The term "Asian physicists" generally refers to physicists from Asia or those of Asian descent who have made significant contributions to the field of physics. This can include a diverse group of individuals representing various countries, cultures, and fields of study within physics, such as theoretical physics, experimental physics, condensed matter physics, and astrophysics. Asia has produced many renowned physicists, including Nobel laureates and influential researchers who have contributed to advancing our understanding of fundamental physical principles and practical applications.

Optical physicists are scientists who study the behavior and properties of light (optics) and its interactions with matter. Their work often involves understanding how light behaves in various mediums, the principles of reflection and refraction, as well as the design and application of optical systems. They may work with lasers, lenses, microscopes, telescopes, and other optical instruments.

The 19th century was a pivotal period for physics, marked by significant advancements and the formulation of theories that laid the groundwork for modern physics. Some of the most notable physicists and their contributions from the 19th century include: 1. **James Clerk Maxwell**: Known for formulating Maxwell's equations, which describe the fundamentals of electricity and magnetism and unify them into the theory of electromagnetism.

The term "20th-century physicists" refers to the numerous influential scientists who made significant contributions to the field of physics during the 1900s. This period was marked by groundbreaking discoveries and the development of new theories that fundamentally changed our understanding of the universe. Some key figures from the 20th century include: 1. **Albert Einstein**: Best known for his theories of special relativity and general relativity, which revolutionized the understanding of space, time, and gravity.

The term "21st-century physicists" refers to the scientists and researchers who are actively engaged in the field of physics in the 21st century. This includes individuals working across various subfields, such as particle physics, condensed matter physics, astrophysics, quantum mechanics, and more. Key attributes and developments characterizing 21st-century physicists include: 1. **Interdisciplinary Research**: Many physicists today collaborate across disciplines, integrating concepts from chemistry, biology, and engineering.

The Fellows of the American Physical Society (APS) is an honorary designation bestowed by the APS to recognize outstanding contributions to physics. The fellowship honors members who have made significant advancements in the field, demonstrated excellence in research, or made notable contributions to the education and public understanding of physics. Each year, nominations for fellowship are made by existing APS members, and the selection is made by the APS Fellowship Committee.