Quantum Physics
Quantum physics is based on quantum theory. The first idea about quantum theory was from Max Planck in 1900. He proposed that energy was not emitted continuously but rather in quanta in black body radiation. He was awarded the 1918 Nobel Prize in physics for this work. In 1905, Albert Einstein extended this idea to the photoelectric effect, which treated light as a flow of particles called photons. This was further proved by the Compton experiment on photon scattering. Einstein was awarded the 1921 Nobel Prize partly because of this work. Erwin Schrödinger developed Schrödinger's equation and wave mechanics at the beginning of the last century. Werner Heisenberg developed matrix mechanics and the uncertainty principle at about the same time. These two mechanics were proven equivalent later. Paul Dirac developed a relativistic version of quantum theory. Their theories became the basis of today's quantum mechanics. Schrödinger, Heisenberg, and Dirac were all awarded Nobel Prizes for their work. Many other physicists have continued to contribute to the development of quantum physics. Today quantum physics has become a very broad area.
Some important points of quantum mechanics are wave-particle duality and the uncertainty principle. Any object, whether it is an electron, a ball, or a human, can act either as a wave or a particle depending on how it is measured. This is what is meant by wave-particle duality. For instance, light will act like a wave in experiments that measure diffraction or refraction and it acts like a particle in experiments that measure reflection. Generally, the wave nature of objects is only evident at the scale of atomic and subatomic physics.
An electron propagates as a quantum wave. This does not mean that the electron is broken into pieces and spreads in space as a water wave does. The electron is still an electron. The value of a quantum wave at a certain position determines the probability that it will be observed at that position. Mathematically the quantum wave has complex (real and imaginary) variables, so the square of modular of the quantum wave value is used to calculate the probability. According to Louis-Victor de Broglie, the wavelength () of a quantum wave of an object is =h/mv, where h is the Planck constant (6.63x10-34 J·s), m is the mass of the object, and v is its velocity. For a flying ball with a mass of 1 lb (0.45 kg) and a speed of 100 ft/s (30 m/s), the wavelength is about 1.6x10-34 ft (4.9x10-35 m). That is much shorter than a trillion trillionth of one foot. This is so small that its wave nature can be safely ignored.
There is a rule of thumb to determine when quantum physics should be used and when classical physics is still good enough. The Planck constant is used to determine this. Its unit is energy multiplied by time, or momentum multiplied by length. We find out the characteristic time and length of the system we are studying, then find the product of energy and time or momentum and length. If the result is much larger than h, then we can use classical mechanics. Otherwise, we must use quantum mechanics. A walking person, for instance, has a mass of about 160 lb (72 kg), a speed of 3 ft/s (0.9 m/s), and a characteristic length (person's height) of 6 ft (1.8 m). The product is 116 joules/s, which is much larger than the Planck constant. Classical mechanics is correct for use in our everyday life.
The uncertainty principle is an important result of quantum mechanics. It says that certain pairs of values, e.g. momentum (or speed) and position, can't be accurately determined simultaneously. The more accurately you can measure one value, the less accurately you measure the other. This seems to completely contradict our everyday experience where both position and speed can be specified simultaneously. Our experience is only approximately correct. The uncertainty principle poses an ultimate limit on how accurately we can measure position and momentum simultaneously. Energy and time is another such pair of variables.
Quantum physics is very important in the microscopic and atomic world. We can see its effects everywhere in the world around us as well. The color of metal, for instance, could not be explained until quantum physics came out because it is a quantum effect. Quantum physics can indeed be used to do calculations in our everyday life although the calculation is usually much more tedious than classical physics. Our everyday experience is only an approximation for the more accurate quantum physics. However, since the quantum wave-like properties of macroscopic objects is imperceptiable to us, classical physics will suffice. It is at the scale of atoms and subatomic particles that quatum physics becomes critically important.
This is the complete article, containing 784 words
(approx. 3 pages at 300 words per page).
