Marathon Fusion, a Silicon Valley start-up, has announced a breakthrough in alchemy by claiming it can transform mercury into gold using nuclear fusion technology. According to an academic paper published last week, the company proposes that neutrons released during fusion reactions could facilitate nuclear transmutation to produce gold. Marathon Fusion suggests that this process could yield tonnes of gold annually as a by-product of its fusion energy efforts. However, the start-up acknowledges that the gold produced would remain radioactive for more than 14 years. While the concept merges two historically challenging and uneconomic ideas—fusion energy and alchemy—experts have expressed skepticism regarding the practicality and profitability of the approach. Critics also highlight that nuclear fusion remains an unproven and highly complex technology, with some dismissing the claims as thermodynamically flawed.