"True science is never speculative; it employs hypotheses as suggesting points for inquiry, but it never adopts the hypotheses as though they were demonstrated propositions."
In science, the word "theory" has a specific meaning—a possible explanation for a phenomenon that is supported by experimental evidence. Scientists speak of the atomic theory, the theory of evolution, and the gravitational theory. They are referring, in each case, to a generally accepted description of atomic structure, or the process of changing life over time, or the functioning of the force that causes us to stay on the planet. All of these theories are based on a body of observations and experimental results.
It is an unfortunate aspect of our language that a single word can have several meanings or shades of meaning. When people say the word "theory" outside the scientific context, they may mean it as a conjecture. People refer to something "in theory" meaning in an abstract case. As a result, when a theory such as evolution or global warming is mentioned, many people think of the theories as guesses or speculation. In reality, the concepts of evolution and global warming are theories in the same sense as the concepts of the atom and gravity.
What is a scientific theory?
Scientific theories generally begin small—someone makes an observation that raises a question. For example, the theory of plate tectonics—the mechanism that moves the continents—began with an observation commonly made by school children: South America and Africa look like they could fit together like pieces of a jigsaw puzzle. Alfred Wegener asked the question: Could the two continents have once been joined? His hypothesis—that the continents float above the inner Earth—was his starting point. We now know that the continents move and the current theory of plate tectonics provides an explanation of how that happens.
A good test of a theory is its ability to predict something that has not yet been observed. For example, Albert Einstein predicted that light would be bent by a large gravitational field such as that of the sun. Specifically, Einstein’s theory of relativity predicted that stars would appear to be slightly out of place in a photograph taken during a solar eclipse, due to starlight being deflected by gravity as it passed the sun. This predicted effect was observed by British astrophysicist Arthur Eddington during a solar eclipse in 1919.
Sometimes a theory leads to predictions that are hard to accept without additional evidence. The Chandrasekhar limit, named after Indian scientist Subrahmanyan Chan-drasekhar, describes the maximum mass that can be supported against gravity before matter is squeezed together enough to collapse into a black hole. Although the existence of the Chandrasekhar limit—and black holes—was predicted in the 1930s, it was not widely accepted by the scientific community, largely due to opposition by Arthur Eddington, who had great influence among his peers. Eddington agreed that accepted theories would allow the existence of black holes but did not believe they could actually develop.
A common misconception is that theories are eventually proven and then become facts. In reality, a scientific theory is never proven. A theory is a model that explains observed facts. As new data becomes available, the theory may be modified to account for the new information, or even replaced by a different theory. For example, John Dalton’s theory of the atom, proposed in the eighteenth century, is very different from the current atomic theory. Our understanding of the nature of the atom has evolved as we learned about subatomic particles and the interaction of matter and energy. It is very likely that the atomic theory of the twenty-second century will be unlike the theory we use today.
A Few Theories That May Sound Familiar
Theories are an integral part of the scientific method. Some current theories, such as the atomic theory that describes the composition of matter on the small scale, have developed over a period of several centuries. Others—for example, string theory— are built on observations made within the past few decades. Other, as yet unnamed theories, may have come together today as a result of recent research.
No one can list all the theories that are used by scientists. There are uncountable theories to explain the results of the experiments performed by millions of scientists. They are constantly developed, modified, and even replaced as additional data becomes available. The atomic theory, the theory of gravity, the cell theory (all living things exist as cells), and kinetic theory (describing the motion of atoms and molecules) are a few of the basic building blocks of our current scientific knowledge.
The following theories have names that may seem familiar. These are theories that you may have seen mentioned in recent discussions about science. That does not necessarily mean that they are more important than other theories.
Evolution (Life Is Change)
In the 1760s, English civil engineer William Smith, while building canals in southern England, observed that fossils found in certain levels of rock strata were also found in different locations. Sir Charles Lyell, whose failing eyesight caused him to turn from law to geology, later made similar discoveries and came to the conclusion that Earth was millions of years old. He published his findings in the three-volume Principles of Geology (1830 to 1833). Charles Darwin studied Lyell’s work during the voyage of the HMS Beagle, and was particularly impressed by his description of rock formations. These observations and discussions provided a background for the conceptual breakthrough that was to become the theory of evolution.
Darwin was also influenced by Thomas Malthus, specifically Malthus’s book An Essay on the Principles of Population. Malthus held that nature produced a great abundance of offspring, yet over time the number of plants and animals remained roughly the same. Darwin reasoned from this that the living things better at getting food and avoiding predators were those most likely to survive and reproduce. He called this "survival of the fittest." When Darwin finally published his book after 20 years of study, he put forth the idea that all life on Earth had common ancestry and that various adaptive environmental reasons were why species changed.
It is commonly believed that the phrase "survival of the fittest" comes from Darwin’s Origin of Species by Means of Natural Selection, published in 1859. It was actually first used by Herbert Spencer in his Principles of Biology in 1864. Darwin did mention the phrase in later editions of his work. The term, as used by these biologists, referred only to the natural selection process in evolution of species. Later usages, in which "survival of the fittest" was applied to human societies and cultures, is completely unrelated to the ideas expressed by Spencer and Darwin.
The key element of the theory of evolution is that life changes as a result of natural selection. Within a species, there are always variations among individual organisms. Organisms that are best adapted to their environment are more likely to survive and reproduce. In each succeeding generation, more individuals are likely to have the traits that are most suited to the environment.
The theory of evolution, as it exists today, is built on several key elements:
♦ There are variations in form and behavior among the members of a species. Some of these variations are hereditary.
♦ Every species produces more offspring than the environment can support.
♦ Some individuals within the population have characteristics that make them better adapted to the environment than other individuals.
♦ Better adapted individuals have a greater likelihood of survival and reproduction.
♦ The favorable traits occur with greater frequency in the next generation.
♦ This process creates a natural selection for organisms possessing traits that are better adapted to the environment.
♦ Genetic change creates new traits that are subject to the natural selection process.
♦ The process of natural selection favors development of new species that are adapted to survival within an environment.
Theories are not static. The current theory of evolution is very different from Darwin’s original theory because a vast body of evidence has been collected since his work was published. The theory of evolution has developed and changed over time based on evidence. Many of the mechanisms of change are not yet known in detail and, within the theory of evolution, there are different theories about some of these mechanisms. Critics of evolution have latched onto some of these differences to claim that biologists cannot even agree on the existence of evolution. However, the key elements of evolution are not in dispute among scientists. It is clear that life evolves through the process of natural selection.
The scientific term for a "missing link" is transitional fossil. These fossilized remains, when discovered, illustrate an evolutionary transition heretofore not found.
Global Climate Change (Not Just Warming)
It is impossible for anyone who reads or watches the news regularly to be unfamiliar with the term "global warming." This concept refers to a rise in the average temperature of Earth’s atmosphere in recent—and if projections are correct, future—decades. Climate scientists, however, generally prefer the more accurate term "global climate change." This is because the effects of global warming do not present themselves as simply a steady increase in temperature every place in the world.
As atmospheric temperatures increase, many processes including global wind patterns and ocean currents can be changed. These alterations in large systems can affect the weather differently around the world. While most parts of Earth’s surface will experience increased average temperatures, some regions could actually experience a decrease. Other predicted aspects of the change in global climate include alterations in patterns of precipitation. Some dry places could begin to experience devastating floods, while other regions could be subject to equally devastating droughts.
It’s not just survival that is threatened by global climate change. In April 2008, Jim Salinger, a climate scientist at New Zealand’s National Institute of Water and Atmospheric Research, told the Institute of Brewing and Distilling convention in Wellington, New Zealand, that climate change portended a decline in the production of malting barley, a key ingredient in making beer. That, coupled with water shortages in certain parts of the world, could mean "pubs without beer or the cost of beer will go up." No reports were forthcoming about public reaction.
According to the theory accepted by an overwhelming majority of climate scientists, the main cause of global warming and the accompanying climate change is a change in the greenhouse effect. The greenhouse effect is an increase in Earth’s temperature due to certain gases in the atmosphere, including water vapor, carbon dioxide, nitrous oxide, and methane. These gases trap energy from the sun. These gases are referred to as greenhouse gases.
What is often lost in reporting about global warming is that the greenhouse effect is a natural part of the functioning systems of Earth. In fact, it is essential to life on Earth. Solar energy passes through the gases of the atmosphere and are absorbed by soil and water. Much of the absorbed energy is radiated back into the atmosphere as long-wave infrared radiation. Without greenhouse gases, heat would escape back into space and Earth’s average temperature would be about 60°F colder. The concern of atmospheric scientists, as related in the film An Inconvenient Truth, is that too much carbon dioxide is being released into the atmosphere by human activities. As industrializing countries, including China and India, increase their patterns of energy consumption, carbon dioxide emissions will continue to accelerate.
Very few scientists dispute the increase in the average temperature of the planet or that climate changes are occurring. The question is, is global climate change mostly caused by human activity? The United States Environmental Protection Agency (EPA) summarizes what is known about climate change on the webpage www.epa.gov/climatechange/science/stateofknowledge.html:
♦ Human activities are changing the composition of Earth’s atmosphere. Increasing levels of greenhouse gases like carbon dioxide (CO2) in the atmosphere since preindustrial times are well-documented and understood.
♦ The atmospheric buildup of CO2 and other greenhouse gases is largely the result of human activities such as the burning of fossil fuels.
♦ An "unequivocal" warming trend of about 1.0 to 1.7°F occurred from 1906— 2005. Warming occurred in both the Northern and Southern Hemispheres, and over the oceans.
♦ The major greenhouse gases emitted by human activities remain in the atmosphere for periods ranging from decades to centuries. It is therefore virtually certain that atmospheric concentrations of greenhouse gases will continue to rise over the next few decades.
Earth’s climate has changed throughout history, switching between ice ages, during which much of the land surface was covered by glaciers, and interglacial periods when ice retreated to the poles, or completely disappeared. A significant change, in either direction, would make the planet less hospitable to humans and the organisms on which they depend for survival. A primary goal of climate scientists is to determine whether human activity has created a risk of such a change and develop techniques to prevent it. The fact that such changes can occur naturally does not make them any more desirable.
Evidence of heating and cooling cycles in Earth’s history show that climates have changed drastically many times in the past, often very rapidly. Most atmospheric scientists are concerned now because of the large increase in carbon dioxide content of the atmosphere since 1750. There may be a "tipping point" at which greenhouse heating causes changes that increase the amount of carbon dioxide produced by natural processes. This could create a loop in which increased temperature leads to more greenhouse gas which causes more increase in temperature, and so on.
Unfortunately, understanding the effects of changes in carbon dioxide concentration is a very tough problem. Climates around the planet result from extremely complex interactions of the atmosphere and the oceans. Some of the world’s largest and fastest computers are devoted exclusively to the study of climate models. The theory of global climate change is one of the most extensively studied scientific topics of recent years. The EPA website mentioned previously also lists the challenges facing climate researchers.
♦ Improving understanding of natural climatic variations, changes in the sun’s energy, land-use changes, the warming or cooling effects of pollutant aerosols, and the impacts of changing humidity and cloud cover
♦ Determining the relative contribution to climate change of human activities and natural causes
♦ Projecting future greenhouse emissions and how the climate system will respond within a narrow range
♦ Improving understanding of the potential for rapid or abrupt climate change
Plate Tectonics
The theory of plate tectonics began with a simple idea and it has grown to become the backbone of modern geological science. The idea at the core of plate tectonics was introduced by Alfred Wegener in the early twentieth century in his theory of continental drift: the continents are in constant motion across the surface of Earth. Key data for the theory included the shapes of the continents, which appear to fit together like puzzle pieces; discovery of identical fossils on several continents; and mountain chains on separate continents that appear to be parts of a single chain.
Wegener hypothesized that the continents were once joined in a single supercontinent, which he called Pangaea. He proposed that Pangaea had broken apart and the continents had moved across the sea floor into the current locations. Acceptance of this hypothesis by geologists was slow because of one missing detail: Wegener could not describe a force capable of driving a continent across the sea floor.
In the 1960s, a key part of the process was found. Scientists studying the floor of the Atlantic Ocean discovered a phenomenon called "magnetic striping." As molten rock cools and hardens, minerals that contain iron tend to line up with Earth’s magnetic field. Scientists discovered that strips of rock parallel to the crests of ridges in the center of the ocean alternate in magnetic polarity. This suggested that, over long periods of time, the direction of Earth’s magnetic field has reversed many times. The observation also suggested that the sea floor is spreading away from the ridges.
Based, in part, on this observation, a mechanism was proposed for the movement of continents. According to the theory of plate tectonics, Earth’s crust (making up both the continents and the sea floor) is actually floating on top of fluid rock. Where pieces of the crust, called tectonic plates, collide, material is pushed down into the layer beneath the crust. Where two plates move apart, molten material moves toward the surface, cools, and hardens, forming a new layer of crust.
Plate tectonics explains why some places are particularly likely to experience geological upheavals such as earthquakes and volcanoes. These events occur at the boundaries between plates, where huge masses of rock collide or grind past one another. Direct collisions between plates can cause the formation of mountain ranges as rock bends and folds. The Himalayan mountain chain, for example, has been built by the slow but continual collision of the Indian subcontinent with the plate on which the continent of Asia rests.
To understand major earthquake zones like the Pacific Coast of the United States, have a look at a map of the tectonic plates of our planet courtesy of the United States Geological Survey’s map at http://pubs.usgs.gov/gip/volc/fig37html.
"I am convinced that, at its best, science is simple—that the simplest arrangement of facts that sets forth the truth best deserves the title of science. So the geology I plead for is that which states facts in plain words—in language understood by the many rather than by the few."
Relativity: Easier to Understand Than You Think
One of the most famous scientific theories is Einstein’s Theory of Relativity. Because the theory is based on complex mathematical calculations, rather than direct observation of familiar phenomena, the theory’s reputation is one of being completely incomprehensible. It really is not that hard to understand the concepts, if you accept that the mathematics support the conclusions.
The uncertainty principle was conceived by Werner Heisenberg in 1927 It holds that the movement of a subatomic particle such as an electron can never be accurately measured, because both speed and position cannot be simultaneously assessed. "The more precisely the position is determined," Heisenberg said, "the less precisely the momentum is known in this instant, and vice versa." This principle frustrated Einstein’s attempts to find a unified field theory.
Einstein actually developed two theories of relativity that combine to form the overall theory: special relativity and general relativity. The special theory of relativity, introduced in the 1905 paper "The Electrodynamics of Moving Bodies" states that all motion is relative and there is no absolute state of rest. A key concept introduced in this theory is that the speed of light is constant for all observers no matter how they are moving relative to one another. This means that time and space are perceived differently by observers depending on their motion. One of the consequences of the special theory of relativity is the equivalence of mass and energy. This equivalence, expressed in one of the most famous equations ever written—E=mc2—provides the basis of nuclear weapons and nuclear power plants. Another consequence of the theory is that nothing can move faster than the speed of light.
The special theory of relativity applies to objects in motion and in the absence of a gravitational field. In the general relativity theory that came over a decade later, Einstein incorporated gravity. In this theory, the three dimensions of space and the dimension of time are combined to form a four-dimensional space-time. As objects accelerate to near the speed of light, the matrix of space and time bends to maintain the speed of light at a fixed value. Gravity is the result of this bend in space and time. Massive objects are attracted to one another by this bending—an attraction that we know as gravity.
"Time and space and gravitation have no separate existence from matter."
One of the consequences of general relativity is that fast-moving matter can create waves in space-time. These gravitational waves can radiate away from a source just as light waves radiate from a glowing body. Although gravity waves have not yet been detected, physicists have built detectors to look for the waves created by dense, spinning stars. These detectors use laser beams that are miles long to try to detect waves that create a motion that is much smaller than the diameter of an atom.
String Theory
You may have heard of string theory because it tends to capture the imagination of science reporters. Physicists who have developed string theory are looking for a pattern in the universe that goes deeper than the subatomic particles that we know and can study. Because matter and energy can be related to one another by Einstein’s theory of relativity, theorists propose that at a basic level, all matter and energy consists of vibrations of loops of material or energy.
Imagine that everything in the universe was part of a constantly moving and changing pictorial tapestry, and that strings make up everything in the universe. However, these strings do not vibrate in three dimensions like a violin string. They vibrate in as many as 11 dimensions. All of the strings are the same. It is the vibrations that differ among the various types of particles. In other words, while we may be able to see atoms and molecules and electrons and photons and other subatomic particles, we cannot see the strings themselves.
String theory is a purely mathematical idea. We cannot see the strings and no test has ever been developed to determine whether they exist. Using the equations of string theory, scientists have attempted to predict energy interactions, even the gravitational activities predicted by Einstein, and weave everything into a unified approach to quantum mechanics.
Quantum mechanics is the branch of physics developed early in the twentieth century to explain the structure of matter at an atomic level. Curiously enough, scientists learned that subatomic matter has a wavelike structure until examined, at which time it takes on particle characteristics.
String theory is not universally accepted by physicists. Lee Smolin, founder of the Perimeter Institute for Theoretical Physics in Waterloo, Ontario, and Columbia University mathematician Peter Woit both published books in 2006 that stated string theory might not only be unproven, but completely wrong. Until the theorists are able to use string theory to make a prediction that can be confirmed experimentally, it is likely that many scientists will consider it to be an untested thought exercise rather than a supported theory.
Chaos Theory (That Butterfly in Brazil)
Chaos theory has captured many people’s imaginations, partly because of an interesting analogy used to explain it. The movie The Butterfly Effect (2004) popularized chaos theory, on which it was loosely based. Chaos theory was first investigated in 1960 when meteorologist Edward Lorenz began using a computer to try to predict the weather. The term "butterfly effect" came from a paper entitled "Predictability: Does the Flap of a Butterfly’s Wings in Brazil Set Off a Tornado in Texas?" The paper was presented by Lorenz in 1972 to the American Association for the Advancement of Science in Washington, D.C. The idea was simple; by flapping its wings, the butterfly made a tiny change in the system in which it existed (the jungle), which might affect, for example, the turn of a leaf, which would affect something else, and so on, eventually changing the trajectory of a larger weather system on the planet.
Although the concept of such a tiny change affecting large-scale phenomena may seem absurd, there are patterns to be found in so-called chaos. Many natural phenomena have patterns that may not be as random as they seem.
Lorenz was not the first person to study chaos. French mathematician Jacques Hadamard published a study in 1898 about the chaotic motion of a free particle gliding unaffected by friction on a surface of constant negative curvature. Chaos theory has been pursued over the years by mathematicians, who use complex formulas to try to make order out of seemingly random events and motion.
A system is classified as chaotic when: (a) it is sensitive to initial conditions, for example, the butterfly; (b) it interacts with the space around it; and (c) related points in an entire system are connected in a complex way. A small motion in the atmosphere meets these criteria. The theory can also be applied to other types of interactions, ranging as widely as the flow of fluids and the movement of money in large economic systems. Chaos theory has also been applied to studying a very large-scale phenomenon—the reasons for the particular locations of planets in the solar system.
