The US Government, and eventually the UN and all nation-states around the world, have realized they are broadcasting their existence to potential enemy civilizations in the nearby galaxy (at least to those that happened to be paying attention to the electromagnetic spectrum, particularly radio waves).

(Most of) The nations of the world want to bring this reckless behavior to a stop. At the very least the US, China, the EU and Russia have all been convinced of the importance of this. They've set a timeline of ten years to bring it about.

What steps would be necessary to stop this constant production of signals? What types of changes would the people on the ground notice? I imagine that radio frequencies would become a lot more regulated and cable and "tight beam" type communications would be explored. Are there frequencies that don't propogate that would still be legal?

Edit: To clarify, I mean any potential civilizations in nearby interstellar space. Not neighboring galaxies.

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    $\begingroup$ I had a post ready for this: got distracted, came back and found that all the points I had to make had already been addressed in other answers. Curse you internet! $\endgroup$
    – Joe Bloggs
    Commented Sep 29, 2015 at 15:44
  • $\begingroup$ AM and shortwave radio would probably be largely unaffected, as these signals reflect off the ionosphere. $\endgroup$ Commented Sep 30, 2015 at 7:57
  • $\begingroup$ Keep in mind parasitic radiation. Every electrical conductor that carries a significant-frequency signal radiates, to a lesser or greater extent. Shielding reduces but does not eliminate the radiation. It's all about what these aliens might be able to detect. Lots of tiny signals add up, and even the presence of any signal whatsoever is valuable information, as it would indicate the existence of an intelligent civilization (at least one similar to what we think of as such). I think we have a question to that effect somewhere here on the site, or possibly on Amateur Radio. $\endgroup$
    – user
    Commented Sep 30, 2015 at 8:36

6 Answers 6


Encrypt all radio traffic. All good encryption algorithms are indistinguishable from random noise. Even if a far-distant alien were able to listen in, they would have a very difficult time distinguishing radio signals from earth in the glare from that giant radio transmitter we call the sun. The entire power output of Earth in the radio spectrum pales in comparison with the sun, so an encrypted signal from Earth just looks like noise from the Sun.

For people on the ground in those countries that move to all-encrypted, all the time they will need to buy new radios and new TV receivers. Cellphone service is already encrypted and relatively short range. WiFi is also encrypted (though there are still some parts of WiFi transmissions sent in the clear).

Ham radio operators will probably be given a pass from buying new gear as the strength of their transmissions are generally pretty low compared to commercial or military transmitters.

Honestly, it's probably not that big of a deal anymore. At great enough distances, the solar system becomes a point source dominated by the Sun. Any transmissions from earth get all jumbled together since frequency ranges are often reused on different parts of the planet. Trying to make any sense of the simultaneous broadcasts from thousands or millions of radio transmitters will tax any signal processor that may be listening.

Signal strength decreases at the inverse square of distance:

$$S_{signal} \propto \frac{1}{d^2}$$

The nearest earth like planet is Tau Ceti at 11.905 light years. Any civilization farther away will have an even harder time detecting Earth's radio traffic. We have

$$S_{signal} \propto \frac{1}{(3\cdot 10^8~\text{m}\cdot\text{s}^{-1} \cdot 3600\cdot24\cdot 365.25~\text{s} \cdot 11.905~\text{Ly})^2}\approx \frac{1}{1.3\cdot 10^{34}}$$

which is about $-340 \,dB$ (assuming a satellite dish 1000 m^2). That is really really freaking tiny.

A ham radio operator friend of mine says that with a sufficiently strong EMP applied to the D-Layer would put a very firm blanket stopping all terrestrial transmissions. The effects would be transitory, lasting only hours or days. To sustain permanent radio silence would require a steady stream of EMPs in the ionosphere. Currently, our only source of EMPs come from nuclear explosions....so not really feasible.

He also said that if we could invent a technology that can control where and when sunspots form on the sun, then direct the proper type and sequence of coronal mass ejections (CME) towards Earth, we could achieve a radio "black out"...but if a civilization has the power to control sunspot activity on a star, they don't really need to worry about encroaching neighbors. CMEs are the natural way of energizing the D-Layer and blocking radio transmissions.

  • $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$ Commented Oct 2, 2015 at 1:27

It is already happening. Cellphone signals are very short range. TV and Radio stations are moving more and more to the Internet. I think the main thing would be cutting off signals to satellites except for tight beam and even that I would probably cut out. No matter how tight beam you make the signal, scattering will always produce stray radiation. I think the US Government and UN would basically just move all communications to the Internet and regulate that all Internet traffic will be wired, except for highly local wi-fi and cell-phone type signals. No more amateur radio, no more local tv stations over the air, no more local radio stations broadcasting over the air. Like I said, most things are moving that way anyway, so just complete the move - force it by law.

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    $\begingroup$ On the conspiracy side, we could easily infer that they already know of the existence of some mean Aliens, right? I mean, for what other reasons governments would want to decrease signals? $\endgroup$ Commented Sep 29, 2015 at 15:11
  • $\begingroup$ @EnzoFerber - Exactly. $\endgroup$
    – user11864
    Commented Sep 29, 2015 at 16:40
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    $\begingroup$ My saying "Exactly" was just purely in jest. The Illuminati have no need to come after me, as I am not aware of their existence. $\endgroup$
    – user11864
    Commented Sep 30, 2015 at 14:12

Give UNOOSA the authority to regulate all space broadcasts.

This is a global effort, and someone's going to have to coordinate it and get everyone to comply. Who's it going to be?

As discussed in another answer, there is already UNOOSA, the UN Office for Outer Space Affairs. They, with the help of SETI and national space agencies, are likely to be the ones to coordinate contact with another civilization. They'd be the natural choice to govern the global effort to darken the Earth.

Don't change the speed of light.

The nearest star is four light years away so it will take our signals four years to get there. Then they have to decide to mount a response and fly all the way here at sublight...

Either they're already on their way, in which case we're screwed in 10-1000 years, or they're really far away, in which case we have even more time.

Stay close to the Sun.

If the Earth were a night light, the Sun would be the giant spotlight right next to it. The Sun is so bright and so electromagnetically noisy that it blots out everything the Earth might transmit. The aliens are blinded.


Unfortunately for us, we're getting really good at detecting exoplanets. We're finding more and more sensitive ways to tease information about a planet out of the noise of its star like the composition of our atmosphere and wavelengths of energy we're reflecting (or transmitting).

Being so close to the Sun helps, but we do have to mind what we transmit and how we alter our atmosphere.

Don't fire focused beams into space, only omni-directional.

Take advantage of the inverse square law, when you double the distance of an omni-directional transmission its power drops four times. By the time something like a radio or TV transmission gets 5 light years out, it's very weak; @Green goes into detail. So long as you stick to omni-directional transmissions, you're probably fine.

If you focus those beams, the effect is greatly lessened. Now who would do that?

Shut down all Active SETI projects!

Seriously guys, stop broadcasting focused beams of energy at other stars! It's like shining a laser pointer at the neighbor's window, the space aliens are going to be really annoyed. And stop sending out star maps!

Unfortunately one message has already arrived at Altair 16 light years away in 1999. A map to our solar system, chemistry, DNA, characteristics... let's hope nobody in Altair was listening.

The next three are set to arrive in the 2020s with another five in the 21st century. They sent out everything from the recipe for photosynthesis, to a bunch of text messages, to a full on navigation beacon. Fortunately these are all directed at specific stars, let's hope we get lucky.

Stop sending probes outside the solar system.

These will probably not be picked up as they're very dark and will eventually be very cold and indistinguishable from the background, but just stop it.

Fortunately there's only five already on the way out, and if we really wanted to we could catch up to them with a rocket and strap an ion engine on it (and the rocket we sent) to put them into a solar parking orbit.

We wouldn't want one of them to fall into a wormhole, be given sentience by an advanced mechanical race, and return to Earth in search of its creator, wrecking havoc in its giant nebula ship when it finds us meatbags made it.

Encrypt all transmissions.

Already covered by @Green, if done correctly encrypted transmissions are indistinguishable from random noise. As correctly pointed out in the comments on that question, the communication protocol itself would still be identifiable; however encrypting the data portion would greatly reduce the signal's detectability as being artificial.

Startalk recently featured Neil Degrasse Tyson and Edward Snowden discussing this very possibility.

Stop radiating on unnatural wavelengths.

Even if you encrypt everything perfectly there's still the problem of spewing out all that radiation on wavelengths which don't occur naturally. We use these frequencies exactly because A) they're not common in nature and B) they're not absorbed by our atmosphere. If aliens see a constant stream of UHF transmissions coming from our planet, they're going to know something is up.

The Earth will have to practice some steganography and hide their signals in plain sight. One way to do this is to use wavelengths already common in the universe. Another is to avoid regular patterns of transmission times.

Return the atmosphere to its pre-industrial state.

We can already take educated guesses at the composition of an exoplanet's atmosphere and we're already looking for signs of life or industry in its composition. There's nothing we can do about showing signs of life, the greatly elevated levels of oxygen are a dead giveaway, but we can do something about all the other dead giveaways we've been pouring into the atmosphere.

Stop dumping heat into the atmosphere.

An industrial civilization generates a lot of waste heat which can be detected as unaccounted for extra infrared radiation. There was recently a SETI survey which did this for entire galaxies searching for Type III civilizations (lucky for us, they found no evidence).

Earth people would have to end the practice of dumping waste heat into the atmosphere. It would either have to be sequestered underground or reused.

Send a transmission about that Hitler guy.

One of the first major TV transmissions was the 1936 Summer Olympics in Berlin featuring speeches by Hitler. It's going to be one of the first video transmissions aliens might pick up. Just to make sure aliens don't get the wrong idea, we should send out a final transmission saying "don't listen to that Hitler guy, he's a ****".

  • $\begingroup$ Apparently there's been some work to find Type II civilizations which have also found no evidence. Unfortunately, they now think they looked for the wrong things :( $\endgroup$
    – Jim2B
    Commented Sep 29, 2015 at 23:30
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    $\begingroup$ With regard to the Hitler point, Carl Sagan includes this specific point as a key story element in his novel Contact. $\endgroup$ Commented Sep 30, 2015 at 9:08
  • $\begingroup$ @MikeofSST You don't say. $\endgroup$
    – Schwern
    Commented Sep 30, 2015 at 9:22

With the distances involved, they would still be hearing the past's radiowaves for quite a long time. Even stopping in ten years, any sufficiently advanced alien race would be able to pick up on our current radio waves and be able to pin-point with pretty decent accuracy our location.

Anyway, society would probably switch to fiber-optic and light communications rather than radio waves.

If that were the case, another race would have to guess towards the usage of light as a communication source. Intercepting communications wouldn't matter because they'd receive light, which can mean any number of things in space (gravitational lensing, stars, reflection of dust, etc), whereas a radio wave is slightly less common and greatly more obvious method of communication.

To give an example, we use a light beam to contact our satellites. Using color as an encryption/encoding style, messages would be easily distinguishable to those who know what to look for, whereas those seeing this light communication from space see a steady stream of slightly changing light, which isn't abnormal in space.

Kind of scary to think that the same thing may be happening to us without our knowledge.


The US Government, and eventually the UN and all nation-states around the world, have realized they are broadcasting their existence to potential enemy civilizations in the nearby galaxy

Given that the nearest galaxy is about 25 thousand light years away, there is no need to do anything - the aliens will receive the signals in 25 thousand years, any reaction would come in another 25 thousand years, and by that time so much can change that any plans will be completely moot (e.g. we can outdevelop the aliens). Moreover, the power mankind radiates into space is steadily decreasing, with lower power spread spectrum broadcasting being the hype now, and military radars being deployed less than during cold war. So the first step would be to go for the low hanging fruit, ban military radars (those are by far the most powerful signals that get into space).

This physics.stackexchange question discusses the distances and dish sizes needed to detect interstellar signals and what is detectable given our technology.

  • $\begingroup$ I think "in the nearby galaxy" means "elsewhere in this galaxy, near us." Otherwise it would have been "nearby galaxies" or "the nearest galaxy." $\endgroup$ Commented Sep 29, 2015 at 19:43
  • $\begingroup$ @MikeKellogg Maybe OP should edit the post and clarify $\endgroup$ Commented Sep 30, 2015 at 2:52

In addition to the previous comments, I'll add these:

  • Radars, both civilian air traffic control and military air/space defense would have to go down. How do you replace them?
  • GPS depends on relatively powerful transmitters so that the receivers can be small and inexpensive. If the military was prepared to abandon that advantage, something strange is happening. There are other radio navigation systems, too.
  • We're changing the spectroscopic profile of our planet by industrial emissions. Could aliens tell that our atmosphere is "not natural"?
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    $\begingroup$ This does not really answer the question. This reads like a comment and you in fact admit that this is exactly that. "In addition to the previous comments" $\endgroup$
    – Jax
    Commented Sep 29, 2015 at 15:44
  • $\begingroup$ This is a seriously incomplete answer. I mentioned three things we'd have to change, among many. $\endgroup$
    – o.m.
    Commented Sep 29, 2015 at 17:20
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    $\begingroup$ GPS transmitters could be focussed so that they only reach Earth. That leaves only stray radiation. $\endgroup$
    – gerrit
    Commented Sep 29, 2015 at 18:02
  • $\begingroup$ GPS satellites are very weak, very slow transmitters using 50 watts and sending in bytes per second. Satellite TV and Internet are far more powerful needing to transmit gigabytes per second using kilowatts of power. All of this is already pointed at the Earth, or the uplink is pointed at a satellite; an omni-directional transmitter would be a waste of power. By comparison the Arecibo Observatory can put out 2.5 terrawatts. $\endgroup$
    – Schwern
    Commented Sep 29, 2015 at 21:33

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