fe. We are grateful on all counts.

We feel a deep personal loss at Per Bak's untimely death.



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