One quantum transition makes light at 21 cm • Hacker News Board

Re: One quantum transition makes light at 21 cm

#171

Post by MaxikCZ » Fri, Apr 25, 2025, 12:43 PM UTC

ttoinou wrote: post #101

MaxikCZ wrote: post #98

Earlier quoted context omitted.

It's not about measuring peak to peak in distance, it's about measuring how long it takes for one spot to encounter second peak after first. The fact that the first peak traveled some distance is irrelevant, as its entirely dependent on propagation speed, which doesn't affect the frequency, only vawelenght.

Would you then say that the wavelength is meaningful for the sound example as its properties are really of a wave propagating, and meaningless for the light as the wave analogy isn’t a full description of the light phenomenon behavior ?

I have pretty strong intuition for how "sound looks". I know how to imagine a wavelength of sound, how the medium works over time etc. I don't have the same intuition about light, as the sound analogy of a wavelength (distance between 2 peaks) clash with the part of photon that behaves like a particle.

From that standpoint I can confidently say that wavelength is meaningful for the sound example, but not so much for light. Someone more knowledgeable than me would probably offer better insight.

Re: One quantum transition makes light at 21 cm

#172

Post by Pixelbrick » Fri, Apr 25, 2025, 1:40 PM UTC

arghwhat wrote: post #99

mjd wrote: post #97

This 21-centimeter transition was chosen by the designers of the Pioneer plaques ( https://en.wikipedia.org/wiki/Pioneer_plaque ) to explain to any alien readers how big we are. At top left is a cartoon of two hydrogen nuclei in opposite spin orientations, and a ruler in between them marked "1". Over on the far right you can see another ruler that measures the height of the female figure, marked with binary numeral "…

If only we could somehow share a physical entity of known dimensions to reference together with the drawing so that we did not need to use a physics riddle to indicate scale...

Banana!

Re: One quantum transition makes light at 21 cm

#173

Post by arghwhat » Fri, Apr 25, 2025, 1:40 PM UTC

arghwhat wrote: post #164

fc417fc802 wrote: post #148

Earlier quoted context omitted.

> our invention of the technology we use to communicate with deep space far predates us learning these concepts ourselves. Maxwell published in 1873. The double slit experiment was 1803, subatomic theory developed throughout the 1800s, and Planck proposed quanta in 1900. The first radio transmission across the Atlantic came approximately 2 years after Planck's theory. I doubt it is plausible to develop anything resem…

The period you're describing is that of old quantum theory, which was hugely inconsistent and predates our theories of modern quantum mechanics which is post 1925 or so. The inventor of the arc converter was 18 at the time radio waves were discovered, 34 at the time he invented the arc converter, but 56 and with only 17 years left till his death when the era of modern quantum mechanics started with the invention of w…

(Not to mention that the hydrogen line was only discovered in 1951, as a result of years of hearing it using radio equipment invented half a century prior. Even things as basic as the proton took until 1932 to discover.)

Re: One quantum transition makes light at 21 cm

#174

Post by RcouF1uZ4gsC » Fri, Apr 25, 2025, 2:52 PM UTC

mjd wrote: post #97

This 21-centimeter transition was chosen by the designers of the Pioneer plaques ( https://en.wikipedia.org/wiki/Pioneer_plaque ) to explain to any alien readers how big we are. At top left is a cartoon of two hydrogen nuclei in opposite spin orientations, and a ruler in between them marked "1". Over on the far right you can see another ruler that measures the height of the female figure, marked with binary numeral "…

They could have also used a 21cm length more directly for the male figure, but they did not.

Re: One quantum transition makes light at 21 cm

#175

Post by apognwsi » Fri, Apr 25, 2025, 3:06 PM UTC

joemag wrote: post #84

Loved this article! I initially was confused by how this transition would work with the conservation of angular momentum (since the electron would be flipping from spin ±½ to the opposite one). But then remembered that photons are spin 1 particles, so the math works out. Neat.

that's not right. if photons were truly spin 1, there would be 3 spin eigenstates available, but in fact there are only 2 (Sz=0 is unavailable). the pithy argument invokes the absence of a stationary frame of reference. for all practical purposes, photons are behave like spin 1/2 particles (despite being bosons). see, for example, the jones algebra / calculus.

Re: One quantum transition makes light at 21 cm

#176

Post by kbelder » Fri, Apr 25, 2025, 4:11 PM UTC

boothby wrote: post #62

raldi wrote: post #37

Earlier quoted context omitted.

That not just imprecise usage of that term; it’s completely incorrect. The correct term would be its exact opposite, “approximately”.

Indiscreet discrete mathematician checking in. If they said "exactly" we'd have a real problem. Instead, "precisely" in this context means "human eye cannot distinguish from exact value at a stone's throw." Yes, physicists and engineers hate me, why do you ask?

"It's precisely 21 cm."

"Is it 21 cm?"

"No."

Re: One quantum transition makes light at 21 cm

#177

Post by freehorse » Fri, Apr 25, 2025, 4:21 PM UTC

mannykannot wrote: post #169

freehorse wrote: post #161

Earlier quoted context omitted.

> is physics highly constrained by what can be observed in the universe It is also very highly constrained by how _we_ observe the universe. Beings with different sensory/cognitive capacities could develop very different models. > equivalences between apparently dissimilar modes of presentation If there was some mathematical equivalence between their models and ours, which is already a leap to assume, there is still…

It seems disproportionate to fuss about "a leap to assume..." when we are talking about a small plaque affixed to a probe on the highly speculative basis that something intelligent might one day retrieve it, as opposed to something that is mission-critical. Would we be better off for not making these "leaps"?

I was answering to a specific comment chain.

Re: One quantum transition makes light at 21 cm

#178

Post by spullara » Fri, Apr 25, 2025, 5:01 PM UTC

monadINtop wrote: post #143

spullara wrote: post #123

Earlier quoted context omitted.

Do you think that physics is somehow subjective? We absolutely would have decoded the message.

As a theoretical physicist, yes physics could definitely be subjective between different species. Physics is the way HUMANS describe nature to themselves. I don't doubt that it describes some greater nature outside of us that is invariant, but it is only a description - not the thing itself. Like mathematics it is an anthropocentric conceptualization that has many arbitrary and historically contingent choices in its…

If they could discover the probe at all and view the plaque, lots of things are already very similar.

Re: One quantum transition makes light at 21 cm

#179

Post by mannykannot » Fri, Apr 25, 2025, 6:05 PM UTC

freehorse wrote: post #177

mannykannot wrote: post #169

Earlier quoted context omitted.

It seems disproportionate to fuss about "a leap to assume..." when we are talking about a small plaque affixed to a probe on the highly speculative basis that something intelligent might one day retrieve it, as opposed to something that is mission-critical. Would we be better off for not making these "leaps"?

I was answering to a specific comment chain.

It would be a leap to assume another culture has something similar to (or, in some cases, anything resembling) one's ethics, sense of humor or taste in music. In comparison to these things, science has something they do not: apparently universal and impersonal 'laws', which, where we can check, appear to hold across the visible universe (putting aside some unresolved issues on the leading edge of our present knowledge.)

For some extra-solar civilization to examine the probe and its plaque intact, it will have to rendezvous with it in space. It seems to me to be the greater leap of faith to suppose this can be done without having knowledge that is isomorphic or equivalent to our formulation of orbital mechanics. Do you have any concrete ideas about how this might be so?

Re: One quantum transition makes light at 21 cm

#180

Post by monadINtop » Fri, Apr 25, 2025, 6:55 PM UTC

spullara wrote: post #178

monadINtop wrote: post #143

Earlier quoted context omitted.

As a theoretical physicist, yes physics could definitely be subjective between different species. Physics is the way HUMANS describe nature to themselves. I don't doubt that it describes some greater nature outside of us that is invariant, but it is only a description - not the thing itself. Like mathematics it is an anthropocentric conceptualization that has many arbitrary and historically contingent choices in its…

If they could discover the probe at all and view the plaque, lots of things are already very similar.

Yeah perhaps, but its really hard to say anything concrete either way