Zahlen, bitte! Up to 4,000,000 alien worlds according to the Drake equation
The Drake equation is used to calculate the probable number of extraterrestrial civilizations in the Milky Way. But it has a huge catch.
"Are we alone in the universe?" – This question is a central component of space research. After all, it would be pretty boring if we were the only beings pondering our existence. Thanks to new research probes, possible candidates for life are being investigated more and more reliably. Not least, the James Webb Telescope examines the composition of the atmospheres of exoplanets regarding traces of life. A much-discussed article in our "Zahlen, bitte!" column was about the Drake equation. For current reasons, we have updated the article and republished it as "Zahlen, bitte! Classic". Have fun!
The Drake equation (also known as the Green Bank formula or SETI equation) is used to estimate how many extraterrestrial civilizations of intelligent beings exist in our galaxy. It was created by the US astrophysicist Frank Drake, who presented it at a conference in Green Bank, West Virginia, in 1961.
Conference as a SETI discussion forum
Only ten participants gathered at the National Radio Astronomy Observatory (NRAO) to hold a conference as part of Project Ozma. Ozma, named after the Princess of Oz, was launched a year before the Green Bank Conference and was the first SETI (Search for Extraterrestrial Intelligence) effort to explore space for signals from possible extraterrestrial civilizations. This small conference was intended to provide the theoretical basis for this research.
(Image:Â CC BY-SA 4.0, Amalex5)
None of the participants were aware that the results and the discussion would attract such public interest that neither souvenir photos nor minutes were taken. The press only stopped by once during the three days because the announcement of the Nobel Prize for Chemistry to conference participant Melvin Calvin happened to fall at the same time as the event.
N = R * fp* ne * fl *fi * fc* L
N - Number of possible developed and communication-ready extraterrestrial civilizations in the Milky Way
Total number of extraterrestrial civilizations that are ready and technically capable of interstellar communication.
=
R* - average star formation rate per year in the Milky Way
The average rate of newly forming stars within our galaxy.
fp - fraction of stars with planetary systems
Fraction of star systems with a planetary structure similar to that of our solar system.
ne - average number of planets (per star) within the ecosphere
Proportion of planets that are at the distance from the sun that makes liquid water, an important element for life, possible.
fl - proportion of planets with life
Proportion of planets on which any form of life exists.
fi - Proportion of planets with intelligent life
Proportion of planets on which intelligent life is being formed.
fc - Proportion of planets whose civilization is interested in interstellar communication
Proportion of planets whose intelligent civilization is willing to communicate beyond its home system.
L - Lifespan of a technical civilization in years
The time span in which an intelligent civilization is able to exist.
Civilizations as endangered species
When Drake presented and described the individual factors on the blackboard, a lively discussion began among the researchers present. The L-factor in particular, which deals with the lifespan of an intelligent species, was controversially discussed, as in addition to natural causes such as natural disasters, for example meteorite impacts, a civilization could also destroy itself through wars among itself.
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In 1961 in particular, in the midst of the Cold War between the Western powers and the Warsaw Pact states, the climax of which was still to come with the Cuban Missile Crisis just under a year later. An existential war was not an unrealistic scenario. Researchers feared that the military would precisely determine the final factor for earthly civilization.
Three different model calculations
In the end, they used the formula to calculate three different outcomes:
- A conservative model calculation: one civilization in our Milky Way.
- A more optimistic model calculation: 100 civilizations in our Milky Way, 5000 light years average distance between two sending civilizations.
- An enthusiastic model calculation: 4,000,000 civilizations in our Milky Way, 150 light years average distance between two sending civilizations.
Between one and four million civilizations, of course, there is a wide range, which highlights the problem that this equation poses: the individual factors cannot be determined with any practical scientific certainty. Although somewhat better data is available on individual points, such as exoplanet research, all figures are ultimately based on assumptions.
(Image:Â NASA)
Further equation calculations over time
And the individual results vary accordingly:
In his book "Civilizations in Space", the German physicist and ESA astronaut Ulrich Walter arrives at a range of between 0 and 100 civilizations (excluding terrestrial ones) via the Drake equation. The well-known astronomer and author Carl Sagan used the equation to calculate 15 civilizations in our galaxy.
Using various computer model calculations, the British astrophysicist Duncan H. Forgan from the University of Edinburgh arrived at values between 361.2 (with a standard deviation of 2) and 37965.97 (with a standard deviation of 20) in his work A Numerical Testbed for Hypotheses of Extraterrestrial Life and Intelligence.
Extended Drake equation arrives at 36 civilizations
According to the latest calculation by the University of Nottingham, 35 other civilizations are thought to exist in our galaxy in addition to the human civilization. The equation was adjusted by the factors of the total number of stars in the Milky Way and the proportion of suns that are at least five billion years old.
What all these calculations have in common is that, over time, observations have made it possible to make one or two orders of magnitude a little more precise, but the values of most of the variables remain fictitious. It is not for nothing that all researchers treat this question with caution. The aforementioned Ulrich Walter even comes to the conclusion that the Drake equation is "still worthless" for answering the question of the existence of further civilizations.
In an interview, Drake himself also expressed his surprise at the great response his equation generated in society: "I am always surprised that this equation is regarded as one of the great icons of science, since it required neither great intellectual effort nor insight from me."
The question of all questions remains unanswered
Consequently, the Drake equation still does not prove the existence of other civilizations. Although investigations by the US military since 2020 appear to provide evidence for extraterrestrial events on Earth, these are not undisputed either. In any case, one reader's assumption that the US military's sudden generosity regarding alleged extraterrestrial phenomena could be linked to the establishment of the Space Force and its raison d'ĂŞtre cannot be dismissed out of hand.
The researchers at the James Webb Telescope caused a sensation in early 2024 with a press release about an exoplanet: they did not entirely disagree as to whether the unusual signature of candidate K2-18b could be the result of life. It later turned out that there was no life after all. Only one thing remains the same: The answer to whether we are alone in the universe is written in the stars!
(mawi)
