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One quantum transition makes light at 21 cm

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Re: One quantum transition makes light at 21 cm

#101

Post by ttoinou »

MaxikCZ wrote: post #98
ttoinou wrote: post #93

Earlier quoted context omitted.

The sound pressure wave does take 17 meters in the air to make a full cycle, no ? It’s real, same for the photon

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 ?

Re: One quantum transition makes light at 21 cm

#102

Post by mjd »

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...

We did that too. There is a cartoon of Pioneer itself, drawn to the same scale.

Re: One quantum transition makes light at 21 cm

#103

Post by hackrmn »

I find it disturbing/puzzling that there is this fundamental physical behaviour like emission of light with wavelength of _exactly_ 21cm -- assuming one centimeter wasn't based on any such property but was just a "random" unit measure that stayed with us historically and through sheer volume of use (in U.S. inches filled the same niche; still do). I mean what are the odds that the wavelength is _exactly_ (the word used in the article) 21cm?

Re: One quantum transition makes light at 21 cm

#104

Post by nomel »

IshKebab wrote: post #77
BurningFrog wrote: post #64

Earlier quoted context omitted.

It does feel a little odd that something the size of 5.29×10⁻¹¹ meter can create something 10 billion times larger. I mean, I understand how and why, but it feels odd.

Wavelength isn't an object though. Like if you walk around the world you haven't made something the size of the world.

Wavelength is a time thing though. To make something that low frequency (1.4GHz or 7ps), things have to happen pretty slowly.

Re: One quantum transition makes light at 21 cm

#105

Post by aylmao »

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...

Unsure what the tone of this message is, so I don't know if you're aware, but that's included too:

> Behind the figures of the human beings, the silhouette of the Pioneer spacecraft is shown in the same scale so that the size of the human beings can be deduced by measuring the spacecraft.

It's good to have redundancy, not just so someone interpreting the plaque can confirm their hypothesis, but also in case one of the messages fail. In this case, the spacecraft could break, but we can assume quantum transitions will always be observable.

[1] https://en.wikipedia.org/wiki/Pioneer_plaque

Re: One quantum transition makes light at 21 cm

#106

Post by tlb »

nomel wrote: post #104
IshKebab wrote: post #77

Earlier quoted context omitted.

Wavelength isn't an object though. Like if you walk around the world you haven't made something the size of the world.

Wavelength is a time thing though. To make something that low frequency (1.4GHz or 7ps), things have to happen pretty slowly.

* 714 ps

Re: One quantum transition makes light at 21 cm

#107

Post by TheOtherHobbes »

nullc wrote: post #96
nine_k wrote: post #85

Earlier quoted context omitted.

That could be some freaky case of Doppler effect. To rule that out, the aliens could send both 21 cm * pi and 21 cm * e .

It's ruled out by the signal being modulated. The question the choice is answering is where do you put a signal where other intelligent minds might look for it, yet which isn't at a frequency where the universe is particularly loud in ways that will make detecting your signal harder.

The signal is always going to be modulated, unless the source is maintaining a position with zero relative velocity to the Earth, or deliberately compensating for same - both of which would be far more impressive as a "hello" than a random-ish number which will always be distorted by orbital and proper motion.

Otherwise it's going to have a varying frequency - maybe not by much, and maybe not quickly, but certainly not static.

Re: One quantum transition makes light at 21 cm

#108

Post by nemomarx »

hackrmn wrote: post #103

I find it disturbing/puzzling that there is this fundamental physical behaviour like emission of light with wavelength of _exactly_ 21cm -- assuming one centimeter wasn't based on any such property but was just a "random" unit measure that stayed with us historically and through sheer volume of use (in U.S. inches filled the same niche; still do). I mean what are the odds that the wavelength is _exactly_ (the word us…

isn't a cm now defined based on the distance light travels in a vacuum in a very small period of time?

so it's not arbitrary really, or rather it probably goes the other way around. a cm used to be based on an arbitrary physical distance but was I think redefined to avoid needing to keep a standard meter cube in Paris.

Re: One quantum transition makes light at 21 cm

#110

Post by petsfed »

hackrmn wrote: post #103

I find it disturbing/puzzling that there is this fundamental physical behaviour like emission of light with wavelength of _exactly_ 21cm -- assuming one centimeter wasn't based on any such property but was just a "random" unit measure that stayed with us historically and through sheer volume of use (in U.S. inches filled the same niche; still do). I mean what are the odds that the wavelength is _exactly_ (the word us…

No more probable than any other value, whole or otherwise. In particular, its (per wikipedia) 21.106cm.

Its funny how our brains find nice whole numbers unsettling in the natural world. I was always sort of weirded out by the distance light travels in a nanosecond: just shy of 1 foot. How weird it is that it flops between systems!

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