Mr. Yang is the physicist that accompanies the trailblazer on the astral express.
Chen Ning Yang (C. N. Yang), the Nobel Prize winner, is perhaps most famous for inventing Yang-Mills gauge theory, a theory that describes three of the forces of nature: the electromagnetic U(1), strong SU(3), and weak SU(2) force. The electromagnetic force follows an abelian guage theory, while the strong and weak forces follow nonabelian gauge theories. These are used in quantum field theory, an area where C. N. Yang did a lot of his most famous work. The modern holy grail of physics is to find a theory that describes the four forces of nature, including gravity. Yang-Mills already describes three of the four, so if somehow gravity can be described using the Yang-Mills framework, then that would be a milestone in physics. But it has not yet been done due to 'technical difficulties'. What he have currently is something called string theory.
The Yang-Mills theory is actually pretty op, being one of the most important contributions to physics in the 20th century (this is no exaggeration).
Some of Yang's skills appear to reference gravity and cosmology. While C. N. Yang's work is related to general relativity and gravity, as stated above, his most famous work is perhaps more related to quantum field theory (qft) and statistical field theory. C. N. Yang specifically won the Nobel Prize for his work on parity violation, a bit more directly related to particle physics and qft than to gravity. But ok, the Yang of Star Rail probably does not even have to have anything to do with C. N. Yang.
Star Rail already did a pretty fine job inviting Didier Queloz to give a lecture on astronomy. The movie Interstellar also invited Kip Thorne to advise them on astrophysics. If Star Rail could invite C. N. Yang to advise them on some detailed physics, hey that would be something. But given how Genshin treated Alhaitham in December 2022, one must question how much respect certain people have towards physicists... These are probably the same people who think the nine familial executions carried out by Yongle contributed more to Chinese history. So if you ever wonder when China can become the leading innovational, technological, and scientific power in the world, it will probably start when the Chinese people give more respect to the contributions of physicists than to a genocidal murderer.
Yang is a nihility character specializing in reducing enemy speed. His skill reduces enemy speed by 10% for 2 turns. His ultimate imprisons enemies, reducing their speed by 10% and delaying their actions. His other talents increase his own damage.
His ultimate is called 'Synthetic Black Hole'. This is funny because a real black hole would destroy/one-shot basically anything in the universe, including video game enemies. But this is a work of fiction, not a phd thesis in astrophysics. His technique is called 'Gravitational Imprisonment'. In relativity, gravity can slow down time (gravitational time dilation), so there is some connection between gravity, slowing down things, and actual physics.
Note, Silver Wolf can plant bugs that reduce speed as well.