Some stars lived for billions of years. Smaller stars could last even longer. But eventually, every star would change, fade, or collapse.
Because civilizations now planned across extremely long time scales, they began studying how life could continue even as the universe itself changed.
The first step was understanding energy more deeply.
Researchers studied many different sources of energy that did not depend entirely on normal stars. They investigated energy from rotating black holes, from particle interactions in deep space, and from extremely efficient matter-energy conversion systems.
Some of these technologies allowed habitats and computing systems to operate using very small amounts of energy.
Efficiency became one of the most important goals in engineering.
In earlier eras, civilizations often focused on producing more energy. In these later eras, they focused on using energy more wisely.
