Science and The Scientific Method
The first task in trying to learn about science is to ask: What is science? (You should write down your answer before you read further).
"Science" means knowledge - or that's where it originated ( from the Latin scientia) - now the term leans toward the more quantitative fields of knowledge. Here we will use a "short list" for the sciences. Our list includes mathematics (including computer science), physics (including astronomy), chemistry and biology. Other legitimate candidates are geology, medicine, psychology, etc. There are also the various fields of engineering and, of course, many others (How about the science of cooking, a fairly quantitative field?). We'll extend our reach beyond the short list on occasion. The order of the short list is not accidental. Mathematics is first because it provides the language which the other sciences use. (Even more fundamental are the concepts of logic, epistemology and metaphysics, since these deal with the universal basis of knowledge, but we'll leave that to others.) After mathematics is physics. Physics deals with the universal properties of Nature. It is the most quantitative of all the sciences, and the workings of all the other sciences are contained with in physics. Today, physical theories based on abstract mathematical formalisms portend to describe all of the laws of Nature in a single unified construct (e.g. superstring theory, or "the theory of everything"). Although there are significant obstacles to overcome before the theory is complete, the mere postulation of such an ambitious attempt at unifying all of Nature is remarkable in itself, and represents an impressive measure of the power of the quantitative approach to science. Chemistry follows physics. The building blocks of the chemist are atoms. These are the atoms that the physicist has dissected into the myriad of sub-atomic particles which are themselves constructed from quarks whose colors and flavors fancifully yet unerringly form the (at least so far) seemingly basic structural underpinning of all matter. The chemist examines the ways these atoms are joined to form molecular structures, and devises new ways to synthesize vast arrays of such structures for a variety of practical applications. Finally (at least for our short list) the biologist' s fundamental working unit is the single living cell, along with its own life-defining structural mix of components. As we move from physics to biology the mathematical formalism becomes less able to explain the systems we study. This is not because new rules come into play, but rather because the systems become so complex that the shear magnitude of the interactions between various part of the system become unmanageable. So... what is science? It is that branch of study which tries to understand the workings of Nature by finding the orderly rules she follows. To search for this understanding requires a faith that the rules are both unchanging and universal. Scientists proceed under these beliefs to describe in as quantitative and simple a manner as possible the basic "laws" under which the world is constrained to function. ( For a somewhat more "official" answer to the question "what is science", look at what the American Institute of Physics has to say).
Is there a scientific method?
In other words, is there a set of defined steps one takes to solve a physical (or any other) problem. Clearly there is not (unless you subscribe to the "try everything" definition). Each problem (hopefully) provides means, by clues or intuition, to its solution. There are, however, some general stages of approach that guide our ordered progress in the research of a problem. These might be listed as1 1. Empirical Observation; 2. Discovery of the Pattern; 3. Formulation of a Theory; 4. Generalization of the Theory. The stages must be repeated and refined until a consistent theory emerges. For a more comprehensive definition of the scientific method, click here. You might also enjoy a link to a game where you can test your understanding of how science is done.
Theory and experiment:
If you talk to a physicist, sooner or later you will find out that he or she considers him/her self to be either a theorist or an experimentalist, especially if the physicist is rather young. Age and circumstance tend to blur the distinction. (When I. I. Rabi, who won the 1944 Nobel Prize in physics in recognition of his resonance method for recording the magnetic properties of atomic nuclei, was asked if he were a theorist or an experimentalist, he replied "well, I'm just a physicist"). Both theory and experiment are necessary ingredients in science. Generally, a phenomenon is observed or contemplated, and experiments are conducted to allow, through observation and measurement, a consistent pattern to emerge from the experimental data. From the data, or sometimes in anticipation of the data, a theory in the form of a physical or mathematical model evolves. The model is then used to predict more general results, and experiments are devised to test the theory (i.e. the scientific method!). Which comes first: theory or experiment? Usually, an idea comes first - an idea often triggered by curiosity about an observation of some physical process. Then the idea is tested by experiment, and finally a theory is formulated. Galileo wondered about the way objects fell under the influence of gravity. He devised experiments involving dropping objects from various heights (Remember the leaning tower of Pisa?) and then with balls rolling down inclined planes since the descent of freely falling objects were not easily timed using his crude clocks, and thus formulated his theory of the motion of falling bodies. There are also notable examples of theory preceding experiment: From a troubling inconsistency in electromagnetic theory Einstein formulated the special theory of relativity. Experimental verification came later. Both theory and experiment are necessary and complementary ingredients in the recipe of scientific investigation. Any scientist, whether theorist or experimentalist, must have a good understanding of both.
The need for quantitative explanations:
Scientific theories gain validity when experiments are conducted to test the theory. Experiments gather information through measurements, and measurements are valid in direct proportion to their accuracy. The measurement and the accuracy of the measurement (and thus the measurement of the accuracy) provide the quantitative basis of science. Of course, the theories themselves must be cast in quantitative form in order to present a comparison of theoretical prediction and experimental results. Without quantitative content science (as well as many other things) loses value. As examples, you might be a bit more assured if you are given directions to a destination as "two miles to the lights then left for three more miles" rather than "over that way." Pollsters are more likely to gain your confidence if they prognosticate with "Gore leads Bush by seven points with a margin of error of plus or minus one point" rather than with "looks like Gore's ahead." Finally, you probably got a better lab grade if you reported "My results were off by 18.5% compared with the predicted values, due to the use of crude equipment" than if your conclusions were reported as "Wow, it was a cool experiment, but I guess something went wrong because my answer was way off."
What constitutes "good" science?
You might say that good science is repeatable science. If the scientific theory is based on facts (rather than assumptions) then experiments can be devised to test these facts over and over. A good scientific theory allows the prediction of the results of future experiments based on that theory. Our science is based on the faith that the rules we discover as we study Nature will not change from time to time or from place to place. We therefore expect the gravitational forces that keep a set of planets in orbit around a star in a distant galaxy to behave the same as holds for our solar system. We also have faith in the inevitability of cause and effect: The requirement that certain events trigger other events routinely and consistently (and so predictably). A scientific theory can explain a natural phenomenon and still not meet the criteria good science. Factors such as simplicity, agreement with experiment and generality are essential.
Of course, what may be considered a successful theory early on can evolve over time into a more complete and useful form. An example of note is the evolution of our model of the solar system itself. To visualize a physical system we often devise a model of the system to work from. Refining our model refines our understanding of the system and so matures our theory. It was Pythagoras who, in the sixth century BC, taught that the earth was surrounded by an arrangement of transparent spheres that carried the sun, moon, planets and stars. His model was prompted by the philosophical requirement of perfect shapes for a perfect world rather than by observations, but it was aesthetically satisfying and a visual first step. As time progressed and measurements were made of the motions of the planets it became clear that the qualitative model of Pythagoras was unable to predict planetary (or even lunar) motion. It was Plato (427- 347 BC) who asked his students to seek out the proper combination of circular motions needed to accurately describe the observed motions of the heavenly bodies. Plato's Problem, as it became known as, occupied the time of mathematicians and astronomers for almost two thousand years, in part because of the important reference to "circular motion". Like Pythagoras, perfect heavens required, in the minds of these ancient thinkers, perfect figures to describe them. Among the most notable of these thinkers was Ptolemy (127 - 151 AD). His mathematical prowess allowed him to devise a model of the solar system that accurately predicted planetary motions. It had the requisite accuracy (for the time) and could predict future positions of the planets, but it was complex and in constant need of modification to maintain accuracy. In about 1530 Copernicus finished his work on a model that placed the sun rather than the earth at the center of the solar system. Although this revolutionary move did little to improve the accuracy of Ptolemy's model it did make the model much simpler, and that is a primary goal of good science. Again, inaccuracies in the prediction of planetary motions, prompted by the availability of accurate experimental (observational) data thanks to the work of Tycho Brahe, prompted Johann Kepler (1571 - 1630) to finally abandon Plato's requirement for circular motions and propose a model that was both simple and accurate in its predictions. More importantly Kepler, after years of seeking out the circles Plato asked for, finally let Tycho's data lead him to the true (elliptical) motions of the planets, unencumbered by preconceived restrictions. Letting the data speak for itself is another requirement of good science. There was still one missing ingredient for good science in Kepler's work: While his laws allow the prediction of planetary motion, there is no underlying cause for the described motions. It was Newton (1642 - 1727) who completed the theory. By introducing the notion of forces causing motion, and the force of gravity as the cause of planetary motion, he arrived at a satisfactory theory of planetary motion. The story ended there, at least for a while. The relativistic theories of Einstein introduced important (although in most instances negligible) modifications to Newton's work. Now, in order to answer questions linking gravity to the world of sub-atomic particles, theorists continue to examine and expand on Einstein's work.
So, were these scientists doing good science?
What is not "good" science?
