Quantum mechanics
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Quantum mechanics is a theory found in physics and chemistry. It explains how very very tiny things work - like atoms and molecules. It is a very accurate and successful theory supported by many experiments.
Some ideas in quantum mechanics can be used to understand how small objects combine into large objects like stars, and even the whole Universe.
Some parts of the theory are controversial. Some results from quantum mechanics seem to disagree with the theory of relativity.
Quantum mechanics describes nature in a way that is different from how we usually think about science, relying on probability rather than certainty.
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[edit] History
Light was first thought to be made of particles. Isaac Newton called these particles "corpuscles". With this idea, he could explain how light behaved. Later, Christiaan Huygens thought that light was made of waves. These theories seemed to be conflicting with one another.
It turns out that both theories are correct - light can have particle and wave properties. We call this "wave-particle duality".
[edit] The Uncertainty Principle
On the level of Quantum mechanics the Uncertainty Principle states that the more we know about something's position, the less we can know about its speed; and the more we know about something's speed, the less we can know about its position.
[edit] Photoelectric effect
In 1905, Albert Einstein proved that although light is like a wave, it is made of particles of energy called photons. This came from the photoelectric effect.
This began quantum theory, where all subatomic particles like electrons, protons, neutrons, and others are both waves and particles at the same time. See picture of atom with the electron as waves at atom.
For other parts of quantum mechanics, see Schrödinger equation and quantum entanglement.
[edit] Observation
A key part of quantum theory is that certain attributes of particles, such as position, speed, direction it moves in, and spin, are not defined until they are observed. It is instead in what is called a “superposition of states”.
[edit] Uses
Quantum mechanics is useful for:
