(Picture from the Washington Post.)
I think most things are knowable, but perhaps not in a lifetime, or even in several lifetimes. In fact, the deeper you get into it, the more effort and the longer it takes. But scientific curiosity should have no limits. We also need more brilliant minds like Einstein’s to carry the search forward.
The video in this link describes in a simple manner the consequences of the recently announced discovery of Gravitational Waves. Their existence is final proof that Einstein’s General Theory of Relativity is correct. It also potentially gives us a new tool for extending astronomical observations so that we can learn more about our universe.
This discovery of gravitational waves also conclusively proves that Newton’s Law of Universal Gravitation, that is used effectively in everyday physics even to this day is only an approximation. This approximation can still be used since it works in almost real life cases that we experience. The application of this law begins to fall apart where there are very large gravitational fields present due to massive objects and short distances between objects. (Approximations are not necessarily a bad thing so long as you recognize them as such, and also recognize their limitations.)
Einstein was the genius who could see things beyond the boundaries of the normal human experiences that are the basis of all of our perceptions. He could then come up with universal laws in this regard, laws that are based on science that can be proved and not simply based on belief. He was an amazing person.
It is fashionable these days in some circles to challenge the scientific approach and scientific results, and to label some of these as beliefs, as if the scientific process is akin to following a religion and a belief system. Such an attitude only shows ignorance, and a laziness when it comes to trying to understand things. This kind of attitude is unfortunately increasing in societies that are supposed to be advanced. Check this comic strip out. (I do not want to reproduce the strip in its entirely here for fear of violating copyright.)