"Pet science project jfc": Elon Musk mocks Earth-based nuclear fusion reactors, calls investment in them "super dumb"

Elon Musk reignited debate over the future of energy research on December 15, 2025, after posting a series of comments dismissing Earth-based nuclear fusion projects as a poor use of resources.

In a message on X (formerly Twitter), the Tesla and SpaceX chief argued that the Sun already functions as a vast, naturally occurring fusion reactor and that attempting to replicate it on Earth makes little sense at scale.

His remarks seem to contrast sharply with the billions of dollars governments and private companies worldwide have invested in fusion research. The comments also aligned with Musk’s long-running emphasis on space-based solar power and orbital infrastructure as the more viable long-term energy path.

Toward the end of his post, Musk summed up his view in stark terms, calling terrestrial fusion efforts a “pet science project”

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More about Elon Musk’s critique of fusion reactors on Earth

In his December 15, 2025 post, Musk described the Sun as “an enormous, free fusion reactor in the sky,” arguing that it dwarfs any conceivable fusion system humans could build on Earth. He wrote that even if multiple gas giants were hypothetically consumed as fusion fuel, the Sun would still account for nearly all the energy produced in the solar system.

Based on that framing, Musk labeled attempts to build “tiny fusion reactors on Earth” as “super dumb,” unless they are openly treated as limited scientific experiments rather than serious energy solutions.

This was not the first time Musk expressed the same idea. In a November 23, 2025 post, he similarly stated that the Sun represents roughly 99.8% of the solar system’s mass and would still “round up to 100% of all energy” even if everything else were hypothetically converted via fusion. He concluded then that “the Sun is all that matters long-term”

Across both posts, Musk’s argument rests on scale rather than physics feasibility. He did not dispute that fusion is scientifically possible, but suggested that Earth-based systems are negligible compared with solar output, making large investments economically irrational in his view.

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Elon Musk on solar power in space

Elon Musk’s criticism of terrestrial fusion seems to be in line with his broader advocacy for large-scale solar energy deployment in space. In a November 20, 2025 post, he outlined a vision in which SpaceX’s Starship could deliver hundreds of gigawatts of solar-powered AI satellites into orbit annually.

SpaceX’s website describes Starship as a fully reusable launch system capable of carrying up to 150 metric tonnes to orbit, designed to support satellite deployment, lunar infrastructure, and beyond.

He estimated that Starship could eventually place 300 to 500 gigawatts per year of such capacity into space, noting that average U.S. electricity consumption is about 500 gigawatts.

According to Elon Musk, the key constraint is not solar cell manufacturing, which he said already exceeds 1,500 gigawatts of annual production capacity for terrestrial use,but chip production and launch capability. He described Starship as the solution to “tonnage to orbit,” while arguing that facilities like Tesla’s proposed Terafab would be required to scale chip manufacturing sufficiently.

He further framed these ambitions in terms of the Kardashev scale, suggesting that even hundreds of gigawatts would be modest by planetary standards, with lunar-based production needed to reach 100 terawatts per year.

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Elon Musk’s comments came as his financial and industrial influence reached new heights. On December 15, 2025 The Guardian reported that Forbes estimated Musk’s net worth had surpassed $600 billion, making him the wealthiest person ever recorded.

The increase was driven largely by SpaceX’s anticipated initial public offering, which could value the company at up to $800 billion, as well as gains tied to Tesla and Elon Musk's AI venture xAI.

Edited by Devangee