The Fermi Paradox: Where are the Aliens?

This question, as much as anything, illustrates why people have trouble thinking through problems when they cannot put their own self-importance to one side. Let us look at this problem not from our point of view.

The Fermi paradox is a statement that since there are so many stars, most of which probably have planets, and a reasonable number of them have life, more than half of those are likely to have been around longer than us and so should be more technically advanced, but we have seen no clue as to their presence. Why not? That question begs the obvious counter: why should we? First, while the number of planets is huge, most of them are in other galaxies, and of those in the Milky Way, stars are very well-separated. The nearest, Alpha Centauri, is a three star system: two rather close stars (A G-type star like our sun and a K1 star) and a more distant red dwarf, and these are 4.37 light years away. The two have distances that vary between 35.6 AU to 11.2 AU, i.e. on closest approach they come a little further apart than Saturn and the sun.  That close approach means that planets corresponding to our giants could not exist in stable orbits, and astronomers are fairly confident there are no giants closer to the star. Proxima Centauri has one planet in the habitable zone, but for those familiar with my ebook “Planetary Formation and Biogenesis” will know that in my opinion, the prospect for life originating there, or around most Red Dwarfs, is extremely low. So, could there be Earth-like planets around the two larger stars? Maybe, but our technology cannot find them. As it happens, if there were aliens there, they could not detect Earth with technology at our level either.  Since most stars are immensely further away, rocky planets are difficult to discover. We have found exoplanets, but they are generally giants, planets around M stars, or planets that inadvertently have their orbital planes aligned so we can see eclipses.

This is relevant, because if we are seeking a signal from another civilization, as Seti seeks, then either the signal is deliberate or accidental. An example of accidental is the electromagnetic radiation we send into space through radio and TV signals. According to tvtechnology.com “An average large transmitter transmits about 8kW per multiplex.” That will give “acceptable signal strength” over, say, 50 km. The signal strength attenuates according to the square of the distance, so while the signals will get to Alpha Centauri, they will be extremely weak, and because of bandwidth issues, broadcasts from well separated transmitters will interfere with each other. Weak signals can be amplified, but aliens at Alpha Centauri would get extremely faint noise that might be assignable to technology. 

Suppose you want to send a deliberate signal? Now, you want to boost the power, and the easiest way to get over the inverse square attenuation is to focus the signal. Now, however, you need to know exactly where the intended recipient will be. You might do this for one of your space ships, in which case you would send a slightly broader signal on a very high power level at an agreed frequency but as a short burst. To accidentally detect this, because you have a huge range of frequencies to monitor, you have to accidentally be on that frequency at the time of the burst. There is some chance of Seti detecting such a signal if the space ship was heading to Earth, but then why listen for such a signal, as opposed to waiting for the ship.

The next possible deliberate signal would be aimed at us. To do that, they would need to know we had potential, but let us suppose they did. Suppose it takes something like 4.5 billion years to get technological life, and at that nice round number, they peppered Earth with signals. Oops! We are still in the Cretaceous. Such a move would require a huge power output so as to flood whatever we were using, a guess as to what frequencies we would find of interest, and big costs. Why would they do that, when it may take hundreds or thousands of years for a response? It makes little sense for any “person” to go to all that trouble and know they could never know whether it worked or not. We take the cheap option of listening with telescopes, but if everyone is listening, nobody is sending.

How do they choose a planet? My “Planetary Formation and Biogenesis” concludes you need a rocky planet with major felsic deposits, which is most probable around the G type star (but still much less than 50% of them). So you would need some composition data, and in principle you can get that from spectroscopy (but with much better technology than we have). What could you possibly see? Oxygen is obvious, except it gives poor signals. In the infrared spectra, you might detect ozone, and that would be definitive. You often see statements that methane should be detectable. Yes, but Titan has methane and no life. Very low levels of carbon dioxide is a strong indication, as it suggests large amounts of water to fix it, and plate tectonics to renew it. Obviously, signals from chlorophyll would be proof, but they are not exactly strong. So if they are at anything but the very closest stars they would not know whether we are here, so why waste that expense. The Government accountants would never fund such a project with such a low probability of getting a return on investment. Finally, suppose you decided a planet might have technology, why would you send a signal? As Hawking remarked, an alien species might decide this would be a good planet to eradicate all life and transform it suitable for the aliens to settle. You say that is unlikely, but with all those planets, it only needs one such race. So simple game theory suggests “Don’t do it!” If we assume they are more intelligent than us, they won’t transmit because there is no benefit for those transmitting.

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