I am working on an earth-like empire (actually, an alternate-universe Earth with Belgium as the global powerhouse) which, instead of using fossil and nuclear fuels, uses light as their principal form of energy. The idea is that, apart from just the raw energy in light, they also use patterns of light and dark for everything, from powering their machines, houses and vehicles to waging war with it. They are about 500 years in the future compared to our time (but still human), and they have figured out a way for feasible interstellar travel using light (they have, I'm still working on it).
I'm currently trying to figure out the following issues:
1) What could push an entire planet to focus on light instead of fossil and nuclear fuel? One option would be a nuclear war that scared people away from using nuclear fuels, but that has been done in Blake and Mortimer and I don't want to use that.
2) What method could they use for interstellar travel? For regular travel, my idea was that they figured out a way to essentially travel through the power grid. However, that method can't work for long-distance travel. I could say that they managed to increase the speed of light and use light beams to travel there, but that's been done in Blake and Mortimer as well as Futurama.
3) How can I use the light-based technology to implement a darker edge to the culture? I don't want to create a purely utopic society. I want the empire to look nice for someone who just entered it, but anyone who spends more than a month starts to sink into a gray-and-gray moral zone.
A solution would likely involve different physics from those in our universe. I don't yet have a plan for these physics, so any suggestions on how they should be changed are welcomed.
background information about the empire
The empire serves as a background for a science-fiction space opera set in a golden age of space exploration: mankind has settled colonies across the Sol system, and is preparing to expand into the stars. Interstellar explorers are sent out to track suitable habitats for humanity. Someone from our time (the protagonist) lands right in there and gets involved in major events.
The empire itself is a combination of history and fiction: The Belgae tribe was a match for the Roman Empire and became a satellite state and a powerful ally of the Romans. After the fall of the Empire, a number of historical figures born in the empire (or one of the states it conquered) started to systematically take over the rest of the world. around 500 years in their past, the entire world has been unified, but already with significant improvements in technology compared to our stage. It is at this point that they started developing light-based technology.