Introduction
Although all of us have taken science classes throughout the course of our study, many people have incorrect or misleading ideas about some of the most important and basic principles in science. We have all heard of hypotheses, theories, and laws, but what do they really mean? Before you read this section, think about what you have learned about these terms before. What do these terms mean to you? What do you read contradicts what you
thought? What do you read supports what you thought?
Hypotheses
One of the most common terms used in science classes is a “hypothesis”. The word can have many different definitions, depending on the context in which it is being used:
. “An educated guess” – because it provides a suggested solution based on the evidence. Note that it isn’t just a random guess. It has to be based on evidence to be a scientific hypothesis.
. Prediction – if you have ever carried out a science experiment, you probably made this type of hypothesis, in which you predicted the outcome of yourexperiment.
. Tentative or Proposed explanation – hypotheses can be suggestions about why something is observed, but in order for it to be scientific, we must be able to test the explanation to see if it works, if it is able to correctly predict what will happen in a situation, such as: if my hypothesis is correct, we should see ___ result when we perform ___ test. A hypothesis is very tentative; it can be easily changed.
Theories
The United States National Academy of Sciences describes what a theory is as
follows:
“Some scientific explanations are so well established that no new evidence is likely to alter them. The explanation becomes a scientific theory.
In everyday language a theory means a hunch or speculation. Not so in science. In science, the word theory refers to a comprehensive explanation of an important feature of nature supported by facts gathered over time. Theories
also allow scientists to make predictions about as yet unobserved phenomena.”
“A scientific theory is a well-substantiated explanation of some aspect of the natural world, based on a body of facts that have been repeatedly confirmed through observation and experimentation. Such fact-supported theories are not "guesses" but reliable accounts of the real world. The theory of biological evolution is more than "just a theory." It is as factual an explanation of the universe as the atomic theory of matter (stating that everything is made of atoms) or the germ theory of disease (which states that many diseases are caused by germs). Our understanding of gravity is still a work in progress. But the phenomenon of gravity, like evolution, is an accepted fact. “
Note some key features of theories that are important to understand from this
description:
. Theories are explanations of natural phenomenon. They aren’t predictions (although we may use theories to make predictions). They are explanations why we observe something.
. Theories aren’t likely to change. They have so much support and are able to explain satisfactorily so many observations, that they are not likely to change. Theories can,
indeed, be facts. Theories can change, but it is a long and difficult process. In order
for a theory to change, there must be many observations or evidence that the theory cannot explain.
. Theories are not guesses. The phrase “just a theory” has no room in science. To be a scientific theory carries a lot of weight; it is not just one person’s idea about something.
Laws
Scientific laws are similar to scientific theories in that they are principles that can be used to predict the behavior of the natural world. Both scientific laws and scientific theories are typically well-supported by observations and/or experimental evidence. Usually scientific laws refer to rules for how nature will behave under certain conditions, frequently written as an equation. Scientific theories are more overarching explanations of how nature works and why it exhibits certain characteristics. As a comparison, theories explain why we observe what we do and laws describe what happens.
For example, around the year 1800, Jacques Charles and other scientists were working with gases to, among other reasons, improve the design of the hot air balloon. These scientists found, after many, many tests, that certain patterns existed in the observations on gas behavior. If the temperature of the gas increased, the volume of the gas increased. This is known as a natural law. A law is a relationship that exists between variables in a group of data.
Laws describe the patterns we see in large amounts of data, but do describe why the
patterns exist.
A model is a description, graphic, or 3-D representation of theory used to help
enhance understanding. Scientists often use models when they need a way to communicate their understanding of what might be very small (such as an atom or molecule) or very large (such as the universe). A model is any simulation, substitute, or stand-in for what you are actually studying. A good model contains the essential variables that you are concerned with in the real system, explains all the observations on the real system, and is as simple as possible. A model may be as uncomplicated as a sphere representing the earth or billiard
balls representing gaseous molecules, or as complex as mathematical equations representing light.
Chemists rely on both careful observation and well-known physical laws. By putting
observations and laws together, chemists develop models. Models are really just ways of predicting what will happen given a certain set of circumstances. Sometimes these models are mathematical, but other times, they are purely descriptive.
If you were asked to determine the contents of a box that cannot be opened, you would do a variety of experiments in order to develop an idea (or a model) of what the box contains. You would probably shake the box, perhaps put magnets near it and/or determine its mass. When you completed your experiments, you would develop an idea of what is inside; that is, you would make a model of what is inside a box that cannot be opened.
A good example of how a model is useful to scientists is how models were used to
explain the development of the atomic theory. As you will learn in a later chapter, the idea of the concept of an atom changed over many years. In order to understand each of the different theories of the atom according to the various scientists, models were drawn, and the concepts were more easily understood.
Chemists make up models about what happens when different chemicals are mixed together, or heated up, or cooled down, or compressed. Chemists invent these models using many observations from experiments in the past, and they use these models to predict what might happen during experiments in the future. Once chemists have models that predict the outcome of experiments reasonably well, those working models can help to tell them what they need to do to achieve a certain desired result. That result might be the production of an especially strong plastic, or it might be the detection of a toxin when it’s present in your food.
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