## Monday, 28 January 2008

### Dark Energy

By;
Arip Nurahman
Department of Physics
Faculty of Sciences and Mathematics
Indonesia University of Education

Dark Energy: Astronomers Still 'Clueless' About Mystery Force Pushing Galaxies Apart By Andrew Chaikin It sounds like something out of a Star Trek episode: Dark energy, a mysterious force that no one understands, is causing the universe to fly apart faster and faster. Only a few years ago, if you'd suggested something like that to astronomers, they would have told you to spend less time in front of the TV and more time in the "real" world.

But dark energy is real or at least, a growing number of astronomers think it is. No one, however, can truly explain it.
"Frankly, we just don’t understand it," says Craig Hogan, an astronomer at the University of Washington at Seattle. "We know what its effects are," Hogan says, but as to the details of dark energy, "Were completely clueless about that. And everybody’s clueless about it."

Dark energy entered the astronomical scene in 1998, after two groups of astronomers made a survey of exploding stars, or supernovas, in a number of distant galaxies. These researchers found that the supernovas were dimmer than they should have been, and that meant they were farther away than they should have been. The only way for that to happen, the astronomers realized, was if the expansion of the universe had sped up at some time in the past.

The Images This chart shows how much of the universe is made up of dark energy, dark matter, and ordinary matter. This diagram reveals changes in the rate of expansion since the universe's birth 15 billion years ago. The more shallow the curve, the faster the rate of expansion. The curve changes noticeably about 7.5 billion years ago, when objects in the universe beg Related SPACE.com STORIES Astrophysics Challenged By Dark Energy Finding Farthest Supernova Detected, 'Dark Energy' Suspected 'Groundbreaking' Discovery: First Direct Observation of Dark Matter Understanding Dark Matter and Light Energy TODAY'S DISCUSSION What do you think of this story?

Until then, astronomers had generally believed that the cosmic expansion was gradually slowing down, due to the gravitational tugs that individual galaxies exert on one another. But the supernova results implied that some mysterious force was acting against the pull of gravity, causing galaxies to fly away from each other at ever greater speeds.

It was a stunning realization.
At first, other researchers questioned the result; perhaps the supernovas were dimmer because their light was being blocked by clouds of interstellar dust. Or maybe the supernovas themselves were intrinsically dimmer than scientists thought. But with careful checking, and more data, those explanations have largely been put aside, and the dark energy hypothesis has held up.

In one sense, the idea is not completely new. Einstein had included such an "anti-gravity" effect in his theory of general relativity, in his so-called cosmological constant. But Einstein himself, and later many other astronomers, came to regard this as a kind of mathematical contrivance that had little relationship to the real universe. By the 1990s no one expected that the effect would turn out to be real.

Still, anti-gravity isn’t the right way to describe dark energy, says Virginia Trimble of the University of Southern California at Irvine.
"It doesn’t act opposite to gravity," Trimble says. "It does exactly what general relativity says it should do, if it has negative pressure."
Trimble has a fairly simple way of imagining the phenomenon.
"If you think in terms of the universe as a very large balloon," she says, "when the balloon expands, that makes the local density of the [dark energy] smaller, and so the balloon expands some more . because it exerts negative pressure. While its inside the balloon its trying to pull the balloon back together again, and the lower the density of it there is, the less it can pull back, and the more it expands. This is what happens in the expanding universe."

The supernova evidence suggests that the acceleration kicked in about 5 billion years ago. At that time, galaxies were far enough apart that their gravity (which weakens with distance) was overwhelmed by the relatively gentle but constant repulsive force of dark energy. Since then, dark energy's continuing push has been causing the cosmic expansion to speed up, and it seems likely now that this expansion will continue indefinitely.

"It means that if you look out at the universe today, and if we wait many billions of years," says Hogan, "everything will be flying away faster and faster, and eventually well be left quite alone."
Aside from such grim forecasts, dark energy is causing quite a bit of upset for astronomers who have to adjust to an unexpected and outlandish new view of the universe. Already, they have had to accept the notion of dark matter, which is now thought to far outnumber ordinary matter in the universe, but which has never been detected in any laboratory. Now, the arrival of an unknown force that rules cosmic expansion has added insult to injury.

"I'm as big a fan of dark matter and dark energy as anybody else," says astronomer Richard Ellis of Caltech. But, he adds, "I find it very worrying that you have a universe where there are three constituents, of which only one [i.e., ordinary matter] is really physically understood."
"When you teach undergraduates, and they say, 'Well, what is dark matter?' Well, nobody's really sure. 'What is dark energy?' We're even less sure. So you have to explain to a student, that 90 percent of the universe, 95 percent, is in two ingredients that nobody really understands," says Ellis. "This isn't really progress."

No one argues that dark energy is difficult to comprehend. And as Trimble points out, it is hardly the first strange idea scientists have had to accept.
"It took two generations for people to be comfortable with quantum mechanics," she says. "The fact that you do not have good intuition about [dark energy] is true for quantum mechanics, general relativity, and lots of other things, because we cant easily mock them up in the laboratory."
And for cosmologists, dark energy has solved at least one cosmological conundrum raised by studies of the Cosmic Microwave Background, or CMB.

## Saturday, 26 January 2008

### Grand Unification Theory

Grand Unification Theory

Arip Nurahman
Department of Physics
Faculty of Sciences and Mathematics, Indonesia University of Education

and

Follower Open Course Ware at Massachusetts Institute of Technology
Cambridge, USA
Department of Physics
http://web.mit.edu/physics/
http://ocw.mit.edu/OcwWeb/Physics/index.htm
&
Aeronautics and Astronautics Engineering
http://web.mit.edu/aeroastro/www/
http://ocw.mit.edu/OcwWeb/Aeronautics-and-Astronautics/index.htm

The Ball-of-Light Particle Model
Introduction, The Picture Puzzle Analogy, Old Intro, More, Summary of the Grand Unification Theory -- "The Ball-of-Light Particle Model", Highlights of information in this Grand Unification, Ball Lightning, Examples of Balls of Light, Balls-of-Light from cracking rock,
Forces
Induction of forces, The Strong Force,

The "Poynting Vector",

Balls-of-Light
Decay Modes, Induction off of a Ball-of-Light's Pole, Induction off of a Ball-of-Light's Pole, The Towers of M16, SS433 (A decaying ball-of-light), The explosion (decay) of small elementary particles, A Large Ball-of-Light Inducing a Small Ball-of-Light, Example: The Artificial Decay of the Lithium Nucleus, Gravitational Induction of an Electromagnetic Wave on a Ball-of-Light,

Gravity

Experiments
Experiments with Balls-of-Light, Example: A Scientist who makes Spherical Sparks,

Problems
What are the problems with the Ball-of-Light Particle Model?,

 Book 1 Book 2 Book 3 Book 4 Book 5 Book 6

Abstract

For years, humanity has always wondered “why are we here?”. Through the creation of God or the Big Bang to the Primordial Soup, either way, humanity was always look for answers. Each culture prior to the scientific age identified a “Creator or God” responsible for the existence of the heavens and the earth. Since the induction of “modern thought”, contemporary explanation concludes the universe was created from a big bang that happened approximately 13.7 billion years ago. From which the expansion and the cooling down resulted in us, a mixture of carbon and gases, with a combination of electric static.

Introduction

A Grand Unified Theory, (GUT), is a model in particle physics in which at high energy, the three gauge interactions of the Standard Model which define the electromagnetic, weak, and strong interactions, are merged into one single interaction characterized by one larger gauge symmetry and thus one unified coupling constant. In contrast, the experimentally verified Standard Model of particle physics is based on three independent interactions, symmetries and coupling constants.

Models that do not unify all interactions using one simple Lie group as the gauge symmetry, but do so using semisimple groups, can exhibit similar properties and are sometimes referred to as Grand Unified Theories as well.

Unifying gravity with the other three interactions would provide a theory of everything (TOE), rather than a GUT. Nevertheless, GUTs are often seen as an intermediate step towards a TOE.

The new particles predicted by models of grand unification cannot be observed directly at particle colliders because their masses are expected to be of the order of the so-called GUT scale, which is predicted to be just a few orders of magnitude below the Planck scale and thus far beyond the reach of currently foreseen collision experiments. Instead, effects of grand unification might be detected through indirect observations such as proton decay, electric dipole moments of elementary particles, or the properties of neutrinos. Some grand unified theories predict the existence of magnetic monopoles.

GUT refers to any of several very similar unified field theories or models in physics that predicts that at extremely high energies (above 1014 GeV), the electromagnetic, weak nuclear, and strong nuclear forces are fused into a single unified field.

Thus far, physicists have been able to merge electromagnetism and the weak nuclear force into the electroweak force, and work is being done to merge electroweak and quantum chromodynamics into a QCD-electroweak interaction sometimes called the electrostrong force. Beyond grand unification, there is also speculation that it may be possible to merge gravity with the other three gauge symmetries into a theory of everything.

## 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,[3] who pioneered the idea to unify gauge interactions.

The acronym GUT was first coined in 1978 by CERN researchers John Ellis, Andrzej Buras, Mary K. Gaillard, and Dimitri Nanopoulos, however in the final version of their paper they opted for the less anatomical GUM (Grand Unification Mass). Nanopoulos later that year was the first to use the acronym in a paper.

## Motivation

There is a general aesthetic among high energy physicists that the more symmetrical a theory is, the more "beautiful" and "elegant" it is. According to this aesthetic, the Standard Model gauge group, which is the direct product of three groups (modulo some finite group), is "ugly". Also, reasoning in analogy with the 19th-century unification of electricity with magnetism into electromagnetism, and especially the success of the electroweak theory, which utilizes the idea of spontaneous symmetry breaking to unify electromagnetism with the weak interaction, people wondered if it might be possible to unify all three groups in a similar manner. Physicists feel that three independent gauge coupling constants and a huge number of Yukawa coupling coefficients require far too many free parameters, and that these coupling constants ought to be explained by a theory with fewer free parameters.

A gauge theory where the gauge group is a simple group only has one gauge coupling constant, and since the fermions are now grouped together in larger representations, there are fewer Yukawa coupling coefficients as well. In addition, the chiral fermion fields of the Standard Model unify into three generations of two irreducible representations ($10\oplus \bar{5}$) in SU(5), and three generations of an irreducible representation (16) in SO(10). This is a significant observation, as a generic combination of chiral fermions which are free of gauge anomalies will not be unified in a representation of some larger Lie group without adding additional matter fields. SO(10) also predicts a right-handed neutrino.

GUT theory specifically predicts relations among the fermion masses, such as between the electron and the down quark, the muon and the strange quark, and the tau lepton and the bottom quark for SU(5) and SO(10). Some of these mass relations hold approximately, but most don't. See Georgi-Jarlskog mass relation. If we look at the renormalization group running of the three-gauge couplings have 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)/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 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.)

## Proposed theories

Several such theories have been proposed, but none is currently universally accepted. An even more ambitious theory that includes all fundamental forces, including gravitation, is termed a theory of everything. Some common mainstream GUT models are:

 minimal left-right model — SU(3)C × SU(2)L × SU(2)R × U(1)B-L Georgi–Glashow model — SU(5) SO(10) Flipped SU(5) — SU(5) × U(1) Pati-Salam model — SU(4) × SU(2) × SU(2) Flipped SO(10) — SO(10) × U(1) Trinification — SU(3) × SU(3) × SU(3) SU(6) E6 331 model chiral color
Not quite GUTs:

Note:

These models refer to Lie algebras not to Lie groups. The Lie group could be [SU(4)×SU(2)×SU(2)]/Z2, just to take a random example.

The most promising candidate is SO(10). (Minimal) SO(10) does not contain any exotic fermions (i.e. additional fermions besides the Standard Model fermions and the right-handed neutrino), and it unifies each generation into a single irreducible representation. A number of other GUT models are based upon subgroups of SO(10). They are the minimal left-right model, SU(5), flipped SU(5) and the Pati-Salam model. The GUT group E6 contains SO(10), but models based upon it are significantly more complicated. The primary reason for studying E6 models comes from E8 × E8 heterotic string theory.

GUT models generically predict the existence of topological defects such as monopoles, cosmic strings, domain walls, and others. But none have been observed. Their absence is known as the monopole problem in cosmology. Most GUT models also predict proton decay, although not the Pati-Salam model; current experiments still haven't detected proton decay. This experimental limit on the proton's lifetime pretty much rules out minimal SU(5).

## Ingredients

A GUT model basically consists of a gauge group which is a compact Lie group, a connection form for that Lie group, a Yang-Mills action for that connection given by an invariant symmetric bilinear form over its Lie algebra (which is specified by a coupling constant for each factor), a Higgs sector consisting of a number of scalar fields taking on values within real/complex representations of the Lie group and chiral Weyl fermions taking on values within a complex rep of the Lie group. The Lie group contains the Standard Model group and the Higgs fields acquire VEVs leading to a spontaneous symmetry breaking to the Standard Model. The Weyl fermions represent matter.

## Current status

As of today, 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.

## Origin of name

The coining of the widely-used acronym GUT has been attributed to a paper published in 1978 by Texas A&M University theorist Dimitri Nanopoulos
(previously at Harvard University).

## References

1. ^ Parker, B 1993, 'Overcoming some of the problems', pp.259-279
2. ^ Hawking, S.W. (1996) A Brief History of Time: the updated and expanded edition. 2nd. edition [from original text]. New York, NY: Bantam Books. ISBN 055338016. pg. XXX.

## Friday, 18 January 2008

### Solving The Mystery of The Missing Netrinos

Solving the Mystery of the Missing Neutrinos
by John N. Bahcall

by:
Arip Nurahman
Department of Physics
Faculty of Sciences and Mathematics
Indonesia University of Education

The three years 2001 to 2003 were the golden years of solar neutrino research. In this period, scientists solved a mystery with which they had been struggling for four decades. The solution turned out to be important for both physics and for astronomy. In this article, I tell the story of those fabulous three years.1

The first two sections summarize the solar neutrino mystery and present the solution that was found in the past three years. The next two sections describe what the solution means for physics and for astronomy. The following sections outline what is left to do in solar neutrino research and give my personal view of why it took more than thirty years to solve the mystery of the missing neutrinos. The last section provides a retrospective impression of the solution.

The Mystery
The Crime Scene
During the first half of the twentieth century, scientists became convinced that the Sun shines by converting, deep in its interior, hydrogen into helium. According to this theory, four hydrogen nuclei called protons (p) are changed in the solar interior into a helium nucleus (4He), two anti-electrons (e+, positively charged electrons), and two elusive and mysterious particles called neutrinos . This process of nuclear conversion, or nuclear fusion, is believed to be responsible for sunshine and therefore for all life on Earth. The conversion process, which involves many different nuclear reactions, can be written schematically as:

(1).

Two neutrinos are produced each time the fusion reaction (1) occurs. Since four protons are heavier than a helium nucleus, two positive electrons and two neutrinos, reaction (1) releases a lot of energy to the Sun that ultimately reaches the Earth as sunlight. The reaction occurs very frequently. Neutrinos escape easily from the Sun and their energy does not appear as solar heat or sunlight. Sometimes neutrinos are produced with relatively low energies and the Sun gets a lot of heat. Sometimes neutrinos are produced with higher energies and the Sun gets less energy.

The neutrinos in equation (1) and the illustration below are the focus of the mystery that we explore in this article.

Neutrinos have zero electric charge, interact very rarely with matter, and – according to the textbook version of the standard model of particle physics – are massless. About 100 billion neutrinos from the Sun pass through your thumbnail every second, but you do not feel them because they interact so rarely and so weakly with matter. Neutrinos are practically indestructible; almost nothing happens to them. For every hundred billion solar neutrinos that pass through the Earth, only about one interacts at all with the stuff of which the Earth is made. Because they interact so rarely, neutrinos can escape easily from the solar interior where they are created and bring direct information about the solar fusion reactions to us on Earth. There are three known types of neutrinos. Nuclear fusion in the Sun produces only neutrinos that are associated with electrons, the so-called electron neutrinos . The two other types of neutrinos, muon neutrinos and tau neutrinos , are produced, for example, in laboratory accelerators or in exploding stars, together with heavier versions of the electron, the particles muon and tau .

Neutrinos Are Missing
In 1964, following the pioneering work of Raymond Davis Jr., he and and I proposed an experiment to test whether converting hydrogen nuclei to helium nuclei in the Sun is indeed the source of sunlight, as indicated by equation (1).

I calculated with my colleagues the number of neutrinos of different energies that the Sun produces using a detailed computer model of the Sun and also calculated the number of radioactive argon atoms (37Ar) these solar neutrinos would produce in a large tank of chlorine-based cleaning fluid (C2Cl4). Although the idea seemed quixotic to many experts, Ray was sure that he could extract the predicted number of a few atoms of 37Ar per month out of a tank of cleaning fluid that is about the size of a large swimming pool.

The first results of Ray's experiment were announced in 1968. He detected only about one third as many radioactive argon atoms as were predicted. This discrepancy between the number of predicted neutrinos and the number Ray measured soon became known as "The Solar Neutrino Problem" or, in more popular contexts, "The Mystery of the Missing Neutrinos."

Raymond David Jr. (left) and John Bahcall in miner's clothing and protective hats. The photograph was taken in 1967 about a mile underground in the Homestake Gold Mine in Lead, South Dakota, USA. Davis is pictured showing Bahcall his newly constructed steel ank (6 meters in diameter, 15 meters long), which contained a large amount of cleaning fluid (40,000 liters) and was used to capture neutrinos from the Sun.
Photo: Courtesy of Raymond Davis, Jr. and John Bahcall

Possible Explanations
Three classes of explanation were suggested to solve the mystery. First, perhaps the theoretical calculations were wrong. This could happen in two ways. Either the predicted number of neutrinos was incorrect or the calculated production rate of argon atoms was not right. Second, perhaps Ray's experiment was wrong. Third, and this was the most daring and least discussed possibility, maybe physicists did not understand how neutrinos behave when they travel astronomical distances.

The theoretical calculations were refined and checked many times over the next two decades by me and by different researchers. The data used in the calculations were improved and the predictions became more precise. No significant error was found in the computer model of the Sun or in my calculation of the probability of Ray's tank capturing neutrinos. Similarly, Ray increased the sensitivity of his experiment. He also carried out a number of different tests of his technique in order to make sure that he was not overlooking some neutrinos. No significant error was found in the measurement. The discrepancy between theory and experiment persisted.

What about the third possible explanation, new physics? Already in 1969, Bruno Pontecorvo and Vladimir Gribov of the Soviet Union proposed the third explanation listed above, namely, that neutrinos behave differently than physicists had assumed. Very few physicists took the idea seriously at the time it was first proposed, but the evidence favoring this possibility increased with time.

Evidence Favors New Physics
In 1989, twenty-one years after the first experimental results were published, a Japanese-American experimental collaboration reported the results of an attempt to "solve" the solar neutrino problem. The new experimental group called Kamiokande (led by Masatoshi Koshiba and Yoji Totsuka) used a large detector of pure water to measure the rate at which electrons in the water scattered the highest-energy neutrinos emitted from the Sun. The water detector was very sensitive, but only to high-energy neutrinos that are produced by a rare nuclear reaction (involving the decay of the nucleus 8B) in the solar energy production cycle. The original Davis experiment with chlorine was primarily, but not exclusively, sensitive to the same high-energy neutrinos.

The Kamiokande experiment confirmed that the number of neutrino events that were observed was less than predicted by the theoretical model of the Sun and by the textbook description of neutrinos. But, the discrepancy in the water detector was somewhat less severe than observed in the chlorine detector of Ray Davis.

In the following decade, three new solar neutrino experiments deepened the mystery of the missing neutrinos. Experiments in Italy and Russia used massive detectors containing gallium to show that lower energy neutrinos were also apparently missing. These experiments were called GALLEX (led by Till Kirsten of Heidelberg, Germany) and SAGE (led by Vladimir Gavrin of Moscow, Russia). The fact that GALLEX and SAGE were sensitive to lower energy neutrinos was very important since I believed I could calculate more accurately the number of low energy neutrinos than the number of higher energy neutrinos. In addition, a much larger version of the Japanese water detector, called Super-Kamiokande (led by Totsuka and Yochiro Suzuki), made more precise measurements of the higher energy neutrinos and confirmed the original deficit of higher energy neutrinos found by the chlorine and Kamiokande experiments. So both high and low energy neutrinos were missing, although not in the same proportions.

The Super-Kamiokande Detector, University of Tokyo. The detector consists of an inner volume and an outer volume which contain 32,000 and 18,000 tons of pure water, respectively. The outer volume shields the inner volume in which neutrino interactions are studied. The inner volume is surrounded by 11,000 photomultiplier tubes that detect pale blue Cherenkov light emitted when electrons are struck by neutrinos.
Drawing: Courtesy of Kamioka Observatory, ICRR, University of Tokyo

Evidence obtained during this decade indicated that something must happen to the neutrinos on their way to detectors on Earth from the interior of the Sun. In 1990, Hans Bethe and I pointed out that new neutrino physics, beyond what was contained in the standard particle physics textbooks, was required to reconcile the results of the Davis chlorine experiment and the Japanese-American water experiment. Our conclusion was based upon an analysis of the relative sensitivity of the chlorine and the water experiments to neutrino number and neutrino energy. The newer solar neutrino experiments in Italy and in Russia increased the difficulty of explaining the neutrino data without invoking new physics.

New evidence also showed that the solar model predictions were reliable. In 1997, precise measurements were made of the sound speed throughout the solar interior using periodic fluctuations observed in ordinary light from the surface of the Sun. The measured sound speeds agreed to a precision of 0.1% with the sound speeds calculated for our theoretical model of the Sun. These measurements suggested to astronomers that the theoretical model of the Sun was so accurate that the model must also predict correctly the number of solar neutrinos.

The last decade of the twentieth century provided strong evidence that a better theory of fundamental physics was required to solve the mystery of the missing neutrinos. But, we still needed to find the smoking gun.

The Solution
On June 18, 2001 at 12:15 PM (eastern daylight time) a collaboration of Canadian, American, and British scientists made a dramatic announcement: they had solved the solar neutrino mystery. The international collaboration (led by Arthur McDonald of Ontario, Canada) reported the first solar neutrino results obtained with a detector of 1,000 tons of heavy water2 (D2O). The new detector, located in a nickel mine in Sudbury, Ontario in Canada, was able to study in a different way the same higher-energy solar neutrinos that had been investigated previously in Japan with the Kamiokande and Super-Kamiokande ordinary-water detectors. The Canadian detector is called SNO for Solar Neutrino Observatory.

Artist's drawing showing cutaway of the Sudbury Solar Neutrino Observatory, encased in its housing and submerged in a mine. The inner detector contains 1,000 tons of heavy water and is surrounded by a stainless steel structure carrying about 10,000 photomultiplier tubes. The outer, barrel-shaped cavity (22 meters in diameter and 34 meters in height) is filled with purified ordinary water to provide support and to shield against particles other than neutrinos.

The Definitive Experiments
For their first measurements, the SNO collaboration used the heavy-water detector in a mode that is sensitive only to electron neutrinos. The SNO scientists observed approximately one-third as many electron neutrinos as the standard computer model of the Sun predicted were created in the solar interior. The Super-Kamiokande detector, which is primarily sensitive to electron neutrinos but has some sensitivity to other neutrino types, observed about half as many events as were expected.

If the standard model of particle physics was right, the fraction measured by SNO and the fraction measured by Super-Kamiokande should be the same. All the neutrinos should be electron neutrinos. The fractions were different. The standard textbook model of particle physics was wrong.

Combining the SNO and the Super-Kamiokande measurements, the SNO collaboration determined the total number of solar neutrinos of all types (electron, muon, and tau) as well as the number of just electron neutrinos. The total number of neutrinos of all types agrees with the number predicted by the computer model of the Sun. Electron neutrinos constitute about a third of the total number of neutrinos.

The smoking gun was discovered. The smoking gun is the difference between the total number of neutrinos and the number of only electron neutrinos. The missing neutrinos were actually present, but in the form of the more difficult to detect muon and tau neutrinos.

The epochal results announced in June 2001 were confirmed by subsequent experiments. The SNO collaboration made unique new measurements in which the total number of high energy neutrinos of all types was observed in the heavy water detector. These results from the SNO measurements alone show that most of the neutrinos produced in the interior of the Sun, all of which are electron neutrinos when they are produced, are changed into muon and tau neutrinos by the time they reach the Earth.

The measurement of the total number of neutrinos in the SNO detector provided the fingerprints on the smoking gun.

These revolutionary results were verified independently in an extraordinary tour-de-force by a Japanese-American experimental collaboration, Kamland, which studied, instead of solar neutrinos, anti-neutrinos emitted by nuclear power reactors in Japan and in neighboring countries. The collaboration (led by Atsuto Suzuki of Sendai, Japan) observed a deficit in the detected number of anti-neutrinos from the nuclear power reactors. A deficit had been predicted for the Kamland experiment based upon the solar model calculations, the solar neutrino measurements, and a theoretical model of neutrino behavior that explained why the previous calculations and measurements seemed to be in disagreement. The Kamland measurements significantly improved our knowledge of the parameters that characterize neutrinos.

Where Did the Missing Neutrinos Go?
The solution of the mystery of the missing solar neutrinos is that neutrinos are not, in fact, missing. The previously uncounted neutrinos are changed from electron neutrinos into muon and tau neutrinos that are more difficult to detect. The muon and tau neutrinos were not detected by the Davis experiment with chlorine; they were not detected by the gallium experiments in Russia and in Italy; and they were not detected by the first SNO measurement. This lack of sensitivity to muon and tau neutrinos is the reason that these experiments seemed to suggest that most of the expected solar neutrinos were missing. On the other hand, the Kamiokande and Super-Kamiokande water experiments in Japan and the later SNO heavy water experiments had some sensitivity to muon and tau neutrinos in addition to their primary sensitivity to electron neutrinos. These water experiments revealed therefore larger fractions of the predicted solar neutrinos.

What Does All This Mean for Physics?
What Is Wrong with Neutrinos?
Solar neutrinos have a multiple personality disorder. They are created as electron neutrinos in the Sun, but on the way to the Earth they change their type. For neutrinos, the origin of the personality disorder is a quantum mechanical process, called "neutrino oscillations."

Pontecorvo and Gribov had the right idea in 1969. Lower energy solar neutrinos switch from electron neutrino to another type as they travel in the vacuum from the Sun to the Earth. The process can go back and forth between different types. The number of personality changes, or oscillations, depends upon the neutrino energy. At higher neutrino energies, the process of oscillation is enhanced by interactions with electrons in the Sun or in the Earth. Stas Mikheyev, Alexei Smirnov, and Lincoln Wolfenstein first proposed that interactions with electrons in the Sun could exacerbate the personality disorder of neutrinos, i.e., the presence of matter could cause the neutrinos to oscillate more vigorously between different types.

Bruno Pontecorvo in his office at the Joint Institute for Nuclear Physics, Dubna, Russia in 1983. Pontecorvo was discussing physics with his collaborator Samoil Bilenky. Later that afternoon, Pontecorvo celebrated his 70th birthday with a party.
Photo: Courtesy of Samoil Bilenky and John Bahcall

Even before the SNO measurement in 2001, phenomenological analyses of all the solar neutrino experimental data suggested with rather high confidence that some new physics was occurring. The preferred neutrino parameters from these pre-SNO analyses agreed with the parameters that were selected later with higher confidence by the SNO and Super-Kamiokande results. But, the smoking gun was missing.

The SNO and Super-Kamiokande results taken together were equivalent to finding a smoking gun, because they referred to the same high-energy solar neutrinos and because the experiments used techniques that were familiar to many physicists. Also, both experiments included many checks on their measurements.

What Is Wrong with the Standard Model of Particle Physics?
The standard model of particle physics assumes that neutrinos are massless. In order for neutrino oscillations to occur, some neutrinos must have masses. Therefore, the standard model of particle physics must be revised.

The simplest model that fits all the neutrino data implies that the mass of the electron neutrino is about 100 million times smaller than the mass of the electron. But, the available data are not yet sufficiently definitive to rule out all but one possible solution. When we finally have a unique solution, the values of the different neutrino masses may be clues that lead to understanding physics beyond the standard model of particle physics.

There are two equivalent descriptions of neutrinos, one that is expressed in terms of the masses of the neutrinos and one that is expressed in terms of the particles with which the neutrinos are associated (electron neutrinos with electrons, muon neutrinos with muon particles, or tau neutrinos with tau particles). The relations between the mass description and the associated-particle description involve certain constants, called "mixing angles," whose values are potentially important clues that may help lead to an improved theory of how elementary particles behave.

Solar neutrino research shows that neutrinos can change their personalities or types. The mathematical description of this malady determines quantities that we hope will be useful clues in the search for a more general theory of how fundamental particles behave.

What Does All This Mean for Astronomy?
The total number of neutrinos observed in the SNO and Super-Kamiokande experiments agrees with the number calculated using the standard computer model of the Sun. This shows that we understand how the Sun shines, the original question that initiated the field of solar neutrino research. The solution of the mystery of the missing neutrinos is an important triumph for astronomy. The standard solar model predictions are vindicated; the standard model of particle physics must be revised. Four decades ago, when the first solar neutrino experiment was proposed, no one would have guessed that this turn of events would be the outcome.

In order to predict correctly the number of neutrinos produced by nuclear reactions in the Sun, many complicated phenomena must be understood in detail. For example, one must understand a smorgasbord of nuclear reactions at energies where measurements are difficult. One must understand the transport of energy at very high temperatures and densities. One must understand the state of the solar matter in conditions that cannot be studied directly on Earth. The temperature at the center of the Sun is about 50,000 times higher than the temperature on Earth on a sunny day and the density in the center of the Sun is about a hundred times the density of water. One must measure the abundances of the heavy elements on the surface of the Sun and then understand how these abundances change as one goes deeper into the Sun. All of these and many more details must be understood and calculated accurately.

