> While I acknowledge the cool factor, I don't like what Boom is doing. We should be looking at making air travel more efficient, reducing the energy/emissions per passenger-mile flown. We don't need to invent ways to make luxury travel by the rarified few ever more expensive and damaging.

Didn't they say it could run on sustainable fuel?

I'm sorry, but I want to maximize my (and really all humans) time on this Earth, if that costs energy, that's the cost. I wouldn't be concerned about emissions per passenger-mile as that's nothing more than a rounding error in "emissions". You're welcome to walk / swim from San Francisco to Europe, but don't expect me to.