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Anonymous Coward writes:
https://www.businessinsider.com/alien-civilizations-may-have-already-colonized-galaxy-study-2019-8
The Milky Way could be teeming with interstellar alien civilizations — we just don't know about it because they haven't paid us a visit in 10 million years.
A study published last month in The Astronomical Journal[$] posits that intelligent extraterrestrial life could be taking its time to explore the galaxy, harnessing star systems' movement to make star-hopping easier.
The work is a new response to a question known as the Fermi paradox, which asks why we haven't detected signs of extraterrestrial intelligence.
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Fermi Paradox Paper: Aliens Could Take Their Time Settling the Galaxy
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The Fine Print: The following comments are owned by whoever posted them. We are not responsible for them in any way.
TOO BAD YOU CAN'T BUY a voodoo globe so that you could make the earth spin
real fast and freak everybody out.
-- Jack Handey, The New Mexican, 1988.
(Score: 2) by Nuke on Tuesday September 10 2019, @08:55AM (3 children)
It has been pointed out that among the first powerful signals emitted from Earth were public radio broadcasts, and they will have reached quite a few stars by now. Prominent among those would have been broadcasts of Hitler's rally speeches. Perhaps he scared them off, which might not be a bad thing.
(Score: 2, Insightful) by Arik on Tuesday September 10 2019, @09:21AM (1 child)
If laughter is the best medicine, who are the best doctors?
(Score: 0) by Anonymous Coward on Tuesday September 10 2019, @09:14PM
Unless they speak German but not Russian or English. ;-)
Or, even if they received _a_ broadcast, what are they odds they translated it right.
(Score: 0) by Anonymous Coward on Wednesday September 11 2019, @03:35AM
They were sent out on long and medium wavelengths. These require immense antennas to receive at the nearest star, maybe comparable to a planet in size. Namely, the free space path loss at 1 MHz is 303 dB, and if we were sending 10 kW (+70 dBm), the sentients over there will need a 170 dB antenna to have -100 dBm at their receiver. We stopped using this band, and the ETs should be smart enough to do the same. Normal (for us) radio astronomy frequencies are in GHz, like SETI's 1420 MHz.
But that number is true only if they use the filter that is matching the spectrum of the signal. If not, the power drops further. Anyway, 170 dB gain, if the antenna can be constructed at all, will result in a very narrow beam. Now the poor ETs have to point this planet-sized antenna exactly to Earth! Do they do that? Well, we certainly don't, we have no orientable MW antennas, and besides the noise floor in this band is pretty bad, good luck pulling an unknown analog signal from tens if not hundreds of dB below.
The TV broadcasts did use a bit higher frequencies like 100-200 MHz, but that is still too low. Arecibo can receive 300 MHz - 10 GHz, but higher frequencies result in higher gain. As a reference, at 430 MHz the Arecibo dish provides 61 dBi gain. If we point two Arecibo dishes, one on Earth and one near Proxima Centauri, toward each other, and transmit 100 kW (+80 dBm), the receiver will get -150 dBm - a signal that could be detected, especially if digitally modulated (adds processing gain.)
There remains one class of RF emission that we are still producing. Radars. They are powerful, have high gain antennas, and operate generally at UHF and above. But who knows how their antennas are oriented, and how often they are used. Also, their frequencies are not linked to nature's constants, so an ET would have to search for a needle not in a haystack, but in a continent that is covered with a mile-thick layer of hay.