The predicted number of high-energy solar neutrinos can be shown by a quantum mechanical calculation to depend sensitively on the central temperature of the Sun. A 1% error in the temperature corresponds to about a 30% error in the predicted number of neutrinos; a 3% error in the temperature results in a factor of two error in the neutrinos. The physical reason for this great sensitivity is that the energy of the charged particles that must collide to produce the high-energy neutrinos is small compared to their mutual electrical repulsion. Only a small fraction of the nuclear collisions in the Sun succeed in overcoming this repulsion and causing fusion; this fraction is very sensitive to the temperature. Despite this great sensitivity to temperature, the theoretical model of the Sun is sufficiently accurate to predict correctly the number of neutrinos.

The research efforts of thousands of researchers in institutions distributed throughout the world have been necessary to achieve the required precision. As a result of this community effort over the past four decades, we now have confidence in our understanding of how stars shine. We can use this knowledge to interpret observations of distant galaxies that also contain stars. We can use the theory of how stars shine and evolve to learn more about the evolution of the universe.

What Is Left To Do?
The chlorine and gallium detectors do not measure the energy of neutrino events. Only the water detectors (Kamiokande, Super-Kamiokande, and SNO) provide specific information about the energies of the solar neutrinos that are observed. However, the water detectors are sensitive only to higher energy neutrinos (with energies > 5 million electron volts).

The standard computer model of the Sun predicts that most solar neutrinos have energies that are below the detection thresholds for the water detectors. If the standard solar model is correct, water detectors are sensitive to only about 0.01% of the neutrinos the Sun emits. The remaining 99.99% must be observed in the future with new detectors that are sensitive to relatively low energies.

The Sun is the only star close enough to the Earth for us to observe the neutrinos produced by nuclear fusion reactions. It is important to observe the abundant low-energy solar neutrinos in order to test more precisely the theory of stellar evolution. We believe we can calculate the expected number of low energy neutrinos more accurately than we can calculate the number of high-energy neutrinos. Therefore, an accurate measurement of the number of low energy neutrinos will be a critical test of the degree of accuracy of our solar theory. There may still be surprises.

At lower energies

## Monday, 14 January 2008

### Astrofisika

Oleh: Arip Nurahman Department of Physics Faculty of Sciences and Mathematics Indonesia University of Education

Astrofisika adalah cabang astronomi yang berhubungan dengan fisika jagad raya, termasuk sifat fisik (luminositas, kepadatan, suhu, dan komposisi kimia) dari objek astronomi seperti planet, bintang, galaksi dan medium antarbintang, dan juga interaksinya. Kosmologi adalah teori astrofisika pada skala terbesar.

Dalam praktek, hampir semua riset astronomi modern mecakup sebagian dari fisika. Nama sekolah program kedoktoran ("Astrofisika" dan "astronomi") di banyak tempat seperti AS seringkali banyak menyangkut sejarah departemen tersebut daripada isi programnya.

Astrofisika pengamatan adalah bidang ilmu yang berurusan dengan pengumpulan, pengukuran, dan analisis kuantitatif dari informasi mengenai benda langit. Bidang ini juga meliputi penjelasan berdasarkan ilmu fisika mengenai instrumentasi astronomi yang digunakan, seperti teleskop, spektrometer, dan detektor yang mengubah informasi tersebut menjadi sinyal.

Informasi yang diperoleh dari pengamatan astrofisika kebanyakan berupa radiasi elektromagnetik. Perbedaan pada rentang panjang gelombang elektromagnetik yang dideteksi membuka cabang-cabang baru dalam astrofisika pengamatan, di antaranya:

* Astronomi inframerah
* Astronomi optik
* Astronomi ultraviolet
* Astronomi sinar-X
* Astronomi sinar gamma

Astrofisika teoretis ialah bidang ilmu yang mencari penjelasan fenomena yang diamati oleh astronom dalam istilah fisika dengan pendekatan teoretis. Dengan tujuan ini, para astrofisikawan teoretis menciptakan dan mengevaluasi model-model dan teori fisika untuk membuat kembali dan memperkirakan observasi. Dalam kebanyakan kasus, mencoba memahami implikasi model fisika tak mudah dan memakan banyak waktu dan usaha.

Astrofisikawan teoretis menggunakan variasi peralatan yang luas yang termasuk model analitik (sebagai contoh, politrope untuk memperkirakan perilaku bintang) dan simulasi bilangan komputasional. Masing-masing memiliki beberapa keuntungan. Umumnya model analitik sebuah proses lebih baik untuk memberikan pengetahuan ke dalam hati apa yang sedang berlangsung. Model numerik dapat mengungkap keberadaan fenomena dan efek yang sebaliknya takkan terlihat.

Para teoris dalam astrofisika berusaha menciptaklan model teoretis dan memperhitungkan konsekuensi pengamatan model-model itu. Bantuan ini memungkinkan pengamat mencari data yang dapat menyangkal model atau bantuan dalam pemilihan antara beberapa model berganti atau yang bertentangan.

Para teoris juga mencoba menghasilkan atau memodifikasi model untuk memperhitungkan data baru. Jika ada ketakkonsekuenan, kecenderungan umum ialah untuk mencoba membuat modifikasi minimal pada model itu untuk mencocokkan data. Dalam beberapa kasus, sejumlah besar data yang tak konsisten yang melebihi waktu bisa menimbulkan tertinggalnya model itu secara keseluruhan.

Dalam komunitas astronomi, secara luas para teoris dikarikaturkan seperti tak pada tempatnya secara mekanis dan tak mujur buat usaha pengamatan. Memiliki seorang teoris di sebuat observatorium mungkin dianggap membawa sial pada observasi yang sedang berjalanan dan menyebabkan mesin rusak atau merasa langit mendung di atas.

Topik-topik yang dipelajari astrofisikawan teoretis termasuk: dinamika bintang; pembentukan galaksi; struktur zat berskala besar di alam semesta; asal sinar kosmik; relativitas umum dan kosmologi. Relativitas astrofisika berjalan sebagai alat untuk mengukur sifat struktur skala besar yang mana gravitasi memainkan peran penting dalam fenomena fisika yang diamati dan berjalan sebagai dasar untuk (astro)fisika lubang hitam dan studi gelombang gravitasi.

Beberapa teori/model yang diterima luas dalam astrofisika termasuk Big Bang, pemompaan kosmik, benda hitam, dan teori fundamental fisika. Teori astrofisika yang memiliki beberapa pendukung namun secara luas nampaknya berbeda dengan observasi ialah kosmologi plasma. Contoh teori astrofisika yang tak diterima luas namun dianggap cukup bisa bertahan untuk karya lanjutan yang pantas ialah MOND.

## Saturday, 12 January 2008

### Voyager Plasma Science Experiment

Voyager Plasma Science Experiment

Solar wind data measured by VOYAGER 2 up through August 30, 2007

Arip nurahman
Department of Physics, Faculty of Sciences and Mathematics
Indonesia University of Education
&
Follower Open Course Ware at MIT-Harvard University, Cambridge. USA.

As of 7 December 2007, Voyager 2 was 7.921 billion miles from Earth (84.293 Astronomical Units from the Sun), well beyond the orbit of Pluto. Voyager 2 is leaving the solar system at 36,000 miles per hour, which is 3.2 AU per year, or 1 light year per 18,600 years.

On the same date, the light travel time from Voyager 2 to Earth was 11 hours, 48 minutes, 41 seconds. Data are returned from the spacecraft at 160 bits per second, using a transmitter with about 25 watts (!) of power.

VOYAGER 2 data up through August 30, 2007
(Daily averages through November 25, 2007)

The outer atmosphere of the Sun expands outward to form the solar wind, with average speeds of 400 km/sec (roughly one million miles per hour). The Plasma Science Experiment on Voyager 2 measures that speed every 192 seconds, and that information is returned to Earth over the Deep Space Net, analyzed, and plotted here within a few days of receipt.
VOYAGER 2 SOLAR WIND SPEED PLOTS

These plots show hourly averages of the solar wind speeds measured by Voyager 2 over the last 500 and 100 days, respectively.
Acquiring the Voyager 1 and 2 Data

Voyager plasma data are available from MIT through the links below or directly through anonymous ftp to space.mit.edu. (cd pub/plasma/vgr). Please look at the README files in each directory before using these data.

Voyager 1: hourly averages and fine resolution data are available by year for 1977-1980.
Voyager 2: hourly averages and fine resolution data are available by year for 1977-present. In addition, a file of daily averages for the entire Voyager 2 mission (de-spiked and then averaged by day) will be updated periodically.
Note that hourly average values for days 2007/240 (28 August 2007) to the present are being re-analyzed.
[go to voyager events page] Show recent events.
VOYAGER 2 SOLAR WIND DYNAMIC PRESSURE

These plots show hourly averages of the solar wind dynamic pressure observed by Voyager 2 over the entire mission (100-day averages) and over the last four years (25-day averages), respectively. These pressures are normalized to 1 AU by multiplying by the square of the spacecraft's distance.
VOYAGER DATA OVERVIEW

These plots show 50-day averages of the solar wind speed, density, and temperature over the life of the Voyager mission (from 1977 to the present), and 1-day averages over the last three years, respectively. The density shown is normalized to Earth by multiplying by the distance to Voyager in AU squared.

## Wednesday, 9 January 2008

### Light and matter united

Light and matter united
Opens the way to new computers and communication systems
By William J. Cromie
Harvard News Office

Arip Nurahman
Department of Physics,
Faculty of Sciences and Mathematics
Indonesia University of Education

Lene Hau has already shaken scientists' beliefs about the nature of things. Albert Einstein and just about every other physicist insisted that light travels 186,000 miles a second in free space, and that it can't be speeded-up or slowed down. But in 1998, Hau, for the first time in history, slowed light to 38 miles an hour, about the speed of rush-hour traffic.

Two years later, she brought light to a complete halt in a cloud of ultracold atoms. Next, she restarted the stalled light without changing any of its characteristics, and sent it on its way. These highly successful experiments brought her a tenured professorship at Harvard University and a \$500,000 MacArthur Foundation award to spend as she pleased.

Now Mallinckrodt Professor of Physics and of Applied Physics, Hau has done it again. She and her team made a light pulse disappear from one cold cloud then retrieved it from another cloud nearby. In the process, light was converted into matter then back into light. For the first time in history, this gives science a way to control light with matter and vice versa.

It's a thing that most scientists never thought was possible. Some colleagues had asked Hau, "Why try that experiment? It can't be done."

In the experiment, a light pulse was slowed to bicycle speed by beaming it into a cold cloud of atoms. The light made a "fingerprint" of itself in the atoms before the experimenters turned it off. Then Hau and her assistants guided that fingerprint into a second clump of cold atoms. And get this - the clumps were not touching and no light passed between them.

"The two atom clouds were separated and had never seen each other before," Hau notes. They were eight-thousandths of an inch apart, a relatively huge distance on the scale of atoms.

The experimenters then nudged the second cloud of atoms with a laser beam, and the atomic imprint was revived as a light pulse. The revived light had all the characteristics present when it entered the first cloud of atomic matter, the same shape and wavelength. The restored light exited the cloud slowly then quickly sped up to its normal 186,000 miles a second.
Communicating by light

Light carries information, so think of information being manipulated in ways that have never before been possible. That information can be stored - put on a shelf, so to speak - retrieved at will, and converted back to light. The retrieved light would contain the same information as the original light, without so much as a period being lost.

Or the information could be changed. "The light waves can be sculpted," is the way Hau puts it. "Then it can be passed on. We have already observed such re-sculpted light in our lab."

A weird thing happens to the light as it enters the cold atomic cloud, called a Bose-Einstein condensate. It becomes squeezed into a space 50 million times smaller. Imagine a light beam 3,200 feet (one kilometer) long, loaded with information, that now is only a hair width in length but still encodes as much information.

From there it becomes easier to imagine new types of computers and communications systems - smaller, faster, more reliable, and tamper-proof.

Atoms at room temperature move in a random, chaotic way. But when chilled in a vacuum to about 460 degrees below zero Fahrenheit, under certain conditions millions of atoms lock together and behave as a single mass. When a laser beam enters such a condensate, the light leaves an imprint on a portion of the atoms. That imprint moves like a wave through the cloud and exits at a speed of about 700 feet per hour. This wave of matter will keep going and enter another nearby ultracold condensate. That's how light moves darkly from one cloud to another in Hau's laboratory.

This invisible wave of matter keeps going unless it's stopped in the second cloud with another laser beam, after which it can be revived as light again.

Atoms in matter waves exist in slightly different energy levels and states than atoms in the clouds they move through. These energy states match the shape and phase of the original light pulse. To make a long story short, information in this form can be made absolutely tamper proof. Personal information would be perfectly safe.

Such a light-to-matter, matter-to-light system "is a wonderful thing to wrap your brain around," Hau muses.

Details of the experiments appear as the cover story of the Feb. 8 issue of Nature. Authors of the report include graduate student Naomi Ginsberg, postdoctoral fellow Sean Garner, and Hau.
In a practical manner

You won't see a light-matter converter flashing away in a factory, business, or mall anytime soon. Despite all the intriguing possibilities, "there are no immediate practical uses," Hau admits.

However, she has no doubt that practical systems will come. And when they do, they will look completely different from anything we are familiar with today. They won't need a lot of wires and electronics. "Instead of light shining through optical fibers into boxes full of wires and semiconductor chips, intact data, messages, and images will be read directly from the light," Hau imagines.

Creating those ultracold atomic clouds in a factory, office, or recreation room will be a problem, but one she believes can be solved. "The atomic clouds we use in our lab are only a tenth of a millimeter (0.004 inch) long," she points out. "Such atom clouds can be kept in small containers, not all of the equipment has to be so cold. Most likely, a practical system designed by engineers will look totally unlike the setup we have in our lab today."

There are no "maybes" in Hau's voice. She is coolly confident that light-to-matter communication networks, codes, clocks, and guidance systems can be made part of daily life. If you doubt her, remember she is the person who stopped light, converted it to matter, carried it around, and transformed it back to light.

## Tuesday, 8 January 2008

### Nuklir Indonesia dan Dunia

Nuklir Indonesia dan Dunia,

Arip Nurahman
Department of Physic Faculty of Sciences and Mathematics
Indonesia University of Education

Pembangunan instalasi reaktor nuklir sebagai pembangkit listrik masih merupakan sebuah wacana yang menciptakan geliat dalam kehidupan masyarakat di Indonesia. Penerimaan masyarakat stagnan dalam tahap antiklimaks terhadap adanya reaktor nuklir di Indonesia.

Paradigma nuklir dalam benak masyarakat Indonesia lekat dengan terorisme atau senjata pemusnah massal yang sangat berbahaya. Seiring melonjaknya populasi manusia, maka kebutuhan energi untuk keberlangsungan hidup manusia itu menjadi alasan pokok untuk menggunakan energi nuklir. Di sisi lain, bukanlah hal yang mudah untuk merumuskan aktualisasi diri nuklir sebagai sumber energi alternatif yang ramah lingkungan untuk menghadapi perubahan iklim yang telah menerpa seluruh belahan dunia.

reaktor

Pintu masuk nuklir

Tahun 1973, negara-negara Timur Tengah melakukan embargo minyak bumi yang mengakibatkan terjadinya krisis energi dan melonjaknya harga minyak bumi OPEC. Peristiwa ini telah membuka mata masyarakat dunia untuk mengurangi esensi penggunaan minyak bumi sebagai energi utama. Kemudian muncul rasa takut masyarakat dunia akan ketersediaan energi di masa depan. Layaknya kuda yang berlari kencang akibat dicambuk oleh sang kusir, beberapa belahan negara di dunia melakukan berbagai penelitian untuk mengeksplorasi sumber-sumber energi alternatif yang masih melimpah di alam. Berbagai sumber energi alternatif seperti energi matahari, angin, batubara,biomassa, air, dan nuklir menjadi proyek terdepan dalam penelitian pada saat itu [Spurgeon, 1987].

Pada awalnya, berbagai penelitian diatas menjadikan aspek ekonomi sebagai entitas utamanya. Namun pada tanggal 28 Maret 1979 terjadi kecelakaan reaktor nuklir yang relatif kecil di Three Mile Island (TMI), AS, yang mengakibatkan reaktor terlalu panas dan akhirnya meleleh (meltdown reactor). Sejak itu, kesadaran masyarakat dunia untuk menciptakan suatu dunia dengan lingkungan yang bersih dan terbentuknya pembangunan yang berkelanjutan mulai terbuka.

Pertanyaannya, apa yang dilakukan oleh negara-negara maju yang sedang mengembangkan teknologi nuklirnya setelah kejadian ini? Mereka menyatakan bahwa akan berusaha menciptakan teknologi nuklir yang lebih baik dan aman. Bahkan Uni Sovyet menyatakan, bahwa kecelakaan ini justru akan menjadi batu penjuru untuk memulai industri nuklir yang baru dan lebih aman. Dengan kata lain, kecelakaan ini hanya sedikit menunda perkembangan teknologi nuklir dunia dan dalam waktu bersamaan menegaskan bahwa segi keamanan manusia adalah pokok terdepan dalam rancangan instalasi sebuah reaktor nuklir. Hasilnya, empat negara maju diatas merupakan negara terdepan dalam bidang teknologi nuklir. Data tanggal 8 Agustus 2007 menunjukan, AS memiliki 104 reaktor, Perancis 59 reaktor, Jepang 55 reaktor, dan Rusia 31 reaktor nuklir yang rutin beroperasi setiap harinya untuk menyuplai energi listrik. Bahkan 76,4% energi listrik di Perancis diperoleh dari energi nuklir. Secara implisit, kecelakaan di Chernobyl telah membawa pengaruh positif terhadap keseluruhan industri nuklir.

Implementasi nuklir di Indonesia

Sejak tahun 1987, pemerintah Indonesia telah mengembangkan program persiapan industri nuklir di kawasan Pusat Penelitian Ilmu Pengetahuan dan Teknologi (Puspiptek), Serpong, melalui pembangunan berbagai jenis instalasi nuklir. Tetapi kegiatan nuklir di Indonesia hingga saat ini belum mengalami kemajuan yang signifikan. Saat ini industri nuklir di Indonesia masih terbatas pada riset dan aplikasi radiasi serta radioisotop dalam dunia kedokteran. Dengan kata lain, Indonesia belum memanfaatkan teknologi nuklir sebagai pembangkit energi listrik yang efisien.

Saat ini, Indonesia masih mengandalkan batu bara sebagai energi alternatif yang utama selain minyak bumi. Pemakaian batu bara untuk suatu PLTU memang memenuhi faktor ekonomi, karena biaya operasionalnya memang murah. Tetapi dibalik itu terdapat bahaya laten seperti gas-gas polutan (SO2, CO2, dan NOX) yang dihasilkan dari proses pembakaran batu bara sebagai pembangkit energi.

PLTN merupakan solusi yang tepat untuk memenuhi kebutuhan energi di Indonesia. Karena jika ditinjau dari besarnya energi, 1 kg bahan bakar nuklir U235 dapat melepaskan energi sebesar 2,5 Terra Joule (1 Terra Joule = 1012 W.s) energi ini setara dengan pembakaran 2,4 juta kg batu bara tanpa menimbulkan emisi gas-gas polutan yang berbahaya bagi kehidupan manusia. Dengan energi sebesar ini, 10% kebutuhan energi listrik Jawa-Bali dapat terpenuhi kurang lebih selama 3 tahun tanpa henti.

Dalam pandangan global, energi nuklir tidak mungkin hilang dari dunia ini, sampai suatu saat ditemukan energi alternatif baru yang lebih aman dan ekonomis, nuklir tetap memegang peranan penting dalam bidang energi. Hanya sekarang mampukah bangsa ini mengundangnya untuk mencegah krisis energi? Jawabannya ada dalam hati tiap masyarakat Indonesia.

## Friday, 4 January 2008

### Superstring Theory

Superstring Theory

By:
Arip Nurahman
Department of Physics
Faculty of Sciences and Mathematics, Indonesia University of Education

and

Follower Open Course Ware at Massachusetts Institute of Technology
Cambridge, USA
Department of Physics
http://web.mit.edu/physics/
http://ocw.mit.edu/OcwWeb/Physics/index.htm
&
Aeronautics and Astronautics Engineering
http://web.mit.edu/aeroastro/www/
http://ocw.mit.edu/OcwWeb/Aeronautics-and-Astronautics/index.htm

Basics

So what is string theory? For that matter, what the heck are elementary particles? If this all sounds totally confusing, try this section first.

 Experiment What progress are physicists making towards experimental tests of string theory predictions? Mathematics What kinds of math do string theorists use and why? And how has string theory changed mathematics? Black Holes Personal safety issues aside, when black holes are tied up in strings, they get even more interesting. Cosmology Was there a String Bang before the Big Bang, or did the Universe simply unwind? History Find out how string theory outlasted the Vietnam War, Mrs. Thatcher and grunge music, in our Timeline section People So who are the people who work on string theory? Check them out in our People section. Links Send us email! Sign our guestbook! Here are a few links to our sympathizers, co-marketers and even the competition. Theatre Now playing in the String Theatre: a Real Audio physics colloquium by Prof. John Schwarz. Bookstore Looking for books on string theory or other topics in modern theoretical physics? Forum Discuss string theory and the legacy of Albert Einstein in our community forum.

Abstract

Superstring theory is an attempt to explain all of the particles and fundamental forces of nature in one theory by modelling them as vibrations of tiny supersymmetric strings. It is considered one of the most promising candidate theories of quantum gravity. Superstring theory is a shorthand for supersymmetric string theory because unlike bosonic string theory, it is the version of string theory that incorporates fermions and supersymmetry.

## Background

The deepest problem in theoretical physics is harmonizing the theory of general relativity, which describes gravitation and applies to large-scale structures (stars, galaxies, super clusters), with quantum mechanics, which describes the other three fundamental forces acting on the atomic scale.

The development of a quantum field theory of a force invariably results in infinite (and therefore useless) probabilities. Physicists have developed mathematical techniques (renormalization) to eliminate these infinities which work for three of the four fundamental forces – electromagnetic, strong nuclear and weak nuclear forces - but not for gravity. The development of a quantum theory of gravity must therefore come about by different means than those used for the other forces.

### Basic idea

The basic idea is that the fundamental constituents of reality are strings of the Planck length (about 10−33 cm) which vibrate at resonant frequencies. Every string in theory has a unique resonance, or harmonic. Different harmonics determine different fundamental forces. The tension in a string is on the order of the Planck force (1044 newtons). The graviton (the proposed messenger particle of the gravitational force), for example, is predicted by the theory to be a string with wave amplitude zero. Another key insight provided by the theory is that no measurable differences can be detected between strings that wrap around dimensions smaller than themselves and those that move along larger dimensions (i.e., effects in a dimension of size R equal those whose size is 1/R). Singularities are avoided because the observed consequences of "Big Crunches" never reach zero size. In fact, should the universe begin a "big crunch" sort of process, string theory dictates that the universe could never be smaller than the size of a string, at which point it would actually begin expanding.

String theory
Superstring theory
This box: view talk edit

## Extra dimensions

Our physical space is observed to have only three large dimensions and—taken together with time as the fourth dimension—a physical theory must take this into account. However, nothing prevents a theory from including more than 4 dimensions, per se. In the case of string theory, consistency requires spacetime to have 10, 11 or 26 dimensions. The conflict between observation and theory is resolved by making the unobserved dimensions compactified.

Our minds have difficulty visualizing higher dimensions because we can only move in three spatial dimensions. One way of dealing with this limitation is not to try to visualize higher dimensions at all, but just to think of them as extra numbers in the equations that describe the way the world works. This opens the question of whether these 'extra numbers' can be investigated directly in any experiment (which must show different results in 1, 2, or 2+1 dimensions to a human scientist). This, in turn, raises the question of whether models that rely on such abstract modelling (and potentially impossibly huge experimental apparatus) can be considered scientific. Six-dimensional Calabi-Yau shapes can account for the additional dimensions required by superstring theory. The theory states that every point in space (or whatever we had previously considered a point) is in fact a very small manifold where each extra dimension has a size on the order of the Planck length.

Superstring theory is not the first theory to propose extra spatial dimensions; the Kaluza-Klein theory had done so previously. Modern string theory relies on the mathematics of folds, knots, and topology, which were largely developed after Kaluza and Klein, and has made physical theories relying on extra dimensions much more credible.

Unsolved problems in physics: Is string theory, superstring theory, or M-theory, or some other variant on this theme, a step on the road to a "theory of everything," or just a blind alley?

## References

1. ^ M. J. Duff, James T. Liu and R. Minasian Eleven Dimensional Origin of String/String Duality: A One Loop Test Center for Theoretical Physics, Department of Physics, Texas A&M University
2. ^ Polchinski, Joseph (1998). String Theory, Cambridge University Press.
3. ^ a b H. Nastase The RHIC fireball as a dual black hole BROWN-HET-1439, ArXiv: hep-th/0501068, January 2005,
4. ^ a b H. Nastase More on the RHIC fireball and dual black holes BROWN-HET-1466, ArXiv: hep-th/0603176, March 2006,
5. ^ a b H. Liu, K. Rajagopal, U. A. Wiedemann An AdS/CFT Calculation of Screening in a Hot Wind, MIT-CTP-3757, July 2006,
6. ^ a b H. Liu, K. Rajagopal, U. A. Wiedemann Calculating the Jet Quenching Parameter from AdS/CFT, Phys.Rev.Lett.97:182301,2006
7. ^ To compare, the size of an atom is roughly 10-10 m and the size of a proton is 10-15 m. To imagine the Planck length: you can stretch along the diameter of an atom the same number of strings as the number of atoms you can line up to Proxima Centauri (the nearest star to Earth after the Sun). The tension of a string (8.9×1042 newtons) is about 1041 times the tension of an average piano string (735 newtons).
8. ^ S. James Gates, Jr., Ph.D., Superstring Theory: The DNA of Reality "Lecture 23 - Can I Have that Extra Dimension in the Window?", 0:04:54, 0:21:00.
9. ^ Simeon Hellerman, Ian Swanson: "Dimension-changing exact solutions of string theory". e-Print: hep-th/0612051; Ofer Aharony, Eva Silverstein: "Supercritical stability, transitions and (pseudo)tachyons". Physical Review D 75:046003, 2007. e-Print: hep-th/0612031
10. ^ The calculation of the number of dimensions can be circumvented by adding a degree of freedom which compensates for the "missing" quantum fluctuations. However, this degree of freedom behaves similar to spacetime dimensions only in some aspects, and the produced theory is not Lorentz invariant, and has other characteristics which don't appear in nature. This is known as the linear dilaton or non-critical string.
11. ^ "Quantum Geometry of Bosonic Strings – Revisited"
12. ^ Aharony, O.; S.S. Gubser, J. Maldacena, H. Ooguri, Y. Oz (2000). "Large N Field Theories, String Theory and Gravity" (subscription required). Phys. Rept. 323: 183–386. doi:10.1016/S0370-1573(99)00083-6. . For other examples see: [1]
13. ^ For example: T. Sakai and S. Sugimoto, Low energy hadron physics in holographic QCD, Prog.Theor.Phys.113:843-882,2005, ArXiv: hep-th/0412141, December 2004
14. ^ See for example Recent Results of the MILC research program, taken from the MILC Collaboration homepage
15. ^ David Gross, Perspectives, String Theory: Achievements and Perspectives - A conference
16. ^ M. R. Douglas,Are There Testable Predictions of String Theory? February 2007 Texas A&M
17. ^ a b Peter Woit's Not Even Wrong weblog
18. ^ a b Lee Smolin's The Trouble With Physics webpage
19. ^ John Baez and responses on the group weblog The n-Category Cafe
20. ^ John Baez weblog
21. ^ Unstrung: The New Yorker
22. ^ See e.g. E. Kiritsis, String theory in a nutshell. Introduction to Modern String theory, Princeton University Press, Princeton, N.Y. (2007)
23. ^ a b c S. Kachru, R. Kallosh, A. Linde and S. P. Trivedi, de Sitter Vacua in String Theory, Phys.Rev.D68:046005,2003
24. ^ P. Woit (Columbia University) String theory: An Evaluation,February 2001, e-Print: physics/0102051
25. ^ P. Woit, Is String Theory Testable? INFN Rome March 2007
26. ^ Prominent critics include Philip Anderson ("string theory is the first science in hundreds of years to be pursued in pre-Baconian fashion, without any adequate experimental guidance", New York Times, 4 January 2005), Sheldon Glashow ("there ain't no experiment that could be done nor is there any observation that could be made that would say, `You guys are wrong.' The theory is safe, permanently safe", NOVA interview), Lawrence Krauss ("String theory [is] yet to have any real successes in explaining or predicting anything measurable", New York Times, 8 November 2005), Peter Woit (see his blog, article and book "Not Even Wrong", ISBN 0-224-07605-1) and Carlo Rovelli (see his Dialog on Quantum Gravity)
27. ^ N. Arkani-Hamed, S. Dimopoulos and S. Kachru, Predictive Landscapes and New Physics at a TeV, SLAC-PUB-10928, HUTP-05-A0001, SU-ITP-04-44, January 2005
28. ^ L. Susskind The Anthropic Landscape of String Theory, February 2003
29. ^ S. James Gates, Jr., Ph.D., Superstring Theory: The DNA of Reality "Lecture 21 - Can 4D Forces (without Gravity) Love Strings?", 0:26:06-0:26:21, cf. 0:24:05-0:26-24.
30. ^ Although two decades ago, it was the other way around.
31. ^ Idem, "Lecture 19 - Do-See-Do and Swing your Superpartner Part II" 0:16:05-0:24:29.
32. ^ Idem, Lecture 21, 0:20:10-0:21:20.