Enrico Fermi's paradox has occupied us more than occasionally in these pages, and for good reason. 'Where are they,' asked Fermi, acknowledging an obvious fact: Even if it takes one or two million years for a civilization to develop and use interstellar travel, that is but a blip in terms of the 13.7 billion year age of the universe. Von Neumann probes designed to study other stellar systems and reproduce, moving outward in an ever expanding wave of exploration, could easily have spread across the galaxy long before our ancestors thought of building the pyramids. Where are they indeed. Kelvin Long, one of Project Icarus' most energetic proponents, recently sent me Poul Anderson's thoughts on the subject. I probably don't need to tell this audience that Anderson was a science fiction author extraordinaire. His books and short stories occupied vast stretches of my youth, and I still maintain that if you want to get not so much the tech and science but the sheer wonder of the...

It's been a week with an exoplanet focus, what with the interesting Kepler results yesterday and the five, or perhaps seven, planets found around the same star by the HARPS instrument. But I can't close the week without recourse to Seth Shostak's recent comments on biological versus machine intelligence. Paul Davies took much the same tack in his recent book The Eerie Silence (Houghton Mifflin Harcourt, 2010), arguing that any civilization we encounter will likely be composed of intelligent machines. Shostak thinks SETI should take that seriously. Searching for Doppelgängers Right now we're searching for what Shostak calls 'doppelgängers of humans' -- i.e., SETI has focused on places that could support life forms that do more or less what we do, which includes not only using radio to communicate, but much broader traits like living for finite lifetimes, following basic biochemical dictates and being subject to evolution. That biases the search toward places that could sustain life as...

Although he doesn't post nearly as often as some of us would like, Caleb Scharf's Life, Unbounded site is always worth reading. Scharf, author of the textbook Extrasolar Planets and Astrobiology (University Science Books, 2008) is the director of the Columbia University Astrobiology Center. As such, he's positioned to offer valuable insights into our investigations of the forms life might take on other worlds. Not long ago he wrote a fascinating post for Scientific American on a statistical approach to astrobiology, a timely idea as we discuss ongoing missions like Kepler and proposed space telescopes like WFIRST. Natural Selection on a Galactic Scale Scharf's latest is a quick take on panspermia, the idea that viable organisms may be exchanged between planets as various early impacts spread debris through a planetary system. We know that surface material moves continually between the rocky moons and planets of our own system, and we've also come to understand that microbial...

Although it seems a long way from interstellar space, the early Earth is a fascinating laboratory for life's development that should yield clues about how life takes hold elsewhere. Thus new work on the movements of the early continents catches the eye. In this case, the Gondwana supercontinent is found to have undergone a 60-degree rotation across Earth's surface during a highly interesting period, the Early Cambrian. This is the fecund era when the major groups of complex animals appeared in relatively rapid succession. Gondwana is what we can call the southern precursor supercontinent, a vast region that would eventually separate from Laurasia roughly 200 million years ago when the Pangaea supercontinent broke into two large areas. This Wikipedia article gives you the basics on Gondwana, noting that it included most of the landmass in today's southern hemisphere, including Antarctica, South America, Africa, Madagascar, Australia, New Guinea and New Zealand, along with the Indian...

It's heartening to see James and Gregory Benford's work on extraterrestrial beacons receiving broader coverage. We've looked at the relevant papers in these pages [run a search on 'Benford' in our database and you'll pull up articles by and about them], but news features like this one in TIME Magazine are pushing the Benford brothers' work out to a much larger audience. That's an important step, because right now the view of SETI most likely held by the average person relates to movies like Contact, in which huge dishes pointed at particular stars seem to be the way to proceed. The Benfords want to re-write that scenario in a big way. We'll have to leave as debatable the question about how far away our own television transmissions can be received. James Benford commented here not long ago that a civilization of approximately our technological level would not be able to receive broadcast signals as weak as those we've sent out carrying the likes of Milton Berle and I Love Lucy....