1924 a PhD thesis by French physicist and aristocrat Louis de Broglie postulated that the particles of matter can also have wave properties.
This image represents a propagation of de Broglie waves in 1d. This new view of matter gives a more definite picture of Bohr’s orbits: They represent stationary wave patterns for an electron is in an atom. The old 19th century distinction; matter is made of particles, light is a wave, completely broke down.
In the quantum world, light and matter both have wave and particle characteristics.
Between 1900 and the mid-1920s, physicists extended quantum theory to a wider and wider range of phenomena. Things that were once thought to be smooth and continuous turned out to be discrete and discontinuous. Things that were once thought to be discrete turned out to have continuous wave properties.
All sorts of quantum phenomena were related to Planks Constant h.
Because h is so very tiny, quantum phenomena occur in the microscopic realm. Despite these successes, not until 1925–1926 did a systematic, mathematical quantum theory emerge.
Austrian physicist Erwin Schrödinger and German physicist Werner Heisenberg developed what looked like completely different quantum theories.
They turned out to be different mathematical forms of the same mechanics. Quantum mechanics is the most successful theory of physics ever created, explaining the nature of light, the structure of matter, and the behavior of particles.
The main features of quantum mechanics are wave-particle duality, indeterminism, and entanglement.
1. wave-particle duality 
2. indeterminism 
3. entanglement 
These 3 basic features take us to some remarkable places. Because Planck’s constant (h) is so small, we sometimes say that quantum physics is only important in the microscopic realm. But of course this is not really true. Many large-scale facts about the world that are determined by quantum physics.
END PART 3
PART 1, PART 2, PART 3, PART 4, PART 5
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