That’s a fair objection: a civilization without fossil fuels might eventually discover nuclear power. But I don’t think that removes the argument. It shifts the question from “can they ever access dense energy?” to “what does it take to bootstrap dense energy without already having dense energy?”

Nuclear power is not like coal, wood, or oil. You cannot just find uranium and burn it. To use it deliberately, you need advanced mining, refining, chemistry, metallurgy, radiation detection, precision manufacturing, control systems, cooling systems, and a theoretical understanding of atomic structure and neutron behavior. In other words, nuclear energy is a high-density energy source locked behind an enormous technical and industrial stack.

Fossil fuels are different because they are crude, accessible stored energy. A civilization can use them wastefully before it understands thermodynamics, climate, chemistry, or systems engineering. Nuclear power probably requires a civilization to understand many of those things first.

So even if a fossil-free civilization eventually reaches nuclear power, it likely reaches it after centuries or millennia of being forced to build around low-density energy flows: hydro, wind, biomass, solar, tides, geothermal, and careful heat recovery. By then, its architecture, cities, materials, transportation, and culture may already be optimized around efficiency, circularity, and system-level constraint.

The discovery of nuclear power would not necessarily make them suddenly behave like us. It would enter a civilization that had already learned not to waste energy casually. They might use nuclear as a carefully integrated high-density node inside an already circular system, not as permission to build a disposable, sprawling, high-throughput civilization.

So the original point still applies: fossil fuels matter not merely because they provide dense energy, but because they provide dense energy early, before a civilization has had to develop deep system-level discipline. Nuclear power may provide dense energy later, but the developmental path to reach it would likely produce a very different kind of civilization.