Alien Technologies

There are many potential ways to detect an advanced alien civilization, but one of the most promising is through observing their technologies. Because they would still be subject to the laws of thermodynamics, these civilizations must obtain and store energy, likely at a much larger scale than we humans have achieved.

If a civilization ultimately derives the majority of its energy from its star, as we do now with every energy source except for nuclear fission, it is beneficial to produce that energy as efficiently (as few changes of the form of energy, for example) as possible, as more can be done with more energy. As such, it can be expected that a sufficiently advanced alien civilization would surround its star with as many solar panels as possible. Any light not captured would be wasted energy. From Earth, such a process would look like a star dimming until it’s invisible, over a long period of time. (The information wouldn’t travel to us instantaneously, and any message sent to such a civilization would reach it years later.) The structure that would eventually be constructed would be a Dyson Sphere, a sphere surrounding a star with the intention of collecting and storing the energy emitted. (A less consolidated effort would result in a Dyson Swarm, which would consist of many orbiting objects as opposed to one large structure.) Multiple layers could even be used to capture the heat radiated from lower layers.

The other main option would be to use energy not ultimately derived from a star. This would be done through nuclear fission and fusion, both deriving from the properties of atomic nuclei, or chemistry. Of these, fusion is by far the most efficient, and the required materials for fusion, hydrogen and helium, are the two most common elements in the universe, so a civilization interested in efficiency would tend to move over to this source of energy. The finiteness of hydrogen and helium within a star system would eventually require a civilization to start harvesting these resources from its gas giant planets (the type of planet with the most hydrogen and helium due to its size), brown dwarfs (objects between the size of gas giants and stars, which also are heavy in hydrogen and helium), and even its own star. Ultimately, this would be seen as the star dimming and disappearing, just like with a Dyson Sphere. Energy storage could be done through batteries or even just storing the raw hydrogen and helium.

Of course, these ideas are based in science as we know it today. If a more accurate model allows civilizations to cheat entropy or to derive energy from some other source, these would be the preferred options.