Portal:Physics/2006 Selected articles

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This is an archive of entries that appeared on Portal:Physics's Selected Article section in 2006.

January 1, 2006 - Soap bubble

A soap bubble is a very thin film of soap water that forms a hollow shape with an iridescent surface. Soap bubbles usually last for only a few moments and burst either on their own or on contact with another object. Due to their fragile nature they have also become a metaphor for something that is attractive, yet insubstantial. They are often used as a children's plaything, but their usage in artistic performances shows that they can be fascinating for adults too. Soap bubbles can help to solve complex mathematical problems of space, as they will always find the smallest surface area between points or edges.

Soap bubbles can exist because the surface layer of a liquid (usually water) has a certain surface tension, which causes the layer to behave as an elastic sheet. A common misconception is that soap increases the water's surface tension. Actually soap does the exact opposite, decreasing it to approximately one third the surface tension of pure water. Soap does not strengthen bubbles, it stabilizes them, via an action known as the Marangoni effect. As the soap film stretches, the concentration of soap decreases, which causes the surface tension to increase. Thus, soap selectively strengthens the weakest parts of the bubble and tends to prevent them from stretching further. In addition, the soap reduces evaporation so the bubbles last longer.

January 17, 2006 - Superconductivity

Superconductivity is a phenomenon occurring in certain materials at low temperatures, characterized by the complete absence of electrical resistance and the exclusion of the interior magnetic field (the Meissner effect). Superconductivity is a popular device in science fiction due to the simplicity of the underlying concept - zero electrical resistance - and the rich technological possibilities. For example, superconducting magnets could be used to generate the magnetic fields used by Bussard ramjets, a type of spacecraft commonly encountered in science fiction. The most troublesome property of real superconductors is the need for extremely low temperatures. Superconductivity is an essentially quantum mechanical phenomenon, and cannot be understood simply as the idealization of "perfect conductivity" in classical physics. (read more...)

June 6, 2006 - Edward Teller

Edward Teller, in 1958

Edward Teller was a Hungarian-born American nuclear physicist of Jewish descent. He was known colloquially as "the father of the hydrogen bomb". Teller was an immigrant to the United States during the 1930s, and was an early member of the Manhattan Project to develop the first atomic bombs. During this time he made a serious push for the first time to develop fusion-based weapons as well, but they were deferred until after the war. After his controversial testimony in the security clearance hearing of his former Los Alamos colleague J. Robert Oppenheimer, Teller became ostracized by much of the scientific community. He continued to find support from the U.S. government and military research establishment. He was a co-founder of Lawrence Livermore National Laboratory, and was both director and associate director for many years. In his later years he became especially known for his advocacy of controversial technological solutions to both military and civilian problems, including a plan to excavate an artificial harbor in Alaska using thermonuclear explosives. Over the course of his long life, Teller was known both for his scientific ability and his difficult interpersonal relations, and is considered one of the key influences of the character Dr. Strangelove in the 1964 movie of the same name. (more...)

September 2, 2006 - H II region

An H II region is a cloud of glowing gas and plasma, sometimes several hundred light years across, in which star formation is taking place. Young, hot, blue stars which have formed from the gas emit copious amounts of ultraviolet light, ionising the nebula surrounding them.

H II regions may give birth to thousands of stars over a period of several million years. In the end, supernova explosions and strong stellar winds from the most massive stars in the resulting star cluster will disperse the gases of the H II region, leaving behind a cluster such as the Pleiades.

H II regions are named for the large amount of ionised atomic hydrogen they contain, referred to as H II (pronounced 'aitch two') by astronomers (H I ('aitch one') being neutral atomic hydrogen, and H₂ (also 'aitch two') being molecular hydrogen). H II regions can be seen out to considerable distances in the universe, and the study of extragalactic H II regions is important in determining the distance and chemical composition of other galaxies. (more...)

Image: NGC 604, a giant H II region in the Triangulum Galaxy.

Week 42

The accelerator chain of the Large Hadron Collider

ATLAS (A Toroidal LHC ApparatuS) is one of the five particle detector experiments (ALICE, ATLAS, CMS, TOTEM, and LHCb) being constructed at the Large Hadron Collider, a new particle accelerator at CERN in Switzerland. It will be 45 metres long and 25 metres in diameter, and will weigh about 7,000 tonnes. The project involves roughly 2,000 scientists and engineers at 151 institutions in 34 countries. The construction is scheduled to be completed in 2007. The experiment is expected to measure phenomena that involve highly massive particles which were not measurable using earlier lower-energy accelerators and might shed light on new theories of particle physics beyond the Standard Model.

The ATLAS collaboration, the group of physicists building the detector, was formed in 1992 when the proposed EAGLE (Experiment for Accurate Gamma, Lepton and Energy Measurements) and ASCOT (Apparatus with Super COnducting Toroids) collaborations merged their efforts into building a single, general-purpose particle detector for the Large Hadron Collider. The design was a combination of those two previous designs, as well as the detector research and development that had been done for the Superconducting Supercollider. The ATLAS experiment was proposed in its current form in 1994, and officially funded by the CERN member countries beginning in 1995. Additional countries, universities, and laboratories joined in subsequent years, and further institutions and physicists continue to join the collaboration even today. The work of construction began at individual institutions, with detector components shipped to CERN and assembled in the ATLAS experimental pit beginning in 2003.

Week 43

The speed of light in a vacuum is an important physical constant denoted by the letter c for constant or the Latin word celeritas meaning "swiftness".

In metric units, c is exactly 299,792,458 metres per second (1,079,252,848.8 km/h). Note that this speed is a definition, not a measurement, since the fundamental SI unit of length, the metre, has been defined since October 21, 1983 in terms of the speed of light: one metre is the distance light travels in a vacuum in 1/299,792,458 of a second. Converted to imperial units, the speed of light is approximately 186,282.397 miles per second, or 670,616,629.384 miles per hour, or almost one foot per nanosecond.

Through any transparent or translucent material medium, like glass or air, it has a lower speed than in a vacuum; the ratio of c to this slower speed is called the refractive index of the medium. In an analogous way, the light speed is also affected by changes in gravity. This gives rise to the phenomenon of gravitational lensing, in which large assemblies of matter can refract light from far away sources, so as to produce multiple images and similar optical distortions.

Week 44

A Feynman diagram is a method for performing calculations in quantum field theory, invented by American physicist Richard Feynman. They are also (rarely) referred to as Stückelberg diagrams or (for a subset of special cases) penguin diagrams. The lines represent particles interacting and mathematical terms correspond to each line and vertex (meeting of lines). The probability of a certain interaction happening is calculated by drawing the corresponding diagrams, and using them to derive the correct mathematical expressions. They are essentially a book-keeping tool with a simple visual physical interpretation of an event.

In this diagram, a Kaon, made of an up and anti-strange quark, decays weakly into three pions, with intermediate steps involving a W boson and a gluon.

The interaction between two particles is quantified by the cross section corresponding to their collision, essentially the probability of the interaction occurring. If the strength interaction is not too large, i.e. if it can be tackled via perturbation theory, this cross section (or more precisely the corresponding time evolution operator, propagator or S matrix) can be expressed as a sum of terms (the Dyson series) which can be described as a short story in time that sounds like the following:

• (once upon a time) two particles were moving freely with some relative speed (one draws two lines --edges -- going upwards),
• they met each other (the two lines meet at a first point -- vertex),
• took a stroll together on a common path (the lines merge in one vertical line)
• and, then separated again (second vertex)
• but they realized their speed had changed and they were not really the same anymore (two lines are drawn upwards coming from the last vertex -- sometimes in a different style to symbolize the change experienced by the particles).

This story can be drawn as a diagram which is generally easier to remember than the corresponding mathematical formula in the Dyson series. These diagrams are called Feynman diagrams. They are meaningful only if the Dyson series converges fast. Their easy story telling character and the similarity with the early bubble chamber experiments have made the Feynman diagrams very popular.

Week 45

The "famous" map of the CMB anisotropy formed from data taken by the COBE spacecraft.

The Cosmic Background Explorer (COBE), also referred to as Explorer 66, was the first satellite built dedicated to cosmology. Its goals were to investigate the cosmic microwave background radiation (CMB) of the universe and provide measurements that would help shape our understanding of the cosmos.

This work helped cement the big-bang theory of the universe. According to the Nobel Prize committee, "the COBE-project can also be regarded as the starting point for cosmology as a precision science". Two of COBE's principal investigators, George Smoot and John Mather, received the Nobel Prize in Physics in 2006.

Week 46

Ernest Rutherford, 1st Baron Rutherford of Nelson, OM, PC, FRS (30 August 1871 – 19 October 1937), was a nuclear physicist from New Zealand. He was known as the "father" of nuclear physics, he pioneered the orbital theory of the atom, in his discovery of Rutherford scattering off the nucleus with the gold foil experiment.

His research, along with that of his protege, Sir Mark Oliphant was instrumental in the convening of the Manhattan Project. He is famously quoted as saying: "In science there is only physics; all the rest is stamp collecting." He is also reputed to have stated that the idea of using nuclear reaction to generate useful power was "moonshine".

Week 47

Assorted transistors

A transistor is a three-terminal semiconductor device that can be used for amplification, switching, voltage stabilization, signal modulation,oscillator and many other functions. The transistor is the fundamental building block of both digital and analog integrated circuits — the circuitry that governs the operation of computers, cellular phones, and all other modern electronics.

The transistor is considered by many to be one of the greatest inventions in modern history, ranking in importance with the printing press, automobile and telephone. It is the key active component in practically all modern electronics. Its importance in today's society rests on its ability to be mass produced using a highly automated process (fabrication) that achieves vanishingly low per-transistor costs.

Week 48

According to the Big Bang, the universe emerged from an extremely dense and hot state (bottom). Since then, space itself has expanded with the passage of time, carrying the galaxies with it.

In physical cosmology, the Big Bang is the scientific theory that the universe emerged from a tremendously dense and hot state about 13.7 billion years ago. The theory is based on the observations indicating the expansion of space (in accord with the Robertson–Walker model of general relativity) as indicated by the Hubble redshift of distant galaxies taken together with the cosmological principle.

Extrapolated into the past, these observations show that the universe has expanded from a state in which all the matter and energy in the universe was at an immense temperature and density. Physicists do not widely agree on what happened before this, although general relativity predicts a gravitational singularity (for reporting on some of the more notable speculation on this issue, see cosmogony).

The term Big Bang is used both in a narrow sense to refer to a point in time when the observed expansion of the universe (Hubble's law) began — calculated to be 13.7 billion (1.37 × 10¹⁰) years ago (±2%) — and in a more general sense to refer to the prevailing cosmological paradigm explaining the origin and expansion of the universe, as well as the composition of primordial matter through nucleosynthesis as predicted by the Alpher–Bethe–Gamow theory.

Week 49

Werner Karl Heisenberg while a student at the Niels Bohr Institute.

Werner Karl Heisenberg (December 5, 1901 – February 1, 1976) was a celebrated German physicist and Nobel laureate, one of the founders of quantum mechanics, and acknowledged to be one of the most important physicists of the twentieth century. He was born in Würzburg, Germany and died in Munich. Heisenberg was the head of Germany's nuclear energy program, though the nature of this project, and his work in this capacity, has been heavily debated. He is most well-known for discovering one of the central principles of modern physics, the Heisenberg uncertainty principle.

Week 50

In particle physics, quarks are one of the two basic constituents of matter (the other Standard Model fermions are the leptons).

Antiparticles of quarks are called antiquarks. Quarks are the only fundamental particles that interact through all four of the fundamental forces. The word was borrowed by Murray Gell-Mann from the book Finnegans Wake by James Joyce, where seabirds give "three quarks", akin to three cheers (probably onomatopoetically imitating a seabird call, like "quack" for ducks).

The names of quark flavours (up, down, strange, charm, bottom, and top) were also chosen arbitrarily based on the need to name them something that could be easily remembered and used.

Image: The 6 quarks and their most likely decay modes. Mass decreases moving from right to left.

Week 51

Richard Phillips Feynman (May 11, 1918 – February 15, 1988) was an American physicist known for expanding the theory of quantum electrodynamics, the physics of the superfluidity of supercooled liquid helium, and particle theory. For his work on quantum electrodynamics, Feynman was a joint recipient of the Nobel Prize in Physics in 1965, together with Julian Schwinger and Shin-Ichiro Tomonaga; he developed a way to understand the behavior of subatomic particles using pictorial tools that later became known as Feynman diagrams.

He assisted in the development of the atomic bomb and was a member of the panel that investigated the Space Shuttle Challenger disaster. Despite his prolific contributions, Feynman wrote only 37 research papers during his career. In addition to his work in pure physics, Feynman is credited with the concept and early exploration of quantum computing, and publicly envisioning nanotechnology, creation of devices at the molecular scale. He held the Richard Chace Tolman professorship in theoretical physics at Caltech.

Feynman was a keen and influential popularizer of physics in both his books and lectures, notably a seminal 1959 talk on top-down nanotechnology called There's Plenty of Room at the Bottom and The Feynman Lectures on Physics, a three-volume set which has become a classic text. Known for his insatiable curiosity, wit, brilliant mind and playful temperament, he is equally famous for his many adventures, detailed in his books Surely You're Joking, Mr. Feynman!, What Do You Care What Other People Think? and Tuva or Bust!. As well as being an inspirational lecturer, bongo player, notorious practical joker, and decipherer of Maya hieroglyphs, Richard Feynman was regarded as an eccentric and a free spirit. He liked to pursue multiple seemingly independent paths, such as biology, art, percussion, and lock picking. Freeman Dyson once wrote that Feynman was "half-genius, half-buffoon", but later revised this to "all-genius, all-buffoon".

Week 52

A rainbow is an optical and meteorological phenomenon that causes a nearly continuous spectrum of light to appear in the sky when the Sun shines onto droplets of moisture in the Earth's atmosphere. It takes the form of a multicoloured arc, with red on the outside and violet on the inside. A double rainbow includes a second, fainter, arc with colours in the opposite order, that is, with violet on the outside and red on the inside.

Even though a rainbow spans a continuous spectrum of colours, traditionally the full sequence of colours is most commonly cited as red, orange, yellow, green, blue, indigo and violet.

Light rays enter a raindrop from one direction (typically a straight line from the Sun), reflect off the back of the raindrop, and fan out as they leave the raindrop. The light leaving the rainbow is spread over a wide angle, with a maximum intensity of 40.6°–42°.