More specifically, it's about what kind of questions are considered worth asking. You can track the changes through history, and philosophy often leads politics and art as much as it does science.
Philosophy looks like the most abstract and possibly trivial pastime, but in fact it's incredibly powerful and influential, because it literally makes some world views thinkable and others unthinkable.
The different interpretations of QM are trying to ask different questions about reality. The fact that they're empirically indistinguishable suggests that either they're literally irrelevant - because they all give the same answer - or that no one knows how to ask a more insightful question yet.
If a more insightful question exists, it may come from some completely unexpected direction.
Physics has had a century to think about the problem, and hasn't gotten any closer to a definitive solution.
That suggests either more time is needed and we just haven't got there yet. Or perhaps the real explanation is literally unthinkable within the world view we have today.
String theory isn't a quantum theory of gravity in the same way that loop quantum gravity (LQG) is, LQG is background independent. String theory assumes there is a flat background spacetime already present and perturbatively builds off of that. LQG doesn't make this assumption and tries to create spacetime from scratch.
LQG did make some testable predictions, as has string theory in recent years. One was regarding the smallest units of area and volume that might have been seen in light scattering in cosmic ray or gamma-ray burst experiments[1]. Another suggesting evaporating black holes could be used to probe LQG [2]. String theory proposed supersymmetry, where each fundamental particle had a supersymmetric partner. Electron => selectron, quark => squark, etc. But none of these proposals have panned out as yet. Thus far supersymmetry has not been found and LQG has not been able to recover general relativity in a classical limit.
> The many-worlds interpretation of quantum mechanics is just that, an interpretation. It doesn’t make any measurable difference from any other interpretation.
In the last couple years, many-worlds researchers have come up with some potentially measurable consequences [3].
[1] https://www.edge.org/conversation/lee_smolin-loop-quantum-gr...
[2] http://dx.doi.org/10.1103/PhysRevLett.107.251301
[3] http://journals.aps.org/prx/abstract/10.1103/PhysRevX.4.0410...
Uhmm, he’s working on quantum gravity too. Just a different approach. The same applies to loop quantum gravity.
> A practical implication is that it doesn't lead to any technology.
Who cares? It’s science not engineering.
> Smolin also doesn't like many-worlds, because it talks about unreachable regions. This he considers too speculative. There's a basic problem in quantum mechanics, which leads to Schroedinger's Cat, the Copenhagen Interpretation, and, in the end, many-worlds.
The string landscape [1] and the many-worlds interpretation [2] are two completely different things. The string landscape indicates that string theory may never be able to make any predictions. Some physicist try to use many universe in combination with the antropic principle to “solve” this problem. But I’m pretty sure this is a very small minority.
The many-worlds interpretation of quantum mechanics is just that, an interpretation. It doesn’t make any measurable difference from any other interpretation. And the Copenhagen interpretation doesn’t lead to many-worlds, they are just two different interpretations of the same theory.
> Physics has been stuck on this problem for almost a century now.
At this time I wouldn’t call it a “problem” of physics. If all predictions are the same it’s just a matter of taste which interpretation you prefer. To bring it into the realm of physics you would need to come up with some kind of theory of the measurement process that actually makes testable predictions.
[1] https://en.wikipedia.org/wiki/String_theory_landscape
[2] https://en.wikipedia.org/wiki/Many-worlds_interpretation