Wolfram: Gosh! And there I was thinking that the octahedra were just supposed to be simple beacons, flashing like lighthouses or something. Not intelligent objects at all. I guess that just shows how difficult it can be to tell whether something is supposed to be intelligent or not!

Anyway, all this stuff about the natural versus the artificial definitely isn't just of theoretical interest. After all, we have picked up all sorts of mysterious radio signals from the cosmos. There were some very regular ones first discovered within a few weeks of when 2001 came out; every few milliseconds an intense radio burst arrived from the Crab nebula, and other places. I guess at first people thought that perhaps this was a sign of extraterrestrial intelligence -- but then they realized it was just a common or garden-variety natural neutron star. Well, now we know that the radio pulses from neutron stars aren't actually perfectly regular; they have little modulations and so on. Are these modulations a sign of extraterrestrial intelligence? A signal superimposed on a carrier? It's incredibly unlikely -- a much better theory is that the modulations come from quakes in the crust of the neutron star. And one reason one might conclude that is that the modulations seem fairly random; they seem too complicated to be artificial. But then, of course, if they were simpler, we'd probably assume they weren't produced by much of an intelligence.

Stork: So what kind of thing would make us sure we had detected extraterrestrial intelligence? What about receiving the digits of pi?

Wolfram: Well, that's a tough one, for two reasons. First, how would we know that there was a complicated intentional intelligence generating those digits? You see, I've found some very simple systems that generate things like the digits of pi -- systems so simple that we could easily imagine they'd occur naturally, without intentional intelligence. So even if we found the digits of pi, we'd have a hard time being sure that the thing that produced them was something like us -- a really complicated, evolved, learning, thing -- rather than just something like a piece of fluid.

Then there's a whole other problem: how would we know that we are receiving the digits of pi? You see, the digits of pi seem effectively random for essentially all purposes. And we certainly don't have any idea how to build some kind of analyzer that would systematically detect the digits as nonrandom. Well, the obvious question is: are there, in fact, radio signals that could be the digits of pi coming from around the galaxy? The answer is definitely yes. If you point a radio telescope in almost any direction, you'll hear radio noise. Maybe it's all thermal emission from hot gas, but maybe -- just maybe -- there are the digits of pi out there. We don't right now have any way to know for sure.

Stork: So, by your definition, do you think there is extraterrestrial intelligence out there?

Wolfram: Oh, I'm sure there are lots and lots of systems that can do computations as sophisticated as working out the digits of pi. We've got lots right here on earth. But we don't call them intelligent. Even though some of them seem to have a mind of their own -- like the weather. But I also think there are probably lots of extraterrestrials out there of the kind you're talking about -- with lots of history, evolution stuff, and so on.

Stork: Will we find them?

Wolfram: I expect so. And probably eventually the argument about whether the signals we get from them are really natural or artificial will die down. But my guess is that history will work out so that we build artificial intelligence in computers before we find extraterrestrial intelligence. And the result of that is that finding extraterrestrial intelligence will be considerably less dramatic to us. Because by then we'll already know that we're not the only intelligent things that can exist.