Ever since the invention of fire, skyrocketing after the industrial revolution, humanity has raced to exploit the energy resources stored on the earth (largely) in the form of hydrocarbons. The Kardashev scale describes civilisations based on the energy they can use: a Type 1 civilisation is able to use all energy available on its home planet. Humanity is advancing towards that stage through techniques such as geothermal energy capture, photovoltaic cells and nuclear power. In the far future, it may be that our needs for energy may even exceed what we can possibly manipulate here on Earth. According to Kardashev, a civilisation reaches the second stage once it can harness the total energy of its home star. Is this advancement even plausible, and if so, is it inevitable? 

An artist’s conception of a partial Dyson Sphere (Image Credit: Kevin McGill, Flickr)

The most popular concept conceived to fulfil this role has been the Dyson Sphere. Named after the physicist Freeman Dyson, it involves a structure that completely encloses the star, collecting the near entirety of its energy output. Only a fraction of that energy reaches any planet. Hypothetically, this structure could supply that space-faring civilisation vast amounts of energy. Our Sun releases on average 3.8 x1028 J/second in various forms of radiation1, from infrared to ultraviolet radiation, including of course visible light. This converts to about 1.05×10^11 terawatt-hours, enough to meet Earths final energy consumption (in 2015) for around 967,000 years2. In fact, even the portion of that energy which reaches the Earth is more than enough, with the energy from the sun reaching Texas alone at noon equivalent to 300 times the world’s total electricity production3. The fact that even harnessing the energy we could get whilst staying from the Earth would eclipse our current production emphasises our distance from becoming even a Type 1 civilisation and the hypothetical nature of the Dyson Sphere. 

In the solar system around 99.9% of mass is in the sun4. Obviously, we can use none of this for construction. Of all the matter in the solar system, around 507 parts per million are metals, or 0.000507%. Considering not all of these are metals we can use, and assuming that we are not willing to cannibalise the Earth itself for its metal core, this drastically reduces the total amount of matter at our disposal. The ore deposits seem to be most prominent on Mars and Mercury, and it seems that if we attempt to build a partial Dyson Sphere (perhaps a Dyson Swarm) than they would be reduced to fields of rubble, as well as much of the asteroid belt. 

Therefore, when Freeman Dyson thought about the Dyson Sphere he largely applied it to the search for extra-terrestrial life. We have no idea how another civilisations energy requirements and technological capacity develops, and as far as we know these civilisations could have existed for millions of years. As a result, the existence of an alien Dyson Sphere cannot be ruled out. He therefore reasoned that the presence of Dyson Spheres could explain the Fermi Paradox, or the lack of evidence for the existence of alien civilisations given the (extremely rough) estimation by some scientists that existence of alien life even in our galaxy is probable5, such as the Drake Equation. The universe has existed for so long a period that any spacefaring civilisation, say, in our galaxy, surely would have been able to even at sub light speeds colonise the entire galaxy. After all, life has proven to be extremely robust, with extremophile bacteria surviving in centrifuges under gravitational forces of 400,000gs.   

The Fermi paradox seems far stranger when we consider the active search we have undertaken as humans for extra-terrestrial life. The organisation SETI (Search for Extra-terrestrial Intelligence) uses various methods, most prominently the Allen Telescope Array, located in the Cascade Mountains in California. It soon will be able to carry out “reconnaissance” of over 1 million nearby stars in the coming future6, and can detect radiation with frequencies between 1,000 and 15,000 Mhz- radio frequencies. Other telescopes, whilst not exclusively devoted to searching for “aliens,” could detect signs of life on multiple other bandwidths.  

The Allen Telescope Array (Image Credit: Seth Shostak, SETI Institute)

Given this, how would we go about finding a Dyson Sphere with our current means? Firstly, we need to determine what a Dyson Sphere would look like. It’s obvious that the popular concept of a solid sphere around a star is an impractical idea. It would be extremely vulnerable to projectiles moving near to the star such as asteroids. There are estimated over 150 million asteroids larger than 100 metres orbiting within the solar system at high velocities. Impact with the sphere would result in a large amount of damage to a large portion of the structure, and any mechanisms attempting to act as a defence (such as for example a laser) would significantly reduce the net output of energy. There will also be structural difficulties as no currently discovered substance seems strong enough to withstand the stress on such a large structure. 

