The following is a list of important unsolved problems organized into different areas of physics.

Some major unsolved problems in physics are theoretical, meaning current theories cannot explain certain observations or experiment results. Others are experimental, involving difficulties in designing tests to check proposed theories or study specific phenomena more closely.

Many important questions remain unanswered in physics beyond the Standard Model, such as the strong CP problem, finding the exact mass of neutrinos, understanding why there is more matter than antimatter, and discovering the true nature of dark matter and dark energy.

A major issue exists within the mathematical structure of the Standard Model itself, which does not agree with general relativity. This disagreement causes both theories to fail in extreme situations, such as at the Big Bang or inside black holes beyond their event horizons.

Historical problems and lists

In 1704, Isaac Newton published a list of 31 questions about light in his book Opticks.

In 1900, Lord Kelvin spoke about two major challenges in classical physics that were important for the physics of the 20th century. These were the lack of proof for the existence of the luminiferous aether and the inability of the equipartition theorem to correctly predict the heat capacity of solids. Both challenges were resolved within a decade through the development of special relativity and quantum mechanics.

In 1984, mathematical physicist Barry Simon created a list of 15 open problems related to quantum operators. About 5 of these problems were solved by the year 2000. A second list of 15 problems was shared in 2000, with at least 3 of them solved by that time.

Nobel laureate Vitaly Ginzburg compiled a list of open physics problems from 1971 to 2005, focusing on challenges near the start of the 21st century. The final list included 30 problems. Ginzburg also included three major questions: the nature of the arrow of time, the interpretations of quantum mechanics, and how life might arise from physics alone.

At the Strings 2000 conference, a group of scientists proposed a list of 10 important problems in theoretical physics. As of 2025, none of these problems have been solved completely.

Some mathematical physics problems are included in well-known lists of unsolved problems in mathematics. These include: