Where are all the Aliens?

milky-way-you-are-here
The Milky Way is a big place. Are we really the only ones here? Source: http://sites.psu.edu/vansonspace/2015/04/10/space-is-the-place/

Are we alone in the Universe? To this day it remains one of the most intriguing questions in Science, and probably one of the most discussed by non-scientists everywhere. It’s likely been around for quite some time, but it wasn’t until 1984 with the birth of the SETI (Search for Extraterrestrial Intelligence) institute that we started making meaningful strides towards finding an answer.

But despite great public visibility and inherent curiosity factor, the institute has been pushed to the edges of scientific research. It has failed to attract any serious funding, and received only small amounts of dedicated observation time on world class telescopes.

Well all that is about to change! Thanks to Russian entrepreneur Yuri Milner and physicist Stephen Hawking, the SETI Institute will receive a total of $100 billion in funding over the next decade. The project is known as “Breakthrough Listen”, and will allow for state-of-the-art radio and optical surveys to take place on some of the world’s best telescopes. The project is actually supposed to start making observations some time this year!

So, now that we have the resources available to do some searching, the next question is – what do we search for? We ideally want to find a planet that shares characteristics with our own. That is, one with a rocky surface, of a similar size, orbiting a similar star, and a surface temperature that can allow for liquid water.

This aspect has not proven to be much of a problem, with observations, primarily from the Kepler Space Telescope, showing that the Milky Way contains around a billion planets that meet these specifications. But once we’ve identified such a planet, how do we go about searching for life?

Well for it to be in any way detectable from a distance, life needs to have evolved to the point where it dominates the planet’s surface chemistry. This will actually change the composition of the atmosphere, creating so-called “biosignatures”. A chemical indication of the presence of life.

An example is an atmosphere of at least 20% O2, since our own planet shows that such a composition can almost entirely be created by biological processes. But there is a very real risk of a false positive with any of these biosignatures, since there is always the possibility of a non-biological source. In the case of O2, the splitting of vaporised H2O by UV radiation could easily create such high levels.

This means that we need to find ways to either back up promising signatures, or identify a false positive. For example, detecting methane (CH4) in the planets atmosphere as well as O2 would significantly strengthen the possibility of a life-based origin. On the other hand, an atmosphere rich in steam would suggest that the splitting of H2O is the most likely source.

But what if we want to be more ambitious? What if we want to, rather than searching for any form of life, jump straight to searching for intelligence? There are a few options available to us here, one of which would be the detection of an intelligent, non-natural radio transmission. This is currently the main aim of the SETI program, and while the risk of a false positive is significantly lower than with biosignatures, it’s not without problems. The main one being that radio communication might be considered archaic by and advanced lifeform, so they might not even be using it.

It would also be possible to search for evidence of energy consumption, a necessity for an advanced civilization that seems impossible to conceal. There are many potential energy sources for a civilization with advanced technology, with nuclear fusion being a likely one. There is also the incredible concept of the “Dyson Sphere”, a megastructure surrounding a star to harvest the energy it emits. In either case the production of waste heat is inevitable, and would produce a detectable mid-infrared (MIR) signal.

But one final problem remains. What if, as so much sci-fi media suggests, biological life is only a brief stage for an evolving intelligence? What if the next logical step is the dominance of artificial, inorganic lifeforms?  If so, we wouldn’t really know where to look. It is likely that they would not be found on a planet, as gravity is only advantageous for emerging biological life, but otherwise a nuisance. They would, however, still need to be close to a power source for energy considerations. A star seems to be the most likely source, so that at least gives us a place to start.

There is also the possibility that such intelligence might be broadcasting a signal in their own attempt to find out if they’re alone in the Universe. But if such an advanced civilization were to do such a thing, it is unlikely that our feeble organic brains would be able to detect or understand it.

So, it looks like this amazing question is no closer to being answered than when the effort first began in 1984, but that’s not really surprising since it’s quite a difficult question. However, given that SETI has just been given a new lease of life, it might have gotten a little bit easier. I hope we’ll be learning a lot about this in the coming decade, and who knows, we might actually find someone.

Sources:

 

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