We often debate real versus not-real things, or concepts, in physics.
In this connection let me quote from "What is Mathematics, Really?"
by Reuben Hersh (1997, ISBN 0-19-511368-3).
"I phone Dr.Caldwell for an appointment. It's fortunate that the
opening ... exists. ... The opening in his schedule can't be weighted,
or measured, or analyzed chemically. It is not a physical object. ...
Is it a mental object? A thought in the receptionist's mind/brain?
No. If she overlooked it, the opening would still be 'there'. A thought
in Dr. Caldwall's mind/brain? No, When you ask about his schedule,
he asks the receptionist. The opining in Dr. Caldwell's schedule really
exists. It's definite, it's recognizable. It has the right to be called 'an
object'. But neither physical, mental nor transcendental object. It exists
in the web of social arrangements, which include doctors, receptionists,
and patients. It's a social-cultural-historic object, and real as can be".
Just sharing a quote which impressed me. Sorry it is not physics.
Ludwik Kowalski