The question is how such an encyclopedia (or other one-time communication) should be designed so that the aliens can actually understand it. They will not speak English and likely will not know to translate radio wave signals into the same sort of audio that a hand-radio here on Earth does. Scientists have attempted to come up with as universal and non-anthropocentric a solution to this problem as possible. One early attempt was made with the Pioneer 11 mission, which attached to the ship the plaque pictured below in case it eventually somehow stumbled upon an alien civilization (chances: way less than slim considering the tiny size of the ship in the immensity of space).

The plaque attempts to represent the hyperfine transition of hydrogen (which would happen in any part of the universe and probably be known by any advanced scientific and technological intelligence) in order to set up a unit of length - the wavelength of this transition.

Built on that, with various scaling, are pictorial representations of the spaceship itself, a human man and woman, our solar system, and the relative position of our sun to the center of the galaxy using the location of pulsars (which could be seen from elsewhere).

The pictures make some sense when they are explained to the reader. For example: the lengths of the lines at the middle left show the relative distances of the pulsars to our sun and a mark at the end of each line gives the Z-coordinate perpendicular to the galactic plane. Ticks above each planet in the layout of our solar system give the distance to the sun in binary. The humans are drawn against an enlarged portion of the image representing the ship in order to establish scale. The ship itself is attached to the representation of Earth by a line to show that it came from Earth.

But simply looking at the picture, how many humans could identify its meaning? Almost none of the human scientists originally shown the message could, so what is the chance an alien species would? Creatures evolving in such a different environment would likely not think or perceive exactly as we do. If they have a sense that might be called vision, it likely is not the same as ours. After all, consider the difference between our vision and that of a squid or a bat. It is almost silly to imagine that they would think pictorially in the same way we do (interpreting scratches on the plaque as geometric lines, when they might perceive and put together their perceptions under a different geometry than ours, e.g.).

Studying the problems of the Pioneer plaque might help understand the anthropocentric pitfalls we run into in trying to design a message for a species about which we know nothing but that it is intelligent and technologically advanced enough to receive our signals. So how then do we go about transmitting ideas and knowledge to an extraterrestrial intelligence?

Chess Grandmaster John Nunn attempts to tackle part of the problem here. He conjectures that because they can receive and interpret our radio signals, they must have some sort of information processing system - in some sense a computer, though likely very different in physical implementation from our own. If we can get them to grasp the few simple logic gates that underlie our own computers, he suggests that the aliens will be able to reconstruct something that functions just like our own computers, even from vastly different materials. He cites the Church-Turing Thesis, which effectively states that any computer can run any algorithm, or as Nunn stretches it: any computer can emulate the operation of any other.

Assuming he is correct, once we got around the problem of explaining our logic gates (certainly not easy, but probably no harder than trying to communicate our sun's distance from the center of the galaxy, as the Pioneer plaque authors did) and they grasp that we want them to emulate a computing machine that can run a program we write, then we can send a program of whatever size and complexity we wish (they need merely load the instructions as they come in).

The sort of program he suggests sending is an artificial intelligence (once we have built or evolved them). An AI could be programmed not only to hold all the knowledge we have stored up and wish to send, but also to adapt to the situation it finds itself in and act as a sort of representative for Earth. A program can be easily transmitted at the speed of light whereas an actual human representative cannot. This seems to allow for the most efficient one-way, one-time communication until many years or lifetimes later when a return signal could reach us.

Of course, I am not sure Nunn's solution has less assumptions than that of the Pioneer plaque's authors. How to communicate the workings of the logic gates on which our computers are built might not be easy - even if they have the concepts of a computer and build their information processing systems on universal mathematico-logical operations similar to our own, how do we make it clear in the first place that that is what we have sent them?

Nunn suggests that it might take a long time for them to analyze our message and deduce its meaning, which sounds reasonable until you imagine humans trying to decode some arcane, mysterious message from aliens. If it were not obvious in a relatively short time, the real meaning would likely be flooded over by countless other crazy hypotheses and there would be too many possibilities to try them all out.

Perhaps, though, we can eventually come up with some way to be more clear what we are suggesting they do with the information. Once this initial hurdle is cleared, feeding the transmitted program into the computer should not be a problem. However, Nunn virtually ignores a major problem with his idea. Once the AI program is up and running, what exactly is its user-interface going to be like? Certainly it will not prompt the aliens in English (or else we would not have had the communication problem in the first place), but then how will it interact with them? It appears things are actually back at square one.

