As Onar Aam is a composer of music,
he has remarked that
Western symphony instruments are linear, and
are easily added together into a coherent whole
that is a linear superposition of each part,
and that
many modern instruments (as rock guitar)
and instruments from other cultures (as sitar) are non-linear, and
have a greatly distorted sound that fills a large part of the spectrum,
making them almost incompatible with other instruments.
He then went on to say that a linear symphonic work (as a string quartet)
could AS A WHOLE be distorted in a non-linear way (as by a bad stereo system)
to produce
A WONDERFUL HOWLING GUITAR INSTRUMENTAL PLAYED WITH CELLOS AND VIOLAS!
THERE IS A BEAUTIFUL ANALOGY IN PHYSICS:
Quantum field theories of electromagnetism, the weak force, and
the color force can be expressed in terms of linear wavefunctions.
The reason these quantum field theories work is that the
linear wavefunctions have the property of superposition,
that is, you can superpose a lot of them and you get another
wavefunction that is a solution of the quantum field equations.
All this takes place in a flat spacetime.
So, quantum field theory of the first 3 forces is like a symphony orchestra.
The 4th force, gravity, is VERY nonlinear - so much so, that it
is hard to express it in terms of a quantum field theory, and
gravity (in most formulations) stands alone because of its nonlinearity.
Gravity is the nonlinear force.
HOWEVER, if you FIRST use the superpositions of linear quantum fields of
the first 3 forces to produce atoms, molecules, etc.,
and THEN apply gravity to the atoms, molecules, etc.,
you see that the atoms, molecules, etc., combine to form stars and
planets and galaxies, AND the flat spacetime is curved by the gravity
so that the stars, planets and galaxies move in orbits as we see them do.
In a sense, OUR UNIVERSE IS A DISTORTED SYMPHONY!