Perhaps we are alone in the universe after all – the outcome of the Fermi paradox and the Drake equation

So many science fiction books, films and television series involve other life forms – often lots of of them – but what are the scientific chances that we are, or we are not, alone in this huge (and expanding) universe? Two of the greatest thinkers on this subject have been the Italian physicist Enrico Fermi and the American astrophysicist Frank Drake.

The first of these men posed what is known as the Fermi paradox which can be summarised as follows:

  • There are billions of stars in the galaxy that are similar to the Sun and many of these stars are billions of years older than the Solar system.
  • With high probability, some of these stars have Earth-like planets and, if the Earth is typical, some may have developed intelligent life.
  • Some of these civilisations may have developed interstellar travel, a step the Earth is investigating now.
  • Even at the slow pace of currently envisioned interstellar travel, the Milky Way galaxy could be completely traversed in a few million years.

And yet, as Fermi noted, there has been no convincing evidence of other life forms, leading him to ask: “Where is everybody?”

The second of our thinkers devised what is known as the Drake equation. This equation attempts to calculate the likelihood of life outside our planet using seven variables:

  1. The average rate of star formations in our galaxy,
  2. The fraction of formed stars that have planets,
  3. For stars that have planets, the average number of planets that can potentially support life,
  4. The fraction of those planets that actually develop life,
  5. The fraction of planets bearing life on which intelligent, civilised life, has developed,
  6. The fraction of these civilisations that have developed communications, i.e., technologies that release detectable signs into space, and
  7. The length of time over which such civilisations release detectable signals,

The first attempt to put figures into the Drake equation in 1961 resulted in the conclusion that there were probably between 1,000 and 100,000,000 civilisations in the Milky Way galaxy. But the most recent attempt to populate the variables in the equation in 2018 – by three philosophers at Oxford University – has come to a radically different conclusion.

If you want to read the Oxford paper of 19 pages, you can access it here. If you want to read a layperson’s summary, you can go here.

If you can’t be bothered to look at either analysis, I can tell you that the latest calculations suggest that, based upon the current state of astrobiological knowledge, there’s a 53 to 99.6 per cent chance we are the only civilisation in this galaxy and a 39 to 85 per cent chance we are the only one in the observable universe.

As an editorial in the “Guardian” newspaper put it:

“The Oxford paper shows that when you take these uncertainties into account and run hundreds of thousands of simulations exploring them, the probability that we are alone in our galaxy, and perhaps in the universe, rises to entirely reasonable levels. The Fermi paradox vanishes. There is quite probably no one out there to rescue or to care about us. What happens to our species is in our hands alone. We had better get on with it.”

My own view is that we are probably the only intelligent life in the universe because, if that were not the case, we should have detected radio waves from other civilisations by now. In any event, even if there is life out there, it is likely that the distances involved in communication would be so great that any meaningful interaction would be impossible.  So, it’s just us guys.

One Comment

  • Pete

    I think this is too pessimistic a view and doesn’t take into account the enormous distances that must separate life-forms in the observable universe. My reasoning is based on the simple fact that the inverse square law comes into the equation.

    As you know this means that an electromagnetic signal will weaken dramatically over distance purely because it is expanding. Even the most powerful laser signal would diverge massively across the unimaginable distances involved. The only reason we see stars that are far away is because they pump out such enormous power! Present technology cannot do that and is unlikely to be able to in the forseeable future. If a reasonable assumption is made that another civilisation faces the same physics limitations in their part of the universe or Milky Way, then we are really not going to see or hear anyone any time soon, because we don’t have an incoming sign to tell us where they were when the signal was emitted. Even if we do, it is going to be a Herculean task to figure out where to point our reply. If a signal took 100,000 light years to cross the Milky Way our reply would do the same. How will we know that they are in the correct place to receive our reply? We won’t. We could only make a best guess… and hope they had remembered they sent the signal in the first place or were even still around.


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