3:Quantum Physics

Quantum Physics

Quantum physics is the study of the essence of the universe at indivisible level, the quantum nature of reality. Unlike classical physics, quantum physics seems unpredictable.
Quanta particles do not behave according to the laws of classical physics.
            ↓ 

Wave-Particle Duality 

This principle states that quanta particles exhibit properties of both a wave and a particle.

Heisenberg Uncertainty Principle

No particle has a definite position, trajectory or momentum. The more precisely one property is known, the less precisely the other is known. 

For example:

You are driving. You can measure your speed or location, but you cannot know both at the same time. To measure your speed, your location must be changing, and to measure your location, your speed must be assumed rather than measured. 

Both of these concepts can be observed in the Double Slit Experiment. Here we see particles act as both particles and waves.  

1) When particles are passed through double slits, they create a pattern of two bands.

2) When waves pass through double slits, an interference pattern occurs where the top of one wave cancels the bottom of the other wave. The lines that are recorded (highest in intensity)

are where the tops of both waves meet. 

...now at the quantum level

3) When photons(particles of light) are passed through double slits, they create an interference pattern like a wave leading to the conclusion that the photon turned into a wave of potential, then passed through the double slits and interfered with itself. (Wave Particle Duality)

4) When a measuring device was added by the slits to see which slit the photon passed, the photons went back into acting like a particle and produced the two bands. The act of observing had an effect on the particle or wave nature of the photon. (Uncertainty Principle)

If you are still confused, this youtube clip explains the Double Slit Experiment!

Dr Quantum - Double Slit Experiment
http://www.youtube.com/watch?v=DfPeprQ7oGc

There are three distinctive features of the quantum world:
1) Quantum Superposition
2) Quantum Entanglement
3) Quantum Coherence

1) Superposition

Superposition is a theory that states that quantum particles (unaffected by coherence) can be in more than one place at the same time. 

"It's like you have a child's swing that goes back and forth," says O'Connell. "We pushed the swing and didn't push the swing at the same time."

This is described by Schrodinger's Cat scenario:

The state of Superposition is thought to collapse and become one wavefunction with the effects of observation. This event of wavefunction collapse is explained by several theories:

The Copenhagen Interpretation (most widely accepted)

States that the act of observing/measuring causes the multiple states (probabilities) to assume one of the possible values. This event is called wavefunction collapse. (as seen in the double slit experiment) This interpretation implies that the consciousness plays an active role in determining reality. 

Many Worlds Interpretation

Denies the idea of wavefunction collapse. Instead of collapsing into one reality, the Many Worlds Interpretation claims that observation/measurement causes an actual split in the universe creating parallel worlds accommodating each of the possible outcomes. 

2) Quantum Entanglement 

Entanglement is a theory that claims the existence of unified particles that when separated, remain connected over distance and time. These quantum particle pairs are intrinsically and absolutely linked; therefore, if one of the particles moves, the other half moves almost instantaneously. This reaction between the two entangled particles is faster than the speed of light and therefore defies the theory of relativity. 

3) Quantum Coherence 

Coherence is when multiple particles can condense into one unified entity that is governed by one wave function and collectively cooperate in a single quantum state.  Coherent waves have the same frequency, phases and amplitude. 

Spacial Coherence describes the correlation between signals at different points in space. An example would be a strong correlation between electrical fields at different locations. 

Temporal Coherence describes the correlation between signals at different moments in time.