Quantization of energy.... We say that electrons have set energy levels, and certain energies they cannot possess whilst in a certain atom. Is it still possible to produce photons / EM waves of any energy we desire? I mean, by looking at the equation E = hf it would appear we can - if we put in any value for f we can get any value for E. (obviously this would mean not being pedantic and talking about -ve numbers, etc. ) We can't just say "yeh we found out a wave with this frequency has this energy - but it doesn't exist!" - can we? Thanks in advance.