Don’t ever ask a physicist the question “What is energy?” You will be stuck for an hour (or more!) listening to words like “fields”, “force particles”, “quarks” and “dark energy.” This blog will show you what I mean [1]. I, however, am an engineer, so I can do it in three minutes without using any big words. I’m sure we will offend the physicist in the process, but that’s just a part of my job.

Everything in the universe is made out of ‘stuff.’ There are probably better words to describe the building blocks of the universe, but physics can’t seem to agree on a term. For our purposes, stuff is anything that has a physical existence – you can see it, touch it, throw it, eat it, etc. But, the word ‘stuff’ alone doesn’t describe the universe completely because all of the stuff in the universe is doing something. That’s where energy comes in. In a sentence, Energy is what makes things happen [2].

I like to think of energy as the fundamental resource – the currency of life. Without it, the universe would be a bunch of very cold things without motion or interaction, like a sandstorm frozen in time. But there is something very important that you must understand – energy doesn’t exist. Let me explain. Happiness does not exist on its own, but instead is a description of the state of an individual – an abstraction that we can possess but can’t pull out of our head and put into a jar to save for later (wouldn’t that be nice). In the same way, energy does not exist on its own but is a description of the stuff in the universe. Just for fun, I’ve included below what the internet or Hollywood has interpreted “pure energy” to look like. It’s so mystical… and blue… and not correct.

We perceive energy in hundreds of different forms [3]. Fundamentally, each form can be described in one of two ways: stuff is moving or stuff is interacting with other stuff, otherwise known as kinetic and potential energy. To give you some examples, thermal energy (temperature) is just atoms vibrating (or moving) back and forth. Likewise, if my two year old holds a rock above my head (potential energy), the rock is interacting with the Earth (gravity) and will fall should he choose to let it go. Unfortunately, it will interact with my head first. Finally, two hydrogen atoms are attracted to (interacting with) an oxygen atom in water. These are only a few of the many ways that energy is expressed.

The most fascinating thing about energy is that, although it doesn’t really exist, it still follows a very basic, fundamental law, known as The First Law of Thermodynamics.