If you feel tempted to recreate this passive cooling experiment yourself, we actually managed to spot the exact copper bullion block for
$170. Yes, a solid brick of copper sitting directly on the CPU does dissipate enough heat to function, but proceed with caution. Just balancing such a monolith on your motherboard is a ticking catastrophe. We're ready for a proper copper CPU cooler to land on the market, hopefully soon.
https://www.amazon.com/dp/B0H2ZRNJGP