Quantum mechanics didn't require $10B (or whatever the equivalent would be in 1930-ish currency) to create. The "inventors" of QM were trying to explain measurements that were already made, quite inexpensively, that did not fit the model of nature that we had at that time.
Basically, the experiments were done, measurements made. Now the theorists were trying to understand what they needed in order to be able to provide a model that fit these results. This required a number of specific mental leaps of faith. Some of these are controversial even today. But they fit the experiments, so the issue for us is one of a mental model.
But ... and this is critical, not all of physics is quantum mechanical. Orbital calculations don't (normally) require QM. Steam engines, heat engines, etc. don't normally require QM.
The objections some of us have with classifying "all of physics being HEP" is that it is not, and the reality is that most physics do not require accelerators. Most new physics won't require accelerators.
A great example from earlier this year is the first sighting of a Majorana fermion[1]. Though this article also makes the mistake of "In particle physics, fermions are a class of elementary particles". Its not in particle (HEP) physics. Its in physics.
[1] https://news.mit.edu/2020/first-majorana-fermion-metal-quant...
Also, look at the military budget and think what is potentially more useful...
That analogy has broken down. It’s not to say that we couldn’t learn something at 100TeV that could be useful or even revolutionary like QM was, but we also don’t really have any reason to believe that right now other than cheery optimism.
I’m all for finding high energy physics, I just don’t think it can justify it’s current budget in the quest for newer bigger colliders at higher and higher energies.
