It may be unlikely to see progress in a subfield even if there are major unsolved problems. Particle physics is one of those branches. But see https://en.wikip

It may be unlikely to see progress in a subfield even if there are major unsolved problems. Particle physics is one of those branches. But see https://en.wikipedia.org/wiki/List_of_unsolved_problems_in_physics https://en.wikipedia.org/wiki/List_of_unsolved_problems_in_p...