It would seem that if life were relatively common in the universe that there would be a cacophony of noise somewhere in the electromagnetic spectrum. Is life so rare and distant that the waves haven't reached us yet, or have they attenuate out, or are they unintelligible, or are we the first, or are we alone?

  • $\begingroup$ Jake, your question has been flagged for closure as it's likely to generate opinions rather than scientific answers. Could I suggest you edit the question to focus on a specific "problem"? For example, it's 2.5m ly to the next galaxy: at that distance, how powerful would a radio transmission need to be for us to detect it? (If we can't detect it from there, what hope have we got to detect anything from the billions of other galaxies?). That's just a suggestion, but hopefully gives you an idea of the kind of question that's ok here. See also How to Ask, and take the Tour. :-) $\endgroup$ Jan 15, 2019 at 7:55
  • $\begingroup$ Well, that depends if you ask about finding "life" - something we might not recognize even if we literally stepped into it, or you're asking why we didn't find some creatures dumb enough to scream with radiowaves in all directions? $\endgroup$
    – Mithoron
    Jan 15, 2019 at 18:21

4 Answers 4


To quote a favourite movie of mine

Pardon me sir, but it's a big-ass sky.

Our current method of detecting life (electromagnetic signals) is by targeting and scanning stars indivdually using radio telescopes.

This method is pretty costly because we don't have a huge amount of them and they can be better used for other (proper) research purposes. Basically, it costs a lot to monopolise a telescope's resources by repeatedly pointing it at stars without a reasonable hope of a result. Understandably, astronomers want to keep their funding by producing results rather than nothing.

The current estimates is that we can stumble upon signals by about 2040


By 2040 or so, astronomers will have scanned enough star systems to give themselves a great shot of discovering alien-produced electromagnetic signals, said Seth Shostak of the SETI (Search for Extraterrestrial Intelligence) Institute in Mountain View, Calif.

But again, this is pure guesswork.

A related question here on SE asks this same question from another direction

how far away could we detect that Earth has life?

One of the answers, quoted in part:

A "blind" search could look for radio signatures and of course this is what SETI has been doing. If we are talking about detecting "Earth", then we must assume that we are not talking about deliberate beamed attempts at communication, and so must rely on detecting random radio "chatter" and accidental signals generated by our civilisation. The SETI Phoenix project was the most advanced search for radio signals from other intelligent life. Quoting from Cullers et al. (2000): "Typical signals, as opposed to our strongest signals, fall below the detection threshold of most surveys, even if the signal were to originate from the nearest star". Quoting from Tarter (2001): "At current levels of sensitivity, targeted microwave searches could detect the equivalent power of strong TV transmitters at a distance of 1 light year (within which there are no other stars)...". The equivocation in these statements is due to the fact that we do emit stronger beamed signals in certain well-defined directions, for example to conduct metrology in the solar system using radar. Such signals have been calculated to be observable over a thousand light years or more. But these signals are brief, beamed into an extremely narrow angle and unlikely to be repeated. You would have to be very lucky to be observing in the right direction at the right time if you were performing targeted searches

I'd really recommend reading the rest of this answer, and other answers for this question.

So, our "noise" isn't really strong enough to be detected over long distances above the greater (and stronger) chatter of the natural universe.

While we could engineer a stronger broadcast message and hope for a reply, it's a long, long project and unlikely to be funded.

  • 3
    $\begingroup$ Space is big. You just won't believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist's, but that's just peanuts to space. $\endgroup$ Jan 14, 2019 at 15:13
  • $\begingroup$ In short, at which distance could be our noise be detected assuming SETI level reception facilities? From your A it seems the project started with little chance indeed. $\endgroup$
    – Alchimista
    Jan 17, 2019 at 9:03

The experimental data only shows that there is no life and no intelligent life in the parameter space where we could detect it.

The experimental data doesn't explain the cause.

That we are alone in the Universe, it is still a possibility.


There are a number of questions here on the Fermi Paradox with answers ranging from an Infinite Universe, the parameters for the Drake Equation and others. Well worth having a read through them.

But my favourite is author Cixin Liu's theory outlined in The Three Body Problem

Civilisations which are noisy draw attention to themselves, and are extinguished by civilisations thinking long term who don't want to have competition for resources in the far distant future.

Obviously that theory is not easily proven or disproven in any useful way, so currently it may be as valid as any other. Well worth a read in any case!

  • $\begingroup$ I think a civilization which is capable to destroy another from many light years away, don't need to think so long term - transferring a lot of nukes to a distant planet is probably not much more harder than transferring a colonization ship. $\endgroup$
    – peterh
    Jan 15, 2019 at 5:00
  • $\begingroup$ You need to read the book. Also, no, the solution is much easier than trying to transfer nukes anywhere. $\endgroup$
    – Rory Alsop
    Jan 15, 2019 at 13:25
  • $\begingroup$ You've made me curious! I'll do that. $\endgroup$
    – peterh
    Jan 15, 2019 at 13:26

I assume you mean "civilization", not "life".

It's a pure speculation that an advanced civilization would emit a "cacophony of noises".

Even our civilization on Earth is already working on reducing the amount of electromagnetic noise it produces. We are reducing light pollution, we are moving communications from radio waves into fiber optic cables and into low-power cellular networks, a lot of our equipment is shielded to avoid unwanted electromagnetic emissions. The general push to conserve energy means less and less will be emitted into space.

So based on our own recent historical experience, a civilization is unlikely to generate an electromagnetic signal noticeable at interstellar distances.


You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .