Monday, May 31, 2010

Dyson Spheres

Finally, here is a post totally unrelated to software or even computer science. It is about a very intriguing concept called Dyson Sphere. Since I don’t have formal education in astrophysics, I guess that the post has very limited value for those who are knowledgeable in this science, but nevertheless I think it would be interesting for rest of us.

Dyson Sphere (named after Freeman Dyson)  is a name for a category of (for now imaginary) mega structures potentially used by advanced civilizations to collect energy from their stars. Before I describe Dyson Sphere(s) in more detail I would like to digress a bit and say a few words about one proposed way to classify advanced civilizations.

Advanced Civilization Types

Since we currently know only one intelligent civilization (us), it is very hard to come up with solid classification of intelligent civilizations. But still, classification called Kardashev scale is frequently used by scientists and other authors. Kardashev scale classifies advanced intelligent civilizations according to their technological level. It was proposed by Russian astrophysicist Nikolai Kardashev, and is well-known, but not widely accepted method (because of its speculative nature). This scale assumes that technological level of civilization is closely related to the amount of energy civilization consumes, that energy demand grows as civilization advances and that astronomical objects are used as primary energy sources. Initially, scale consisted of three types only (Type I, Type II and Type III), but later, as astrophysics advanced it became evident that Types IV and V can be added too.

  • Type I: civilization uses all resources on its own planet.
  • Type II: civilization uses all resources of its star system, primarily its star.
  • Type III: civilization uses all resources of its galaxy.
  • Type IV: … all galaxies in the universe.
  • Type V: … all universes.

Of course, it is obvious that this method is highly speculative. First of all, types III, IV and V indirectly assume that speeds above c (light speed) or some other means of large distance transportation are possible in our universe. Otherwise colonization of entire galaxy / other galaxies would not be feasible. Further, Type V assumes that others universes exist which is very likely according to many scientists but isn’t proven yet. Finally, maybe there is a way to get all this energy without going that far. Attaching to most of the stars in the galaxy or even universe sounds like very pedestrian and unintelligent approach, and maybe it is possible to get the same amount of energy by using resources from own planet only and some process we are still unaware of.

Our civilization

One interesting question is: what type our civilization belongs to? And answer is really obvious: currently we are civilization Type 0. In other words, we really don’t meet all requirements of Type I. According to Kardashev Scale wikipedia article, as of year 2010,  our energy consumption is about 72% of the amount required to “qualify” as Type I civilization. And it is possible that we will qualify as Type I civilization (again according to our energy consumption) around the year 2100.

Another interesting thing is that some scientists think transition from Type 0 to Type I is probably the most dangerous period for every intelligent civilization. This is the period when civilizations might be very prone to self destruction. Simply, at that point, civilization finally acquires almost complete control of its planet, and if its “spiritual” level doesn’t match its technological advancements, self destruction is unfortunately very likely.

One of the explanations for seeming absence of intelligent civilizations is that the greatest number of them self-destroy exactly during this transition and never achieve higher levels. In my humble opinion, this is not very good explanation, because even if these advanced civilizations existed, most likely we wouldn’t be able to notice them. One of the scientists from highly-recommended The Universe series noted the anthill paradox: ant civilizations don’t notice big highways passing nearby their anthills and we as members of more advanced civilization are very uninterested in approaching to tell them more about us, let alone share some of our scientific discoveries.

Back to Dyson Sphere

Now, after really big digression, let’s go back to the original topic – Dyson Sphere. It is obvious that if we take a look at Kardashev scale, Dyson Sphere can be used by civilization Types II and above. I already mentioned that Dyson Sphere represents entire class of imaginary structures that serve the same purpose. They don’t have to have necessarily be of spherical shape. So any structure that your imagination might come up with might qualify as Dyson Sphere. Our civilization is obviously not ready for creating one, so most of ideas about this subject are in the realm of science fiction. The idea itself was inspired by a science fiction novel, so don’t be afraid to think about new ideas in this area, you don’t have to be an astrophysicist to come up with an good idea (after that astrophysicists will be glad to explain why your idea is impossible :-) ).

Dyson Sphere Variants

The most popular form of Dyson Sphere is Dyson Shell. It gained popularity through frequent mentioning in science fiction literature. It consists of single spherical structure built around a star. This structure would therefore absorb 100% of emitted energy. It is not hard to conclude that structure like this is not feasible for many reasons. Dyson himself said that  it is mechanically impossible to build a solid one-piece shell or ring structure surrounding a star. Many proposals suggest that internal surface of shells should be populated by humans. One step further is actually terraforming the internal surface of the shell. It is obvious that the perimeter of the shell should be close to average Sun-Earth distance or some other value in habitable zone of our solar system. Needless to say, this is just a interesting thought experiment, it is not hard to list many potential issues with this design. For example, Sun’s gravitation wouldn’t hold the shell in place and we would have to find the separate collision preventing mechanism. Shell would be vulnerable to impacts of outer bodies such as asteroids and comets. There would be no nights except if not simulated, perhaps by eclipsing sun with collectors.

Dyson Swarm is a more feasible approach in which we have many star satellites orbiting the sun and collecting the energy. These collectors would have to be arranged in ring or spherical structure and orbit around the sun. Collectors could be built and deployed one by one so the Dyson Swarm could grow gradually. This approach is closest to our current capabilities.  Dyson Bubble is Dyson Swarm variation where collectors are intentionally kept static. In this case separate mechanism is used to neutralize the effect of star’s gravity on collectors. Main benefit we get from this variation is that we lower the chance of potential collisions.

If you go through the scientific and science fiction literature you will find dozens of Dyson Sphere variations. They range from ones used solely for energy collection to ones used primarily for habitation. Each proposed variation has serious drawbacks, and no matter how feasible it looks at the first glance we are far from being able to implement something like that. But it is possible that sometime in the future human civilization will have the need to build mega structures like these in order to fill its energy or habitat needs.

Search for Extraterrestrial Intelligence

Here is another reason why concept of Dyson Sphere is so interesting. Many scientists believe that intelligent civilizations at some point need to build mega structures like Dyson Sphere, so it is reasonable to believe that some other, more advanced civilizations already use them. Dyson Spheres would be easy to detect and this is why searching for them is really great idea for detecting extraterrestrial intelligence. Basically, light spectrum emitted by a star would be analyzed to find unusual alterations that suggest presence of collectors. Fermilab Dyson Sphere Search Program has been conducting this search for several years. Basically they are analyzing star by star and looking for patterns that resemble full or partial Dyson Spheres. The sensitivity of their analysis is enough to detect solar-sized Dyson Spheres. And… did they find something? The answer is: no, they didn’t find anything thus far. They used 250,000 source database of the IRAS infrared satellite that covers about 96% of the sky. After reviewing all results they were very skeptical, they couldn’t find any likely candidates.

Search continues, scientists are using all kinds of methods to detect extraterrestrial life and this is only one of them. Thus far, every our attempt was a disappointment. But in my opinion that shouldn’t make us think that intelligent extraterrestrial life doesn’t exist. Our search methods and assumptions about how advanced civilizations look like (such as assumption that they use of Dyson Sphere) might be really naive. It is very possible that advanced civilizations don’t want to be easily detectable by potentially unfriendly civilizations. Perhaps, it is not realistic to believe that a civilization far ahead of ours would build a Dyson Sphere easily detectable by humans. This shouldn’t however prevent us from theorizing and searching further! 

Useful links:

No comments: