Schrodinger's cat

Quantum mechanics is considered as one of the foundations of modern physics (the other one is relativity). This theory is the work of many scientists in 20th century, so the creation of theory can not be attributed to a single person. Quantum mechanics started from the experiment results that classical mechanics can't explain. Scientists, found that they need a new mathematics model, because the classic mechanics doesn't work in the microscopic world. The discoveries and the research of the world of particle are the foundation of quantum mechanics.

There are three principles that are important to quantum mechanics. One of them is the quantized property. Before the development of quantum mechanics, scientists thought that the energy is always continuous However, scientists found that the spectrum of the light is consist of specific color and wave length of light instead of a continuous spectrum. Scientists' explanation of this property is that electrons of atoms have different level of orbits. When electrons absorb the energy, specific wave length of light, they will move to other orbits that have higher energy. The electron that jump to another level of orbit will eventually fall back to the its original level when it doesn't receive energy. When it falls back to the original level, it emit light. The wave length of the emitted light, is identical to the wave length of light it absorb when it jumps to the another level. Only in this way, the energy can be conservative.

A interesting property of quantum mechanics is that we can not know both the speed and the position of particles. Why is that? Take observing electron for example, when we observe the position of electron, we use photons to hit that electron. Once the photons hit the electron and bounce back, we can know the position of the electron by catching those reflected photons. However, although we know the position of that electron at the moment we observe it, we are not able to know the velocity of that electron, because we change its speed when we use the photon to hit it. On the other hand, if we want to observe the velocity of that electron precisely, we must not use the photon to hit it. Hence, even though we know the speed of that electron, we can not tell where it locates. This bizarre property is called "uncertainty principle"    In the past, scientists thought that electrons of atoms orbit the nuclei, but if we apply the uncertainty principle, we will know that this model was wrong. If we can not know both the position and the velocity of electron, how can we even predict that they orbit the nuclei of atoms. As a result, the old model which describe that electrons orbit the nuclei was modified to a model that indicates the domain that electrons may appear. In other worlds, the present model of atoms tell us that there are some specific areas where electrons exist, before we observe them, they can be anywhere in those areas.

After we understand this idea, we can try to extend it. In addition to the position and velocity, other properties of electrons also contain lots of possibilities. Just like the idea that electrons can be anywhere before we observe them, electrons also exist in any state before we observe it. The situation that a particle can exist in multiple state at the same time is called 'superposition'. To explain this idea, a physicist named Schrodinger set up an imaginary experiment. The experiment goes like this: Assume that we put a cat in a box, and also put a bomb which has 50% chance to explode. After we put both cat and bomb inside the box, we close the top and leave the box for a while. A few hours past, the cat in the box would have 50% to be dead and 50% chance to be alive. We have to open the box to find out. Before we open the box, the cat was in the state of both dead and alive, just like a electron exist in multiple state at the same time. We have to make an observation in order to pin point the state of the cat or electron.

Quantum mechanics is really interesting. Also it can describe the microscopic world nearly flawlessly, no one can fully understand it. In the other hand, classical mechanics is not perfect, but nearly everyone can understand its idea. I think this is because of the strange and mysterious property of the nature. We never know if we can fully comprehend it.