Pop up some more popcorn: Billionaire Elon Musk has gotten himself into another CEO vs. CEO challenge, this time with Uber’s Dara Khosrowshahi over air taxis.

Uber and many other companies are working on electric-powered, flying vehicles that could carry passengers autonomously between landing pads, circumventing traffic jams. Uber has said it could start testing what are basically flying cars by 2020 in Los Angeles, Dallas-Fort Worth and Dubai.

Khosrowshahi — who left Bellevue, Wash.-based Expedia last year to become Uber’s CEO — is sold on the idea. Musk isn’t. Instead, the CEO of SpaceX and Tesla is partial to tunnels that let cars or electric-powered pods zip beneath surface roads. Musk’s tunneling venture, The Boring Company, is involved in experimental projects in the L.A. area as well as Chicago and Baltimore-Washington, D.C.

Other ventures, Virgin Hyperloop One and Hyperloop Transportation Technologies, are following up on Musk’s Hyperloop concept for near-supersonic travel through low-pressure tubes.

With that background, an Indian journalist got today’s party started with a tweet:

It didn’t take long for Musk to respond, even though he was gearing up for the first launch of SpaceX’s prototype Starlink broadband satellites:

If you love drones above your house, you’ll really love vast numbers of “cars” flying over your head that are 1000 times bigger and noisier and blow away anything that isn’t nailed down when they land — Elon Musk (@elonmusk) February 22, 2018

Khosrowshahi is in India for a tech conference and business meetings, including a sit-down with India’s aviation minister to discuss flying cars. But he did take the time to reply to Musk’s tweet:

Challenge accepted. Improved battery tech (thx 2 @elonmusk) and multiple smaller rotors will be much more efficient and avoid noise + environmental pollution. https://t.co/563U0RqDYF — dara khosrowshahi (@dkhos) February 22, 2018

Will going high or going low win out when it comes to alternatives to surface traffic congestion? Los Angeles could serve as the perfect laboratory for the experiment, determining whether Khosrowshahi or Musk has the better idea.

Check out these dueling visions:

Today’s exchange means you can now add Uber to the list of companies whose feathers have been ruffled by Musk. That list also includes: