Light and matter united

Light and matter united

Opens the way to new computers and communication systems

By William J. Cromie

Harvard News Office

Edited and Add By:

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.

Nuklir Indonesia dan Dunia

Nuklir Indonesia dan Dunia,

Edited and Add By:
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.

Beberapa tahun kemudian, negara-negara maju seperti AS, Perancis, Jepang dan Rusia tengah beradu cepat guna menciptakan reaktor nuklir yang aman dan memiliki efisiensi yang tinggi. Kemudian pada tanggal 25-26 April 1986 terjadi kecelakaan terbesar dalam sejarah reaktor nuklir dunia yang terjadi di Chernobyl, Uni Sovyet (sekarang Rusia). Dalam kecelakaan ini 135000 jiwa terlibat secara langsung, 24403 jiwa diantaranya divonis terkena radiasi yang cukup berat dan 31 jiwa meninggal. Peristiwa ini menjadi titik balik dari era keemasan teknologi nuklir pada saat itu. Dalam survei yang dilakukan beberapa tahun setelah kejadian ini, ditemukan bahwa pihak oposisi telah meningkat dari 26% menjadi 42% dan pihak pendukung telah menurun dari 57% menjadi 49%. Secara tidak langsung, kejadian ini mengakibatkan paradigma masyarakat dunia terhadap teknologi nuklir merupakan sesuatu yang tidak menghargai nilai kemanusiaan.

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.

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 [hide]Theory String theory Superstrings Bosonic string theory M-theory (simplified) Type I string · Type II string Heterotic string String field theory Holographic principle [show]Concepts Strings · Branes Calabi–Yau manifold Kac–Moody algebra D-brane E8 Lie group [show]Related Topics Supersymmetry Supergravity Quantum gravity [show]Scientists Veneziano · Susskind · Greene · Ramond · Schwarz · Mandelstam · Scherk · Polyakov · Green · Witten · Gross · Polchinski · Vafa · Sen · Townsend · Duff · Maldacena · Kaku

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Extra dimensions

See also: Why does consistency require 10 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. http://arxiv.org/abs/hep-th/9905111. . 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.