Why Kepler (and Fermi) give me Fear

NASA have a magically sensitive light meter in orbit, pointed permanently at a sliver of the sky in Cygnus. This instrument is called Kepler and its purpose is to search for planets orbiting those stars it can see. And that is what it has been doing: it's found fifteen so far, and it's got hundreds of candidates and years to run. Right now it's finding huge planets in close orbits, because they cause frequent big bobbles in the light curve; as time goes on and the data piles up it will be able to find smaller planets further from their suns: planets like Earth. We don't know how many it will find -- data from Kepler and others suggests that solar systems are typically tighter than ours -- but it will certainly find some. And the geometry of transits means that for every world it finds, it'll miss dozens more.

Up till now, it's been possible to believe that planets were rare, that the universe is overwhelmingly plasma: hot or wildly diffuse or both. It's true that planets are insignificant in the total mass of the universe, but we care about them and Kepler tells us that there's plenty to care about. In all probability, scaling from Kepler, the galaxy has countless thousands of rocky worlds with suns that keep them at or near liquid-water temperatures for billions of years. Life worlds in fact -- not worlds we'd necessarily like very much, but suitable homes for whatever's evolved there.

Sixty years ago, most of this was already known. The astronomers had won the long argument: the stars are billions, not millions, of years old. The physicists conceded once they realised that stellar cores are nuclear fusion furnaces that can hold a star like the sun at a roughly constant heat output for eight or ten billion years. That discovery made it intellectually respectable to discuss billion-year ages for the earth, and the life on it.

And that brings us to Enrico Fermi: the great synthesist, father of nuclear power and asker -- sixty years ago -- of the question that's worried me since I heard it. It's called Fermi's paradox. He estimated the number and age of earthy planets -- planets that should build advanced cultures in a few billion years -- and asked:

• "Where Is Everybody?" 

Does that seem strange? Discovery or contact with extraterrestrials is generally imagined as a rare or impossible event. But Fermi was asking why we didn't see them everywhere we looked. He knew that a technical culture -- like ours -- was already conspicuous on a stellar scale, just a hundred years since we started using electricity. The broadcast stations and air defence radars of the war just finished had sent obviously artificial signals that were already passing the nearest stars. In thirty thousand years, the people of Earth will have announced themselves to every planet in the galaxy. That seems like a long time, but against the age of the stars it's infinitesimal. Given the likely number of worlds -- confirmed by Kepler -- there should be many technical civilisations active in the galaxy at once, and since ours is so young most of them will be more advanced -- more conspicuous -- than us.

We can't really tell what an advanced civilisation would do. Perhaps we would see radio emissions. Perhaps we would see large-scale engineering like ringed stars, or even the glare from the engines required to move from star to star. But we all know that there's nothing. The universe looks wild, natural, at every wavelength, at every scale. There may be life on other worlds, there may even be sentience, but to all appearances there are no engineers.

• So. Why is that? Where ARE the aliens?

There are plenty of answers to Fermi's question, but they can be lumped into just two categories: reasons why technical cultures like ours never arise, or why they always fail:

• The"never arise" list is a ragbag -- dozens of improbable or ad hoc claims: "By chance we are the first;" "Life can never develop without a moon that exactly eclipses the sun;" or there's my favourite: "Eukaryotic cells are highly unlikely to evolve." But we are here, so we know that none of these can be absolute. Explaining our loneliness with one of these, or even the whole list, it boils down to being a matter of chance, a fluke. It may BE so, but we don't know, and I struggle to believe that any of these could be true enough, in a galaxy with the countless potential worlds revealed by Kepler.

• The "always fail" list is just as long but much grimmer, because any or all of the reasons could be true,  up in our future, and not far off either. It's not enough to say "Technical civilisations cannot last." They have to disappear quickly, so there's only one at any time, and they can't leave a mark that we would see. Within a generation or two -- it has to be really soon because there are so many candidate planets -- we stop broadcasting. We never terraform the solar system. We never cross to other stars. We are now seeing the height of human development, and soon war, environmental degradation, philosophical attitudes, energy prices, the galactic empire's pest exterminators, or whatever ambush it is, will knock us so far back that tens of millions of years will pass before Earth (it won't be Us) tries, and fails, again. For my money, the "always fail" list seems much more plausible -- any or all of them could be true.

The "always fail" list is horrifying. We're doomed. The fall may be so close that people alive today may have to handle the consequences, and if it's that fast it will not be pleasant. Having those children may turn out to have been a serious moral error.


If you want hope for the future, you need to find an adequate answer somewhere in the "never arise" list. Because, if that's right, then once we're past those hazards (and we already ARE), there's no telling what we'll do, in a galaxy that we own. It's up to us.


The problem is that the best chance, the most plausible reason to permit us to be an oddity, was "planets are rare." It could have been true, but Kepler results show that it's not. We have to look again, to find something improbable in the long history from the lifeless Earth to our technical civilisation. The origin of life seemed a good choice, but we can date that now, and it seems to go back to just a short time after the formation of liquid water: Unless that's a huge fluke, life isn't improbable at all, and it will arise on every water world. 


That's why I know more than I should about eukaryotes. I'm hoping that the step from simple cells to structured ones that can gang up into organisms was difficult, implausible. It took a good few billion years in our history, and I take that as a sign that it was far from inevitable, but I can't really persuade myself that that's true. Effectively, I'm hoping that we can look at  world after earthy world, each with oceans teeming with bacteria, and nothing but slime on the land.


We'll know soon. Here's another name: James Webb. That's the NASA administrator whose name adorns the successor to the Hubble telescope. When Kepler starts listing earthlike worlds, the huge objective mirror of the Webb telescope will be turned towards them, and its spectroscopes will analyse, photon by photon, light that has glanced off alien oceans and strange leaves. Results from each individual planet will tell us little, but as the numbers pile up, we'll know: bacteria, or plants.


If it's plants, that will tell us that eukaryotes are common, and to my mind a world with eukaryotes will have engineers in time. And that says that the reason we seek, the answer to Fermi, is in the always "fail list." I won't be surprised. The "never arise" reasons all boil down to saying that Earth or the Sun or life here is special in some way. In the whole history of modern astronomy, from Copernicus on, that's never been the way to bet. Kepler's observations have taken us one stage further down that road, and there is extinction at the end.