We humans have a lot of reason to be proud. In the short span of a few million years we have become self-aware and clever, learning to manipulate our world in ways that have greatly enhanced our survival. The last 100,000 years have seen the evolution of anatomically modern humans, which migrated from our African birthplace to colonize and populate essentially all corners of the globe. Using sophisticated brains we learned about the world, deciphering patterns in nature, designed and constructed tools, and formed societies and civilizations.
Unfortunately, there has also been much about our success that is less praiseworthy. At the same time that we have been building ingenious devices to better feed, clothes, shelter, and move ourselves from point A to point B, we have also been in the business of making ever more efficient weapons to destroy one another. As our technological progress seems to outpace our societal ethics and maturity, we now have it in our power to completely annihilate our entire species. In the not too distant future it could conceivably be possible to extinguish all life on planet earth, whether through horrible accident or intentional destruction.
While we sit on this world powder cake of self destruction, perhaps at times in a little more danger, and at times in a little less, we often wonder if we are alone in the universe. Not only are we the only example of intelligent life that we know of in the universe, but our little planet is home to the only example of life we know of anywhere. All evidence seems to indicate that there are a vast number of planetary systems and potential habitable worlds in the universe. We have detected over 2000 exoplanets, so far, with the first one being discovered only as recently as 1992, and with advancing techniques the numbers have been skyrocketing in recent years. Yet, there is still no sign of alien life, and even with SETI (Search for Extraterrestrial Intelligence) listening for alien radio transmissions since 1960, we have not detected any confirmed signs of intelligent aliens.
In the October 23, 2015 issue of The International Journal of Astrobiology, authors Adam Stevens, Duncan Fogan, and Jack O’Malley James, make an interesting case that we may soon have the technology necessary to detect alien civilizations in the act of self-destruction. In fact, alien armageddon may provide us with our most likely opportunity to detect the presence of intelligent alien life – even if we are only witness to their last moments. The authors summarize some of the possible ways that an intelligent civilization could go horribly wrong, and how evidence for these tragic events could potentially be detected by our instruments here on earth.
The first major scenario would be that of global nuclear war. There are several characteristics of a world that has been annihilated by an intense exchange of nuclear weapons that might be detectable from our distant vantage point. The detonation of the devices would emit high energy gamma radiation that would last for a short period of time – on the order of thousandths of a second. Even given the high energy involved in the detonation of a world arsenal of nuclear devices, it is not very likely we could detect the energy output from so many light years away. Naturally occurring gamma ray bursts (GRBs) are some of the most intense energy generating events in the universe, and can be observed at the edges of the visible universe, but they are also around 10 billion billion billion times more energetic than the predicted energy release of all the nuclear weapons on earth combined.
The intense radiation from global nuclear war would, however, ionize the planet’s atmosphere, resulting in an “air glow” due to light emission from energized nitrogen and oxygen. The atmosphere would have a lovely green glow in the the visible spectrum, is predicted to last several years, and could be observed as an increase in the light intensity at the expected wavelength. There would also be a depletion of the planet’s ozone layer as reactive chemicals are produced by the explosions. This too, might be observable as a change in the planet’s atmosphere. Nuclear war would also generate a great deal of dust and small particles that enter the air, altering the transparency of the atmosphere. A combination of a gamma ray burst, air glow, drop in ozone concentration, and loss of transparency of the atmosphere would be good evidence for this alien-made disaster. Any one event on its own might not be enough evidence to be certain of an artificial event. For example, a change in the atmosphere from transparent to opaque could also be caused by natural events like a large asteroid impact.
Second on the list for a self-induced civilization-stopping calamity would be use of potent biological weapons. Genetically engineered organisms, like viruses and bacteria, would potentially be much more deadly than any naturally occurring epidemic. If the infectious agent was designed to attack all animals and plants, the entire biosphere would be jeopardized. How would such a horror be detected by us? Well, a rapid demise of the planet’s multicellular life would result in a huge amount of organic material for bacteria to consume. The result of this massive decay would be the release of certain chemicals such as methane and ethane, that could be observed by spectroscopic analysis of the atmosphere.
The next deadly scenario is the so called, “grey goo” event. This involves the engineering of self-replicating nanomachines – tiny machines that use some building material as substrate and convert it into more tiny nanomachines. The authors of the paper point out that this could be the result of either “goodbots” or “badbots”. In the goodbot case the self-replicating nanomachines were never intended for destruction, but due to poor system controls, got out of hand leading to world destruction. Badbots, on the other hand, were designed to cause complete and total destruction – the ultimate doomsday machine! These replicators would take all carbon containing material on the planet’s surface, (ie. living organisms), and convert them into a growing mass of more replicators that do the same. K. Eric Drexler – who coined the term nanotechology- pointed out in his ‘Engines of Creation’: “Replicators can be more potent than nuclear weapons: to devastate Earth with bombs would require masses of exotic hardware and rare isotopes, but to destroy all life with replicators would require only a single speck made of ordinary elements.”
It might take as little as a few weeks to convert the worlds living biomass into a lifeless desert of tiny replicators – grey goo! Pretty scary!! From earth we might be able to detect this as a large increase in atmospheric dust (the masses of nanomachines). The nanomachines would form giant sand dunes (bot dunes in this case) and would change the apparent brightness of the planet as we observe it. There would be visual effects of shadowing, as the planet orbits its star due to the changing angle that light hits the grains of nanomachines in the bot dunes. This is similar to the effect we see as light passes through the small particles in Saturn’s rings at different angles. Over a period of thousands of years the nanomachines would be recycled through the planet’s interior, as the planet’s normal geological processes continue to operate.
Another apocalyptic possibility would be intentional pollution of the planet’s star. To dispose of harmful radioactive waste, a civilization might launch such materials into its parent star. Detecting uncommon radioactive elements in the star’s atmosphere would be evidence for this unnatural process. Carl Sagan, called this “salting” the star. We would know that this was an artificial process by the fact that elements present would be produced only in such high amounts by nuclear processes that don’t occur naturally. Models have shown that if this was carried out to extremes, it would affect the star’s internal balance of forces and cause it’s size to increase, while dropping the surface temperature. This change in the star’s characteristics could change the location of the habitable zone around the star, making life difficult or impossible on the alien planet that did the salting. The authors suggest that, “compiling a sample of stars that are bright, cool, and slightly larger than expected as an initial step to search for this particular death channel.”
Finding evidence for intelligent life in the cosmos would radically change our view of ourselves, and our place in the universe. If aliens have a similar psychology to ourselves (a big if to be sure), they could be prone towards potentially fatal flaws that could escalate to total catastrophe. Their demise at their own hands (or equivalent body structures) might also be the signal that informs us that they were ever there at all. Finding one or more civilizations that self-destructed might also give us a way to prognose the long-term health of the human race. Do civilizations reach a point where their technological power is too great for their wisdom? Could Homo sapiens one day end up as a signal to the stars that we were here for a brief time, an intelligent species, but just not quite intelligent enough to solve the problem of surviving peacefully with one another?
“Observational signatures of self-destructive civilizations.” Oct. 23, 2015, The International Journal of Astrobiology. Adam Stevens, Duncan Forgan and Jack O’Malley James.