Where is everyone?

With all the kerfuffle surrounding the unidentified flying objects (UFOs) shot down by assorted US aircraft in recent days, the tinfoil hat brigade have gone off the deep end again, perhaps aided and abetted by the US Airforce spokesman who said he could not deny the possibility that thy were aliens (as in extra-terrestrials)¹. Not only have the cookers gone off the deep end regarding these shot-down UFOs but UFO sightings have skyrocketed across the US². 

Despite all these alien conspiracy theories there has been a distinct paucity of alien contact of any sort outside the tinfoil hats. This brings to mind the Fermi Paradox. Back in 1950, Enrico Fermi, the Nobel Prize winning Italian physicist, during a discussion of sightings of Unidentified Flying Object, asked ‘Where is everybody’, alluding to the fact that the universe is huge, so why do we only know of life on one planet?³

Frank Drake (he died in September 2022) was a Harvard-trained radio astronomer who pioneered the use of radio telescopes in the Search for Extra-Terrestrial Intelligence (SETI). He is more widely known for his 1961 equation ‘The Drake Equation’ which was a probabilistic way of estimating the possible number of civilisations in our galaxy^{4, 5}. 

The Drake Equation is as follows:

N = R_* x f_p x n_e x f_l x f_i x f_c x L

where:

N = the number of detectable civilizations in our galaxy

R* = the rate at which new stars form in our galaxy

f_p = the fraction of stars with planets

n_e = the number of planets per star where conditions are suitable for life

f_l = the fraction of planets where life actually emerges

f_i = the fraction of life-containing planets where an intelligent civilization develops

f_c = the fraction of intelligent civilizations that produce communications technology we can detect

L = is the length of time the communicating civilization remains detectable⁵.

While it reeks of mathematical precision, Drake himself admitted that he did not have real values for most of these factors. Indeed, he looked upon it mostly as a way to summarise the factors involved in the determination of the number of detectable civilisations⁵.

At the time, most ‘reasonable’ values for these variables suggested the galaxy should be teeming with life and we should already have detected a civilization or two. Drake himself suggested an extra-terrestrial civilization was likely to be detected by the year 2000. Of course, that has not happened⁵. At the time of the development of the equation, the various estimates of the variables gave an estimate of 20 civilisations as a minimum and 50 million as a maximum⁶.

Astronomical research has continued at an increasingly rapid rate in the years since Drake developed his equation and some of the values of the variables are becoming more precise estimates. For instance, when Drake developed his equation the proportion of stars with planets (f_p) was unknown, but was estimated to be about 0.2 to 0.5. It is now estimated to be approaching 1.0. Similarly, R* was estimated to be 1 star per year in our galaxy. It is now estimated to be between 1.5 and 3.0⁵.

There has only been one advanced civilisation in the entire universe that we know of: ours. In the 60-plus years since the Drake Equation was first proposed, no one has been able to determine L, the length of time that an advanced civilization is able to communicate its existence into space after developing the technology to do so. We know that might be more than 100 years, which is how long humans have been using radio waves to broadcast signals, but are we outliers? Nobody knows⁷.

Scientists have been trying to argue one way (we are alone) or the other (we are not alone) ever since Fermi first posed his question. In Fermi’s day the only planets we knew of were those in our own solar system. However, since 1992, over 5,000 planets have been discovered orbiting other stars in our galaxy⁸. Of these ‘exoplanets’, it has been estimated that 20% of them lie within the habitable zone⁹.

Why haven’t we discovered any other civilisations? The short answer is: we don’t know. However, it could simply be the vastness of the universe which decreases the chances of detection. For instance, humans have been emitting radio waves for about 100 years. Therefore, that radio ‘bubble’ is only 200 light years in diameter. That is minuscule in a galaxy that is about 100,000 light years across, and a universe that is 94 billion light years across¹⁰.

Sources

1. https://www.dnaindia.com/world/report-aliens-inside-china-spy-balloon-over-america-top-us-air-force-commander-makes-shocking-claim-3023402
2. https://www.tmz.com/2023/02/11/tiktok-conspiracy-theories-ufo-high-altitude-object-shot-alaska/
3. https://cosmosmagazine.com/space/what-is-the-fermi-paradox/
4. https://public.nrao.edu/gallery/frank-drake/
5. https://www.famousscientists.org/frank-drake/
6. https://en.wikipedia.org/wiki/Drake_equation
7. https://interestingengineering.com/science/the-drake-equation-and-the-probability-of-alien-intelligence
8. https://exoplanets.nasa.gov/faq/6/how-many-exoplanets-are-there/
9. https://www.space.com/25325-fermi-paradox.html
10. https://time.com/6242921/why-extraterrestrials-havent-contacted-earth/