One of the greatest scientific achievements of physics in the 20th century is
the discovery of quantum mechanics. It governs the dynamics of microscopic objects
such as atoms and electrons. In this tiny world, things behave differently from
the macroscopic world where classical mechanics rules.
Few people realize how much our picture of the universe has changed in 100 years.
At the end of the 19th century, the universe was thought to contain only hundreds
of thousands of stars arranged in no particularly interesting patterns. The most
distance stars were thought to be about 100,000 light years away
(meaning that it would take light 100,000 years to travel from Earth to such distant
stars; 1 light-year is about 10 trillion kilometers or 6 trillion miles).
Isaac Newton changes our understanding of the universe by formulating
three laws to describe the movement of objects. 1) An object in motion remains
in motion unless an external force is applied to it. 2) The relationship
between an object's mass (m), its acceleration (a) and the applied force (F) is F = ma. 3)
For every action there is an equal and opposite reaction.
Electromagnetism is one of the four fundamental interactions of nature, along
with strong interaction, weak interaction and gravitation. It is the force
that causes the interaction between electrically charged particles; the areas in
which this happens are called electromagnetic fields.
Energy is equal to mass times the speed of light squared.
Albert Einstein's famous formula proves that mass and energy
are different expressions of the same thing, and that a very small
amount of mass can be converted into a very large amount of energy.
Thought and experimentation by Isaac Newton, Thomas Young and Albert Einstein
lead to an understanding of what light is, how it behaves, and how it is transmitted.
Newton uses a prism to split white light into its constituent colors and another prism to
mix the colors into white light, proving that colored light mixed together makes white light.
Young establishes that light is a wave and that wavelength determines color. Finally,
Einstein recognizes that light always travels at a constant speed.
The unexpected discovery that some materials have no resistance
to the flow of electricity promises to revolutionize industry and
technology. Superconductivity occurs in a wide variety of materials,
including simple elements like tin and aluminum, various metallic alloys and certain ceramic compounds.
Of the basic forces at work on the subatomic level lead to the realization
that all interactions in the universe are the result of four fundamental
forces of nature — the strong and weak nuclear forces, the electromagnetic force and gravitation.