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Comment by BjoernKW | Hacker News Reader

The question is: What could they possibly be using instead of some sort of electromagnetic signals?

There are only a limited number of fundamental forces in the known universe (unless our current understanding of physics is completely wrong), not all of which lend themselves to being used for long-range communication.

Gravity possibly could be used as a means of communication but I suppose it’d be rather slow and have a low bandwidth.

Some sort of quantum entanglement-based form of communication might be possible though that contradicts our current understanding of how information can be transmitted in the universe.

So, barring some fundamental shortcut such as Star Trek subspace, there aren’t too many options for interstellar communication.

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Why not expect new physics we simply don't have the tools to see yet? Maybe something that only shows itself at very high energy or interacts only with neutrinos or antimatter or some exotic matter that isn't produced with fusion or supernovas.

What about beings that operate at very different time scales? What if there is some encoding scheme that blows our information theory out of the water so communication just looks like white noise?

What if evolution converges to a single shared consciousness or fierce independence and communication just stops being interesting after a certain stage? Or if non-interference is the very well enforced law of our corner of the galaxy?

I think it's hubris to think that we know the answers to all of the questions for physics or at least we know what we don't know. My assumption is that there are questions/problems/phenomena that we don't even have the context yet to imagine.

Then the answer is: we can only rule out intelligent life as we CAN immagine it. Sure, there could exist intelligent life of sorts that we cannot comprehend, that use physics outside of the standard model; God perhaps?

> What if there is some encoding scheme that blows our information theory out of the water so communication just looks like white noise?

You don't even need a new encoding scheme for that. Compressed data looks like white noise unless you know the decompression algorithm.

Compressed data doesn’t looks like noise correctly encrypted data can.

That said however metadata will often be unencrypted and even encrypted data will have discernible patterns for example the transmission of say a 2.4ghz radio network with packets will look like white noise even if all packets are encrypted as you need to somehow modulate the signal for transmission control.

Under _our_ technology, yes. Why would that be so for a civilization even a hundred years more advanced than ours, never mind millions? Why would they be doing planet-scale broadcasts _ever_, instead of focussing the communication as tightly as they could in the right direction?

There's so many assumptions that they'll basically use a version of modern technology but bigger in the "why can't we hear them?" question. Tight-beam, fully encrypted data with sensitive receivers could easily be utterly undetectable by our understanding.

Well the beauty of the universe is that cannot be used as a good reason.

If civilizations are common then there are just as many less advanced civilization than us than they are more. Heck if technological progression leads to the downfall of a species than by default everyone we should be seeing is around our own level of development if not lower.

If intelligent life is an anomaly then it can be very well be that in the life span of an existing civilization they would be the only intelligent one in the galaxy or even beyond that and they would simply die out even 1M years is a blink of an eye for universal time scale.

And lastly regardless of what the civilization is today if they are on the other side of the galaxy we see a 100,000 year snapshot if they are in say another galaxy even a close one like the Andromeda galaxy we see them as they were 2.5M years ago.

Tight-beam, tachyon transmission, quantum entanglement with retro-causality suspension or w/e they might be using if they are so advanced beyond us that we look like anthills to them is fine but at some point they were just as advanced as we are and less so that's the noise that we should be hearing and we aren't.

I always wonder, if you draw a sphere around earth, some amount of light years away. How much surface of that outside sphere has our signal gotten in contact with. (for the sake of making it easier, say that all signals capable or reaching this distance, have done so)

Something like this:

http://www.planetary.org/blogs/emily-lakdawalla/2012/3390.ht...

That's assuming the exact opposite of this paper; that there's _infinite_ other civilisations, which is as obviously untrue as the idea that there are none.

If the period of time before all high-power communication is encrypted is short, then the likelihood that the period of our ability to pick up unencrypted high-power communications will intersect it is potentially very low.

The universe is _huge_. Most of our communications will not be audible above background radiation after a little way out - this could be no different for any other civilisation's communication technology. You don't use a nuclear reactor to power a cell tower, and if you don't put that much power into it then it's not gonna be detectable ten light years out.

Encoded data can sounds just like noise. Take Olivia for instance. It can transmit digital data at 14dB BELOW the noise floor. It's just a digital mode that hams use to try to transmit between countries for around 1 watt.

A signal with compressed data does not look like white noise. It looks like a sine or cosine wave that is around a well defined frequency, and the intensity/phase/frequency changes from time to time. The hops may look random, but the carrier signal is easy to spot.

If they use frequency hoping, the changes in the frequency are even more regular. It's more difficult to measure the exact signal, but all the hops are inside an interval.

You’re probably more of an expert but what you’re saying is totally unintuitive to me.

If a signal carries the “this looks like a signal” information in addition to the source information itself... isn’t that a waste of bandwidth? Wouldn’t an ideally encoded stream be indistinguishable from noise?

I can understand for practical reasons leaving some bandwidth on the table to make it easier to detect signals, but when talking about advanced alien life forms we have to assume they are playing closer to the limits of physics.

You are describing FM, which does dump quite a bit of power into the carrier wave.... which is exactly why it's not used if you care about range/efficiency.

Check out things like "Olivia_MFSK" on wikipedia for something more current. It can transmit even with 14dB below the noise floor.

Seems like a any sane communication method for any galaxy spanning civilization would be: * encoded in such an advanced way that we wouldn't see it, even if using signals within our physics. * be highly directional

Maybe something like 1% of the asteroid belt would be converted into communication sats that could form a swarm that would over a few ns significant outshine the sun by focusing a signal on whoever you want to communicate with.

Of course typically the cloud of sats would be handling within the solar system communications or nearby stars that didn't require the entire cloud.

I do wonder if you could capture say 0.01% of the solar radiation for 24 hours and with 50% conversion frequency generate a single for 1 ns on the ideal frequency... could you outshine the galaxy on that frequency?

Of course the ideal frequency would be minimally blocked by dust and minimally generated by stars. The "Water hole" as mentioned by Seti (among others) would be a good start.

The fundamental forces are a starting point, but it's not right to assign special significance to EM. The great majority of mass in the universe does not feel electromagnetism. It's dark matter.

Humanity's expertise in electromagnetism is driven by our biologically EM-sensitive eyes, our physical size, the energy levels that permit classical chemistry, and the timeframe in which we live our lives.

Perhaps aliens exist with much larger physical forms, communicating with neutrinos over vast distances and larger time scales. Humanity would be completely blind to these signals.

EM is much easier, any moron wit a HAM radio can broadcast to the whole Earth, and a similar upgraded version that is still small and cheap can be used for interplanetary communication. So I'd guess EM for usual communications, but the idea of something weird like neutrinos for special purposes is nice.

I don't know the size of the current neutrino transmitter/receivers, but IIRC the size is about a big building. Even the initial EM device where smaller.

About dark matter, the current understanding is that it is diffuse and there are no "dark star" or "dark planets", but I always prefer to wait 10-50 (100?) years to call it definitive.

> Gravity possibly could be used as a means of communication but I suppose it’d be rather slow

Doesn't gravity "travel" at the speed of light just like EM radiation?

Yes but the frequency is way lower, so maybe less information/time.

Or an advanced civilization uses low power transmission with high compression codecs, maybe with spacial (cellular) dispersion.

Which of our modern transmissions would be decoded by someone from 75 years ago?

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