What exactly is the Ultraviolet Catastrophe?

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Discussion Overview

The discussion centers around the Ultraviolet Catastrophe, exploring its implications in classical and quantum theories of black body radiation. Participants seek to clarify the original theory and how quantum mechanics, particularly Planck's contributions, address the issues arising from classical interpretations.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants express confusion about the concept of intensity approaching infinity in classical theory.
  • One participant notes that classical theory leads to an infinite result for black body radiation, while quantum theory via Planck resolves this issue.
  • There are discussions about the analogy of string lengths used in explanations, with some participants questioning its relevance to the concept of photons and energy.
  • Another participant explains that in classical theory, energy can be distributed among waves of all frequencies, leading to a higher expectation of energy at high frequencies, while Planck's theory introduces the idea of energy being quantized in packets called photons.
  • Concerns are raised about the clarity and effectiveness of a YouTube video that attempts to explain these concepts, with participants expressing dissatisfaction with its production quality and content.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the effectiveness of certain analogies used in explanations, and there are mixed feelings about the clarity of external resources like videos and articles. The understanding of the Ultraviolet Catastrophe and its resolution through quantum theory remains a topic of exploration and debate.

Contextual Notes

Some participants highlight the complexity of the relationship between classical and quantum theories, noting that assumptions about energy distribution and the nature of waves may not be fully resolved in the discussion.

JoshBuntu
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I tried looking it up, but I just don't get it. Something about intensity going to infinite(?)

What exactly was the original theory and how does the "quantized" theory account for stuff?

I'm sorry if this is a dumb question :/
 
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the intensity is decreasing for higher frequency. see this explanation
 
Last edited by a moderator:
Naty1 said:
The problem was that classical theory gave an infinite (silly) answer for black body radiation...quantum theory via Planck solved the riddle...

This is a good explanation...

http://en.wikipedia.org/wiki/Ultraviolet_catastrophe

That bit involving lengths of string is a bit fanciful. How ever is it supposed to show the difference in powers? The rms power is the same for all frequencies of waves of similar shape and same amplitude. What has the length of a piece of string got to do with it? How does the string relate to photons?
 
sophiecentaur said:
That bit involving lengths of string is a bit fanciful. How ever is it supposed to show the difference in powers? The rms power is the same for all frequencies of waves of similar shape and same amplitude. What has the length of a piece of string got to do with it? How does the string relate to photons?

Are you talking about the wiki link? I don't see such contradictions in the very brief mention of harmonics on a string. They just used it as a brief analogy to help show that the density of states for a classical harmonic oscillator increases with the frequency.
 
Born2bwire said:
Are you talking about the wiki link? I don't see such contradictions in the very brief mention of harmonics on a string. They just used it as a brief analogy to help show that the density of states for a classical harmonic oscillator increases with the frequency.

Wow - I'm sorry. I was referring to (complaining about) the UTube clip in the other post. I just quoted the wrong post - durr.
In the UTube movie, they were showing a progressive wave with the string (referring to light ) and relating the length of the string that they unwound off some pins to the energy of the wave. That passage made no sense to me as the string was no more than a graph of displacement (possibly?) with distance. How does that relate to energy? It was so bad that I really couldn't go along with any more of it.
The Wiki link was fine btw.
 
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In classical theory energy can be shared amongst waves of all frequencies. If a box contains electromagnetic waves there will be more waves in a range of frequencies at the high frequency end than at the lower frequency end and this suggests that more of the energy will be at the high frequency end (ultra violet is high frequency waves).
Plancks theory states that energy can only be emitted or absorbed in packets called photons. The energy of a photon is proportional to the frequency. ALSO the probability of getting a high energy photon (compared to the average energy) is lower. Just like the probability of finding a very high energy molecule in a gas at a certain temperature (average energy). This accounts for the shape of the black body spectrum just like the Boltzmann distribution accounts for speed distribution of molecules.
 
sophiecentaur said:
Wow - I'm sorry. I was referring to (complaining about) the UTube clip in the other post. I just quoted the wrong post - durr.
In the UTube movie, they were showing a progressive wave with the string (referring to light ) and relating the length of the string that they unwound off some pins to the energy of the wave. That passage made no sense to me as the string was no more than a graph of displacement (possibly?) with distance. How does that relate to energy? It was so bad that I really couldn't go along with any more of it.
The Wiki link was fine btw.

Yeah, that was my guess but I wasn't willing to sit through an 8 minute video to find out.
 
Zero out of ten for production values and not much more for content, I think!
 

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