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number 04.             June 15, 1996

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a forum for virtual meetings of scientists and students involved in a research activity on:
THE SOLID STATE PHYSICS AND SUPERCONDUCTIVITY

Editors: Dr. Zbigniew J.Koziol, (Editor-in-Chief) webex@ra.isisnet.com, WebExperts Inc.
Dr. Michal Spalinski, Michal.Spalinski@fuw.edu.pl, Institute of Theoretical Physics, Warsaw University
Copyright (C) 1996 by Zbigniew Koziol.
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IN THIS ISSUE:

LETTER FROM THE EDITOR
TRANSGRESSING BOUNDARIES AND TRANSFORMATIVE HERMENEUTICS OF QUANTUM GRAVITY
BOSE-EINSTEIN CONDENSATION
CANADIAN INTERNET AWARDS

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LETTER FROM THE EDITOR

Dear Readers of Virtual Physics,

As usual with every new issue of Virtual Physics published, we wish to welcome all new readers with a hope that they will become interested in this journal.

This time, please have a brake from the stricte physical material. A bit of philosophy of science emerges from the articles found on the Usenet discussion groups and related to the recent publication of Allan Sokal. After reading my compilation on that subject, I am sure you will find the second article, a very brief description of the last-year experiments with Bose-Einstein Condensation, refreshing and interesting.

Sincerely yours,
Zbigniew Koziol

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TRANSGRESSING BOUNDARIES AND TRANSFORMATIVE HERMENEUTICS OF QUANTUM GRAVITY

Many of you, especialy in North America, know already this story, aren't you? Let me provide this compilation for other readers of Virtual Physics.

After NAS SCIENCE NEWS: Vol. III, issue 5 of 22 May 1996:

NYU physicist Alan Sokal's clever article -- "Transgressing the Boundaries: toward a Transformative Hermeneutics of Quantum Gravity"--that the editors of Social Text (circulation 800) included in their most recent edition on the "science wars," has been making news far beyond the pages of the May/June Lingua Franca in which the parody was initially exposed. Last Friday, 17 May 1996, the hoax was released as an Associate Press Story; on Saturday it was front page news in The New York Times (by Janny Scott; Copyright 1996 The New York Times Company ):

The dispute over the article--which was read by several editors at the journal before it was published--goes to the heart of the public debate over left-wing scholarship, and particularly over the belief that social, cultural and political conditions influence and may even determine knowledge and ideas about what is truth.

In this case, Sokal, 41, intended to attack some of the work of social scientists and humanists in the field of cultural studies, the exploration of culture--and, in recent years, science--for coded ideological meaning.

In a way, this is one more skirmish in the culture wars, the battles over multiculturalism and college curriculums and whether there is a single objective truth or just many differing points of view.

Conservatives have argued that there is truth, or at least an approach to truth, and that scholars have a responsibility to pursue it. They have accused the academic left of debasing scholarship for political ends.

"While my method was satirical, my motivation is utterly serious," Sokal wrote in a separate article in the current issue of the magazine Lingua Franca, in which he revealed the hoax and detailed his "intellectual and political" motivations.

"What concerns me is the proliferation, not just of nonsense and sloppy thinking per se, but of a particular kind of nonsense and sloppy thinking: one that denies the existence of objective realities," he wrote in Lingua Franca.

Here is some sparkled reaction spotted at the Usenet group sci.physics, at the end of May 1996. It is certainly presented in a distorted manner (though not intentionally). Original articles still might be available at some newsgroups, like sci.physics, sci.philosophy.meta, sci.philosophy.tech, and at their repositories.

From Michael Tobis, tobis@scram.ssec.wisc.edu

[ ... ] My concern is that the weaponry of relativism is only coincidentally and temporarily associated with the rhetoric of freedom and dignity. Less developed versions of the same thing have been used in the Stalinist and Nazi tyrannies. This is a central fact of the history of twentieth century science. In developing a rhetoric of willful uncertainty and confusion (somehow ignoring manifest and spectacular success) and conferring some sort of academic respectability upon it, the relativists are developing a weapon that can and would be used by spectacularly malevolent forces in the process of subverting and eliminating the very sorts of human dignity contemporary proponents believe themselves to be promoting. Ultimately it comes down to the triumph of the ad hominem over the substantive. In that case, it is a trivial matter to move the trusted class from tofu munching bicycle commuting book collecting casual buddhist environmentalist utopians (I have described the class so as to include myself) to gun totin beer guzzlin angry racist tax paranoids. If such people ever get the sort of power they aspire to, they will need a front of intellectual respectability, and the machinery of radical relativism will prove remarkably malleable. [ ... ]

* * *

[ ... ] Of course the process of science should be studied, but for it to be be mocked by people who haven't the slightest understanding of why scientists do what they do, and why the process is so successful, doesn't constitute such a study. Note that the whole movement stems from literary criticism. Of course it is possible to object to the deconstructionist view of the arts as well - that there is no aesthetic save what is projected. Psychological studies (ah, evidence) refute this, showing considerable cross-cultural agreement on what is beautiful and what is ugly. However, the idea that science is text and that its principal (not to say only) message is its cultural context is not merely willfully ignorant and astonishingly stupid, but is also evil and dangerous; more dangerous, I think, than its obvious gooselike silliness leads the scientifically educated observer to immediately suspect.

* * *

[ ... ] Suppose there is a universal truth toward which science is striving. How does this enter into the process of doing science? It enters in by determining the results of the experiments scientists perform. The important thing here is that the experiments have results which are used. Whether these results come from objective reality, divine intervention, or electric signals transmitted to your brain in a mad scientist's lab is completely irrelevant. You can study the process of science anyway.

It's true that, in practice, many of the people who reject an objective reality also reject science in general, so they won't make good science sociologists. But someone who can take a dispassioned view towards science and decide "I'm going to study this sociological event, and frankly I don't care whether it corresponds to any kind of objective reality or not." could be fine.

From Jacques Distler, distler@golem.ph.utexas.edu

[ ... ] To the experimental precisions of the day, Einstein's and Galileo's theories give IDENTICAL predictions. Aristotles' theory gives flagrantly wrong predictions. It is (relatively) easy to eliminate WRONG theories.
But, [ ... ] under the circumstances of the day, it would have been impossible to decide experimentally between Galileo and Einstein (which puts them in a very different class, "right" and "righter", from Aristotle's, "wrong").

If one had to choose between Einstein and Galileo at that time (at the time of Galileo - Editors note), the best one could have done would have been to envoke some extra-empirical principle (Occam's Razor, "elegance", ... ). It is an interesting question to speculate on, but I personally expect that "physicists of the day" would have overwhelmingly chosen Galileo.

Anyone who knows anything about how science works (such as a practicing physicist like yours truly) knows that we make such judgements all the time. And, as practicing scientists, we're very aware that history may prove these judgements wrong (or right, that where the fun comes in!). Nevertheless, we make them because we HAVE to make them in order to proceed.

Historians and Sociologist of Science (the serious ones, not the Andrew Ross's and Stanley Aronowitz's, who are nothing but clowns) spend their time trying to understand HOW we make those judgements, how we decide whether those judgements were right or wrong, in short, how the day-to-day progress of Science WORKS.

Some take a "Social Constructivist" approach. Not surprising; Science is a social activity, and we don't make these judgements in a vacuum. This is not even REMOTELY the same thing as alleging that (to quote that great sage, Andrew Ross) "scientific knowledge is ... not a version of some universal truth that is the same in all times and places." Indeed, it is perfectly compatible with scientists' self-description, that we are producing successively better approximations to just such a universal truth. The issue for the Historian or Sociologist of Science is HOW, not whether, we are getting there.

If you start out with the contention that there IS no "universal truth", that Science is striving towards, then the likelihood that you will come to ANY sensible conclusions about how scientists do what they do is NIL.

If you suplement this nutty epistemology with a near-total (and proud!) ignorance of science, then your chances are . . . (whoops! they were already nil).

Ross, Aronowitz, and their "Fish"y postmodernist friends, in their response to the Sokal hoax, have done much to discredit the discipline of the Sociology of Science.
But then, they were never seriously interested in the subject in the first place. (Anyone who wants to judge their seriousness is invited to check out some of their writing. There is, I'm sure, much more risible stuff in print, but http://zelda.thomson.com/routledge/cst/ross.html and http://zelda.thomson.com/routledge/cst/arnowitz.html will serve well for those too lazy to troop to the library.)

Their interest in Science is political and polemical.
Those who live by the sword . . .

Compiled by Zbigniew Koziol

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BOSE-EINSTEIN CONDENSATION

The Discovery

Last year, three groups: at JILA, a lab run jointly by the National Institute of Standards and Technology and Colorado University, at Rice University, and a group at MIT have observed Bose-Einstein Condensation (BEC) in supercooled, magnetically trapped diluted vapoures of rubidium, lithium and sodium atoms, respectively. A combination of laser cooling and evaporative cooling has been used by all of them in order to achieve the lowest up to day temperatures required.

The Bose-Einstein condensation was first postulated more than 70 years ago by Satyendra Nath Bose and Albert Einstein. This new state of the matter was observed long ago in liquid helium and in superconductors. In semiconductors, pairs of electrons and electron holes, known as excitons, have been observed to form condensates but these last only a few millionths of a second. In liquid helium the condensate is modified by the classical forces between atoms, so the quantum-mechanical effects are smeared out.
A significant step forward was done in June 1995 when a team at the University of Colorado led by Eric A. Cornell and Carl E. Wieman first observed BEC in a dilute atomic gas of 87Rb.

[ Velocity distribution of the cloud of rubidium atoms ] False-color images display the velocity distribution of the cloud of rubidium atoms at (a) just before the appearance of the Bose-Einstein condensate, (b) just after the appearance of the condensate and (c) after further evaporation left a sample of nearly pure condensate. The field of view of each frame is 200 x 270 micrometers, and corresponds to the distance the atoms have moved in about 1/20 of a second. The color corresponds to the number of atoms at each velocity, with red being the fewest and white being the most. Areas appearing white and light blue indicate lower velocities. (published with permission from Colorado University: click on the image to reach the original site)

Unlike liquid helium, the only degenerate boson fluid thus far investigated, the dilute Bose gases are weakly interacting. This allows for large condensate fractions and an exceptionally transparent physical picture of many-body quantum behaviour. Not surprisingly, the quantum gases have intrigued and inspired physicists throughout this century.

There are two kinds of particles in nature: bosons (with integer spin) and fermions (carying a half integral spin). Let us take a hydrogen atom. It consists of a nucleus of only one proton and one electron around this nucleus. The whole system is a boson because the half integral spin of the proton and the electron combine to an integral total spin. Among all the different atoms you can find bosons as well as fermions. If an atom has different isotopes there can even be bosons and fermions among the same atom species.

Atoms are normally considered as particles but, according to quantum mechanics, they also have wave-like properties characterised by the deBroglie wavelength, which is inversely proportional to the atom's momentum. As atoms are cooled they slow down and their deBroglie wavelength increases. At a low enough temperature the wavelength exceeds the inter-particle spacing and the atoms begin to overlap and they become indistinguishable. Then according to Bose statistics the particles "fall" into the lowest quantum state, entering a coherent state (BEC) and the rules of quantum mechanics determine the behaviour of the macroscopic system.

Experiment

Here is how J.T.M. Walraven describes the three stages of the JILA experiment (from an article published in Europhysics News.

A - optical loading, (pre)cooling & polarization;
B - magnetic trapping & evaporative cooling in the absence of light;
C - optical detection.

A - laser cooling stage.
For 300 s, about 107 atoms are gathered from the low-velocity tail of a room-temperature Rb-vapour at some 10-11 mbar into a so-called "dark" magneto-optical trap (MOT), which is most efficient in collecting a large number of atoms by optical forces. The gas is rapidly (pre)cooled in the MOT to about 20 *K and subsequently magnetically polarized in a small magnetic bias field by optical pumping.

B - trapping and cooling.
Polarized atoms are magnetically trapped in a rapidly applied time-orbiting potential (TOP) trap, which consists of a set of coils in anti-Helmholtz configuration with a small, uniform transverse field, rotating at 7.5 kHz, superimposed. The TOP provides an effectively harmonic potential with an axial frequency of about 120 Hz and radial frequency of about 42 Hz. In the, TOP the gas is adiabatically compressed to reach the starting conditions for evaporative cooling at about 90 *K with a number density of about 2x1010cm-3, sufficiently large to have the elastic collision rate dominate over the loss rate in the gas. The evaporation takes 70 s and BEC is achieved with 2x104 atoms at approximately 170 nK. The evaporation is induced by a RF transition to an untrapped state of the atoms at the edge of the sample.

C - optical detection.
At the start of the detection stage the trap is expanded adiabatically to a larger size to allow a fast (destructive) absorption measurement in which the sample is imaged on a CCD camera. The appearance of a diffraction ring marks the growth of a partially resolved structure in the sample. This is consistent with BEC in an inhomogeneous sample, where the condensate is expected to appear as a very small dense gas cloud at the centre of the potential well (see figure). To confirm this interpretation, the momentum distribution in the sample was measured by suddenly switching-off the trap and observing the expanding gas cloud. In this process both isotropic expansion of the (thermal) non-condensate fraction was observed as well as an anisotropic expansion, as is to be expected for a suddenly released anisotropic single quantum state.

Implications

The implications of the dicovery for physics and for society are not yet determined. There are numerous speculations that the BEC state can be used to create the atomic equivalent of lasers. Such lasers could permit the nanoscale sculpture of computer circuitry and perhaps other advances that are currently impossible.
Many intriguing problems await experimental investigation. Most prominent among them are the relation between BEC and superfluidity, the kinetics of BEC, the size and number dependence of the transition, optical properties, dimensionality aspects, the interaction between two condensates, the use of the condensate as a source for a coherent atomic beam, and the differences with respect to Fermi systems.

