Sir Richard Branson speaking at the Innovation Summit in Brooklyn, New York on July 14, 2017.

When Richard Branson invested in futuristic transportation start-up Hyperloop One this week, he jumped into yet another market that's of deep personal interest to fellow billionaire entrepreneur Elon Musk.

Musk is credited with creating the idea of the hyperloop, a super speedy method of passenger travel that involves pressurized capsules. He also founded The Boring Company, which is setting out to build hyperloop tunnels.

Whether it's the space race or the future of high-speed underground travel, Branson and Musk are charting parallel paths into these speculative technologies. Branson's Virgin Galactic claims to be the world's first commercial spaceline, while Musk's SpaceX is already designing and launching rockets and spacecraft for NASA.

When Virgin Group announced a stake in Hyperloop One — now Virgin Hyperloop One — Branson said, "I think it's more likely that I will go into space before I get into my pod," noting that he expects to ride in space within six months.

While many have questioned the viability of a system to zoom humans around underground in high-speed pods, Musk has indicated on Twitter that he's already received "verbal approval" for a route between New York and Washington.

In a July 20 tweet, he laid out his plans in brief: