Nutrinos Are Stable, but You Can't Build Anything Out of These

Nutrinos are stable. They can last for a long time. If you produce an electron nutrino and you shoot it through the universe, it might end up as a anutrino or a tow nutrino. These particles sort of mix into each other, which is sort of cool. It's this crazy quan mechanical effect that you can learn about if you check out that episode. But yes, we do think that there were other different, weird states in the very early universe that might have involved some of these heavier particles.