Lex Fridman Podcast
#485 – David Kirtley: Nuclear Fusion, Plasma Physics, and the Future of Energy
17 Nov 2025
Full Episode
The following is a conversation with David Kirtley, a nuclear engineer, expert on nuclear fusion, and the CEO of Helion Energy, a company working on building nuclear fusion reactors and have made incredible progress in a short period of time that make it seem possible like we could actually get there as a civilization.
This is exciting, because nuclear fusion, if achieved commercially, would solve most of our energy needs in a clean, safe way, providing virtually unlimited clean electricity. The problem is that fusion is incredibly difficult to achieve. You need to heat hydrogen to over 100 million degrees Celsius and contain it long enough for atoms to fuse.
That's why the joke in the past has been that fusion is 30 years away and always will be. Just in case you're not familiar, let me clarify the difference between nuclear fusion and nuclear fission.
By the way, I believe according to the excellent sample size subreddit post by PM Goodbeer on this, the preferred pronunciation of the latter in US is nuclear fission, like vision, and in the UK and other countries is nuclear fission, like mission. I prefer the nuclear fission pronunciation because America. So today's nuclear power plants use nuclear fission.
They split apart heavy uranium atoms to release energy. Fusion does the opposite. It combines light hydrogen atoms together, the same reaction that powers the sun and the stars. The result is that it's clean fuel from water, no long-lived radioactive waste, inherently safe because a fusion reactor can't melt down. If something goes wrong, the reactor simply stops. And there's no carbon emissions.
On a more technical side, Helion uses a different approach to fusion than has traditionally been done. Most fusion efforts have used tachymax, which are these giant donut-shaped magnetic containment chambers. Helion uses pulsed magneto-inertial fusion. David gets into the supertechnical physics and engineering details in this episode, which was fun and fascinating.
I think it's important to remember that for all of human history, we've been limited by energy scarcity. And every major leap in civilization, agriculture, industrialization, the information age, came in part from unlocking new energy sources. If someone is able to solve commercial fusion, we would enter a new era of energy abundance that fundamentally changes what's possible for us humans.
I'm excited for the future. And I'm excited for super technical physics podcast episodes. And now a quick few second mention of each sponsor. Check them out in the description or at lexfriedman.com slash sponsors. It is the best way to support this podcast. We got Uplift Desk for my favorite office desk that I'm behind right now. Finn for customer service AI agents.
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