There are lots of obvious answers - astrology is one. Here is another, but perhaps not as obvious: UFO's. Stories of UFO's can be found on any news stand and are prime candidates for movies. They have also been studied by scientists, and while most UFO sightings can be explained as natural (i.e. earthly) events, some cannot. The difficulty arises because the scientific method cannot be applied. If we could convince potential visitors to announce their arrival in advance, so that we could set up our instruments and gather data when they make their appearance, we could turn UFO experiences into good science. Without that, we are faced with consideration of a series of isolated events, narrated by observers and supported in some cases by photographs and video tapes (of often questionable authenticity). What can we do? We can apply logic and our understanding of the laws of Nature. Do these laws allow for visitors from distant galaxies? Yes, they do. Is the probability that we are being visited outweigh the probability of other more earthly causes for these events? Again, I leave the answer to you.
Forces
The Jedi had access to "The Force" and it carried them through all sorts of predicaments. What is a force? Where do forces come from, and where do they go? You push on a door, and the force you exert opens it. How many forces are there? How different is the force of Sammy Sosa's bat on a baseball from Tiger Woods' driver on a golf ball? A familiar and puzzling force is that of gravity as it pulls things to Earth. Chemical forces seem to hold molecules together. Is the force of the wind a special kind of force (as gravity seems to be)?
Here's a seemingly simple problem: I sit on a table and the table supports my weight. How does it do this? Clearly, the table pushes up on me by just as much as I (with the help of gravity) push down, and we come to a state of equilibrium. Now I lay my book on the table beside me. The book pushes down and the table pushes up and the book, like me, is at rest on the table. Question: How does the table know just how hard to push on me and how hard to push on the book? It's reasonable to expect the table to push harder on me (i.e. exert a larger force), but how does it know how much harder? Think about it - we'll find the answer soon enough.
The first two
Getting back to our list of forces, it seems that it can get quite long: What forces make a car go, or an electric train? It would seem that the force to keep an electric train moving should be electrical and a car's forces should derive from the gasoline it its tank. How different are these? It begins to look as if the list is an enormous one, but it turns out that the list is not very long at all. There are, in fact only four forces we have to deal with. One we've mentioned, gravity. We need to understand more about the gravitational force, but for now we just want to establish our list. The next force is the electrical, or more properly the electromagnetic force. It's much stronger than the gravitational force, as you can easily show: Run a rubber comb through your hair and move it close to a small piece of paper lying on the table. When the comb passed through your hair some electrons from your hair were transferred to the comb, so it had a net negative charge. This relatively small amount of charge, when put near the piece of paper, provides a force strong enough to lift the paper right off the table, in spite of the fact that the whole earth, through its gravitational influence, is trying to keep it down! Later on we'll calculate how much the difference between the two forces are, but for now it suffices to say that the difference is enormous. Now, as far as our every day experience is concerned, we've exhausted the list - there's only two! Well, there's really four, but the other two, which I'll talk about later, are only noticeable on an atomic scale. Wait a minute - what about the Sosa's baseball and Tiger Woods' golf ball? These forces are electrical. Take a close-up look at a bat hitting a ball: the two objects come so close to each other that the atoms in the bat interact with the ones in the ball. Atoms are tiny positively charged things (nuclei) surrounded by a swarm of negatively charged electrons. Well, that's a crude description of an atom, but it serves our purpose here. It's an experimentally verified and well known fact that like electrical charges mutually repel each other, and opposite charges attract. As the ball and the bat come together, the first each sees is the electrons of the other. (The electrons are, after all, on the outside of their atoms). The electrons repel each other and the ball heads for the bleachers. I'm ready to admit that no one uses this electrical interaction to actually calculate the effect of bat on ball - there are way too many electrons involved - but the fundamental process is electrical. As for the other forces mentioned above, and in fact all the other forces we encounter on a macroscopic scale, they too are electrical. For example, the intermolecular forces that are released when gasoline is combusted by our car engines are there due to the electrical make-up of the atoms that comprise the molecules of the fuel.
The other two
There are two more forces. One is fairly easy to figure - at least it's easy to see that it should exist. The model of the atom mentioned the previous paragraph is the one everyone learns about in school: A nucleus made of protons and neutrons surrounded by rings of electrons. We also learn that the electrons carry negative charges and the protons have an equal positive charge. As the electrons move in their orbits they spread themselves out as much as possible because they mutually repel each other. How about the protons? They're all positively charged and they are really close together. Why don't they fly apart? Answer: They must be trying to, and since they don't it must be that something (a force!) is holding them together. Rule gravity out - it's much too weak. It must be another, very strong force. We call it, well ..., the "strong" force (or, more formally, the "strong interaction"). How strong is this force? It must hold the nucleus together against the electrical repulsion of the protons. Check out the periodic table of the elements. There are about 100 elements. That means 100 protons pushing each other apart. The strong force is able to withstand the force of 100 protons, but not more, otherwise we would have more elements. Conclusion: the strong force is (roughly) 100 times that of the electrical force.
