It's impossible to definitively say which physical science is the most fundamental because each branch builds upon and interacts with the others. However, many argue that physics holds a strong claim for this title due to its focus on the most basic building blocks of the universe and the fundamental laws governing them.

Here's why physics is often considered the most fundamental:

* Focus on the Universe's Foundations: Physics explores the nature of matter, energy, space, time, and the forces that govern their interactions. These are considered the most basic elements of reality.

* Underlying Other Sciences: Many other sciences, such as chemistry, biology, and geology, build upon the fundamental principles of physics. For instance, chemistry relies on the laws of physics to explain chemical reactions and the properties of matter, and biology uses physics to understand processes like energy flow and movement.

* Unifying Principles: Physics seeks to discover universal laws that can explain phenomena across different scales, from the subatomic realm to the vastness of the cosmos.

However, it's important to remember that all scientific disciplines are interconnected and contribute to a deeper understanding of the universe. While physics may be considered the most fundamental in terms of its scope and focus on the basic building blocks, other fields, like chemistry and biology, are equally essential for exploring the complexity and diversity of our world.

Ultimately, the question of which science is most fundamental depends on your perspective and what aspects of the universe you're most interested in exploring.