Recently I listened to a Quantum Physicist speak about reality, and how it is now understood as being completely misunderstood. When asked in the documentary about the nature of existence, he noted the science is now bordering on philosophy, and extended the notion that the physical universe seems to present more ontological problems than once realized until Quantum Entanglement and Electron Orbits were measured. That every atom in the universe, specifically the electrons, is "aware" of what every other electron is doing and where it is. Entangled, in that the measured electron motion influences the motion of other electrons no matter how far apart the atoms are from one another. The mystery is the "HOW" this can be so. If two gears are torn apart from one another, their motion no longer influences the the motion of the other gear. But the opposite is true for atoms, whose motion in separate locations isolated from one another still influences the measurable motion of other atoms.
Now, back to your question, the QPhysicist in his discussion said to the interviewer, "try to imagine nothingness", adding to that that our existence is far more probable to be than not to be. I believe that nihilism is impossible to define, as science with its new ontological problems put forth is "geared" toward causality, not a-causality. The big bang presents a problem that "time" at the moment of the big bang held to no Universal Law... real chaos existed. The closest thing to nihilism that I can think of was the moment that Ex Nihilo, Nihil Fit.
Be it real, or not, it is still measurable, the universe. But my thoughts can be measured as being, or, having being. In spite of all, there is still thought. Moreover, there is the thought that all is thought, and if so, who is thinking... who thinks, therefore -- I AM? A thing to be considered is how thought does make manifest, and thoughtlessness encourages no thing, influences no thing and is in fact probably, nothing at all. Whether we are thinking or not, the mind is always involved as the observer, even if only it observes its own thoughts. To the schizophrenic, its thoughts are very much real to the extent that they are born witness to. While we cannot see the manifestations of the schizoid mind, we can say emphatically that what is perceived is very real to the one encumbered by such a state. In a universe of either good, or evil, it is both nihilistic and not -- schizoid, as it were. Nil as it seems