All Alone in Space

During his time at the Los Alamos National Laboratory, nobel laureate Enrico Fermi (1901–1954) is said to have discussed with some colleagues on their way to the staff canteen why mankind has not yet seen any evidence of extraterrestrial civilisations. Fermi assumed that the emergence of life and its development into intelligent species was not a singular event on mother Earth, but had already happened several times in the universe and even in our galaxy. But why then have we not yet found any traces of these alien civilisations, such as alien spaceships or radio signals from inhabited planets?

The question raised by Fermi was later explored in greater depth by other researchers such as Michael H. Hart (born 1932), Frank J. Tipler (born 1947) and Frank D. Drake (1930–2022). A look at the evolution of life and human civilisation on Earth reveals the developmental steps that must be successfully completed in order to bring about a technological civilisation. Based on these considerations, American astronomer Frank D. Drake derived a formula in 1961 that can be used to estimate the number of extraterrestrial civilisations in our home galaxy. In a slightly modified form, this formula can be written as follows:

Number of Civilisations ∼ R_stars⋅ f_sun ⋅ f_planets ⋅ n_habitable ⋅ f_life ⋅ f_intelligent ⋅ f_{ciivilisation} ⋅f_detectable ⋅ L

In this formula, R_stars denotes the average star formation rate in the galaxy and f_sun denotes the percentage of stars that are approximately the size of our Sun. Both variables can now be estimated quite accurately on the basis of astronomical observations. According to these, approximately a dozen new stars are formed in the Milky Way each year, and approximately 7% of stars are of the same size class as our Sun, i.e. these stars have a stable and sufficient luminosity for several billion years. However, most stars form binary star systems, and stable planetary systems such as our solar system are rather rare. However, it is only in the last few years that astronomical observation capabilities have become precise enough to detect planets around stars other than our Sun. The proportion f_planets of stars that have a stable planetary system is therefore still known only with great uncertainty and is probably smaller than previously thought. In the first generation of stars, there were no rocky planets as the heavy elements required for their formation are only created at the end of a star's life and released during stellar explosions. 

Only a few planets, such as Earth, possess a solid surface and an atmosphere, and orbit their central star in such a way that the energy radiation emitted by it enables the existence of water in liquid form on the planet's surface. The number n_habitable indicates how many planets in a planetary system on average meet these conditions and would therefore be fundamentally habitable for life forms as we know them on Earth. In the case of our solar system, Mars and Venus have also met these conditions at least temporarily, in addition to Earth. However, it is possible that our solar system is rather atypical and that the number 3 is significantly too high for n_habitable.

Entirely unknown in the equation is the variable f_life which indicates the proportion of planets on which life arises. Apart from our home planet Earth, we know of no other cases. Equally unknown is the variable f_intelligent which indicates the proportion of inhabitad planets that also produce intelligent life forms. The same applies to the variable f_{civilisations} which indicates the proportion of technical civilisations among intelligent species, of which only a certain proportion f_detectable may provide detectable evidence of their existence – e.g. through radio waves or alien spaceships landing on Earth.

The equation also takes into account the average lifespan L of a technological civilisation. It is at best 200 years since mankind reached a level of technological advancement that leaves traces that can be detected from distant planets – for example, radio waves, satellites or changes in the composition of the atmosphere. Pessimists assume that our human civilisation will not enjoy a long existence because mankind will destroy itself through wars or environmental disasters. If this assumption also applies to alien civilisations, there would be virtually no chance of two neighbouring civilisations encountering each other during the short time of their existence.

For several decades, the sky has been scanned for radio signals that could originate from alien civilisations in the Milky Way. However, no reliable evidence has yet been found that there is currently another technologically advanced civilisation in the Milky Way besides our own. Aliens have so far only appeared in movies and science fiction literature - they have not yet been sighted on Earth, even though some miracle believers claim the opposite.

So is mankind the only technological civilisation in space? Has no other life form reached this stage of development before us?  

Life on distant planets

Our current scientific knowledge suggests that the emergence of life is almost inevitable if conditions on a planet are similar to those on Earth, provided there are sufficiently long periods without life-threatening catastrophes. There are probably large numbers of planets with Earth-like conditions in our home galaxy, the Milky Way. This is evident from cosmological models for the formation of stars and planets, and for several years now, exoplanets have also been detectable using indirect observation methods. If a planet circulates at a moderate distance around its parent star, the radiation of light and heat is strong enough that the temperatures on the planet's surface are within a range where water can exist in liquid form. If it is a rocky planet with an atmosphere similar to that of the early Earth, containing carbon dioxide, methane and water vapour, complex organic molecules are likely to form on this planet, as they did on the young Earth. The emergence of organic life forms is then probably only a matter of time.

Hence, the emergence of life is not the bottleneck. According to our considerations, the gradual evolution from initially primitive life forms to intelligent beings is also almost inevitable, provided that sufficient time is available. On Earth, it took around 500 million years from the emergence of multicellular organisms to the emergence of humans. Since this period is much shorter than the total age of the universe, which is around 14 billion years, it would be surprising if intelligent life forms had not long since emerged in other planetary systems in the Milky Way, and even more so in other galaxies. Even on Earth, humans are not the only living beings that possess self-awareness and communication skills. Other mammals such as whales and dolphins, as well as some birds, can recognise themselves in mirrors and communicate extensively with members of their own species.

However, it is unclear how long other planets can offer conditions favorable for life. Our own solar system may be something of an exception in this regard. In our solar system, the four inner planets – Mercury, Venus, Earth and Mars – are very well shielded from cosmic debris by the gas giants Jupiter and Saturn, which are located further out. Nevertheless, Earth has also been hit by large asteroids from time to time – such as the asteroid impact 60 million years ago that heralded the end of the dinosaurs and the rise of birds and mammals. If other planets are hit by asteroids much more frequently, this could prevent the life forms there from developing undisturbed for long enough to reach higher levels of development. On the other hand, it appears that during evolution on Earth, life forms developed rapidly after cosmic impacts, and some evolutionary dead ends could only be overcome thanks to such leaps after cosmic impacts. According to the latest findings, the solar system crosses a debris-rich area on its orbit around the centre of the galaxy approximately every 30 million years, which leads to regularly recurring impacts on Earth, followed by a longer period of calm. The driving forces of cosmic and biological evolution seem to be governed by what German poet Johann Wolfgang Goethe (1749-1832) had the devil say in his master piece ‘Faust’: ‘I am part of that force which always wants evil and always creates good. I am the spirit that always denies. And rightly so, for everything that comes into being is worthy of destruction!’

Transition to a technological civilisation

In my opinion, a major bottleneck lies in the transition from an intelligent life form to a technological civilisation. This is because biological evolution generally produces organisms that can cope excellently in their habitat without aids such as tools and clothing. Whales, dolphins and birds do not need tools to survive and reproduce. Apart from that, they do not have an organ comparable to the human hand, which is perfectly designed for using tools. The fact that humans have free hands is only due to a coincidence in evolutionary biology: human ancestors were initially tree dwellers, whose habitat then became the savannah, where walking upright was an advantage. This freed up the hands, which had previously been important grasping organs for tree dwellers. Without this coincidence, humans would not have hands suitable for using tools.

However, humans not only have the ability to use tools, but also the necessity to do so. We like to see ourselves as the ‘crown of creation,’ but in fact, our biological fitness is rather bad. German philosopher Arnold Gehlen (1904-1976) described humans as ‘deficient beings’ for good reason. Alone and naked, we would hardly be able to survive for long. We need clothing to protect us from the cold and wet. We need fire to keep us warm and cook our food. We need weapons to hunt animals and defend ourselves. We need tools to grow crops and process them into food.

The fact that we do not have natural fur to protect us from the elements is probably an unlikely evolutionary coincidence. As described in the article ‘The Evolution of Human Intelligence’, our ancestors probably lost their protective fur because some of the females chose mates who were less aggressive than other males. When humans began to domesticate pigs, they took a similar approach and selected the less aggressive individuals for breeding. The result: domestic pigs are not only less aggressive than wild boars, but they have also lost their fur and developed a shortened facial skull, which is otherwise typical of young animals. The same pattern can be observed in humans. Our ancestors also lost their fur and developed a shortened facial skull in the course of evolution. This is why we talk about the ‘self-domestication’ of humans. Without fur, however, our ancestors had a real disadvantage in the ‘survival of the fittest’. But they were able to compensate for this disadvantage by making clothing and harnessing fire. They were able to put their intelligence and their newly freed hands to good use. From a biological point of view, evolution had manoeuvred our ancestors into a dead end from which they could only escape because they happened to have an organ that was ideally suited to the use of tools.

The fact that evolution on Earth has brought forth a species that depends on the use of tools for survival was therefore merely a coincidence between biological traits that had nothing to do with each other. Such combinations occur occasionally, but it is unlikely that life forms on other planets would exhibit a combination similar to that found in terrestrial mammals. The transition from intelligent life forms to a technological civilisation would therefore be a very unlikely step in evolution. Perhaps we are indeed pioneers in this respect in our galaxy and even beyond.

Colonisation of space

Some tech billionaires dream of leaving our home planet Earth and colonising space. This dream is unlikely to become reality. First of all, other planetary systems are very far away; spacecraft would take many years to reach them. According to estimates, the nearest 20 habitable exoplanets are between 4 and 40 light years away from us. The spacecraft needed to travel such distances would have to be gigantic and would require vast amounts of fuel to transport everything needed for the long journey and to start a new civilisation on a different planet. Nutrition is likely to be a major hurdle. We depend on consuming organic substances such as essential amino acids, carbohydrates, fats, nucleic acids, vitamins and trace elements in our food. If we encounter organic life on a life-friendly distant planet, these life forms will most likely be composed of different organic substances than the life forms on Earth. This means, however, that we would not be able to feed ourselves from these extraterrestrial life forms. We would have to bring our own plants and animals with us in the spaceships – similar to how Noah once brought a seed stock for agriculture and livestock through the floods in his ark. However, our plant and animal species are adapted to Earth's conditions – they would certainly cope less well with the conditions on an different planet than the native life forms there. We would therefore first have to re-engineer the crops we brought with us and suppress the life forms of the alien planet. Alternatively, we could produce our food artificially in a test tube – but that is extremely costly. I therefore consider it virtually impossible for organic life forms to successfully colonise other planets. If, on the other hand, we decide at some point to create a technical life form that does not require organic food and is able to feed itself from other energy sources such as light, it would be conceivable to send it on a journey to distant planets to colonise them. However, we do not yet have the necessary knowledge to develop such technical life forms. With our current engineering knowledge, it is not possible to build self-replicating machines. And the question arises as to why we should do this at all. Why should we create technical life forms that may be superior to us and could displace us? Other intelligent beings will have asked themselves the same question, assuming that intelligent beings who have created a technical civilisation already existed on another planet in the vastness of space before us.

Conclusion

The fact that we have not yet discovered any traces of extraterrestrial civilisations suggests that such civilisations do not currently exist, at least not in our home galaxy, the Milky Way. Although organic life probably exists on many other planets, the step towards a technological civilisation is highly unlikely from an evolutionary point of view. And leaving one's home planet and colonising space is practically impossible. Therefore, we should probably not expect extraterrestrials to visit us on Earth. We should get used to the idea that we are all alone in space.