LordOfTheBorg 1 Posted March 17, 2004 Ok, read this only if you can take Science-Dense things. Response is welcomed. Click for Spoiler: Heat a liquid or solid until it glows, and the light produced will have a continuous spectrum, the color changing from red to orange to white to blue as the temperature increases; this incandescent glow is the same for all elements. In 1900, Max Planck developed a formula to describe these phenomena; there was, however, no known theory to describe why it should fit the data. So Planck derived one. In the process, however, he had to reconsider the very nature of the conversion of light into heat: that there were discrete values at which it could occur and a smallest unit of exchange, which came to be known as the quantum. (The energy E of this exchange equals Planck's constant, or approximately 6.6 x 10^-34, times the frequency f of the light, or E=hf.) Einstein in 1905 used Planck's idea of light quanta, or photons, to explain the photoelectric effect, wherein blue light shined on negatively charged metal would cause the charge to leak away, thus indicating that there might be a far broader significance to Planck's theory than simply explaining incandescence. Light, therefore, behaved like a particle in addition to a wave; quantum physics was born. Einstein in 1905 used Planck's idea of light quanta, or photons, to explain the photoelectric effect, wherein blue light shined on negatively charged metal would cause the charge to leak away. For an explanation, please see http://www.cmmp.ucl.ac.uk/~ajf/1B23/qm1/node3.html This showed that Planck's theory might be far more important than simply explaining one phenomenon, incandescence. Light behaved like a particle in addition to a wave; quantum physics was born. Atomic Models from Aristotle to Schroedinger Aristotle Although the idea of the atom, the smallest, indivisible component of matter, was first proposed in 400 BC, Aristotle didn't like it. He claimed that there was no smallest part of matter and that different substances were made up of proportions of fire, air, earth, and water. As there were of course no experimental means available to test either view, Aristotle's prevailed mainly because people liked his philosophy better. Dalton It was not until 1850 that another atomic theory was proposed, this time to explain experimental evidence rather than because it seemed philosophically nice. Dalton stated that all matter is made of indivisible and indestructible atoms, which differ from element to element.The atom, it was assumed, was of uniform density and constitution. Bohr That pesky atom, however, refused to cooperate completely. Using the famous gold foil experiment, British experimental physicist Rutherford found evidence that the atom really consisted of a highly dense nucleus and a vast empty space in which the electrons orbited. Bohr seized upon this data and Planck's beginnings at quantum theory and theorized distinct energy levels where electrons could exist. The ground state was where an atom normally was found; the higher energy levels could only be obtained by electrons if they were excited (ie, gained energy, as through a collision). He also discovered that Planck's constant determined the diameter of the atom, and that the atomic spectrum unique to each element was determined by transitions between energy levels (quantum leaps, which are accompanied by the release of a photon.) de Broglie Louis Victor Pierre Raymond duc de Broglie added to Bohr's model of the atom by reasoning that, since light could act like a particle, an electron could act like a wave. Since the energy E of a photon equals Planck's constant times the frequency f, or E=hf, de Broglie reasoned that the momentum p of an electron would equal Planck's constant divided by the wavelength l, or p=h/l. Using this and the reasoning that only a whole number of wavelengths (see picture) would be possible, de Broglie arrived at the same rule for electron orbits as had Bohr. In other words, a wavelength associated with an electron and derived from its momentum yields a standing-wave pattern identical to Bohr's allowed energy levels. As Einstein put it: "It may look crazy, but it really is sound!" (In 1929, de Broglie received the Nobel Prize -- the first physicist to do so for his doctoral dissertation.) Evidence for the de Broglie model came through the Young double slit experiment, an explanation of which can be found at http://www.cmmp.ucl.ac.uk/~ajf/1B23/qm1/node8.html Schroedinger But more was still to come: a mathematical model of the atom, provided by Erwin Schroedinger (of cat fame) The Heisenberg Uncertainty Principle It's not just us: there are mathematical reasons why we can never be completely accurate about the world around us. Part of this is because the quantum level is expressible only in probabilities (ie, Schroedinger's cat). Part of this is also because of Heisenberg's famous Uncertainty Principle. Certain physical properties exist in pairs: position and momentum, energy and time, and others. No matter how accurate the measurements, both qualities cannot be known accurately (on the atomic level; in everyday life objects are enough greater than the possible error to make it negligeable, but in quantum physics it becomes critical). Since the measurements depend at the very least on the interaction of a photon with the particle under observation, they can get no more accurate than the wavelength of the photon used to observe. As the wavelength of the photon decreases, however, the momentum increases, meaning that when the photon interacts with the particle both will change momentum, thus messing with the observed phenomena. It is impossible to know both where a particle is and at what velocity it is traveling with enough accuracy to predict its actions very far into the future, or to reconstruct its behavior very far into the past. This ignorance, according to Heisenberg, was the inevitable result of observation: thus the famous quantum principle that the act of observation changes both observer and observed. Quantum mechanics, also referred to as quantum physics, is a physical theory that describes the behavior of matter at short length scales. The quantum theory provides a quantitative explanation for two types of phenomena