laser, maser, like, other excitation / energy saturation does not work here ?

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

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

Yeah. It would be pretty funny if an alien reader of the plaque concluded that 1 refers to the actual length of the line between the two circle thingies and concluded, therefore, that we're only a few cm tall.

The plaque also provided a drawing of the probe itself next to the two human figured, at scale.

> 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.

What helps me is thinking of it in term of period instead given that the wavelength is the spatial propagation of a change in field. It’s big, but that’s because C is high.

Segmentation fault! Core dumped

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

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

It started with the grandfather clock. Everyone's clock pendulum needed to be the same length to have the same length of a second. So a meter also happens to (approximately, this was before we could easily be precise to several decimal places) be the length of pendulum that cycles at 0.5 hz (each swing back and fourth is a second) in 9.8 m/s^2 gravity.

The standard metre was a rod 1 metre long, you might be thinking of the standard kilo which is a compact cylinder?

SETI uses the gap between the H line and the OH line (the "water hole"). The whole region of the spectrum is kind of quiet for reasons, and the H/OH area is (perhaps parochially) thought to be a natural place for other water-chemistry life forms to look.

1.4 GHz = 21 cm. Masers use the same transition AFAIK.

In fact, natural H-masers have been found: https://www.cfa.harvard.edu/news/hydrogen-masers-space

Don't need to. It's the hydrogen wavelength / pi.

Wouldn’t be required. Take any frequency, Hydrogen in this case, and multiply it by pi which is unitless. The resulting frequency is pi times whatever you started with no matter how you count the passage of time.

Out of the question, it has no definition which is only related to physics. Well, there's the "the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom" definition, but this was chosen to match the celestial-based unit related to the Earth's rotation (which does not tell anything to extraterrestrials).

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.

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?

I expect the non-technical author/editor was playing the telephone game and originally wanted to emphasize that the frequency is always the same value, not that the hydrogen emissions frequency is related by arbitrary factors of 9192631770.000 Hz, 1/299792458.000 seconds, and then exactly 21.000/100.000 to the caesium-133 frequency.

so the claim is inaccurate by 1mm and missing precision data. I'd call it inaccurate and imprecise XD

The exact opposite would be ”imprecise” or ”inaccurate”

I was expecting some spectacular revelation that the definition of the second, the period of a Cesium atom, and the speed of light were somehow related to the definition of a meter by a factor of 0.21.

If our system was based on Planck units then it would be interesting. It would also cause tons of other fundamental constants to be greatly simplified to either integers or integer multiples of known transcendental constants.

then cm will become a bit longer and it'll break many things

I still have my nanowire, received directly from Grace herself during one of her last lectures I attended in the 80’s.

Of course, it’s in among about a thousand other wires and cables and nonsense.

One of these days I should sort it out and try to identify it by length.

She had a very firm handshake, and a very definite glint in her eye as she handed those out to her star struck fans ..

I'm sure that's what it was. I probably should have remembered that, but it was such a small part of one of his lectures it didn't resonate as deeply as it should have.

It's ultimately what killed having a memory controller on the northbridge of a motherboard. Having the CPU talk to a separate chip to ultimately talk to the RAM simply added too much latency into the entire process.

She didn't use string, she used wires, and would sometimes hand them out after lectures.

Woah. Imagine extrapolating that for life. What does it mean to throw away a day?