Without it, radiation would be chaotic and uncommunicative. It would be noise that could not bear a signal. Yet communication can never exceed this speed, a fact that will keep us forever distant from other planets and even from ourselves. There are no practical limits to the spectrum's range of possible wavelengths and frequencies. Nor is the spectrum expressed only by the physics of electromagnetic waves.
Spectral frequencies translate into temperatures, into atomic signatures, and into photon energies.
Slowly accelerate the drumming to the fast be-bop rattle of a Max Roach or Buddy Rich, perhaps 16 beats per second. That is 16 hertz, around one fourth of the rate of an electrical power station. At some 30,000 hertz you have broken the sound barrier because you are sending out wave crests faster than they can be heard. Nonetheless, you remain near the very bottom of the electromagnetic spectrum. At the other extreme are gamma rays, creatures of cosmic explosions and giant particle accelerators, a frequency of 10 to the 24th hertz.