Is there a definite end to the electromagnetic spectrum?
The electromagnetic spectrum has no theoretical limit at either end. You can create as long a wavelength (ie. as low a frequency) as you want simply be moving an electric charge back and forth in as long a period of time as you choose. Given the proportionality of energy and frequency, long wavelengths such as this represent very low energies.
At the other end of the spectrum, it takes higher energies to create higher frequencies (shorter wavelengths). That means you are limited only by the energy available. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the
maximum frequency attainable.
The highest frequency EM waves are labelled 'Gamma' rays.
Paul Walorski, B.A., Part Time Physics Instructor
'The atomic bomb ... made the prospect of future war unendurable. It has led us up those last few steps to the mountain pass; and beyond there is different country.'