Quantum mechanics

Main thing

Quantum mechanics is the theory that describes the bizarre behavior of matter and energy at the atomic and subatomic scale. The core idea is that at this tiny scale, particles exhibit both wave-like and particle-like properties, and everything is quantized into discrete packets. This leads to very strange phenomena that seem to defy common sense, like particles being in multiple states at once (superposition) and instantly affecting each other at a distance (entanglement). But despite how weird it is, quantum mechanics has been validated to extreme precision and forms the foundation of fields like chemistry and modern technologies.

Terms

• Theory: A scientific explanation of some aspect of the natural world that is supported by evidence and can be tested.

• Mechanics: The branch of physics that deals with the behavior of physical bodies when subjected to forces or displacements.

• Matter: Physical substance that occupies space and possesses rest mass, especially as distinct from energy.

• Energy: The capacity for doing work, which may exist in potential, kinetic, thermal, electrical, chemical, nuclear, or other forms.

• Atomic scale: The size range of individual atoms, typically measured in picometers or Ångströms.

• Subatomic scale: Referring to particles smaller than atoms, such as electrons, protons, and quarks.

• Quanta: The smallest discrete unit that properties like energy come in at the quantum scale.

• Wave-particle duality: How particles exhibit both wave-like and particle-like characteristics.

• Superposition: A particle existing in multiple possible states at once until measured.

• Entanglement: When particles interact such that measuring one instantly affects the other, even at great distances.

• Uncertainty principle: You can't simultaneously know a particle's exact position and momentum - measuring one reduces precision of the other.

An analogy

Imagine a pixelated video game world. From far away it looks smooth and continuous, but zooming in reveals it's made of discrete blocks with set properties. Quantum mechanics says our reality is similar - seemingly smooth and predictable on our scale, but quantized and probabilistic when you zoom into the atomic realm.

A main misconception

Many think quantum mechanics says "anything can happen" or that it allows faster-than-light communication. This is wrong. Quantum mechanics is strange but precisely predictable using math. Effects like entanglement can't actually send information faster than light.

The history

1. 1900 - Max Planck discovers energy is quantized to solve the blackbody radiation problem

2. 1905 - Einstein explains the photoelectric effect using light quanta (photons)

3. 1924 - de Broglie proposes wave-particle duality

4. 1925-1926 - Heisenberg and Schrödinger create the first complete mathematical frameworks of quantum mechanics

5. 1935 - The EPR paper by Einstein, Podolsky and Rosen highlights the seeming paradox of entanglement

6. 1940s-1960s - Quantum mechanics enables the development of transistors, lasers and modern electronics

7. 1964 - Bell's theorem shows that quantum mechanics is incompatible with local hidden-variable theories

8. 1970s-1980s - Experiments confirm quantum entanglement and violations of Bell's inequalities

9. 1980s-2000s - Quantum information theory and quantum computing begin to emerge as fields

10. 2000s-present - Quantum technologies like cryptography, sensing, and simulation continue to advance

Three cases how to use it right now

1. Quantum random number generators use the inherent randomness of quantum processes to create truly random numbers, crucial for encryption.

2. MRI machines use the quantum property of spin to image soft tissues in the body without radiation.

3. Quantum computers, while still early stage, are expected to someday solve certain problems far faster than classical computers by utilizing superposition and entanglement.

Interesting facts

• A particle can tunnel through a barrier it shouldn't have the energy to pass through, thanks to quantum mechanics.

• Quantum entanglement has been demonstrated between particles separated by over 1200 km.

• Quantum mechanics says there is a tiny but non-zero chance you could quantum tunnel through a wall.

• The quantum Zeno effect says observing a particle can keep it from decaying.

• Quantum mechanics was developed by at least 12 Nobel Prize winning scientists.