From the inhabitants of the stars

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There is a text by the philosopher Immanuel Kant about the inhabitants of the stars . It forms the appendix and third part of the General Natural History and Theory of Heaven , published in 1755, and deals with the question of extraterrestrial life .

According to Kant, the existence of living beings on other planets in our solar system is very likely. In addition, he formulates a law of distance to the sun , according to which the mental abilities of living beings increase the further away they live from the sun. According to this, living beings on Jupiter are spiritually far superior to humans, while Mercury inhabitants are intellectually clearly inferior to those on earth. From a spiritual superiority also follows a moral superiority, which is why people are no longer to be regarded as the "crown of creation" from a spiritual and moral perspective.

Kant's theory of extraterrestrial life received little attention in the history of philosophy and astronomy, also because his theses have turned out to be implausible from today's perspective.

Context of the theory

Drawing by the philosopher Immanuel Kant around 1755 by Caroline von Keyserling

Natural philosophical thoughts on the existence of extraterrestrial life can be traced back to antiquity. For example, in Plutarch's work Das Mondgesicht or Lukian from Samosata's writing Ikaromenipp or the cloud journey, thoughts about living beings beyond the earth can be found. Such texts, however, relate essentially to mythical motifs and do not claim to develop theories about extraterrestrial life with the help of rational argumentation.

This changes at the latest in the late 17th century, among other things by the astronomer Christiaan Huygens and his work Weltbeschauer, or reasonable assumptions that the planets are no less decorated and inhabited than our earth. Huygens, at the same time one of the founders of the theory of probability , realized that he could not come to any certain knowledge about extraterrestrial life. Nevertheless, some assumptions are more likely than others, so one can at least come to "reasonable guesses".

The idea of ​​such “reasonable guesswork” strongly influenced the natural philosophy of the 18th century. With the help of analogy arguments and “reasonable assumptions”, Christian Wolff even calculated the size of the inhabitants of Jupiter to be 13,819 1440ths of a Parisian foot , i.e. about four meters. Kant's hypotheses about life on foreign planets are also based on the methodological basis of analogies and “reasonable assumptions”. Kant's preoccupation with the question of extraterrestrial life is by no means unusual in the context of contemporary natural philosophy and astronomy.

Although Von den In der Kestirne belongs to Kant's early, pre-critical writings, there is no evidence of a later distancing from belief in extraterrestrial life. In this context, there are numerous passages in later works that emphasize the validity of principles for all beings gifted with reason. In the Critique of Pure Reason, for example, it says : "The human mind takes (as I believe that it necessarily happens in every rational being) a natural interest in morality". In Kant's late book Anthropology in a pragmatic way from 1798, even explicit reference is made to inhabitants of other stars:

“It is remarkable that we cannot think of any other suitable form for a rational being than that of a human being. Any other would at best be a symbol of a certain human characteristic - e.g. B. the snake as an image of malicious cunning - but do not represent the rational being itself. So we populate all other world bodies in our imagination with nothing but human figures, although it is probable that they may be very differently shaped according to the differences in the soil that supports and nourishes them and the elements of which they consist. "

Existence of extraterrestrial life

Kant does not doubt the existence of life on other planets. Some planets may be uninhabited, but this is an exception. On the one hand, some planets may not yet be fully developed and therefore not yet offer the conditions for organic life - Jupiter is a candidate for such a star. Also "there could be barren and uninhabitable areas", but it would be an "inconsistency" to deny that most of the planets are inhabited.

Kant is so sure of this fact that he does not even argue in detail for the existence of extraterrestrial life. He only gives a satirical story about lice to illustrate his thesis:

"Those creatures [...] who inhabit the woods on the head of a beggar had long considered their abode for an immeasurable sphere and themselves as the masterpiece of creation, as one of them whom heaven had endowed with a subtle soul, a little Fontenelle of his sex, the head of a nobleman, was unexpectedly noticed. Immediately he called all the witty people in his quarters together and said to them with delight: We are not the only living beings in all of nature; see a new country here, more lice live here. "

From Kant's perspective there are two arguments for the existence of life on other planets. One argument is based on the principle of analogy, the other on Kant's cosmogonic theory.

Analogy argument

The fable about the lice already suggests the analogy argument that seems to speak for the existence of life on other planets: If there are different heads and one finds lice on one head, one can reasonably assume that one is also on other heads Will find lice. Only ignorance could lead the fable's lice to assume that only their head is inhabited. Likewise, it would be ignorant if humans assumed that only their planet was inhabited.

