Alternate View Column AV-01
Keywords: particle, physics, quark, monopole, proton, decay
Published in the July-1984 issue of Analog Science Fiction & Fact Magazine;
This column was written and submitted 12/16/83 and is copyrighted © 1983, John G. Cramer. All rights reserved.
No part may be reproduced in any form without the explicit permission of the author.
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The universe is slowly coming unglued. Thermodynamics tells us that its disorder is slowly increasing to an ultimate "heat death". Astrophysics tells us that all stars are slowly burning up their nuclear fuel and all will collapse to cooling "black dwarf" stars, neutron stars, and black holes. Quantum mechanics tells us that the black holes themselves are slowly fizzing away to nothingness by boiling off Hawking radiation. But perhaps most devastating of all, we now have reason to believe that a fundamental building block of the universe, the proton which is the core of every hydrogen atom, has only a "limited warranty" which runs out in about 1032 years. With about that half-life protons (and all of the more complicated nuclei containing protons) will "decay", releasing much energy as they are transformed into lighter particles. The process ends with a positron and some neutrinos and gamma rays replacing the proton.
Every year our sun should be losing about 1020 protons (about a milligram's worth) in this way. This is not much of a loss, but it is irreversible, and it adds up. In 1035 years or so all of the protons in the universe will be gone. The universe will then be empty of all complex matter. There will be no galaxies, no stars, no planets, no organisms, no molecules, no atoms, no nuclei. No matter at all will be left except for some miscellaneous electrons and positrons seeking a final annihilation and leaving behind only gamma rays.
This dismal eventuality is a prediction of "GUTs". (GUTs is short for Grand Unified Theories; the plural s is because there are several rival theories with more or less the same predictions.) GUTs ties together three of the four fundamental forces of the universe, omitting only gravity while connecting electromagnetism (the force acting in chemical bonding) with the strong force (which holds nuclei together) and with the weak force (which acts in "beta decay" when a radioactive nucleus spits out an electron and a neutrino). GUTs says that in the ultra-hot era of the early Big Bang the strong, weak, and electromagnetic forces were completely indistinguishable. All were symmetric manifestations of the same force. Only when the pristine simplicity of the initial Big Bang degenerated by cooling did this change. After the early universe expanded a bit, the average energy dropped below 1014 GeV and the symmetry of forces "broke". The strong force became distinguishable from the still-symmetric electromagnetic + weak forces. And later when the average energy dropped below 100 GeV a further symmetry break occurred and the electromagnetic and weak forces became separate and distinguishable. In our present "cold" era these three forces are very different in their effects, but the bridge of their original symmetry still tenuously remains. Protons can use this bridge to decay.
GUTs tells us that even now, in the veritable youth of our universe (which is only about 1010 years old) some of the protons around us are decaying. The GUTS estimate of the proton half-life (about 1032 years) is just on the hairy edge of what can be measured. And so in deep mines and tunnels in Japan, India, France, Italy, and the USA physicists have mounted expensive and "heroic" proton decay experiments. Enormous tanks of water are being watched by the electronic eyes of tens of thousands of photomultiplier tubes, awaiting the telltale light flashes which signal the death of a proton. At this writing (12/83) no group has formally reported such an observation. But there are rumors that several groups have "candidate events" which are being studied and which may signify protons in the act of decay.
But why should something as obviously stable as a proton be unstable at its roots? The Buddha gave the reason in about 485 BC: "All composite things decay." And protons indeed decay because they are composite. We have learned in the past two decades that protons are not "fundamental" as has been previously supposed, but rather are composite particles made of three "quark" constituents. It is the interactions and transformations of these quarks which permits the proton to occasionally decay. So let us talk about quarks.
The quark model, the present theory of "elementary" particles (which is well supported by experiment) tells us that quarks are "point-like" objects with a "fractional" electrical charge Q (where electrons have Q=-1). Quarks come in a sort of "six-pack" of possible "flavors". These flavors are "up", "charmed", and "top*" (each having Q=+2/3), and "down", "strange", and "bottom*" (each having Q=-1/3). The lightest quarks (up and down) have only 37% of a proton's mass. The heaviest quarks are the bottom quark with more than 5 times the proton's mass and the as yet unobserved top quark. As I write this I have just heard a rumor that physicists at CERN laboratory in Switzerland have found the top quark and determined its mass to be about 34 times greater than the mass of the proton. The family of six quark flavors (abbreviated u, c, t, d, s, and b) come in three "colors" (a sort of 3-value "strong" analog of electric charge) and in matter and antimatter varieties.
Before the quark model came along, physicists were troubled by the bewildering "zoo" of hadronic particles which had been discovered and which seemed to have little systematics or interrelation. Hadrons are particles which respond to the strong force. The quark model brought order to this area by demonstrating that all of the many hadron particles were made of two or three quarks. Quarks combine in matter-antimatter pairs to make medium-weight "meson" particles like pi's, rho's and K's. A pi+ meson, for example, is made of a u quark and an anti-d quark (Q=2/3+1/3=1). Quarks combine in triplets of the same matter/antimatter type to make heavier "baryon" particles like protons, neutrons, lambdas, and omegas. A proton contains one d and two u quarks [Q=(-1/3)+(2/3)+(2/3)=1], and a neutron contains one u and two d quarks [Q=(2/3)+(-1/3)+(-1/3)=0]. The quark model requires that these two or three quark combinations must always give a charge Q which is an integer (or zero). No fractionally charged particles are allowed. (See, however, my article New Phenomena, Analog, February, 1983 which discusses an apparent observation of fractional charge).
Single quarks cannot be found in isolation. The strong force that holds quarks together is very strong indeed. It is so strong that if you try to pull a quark out of a proton, you have to pull very hard, supplying in the process a large amount of energy. So much energy is provided that more
quarks and anti-quarks are created, one of which will immediately pair off with the quark that you are attempting to remove. Therefore, no matter how hard you try to grab a quark and pull it loose, you cannot end up holding an isolated quark. You will instead find that you are holding quark stuck to an antiquark to form a meson. In this way the quark groupings of two or three are always preserved. It is possible to rearrange the groups but not to completely free an isolated quark from its associates.
The strong force binds groups of quarks together, but it cannot change one flavor of quark to another. This flavor-changing can, however, be done by the weak force. In analogy with the "six-pack" of quark flavors, there is a corresponding "six-pack" of leptons. Leptons are the light particles of the weak interaction. They are the electron (e), muon (µ), and tau lepton (tau), all with unit charge, and their corresponding neutrinos (e, µ, and tau), all with charge zero.
The GUTS theories go a step beyond the quark model by matching up the six leptons of the weak interaction with the six quark flavors of the strong interaction. The assertion of GUTS is that leptons and quarks are the same kind of objects, obeying similar general rules and which under some circumstances can be converted into one another. The leptons are cousins of the quarks, but there are differences. Leptons have only one color (or none). There are no leptons with fractional charge but only charge one or zero. Figure 1 shows the family album of the quark clan and their lepton cousins.
The proton decay can occur because GUTS provides a connection between quarks and leptons as members of the same extended family. It is possible for two of the quarks within a proton to simultaneously forget who they are and to trade places with their brothers or cousins. In particular, a u and a d quark may suddenly become a positron and an anti-u quark, as illustrated in Fig. 2. This means that the proton abruptly becomes a positron and a pi-0 meson in loose association. Further, the pi-0 is unstable and in about 10-16 seconds becomes a pair of very energetic gamma rays. This process is not very likely because it requires two quarks to change at the same time, but in the fullness of time it will happen to every proton in the universe. And each time it happens, most of the proton's mass-energy is liberated. This is not a good way of getting free energy, however, because proton decay is an infinitesimally slow process.
But it now appears that there may be a way of speeding things up. The way involves using a very peculiar particle that (probably) no one has ever seen, the magnetic monopole. (The reader is referred to my article Again Monopoles, Analog, October, 1983). The GUTs theories applied to the origins of the universe point to a curious happening. Just after the Big Bang, the density of the universe is truly enormous, and small regions of space contain so much mass-energy that they are rapidly collapsing to black holes and as rapidly un-collapsing back into normal space. Some of these mini-black-holes can develop a sort of indigestion by eating some magnetic flux. Lines of magnetic flux can be left threading into or out of a small black hole.
The "normal" small black hole has a very short lifetime. If it is near minimum size it will rapidly evaporate by Hawking radiation and shrink to a rock-bottom mass (the so called Planck mass of 10-8 grams or so) and then disappear altogether in a final burst of energy. However, those black holes which have an excess of magnetic flux cannot do this. Before they can disappear, a way must be found to dump the magnetic flux excess. But no light particle can carry away this net flux, so the black hole is "stuck". It is like the loser in a game of Old Maid, stuck with a card it cannot unload. But it cannot quit the game. It therefore becomes a new and a unique kind of particle with a mass of the Planck mass and a net magnetic charge. This kind of particle is called a "massive monopole" or simply a "monopole". If its lines of flux are coming out, it is a north monopole (a positive magnetic charge), and if the flux lines go in it is a south monopole (a negative magnetic charge). Only if one monopole were to encounter another monopole of the opposite magnetic charge, north monopole meeting south monopole, could their burdens of magnetic flux be released so that the monopole pair could annihilate in a burst of energy and disappear.
All recent models of Big Bang cosmology predict an uncomfortably large number of massive monopoles should be produced in the Big Bang in equal numbers of the north and south varieties. The near-chaos at the Beginning should twist magnetic flux into very many knots which become monopoles. And yet, (with the possible exception of the Cabrera event discussed in Again Monopoles) no monopole has yet been seen. We won't, for the moment, worry about why they have not been found. Let's instead assume that they are lurking around somewhere (in the bowels of the Earth, perhaps) and that they can be used if we are clever enough to find them.
Essentially then, a monopole is a tiny "replica" of the Big Bang. In its tiny heart is a minute region of space which still retains the enormous energy density which was once present in the Big Bang itself. And within this core the forces of the universe are still indistinguishable from one another: the strong, weak, and electromagnetic forces all are the same. There the quarks and their lepton cousins are, in this domain, the same particles.
Consider then what will happen if a massive monopole comes very close to a proton, attracted perhaps by the small magnetic dipole field which every proton has. The quarks within the proton would have a reasonable probability of encountering the core region of the monopole. And when this happens, the quarks are very likely to "forget" their identity and to be changed to some other flavor of quark or lepton. If this happens, proton decay becomes a near certainty. But the monopole, the cause of it all, is unaffected. It is still "stuck" with its surplus of magnetic flux, so it cannot participate in the decay process.
Thus the monopole is the analog of a chemical catalyst. It is an agent provocateur. It wanders through matter stimulating proton decay and nuclear breakup without being changed itself. A single monopole can do this over and over again as rapidly as it can find its way into successive protons or nuclei. And with each such event, a quantity of energy is liberated which is far greater than that released in uranium fission. The implications of monopole catalysis are enormous. All matter, be it garbage or junk or gold ingots, becomes a source of unlimited energy. Given a suitable supply of monopoles the energy needs of the world are limited only by the supply of matter to be catalyzed into energy. If massive monopoles are ever found, they will be of incalculable worth for physical research and for energy production.
Beyond their utility as producers of energy, monopoles could probably be used directly in a spaceship engine. There have already been studies by Robert W. Forward and others showing that antimatter annihilating with matter in a magnetic "hemi-bottle", an intense magnetic field pinched at one end and open at the other would serve as an extremely efficient spaceship drive. The problem is that the needed amount of antimatter fuel would require a truly staggering investment, because the antimatter would have to be manufactured by earth-based or orbiting "antiproton factories" of monumental size.
The same basic scheme, however, could be applied using monopole catalysis. The "fuel" would then be atoms of normal matter caused to explode because their protons and neutrons undergo catalyzed decay as a flux of monopoles is passed through them. The hemi-bottle magnetic nozzle then provides the dual function of guiding the charged nuclear fragments from the exploded nuclei out the exhaust port of the engine and at the same time collecting the monopoles at the pinch point for re-use in the next engine cycle.
There is another side-effect of monopole catalysis that is worrisome: with monopoles around, the average life-expectancy of protons is reduced by a factor of 1012 and becomes only about 1010 years. This is because if one presumes that there are massive monopoles around which are chewing away at the hearts of stars and planets, an average proton is far more likely to decay by monopole catalysis than by "normal" decay. But since this reduced life expectancy is still 10 billion times the present age of the universe, it should not be a matter of immediate concern. So cheer up!! The news of the ultimate death of matter-as-we-know-it in 1035 or 1020 years is not all that bad. Most of us won't be around by then anyhow. And maybe we can use the intrinsic instability of the proton to take us to the stars and give us lots of free energy in the meantime.
* The t and b quarks are also sometimes called "truth" and "beauty", but these names seem to me presumptuous and lead physicists to indulge in phrases like "naked truth" and "bare beauty". The top quark is predicted but not yet detected.
Followup note: The top quark was detected in 1994 by the CDF
group at Fermi Lab and found to have a mass of about 185 GeV.
N. Isgur and G. Karl, Physics Today 36 #11, 36 (1983).
Big Bang Monopoles:
D. N. Schramm, Physics Today 36 #4, 24 (1983).
M. Goldhaber, Physics Today 36 #4, 35 (1983).
Proton Decay Catalysis:
F. Wilczek, Phys. Review Letters 48, 1144 (1982).
Figure Captions: (Note: figures presently unavailable.)
Figure 1 - The family album: The Magnetic Monopole (above); The Quark Family (mid): top and bottom, charmed and strange, up and down; The Lepton Family (below): tau lepton (tau) and tau neutrino (tau), muon (µ) and mu neutrino (µ), electron (e) and electron neutrino (e). Quarks to the left have charge +2/3, quarks to the right have charge -1/3, leptons to the left have charge -1, and leptons to the right (neutrinos) have no charge and always travel with the velocity of light. The heavier particles are above and to the left. All particles have corresponding anti-particles (not shown) of the same mass but opposite charge.
Figure 2 - A wandering monopole induces proton decay: A proton with two u and one d quarks encounters a monopole. One u and d quark, under the influence of the monopole, "forget" their identities and become an anti-electron (positron) and an anti-u (antiparticles represented by reversed images). The proton has thus become a positron (e+) and a o meson, which immediately decays into two gamma rays. Notice that electrical charge is preserved during the decay process.
This page was created by John G. Cramer on 7/12/96.