Forget SETI, this is how you find aliens: Hefty prof speaks
The truth is out there. Or maybe in here, actually
Magnetic monopole thieves may have left an IOU at the L4 point
However, if intelligence is not in fact an evolutionary dead end, we might look instead for the marks and signatures that super-advanced technology might leave. Rather then primitive radio signals, Davies thinks better results might be obtained by probing for the unique signatures of mighty astro-construction works such as "Dyson Spheres"***. Alternatively, near-future planet hunter telescopes and techniques might be used to probe alien atmospheres for industrial pollution of various kinds. Or, puissant ETs might be sniffed out by the neutrinos or gamma-rays belching from their advanced nuclear or antimatter powerplants.
Davies has pondered, too, on the so-called "Fermi Paradox", which suggests that if there are any interstellar-colonizing alien empires about they ought to have expanded through our solar system - or at least visited it - long ago. So where are they?
The professor points out that they may well have been and gone millions of years ago, perhaps mining our solar system bare of some valuable resource we don't even know about (naturally, as the thieving aliens have nicked it all) and departing while our remote microbial ancestors were still thinking about assembling themselves into primeval slime.
Davies thinks it's plausible, though, that the ancient visitors may very well have left behind a message, monument or probe of some kind. This would not be on Earth's surface, of course, as the smart aliens would know that would lead to it being destroyed or buried by the constant churning or the planetary crust as seen over these terrifically long timescales.
Rather, says the prof, it would make more sense to look for such a thing on the Moon or at the gravitationally-stable L4 and L5 points, where a spacecraft needs to expend no power to hold position. Beaming an active-SETI radio message at these positions, speculates the prof, might awaken some aeons-dormant machine left behind by the aliens who snaffled all our magnetic monopoles, which would then automatically hook up to the internet and brief us on the galactic scene.
If that's not enough to be going on with, Professor Davies has more - messages written in our own or other organisms' genetic code, "post-biological" aliens who have abandoned their flimsy flesh bodies to live as augmented computer intelligences in superconducting quantum computers (situated in intergalactic space to benefit from the cold there, naturally) etc etc.
Much of it is laid out in the IOP article here. Alternatively there's more detail in the prof's latest book, The Eerie Silence: Are We Alone in the Universe?, available this month from Penguin. ®
*So named for the notation made on the margin of the "Big Ear" telescope's data printout by the discovering boffin, Jerry Ehman.
**WARNING: IT angle.
***In which a powerful civilisation might enclose its sun in a colossal sphere, so creating unbelievably huge amounts of useable land area compared to measly little planets.