I think that it’s easy to deride the ‘let’s just do what we’ve already done, but an order of magnitude bigger/better/more expensive’ (BBME). But really it’s more subtle.
In particular I think there clearly are times and areas where BBME works really well for quite a long time. I don’t know the history of particle physics experiments well enough, but I bet that between, say, 1945 and whenever LEP was commissioned BBME worked brilliantly: build a BBME synchrotron and huge amounts of new physics poured out and the price was not extortionate. The same is true for gravitational wave detectors – when I was in the process of stupidly abandoning my PhD in GR in the 1980s people pretty much knew that although there was no chance of any detector we could build then seeing (hearing, really) anything, it kind of was the case that some future detector should be able to. And the only real way to build that future detector was to work up through a sequence of, really, technology development systems which would not be adequately sensitive but would let people do the engineering. And we ended up with LIGO / VIRGO & their friends. And you are not going to persuade me that direct detection of gravitational waves was not a prize worth having.
But I think there comes a point where BBME stops working for at least three reasons: you can reach a point where there’s a big hole in the physics so that to see anything really new you need something absurdly bigger so your BBME system just ends up doing the same thing but a bit more accurately; the ME becomes too expensive – when your proposed experiment will use the entire GDP of the planet it is probably too expensive; and finally the spin-off benefits become not interesting enough.
Maybe particle physics is at that point (I suspect strongly it is but I am not a particle physicist). Is gravitational wave astronomy there yet? I don’t think so, but it will get there one day. Are space telescopes, say, there yet? Well it’s tempting to say yes given what JWST has cost, except that JWST is not a BBME Hubble: it’s a different thing altogether, so it doesn’t provide evidence either way. I suspect absurdly large ground-based optical telescopes may be close to or at that point though.
I think humans are also really bad at seeing when BBME has run its course. Hi-Fi is a good example. For a long time BBME worked really well for Hi-Fi – if you’ve listened to Hi-Fi made in the 1950s it is immediately apparent that it is not as good as Hi-Fi made in the 1970s. But then it all hit a wall, in this case because many components became essentially perfect (they got better than the human auditory system). But BBME carried on leading to all the absurdities of speaker cables with all the spins lined up or something we see today.
And of course coming to the end of BBME is awkward for another reason. BBME is typically an exponential process (make one twice as good and four times as expensive every ten years) and exponential processes have nice properties: they are self-similar so that everythig is the same, just scaled up, from one year to the next, and humans don’t like change. There are always enough jobs that each tranche of good students gets employed, for instance. When BBME stops, then suddenly everything is different, and a huge wave of students don’t get employed (and since the exponential process has run for many years, it is a huge wave). Suddenly lots of people who thought they had careers now don’t and lots of courses which turn out those people stop getting students signing up to them. This is a tiny version of the much bigger problem of the end of various other exponential processes which humans have relied upon since there were humans and on which our entire economic system is built. We are completely failing to understand how to negotiate the end of any of these processes without very awkward, and very likely civilisation-ending consequences. Maybe there is no way to end them without these very awkward consequences: just because we need there to be a way to do that does not mean there is. For physics at least the awkward consequences are pretty small unless you are a particle physics PhD student who was expecting a career.
It probably also matters that coming off the end of BBME means that people need to start actually being clever again: brute force and money has failed so cunning and cheap is needed. That’s a big change in thinking. Although I’ve not been able to find details of the total cost, I suspect that the EHT is an example of cunning and cheap: you want to make a telescope as big as the Earth? well, it turns out you can cheat. Hi-Fi provides another example again: could you make, today, Hi-Fi that was actually better rather than just more gold-plated? Yes, it turns out you could, because loudspeakers have really significant levels of distortion (this makes the depleted-uranium–24-bit-speaker-cable-thing even more of a joke than it already is). Current speaker designs are never going to get much better: perhaps there’s a cheap and cunning alternative2?
Finally I think it’s worth remembering the spin-off thing. Everyone else thinks that the LHC is doing research into particle physics: I think it’s doing research and development into production-quality large-scale high-power superconducting systems. And given my take that we’re going to need to ship huge amounts of electric power over many thousands of miles (half way around the world in fact) if we’re going to have a medium-term future as a civilisation I’m kind of interested in those. Would a BBME collider further that goal? I don’t know.