[Mithaldu]

This seems nonsensical to me. Just like internet protocols, any radio transmission is built on a layer of protocols that envelope the actual data being transmitted.

Encryption is applied on the data layers not to hide that something is being transmitted, but what is being transmitted.

However scientists aren't even trying to detect signals with any sort of data in it, but merely radio emissions that look like they might come from something with an intellect.

If we haven't found anything like that yet, and encryption is supposed to be the reason, then that means that encryption would have to be applied at the most basic protocol layer in such a way that even the physical properties of the emission look like the universe's background radiation. Is there currently human technology that does anything similar to this?

[jjoe]

What if it's such advanced protocol layering and encryption that those alien signals appear to us to be "cosmic noise"? Surely an advanced civilization would have advanced communication capabilities we haven't even considered.

[kanzure]

> What if it's such advanced protocol layering and encryption that those alien signals appear to us to be "cosmic noise"?

Another interesting way to speculate is the "under our nose" concept, which is the concept that the existing distribution of stars and galaxies, as well as the recorded background noise, might be the byproduct of alien intervention. Binary star systems are a popular speculative example of "starivore" civilizations that consume entire stars that have been moved into the alien civilization's own star system, and perhaps some combination of multiple stars in a single system are not "naturally" occurring in the absence of alien influence. To an unsuspecting observer, some forms of distant astronomical-scale engineering could be mistakenly interpreted as natural astrophysics that the observers then incorporate into their standard models when refactoring to account for all of the observed data... Usually the simple explanations are correct, but when your models require really insane updates to handle the observed data, perhaps there are other explanations? At the same time though, what recourse would we have if 99% of the visible universe was already astro-engineered?

[cgriswald]

If binary star systems were systems in which stars were moved into the system, we should see evidence of stars being moved and consumed. I have also read about stars being created (e.g., starting a fusion process with all the hydrogen and helium in Jupiter, Saturn, etc.).

There is currently no evidence which suggests stars are being moved. We should see either large gravitational tugs or engines such as Shkadov thrusters. The latter should be plainly visible. The former should be easily detected by extrasolar planet detection methods. Unless the tugs are spherical, the light curves of the tugs would definitely pique interest. In any case, moving a star seems a rather extreme and expensive measure. It is probably more effective to consume the star onsite and use the energy locally or send only the energy back.

There seems to be no evidence of stars being consumed, either. Dyson spheres (or swarms) have actually been searched for locally by comparing visible and infrared wavelengths over sections of the sky. None have been found. Intergalactic searches have also been done by looking for galaxies which glow too brightly in the far infrared. No luck.

It is not just a question of a mistaken belief that the artificial is natural. The properties of light are the same here on Earth as they are billions of light years away. Further, for all those galaxies and stars to be engineered in the same way aross billions of light years (with some points being unable to communicate with others since the Big Bang), is all but impossible. Life would have to evolve at effectively the same rate and come up with the same solutions in all those hundreds of billions of galaxies (and yet somehow be different here in the Milky Way). Given the variety of life on Earth and the variety of solutions it has evolved, that seems unlikely.

[blackorzar]

And three more strange ones: http://articles.latimes.com/2009/aug/27/science/sci-planet27

http://news.discovery.com/space/alien-life-exoplanets/kepler...

http://astronomynow.com/2015/05/24/hubble-observes-one-of-a-...

Edit: to include the third link for Nasty1

[blackorzar]

These are my favorite candidates for stars being consumed in our own Milky Way: http://www.space.com/20286-star-whips-around-black-hole-at-r... http://www.space.com/20303-black-hole-star-speed-record.html http://www.space.com/24290-quiet-black-hole-discovery.html

[talmand]

What if these things were done so long ago that we missed our chance to witness them?

[cgriswald]

There are hundreds of billions of galaxies at various distances from Earth. When we look out at those different distances, we are also looking out at time. So we have something of the full spectrum of galactic evolution. Even if these events happened "long ago" we should be witnessing them somewhere.

Locally, if these events happend long ago, surely they would have been here by now, harvesting our star.

[talmand]

That's also assuming such things are being being done on a large scale. My point is that we've only had the capability to see such things recently, while the universe is really old.

I personally just don't like definitive statements when there's no way for us to know the whole story.

[kabouseng]

Such as spread spectrum techniques

https://en.wikipedia.org/wiki/Spread_spectrum

[geomark]

Yeah, I was gonna say. In addition to making it hard to detect it also makes the channel robust to some kinds of noise and fading. See Chirp Spread Spectrum for example http://nanotron.com/EN/CO_techn-css.php

[mojuba]

Someone said that if any object in the Universe has a non-zero second derivative of velocity (aka jerk, or "acceleration of acceleration") it's a sign of intelligent life.

Something similar should exist in the information theory. An encrypted signal can't be "too random", there should be some metric that distinguishes an intelligently designed signal from a random one. With spread spectrum and other tricks they can make it harder but not impossible to detect and separate from pure noise.

What is that metric? I have no idea, just trying to theorize. At least the opposite should be true, that for example the cosmic microwave background can not carry any useful/meaningful information other than just "signatures" of the particles that emitted the signal. So there should be some metric that's different for CMB and any signal that has something else in it.

Edit: I don't think the metric in question is entropy, although someone might convince us that it is. The problem with entropy is that, an object that consists of just a few types of atoms may emit a signal that would look very "orderly". That signal would be the spectrum with a few distinct frequencies in it typically emitted by those atoms.

[romaniv]

>An encrypted signal can't be "too random"

It should if encryption is good. After all, security proofs for encryption define "secure" as "indistinguishable from random".

[mojuba]

A signal that contains anything other than noise can not be absolutely indistinguishable from noise. Otherwise you won't be able to decrypt it.

[stouset]

It's computationally distinguishable from noise iff you have the decryption key.

The key word here is "computationally". A signal encrypted with a non-OTP symmetric key can be distinguished from noise without the key — unfortunately, for modern key sizes (128, 196, or 256 bits), the cost of doing so is prohibitively expensive for even arbitrarily advanced civilizations, unless (as Brice Schneier put it) they are building computers out of something other than matter that occupy something other than space.

[DanBC]

> Otherwise you won't be able to decrypt it.

Why not?

[mojuba]

Because the only way to make your signal appear more random is to add more redundancy. In order to make it look like an absolute random signal you'd have to add infinite redundancy.

[DanBC]

Redundant data is compressible data.

Random data is not compressible.

Adding redundant data to random data will make it more compressible - less random.

[toth]

> Someone said that if any object in the Universe has a non-zero second derivative of velocity (aka jerk, or "acceleration of acceleration") it's a sign of intelligent life.

Not sure what someone could possibly mean by that. Pretty much every celestial body has non-zero jerk. For instance, earth's acceleration is (to pretty good approximation) a constant times the $-e_r/r^2$, and the time derivative of that is definitely not zero.

[78666cdc]

The time derivative of that expression is indeed zero.

[toth]

It is not. $e_r$ is a rotating vector, not constant. Also $r$ is not really constant either.

Actually, if you think about it, the only plausible way you could have something in space with zero jerk and non-zero acceleration would be an interstellar ship maintaining constant acceleration, so the suggested rule is almost exactly wrong.

[78666cdc]

I'm afraid you'll have to explain your perspective to me as if I'm five years old. In your original comment, you say,

>a constant times the $-e_r/r^2$, and the time derivative of that is definitely not zero.

I don't see a term there that is time-dependent.

[lotyrin]

A more advanced civilization will have gotten much better at avoiding the energy waste of sending a signal except to where they want it to go.

The Drake equation of detecting intelligent life based on their signal emission needs a few extra terms for accounting for energy efficiency or perhaps even deliberate discretion (https://xkcd.com/1377/).

If we did pass through their data laser or whathaveyou, then perhaps it would be unintelligible encrypted information, but that's not something that seems likely to happen (even if things aligned perfectly, other star systems - particularly those with radio emitting civilizations - are probably too noisy to try to transmit through).

[norea-armozel]

The physics of electromagentism doesn't diverge all that much when you're talking about stray signals from alien satellites or radio arrays. So long as you use the radio spectrum to send signals out to satellites or interplanetary systems (probes, colonies, whatever) you're going to get spotted. Laser signaling may be the only alternative I can think of that wouldn't be so easily detected and probably lower power too, but that's it.

The only other alternative I can hazard speculation on is possibly gravity wave signaling? It's a bit of a stretch in my mind since the only real way to do that is to assume certain kinds of unproven particles like gravitinos (these are supposedly able to be interacted with in superconducting materials last time I read about them).

[toth]

Even without any encryption, a perfectly compressed signal will be indistinguishable from random noise. Of course, it might still be distinguishably artificial depending on how it is encoded, but I believe that the SETI searches that have been done to date would not find that kind of signal.

[autotravis]

> Is there currently human technology that does anything similar to this?

Steganography. Not "background", in the sense that images are generally considered useful, but it is hiding information in a place that a casual onlooker would not think to look.

> Encryption is applied on the data layers not to hide that something is being transmitted, but what is being transmitted.

That's exactly why this encryption would be strong. Initially, no one thinks to look for signals that don't look like signals.

[karmakaze]

Yes, I believe so. Suppose the form of encryption is a one-time pad which specifies which frequencies upon which to transmit each bit. The signal on each frequency is well within the range of background noise. However if listening on a expected successive sets of frequencies bits may be read.

[romaniv]

> Is there currently human technology that does anything similar to this?

Any sort of steganography tries to achieve something similar. I wouldn't be surprised if something similar would be used in military radio communications.

[JulianMorrison]

Yeah, we do it that way, but Moties wouldn't.