Wednesday, 14 April 2010

Quantum Quotes

Quotes from scientists from 'Entanglement: The Greatest Mystery In Physics' by Amir D. Aczel

"Entanglement is not one but rather the characteristic trait of quantum mechanics"
- Erwin Schrodinger

"So farewell, elements of reality!"
- David Mermin

"Einstein said that is quantum mechanics were correct then the world would be crazy. Einstein was right - The world is crazy."
- Daniel Greenberger

Notes from book:

Wener Heisenberg - a founder of quantum theory

Light is both particle and wave
Some experiments reveal light as particle, others reveal it as a wave. But never both at the same time. But before we observe a ray of light, it is both wave and particle. Particles and photons are both wave and particle and each has its wave function. (QUANTUM PARADOX)

Electrons live in HILBERT SPACE
abstract algebra, probability theory

Quantum mechanics - we can predict outcomes, but can't understand the underlying processes. Einstein said - it (quantum theory) does not constitute a complete description of physical reality. The theory is incomplete - based their argument on the "unreal" phenomenon of entanglement. If quantum mechanics allowed such bizarre effects to exist, then something must be wrong or incomplete. Einstein felt that what happens in one place could not possibly be directly and instantaneously linked with what happens at a distant location.

Entangled entities (particles or photons) are linked together because they were produced by some process that bound them together in a special way. E.g. 2 photons emitted from the same atom as one of its electrons. They remain intertwined forever, once one is changed, the other changes immediately.

Entangled particles transcend space. The 2 or 3 entangled entities are really parts of one system, and that system is unaffected by physical distance between its components. The system acts a single entity.


A <--> B Alice is married to Bob
D <--> C Dave is married to Carol

Alive and Dave go away on separate business trips.
Whilst they are away, Bob and Carol fall in love and become entangled.
Now Alice and Dave are entangled, despite never having met.

Quantum theory is based on probabilities rather than exact prediction.
Uncertainty Principle: It is impossible to know both the momentum of a particle and its location. If one is known with some precision, the other can only be known with uncertainty.

When we measure, we force some quantum system to 'choose' an actual value, thus leaping out of the quantum fuzz into a specific point.
Observing a particle destroys some of its information contents (wave-function collapse).

Where does the boundary lie separating the macro-world we know from everyday life and the micro-world of photons, electrons, atoms, protons and molecules?
Is a person the sum of many elementary particles, each with its own wave function, or a single macro-object with a single wave-function?

Entanglement teaches us that our everyday experience does not equip us with the ability to understand what goes on at the micro-scale which we do not experience directly.

Greenstein and Zajonc (The Quantum Challenge):
A baseball hit against a wall with two windows can not get out of the room by going through both windows at once. This is something that every child knows instinctively. And yet an electron, neutron, or even an atom, when faced with a barrier with two slits, will go through both of them at once.

Notions of causality and the impossibility of being at several locations at the same time are shattered by quantum theory. The idea of superposition - of "being at two places at once" - is related to the phenomenon of entanglement.


I have highlighted the bits that I found most interesting. As I thought, they seem to point more to the philosophy behind the science and their implication in our world. Without the science and the equations and other stuff I don't understand or care to understand, Quantum Theory is a really amazing piece of work. It is now a completely valid theory, despite the fact that it explains HOW some certain things happen, but absolutely no-one can explain WHY. It really does shatter logic, breaking all the rules we thought just 'were', no questions asked.

Imagine the quantum world was our macro world? We could be in two places at once, or several places at once, doing everything at the same time, be irrevocably attached to someone else and acting as a 'single entity'. It would be crazy. Imagine we were neutrons or particles and behaved so, we could walk through two doors at once...

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