Effective Theories in Physics:

Abstract

Effective Theories have been with us since the dawn of science, but it has only been in recent decades that we have found it important enough to give it a clear and voiced name. This new found desire is due in part to our understanding that no finitely written theory is complete. There was a proselytizing impulse among all those who first grasped the vision of Effective Theories. I recall as a Ph.D. student that many fellow students coming out of Boston would repeatedly pepper their conference talks with the words ‘‘Effective Theory’’, and others sometime joked that they were curiously keen on celebrating their ignorance and lamented how sad it was that they had such weak ambition. It was at the time that many particle physicists were proudly espousing their faith in the ‘‘Theory of Everything’’ being around the corner. The extremes of the two camps were in stark contrast. Today, the culture and language of Effective Theories have permeated all of physics. It is not controversial and not lamentable. The concepts are deeply ingrained in many other areas of theoretical physics. In the subsequent chapters, several different physics subareas are touched upon but the discussions all revolve around Effective Theories. An abstract definition of the term is given in the first chapter, and fleshed out through examples in the following chapters. It is hoped that by the end the reader will have a good feel for how the concepts of Effective Theories affect the thinking of practicing scientists, and can see the power that explicitly agreeing to the Effective Theory mindset can have in developing richer theories of nature and achieving a deeper understanding.