Space Phenomenon

1.4 Gravity

In the late eighteenth century an experiment was conducted in a stone house
on the outskirts of London to measure the mass of the Earth by knowledge of the
gravitational attraction of spheres of known mass. The work was completed by
Henry Cavendish who watched as a small lead barbell suspended by a fiber twisted
minutely under the gravitational tug of two bowling ball-sized weights. The size
of the twist revealed the strength of gravity between the two known masses, the
barbell and the balls. Because Cavendish knew how strong the Earth's
acceleration would be, he could then precisely resolve its mass. The experiment
rested on a knowledge of the gravitational constant of the Universe. This is one
of the fundamental quantities in nature but its exact resolution is not known.
Though constants such as the charge of the electron can be resolved to seven
decimal places, physicists are unable to measure G accurately after only the
third.

"It (the lack
of resolution) grates on me like a burr in the saddle,"

Science
December 1998

There has been continuing research to find an accurate answer for G
that has continued over many decades. To the dismay of the various teams instead
of producing work that has brought them collectively closer to a final answer
they have come up with significantly different values.

"You might say we've had negative progress,"

says Barry Taylor, a physicist at the National Institute of
Standards and Technology (NIST) in Gaithersburg, Maryland. However, the November
1998 meeting to honour the Cavendisg anniversary the 45 members of the Big G
community had a pleasant surprise. Six groups using a variety of techniques
weighed in with new values of G, and they were all in rough agreement. Though
the numbers seem to be converging there is slight skepticism from many members
of the scientific community because the data points represent a divergence from
the previous data (see figure 1). The general explanation offered at the present
time for the divergence is simply the continued refining of the empirical
results.

Figure 1 Diagram From Science December 1998 Showing the
New Experimental Data (red) Contrasting Previous Data (blue) For the Exact
Resolution of The Universal Gravitational Constant.

The problem of measuring G is that it is not possible to shield out the
gravitational attraction of other objects. Riley Newman, a physicist at the
University of California, Irvine, likes to tell the story of how his group
once discovered a peculiar early morning wiggle in gravity's strength. After
months of head-scratching, a graduate student leaving the lab at 3 a.m. was
literally doused by the answer: The sprinkler system on the surrounding lawn,
set on a regular clock, was soaking the ground with enough water to create an
additional nearby mass, which skewed the morning readings.

Science December 1998

The official value for G chosen by an international panel in 1986 comes from
a 1982 measurement by Gabe Luther, now at Los Alamos National Laboratory in New
Mexico, and William Towler of the University of Virginia. They deduced their
value by means of a setup not dissimilar to Cavendish's. In the Luther-Towler
experiment (in blue at the top of figure 1) a tiny barbell was hung from a long
fiber made of quartz or tungsten. When disturbed, the barbell would rotate
lazily back and forth about once every 6 minutes, driven by the fiber's
resistance to twisting. The addition of two large tungstun balls added an a
gravitational pull to the barbell a force that slowed the swing time by a split
second. By measuring that difference, Luther and Towler resolved G with an
estimated accuracy of better than a hundredth of a percent. This was excepted as
canon until 1994, when field leaders at the German standards lab, the PTB in
Braunschweig, announced a value of G that was purported as being equally as
accurate (far right blue plot on figure 1). Instead of suspending test weights
from a delicate fiber, they floated them on a layer of mercury. That allowed the
researchers to use larger masses and generate a stronger pull. To the surprise
of the community the German value came out considerably above the Luther-Towler
number a full half-percent larger. Things got worse in 1995 when New Zealand's
MSL came out with a number that significantly undercut the accepted value. Given
that the new values are converging it seems more likely that the debate will
soon be resolved.

A gravitational field is not as is often quoted a force, but more the warping
of space-time in relation to a mass or energy. This warping is a disturbance
moving out away from the object and extends theoretically to infinity. However,
the warping falls off as an inverse square function, thus becoming rapidly less
intense the further from the source. (Gribbin 1996) The communication of
gravitational fields between objects is by a hypothetical boson known as the
graviton. They carry the field strength for gravitational fields in a manner
identical to the way photons are used in electromagnetic fields.
(Kaufmann 1991) For a long time, there have been discussions on whether
the Universal
Gravitational Constant is constant or if there is not a slow variation with
time. It appears that these claims are unsupported empirically.

