I read this when I was a child (late 90's to early 00's) so my memory of the details is a bit hazy, but the story concerned an alien race making contact with humans.
The main details I recall are that the aliens had not had predators on their planet (?) and so had not evolved to be competitive, and that they discussed with humans that their space-travel technology was based on the idea that the Law of Conservation of Matter/Energy was slightly wrong, and that the largely unnoticed destruction of minuscule amounts of stuff created gravity, a process they induced artificially for faster-than-light travel.
I had thought it was by Arthur C. Clarke, but none of his titles are ringing a bell with me. Any ideas?