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If there is a faster-than-light particle in this universe, then that is what intelligent life would use to communicate.

SETI-like efforts have a big handicap for a different reason. To oversimplify a bit: any signal that is distinguishable from noise is a waste of energy.

Right now, in the name of spectral efficiency, we're migrating our legacy systems (such as TV broadcast) to modulation formats that sound exactly like white noise to a receiver that doesn't know the coding scheme... and never mind encryption, which has the same effect. Other races will be confronted with the same problems, and will use the same solutions, to the extent they use wireless for medium- to long-range communications at all.

So, the only way we'll detect intelligible signals from an alien world is if we happen to catch them between their development of communications technology and information theory. This is a pretty narrow window -- only about 100 years in our case.

If SETI has any hope at all, it will lie in detecting deliberate beacon transmissions, not incidental RF. But some smart people have argued that attracting attention with such a beacon would be a mistake, possibly the last one the species in question ever makes.

"Other races will be confronted with the same problems, and will use the same solutions, to the extent they use wireless for medium- to long-range communications at all."

This seems a little ahistorical and antropocentric to me.

Ahistorical because even humans have avoided using certain technologies for a variety of reasons -- from certain weapons (chemical/biological, cluster bombs, nuclear weapons, etc) to pesticides, communications technologies, certain programming languages, etc. despite their arguable technological superiority or ability to get the job done.

Anthropocentric because, really, who knows how aliens would think or what they would do? Your argument applies, if it applies at all, to species that think and act much like us. It is debatable whether radically different intelligent (a term which we don't understand even when we apply it to ourselves) species would even understand something as "fundamental" as mathematics the way we do, nevermind actually use technical artifacts in a way recognizable to us.

On the subject of recognizability, could bacteria recognize the humans that they dwell on as intelligent or even living? Can they recognize anything at all? As bacteria are to us, so we may be to alien intelligent life, or even to potentially intelligent life here on earth such as trees, superorganisms like insect or fungal colonies, etc. Organisms that operate at radically different time scales or radically different ways of relating to the world.

Some have argued that the Earth is an organism with agency, or the Internet is one. If that is so, how would we recognize these as such, how would we communicate with them, if it is possible? And if communicating with these on Earth is so unlikely, how much less the likelihood of communicating with beings from other star systems or galaxies utterly unlike that of our own?

If they don't use radio technology we'll of course never hear from them - at least not via SETI. So, when it comes to SETI being effective, the interesting case is where the aliens are using radio technology but never advance their modulation technology to the point where the signal is no longer obviously artificial to an observer without knowledge of the coding scheme. It is of course difficult to say whether this is likely to happen; however, it seems contrived for a species to exist that is okay with using math and physics to construct and operate high-power radio transmitters, but refuses (or is unable to) use math to reach the next level of spectral efficiency.

This seems a little ahistorical and antropocentric to me.

No, the principles involved are absolutely universal. They have to deal with the Shannon limit on Altair 4 just like we do here.

Stanislaw Lem used the idea of neutrinos-for-communication as the cause of the "silent universe" in His Master's Voice, which is possibly the best fictional account of how science actually works that I have ever read. Highly recommended.

It possibly gives an excuse for the lack of transmissions visible, but simple efficiency considerations already explain that. You transmit with the minimum power that works (plus margin), with as much focus as you can get.

Tachyons cannot be used to communicate FTL even though they have v > c. See http://math.ucr.edu/home/baez/physics/ParticleAndNuclear/tac... for a cool explanation.

Regardless, neutrinos would seem to be a viable communication medium. SETI is considering how they may be used: http://www.seti-setr.org/SETI/neutrinos.html

"When a distinguished but elderly scientist states that something is possible, he is almost certainly right. When he states that something is impossible, he is very probably wrong." -- Arthur C Clarke

Funny thing is there has already been some success towards using neutrinos to communicate here on earth (http://physicsworld.com/cws/article/news/2012/mar/19/neutrin...). While it's nowhere near efficient currently; I won't dare imagine what could be achieved given a few more years of research.

Interesting. I had to look up what the Fermi paradox is: http://en.wikipedia.org/wiki/Fermi_paradox

But this doesn't solve why the Earth wasn't already visited/colonized, correct?

The nearest life-bearing planet is most likely hundreds of light-years away. Faster-than-light communication doesn't mean faster-than-light travel, and nobody wants to sit in a spaceship for 200 years.

True, but the Fermi paradox is about the question of where's everybody, not where's the next galactic pub.

You take a right at Barnards star.

But suspended animation, often used in science fiction films with long spaceflights in them, would make a 200-year-long trip seem an awful lot shorter. I don't think it's too unreasonable to assume that a life-form that achieved near-light-speed travel will have also discovered a way to lie dormant during the trip if necessary.

Also, there's no telling how long an alien life-form might live, or how patient they might be. Basing things on human lifetimes and personalities seems a little anthropocentric given that we know practically nothing about alien life.

As long as we're doing away with assumptions, we should also throw out the one that aliens have a desire to propagate and colonize across the universe.

If you can get near light speed travel, then time dilation means that you won't experience a 200 year trip, only those you left behind. So any species venturing on a one-way trip wouldn't even blink at the prospect of light speed getting in their way.

I'm not a physicist, but as I understand it, it takes light 1 year to travel 1 light-year.

If the nearest life-bearing planet is hundreds of light-years away, even if you could travel at the speed of light, it would still take you hundreds of years to get there, from your frame of reference.

Time dilation just means it would appear to take even longer from the frame of reference of those you left behind (or those you were headed towards).

In the frame of reference of a photon, no time passes between emission and absorption, regardless of the distance it travels.

We haven't even ruled out life on the closest planet to us yet. (Or Mars.)

>We can assume that aliens that are smart enough to reach the level that they figure out what a neutrino is, would also, eventually, figure out a way to use it to communicate.

You can't just assume that understanding a law allows you to violate it. Understanding leads to some advantage, but it may well just be a diversion of resources away from trying the impossible. If it is inherently contradictory that FTL neutrinos can be used for communication, then what you are suggesting is obviously wrong. And seeing as how you don't know that, you'd be foolish to assume it.