ScienceWeek

SCIENCE-WEEK

A Weekly Email Digest of the News of Science

A journal devoted to the improvement of communication
between the scientific disciplines, and between scientists,
science educators, and science policy makers.

November 19, 1999 -- Vol. 3 Number 47

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To the first flaker of flints who forgot his dinner.
-- W.H. Auden (1907-1973)

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Contents of This Issue:

1. On Proteolytic Enzymes
2. Zoology: A Polarized Light Compass Organ in Spiders
3. Medical Biology: A Possible Cause of Multiple Sclerosis
4. Astrophysics: On the Determination of the Hubble Constant
5. Earth Science: Atmospheric Oxygen over Phanerozoic Time
6. Theoretical Physics: On Pascual Jordan and Nazi Physics

In Focus: On Prokaryotic and Eukaryotic Cells

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1. ON PROTEOLYTIC ENZYMES
Proteolytic enzymes (also called proteases, peptidases, peptide
hydrolases) are enzymes that catalyze the hydrolysis of the
peptide bonds of proteins, thus breaking the proteins down into
their amino acid constituents. These enzymes are now recognized
to be among the most important enzymes found in biological
systems, and they are intensively studied in many laboratories.
... ... Hans Neurath (University of Washington Seattle, US)
presents an essay on the past, present, and future of research on
proteolytic enzymes, the author making the following points:
     1) Research on proteolytic enzymes 60 years ago was quite
different than today. In the first place, these enzymes had just
been recognized as distinct chemical entities with constant
solubilities, pure compounds in their crystalline forms. At that
time, the proteolytic enzymes known, most of which were enzymes
involved in digestion, included pepsinogen, pepsin, a pepsin
inhibitor, chymotrypsin, trypsin, their *zymogens and inhibitors,
carboxypeptidase, ribonuclease, hexokinase, *diphtheria toxin,
and several others. Secondly, because these proteins were
commercially unavailable, researchers interested in studying them
had to isolate the compounds in the laboratory.
     2) The field of proteolytic enzyme chemistry lay relatively
dormant from 1940 until the 1960s, awaiting the development of
more effective and specific methods of isolation, purification,
and characterization of proteins, new methods such as
*chromatography, *gel electrophoresis, *gel filtration,
*ultracentrifugation, amino acid analysis, and protein amino
acid- sequencing. An important improvement was the development of
synthetic low molecular weight polypeptide substrates for
proteolytic enzymes. Another important landmark was the discovery
of natural and synthetic protease inhibitors, and the
introduction of organic phosphate isotope label into the active
site of a proteolytic enzyme. During the past 30 years, chemical
characterization of active sites, together with x-ray structure
analysis of proteases, has demonstrated that these enzymes can be
grouped into families of common mechanism, similar structural
features, and hence common evolutionary origin.
     3) The number of proteases under investigation in the early
days of protease biochemistry was minuscule compared with the
current inventory of several thousand proteolytic enzymes that
are coded by as much as 2 percent of the structural gene pool.
     4) Interest in proteases has been considerably stimulated by
the recognition that aside from their digestive action proteases
are involved in the regulation of a great many physiological
processes. In many cases, regulation is mediated by the
association of proteases with non-proteolytic domains that confer
specificity to their interaction with receptor sites.
     5) In recent years, the term "limited proteolysis" was
coined to differentiate the restricted specificity of certain
enzymes under certain conditions from the random proteolysis
accompanying protein degradation. It is now recognized that
proteolytic processing can be limited by the specificity of the
protease, the accessibility of the susceptible peptide bond of
the substrate, the obligatory activation of an enzyme precursor,
the action of protease inhibitors, or a combination of these
factors.
     6) One important generalization that has emerged is that
most proteases are synthesized as inactive precursors (zymogens)
that require limited proteolysis for activation. Because
proteolysis is irreversible under physiological conditions, the
generation of the uncleaved precursor requires de novo synthesis.
     7) Two major factors have expanded our conceptual horizons
and endowed us with experimental tools of previously unimaginable
powers of resolution. One factor is the application of the newly
emerging concepts and methodologies of molecular and cell
biology. The other major impetus comes from a group of newly
developed concepts and experimental approaches to the structure
and function of proteins by mass spectroscopy, multidimensional
nuclear magnetic resonance, and the use of computers for the
prediction of protein structure based on various types of
algorithms. A third factor of almost equal importance in this
context is the use of combinatorial chemistry to scan and
identify protein ligands of physiological significance.
     8) Although we are still far from understanding the rules of
the in vivo folding of nascent polypeptide chains, the challenge
lies in deriving the function of a protein from its known
chemical and biological parameters, and in learning how to design
proteins of predetermined physiological properties.
-----------
Hans Neurath: Proteolytic enzymes, past and future.
(Proc. Natl. Acad. Sci. US 28 Sep 99 96:10962)
QY: Hans Neurath [neurath@u.washington.edu]
-----------
Text Notes:
... ... *zymogens: (proenzymes) The term "zymogen" refers to the
inactive precursor of an enzyme, often convertible to the enzyme
by partial proteolysis. The term is used especially for the
inactive forms of pancreatic enzymes such as trypsinogen,
chymotrypsinogen, peptidase, etc. These particular zymogens are
cleaved to remove a peptide to produce the active enzyme after
their secretion from zymogen granules in certain cells of the
pancreas.
... ... *diphtheria toxin: This toxin is secreted (i.e., it is an
"exotoxin") by the bacterium C. diphtheriae and is lethal to
humans in doses as small as 40 nanograms. The toxin molecule has
a molecular weight of 62,000, and is secreted as a single
polypeptide which degrades into two fragments linked by a
disulfide bond. The heavier proteolytic fragment binds to
specific host cell receptors and facilitates the entry of the
lighter companion fragment into the cell cytoplasm. The lighter
fragment inhibits protein synthesis, disrupting normal cellular
physiological functions.
... ... *chromatography: In general, this refers to any technique
involving separation of components of a mixture in solution
through differential solubilities in a moving solvent and a
stationary phase (e.g., a gel).
... ... *gel electrophoresis: A type of "zone electrophoresis" in
which the supporting medium is a gel of uniform concentration. In
zone electrophoresis, a solution of protein (or other molecules)
is placed at the starting position as a thin band or spot in an
inert supporting medium (paper, starch gel, polyacrylamide gel,
etc.) containing buffer solution. An electric potential is then
applied to the supporting medium, causing the proteins (or other
substances) to migrate to give distinct bands or zones which can
be located in situ by staining, light absorption, etc., or by
analysis after elution of discrete pieces of the supporting
medium.
... ... *gel filtration: (gel-permeation chromatography) A
separation method in which a mixture to be separated into
components is poured into a column containing beads of inert gel
and then washed through with solvent. Speed of passage depends on
relative solubilities in the solvent and ability to pass through
pores in the gel (i.e., on molecular size).
... ... *ultracentrifugation: In general, high-speed
centrifugation capable of sedimenting (and separating) particles
as small as protein or nucleic acid molecules. The technique was
first devised by T. Svedberg in 1925 (Nobel Prize for Chemistry
1926).
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 19Nov99
[For more information: http://scienceweek.com/search/search.htm]
-------------------
Related Background:
PROTEASES AS MEDIATORS OF APOPTOSIS
Proteases are a class of enzymes that hydrolyze proteins,
splitting them into various groups of subunits, with the sites of
hydrolysis dependent on the particular enzyme and the protein
substrate. Actin is a structural protein present in all cells 
as a constituent of the cell cytoskeleton, and gelsolin is a
protein that breaks actin filaments and causes a gel-sol
conversion -- a conversion of a gelatin-like system to a solution
(liquid) system. This type of conversion is ordinary in certain
cell types under certain conditions, but it is also seen in
apoptosis (programmed cell death) when the cytoskeleton is
destroyed and the cytoplasm liquified. Srinivas Kothakota et al
(11 authors at 3 installations, US) report that the protein
gelsolin is the primary substrate for the caspase-3 protease
family that has been implicated in apoptosis. Gelsolin cleavage
products cause multiple cell types to round up, detach from the
cell culture plate, and undergo nuclear fragmentation. Cells
isolated from genetically engineered mice lacking gelsolin showed
marked delays in apoptosis onset following apoptosis induction,
while wild-type cells did not show these delays. The authors
suggest that cleaved gelsolin may be one of the physiological
effectors that produce morphological changes during apoptosis.
QY: David J. Kwiatkowski [kwiatkowski@calvin.bwh.harvard.edu]
(Science 10 Oct 1997) (Science-Week 31 Oct 97)
-------------------
Related Background:
NEW SYNTHESIS OF AN IMPORTANT PROTEASE INHIBITOR
A protease is an enzyme that splits proteins and thereby degrades
them. Many pathogens use proteases as part of the pathogenic
disease process, one such pathogen being HIV. Palinavir is a
powerful protease inhibitor and a potential agent for the
treatment of AIDS. Until now, the synthesis of palinavir has been
tricky, involving hazardous diazomethane, requiring elaborate
purifications by chromatography, resulting in low overall yields
and the ability to prepare only small amounts. Now Pierre L.
Beaulieu and Pierre Lavallee (Boehringer Ingleheim, Quebec CA)
have developed a new synthesis of palinavir that does not require
elaborate purification, and that can be used to prepare kilogram
quantities for preclinical studies. Boehringer Ingleheim has
stopped development of palinavir, and instead will license the
new technology.
(J. Organic Chemistry, v62, 3440/1997)
(Science-Week 26 Jun 97)
[For more information: http://scienceweek.com/search/search.htm]


2. ZOOLOGY: A POLARIZED LIGHT COMPASS ORGAN IN SPIDERS
In all but the most primitive animals, the ability of the nervous
system to respond to the internal and external environment
depends on specialized sensory cells (sensory receptors) that in
general can be grouped into four principal types: a)
photoreceptors (sensitive to light); b) mechanoreceptors (which
respond to physical pressure or movement, e.g., sound and touch);
c) chemoreceptors (which detect chemical substances, e.g., odor
and taste); d) thermoreceptors (which monitor temperature. In
addition to the above major types, there are also sensory cells
that have evolved to specifically respond to electric and
magnetic fields (see background material below). In general, for
most sensory modalities the sensory cell acts as an energy
transducer, transforming the energy of the environmental stimulus
into a change in the electrical potential difference across a
biological membrane. Energy transduction is thus the fundamental
physical basis of the sensory response of most biological systems
to their environments, but within each of the evolved sensory
modalities there exists an enormous variety of structure and
function produced by evolutionary pressures. Some insects and
vertebrates, for example, use the pattern of polarized light in
the sky as an optical compass. In the case of bees and ants, only
a small section of clear sky must be visible in order for these
insects to obtain a compass bearing for accurate navigation. The
receptors involved in the polarization compass are confined to a
small part of the animal's retina, and the eyes are for the most
part constructed for other visual tasks.
... ... M. Dacke et al (6 authors at 4 installations, SE AU UK
US) now report the discovery of a unique compass organ in the
spider Drassodes cupreus, in which a pair of specialized
secondary eyes cooperate to analyze skylight polarization. These
eyes do not form images, but use a built-in polarization filter
to determine precisely the direction of polarization. The authors
report that measurements using a model eye indicate that this
compass organ is best suited for navigation at dusk and dawn.
Behavioral experiments demonstrate that the spiders are primarily
active after sunset, and that they use polarization cues to find
their way back to the nest after foraging trips. The authors
suggest that a similar organization of the secondary eyes in
several spider families indicates that such compass organs may
not be an isolated phenomenon. The authors also suggest that
since this compass organ appears to be involved in no other
visual tasks, it offers an interesting model for studies of the
neural processing underlying polarization navigation.
-----------
M. Dacke et al: Built-in polarizers form part of a compass organ
in spiders.
(Nature 30 Sep 99 401:470)
QY: M. Dacke [dacke@zool.lu.se]
-------------------
Summary by SCIENCE-WEEK [http://scienceweek.com] 19Nov99
-------------------
Related Background:
STRUCTURE AND FUNCTION OF VERTEBRATE MAGNETIC SENSE ORGANS
One of the more exhilarating moments in science occurs when a
long-standing mystery is finally solved. It has been thought for
some time that many diverse animals are able to use the Earth's
magnetic field for navigation during migration and homing, but
both the detection mechanism and the neural pathways involved
have never been elucidated. There have been theories linking the
detection of magnetic fields to vision, electroreception, and
magnetite particles, but until now no evidence has been forth-
coming to support any theory, and there is contrary evidence for
the involvement of both vision and electroreception. Magnetite is
an iron ore strongly attracted by a magnet, and now it appears
that magnetite particles are indeed the essential components of
magnetic field detection, at least in one vertebrate. Walker et
al (6 authors at Univ. of Auckland, NZ) describe the key comp-
onents of the magnetic sense ability of the rainbow trout
(Oncorhynchus mykiss), identify an area in the nose of the trout
where candidate magnetoreceptor magnetite-containing cells are
located, and present results of behavioral and electrophysiolog-
ical studies of trout responses to magnetic fields. The authors
suggest their work provides experimental support for the idea
that animals use the magnetic sense for navigation.
QY: Michael M. Walker 
(Nature 27 Nov 97) (Science-Week 19 Dec 97)


3. MEDICAL BIOLOGY: A POSSIBLE CAUSE OF MULTIPLE SCLEROSIS
In the vertebrate central nervous system, the axons of nerve
cells involved in physiological functions that require rapid
signaling (for example, the neural control of voluntary muscle)
are wrapped in a special sheath called myelin. The myelin sheath
consists of concentric layers of electrically insulating lipid-
protein material, but the sheath is periodically interrupted
along the length of the axon, and at the points where the sheath
is interrupted so is the electrical insulation interrupted. The
result, predictable from the classical physics of electrical
transmission lines and the electrical parameters of nerve fibers,
is that the propagation of an electrical pulse along such nerve
fibers occurs at a velocity much higher than that found in
unmyelinated fibers. Multiple sclerosis is a human disease
characterized by the progressive loss of the myelin of the brain
and spinal cord, with the physiological disruptions to be
expected from such loss, considering the significance of myelin
in the functioning of nerve cells. The cause of the disease is
unknown, but an immunological abnormality is suspected. It has
also been postulated that the cause is infection by a latent
virus, with viral activation and expression triggering a
secondary immune response. There is some evidence for genetic
susceptibility, and there is also evidence that environment may
be a factor, since the disease is 5 times more common in
temperate climates than in the tropics.
... ... D.C. Shields et al (4 authors at 2 installations, US JP)
now present a study of the mechanism of demyelinization in
multiple sclerosis, the authors reporting the following:
     1) In autoimmune demyelinating diseases such as multiple
sclerosis, the degradation of myelin proteins results in the
destabilization of the myelin sheath. Protein-degrading enzymes
(proteases, proteinases) have been implicated in myelin protein
degradation, and recent studies have demonstrated increased
expression and activity of a calcium-activated neutral proteinase
(calpain) in experimental allergic encephalomyelitis, the
corresponding animal model of multiple sclerosis.
     2) In the present study, calpain activity and expression
were evaluated in white matter from human patients with multiple
scelerosis and Parkinson's and Alzheimer's diseases and compared
with that of white matter from normal controls. Analysis
indicates that the active form of calpain and calpain-specific
degradation products were increased by 90.1 percent and 52.7
percent, respectively, in multiple sclerosis plaques compared
with normal white matter, and that calpain expression increased
by more than a factor of 4 compared with normal white matter.
Calpain activity and expression were not increased significantly
in white matter from patients with Parkinson's or Alzheimer's
diseases compared with that of normal controls.
     3) The authors suggest that because calpain degrades all
major myelin proteins, the increased activity and expression of
this proteinase may play a critical role in the degradation of
myelin in autoimmune demyelinating diseases such as multiple
sclerosis.
-----------
D.C. Shields et al: A putative mechanism of demyelination in
multiple sclerosis by a proteolytic enzyme, calpain.
(Proc. Natl. Acad. Sci. US 28 Sep 99 96:11486)
QY: Naren L. Banik [baniknl@musc.edu]
-------------------
Summary by SCIENCE-WEEK [http://scienceweek.com] 19Nov99
[For more information: http://scienceweek.com/search/search.htm]
-------------------
Related Background:
ON THE MANAGEMENT OF MULTIPLE SCLEROSIS BY DRUG THERAPY
Multiple sclerosis is a disease of the central nervous system
affecting approximately 1 million people worldwide, most of them
young female adults. The disease is characterized by episodic
neurologic symptoms, often permanent neurological deficits, and
progressive decline over a period of 3 or 4 decades. At the
cellular level, the disease involves spreading patches of
demyelination in the brain and spinal cord. Since the myelin of
myelinated axons is essential to the axons for their proper
physiological functioning, the neurologic symptoms of multiple
sclerosis are a logical consequence of the disease process. There
is no cure, and until recently there was hardly any treatment for
this disease. The present consensus is that multiple sclerosis is
an autoimmune process occurring in genetically susceptible
persons after an environmental exposure. But no specific pathogen
has been linked to the disease. Several types of multiple
sclerosis are recognized, the categories based on symptomatology.
The type that responds most favorably to treatment is the so-
called relapsing-remitting type, a variant with periods of stable
remission that may last as long as decades. The interferons are
proteins produced by white blood cells when invaded by viruses,
and are important in the immune response. There are several types
of interferon depending on their source: interferon-alpha (leuko-
cytes), interferon-beta (fibroblasts), and interferon-gamma
(lymphocytes). Recombinant DNA technology has made interferon
from bacterial cells available in adequate quantities for clin-
ical trials. Glatiramer acetate is a mixture of random synthetic
polypeptides with an amino acid composition that mimics the
myelin basic protein that appears to be the autoantigen in
multiple sclerosis. The rationale for the pharmacological use of
glatiramer is that synthetic autoantigen in extracellular fluid
acts as a decoy for immune system cells that would attack myelin.
Glial cells are the cells of the central and peripheral nervous
system that produce the multiple membrane layers called myelin
and enfold nerve cell axons with it. Growth factors are peptide
hormones that regulate the growth of cells and tissues, and
recombinant growth factors are simply such factors produced by
recombinant gene technology. Rudick et al (5 authors: Cleveland
Clinic Foundation, US), in a review of therapeutic management of
multiple sclerosis, conclude that long-term placebo-controlled
trials may no longer be ethically justifiable in patients with
relapsing-remitting multiple sclerosis given the evidence of the
efficacy of interferon-beta and glatiramer acetate. The authors
suggest that in the future glial-cell transplantation or treat-
ment with recombinant growth factors could be used to stimulate
regeneration and functional recovery.
QY: Richard A. Rudick, Dept. of Neurology, Cleveland Clinic
Foundation, Cleveland OH 33106 US.
(New England J. Med. 27 Nov 1997) (Science-Week 5 Dec 97)
[For more information: http://scienceweek.com/search/search.htm]


