Physics is the most fundamental of the experimental sciences, as it seeks to explain the universe itself, from the very smallest particles—quarks (perhaps 10–17 m in size), which may be truly fundamental—to the vast distances between galaxies (1024 m).
Newtonian mechanics, electromagnetism and thermodynamics went a long way in deepening our understanding of the universe.
However, experimental discoveries dating from the end of the 19th century and more recently, developments in chaos theory, in which it is now realized that small changes in the initial conditions of a system can lead to completely unpredictable outcomes, have led to a fundamental rethinking in thermodynamics.
Quantum mechanics and QED show that the nothing is certain and everything is decided by probability. But there is still much that is unknown and there will undoubtedly be further paradigm shifts as our understanding deepens.