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        We saw through a study of the models leading to a description of various phenomena in nature that the Greeks were the first who showed us that the world is not just the playground of the gods, but accessible to human reason, to the power of observation and deduction. The literate came to know the Earth no longer as flat, but rather as a sphere with a predictable radius and circumference. (Erastothenes, 3rd Century BC). Later, Galileo became the father of modern science when he added the perspective that experiment must verify the model. Newton elaborated on this. In fact his models agreed very well with experiment that nearly every phenomena was described in terms of his mechanical universe. His models of motion and gravitation stood until Einstein who showed us that phenomena depends on the observer. Later in this text we will examine the Special and General Theories of Relativity, but for now, his intellectual triumphs did alter our perspectives drastically. He contributed immensely to the large scale models of the universe, forming the foundations of the standard theories of today, and helped to formulate our very picture of the quantum world. Yet he was never really satisfied with the quantum theory, somehow not able to accept that God might actually be playing dice with the Universe. Instead he felt the world was more deterministic and was gradually recognized as the last of the classical physicists.

        Our study, then, is an inheritance of a tradition of Greek thought, refined by intellects during the past two millenia. While the list of people is impressive, the positive contribution of each was in fact built on the works of their predecessors. Today, the two extremes of physics -the search for the basic nature of the most elementary forms of matter and the nature of the cosmos itself need to complement each other to provide satisfactory answers to our questions. We really seek a comprehensive picture so that we can describe our world, from elementary particles to nuclei, to atoms, to molecules, to cells, to people, to the earth, the stars, galaxies, and to the universe.

The Search for Simplicity

        We seek a simple picture. It the task before us to draw together, all the disparate elements of physics into a simpler theory. The story of physics is one of increasing (???) simplicity. Even so, the search for the nature of matter itself is relatively recent. We have just completed an examination of the nature of the atom. Now we wish to peel off the next layer of matter to look inside the atom into the very components that make it up. We ultimately wish to get into the bottommost layer. Leon Lederman,  former Director of Fermi Lab (World's foremost particle accelerator in Batavia, Illinois) and Nobel Laureate, tells the following story. This process is parallel to entering a library - the library of matter.

When we look at the library, we can tell at a glance that it is made up of books. Ah: Then we can describe it in terms of all the books it contains. But a closer look tells us that books are made of pages and, even the pages are made of words. Aha: Since a dictionary contains all the words in the language, surely we can describe our world of the library with just a dictionary. But as we do this, we notice that we need some rules, to put the words together properly. We call these rules grammar. We actually needed rules even with the books themselves, perhaps the Dewey Decimal System or the Library of Congress Classification Scheme. Now our rules have become more complex, but the description of what makes it up is simpler. Now it is brought to our attention that even the words can be simplified. They are made up of merely twenty six letters. While we are concerning ourselves with this level of matter, perhaps a Girl Scout shows us that all the letters and numbers can be made from the Morse Code, simple Dots and Dashes. These then, are the most elementary forms that can be used to construct this entire library. Well, it certainly seems so. And the search into matter is somewhat parallel to this. We are searching for the elementary dot and dash to describe matter. After peeling off many layers of matter we think that we may have found the most elementary dot and dash. But at the same time, as the substance becomes simplers, the rules of combination become more complex. There is always that caveat as we simplify the world. Let us share these ideas in the following paragraphs.

Particle Accelerators

        When we look out into the universe around us we need bigger and better telescopes. When we look into matter we need microscopes. Actually optical microscopes are somewhat limited in what they can see. We only get several hundred power magnification. The electron microscope can see smaller objects because the de Broglie wavelength of the electron is much smaller than wavelengths of visible light which we see optically. To observe really small effects, we use particle accelerators. These are hardly "elegant", but they work. Some scientists say that using particle accelerators to "smash" atoms and particles together at high energies is a lot like throwing a fine Swiss made watch against the wall to see what it is made of. As we observe gears, spindles and minute and hour hands being ejected we conclude these are the components. Still missing of course is some overall.plan on how the parts go together, or the rules. It is not an easy process. Some say we need more philosopher-physicists to give us better models. From observing results of high energy collisions we do hope to describe what makes up the nucleus, until all the components are known.

or 3.6 X 10⁶ Joules. This costs us about a dime if we include taxes and special charges. It will keep a 100 watt light bulb on for 10 hours. ( 100 X 10 = 1000) By contrast,

        Remember, if you will, that it took about 13.2 eV of energy to remove the electron from the hydrogen atom, even less to excite it. But on the atomic scale, the eV is a good amount to compare with. The first particle accelerator was used by Galileo. It might be called the NVLA, or Nearly Vertical Linear Accelerator. Basically, his particles were rocks, and he dropped them off the leaning tower. This generated an energy of about 0.1 eV as the rocks fell straight down and gained kinetic energy.

        A Bunsen Burner can be used to excite atomic electrons. Chemists use these for flame tests in qualitative analysis. You may have done this by dropping some salt in a fire. We observe a yellow light. That's the flame test for Sodium. Potassium gives a red flame. Copper gives a bluish-greenish color. We are observing the light emitted as the excited electrons spontaneously return to the ground state. During this transition they emit photons of characteristic wavelengths. They can typically generate a few eVs.

       X-Ray tubes generate about a thousand to ten thousand eVs of energy. This is still small to us, but large atomically. It has been about 50 years since the Cockcroft Walton or Van de Graaf Generators were introduced. They gave us a large boost in energy available, developing up to 500 keV (thousand electron volts) of energy.

         The cyclotron was invented in 1932 by E.O. Lawrence and M.S. Livingston. It is the simplest of the accelerators in use today. Particles such as protons or atomic nuclei are injected into the center of two "D" shaped hollow conductors called "dees". They are subjected to a magnetic field perpendicular to the plane of the particle's motion and accelerated across the space between the Dees by a varying electric field. That way it accelerates one way and then as it goes one-half circle it is accelerated across to the other side. The path gets larger and large and eventually after the particle gains enough energy it is ejected to the target. These generate from 1 to 10 MeV (Million electron Volts) of energy.
 
 

        Today the foremost particle accelerator in the world is the one at Fermi-Lab in Batavia, Illinois. It generates 400 GeV of energy, in a tunnel no larger than a fire hose, (the actual tunnel for magnets, equipment and personnel access is much larger) and has been converted to develop 1 TeV by sending particles in one direction and anti-particles in the same tunnel but in the opposite direction. The electrical costs are phenomenal to keep the electromagnets working for the nearly three mile in circumference path. From the highway, a visitor can see the large underground tunnel looking like a giant mole tunnel. We expect our greatest advances to come from this device. A similar facility is CERN, an international lab run by 13 countries. It is located in Switzerland, near the French border.
 
 

Figure 6-3. Fermi Lab National Accelerator; The four-mile circle is the Tevatron, the world's most powerful accelerator.  The smaller oval is the Main Injector, to begin operating in 1999.  The tangential lines reaching to the northeast from theTevatron are particle beamlines.

        The higher the energy we can develop, the more layers of matter we can penetrate. While a few eVs can excite electrons, we need Keys to get to the lowest layer of them. A few MeVs can get to the Nucleusi It takes a GeV or more to break up the nucleus. With about 100 GeVs we observe protons and neutrons to break up. At 1000 GeVS we can "see" quarks, the heros of our story.

The congress of the United States has decided the future of funding the Superconducting Super Collider particle accelerator. If built, it would dwarf even Fermi Lab size machines. In current dollars,  it would require $4.4 Billion so it became a victim of a Congress eager to look fiscally responsible. Someday, it might be built. It would be more than 50 miles in circumference and built far underground since purchasing that much real estate would be almost unthinkable. It should achieve energies 20 times greater than any ever developed, 40 TeVs: This machine would allow physicists to probe ever deeper into the layers of the nucleus to find secrets of the nature of matter itself and perhaps unlock undreamt of ideas about the universe itself. It would truly be the world's biggest machine.

        An additional "instrument" is used to determine the basic properties of the proton. We will see much later that the estimated lifetime of the proton is  10³¹ years. Since the universe is only 10⁹ years old, it will take a long time to observe even one decaying proton. Statistically, if we can assemble 10³¹ protons, perhaps we will see one decay in a year. Now, 10³¹ protons is a lot of protons. If water is the source (good reasons for this) it would take a swimming pool the size of a 4 story building to contain that amount of water. The problem of detecting that one decay and conclusively verifying that indeed the count on a detector is due to a decaying proton is not a trivial matter. Such experiments are being conducted in the Soudan Tower Mines in northern Minnesota. If protons are found to decay, then one must conclude that matter itself is merely a temporary phenomena.

