What is the greatest challenge today in modern physics , astronomy or astrophysics?

In your opinion What is the greatest challenge today in modern physics , astronomy or astrophysics that would have the most beneficial effect on mankind ?

















|||As far as I know, particle physics and astrophysics--the most far-out fields of physics, do absolutely nothing that contributes directly to the benefit of mankind. Higgs bosons, dark matter, dark energy, the early universe--all this is terribly interesting, but not applicable in any way that we can forsee (although one never knows).





Nano-technology--which is really on the edge between physics and chemistry and between physics and biology--is where applications are being made that are likely to have impacts on mankind.





The other field of physics that is working for a beneficial effect is plasma physics. That is the effort to make controlled fusion reactions a reality. If they succeed, it will make energy crises a thing of the past. Unfortunately, they have been "about 20 years away from success" for approximately the past 40 years. But I believe they will turn the corner on that eventually.|||These days it would have to be cold fusion. Were such a thing possible it would mean almost limitless amounts of cheap energy. As it is now, fusing even simple atoms like hydrogen involves the simultaneous detonation of three nuclear bombs to achieve the pressures necessary. |||Finding an inexpensive way to produce and distribute hydrogen.|||Building a commercially viable fusion reactor would bring massive benefits to mankind. We'd be freed from our current dependence on hydrocarbons.





|||To explain all forces, including gravity.|||The Grand Unification Theory or The Theory of Everything is said to be the Holy Grail of modern physics.





At the moment, relativity and quantum theory contradict each other in some fundamental ways. A theory that they both fit into would, potentially, explain the entire workings of the universe..."for then we should know the mind of God", according to Stephen Hawking (who isn't religious anymore than I am).|||Astrophysics is mainly the study of meteors and astronomy is the study of heavenly bodies so by my point of view astronomy and astrophysics both have a great challenge