The subject presents an interesting challenge both theoretically and experimentally. Important role in the condesation process is played by the microscopic parameter specific for various atoms, known as the scattering amplitude. It is of great importance to determine the value of this parameter and in particular its sign. This parameter was until recently only known for atomic hydrogen, in which case the interaction potential has been rigorously calculated. For the various alkali gases for which BEC is being attempted experimentally, no reliable theoretical potentials are available and a vast gap in experimental knowledge exists as well.

Literature

  • C.R. Monroe et al., Phys.Rev.Lett 70, 414-417 (1993).
  • A. Lagendijk et al., Phys.Rev.A 33, 626-628 (1986).
  • T.D. Lee et al., Phys.Rev. 106, 1135-1145 (1957).
  • A.L. Fetter, and J.D. Walecka, Quantum Theory of Many-Particle Systems, New York: McGraw-Hill, 1971, p. 222.
  • D.G. Friend, and R.D. Etters, J.Low.Temp.Phys. 39, 409-415 (1980).
  • A.J. Moerdijk et al., Phys.Rev.Lett 72, 40-43 (1994).
  • A.J. Moerdijk, and B.J. Verhaar, Phys.Rev.Lett. 73, 518-521 (1994).
  • E.R.I. Abraham et al., Phys.Rev.Lett. 74, 1315-1318 (1995).
  • M. H. Anderson et al., "Observation of a Bose-Einstein Condensation in a Dilute Atomic Vapor," Science 269, 198 (1995).
  • G. Taubes, "Physicists Create New State of Matter," Science 269, 152 (1995).
  • C. C. Bradley et al., "Evidence of Bose-Einstein Condensation in an Atomic Gas with Attractive Interactions," Physical Review Letters 75, 1687 (1995).
  • K. B. Davis et al., "Bose-Einstein Condensation in a Gas of Sodium Atoms," Physical Review Letters 75, 3969 (1996).
  • GSU Bose-Einstein Condensation (BEC) Home Page
  • Bose-Einstein condensation by J.T.M. Walraven
  • MIT press release on the condensate formed there
  • Molecule of the Year: A New Form of Matter Unveiled
  • Introduction to BEC in trapped atomic vapors
Compiled by Zbigniew Koziol

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CANADIAN INTERNET AWARDS

Received June 15, 1996
Please vote for The Physics of Superconductivity page maintained by the Editor of Virtual Physics, in a competition for the Canadian Internet Awards (Our page can be found under the category Best Science Site)

The Canadian Internet Awards honour a number of national and international sites and developers who have made a significant contribution to the net either through providing unique public services or for technical expertise and performance

Voting can be performed until June 21, 1996 only. The number of public votes is supposed to decide about the outcome of this competition. Please do not be surprised that there is a little only about the rules and appearantly - no public control of the whole process. This is a ususal situation nowadays, unfortunately. Nethertheless, it is worth to visit the site since indeed links to several interesting places on the Canadian internet landscape can be found there.

Thank you for your support.

Zbigniew Koziol
WebEx@ra.isisnet.com
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Virtual Physics: a forum for virtual meetings of scientists and students involved in a research activity on THE SOLID STATE PHYSICS AND SUPERCONDUCTIVITY is available for a free subscription in an e-mail version. To subscribe: send a request to the Editor.

Editors:

Dr. Zbigniew J. Koziol (Editor-in-Chief), WebEx@ra.isisnet.com, WebExperts Inc.,
2-6032 Compton Ave., Halifax, Nova Scotia, B3H 1E7 Canada, tel. (902) 423 2149
Dr. Michal Spalinski, Michal.Spalinski@fuw.edu.pl, Institute of Theoretical Physics,
Warsaw University, Hoza 69, 00-681 Warsaw, Poland, tel. (+48)(2) 628 3031
Virtual Physics URL address: http://www.isisnet.com/MAX/vp.html
To subscribe a F R E E e-mail version or submit materials for publication, write to the Editor.
Copyright (C) 1996 by Zbigniew Koziol.
this copyright notice concerns the whole of the Virtual Physics edition but not specific articles published there which are property of their respective copyright holders
No responsibility is assumed by the publisher for any damage to persons or property as a matter of the product liability, negligence or otherwise, or from any use of methods, instructions or ideas contained in the material herein. The opinions expressed in this publication do not necessarily reflect the opinions of the Editor and certainly they have nothing to do with WebExperts Inc.
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