It is theorized by scientists that advanced alien civilizations would use a large percentage of the energy of their parent star. This would result in a lot of waste heat being generated on an enormous scale, which has the potential of being detectable using telescopes here on earth. Explain how this theory makes sense from a thermodynamics sense, using our civilization as an example.
Answers
If aliens somewhere in the universe are using a significant portion of a star's energy to power their civilization, a very large amount of waste heat would be produced as a result, which would lie in the mid-infrared portion of the electromagnetic spectrum. This is an inescapable consequence of the laws of thermodynamics. Energy cannot be destroyed, it can only change forms, and the common form of energy after being used is to end up as waste heat. Take a car for example; most of the energy of the fuel is lost as heat, and the remaining energy is used to move the car (i.e. perform useful work). However, to move the car, friction with the road and air must be overcome, along with internal friction of the engine and other moving parts in the car. Ultimately, this ends up as wasted heat as well. So essentially all the energy of the car's fuel ends up as waste heat. You can argue the same principle would apply for aliens using a large fraction of star energy. That energy is used to "do something", and after that task, or tasks, are performed, and assuming none of the energy is stored anywhere, that energy will end up as waste heat in the mid-infrared. You can go much deeper than this to explain the precise reasons why, but it's a basic consequence of the laws of thermodynamics.
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