A Unified Physics By 2050 Part III

 

"Kasih hanya akan datang kepada mereka yang mengenal dirinya dan Tuhannya"

~arip~

A Unified Physics by 2050?

Experiments at CERN and elsewhere should let us complete the Standard Model of particle physics, but a unified theory of all forces will probably require radically new ideas.

By: Prof. Steven Weinberg, Ph.D.

Suppressed Interactions 

What then? There is virtually no chance that we will be able to do experiments involving processes at particle energies like 10^16 GeV. With present technology the diameter of an accelerator is proportional to the energy given to the accelerated particles. To accelerate particles to an energy of 10^16 GeV would require an accelerator a few light-years across. Even if someone found some other way to concentrate macroscopic amounts of energy on a single particle, the rates of interesting processes at these energies would be too slow to yield useful information. 

But even though we cannot study processes at energies like 10^16 GeV directly, there is a very good chance that these processes produce effects at accessible energies that can be recognized experimentally because they go beyond anything allowed by the Standard Model. The Standard Model is a quantum field theory of a special kind, one that is "renormalizable." This term goes back to the 1940s, when physicists were learning how to use the first quantum field theories to calculate small shifts of atomic energy levels. 

They found that calculations using quantum field theory kept producing infinite quantities, a situation that usually means a theory is badly flawed or is being pushed beyond its limits of validity. In time, they found a way to deal with the infinite quantities by absorbing them into a redefinition, or "renormalization," of just a few physical constants, such as the charge and mass of the electron. (The minimum version of the Standard Model, with just one scalar particle, has 18 of these constants.) Theories in which this procedure worked were called renormalizable and had a simpler structure than nonrenormalizable theories.

Image: Johnny Johnson

THE HIERARCHY PROBLEM is a measure of our ignorance. Experiments (yellow band) have probed up to an energy of about 200 GeV and have revealed an assortment of particle masses (red) and interaction energy scales (green) that are remarkably well described by the Standard Model. The puzzle is the vast gap to two further energy scales, that of strong-electroweak unification near 10^16 GeV and the Planck scale, characteristic of quantum gravity, around 10^18 GeV.

It is this simple renormalizable structure of the Standard Model that has let us derive specific quantitative predictions for experimental results, predictions whose success has confirmed the validity of the theory. In particular, the principle of renormalizability, together with various symmetry principles of the Standard Model, rules out unobserved processes such as the decay of isolated protons and forbids the neutrinos from having masses. Physicists commonly used to believe that for a quantum field theory to have any validity, it had to be renormalizable. This requirement was a powerful guide to theorists in formulating the Standard Model. It was terribly disturbing that it seemed impossible, for fundamental reasons, to formulate a renormalizable quantum field theory of gravitation. 


Today our perspective has changed. Particle physics theories look different depending on the energy of the processes and reactions being considered. Forces produced by exchange of a very massive particle will typically be extremely weak at energies that are low compared with that mass. Other effects can be similarly suppressed, so that at low energies one has what is known as an effective field theory, in which these interactions are negligible. Theorists have realized that any fundamental quantum theory that is consistent with the special theory of relativity will look like a renormalizable quantum field theory at low energies. But although the infinities are still canceled, these effective theories do not have the simple structure of theories that are renormalizable in the classic sense. Additional complicated interactions are present; instead of being completely excluded, they are just highly suppressed below some characteristic energy scale.

Image: Slim Films

WHAT COMES NEXT? There are several possibilities for the unified physics that lies beyond the Standard Model. Technicolor models (a) introduce new interactions analogous to the "color" force that binds quarks. Accompanying the interactions are new generations of particles unlike the three known generations. Supersymmetry (b) relates fermions to bosons and adds the supersymmetric partners of each known particle to the model. M-theory and string theory (c) recast the entire model in terms of new entities such as tiny strings, loops and membranes that behave like particles at low energies.

Gravitation itself is just such a suppressed nonrenormalizable interaction. It is from its strength (or rather weakness) at low energies that we infer that its fundamental energy scale is roughly 10 ¹⁸ GeV. Another suppressed nonrenormalizable interaction would make the proton unstable, with a half-life in the range of 10 ³¹ to 10 ³⁴ years, which might be too slow to be observed even by 2050 [see my article "The Decay of the Proton"; Scientific American, June 1981]. Yet another suppressed nonrenormalizable interaction would give the neutrinos tiny masses, about 10^-11 GeV. There is already some evidence for neutrino masses of this order; this should be settled well before 2050. 

