furthest

To the greatest distance in space or time (`farthest' is used more often than `furthest' in this physical sense).

“he swam the furthest”

To the greatest degree or extent or most advanced stage (`furthest' is used more often than `farthest' in this abstract sense).

“went the furthest of all the children in her education”

“furthest removed from reality”

(comparatives of `far') most remote in space or time or order.

“explored the furthest reaches of space”