> To untutored common sense, the natural world is filled with irreducibly different kinds of objects and qualities: people; dogs and cats; trees and flowers; rocks, dirt, and water; colors, odors, sounds; heat and cold; meanings and purposes.
It's too early to declare that there are irreducible things in the universe. All of those things mentioned are created in the brain and we don't know how the brain works, or consciousness. We can't declare victory on a topic we don't fully understand. It's also a dubious notion to say things are irreducible when it's quite clear all of those things come from a single place (the brain), of which we don't have a clear understanding.
We know some things like the brain and the nervous system operate at a certain macro level in the universe, and so all it observes are ensembles of macro states, it doesn't observe the universe at the micro level, it's then quite natural that all the knowledge and theories it develops are on this macro scopic / ensemble level imo. The mystery of this is still unsolved.
Also regarding the physics itself, we know that due to the laws of physics, the universe tends to cluster physical matter together into bigger objects, like planets, birds, whatever. But those objects could be described as repeating patterns in the physical matter, and that this repeating nature causes them to behave as if they do have a purpose. The purpose is in the repetition. This is totally inline with reductionism.
> It's too early to declare that there are irreducible things in the universe. [...] We can't declare victory on a topic we don't fully understand.
This isn't a matter of discovering contingent facts that may or may not be the case. This is a matter of what must be true lest you fall into paradox and incoherence and undermine the possibility of science and reason themselves. For instance, doubting rationality in principle is incoherent, because it is presumably reason that you are using to make the argument, albeit poorly. Similar things can be said about arguments about the reliability of the senses. The only reason you can possibly identify when they err is because you can identify when they don't. Otherwise, how could you make the distinction?
These may seem like obviously amateurish errors to make, but they surface in various forms all over the place. Scientists untutored in philosophical analysis say things like this all the time. You'll hear absurd remarks like "The human brain evolved to survive in the universe, not to understand it" with a confidence of understanding that would make Dunning and Kruger chuckle. Who is this guy? Some kind of god exempt from the evolutionary processes that formed the brains of others? There are positions and claims that are simply nonstarters because they undermine the very basis for being able to theorize in the first place. If you take the brain to be the seat of reason, and then render its basic perceptions suspect, then where does that leave science?
We're not talking about the products of scientific processes strictly, but philosophical presuppositions that affect the interpretation of scientific results. If you assume that physical reality is devoid of qualitative properties, and possesses only quantifiable properties, then you will be led to conclusions latent in those premises. It's question begging. Science no more demonstrates this is what matter is like than the proverbial drunk looking for his keys in the dark demonstrates that his keys don't exist because they can't to be found in the well-lit area around a lamp post. What's more, you have now gotten yourself into quite the pickle: if the physical universe lacks qualities, and the brain is physical, then what the heck are all those qualities doing inside of it! Consciousness has simply been playing the role of an "X-of-the-gaps" to explain away anything that doesn't fit into the aforementioned presuppositions.
You will not find an explanation of consciousness as long as you assume a res extensa kind of matter. The most defining feature of consciousness is intentionality, and intentionality is a species of telos, so if you begin with an account of matter that excludes telos, you will never be able to explain consciousness.