Planck mass; time; length derived out of air?

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Discussion Overview

The discussion revolves around the derivation of Planck mass, Planck time, and Planck length, exploring the underlying constants of nature and their relationships. Participants seek to understand the mathematical and experimental foundations of these concepts, as well as the historical context of Planck's constant.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants note that Planck mass, time, and length are derived from algebraic combinations of the speed of light (c), Planck's constant (h), and Newton's gravitational constant (G), which have been measured extensively.
  • One participant emphasizes that these combinations are the only ones that satisfy dimensional analysis.
  • Another participant questions the derivation of Planck's constant (h), seeking specific experiments or observations that led to its value.
  • A participant explains that the concept of h originated from issues in thermodynamics and electromagnetism around 1900, particularly related to black body radiation, where Max Planck proposed that light consists of particles with energy proportional to their frequency.
  • There is mention of experiments, such as those involving Josephson junctions, which may provide accurate measurements of h, although the participant expresses uncertainty about this detail.
  • A follow-up question is raised regarding the implications of infinite energy in the context of black body radiation and the modes within a heated cavity.

Areas of Agreement / Disagreement

Participants generally agree on the algebraic relationships involving the constants but express differing views on the derivation and implications of Planck's constant, indicating that multiple perspectives remain in the discussion.

Contextual Notes

Some limitations include the need for clarity on the distinction between the concept and the value of Planck's constant, as well as the historical context surrounding its derivation. The discussion also highlights unresolved aspects of how these constants relate to physical phenomena.

Chaos' lil bro Order
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Greetings,

Anyone know how the Planck mass, Planck time, and Planck length were derived in the first place? Please cite experiments or mathematics to support your comment as I'd like to intimately understand this, not just from a metaphorical standpoint.

Thanks a bunch,

Chaos' lil bro.
 
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Chaos' lil bro Order said:
Greetings,

Anyone know how the Planck mass, Planck time, and Planck length were derived in the first place? Please cite experiments or mathematics to support your comment as I'd like to intimately understand this, not just from a metaphorical standpoint.

Thanks a bunch,

Chaos' lil bro.

The http://en.wikipedia.org/wiki/Planck_length" are algebraic combinations of three measured constants of nature, the speed of light, c, Planck's constant, h, and Newton's constant of gravity, G. Those constants have been measured many many times.
 
Last edited by a moderator:
They are the only possible algebraic combinations of those 3 constants which obey dimensional analysis.

Daniel.
 
Ok, then how was 'h' derived?

Ok, C, G, h.

Then how was Planck's constant 'h' derived? If possible please site an experiment, observation, or derivation since to help me understand the meaning beyond a google cut and paste.

Thanks.
 
Do you mean the concept of h or the value of h?

The concept of h came from problems in thermdynamics/electromagnetism around 1900 which predicted that the black body radiation spectrum for a cavity (like a heated oven) should have infinite energy. In order to solve this Max Planck realized you could get the right spectrum if you assumed light was made up a particles which had energy hf, where f was their frequency and h a constant. He didn't initially agree with his own work, but the results were undeniable.

To get the value of h, experiments are done. I seem to remember reading a few years ago that Josephson junctions are excellent for determining h to a very high accuracy, but solid state physics isn't my thing and I can't be sure I'm remembering that correctly.
 
Alpha, great post!

One little question:
Are you saying that the oven contains infinite energy because there can be infinite modes within it? As in a curve that extends towards but never reaches the x line?
 

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