turbo
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Broadcasting and listening on the 21 cm band may ultimately be fruitless, but it's a pretty smart way to attract attention for two reasons.MonstersFromTheId said:I DO take issue with the idea that "broadcasting on 21 cm would be like dialing 911 on your cell phone". That's a pretty over the top assumption to make imo. Broadcasting on 21 cm could very well be more like beating on a phone wire with a stick. IF the phone company had sensors installed on phone wires to detect attempts at communication by people far too primitive to figure out how to tap into the line somebody might notice. But I'm not sure that that's all that likely.
1) Neutral hydrogen is pretty fundamental, and it's a good bet that anybody mapping the universe in EM will pay special attention to that wavelength and actually conduct surveys (large-area studies) in that wavelength.
2) Patches of neutral hydrogen do not exhibit modulations in complex repeating patterns, and any such broadcast would be a pretty good indication of intelligence behind the source.
You might not like Chronos' comparison of 21 cm to 911, but it is a valid point. Anywhere in the US, you can dial 911 on your cell phone and it will be universally recognized as a call for assistance. I don't know how many other countries might have adopted that code (ignorant on that count) but it is very handy here. Not being able to communicate with other civilizations yet (and set up a common meeting ground), we have to guess where they might be looking for signs, and 21 cm is a very logical place to look.
Compared to putting plaques and phonograph records on interplanetary probes, broadcasting and searching at 21 cm is just a little (maybe 1010 times
) likely to yield something, if only a qualified negative result.
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