If the fable is to become a convincing argument, it must be justified why people are ignorant when they assume that only the earth is inhabited. The existence of other planets does not imply the existence of other inhabited planets. This is where the analogy principle comes into play: If you compare planets with other celestial bodies such as the sun, comets, moons or stars, you will find many astronomical similarities between planets. Now the principle of analogy can be formulated as follows: If two cases are similar in many known aspects, one can assume that they are also similar in unknown aspects. Since planets are now similar in many respects, one can assume that they are also similar with regard to the question of the existence of life. And since we already know of one planet - the earth - that life occurs on it, it is reasonable to assume that life has also evolved on the other planets.

Such an argument by analogy can seem absurd from today's perspective, as it leads to incorrect results. It should be noted, however, that analogy arguments are common in many sciences. A simple example is the assignment of paintings. If you ask yourself whether a painting can actually be assigned to a particular painter, you will argue according to the principle of analogy: If two cases are similar in many known aspects, one can assume that they are also similar in unknown aspects. The more the painting in question matches the known paintings (dating, material, style, etc.), the more likely it is that the paintings match in terms of their originator as well. Modern astrobiology also argues on the basis of analogy arguments: We are looking for places that match the earth in as many relevant aspects as possible.

Kant's assumptions about the existence of extraterrestrial life are therefore not wrong because they are based on dubious argument structures. On the one hand, Kant did not have the data available today on differences between the planets, and on the other hand he did not know which similarities are relevant for the origin of life, for example temperature or atmosphere.

Cosmogony argument

Kant's astronomical theory makes the existence of extraterrestrial life plausible for another reason: the young Kant is an enthusiastic Newtonian and his General Natural History and Theory of Heaven is based on the theoretical innovations of the Philosophiae Naturalis Principia Mathematica . However, Kant goes beyond Newton in one crucial point: Newton was able to explain the movements of the planets with the help of the theory of gravity, but he had no theory for the development of the universe and postulated the direct intervention of God at this point. Within the framework of the Kant-Laplace theory , Kant is now able to provide an explanation for the development of the universe on the basis of Newton: Kant does not assume an empty space as the initial condition, but a material nebula ( solar nebula ) that does not yet have any shape owns. Now, however, this initial state would change rapidly through attraction and repulsion and would eventually reach the present state of the universe. In the context of this theory, the following famous saying by Kant is to be understood: "Give me matter, I will build a world out of it!"

Now this evolution of the cosmos does not stop at inorganic matter; rather, Kant imagines the emergence of organic life as a further stage in the development process, which is guided solely by the laws of nature . The direct intervention of God is not necessary in the formation and development of the planets, nor in the formation and development of organic life. Kant's remark that there may not yet be any life on Jupiter because it is not yet in a sufficiently advanced stage is to be understood in this sense.

Properties of extraterrestrial life

Mental abilities and the distance from the sun

Solar system, not to scale

In the text On Inhabitants of Alien Stars , Kant very quickly moves from the question of the existence of extraterrestrial life to a theory about the shape of this life. Newton's theory of gravity is central here again. According to Newton's law of gravitation , the force of attraction between two bodies decreases with increasing distance. Since the planets are located at different distances from the sun, the bodies on the planets are also exposed to different forces. According to his general astronomical theory, these differences mean that denser matter sinks further towards the sun, while lighter parts are further away from the central star. Now Kant argues that these differences in the material constitution of the planets must certainly have an influence on the shape of life.

“The material from which the inhabitants of the most varied of planets, indeed even the animals and plants on them, are formed, must be all the lighter and finer, and the elasticity of the fibers, including the advantageous structure of their structure, must be all the more perfect, according to the measure as they stand further from the sun. "

In a second step of the argument, Kant deduces from the advantageous physical constitution to an advantageous mental constitution. This step assumes that the mental abilities are determined by the physical characteristics of living beings. Kant agrees with the premise that “the ability to think [...] depends entirely on the nature of this matter.” Kant thus formulates a law of distance to the sun, according to which the physical and mental abilities of living beings increase with distance from the central star.

The reasoning for the law of distance from the sun can be criticized from many perspectives. Even if one accepts the dependence of physical properties on the distance from the sun, one can still ask why the "elasticity of fibers" should be decisive for the mental abilities of living beings. Kant meets this argument again with an analogy: With increasing age, the fibers of people become less flexible, the juices thicker. However, according to Kant, these physical phenomena also lead to increasing mental immobility in old age. If one can now observe in people on earth that the mental abilities are dependent on these physical phenomena, then one can reasonably assume that it behaves in the same way with other living beings.

Moral mediocrity of man

In the middle of the 18th century, the Copernican worldview was recognized, according to which the earth was one of the other five classical planets in the solar system, Mercury is closest to the sun and Jupiter is further away from the sun than the earth. The earth stands between these planets and according to the law of the distance from the sun, the inhabitants of the earth only have average mental abilities. Kant explains this situation with the following comparison: Everyone would appear to the inhabitants of Mercury like a Newton - for Kant Newton is an outstanding example of a genius. Conversely, even Newton would appear to the inhabitants of Jupiter to be very intellectually unskilled. One consequence of the Kantian conception is that people no longer appear as the “crown of creation”, they are hopelessly inferior to many extraterrestrial living beings.

