Joe Rogan Experience #2554 - Carlo Rovelli

Mountain lions are roughly half the size of jaguars.

Jaguars are stockier and can grow heavier, but they are not twice the size. The San Diego Zoo's profiles put jaguars at 70 to 249 pounds and male mountain lions at 116 to 158 pounds, so the two ranges overlap and a typical jaguar is nowhere near double a typical male cougar. Only the largest jaguars, such as those in South America's Pantanal, open up that kind of gap.

When the United Nations was founded in the 1940s and 1950s, eliminating poverty was declared a global interest by all member countries.

There is a real basis for this. Article 55 of the 1945 UN Charter commits the organization to promoting "higher standards of living" and "conditions of economic and social progress and development," and Article 56 has members pledge joint action toward it. But nothing in those founding documents declares the elimination of poverty as a goal, and it was not all the countries together: the UN had 51 founding members. Ending poverty became an explicit worldwide target much later, with the Millennium Development Goals in 2000 and the Sustainable Development Goals in 2015.

The guest's grandmother was born at a time when there was no electric light, no trains, no cars, no washing machines, no television, and no radio.

Most of the list works. Rovelli was born in 1956, so a grandmother born in the late 1800s would indeed have arrived before electric light reached homes, and before cars, radio, television and washing machines. Trains are the exception. Italy's first railway, the line from Naples to Portici, opened on October 3, 1839, decades before any grandmother of a man born in 1956 could have been born, and the country had a growing network by the 1880s.

The United States is currently the world's largest military power and controls all oceans and seas.

The first half holds up. The United States spends roughly a third of all the military money on Earth and is the only country with carriers and bases spread across every ocean. But "controls all the oceans, all the seas" overstates it. China now fields more battle force ships than the US Navy, and as of September 2026 the Houthis control Yemen's Red Sea coast and the Bab al-Mandeb strait, a chokepoint carrying about 12 percent of world trade, with shipping still rerouting around Africa.

There are 12,000 nuclear warheads in existence that could annihilate humankind within 10 minutes.

The warhead count is close to right. The Federation of American Scientists and SIPRI both put the world total at roughly 12,200 at the start of 2026, though about 2,400 of those are retired and waiting to be taken apart, fewer than 4,000 are actually deployed, and about 2,100 sit on high alert. The rest is overstated: land-based missiles take roughly 30 minutes to cross between Russia and the United States, and the leading peer-reviewed study of a full US-Russia exchange estimates more than 5 billion deaths, most of them from famine over the following years rather than in the first minutes. Researchers who study nuclear winter, including Alan Robock, consider complete human extinction unlikely.