The Academy
One Family of Waves
The electromagnetic spectrum, end to end
Only the size of the wave changes
Radio, microwaves, infrared, visible light, ultraviolet, X-rays and gamma rays are one phenomenon. Maxwell's equations, written in the 1860s, predicted that a changing electric field makes a magnetic field and vice versa, that the disturbance travels at a speed computable from two electrical constants, and that this speed matched the measured speed of light — from which Maxwell concluded that light *is* an electromagnetic wave. Hertz produced and detected radio waves in his laboratory in 1887, and the case was closed.
Wavelengths run from kilometres at the radio end to less than the width of an atomic nucleus at the gamma end. That is more than eighteen powers of ten, which is why any honest drawing of the spectrum uses a logarithmic scale.
The sliver you can see
Human vision occupies roughly 380 to 700 nanometres — about one octave, a single doubling of frequency, out of that entire range. Everything anyone has ever seen with their own eyes, every colour in every painting, arrived through that one thin band.
It is not an accident. Water is transparent in almost exactly this window, the Sun's output peaks here, and the atmosphere lets it through. Eyes evolved to use the light that was available.
What each part does to you
Below visible, photons are too weak to break chemical bonds; they mostly heat things. Infrared is felt as warmth. Microwaves shake water molecules, which is your oven. Radio passes through walls and through you.
Above visible, photons carry enough energy to do damage. Ultraviolet breaks bonds in dna, which is sunburn and, eventually, skin cancer. X-rays pass through soft tissue and are stopped by bone, which is the whole of radiography. Gamma rays come from nuclear transitions and the most violent events in the universe. The dividing line — ionising or not — falls just past the colour violet.
Seen in the game · Stage 4 · spectral analysis
Where this comes from
Enspinors is a ten-minute investigation built out of real instruments — a true compass bearing, a shortwave band that behaves like one, a time signal modelled on wwv in Fort Collins. This article is one of the Academy lessons inside it, published here in full and free.
Enspinors on the App Store · $4.99 · no ads, no in-app purchases, no tracking