Question

What practical application can we expect from particle physics a century or two from now? What use can we make of quark-gluon plasmas or strange quarks? How can we harness W- and Z-bosons or the Higgs boson? Nuclear physics has given us nuclear plants and the promise of fusion power in the near future. What about particle physics? If we extend our timeframe, what promise does string theory give us? Can we make use of black holes?

Answer 1

You asked for speculation, so here is outlandish speculation:

We can do engineering all the way down to the atomic scale. The reason is that life is made of atoms, and biology is complicated processes capable of general purpose computation, so atoms can do complicated things. There is no reason that we should be able to do engineering with nuclei, because our universe doesn't embed life in nuclear structures.

But that doesn't mean that you can't try. Suppose you could build a pion laser, and stabilize it by the appropriate methods, by surrounding it with the appropriate reflectors to prevent 2-photon decay, or change to charged pion very quickly to prevent decay, or ... I don't know, or else this wouldn't be speculation. Then you would be able to do nuclear engineering, meaning move nuclei around like you move atoms with light lasers, and pump energy into hadronic states at will, not by collisions, but by engineering. Without good bosonic fields which you can manipulate over relatively large scales, there is no hope for any of this.

Using a pion laser, you might be able to blow up elementary particles in a spherically symmetric way, like balloons, and let them collapse onto themselves to make black holes. This requires a controlled implosion, because the mass of a nuclear scale black hole is that of a mountain. If you can somehow make a symmetric implosion which shrinks the pumped up hadron by 10 orders of magnitude, to get some black hole states at some heavy but achievable mass, you can make monopoles, black holes, strings, and turn anything into energy.

I spent many hours of my youth trying to make this hopelessly futuristic idea work, because it is the only hope we have of investigating the Planck scale by even speculatively achievable technology. I think this type of thing might work out in 200 years, and produce a monopole-driven total mass-energy converter