Farther or further?

I think the Star should have used "further" here, but there's room for debate so let's give them the benefit of the doubt and say this isn't necessarily an error.

Most grammar nerds say farther means "more far" (as in distance), while further means "more extreme" or "deeper" (in a metaphorical sense).  Some say farther is archaic and should no longer be used.  And a few say who cares, both are interchangeable.