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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

#91

Post by justlikereddit »

BurningFrog wrote: post #64
kccqzy wrote: post #10

Amazing article! It seems incredibly to weird to hear about transitions causing photons at 21cm wavelength; I guess I'm only used to seeing (no pun intended) much shorter wavelengths at hundreds of nanometers.

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.

My subwoofer is approximate cubic with 30 cm to a side.

But the wavelength of sound it makes at 20Hz is approximately 17 meter.

Wavelength is merely a human conceptualization. If we reconceptialize it as peak-to-peak interval it suddenly stops being length and becomes a time instead

Re: One quantum transition makes light at 21 cm

#93

Post by ttoinou »

justlikereddit wrote: post #91
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.

My subwoofer is approximate cubic with 30 cm to a side. But the wavelength of sound it makes at 20Hz is approximately 17 meter. Wavelength is merely a human conceptualization. If we reconceptialize it as peak-to-peak interval it suddenly stops being length and becomes a time instead

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

Re: One quantum transition makes light at 21 cm

#94

Post by jpmattia »

AnimalMuppet wrote: post #82
kccqzy wrote: post #10

Amazing article! It seems incredibly to weird to hear about transitions causing photons at 21cm wavelength; I guess I'm only used to seeing (no pun intended) much shorter wavelengths at hundreds of nanometers.

Yeah, it's weird to me that an atomic transition can create something with a wavelength so much longer than the atomic radius. (Yeah, I know that it's a really low-energy transition, and I know about the relationship between energy and wavelength. But the net result I still find highly counter-intuitive.)

> Yeah, it's weird to me that an atomic transition can create something with a wavelength so much longer than the atomic radius.

Then it will be even weirder during an MRI: The protons in your body produce a wavelength that can be of order 1-10 meters.

Re: One quantum transition makes light at 21 cm

#95

Post by o11c »

simiones wrote: post #72
omegacombinator wrote: post #68

Earlier quoted context omitted.

Ah, so the answer to life, the universe, and everything was actually 42/2 …

Is this going to be τ vs π all over again?

I recently did a bit of programming exploration using tau exclusively instead of pi (and `sintau` instead of the new `sinpi` function etc.)

In almost every aspect this was far simpler, but there was the curious case of the constant `M_2_SQRTPI = 2 / sqrt(π)`. Even after looking up what weird formula that constant is used in, it wasn't at all clear to me where would be the most sensible place to put the constant.

Re: One quantum transition makes light at 21 cm

#96

Post by nullc »

nine_k wrote: post #85
belter wrote: post #36

In Contact the alien beacon arrives at 4.4623 GHz. Pi times the Hydrogen line...

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.

Re: One quantum transition makes light at 21 cm

#97

Post by mjd »

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 "8" ("|---") to indicate that she is approximately 8×21 = 168 cm tall.

Re: One quantum transition makes light at 21 cm

#98

Post by MaxikCZ »

ttoinou wrote: post #93
justlikereddit wrote: post #91

Earlier quoted context omitted.

My subwoofer is approximate cubic with 30 cm to a side. But the wavelength of sound it makes at 20Hz is approximately 17 meter. Wavelength is merely a human conceptualization. If we reconceptialize it as peak-to-peak interval it suddenly stops being length and becomes a time instead

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.

Re: One quantum transition makes light at 21 cm

#99

Post by arghwhat »

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...
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