Really?
I've read some pretty authoritative writings about how humanity always thinks The End is Near, that we live in an era of decay after a lost Golden Age, that today's youth is a uniquely corrupted lost generation and so on.
Blockchains are one that I would present. I'm sure experts in other fields would have examples from their worlds as well. We just haven't had time yet to appreciate how dramatic some of the discoveries are going to be.
In that regard, the number of inventions (as subset of all sets of configured matter)- is similarly bound. We might argue that such a bounding is infinitely expanding along with the universe, as space is a important variable in the equation. Even so, my assumption is that space becomes irrelevant after a certain point of expansions. (If I have 2 atoms in a field of a billion of square miles, the number of configurations is only trivially changed by adding a few more square miles.
Once more, even if an infinitely expanding universe equates to an infinitely expanding art of inventions (configurations) - the fact remains that the set is fixed for any given time point.
No, they really haven't. In fact for a good chunk of centuries (from 16th century onwards), the optimism for the eventual future developments was endless. At some point there was a few scholars saying that during the end of 19th century, but still not some widespread belief.
That said, discovery probably also follows an 80/20 rule, and we're somewhat at the tail end now. We haven't had any major new discoveries, of the kind that we had regularly until the 60s-70s, for decades now.
Progressive refinement (like going from the workstation to mobile phones and watches) yes. But nothing like the advent of the computer, the internet, and so on.
And even less earth-shattering stuff than the time before that (which got us from the steam engine and electricity, to nuclear energy, radio and tv, flight, space exploration, the digital computer, QM and relativity, the DNA, and so on). Stuff like that was coming decade after decade up until the 60s-70s. After that, not so much.
>"We might have invented everything" would imply that the space of all possible inventions is bounded, and we're running up against the edges of the box. But I don't see any reason it should be bounded.
While there's some quasi-religious optimism (like the universe owe us endless discoveries forever), there are real limits, and notions like "low hanging fruit" and "marginal returns" do come into play.