Observations of this kind will yield valuable clues to the unified theory of all forces, but the discovery of this theory will probably not be possible without radically new ideas. Some promising ones are already in circulation. There are five different theories of tiny one-dimensional entities known as strings, which in their different modes of vibration appear at low energy as various kinds of particles and apparently furnish perfectly finite theories of gravitation and other forces in 10 space-time dimensions. 

Of course, we do not live in 10 dimensions, but it is plausible that six of these dimensions could be rolled up so tightly that they could not be observed in processes at energies below 10 ¹⁶ GeV per particle. Evidence has appeared in the past few years that these five string theories (and also a quantum field theory in 11 dimensions) are all versions of a single fundamental theory (sometimes called M-theory) that apply under different approximations ["The Theory Formerly Known as Strings"]. But no one knows how to write down the equations of this theory.

Further Reading:

1. Unified Theories of Elementary-Particle Interaction. Steven Weinberg in Scientific American, Vol. 231, No. 1, pages 50-59; July 1974.

2. Dreams of a Final Theory. Steven Weinberg. Pantheon Books, 1992.

3. Reflections on the Fate of Spacetime. Edward Witten in Physics Today, Vol. 49, No. 4, pages 24-30; April 1996.

4. Duality, Spacetime and Quantum Mechanics. Edward Witten in Physics Today, Vol. 50, No. 5, pages 28-33; May 1997.

5. The Elegant Universe: Superstrings, Hidden Dimensions, and the Quest for the Ultimate Theory. Brian Greene. W. W. Norton,1999.

http://hera.ph1.uni-koeln.de/~heintzma/Weinberg/Weinberg.htm 

The Author
 

STEVEN WEINBERG is head of the Theory Group at the University of Texas at Austin and a member of its physics and astronomy departments. His work in elementary particle physics has been honored with numerous prizes and awards, including the Nobel Prize for Physics in 1979 and the National Medal of Science in 1991. 

The third volume (Supersymmetry) of his treatise The Quantum Theory of Fields is out from Cambridge University Press. The second volume (Modern Applications) was hailed as being "unmatched by any other book on quantum field theory for its depth, generality and definitive character."

Beyond Superstring Theory

 

 

It is commonly believed that the 5 superstring theories are approximated to a theory in higher dimensions possibly involving membranes. Unfortunately because the action for this involves quartic terms and higher so is not Gaussian the functional integrals are very difficult to solve and so this has confounded the top theoretical physicists. Edward Witten has popularised the concept of a theory in 11 dimensions M-Theory involving membranes interpolating from the known symmetries of superstring theory.

It may turn out that there exist membrane models or other non-membrane models in higher dimensions which may become acceptable when new unknown symmetries of nature are found, such as noncommutative geometry for example. It is thought, however, that 16 is probably the maximum since O(16) is a maximal subgroup of E8 the largest exceptional lie group and also is more than large enough to contain the Standard Model. Quartic integrals of the non-functional kind are easier to solve so there is hope for the future. This is the series solution which is always convergent when a is non-zero and negative:

In the case of membranes the series would correspond to sums of various membrane interactions that are not seen in string theory.

Compactification

 

 

Investigating theories of higher dimensions often involves looking at the 10 dimensional superstring theory and interpreting some of the more obscure results in terms of compactified dimensions. For example D-branes are seen as compactified membranes from 11D M-Theory.

Theories of higher dimensions such as 12D F-theory and beyond will produce other effects such as gauge terms higher than U(1). The components of the extra vector fields (A) in the D-brane actions can be thought of as extra coordinates (X) in disguise. However, the known symmetries including supersymmetry currently restrict the spinors to have 32-components which limits the number of dimensions to 11 (or 12 if you include two time dimensions.) Some commentators (e.g. John Baez et al) have speculated that the exceptional lie groups E₆, E₇ and E₈ having maximum orthogonal subgroups O(10), O(12) and O(16) may be related to theories in 10, 12 and 16 dimensions; 10 dimensions corresponding to string theory and the 12 and 16 dimensional theories being yet undiscovered but would be theories bases on 3-branes and 7-branes respectively. However this is a minority view within the string community.

Since E₇ is some sense F₄ quaternified and E₈ is F₄ octonified, then the 12 and 16 dimensional theories, if they did exist, may involve the noncommutative geometry based on the quaternions and octonions respectively. From the above discussion it can be seen that physicists have many ideas for to extend superstring theory beyond the current 10 dimensional theory but so far none have been successful.

Kac-Moody algebras

 

Since strings can have an infinite number of modes, the symmetry used to describe string theory is based on infinite dimensional Lie algebras. Some Kac-Moody algebras that have been considered as symmetries for M-Theory have been E₁₀ and E₁₁ and their supersymmetric extensions.

Levels of magnification:

1. Macroscopic level - Matter
2. Molecular level
3. Atomic level - Protons, neutrons, and electrons
4. Subatomic level - Electron
5. Subatomic level - Quarks
6. String level

Astrobiology and Space Exploration

"Mungkin saja kehidupan lain di luar bumi sana sedang menunggu kita untuk dikunjungi"

~Arip~

3. From Astrochemistry to Astrobiology

Stanford University Course

In the Stanford Astrobiology Course, our lectures follow a more or less linear path from the Big Bang all the way to the development of complex life and, finally, space exploration. It is truly amazing how evolutionary principles have operated at the macro, and micro, level ever since the birth of the universe we reside in today.

Physics, research, experimentation, astronomy, extraterrestrial life, planets, asteroids, cosmology, measurements, data, innovation, development, history, science, telescopes, observations, theories, predictions, telescopes, instruments, light, expansion.

 A syllabus for the Winter, 2010 Astrobiology Course can be downloaded here.

The Big Bang created the physical universe. Of course life is part of this physical universe, but the immediate building blocks of life are chemicals. Before the Big Bang, words such as “time” had no meaning, but even in the first few minutes there could be no chemistry since there were no atoms. The nuclei of some of the lighter elements formed within minutes, atoms some time later, and elements heavier than lithium were forged in the supernovae of stars. Thus, we are primarily star dust, although the hydrogen atom you drink tonight may be nearly as old as the Big Bang.

But living organisms are more than a collection of atoms. They are a cauldron of molecules in a solvent. For life on earth, that solvent is water. The building blocks of chemical compounds had to form other molecules as well, especially ones based on carbon. Where could these compounds have been formed? Were they formed on earth or transported from elsewhere?

Most stunning are the recent discoveries in astrochemistry showing that the organic compounds that make up life on earth may possibly be THE language of the universe. In September 2010, the NASA Ames IR Spectroscopic Database was released, along with tools to access it. See the press release.

Recommended Reading

“Chemical Evolution across Space and Time: From The Big Bang to Prebiotic Chemistry”  Eds Lori Zaikowski and Jon Friedrich; Published by American Chemical Society, Wash. DC ISBN 978-0-8412-0

Amallondalla’s is chapter 5: ” Chemical Evolution in the Interstellar Medium:  Feedstock of Solar Systems.
The next volume is entitled:

“Chemical Evolution across Space and Time: From Origins of Life to Modern Society”  Eds Lori Zaikowski and Jon Friedrich; Published by American Chemical Society, Wash.

This Scientific American article  is geared to the general scientifically literate audience:  ”Life’s Far-Flung Raw Materials”,

Bernstein, Sandford, Allamandola, Scientific American, July 1999


"The space effort is very simply a continuation of the expansion of ecological range, which has been occurring at an accelerating rate throughout the evolutionary history of Man..."
~Ward J. Haas, "Biological Significance of the Space Effort," in Annals of the New York Academy of Science, 1966 ~

Below you will find a list of recommended resources. If you would like to learn more about the Big Bang, check out these books, videos, and articles.

Further Resources:
Singh, Simon. “The Big Bang: The Origin of the Universe”. New York: Fourth Estate, 2005.
Riordan, Michael and William A. Zajc. “The First Few Microseconds”. Scientific American Magazine: May, 2006.
Roos, Matts. “Expansion of the Universe – Standard Big Bang Model”. UNESCO Encyclopedia of Life Supporting Systems, 14 Feb. 2008.

Sumber:
1. Stanford University
2. NASA

Ucapan Terima Kasih:

1. Bapak. Prof. Dr. Ing. H. B. J. Habibie.

2. Departemen Pendidikan Nasional

3. Kementrian Riset dan Teknologi

4. Lembaga Penerbangan dan Antariksa Nasional


Disusun Ulang Oleh:

Arip Nurahman

Department of Physics, Indonesia University of Education

&

Follower Open Course Ware at MIT-Harvard University, Cambridge.USA.

Semoga Bermanfaat dan Terima Kasih