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When we think to interstellar communications, we immediately think to radio signals with medium or large antennas :

  • We all know about radio signals in seti.
  • In the case of fictional stories, some peoples will even rememberer the broken antenna of Obi‑Wan in Star Wars episode 2 where he finally manage to contact coruscant half of the galaxy away (through radio signals).

However, we know the drawbacks :

  • the farther the target is, the more the required energy is. This start to heart our space exploration : for example, we disable many instruments on voyager probes only for few extra energy saving whereas the antenna consume more than all combined instruments.
  • transfer speeds happen at speed of light : this may sound fast but at the galaxy level, things can take centuries in order to travel. Everyone know the case of the philæ probe that landed at 90° angle because as it happened in automatic mode, gyroscopic stabilizers being stopped on the first touch (not to mention the rosetta relay requirement that prevented the primary mission objective to complete).

So at some point, the use of radio signals become a strong STOP (definitely aborting the idea to send data between galaxies and well shorter before that).

In the same time, there are reports of communication using quantum nonlocality over short distances (this might only solve the energy problem, speed being only one among others).
Of course I read about the theoretical possibility of quantum nonlocality in use in communications before asking this question : that’s why I think surveys like this one are hoax.

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    $\begingroup$ The thing is, I think you're going to be limited by the speed of light no matter what. Causality is a bitch. $\endgroup$ – Draco18s Feb 1 '16 at 21:56
  • $\begingroup$ @Draco18s : this was only an example to highlight thetoo human centric at current technologieseffect. Again, speed is only one of the drawbacks of radio signals with directionals antennas. $\endgroup$ – user2284570 Feb 1 '16 at 23:18
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    $\begingroup$ I think using a fantasy movie (Star Wars doesn't have much of the "science" part of sci-fi) as your primary example doesn't help the question. Maybe pick something based in reality? $\endgroup$ – Schwern Feb 1 '16 at 23:22
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    $\begingroup$ @user2284570 Using Star Wars as an example of the current thinking of SETI is like using CSI as an example of good police work. It's concern is entertainment and only enough accuracy to be plausible to the general public. SETI doesn't ignore ansibles because of human-centrism, they ignore them because all evidence says it would violate the laws of the universe. And if they did exist we'd have no idea how they worked and how to detect them. $\endgroup$ – Schwern Feb 1 '16 at 23:38
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    $\begingroup$ @user2284570 The Rare Earth Hypothesis (not a theory) has come under fire in part because of the discovery of large numbers of exoplanets in the last decade makes Earth look not-so-rare. The idea of a Galactic Habitable Zone is just an idea. Even then it's a ring around the center of the galaxy which does mean tens of thousands of light years to communicate from one end of the galactic habitable zone to the other. $\endgroup$ – Schwern Feb 2 '16 at 1:33
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Yes, I've often thought the same thing. If there are intelligent aliens out there, who says they use radio?

Perhaps radio is just a brief step that civilizations take on the road to more advanced technologies. Like vacuum tubes. There was an era when vacuum tubes were the latest, cutting-edge technology. That lasted for, what, 40 years or so? Then they became obsolete and we've moved on to transistors and integrated circuits. (Not to say that that's the ultimate technology either.) Maybe radio is something that intelligent being use for a century or two and then naturally move on to something better. I don't know what that "something better" would be. But then lots of people in the 1940s had no idea what could be better than vacuum tubes. (I always get a chuckle today when I read a science fiction story that was written in the 1940s or 1950s and that talks about the computer on the star ship or at the capital of the galactic empire having vacuum tubes.)

Or, maybe other civilizations would have different communications technologies, not because they are inherently better, but just because their technology took a different route. If aliens were truly different from us -- if they lived in water or breathed methane or can "see" microwaves but not visible light or whatever -- their technology might be different in many ways.

The problem is that we have never met an intelligent alien. We don't even know if such creatures exist, much less what they are like if they do. We're just piling speculation on top of speculation. Not that that isn't fun, but unless and until we actually meet such creatures, it's impossible to know.

Well, when I say "impossible", we can presumably put constraints on it. Years ago I read that we know for a fact that aliens do not play games using regular polyhedral dice of a shape unfamiliar to us, because Plato proved that there are only 5 possible such shapes, the Platonic solids. Likewise, current science indicates that the speed of light is the absolute limit for transmitting information. So aliens might have an alternate means of sending information, but it can't be faster than light. On the other hand, I'd be very reluctant to say that aliens might not have, say, more efficient ways to produce energy than we do. Just because we don't know a better way doesn't mean it doesn't exist. My point is, there's a big difference between "I can't think of a solution to this problem other than X, Y, and Z", and "I have proven logically and mathematically that there is no solution to this problem other than X, Y, and Z."