The other force is called the "weak" force (or weak interaction). This force is involved in the process whereby a neutron decays into a proton and in so doing ejects an electron and a neutrino in a process called beta decay. (Actually, its an antineutrino and the process can also start with a proton and eject a positron, but here we just want to establish the list). The force that is involved in these processes is the weak interaction. It is weak indeed, but not so weak as gravity.
The four forces differ greatly in strength and range. Of the two we experience every day, the electromagnetic force is by far the greater. As an example, two protons are electrically repelled and gravitationally attracted. The electrical repulsion is over one million trillion trillion times greater than the gravitational attraction. That's 10,000,000,000,000,000,000,000,000,000,000,000,000 greater or (as a demonstration of why we like to use "scientific notation") 1037 times greater. If the two protons could get next to each other the attractive force would overcome the electrical force by about 100 times, but this force doesn't extend for distances much beyond the diameter of a proton (electromagnetic and gravitational forces extend to infinity). The weak force is much greater than gravity, but tiny compared with the other two, and extends over an even shorter range than the strong interaction.
Dealing with forces
Aside from the strikingly short list of fundamental forces, on a more mundane level we deal with forces every day. Gravity is fundamental and familiar, as is electricity (or electromagnetism), but often not as a force. Forces like those between bats and balls are called mechanical forces and its more practical to deal with them as the kind of forces Newton described rather than as the electromagnetic interactions they fundamentally are. Nuclear forces are not things we deal with very often, so we won't consider them now. A good working definition of a mechanical force is a push or a pull. This definition also illustrates an important characteristic of forces, and one we will have occasion to use: If a force is a push or a pull, how do you quantify it? You can describe how hard you push, but that's not enough. You also need to tell the direction of the push. I can ask you to push on something with a force of 10 N, but if I don't specify a particular direction you may not provide the desired results. Both magnitude (how hard you push) and direction are required to completely define a force. (Try to push on something without involving a direction). In the business of science we call things requiring magnitude and direction "vectors". By the way, the unit 'N' for our 10 N force is called a Newton in honor of Sir Isaac Newton. It's the metric counterpart of the English pound. To convert between the two, 1 N = .2248 lb, or in the other direction 1 lb = 2.448 N (or roughly two and a half Newtons per pound). Although pounds may be more comfortable for you, its time to bite the bullet and go metric. Only the United States hasn't already made the move to measuring things in metric units. Maybe after you take this course, graduate and make it to congress you will have seen the light and so push (no pun intended) us along to metric sanity.
Categories of Phenomena
When Newton published his laws of motion in 1687 he brought a means of predicting, to any (at least in principle) degree of accuracy, the motions of planets in their orbits about the sun as well as the flight of a cannon ball over the surface of the earth. Using his laws the world could be considered as a fine clock, which when wound up in a known way would tick away predictably and flawlessly into the distant future. Given a few pieces of critical information about how a physical system started out, Newton's equations accurately predicted the future of the system from that time forward. If the system became complicated by virtue of the number of its parts, the equations would become cumbersome but solvable: Even the mutual interactions (via gravity) of all the planets and all their moons are determined by (simultaneously) solving a single set of equations (Newton's famous universal law of gravitation Fg = Gmm'/r2). But what if the number of interacting particles becomes enormous, as in the case of the air molecules in a room? Here the number becomes very large, on the order of Avogadro's number (6.022 x 1023). In principle you might suppose that the picture doesn't change fundamentally, even though the number of simultaneous equations becomes so large that there is no hope of ever solving them, even with the help of the most powerful computers.
On the other hand, there is hardly any motivation to find out how molecules in a gas move in such fine detail. We want to know how the gas behaves as a whole, and very precise information about its behavior can be obtained statistically using methods introduced by Boltzmann. The question now arises, which approach, the Newtonian regime of a clock-like world or the statistical methods of Boltzmann are more fundamental? The question becomes more puzzling in the quantum mechanical world where even the most elementary interactions of a single particle (e.g. an electron) yield better to a statistical interpretation than to a precisely deterministic one. The matter is still under question.