I want to believe (but the math says no)

Illustration by Eliza Stribling

Almost a year ago, civilisation was shattered when citizen astronomers prepublished a paper on arXiv titled: Planet Hunters X. KIC 8462852 – Where’s the Flux? What originally appeared to be a tepid report of a tedious astronomical phenomena detected by the Kepler telescope between 2009 and 2013 soon became the subject of global gossip and speculation.

KIC 8462852 (now known as Tabby’s Star after the lead author of the paper) lies roughly 1,400 light years away in the constellation of Cygnus, the swan*. The paper reported“aperiodic dips in flux of up to ~20\%. The dipping activity can last for between 5 and 80 days. They concluded that the most likely explanation was the passage of a family of exocomets or planetesimal fragments in front of the star.

That would have been fine, if the boffins had left it alone. However, Professor Schaefer from Louisiana State University examined half a million photographs of the sky taken between 1890 and 1989 and found that the star had been dimming consistently over that hundred years.

Not to be outdone, a grad student at CalTech published a study showing that the dimming of the star was even more excessive than that. Over the first thousand days of the Kepler mission, Tabby’s Star dimmed at 0.34% (twice as fast as over the period looked at by Professor Schaefer) then dimmed by more than 2% over the next 200 days, and then steadied out. As the authors wrote: “No known or proposed stellar phenomena can fully explain all aspects of the observed light curve.”

So, what explanation does that leave? That’s right: Aliens. As Jason Wright, an astronomer from Penn State University, said: “this looked like something you would expect an alien civilization to build”. The idea was that the dimming was caused by an alien civilisation building a Dyson Swarm, which is a large number of objects orbiting a star and capturing its energy, such as solar powered space stations with vast solar panels. Don’t worry, maths proves that it’s not an alien megastructure.

Our galaxy, the Milky Way, contains about 100 billion stars. That’s a whopping big number. While we don’t know how many alien civilisations there are in the galaxy, Frank Drake once proposed an equation to estimate how many we could detect. He argued that the number would be equal to the average rate of star formation in our galaxy multiplied by the fraction of formed stars that have planets, multiplied by the average number of planets per star that has planets that can support life, multiplied by the fraction of those planets that actually develop life, multiplied by the fraction of those planets bearing life on which intelligent, civilised life has developed, multiplied by the fraction of those that have developed communications, multiplied by the length of time over which such civilisations release detectable signals.

That’s a lot of things to take into account, but the important thing is to notice how many of those are fractions. Most stars seem to have planets, but very few of those planets would be capable of supporting life. They have to be the right size, with the right components, at the right distance from the star. Even those planets that could support life don’t automatically generate it – as far as we know life has spontaneously generated exactly once, even though other planets in our solar system have been capable of supporting life in the past. So I think it’s safe to say that only a small fraction of planets that can sustain life actually develop it.

How many planets that have a genesis event actually go on to develop an advanced civilisation that we could detect? The formation of eukaryotes and multicellular organisms is not a given, and most life events would stay at the primordial ooze stage. If intelligent life develops, but finds itself on a planet without an easy fuel source or without many metals, it’s not going to get very far.

I won’t put any numbers in here – you can play with that – but it’s safe to say that for every star that contains an advanced civilisation building a Dyson Swarm, there are hundreds of millions – or even billions – of stars that are just doing their own thing based on non-living processes. Remember, Kepler only looked at 145,000 stars.

So any time we detect an irregularity, no matter how difficult it is for us to come up with an explanation that fits its peculiarities, the chances of the cause being alien civilisations rather than astronomical processes is in the order of 1 in billions. If we found a strangely behaving star every day we would, on average, have to look for hundreds of thousands of years before we found a peculiarity that was actually the result of aliens. This argument applies to everything regarding aliens.

If a strange craft floats down before you one lonesome night, and a little green man with silly antennae on his head struts up and down in front of you making “meep meep” noises, it’s far more likely that you ate the wrong mushrooms than that you’ve made inter-planetary contact. If this craft came down in a city and thousands of people saw and took photos and videos and posted them to instagram, it is statistically far more likely to be a hoax perpetrated by Russia or Coca Cola than alien life forms popping over to say “hey gurl”.

*Of course, everyone missed the obvious “Black Swan” pun. This is because news organisations keep firing sub-editors.

Tags : astrobiologyastrophysicsseti

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