Please elaborate on this.
To describe the behavior of large objects like solar systems and galaxies or objects moving close to the speed of light, physicists use relativity theory. The experimental data and the theoretical predictions are close enough.
But for subatomic particles, relativity gives wrong results. So scientists use quantum mechanics. And then the experimental data and theoretical predictions are close enough.
But that means these two theories contradict each other. Science strives to find theories that are universal and apply everywhere in the universe. Einstein was aware of the contradiction and spent the last 30 years of his life looking for a unified field theory that would apply to both parts of the universe. He failed in that attempt.
That is the Holy Grail of physics today, to find one theory to describe both objects that are very large (or moving very fast) and objects that are very small. One theory they have come up with is superstring theory. It says that the universe is composed of very small strings, which are more like little rubber bands that vibrate at different frequencies. It is a very elegant theory, but it is also impossible to verify that they exit, at least for the time being.
If you like to read about science, I recommend The Elegant Universe by Brian Greene.