Understanding the Universe

From Quarks to the Cosmos

Don Lincoln

• Publisher: WSPC
• Year: 2004
• ISBN:
  9789814338110
• Topic: Scienze fisiche
• Subtopic: Astronomia e astrofisica

The Big Bang, the birth of the universe, was a singular event. All of the matter of the universe was concentrated at a single point, with temperatures so high that even the familiar protons and neutrons of atoms did not yet exist, but rather were replaced by a swirling maelstrom of energy, matter and antimatter. Exotic quarks and leptons flickered briefly into existence, before merging back into the energy sea.

This book explains the fascinating world of quarks and leptons and the forces that govern their behavior. Told from an experimental physicist's perspective, it forgoes mathematical complexity, using instead particularly accessible figures and apt analogies. In addition to the story of quarks and leptons, which are regarded as well-accepted fact, the author who is a leading researcher at the world's highest energy particle physics laboratory also discusses mysteries on both the experimental and theoretical frontier, before tying it all together with the exciting field of cosmology and indeed the birth of the universe itself.

The text spans the tiny world of the quark to the depths of the universe with exceptional clarity. The casual student of science will appreciate the careful distinction between what is known (quarks, leptons and antimatter), what is suspected (Higgs bosons, neutrino oscillations and the reason why the universe has so little antimatter) and what is merely dreamed (supersymmetry, superstrings and extra dimensions). Included is an unprecedented chapter explaining the accelerators and detectors of modern particle physics experiments. The chapter discussing the hunt for the Higgs boson, currently consuming the efforts of nearly 1000 physicists, lends drama that only big-stakes science can give. Understanding the Universe leaves the reader with a deep appreciation of the fascinating particle realm and just how much it determines the rich beauty of our universe.

Contents:

• Early History
• The Path to Knowledge (History of Particle Physics)
• Quarks and Leptons
• Forces: What Holds It All Together
• Hunting for the Higgs
• Accelerators and Detectors: Tools of the Trade
• Near Term Mysteries
• Exotic Physics (The Next Frontier)
• Recreating the Universe 10,000,000 Times a Second
• Epilogue: Why Do We Do It?

Readership: Students, scientists and lay people.

chapter 1

Early History

Whatever nature has in store for mankind, unpleasant as it may be, men must accept, for ignorance is never better than knowledge.

—Enrico Fermi

Billions of years ago, in a place far from where you are sitting right now, the universe began. An enormous and incomprehensible explosion scattered the matter that constitutes everything that you have ever seen across the vast distances that make up the universe in which we live. It would not be correct to call the temperatures hellish in that time following the Big Bang…it was far hotter than that. The temperature at that time was so hot that matter, as we generally understand it, could not exist. The swirling maelstrom consisted of pure energy with subatomic particles briefly winking into existence before merging back into the energy sea. On quick inspection, that universe was as different from the one in which we live as one can imagine. Basically, everywhere you looked, the universe was the same. This basic uniformity was only modified by tiny quantum fluctuations that are thought to eventually have seeded the beginnings of galaxy formation.

Fast forward to the present, ten to fifteen billion years after the beginning. In the intervening years, the universe has cooled and stars and galaxies have formed. Some of those stars are surrounded by planets. And on an unremarkable planet, around an unremarkable star, a remarkable thing occurred. Life formed. After billions of years of change, a fairly undistinguished primate evolved. This primate had an upright stance, opposable thumbs and a large and complex brain. And with that brain came a deep and insatiable curiosity about the world. Like other organisms, mankind needed to understand those things that would enhance its survival—things like where there was water and what foods were safe. But, unlike any other organism (as far as we know), mankind was curious for curiosity's sake. Why are things the way they are? What is the meaning of it all? How did we get here?

Early creation beliefs differed from the idea of the Big Bang, which modern science holds to be the best explanation thus far offered. One people held that a giant bird named Nyx laid an egg. When the egg hatched, the top half of the shell became the heavens, while the bottom became the earth. Another people believed that a man of the Sky People pushed his wife out of the sky and she fell to Earth, which was only water at the time. Little Toad swam to the bottom of the ocean and brought up mud that the sea animals smeared on the back of Big Turtle, which became the first land and on which the woman lived. Yet a third group asserted that the universe was created in six days. A common theme of all of these creation ideas is the fact that we as a species have a need to understand the pressing question: “From where did we come?”

While the modern understanding of the origins of the universe fulfills a need similar to that of its predecessors, it is unique in a very important way. It can be tested. It can, in principle, be proven wrong. In carefully controlled experiments, the conditions of the early universe, just fractions of a second after the Big Bang, can be routinely recreated. This book tries to describe the results of those experiments in ways that are accessible to all.

First Musings

The path to this understanding has not been very straight or particularly easy. While much of the understanding of the universe has come from astronomy, the story of that particular journey is one for another time. An important and complementary approach has come from trying to understand the nature of matter. Taken on the face of it, this is an extraordinary task. When you look around, you see a rich and diverse world. You see rocks and plants and people. You see mountains, clouds and rivers. None of these things seem to have much in common, yet early man tried to make sense of it all. While it is impossible to know, I suspect that an important observation for early man was the different aspects of water. As you know, water can exist in three different forms: ice, water and steam. Here was incontrovertible proof that vastly different objects: ice (hard and solid), water (fluid and wet) and steam (gaseous and hot); were all one and the same. The amount of heat introduced to water could drastically change the material's properties and this was a crucial observation (and probably the most important idea to keep in your mind as you read this book). Seemingly dissimilar things can be the same. This is a theme to which we will often return.

The observation that a particular material can take many forms leads naturally to what is the nature, the very essence, of matter. The ancient Greeks were very interested in the nature of reality and offered many thoughts on the subject. While they preferred the use of pure reason to our more modern experimental approach, this did not mean that they were blind. Like Buddha, they noticed that the world is in constant flux and that change seems to be the normal state of things. Snow comes and melts, the Sun rises and sets, babies are born loud and wet and old people die and fade into dry dust. Nothing seems to be permanent. While Buddha took this observation in one direction and asserted that nothing physical is real, the early Greeks believed that there must be something that is permanent (after all, they reasoned, we always see something). The question that they wanted answered was “What is permanent and unchanging among this apparent turmoil and chaos?”

One train of thought was the idea of opposing extremes. The thing that was real was the essence of opposites: pure hot and cold, wet and dry, male and female. Water was mostly wet, while ice had a much higher dry component. Different philosophers chose different things as the “true” opposing extremes, but many believed in the basic, underlying concept. Empedocles took the idea and modified it somewhat. He believed that the things we observe could be made from a suitable mix of four elements: air, fire, water and earth. His elements were pure; what we see is a mix, for instance, the fire that we observe is a mixture of fire and air. Steam is a mix of fire, water and air. This theory, while elegant, is wrong, although it did influence scientific thinking for thousands of years. Empedocles also realized that force was needed to mix these various elements. After some thought, he suggested that the universe could be explained by his four elements and the opposing forces of harmony and conflict (or love and strife). Compare the clouds on a beautiful summer day to a violent thunderstorm and you see air and water mixing under two extremes of his opposing forces.

Another early philosopher, Parmenides, was also an esoteric thinker. He did not worry as much about what were the fundamental elements, but more on the nature of their permanence. He believed that things could not be destroyed, which was in direct conflict with observation. Things do change; water evaporates (maybe disappears or is destroyed), vegetables rot, etc. However, he might have offered in counterpoint a wall surrounding an enemy citadel. After the city is captured and the wall pulled down by the conquerors, the wall, while destroyed, still exists in the form of a pile of rubble. The essence of the wall was the stones that went into it. The wall and rubble were just two forms of rock piles.

This prescient insight set the stage for the work of Democritus, who is traditionally mentioned in these sorts of books as the first to offer something resembling a modern theory of matter. Democritus was born circa 400 B.C., in Abdera in Thrace. He too was interested in determining the unchanging structure of matter. One day during a prolonged fast, someone walked by Democritus with a loaf of bread. Long before he saw the bread, he knew it was there from the smell. He was struck by that fact and wondered how this could work (apparently fasting made him dizzy too). He decided that some small bread particles had to travel through the air to his nose. As he couldn't see the bread particles, they had to be very small (or invisible). This thought led him to wonder about the nature of these small particles. To further his thinking, he considered a piece of cheese (he seemed to have a thing with food, perhaps because of all of those fasts). Suppose you had a sharp knife and continuously cut a piece of cheese. Eventually you would come to the smallest piece of cheese possible, which the knife could no longer cut. This smallest piece he called atomos (for uncuttable), which we have changed into the modern word “atom.”

If atoms exist, then one is naturally led to trying to understand more about them. Are all atoms the same? If not, how many kinds are there and what are their properties? Since he saw that different materials had different properties, he reasoned that there had to be different types of atoms. Something like oil might contain smooth atoms. Something like lemon juice, which is tart on the tongue and hurts when it gets into a cut, would contain spiny atoms. Metal, which is very stiff, might contain atoms reminiscent of Velcro, with little hooks and loops that connected adjacent atoms together. And so on.

The concept of atoms raised another issue. It concerned the question of what is between the atoms. Earlier, some philosophers had asserted that matter always touched matter. They used as an example the fish. Fish swim through water. As they propel themselves forward, the water parts in front of them and closes behind them. Never is there a void that contains neither water nor fish. Thus, matter is always in contact with matter.

The idea of atoms somehow belies this assertion. If there exists a smallest constituent of matter, this implies that it is somehow separate from its neighbor. The stuff that separates the atoms can be one of two things. It can be matter, but a special kind of matter, just used for separating other matter. But since matter is composed of atoms, then this material must also contain atoms and the question arises of just what separates them. So this hypothesis doesn't really solve anything. An alternative hypothesis is that the atoms are separated by empty space, not filled with anything. This space is called the void.

The idea of nothingness is difficult to comprehend, especially if you're an early Greek philosopher. While today we are comfortable with the idea of the vacuum of outer space or in a thermos bottle, the Greeks had no such experience. Try as they might, they could find no place where they could point and say, “There is nothing.” So the void idea wasn't very popular. Democritus finally reasoned that the atoms must be separated by an empty space, because one could cut a piece of cheese. There had to be a space between the cheese atoms for the knife-edge to penetrate. This argument is interesting, but ultimately not completely compelling.

The ideas of the Greeks came into being during the Golden Age of Greece, circa 500 B.C. This time was exceptional in that it allowed (and even encouraged) people (mostly rich, slave-owning men, it's true) to think about the cosmos, the nature of reality and the very deep and interesting questions that still cause modern man trouble. For the next 2000 years, there was not the right mix of circumstances to encourage such a lofty debate. The Roman era was marked by a concern for law, military accomplishments and great feats of engineering. The Dark Ages, dominated by the Catholic Church and small kingdoms, was more concerned with matters spiritual than scientific and even learned men of that time deferred to the Greeks on these topics. Even the lesser-known Golden Age of Islam, notable for its remarkable accomplishments in arts, architecture, cartography, mathematics and astronomy, did not add appreciably to mankind's knowledge of the nature of reality. (A mathematical smart-aleck might say that it added zero.)

Before we switch our discussion to the next era in which substantial progress was made in these weighty matters, some discussion of the merits of the Greeks’ early ideas is warranted. Books of this type often make much of the success of some of the Greeks in guessing the nature of reality. Some guesses were right, while most were wrong. This “canonization” is dangerous, partially because it confuses non-critical readers, but even more so because writers of books on the subject of New Age spirituality usurp this type of writing. These writers steal the language of science for an entirely different agenda. Using crystals to “channel” makes sense because scientists can use crystals to tune radio circuits. Auras are real because scientists really speak of energy fields. Eastern mysticism uses a language that sounds similar to the non-discerning reader to that of quantum mechanics. Somehow it seems enough to see that the ancients had many ideas. Some of these ideas look much like the results of modern science. It's clearly, they would assert, just a matter of time until other ancient beliefs are proven to be true too.

Of course the logic of this argument fails. Most speculative ideas are wrong (even ours…or mine!) The ancient Greeks, specifically the Pythagoreans, believed in reincarnation. While the experimental evidence on this topic is poor, it remains inconclusive. But the fact that the Greeks predicted something resembling atoms has no bearing on, for instance, the reincarnation debate.

I think that the really interesting thing about the Greeks’ accomplishments is not that a Greek postulated that there was a smallest, uncuttable component of matter, separated by a void; after all, that model of the atom was wrong, at least in detail. The truly astounding thing was that people were interested in the nature of reality at a size of scale that was inaccessible to them. The fact is that their atoms were so small that they would never be able to resolve the question. Reason is a wonderful skill. It can go a long way towards helping us understand the world. But it is experiment that settles such debates. A primitive tribesman, living in the Amazon jungle, could no more predict ice than fly. Thus it is perhaps not at all surprising that the generations following the Greeks made little progress on the topic. The Greeks had used reason to suggest several plausible hypotheses. Choosing among these competing ideas would await experimental data and that was a long time coming.

The next resurgence of thought on the nature of matter occurred in the years surrounding the beginning of the Italian Renaissance. During this time, alchemists were driven to find the Philosopher's Stone, an object that would transmute base metals (such as lead) into gold. What they did was to mix various substances together. There was little understanding, but a great experimental attitude. Along the way, dyes were discovered, as were different explosives and foul-smelling substances. While the theory of what governed the various mixings (what we call chemistry) was not yet available, the alchemists were able to catalog the various reactions. Centuries of experimentation provided the data that more modern chemists would need for their brilliant insights into the nature of matter. There were many deeply insightful scientists in the intervening centuries, but we shall concentrate on three of the greats: Antoine Lavoisier (1743–1794), John Dalton (1766–1844) and Dmitri Mendeleev (1834–1907).

Better Living through Chemistry

Lavoisier is most known in introductory chemistry classes because of his clarification of the theory of combustion. Prior to Lavoisier, chemists believed that combustion involved a substance known as phlogiston. He showed that combustion was really the combination of materials with oxygen. However, in the context of our interest, the ultimate constituents of matter, he actually should be known for other things. One of his accomplishments was notable only long after the fact. He completely revamped the chemical naming convention. Prior to Lavoisier, the names of the various substances manufactured by the alchemists were colorful, but not informative. Orpiment was a particular example. What Lavoisier did was rename the substances in such a way that the name reflected the materials involved in the reaction. For instance, if one combined arsenic and sulfur, the result was arsenic sulfide, rather than the more mysterious orpiment. While Lavoisier was more concerned with the fact that arsenic and sulfur were combined to make the final product, we now know that the final product contains atoms of arsenic and sulfur. Just the more organized naming somehow helped scientists to think atomically.

Another important discovery by Lavoisier concerned water. Recall that the ancients treated water as an element (recall fire, air, earth and water?). Lavoisier reacted two materials (hydrogen and oxygen gas) and the result was a clear liquid. This experiment is repeated in high-school chemistry labs today. Hydrogen and oxygen are first isolated (another Lavoisier effort) and then recombined using a flame. After a “pip” (a little explosion), the same clear liquid is observed. This liquid is water. So first Lavoisier proved that water was truly not elemental. An even greater observation was the fact that in order to get the two gases to react fully, they had to be combined in a weight ratio of one to eight (hydrogen gas to oxygen gas). No other ratio would use up all of both reactants, which somehow suggested pieces of hydrogen and oxygen were coming together in fixed combinations. Lavoisier also reversed the process, separating hydrogen and oxygen from water and also observed that the resultant gases had the same ratio by weight: eight parts oxygen to one part of hydrogen. While Lavoisier was not focused on the atomic nature of matter, his meticulous experimental technique provided evidence that lesser scientists could easily see as consistent with the atomic nature of matter. Lavoisier's brilliance was tragically extinguished on the guillotine in 1794 as part of the blood purge that was France's Reign of Terror.

John Dalton was an amateur chemist who expanded on Lavoisier's earlier observations. Although Lavoisier did not focus on the theory of atoms, Dalton did. While some historians of science have suggested that Dalton has received an undue amount of atomic glory, he is generally credited with the first articulation of a modern atomic theory. Democritus postulated that the basic difference between different kinds of atoms was shape, but for Dalton the distinguishing factor was weight. He based his thesis on the observation that the products of a chemical reaction always had the same weight as the materials that were reacted. Like Lavoisier's earlier observations of the mixing ratio of oxygen and hydrogen, Dalton mixed many different chemicals together, weighing both the reactants and the products. For instance, when mixing hydrogen and sulfur together, he found that by weight one needed to mix one part of hydrogen to sixteen parts of sulfur to make hydrogen sulfide. Mixing carbon and oxygen together proves to be a bit trickier, because one can mix them in the ratio of twelve to sixteen or twelve to thirty-two. But this can be understood if there exist atoms of oxygen and carbon. If the ratio of weights is 12:16 (twelve to sixteen), then this can be explained by the formation of carbon monoxide, which consists of one atom of carbon and one atom of oxygen. If, in addition, it was possible to combine one atom of carbon with two atoms of oxygen, now to make carbon dioxide, then one could see that the ratio of weights would be 12:32. The mathematically astute reader will note that the ratio 12:16 is identical to 3:4 and 12:32 is identical to 3:8. Thus the reason that I specifically chose a ratio of twelve to sixteen was due to additional knowledge. In the years since Dalton, scientists have performed many experiments and shown that hydrogen is the lightest element and thus its mass has been assigned to be one. This technique is moderately confusing until one thinks about more familiar units. A one-pound object is a base unit. A five-pound object weighs five times as much as the base unit. In chemistry, the base unit is the hydrogen atom and Dalton and his contemporaries were able to show that a unit of carbon weighed twelve times more than...

Table of contents

• Cover Page
• Title Page
• Copyright Page
• Dedication Page
• Contents
• Foreword
• Preface
• Acknowledgments
• 1 - Early History
• 2 - The Path to Knowledge (History of Particle Physics)
• 3 - Quarks and Leptons
• 4 - Forces: What Holds it All Together
• 5 - Hunting for the Higgs
• 6 - Accelerators and Detectors: Tools of the Trade
• 7 - Near Term Mysteries
• 8 - Exotic Physics (The Next Frontier)
• 9 - Recreating the Universe 10,000,000 Times a Second
• 10 - Epilogue: Why Do We Do It?
• Appendix A: Greek Symbols
• Appendix B: Scientific Jargon
• Appendix C: Particle-Naming Rules
• Appendix D: Essential Relativity and Quantum Mechanics
• Appendix E: Higgs Boson Production
• Appendix F: Neutrino Oscillations
• Further Reading
• Glossary
• Index