I haven’t quite given up on my childhood dream of meeting an alien. The nice sort, a Vulcan like Mr Spock, from Star Trek – not the nasty kind that Scully and Mulder always encountered in the X-Files, or those featured in lurid accounts of UFO abduction stories that I read as a wide-eyed adolescent. I was thinking more of ‘The Alien Who Came to Tea’.
The possibility of there being other sentient life in the universe is something that still fascinates me. Despite, that in the intervening time, I have learned that the universe is much bigger than my imagination can contain, and the the likelihood of there being another planet hosting sentient life within spitting distance of Earth is perhaps much smaller than I could have hoped. But this doesn’t stop me thinking about the science of it, even as a dilettante. Exoplanets are popping up like daisies in the cosmic grass, and it is likely that most stars have planets. Pretty well all of the planets discovered so far are not obviously habitable by humans, or humanish tea-drinking aliens. These include: crazy hot Jupiters, mad eccentric Neptunes and unfriendly star-hugging super-Earths. However, it is important to note that the detection of Earth-size planets at Earth-like distances from the sun is very much harder to achieve than for the larger ones close to their stars, but the detection of exoplanets is improving rapidly with technology and methodology, and the next few years will change this profile significantly. There is no good reason that there is not an extended family of sister-Earths out there.
Going back to my musing on possibilities – what do I mean by ‘bigger’ and ‘smaller’? These scales are all orders of magnitude from our ordinary experience. Perhaps a benchmark is that it takes eight minutes for light from the sun to reach our planet, which is about 150 million kilometers away. It is often scaled as ‘one astronomical unit’ – 1 AU. Our solar system out to the Kuiper Belt (the outermost rubble of our solar system) is about 100 AU across. That’s about 800 minutes in light terms. To the Oort cloud – a roughly spherical shell of scattered icy planetessimals that surrounds our system – extends out to 100s of thousands of AUs from the sun. For light to get to the Oort Cloud will take of the order of 10 to the power of five (one with five trailing zeroes – or 100, 000) times eight minutes to reach us – around 13 thousand hours or 1.5 years. That’s a good chunk of the distance to our nearest star – Proxima Centauri, from which light reaches us in four years. A radio signal from Earth to the centre of our galaxy would take 27,000 years. Travelling edge to edge of our galaxy would take about 200, 000 years at the speed of light. Our galaxy is one of a ‘local group’, which is in turn part of a supercluster of galaxies. In each galaxy there are about ten to the power of eleven or twelve stars, and we can see a similar number of galaxies in the visible universe. So we are talking of a very large number of stars. And another factor of ten or so more planets. So given, say ten to the power twelve stars in our own galaxy, perhaps we could come up with a few habitable planets scattered within it.
But even with light speed travel, one cannot evade the relativistic puzzle of space-time, wherein the act of going fast to somewhere, means that your own world – home, family, friends, is going into the past. For, by the time you get back home again – experiencing a few years’ absence on board the Starship Whatever to get halfway across the galaxy, the Earth has aged tens of thousands of years. For human scales, this is a bit of a downer.
There are arguments as to whether relativity is a complete explanation, and whether consciousness could survive going at light speed. We could invent the warp drive or uncover a wormhole, but even if we could get round all these problems, the galaxy is still a pretty big nut, and the universe is staggering on any scale, and I haven’t considered fuel costs to drive the starship. But – hey – we are just a bunch of intelligent apes who have the audacity to take on the universe.
Fermi’s paradox is maybe a good starting point for a discussion – it goes something like: if there was a lot of intelligent life out there, some of it would have developed interstellar capability and surely this race of intelligent beings would have populated the universe by now? Extreme views on answering this question often invoke self-fulfilling admonitory caution for man’s/alien’s wickedness ‘destruction by apocalypse’ before they got that far (The Great Filter), or a gnomic with raised eyebrow, ‘perhaps they did…’ These kinds of arguments have a tendency to become the means to their own ends.
To do a scoping exercise based on scales. The universe came into being on (any reasonable scale) an infinitesimally small time, but took a very long time indeed to get to a point where we had available the building blocks for life as we know it. (I am thinking here about the simplest ideas of having the right sort of atoms, but there is more that needs to be considered). The universe shortly after the big bang had no elements more massive than lithium (ignoring some unstable beryllium). Synthesis of heavier elements occurred in successive generations of stars. At the end of the life of these later stars, some of became supernovae with the energy to make the really heavy atoms, such as uranium. To make the materials necessary for complex life, it took billions of years.
