i) To my knowledge, there are roughly two longstanding problems with relativity and quantum physics. One is how to harmonize the two. The other is that, even on its own terms, there appears to be a intractable weirdness to quantum mechanics. Some of what it posits seems to be physical impossible, yet there's evidence for it.
There's also some weirdness with relativity (e.g. the twin paradox), but that seems less baffling.
ii) So we have two world pictures (relativity, quantum mechanics) that are powerful, accurate, well-confirmed theories. Theories that make testable and tested predictions.
But thus far they don't mesh, and even on its own, there are things about quantum mechanics that defy comprehension. It just doesn't seem to be realistic in some respects, even though it works.
iii) What this suggests to me is that we need a new world picture that transcends these two world pictures. A picture that captures the best of both.
For a time, string theory was the holy grail, but many physicists have become disenchanted with its prospects, not to mention physicists who were skeptical from the get-go.
iv) Let's toy a thought-experiment. Suppose humans can't perceive the physical world directly. Suppose we can only perceive the effects of an indetectable physical reality. All we have to go by are the effects. Something physical is producing them, but it's out of range.
v) Apropos (iv), suppose the sensible world is like a house of mirrors. The mirrors simultaneously reflect reality and distort reality.
There are different kinds of mirrors, viz. right-angled mirrors, convex mirrors, concave mirrors, infinity mirrors.
Suppose we were born into a world in which we only saw reflections. Complex reflections.
In one respect, these would be realistic. They'd be projections of a physical reality. Grounded in reality.
But in another respect, they'd be unrealistic. Mirror images can depict spatial relationships that are physically impossible to instantiate in 3D.
For instance, mirrors can illustrate nonlocality or action at a distance (quantum entanglement). The same object instantly appears to be in more than one place at the same time.
Our cosmic house of mirrors would be mathematically complex to describe, yet mathematically elegant.
The images would correlate with reality. But because we couldn't compare the reflection to what it reflected, it would be hard to say when reality ends and distortion begins. On this scenario, we lack direct access to the objective standard of comparison.