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ARRoGANT CoURiERS WiTH ESSaYS
Grade Level: Type of Work Subject/Topic is on:
[ ]6-8 [ ]Class Notes [Origins and Bibliography]
[x]9-10 [ ]Cliff Notes [of the Big Bang Theory ]
[ ]11-12 [x]Essay/Report [ ]
[ ]College [ ]Misc [ ]
Dizzed: 10/94 # of Words:4067 School: ? State: ?
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ORIGINS: Background & Bibliography
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Assembled for the PHILOsophy Conference of:
Computer Connection PO Box 382
BBS (609) 784-9404 Voorhees, NJ 08043
by T.A. Hare Nov. 13, 1985
Topic: Areas of interaction between philosophy, science, and<6E>religion.
Part I - Big Bang (Astronomy)
Part II - Unified Field (Particle Physics)
Part III - Evolution (Biology).
Part IV - Theologic interaction
- - - -
Part II - Unified Field Theory of Particle Physics:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
And God said, "Let there be an expanse between the waters
to separate water from water." (Gen. 1:6)
And God said, "Let the water under the sky be gathered to one place,
and let dry ground appear." And it was so. (Gen. 1:9)
- - - -
Further reading:
1. John H. Schwartz, "Completing Einstein", SCIENCE 85, vol 6, pp 60-64,
1985.
2. Robert Palmer, "What's a Quark?", SCIENCE 85, VOL 6, pp 66-71, 1985
3. Bruce Schechter, "The Moment of Creation", DISCOVER, April 1983,
pp 18-25.
4. Lawrence R. Sulak, "Waiting for the Proton to Decay", AMERICAN
SCIENTIST, 70, 616-625, 1982.
5. Mary K. Gaillard, "Toward a Unified Picture of Elementary Particle
Interactions", AMERICAN SCIENTIST 70, 506-514.
- - - -
The following background articles were downloaded from American Adacemic
Encyclopedia via Dow Jones News Retrevial Service; Nov 12, 1985
UNIFIED FIELD THEORY
Classical attempts at devising a unified field theory, principally those
of Einstein, were concerned with the combination of gravitation (the
general theory of RELATIVITY) and electromagnetism into the same
theoretical framework. Electromagnetism is described by MAXWELL'S EQUATIONS
for an antisymmetric tensor, whereas Einstein's theory of gravitation
centers about a symmetric metric tensor; Einstein's idea was to combine
both descriptions into a single, nonsymmetric tensor, thereby treating both
subjects from an essentially geometric point of view. Other attempts to
incorporate electromagnetism into the basically geometric formalism of
general relativity were made by Hermann Weyl (1918) and more recently by
John Wheeler; although some theories are more esthetic than others, all
lack the connection with quantum phenomena that is so important for
interactions other than gravitation.
More-recent attempts at unification have been made from the quite
different point of view of merging the quantum field theories that (are
supposed to) describe the four FUNDAMENTAL INTERACTIONS of gravity,
electromagnetism, and the weak and the strong nuclear interactions. The
most palatable unification so far has been given by Steven WEINBERG of
Harvard University and independently by Abdus SALAM of Imperial College,
London, joining electromagnetism and the weak interactions. In the simplest
version of this type of unified gauge theory, forces are transmitted by the
exchange of four different types of particles called bosons, which are
assumed to be massless. By means of a "broken symmetry" an effective
generation of masses occurs, so that the Weinberg-Salam theory envisages
the weak interactions as being transmitted by massive "W" mesons, in which
one meson, identified with the photon, remains massless, while the other
three, identified with the quanta that transmit the weak interaction, are
estimated to be quite heavy. Their rest-mass energies are on the order of
50 to 100 times the mass of the proton, and their observation should become
possible with the next generation of high-energy accelerators. So far, the
Weinberg-Salam theory has passed every unambiguous test to which it has
been subjected. Weinberg and Salam shared the 1979 Nobel Prize for physics
for their model.
Many other unified theories, involving strong interaction and even
gravitation, have recently been proposed. Such grand unification schemes to
date have unavoidable and questionable consequences, such as the removal of
the separate conservation of baryon and lepton number; they predict a
proton could decay into a lepton plus pions--an improbable event that is
actively being searched for at present. Recent grand unification schemes
require the existence of magnetic MONOPOLES. These hypothetical particles,
also called grand unification monopoles (GUMs), are thought to be very
massive, with a mass ranging from 10 to the 16th power to 10 to the 19th
power GeV. No experimental evidence of monopoles has yet been found. H.
M. FRIED
Bibliography
Bergmann, Peter G., Introduction to the Theory of Relativity (1942;
repr. 1976)
Einstein, Albert, The Meaning of Relativity, 5th ed. (1956)
Hadlock, Charles, Field Theory and Its Classical Problems (1979)
Tonnelat, Marie A., Einstein's Theory of Unified Fields (1966).
- - - -
RELATIVITY
Albert Einstein's theory of relativity has caused major revolutions in
physics and astronomy during the 20th century. It introduced to science the
concept of "relativity"--the notion that there is no absolute motion in the
universe, only relative motion--thus superseding the 200-year-old theory of
mechanics of Isaac Newton. Einstein showed that we reside not in the flat,
Euclidean space and uniform, absolute time of everyday experience, but in
another environment: curved space-time. The theory played a role in
advances in physics that led to the nuclear era, with its potential for
benefit as well as for destruction, and that made possible an understanding
of the microworld of elementary particles and their interactions. It has
also revolutionized our view of COSMOLOGY, with its predictions of
apparently bizarre astronomical phenomena such as the BIG BANG, NEUTRON
STARS, BLACK HOLES, and gravitational waves (see GRAVITATION).
Scope of Relativity
The theory of relativity is a single, all-encompassing theory of
space-time, gravitation, and mechanics. It is popularly viewed, however,
as having two separate, independent theoretical parts-- special relativity
and general relativity. One reason for this division is that Einstein
presented special relativity in 1905, while general relativity was not
published in its final form until 1916. Another reason is the very
different realms of applicability of the two parts of the theory: special
relativity in the world of microscopic physics, general relativity in the
world of astrophysics and cosmology.
A third reason is that physicists accepted and understood special
relativity by the early 1920s. It quickly became a working tool for
theorists and experimentalists in the then-burgeoning fields of atomic and
nuclear physics and quantum mechanics. This rapid acceptance was not,
however, the case for general relativity. The theory did not appear to have
as much direct connection with experiment as the special theory; most of
its applications were on astronomical scales, and it was apparently limited
to adding miniscule corrections to the predictions of Newtonian gravitation
theory; its cosmological impact would not be felt for another decade. In
addition, the mathematics of the theory were thought to be extraordinarily
difficult to comprehend. The British astronomer Sir Arthur Eddington, one
of the first to fully understand the theory in detail, was once asked if it
were true that only three people in the world understood general
relativity. He is said to have replied, "Who is the third?"
This situation persisted for almost 40 years. General relativity was
considered a respectable subject not for physicists, but for pure
mathematicians and philosophers. Around 1960, however, a remarkable
resurgence of interest in general relativity began that has made it an
important and serious branch of physics and astronomy. (By 1977,
Eddington's remark was recalled at a conference on general relativity
attended by more than 800 researchers in the subject.) This growth has its
roots, first, beginning around 1960, in the application of new mathematical
techniques to the study of general relativity that significantly
streamlined calculations and that allowed the physically significant
concepts to be isolated from the mathematical complexity, and second, in
the discovery of exotic astronomical phenomena in which general relativity
could play an important role, including quasars (1963), the 3-kelvin
microwave background radiation (1965), pulsars (1967), and the possible
discovery of black holes (1971). In addition, the rapid technological
advances of the 1960s and '70s gave experimenters new high-precision tools
to test whether general relativity was the correct theory of gravitation.
The distinction between special relativity and the curved space-time of
general relativity is largely a matter of degree. Special relativity is
actually an approximation to curved space-time that is valid in
sufficiently small regions of space-time, much as the overall surface of an
apple is curved even though a small region of the surface is approximately
flat. Special relativity thus may be used whenever the scale of the
phenomena being studied is small compared to the scale on which space-time
curvature (gravitation) begins to be noticed. For most applications in
atomic or nuclear physics, this approximation is so accurate that
relativity can be assumed to be exact; in other words, gravity is assumed
to be completely absent. From this point of view, special relativity and
all its consequences may be "derived" from a single simple postulate. In
the presence of gravity, however, the approximate nature of special
relativity may manifest itself, so the principle of equivalence is invoked
to determine how matter responds to curved space-time. Finally, to learn
the extent that space-time is curved by the presence of matter, general
relativity is applied.
Special Relativity
The two basic concepts of special relativity are the inertial frame and
the principle of relativity. An inertial frame of reference is any region,
such as a freely falling laboratory (see FREE FALL), in which all objects
move in straight lines with uniform velocity. This region is free from
gravitation and is called a Galilean system. The principle of relativity
postulates that the result of any physical experiment performed inside a
laboratory in an inertial frame is independent of the uniform velocity of
the frame. In other words, the laws of physics must have the same form in
every inertial frame. A corollary is that the speed of light must be the
same in any inertial frame (because a speed-of-light measurement is a
physical experiment) regardless of the speed of its source or that of the
observer. Essentially all the laws and consequences of special relativity
can be derived from these concepts.
The first important consequence is the relativity of simultaneity.
Because any operational definition of simultaneous events at different
locations involves the sending of light signals between them, then two
events that are simultaneous in one inertial frame may not be simultaneous
when viewed from a frame moving relative to the first. This conclusion
helped abolish the Newtonian concept of an absolute, universal time. In
some ways the most important consequences and confirmations of special
relativity arise when it is merged with quantum mechanics, leading to many
predictions in agreement with experiments, such as elementary particle
spin, atomic fine structure, antimatter, and so on.
The mathematical foundations of special relativity were explored in 1908
by the German mathematician Hermann Minkowski, who developed the concept of
a "four-dimensional space-time continuum," in which time is treated the
same as the three spatial dimensions--the fourth dimension of Minkowski
space-time.
The Principle of Equivalence and Space-time Curvature
The exact Minkowski space-time of special relativity is incompatible
with the existence of gravity. A frame chosen to be inertial for a particle
far from the Earth where the gravitational field is negligible will not be
inertial for a particle near the Earth. An approximate compatibility
between the two, however, can be achieved through a remarkable property of
gravitation called the weak equivalence principle (WEP): all modest-sized
bodies fall in a given external gravitational field with the same
acceleration regardless of their mass, composition, or structure. The
principle's validity has been checked experimentally by Galileo, Newton,
and Friedrich Bessel, and in the early 20th century by Baron Roland von
Eotvos (after whom such experiments are named). If an observer were to ride
in an elevator falling freely in a gravitational field, then all bodies
inside the elevator, because they are falling at the same rate, would
consequently move uniformly in straight lines as if gravity had vanished.
Conversely, in an accelerated elevator in free space, bodies would fall
with the same acceleration (because of their inertia), just as if there
were a gravitational field.
Einstein's great insight was to postulate that this "vanishing" of
gravity in free-fall applied not only to mechanical motion but to all the
laws of physics, such as electromagnetism. In any freely falling frame,
therefore, the laws of physics should (at least locally) take on their
special relativistic forms. This postulate is called the Einstein
equivalence principle (EEP). One consequence is the gravitational redshift,
a shift in frequency f for a light ray that climbs through a height h in a
gravitational field, given by (delta f)/f = gh/cc where g is the
gravitational acceleration. (If the light ray descends, it is blueshifted.)
Equivalently, this effect can be viewed as a relative shift in the rates of
identical clocks at two heights. A second consequence of EEP is that
space-time must be curved. Although this is a highly technical issue,
consider the example of two frames falling freely, but on opposite sides of
the Earth. According to EEP, Minkowski space-time is valid locally in each
frame; however, because the frames are accelerating toward each other, the
two Minkowski space-times cannot be extended until they meet in an attempt
to mesh them into one. In the presence of gravity, space-time is flat only
locally but must be curved globally.
Any theory of gravity that fulfills EEP is called a "metric" theory (from
the geometrical, curved-space-time view of gravity). Because the
equivalence principle is a crucial foundation for this view, it has been
well tested. Versions of the Eotvos experiment performed in Princeton in
1964 and in Moscow in 1971 verified EEP to 1 part in 10(12). Gravitational
redshift measurements using gamma rays climbing a tower on the Harvard
University campus (1965), using light emitted from the surface of the Sun
(1965), and using atomic clocks flown in aircraft and rockets (1976) have
verified that effect to precisions of better than 1 percent.
General Relativity
The principle of equivalence and its experimental confirmation reveal
that space-time is curved by the presence of matter, but they do not
indicate how much space-time curvature matter actually produces. To
determine this curvature requires a specific metric theory of gravity, such
as general relativity, which provides a set of equations that allow
computation of the space-time curvature from a given distribution of
matter. These are called field equations. Einstein's aim was to find the
simplest field equations that could be constructed in terms of the
space-time curvature and that would have the matter distribution as source.
The result was a set of 10 equations. This is not, however, the only
possible metric theory. In 1960, C. H. Brans and Robert Dicke developed a
metric theory (see GRAVITATION) that proposed, in addition to field
equations for curvature, equations for an additional gravitational field
whose role was to mediate and augment the way in which matter generated
curvature. Between 1960 and 1976 it became a serious competitor to general
relativity. Many other metric theories have also been invented since 1916.
An important issue, therefore, is whether general relativity is indeed
the correct theory of gravity. The only way to answer this question is by
means of experiment. In the past scientists customarily spoke of the three
classical tests proposed by Einstein: gravitational redshift, light
deflection, and the perihelion shift of Mercury. The redshift, however, is
a test of the equivalence principle, not of general relativity itself, and
two new important tests have been discovered since Einstein's time: the
time-delay by I. I. Shapiro in 1964, and the Nordtvedt effect by K.
Nordtvedt, Jr., in 1968.
The confirmation of the deflection of starlight by the Sun by the solar
eclipse expedition of 1919 was one of the triumphant moments for general
relativity and brought Einstein worldwide fame. According to the theory, a
ray of light propagating through the curved space-time near the Sun should
be deflected in direction by 1.75 seconds of arc if it grazes the solar
surface. Unfortunately, measurements of the deflection of optical starlight
are difficult (in part because of need for a solar eclipse to obscure the
light of the Sun), and repeated measurements between 1919 and 1973 yielded
inaccurate results. This method has been supplanted by measurements of the
deflection of radio waves from distant quasars using radio-telescope
interferometers, which can operate in broad daylight. Between 1969 and
1975, 12 such measurements ultimately yielded agreement, to 1 percent, with
the predicted deflection of general relativity.
The time-delay effect is a small delay in the return of a light signal
sent through the curved space-time near the Sun to a planet or spacecraft
on the far side of the Sun and back to Earth. For a ray that grazes the
solar surface, the delay amounts to 200 millionths of a second. Since 1964,
a systematic program of radar ranging to the planets Mercury and Venus, to
the spacecraft Mariners 6, 7, and 9, and to the Viking orbiters and landers
on Mars has been able to confirm this prediction to better than half of 1
percent.
Another of the early successes of general relativity was its ability to
account for the puzzle of Mercury's orbit. After the perturbing effects of
the other planets on Mercury's orbit were taken into account, an
unexplained shift remained in the direction of its perihelion (point of
closest approach to the Sun) of 43 seconds of arc per century; the shift
had confounded astronomers of the late 19th century. General relativity
explained it as a natural effect of the motion of Mercury in the curved
space-time around the Sun. Recent radar measurements of Mercury's motion
have confirmed this agreement to about half of 1 percent.
The Nordtvedt effect is one that does not occur in general relativity but
is predicted by many alternative metric theories of gravity, including the
Brans-Dicke theory. It is a possible violation of the equality of
acceleration of massive bodies that are bound by gravitation, such as
planets or stars. The existence of such an effect would not violate the
weak equivalence principle that was used as a foundation for curved
space-time, as that principle applies only to modest-sized objects whose
internal gravitational binding is negligible. One of the remarkable
properties of general relativity is that it satisfies EEP for all types of
bodies. If the Nordtvedt effect were to occur, then the Earth and Moon
would be attracted by the Sun with slightly different accelerations,
resulting in a small perturbation in the lunar orbit that could be detected
by lunar laser ranging, a technique of measuring the distance to the Moon
using laser pulses reflected from arrays of mirrors deposited there by
Apollo astronauts. In data taken between 1969 and 1976, no such
perturbation was detected, down to a precision of 30 cm (1 ft), in complete
agreement with the zero prediction of general relativity and in
disagreement with the prediction of the Brans-Dicke theory.
A number of secondary tests of more subtle gravitational effects have
also been performed during the last decade. General relativity has passed
every one, while many of its competitors have failed. Continuing to test
general relativity is important, in order to strengthen confidence in its
use as a tool for analyzing many of the newly discovered phenomena in
astronomy and astrophysics.
Cosmology
One of the first astronomical applications of general relativity was in
the area of cosmology. The theory predicts that the universe could be
expanding from an initially condensed state, a process known as the big
bang. Despite many challenges (including the popularity during the 1950s
of the steady-state theory), the big bang is now accepted as the standard
model of the universe. Three important pieces of evidence, accumulated
mainly since 1960, support this conclusion: (1) more precise measurements
of the universe's expansion rate, first measured by Edwin Hubble in 1929,
indicating that the big bang occurred between 10 and 20 billion years ago;
(2) the discovery in 1965 of the 3K (3 degrees above absolute zero)
microwave background radiation, a uniform "sea" of electromagnetic
radiation left over from the earlier hot phase of the universe (700,000
years after the big bang); and (3) the realization that the observed cosmic
abundance of helium (20 to 30 percent by weight) is necessarily produced in
the conditions of the big bang. One aspect of the model that is still
uncertain is whether the universe will continue to expand indefinitely or
whether it will slow down and eventually recollapse to a "big crunch."
Astronomical observations may yield an answer.
Another important application of general relativity is to the theory of
neutron stars, bodies that have been so compressed by gravitational forces
that their density is comparable to that within the atomic nucleus, and
their composition is primarily neutrons. (A neutron star whose mass equals
that of the Sun has a radius of only 10 km/6 mi.) They are thought to occur
as a by-product of such violent events as supernovae and other
gravitational implosions of stars. Pulsars, first discovered in 1967, are
generally believed to be rapidly spinning neutron stars. Pulsars are
objects that emit pulses of radio waves at regular intervals, ranging from
about 30 milliseconds to 3 seconds; as of 1979, 200 have been discovered.
According to one model, the neutron star acts as a lighthouse, emitting a
narrow beam from its surface that sweeps by an observer's telescope once
each rotation period.
One of the most exotic predictions of general relativity is the black
hole. Implosions of extremely massive stars can proceed beyond the neutron
star configuration. As the matter continues to implode, it crosses an
imaginary spherical surface known as the event horizon, located at a radius
given by 2MG/cc, where M is the mass that has imploded and G is Newton's
constant of gravitation; for one solar mass, this radius is about 3 km (1.9
mi). Once inside the event horizon, nothing--not even light--can escape.
The exterior space-time geometry of the black hole is described by the
Schwarzschild solution of the field equations if it has no rotation, and by
the Kerr solution if it rotates (solutions discovered respectively in 1916
by Karl Schwarzschild and in 1963 by R. Kerr). Rather strong evidence now
exists that the companion of the star denoted HDE 226868 in the
constellation Cygnus is a black hole. According to the most favored model,
gas from the atmosphere of HDE 226868 is stripped off by the gravitational
field of the hole, heats up as it falls toward the hole, and emits copious
amounts of X rays just before plunging across the event horizon. The X rays
from this source, called Cygnus X-1, were detected in 1971 by a telescope
on a satellite called Uhuru. Some theorists have speculated that
supermassive black holes may exist at the centers of some clusters of stars
(with masses of 1 thousand solar masses) and of some galaxies (with masses
of 1 million to 1 billion solar masses), including perhaps our own.
One prediction of general relativity has not yet been verified:
gravitational radiation, a wave of gravitational force that travels at the
speed of light, transports energy, and induces relative motion between
pairs of particles in its path or produces strains in bulk objects.
Astrophysicists believe that it should be emitted by dynamic sources such
as supernovae, double-star systems, and black-hole formations and
collisions. Although experiments around 1970 using 1.5-ton aluminum
cylinders fitted with strain gauges were thought to have detected it,
subsequent experiments by other groups did not confirm the detection. A
worldwide effort is now in progress to build gravitational radiation
antennas, not only to detect this phenomenon but also, ultimately, to make
use of it as a new window on the universe.
Recently, indirect evidence for the existence of gravitational radiation
has been discovered in a system known as a binary pulsar, a pulsar in orbit
around a companion star. Careful measurements, by radio telescopes, of the
motion of the pulsar have shown that the orbit is losing energy and is
decaying at just the rate to be expected from the loss of energy by means
of emission of gravitational waves by the system. CLIFFORD M. WILL
Bibliography
Barnett, Lincoln, The Universe and Dr. Einstein, rev. ed. (1968)
Born,Max, Einstein's Theory of Relativity, rev. ed. (1962)
Einstein, Albert, The Meaning of Relativity, 5th ed. (1956)
Gardner, Martin, Relativity for the Millions (1962)
Reichenbach, Hans, The Philosophy of Space and Time, trans. by
Maria Reichenbach (1958)
Russell, Bertrand, The A B C of Relativity, 3d ed. (1969)
Struble, Mitch, The Web of Space-Time: A Step by Step Exploration
of Relativity (1973)
Taylor, E. F., and Wheeler, J. A., Spacetime Physics (1966)
Weinberg, Steven, The First Three Minutes (1977).
See also - CLOCK PARADOX; SPACE-TIME CONTINUUM; WORLD LINE.
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