One such entity is the "wavefunction" & matrix representations of the same.
Schrödinger associated the wavefunction with the Electron as a an electric Charge Density, a physical field spread out over infinite Space [though very thinly outside the conventional "size" of the Electron.
On the other hand, Max Born interpreted the same wavefunction as a Probability Distribution (more specifically – complex, in the Math function sense, Probability Amplitude whose mathematically real squared absolute value renders Probability).
Adding the now-so-controversial Wigner-Neumann Consciousness-created Quantum Reality to Born's Probability interpretation, the long-time, nearly unanimous "Copenhagen" (home of Quantum Mechanics committee chairman Neils Bohr) interpretation initially "competed" with some initially-unpopular Realist versions by David Bohm & Louis de Broglie, & others that followed in that vein. Also increasing have ever been the Instrumentalist positions that ignored all explanation & the accepted abstract mathematical structure of Hilbert spaces & Quantum Mechanical operators.
The culture of Science veered away from the Copenhagen Quantum Idealism in parallel with 2 inspirations to do so, One was the Analytical Philosophy that succeeded Logical Positivism (which had some idealist roots), with the former dedicated to annihilate the reigning Idealism of the previous century. The other was a aversion to fundamentalist religion & a dominant "sophistication" of Atheism among Scientist (to a degree contrasting with prior generations, including the
group). Atheist Pragmatist Philosophy's dominance in higher education was
instrumental in this shift. Copenhagen
[Steve Martin's 2nd comedy album included a skit were he dies & is shocked to find himself at some Last Judgment before the Pearly Gates. He complains: "but in college they said all this was bullshit."]
Grasping for any Realist alternative, over the same decades up through many Modal wing-clipped theories of Quantum Mechanics, decades in which Darwinism fought "Armageddon" with Creationism, one fantastic Realist alternative that gained majority standing was Hugh Everett's Many-Worlds interpretation, considered now by Max Tegmark & Michio Kaku to be 1 of 4 "levels of Multi-Verse".
Recognition of Anthropic Fine Tuning of the Universe & studies of Quantum Entanglement & Delayed-Choice Quantum Eraser Double-Slit experiments have themselves exerted 2 opposing influences. On the one hand, they have hardened minority Quantum Idealist positions such as the Wheeler–Stapp Participatory-type Universes. At the same time those advances & others in Particle theory & Big-Bang Fundamental Forces issues have encouraged majority Realisms that are increasingly "unrealistic". The latter include String Theory, the Multi-Verse & also other complex Mathematical sleight-of-hand like Quantum Decoherence, Ensemble, Relational, Transactional, & Stochastic approaches, as well as Computational or Hologramic Universes (not that similar to David Bohm's earlier Holoverse Realism). Objective collapse theories attempt to "split the difference" by upholding Realism while including Idealist–like indeterminism without hidden-variables.
The above themes & 1600 pages more are freely available as perused or downloaded PDF’s, the sole occupants of a Public Microsoft Skydrive “Public Folder” accessible through: