Robert McNees
Happy #QuantumDay!
Max Planck presented his work on blackbody radiation to the German Physical Society #OTD in 1900. His novel “quantum hypothesis” suggested that matter emits and absorbs light with frequency f only in discrete chunks of energy E=hf.
Image: AIP
Robert McNees
Planck’s quantum hypothesis would revolutionize physics, but he initially thought it wasn’t real. He suspected that the interaction of matter and radiation was tremendously complicated but still governed by the physics known at the time — what we now call “classical physics.”
Invoking quanta of radiation to derive the blackbody emission spectrum was, it seemed to Planck, just a mathematical trick that somehow encapsulated all that complication.
Robert McNees
But it was a trick that *worked*. Previous efforts to derive the blackbody emission spectrum using classical physics gave nonsensical results at high frequencies. Replace continuous emission with discrete quanta and things work out perfectly.
Evidence for the reality of quanta began with Einstein’s explanation of the photoelectric effect in 1905. The proposal that radiation of frequency f exists only in discrete chunks of energy E=hf was the first result of Einstein’s “Miracle Year.”
jessica, fission girl
@mcnees I will enjoy things only in discrete amounts today
Robert McNees
@rooster This is the proper way to observe Quantum Day!
Robert McNees
Many physicists remained skeptical. But Arthur Compton’s 1923 explanation of X-rays scattering off electrons was near-incontrovertible evidence that quanta were real.
Robert McNees
Here's a great APS Landmarks entry where you can read more about Compton Scattering and the reality of photons:
https://physics.aps.org/story/v13/st8
Robert McNees
Anyway, this was a not uncommon narrative in the transformative years of late 19th and early 20th century physics.
Some experimental result wouldn't make sense, a physicist would propose a radical solution, the solution would seem too weird to be true so they'd write it off as a convenient "trick," and then eventually everyone would realize that it wasn't a trick at all and reality was in fact weirder than they'd expected.
Robert McNees
Planck’s hypothesis was in fact a deep statement about the way Nature works. Radiation of frequency f comes in discrete chunks of energy E=hf. It's the nature of radiation, not some artifact of a complicated interaction with matter.
Nowadays we refer to the proportionality constant h as "Planck's constant." In the SI system it takes the value h=6.626 x 10⁻³⁴ kg*m²/s, or 4.136 x 10⁻¹⁵ eV*s.
As far as we can tell, h is a fundamental constant that is hardwired into our Universe.
Robert McNees
The results of Planck’s December 14th lecture were submitted to Annalen der Physik a few weeks later, on January 7th, and published not long after that.
You can see the original (in German) here:
https://onlinelibrary.wiley.com/doi/epdf/10.1002/andp.19013090310
An English translation of Planck’s paper, taken from Dirk ter Haar’s “The Old Quantum Theory,” is available here:
http://hermes.ffn.ub.es/luisnavarro/nuevo_maletin/Planck%20(1900),%20Distribution%20Law.pdf
Robert McNees
Something that isn’t as widely known is that “h” is not the only fundamental constant that was introduced during Planck’s presentation to the German Physical Society #OTD in 1900!
Planck was investigating emission and absorption by blackbodies, so he needed a way to relate energies and temperatures. Thus, he had to introduce what we now refer to as “Boltzmann’s constant.”
Robert McNees
That’s right, the factor of “k” that appears in the formula “S = k log W” — the formula engraved on Boltzmann’s memorial! — was actually introduced by Max Planck. Boltzmann expressed his results in terms of the ideal gas constant R.
Image: user Daderot on Wikipedia
Robert McNees
The transition from classical to quantum physics went very smoothly. Happy #QuantumDay.
(Sorry, I don’t know who made this image!)
Robert McNees
FYI, "quanta" is an outdated term. Most physicists now say "chonks." (The singular is "chonk.")
This is important if you are emailing a physicist out of the blue with your new theory. Be sure to refer to "chonks" and "chonky mechanics" so they know what you are talking about.
Joyous chonk-iversary!
Robert McNees
@desdinova I believe they call it Chonky Rainbowdynamics.
Desdinova
Chonky Chromodynamics rolls off the tongue perfectly, and is a far more self-descriptive term :)
Alex
@mcnees Isn't #QuantumDay April 14th?
Robert McNees
@mentallyalex Huh, I had no idea. "Quantum Day" here isn't anything official, just a name some of us attach to the anniversary of Planck publicly presenting the idea of the quantum.
RD Hall
@mcnees , 🤣🤣🤣🤣🤣
Andy Beaton✅
@mcnees ah hell, I always call them thingies. No wonder no one will review my theories. I even write them in different coloured crayons to make the concepts clear!
Level 98
@mcnees Kind of similar to... a bright, young, slender, cheery(ish) Einstein in 1905 having explained special relativity to the world vs an older, more sombre, world-weary, slightly portly Einstein in 1915, having grappled with general relativity for 10 years!
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