The Strongest Force This article by one of the co-discoverers of 'the eightfold way' of classifying strongly interacting particles, first appeared in 'Science Year 1968' and is reproduced here by kind permission of the publishers. Yuval Ne'eman by K. Unser. It has two channels, one for When that visionary, Jules Verne, described the search for an understanding of it is high and one for low frequencies, each the launching of the first manned space the greatest challenge in physics. with its own beam current transformer, flight in his science fiction novel 'From At Serpukhov, Russia, on the other side and the channels are coupled in such a the Earth to the Moon' in 1865, he calcu­ of the earth from the Saturn's base on way that there is an automatic and con­ lated the height of Captain Barbicane's Merritt Island, Florida, is the world's largest tinuous transition between the two to cover monstrous gun, the 'Columbiad', at 880 proton accelerator. Its proton beam acts the whole range. feet. When the gunpowder that filled a like the first stage in a multi-stage rocket. Beam current transformers for moni­ quarter of this gun was ignited, the space But each proton in the beam is boosted toring fast ejected beams have been capsule, in an earth-shattering blast, shot to 50 million times the energy it would developed by S. Battisti and R. Bertolotto. instantly to the 36 000 foot-per-second take to lift it#to the moon. It has 76 000 (At the synchro-cyclotron, R. Hohbach and velocity required to escape the earth's million electronvolts (76 000 MeV) of S. Mango have achieved monitors of high gravity. It was a jolting beginning to a kinetic energy. Remembering the Saturn's sensitivity — down to about 0.5 LIA — for remarkable lunar voyage. energy needs, it is obvious that physicists the extracted proton beam.) The particular studying this stronger force, needing so In 1968, Verne's prophecy has become problem with ejected beams is the low much more energy, must settle for an reality. Men of another century were con­ beam current and an accurate device for extremely small payload. When a small structing the Saturn V moon rocket, the slow ejected beams with a long spill-time bunch of protons strikes a metal target, most powerful machine ever built, to send has not yet been operated. the collision produces a multitude of tiny an Apollo spacecraft soaring to the moon. More difficulties come in when faced new particles called pions, kaons, and To overpower gravity's enormous re­ with the problem of monitoring the beam antiprotons. These are separated and sistance, the Saturn's engines burn almost in storage rings. The aim is to provide a collected in secondary beams, which are 4 000 gallons of fuel and oxidizer every monitor for the ISR which will be capable sent to destinations located deep within second. both of measuring the total stacked beam the nucleus of the atom. current (with values up to 20 A circulating Man has thus learned how to overcome Even as man explores the moon, so for many hours) and which will also be gravity — the gross force of afl the earth's will particles in those secondary beams sensitive to small changes, so that the atoms. But within each small atom, there explore a new world — the world of the addition of an extra pulse (say 50 mA) is a much larger force — electromagnet- strong nuclear force. Physicists call it from the PS during the stacking process ism. Imagine that tiny rocketeers living the strong interaction. It binds together can be monitored, and so that any beam within an atom wished to launch a nega­ neutrons and protons in atomic nuclei. Its losses can be detected. A paper on this tively charged electron against the electro­ pull, particle for particle, is more than a work by Unser entitled 'Beam Current magnetic pull of its positively charged hundred times stronger than electro- Transformer with D.C. to 200 MHz Range' atomic nucleus. They would need 10 000 magnetism, and a hundred followed by was read at the 1969 Particle Accelerator times more fuel than the amount needed 35 zeros times stronger than gravity. to lift a single electron from the earth to Conference at Washington on 7 March. These forces — gravitation, electro- the moon. To further illustrate the strength The response of the monitor is extended magnetism, and the strong nuclear force of this force, imagine that a Space Age to the d.c. condition (to measure the (plus a little-understood weak nuclear imp had removed all the electrons from steady stacked beam in the ISR) by adding force) — cause all of the variety, change, only one-tenth of a cubic millimeter of the a magnetic modulator to the system and beauty in the universe. Without them, Apollo capsule's metal skin and had already used on the PS (which measures objects would never be aware of one carried them down to the launch pad. the rapid changes). It consists of a pair another. They would never attract or repel, The electromagnetic force now attracting of toroids which are excited by an aux­ and they would not collide, but would the positively charged capsule to the iliary oscillator in opposite senses so that effortlessly pass through each other. How electrons on the ground would be so their signals, in a winding around both do forces, which somehow act through overwhelming that, at blast-off, the toroids, cancel. When a beam passes what seems to be empty space, account 7 500 000 pound thrust of the Saturn's through, it introduces an asymmetry giving for this ? One of the great theoretical fiery engines could not budge the space­ an output signal proportional to the current. achievements in physics tells us the craft. The imp, to the bewilderment of the A prototype has given very encouraging answer, and allows us to see how the astronauts, would have matched the gravi­ results. It has been tested up to currents strong nuclear force — the strongest tational force of the whole earth with of 20 A and over a wide frequency range force — behaves. only a millionth of a gram of electrons. down to d.c. The accuracy was about 0.01 %>. When electrons violently collide, as they Within the nucleus of the atom there do in the sun or in the hot filament of is a force even stronger than electro- a light bulb, small bundles of kinetic magnetism. Scientists have known of this energy are knocked free. The electrons force for just over 30 years, and, today, slow down, due to dispersion of some 69 l/l/e can detect a proton only through its forces. It is the sum of four effects. The gravitation force, surrounding all matter in all directions to infinity, controls the stars and galaxies. The much stronger electromagnetic force cancels out at long range, since there are equal numbers of positive and negative charges in the universe. It controls the world of atoms and molecules. The weak nuclear force is known to exist, but its carrier has not yet been detected. The strongest force — the strong nuclear force — controls most effects in the compacted nuclear and sub- nuclear world. photon of green light, 2 x 1CT6 MeV of massive particle. He first assumed that energy, can-be observed only if it exists the new force could not spread faster than longer than a million-billionth (10-15) of light, which was not proved experimentally a second of time. When this photon exists until 1967 by Seymour Lindenbaum at for a shorter time, it cannot be detected. Brookhaven National Laboratory. A pho­ No photon having measurable energy ton moves 1 fermi in 10-tri I Months of a can be emitted by a static charge on my trillionth (10~23) of a second. Yukawa then shirt, but unobservable photons can freely used the uncertainty principle to calculate emerge from it at the speed of light and the minimum energy of a virtual particle act on a hair. Thus, a stream of 'virtual' that can act only tjpis very short amount photons — so called to distinguish them of time. He found it to be about 100 MeV, from the 'physical' photons that we can roughly one-ninth of the energy — and observe — carries the charges' attraction thus one-ninth of the mass — of a or repulsion. The less energy a virtual nucléon. This hypothetical force-carrying photon has, the longer the time it can act. particle was called a meson. Thus the farther apart two charges are, Scientists could hope to check Yukawa's the longer the virtual photons take to leap theory by producing physical, rather than between them, the smaller the energy the virtual, mesons in violent collisions be­ photons can possess, and the weaker the tween nucléons, just as physical photons force they transmit. The electromagnetic emerge from collisions of electrons. With force has an infinite range ; infinitely weak their sizable mass, the new mesons virtual photons reach out from each charge should, in fact, be easier to observe. to the very horizon of the universe. Further, when scientists had bombarded This also holds for the gravitational nuclei with neutrons, they found the force force. Its action is transmitted, also at that scattered the neutrons had turned the speed of light, by particles of energy some of them into protons, leaving the called gravitons. Though virtual when corresponding nuclei with one less positive simply binding the earth to its orbit around charge.