Dyson Spheres and Carl Sagan’s Golden Rule

Thanks to recent astronomical observations the topic of Dyson spheres is back in the limelight.

What are they and what caused this renewed interest?

Dyson Spheres

Dyson spheres would be alien megastructures built around a star with the aim of collecting a large amount of energy emitted by the star itself.

The first who speculated about this kind of structures was the philosopher and science fiction writer Olaf Stapledon in a novel published in 1937.

Later the idea was popularized by the renowned physicist Freeman Dyson. In an article published in 1960 he considered this kind of structures the most natural way in which a highly advanced alien civilization could meet its energy needs.

He hypothesized that these structures could be observable thanks to a couple of clues

  1. a periodic variation in the star brightness caused by a partial obscuration by the Dyson sphere
  2. the emissions of electromagnetic waves in the infrared caused by the overheating of the structure. These emissions would make the electromagnetic spectrum of the star different from that of similar stars not surrounded by a Dyson sphere.

In the following years, many different geometric shapes were hypothesized for this kind of structures, for example Dyson swarm, Dyson Bubble, and Dyson Shells.


Dyson swarm
Dyson bubble
Dyson ring

Our current technology is far from the possibility of building even small versions of this kind of structures, but other extraterrestrial civilizations may already be able to build something similar.

Dyson Spheres in the News!

In recent years a couple of astronomical observations had a certain media coverage because, among the many hypotheses made to explain some weird phenomenon, also the presence of a Dyson sphere has been considered.

The most interesting case is a star called KIC 8462852 or Tabby’s star, 1280 light years away. The star, not visible to the naked eye, had already been discovered in the 19th century but its strange properties had never been noticed.

Between 2009 and 2013 the Kepler spacecraft monitored the brightness of a lot of stars searching for evidence of exoplanets. After some time this data were analyzed in a citizen scientist project and an odd variability in the brightness of Tabby’s star was noticed.

The star has small and irregular brightness oscillations on a daily scale and much bigger brightness decreases with intervals of a few years.

During these periods its brightness can drop up to 22%. This is a very high percentage considering that Jupiter, the largest solar system planet, would obscure a fraction of about 1% of Tabby’s star.

Tabby’s star brightness variability between 2 May and 4 October 2017.

For this reason some have suggested that the change in brightness is due to the presence of a giant alien structure.

The SETI Institute has pointed radio antennas at the star and no particular signal has been found although the star is so far away that alien signals could be too weak to be detected.

Even the infrared emissions caused by the heating of the structure hypothesized by Dyson has not been observed.

By now, however, also other possible natural explanations don’t completely satisfy scientists.

The most plausible cause seems to be the presence of a large cloud formed by the debris of a comet or planet, as a result of an impact with an asteroid.

The probability of this phenomenon being caused by a Dyson sphere is rather low, and we don’t have to fall into the trap of believing something is true just because we like that kind of explanation!

Carl Sagan’s Golden Rule

Something similar happened when pulsars were observed for the first time. It was 1967, and among the various possible explanations of their highly regular pulsating electromagnetic emissions, also the presence of an alien civilization was taken into account.

Then, in a short time, it became clear that the signal was due to a natural phenomenon.

We must learn from past experiences and always remember the golden rule popularized by Carl Sagan which states that extraordinary claims require extraordinary evidence.

Carl Sagan with a model of the Viking lander.

One day maybe we will have stronger evidence and we could say that we have identified an alien civilization.

At the moment we have nothing more than a strange change in a star brightness, not a strong evidence at all for such an extraordinary claim.

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P.S. I’m currently working on the 2018 math and physics calendar, stay tuned!


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