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  • $\begingroup$ That last paragraph about Platonic Solids and games is nonsense. It doesn't even hold true on Earth, I have at least six different types of dice and the d10 is not a Platonic Solid. It also has nothing to do with the speed of light; games are a cultural choice, the speed of light is a universal constant. $\endgroup$ – Schwern Feb 1 '16 at 23:15
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    $\begingroup$ @Schwern I didn't say that the shape of dice had anything to do with the speed of light. They were two unrelated examples. And yes, you can make dice that are not Platonic solids. I didn't say that aliens can't have objects in shapes that we've never seen. That would be absurd, the number of possible shapes is infinite. They can't have REGULAR POLYHEDRAL shapes that we've never seen, where "regular polyhedral" is defined as all sides being the same 2D shape and all vertices connecting the same number of sides. $\endgroup$ – Jay Feb 1 '16 at 23:29
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    $\begingroup$ I see, I misread. Objection withdrawn. $\endgroup$ – Schwern Feb 1 '16 at 23:34
  • $\begingroup$ @Schwern : not the downvote. :‑) $\endgroup$ – user2284570 Feb 1 '16 at 23:39
  • $\begingroup$ @user2284570 Can't do that without an edit. $\endgroup$ – Schwern Feb 1 '16 at 23:42
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A qualified yes, because we're pretty sure there's no faster way to transfer information even with quantum whatever. The qualification is they might not use radio waves, but they're going to use some sort of light.

What is likely is they won't use omni-directional antennas for very long. Radiating energy in an expanding sphere is extremely wasteful, its power will diminish with the square of the distance. Instead, focused energy transmissions are much preferred. The ultimate expression is using a laser, which is great for talking to things in space, but not so great for talking to the next city over because the curvature of your planet gets in the way.

However, there's always a need for omni (or nearly omni) directional transmissions. A simple example is wifi Internet and cell phones, though even those are somewhat directed.

This is taken into account by the Drake equation in two parts. Fc is how many alien civilizations reveal their existence via signals into space, and L is how long their civilization sends detectable signals into space. Though we have little idea what those numbers are.

In the end, while SETI is looking for stray radiation, it's also hoping somebody else looks at the Earth and says "hmm, there's something fishy going on with their chemistry over there... too much methane and oxygen and it's absorbing too much red light. Let's beam them a hello!"


In the same time there are (probably hoax) reports of communication using Quantum nonlocality over short distances (this might only solve the energy problem).

This won't work. The speed of light is not just the speed of light, it is the maximum speed which information can be transmitted. This is called the no-communication theorem.

In physics, the no-communication theorem is a no-go theorem from quantum information theory which states that, during measurement of an entangled quantum state, it is not possible for one observer, by making a measurement of a subsystem of the total state, to communicate information to another observer.

In the example of quantum entanglement, if you and I carry two entangled particles away from each other and then observe them it is true that my observation causes your particle to also collapse to the opposite spin. However no information is conveyed. The original particle is in a superimposed state, and I cannot control which state it collapses to.

To use an analogy, suppose we each carried a special coin in a box. When you open the box, the other coin would immediately show the opposite. We travel away from each other and I look in the box. Mine says heads. When you look in your box yours will say tails. Because I cannot choose what face my coin will show, you can glean no information. You can't even tell when I looked at my coin, because as soon as you check inside your box you force the coin to manifest.

Veritasium has a more technical and better illustrated video on the subject.

A note on Space-QUEST. It is not a hoax. It was published in the International Astronomical Congress Proceedings. It's purpose is to eliminate some of the final loopholes which might allow quantum entanglement to communicate faster than light.

There is one way to settle the matter for sure: send entangled photons to two orbiting astronauts on board different spacecraft with large relative velocities. That leaves no room for hidden variable theories or any other fix because the peculiarities of special relativity allow both astronauts to claim the measurement on their photon was performed before the other.

Even when we're pretty sure about something, we still need experimental data to verify the theory.


Somebody mentioned neutrinos. They'd make a terrible interstellar communications medium. They're created by fusion which requires tremendous energies. They have almost no mass. They interact only via the weak nuclear force making them extraordinarily elusive. You'd need four light years of lead to reliably stop a neutrino. And they're spewed out by stars and supernova and even the cosmic background radiation causing a tremendous amount of interference.

And they only go at the speed of light giving them no advantage over photons.

I seriously doubt a civilization would discover how to create, control and detect neutrinos before they figured out electromagnetism. This is more than human-centric thinking. EM interacts with lots of things easily, is created and interacted with naturally, evolution has taken advantage of electricity independently many times, and is the simplest force to detect, create and manipulate.

Here's a great video on neutrinos by Sixty Symbols.


What is theoretically maybe possible is using a system of wormholes. Wormholes bend space itself and so avoid violating the speed-of-light. If a permanent wormhole could be established between two points, then it could be used to communicate. But that communication would still be using plain old light.

