> That's not what irreducibility means.

I don't want to argue about this or any word, but I think what was meant - and what I too would say - is that some things are emergent properties of interacting things. Yes, they consist of "physics stuff" following "physics rules", but also, together they create something new, on a higher level. If you take it apart it's gone, of course, and you go back to the physics. To give an example, something deliberately slightly extreme or ridiculous (depending on your POV): Try to examine the game of chess by looking at the atoms involved in a physical game.

Or, when I zoom in too far the forest disappears and I end up with first trees, then branches, then cells, then "physics". But someone who gets a degree in forest management does not benefit from learning particle physics, aside from the intellectual exercise of course. Some things stop existing if you zoom in too far, there is no "forest" or "love" or "chess" any more all the way "down there".

I think there is a misunderstanding, people talking past one another. Some people (here, but in general) think what is meant is something "meta-physical", esoteric. At least for me that's not true at all. There isn't anything magic, there is physics. But it took me decades to get to the POV that I tried to present here, which is just a different angle - and "POV" (literally, just shifting position, still looking at the same physical scientifically explorable universe). I think this is like what I remember from many higher math education revelations - you fail to see what the teacher is trying to say, and when you finally see it it' sooooo simple, just a different point of view, not actually different from what you know. What I'm trying to say is, if you don't understand what someone might mean like in this case, talking about "emergent properties" and the like, please don't assume they leave known science behind to go on an esoteric trip. It's got something to do with us not being "god", seeing the entire universe at once, but only being able to shine an extremely tiny extremely focused beam at one extremely tiny detail. So even if we had a few formulas for _everything_ (all energy, all matter, incl. what now is the dark stuff), it would not help us when we try to shine our tiny light at a higher level, so we need a different model even though the components everything is made of are more "fundamental". When you have surgery, you don't want a particle physicist wielding the knife, and you probably don't care if the surgeon would fail every elementary quantum physics question. It is just not useful if you want to do something on a much higher level.

It may not be so to a "god", but to our small minds all those basic tiny "physics things" working together create something new on top of them, and it gets lost if you start looking at the parts. Of course those components, atoms and below, are still explainable using nothing but physics. Just not a huge amount all of them together, interacting in ways for which we have created models far above physics, unless you look at mass/force/etc. Each time you zoom in you see the physics (or if you drop tree and measure the force of its impact, but even the part of physics you use there is far above the low level stuff).

Last example: Imagine all models gone, in all fields. Only the most low level physics exists. Try to explain the chess rules :)

Anyway, that's just my interpretation.