Okay, I am not a physicist but I am wondering about where Planck's constant came from? I understand that he was attempting to explain "black body radiation" and that he got frustrated with the math of this endeavor. So in a stroke of genius, he introduced a number $6.55×10^{−34}$ J⋅s and it made sense of the "Black Body Radiation" and worked perfectly, great. My question is, where or how did he derive this number and does it affect us?

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    $\begingroup$ also it's $6.63\times 10^{-34}$, not $6.55$. Well if you want to be a constant nerd it's $6.62607004081\times 10^{-34}$, but who's experiment is that accurate anyway. $\endgroup$ Aug 11, 2017 at 18:45
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    $\begingroup$ Which books or articles, there are lots (and lots) of them, have you read relating to this? Then you can create a better question regarding which aspect of the topic you would like to pin down as a problem in understanding it. $\endgroup$
    – user163104
    Aug 11, 2017 at 18:48
  • $\begingroup$ The size of atoms, based on the Bohr radius, goes like the square of the Planck constant. So yes, it affects the size of your and everything else's atoms... and... and... $\endgroup$ Aug 11, 2017 at 19:30
  • $\begingroup$ Is there some specific part of the corresponding Wikipedia article that you find confusing? $\endgroup$ Aug 11, 2017 at 19:51
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    $\begingroup$ @Countto10 Of course I have nothing to say about Panck himself and what he thought or didn't. I am "reminding" the OP of the evident in his "does it affect us" dangler. It is not about Planck, really. $\endgroup$ Aug 11, 2017 at 22:38

1 Answer 1


The experimental black body radiation curve

black body

followed the quantum curve ( named a posteriori) in the above diagram. Classical calculations could not fit the data for intensity of radiation versus frequency.

Planck had the out of the box idea to model black body radiation as a cavity with discrete energy oscillators, since continuous ones of classical electromagnetism led to the ultraviolet catastrophe..

class versus quantum

The h is a proportionality constant between energy of the mode ( we now call photon) and frequency. I.e., since continuous frequencies did not fit the data, he tried discrete, and fitted them with just a constant measured from data and in the end given Plack's name.

The success of solving the ultraviolet catastrophy for black body radiation is one of the basic reasons that quantum mechanics was discovered to be necessary to explain the data in the microcosm of atoms..

  • $\begingroup$ Thank you, I now understand, it was not a guess but derived. That's what I was looking for! $\endgroup$ Aug 13, 2017 at 18:30

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