What is the blackbody problem and the ultraviolet catastrophe?

  1. Hello! I'm trying to research about the history and development of Quantum theory, especially with regards to Max Planck's energy quanta.

    I don't understand what was the problem in classical physics that required Planck to formulate quantum theory/energy quanta, which seemed to have revolutionized physics at the time.

    I read about the blackbody radiation problem and the ultraviolet catastrophe that Planck had tackled on, but I'm having a hard time understanding it. All I could pick up is about some infinite energy in the body's system when it absorbs all incoming radiation. I don't know if that's even right.

    Anyway, if somebody could explain it to in layman's terms (if possible, with analogies), as I don't really have a working technical knowledge of physics and mathematics. Thanks you very much!
     
  2. jcsd
  3. According to Wiki
    http://en.wikipedia.org/wiki/Ultraviolet_catastrophe
    Plank did not develop his theory in response.
    So, for historical accuracy, you might want to investigate that aspect.
     
  4. Here's the Planck's paper.
    And here's a paper which may be useful.
     
  5. I knew I was being inaccurate somehow and was missing something, thank you!

    So the blackbody problem/UV catastrophe had nothing to do with Planck and the development of "quanta"?

    But still, my question remains, what was the motivation of Planck behind introducing the concept of "quanta"? Did it stil have someting to do with rising problems in classical physics? I know you said in your quote that Planck's actual motivations are difficult to explain to a lay audience, but maybe you (or somebody out there :D) could give a general idea? Thanks so much, sorry for my persistence. :)
     
    Last edited: Jan 29, 2014
  6. Okay, I think I just found the answer to my own question from this website/blog:

    http://www.daviddarling.info/encyclopedia/Q/quantum_theory_origins.html

    As it turned out, Max Planck was really "into" the concept of Entropy and the 2nd law of Thermodynamics, and the Time's arrow (the Universe only going forward in one direction); and that he doubted the existence of atoms (which is pretty ironic considering the concept of "quanta").

    To quote the site/blog post:

    Anyway, it did has "indirectly" something to do with blackbody, but Planck's true motivation behind the concept of "quanta" was to provide a link between irreversibility and the absolute nature of entropy, by using the blackbody formula:

    So is this right? Planck's goal was to study more about Entropy and the arrow of time, and its related concepts?

    Finally, Planck's "quanta" was not in fact a direct response to the Ultraviolet Catastrophe:

    But Planck's formulation of the "quanta" and the Planck's Constant & Law, did turn out to resolve the UV Catastrophe issue (accidentally, if that's safe to say)?
     
  7. That is a Wiki quote - their words, not mine.

    This should give you an insight and make some sense out of it, contrary to what wiki says.
    http://www.daviddarling.info/encyclopedia/Q/quantum_theory_origins.html

    a few paragraphs down,
    Mostly Planck was trying to work from a thermodynamics point of view and comprise entropy and the second law. The breakdown of Wein's law for a blackbody gave him impetus for his endevour. He actually was not trying to solve the ultraviolet catastrophe per se - it just so happened that he did. It is ironic that Planck, who did not believe in tiny bits of matter called atoms, actually proved that energy came in tiny bits, subsequently called quanta.

    EDIT: I see you found the same reference.
     
  8. Or maybe is it because Planck himself was not even sure what his suggestion of quantum energy had meant?

    Because he "really did not give it much thought" except to bring a positive result, and that he didn't see his work at the time as representing any kind of threat to classical mechanics or electrodynamics. That's why some historians question whether Planck really ought to be considered the founder of quantum theory, that it wasn't until years later when the "physical"concept of energy quanta was fully realized, when Albert Einstein published his Nobel-winning work on the Photoelectric effect (where he quantized light as packets called photons).

    To quote:

     
  9. Point taken, thanks. But where can we find reliable sources? I checked out the Wikipedia page, and it led me to an "offical" article by Physics world: http://physicsworld.com/cws/article/print/2000/dec/01/max-planck-the-reluctant-revolutionary , which is the same article Shyan posted above as PDF.

    Thanks :D Yes, I'm as surprised as you are. Too bad there are only few written works/articles about this subject made available online. Seemed we must have come across it coinidentally from the search engines.

    I see. This is also from the "daviddarling" source:

    Planck believed that such a formula (blackbody) might provide the link between irreversibility and the absolute nature of entropy: his scientific holy grail.

    But what was the "problem" or "idea" about Entropy/2nd law of Thermo, that he intended to "solve" or "achieve"?

    I see thanks! Helped a lot.

    Our source also explained it in detail: (Note the bold's)

    Is it true that he just "guessed" the formula, without formal derivation or possibly rigorous math proofing?

    Oh wow okay, that's so cool for Planck! (forgive my rather informal/juvenile-like remark). I see now why they chose the UV Issue as a historical basis to introduce and explain Planck's physics.

    But anyway, I still don't understand the problem behind the UV Issue, and how his quantum energy had resolved it. So maybe, if it's okay with you to explain it to me briefly and simply? I'd appreciate it.

    Yes, I find that very ironic, yet also funny.

    Thanks very much for posting and your help!
     
  10. Loosely described, and baring the actual physics, which I think you can look up Wein, Raleigh, and some of the other terms that you have seen, it became apparent that a radiating body due to the classical investigation of radiation, that a blackbody should emit energy at all wavelengths, and more so at the shorter wavelengths on into an emission of energy on into infinity. Of course, if you take a blackbody, the emission spectrum does not behave that way, but has a peak at a certain frequency, and falls lower at higher and lower wavelengths.

    Wiki uses an analogy as a vibrating string, onto of which countless standing waves could be imposed, with each standing wave wavelength, or frequency, if you prefer, as having equal energies. The string would then have limitless energy as the number of standing waves would also be limitless.

    You could relate it to sound waves also. A musical instrument giving a note, emits that note, and harmonics, the strength of which is less than the previous harmonic (or note). The sound level of the harmonic(s) decays the farther it is from the basic note. That is the reality.

    For an "ultraviolet catastrophe" of the musical instrument, each harmonic would not be at a lessor strength but of the same level as the basic note. Since there are many harmonics, a musician playing an "ultraviolet catastrophe" musical instrument, would have the sound levels of each harmonic add ( which is not additive in the usual sense but of some formula ), and you and your fellow audience members would not enjoy having your eardrums burst with a high decibel output.

    For sure there are some analogical errors there, but I hope you get the sense of it.

    PS. Re-reading that, it sounds like someone writing from the 1880's
     
  11. jtbell

    Staff: Mentor

    <nitpick> That guy's name was Wien, not Wein. </nitpick>
     
  12. Hehe, I think we once derived both results in a statistical mechanics class, the Rayleigh-Jean and Plancks law. I think deriving them will let you understand why one is wrong and the other isn't - or just finding the deriviation in a book with some good explanations, of why they did as they did, and which assumptions they made (and thus which were wrong).
     
  13. Ha. That's a hooch. How did any grapes get tossed in there?

    ( yes. I looked up wein - grape, wine in german and Yidish )
     
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