Astronomical Answers! – Why hasn’t ET phoned home?

Keeping up with the theme of the unanswerable paradoxes I’ve been asked to explain Fermi’s Paradox. Now, I wasn’t really asked a specific question in this request – and to the submitter of this particular topic, I would definitely not describe Fermi’s Paradox as ‘fun’. (In fact, I would go as far as saying the idea of forming a scientific argument based on an abundance (read: no) data, all with error margins that would make even the most foolhardy scientist tremble, is just plain silly. That being said, there’s no reason to not discuss the arguments put forward by this paradox.)  In lack of a specific question, I’ll try explain what Fermi’s paradox is, and how we can possibly explain its occurrence. This is a very small overview of the full picture surrounding this paradox- it’s very hard to condense what is a life time of work for some people into a single blog post!

The Fermi Paradox, originally proposed by Enrico Fermi and Michael H. Hart, highlights an observed contradiction between the estimated number of intelligent civilizations in the universe and the observed number of civilizations in the universe. Their argument suggests: There are billions of stars in the galaxy, many of which are much older than the Sun, it is highly unlikely that the Earth is completely unique and much more likely that earth-like worlds exist around some of these stars. Some of these worlds may develop intelligent life. Using humanity as our only frame of reference to intelligent life, it is likely these intelligent civilizations will develop inter-stellar travel. Even at a modest pace, the galaxy would be completely colonized within a few tens of millions of years. So, where are all these civilizations?

The first thing I want to point out with all of this is, the principles behind this paradox are part of a thought experiment which science has been attempting to quantify since the argument was first proposed. But where are these estimates from and how do we arrive at the number that we do? Many attempts have been made to derive numbers from the situations we observe, and despite my personal reservations about the paradox, it is a very active and hotly debated problem. Using theories and ideas that humanity has already started researching, it is plausible to assume some, if not all  advanced civilizations will develop technologies similar to the aforementioned ideas. Concepts like the Von Neumann probe would drastically reduce the time it would take to colonize, or at least leave an observable mark on, the galaxy.

So, all things considered, these estimates suggest ET should be dropping by for tea every second Wednesday- So why do they have the same punctuality as [insert your chosen doomsday scenario here]? Well, there are actually a few well grounded explanations to this dilemma.


Looking the Wrong Way

It may come as a surprise that the amount of the sky being observed at any given point in time is actually quite small. Taking into account the different forms of communication we are able to use ourselves- by which I mean the different wavelengths that communications technology use nowadays. Maybe we’re just not looking in the right places within space?


The Prime Directive… of sorts

Throughout science fiction there are many examples of space based stories involving directives which prohibit the contacting of civilizations that are not at the inter-stellar travel stage of development. It is conceivable that these directives will one day govern our expansion into the cosmos and are also found in other civilizations. Maybe we don’t see evidence of these civilizations because they don’t want us to see them?


E-M Communications? …That’s so last century!

One line of reasoning that I personally see a great deal of worth in is the idea that we are listening to the wrong forms of communication. It seems almost arrogant of humanity to expect advanced civilizations to be using the same forms of communication as we use currently. Perhaps we don’t have the technology to pick up the signals these civilizations send out, or perhaps the future of communications technology lies along more directed signal transmission route. By which I mean ideas like quantum entanglement or laser based communication methods rather than broadcasting wave based transmissions in every direction.


Boldly Going Where No-One Has Gone Before…

As much as the statistical odds seem to reject this notion, it is possible that we are the first civilization to develop this far- we could in fact be the leaders across the universe in terms of technological development. However, on account of the age of the Sun relative to the age of the Universe, this seems implausible.


Catastrophic Ends…

The periodic destruction of life is possibly the most pessimistic interpretation of the estimates. It follows the idea that either periodic natural disasters can and do scour intelligent life from planets at a faster rate than they expand into the cosmos, or alternatively, that the eventuality of every intelligent civilization is to destroy itself.


Inside, Looking in?

Anthropic selection may well play a part in this paradox. The idea that, because we are internal to the situation we are observing, our conclusions must be biased. The idea that, by being able to observe and theorise about these ideas, we alter the balance of the problem – but at the same time, the problem could not be considered without us here to consider it! (And if your head hurts when you try to think about that, don’t worry- it’s a sign you’re sane). The ultimate implication of this anthropic selection principle is that the numbers we use in equations (like the Drake equation), to work these estimates out, may be fundamentally flawed.


As I set out at the start of this post, this is by no means an exhaustive list of theories surrounding the Fermi Paradox. There are a great deal of resources out there discussing the finer details of the work surrounding it- check them out!


About Mark Nottingham

Mark is a PhD student in the Isotope Geochemistry and Cosmochemistry group at UoM. Primarily working on the RIMSKI and RELAX noble gas instruments.
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