The Fermi Paradox focuses on the existence of advanced civilisations elsewhere in the galaxy. If these civilisations are out there--and many analyses suggest the galaxy should be teaming with life--why haven't we seen them?
Today Carlos Cotta and Álvaro Morales from the University of Malaga in Spain add an another angle to the discussion. One line of thought is the speed at which a sufficiently advanced civilisation could colonise the galaxy. Various analyses suggest that using spacecraft that travel at a tenth of the speed of light, the colonisation wavefront could take some 50 million years to sweep the galaxy. Others have calculated that it may be closer to 13 billion years, which may explain ET's absence.
Cotta and Morales take a different tack by studying how automated probes sent ahead of the colonisation could explore the galaxy. Obviously, this could advance much faster than the colonisation wavefront. The scenario involves a civilisation sending out 8 probes, each equipped with smaller subprobes for studying regions that the host probe visits.
This is not a new scenario. One previous calculation suggests that in about 300 millions years these 8 probes could explore just 4 per cent of the galaxy. The question that Cotta and Morales ask is: what if several advanced civilisations were exploring the galaxy at the same time? Surely, if enough advanced civilisations were exploring simultaneously, one of their probes would end up visiting the solar system. So that fact we haven't seen one places a limit on how many civilisations can be out there.
The numbers that Cotta and Morales come up with depend crucially on the lifetime of the probes doing the exploring (and obviously on the number of probes each civilisations ends out). They say that if each probe has a lifetime of 50 million years and that evidence of them visiting the solar system lasts for about a million years, there can be no more than about 1000 advanced civilisations out there now.
But if these probes can leave evidence of a visit that lasts for 100 million years, then there can be no more than about 10 civilisations out there.
Oh good grief.
First off, a space probe that lasts 50 million years. I'd be impressed if we - or any civ within 2k years - would be able to produce one that lasted for 10k years. Sheesh.
Second of all, we have no evidence that the space exploring critters will last that long. Criminy! There's not been a single synapsid or diapsid that's lasted even 10 million years. Please keep in mind, 7 million years (+/-) is the time frame we split from other apes in our evolution and the longest living species ancestral to us was Homo erectus...and it lasted almost 1 million years. Between 7 mya and now we've had at least 6 species "generations" (mostly likely a lot more).
Do we really expect our descendents 6 to 20 speciesial generations later to be doing the same things we will be? Or try to be? How can we make an assumption that any other race will be doing the same through x number of speciesial generations?
The scenario involves a civilization sending out eight probes, each equipped with smaller subprobes for studying the regions that the host probe visits.
ReplyDeleteOr a total number of probes ever equal roughly to one tenth as many probes as humans have launched since the beginning of the space age a few decades ago.
The numbers in the putatative scenarios are ludicrous as you point out. I'd be embarrassed to be an author of that study.
ReplyDeleteOne reason I read this excellent blog is the intriguing mix of evolutionary science and space science. Too many of us physics oriented space cadets spout nonsense like "It's inevitable that intelligence and technical civilizations evolve because evolution proceeds towards evolving high intelligence. Therefore the Milky Way is filled with technical (radiotelescope savvy) civilizations."
It's refreshing to look at these fun unanswered questions from an evolutionary biologist perspective.
The funny part, Phil, is that I am not a space scientist[1] nor am I a evolutionary biologist.
ReplyDeleteI am actually a sysadmin of big monster computers and have some background in physics.
I just like this stuff and learn about it as much as possible.
1. Rocket scientist I may actually count as. lol.
Yes, you've posted your computer sysadmin job info many times in this blog. In my brief comment I didn't mean to give you creds you don't claim. I do love the elcectic mix of topics here.
ReplyDeleteNot only does one have to realize that not all life-sustaining planets with mutlicellular life (or else the potential to develop sentience) will even develop sentience.
ReplyDeleteThen one must realize the span of time which a civilization is able to point telescopes at the stars (we were sapient for over a hundred thousand years, but didn't even start leaving a footprint on space until the sixties. And while we did have telescopes before then, I'm not sure if they were incredibly useful if we wanted to find any alien species). One has to consider that we may be abnormal for having only a single "Dark Age", other species may develop to Rome, Rennaisance, or even further levels culturally, and then get knocked back to the Stone Age by some minor extinction or such.
Now consider this: maybe a species that can go interstellar just doesn't want to. We assume that all alien species have our mindset, and have first contact on their mind the minute they set off into the "final frontier". There could be species out there who ventured around their solar system, got bored, and then decided to stay on their homeworld (we, ironically, have parallels to this). Or they preferred to eschew space technology in favor of feeding their population or eliminating diseases.
The final point is that space is big. "Really big. You just won't believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist, but that's just peanuts to space". If a sapient alien species starts chucking interstellar probes out there, what are the chances that we'll see it unless its lucky enough to get stuck in our gravity or come crashing to Earth. I mean we've just been able to detect planets that are the size of Earth, how could we spot a dinky little satellite.