New Phenomena

One of the most delightful things about the physical sciences is that every year or so a new phenomenon comes along which “doesn't fit." The best of these are experimental results or observations which are completely unanticipated by contemporary understanding and without precedent on the basis of established theory or past results. Perhaps half of these reports of new phenomena turn out to be wrong. The recent “discoveries” of magnetic monopoles in Berkeley , of super-heavy elements in Tallahassee , and of cosmic-ray “quarks” in a cloud chamber in Australia are notable examples of reported discoveries which failed to withstand close examination.

However, while some “discoveries” have been found to arise from instrumental problems or from unduly optin1istic.analysis, there are others such as the Mössbauer effect (Mössbauer, Nobel Prize, 1961), the CP violation of the K₂⁰ meson decay (Fitch and Cronin, Nobel Prize, I980), or the observation of the 2.7° radiation from the Big Bang (Penzias and Wilson, Nobel Prize, I978), which have turned a field on its head and demanded a thorough revision of current ideas to accommodate the new phenomenon.

Among experimental physicists, this is the Mother Lode, the Holy Grail, the payoff for a lifetime of all-night runs, lavish attention to minute experimental detail, and plain hard work. The chances of a given group of scientists making such a discovery are, of course, very small, and there are no guaranteed paths to such discoveries. Not even the most carefully planned experimental program is assured of striking the “pay dirt” of a new result. Nevertheless, it is the possibility of finding a new phenomenon which provides a sizable part of the excitement and intellectual stimulation of experimental science and which compensates for the long hours and the less-than-you-could-get-as-a-plumber pay scale.

This article describes three experimental/observational results that seem to qualify as “new phenomena.” Each of them has already been around for a few years, first as a suspected “glitch,” then as an un-understood result that has stubbornly refused to go away. Any of these results may yet prove to be spurious, but they also have the potential for causing revolutions in their respective fields. These phenomena are (l) the discovery at Stanford of “something” having only a fraction of the charge of an electron, (2) the observation at    Berkeley of “accident-prone" fragments of nuclei with five or so times the normal chance of collision, and (3) the observation by several groups of radio astronomers of objects that appear to be moving faster than the speed of light.

I. Quarks in a Jukebox?

Fifteen years ago the theoretical physicist Murray Gell-Mann of CalTech suggested that there might exist a new kind of fundamental particle that he called a quark. These new particles were supposed to have the peculiar property of fractional charge, in that they would have only l/3 or 2/3 of the electrical charge of a proton or an electron. They were supposed to be the constituent particles from which all of the heavy particles previously considered to be fundamental (protons, neutrons, p mesons, etc.) were constructed.

This prediction set off a veritable gold rush among experimental physicists to try to discover the first free or “bare” quark.  They tried to produce quarks with high energy particle accelerators, and while they saw evidence of quarks within neutrons and protons, they saw none in isolation.  They tried to find quarks that had been produced by cosmic rays.  They looked for quarks in the material of “beam stops” from large accelerators. They tried to find quarks attached to oil drops. They looked for quarks in oyster shells, in nodules from the bottom of the ocean, in the sewer sludge of the city of Chicago . And they didn't find any bare quarks anywhere by any technique.

After this plethora of negative results, theoretical physicists began to devise reasons why nobody should find any bare quarks. At first they said that perhaps the quarks were just too heavy and therefore required too much energy to make.  But that idea didn't fit the facts. So they came to the concept of quark confinement. The gimmick here is that the force that sticks quarks together to make protons and mesons, the so-called color force, is so strong and so long in its range of influence that when you try to pull two quarks apart you have to put in enough energy to make two more quarks. So each of the two original quarks that you have separated now has a new quark stuck to it, and they aren't really separated at all. The concept of quark confinement is now generally accepted by physicists and is the basis for the new field of Quantum Chromodynamics, a self-consistent theory of the color-force interactions of quarks and the ways in which they combine to produce the “old” fundamental particles and their properties. This theory has been able to explain a large body of previously undigested facts in particle physics. Its success has produced a great deal of confidence among physicists that quarks are indeed confined and that no one will ever be able to find a bare quark lying around.

However, there is an unsightly fly presently resting atop the lovely confection of quantum chromodynamics, and it was placed there by Professor William Fairbank of Stanford.  Fairbank and his collaborators, like a number of other groups of experimental physicists, set out some years ago to look for particles of fractional charge. The technique that they devised is a greatly improved version of the famous Millikan Oil Drop Experiment. They place small spheres made from the element niobium in a magnetic field. These spheres are cooled to near absolute zero and become superconductors, i.e., perfect electrical conductors. A superconductor has the property that it will not permit a magnetic field to penetrate its volume.  It generates an electrical current on its surface that nullifies the interior magnetic field. The external effect of this superconducting current is to push against the external magnetic field. This can be used to make the superconducting sphere “float” on the magnetic field, with the magnetic force exactly cancelling the force of gravity.

This magnetic levitation permits Fairbank and his group to measure the electric charges on the spheres by observing their motion while pushing on them with an electric field, causing them to vibrate in a way that depends on their electric charge. The group has developed a sort of “jukebox” that will remove a selected niobium sphere from a storage rack, place it in the magnetic field, and set it into an oscillating "dance step" that measures its charge. They now have several spheres that consistently show a measured charge of l/3 or 2/3 of an electron’s charge. They can demonstrate this result repeatedly, alternating the fractionally charged spheres with those having normal integer charges.

This result was first announced several years ago and was met with great skepticism. However, the group has persisted and now has very convincing evidence that they are observing something that gives at least the appearance of fractional charge. As with many sci64 entific results, this one does more to raise questions than to provide answers. Are they seeing quarks? If so, why aren’t the quarks confined? Why are not the effects of the “color force” seen? If they are not observing quarks, then what are they seeing? Some instrumental effect? Another, previously unsuspected particle that is not a quark but that has fractional charge? As we sometimes say in Physics, “This result has very far-fetching implications!"

II. Accident-Prone Nuclei

When an atomic nucleus moving with a sizable fraction of the velocity of light strikes solid matter, it rapidly loses its large velocity through a series of collisions with atoms of the material. These “atomic collisions" knock electrons loose from one atom after another, causing the fast nucleus to slow down in the process.

Occasionally there is another more violent event called a “nuclear collision,” in which the fast particle makes a direct hit on the nucleus of an atom. This produces a far more dramatic result. Both colliding nuclei literally fly apart, producing fast and slow “fragments” in a variety of sizes. This happens perhaps a million times less frequently than an atomic collision, because the nucleus of an atom presents a far smaller target and is therefore harder to hit than the diffuse cloud of electrons surrounding the nucleus.

Cosmic rays are super-energetic fast particles and nuclei that come into our atmosphere from the depths of space. Some years ago, physicists reported a very interesting but elusive effect in the nuclear collisions produced by the weak heavy-nucleus component of cosmic rays. They had been using photographic emulsions carried by high altitude balloons to study the “history” of collisions between the fast cosmic ray particles and the silver and bromine atoms of the emulsion, as the collision products show up as dark “tracks” when the emulsion is photographically developed.

The cosmic ray particles passing through the emulsion typically show a track of atomic collisions punctuated by an occasional nuclear collision. Nuclear fragments arising from the breakup of the colliding nuclei appear as a “fork” in the track. The cosmic ray physicists reported on a number of occasions (first in 1954) that there appeared to be something strange going on immediately after a nuclear collision. The pieces of the original fast nucleus appeared be much more “accident-prone,” to be much more likely to have another nuclear collision in the next centimeter or so of the track. Because these cosmic ray experiments had provided only a few measured collisions to support this observation, however, the result was not taken very seriously.

Recently a group of nuclear physicists led by E.M. Friedlander and Harry Heckman of the Lawrence Berkeley Laboratory and cosmic ray physicist Barbara Judelc of Ottawa decided to try producing the same effect artificially by accelerating heavy nuclei in a particle accelerator instead of waiting for them to come “naturally” as cosmic rays. They accelerated oxygen and iron nuclei to very high energies in the Bevalac accelerator at Berkeley , so that these particles were travelling at 95% of the New Phenomena velocity of light. They then allowed these fast nuclei to strike the same kind of emulsions that had been used in the cosmic ray experiments. And they observed the same “accident-prone” behavior in the fast collision fragments. There was a definite increase in the occurrence of further nuclear collisions in the next few centimeters of track immediately after a nuclear collision “fork.” This time the effect was observed in 1,460 events, and so was convincing even to most skeptics.

The analysis of their data shows that about 6% of the time the fast fragments from the collision, which are pieces of the original fast nucleus, appear to be in some peculiar accident-prone “state.”  These nuclei are about five times more likely to have another nuclear collision than are the same kinds of nuclei moving with the same speeds through the same material when no previous collision is involved. The group has estimated that this “accident-prone” condition persists for about 10 picoseconds (l0^-11 seconds) before the nuclei return to more normal behavior. This result cannot be explained in terms of our present understanding of nuclear physics.

Since the forces between nuclei are very short in their range of influence, the pair of colliding particles must be essentially “touching” on a nuclear scale before they even “notice” one another. Therefore the probability of scattering depends directly on the sizes of the colliding nuclei. But a nuclear fragment, even in a very highly excited and energetic state, has never been observed to change its size by even a fraction of a percent. Therefore, a change in the size (or cross-sectional area) of a particle by a factor of five is unacceptable as an explanation.

The only other simple explanation of this effect is that the range of the force between the particles has somehow become larger, and that the particle fragment is colliding with nuclei that are some distance away rather than “touching.” There is no known force in the universe that can produce this behavior. Perhaps we are on the threshold of discovering a new force.

III. Faster than a Speeding Sunbeam

A large fraction of all science fiction stories and novels involves, at least incidentally, some way of travelling faster than the speed of light (c). The need of the authors for this device is quite understandable. The universe is a far more interesting place when one can travel from one region of it to another in less than a lifetime. But the question that remains is, “How can faster-than-light travel be accomplished?”

The gimmick used in a SF story might be a space warp, or a detour through hyperspace where the speed limit is higher, or a quick orbit around a black hole and through a “wormhole” connection to another part of the universe, or conversion of the space ship into tachyons and back, or it might be simply some de facto FTL drive that allows you to go from Point A to Point B in the universe without having to travel below the “statutory limit” of one light year per year. While most of these gimmicks were borrowed from physics, at the moment physicists know of no way of producing FTL travel and can tell you a number of reasons why it is impossible. Therefore, the new result described here, an apparent violation of the light-speed barrier, is likely to create great excitement for physicists and science fiction readers alike.

The light-speed limit is a very difficult speed limit to violate because, according to Einstein's Special Theory of Relativity, it must hold not only for material objects (like protons and spaceships) but also for the speed at which information or messages can be sent from one place to another. Special Relativity implicitly forbids not only travel faster than c but also communication faster than c.

The reason for this limit on information speed is that if a message could be sent even slightly faster than the speed of light, then physical laws would not be the same in all non-accelerating “reference frames." This is true even if the message were hand-carried aboard a spaceship travelling through “hyperspace” under “warp-drive”! The reference frame lingo mentioned above refers to any system in which an observer is moving with a fixed speed (or not moving at all) and in which he might decide to make some physical measurements. This identity of the laws of physics in all non-accelerating reference frames lies at the very foundation of Special Relativity and seems to be on a very firm experimental foundation.

Among the many phenomena of Nature, however, one can find apparent violations of the light-speed limit. For example, radar waves travelling down a kind of rectangular pipe called a wave guide will travel so that their wave fronts actually move faster than the speed of light. Physicists call this the phase velocity of the waves.  The phase velocity easily can he made greater than c under the proper conditions.  But due to a conspiracy on the part of Nature, this phenomenon and other similar ones cannot be used to send messages (or material objects) at speeds faster than c. The message always travels with a speed called the group velocily. This is the speed at which, for example, dots and dashes of Morse code superimposed on the waves would travel. A group velocity greater than c has never been observed, even when the waves carrying the message travel faster than c. This leaves the would-be violator of the lightspeed limit completely frustrated.

In recent years, there has been some discussion among theoretical physicists of another faster-than-light possibility. It was recognized that the relativistic equations describing the motion of physical objects have faster-than-light solutions that appear to give a consistent description of some most peculiar “objects.” These hypothetical objects have been given the name tachyons. If tachyons really existed, they would have the property of always moving at speeds greater than c and of slowing down (and approaching I) as they were given more and more energy. Operating on the principle of modern particle physics that “everything which is not forbidden is required,” some experimental physicists have decided to take the idea of tachyons seriously enough to begin experimental searches for them. These searches have so far yielded uniformly negative results, however, and some fairly convincing arguments have been made which demonstrate why, if tachyons did exist, they could have no interactions with more normal kinds of particles like protons and electrons.

But the most provocative indication that perhaps the light-speed barrier may have a crack in it comes from the cumulative work of radio astronomers over the last decade. The most distant visible objects from the Earth, in the opinion of most astronomers, are the quasars. They are relatively small objects which are moving very rapidly away from us and which, for some unknown reason (black holes converting matter to energy?), are- emitting the enormous amounts of light energy which allow us to see them with large telescopes despite their great distances. Quasars have been carefully observed since the late 1960s, both as visible objects and as sources of radio waves.

Their detailed study as radio wave sources is made possible by the technique of “long-baseline radio interferometry.”  This involves the simultaneous use of several radio telescope antennas at widely separated locations around the world, adding up the signals from all of these to study radio sources that are very close together. It provides extremely precise information on the relative positions of radio wave sources within the object being observed. In this case, the technique indicated that the quasar 3C 345 had two distinct radio “hot spots” that were the sources of its radio emissions. Persistent observation of these hot spots from 1969 to I976 revealed that the separation of the two source points was rapidly growing. But most surprising of all, when the velocities of the two sources were calculated, each appeared to be moving away from their common center at about four times the velocity of light!

Reports in 1976 by two different groups of radio astronomers announced this unexpected result. Since then, two other quasars (3C 273 and 3C 279) and one radio galaxy (3C 120) have been observed to exhibit the same phenomenon. In all cases, the radio sources are separating rather than moving together. This, then, is evidence for objects which appear to be travelling at velocities that exceed the speed of light. They have been given the name “superluminal objects” to indicate this.

One possible explanation of the superluminal objects is that perhaps we have the distance scale for quasars wrong, and that they are really much closer than we think, perhaps even within our own galaxy. This would clear up the mystery of their enormous light output, making it much smaller. Further, the distance between the hot spots would be smaller and so would their speed of separation. There are, however, problems with that explanation. The distance scale for quasars is based on their large Doppler shift, which indicates that the quasars are moving away from us at a very high velocity. This large recession velocity is assumed to be “cosmological,” or arising from the effect of the overall expansion of the universe on distant objects. The quasar distance scale continues to be a hotly debated topic among astronomers, as it has been ever since their discovery. However, an impressive structure of evidence and logic supports the large distance scale which was used in the “superluminal” analysis.

Another possibility is that the speed limit violation which is observed is not a “moving violation.” Astrophysicists supporting this view argue that we are observing a so-called searchlight effect. Their description is that the quasar is somehow generating two beams of particles or radiation which are striking nearby hydrogen clouds to make the observed radio waves. The quasar is rotating so that these beams are sweeping across the gas clouds. This is like New Phenomena a searchlight on the ground sweeping across clouds in the sky to give the appearance of a moving object (a bright spot) in the clouds. If the beams from the quasar sweep fast enough, heat the hydrogen cloud hot enough, and the hydrogen is far enough away from the quasar, this could produce radio sources which have a speed greater than c. In that situation, the apparent speed of the radio hot-spot would be greater than c, but no material object or information transfer would be moving at this speed. This explanation, however, does not explain why in all cases the hot-spots move apart.

 

 

Fig.1 Apparent velocity of superluminal objects:  Consider a very hot object that has been ejected from a quasar so violently that it is travelling essentially at a velocity V=c. At time T=0 it emits a burst of light at position 1, which travels to the eye of an observer on Earth. It then travels at a slight angle q to the Earth line-of-sight and at time T=t it emits a second burst of light at position 2, when it is a distance D from the Earth. The time required for the first light burst to reach the Earth is T₁=(ct Cosq + D)/c and the time for the second burst to reach the Earth is T₂= t + (D/c). To the Earth observer, the object appears to have travelled a distance Dx=ct Sinq in a time DT=T₂-T₁. Therefore, its apparent velocity is V=(c Sinq)/(1-Cosq)»2c/q (using the small angle approximation for q in radians that Sinq » q and Cosq » 1-½q². So the apparent velocity is: V = Dx/DT = ct Sinq/t(1-Cosq) » ctq/½tq² » 2c/q.  Therefore, if we make q small enough, we can make V as much larger than c as we like. This works (but is somewhat more complicated) even if the hot object is moving with a velocity somewhat less than c.  It is also somewhat more complicated when one considers some of the relativistic effects, but the above derivation is essentially correct.