Problems from the Classical

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-- "In a few years, all the great physical constants will have been approximately estimated and the only occupation which will then be left to the men of science will be to carry these measurements to another place of decimals." Back in 1871, this quote from the Scottish physicist James Clerk Maxwell sounds discouraging and disappointing since it was thought that classical physics have come to the end of the road, nearly explaining all phenomena known with success. However, in the early 20th century, Max Planck introduced an interesting idea which is weird and new to classical physics but a prerequisite to create his blackbody spectrum formula. The formula included an assumption that energy was emitted only in finite lumps called quanta, i.e. you can only have 1, 2 or any integral number of lumps, but not 0.5 lumps or 12.3 lumps. This odd assumption proved to be mathematically successful, but was not well received. No classical radiation theory was able to explain the spectrum. In 1905, Albert Einstein used the same idea to explain a new physical phenomenon, the photoelectric effect, i.e. the emission of electrons when light strikes a surface, treating light as being quantized in terms of photons.

��Old model of an atom showed that electrons moved around the positively charged nucleus in a circular orbit, somewhat like a little solar system. This was a great blunder because according to classical electromagnetic theory, an orbiting electron or any accelerating charged body would continuously radiate away their energy in the form of electromagnetic radiation and thus will spiral into the nucleus and as a result, there wouldn't be anymore atom. In 1913, Niels Bohr postulated that an electron in an atom can move around in certain circular stable orbit, without emitting radiation contrary to the prediction of classical electromagnetic theory. According to him, there is a definite energy, associated with each stable orbit, and any radiation of energy from an atom occurs only if there is a transition from one orbit to another. Following this argument, Bohr found that an electron's angular momentum should be quantized. The Bohr model had tremendous successes in describing the properties of the hydrogen atom and its spectrum. But the modern model of an atom have some slight differences with Bohr's showing that electrons do not orbit but form some clouds of statistical probabilities around the nucleus called orbitals.-

��Just as Newton's equations describe the behavior of mechanical phenomena, Maxwell's equations govern the behavior of electromagnetic phenomena. From these equations, the speed of electromagnetic waves was able to be calculated. But we knew from Newton that speed is relative, not absolute. So relative to what was this speed to be measured? One question that arose was that the Maxwell's equations need changes in their mathematical form under a Galilean transformation. Scientists then were led to the prediction that a medium called an ether was needed as a prerequisite for the propagation of electromagnetic waves including light just as sound waves propagating through mediums like the air. In 1887, the Michelson-Morley experiment showed that the velocity of light has the same magnitude, c (approximate value = 3.0 x 10⁸ m/s), contrary to the ether- theory's prediction and the changes in the Maxwell's equations under Galilean transformation that light should have different velocities in different directions relative to the direction of motion of the observer through the ether. This encounter led to the development of Einstein's theory of relativity but with distinct differences from the classical one of which one of his postulate that the speed of light is always c in vacuum independent of the motion of the source, contradicting to our simple elementary notion of relative velocities and its simple addition and subtraction laws.

�� Newtonian physics commonly referred to as classical physics fail completely to explain the subatomic world of particles like electrons and high speed motions approaching the speed of light. Today, the subatomic world is explained by quantum physics while motions of speed approaching speed of light and the world of extremely massive objects like planets are explained by Einstein's theory of relativity.

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