The Mountains on a Proton

Protons are not smooth spheres.

If a proton could be magnified, making it as big as a basketball, what would it look like? Not like a basketball. Protons, and other particles too, are complicated.

If a proton could be blown up to the size of the earth, it might have just as many features: mountains, fault zones, hurricanes, volcanoes. It might even be found to contain some form of life! No one can mathematically prove otherwise.

If a proton could be expanded till it was as big as the known universe, would it have its own galaxies, quasars, black holes, stars and planets? Scientists as credible as Carl Sagan have imagined the possibility.

No one has seen a proton, neutron or other subatomic particle, and no one ever will. They're too small for optical microscopes. Light waves are too long to resolve them, passing by these bits of matter like ocean swells past corks. Still, scientists know that protons aren't smooth. The harder a proton is looked at, the weirder it looks.

How have scientists progressed from ancient alchemy to the point where they can peer into the innards of subatomic specks? Their strategies would make any brilliant detective envious.

What an increase in human knowledge and awareness has taken place in the past several hundred years! Most of this has been since about the year 1850. What will humankind's theories of matter and energy be like a thousand years from now? Will schoolchildren look back and wonder at the myopia of today's physics professors?

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Upon casual observation, you might not guess that matter is made of submicroscopic specks. Gases, liquids and solids all seem continuous and homogeneous to the unaided eye. Yet this very notion of matter is, upon scrutiny, harder to believe than the idea that things are made of myriad particles. A few moments' thought brought this even to olden minds. The ancients made some astonishing deductions.

How, for example, would friction be explained if matter were perfectly smooth and continuous? Why the tendency for solids to shear apart along geometric planes, forming beautiful crystals? If material things were homogeneous and could be cut in half again and again ad infinitum, surfaces would have no roughness and there would be no friction. All solids would break apart in the same fashion. Little pieces of any substance would look and behave just like big pieces, except smaller. This is not the case.

Aside from these problems, how could heat be physically explained? How could some things have great mass in a small volume, while other things have a small mass in a large volume? Why is it that gases can be compressed, while liquids and solids usually cannot?

All of these phenomena, observed by scientists and their forebears over the centuries, can be neatly explained if matter is imagined to be made of particles. For these reasons, even the ancients generally believed in atomic theory, although they didn't know the details.

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There are definite reasons to think that matter is composed of atoms or molecules, rather than being continuous stuff. Isaac Newton believed that matter must be made of hard, solid, tiny and dense particles. He envisioned atoms as something like lead shot, constantly in motion. But even Newton based his idea on intuition.

Early in the 1800s, John Dalton noticed that different chemical elements combine in predictable ways, with behavior and end products that are always the same. For example, a highly reactive metal will combine with a corrosive, toxic gas to make the condiment you put on your food to make it taste better: salt. Whenever sodium is exposed to chlorine at room temperature and pressure, this happens. The whitish, crystalline stuff is the same every time. The most abundant element in the universe, hydrogen, combines readily with another gas, oxygen, to make water. Other examples abound.

This exact, repeatable behavior caused Dalton to suspect that each element is comprised of a type of particle unique to itself. If matter were continuous, there would, it seemed, be only one real type, perhaps with variable density, but without the observed idiosyncrasies, the affinities for certain other chemicals.

Late in the nineteenth century, Sir William Crookes began to experiment with electricity passing through glass tubes from which most of the air had been removed. Crookes was one of the early maverick-type experimentalists. It has been said that one experimeter can keep a dozen theorists busy; this was true of nobody if not Sir William Crookes. He made diamonds artificially, becoming a modern alchemist, and discovered the element thallium.

In his evacuated glass tube, Crookes had inserted wires, one for a positive electric charge and the other for a negative charge. When a high voltage was applied between these electrodes, current flowed through the tube. This indeed seemed bizarre: Why should no current flow through air, but electricity conduct through a near vacuum? The current flowed in rays that seemed to travel in straight lines. These rays were visible inside the tube, glowing with an eerie light. When this effect was first seen, it caused a scientific sensation. A new, mysterious type of radiation, visible only under special circumstances, had been found. Could it be dangerous? What caused it? What did it signify?

Joseph John Thomson, known to his friends and colleagues as J.J., believed that the cathode rays seen in an evacuated tube were made up of particles having constant ratio of charge to mass. He was convinced that all of the particles were alike, and that they were commonly found in many places in the physical world. But how could their nature be explored, when they were far too small to be seen even with the most powerful microscopes, and when they never stood still, but insisted on buzzing around with blinding speed?

When subjected to magnetic or electric fields, the cathode rays were bent. They were attracted to a positive electric charge, and their curvature was at right angles to magnetic lines of flux. By the time of J.J. Thomson's experiments, knowledge of electromagnetic phenomena was beginning to unfold, and the secrets of long-range wireless communication were about to be discovered. The actual electrical charge of a cathode-ray particle was measured by Robert Millikan. This was found to be the smallest possible quantity of negative charge. Because the particles carry electric charge, they became known as electrons.

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Cathode rays, comprised of electrons, were not the only types of rays that were discovered around the end of the nineteenth century. Radioactive substances were found to emit particles with charge opposite that of the electron. These were called alpha particles, and a barrage of them were referred to as alpha rays. In addition, negatively charged particles were cast off, and these produced beta rays. Beta particles were later found to be electrons, like cathode rays.

A third type of radiation seemed to have no charged particles associated with it, and these were called gamma rays. These are energetic and penetrating, like X rays but stronger. It takes several inches of solid rock or concrete to stop them. They present significant danger to living things, causing violent illness and death in large doses, and genetic mutations long-term. Gamma rays emanate from nuclear fallout, and are the main reason people built fallout shelters during the height of the Cold War.

The alpha particles are known nowadays to be the nuclei of helium atoms, consisting of two protons and two neutrons. At the end of the nineteenth century, all that was known about them was that they have a positive electric charge, and their ratio of mass to charge is much greater than that of electrons. That is, they are heavy. A high-speed electron might be compared to a major-league baseball pitcher's fastball. An alpha particle at the same speed, in this analogy, would be the same fastball if the ball weighed a quarter of a ton.

Thomson's particles were thought to be fundamental building blocks of matter. Atoms usually have no electric charge, either plus or minus. It was imagined that atoms were balls of positively charged stuff like bread or cake, with electrically negative electrons embedded like raisins. There were just enough negatively charged raisins to balance the positive charge of the bread. Most of the time.

This model of the atom didn't last long. It was formed by speculation. It was up to Ernest Rutherford to show that it was wrong, and that atoms are nothing at all like raisin bread.

A laboratory exercise, supposedly routine and designed to train Rutherford's lab assistants, was set up to show that atoms could not deflect fast-moving alpha particles. It was thought that these high-speed projectiles would bluster their way through a thin sheet of metal foil almost unaffected. The results were startling. But it was not because anything had been done wrong by the lab assistants. Instead, an important property of atoms had been accidentally found.

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Hans Geiger was a young physics student from Europe. Today we recognize his name in the Geiger counter, a device for detecting particles of radioactivity. Actually, Geiger worked with Ernest Rutherford to design several types of radiation counters. Another young student, Ernest Marsden, joined Geiger and Rutherford and set up the famous "gold-foil experiment" that gave scientists their first detailed glimpse of the atom.

Alpha particles were directed at a thin piece of foil. This radiation is not normally very penetrating, but the foil was made thin enough so that the radiation could pass through. It was expected that the foil would behave almost as if nothing were in the way of the dense, charged particles. True, the atoms in the foil were potential obstructions, but the alpha particles ought to get through with little trouble, like bullets through tissue paper.

Detecting screens were set up opposite the source of particles. Screens were also placed at all angles around the foil, even on the same side as the source. The intent was to show that all the alpha particles would pass straight on through the foil. Most did. But some careened off every which way. Some came off sideways, and some were actually knocked backwards.

Surely, at first, Rutherford must have thought that his lab assistants had not done the experiment correctly. But there could be no mistake: Something in the foil was causing the alpha particles, dense and fast as they were, to be scattered, rather than letting them all pass through.

Clearly, the raisin-bread model of J.J. Thomson could not be an accurate representation of the atom, at least not for gold foil. The Thomson model envisioned a soft, fuzzy atom, hardly the kind of thing that would knock massive, high-speed particles sideways and backwards! It was like shooting a gun at a piece of paper and having the bullets bounce off.

Rutherford tried to envision how this might take place. Perhaps the atoms were made of some extremely dense substance, just as dense as the alpha particles but much heavier. Most of the atoms would have to consist of empty space; the mass would have to be almost entirely contained in the dense centers. Rutherford gave the name nucleus˙20to the atomic center, presumably after the nucleus of a living cell. The nucleus, surmised Rutherford, had to carry a positive electric charge, like the alpha particles. Then, if an alpha particle came very close to a nucleus of gold foil, the repulsive electric force, caused by like charges, would throw the comparatively light alpha particle off course. The closer the approach, the greater the deviation. In case of a head-on hit, the alpha particle would be thrown right back toward the source.

Refinements were made to atomic theory, until today, physicists envision a hard, dense center made of protons and neutrons, and a cloud of electrons whizzing around. The electrons and protons usually balance each other, so that the atoms are neutral, but sometimes there is a slight deficiency or excess of electrons. There can be some variation in the number of neutrons in the nucleus. The most important feature of an atom, and the one that gives it its unique chemical identity, is the number of protons.

Neutrons live, on the average, only about fifteen minutes unless they are part of an atomic nucleus, and then they might live for millions of years. But protons live far longer than even the most hardy neutrons. In fact, the universe is an infant according to the time frame of the typical proton, which lives something like a hundred quadrillion (100,000,000,000,000,000) times longer than the cosmos' age according to recent estimates.

Neutrons decay quickly in isolation, but, in practical terms, protons are forever! A man could give a woman an engagement ring made of anything, even brass and glass, and tell her that the protons will last a hundred nonillion years, and that all the stars will have burnt out long before those humble specks have lost their identities. She might not marry him, but he would, at least, not be a liar.

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In the beginning, say cosmologists, there was energy. Then there was an explosion, and matter congealed in the form of particles. There are so many different kinds of particles that cataloging them has proven quite a challenge for the name makers.

You have heard some of these names: leptons, hadrons, neutrinos, antimatter, positrons. They have properties like mass, charge, spin, energy content, wavelength.

Albert Einstein said that God is sophisticated. Whatever you believe God to be, it is hard to think otherwise. Einstein also said that God is not malicious, that things are not complicated to spite human beings. You might wonder about that. Why can't matter and energy, the stuff of the cosmos, be simpler?

Perhaps the answer is that infinite complexity is the only way things can be.

If there were a fundamental, indivisible material speck, it would have to be made, in a sense, of continuous matter. It couldn't be broken apart. The glue inside it would have to be infinitely strong. It's hard to believe there can be any such thing. It's almost easier to think that particles just keep getting smaller and smaller.

It's like the number line. You can keep finding new numbers in between other numbers, no matter how strong the "magnification" you use to look at the line. There is no end to this. Although it's difficult to see how this can be, it's harder to imagine how it could not be.

Recent research has shown that protons consist of subparticles called quarks and antiquarks, and these are held, or "glued," together by gluons. The innards of a proton really do seem something like raisin bread, the model of the atom once propounded by J.J. Thomson and his colleagues.

The name "quark" comes from the story Finnegan's Wake by James Joyce, in which someone says, "Three quarks for Muster Mark." As the number of known particles has proliferated, physicists have resorted to ever more creative names for them. Quarks were first thought to come in three types, or flavors, called up, down and strange. Then there emerged charmed quarks, and of course all of these particles had to have their antimatter counterparts.

Evidently, quarks cannot, or will not, exist all by themselves. They must be part of something, or they lose their identities. In this way quarks are a little like mountains. You cannot rip a mountain away from the earth and still have a mountain; it has to be part of the earth. If torn free, it would be an asteroid, perhaps.

The same holds for gluons, those bizarre particles that serve to hold the quarks together. They are like the doughy part of a slice of raisin bread. You can't rip the bread away from the raisins and still have bread; you'd only have junk.

In future generations, protons might be resolved into things similar to atoms as we know them today. Or an entirely new, and heretofore undreamed-of, structure might emerge. Only time will reveal the details.

In Chapter 4 of his book The Nature of Matter, D. H. Perkins delves into the proton, using an imaginary supermicroscope that can resolve objects down to 1/100 of the diameter of a proton. *  Using a microscope that can see things as small as a proton itself, the particles look like blobs, and no detail is observable. A fantastically tiny length is being "seen," a ten-trillionth of a centimeter, or a quadrillionth of a meter. Compare this with a wavelength of red light, for example, that measures a little less than a millionth of a meter. A proton is a billionth as wide as the wavelength of red light.

If the supermicroscope gets ten times more powerful, things are seen that are just a tenth the diameter of the proton. Then, the proton looks like a cell with three different nuclei, or points where matter is congealed. These are called valence quarks. Sometimes a gluon, normally invisible, turns into a quark-antiquark pair.

Ultimately, Perkins depicts the proton with an imaginary micromicroscope--call it a picoscope--still ten times more powerful. The inside of the particle now appears alive with quark-antiquark pairs! The gluons look like threads. The three valence quarks appear as well-defined blobs or specks. This is the greatest detail that has been resolved to date, with the most powerful particle accelerators.

The limit of resolving power is determined only by how much energy can be mustered for the purpose of accelerating particles. Someday, whole batteries of power plants might be bent to the task of smashing atoms and looking at protons. That will depend on the willingness of governments to spend money on subatomic physics experiments when the people demand more fundamental things, such as food, shelter and medical care. Knowledge is limited by necessity, perhaps more than anything else.

Perkins makes a prediction as to what would be seen at these greater levels of resolution: more and more pairs of quarks and antiquarks, connected by gluons, which are inherently themselves quarks and antiquarks. It is the infinite progression of particles that some scientists have expected all along. Yet, it is a finite potpourri. The smallest particle, in such a model, is made of copies of itself.

In the quest for finding that elusive wisp, the particle that cannot be subdivided, scientists have resorted to machines that muster ever greater levels of energy. These are the giant particle accelerators, or atom smashers.

Breaking up a subatomic particle is a little like shattering a piece of china. The more violently you throw the china against the wall, the tinier the resulting fragments will be. If you could hurl a china plate against a wall at almost the speed of light, it might be pulverized into its constituent atoms.

It's a fundamental rule that the greater the energy with which particles are rammed against each other, the tinier are the resulting fragments.

The power supplies needed for the largest particle accelerators could supply the needs of many households for a long time. These are mere popguns compared to what could be generated if all the industrial plants on Earth were committed to the task at once. If that were done, scientists might find things smaller than quarks, antiquarks and gluons. No one will know, unless and until it is tried.

Imagine focusing all of the power in the sun, or in all the stars in the whole galaxy, or in all the stars in the observable universe. Humankind will, of course, never do any such thing. But presumably, if it were done, particles might be found that would make quarks, antiquarks and gluons seem like huge globs by comparison. Then, the idea of a fundamental particle would have to be revised inward--again.

The smallest particles imaginable would be generated by means of an atom smasher that uses, as its source of power, all the energy in the entire universe. Beyond this, it is pointless to brainstorm.

One of the worst forms of madness is the belief that one has found the absolute in any sense. Over and over again, throughout history, people have thought they had gotten to the end of knowledge in some vein. They have always been proven wrong.

* * *

Albert Einstein, probably the greatest physicist in history, said that matter is energy. He wedded them by his famous equation, now known even to some first-graders: e = mc2. Energy and mass are related by a constant factor, the speed of light multiplied by itself.

Just as matter is made of particles, rather than existing as a continuous, homogeneous ooze, so energy is also a fantastic array of packets or specks, each carrying a constant, although tiny, punch. Isaac Newton, who imagined matter as consisting of atoms, also thought of light as a barrage of invisible, submicroscopic specks. Today we call these particles photons.

Photons aren't all alike. They can vary greatly in the amount of energy they carry. Feeble photons produce radio waves; stronger ones give us microwaves. Still stronger photons produce infrared, visible light and ultraviolet rays. The most powerful yield X rays and gamma rays, capable of altering atoms and damaging the chromosomes in living cells.

Any photon has a specific wavelength associated with it. And any wave disturbance has a corresponding photon, with a certain constant energy level. The particle/wave dichotomy, as it has been called, is another face of the matter/energy duality, different manifestations of the same thing.

How is matter ultimately made? Is there a smallest particle? Or are there tinier and tinier bits of matter, the process going forever inward?

Some scientists today believe that quarks, antiquarks and gluons are the elementary particles of matter so long sought. But some warn that such a belief, or confidence, is dangerous in the intellectual sense, because this attitude has been held before. Newton regarded atoms as fundamental particles, and he was mistaken.

Science history is replete with theories that have been firmly believed and later disproved or shown to be too simple. There exists no mathematical proof that quarks, antiquarks and gluons are the fundamental particles of matter. Likewise, there is no logical certainty that they are not. Not yet.

Suppose, once again, that it were possible to muster all of the energy available in the universe, and to use it solely to search for the smallest possible particles. Then indeed, the specks found would be ultimate, since they would be unbreakable by any means cosmically attainable. You might say that even the God of this cosmos could not split such things apart. Are quarks these specks? And quark-antiquark pairs, and gluons? If so, then humankind has succeeded in finding elementary particles without reaching a limit as to how far matter can be subdivided! For if this is the secret of matter, then all things are made of littler things just like them: universes within universes.

Strange mountains!
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* Mulvey, J.H., Editor, The Nature of Matter (New York: Oxford University Press, 1981), pp. 97-103, by D. H. Perkins.

Copyright 1998, 1999, 2000 by Francisco Carrera.