4. ASTROPHYSICS: ON THE DETERMINATION OF THE HUBBLE CONSTANT
     Far down the road, it will be written that five centuries
after the astronomer Copernicus placed the Earth as a small
object in orbit around the Sun, the astronomers of the 20th
century placed the Sun as an ordinary star in our Milky Way
galaxy, and then placed that galaxy as an ordinary galaxy in the
local cluster of galaxies, and then placed that local cluster as
an ordinary cluster in an even vaster supercluster, and that
supercluster as an apparent ordinary supercluster in an apparent
limitless population of superclusters in a Cosmos without
apparent boundaries. Whenever in the far future there will be
talk of the human species and where it is, our time will be noted
as the time of the Second Displacement after the First
Displacement by Copernicus.
     Since we are still in the Second Displacement, it is often
difficult to comprehend its nature and signficance, but one
advantage of our presence in this time is that the important
events are clear, the remarkable achievements of the astronomers
and astrophysicists of this century still fresh and vibrant.
     In this context, three signal events occurred early in this
century. The first, in 1918, was the demonstration by Harlow
Shapley (1885-1972) that the Sun was not, as many believed, at
the center of our galaxy, but was in fact 50,000 light-years
distant from the center (the figure was later reduced to 30,000
light-years by the work of J.H. Oort [1900-1992]).
     The second signal event, in 1924, was the demonstration by
Edwin Hubble (1889-1953) that the Andromeda Nebula was not in
fact, as nearly everyone then believed, a mass of gas and dust in
our Galaxy, but a galaxy like our own and 800,000 light-years
away (a figure later determined to be an underestimate), the
nearest of many galaxies outside the Milky Way Galaxy, each
galaxy containing millions or billions of suns.
     The third signal event occurred in 1929, but this requires
some elaboration since it was the culmination of years of work by
many people. The essential story is that following the
realization that the so-called "nebulae" were in fact galaxies,
astronomers began studying the spectra of these galaxies, and it
was soon apparent that almost all the spectra had spectral lines
shifted toward longer wavelengths (shifted to the red =
"redshift"). At that time, this was interpreted as a consequence
of the Doppler effect, these redshifts implying that the galaxies
were receding [*Note #1]. In 1929, Edwin Hubble announced a
general law of redshifts now known as the "Hubble law", the law
stating that the velocity of recession of a galaxy equals a
constant times its distance. Thus, the more distant a galaxy, the
faster its apparent recession from us. The constant, now denoted
as H(sub0), is called the "Hubble constant" (or Hubble parameter,
since in some models it is time dependent), is a critical
quantity in all current cosmological models, and enormous efforts
have been made to determine its exact value.
     One important aspect of the Hubble constant is that with
certain simplifying assumptions this constant allows one to
estimate the age of the universe. There are a number of methods
to do this, some more direct than others, and at present no one
in cosmology is apparently satisfied with the results [*Note #2].
... ... W.L. Freedman and L.L. Feng (2 installations, US CN)
present a review of current efforts to determine the Hubble
constant, the authors making the following points:
     1) What is required to measure an accurate value of the
Hubble constant? According to the Hubble law, what is needed are
measurements of both redshifts of galaxies (via spectral lines),
and distances to galaxies (at sufficiently large distances where
peculiar motions relative to the smooth *Hubble flow are slow).
The Hubble constant then follows immediately from the slope of
correlation between the redshift and distance. However, the
precise determination of galaxy distances remains a longstanding
fundamental problem in astronomy. In principle, measuring the
distance of a distant galaxy relies on a particular property of
the propagation of light in space: the apparent brightness of a
light source varies inversely with the square of distance.
Accordingly, the distance to an object may be determined by
knowing the intrinsic luminosity and then comparing that with its
apparent brightness.
     2) Establishing accurate extragalactic distances has
provided an immense challenge to astronomers since the 1920s. The
situation has improved dramatically as better detectors have
become available, and as several new and promising techniques
have been developed. For the first time in the history of this
difficult field, relative distances to galaxies are being
compared on a case-by-case basis, and their quantitative
agreement is being established. New instrumentation, the
developmeent of new techniques for measuring distances, and
recent measurements with the *Hubble Space Telescope all have
resulted in new distances to galaxies with precision at the +- 5
to 20 percent level. The current statistical uncertainty in some
methods for measuring the Hubble constant is now only a few
percent, and with systematic errors, the total uncertainty is
approaching +- 10 percent. Thus, the authors state, "the
historical factor-of-two uncertainty in the value of the Hubble
constant is behind us."
-----------
W.L. Freedman and L.L. Feng: Determination of the Hubble
constant.
(Proc. Natl. Acad. Sci. US 28 Sep 99 96:11063)
QY: Wendy L. Freedman, Carnegie Observatories Pasadena US.
-----------
Text Notes:
... ... *Note #1: Redshift (symbol: z) is a lengthening of the
wavelengths of electromagnetic radiation from a source caused
either by the movement of the source (Doppler effect) or by the
expansion of the universe (cosmological redshift). Redshift is
defined as the change in wavelength of a particular spectral line
divided by the unshifted wavelength of that line. Large redshifts
imply large radial velocities (which imply large distances,
according to current cosmological theory), but at redshifts
greater than about 0.2 there is a relativistic divergence from a
linear relation. A redshift of 4.0 corresponds to an object
receding with a radial velocity 92% that of the velocity of
light. The largest astrophysical redshifts so far observed are of
the order of z = 4.9.
... ... *Note #2: Concerning the age of the Universe in this
context, the relevant term is the "Hubble time", i.e., the time
required for the Universe to expand to its present size, assuming
that the Hubble constant has remained unchanged since the
Universe came into existence. The Hubble time is defined as the
reciprocal of the Hubble constant, and according to current
estimates is between 9 and 18 billion years, depending on both
the value of the Hubble constant and on the cosmological model in
which it is applied.
... ... *Hubble flow: The general outward motion of galaxies
resulting from the uniform expansion of the Universe. All motions
lie in a radial direction from the observer, and the apparent
velocities are proportional to the distances of the galaxies. The
actual pattern of galaxy motions is perturbed by gravitational
interactions, but these gravitational interactions are
significant only locally and are small compared with the overall
Hubble flow.
... ... *Hubble Space Telescope: The Hubble Space Telescope was
launched from a space shuttle in 1990 into a 600-kilometer
low-Earth orbit and has been providing extensive imaging and
spectroscopic observations critical for the development of
astronomy and astrophysics. The new information has concerned hot
stars, stellar chromospheres and coronas, the interstellar
medium, galaxies and galactic clusters, quasars, etc. -- all of
it information uncorrupted by the Earth's atmosphere, which is
the problem for ground based telescopes.
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 19Nov99
[For more information: http://scienceweek.com/search/search.htm]
-------------------
Related Background:
ON EDWIN HUBBLE
At the time of his death, Edwin Hubble (1889-1953) was the most
eminent and celebrated observational astronomer in the world, a
man as well-known to the public as to the scientific community.
Essentially, Hubble made 3 major contributions during his
scientific career: 1) He provided the first evidence (1923) of
the existence of galaxies other than our own; 2) he proposed (in
the 1920s) a classification of galaxies as ellipticals, spirals,
and *barred spirals, a classification scheme still in use; 3) he
provided observational evidence (1928) for the recession of
galaxies (the expansion of the Universe), and he proposed (1929)
what is known as "Hubble's Law" relating the observed recession
rate of galaxies to their distance. The first and last of these
contributions have certainly been a most important part of the
foundation of 20th century cosmology. In much of his telescope
observational work, Hubble was assisted by Milton Humason (1891-
1972), an accomplished astronomer who was something of a Michael
Faraday in American astronomy: Humason had little formal
education and he first worked for Hubble as a janitor at the
Mount Wilson Observatory [*Note #1]. ... ... Gale E. Christianson
(Indiana State University) presents a biographical essay on
Hubble, the author making the following points: 1) Hubble was 6
feet 2 inches tall, weighed 190 pounds, constantly smoked a pipe,
favored a tightly-belted military trenchcoat, sported an English
accent acquired during his days as a Rhodes scholar at Oxford
University (where he studied law, not astronomy), and had a
special observatory wardrobe consisting of knickers, jodhpurs,
high-topped military boots, and a *Norfolk jacket. The author, in
fact, states that Hubble was disappointed when he arrived in
France during World War I only days before the November
armistice, "ending his dreams of leading men into battle." 2)
Hubble settled at the Mount Wilson Observatory in 1919, and
immediately began working with the 100-inch Hooker telescope. In
1923, working with the Hooker telescope, Hubble discovered
*Cepheid variable stars in the Andromeda *nebula M31 (later to be
called the Andromeda galaxy). Using the well-known period-
