Friday, May 09, 2008

A brief history of Physics: The development of Quantum Mechanics

I had read this so many times now that I can retell the story spontaneously. So, if you're not a physics student, and had very little to do with physics since Form 5, you'll know Classical Physics, that is:
  • Mechanics: the study of Forces, Movements, and Mechanical Energy includes Newtonian Gravity.
  • Optics: the study of light and it's wave Properties.
  • Thermodynamics: The study of Heat.
  • Electromagnetic: Electricity and Magnetic and it's combination with light by Maxwell.
So here's a bit of Modern Physics, developed at the beginning of the 20th century and now about 100 years old.

Quantum mechanics started with Planck, Max Planck. He solved the problem of Ultraviolet Catastrophe in 1900 by assuming the Energy of the electromagnetic wave, previously assumed to be able to take any value of energy, is proportional to its' frequency. That way, quantization is introduced into a previously continuous physics.

Albert Einstein in1905, used this principle to explain the photoelectric effect, thus once and for all really put in the reality that light is both a wave and a particle into physics. This is also the paper for he got the Nobel Prize for, not the relativity paper!

Neils Bohr used this principle: the postulate that angular momentum is quantized to give the most accurate version of the hydrogen atom then available. He predicted the value of the ionization energy of hydrogen from this theory!

From now on Quantum theory is known as the new quantum theory, the above are classified as the old quantum theory.
Then Heisenberg had a powerful maths to really explain the full theory of Quantum Mechanics. He developed matrix mechanics. His uncertainty principle is also fundamentally changed Physics. He told us that there is no way you can had a infinitely precise position and momentum at the same time. It's because of this that the electrons you now see in atoms are fuzzy clouds and not small balls orbiting the nucleus. It's fuzzy because you don't know where it is exactly or what velocity it has at that time.

Schrodinger then developed the most familiar equations that University students uses: the Schrodinger equation. With this equation, all properties of an object that can be observed can be predicted by theory so long as the boundary conditions or the situation of the object is clearly known. So from this equation, the chemical bonds of molecules are explained and calculated by theory! How molecules interact with each other can also be predicted.

Finally Paul Dirac had combined quantum mechanics with special relativity, thus predicting the existence of anti-matter. Years later the positron, the antimatter of electron is observed experimentally!

All this achievement are done in the span of 30 years, from 1900 to 1930. There are certainly more than this few in the full history of quantum mechanics but for now all I can write are these. I am sorry for not explaining most of the things here, I hope that you'll have enough interest from reading it here to find out yourself in Wikipedia or HyperPhysics. Now one last thing you should know: you are all benefiting from this theory as the science of electronics is born from quantum mechanics. Therefore, the computer, the cellphones and anything electronic are because of quantum mechanics. We should be grateful for all these physicist for developing this revolutionary theory of Quantum Mechanics.

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