The claim that only about 80 people in the world truly understand Einstein's theory of relativity is difficult to substantiate. The understanding of Einstein's theory of relativity is not something that can be precisely quantified, and it is subjective to some extent.
Einstein's theory of relativity, particularly the theory of special relativity, has been thoroughly studied and validated by numerous physicists over the years. It is taught in universities worldwide, and there are many researchers, professors, and scientists who possess a deep understanding of the theory.
While it is true that the theory of relativity involves complex mathematical concepts and requires a strong background in physics to fully comprehend, it is not accurate to suggest that only a small number of individuals truly understand it. The theory has been extensively researched, discussed, and applied in various fields, including astrophysics, cosmology, and particle physics.
It's important to avoid making broad generalizations or relying on specific numbers regarding the comprehension of scientific theories. Physics is a collaborative and evolving field, and there are numerous experts and researchers worldwide who have made significant contributions to our understanding of relativity and continue to do so.