### Explaining the electromagnetic spectrum in less than 550 words

#### It’s intriguing how we always talk about stuff like radio, microwaves, light, x-rays and the rest – as if all these were different things.

Well guess what – they’re not. They’re all exactly the same thing. Electromagnetic energy. That’s it, really. Well, there are differences – as we’ll see in this post. But in terms of fundamental physics, all of these things are one and the same.

Electromagnetic energy is one of the four fundamental forces – the others are strong nuclear, weak nuclear (both working at atomic level) and gravity, though gravity is a function of the curvature of space-time, and try as we might, we haven’t found a particle that carries it …yet.

The one I’m on about today is electromagnetic energy. It exists as a ‘wavicle’ – both a particle and a wave. The wavelength is the crucial part for our purposes because the energy – and how we perceive it – depends on that wavelength. It starts with low-frequency radio waves that are 1000 metres or more long. It finishes with gamma radiation whose wavelength is less than 0.000000000001 of a metre.

For our own purposes we divide the electromagnetic spectrum up into ‘octaves’. There are 88 in all – of which visible light is but one.

I’ll start there because it’s what you’re using to read this post with (mostly blue light, as it happens, from computer monitors). Visible light extends from red (longest wavelength) to blue (shortest wavelength).

Bracketing visible light are ultraviolet (which we call ultra-violet because it’s just above violet on the spectrum) and heat – which we call ‘infra-red’ because it’s just below red) behave slightly differently to light because of the wavelength. Our retinas are actually sensitive to ultraviolet, but it’s blocked by the cornea. And we feel heat through our skin.

Drop the wavelength below infra-red and you get microwaves, which are more of the same thing – and which penetrate organic matter more easily. That’s why a microwave oven heats things more efficiently than a standard infra-red one.

It’s also why radar sets – which work at microwave frequencies – are known for being able to cook anything in the beam, if it’s close enough. Both use the one device, the cavity magnetron, to generate electromagnetic radiation at those frequencies.

Go down further down and you get into radio waves. These don’t just let us broadcast information – they are also naturally generated. The biggest radio transmitter in the solar system is the Sun.

Above visible light the spectrum climbs quickly from ultraviolet into X-rays, which penetrate skin and bone; and then gamma. Photons at these higher frequencies carry enormous energy – up to 1,000,000 electron volts per photon. As a result, the most violent and energetic natural phenomenon (yet) known to physics is the gamma ray burst (GRB), produced by a supernova: one can shine across half the known universe.

If we’re caught in the way of a nearby one – well, let’s put it this way, Earth was a planet that ONCE hosted life…

So there you have it – the wonders of electromagnetic spectrum in less than 550 words!

## 8 thoughts on “Explaining the electromagnetic spectrum in less than 550 words”

1. What a glorious post. I hated physics when I was younger but now I find it fascinating. What about those neutrinos! So small they can pass through a light year of lead without touching anything. All the very best. Kris.

1. Physics is my favourite subject. Weird, given my degrees are in other fields… But the fascination never dims.

2. Sorry, total moron here but I was caught by the idea of your continuum. When we say travelling ‘at the speed of light’, what exactly are we talking about? Visible light? But does that then mean it’s the fastest ‘thing’ on the continuum? Or is there something faster? As I said, I’m a real dunce at this. 😦

1. Visible light is the bit of the electromagnetic spectrum we perceive with our eyes. We use the term ‘light’ purely because that’s the part of the spectrum we see with. But all electromagnetic radiation moves at that speed. Nothing goes faster and no material thing can go as fast. However, time also moves at the speed of light and we now think gravity waves do too. All of this was originally worked out by Albert Einstein in 1906 and 1916. He was one clever dude!

1. Aaaaah, I see. I really do. I knew ‘about’ the other forms electromagnetism but somehow I just didn’t/couldn’t connect the dots. Thank you so much. 😀

1. Thanks! It’s a fascinating subject. I hadn’t done a physics post for a while and figured it was time…