# Why are we looking for alien signals from radio waves?

Is the only reason we are scanning the radio frequency bands for signs of aliens simply as this is all we have technologically able to do?

It seems that any civilization capable of interstellar flight would have better communications than radio. Correct me if I am wrong, but even modern radio signals are not able to make it more than 60 light years due to their strength.

The wiki for systems within 60 light years only lists like 20 or so planets. (though there are more when you look at the individual star wiki's)... We would think that if there is intelligent life there using radio we would have heard them....

• Can you please explain what the 60 light years number has to do with anything? Why can't modern radio signals travel more than 60 light years due to their strength? Are they attenuated by interstellar matter? Do they just become so low in intensity due to $\frac{1}{r^2}$ that they are below the CMB noise floor or something? There is no reason an alien civilization couldn't have begun sending very very powerful radio waves in Earths direction very long ago. May 26, 2019 at 22:25
• "Is the only reason we are scanning the radio frequency bands for signs of aliens simply as this is all we have technologically able to do?" Yes. We our looking for our lost keys under the street light because we can't see them if they are in the alley where they are much more likely to be. May 27, 2019 at 5:57

We look for three reasons :

• If you don't look, you won't find anything even if it's there and not finding something is useful information as well. To be a scientist is to search for you know not what.

• Just because the nearest planets may not suit our needs doesn't mean that they won't suit some alien life form. We know next to nothing about "how to build life" and what is possible or likely.

• Even if no aliens live on these planets that does not mean that they don't visit them (if that's possible), may not have left automated systems to tell the universe "we lived once and came here once" or may not simply be traveling and searching themselves.

We would think that if there is intelligent life there using radio we would have heard them

Which presumes they broadcast. Maybe they only listen. People here have made arguments that broadcasting is potentially dangerous because you don't know what might be listening and how they might react.

It seems that any civilization capable of interstellar flight would have better communications than radio

Wild speculation. There's no reason for us to think there is anything better that flinging photons into the void. Even if they have "better than radio" for their own uses, that doesn't mean they're dumb enough to look for only those signals and would not use "good old fashioned" radio, which they know (with reasonable assurance) any technological civilization would develop and use at some point.

Correct me if I am wrong, but even modern radio signals are not able to make it more than 60 light years due to their strength.

You're wrong. See, e.g., http://www.setileague.org/askdr/range.htm   ....

"Frank Drake once calculated that as a telecommunications facility, Arecibo could communicate with its theoretical twin anywhere in the Milky Way galaxy. That 100,000 light year range seems overly optimistic to me. When I ran the numbers, I came up with a more modest result of perhaps 10,000 LY (still a substantial distance)."

I recall the estimate that "Arecibo could communicate with its theoretical twin anywhere in the Milky Way galaxy" from another source many years ago. But I can't recall nor google where I read it. However, see, e.g., https://en.wikipedia.org/wiki/Arecibo_message for a different story: "the Arecibo message is a 1974 interstellar radio message carrying basic information about humanity and Earth sent to globular star cluster M13", which is some 25,000LY from Earth.

In any case, 60LY is a vast underestimate, probably by some four orders of magnitude.

• Yes but that is a single focused purposeful interstellar signal. Not a wide area unfocused terrestrial signal.
– Rick
May 27, 2019 at 21:51
• @Rick Oops, looks like "I'm wrong." But note that attenuating your signal by sending it out isotropically isn't really the best idea in the first place. Better to choose a well-populated chunk of sky, like that M13 Arecibo_message. So your "systems within 60 light years only lists like 20 or so planets" isn't really relevant. With a directional antenna, like Arecibo, we could easily contact every planetary system discovered so far (and plenty more). Just not all of them simultaneously and continuously.
– user89220
May 29, 2019 at 3:51

The answer to your question, simply put, is that searching for extra-terrestrial intelligence in radio waves is what has paradigmatically been done for the longest time. Put another way, it's what has got the most traction. Specifically, we can draw this back to the Drake Equation

$$N = R_* \times f_p \times n_e \times \times f_l \times f_i \times f_c \times L$$

which has motivated SETI's searches since it was first postulated in 1961. Now, the Drake Equation is nothing more than a wild guess. Out of the seven terms involved, only the first two--the average rate of star formation in our galaxy and the fraction of stars that have planets--are things that modern astrophysics has given us quantitative estimates for. The remaining terms involve very vague notions such as the fraction of planets that can develop life, the fraction of planets that actually develop life, the fraction of those that evolve into civilizations, etc. Crucially, $$f_c$$ is the fraction of civilizations that can communicate via radio waves.

There is no ground for this other than Drake thought it was a good idea to search in the radio band, and by now millions of dollars have been invested into these searches. I actually attended a talk given by someone from SETI about their recent work and frankly, I found their entire approach to be seriously wanting.

Shortly put: they keep doing it because they can still get funding to do it and nobody has argued for more effective use of those resources.

Who says there are any civilisations capable of interstellar flight? There almost certainly aren't, especially when journeys of hundreds of light years are involved. Few people have any idea how difficult interstellar space travel is to achieve. Our best hope, admittedly a rather forlorn hope, is to detect their everyday radio, TV or radar transmissions. As you point out, this would require the extra-terrestrial civilisation to be within about 60 light years of us, but the upside is that in our search for very faint radio signals we may detect things of great scientific interest even though they are not signals from intelligent beings orbiting distant stars.

• That second sentence is definitely one no one can make with any certainty. That's basically the thing we definitely don't know, just because we don't have interstellar flight doesn't mean another civilization couldn't. May 26, 2019 at 22:22
• I can say it with certainty,but to explain why would take too long. Basically the reason why is summed up in my third sentence. May 26, 2019 at 22:30
• No it cannot be said with certainty at all, we have no idea what's out there so there is no way to assert that there are not May 26, 2019 at 23:09
• @Triatticus It is possible to say with near certainty. Even at a significant fraction of the speed of light, it would only be possible to travel very tiny distances at the galactic scale. May 27, 2019 at 2:42
• You can't reach any conclusion that aliens don't exist just by your thought. Research is being going on using AI to study various cosmic signals reaching us. And it's a long way ahead to reach any conclusion. May 27, 2019 at 6:45

I believe what StephenG said about looking somewhere is better than looking nowhere is the key answer here. However, i also feel that one possible reason for this is that when this search started, the number of sattellites around orbit available or such a mission was few if any, and radiowaves are within a part of the electromagnetic spectrum referred to as the "radio window", which refers to the fact that radiowaves generally makes it through the atmosphere without being attenuated along the way, meaning that the signals make it through to the surface.

More or less, the distance a signal travel generally depends on the receiver. The receiver will have a "noise-floor" which is the average level of the electrical noise in the receiver. As long as the signal is above this level and the receiver would conclude that it's a signal and not a spontaneous nosie burst, the signal would be detected as such.

I think the OP is referring to the mysterious Fast Radio Bursts (FRBs) which are radio bursts that lasts a few milli-seconds, but the pulses are incredibly bright. Also this is not the first time that aliens have been suggested.

The repeater FRB 121102 has been theorized as alien signals because natural origin explanation would most likely produce a single burst. Research is going on using artificial intelligence (AI) to study the hidden patterns in cosmic signals that come our way. However there is no idea about how alien signals look like and AI could come to the rescue due to its broad pattern recognition abilities. For this purpose it is important to a wider range of cosmic signals coming from nearby stars and galaxies.

So this is just a prediction that repeating FRBs are alien signal and it's a long way to reach a conclusion.