After some research, it seems apparent to me that the EM spectrum is continuous, but this would contradict a physics fundamental that energy is discrete. Is there a conflict here?

  • $\begingroup$ You seem to be interpreting restricted claims in an unduly broad fashion. There is no general claim that "energy is discrete". There are many claims about discrete emission. Perhaps you can point us at the sources you are reading. Otherwise this is simply too broad. $\endgroup$ Apr 30, 2017 at 17:27
  • $\begingroup$ @daniel "Wasn't this question just asked?" Well the OP's previous question physics.stackexchange.com/q/330025 arises from the same misunderstanding, but this version makes the exact nature of the disconnect clearer. $\endgroup$ Apr 30, 2017 at 17:33
  • $\begingroup$ I am temped now to answer this question of mine too. I think the lesson for me and perhaps others is this: There is a lot of misinformation out the on the web, youtube in particular. Tons of sites saying that energy is discrete. Good thing this site is here. $\endgroup$
    – Lambda
    Apr 30, 2017 at 17:41
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    $\begingroup$ The two most common bases for this mis-claim are the photoelectric effect (which says that energy emission in a particular wavelength occurs in discrete chucks) and the line spectra of atoms (which is related to the steady-state energies available to bound systems being discrete). Both of these things are limited claims. $\endgroup$ Apr 30, 2017 at 17:48

1 Answer 1


No, there isn't a contradiction. From the very inception of the idea of quantization of energy (in Planck's explanation of the continuous blackbody spectrum) the two ideas have been compatible.

The "physics fundamental" that "energy is discrete" that you refer to, when applied to the electromagnetic field, says that each mode of electromagnetic radiation at frequency $\nu$ can only hold energy in discrete lumps of size $h\nu$. However, there is a continuous infinity of possible modes spanning all possible frequencies $\nu\in(0,\infty)$.

There are additional aspects of energy quantization when matter is involved (most commonly the photoelectric effect and the discrete nature of atomic emission and absorption lines) but these refer to the nature of the energy transitions that matter itself can perform and interact with, and they say nothing about the nature of the frequency and energetic spectrum that the EM field itself can accommodate.

  • $\begingroup$ Thanks for the answer, Emilio. I lost some points on this question, but that's the way it goes. $\endgroup$
    – Lambda
    Apr 30, 2017 at 18:22

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