This is an interesting historical question, but I’d like to challenge your initial motivation ;) So the idea that sciences used to be pursued more effectively a century ago. Intuitively speaking, I don’t see why this would be the case, so I’d first have to see some evidence (including the measure of effectiveness) for this claim. My impression is rather that due to immense fragmentation of today’s science into sub-disciplines, there are more people working on particular problems who are effective in their own domains, while remaining largely unknown to the wider audience.
In fact, I would link a lower degree of interaction in the past science, in comparison to today’s science (we have peer-review system, there are more conferences, there is an easier access to publications, etc.) with a lower degree of effectiveness. But of course, how exactly interaction and effectiveness/efficiency are related is an empirical question, so I’m open to be surprised :)
This is a nice summary of Kuhn’s ideas from his SSR (with some really great examples). Your main question (where is in all this objectivity and how to get rid of relativism?) puzzled both Kuhn as well as the post-Kuhnian philosophers of science. In his later work (The Road Since Structure) Kuhn tried to answer these questions in more detail, leaning towards a Kantian interpretation of the world (roughly: even though we do not have an access to the world as such, the world does give a “resistance” to our attempts at forming knowledge about it, which is why not anything goes; a good guide for this is Paul Hoyningen-Huene’s excellent book on Kuhn “Reconstructing scientific revolutions: Thomas S. Kuhn’s philosophy of science”).
I don’t know enough about predictive coding to comment on that comparison, but here are two comments on some of the above issues:
1) While the shift from one paradigm to another often appears to be a matter of “mob psychology” (as Lakatos put it), Kuhn actually discusses elsewhere the process of ‘persuasion’ and ‘translation’ that the proponents of rivaling paradigm can employ. Even though scientists may belong to mutually incommensurable paradigms, the ‘communication breakdown’ can be avoided via these processes (for more on this see this, also available here).
2) Concerning the objectivity of the world, the reason why this issue is not so simple for Kuhn is that he rejects the idea of the “mind-independent world”. This point is often misunderstood and either ignored or placed under Kuhn’s ‘obscure ideas’ mainly because in his attempts to explicate it, Kuhn gets very close to the so-called continental philosophical style, which sometimes irks the shit out of analytically-minded philosophers ;) The following passage from a discussion on Kuhn may not make things much clearer without an additional context, but it points to the relevant parts of Kuhn’s work on this and it hopefully shows why Kuhn doesn’t accept a simple dichotomy between the mind-dependent and mind-independent world (bold emphasis added):
This sums up some parts of late Kuhn’s thoughts on the growth of knowledge and its non-additive character. Now, one can ask: but what does this practically mean? What kind of methodological guidelines does this give us? And this is where issues are perhaps not so surprising (or disturbing). I think the most important points here are:
1) a complex defeasible character of scientific models and theories (complex in the sense that falsifying a theory may not be a matter of deciding in view of one or two experiments, as discussed in the article; instead Kuhn speaks of the importance of ‘epistemic values’, such as scope, adequacy, simplicity, consistency, fruitfulness—which guide scientists to prefer one theory over another, and which at the end of the day lead the community to replace one paradigm with another; this is closely related to the next point);
2) instead of assessing the truthfulness of scientific knowledge, post-Kuhnian philosophers of science prefer to speak of the assessment of their performance in terms of epistemic (or as sometimes called ‘cognitive’) values, based on empirical evidence (in other words, scientists are considered as accepting a theory not because it is ‘true’ or ‘truth-like’ but because it scores highly with respect to its predictive accuracy, explanatory scope, etc.
3) the presence of conceptual frameworks underlying scientific theories, which complicate their unification and integration (and which have inspired a whole range of accounts proposing ‘scientific pluralism’), and which may also give rise to rational disagreements in science, make the learning and communication across paradigms cumbersome, etc.