Scope and Excitement of Physics

Physics — The Study of Nature at Every Scale

Physics is the branch of natural science that studies matter, energy, and the fundamental

interactions between them. What makes physics genuinely exciting is its enormous range: the

same subject that explains how a quark behaves inside a proton (a distance of about

$10^{-15}$ m) also explains how galaxies orbit one another across distances of $10^{26}$ m

— a span of forty-one orders of magnitude in length alone, and a comparable span in time,

from the lifetime of an unstable sub-atomic particle to the age of the universe.

This scope is usually organised into two broad domains:

• Macroscopic physics — the physics of everyday, laboratory and astronomical scales: mechanics, thermodynamics, electromagnetism, and optics as they operate on objects you can see, touch or track with ordinary instruments (falling stones, flowing currents, planets).
• Microscopic physics — the physics of the very small: atomic structure, nuclear physics and particle physics, where the rules of quantum mechanics replace the familiar rules of everyday mechanics.

What Makes Physics "Exciting"

Three things repeatedly draw students and researchers to physics:

1. Unification. Physics keeps finding that phenomena which look completely unrelated are in fact the same underlying law seen from different angles — electricity and magnetism turned out to be a single electromagnetic force; the fall of an apple and the orbit of the Moon turned out to obey the same law of gravitation.
2. Predictive power. A correct physical theory does not just describe what has already been observed — it predicts what has not yet been seen. The existence of the neutron, radio waves, and gravitational waves were all predicted by theory before they were confirmed by experiment.
3. Universality. The laws discovered by studying objects on Earth (falling apples, spinning wheels) turn out to govern the entire observable universe — a rock on the far side of a distant galaxy obeys the same law of gravitation as a stone dropped in a laboratory.