Anti-Matter in the Universe

        Recall if you will, the Schrodinger's Equation. Remember that this model served as a wave description of particles in the microscopic world, where we interpreted the waves in the form of probability distributions. In 1928 Dirac modified this equation to include relativistic effects. Remember that we usually model a~phenomena in its simplest forms and then add real world constraints that more closely represent the situation we are observing. This was the next logical step with the newly accepted mathematical model. Up to this time the world of the atom and consequently that of matter itself and the universe was relatively simple. It said that everything was made of electrons, protons and neutrons. Sounds a bit like the kinds of models we learned about in the fourth grade, doesn't it? This seemed nice, but it didn't explain phenomena like why the sun burns or why we have radioactivity.. Dirac's solutions predicted the existance of antimatter. i.e.; for every electron there was an anti-electron, or more commonly called the positron. For every particle there was an antiparticle.
 
 
 
 
 
 
 

 1965 TM New Yorker Magazine, inc.

         Experiments do verify this concept. We do not actually "see" positrons, or anti-electrons. We always measure quantities in terms of their effects on something else. For example, we can't exactly hold an electron in our hands and determine its mass and charge. In fact we could question what mass and charge even mean themselves. But we can measure the mass of the electron by its effect on other masses. We can measure the charge on the electron by how it affects other charged particles. We see the antiparticle by their effects on the rest of the world.

        As we discovered a new particle that came from the nucleus we named it after the Greek alphabet. It wasn't very long before the Greek alphabet was exhausted. In fact, by 1963 we had over one hundred "elementary" particles that came from the nucleus. The picture of the world seemed to be getting more complicated than simple. It was in 1964 that Murray Gellmann (Cal Tech) suggested that all the nuclear particles could be made of three particles called quarks. Their name comes from James Joyce's Finnegan's Wake - "... three quarks for Muster Mark."

Hadrons and Leptons

        Today we better describe the elementary particles existing within the nucleus in terms of the two major forces that bind them. Quarks are elementary particles. All Hadrons, from the Greek word Hadros , meaning strong, are made of quarks. They are bound (together) by the strong nuclear force. They are typically the heavier particles. Leptons are also elementary particles, but aren't bound by the strong force. Lepton comes from the Greek word for weak, and they experience the weak nuclear force.

        We give certain characteristics of nature names that seem appropriate. Mass and charge are two fundamental quantities. In the hydrogen atom the electron acts like it spins on its axis much like the earth rotates in its motion about the sun. Now, whether it really spins or not, the effect on the rest of the world is much as if it does. Thus it is natural to describe that characteristic the spin of an electron. Atomic and nuclear particles all have spin. There are some other properties too.

         Physicists almost immediately found three quarks, the up, down and strange quarks. Four leptons were already known, the electron, the positron, the electron neutrino (we will describe it later) and its antiparticle. Basically, it requires two up quarks and a down quark with charges +2/3 and -1/3 respectively to make a proton with charge +1. The neutron can be made of one up (charge = +2/3) and two down quarks (charge = -1/3 each):
 

        The world now was simpler, but not symmetrical. The up was symmetrical to the down quark, but the strange quark was all alone. In 1974 the 4th quark, called charm was found. This gave some added symmetry. Two years later a fifth quark was found, called the top quark. Now we are still searching for its counterpart, the bottom quark. Today we believe there are the six basic quarks: Up and Down, Strange and Charm, Top and Bottom. We think they come in three types each called flavors or colors. (This is analogous to the three primary colors) and that each quark has an antiparticle or antiquark. Thus there are:

6(quarks)  X 3(flavors) X 2(particle & anti-particle) = 36 particles total

 The following chart show the basic properties of the quarks:

        The Up and Down quarks account for 99% of matter in the universe. This is column I. Smaller effects are observed in column II, namely by the Strange and Charm quarks. Even smaller effects are found in column III by the Top and Bottom quarks. We have not yet found the bottom quark. We expect to find it when the super collider at the National Accelerator of Fermi Lab is in operation. We have looked for, but not yet found and smaller effects, column IV. We don't think they exist. At this time we also don't think there is any structure to the quarks. They seem to be elementary. However, O.W. Greenberg (Sept 85, Physics Today suggests that some observed irregularities that quarks an leptons exhibit may indicate that they themselves may be composites. At this time there is not convincing evidence that this is true. In 1998 the last quark to complete this picture, the Top quark, was found at Fermi Lab.

        Leptons are fundamental particles that are not bound by the strong nuclear force. The six known types of leptons are shown in the table below. Like the anti-particles for hadrons, there are also six anti-lepton types, one for each lepton.

Particle Type	Electron     e-1	Muon     m	Tau        t
Neutrino	ne	nm	nt

Electrons and Positrons

           The electron is the least massive charged particle of any  type. It is absolutely stable because conservation of energy and electric charge together forbid any decay.  The antiparticle of the electron is called a positron. It has exactly the same mass as the electron, but the opposite sign (+1) for its electric charge. Positrons are also stable particles. However, positrons can  annihilate when they meet an electron. Both the electron and the positron vanish, and their energy goes  into photons and, possibly, more massive particles. Conversely, photons with sufficient energy (E > 2 m_e c² as per Einstein's matter-energy equivalence) can produce an electron and a positron -- this is called pair production. The net charge is still conserved (zero) while the energy is transformed into mass.
 

Muons

         The muon has a mass of 0.106 GeV/c2. The negatively charged muon (mu-minus) is just like an electron, except it is more massive. Muons are unstable -- they decay to produce a virtual W-boson and the matching neutrino type. The W-boson then decays to produce an electron and an electron-type
anti-neutrino.

         The antiparticle of a mu-minus is a mu-plus. Particle physicists use the name muon for either mu-plus or a mu-minus a muon. The mu-plus decays to produce an anti-muon type neutrino and a W-plus boson, which
then decays to a positron and an electron-type neutrino.

         Muons are produced in particle physics experiments. They also are produced by cosmic rays. Because they are much more massive than electrons, muons readily pass through the electric fields inside matter with very little deflection. So, muons do not radiate and slow down as electrons do. However, they can cause ionization and this makes them readily detectable in matter, for example, with a Geiger counter.

Tau Leptons

         The tau-minus is a electron-like particle with a mass of 1.784 GeV/c2.  Its antiparticle, the tau-plus, has the
same mass but a positive electric charge. These particles were discovered at SLAC in experiments at
SPEAR . The 1995 Nobel Prize was awarded for this discovery.

         This third type of charged lepton is also unstable. The tau-minus decays to produce its matching neutrino
and a virtual W-minus boson. The W-minus has enough energy that there are several possible ways for it to
decay, such as:

            1. An electron and an electron-type antineutrino.
            2. A mu-minus and an muon- type antineutrino.
            3. A down quark and an up-type antiquark.
            4. An strange quark and an up-type antiquark.

         The quark and antiquark do not emerge individually. One or more mesons emerge from the decay that contain the initial quark and antiquark, and possible additional quark-antiquark pairs produced from the
energy in the strong force field between them.

         For tau-plus, a similar set of decays occurs -- just replace every particle by its antiparticle (and vice-versa, every antiparticle by the matching particle.) Thus, for example, tau-plus can decay to give a tau type
anti-neutrino and a positron and an electron-type neutrino.

Neutrinos

         There are three types of neutrinos, one associated with each type of charged lepton. All are particles that are somewhat like electrons: they have half a quantum unit of spin angular momentum, and do not
participate in strong interactions.

         However, neutrinos differ from electrons in that they have zero electric charge and, as far as we know today, zero mass or at least a very small mass. If they have any mass at all, they are so pervasive throughout the universe that they could account for a significant part of the mass of the universe as a whole. Experimentally, all we can do is set an upper limit on their masses -- they are smaller than some value. Larger masses would have  had observable effects in some experiment. The only known difference between the three neutrino types is which type of the charged lepton they are associated with during production or decay processes. The Oct 2000 issue of Physics Today reported confirmation of discovery of the Tau neutrino. This completes the expected classification scheme of lepton particles.

         Since neutrinos have no electric charge, they can participate only in weak interaction or gravitational processes.  For this reason, they are very difficult to detect. We observe them only by the effects they have on other particles with which they interact.

         For example, a high-energy electron-type neutrino can convert to an electron by exchanging a W-boson
with a neutron (which becomes a proton when it absorbs the W boson). This rarely happens. With an
intense source of neutrinos and a large detector containing many neutrons, one can observe events with
no visible initiating particles that can only be explained as neutrino-initiated processes. What is seen in the
detector is the recoiling electron and proton after the process occurs.   (Experimental work demonstrating
this process resulted in Frederick Reines sharing the 1995 Nobel Prize with Martin Perl.)

         Even harder to see is the process where the neutrino is deflected by exchanging a Z-boson with a proton or  neutron. The proton or neutron gains energy from this exchange, so one searches for events where a
recoiling proton or neutron is seen with no associated electron and no visible initiating particle. 

         In high-energy particle experiments, we often use energy and momentum conservation to infer that
production of one or more neutrinos occurred. If the detector detects everything but neutrinos, then an
event where the total final energy detected (or the total final momentum) does not match the initial energy
(or momentum) in the incoming particles, then neutrinos must have been produced.  The neutrinos carried
off the missing energy (and momentum).

        Let us for a moment revisit those four basic forces in nature. The effects of the forces themselves may be likened to virtual particles "carrying" the forces. I do not mean carrying in a literal sense. When I was in the Air Force and stationed in the South, a common expression was "I'll carry you downtown". Obviously no one would literally carry someone anywhere. It was a friendly way of agreeing to escort or drive a guest somewhere. Here we have a meaning that means more like an attached property, connected in some intimate way but not just as an attachment. It describes more the nature of interaction of forces and particles.

        Suppose you are in a very dark room. Even though your eyes have had time to acclimate, there is no source of light and it is dark. Now, suppose I turn on a light at the other end of the room. You of course see it almost simultaneously* Hut light travels at a finite speed. It travels at 3 X 10 metres per second. That means it would take a second to travel 3 X 10⁸  metres. It takes eight minutes for light to reach us from the sun. It takes hundreds of thousands and in some cases, even billions of years to reach us from distant star and galactic systems. In any case it takes some time to get there. It is not instantaneous. Consider that the photon, the particle aspect of light, carries the effect we notice. In fact this may be easier to visualize at other electromagnetic wavelengths. For us, we can consider that the photon "carries" the electromagnetic force. We could also describe this effect as a field. But do think of this photon only as a virtual particle. It exists only because the electromagnetic force is there. And the electromagnetic force is there because the photon
carries it. A Photon is both its real and virtual particle.

        Now, let us look -at the Strong Nuclear Force. The carrier of it is the Gluon. Quarks are held together by gluons to make heavier hadrons, like protons and neutrons. These "gluons" are comparable to the field of the strong nuclear force. As we examine the nature of the strong force we should realize that we have to have it. There must be something that keeps the nucleus from flying apart, as it surely would if only protons (positive charges) and neutrons (no charge) acted electromagnetically. This is obviously a  very short range interaction. The proton is about 1 X 10^-15 metres in radius so it must be that small anyway, and the largest nucleus we see are less than 8 X 10^-15 m in radius. If it were any longer in range, we might see even larger atoms in the world.

       Weak Forces are carried by the GUTS family of virtual particles. They account for radioactivity, primarily beta, neutrino, and gamma decay. These include particles called W, Z and Higgs Bosons. Their nature is far beyond the scope of this writing.

        Keeping up our analogy, gravitational forces must be carried by "gravitons." They must be so big we can't see them.  Attempts to measure these "critters" are in process. Antennae (see below) must pick up very weak signals from far reaches of the universe. The existence of gravitons has not been experimentally determined yet.

        The effects of the four basic forces can be described using the concept of a field. The field itself, rather than a source, carries momentum and energy. The gravity field, for example, is typically viewed as caused by the mutual interaction of two masses. Given these two objects, each causes a force to be exerted on the other object. Similarly for electromagnetism. Two charges mutually affect each other. Whether the fields themselves are real, or are a useful mathematical construct is being debated heavily. We know, for example, that a charge causes an electric field around it which then exerts forces on other charged objects. We also use this idea to show that for oscillating charges, the field emitted can propogate outward without the source being present anymore. So microwaves and TV and radio waves, as well as visible light from star system billions of light years away come to us. It is certainly possible that a galaxy whose light left it 20 billion years ago and is just reaching us now, may no longer exist. The idea of a field, then, is a mechanism to carry forth energy and force. If the concept is valid, we ought to be able to "see" (detect) gravitational waves detached from the gravitational source itself. We have, in fact, built gravity antennae to look for such waves. They are simply two masses connected by a spring (as are charges that oscillate in wires serving as electrical antennae.) Such a device is merely a big, solid cylinder that can be compressed aj!qng its axis. Since the effect is something like 10⁴⁰ times weaker than electromagnetism, it is not easy to detect. Only an explosion of cataclysmic proportions, such as a supernova, could produce such results. They have not as yet been confirmed, but there is indirect evidence. A special pulsar, 1913+16 makes 16.94 revolutions per second observed at the earth. It has a companion star orbiting it with a 7.75 year period. The period is decreasing slowly (1/10 th second per year) which could be due to loss of gravitational energy. We still have a lot of work to do with this ones

        Today we are looking for the smaller, more subtle effects, for that column IV effects. So far we haven't seen any. Nor have we observed any signs of quark or lepton structure. We are looking to find free quarks and other
totally new phenomena.

        Remember that picture we took at the racetrack? We want to tell from it where all the horses were at some time earlier and in the future. It would be especially nice to be able to predict the winner. In our picture of the world of matter that we are-.seeing for a moment in the entire history of mankind, consider a comparison of temperature of matter and the kind of energy it corresponds to:
 
 

         No lab on earth is capable of producing the energies needed to "see" the. unification of all four  forces of
nature. Such energies and temperatures were available at  the genesis of the universe. Now, the hottest places are   the interior of stars with temperatures of 10⁷ to   10⁹ Kelvins! (The latter may be approached in the interior of a supernova event.) These are so many orders of magnitude higher than earth based laboratories achieve. Only at the birth of the universe did such temperatures exist. (See Weinberg's The First Three Minutes) At the start of the universe all matter was a primordial soup of quarks and leptons. Matter did not exist as we know it today in the form of protons, neutrons, and atoms, etc. Later, in the chapter on Cosmology, we will examine the evolution of the universe from the first instant, through the modern epoch and into the future, through the ultimate destiny of it. That is not our intent right now.

         In the early universe (the first few minutes) we had photons, quarks and leptons in equal numbers. In cooling, quarks and antiquarks annihilated each other, producing gamma particles and energy. There does not seem to be enough energy for the reverse process, unless it comes from gravity. If there is enough mass in the universe, the universe will expand and then because of the mass, it will stop expanding and finally collapse back to a point, perhaps. If there is not enough mass, it will remain open and expand forever. We are very interested in finding out if there is enough mass to close the universe, however many billions of years it may take. The answer to this question appears to lie in the mass of the neutrino. It was initially thought to be zero, but now has a limit on it of something less than 1/5000 th that of the mass of the electron.

        Interestingly enough, the answer to the mass of the neutrino may come from astrophysicists observing the universe rather than elementary particle physicists with particle accelerators. February 23, 1987 is the date that light from a Super Nova (SN1987a) in the Large Magellenic Cloud (LMC) reached earth. The LMC is 163,000 light years away. This is the first such super nova visible to the naked eye since Kepler's of 1604. At this writing neutrino detectors around the world have sensed neutrinos from the blast (the universe itself can be likened to a gigantic, highest of energies, particle accelerator) and an upper limit is being determined for the mass of a neutrino. Perhaps answers to some of our questions about the basic structure of matter as well as the universe will be discovered.

        One other interesting aspect of study in this arena of physics is the search for a unified field theory. Einstein searched for such a grand theory. He had less to work with then than we have today. The nature of the nuclear forces was not known and the combination of the electromagnetic to the gravitation is not easy to recognize. It would certainly be a simpler theory of the world if all the forces in nature were really limiting examples of on grand force. We are searching for a Grand Unified Theory. (This is where the GUTS particles got their names) So far some progress has been made at unifying the weak nuclear and the electromagnetic forces together. Perhaps this is a start to join the others with them.

QUESTIONS

1. Distinguish between hadrons and leptons.

2. List the six different kinds of quarks.

3. When matter and antimatter come together, they annihilate each other and gamma (light) is given off.  How could you substantiate the statement that the universe is all matter and no antimatter systems exist?

4. What force is responsible for radioactivity?

5. Describe neutrinos and their role in the "scheme" of nature.

6. What is meant by a virtual particle?

7. What is meant by a Grand Unified Theory?

8. Explain how a cyclotron works.

9. Make up a good, fair question

BIBLIOGRAPHY

1. Elementary Particle Physics, Chautauqua Short Course, Argonne National Laboratories, 1984

2. Fisher, Arthur, "The World's Biggest Machine," Popular Science, June, 1987. ',

3. Segre, Emilio, From X-Rays to Quarks, W.H. Freeman and Company, New York, 1990.

4. Greenberg, O.W., Physics Today