On the ontology of "Absence makes the heart grow fonder."

"What would not I give to wander
Where my old companions dwell?
Absence makes the heart grow fonder;
Isle of Beauty, fare thee well!"

-- Thomas Haynes Bayly, 1844

What is this thing called an absence? Does an absence exist?

Absences, like holes, have an uncertain kind of existence, since some deny they actually exist, except as conformations of the stuff around them, of which they they are holes, or absences. But no one can deny that holes and absences can be measured and counted. From a scientific point of view, holes thus exist as much as any other objective phenomena that can be measured and counted can be said to exist.

And holes, of course, are emergent. They could not exist without the stuff of which they are NOT made.