Some of the major unsolved problems in physics are theoretical, meaning that existing theories seem incapable of explaining a certain observed phenomenon or experimental result. The others are experimental, meaning that there is a difficulty in creating an experiment to test a proposed theory or investigate a phenomenon in greater detail. Can quantum mechanics and general relativity be realized as a fully consistent theory (perhaps as a quantum field theory)? [1] Is space-time fundamentally continuous or discrete? Would a consistent theory involve a force mediated by a hypothetical graviton, or be a product of a discrete structure of space-time itself (as in loop quantum gravity)? Are there deviations from the predictions of general relativity at very small or very large scales or in other extreme circumstances that flow from a quantum gravity theory? [2] In general, there are some unanswered questions or complex concepts in modern physics. These issues are divided into two categories: A: The questions that modern physics does not have answers for, and the physicists believe that it is due to the inability of theories. B - Complex concepts that seem unrealistic, but physicists have admitted they do not know the problems of modern physics. There are concepts and equations in physics (classical mechanics, relativity and quantum mechanics) that we can use to reach an understanding that is able to be experienced and by which we can review relativistic Newton's second law. Using the revised relativistic Newton's second law, we can make it easier to express complex concepts in modern physics and respond to many unanswered questions in modern physics. Reconsidering the relativistic Newton's second law is a powerful tool that deepens our understanding of space-time and can be an important step in understanding the nature of interactions and unifying them easier.