An alternative to the conventional sphere is a Dyson “Swarm,” composed of a vast number (in the quadrillions) of independent collectors somehow kept around the star in independent orbits. Each collector would be an essentially vast mirror reflecting light to a smaller number of converters. Given the nature of orbital mechanics, to avoid collisions it would require extremely complex arrangements. Even with all collectors in polar orbits, the meeting point above the star would require them to each orbit at slightly different altitudes. Obviously, many would continuously be eclipsed. Therefore, even more would have to be constructed.  

This simply increases the amount of material required, and thus makes it unlikely that there would be enough to reach full coverage. However, given the sheer amount of energy released by the sun, even managing to capture 1% of that energy would provide vast amounts of energy. Note that for civilisations that have been developing for long periods time it seems likely that their energy requirements would outstrip the possible production of their home planet and thus at least some measures would have to be taken to harness the energy of a star. A full or partial Dyson Swarm is a very possible way of achieving this for civilisations with advanced space technology. This is especially true for our Solar System, given Mercury’s large metal deposits whilst close to the sun and with low gravity, reducing exit velocity and therefore the energy required for construction and transport.  

However, any megastructure would have a large impact on the habitability of planets in the system. If energy from the sun were no longer reaching us, little would prevent massive temperature drops (even though our atmosphere retains heat quite well) other than the heat of the earth’s core and temperature at the Earth’s surface would eventually reach around 50 degrees above absolute zero.7 Whilst researchers at the Potsdam Institute for Climate impact research argue that for complex multi-cellular organisms to evolve, photosynthesis on a planet is necessary, it is obvious that any civilisation advanced enough to undertake this project could mitigate the impact a reduction of light would have on the synthesis of food on a necessary scale. Therefore overall the only possible solution we can envision is the construction of artificial habitats on planets or in space. Once again, it is impossible for us to make any assumptions about the motives of any aliens other than the most basic.  

Therefore, what interest us are locations where stars should be present but no or little visible light reaches us as small or large proportions as well as possibly the entirety of the star is surrounded. What would this look like for us? Whilst less visible light would escape, some of the energy would be radiated away as infrared radiation, or heat, so that the material maintains a constant temperature. Therefore, we would want to find stars that release unusually high levels of infrared radiation compared to visible light. 

However, as of yet searches for Dyson “Spheres”(as I will refer to all Dyson structures for convenience) based on the above principles have turned up nothing. A new study by Erick Zackrisson at Uppsala University in Sweden has proposed a method to find partial Dyson Spheres with “weak or even absent waste heat signatures,” such as ones which release radiation outside infrared wavelengths, store heat energy, or radiate it in a different direction than towards us8. This works on the assumption that it is impossible or impractical to build a Dyson Sphere that entraps the entirety of all radiation of a certain wavelength. At least some, be it visible light or infrared radiation, will get through. It uses the Gaia Project, “an ambitious mission to chart a three-dimensional map of our Galaxy.9”  

Since a partially covered star would seem much more faint to us as less of its energy reaches us at wavelengths of visible light, we would receive the impression that it is further away because of spectrophotometric measurements. Spectrophotometry is used to determine the distance of bright stars by at first finding out the colour spectrum of the light given off by the star. Given that we can predict exactly how a star’s colour changes as it increases brightness, we can use that colour to accurately ascertain its brightness. Apparent brightness has an inverse square relationship with distance- with two identical stars, if one is 10x further away, it will appear 1/100 times as bright. Calculations using the brightness of the sun and its distance can be applied to roughly work out the distance of the star. If a Dyson Sphere is present, then the star will appear to us less bright and therefore much further away.  

However, the Gaia program uses the parallax method employing extremely precise measurements from a satellite not in Earth’s orbit but at the L2 Lagrangian point- in other words constantly suspended on the opposite side of the Earth to the sun can ensure an actually accurate measurement of distance. The way stellar parallax is used to find the distance of a star is as follows: two measurements are taken of the star’s location on the night sky at two points in time, exactly six months apart. These are taken at the two points when the angle formed by the lines between Earth and the Sun and the star and the Sun is 90 degrees.  