Paul A.M. Dirac, among the greatest theoretical physicist this century if not
of all time, once suggested that the universal gravitational constant, G,
weakened with time, in proportion to the age of the universe. Dirac's theory
stated that the force of gravity would be only half as strong in 10 billion
years as it is today. This became possible to assess empirically in the late
1960s. The moon’s distance from the Earth is understood to be slowly increasing
because of its tidal interaction with the Earth. If gravity were growing weaker
with time, the moon would recede from the earth even faster than conventional
theory predicted. Using laser pulses reflected from mirrors placed by Apollo
astronauts scientists showed that though the moon is indeed slowly receding it
is only at the expected rate, not the faster one Dirac's theory would imply.

Robert Ehrlich George Mason University

Scientific American Web Site

Robert Ehrlich in the physics department of George Mason University responds
to questions in Scientific American regarding the change of the Gravitational
Constant by explaining:

"Scientists do continually try to measure the constants of physics, but the
usual motivation is to get more precise values, rather than to check whether
those values have changed. If you had a technique to measure the speed of light
that was no better than one that was previously used, you might not bother to
make another measurement unless there were some reason to believe the previous
value was in error. Moreover, if you did measure the speed of light and got an
anomalous value, the odds are good that you would conclude that you had made a
mistake in the measurement, rather than that the speed of light 'hiccupped' that
particular day. State-of-the-art measurement techniques are extremely complex
and require all sorts of checks to be sure they have been performed correctly.
If in fact the constants of nature were changing, it would be very difficult to
know how precise your experiment needed to be to detect such a change, unless
you had some way of estimating the expected rate of change. Random, occasional
hiccups in the constants almost certainly would go undetected."

Scientific American Web Site

However, recent developments in an unrelated field may call into question
some previously adhered to theory concerning gravitational acceleration and
perhaps even the Gravitational Constant. Though these do not seem to suggest a
notable decrease with time exceptionally accurate measurements by JPL no longer
correspond to accepted values. (New Scientist No 2151). JPL in Pasedena
has been working for over a decade on the anomalous results and have so far been
unable to come up with an answer. It appears that data from space probes points
to an unknown gravitational attraction within our solar system. Close
observations of the trajectory of spacecraft reveals perturbations that some
scientists are seriously considering as evidence that our current theories of
gravity are wrong.

John Anderson of NASA's Jet Propulsion Laboratory in Pasadena:

"We've been working on this problem for several years, and we accounted for
everything we could think of,"

The Pioneer 10 probe has been sending messages to Earth since its launch in
1972. By studying the red shift of the returning radio-waves, one can calculate
the probe’s speed. Unusually Pioneer 10 seems to be slowing more quickly than it
should.

Anderson notes that the signals from Pioneer 10 are far from "clean". The
movement of the Earth around the Sun periodically alters the apparent redshift of
the waves. The probe also occasionally corrects its course so that its antenna
remains pointing towards the Earth. Scientists believe that all these factors
have been accounted for.

However, in 1987 the team working on the Pioneer 10 data found a systematic
anomaly that appeared to imply the probe was receiving additional deceleration
from the Sun. The disagreement is 80 billionths of a centimeter per second
squared. However JPL said to scientists used to working with absolute precision
it is a glaring discrepancy.

Pioneer 10's gauges show no unexpected loss of fuel so that could not be
responsible for the deceleration and it is not believed possible that the
interstellar could cause such a large deceleration. Thermal radiation from the
batteries of the spacecraft would be too small and would emit in all directions
not causing the kind of deceleration observed. The team also examined the
possibility of gravitation from an unknown asteroid but this too was deemed
impossible.

What gives their findings credence is that the effect is not limited to a
single space craft. If this phenomenon was observed only on Pioneer 10 then it
would be most likely an error or problem with the probe. However, Pioneer 11,
launched in 1973 is also slowing at about the same rate. The Ulysses probe,
launched in 1990 sent originally to slingshot over Jupiter appears to display
similar anomalies, as does data from Galileo.

New Scientist 12 September 1998 No. 2151 page 4

Figure 3 Diagram Showing the Positions of the Two Major
Probes Studied In the Gravitation Report.

The problem with what the JPL team is suggesting is that it is not observed
to affect anything else in the solar system:

Clifford Will, a physicist at Washington University in St Louis states:

"They're extremely good at what they do, but I think there's some kind of
systematic effect that has corrupted the data."

John Ries, a planetary scientist at the University of Texas at Austin,
expressed skepticism given that even a small acceleration would affect the
planets over a period of 4 ½ billion years. Anderson and his colleagues are
still cautious and have not ruled out a systematic error. More recent work seems
in agreement with the thoughts of John Rie. It has been suggested that the
retardation of distant spacecraft as documented in New Scientist 12 September
1998 No. 2151 page 4 may have a more straight forward explanation.

Since John Anderson of NASA's Jet Propulsion Laboratory in Pasadena came
forward with the evidence that as probes moved away from the Sun they slowed
down two scientists have suggested an alternative solution.

All the spacecraft have plutonium-based radioisotope thermoelectric
generators (RTGs) to power them. It is believed that resistance in the
spacecraft's circuits turns some of the electrical power produced by the RTGs
into heat. All probes are fitted with louvered fin heat sinks to radiate the
excess heat away. According to Edward Murphy, an astronomer at Johns Hopkins
University in Baltimore, Maryland.

The heat sinks appear to face away from the Sun, Murphy says the departing
photons give an acceleration according to Newton's Third Law. This would act as
a retardation to the overall speed slowing the probes down.

He concluded his findings of the radiation and retardation by saying:

"It's pretty close, and within observational errors,"

Jonathan Katz of Washington University in St Louis, Missouri, also blames
heat--in this case, the heat wasted because of the RTGs' inefficiency at turning
thermal energy into electricity. He points out that the satellites have large
antennas that point to the Earth, and that the RTGs sit just off to the side.
"The radiation can bounce off the back of the antenna and push the spacecraft
towards Earth," he says.

Anderson who as discussed above claims to have ruled out a heat effect as the
cause of the deceleration, is still unconvinced by the new arguments. "You can't
get the force you need," he says.

From New Scientist, 17 October 1998

Gravity and Antigravity

The ships of the Federation employ an artificial gravity system to allow
movement along planform decks. This is accomplished through the use of a network
of small gravity generators. The network is divided into four regions two within
the saucer section and two in the star drive section. All four networks are tied
to the Inertial Dampening System to allow effective "shock absorption" during
movement. The networks employ a series of graviton generators that create
short-lived graviton pulses. This allows the creation of artificial gravity in a
manner similar to the tractor beam emitters.

Early human-built interstellar ships used rotating centrifuges to mimic the
effects of gravity, though more modern Starfleet vessels use antigravity. Even
the very early ships used by the Federation including the Daedalus Class
launched prior to 2167 only 6 years after the founding of the United Federation
of planets would appear to have been equipped with antigravity generators given
the absence of rotating centrifuges in their hull geometries. The theory of
antigravity is being considered in the scientific community and periodically
claims arise from scientists claiming to have discovered the principles behind
nullifying gravity.

Figure 4 Diagram of Synthetic Gravity Generator From the
USS Enterprise NCC 1701 D

Sternbach and Okuda 1991

Andrew Trupin, in an interview with Scientific American stated his
belief that though it was possible to produce an equal and opposite magnetic
force to counterbalance the pull of gravity. Gravity its self was not a force
more a warping of space time and therefore nullifying gravity would require the
realignment of space time. This can not be achieved with magnetic fields that
can however, give an illusion of antigravity. At present no such "force" exists
that can undo the warping of space time.

Scientific American Web Site

Steinn Sigurdsson of the Institute of Astronomy at Cambridge University
addressed the general feasibility of counteracting the pull of gravity:

"One can imagine three ways of countering gravity."

The first method spoken of was similar to that dismissed by Turpin. This
was that something can provide a force opposing that of gravity. This as we
have addressed gives the illusion of antigravity because objects can seemingly
be made to levitate or otherwise act as if not under the pull of gravity.

The second way would be to find a new kind of force, unrelated to either
the electromagnetic or nuclear forces known to science, which would provide
repulsion on human scales. Searches for such a force have proved fruitless,
and the properties of any such undiscovered forces are severely constrained by
the many negative experiments.

Third, one can try to turn gravity against itself--that is, one can look
for non-intuitive effects in relativity theory or the little understood
quantum theory of gravity, which most physicists think may be formulated.

Solutions in relativity allow for the existence of repulsive forces related
to gravity. A curious solution exists in which infinite ‘walls’ of high density
are postulated, existing under very high surface tension. Such walls would repel
all matter with a constant acceleration. It has been conjectured by some
theorists that finite pieces of such walls could exist in the real universe and
provide local repulsion. Such objects have been invoked to explain some puzzles
of cosmology, although most physicists consider conventional explanations to be
more likely. In a related vein, a universal repulsive ‘force’ is also postulated
to have existed during the era of inflation. In this view, the early universe
swelled enormously because of a repulsive 'force' pervading the vacuum.

Smoot 1995

Creating Antigravity

Dutch physicist, Hendrik Casimir in 1948 put forward the first evidence for
the existence of a form of antigravity. Casimir, who was born in The Hague in
1909, He put forward his theory in the years from 1942 while working for the
electrical company Philips. The Casimir effect involves two parallel metal
plates, placed very close together with nothing in between them. The basis of
the effect is that what one would normally define as empty space is actually a
turbulent mass of virtual particles. This phenomenon is known as zero point
momentum.

Figure 5 Diagram Showing the Casimir Effect

Scientific American December 1997

Photons will be among the most common particles created in the vacuum.
Photons being the particles responsible for carrying the electromagnetic force.
Virtual photons are common, partly because a photon is its own antiparticle, and
partly because photons have no "rest mass. Photons with different energies are
associated with electromagnetic waves of different wavelengths, with shorter
wavelengths corresponding to greater energy.

Diagram 6 Illustration to Show the Electromagnetic
Spectrum

This series of virtual particle fluctuations gives the vacuum energy.
Unfortunately, this energy is the same everywhere, and so it cannot be detected
or used. Energy can only be used to do work, and thereby make its presence
known, if there is a difference in energy from one place to another.

However, though the above is true for virtual particles in an unbounded
vacuum; between two electrically conducting plates, electromagnetic waves would
only be able to form certain stable patterns. Such waves can only vibrate in
certain ways. The allowed vibrations are in the electromagnetic spectrum are
similar to the fundamental note for a particular length of string, and its
harmonics, or overtones

Diagram 7 Standing Wave Diagrams For Energy Bounded By Two
Plates.

Fundamental or First Harmonic

First Overtone Second Harmonic

Second Overtone third harmonic

Quite simply, no photon corresponding to a wavelength greater than the
separation between the plates can fit in to the gap. This means that some of the
activity of the vacuum is suppressed in the gap between the plates, while the
usual activity goes on outside. The result is that in each cubic centimeter of
space there are fewer virtual photons bouncing around between the plates than
there are outside, and so the plates feel a force pushing them together. Several
experiments have been carried out to measure the strength of the Casimir force
between two plates, using both flat and curved plates made of various kinds of
material. The force has been measured for a range of plate gaps from 1.4
nanometers to 15 and exactly matches Casimir's prediction.

Scientific American December 1997

Further Research Into Zero Point Motion

Zero
point motion in a Bose-Einstein Condensate
was quantitatively measured for the first time in May 1999, allowing
researchers, in effect, to study matter at a temperature of absolute zero.
materials cooled to absolute zero will never cease all motion due in effect to
the quantum mechanical principle of indeterminacy they will always be in slight
motion. MIT researcher Wolfgang Ketterle, measured such "zero-point motion" in a
sodium BEC, a collection of gas atoms that are collectively in the lowest
possible energy state. According to Ketterle,

"the
condensate has no entropy and behaves like matter at absolute
zero."

The
MIT physicists measured any form of motion by analysing the manner in
which   atoms absorb light at slightly lower or higher frequencies if
they are moving away from or towards the light. To determine these Doppler
shifts, the researchers used a technique known as Bragg scattering. In this
technique, atoms absorb photons at one energy from a laser beam and are
stimulated by a second laser to emit a photon at another energy which can be
shifted upward or downward depending on the atoms' motion towards or away from
the lasers. Measuring the range in energies of the emitted photons allowed the
researchers to determine the range of momentum values in the condensate.
Multiplying this measured momentum spread (delta p) by the size of the
condensate (delta x) gave an answer of approximately h-bar (Planck's constant
divided by 2 pi)--the minimum value allowed by Heisenberg's uncertainty relation
and quantum physics. While earlier BECs surely harvested this zero-point motion,
previous measurements of BEC momentum spreads were done with exploding
condensates having energies hundreds of times larger than the zero-point
energy.

Physical
Review Letters, 7 June 1999

The Existence of Antigravity

The uses of antigravity would be far reaching but and relates to the
discussion on an accompanying page where by the use of antigraviton fields are
discussed with respect to holing the "throat" of Einstein Rosen Bridges
open. In 1987, Morris and Thorne drew attention to such possibilities. In the
same paper, they concluded that:

"one should not blithely assume the impossibility of the exotic material that
is required for the throat of a traversable wormhole."

Gribbin Homepage

When
attempting to determine cosmological distances astronomers have techniques to
map the parameters of the Universe. many of these techniques rely on the use of
light or other electromagnetic wave.  what are commonly used are "standard
candles", instances where sources of known intrinsic strength can be used as a
function with red shift. It was Henrietta
Leavitt's 1912 discovery of the relation between the period and luminosity of
Cepheid variable stars allowed the construction of these standard candle
techniques. That is, certain events will always have the same intrinsic
energy if we know certain specifics. Stellar nova will always follow certain set
rules determined by their colour and frequency. By using Type 1a supernova it
was believed that distant galaxies could be charted and from any changes in
these the distances and recession of objects could be mapped. However in late
1997 it was realised that certain nova events were far fainter than they should
have been. A distant supernovae observed by Perlmutter and colleagues
towards the end of that year gave a result that contradicted the current
Universe model. It suggested that the expansion rate was actually increasing
rather than decreasing (Nature 391 51). Further research by other
groups confirmed their results. This suggested the
bodies were further away and retarding faster than had previously been believed.
two
team of astronomers - one led by Saul Perlmutter from the Lawrence Berkeley
National Laboratory, the other by Alex Filippenko of the University of
California at Berkeley - have found that the remnants of nearly all type 1a
supernovae are at least 15 % further away than the standard model of the
Universe predicts. The problem became that the Universe was
expanding more quickly than it should have been and the suggestion was that some
force was pulling the fabric of space apart. It looked like a form of
fundamental force that worked only on very macroscopic scales to push the
Universe apart.

Many astrophysicists believe that the Universe underwent a period
of incredibly rapid expansion shortly after the big bang. One consequence of
this "inflationary" model is that the Universe is "flat" with a value of Omega
equal to one. However, when all the visible mass in the Universe is added up, it
is much less than that needed to give a flat Universe. This is one of the main
motivations of the search for invisible or "dark" matter in the Universe.

Some cosmologists believe that the acceleration is caused by
quantum effects, which result in a non-zero cosmological constant, Lambda. If
the sum of Lambda and Omega equals 1, then the Universe will remain "flat", as
predicted by inflation theory.

Some groups have tried to measure Lambda by studying
gravitational lensing. If Lambda is non-zero, then astronomers should see more
lensing events than if Lambda were zero. According to Matthias Bartelmann of the
Max Planck Institute for Astrophysics in Garching, Germany, computer simulations
can predict the number of lensing events you should see for different values of
Lambda. His results approximately match observations of the gravitational
lensing of radio galaxies carried out by Chris Kochanek and colleagues from the
Harvard-Smithsonian Center for Astrophysics in the US (Astrophys J. 495 157). Their results place an upper
limit of 0.7 on Lambda and a lower limit of 0.3 on Omega. Both these figures
match the supernova data.

However, more recently (21 August
1999) warnings have been issued that scientists have noticed a new source of
bias in tracking supernovae. While the bias does not necessarily affect
arguments for a cosmological constant, it suggests that astronomers have
probably not yet pinpointed every possible source of error. The significance of
this finding was thrown into question when astronomers discovered that the most
distant of these supernovae might be inherently dimmer (New Scientist, 17 July,
p 4). Now Dale Howell, a graduate student at the University of Texas at Austin,
points out another possible problem in a paper to appear later this year in The
Astrophysical Journal.

Howell says that the central region of galaxies on
older photographic plates are usually overexposed, so supernovae are less likely
to be discovered there. In contrast, more modern digital photography exposes
galaxies evenly.

This is a problem because supernovae in the center of
galaxies vary much more in brightness than those on the edge. This leads to a
selection bias: closer supernovae discovered via photography might have
different properties from faraway supernovae found by more modern
methods.

"It makes it easier still to imagine that there's some
systematic error," says Adam Riess, a supernova spotter at the University of
California at Berkeley. However, Riess says that he and his team have attempted
to allow for such a bias in their measurements.

(New Scientist 21 August
1999)

Einstein Rosen
Bridges.

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