luminosity relationship established for Cepheid variables, Hubble
estimated the distance of the Andromeda galaxy as 300,000
*parsecs from Earth, a distance which apparently astounded
everyone. 3) Following the Andromeda galaxy work, in search of an
understanding of the formation and evolution of galaxies, Hubble
proposed what is now known as the "tuning fork diagram", a galaxy
classification scheme: the handle of the tuning fork consists of
an evolving sequence of elliptical galaxies (from spherical to
true elliptical), with one arm of the tuning fork diagramming the
evolution of spiral galaxies, and the other arm of the tuning
fork diagramming the evolution of the "barred" spiral galaxies.
4) In 1928, Hubble and Humason began a systematic study of the
*redshifts of galaxies, and in 1929 this resulted in the proposal
that the distances and recessional speeds of the nebulae
(galaxies) are in direct proportion to each other ("Hubble's
Law"): double the distance to a galaxy and the speed of recession
doubles; triple the distance and the speed triples [*Note #2]. 5)
In 1931, Einstein visited Hubble in Pasadena, and apparently when
Hubble was working at the observatory, Grace Hubble, Edwin
Hubble's wife, drove Einstein to his meetings and appointments.
The author concludes: "He [Einstein] was silent sometimes, and
sometimes he would talk in French or English, for Grace knew no
German. One afternoon he broke his silence to say, 'Your
husband's work is beautiful.'" [Editor's note: It was Hubble's
demonstration of the apparent expansion of the Universe that
caused Einstein to call his rather ad hoc introduction of the so-
called "cosmological constant" into his relativity equations "the
greatest aesthetic blunder of my life." Einstein's relativity
model proposed a non-expanding Universe essentially held static
by the cosmological constant term. In addition to the background
material below, considerably more background material can be
found in various SW Focus Reports located at the SW website:
[http://scienceweek.com/swfr.htm]].
-----------
Gale E. Christianson: Mastering the Universe.
(Astronomy February 1999)
QY: Gale E. Christianson, Indiana State University 812-237-2121.
-----------
Text Notes:
... ... *barred spirals: In general, a barred spiral galaxy is a
type of galaxy with spiral arms extending from an almost
rectangular or cigar-shaped bar of stars across its central
region.
... ... *Norfolk jacket: From Norfolk UK (c. 1866). A loose-
fitting belted single-breasted jacket with box pleats.
... ... *Cepheid variable stars: These are variable stars that
pulsate periodically, expanding and contracting with as much as a
30% change in size in each cycle, with a typical average luminos-
ity about 10,000 times that of our Sun. In 1912, Henrietta Swan
Leavitt discovered a simple relationship between the period of
light variation and the absolute magnitude of a Cepheid variable.
This relationship, called the "period-luminosity law", enabled
the calculation of distances to the stars in our own galaxy and
to the stars in other galaxies. In 1952 it was discovered that
there are two types of Cepheid variables, which meant an error
had been introduced in the earlier calculations of distances, and
when the correction was made, the apparent size of the universe
abruptly doubled. During 1908-1912, Leavitt (1868-1928), a
graduate of Radcliffe College on the staff of the Harvard
Observatory, discovered 2400 variable stars, doubling the number
known in her time. In the early years of stellar spectroscopy,
particularly at the Harvard Astronomical Observatory, nearly all
the data was catalogued and analyzed by female astronomers,
called "computers", who were forbidden because of their sex to
use the telescopes. It is an irony of the social history of
science that the work of such female astronomers as Henrietta
Swan Leavitt and Annie Jump Cannon (1863-1941) came to be of
greater significance than the work of many of the male
astronomers who considered these female astronomers to be no more
than menial assistants.  
... ... *nebula: Before Hubble, all of the fuzzy astronomical
objects that appeared in telescopes, many of which are now known
to be galaxies, were thought to be clumps of gas and dust. There
are indeed clumps of gas and dust everywhere in the Universe, and
they are correctly termed "nebulae". But since the work of
Hubble, which means since the 1920s, the use of the term "nebula"
for a galaxy is obsolete and incorrect.
... ... *parsecs: 1 parsec equals 3.262 light-years, or 30.86 x
10^(12) kilometers.
... ... *Note #1: In general, the Hubble tuning fork diagram
contains 10 galaxy categories. An 11th category, "irregular
galaxies", is usually diagrammed as an extending tine between the
two tuning fork arms. The result is a 3-prong "pitchfork"
diagram, rather than a "tuning fork" diagram.
... ... *redshifts: See main report.
... ... *Note #2: Humason measured the speed of recession of
approximately 800 galaxies. In 1956, three years after the death
of Hubble, Humason and others refined Hubble's Law, making the
proportionality constant (Hubble constant) in the relationship
between recession velocity and distance essentially time-
dependent. The "Hubble constant" is thus more properly called the
"Hubble parameter".
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 26Feb99
-------------------
Related Background:
RED GIANT STARS AND CONSTRAINTS ON THE HUBBLE CONSTANT
In cosmology, according to the Hubble law that describes the
expansion of the Universe, a law first proposed by Edwin Hubble
in 1929, the apparent recession velocity of galaxies is
proportional to their distance from the observer, with the
proportionality factor denoted as H(sub0). This proportionality
factor is called the "Hubble constant", but in the *Big Bang
theory it varies with time and is really a parameter rather than
a constant. This important cosmological parameter is usually
measured in units of kilometers per second per megaparsec, which
is identified dimensionally as a variation of velocity with
distance. Assuming the Big Bang origin of the expansion, the
"Hubble time" is defined as the reciprocal of the Hubble
constant, and is the time required for the Universe to expand to
its present state, assuming the Hubble constant has remained
unchanged since the Big Bang. Determination of the Hubble time
has been far from unequivocal, with estimates of the Hubble time
ranging between 9 and 18 billion years, depending on various
measurements, models, assumptions, and so on. In the standard Big
Bang theory, the actual age of the Universe is always less than
the Hubble time, because the expansion was faster in the past.
... ... W.E. Harris et al now present a report of observations of
the brightest *red-giant stars in a *Virgo-cluster galaxy, and
the use of these observations to determine constraints on the
Hubble constant. The authors make the following points: 1) The
nearest large groups of *elliptical galaxies (in the Virgo and
*Fornax clusters) play a central role in determinations of the
Hubble constant, and hence the cosmological rate of expansion.
Because the relative distances between these two clusters and
more remote clusters are well known, absolute distance
determinations to Virgo and Fornax should establish the Hubble
constant for the local universe. 2) In addition, elliptical
galaxies reside predominantly in the cores of galactic clusters,
so distance calibrations for ellipticals should minimize the
uncertainties due to the possibly large extent of the clusters
along the line of sight. 3) The authors suggest that a powerful
and direct way of establishing such distances is to use the
brightest red-giant stars, which have nearly uniform
luminosities. 4) The authors report the direct observation of old
red-giant stars in a *dwarf elliptical galaxy in the Virgo
cluster. They determine a distance to this galaxy, and thus to
the core of the Virgo cluster, of 15 megaparsecs, from which they
estimate a Hubble constant of H(sub0) = 77 +- 8 kilometers per
second per megaparsec. Under assumptions of a *low density
Universe with the simplest cosmology, the authors suggest the age
of the Universe is no more than 12 to 13 billion years.
-----------
W.E. Harris et al (4 authors at 4 installations, CA US):
Constraints on the Hubble constant from observations of the
brightest red-giant stars in a Virgo-cluster galaxy.
(Nature 3 Sep 98 395:45)
QY: William E. Harris 
-----------
Text Notes:
... ... *Big Bang theory: The Big Bang theory is the general
cosmological model that proposes that all matter and radiation in
the universe originated in an explosion at a finite time in the
past.
... ... *red-giant stars: A red giant star is a star in a late
stage of evolution, having exhausted the hydrogen fuel in its
core. It has a surface temperature of less than 4700 degrees
Kelvin and a diameter 10 to 100 times that of the Sun.
... ... *Virgo-cluster galaxy: The Virgo cluster is a giant
irregular cluster of galaxies in the constellation Virgo. It is
the nearest large cluster, and approximately 2500 galaxies have
been identified in it.
... ... *elliptical galaxies: These are galaxies that have no
disc component, the shape varying from almost circular to narrow
ellipses. The stars within elliptical galaxies are predominantly
old stars. Elliptical galaxies display the greatest variation in
mass, ranging down to extreme dwarfs (approximately 10^(6) solar-
masses.
... ... *Fornax: The Fornax system is a dwarf elliptical galaxy
in the Fornax constellation. 
... ... *dwarf elliptical galaxy:  A dwarf galaxy is one that is
unusually faint because of small size or low surface brightness
or both. Dwarf galaxies contain only a few million stars, and
they are usually difficult to observe against foreground stars
because they are almost completely transparent. Dwarf galaxies
apparently make up the bulk of the cosmic population.
... ... *low density Universe: The apparent mean density of
matter in the Universe, as determined from both theory and
observation, is a critical parameter that constrains the geometry
and future history of the Universe, and also the age of the
Universe.
-------------------
Summary & Notes by SCIENCE-WEEK  25Sep98
[For more information: http://scienceweek.com/search/search.htm]


5. EARTH SCIENCE: ATMOSPHERIC OXYGEN OVER PHANEROZOIC TIME
The term "Phanerozoic time" refers to the past 550 million years,
the time during which most higher organisms arose and evolved,
both in the oceans and on the continents. The evolution of
atmospheric oxygen over geologic time is believed to have been
both a major cause and a major effect of biological evolution,
since oxygen is both consumed by plant and animal respiration and
produced by photosynthesis. On a geologic time scale (i.e.,
millions of years) the global biogeochemical cycles of carbon and
sulfur, involving the exchange of reduced carbon and sulfur
between rocks and the atmosphere-plus-oceans, constitute the
major controls on the levels of oxygen. Therefore, the study of
these cycles and how they may have varied in the geological past
is important to the history of both the atmosphere and of Earth
surface environments.
... ... Robert A. Berner (Yale University, US) presents a review
of recent work in the field, the author making the following
points:
     1) The processes that affect the evolution of atmospheric
oxygen as it relates to the carbon and sulfur cycles over
geologic time include the following:
... ... a) Input to the oceans of carbon dioxide and dissolved
carbonate and sulfate derived from oxidation, during chemical
weathering on the continents, of ancient organic matter and
pyrite [FeS(sub2)] in *sedimentary rocks.
... ... b) Reduction and removal of dissolved inorganic carbon
from sea water and fresh water via the synthesis of organic
matter, followed by a burial of dead organic remains in bottom
sediments.
... ... c) Removal of sulfate from seawater via bacterial
reduction to hydrogen sulfide followed by the reaction of
hydrogen sulfide to form sedimentary pyrite.
... ... d) The reaction of hot *basalt with sulfate in seawater
at midoceanic rises.
... ... e) Degassing of reduced carbon- and sulfur-containing
gases to the atmosphere-plus-oceans as a result of the thermal
decomposition of deeply buried organic matter and pyrite by
*diagenesis, *metamorphism, and volcanism. On arriving at the
Earth's surface, these reduced gases are rapidly oxidized by
oxygen.
     2) In addition to the above carbon and sulfur cycles which
involve atmospheric oxygen, there are cycles important to carbon
and sulfur mass balance, particularly isotope mass balance, but
which do not involve atmospheric oxygen. These cycles include a)
the weathering of calcium carbonate and calcium sulfate minerals
on the continents, and b) the formation of these minerals in the
oceans followed by burial in sediments.
     3) Calculation of the effect of changes in the global carbon
and sulfur cycles over geologic time on atmospheric oxygen has
been attempted with various models:
... ... a) Sediment composition models: In these models, the
chemical composition of sedimentary rocks of various ages is
combined with the abundance of these rocks (corrected for
postdepositional erosional/metamorphosic loss) to calculate the
original rates of burial of organic carbon and pyrite sulfur in
sediments.
... ... b) Nutrient models: In thes models the burial rate of
organic carbon is assumed to be limited by the availability of
the nutrients nitrogen and phosphorus, which leads to
consideration of the cycles of these elements, as well as those
of carbon and sulfur.
... ... c) Isotope mass balance models: In these models, carbon
and sulfur isotopic data for seawater composition over geologic
time are used to calculate the values of fluxes.
     A major problem with all models is the extreme sensitivity
of the mass of atmospheric oxygen to very small imbalances in the
burial and weathering fluxes.
     4) One study using sediment abundance data, along with
assumed rapid recycling of sediments to stabilize oxygen, shows a
pronounced and extended rise in atmospheric oxygen over the
period 375 to 275 million years ago, spanning the *Carboniferous
and Permian periods. What could have brought this about? The
modeling indicates that increased oxygen production caused by
increased burial of organic carbon is the chief suspect. This
increased burial is attributed to the rise and spread of large
woody vascular plants on the continents beginning at about 375
million years ago. The plants supplied a new source of organic
matter to be buried on land and carried to the oceans via rivers.
This "new" carbon was added to that already being buried in the
oceans, thus increasing the total global burial flux.
-----------
Robert A. Berner: Atmospheric oxygen over Phanerozoic time.
(Proc. Natl. Acad. Sci. US 28 Sep 99 96:10955)
QY: Robert A. Berner [berner@hess.geology.yale.edu]
-----------
Text Notes:
... ... *sedimentary rocks: These are rocks formed by the
hardening of accumulated particles (sediments) that were
transported by agents such as wind and water. Such rocks are the
prime source of fossils.
... ... *basalt: Basalt is a dark gray to black igneous
rock of volcanic origin that cools rapidly. "Igneous rocks" are
rocks that have congealed from a molten mass.
... ... *diagenesis: In general, the term "diagenesis" refers to
all the changes that occur in a sediment at low temperature and
pressure after deposition. With increasing temperature and
pressure, diagenesis grades into "*metamorphism".
... ... *metamorphism: In general, the process of changing the
characteristics of a rock in response to changes in temperature,
pressure, or volatile content. Most metamorphic changes do not
include bulk chemical changes, but merely the crystallization of
new mineral phases. Examples of the transformation of of
sediments through diagenesis and metamorphism are sand to
sandstone and peat to coal.
... ... *Carboniferous and Permian periods: The "Carboniferous
period" is the time-frame 362.5 to 290 million years ago. The
"Permian period" is the time-frame 290 to 245 million years ago.
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 19Nov99
[For more information: http://scienceweek.com/search/search.htm]


6. THEORETICAL PHYSICS: ON PASCUAL JORDAN AND NAZI PHYSICS
The individual human brain is an extremely complex natural
system, and the individual human mind, the manifestation of the
dynamics of that system, is at least of an equal order of
complexity and also a domain where paradox is commonplace.
(Ernst) Pascual Jordan (1902-1980) was one of the great
theoretical physicists of this century, the principal architect
of the Born-Heisenberg-Jordan matrix quantum mechanics (see Note
#1 below), the essential inventor of *quantum field theory, and a
20th century tour de force in mathematical physics -- but he was
also an ardent Nazi storm trooper, "complete with brown uniform,
jackboots, and swastika armband..." And if that paradox is not
enough, add to it the fact that Jordan not only defended the
physics of Albert Einstein to the Nazi regime which despised
Einstein because Einstein was a Jew, but also devoted
considerable effort to developing the details of Einstein's
general theory of relativity.
... ... Engelbert L. Schucking (New York University, US),
theoretical physicist and a former student of Pascual Jordan
(beginning in 1952), presents a biographical essay on Jordan,
with Schucking making the following points:
     1) Pascual Jordan was the originator of the quantum theory
of fields, "which we now take to be the basis of all physics." He
was the first to realize that all things in the Universe --
photons, electrons, protons, atoms, and elephants -- are field
quanta. Of the triumvirate Pascual Jordan, *Max Born, and *Werner
Heisenberg that formulated matrix quantum mechanics in 1925,
Jordan was the principal architect of the theory. But in spite of
his revolutionary contributions, Jordan never achieved the
acclaim of his colleagues Heisenberg and *Wolfgang Pauli, perhaps
because Jordan was looked down upon by Pauli and Heisenberg as
more of a mathematician than a physicist.
     2) Schucking points out that Jordan also made the first
formulation of what is now called *Fermi-Dirac statistics. The
story is that in 1925 Max Born, who was then editor of the
_Zeitschrift fur Physik_ was given a paper by Jordan for
publication in the journal. Born put the paper in his briefcase
and then left for the US to give lectures at MIT. Born forgot
about the paper, and when he returned to Germany six months
later, he found the paper at the bottom of the suitcase.
According to Max Born: "It contained what came to be known as the
Fermi-Dirac statistics. In the meantime, it had been discovered
by Enrico Fermi and, independently, by Paul Dirac. But Jordan was
the first."
     3) In May 1933, Jordan joined the Nazi party. But even
before the Nazis came to power in January 1933, Jordan had been a
conservative nationalist, and under the pseudonym "Domeier" he
had published his elitist views in the right-wing journal
_Deutsches Volkstum_ (_German Heritage_). In November 1933,
Jordan joined an SA (Sturmabteilung) unit and became a storm
trooper. He volunteered for the Luftwaffe in 1939, worked mostly
as a meteorologist at airfields, and also at the notorious
Peenemunde rocket center. In 1953, thanks to the intercession of
Wolfgang Pauli, Jordan was "rehabilitated" and advanced from
visiting to full professor at the University of Hamburg.
     4) The Schucking article includes an amusing extract from a
play by *Bertolt Brecht (_Fright and Misery in the Third Reich_)
in which Brecht satirizes Nazi physics in a scene in which two
physicists execute tortuous verbalizations in an attempt to avoid
mentioning the dangerous "E-word" (Einstein). In fact, most
German physicists, when writing about relativity during the Nazi
era, shunned the dangerous E-word. Schucking notes: "A
circumspect Heisenberg managed to avoid it." Jordan, however, did
use Einstein's name when writing about relativity.
     5) Schucking notes that the contributions of Pascual Jordan
are for the most part still widely unknown. "The bulk of the
monumental 1925 Born-Jordan paper 'Zur Quantenmechanik' was
written by Jordan [*Note #1]." It has also been argued that
Jordan's habilitation lecture was crucial for Heisenberg's
discovery of the uncertainty principle. "Even Jordan's pioneering
work in quantum field theory was not immediately appreciated. His
formalism of *creation and annihilation operators, now the basic
language of physics, was still viewed with suspicion by Pauli in
1933." In a seminal paper in 1935, Jordan showed how his
formalism could treat the physics of multiparticle systems -- now
the standard treatment in condensed matter physics -- and
generate the representations that are now used in particle
physics.
     6) In 1979, *Eugene Wigner proposed Jordan for the Nobel
Prize in Physics, but the Swedish Academy awarded the prize that
year to *Sheldon Glashow, Abdus Salam, and Steven Weinberg --
according to Schucking, "three practitioners of the art that
Jordan had invented." Less than a year later, Jordan died at the
age of 78 while filling in formulae in a manuscript at his
kitchen table.
-----------
[Editor's note: The 1997 edition of _Chambers Biographical
Dictionary_ contains a short paragraph on "(Ernst) Pascual Jordan
(1902-  ) German theoretical physicist". Evidently, 17 years
after Jordan's death, the editors of the dictionary were not
aware of it. Several current popular biographical dictionaries of
scientists contain no mention of Pascual Jordan at all. David
Bohm's 1951 textbook _Quantum Theory_ does not mention Jordan at
all. The 1958 4th edition of Paul Dirac's _The Principles of
Quantum Mechanics_ does not mention Jordan at all. Jordan is also
not mentioned anywhere in Richard Feynman's _Lectures on Physics_
(1965). Additional note: Pascual Jordan (1902-1980) should not be
confused with the noted mathematician Camille Jordan (1838-1922).
Camille Jordan was the foremost specialist in algebra of his
time, publishing research in topology, analysis, and particularly
in group theory. The so-called "Jordan curve" in analysis is the
curve of Camille Jordan.]
-----------
Engelbert L. Schucking: Jordan, Pauli, politics, Brecht, and a
variable gravitational constant.
(Physics Today October 1999)
QY: Engelbert L. Schucking, Dept. of Physics, New York
University, US.
-----------
Text Notes:
... ... *quantum field theory: The mathematical fusion of quantum
mechanics with special relativity theory. It is now the overall
theory of fundamental particles and their interactions, with each
type of particle represented by appropriate operators which obey
specific algebraic commutation laws.
... ... *Max Born: (1882-1970) Nobel Prize in Physics 1954. Born
did fundamental work in quantum theory, particularly work linking
the wave function of the electron to electron distribution
probability. It was Born who apparently coined the term "quantum
mechanics". Heisenberg was one of Born's students.
... ... *Werner Heisenberg: (1901-1976) Nobel Prize in Physics
1932. Developed quantum theory (matrix quantum mechanics) and
formulated the uncertainty principle, which concerns matter,
radiation, and their reactions, and which places absolute limits
on the achievable accuracy of measurement of physical phenomena
in the quantum domain.
... ... *Wolfgang Pauli: (1900-1958) Nobel Prize in Physics 1945.
Originated the exclusion principle, which states that in a given
system no two fermions (electrons, protons, neutrons, or other
elementary particles of half-integral spin) can be characterized
by the same set of quantum numbers. He also predicted the
existence of neutrinos.
... ... *Fermi-Dirac statistics: The statistics of an assembly of
identical half-integer spin particles. Such particles satisfy the
Pauli exclusion principle, i.e., no two particles of the same
kind in the system may simultaneously occupy the same quantum
state.
... ... *Bertolt Brecht: (1898-1956) Considered by many to be
Germany's greatest dramatist, Brecht presented his plays as
instruments of sociological analysis. When Hitler came to power
in 1933, Brecht left Germany and in 1941 finally settled in
Hollywood (US). The play in question, _Fright and Misery under
the Third Reich_, is also called _Fear and Loathing under the
Third Reich_ (Furcht und Elend des dritten Reiches, 1945). In
1948, Brecht moved to East Berlin to direct a theater. Always in
conflict with bureaucratic authority, Brecht's years in East
Germany proved difficult for both himself and the East German
government.
... ... *Note #1: What is known as "Heisenberg's matrix
mechanics" (matrix quantum mechanics) is a particular formulation
of quantum mechanics in which the vector aspect of quantum theory
is emphasized, whereas the wave aspects of quantum phenomena play
a secondary role. Although wave quantum mechanics (subsequently
developed by Schroedinger, see below) and matrix quantum
mechanics appear superficially to be very different, the two
theories are in fact completely equivalent and lead to the same
physical predictions. Werner Heisenberg's first paper on the
subject appeared in 1925, and in this paper matrix theory is not
mentioned explicitly because Heisenberg did not realize yet that
his mathematical operations had a matrix theory interpretation.
The connection with matrix theory was demonstrated the same year
in the already mentioned important paper by Max Born and Pascual
Jordan (Z. fur Physik 1925 34:858). In a second paper a short
time later, Born and Jordan and Heisenberg all published together
and clarified the principles of matrix quantum mechanics (Z. fur
Physik 1926 35:557). The wave quantum mechanics of Erwin
Schroedinger was not published until 1926 (Annalen der Physik
1926 79:361), so that historically matrix mechanics was invented
and developed before Schroedinger invented wave mechanics. Given
wave mechanics, the invention of matrix mechanics might be viewed
as inevitable, since the set of all solutions of a linear
differential equation can be regarded as a vector space. The fact
that matrix mechanics was invented _without_ wave mechanics is
considered by some physicists to be an astounding theoretical
accomplishment.
... ... *creation and annihilation operators: These are quantum
mechanical operators which increase or reduce, respectively, the
occupation of a single quantum state by one. For example, an
annihilation operator applied to a state of one particle yields
the vacuum. In this context, "operators" are abstract
representations of certain specific mathematical operations, and
consideration of the various algebras of such operators has
proved to be of immense importance in theoretical physics.
... ... *Eugene Wigner: (1902-1995) He introduced the idea of
parity, or symmetry theory, into nuclear physics. He shared the
1963 Nobel Prize for Physics with Maria Goeppert-Mayer
(1906-1972) and Hans Jensen (1907-1973).
... ... *Sheldon Glashow, Abdus Salam, and Steven Weinberg:
Shared the 1979 Nobel Prize in Physics for the unified theory of
weak and electromagnetic fundamental forces, and for the
prediction of the existence of the weak neutral current. Abdus
Salam (1926-1996).
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 19Nov99
[For more information: http://scienceweek.com/search/search.htm]