The only thing I can think of is that whatever way we found to make clear our intentions for having them put together the computer would give enough of a communication basis on which to start off some other very simple communication which is independent of the input-output interface (their information processing systems may be able to emulate our own as far as computing any algorithm and thus running any program, but they surely will not have pixel-displaying monitors like our own). At least once some basic start has been made, an intelligent enough AI could theoretically keep adapting to their attempts until it was able to establish a workable method of more in-depth communication.

While the suggestion of sending an artificial intelligence program in the end does not actually get around the initial problem of establishing the simplest communication (getting from a radio signal to meaningful symbolic information), it does seem to present a more thoughtful and useful alternative to just broadcasting a larger and more complicated version of the Pioneer plaque (i.e. Encyclopedia Earth). Whether the AI would fairly represent our own intelligence and civilization is another question, but surely it will come closer than a static 'book'.

Of course, Nunn suggests another reason why we should send an AI program: it could bargain and trade with the alien species in what he suggests is the only viable interstellar commodity between two civilizations which are merely broadcasting to each other over vast distances and not actually meeting in person: information. We share certain parts of our knowledge in exchange for their verification to the AI that they have broadcast some of their knowledge back toward Earth to eventually be received by us.

This entire notion of Nunn's seems absurd though. He thinks that our knowledge could be encrypted in such a way that only the AI could access it to dole it out as necessary. Perhaps that is so, though I suspect a sufficiently advanced civilization might be able to break our own attempts at encryption since we are handing them the source code to the tool that does the decrypting. However, even if things could work as he suggests, there is a fundamental flaw in his premise that knowledge is a viable commodity.

Any other civilizations out there will have come about at different times in different solar systems and the chance that any species we communicate with has been around for roughly the same amount of time as our own civilization is miniscule. Look how much we have adapted and changed in just the few decades since radio technology was invented: imagine how we will change in a thousand more years if we do not destroy ourselves. Surely an alien civilization which has been technologically improving for thousands or even millions of years longer than us will be far beyond our own in terms of scientific knowledge and the like. Given our own youth (a mere newborn civilization in the cosmic scale of things), it is of course most likely we would be the younger of the two if this communication happened anytime relatively soon.

Since the other civilization is likely much more advanced than us, it is laughable that we would have much to offer them in terms of bargaining knowledge for knowledge. Consider how out of date our knowledge will be to ourselves in fifty years time - if it takes fifty years to send our signal and fifty years to get back their response, what we had to offer will be old news and it is doubtful it will be worth any of their knowledge which would be useful to us one hundred years later. I think in all honesty we have to assume that if we are going to get any knowledge from them, it will be a choice made based on their own benevolence (or other motives) and not because of the knowledge we can offer.

Should the entire AI idea be scrapped them? Of course not. For one thing, there might just be benevolent civilizations out there. Our own history shows how quickly a technological civilization can gain the power to destroy itself (nukes and pollution now, perhaps nanotech grey-goo overrunning the planet before long), so it is plausible that those civilization which can successfully find a way not to destroy themselves have found a way around the simplistic malevolence and greed that would closed-fistedly keep a tight grip on all knowledge.

More than that, though, it is arguable that it would be worthwhile to share our knowledge and thoughts and collective experience with another species even if it is not going to send us back new technology or scientific information. There is something amazing about sharing and communicating with another intelligent civilization in the first place which is valuable in and of itself.

Imagine if you were one of only a few disparately located humans stranded on islands across an uninhabited Earth. Would you not find something rewarding in sending out a message in a bottle and knowing it will reach someone else, even if you never meet them in your lifetime, even if they are unable to send you back food or tools in exchange?

To share and communicate with an intelligence which evolved half way across the galaxy seems vastly more amazing. So sharing our knowledge freely does seem a reasonable direction for our attempts at interstellar communication to move in once we have developed a reasonable artificial intelligence.

Of course, if this is such a logical solution to the problem of talking to extraterrestrial intelligences, no doubt other civilizations more advanced than our own will have stumbled upon the idea (if not a better one, that is) and will send or have sent their AI blueprints our way (depending on whether they know of us yet or are just sending out a blanket signal).

Which means if we get a message from the stars it likely will not just be a simple hello like the Pioneer plaque, showing the shape and size of their bodies and what solar system they come from (the latter information probably being obvious for radio or light signals). Instead it might be a method for constructing some sort of technology for establishing instantaneous communication with a representative from their solar system.

Finding any such signals which are aimed at us and arriving right about now - let alone deciphering them - is another problem we will have to tackle when we get to it, but for now the search for a clear communication signal among all the static is still going on.