Thu, 13. December 2012
Do You Think We Are Alone in the Universe?
Recently I followed a Facebook discussion in response to the question: "Do you think we are alone in the Universe." Of the fifty or so responses, most of them - with no evidence except a diet of tv science fiction - were decisively convinced that we are not alone. Only two of them thought to the contrary.
Many answers to the question were glib and ignorant:
- "I think aliens made us by some genetic engineering."
- "People don't realise our radio signals haven't gotten far at all. Probably not even to the next solar system."
- "I still buy into an idea that homo sapiens are the direct result of a deliberate genetic mutation."
- "Absolutely not - though probably not sharing our physical laws."
- "Not because one cannot prove that something does exist, then it does not really exist. So far, there is no known evidence, but induction does not always work!"
- "You must be kidding, right? I mean this is a VERY illogical question considering the IMMENSITY of THIS Universe. Alone... LOL."
<sigh> There goes that same old accusation of arrogance again! Star Trek has a lot to answer for....
I was beginning to think that none of them cared to really think about the existing knowlege we have about alien life-forms so far (i.e. nothing) before rushing into print, until I saw one person out of the fifty give a very sensible answer:
"Depends what you mean by, "alone". The odds of there being other life forms in the universe are pretty high. The odds of there being life forms with the potential to develop communication and spacefaring technologies is probably comparatively rarer. The odds of any of those life forms existing anywhere near us or during the same time frame as us, is probably extremely remote. And the odds of any of those beings visiting us right now... I wouldn't bet on it. So ultimately yes, I think for all intents and purposes, we are alone."
Spot on. The chances that life has arisen elsewhere in the Universe during its 13.7 Gigayear history are probably fairly good but the freakish series of evolutionary accidents which led to human beings on Earth may not easily replicate everywhere else. So it is quite likely that a planet which does develop life might go through it's entire biological history without ever being dominated by intelligent beings.
So many people assume that "intelligent" civilisations are inevitable in large quantities - in our galaxy and in our neighbourhood right now. We really don't know - but intelligent civilisations could be much rarer than most people think. SETI defines intelligence as a communicating civilisation - a civilisation which has developed the means for inter-stellar communication.
It also hinges on the average lifetime of such civilisations. We have been a communicative civilisation for only a few decades, so the chances of finding another communicative civilisation of at least the same level of advancement as us would be extremely remote. Communicating with a civilisation beyond, say, fifty light years can have little meaning, because we could respond but it would take more than a century to get a reply.
A fifty light year radius is nothing compared with the size of the galaxy and the chances of finding a communicative civilisation within fifty light years at the same point in time as us are very small. Within this huge volume of space, there are roughly 1400 star systems, containing 2000 stars according to this website. It's not many!
Whilst there are an enormous number of stars in the galaxy, their lifetimes cover an immensity of time. The Milky Way is 13 Gigayears old. If we took what I consider to be an optimistic view, that a communicative civilisation might, on average, last for 1,000 Earth years (before it is destroyed either by natural disaster, technology or religion), and if we modestly assume that an average of just two civilisation exist in the galaxy at any one time, then the rise and fall of a monstrously high number of 26 million communicable civilisations would have occurred in the galaxy over its entire history. That's a lot.
We could very easily be alone in the galaxy right now but on the other hand we might not. How awesome to imagine the entire galaxy of billions of stars with only us looking out in wonder at it - but how much more awesome still, to learn one day that others have evolved to unravel the mysteries of science as we do and seek a dialogue with us. It seems enigmatic, whichever way you look at it.
We must keep on trying but I am very pessimistic about hearing from an advanced civilisation in our galactic neighbourhood. The chances of chatting with civilisations beyond fifty light years is not much higher because of the weakening and degradation of signals over immense distances and the time lag between each response.
So, are we alone? I really don't know but it seems increasingly likely that we could be.