Fusion may still sound like science fiction—but it might not be for much longer. With AI pushing demand for clean power to new highs, a breakthrough may finally be close. In this episode of YC Decoded, General Partner Gustaf Alströmer explains the history of fusion, the physics behind it, and the engineering challenges that stalled it for nearly a century. He also looks at how Helion Energy is approaching the problem differently, as they develop a new fusion system expected to deliver power to Microsoft by 2028.