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  • $\begingroup$ While laser can use radio length, I don’t consider it as the definition of radio signals in my question (by radio signals I think to the use of some kind of antenna). I already know about the theoretical possibility of quantum nonlocality : that why I qualified this as on of many existing hoax in my question. I also told that even if they were possible, they could only solve the energy problem. $\endgroup$ – user2284570 Feb 1 '16 at 22:34
  • $\begingroup$ @user2284570 The simple, literal answer to "will they be using omni-directional energy radiation in the 300 GHz to 3 kHz bands" is "probably not" because even we're getting rid of it. I made the answer more interesting. However, a radio telescope search isn't just looking for incidental transmissions, it's looking for any transmission. Some might be deliberately directed at us. The hope is that an alien civilization will use a frequency that is transparent to the interstellar medium such as the water hole. $\endgroup$ – Schwern Feb 1 '16 at 22:42
  • $\begingroup$ @user2284570 Also, Space-QUEST is not a hoax. I've added some info to the answer. $\endgroup$ – Schwern Feb 2 '16 at 0:00
  • $\begingroup$ This is just I didn’t used the right example. $\endgroup$ – user2284570 Feb 2 '16 at 1:17
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    $\begingroup$ @user2284570 It may be helpful to blur the line between light and radio. There is no actual dividing line between them, so trying to create such a separation is likely to cause unnecessary confusion. An "antenna" is just an artifact of how humans currently go about the process of making EM emissions. $\endgroup$ – Cort Ammon Feb 3 '16 at 21:37
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People (by which I mean an intelligent life form, and not necessarily Earth-based humanity) tend to use whatever forms of communication are sensible. For instance, according to Henry Wadsworth Longfellow, Paul Revere used a lighthouse to shine line with the code, "one if by land, two if by sea".

If he did so, people a hundred miles away (in the next state, the American equivalent of a province), much less anyone on another continent, or the moon, or another planet in our solar system, or a galaxy away.

The reason why radio emissions were sought by Earth sensors is not a belief that Aliens were likely to embrace radio instead of other forms of communication. The biggest reason is that radio waves don't tend to diminish over distance as much as other things. Also, radio is fairly simple, on a technological level, so it is sensible to believe that another species may dabble with radio, at least temporarily (before they come up with something more advanced).

Would advanced extraterrestrial life really use radio signals

The assumption is that they would be likely to use whatever seems to work best for them. We built our big satellite dishes with the assumption that, at some point, using radio technology may be the actions that they may be most likely to do, which we would be likely to detect from a great distance away.

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  • $\begingroup$ The assumption is that they would be likely to use whatever seems to work best for them. We built our big satellite dishes with the assumption that, at some point, using radio technology may be the actions that they may be most likely to do, which we would be likely to detect from a great distance away. While I didn’t wrote it in my question, I thought to it. Your answer isn’t a real clear one. $\endgroup$ – user2284570 Feb 1 '16 at 23:22
  • $\begingroup$ I will add this as a re-phrase: Aliens might communicate with written mail, smoke signals, telegraph, hard-wired telephone, radio, lighthouses, tin-cans-and-strings, and underground cables, and maybe other approaches (unique to them). Of those, radio is the absolute best thing for us to scan for, because it's the method which we are likely to be able to notice from far away. They may use other things, like wired communications, but we won't be likely to scan for those other things. Compared to other options simple for them to implement, radio is very detectable (by us) over great distance. $\endgroup$ – TOOGAM Feb 1 '16 at 23:53
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Maybe not, the path to radio requires electricity which might be an unlikely thing to stumble across some environments. An aquatic species might become very advanced even starfaring and not come up with it. Same with a species that evolved on a metal poor planet or moon. I think assuming radio is human-centric to a fault. The equivalent of believing that life on other worlds has ford pick-up trucks.

Who knows maybe the rest of the universe found that the creation and detection of neutrinos are simple and they use that. (neutrinos go farther and bend less in gravitational fields) We are just too dopey to figure it out.

Or and this is the stunner. There is no good way to communicate or travel interstellar distances or Alien life is too alien to communicate with or does not hold the value of exploration or communication.

enter image description here

MR. SNIFF: What are you looking for? MR. SNOOP: A five-dollar bill. MR. SNIFF: Are you sure you lost it on this street? MR SNOOP: Oh no! I lost it in the next block, but I’m lookin’ up here because the light is better.

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  • $\begingroup$ Yeah, when I heard about radio signals for extraterrestrial search, I wondered if the idea is too human centric making things like this stupid. Please also note my edit to the title. $\endgroup$ – user2284570 Feb 1 '16 at 22:16
  • $\begingroup$ Do my tenses still work? Tech is my opinion is path-dependant and branching whenever I hear "an advanced alien race would have X tech" or that there are levels of technological advancement I giggle. $\endgroup$ – King-Ink Feb 1 '16 at 22:21
  • $\begingroup$ You site things like liquid water : as soon as you leave it (or the planet) other ways of communications might get quickly highlightable because they would only work in the presence of matter (instead of infrasound based for water). $\endgroup$ – user2284570 Feb 1 '16 at 22:23
  • $\begingroup$ what is highlightable? $\endgroup$ – King-Ink Feb 1 '16 at 22:28
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    $\begingroup$ It means tohighlight it possible. An incorrect translation of mettable en evidence. $\endgroup$ – user2284570 Feb 1 '16 at 22:31

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