Tesla CEO Elon Musk fired back at Mark Zuckerberg on Tuesday, calling his understanding of AI "limited." TED The billionaires Mark Zuckerberg and Elon Musk are fighting publicly about the future of artificial intelligence.

On Sunday afternoon, while smoking some meats in his back garden, Zuckerberg, the Facebook CEO, questioned why Musk, the CEO of Tesla, SpaceX, and OpenAI, was being so negative about AI.

Musk responded on Tuesday with a tweet saying Zuckerberg's "understanding of the subject is limited."

Musk is concerned that supersmart machines powered by AI could one day pose a threat to humanity. In 2014, he said AI could be even more dangerous than nuclear weapons.

During a Facebook Live broadcast, a person who said they'd recently watched an interview with Musk in which he said his largest fear for the future was AI asked Zuckerberg about his thoughts.

"I have pretty strong opinions on this," Zuckerberg said. "I'm really optimistic. I'm an optimistic person in general. I think you can build things and the world gets better. With AI especially, I'm really optimistic, and I think that people who are naysayers and try to drum up these doomsday scenarios ... I don't understand it. It's really negative, and in some ways, I actually think it's pretty irresponsible."

Zuckerberg added that he believed AI would save lives by making cars safer, and he highlighted how AI was already helping to diagnose medical conditions and match people with the right treatment.

"Whenever I hear people saying AI is going to hurt people in the future, I think: Yeah, technology can generally always be used for good and bad, and you need to be careful about how you build it, and you need to be careful about what you build and how it's going to be used.

"But people who are arguing for slowing down the process of building AI — I just find that really questionable. I have a hard time wrapping my head around that. If you're arguing against AI, then you're arguing against safer cars that aren't going to have accidents, and you're arguing against being able to better diagnose people when they're sick."

On Tuesday, Musk hit back at Zuckerberg's comments, saying: "I've talked to Mark about this. His understanding of the subject is limited." Musk also teased a "movie on the subject coming soon."

The consensus of AI leaders is that it'll be several decades before computers come close to achieving human levels of intelligence, and some question whether they'll get there at all. However, experts believe that if computers became as smart as us, they would quickly become superintelligent.

Here's the full Facebook Live video: