Learn Physics Online: 2010

Sunday, August 15, 2010

Where the mind is without fear …

Where the mind is without fear and the head is held high;
Where knowledge is free;
Where the world has not been broken up into fragments by domestic walls;
Where words come out from the depth of truth;
Where tireless striving stretches its arms towards perfection;
Where the clear stream of reason has not lost its way into the dreary desert sand of dead habit;
Where the mind is led forward by thee into ever-widening thought and action
Into that heaven of freedom, my father, let my country awake.

Thursday, August 5, 2010

BIG BANG

Big Bang Theory -

The Premise

The Big Bang theory is an effort to explain what happened at the very
beginning of our universe. Discoveries in astronomy and physics have
shown beyond a reasonable doubt that our universe did in fact have a
beginning. Prior to that moment there was nothing; during and after that
moment there was something: our universe. The big bang theory is an
effort to explain what happened during and after that moment.
According to the standard theory, our universe sprang into existence as
"singularity" around 13.7 billion years ago. What is a "singularity" and
where does it come from? Well, to be honest, we don't know for sure.
Singularities are zones which defy our current understanding of physics.
They are thought to exist at the core of "black holes." Black holes are
areas of intense gravitational pressure. The pressure is thought to be
so intense that finite matter is actually squished into infinite density
(a mathematical concept which truly boggles the mind). These zones
of infinite density are called "singularities." Our universe is thought to
have begun as an infinitesimally small, infinitely hot, infinitely dense,
something - a singularity. Where did it come from? We don't know.
Why did it appear? We don't know.

After its initial appearance, it apparently inflated (the "Big Bang"), expanded
and cooled, going from very, very small and very, very hot, to the size and
temperature of our current universe. It continues to expand and cool to this
day and we are inside of it: incredible creatures living on a unique planet,
circling a beautiful star clustered together with several hundred billion other
stars in a galaxy soaring through the cosmos, all of which is inside of an
expanding universe that began as an infinitesimal singularity which appeared
out of nowhere for reasons unknown. This is the Big Bang theory.
Big Bang Theory - Common Misconceptions

There are many misconceptions surrounding the Big Bang theory.
For example, we tend to imagine a giant explosion. Experts however say
that there was no explosion; there was (and continues to be) an expansion.
Rather than imagining a balloon popping and releasing its contents, imagine
a balloon expanding: an infinitesimally small balloon expanding to the size
of our current universe.

Another misconception is that we tend to image the singularity as a little
fireball appearing somewhere in space. According to the many experts
however, space didn't exist prior to the Big Bang. Back in the late '60s and
early '70s, when men first walked upon the moon, "three British astrophysicists,
Steven Hawking, George Ellis, and Roger Penrose turned their attention
to the Theory of Relativity and its implications regarding our notions of time.
In 1968 and 1970, they published papers in which they extended Einstein's
Theory of General Relativity to include measurements of time and space.
1, 2 According to their calculations, time and space had a finite beginning
that corresponded to the origin of matter and energy."3 The singularity didn't
appear in space; rather, space began inside of the singularity. Prior to the
singularity, nothing existed, not space, time, matter, or energy - nothing. So
where and in what did the singularity appear if not in space? We don't know.
We don't know where it came from, why it's here, or even where it is. All we
really know is that we are inside of it and at one time it didn't exist and
neither did we.

Big Bang Theory - Evidence for the Theory

What are the major evidences which support the Big Bang theory?

First of all, we are reasonably certain that the universe had a beginning.
Second, galaxies appear to be moving away from us at speeds proportional to
their distance. This is called "Hubble's Law," named after Edwin Hubble (1889-1953)
who discovered this phenomenon in 1929. This observation supports the
expansion of the universe and suggests that the universe was once compacted.
Third, if the universe was initially very, very hot as the Big Bang suggests,
we should be able to find some remnant of this heat. In 1965, Radioastronomers
Arno Penzias and Robert Wilson discovered a 2.725 degree Kelvin
(-454.765 degree Fahrenheit, -270.425 degree Celsius) Cosmic Microwave
Background radiation (CMB) which pervades the observable universe. This is
thought to be the remnant which scientists were looking for. Penzias and Wilson
shared in the 1978 Nobel Prize for Physics for their discovery.
Finally, the abundance of the "light elements" Hydrogen and Helium found in the
observable universe are thought to support the Big Bang model of origins.

Big Bang Theory - The Only Plausible Theory?

Is the standard Big Bang theory the only model consistent with these evidences?
No, it's just the most popular one. Internationally renown Astrophysicist George F. R.
Ellis explains: "People need to be aware that there is a range of models that could
explain the observations….For instance, I can construct you a spherically symmetrical
universe with Earth at its center, and you cannot disprove it based on observations….
You can only exclude it on philosophical grounds. In my view there is absolutely nothing
wrong in that. What I want to bring into the open is the fact that we are using philosophical
criteria in choosing our models. A lot of cosmology tries to hide that."
In 2003, Physicist Robert Gentry proposed an attractive alternative to the standard
theory, an alternative which also accounts for the evidences listed above.5 Dr. Gentry
claims that the standard Big Bang model is founded upon a faulty paradigm
(the Friedmann-lemaitre expanding-spacetime paradigm) which he claims is
inconsistent with the empirical data. He chooses instead to base his model on
Einstein's static-spacetime paradigm which he claims is the "genuine cosmic
Rosetta." Gentry has published several papers outlining what he considers to be
serious flaws in the standard Big Bang model.6 Other high-profile dissenters
include Nobel laureate Dr. Hannes Alfvén, Professor Geoffrey Burbidge, Dr. Halton Arp,
and the renowned British astronomer Sir Fred Hoyle, who is accredited with first
coining the term "the Big Bang" during a BBC radio broadcast in 1950.

Big Bang Theory - What About God?

Any discussion of the Big Bang theory would be incomplete without asking the question,
what about God? This is because cosmogony (the study of the origin of the universe) is
an area where science and theology meet. Creation was a supernatural event. That is, it
took place outside of the natural realm. This fact begs the question: is there anything else
which exists outside of the natural realm? Specifically, is there a master Architect out there?
We know that this universe had a beginning. Was God the "First Cause"? We won't attempt
to answer that question in this short article. We just ask the question:
Does God Exist?

------------- the decision is up to u to say whether god exists or not ....................

Footnotes:
wikipedia
Steven W. Hawking, George F.R. Ellis, "The Cosmic Black-Body"

GRAND UNIFIED THEORY

GUT

The term Grand Unified Theory or GUT, refers to any of several
similar models in particle physics in which at high energy scales,
the three gauge interactions of the Standard Model which define
the electromagnetic, weak, and strong interactions, are merged
into one single interaction characterized by a larger gauge
symmetry and one unified coupling constant rather than three
independent ones
History :
Historically, the first true GUT which was based on the simple
Lie group SU(5), was proposed by Howard Georgi and Sheldon Glashow
in 1974.The Georgi–Glashow model was preceded by the Semisimple Lie
algebra Pati–Salam model by Abdus Salam and Jogesh Pati,who pioneered
the idea to unify gauge interactions.

Unification of forces and the role of supersymmetry :
The renormalization group running of the three-gauge couplings has been
found to nearly, but not quite, meet at the same point if the hypercharge
is normalized so that it is consistent with SU(5) or SO(10) GUTs, which
are precisely the GUT groups which lead to a simple fermion unification.
This is a significant result, as other Lie groups lead to different
normalizations. However, if the supersymmetric extension MSSM is used
instead of the Standard Model, the match becomes much more accurate.
It is commonly believed that this matching is unlikely to be a coincidence.
Also, most model builders simply assume supersymmetry (SUSY) because it
solves the hierarchy problem—i.e., it stabilizes the electroweak Higgs mass
against radiative corrections. And the Majorana mass of the right-handed
neutrino SO(10) theories with its mass set to the gauge unification scale
is examined, values for the left-handed neutrino masses (see neutrino oscillation)
are produced via the seesaw mechanism. These values are 10–100 times
smaller than the GUT scale, but still relatively close.
(For a more elementary introduction to how Lie algebras are related to
particle physics, see the article Particle physics and representation theory.)

Current status :

As of 2009, there is still no hard evidence that nature is described by a Grand
Unified Theory. Moreover, since the Higgs particle has not yet been observed,
the smaller electroweak unification is still pending.The discovery of
neutrino oscillations indicates that the Standard Model is incomplete and
has led to renewed interest toward certain GUT such as SO(10). One of the few
possible experimental tests of certain GUT is proton decay and also fermion
masses. There are a few more special tests for supersymmetric GUT.
The gauge coupling strengths of QCD, the weak interaction and hypercharge
seem to meet at a common length scale called the GUT scale and equal
approximately to 1016 GeV, which is slightly suggestive. This interesting
numerical observation is called the gauge coupling unification, and it works
particularly well if one assumes the existence of superpartners of the
Standard Model particles. Still it is possible to achieve the same by postulating,
for instance, that ordinary (non supersymmetric) SO(10) models break with
an intermediate gauge scale, such as the one of Pati-Salam group

The research still continues...........................

superconductivity - Jihin

Superconductivity: So simple, yet so hard to explain!

For half a century the world's most brilliant physics theorists tried
scribbling equations, only to crumple the paper and hurl it at a
wastebasket. Bend a metal wire into a circle, make it as cold as
you possibly can, and set an electric current moving around it.
The current can persist. Put the circle of wire above a magnet,
and it will float there until the end of the world.
In the decades after this strange discovery, physicists figured
out the laws of relativity and quantum mechanics. They worked
out equations to calculate all the colors and chemistry of the
natural world, they cracked open the atomic nucleus, they
uncovered the forces that light the stars... and still nobody had
explained that little floating wire.

This exhibit tells how three extraordinary minds worked together
to finally solve the puzzle. You will see that getting to a new theory
may take not just one "Moment of Discovery" but a string of dozens
of such moments among many people. For a personal account,
listen to Bob Schrieffer, the youngest of the team, tell what happened
in his own words. To get the full background, you can read or listen
to how a noted physicist saw the story from an outside perspective.
You can also read a detailed account by a historian of physics, and
explore other supplementary materials.

Monday, July 19, 2010

SUPERCONDUCTIVITY

“The experiment left no doubt that, as far as accuracy of measurement went, the resistance disappeared. At the same time, however, something unexpected occurred. The disappearance did not take place gradually but abruptly. From 1/500 the resistance at 4.2K, it could be established that the resistance had become less than a thousand-millionth part of that at normal temperature. Thus the mercury at 4.2K has entered a new state, which, owing to its particular electrical properties, can be called th state of superconductivity. “— Heike Kamerlingh Onnes

A GLIMPSE

SUPERCONDUCTIVITY is a fascinating and challenging field of physics. Scientists and engineers throughout the world have been striving to develop an understanding of this remarkable phenomenon for many years. For nearly 75 years superconductivity has been a relatively obscure subject. Today however, superconductivity is being applied to many diverse areas such as: medicine, theoretical and experimental science, the military, transportation, power production, electronics, as well as many other areas. With the discovery of high-temperature superconductors, which can operate at liquid nitrogen temperatures (77 K), superconductivity is now well within the reach of high school students. Unique and exciting opportunities exist today for our students to explore and experiment with this new and important technological field of physics.

HISTORICAL BACKGROUND

Major advances in low-temperature refrigeration were made during the late 19th century. Superconductivity was first discovered in 1911 by the Dutch physicist,Heike Kammerlingh Onnes. Onnes dedicated his scientific career to exploring extremely cold refrigeration. On July 10, 1908, he successfully liquified helium by cooling it to 452 degrees below zero Fahrenheit (4 Kelvin or 4 K). Onnes produced only a few milliliters of liquid helium that day, but this was to be the new beginnings of his explorations in temperature regions previously unreachable. Liquid helium enabled him to cool other materials closer to absolute zero (0 Kelvin), the coldest temperature imaginable. Absolute zero is the temperature at which the energy of material becomes as small as possible.

In 1911, Onnes began to investigate the electrical properties of metals in extremely cold temperatures. It had been known for many years that the resistance of metals fell when cooled below room temperature, but it was not known what limiting value the resistance would approach, if the temperature were reduced to very close to 0 K. Some scientists, such as William Kelvin, believed that electrons flowing through a conductor would come to a complete halt as the temperature approached absolute zero. Other scientists, including Onnes, felt that a cold wire's resistance would dissipate. This suggested that there would be a steady decrease in electrical resistance, allowing for better conduction of electricity. At some very low temperature point, scientists felt that there would be a leveling off as the resistance reached some ill-defined minimum value allowing the current to flow with little or no resistance.Onnes passed a current through a very pure mercury wire and measured its resistance as he steadily lowered the temperature. Much to his surprise there was no leveling off of resistance, let alone the stopping of electrons as suggested by Kelvin. At 4.2 K the resistance suddenly vanished. Current was flowing through the mercury wire and nothing was stopping it, the resistance was zero.FIG 1 is a graph of resistance versus temperature in mercury wire as measured by Onnes . According to Onnes, "Mercury has passed into a new state, which on account of its extraordinary electrical properties may be called the superconductive state". The experiment left no doubt about the disappearance of the resistance of a mercury wire. Kamerlingh Onnes called this newly discovered state, SUPERCONDUCTIVITY

Onnes found that the superconductor exhibited what he called persistent currents, electric currents that continued to flow without an electric potential driving them. Onnes had discovered superconductivity, and was awarded the Nobel Prize in 1913.

UNLOCKING THE MYSTERIES OF SUPERCONDUCTIVITY

Whenever a new scientific discovery is made, researchers must strive to explain their theories. By 1933 Walther Meissner and R. Ochsenfeld discovered that superconductors are more than a perfect conductor of electricity, they also have an interesting magnetic property of excluding a magnetic field. A superconductor will not allow a magnetic field to penetrate its interior. It causes currents to flow that generate a magnetic field inside the superconductor that just balances the field that would have otherwise penetrated the material.

This effect, called the Meissner Effect, causes a phenomenon that is a very popular demonstration of superconductivity. Figure (2) is an image of magnetic field lines from a magnet levitating above a superconductor. The Meissner Effect will occur only if the magnetic field is relatively small. If the magnetic field becomes too great, it penetrates the interior of the metal and the metal loses its superconductivity. In 1957 scientists began to unlock the mysteries of superconductors. Three American physicists at the University of Illinois, John Bardeen, Leon Cooper, and Robert Schrieffer, developed a model that has since stood as a good mental picture of why superconductors behave as they do. The model is expressed in terms of advanced ideas of the science of quantum mechanics, but the main idea of the model suggests that electrons in a superconductor condense into a quantum ground state and travel together collectively and coherently. In 1972, Bardeen, Cooper, and Schrieffer received the Nobel Prize in Physics for their theory of superconductivity,which is now known as the BCS theory, after the initials of their last names.

In 1986, Georg Bednorz and Alex Müller, working at IBM in Zurich Switzerland, were experimenting with a particular class of metal oxide ceramics called perovskites. Bednorz and Müller surveyed hundreds of different oxide compounds. Working with ceramics of lanthanum, barium, copper, and oxygen they found indications of superconductivity at 35 K, a startling 12 K above the old record for a superconductor.Soon researchers from around the world would be working with the new types of superconductors. In February of 1987, a perovskite ceramic material was found to superconduct at 90 K. This discovery was very significant because now it became possible to use liquid nitrogen as a coolant. Because these materials superconduct at significantly higher temperatures they are referred to as High Temperature Superconductors.

Fundementals of superconductors

¯ Superconductors have the ability to conduct electricity without the loss of energy. When current flows in an ordinary conductor, for example copper wire, some energy is lost. In a light bulb or electric heater, the electrical resistance creates light.

¯ Inside a superconductor the behavior of electrons is vastly different. As the superconducting electrons travel through the conductor they pass unobstructed through the complex lattice .As these electrons do not bump with anything( unlike the electrons of metal conductors Cu and which collide with tiny impurities and imperfections in lattice), these create no friction and they can transmit electricity with no appreciable loss in the current and no loss of energy.

¯ BCS THEORY by three American physicists-John Bardeen, Leon Cooper, and John Schrieffer explains superconductivity at temperatures close to absolute zero. According to the theory, as one negatively charged electron passes by positively charged ions in the lattice of the superconductor, the lattice distorts. This in turn causes phonons to be emitted which forms a trough of positive charges around the electron illustrates a wave of lattice distortion due to attraction to a moving electron. Before the electron passes by and before the lattice springs back to its normal position, a second electron is drawn into the trough. It is through this process that two electrons, which should repel one another, link up.

¯ The BCS theory successfully shows that electrons can be attracted to one another through interactions with the crystalline lattice. This occurs despite the fact that electrons have the same charge. The electron pairing is favorable because it has the effect of putting the material into a lower energy state. When electrons are linked together in pairs, they move through the superconductor in an orderly fashion.

¯ As the superconductor gains heat energy the vibrations in the lattice become more violent and break the pairs. As they break, superconductivity diminishes. Superconducting metals and alloys have characteristic transition temperatures from normal conductors to superconductors called Critical Temperature (T _c)

¯ Below the superconducting transition temperature, the resistivity of a material is exactly zero. Superconductors made from different materials have different( T _c) values.

¯ There is a certain maximum current that these materials can be made to carry, above

which they stop being superconductors. If too much current is pushed through a superconductor, it will revert to the normal state even though it may be below its transition temperature.

¯ There are two types of superconductors, Type I and Type II. Very pure samples of lead, mercury, and tin are examples of Type I superconductors. High temperature ceramic superconductors such as YBa_2CU_3O_7 (YBCO) and Bi_ CaSr _ 2Cu_2O_9are examples of Type II superconductors.

¯ The superconducting state is defined by three very important factors: critical temperature (Tc), critical field (Hc), and critical current density (Jc). Each of these parameters is very dependant on the other two properties present. Maintaining the superconducting state requires that both the magnetic field and the current density, as well as the temperature, remain below the critical values, all of which depend on the material

¯ Tunneling is a process arising from the wave nature of the electron .It is the passage of electrons through a potential barrier which they would not be able to cross according to classical mechanics, such as a thin insulating barrier between two superconductors.

¯ The tunneling of a pair of electrons between superconductors separated by an insulating barrier was first discovered by Brian Josephson in 1962. Josephson discovered that if two superconducting metals were separated by a thin insulating barrier such as an oxide layer 10 to 20 angstroms thick, it is possible for electron pairs to pass through the barrier without resistance. This is known as the dc Josephson Effect.

¯ A Josephson junction consists of two superconductors separated by a thin insulating barrier. Pairs of superconducting electrons will tunnel through the barrier. The Josephson junction is a superfast switching devise. the junction devices' exceptional switching speed make them ideal for use in super fast and much smaller computers.

APPLICATION OF SUPERCONDUCTORS

Ø Magnetic-levitation is an application where superconductors perform extremely well. A landmark for the commercial use of MAGLEV technology occurred in 1990 when it gained the status of a nationally-funded project in Japan. The Minister of Transport authorized construction of the Yamanashi Maglev Test Line. the wider use of MAGLEV vehicles has been constrained by political and environmental concerns (strong magnetic fields can create a bio-hazard).

Ø superconductors can perform a life-saving function in the field of biomagnetism. By impinging a strong superconductor-derived magnetic field into the body, hydrogen atoms that exist in the body's water and fat molecules are forced to accept energy from the magnetic field. They then release this energy at a frequency that can be detected and displayed graphically by a computer- Magnetic Resonance Imaging (MRI)

Ø superconducting wire are made use in electric generators and their efficiency is above 99% and is half the size of conventional generators.

Ø Recently, power utilities have also begun to use superconductor-based transformers and "fault limiters". The Swiss-Swedish company ABB was the first to connect a superconducting transformer to a utility power network in March of 1997. ABB also recently announced the development of a 6.4MVA (mega-volt-ampere) fault current limiter - the most powerful in the world.

Ø Superconductors can be employed in transmission of power to cities.But due to the high cost and difficulty of cooling miles of superconducting wire this has only happened with short "test runs".

Ø In the electronics industry, ultra-high-performance filters are now being built.

Ø Superconductors have also found widespread applications in the military. HTSC SQUIDS are being used by the U.S. NAVY to detect mines and submarines. And, significantly smaller motors are being built for NAVY ships using superconducting wire and "tape". In mid-July, 2001, American Superconductor unveiled a 5000-horsepower motor made with superconducting wire (below). An even larger 36.5MW HTS ship propulsion motor was delivered to the U.S. Navy in late 2006.

Ø The newest application for HTS(high temperature superconductor) wire is in the degaussing of naval vessels. In addition to reduced power requirements, HTS degaussing cable offers reduced size and weight.

Ø Superconducting x-ray detectors and ultra-fast, superconducting light detectors are being developed due to their inherent ability to detect extremely weak amounts of energy.

Ø Soon superconductors may even play a role in Internet communications also. , superconductor technology may be called upon to meet this need.

Superconductivity milestones

ª 1911 - Dutch physicist Heike Kamerlingh Onnes discovers superconductivity in mercury at temperature of 4 K.

ª 1913-Kamerlingh Onnes is awarded the Nobel Prize in Physics for his research on the properties of matter at low temperature

ª 1933 – W. Meissner and R. Ochsenfeld discover the Meissner Effect.

ª 1941- scientists report superconductivity in niobium nitride at 16 K.

ª 1953- Vanadium-3 silicon found to superconduct at 17.5 K.

ª 1962- Westinghouse scientists develop the first commercial niobium- titanium superconducting wire.

ª 1972- John Bardeen, Leon Cooper, and John Schrieffer win the Nobel Prize in Physics for the first successful theory of how superconductivity works.

ª 1986- IBM researchers Alex Müller and Georg Bednorz make a ceramic compound of lanthanum, barium, copper, and oxygen that superconducts at 35 K.

ª 1987- Scientific groups at the University of Houston and the University of Alabama at Huntsville substitute yttrium for lanthanum and make a ceramic that superconducts at 92 K, bringing superconductivity into the liquid nitrogen range.

ª 1988- Allen Hermann of the University of Arkansas makes a superconducting ceramic containing calcium and thallium that superconducts at 120 K. Soon after, IBM and AT&T Bell Labs scientists produce a ceramic that superconducts at 125 K

ª 1993- A. Schilling, M. Cantoni, J. D. Guo, and H. R. Ott from Zurich, Switzerland, produces a superconductor from mercury, barium and copper, (HgBa _Ca _C u_ O) with maximum transition temperature of 133K.