The situation is exacerbated as Kant ties the moral faculties of living beings to their general intellectual faculties. So humans are not only spiritually inferior to the inhabitants of Jupiter, but are also morally on a lower level. Kant speculates that the human situation may be unique, as only they have the "unhappy ability" to sin:

“Who knows, then, the inhabitants of those distant celestial bodies are not too lofty and too wise to surrender to the folly that is in sin, but those who dwell in the lower planets are too firmly attached to matter and provided with too little faculty of spirit to be allowed to bear the responsibility of their actions before the judgment seat of justice? "

Reception and perspective of bioastronomy

The assertions of the text have largely turned out to be false or implausible: It is not the case that intelligent life forms can be found on most of the planets in the solar system, and the law of the distance from the sun seems extremely implausible from today's perspective. The reception is shaped by these facts: Occasionally Von The Inhabitants of Alien Stars is an example of the fact that even strict, systematic thinkers like Kant come up with absurd and speculative theses. In addition, there is a tendency in Kant research to ignore Kant's theory of extraterrestrial life. Also in many discussions of his pre-critical natural philosophy there is no mention of this subject.

However, Kant was well aware that with some of his theses he was on the verge of what could reasonably be discussed: "Who shows us the limit, where established probability ends and the arbitrary fictions raise?" However, Kant's doubts refer to his speculations about He certifies the moral properties of living beings, other considerations, to be “not far from an established certainty”.

Indeed, the structure of Kant's arguments is often quite modern and stands out from many mythical and theological speculations about extraterrestrial life. Modern astrobiology is also often faced with challenges similar to those of Kant and also refers to arguments by analogy. When bioastronomers discuss life outside the solar system, they have no direct data on the conditions on the planets and have to come to their conclusions indirectly. It is considered how likely the existence of planets is that are sufficiently similar to the earth to infer a possible form of life by analogy. The best-known example of such a train of thought is the Drake equation .


Primary literature

  • Immanuel Kant: General natural history and theory of the sky , 1755. Parts I and II contain Kant’s general astronomical theory, part III / appendix the considerations for life on other planets
  • Immanuel Kant: Metaphysical Beginnings of Natural Science , 1786. Kant's central writing on natural philosophy from his critical time
  • Isaac Newton: Philosophiae Naturalis Principia Mathematica , 1683. Basis for the astronomical considerations of Kant

Secondary literature

  • Eberhard Knobloch: "Multiplicity of Worlds - Extraterrestrial Intelligence.", In: Wilhelm Vosskamp: Ideale Akademie , Berlin, Akademie Verlag, 2002, ISBN 3-05-003739-3 . Overview article on extraterrestrial life in the history of science, contains a section on Kant
  • Mary Hesse : Models and analogies in science , Notre Dame, Ind., Univ. of Notre Dame Press, 1966, ISBN 0-268-00337-8 . Standard work on arguments by analogy in the sciences. However, without direct reference to Kant

Web links

Individual evidence

Quotations from general natural history and the theory of heaven only contain the page numbers of the work edition.

  1. Plutarch: The moon face , trans. by Herwig Görgemanns, Zurich, 1968
  2. Lukian of Samosata: Ikaromenipp or the cloud journey , bilingual edition, ed. and over. by Karl Mras , Munich, 1980
  3. Christian Wolff: Elementa matheseos universae. Edito Nova , Halle, Renger, 1735
  4. For an overview of Kant and the history of science the search for extraterrestrial life has: Eberhard Knobloch: "plurality of worlds - extraterrestrial intelligence.", In: William Voßkamp: Ideal Academy , Berlin, Akademie Verlag, 2002, ISBN 3-05-003739- 3 , pp. 185-187. For Wolff's calculation, see there, p. 167 Googlebooks
  5. Immanuel Kant: Critique of Pure Reason , AA III p. 537, footnote.
  6. Immanuel Kant: Anthropology in a pragmatic way , p. 172.
  7. A 175f.
  8. A 177f.
  9. Mary Hesse: Models and analogies in science , Notre Dame, Ind., Univ. of Notre Dame Press, 1966, ISBN 0-268-00337-8
  10. Isaac Newton: Philosophiae Naturalis Principia Mathematica , 1683, digitized version  ( page no longer available , search in web archivesInfo: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice.@1@ 2Template: Toter Link /  
  11. A XXXII
  12. A 186
  13. a b A 180
  14. A 198
  15. A 197
  16. A 195
  17. An overview is provided by: Jean Heidmann: Extraterrestrial Intelligence , Cambridge, Cambridge University Press, 1197, ISBN 0-521-58563-5
This version was added to the list of articles worth reading on May 4, 2008 .