Conceptualized by Nikolai Kardashev, a Russian astronomer, the Kardashev Scale is a way to determine how advanced a civilization is, based on the amount of energy the civilization consumes. Kardashev had initially made three categorizations, Type 1 is a planetary civilization which is able to store and use all the energy available on its own planet from its own star, Type 2 being a stellar civilization which is able to harness and utilize the energy of its entire star and a stellar system (a close group of stars) and Type 3, a galactic civilization which is capable of harvesting all the energy from across its own galaxy.
The Kardashev Scale has since been extended with proposals by numerous noted physicists like Michio Kaku and Carl Sagan who suggested adding ‘information available to a civilization’, as an additional measure. A Type 4 civilization might be able to latch onto all the energy in the universe including dark energy as suggested by Michio in his book Parallel Worlds (find it on Amazon US, UK, IN). Zoltán Galántai, a noted futures-research faculty member at the Budapest University suggests that a Type 4 civilization might be unrecognizable (given present and near future human technology) since it’s mechanizations might be indistinguishable from nature. Going further up the scale, a Type 5 civilization may be able to utilize energy from across universes or from the multiverse. A Type 0 civilization has also been proposed, which would have access to and utilize 1 megawatt of energy.
Human civilization had notched in at Type 0.7 on the Kardashev Scale with an estimated consumption of ~10 terawatts by 1973, calculated using Carl Sagan’s formula. We’d got to Type 0.73 by 2018 with a utilization of ~18.4 terawatts of energy. Carl Sagan’s book Pale Blue Dot: A Vision of the Human Future in Space (find it on Amazon US, UK, IN), is an eye opener about how humans may need to colonize space, just to survive.
Kardashev Scale civilizations
Type 1 Civilization
Getting to this point is dodgy. Professor Stephen Hawking in his last book Brief Answers to the Big Questions (find it on Amazon US, UK, IN) stated that for our species to survive, we need to get off planet and begin colonizing other worlds, within the next hundred years. The problems we will face are numerous, of which one of resource pressure. Human population may continue to rapidly expand, resource extraction and consumption might then continue to increase and the planet will be stressed. That’s assuming all continues as is without a global catastrophe like an asteroid or disease wiping everyone and thing off the planet. But we’re getting to Type 1.
A Type 1 civilization will be able to capture, store and utilize all the energy arriving on its planet, from the local star. In our case, this would be ~1.740 x 1017 Watts. This might be achieved through a combination of technologies and sources of energy ranging from on-planet non-renewable and renewables like solar, to an off-planet radiation harvesting constellation of satellites. A Type 1 civilization would have access to and be occupying planets other than its own home-world. Controlling planetary weather, mastering geological activity and managing local space would be par for the course. To get to Type 1, we’d likely have to master our own biologies and become transhumans.
Type 2 Civilization
Not only would a Type 2 civilization consume the equivalent energy of its host star, it would likely be able to control its star to extract energy and perhaps manipulate gravity. Such a civilization might build a Dyson Sphere around its star and around stars near its own planetary system. From the Earth-human perspective, the amount of energy required to be captured and consumed would be that of The Sun, ~ 3.846 x 1026 Watts.
Star matter itself might be utilized for matter generation or even construction of planet-sized objects. It is likely that a Type 2 civilization would have safely harnessed antimatter and consolidated its uses. The expansion of the civilization would be rapid across its galaxy with world modification techniques like planetary engineering and terraforming becoming commonplace. Mega-scale engineering like construction of Dyson swarms and spheres or Larry Niven’s mega-structure concept in Ringworld (find it on Amazon US, UK, IN). Micro-gravity environments and gravity control would be integral to a Type 2 civilization.
To operate their macro-engineering systems, the civilization would have adequate computing, likely using Robert J. Bradbury's hypothetical Matryoshka brain described in Year Million (find it on Amazon US, UK, IN), is a mammoth computing systems which would be required to manage the civilization's advanced artificial intelligence and automation. Such a computing system would be large enough to require the entire energy output of a star. This would be a civilization that would have occupied its entire galaxy just before transitioning to the next level on the Kardashev Scale.
Most of the Star Trek Next Generation series (find it on Amazon Prime US, UK) is based on the idea that humanity and the federation has achieved Type 2 status and has become an interstellar civilization. By this point it’s entirely likely that we’d have long since crossed over from being mere transhumans, opting for biological and technological augmentation, making us posthumans.
Type 3 Civilization
By the time a civilization has edged itself to Type 3, it’s already tapping into the energy equivalent of its entire galaxy. For Earth-humans, this would be ~ 5 × 1036 Watts, the luminosity of the Milky Way. To achieve such a feat, the civilization may actually need to traverse and occupy multiple galaxies, possibly tapping into the energy of quasars, super-massive black holes, white-holes as hypothesized by Stephen Hawking and even capturing gamma-ray bursts by colliding neutron stars with blackholes or merging two or more blackholes. The scale of such operations would be at the edge of current comprehension. Stephen Baxter's Xeelee Sequence series (find it on Amazon US, UK, IN) set billions of years into the future describes such a species which conflicts with humans for control of the galaxy.
It’s unlikely that a species will retain its original shape or form by the time it has established itself as Type 3. With mastery over elementary particles, artificial life, complex intelligence, information and knowledge of everything, a Type 3 species would already be geared to rapidly out-evolve itself, by controlling space-time in their own universe and experimenting with extending their reach into the multiverse. Such a species may not even be detectable by 21st century humans. By the time we’re at this stage, we’d have left post human form/s behind, likely becoming energy-information beings.