This is, of course, an extremely simplified description. I have made no reference to galaxy formation or grand structure of any kind. But my point is, that this preliminary to the genesis on Man (radiant music of your own choosing) occupied a big chunk of the first ten billion years of the existence of our universe. Our solar system, and its particular kit of matter, required the deaths of many earlier stars. Our solar system, with its one habitable planet, is a delicate matter of balance of physics, geology, chemistry and biology over long periods of time. Although life – of a primitive kind – is believed to have been around for much of the history of the planet, it took billions of years before this life became complex enough for the possibility of sentience to become a glimmer in the eye. The first mammals appeared less than 200 million years ago, co-extant with dinosaurs. Modern humans appeared about 200 thousand years ago. We will never know if a dinosaur descendant would have made an equivalent transition to intelligence on a par with modern humans. The bottom line is that it has taken almost 14 billion years to get us to the point where we are asking questions about aliens who may be peering in our direction from thousands of light years away. A lot could have gone awry in the process of making Earth fit for anthropomorphs to live and love and make tea upon, and – in our case – begin to seriously trash the joint, but I suspend judgement as to whether this is a necessary consequence of ‘intelligence’ or merely an enhanced drive to promulgate one’s own kind. Assuming comparable timescales elsewhere in an effectively infinite universe, I believe that there is almost certainly another planet elsewhere/when, where an alien someone asks the same kind of question. However the scales in terms of distance do not stack up with the human timeframe, unless warp drive or other unknown technologies become available. But, let’s be optimistic – physics has perhaps never been so exciting – ideas are being shaken, rattled and stirred and the bookies could have a field day (bad cosmic joke) if they knew enough science to take bets, and lived long enough to pay out.
But this little excursion has a point, albeit a fuzzy one. Humans are very blinkered to human scales and motivations. I’m not going all new-agey here – but we do need to keep going at the science to get closer to ‘The Answer’. (If you haven’t read Douglas Adams, you are missing out.) I suggest that we consider things in terms of scales – one civilisation takes ten billion years and a million dead stars, for instance. And it’s possible to speculate that a solar system making kit capable of making life could be spawned in a local group with similar atomic profile, so there is perhaps a likelihood that life – and maybe – civilisations could form in clusters, so we could have neighbours in a radius of a few tens or hundreds of light years. But that is a long way for an intelligent ape with a life span of tens of years, and whose civilisations last a few centuries.
On the grand scale, if I am asked to bet abut the incidence of life and intelligent civilisations in the universe, my own feelings have to do with thermodynamics – and here I am soon out of my depth, so I am not making a very cogent case. I think that basic life will be prevalent. Intelligence and consciousness are harder to predict. We have no definitions for these things and poor understanding of how they relate to the way the universe operates. It could be that life is not particularly relevant on the grand scale of things, or – indeed – when the beans are counted – it could be that the organic scum on the surface of small rocks (or other habitats) is disproportionately good at balancing the energy of the universe. In which case, there is an argument that there is more of it elsewhere in our universe, or in alternative universes if one is disposed towards this line of thought. Maybe there are thousands of planets within our own galaxy bursting with alien tea shops waiting for our custom. Or maybe they are so parochial that they don’t want ‘riff-raff’ in their premises so don’t advertise on a cosmic scale. Or – maybe we are being parochial about life based on planets – and even matter. Information can be coded in other ways than molecular form. My thoughts go in the direction of complexity of structure and the grand scheme of things. A top down argument for life emerging when a certain level of structure is possible. And when it is, it will, perhaps, bloom like a weed. And it could be that there are layers of the informational universe that operate on galactic scales. (And there are ideas that the universe is some sort of super computer. But I would be careful to take this metaphor too far, as this seems like a means to its own end.)
When I was a student of physics in the seventies, some lecturers talked blithely of a ‘theory of everything’ within their lifetimes, and unification of all the forces of nature into one beautiful whole. I think that they were either optimistic, or unimaginative. The intervening years have opened up the lid of our teapot of ignorance and the cosmic brew is looking very inviting, but we are perhaps over-ambitious to imagine that our small minds can work it all out within our scales of human experience. We perhaps need a much bigger frame upon which to join the multidimensional dots.
There must be infinite numbers of planets in the universe capable of sustaining life, and infinite incidences of intelligent civilisations. But that has a limited relevance to us in our small corner. As for our own galaxy, concurrent as far as we can make it with our own timeframe – we could be alone, or we could be part of a select band of organised intelligences. I won’t attempt to put a number on it, partly because – it would be a big finger in the sky guess, even for orders of magnitude. But – not for a moment – and for many reasons – would I suggest that we stop looking and thinking about it. The process bears its own fruit.