This originally appeared in Asimov's Science Fiction. Gardner Dozois selected it for a themed reprint anthology on time. It appear in the collection Slow Birds and Other Stories by Ian Watson. Dozois describes Watson's work as "vivid and highly original conceptualization" with this story changing "quite literally--the way we see the world."
Jim Roseberry's time machine plucks Titus Lucretius Carus from the Roman era into the future, right before death although he looks healthy enough. They introduce him to the present--Jim, especially, being a little pompous about the present science being better. This changes, however, when the colleagues at the Institute see the world as Lucretius reasoned it was. Jim puts up with this awhile but when--through jealousy or preservation of the modern status quo--he takes matters in his own hands. This doesn't quite go as planned, either.
Interesting mix of SF and fantasy--although it could be argued that Lucretius' thought would be science of his day. This plays with the idea that ideas can be equally powerful--tinting more than the way we see the world. It isn't clear why this narrator, but nearly everything Ian Watson writes is interesting. It's never enough to develop just one idea when two or three could make it cooler.