Other Worlds
About 20 years ago, Isaac Asimov’s book ‘Extraterrestrial Civilisations’ theorised the existence of approximately 570,000 advanced civilisations within the Galaxy, even though he postulated a mean duration for civilisation on a world of only 1 million years. Applying the same approach but allowing for more recent developments in our understanding of the emergence of land life and intelligence on Earth, my own figures are less rosy.
1. Stars capable of supporting living worlds.
The Sun is a not uncommon star type (G2), although most stars are in binaries and this may often prevent the stable conditions necessary for life. Most G and K-type single stars outside the core should be potentially capable.
Guess: 1/20 in population 2 stars outside the galactic core. In our Galaxy: 5 billion.
2. Planets in habitable zone.
There are indications that the zone is fairly narrow - Venus and (probably) Mars lying outside it. However a volcanically active planet is surprisingly good at mitigating temperature extremes.
Guess: 1/5 life zones contain usable planet. In our Galaxy: 1 billion.
3. Life on planet
There seems a strong urge to life throughout the universe. Only repeated meteor bombardment can keep it at bay.
Guess: 9/10 (excluding very young worlds). In our Galaxy: 0.9 billion.
4. Multicelled life on planet.
It took 4 billion years to evolve on Earth, it has existed for only 1/9 the life of Earth. indicating it may be rare. It may take just the right level of meteor impacts to provoke without destroying everything.
Guess: 1/10. In our Galaxy: 90 million
5. Land life on planet.
The development of land life likely was greatly speeded up on Earth by the tidal processes of Earth’s unusually large moon. Furthermore, the planetary impact that created the moon also ripped chunks from Earth’s surface, creating the deep-sea (non-continental shelf) area that enables the existence of large amounts of dry land on the Earth’s suface. This event and its fortunate consequence, the creation of a huge moon in close orbit to Earth, more than any other may be responsible for Earth’s apparent relative uniqueness. Without a large moon, land life could still have developed, but possibly at 1/10 or 1/100 the actual rate.
Guess: 1/1000 In our Galaxy: 90 000
6. Intelligent life on planet’s surface
Intelligent life in a planet’s ocean may be relatively common (look at dolphins), but it seems highly unlikely that it would develop a technologically advanced civilisation capable of interacting with Earth. The relative scarcity of land life postulated in (5) makes the probability of the existence of land civilisations much lower. On Earth the development of human intelligence was spurred on by the Ice Ages, an unusual phenomenon caused by land masses simultaneously appearing over both poles about 5 million years ago. It has only existed for about 1/45000th of the Earth’s existence, or 1/5000th of the time since the development of multicelled life. Given these preconditions, we can guess the figure will be within a similar order of magnitude.
Guess: 1/5000 In our Galaxy: 18
7. Persistence of Intelligent Life on the Planet
How long is intelligence likely to exist, once evolved? On the evolutionary principle that ‘you can never start from a blank slate’, the de-evolution of intelligence among an existing intelligent species seems unlikely, bar selective breeding by an outside controlling entity (presumably intelligent). Barring this, only the destruction of the entire intelligent species will suffice - this might be accomplished by a massive planetary impact or by unsuccessful war with another species that decides to eliminate it - but given the apparent scarcity of intelligent life in the universe, the latter may be very unlikely (barring widespread use of Berserker probes by a hostile and indiscriminatory intelligent species). At a conservative estimate, we can guess that perhaps ½ of intelligent species are wiped out after evolving, probably in the main by natural causes, within the lifetime of their star.
Guess: ½ In our Galaxy: 9
The final figure is very low, and implies that the nearest intelligent alien civilisation may well be 30,000 light years away. If wrong by an order of magnitude, there may be no other intelligent life in our Galaxy - or there may be some within a few thousand light years. In either case, though, it is not surprising that we are not aware of any.
About 20 years ago, Isaac Asimov’s book ‘Extraterrestrial Civilisations’ theorised the existence of approximately 570,000 advanced civilisations within the Galaxy, even though he postulated a mean duration for civilisation on a world of only 1 million years. Applying the same approach but allowing for more recent developments in our understanding of the emergence of land life and intelligence on Earth, my own figures are less rosy.
1. Stars capable of supporting living worlds.
The Sun is a not uncommon star type (G2), although most stars are in binaries and this may often prevent the stable conditions necessary for life. Most G and K-type single stars outside the core should be potentially capable.
Guess: 1/20 in population 2 stars outside the galactic core. In our Galaxy: 5 billion.
2. Planets in habitable zone.
There are indications that the zone is fairly narrow - Venus and (probably) Mars lying outside it. However a volcanically active planet is surprisingly good at mitigating temperature extremes.
Guess: 1/5 life zones contain usable planet. In our Galaxy: 1 billion.
3. Life on planet
There seems a strong urge to life throughout the universe. Only repeated meteor bombardment can keep it at bay.
Guess: 9/10 (excluding very young worlds). In our Galaxy: 0.9 billion.
4. Multicelled life on planet.
It took 4 billion years to evolve on Earth, it has existed for only 1/9 the life of Earth. indicating it may be rare. It may take just the right level of meteor impacts to provoke without destroying everything.
Guess: 1/10. In our Galaxy: 90 million
5. Land life on planet.
The development of land life likely was greatly speeded up on Earth by the tidal processes of Earth’s unusually large moon. Furthermore, the planetary impact that created the moon also ripped chunks from Earth’s surface, creating the deep-sea (non-continental shelf) area that enables the existence of large amounts of dry land on the Earth’s suface. This event and its fortunate consequence, the creation of a huge moon in close orbit to Earth, more than any other may be responsible for Earth’s apparent relative uniqueness. Without a large moon, land life could still have developed, but possibly at 1/10 or 1/100 the actual rate.
Guess: 1/1000 In our Galaxy: 90 000
6. Intelligent life on planet’s surface
Intelligent life in a planet’s ocean may be relatively common (look at dolphins), but it seems highly unlikely that it would develop a technologically advanced civilisation capable of interacting with Earth. The relative scarcity of land life postulated in (5) makes the probability of the existence of land civilisations much lower. On Earth the development of human intelligence was spurred on by the Ice Ages, an unusual phenomenon caused by land masses simultaneously appearing over both poles about 5 million years ago. It has only existed for about 1/45000th of the Earth’s existence, or 1/5000th of the time since the development of multicelled life. Given these preconditions, we can guess the figure will be within a similar order of magnitude.
Guess: 1/5000 In our Galaxy: 18
7. Persistence of Intelligent Life on the Planet
How long is intelligence likely to exist, once evolved? On the evolutionary principle that ‘you can never start from a blank slate’, the de-evolution of intelligence among an existing intelligent species seems unlikely, bar selective breeding by an outside controlling entity (presumably intelligent). Barring this, only the destruction of the entire intelligent species will suffice - this might be accomplished by a massive planetary impact or by unsuccessful war with another species that decides to eliminate it - but given the apparent scarcity of intelligent life in the universe, the latter may be very unlikely (barring widespread use of Berserker probes by a hostile and indiscriminatory intelligent species). At a conservative estimate, we can guess that perhaps ½ of intelligent species are wiped out after evolving, probably in the main by natural causes, within the lifetime of their star.
Guess: ½ In our Galaxy: 9
The final figure is very low, and implies that the nearest intelligent alien civilisation may well be 30,000 light years away. If wrong by an order of magnitude, there may be no other intelligent life in our Galaxy - or there may be some within a few thousand light years. In either case, though, it is not surprising that we are not aware of any.