The Parallax Method  (Image credit: Alexandra Angelich, NRAO/AUI/NSF)

Given that we know the distance from Earth to the Sun, we can use the tiny shift in angle as we perceive the star in relation to the horizon and trigonometry to determine its distance. Whilst parallax decreases with distance, Gaia can measure parallax angles to an accuracy of 10 microarcseconds10, about 1/360 of a degree. This is enough to reliably measure the position of 1 billion nearby stars, according to the European Space Administration11. This is also true for its relative velocity to us, as we take several measurements of the star over time and compare its distance. So far it has recorded information about 1.7 billion12, including radiation footprints.  

As a result, we can identify possible Dyson Spheres that don’t have large heat signatures by finding stars whose distance working from spectrophotometry are very different to the value provided by a more accurate trigonometric parallax calculation. In fact, we can work out the exact percentage of the star that is obscured by predicting the nature of the radiation reaching us had it been at the location suggested by spectrophotometric readings.  

The results have been analysed and potential candidates for locations of Dyson Spheres have been identified in our galaxy. 6 candidates were initially chosen, each of which had a potential “blocking fraction,” or proportion of energy blocked, of 0.7. This was eventually narrowed down to two, and then finally one star, “the late F-type dwarf TYC 6111-1162-1.” However, a potential alternative explanation is the presence of a massive white dwarf, undetected by us, in a binary system with our candidate, therefore massively throwing off the parallax measurement used. Future data collection by the Gaia satellite could determine the movement of the star and therefore perhaps confirm this. 

The alternative is, of course, that we haven’t searched enough space yet. Only main-sequence stars were fully considered because for large giants spectrophotometric distances tend to be vastly overestimated. Future technology could more accurately measure discrepancies for all stars. Astronomers at Penn State have said that the amount of observable space SETI has so far searched is  “comparable to searching the volume of a large hot tub for evidence of fish.13 “In our case this is less applicable as it refers to searches by SETI’s own more comprehensive equipment, whilst independent analysis of Gaia data has covered a larger number of stars specifically looking for Dyson Spheres. 

In addition, far more efficient methods of possible future energy production have been discussed. Why would an extremely advanced civilisation spend vast amounts of resources and time constructing a Dyson Sphere whilst they could attempt developing cold fusion reactors, antimatter generators and a means of energy generation known as the “kugelblitz”. Each has received large amounts of attention from the scientific community and are potentially viable, as well as extremely far-fetched, potential means of meeting a civilisation’s energy demands. 

In conclusion, whilst the Dyson Sphere has been represented as an awe-inspiring mega-structure in science fiction, featuring in for example Star Trek, not only is it for us outside the realm of practicality given the rare nature of metals in our solar system, but also the manner in which it is described as a solid sphere is incredibly unrealistic. Dyson Spheres could be a potential reason for a lack of evidence for alien intelligence even though we have discovered means of finding them, given how little space we have searched. Finally, although we can never assume the motives of any alien civilisation, it seems unlikely that they would turn to constructing a Dyson Sphere as opposed to other more efficient futuristic means of energy generation, dooming all (remaining) planets in the system to near darkness. 

References

[1] https://www.gocamsolar.com/blog/how-much-energy-does-sun-generate

[2] https://en.wikipedia.org/wiki/World_energy_consumption

[3]https://ag.tennessee.edu/solar/Pages/What%20Is%20Solar%20Energy/Sun%27s%20Energy.aspx

[4] http://earthguide.ucsd.edu/virtualmuseum/ita/08_1.shtml

[5] http://www.astrodigital.org/astronomy/drake_equation.html

[6] https://www.seti.org/ata

[7] https://www.spaceanswers.com/astronomy/why-is-venus-so-bright/

[8] https://arxiv.org/pdf/1804.08351.pdf

[9] http://sci.esa.int/gaia/

[10] https://en.m.wikipedia.org/wiki/Stellar_parallax

[11] http://sci.esa.int/gaia/

[12] https://www.forbes.com/sites/startswithabang/2018/05/03/dyson-spheres-the-ultimate-alien-megastructures-are-missing-from-the-galaxy/#5d3e03793138

[13] https://www.smithsonianmag.com/smart-news/search-aliens-weve-only-examined-cosmic-hot-tub-180970447/

About the author