Sorry, I don't understand this point.
If a model of the universe was completely correct, wouldn't it have equivalent complexity to the universe and hence not be a model?
If a model of the universe was completely correct, wouldn't it have equivalent complexity to the universe and hence not be a model?
This is false both due to the nature of mathematical modelling in physics, and the ad-hoc nature of the term "complexity" when comparing the universe and the science we use to understand (or, perhaps, only model it).
To elaborate on the first point: No measurement can be perfect enough for their to be no uncertainty on it. It is therefore impossible for a model to be completely correct, although it can (obviously) agree with experiment to within current experimental uncertainties - like the standard model is now, so far.
For example, we had Newtonian Mechanics and that looked good for a couple of centuries, but then it turned out that it was too simple and we needed to add more laws.
We would have to settle for merely being able to explain every single phenomena in the observable universe at every scale.
Then see a recent essay at Quanta Magazine that explains that physics has long looked to some largely esthetic concerns especially about symmetry to pick and choose among alternate theoretical explanations -- again my rough summary from my rough memory.
https://www.quantamagazine.org/there-are-no-laws-of-physics-...
Sabine Hossenfelder, Lost in Math: How Beauty Leads Physics Astray
at
https://www.basicbooks.com/titles/sabine-hossenfelder/lost-i...
and is an excerpt from her book of the same name.
I was led to that excerpt by page
https://www.quantamagazine.org/authors/sabine-hossenfelder/
from page
Sabine Hossenfelder, "The End of Theoretical Physics As We Know It", August 27, 2018.
at
https://www.quantamagazine.org/the-end-of-theoretical-physic...
It's not currently (maybe ever?) possible to know when you're 'done' with an experimental science. With newtonian mechanics, we didn't know we needed something better until we did.
So when you go from particle physics to chemistry, new complexities emerge that can't be explained in the realm of particle physics alone (iirc).
sadly certain "sciences" still cling to the idea that they can simply aggregate the results from multiple of their "particles" and get a solution for larger systems.
Correct me if I'm misunderstanding, but I think you're confusing general theory vs practical applicable models here maybe? Yes, fundamental principles of interaction can combine at scale to create new large scale effects, but that doesn't change the fact that they came out of fundamental principles nor that they can't be "explained" via those principles. There is no magic that pops into existence up the chain. The asymmetry of water molecules and the way their electron clouds distribute create all sorts of fascinating effects in bulk water, but they're still directly coming out of physics of course.
The issue in practice however is that the level of computing necessary to accurately model reality at scale from fundamentals matches or exceeds actually doing it in reality, and for us rapidly becomes absolutely, utterly infeasible for anything but the simplest systems. "New emergent complexities" absolutely "can be explained" from a correct lower level set of principles, but that doesn't mean we can actually crunch the math at any scale we want. So we need higher level bulk models too, at many levels all the way up, which are good enough to be effective approximations to a given level of accuracy in practical computing time. The low level fundamentals often at bulk average out due to random variance in sufficient quantity and are irrelevant to whatever we care about, so there is no need to do it that expensively (even if we could). But that isn't the same thing as the fundamentals being wrong somehow or not being at the root of everything above.
But why would a non-reducible universe be so predictable?