Maybe energy can be created and destroyed, or maybe the notion doesn’t quite make sense.
Daniel Sudarski | NAUTILUS
Physics is often baffling, but one principle seems rock-solid: the law of conservation of energy. The world contains this thing called “energy” whose amount never changes. It can change its form or go from one body to another, but its total amount remains constant. Everything from the arc of a well-kicked football to the purring of a car engine depends on this law. It makes energy a precious commodity, counted, hoarded, and fought over.
The quantum world is uncertain; attributes such as energy are ill-defined or fuzzy.
We physicists have learned that our bodies do not merely use energy, but consist of it. Einstein’s formula E=mc2 identifies mass as a form of energy, one that can be converted to other forms (by a nuclear bomb, say) or created from those forms (in a particle collider). The formula strengthens our intuition that energy is the basic stuff of which things are made. When one gets deeper into physics, one also learns that conservation laws are intimately tied to symmetries, as first appreciated by the German mathematician Emmy Noether nearly a century ago. Energy is conserved because the laws of nature are symmetric in time—they do not change from moment to moment.
But physics wouldn’t be physics if it did not continually question itself. Not long after Einstein derived his famous formula, he began to create a theory of gravitation, his general theory of relativity. Energy conservation became a bit dicey. Although individual observers can measure the energy density immediately around them and confirm that the total energy of localized systems remains constant, it is impossible to define an overall energy that is strictly conserved. It might sound strange to be able to define a local quantity of energy and not a global one. And it is.