A new Silicon Valley, billionaire battle is brewing between Tesla's (TSLA  ) Elon Musk and Amazon's (AMZN  ) Jeff Bezos. Both have achieved remarkable success in their domains but their paths are colliding in adjacent fields.

Last week, Musk commented on Amazon rejecting journalist Alex Berenson's book being rejected for self-publication. Musk tweeted that Amazon's decision was "insane" and added, "Time to break up Amazon."

Berenson has been controversial due to his dismissal of politicians and public health officials' warnings about the coronavirus especially in terms of the tradeoff with the economic and health consequences of the shutdown. Musk has also been vocal on this topic. He has described government policies during the coronavirus as "fascist" and publicly funded with local officials about reopening his factory even threatening to move Tesla's headquarters out of California.

Self-Driving

While Twitter barbs aren't that meaningful, a more significant front between the two titans is opening up in self-driving cars. Amazon is reportedly close to buying Zoox which is a private company developing its own self-driving car. Amazon already is a market leader in so many niches like e-commerce and cloud computing and has a foothold in other areas like home assistance devices, logistics, and shipping.

Amazon's interest in buying Zoox is largely to reduce its shipping costs by taking advantage of the company's technology. According to Morgan Stanley (MS  ), Amazon will spend $90 billion on shipping costs over the next decade and interesting autonomous technology could save the company $20 billion.

Further, Amazon has the resources to pour money into development and distribution. It's also willing to lose money on a project which it perceives as having long-term potential to win market share and starve its competitors. Of course, Tesla is the leader in self-driving cars with its autopilot software that is already running on many cars.

Zoox along with Uber (UBER  ), Google (GOOG  ), and General Motors (GM  ) are its main competitors. Due to Tesla's early advantage, many have pegged it as the favorite, and it's one reason for its sky-high valuation.

Space

Another arena in which Bezos and Musk are competing is space exploration. In this, Musk also has a lead especially with SpaceX's launch of humans to the International Space Stations and routine launches of satellites. Both companies are building relaunchable vehicles that can transport people and cargo into space.

SpaceX was started in 2002, while Bezos started Blue Origin in 2004. Musk's goal for SpaceX is to eventually colonize Mars. However, Bezos has been critical of this plan, stating that it's not plausible and Mars is inhospitable for humans.

In Bezos' view, the battle between SpaceX and Blue Origin is like the tortoise vs the rabbit, so he is not daunted by Musks' early success. Both companies have intensely battled for talent, leases on rocket launch platforms, and patents. Of course, there's also been some acrimony on Twitter as well.