量子物理 - 《理論物理學》

量子物理史話〈曹天元)
1935年5月15日，愛因斯坦和波多斯基、羅森三人共同發表了一篇論文《物理實在的量子力學能被視為完備的嗎？》這篇論文後來被以他們三人的姓氏開頭簡稱為EPR悖論。

這篇論文中設想了一個思想實驗來指出 #不確定性原理的不完備性。假設有兩個粒子經過交互作用後彼此遠離，從不確定性原理我們知道，我們無法同時測得粒子的動量和位置，但若我們只測量A粒子的動量，並同時只測量B粒子的位置，就能用動量守恆的方式同時得知兩者的位置和動量，這與不確定性原理中的原則不相符。

薛丁格用了「#量子纏結」這個詞來稱呼這兩個產生交互作用的粒子。

什麼是量子纏結呢？兩個經過交互作用的粒子移動離彼此到相當遠的地方，透過測量其中一個粒子，我們卻能馬上知道另一個粒子的狀態，A粒子今天是自旋向上，B粒子馬上自旋向下；A粒子今天喝了一杯咖啡，B粒子馬上也喝一杯咖啡；A粒子跟她媽吵架；B粒子馬上也找件事跟他媽吵；A粒子跟她男朋友分手，B粒子立馬跟他女朋友分手。

在宏觀的物理世界裡，兩個粒子相相隔兩地，但在微觀的量子世界裡，卻是緊緊的糾纏在一起。達到了100%的同步率。這樣「#鬼魅般的超距作用」，違反了狹義相對論已經證明的「光速是速度的最高極限」的原則，但卻真實存在，令人匪夷所思

然而愛因斯坦等人為了駁斥不確定性原理而提出的EPR悖論，反倒讓人們開始了一連串的研究，並證實了「量子纏結」的現象。

〈量子纏結＝超距作用〉
>>https://bit.ly/2SVBnXs
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Quantum Physics I (Prof Young Lee).pdf

Quantum Physics II (Prof Krishna Rajagopal).pdf

Quantum Physics III (Prof Krishna Rajagopal).pdf

There were two groundbreaking experiment that explained the most basic properties of light and matter, even universe.
1). Double slit experiment
2). PHOTO ELECTRIC effect.

This is the PART-1 of quantum mechanics.
There will be more discussion on this topic.
But for now, starting it from basics.

QUANTUM MECHANICS
PART-I

How did it all begin?

EVIDENCE

There was time in history when scientists thought they have the knowledge of everything in this universe. But some experiments and concepts destroyed this thought. And after these experiments, we got to know, we can never be perfect in science. And that’s because of Quantum Mechanics.

DOUBLE SLIT EXPERIMENT

This experiment was performed by passing light through two slits. After this experiment, we got to know light behaves as wave, as it was creating interference pattern. Later, this experiment was performed by passing electrons. And it was strange to observe that, electrons were also making interference pattern. But even strange thing was the disappearance of interference pattern on observing it. So, now electrons were also showing properties like wave. But on observation, it starts behaving like particle.

PHOTOELECTRIC EFFECT

This experiment gives the proof for particle like behaviour of light. In this experiment, light of particular wavelength was allowed to fall on metal. During this, electric current started to flow through circuit. This explained the quantization of energy or, shows the particle nature of light.

E=hν

After these two experiments, the concept of wave particle duality was highlighted. This means for the dual behaviour of light and matter (as wave and particle).

Image credit: Energy Wave Theory
QUANTUM MECHANICS PART 2
In this Part, I have discussed about the basic and fundamental understanding of Quantum Mechanics.
Today these things are very common and comfortable for science. The complexity has increased and this is resulting as new Discovery and invention.
Actually, the concept of probability in Quantum Mechanics can destroy the static mindset for our universe and may seems as absurd but that’s the fundamental nature of it.
These uncertainty is not due to the lack of technology or we cannot measure it but these uncertainties are intrinsic property of our universe.
WE ARE UNCERTAINS LIVING IN UNCERTAINTIES. BUT REALITY IS THE COLLAPSED WAVEFUNCTION.

What’s the basic nature of Quantum mechanics?

WAVE NATURE OR SOMIETHING ELSE?
After the double slit experiment, we got to know matter also behaves as wave. And if it is a wave we cannot be so sure about the coordinates of that particle. So, it was only possible to calculate the probability of that particle on specific coordinates or we have to deal with uncertainties. Hence, we got HEISENBERG’S UNCERTAINTY PRINCIPLE.

HEISENBERG’S UNCERTAINTY PRINCIPLE
∆x∆p ≥ ℏ/2
This inequation can give us the data about the uncertainty of position and velocity. Here, ∆x is uncertainty in position, ∆p is uncertainty in momentum and ℏ is reduced Planck’s constant. But! But! But!! There’s not only position and velocity uncertainty but there’s UNCERTAINTY INEQUATION for Energy and Time also.

NEED FOR A NEW EQUATION
Now these all things were different from the laws of Classical Mechanics. So, there was the need for a new equation which can make us understand about the Dynamics of these probabilistic waves. After these all events, one can hardly say what is going to happen because now Mechanics was not accurate to state the outcomes. Actually, there is only Probability of it. So, it may or may not occur.

SCHRÖDINGER’S WAVE EQUATION
Schrodinger’s Wave Equation is highly complex mathematical equation which can explain about the Dynamics of electronic waves. It has given many results which are core of Quantum Mechanics And that’s why this equation is called as heart of Quantum Mechanics. Integrating it three times have given three Quantum Number. These are Principal Quantum number, Azimuthal Quantum number and Magnetic Quantum number. This part needs much more explanation. So, there will be a separate post about it.
iℏ(∂ψ/∂t) = Ĥψ
How are Photons Created and Destroyed?

The photon is a type of elementary particle. It is the quantum of the electromagnetic field including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force. The invariant mass of the photon is zero; it always moves at the speed of light in a vacuum
: Dave Kornreich

How are photons created and destroyed?

The simplest answer is that when a photon is absorbed by an electron, it is completely destroyed. All its energy is imparted to the electron, which instantly jumps to a new energy level. The photon itself ceases to be. In the equations which govern this interaction, one side of the equation (for the initial state) has terms for both the electron and the photon, while the other side (representing the final state) has only one term: for the electron.

The opposite happens when an electron emits a photon. The photon is not selected from a “well” of photons living in the atom; it is created instantaneously out of the vacuum. The electron in the high energy level is instantly converted into a lower energy-level electron and a photon. There is no in-between state where the photon is being constructed. It instantly pops into existence.

So the question is: where does the photon come from?

Strangely, it doesn’t seem to come from anywhere. The universe must put the extra energy somewhere, and because electrons in atoms are electromagnetic phenomena, a photon is born with the required energy. In a weak-force interaction, say the decay of a neutron, that energy goes into a neutrino particle which is also instantaneously created. Each force has its own carrier particles and knows how to make them.

That’s really all we can say about it. There are many interpretations of what this and other phenomena in quantum mechanics mean on a deeper level, and whole libraries worth of books which argue points of view on the matter. But my personal philosophy is that of the famous physicist Richard Feynman, who said: “Shut up and calculate.”