Bill Gates and Richard Branson have some big goals.

Branson wants to go to space and send hyperloop pods shooting through underground tunnels at the speed of airplanes. Gates wants to rid the world of Polio and Alzheimer's disease, as well as implement the Bill & Melinda Gates Foundation's extensive list of other moonshots. Both the Microsoft founder and Virgin Group founder backed a start-up that grows meat in a lab and hopes to reduce the environmental impact of raising livestock.

And while some challenges seem insurmountable — even for a pair of the world's most powerful people — Branson and Gates agree it's crucial to chase big ideas, even if success isn't immediate.

"Bill and I spoke about the importance backing long-shot projects," Branson writes on his blog about a meeting the billionaires had Tuesday. The two met in Paris for a summit focused on one such challenge, climate change.

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"Not all ideas will work," Branson writes. "But if we back enough of them, then the more likely it is that there will be a handful that can have a huge impact."

Gates' willingness to act on his dreams to improve the world is an inspiration for Branson.

"I've learned so much from Bill. He built a formidable company and decided to put his vast wealth into solving the problems of the world," Branson writes.

For Branson himself, dreaming big has also been key to his success.

"Dreaming champions aspiration, spurs innovation, leads to change, and propels the world forward. Dream big and you will be rewarded… trust me," he writes in an earlier post.

But he says it can't be done alone: "I believe that we can truly achieve great things when we all come together."

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