Editorial
Authors: Munawar Karim  
Published: August 2002

The 20th Century saw a renaissance in experimental gravitation:
some recent results were presented in a symposium organized by Hu Enke
and Peter Michelson in Guangzhou, in 1987, followed by the symposium
organized by Asghar Qadir and myself in Nathiagali in 1993, and in the
latest gathering in Samarkand in August 1999. An interval of six years
seems appropriate in reviewing landmarks in this field.

This issue of Classical and Quantum Gravity is devoted to
topics covered in the Samarkand symposium. The subject of the symposium
is broadly classified as experimental gravitation: included in it are
experiments from many different areas
of physics, that generally aim to test and
interpret Einstein's theory of gravity. Contributors to this issue have
provided comprehensive reviews of experiments placing each within a
theoretical framework.

Advances in several branches of physics have made possible experiments
of unprecedented precision to the extent that one can devise tests of
many aspects of general relativity, using in some cases,
laboratory-scale apparatuses. Sometimes
these advances have occurred in fields as
diverse as atomic physics, physics of condensed matter, metrology and
measurement theory to name a few; the symposium provided a synergic
forum for scientists from different specializations. Experiments were
described that test the predictions of general relativity over a range
of phenomena from the classical to the quantum, over distances of
millimetres to the astronomical, over timescales from the present to
the early Universe and from the weak to the strong-field approximation.

Papers in this issue are loosely grouped under the following broad
categories: tests of the equivalence principle, with Pound's description of
a classic, Bantel and Boynton reporting on new methods to push
back the
limits of the equivalence principle using the venerable torsion balance,
and separate proposals by Iafolla, Sanders and Nobili to refine
Galileo's free-fall experiments on Earth and in space. Difficult and
ingenious experiments to measure `G' are reviewed by Luo. One can
observe the sometimes erratic progress in the measured value; great
efforts are underway to improve the accuracy. Ruoso reports on an
experiment to verify, on a submillimetre scale, Newton's law of gravity
and attempts to link the results to supersymmetry physics. Rotating
fields are covered next: Ciufolini describes his discovery of the
Lens-Thirring effect using, as a gyroscope, a pair of satellites.
Gustavson reports on an atom interferometer gyroscope, a device meant to
extend, to general relativity, earlier work on the effect of rotating
frames on quantum systems. Mashhoon proposes an experiment to measure
the effect of a rotating mass on intrinsic spin. Astrophysical phenomena
have revealed new insights associated with strong field effects close to
black holes. Chakrabarti describes matter under extreme conditions in
the vicinity of black holes and shows that spectral signatures can
distinguish between a black hole and a neutron star, and how the
centrifugal barrier oscillates to produce the quasi-periodic
oscillations of x-rays from black-hole accretion disks. Partridge has
reviewed the status of measurements of cosmic background radiation
as well as recent observational evidence requiring a cosmological
constant, necessitating an accelerating expansion of the Universe.
Saulson reports on the status of interferometeric detectors of
gravitational radiation. Little is known about quantized fields in
curved metrics; the last contribution points to an intriguing
possibility.

The symposium provided those engaged in experiments with gravitation an
opportunity to exchange ideas with scientists from a part of the
World emerging from a long period of isolation.

Samarkand is a city of spectacular monuments, both architectural and
intellectual. It was the city where the great medieval astronomer Ulugh
Bek (1394 - 1449) established an observatory. His aim was to measure the
length of a year in order to revise the calendar. Following the
tradition of the scientific method established by Ibn Al-Haytham (d.
1039), he designed and built an instrument before engaging in
measurements. His log books have survived, as has his observatory. Among
his discoveries were a number of errors in the computations of the 2nd
Century Alexandrian astronomer Ptolemy. Ulugh Bek compiled a
catalogue of
stars (the third such catalogue after Hipparchus (129 BC) and
Ptolemy's
Almagest (140 AD)) which circulated in Europe in the 1500s. Ulugh Bek
was Tycho Brahe's predecessor.

Omar Khayyam also enriched Samarkand's intellectual history. Omar solved
the general problem of extracting roots of any desired degree. He was an
avid astronomer. As a result of his observations he suggested a scheme
which made 8 of every 33 years leap years, with 366 days each, and
produced a length of the year closer to the true value than does the
present Gregorian calendar. Among his quatrains was one that may
describe the typical contemporary relativity conference:

Myself when young did eagerly frequent

Doctor and Saint, and heard great Argument

About it and about: but evermore

Came out by the same Door where in I went.

This symposium, I hope, is an exception.

During the 9th Century the city of Khiva, a day's drive from Samarkand,
was home to the mathematician Al-Khwarizmi. Among his many achievements
was a book explaining Hindu arithmetic and a systematic introduction to
algebra and a theory of quadratic equations. He also made an accurate
measurement of 56 2/3 miles/degree.
The word algorithm is derived from a
Latinized version of his name.

A millennium ago the introduction of decimal arithmetic caused a
revolution in computing power which influenced all of science, much as
personal computers today are revolutionizing our civilization.

Contemporaneous with Al-Khwarizmi were Al-Biruni and Avicenna, equally
luminous for their measurements of longitudes and latitudes of locations
in this region and for inventing the azimuthal equidistant and globular
projections. Al-Biruni was pressed into service as a diplomat; of this
he wrote, `I was compelled to participate in worldly affairs, which
excited the envy of fools, but made the wise pity me'. Avicenna's
treatise on medicine was a standard text for 900 years. This symposium
closes the circle of scientific activity in Samarkand.

Paper, which was invented in China in the 2nd Century, was brought to
Samarkand in the 8th Century and from there it travelled along the Silk
Road to Arab lands in the 11th Century and thence to Fabriano in Italy
in the 13th Century, its first appearance in Europe. Paper was not the
first product from China to travel west on the Silk Road, silk has that
distinction because it was used in Pharonic times.

I mention these examples from previous eras to remind us all to value
experiments. Physics is an experimental science, an aspect emphasized by
Newton, Einstein, Landau and Feynman among others.

On behalf of the participants I wish to express my gratitude to the
organizations which sponsored the Samarkand symposium. These are: the
United States National Science Foundation, the Abdus Salam International
Centre for Theoretical Physics, Turkish Airlines, COMSTECH, Samarkand
Business Centre, Samarkand State University, Samarkand Ziyolilar Saroy,
Institute of Nuclear Physics (Tashkent) and the Local Organization
Committee. Among the many individuals who provided much of the invisible
logistical support I wish to recognize Bobomurat Ahmedov, my
co-organizer, and his family for their friendship and
hospitality; Umar
Salikhbaev, Shahriyor Safarov and Abdullah Kuvatov of Samarkand State
University, for hosting the Symposium and for the special honour
conferred on Professor Pound; Bahtiyor Allayarov for the excursion to
Bukhara and hotel arrangements; Mohammad Shafique for producing the
conference stationery; St John Fisher College, especially the Business
Office for administrative support; and Nic Marinaccio for rendering the
symposium poster. Andrew Wray of the Institute of Physics Publishing
deserves appreciation for his advice in preparing this special issue.