Ephraim FISCHBACH, et al.

Hypercharge -- Fifth Force 

Fifth Force

Occasionally, physicists have postulated the existence of a fifth force in addition to the four known fundamental forces. The force is generally believed to have roughly the strength of gravity (i.e. it is much weaker than electromagnetism or the nuclear forces) and to have a range of anywhere from less than a millimeter to cosmological scales.

The idea is difficult to test, because gravity is such a weak force: the gravitational interaction between two objects is only significant when one is very heavy. Therefore, it takes very precise equipment to measure gravitational interactions between objects that are small compared to the Earth. Nonetheless, in the late 1980s a fifth force, operating on municipal scales (i.e. with a range of about 100 meters), was reported by researchers (Fischbach et al.) who were reanalyzing results of Loránd Eötvös from earlier in the century. The force was believed to be linked with hypercharge. Over a number of years, other experiments have failed to duplicate this result, and physicists now believe that there is no evidence for a fifth force.

Theory and Experiment

There are at least three kinds of searches that can be undertaken, which depend on the kind of force being considered, and its range.

One way is to search for a fifth force with tests of the strong equivalence principle: this is one of the most powerful tests of Einstein's theory of gravity, general relativity. Alternative theories of gravity, such as Brans-Dicke theory, have a fifth force — possibly with infinite range. This is because gravitational interactions, in theories other than general relativity, have degrees of freedom other than the "metric," which dictates the curvature of space, and different kinds of degrees of freedom produce different effects. For example, a scalar field cannot produce the bending of light rays. The fifth force would manifest itself in an effect on solar system orbits, called the Nordtvedt effect. This is tested with Lunar Laser Ranging Experiment and very long baseline interferometry.

Another kind of fifth force, which arises in Kaluza-Klein theory, where the universe has extra dimensions, or in supergravity or string theory is the Yukawa force, which is transmitted by a light scalar field (i.e. a scalar field with a long Compton wavelength, which determines the range). This has prompted a lot of recent interest, as a theory of supersymmetric large extra dimensions — dimensions with size slightly less than a millimeter — has prompted an experimental effort to test gravity on these very small scales. This requires extremely sensitive experiments which search for a deviation from the inverse square law of gravity over a range of distances. Essentially, they are looking for signs that the Yukawa interaction is kicking in at a certain length.

Australian researchers, attempting to measure the gravitational constant deep in a mine shaft, found a discrepancy between the predicted and measured value, with the measured value being two percent too small. They concluded that the results may be explained by a repulsive fifth force with a range from a few centimetres to a kilometre. Similar experiments have been carried out onboard a submarine (USS Dolphin (AGSS-555)) while deeply submerged.

The above experiments search for a fifth force that is, like gravity, independent of the composition of an object, so all objects experience the force in proportion to their masses. Forces that depend on the composition of an object can be very sensitively tested by torsion balance experiments of a type invented by Loránd Eötvös. Such forces may depend, for example, on the ratio of protons to neutrons in an atomic nucleus, or the relative amount of different kinds of binding energy in a nucleus (see the semi-empirical mass formula). Searches have been done from very short ranges, to municipal scales, to the scale of the Earth, the sun, and dark matter at the center of the galaxy.

Other Interactions

A few physicists think that Einstein's theory of gravity will have to be modified, not at small scales, but at large distances, or, equivalently, small accelerations. They point out that dark matter, dark energy and even the Pioneer anomaly are unexplained by the Standard Model of particle physics and suggest that some modification of gravity, possibly arising from Modified Newtonian Dynamics or the holographic principle. This is fundamentally different from conventional ideas of a fifth force, as it grows stronger relative to gravity at longer distances. Most physicists, however, think that dark matter and dark energy are not ad hoc, but are supported by a large number of complementary observations and described by a very simple model.


Ephraim Fischbach, Daniel Sudarsky, Aaron Szafer, Carrick Talmadge, and S. H. Aronson, "Reanalysis of the Eötvös experiment", Physical Review Letters 56 3 (1986).
University of Washington Eöt-Wash group, the leading group searching for a fifth force.
Lunar Laser Ranging [1]
Satellite Energy Exchange (SEE) [2], which is set to test for a fifth force in space, where it is possible to achieve greater sensitivity.
The Tech Online -- Volume 105, Issue 58 (January 22, 1986)

Physicists Discover Fifth Force


David P. Hamilton

Physicists at Purdue University believe they have discovered a fifth elementary force of nature. This postulated force, named hypercharge, may oppose the force of gravity.

Dr. Ephraim Fischbach and his colleagues have reinterpreted the results of the experiments of Roland von Eotv"os, a Hungarian scientist of the early 20th century. Eotvos' work involved a test of the principle of equivalence, an Einsteinian postulate stating that gravity affects objects independently of their composition. Eotv"os found a small but systematic error in his calculations and declared a null experiment.

The principle of equivalence is one of the fundamental assumptions of Einstein's General Theory of Relativity. Even the verification of hypercharge is unlikely to seriously affect the principle, according to Peter Saulsan, a principle research scientist for the MIT Department of Physics.

Fischbach declared in the Jan. 6 issue of Physical Review Letters that Eotvos' error is systematic enough to prove the existence of an ephemeral force opposed to that of gravity.

Saulson said that Fischbach had found an "astoundingly good" correlation between the degree of the error and the baryon number of the tested materials. The baryon number of a material is equal to the total number of protons and neutrons in its nucleus.

The extremely localized effect of the hypercharge force would not significantly damage the theory of relativity, Saulsan said.

The principal differences between hypercharge and gravity appear to lie in the forces' effective range and strength, Saulsan said.

Unlike gravity, whose effects seem to extend to an infinite distance, hypercharge appears to have a finite range of approximately 200 meters, he continued.

Two other elementary forces, the strong and weak nuclear forces, also have finite ranges, although the range of these forces is more on the order of the diameter of the atomic nucleus, Saulsan said.

Fischbach also quoted the results of more recent experiments which seem to support the existence of hypercharge, Saulsan said.

Experiments conducted as far as one kilometer underground by Frank D. Stacey of the University of Queensland in Australia indicate that the force of gravity varies by as much as seven-tenths of one percent at different depths in the earth.

Other scientists have reported the apparent effects of another elementary force in experiments conducted at the Fermi National Accelerator Laboratory in Batavia, Illinois, according to a Jan. 8 article in the New York Times.

The theory of hypercharge could still face some problems, Saulsan claimed. For instance, Eotvos' "systematic trend" of error is greater than Stacey's reported gravitometric anomaly by a factor of more than 20.

Reasonable explanations for this disagreement exist, Saulsan suggested. He elaborated on the difficulty of Eotvos' original experiment, which involved the use of a torsion balance which would respond to gravity while taking the rotation of the earth into account.

Interpreting data from a 60-year-old experiment is also rather difficult, Saulsan said. In addition, Stacey's work required him to estimate the density of the rock above him as he conducted his experiments. These estimates could easily have been in error, he continued.

Four elementary forces have already been identified. In order from weakest to strongest, they are: gravity, electromagnetic, the weak nuclear force, and the strong nuclear force. Scientists believe that these forces can explain any phenomenon, including the creation of the universe.

If hypercharge actually does exist, it would be a step away from physicists' attempts to mathematically unify the elementary forces of nature, Saulsan said. But widespread acceptance of the theory would not threaten any physicist's "dearly-cherished notions," he added.

The theory would still be a "first-rate" discovery if verified, Saulsan said.,9171,1074978,00.html
Tuesday, Jun. 21, 2005

A Fifth Force?

In the famous anecdote, Galileo Galilei clambered to the top of the Leaning Tower of Pisa, simultaneously dropped cannonballs of different sizes and found that they all hit the ground at the same time. He thus convinced the world -- and in the years to come, Sir Isaac Newton and Albert Einstein as well -- that in a vacuum all objects, regardless of mass, fall at the same speed. Galileo's work went unchallenged until last week, when Purdue University Physics Professor Ephraim Fischbach, three of his graduate students and S.H. Aronson, a physicist at Brookhaven National Laboratory in New York, reported discerning a previously unknown force that causes objects of different masses to fall at different rates.

If Fischbach is proved right, his hypothetical force, which he calls hypercharge, would be the fifth known basic force. (Four forces are known to exist: gravity; electromagnetism; the strong force, which binds the atomic nucleus; and the weak force, which is responsible for certain types of radioactivity.) Hypercharge, Fischbach reports in Physical Review Letters, is an extremely weak repulsive force that acts between objects no more than about 600 feet apart and varies in strength from element to element. It is strongest in iron and weakest in hydrogen. Thus, the physicists contend, if an iron ball and, say, a feather were released simultaneously in a vacuum, the iron's repulsive hypercharge would act more strongly than the feather's to counteract the earth's gravity--and the feather would hit first.

The team began looking for evidence of hypercharge after perceiving what Fischbach calls "funny results" in two contemporary experiments, one involving gravity tests in a deep mine, the other the behavior of subatomic particles. "We felt the results could be explained with an additional force," says Fischbach, "so we went back to the data published by Baron Roland von Eötvös in Hungary in 1922 to see if we could find evidence." Eötvös had indirectly measured the speeds at which objects fall and found small discrepancies, which he attributed to limitations in his equipment. Re-examining the data, the team decided that the aberrations were caused by hypercharge. But other physicists caution that more experiments are necessary before a firm conclusion can be reached. Says Harvard University's Sheldon Glashow: "The work suggests an interesting direction, but by no means should be taken as a real discovery."
Phys. Rev. Lett. 56, 2347 - 2349 (1986)

Hypercharge Fields and Eötvös-Type Experiments

P. Thieberger
Department of Physics, Brookhaven National Laboratory, Upton, New York 11973

It is shown that Eötvös-type torsion-balance experiments performed in the vicinity of a large cliff may be used as sensitive tests for the recently postulated existence of a medium-range hypercharge force. The residual nonzero effect found in the original Eötvös results could be mainly due to terrain irregularities and thus be larger than, but still correlated to, the effects expected from the Earth's rotation and the hypercharge hypothesis.
Phys. Rev. Lett. 56, 3 - 6 (1986)

Reanalysis of the Eoumltvös experiment

Ephraim Fischbach
Institute for Nuclear Theory, Department of Physics, University of Washington, Seattle, Washington 98195

Daniel Sudarsky, Aaron Szafer, and Carrick Talmadge
Physics Department, Purdue University, West Lafayette, Indiana 47907

S. H. Aronson
Physics Department, Brookhaven National Laboratory, Upton, New York 11973

We have carefully reexamined the results of the experiment of Eötvös, Pekár, and Fekete, which compared the accelerations of various materials to the Earth. We find that the Eötvös-Pekár-Fekete data are sensitive to the composition of the materials used, and that their results support the existence of an intermediate-range coupling to baryon number or hypercharge.

Antigravity II: A Fifth Force?


John G. Cramer

Sometimes physics moves surprisingly fast, sometimes dismayingly slowly. In mid-December I wrote my AV column (Analog, 7/86) on antigravity, a familiar SF concept. That column was based on a 1957 paper by Bondi on negative mass. Almost nothing had been published on gravitational repulsion in the almost 30 years since the appearance of Bondi's paper. The scientific "field" of antigravity research was essentially non-existent.

Then, as soon as my column was safely submitted, hot new results on antigravity appeared. The lead article in the January 6, 1986 issue of Physical Review Letters had the unassuming title: "A Reanalysis of the Eötvös Experiment" by E. Fischbach, et al. Two days later the New York Times ran an article with the headline: "Hints of Fifth Force in Universe Challenge Galileo's Findings" describing the importance of Fischbach's work. Peculiar experimental results from terrestrial gravity measurements and from the behavior of "strange" K-mesons (kaons) had been explained by a new theory proposing a "hypercharge" force, a new fifth force of nature which is gravity-like but which repels rather than attracting nearby masses. This new antigravity force is the subject of this AV column.

The first thread of this story goes back two centuries to Sir Isaac Newton. Newton discovered the famous gravitational "inverse square-law" relation, F12 = Gm1m2/r2, which proved equally useful in predicting the orbit of the Moon and the force of gravity at the surface of the Earth. In Newton's equation G is a fundamental quantity called the universal gravitational constant. Among the physical constants of nature, G stands out as being the most uncertain. Fundamental constants (the velocity of light, the electron charge) are usually known to a few parts per million, but G, with a value of 6.673 × 10-11 m3/kg-s2, is known to only about 1 part in 2000.

In a way, it is surprising that G is so poorly known. The orbits of planets in our solar system depend directly on G and are both observed and calculated to parts per billion. The problem is that to obtain G from these data we must have a completely independent knowledge of the masses involved in the gravitational attraction. Unfortunately, we have no way, independent of orbital dynamics, of measuring the masses of the Earth, Moon, Sun, Jupiter, etc. Therefore, our imprecise knowledge of G must come from the very weak force of gravitational attraction observed in the laboratory between two masses, for example two large lead spheres placed close together.

But there is another way of measuring G. The oil industry has developed extremely precise devices for measuring g, the acceleration due to gravity, both on and beneath the Earth's surface. The dependence of the acceleration g on depth can be used to determine the gravity constant G. When the densities of the rock strata have been well mapped, this determination has an accuracy comparable to laboratory measurements of G. One would expect both methods to give the same value of the "constant". It is a big surprise, therefore, that the geological technique gives a value of 6.734 × 10-11 m3/kg-s2 (instead of 6.673 × 10-11). It would appear that this "universal constant" has significantly different values below the Earth's surface and in a surface laboratory.

The second thread of the story comes from modern particle physics. The species of particles called K-mesons or kaons are unusual among mesons in having a characteristic called hypercharge, a conserved property of certain particles. The neutral "matter" kaon is the Ko theoretically a system composed of a "down" quark and an "anti-strange" quark, has a hypercharge of +1. Its antimatter twin, the Kő, a strange quark and an anti-down quark, has a hypercharge of -1. Both Ko's have the same electrical charge (Q=0), the same spin (s=0), and the same mass (about half that of a proton). From all external clues these two theoretical particles are indistinguishable except in their hypercharge, which is not directly observable.

In this situation where two states of matter cannot be distinguished externally, quantum mechanics tells us that a very interesting thing happens. The two indistinguishable states are "mixed" to make two new states of matter which are distinguishable. This mixing produces from the combination (Ko-Kő) the particle KS which decays in about 10-10 seconds (and so is called K-short). And it produces from the combination (Ko+ Kő) the particle KL which decays 581 times more slowly (and therefore is called K-long). The KL particle has been found to be very peculiar in its decay into other particles, showing a favoritism for one direction of time over another and for matter over antimatter. These violations of symmetry principles of nature (time-reversal and charge invariance) are not understood in any fundamental way.

But more recently another peculiarity of the kaon system has been discovered which is even more of a puzzle. Detailed studies of the KL and KS mesons have been made at a number of accelerator laboratories under a variety of experimental circumstances. When these experiments are reduced to the few basic "constants" of the kaon system, for example the KL-KS mass difference and the KS half-life, these "constants" are found to depend on the velocity of the kaons with respect to the laboratory frame of reference. This is not a special relativity effect; those are already included in the data analysis. In fact, this velocity dependence cannot be readily accounted for by any of the four known forces or by any known physical effects.

Prof. Ephriam Fischbach and his colleagues, in the paper mentioned above, have sought to explain both of these curious results, the variation of G and the velocity dependence of the kaon system, with a single theory. They start with the fact that kaons, neutrons, and protons all have hypercharge. Perhaps, the paper speculates, there is new and very weak force associated with hypercharge which is responsible for the anomalies in both the gravitational and the kaon measurements. Starting from this point, they calculate the properties which such a "fifth" force must have to be consistent with these observations. They conclude that this new force would be very much like gravity, but with four important differences: (1) it depends on hypercharge rather than mass; (2) it is a repulsive force, in that objects with the same hypercharge are repelled from each other; (3) it has a strength only 0.7% that of gravity; and (4) it is a "short range" force which cuts off exponentially at distances on the order of 200 meters.

This last point requires some explanation. Two of the four known forces of nature, gravity and electromagnetism, are "long range" forces which fall off as 1/r2 with the distance from a massive or charged object but otherwise extend to infinity. The other two known forces, the weak and strong interactions, are "short range" and cut off to zero at distances on the order of the size of a nucleus. These differences in range are attributed to the masses of the "mediating particles" which produce the forces. Electromagnetism is mediated by the photon and gravity by the graviton, both particles with zero rest-mass which give their corresponding forces infinite range. The strong interaction is mediated by the gluon and the weak interaction by the Z and W particles, all of which have masses on the order of that of the proton and give their corresponding forces very short ranges. According to the "fifth force" hypothesis, the range of the force which would account for the G measurements and the kaon anomalies would have to be about 200 meters. This corresponds to a very light mediating particle (the "hyper-photon") with a mass about 10-14 that of the electron.

This hypothesis can explain the G difference. Gravitating objects within a few hundred meters of each other, for example, the lead spheres in a laboratory measurement of G, feel a 0.7% repulsion from the hypercharge force which reduces the attraction slightly and leads to a slightly low measured value for G. The geological measurements of g, however, record the gravitational attraction of masses which are typically much more distant than a few hundred meters and give a value of G unmodified by hypercharge repulsion.

The hypothesis can also explain the kaon energy dependence. The Ko and Kő, with opposite hypercharges, are mixed in slightly different proportions at different velocities because the extra hypercharge force from the nearby neutrons and protons of nuclei in the laboratory acts oppositely on them. Thus their invariant properties become variables. The "true" properties of the kaons, according to the hypercharge theory, would be obtained if measurements were made in empty space with no hypercharge field from nearby matter to modify the Ko+ Kő mixing.

Like any theory, this one need testing. And one "test" has already been done and seems to agree with the predictions of the theory. This test was not a new experiment but a re-analysis of the Eötvös Experiment, the famous experimental comparison of inertial and gravitational mass performed by a Hungarian count in the early decades of this century and published only after his death in 1922. Fischbach and his collaborators realized that Eötvös should have seen some evidence for the hypercharge force. The reason is that the hypercharge of a nucleus depends strictly on the number of neutrons and protons in the nucleus, while the mass of a nucleus depends also on the binding energy of the system. Thus an iron nucleus with large binding energy has a larger hypercharge-to-mass ratio than does a hydrogen nucleus. To put it another way, a kilogram sphere of water contains fewer neutrons and protons and has a smaller hypercharge than a kilogram sphere of iron. Therefore the sphere of water should fall slightly faster in vacuum than the iron sphere because there would be a smaller hypercharge force acting on the water than on the iron. The Eötvös experiment should have shown the effects of these small modifications of the force of gravity. And Fischbach's re-examination of the Eötvös data reveals that indeed the predicted effect does seem to be present in the old data.

This new theory has had its first experimental confirmation. Much more work in testing for the hypercharge force needs to be done, of course, before it can be considered as established. This is a "hot" topic and many experimental groups, including one in my own laboratory, are swinging into action to do the testing.

But in the nature of this column, let's assume for the moment that the hypercharge force is real and consider its science fiction implications. First, by damn, we have antigravity! But no dancing in the streets just yet, please! For use in the "normal" antigravity way in science fiction, the hypercharge force does have a few problems: (1) it's too weak, and (2) it only works over a few hundred meters of distance. So we need some hypercharge "amplifier", some way for getting more hypercharge without getting more mass. That might be possible if there were massless particles (maybe hyper-photons or neutrinos), that had hypercharge without having a proton-size mass, but none-such are known. Or perhaps there are "hyper-magnetic" effects when a hypercharged object is moved at a goodly velocity.

Anyhow, suppose we can overcome this obstacle and produce vehicles using hyper-repulsion. How might they work? Well, first of all the range is a problem. At 600 meters above the ground, the range effect will cut down the hyper-repulsion to only 5% of what it is at the surface. So the vehicle would be most effective at distances of 50 meters or less above the surface. It would resemble the "floaters" and "grav sleds" which are common SF techno-props, but it would not be directly useful in space travel or propulsion.

It's worth considering also that in the process of repelling the ground, the hyper-force on our hypothetical floater would also tend to repel the passengers. This unpleasant side effect might be avoided by placing the repulsion sources for minimum effect on the passengers, perhaps at many points which lie on the same spherical surface. But passenger-repulsion might also be turned into an advantage by using it to reduce or nullify the forces of acceleration. With a suitable hyperfield system high-performance spacecraft or aircraft might might, by balancing inertial forces with hyper-repulsion, be able to accelerate at many g's without squashing pilot and passengers. Free-fall space habitats might produce simulated gravity with hyperfield units mounted in the ceilings, with hyper-repulsion pushing the occupants toward the floor.

Anyhow, stay tuned to this column for further developments on the hypercharge force. The definitive tests of the theory will be well in progress by the time you read this column.


G Measurement Anomaly:
S. C. Holding and G. J. Tuck, Nature 307, 714 (1984).

Kaon Anomaly:
S. H. Aronson, G. J. Bock, H. Y. Cheng, and E. Fischbach, Physical Review D28, 476 (1983).

Fifth Force Theory:
E. Fischbach, D. Sudarsky, A. Szafer, C. Talmage, and S. H. Aronson, Physical Review Letters 56, 3 (1986).

Eötvös Experiment:
R. von Eötvös, D. Pekár, and E. Fekete, Ann. Phys. (Leipzig) 68, 11 (1922).

Was a fifth force felt? - Hypercharge or Baryon Number Theory

Dietrick E. Thomsen

Was a fifth force felt?

Physicists have divided all the motions in the universe into the domains of four kinds of force: gravity, electromagnetism, the weak subatomic force and the strong subatomic force or color force. Each of these has its source in a different property of material objects --for example, the source of gravity is mass, while that of electromagnetic forces is electric charge. Now, a fifth force is suggested.

Such proposals tend to arise from experimental anomalies that suggest an unknown force may be acting. In the Jan. 6 PHYSICAL REVIEW LETTERS, Ephraim Fischbach (temporarily at the University of Washington in Seattle), Daniel Sudarsky, Aaron Szafer and Carrick Talmadge of Purdue University in West Lafayette, Ind., and S. H. Aronson of Brookhaven National Laboratory in Upton, N.Y., propose that a fifth force was operating in a famous experiment done in Hungary in 1922 by Roland von Eotvos, D. Pekar and E. Fekete. The Eotvos experiment, as it is called, tested the law of gravity by measuring the gravitational attraction between the earth and various materials, including metals, woods and even grease or suet. Fischbach and his co-workers suggest that, unbeknownst to Eotvos and colleagues, slight differences in the responses of different materials indicate that in addition to gravity, a small, repulsive force was acting.

Fischbach and his co-workers relate this suggested force to a quality of matter called phpercharge or baryon number. The baryon number is related to the number of neutrons and protons, and therefore to the chemical composition of a material--thus explaining the difference in force for different materials. The researchers propose a formal similarity between this hypercharge force and electromagnetism. Just as electromagnetic forces are carried from object to object by intermediary particles called photons, so this hypercharge force would be carried by "hyperphotons.' A number of experiments could test for the existence of the hypercharge force, including a direct search for the hyperphotons themselves.
Astrophysics and Space Science,  Volume 126, Number 2 / October, 1986

A Scalar-Tensor Theory and the New Interaction

Luis O. Pimentel and Octavio Obregón

[ Department of Physics, Universidad Autónoma Metropolitana-Iztapalapa, P.O. Box 55-534, CP 09340 Mexico, D.F., Mexico ]

Abstract --- We present a scalar-tensor theory whose weak field limit gives exactly the potential proposed by Fischbach et al. (1986). The three experimental constants G infin, agr, and lambda are related to three parameters in our theory. At the level of the theory we have obtained the field produced by a source. The way this field should couple with a massive and lsquochargedrsquo particle (baryonic hypercharge) is a matter beyond the scope of this work.

The Search for Non-Newtonian Gravity


Ephraim Fischbach & Carrick L. Talmadge

Newton's inverse-square law of gravitation has been one of the cornerstones of physics ever since it was proposed 300 years ago. One of its most well known features is the prediction that all objects fall in a gravitational field with the same acceleration. This observation, in the form of the Equivalence Principle, is a fundamental assumption of Einstein's General Relativity Theory. This book traces the history of attempts to test the predictions of Newtonian Gravity, and describes in detail recent experimental efforts to verify both the inverse-square law and the Equivalence Principle. Interest in these questions have increased in recent years, as it has become recognized that deviations from Newtonian gravity could be a signal for a new fundamental force in nature. This is the first book devoted entirely to this subject, and will be useful to both graduate students and researchers interested in this field. This book describes in detail the ideas that underlie searches for deviations from the predictions of Newtonian gravity, focusing on macroscopic tests, since the question of gravitational effects in quantum systems would warrant a separate work. A historical development is combined with detailed technical discussions of the theoretical ideas and experimental results. A comprehensive bibliography with approximately 450 entries is provided.,9171,968137,00.html
Monday, Aug. 15, 1988

Was Sir Isaac All Wet?

By John Langone

As every physics student learns, there are four known forces of nature: gravity, electromagnetism, a "strong" force that binds atomic nuclei and a "weak" one that governs certain types of radioactive decay. Last week researchers at the Los Alamos National Laboratory announced that they may have found the best evidence yet for a hypothetical, elusive "fifth force." If confirmed, their findings could mean that Sir Isaac Newton's famous inverse- square law of gravity* is in danger of losing the exalted position it has held for three centuries. "It's like saying Mom and apple pie's no good anymore," admits the leader of the gravity project, Geophysicist Mark Ander. "You just don't do that lightly."

The physicists reached their conclusion as the result of an experiment conducted in Greenland last summer. They lowered a supersensitive gravity meter into a mile-deep hole bored in glacial ice -- chosen because its density is more uniform than that of rock -- and monitored the gravitational pull as the meter descended. What occurred was startling: the expected increase in gravitational force predicted by Newton was there, but it got stronger faster than expected. Either something was enhancing the force of gravity or the researchers had come upon a heretofore unknown, far more complex working of gravity itself. Or, just possibly, they had made a mistake.

The fifth force, if that is what it is, has been a source of debate among physicists since its existence was suggested in 1981 by Australian mineshaft experiments. Five years later, Purdue University Physics Professor Ephraim Fischbach measured a weak force he called "hypercharge" and theorized that it caused objects of different composition to fall at different rates. Since Fischbach's finding, as many as 45 experiments have sprung up in search of the mystery force, and so far each has served only to confound rather than clarify the issue.

In some, for example, gravity appears to be enhanced, while in others it seems to be counteracted. Moreover, findings from a U.S. Air Force gravity study were even interpreted by some scientists as evidence of a "sixth force." But if the existence of an additional force was proved, scientists would have to readjust their calculations of gravitational force. "It's like something completely out of left field," notes Los Alamos Physicist Terry Goldman. "You don't know quite what to do with it."

Jim Thomas, a physicist at the California Institute of Technology, praises the technical precision of Ander's experiment, but cautions that measuring gravity in holes is inexact at best. He points out, for example, that an aberration in the earth's crust might have caused the unusual measurements. "What we're really talking about is the possible modification of gravity, which is the fourth force," adds Thomas. Even Ander stresses that rigorous confirmation is needed before he accepts the results of his Greenland experiment. Says he: "You keep saying to yourself, 'Gee, I've gotta be wrong -- Newton certainly can't be wrong.' "

FOOTNOTE: *Newton's law holds that gravitational pull increases in inverse proportion to the square of the distance between two bodies.

Energy Citations Database
( 1986 Mar 31 )

Experimental signals for hyperphotons

Aronson, S.H. ; Cheng, H. ; Fischbach, E. ; Haxton, W.

We discuss experiments for detecting hyperphotons (..gamma../sub Y/), which are the real quanta of a hypercharge field whose existence has been suggested by a recent reanalysis of the Eoetvoes experiment.^It is shown that ..gamma../sub Y/ is best detected as an unobserved neutral in the decays K/sup + -/..--> pi../sup + -/..gamma../sub Y/ and K/sub S//sup 0/..--> pi../sup 0/..gamma../sub Y/, and that existing experimental limits provide nontrivial constraints on the strength and range of possible hypercharge couplings.

By Fischbach, Ephraim    Sudarsky, Daniel    Szafer, Aaron    Talmadge, Carrick    Aronson, S. H.

By Fischbach, Ephraim    Sudarsky, Daniel    Szafer, Aaron    Talmadge, Carrick    Aronson, S. H.

By Milgrom, Mordehai

By Goldman, T.    Hughes, Richard J.    Nieto, MichaelMartin

By Fayet, P.

By Talmadge, Carrick    Aronson, S. H.    Fischbach, Ephraim

By Glashow, S. L.

By Moffat, J. W.    Savaria, P.    Woolgar, E.

By Elizalde, E.

By De Rujula, A.

By Fischbach, Ephraim    Sudarsky, Daniel    Szafer, Aaron    Talmadge, Carrick    Aronson, S. H.

By Fischbach, Ephraim    Sudarsky, Daniel    Szafer, Aaron    Talmadge, Carrick    Aronson, S. H.

By Talmadge, Carrick    Fischbach, Ephraim    Aronson, S. H.

By Talmadge, Carrick    Fischbach, Ephraim

By Fischbach, Ephraim    Talmadge, Carrick

By Talmadge, Carrick    Fischbach, Ephraim

By Fischbach, Ephraim    Talmadge, Carrick

Isis, Vol. 86, No. 2 (Jun., 1995), pp. 355-356

Book Review: R. Corby Hovis

The Rise and Fall of the Fifth Force: Discovery, Pursuit, and Justification in Modern Physics


Allan Franklin

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