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A, B, C



Accelerator mass spectrometry ACCESS SCIENCE ONLINE

The use of a combination of mass spectrometers and an accelerator to measure the natural abundances of very rare radioactive isotopes. These abundances are frequently lower than parts per trillion. The most important applications of accelerator mass spectrometry are in archeological, geophysical, environmental, and biological studies, such as in radiocarbon dating by the counting of the rare carbon-14.



Strongly interacting composite particle that accounts for almost all of the visible mass of the universe. The proton and neutron that make up the atomic nucleus are examples of baryons. Strongly interacting particles (hadrons) are either baryons, which are fermions with half-integral spin, or mesons, which are bosons with integer spin.  Although baryons are very small (roughly 10?15 m in diameter), they consist of even smaller, elementary particles called quarks, together with the exchange particles of the strong interaction between the quarks, the gluons.


Big Bang



A theory of the origin and evolution of the universe which holds that approximately 1.4 ? 1010 years ago all the matter in the universe was packed into a small agglomeration of extremely high density and temperature which exploded, sending matter in all directions and giving rise to the expanding universe. Also known as superdense theory.



Black holes are the remnants after heavy stars burn out and collapse. The gravitational pull of a black hole is so strong that not even light can escape. Moreover, craters and other distinctive features are impossible because of the crushing forces exerted on matter in the black hole. The contrast between the initial complexity of a star and the final, apparently structureless state of a black hole is dramatic and puzzling. Indeed, if the black hole shows no hint of its complex past, there is an apparent conflict with determinism. According to determinism, the present state of the world developed from some past state that should be deducible from the present one, at least in principle. Theoretical physicists are strong believers in determinism and therefore are inclined to suspect that the complexity of the star has been transformed into some kind of internal structure of the black hole, rather than having disappeared.



A force whose line of action is always directed toward a fixed point. The central force may attract or repel. The point toward or from which the force acts is called the center of force. If the central force attracts a material particle, the path of the particle is a curve concave toward the center of force; if the central force repels the particle, its orbit is convex to the center of force.



A fictitious or pseudo outward force on a particle rotating about an axis which by Newton's third law is equal and opposite to the centripetal force. Like all such action-reaction pairs of forces, they are equal and opposite but do not act on the same body and so do not cancel each other. Consider an experimenter in a windowless, circular laboratory that is rotating smoothly about a centrally located vertical axis. No object remains at rest on a smooth surface; all such objects move outward toward the wall of the laboratory as though an outward, centrifugal force were acting. To the experimenter partaking in the rotation, in a rotating frame of reference, the centrifugal force is real. An outside observer would realize that the inward force which the experimenter in the rotating laboratory must exert to keep the object at rest does not keep it at rest, but furnishes the centripetal force required to keep the object moving in a circular path.


CERN "Encyclopædia Britannica. 2008.

Conseil Européen pour la Recherche Nucléaire , English European Organization for Nuclear Research, international scientific organization established for the purpose of collaborative research into high-energy particle physics. Founded in 1954, the organization maintains its headquarters near Geneva and operates expressly for research of a “pure scientific and fundamental character.”



Resonance absorption of energy from an alternating-current electric field by electrons or ions in a uniform magnetic field when the frequency of the electric field equals the cyclotron frequency, or the cyclotron frequency corresponds to the effective mass of electrons in a solid. Also known as diamagnetic resonance.



D, E, F

Expanding Universe



Dark matter consists of particles or objects that exert a gravitational force but do not emit any detectable light. Dark matter is the dominant form of matter in our Galaxy. Astronomers have detected the presence of dark matter through its gravitational effects and have shown that dark matter is not composed of ordinary atoms. Particle physicists have suggested several plausible candidates for dark matter; planned experiments are capable of detecting these new particles.


Dark Matter: (Astronomical evidence for) ACCESS SCIENCE ONLINE

A variety of astronomical observations imply that dark matter is ubiquitous; it is detected in dwarf galaxies, in spiral galaxies, and in elliptical galaxies. It is the dominant form of matter in galaxy clusters and leaves clear signatures in the large-scale distribution of galaxies and in the microwave background. Astronomers infer the presence of matter through its gravitational effects. Since they have not been able to detect any light directly associated with this matter, they have labeled it “dark matter.” Dark matter is also sometimes called the “missing matter.” This is a misnomer since astronomers detect the mass but they are unable to detect the light associated with the matter.



The Doppler effect for sound waves is now a commonplace experience: If one is passed by a fast car or a plane, the pitch of its noise is considerably higher in approaching than in parting. The same phenomenon is observed if the source is at rest and the receiver is passing it.



