Ask Ethan: What Is Energy?
“We talk about energy and we know that there are various forms of energy (PE, KE …) and you can do work with it, and it has to be conserved, and energy and matter are interchangeable, etc. But what is energy?”
Energy is something that touches all aspects of our lives. Yet if you try defining it, you’ll wind up tying yourself in knots. It’s not something we can isolate in a laboratory, but rather is a property inherent to all matter, antimatter, and radiation particles. It can only be defined relative to other particles, rather than absolutely. The definition we use in physics, that it’s the ability to do work, is over 300 years old and is rather circular.
A little over a century ago, the esteemed physicist Henri Poincaré noted the following, “science is built up of facts, as a house is built of stones; but an accumulation of facts is no more a science than a heap of stones is a house.” We speak all the time of what energy can do, how it’s used, where it appears and in what quantities, and how to accomplish a myriad of tasks with it. But a fundamental, universal definition?