that classical mechanics and classical electrodynamics cannot account for: Some observable physical quantities, such as the total energy of a blackbody, take on discrete rather than continuous values. This phenomenon is called quantization, and the smallest possible intervals between the discrete values are called quanta (singular: quantum, from the Latin word for "quantity", hence the name "quantum mechanics.") The size of the quanta typically varies from system to system. Under certain experimental conditions, microscopic objects like atoms or electrons exhibit wave-like behavior, such as interference. Under other conditions, the same species of objects exhibit particle-like behavior ("particle" meaning an object that can be localized to a particular region of space), such as scattering. This phenomenon is known as wave-particle duality. The foundations of quantum mechanics were established during the first half of the 20th century by the work of Max Planck, Niels Bohr, Werner Heisenberg, Erwin Schrödinger, Paul Dirac, and others. Some fundamental aspects of the theory are still being actively studied. Quantum mechanics has also been adopted as the underlying theory of many fields of physics and chemistry, including condensed matter physics, quantum chemistry, and particle physics. Mathematical formulation In the mathematically rigorous formulation developed by Paul Dirac and John von Neumann, the possible states of a quantum mechanical system are represented by unit vectors (called state vectors) residing in a complex separable Hilbert space (called the state space.) The exact nature of the Hilbert space is dependent on the system; for example, the state space for position and momentum states is the space of square-integrable functions. The time evolution of a quantum state is described by the Schrödinger equation, in which the Hamiltonian, the operator corresponding to the total energy of the system, plays a central role. Each observable is represented by a densely-defined Hermitian linear operator acting on the state space. Each eigenstate of an observable corresponds to an eigenvector of the operator, and the associated eigenvalue corresponds to the value of the observable in that eigenstate. If the operator's spectrum is discrete, the observable can only attain those discrete eigenvalues. During a measurement, the probability that a system collapses to each eigenstate is given by the absolute square of the inner product between the eigenstate vector and the state vector just before the measurement. We can therefore find the probability distribution of an observable in a given state by computing the spectral decomposition of the corresponding operator. Heisenberg's uncertainty principle is represented by the statement that the operators corresponding to certain observables do not commute. The details of the mathematical formulation are contained in the article Mathematical formulation of quantum mechanics. Philosophical debate Since its inception, the many counter-intuitive results of quantum mechanics have provoked strong philosophical debate and many interpretations. See interpretation of quantum mechanics for more detail. The Copenhagen interpretation, due largely to Niels Bohr, was the standard interpretation of quantum mechanics when it was first formulated. According to it, the probabilistic nature of quantum mechanics predictions cannot be explained in terms of some other deterministic theory, and do not simply reflect our limited knowledge. Quantum mechanics provides probabilistic results because the physical universe is itself probabilistic rather than deterministic. Albert Einstein, himself one of the founders of quantum theory, disliked this loss of determinism in measurement. He held that quantum mechanics must be incomplete, and produced a series of objections to the theory. The most famous of these was the EPR paradox. John Stewart Bell's theoretical solution to the EPR paradox, and its later experimental verification, disproved a large class of such hidden variable theories and persuaded the majority of physicists that quantum mechanics is not an approximation to a nominally classical hidden-variable theory. The many worlds interpretation, formulated in 1956, holds that all the possibilities described by quantum theory simultaneously occur in a "multiverse" composed of mostly independent parallel universes. While the multiverse is deterministic, we perceive non-deterministic behavior governed by probabilities because we can observe only the universe we inhabit. The Bohm interpretation postulates the existence of a non-local, universal wavefunction (Schrödinger equation) which allows distant particles to interact instantaneously. It is not popular among physicists largely because it is considered very inelegant. Some Quotations I do not like it, and I am sorry I ever had anything to do with it. Erwin Schrödinger, speaking of quantum mechanics Those who are not shocked when they first come across quantum mechanics cannot possibly have understood it. Niels Bohr God does not play dice with the cosmos. Albert Einstein Who are you to tell God what to do? Niels Bohr in response to Einstein I think it is safe to say that no one understands quantum mechanics. Richard Feynman It's always fun to learn something new about quantum mechanics. Benjamin Schumacher If that turns out to be true, I'll quit physics. Max von Laue, Nobel Laureate 1914, of de Broglie's thesis on electrons having wave properties. Anyone wanting to discuss a quantum mechanical problem had better understand and learn to apply quantum mechanics to that problem. Willis Lamb, Nobel Laureate 1955 Share this post Link to post Share on other sites
WEAREBORG4102 0 Posted March 18, 2004 all I can say is that that richard feynmen was right in that we cannot understand the multiverse.... I believe hat only God can.. Quantum mechanics and other theories of the universe have coided over the past century... That is what makes science... Then you can consider the theories about strings, quantum foam, dark matter, microwormholes, macrouniversal expansion.... etc... We have too many theories... Then you have to consider the Laws of thermodynamics.... We'll never truly prove Entropy.... Share this post Link to post Share on other sites