Einstein's Miracle Year EINSTEIN FOR DUMMIES

Einstein's Miracle Year was the year Einstein wrote five important physics papers that revolutionized the field of physics.  In 1905 Einstein published five papers that eventually won him the Nobel prize.  His first paper ("On a heuristic point of view concerning the production and transformation of light", March 17) laid the foundation for quantum theory with the introduction of a theoretical particle called a "photon".  This paper was nominated for the Nobel prize in 1921 and won.  His next two papers dealt with the existance of molecules and an explanation of a related form of motion called "Brownian motion".  These papers, while remarkable, didn't revolutionize physics as much as the next two.  On June 30, 1905, Einstein published a paper called "On the electrodynamics of moving bodies" which was his first paper on the theory of relativity.  His final paper published in 1905 was titled, "Does an object's inertia depend on its energy content?" and included his famous equation E=mc2.


Einstein's Principle of Relativity ACCESS SCIENCE ONLINE

The principle that all the laws of physics must assume the same mathematical form in any inertial frame of reference; thus, it is impossible to determine the absolute motion of a system by any means.


Expansion of the universe ACCESS SCIENCE ONLINE

Only in the 1920s did it become clear that the “spiral nebulae,” clouds of gas with arms spiraling outward from a core, were galaxies on the scale of the Milky Way Galaxy. This was established in 1925, when observations of variable stars in several galaxies by E. Hubble enabled the distance to these galaxies to be determined with some accuracy.

Starting in 1912, the spectra of many of these spiral nebulae were found to have large redshifts. According to the Doppler effect, these large redshifts correspond to large velocities of recession from the Earth. Estimates of distances to these objects by Hubble and colleagues established a direct relation between the distance to a galaxy and its velocity of recession. It was soon interpreted as the result of an expanding universe. 



G, H

General Relativity


Glueballs Frank E. Close Scientific American  11-01-1998 Elibrary Online

There are no atoms of light. That is, photons do not attach to other photons, forming composite entities. But gluons, the particles that bind quarks--the basic units of matter--into objects such as protons, may indeed stick just to one another. Physicists call the resulting glob a glueball.



The hypothetical force particles believed to bind quarks into strongly interacting particles. Theoretical models in which the strong interactions of quarks are mediated by gluons have been successful in predicting, interpreting, and explaining many phenomena in particle physics, but free gluons remain undetected in experiments (as do free quarks). According

to prevailing opinion, an individual gluon cannot be isolated


Higgs Boson “Mathematics and Physical Sciences." Encyclopædia Britannica. 2008.

The hunt continued for the elusive Higgs boson, the hypothetical subatomic particle proposed by theoretical physicists as a mechanism to account for the reason that the elementary particles exhibit the rest masses that they do. The standard model, the current mathematical theory describing all of the known elementary particles and their interactions, does not account for the origin of the widely differing particle masses and requires an “invented” particle to be added into the mathematics. Confirmation of the existence of the Higgs boson would make the standard model a more complete description.


I, J, K

Inflationary Universe


L, M


An elementary particle having no internal constituents. There are three known charged leptons: the electron (e?), the muon (??), and the tau (??). In addition, the corresponding antiparticles e+, ?+, ?+ are known. Each experiences electromagnetic, weak, and gravitational forces, but not the strong (nuclear) force. Associated with each charged lepton is a corresponding neutral lepton, called a neutrino (?e, ??, ??) or antineutrino: (, , ); these have only weak and gravitational interactions. A charged lepton and its associated neutrino form a lepton generation; thus there are three known lepton generations. Leptons are very small, less than 10?18 m in radius. This is less than 10?3 of the radius of a nucleus and less than 10?8 of the radius of an atom. Indeed, all existing measurements are consistent with the assumption that leptons are point particles.



Like baryons, mesons are very small (roughly 10?15 m in diameter) and consist of even smaller elementary particles: quarks, antiquarks, and gluons. Mesons are neither matter nor antimatter: they are made of quarks and a balancing number of antiquarks (in the simplest case a single quark and a single antiquark). Over 200 examples are known of such q–q-bar combinations (q being the generic symbol for a quark; and q-bar, denoted here by , for an antiquark).


N, O




An elementary particle having approximately the same mass as the proton, but lacking a net electric charge. It is indispensable in the structure of the elements, and in the free state it is an important reactant in nuclear research and the propagating agent of fission chain reactions. Neutrons, in the form of highly condensed matter, constitute the substance of neutron stars. 


Neutrons in nuclei ACCESS SCIENCE ONLINE

Neutrons and protons are the constituents of atomic nuclei. The number of protons in the nucleus determines the chemical nature of an atom, but without neutrons it would be impossible for two or more protons to exist stably together within nuclear dimensions, which are of the order of 10-13 cm. The protons, being positively charged, repel one another by virtue of their electrostatic interactions. The presence of neutrons weakens the electrostatic repulsion, without weakening the nuclear forces of cohesion. In light nuclei the resulting balanced, stable configurations contain protons and neutrons in almost equal numbers, but in heavier elements the neutrons outnumber the protons; in 238U, for example, 146 neutrons are joined with 92 protons. Only one nucleus, 1H, contains no neutrons. For a given number of protons, neutrons in several different numbers within a restricted range often yield nuclear stability—and hence the isotopes of an element. 


P, Q


A positively charged particle that is the nucleus of the lightest chemical element, hydrogen. The hydrogen atom consists of a proton as the nucleus, to which a single negatively charged electron is bound by an attractive electrical force (since opposite charges attract). The proton is about 1836 times heavier than the electron, so that the proton constitutes almost the entire mass of the hydrogen atom. Most of the interior of the atom is empty space, since the sizes of the proton and the electron are very small compared to the size of the atom. 



Theory of physics that discribes matter as having a wavelike character on very small length scales (usually the size of atoms or smaller).



One of the hypothetical basic particles, having charges whose magnitudes are one-third or two-thirds of the electron charge, from which many of the elementary particles may, in theory, be built up; for example, nucleons may be formed from three quarks and mesons from quark-antiquark combinations; no experimental evidence for the actual existence of free quarks has been found.


Quarks: Discovery of ACCESS SCIENCE ONLINE

Quarks were originally postulated by M. Gell-Mann and others in the early 1960s mainly as a mathematical device to explain the observed symmetries in elementary particles known at the time. Deep inelastic scattering provided the first hard evidence of their actual existence inside protons and neutrons, giving quarks a new measure of reality.


R, S



Redshift “The Five Ages of the Universe” by Fred Adams

If a source of light, such as a star or galaxy, moves away from us, its radiation is shifted toward lower frequencies or longer wavelengths (toward the red end of the spectrum).



Theory of physics which recognizes the universal character of the propagation speed of light and the consequent dependence of space, time, and other mechanical measurements on the motion of the observer performing the measurements; it has two main divisions, the special theory and the general theory.


Relativity: (special) ACCESS SCIENCE ONLINE

The division of relativity theory which relates the observations of observers moving with constant relative velocities and postulates that natural laws are the same for all such observers.


Relativity: (general) “The Five Ages of the Universe” by Fred Adams

A comprehensive theory of space, time, and mass. As first developed by Albert Einstein, general relativity holds that gravitation is an effect of the curvature of the space-time continuum.


Space-time “Black Holes & Time Warps” by Kip S. Thorne

The four-dimentional “fabric” that results when space and time are unified.



A four-dimensional space used to represent the universe in the theory of relativity, with three dimensions corresponding to ordinary space and the fourth to time. Also known as space-time continuum.


Steady State Model Giancoli, Douglas C. Physics. 6th ed. Upper Saddle River: Pearson Education Inc., 2005. 930-35.


The main universal model competing with the Big Bang Theory in the mid-twentieth century.  This theory is that the universe is

infinitely old and on averafe always has and always will look the same, with no large-scale changes in the universe as a whole.  Because of the observation that the galaxies were moving apart, to be true, matter was believed to be created continuously (violating the conservation of matter and energy law). 


The main universal model competing with the Big Bang theory in the mid-twentieth century. This theory is that the universe is infinitely old and on average always has and always will look the same, with no large-scale changes in the universe as a whole. Because of the observation that the galaxies were moving apart, to be true, matter was believed to be created continuously (violating the conservation of matter and energy law).


String Theory "string theory." Encyclopædia Britannica. 2008. Encyclopædia Britannica Online School Edition. 7 Feb. 2008

The name string theory comes from the modeling of subatomic particles as tiny one-dimensional “stringlike” entities rather than the more conventional approach in which they are modeled as zero-dimensional point particles. The theory envisions that a string undergoing a particular mode of vibration corresponds to a particle with definite properties such as mass and charge.


Superstring theory ACCESS SCIENCE ONLINE

Superstrings are extremely small, approximately 10?20 times the size of an atomic nucleus. Ordinary experiments would therefore fail to observe their vibrating nature, and would be able to discern only some gross features, such as the mass.


T, U

Time Dilation "time dilation." Encyclopædia Britannica. 2008. Encyclopædia Britannica Online School Edition. 7 Feb. 2008

In the theory of special relativity, the “slowing down” of a clock as determined by an observer who is in relative motion with respect to that clock.


Unified Field theory "unified field theory." Encyclopædia Britannica. 2008. Encyclopædia Britannica Online School Edition. 7 Feb. 2008 ''

In particle physics, an attempt to describe all fundamental forces and the relationships between elementary particles in terms of a single theoretical framework. In physics, forces can be described by fields that mediate interactions between separate objects...Einstein and others attempted to construct a unified field theory in which electromagnetism and gravity would emerge as different aspects of a single fundamental field. They failed, and to this day gravity remains beyond attempts at a unified field theory.


Twins paradox




V, W


X, Y, Z



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