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Fig. 1

image

Two-dimensional classification of the ETCs. Top: horizontal axis expresses the capabilities of an ETC to interact with its environment. Vertical axis quantifies the amount of energy available to them, as defined by the classical Kardashev scale. Bottom: generalized two-dimensional classification. Horizontal axis shows the level of integration with the environment. The approximate locations of humanity throughout history and of a few hypothetical civilizations are shown and labeled. For details, see Sect. 3.

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