The Electromagnetic Spectrum

Radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays are not different substances. Each is an electromagnetic wave: a self-propagating ripple of electric and magnetic fields, generated whenever a charge accelerates. Every one of these waves travels through vacuum at the same speed, c = 3.0 x 10⁸ m/s. What separates a radio wave from a gamma ray is purely wavelength and frequency, linked by c = f·lambda. Stretch the wavelength out to kilometers and you get radio waves; squeeze it down to picometers and you get gamma rays. Walk the spectrum continuously from one end to the other and nothing physically changes except that ratio of wavelength to frequency.

Visible light, roughly 400 to 700 nm, looks special only because it happens to match the narrow window of wavelengths that trigger chemical reactions in the retina. Swap in a creature with different eyes and a different slice of the spectrum would feel 'normal' instead. Physics draws no line around visible light; it is an accident of biology, not a boundary in nature.

What does shift as you climb from radio to gamma is how the wave interacts with matter, because higher frequency means more energy per photon. Radio waves pass through walls and barely disturb atoms. Infrared warms them by exciting molecular vibrations. Visible and ultraviolet can kick electrons into higher energy levels or break weak bonds. X-rays and gamma rays carry enough energy to eject electrons entirely and damage tissue. This same spectrum is what later shows up in diffraction and interference patterns, since wavelength is exactly what determines how a wave bends around obstacles or spreads through slits.