=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=

IN FOCUS: ON PROKARYOTIC AND EUKARYOTIC CELLS
"The oldest fossils known on Earth, found in South Africa,
Australia, and Siberia, indicate that the earliest forms of life
were individual (not colonial), single-celled, prokaryotic (pro
-- before; karyo -- kernel, a reference to the nucleus, or
central "kernel" of the cell) organisms. Prokaryotic cells are
small, have no nucleus or other internal partitions, and are the
type of cell found in bacteria. Today, along with prokaryotes,
however, there is a second very different kind of cell on Earth:
eukaryotes (eu -- true). Eukaryotic cells are larger and more
complex, and they have a nucleus and a variety of internal
chambers called 'organelles', each with specific functions. All
single-celled organisms [other than prokaryotes], as well as
multicellular life, are eukaryotic. The evolution of eukaryotes
from prokaryotes, arguably the single most significant event in
the history of life, probably occurred about 1.5 billion years
ago. An evolutionary step of this magnitude is hard to explain,
but one very plausible scenario, proposed in the late 1960s by L.
Margulis of the University of Massachusetts, suggests that
eukaryotic cells are in fact the products of prokaryotic cells
initially having having been swallowed by other prokaryotes. This
theory, called the 'endosymbiotic theory' of the origin of
eukaryotes (endo -- inside; symbios -- living together), proposes
that the ingested prokaryotes continued to live with within their
hosts in a mutually beneficial arrangement, adopting specialized
functions as organelles. A large body of evidence supports this
theory. For example, the DNA and RNA of certain organelles is
like that of prokaryotic cells and different from that of the
nucleus; certain organelles have a separate cell membrane; and
organelles have separate reproductive mechanisms. Moreover,
chemical reactions within the tissue of eukaryotic cells are not
like those of certain organelles, whose own chemical reactions
more closely resemble those found in prokaryotes. Clearly,
evolution does not necessarily proceed in tiny mutation-based
steps occurring over millions of years!"
-----------
D.E. Fastovsky and D.B. Weishampel: _The Evolution and Extinction
of the Dinosaurs_.
(Cambridge University Press, New York 1996, p.67)


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