Book Review on Per Bak By Erin Tomlinson & Maree Vincent

Overview of Per Bak’s: How Nature Works Per Bak puts forth the theory of how complex systems work by describing many complexity and criticality formations such as fractal geometry, power laws, equilibrium models, and general laws of nature.

Continued: He discusses self-organization and its criticality. This concept can be related to the process of evolution and complex systems. For example, how one’s nervous system works in their own body. It can also be related to the relationship in the fluctuation of world economics.

Continued: Throughout this presentations, we will discuss the many questions Per Bak proposes to his readers.

Chapter one: Questions Proposed Could a rock slide be a complex system? Could this motion be understood in terms of their individual, physical properties? One rock could, one day, slip and fall or even dislodge another rock causing them to slide. This rock slide shows how nature works in its self- organized state by action and reaction.

Chapter One: Questions Is a complex system man-made like the sandpile analogy or are they laws or equations of physics? In terms of a man- made sandpile, a hand drops grains of sand to create a pile, which results in an avalache effect. The properties of the entire pile that came from the hand, can be understood as a holistic description.

Holistic Description: This describes that each individual grain conforms to the rest of the grains in the pile, resulting in the pile becoming one. Thus, moving as one, hence the sandpile creates an avalache.

The Laws and Equations of Physics: As Newton’s and Maxwell’s equations describe, the laws of physics are, in fact, simple but nature, as a whole, is complex. Newton’s law, f=ma, according to the book, it simply tells us that an object that is subjected to a force responds by accelerating at a rate proportional to that force. (I.e. an apple falling to the ground, a planet orbiting the sun, and how galaxies are attracted to one another by the force of gravity

Continued: The laws and equations of physics: Maxwell’s equations, according to the book, describe the interactions between electrical currents and magnetic fields. (I.e. how an electric motor or dynamo works) Both of these laws deal with simple mathematical equations but can be complex within themselves resulting in complex systems.

CHAPTER 3: The Sandpile Paradigm What exactly does the sandpile represent in nature? The sandpile can be related to the swinging of a pendulum; the pendulum, as Bak explains, is an analogy to how grains of sand can pile up after time and, at some point, create an anvalache.

Chapter 3: Continued Sandpiles are a part of our everyday life giving us many degrees of freedom. One grain of sand landing on the pile represents potential energy. When the grain topples, this energy is transformed into kinetic energy. When the grain comes to a rest, the kinetic energy is transformed into heat in the pile.

Continued: As the slope of the sandpile increases, the steepness of the pile can help determine when the avalache may occur. Like one would expect, the steeper the slope, the more likely the grain will topple over. The Stationary State is when the average amount of sand and the average slope are constant or equal to each other in time.

Continued: When there are avalaches that span the whole pile, it is called the self-organized Critical State. There must always be communication throughout the entire system.

Continued: The sandpile mataphor has reach well beyond the world of physicists thinking about complex phenomena; it contains EVERYTHING According to Al Gore in Bak’s book, he states that “the sandpile theory---self-organized criticality--- is irresponsible as a metaphor; one can begin by applying it to the developmental stages of human life.” It is his new way of viewing the world.

Hope you enjoyed it!!! The End