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Biology LibreTexts

1.0: Introduction

In which we consider what makes science a distinct, productive, and progressive way of understanding how the universe works and how science lets us identify what is possible and plausible from what is impossible. We consider the “rules” that distinguish a scientific approach to a particular problem from a non-scientific one.

A major feature of science, and one that distinguishes it from many other human activities, is its essential reliance upon shareable experiences rather than individual revelations. Thomas Paine (1737-1809), one of the intellectual parents of the American Revolution, made this point explicitly in his book The Age of Reason10. In science, we do not accept that an observation or a conclusion is true just because another person claims it to be true. We do not accept the validity of revelation or what we might term “personal empiricism.” What is critical is that, based on our description of a phenomenon, an observation, or an experiment, others should, in practice or at the very least in theory, be able to repeat the observation or the experiment. Science is based on social (shared) knowledge rather than revealed truth.

Revelation is necessarily limited to the first communication – after that it is only an account of something which that person says was a revelation made to him; and though he may find himself obliged to believe it, it can not be incumbent on me to believe it in the same manner; for it was not a revelation made to ME, and I have only his word for it that it was made to him.  –Thomas Paine, The Age of Reason.

As an example, consider sunlight. It was originally held that white light was “pure” and that somehow, when it passed through a prism, the various colors of the spectrum, the colors we see in a rainbow, were created de novo. In 1665, Isaac Newton (1642–1727) performed a series of experiments that he interpreted as demonstrating that white light was not pure, but in fact was composed of light of different colors11. This conclusion was based on a number of distinct experimental observations. First, he noted that sunlight passed through a prism generated a spectrum of light of many different colors. He then used a lens to focus the spectrum emerging from one prism so that passed through a second prism; a beam of white light emerged from the second prism. One could go on to show that the light emerging from the prism 1 lens prism 2 combination behaved the same as the original beam of white light by passing it through a third prism, which again produced a spectrum. In the second type of experiment, Newton used a screen with a hole in it, an aperture, and showed that light of a particular color was not altered when it passed through a second prism - no new colors were produced. Based on these observations, Newton concluded that white light was not what it appeared to be – that is, a simple pure substance – but rather was composed, rather unexpectedly of light of many distinct “pure” colors. The spectrum was produced because the different colors of light were “bent” or refracted by the prism to different extents. Why this occurred was not clear nor was it clear what light is. Newton’s experiments left these questions unresolved. This is typical: scientific answers are often extremely specific, elucidating a particular phenomenon, rather than providing a universal explanation of reality.

Two basic features make Newton’s observations and conclusions scientific. The first is reproducibility. Based on his description of his experiment others could reproduce, confirm, and extend his observations. If you have access to glass prisms and lenses, you can repeat Newton’s experiments yourself, and you will come to the same empirical conclusions; that is, you would observe the same phenomena that Newton did12. In 1800, William Herschel (1738-1822) did just that. He used Newton’s experimental approach and discovered infrared (beyond red) light. Infrared light is invisible to us but its presence can be revealed by the fact that when absorbed by an object, say by a thermometer, it leads to an increase in the temperature of the object13. In 1801, inspired by Herschel’s discovery, Johann Ritter (1776 –1810) used the ability of light to initiate the chemical reaction: silver chloride + light → silver + chlorine to reveal the existence of another type of invisible light, which he called “chemical light” and which we now call ultraviolet light14. Subsequent researchers established that visible light is just a small portion of a much wider spectrum of “electromagnetic radiation” that ranges from X-rays to radio waves. Studies on how light interacts with matter have led to a wide range of technologies, from X-ray imaging to an understanding of the history of the Universe. All these findings emerge, rather unexpectedly, from attempts to understand the rainbow.

The second scientific aspect of Newton’s work was his clear articulation of the meaning and implications of his observations, the logic of his conclusions. These led to explicit predictions, such as that a particular color will prove to be homogenous, that is, not composed of other types of light. His view was that the different types of light, which we see as different colors, differ in the way they interact with matter. One way these differences are revealed is the extent to which the different colors of light are bent when they enter a prism. Newton used some of these ideas when he chose to use mirrors rather than lenses to build his reflecting (or Newtonian) telescope. His design avoided the color distortions that arose when light passes through simple lenses.

The two features of Newton’s approach make science, as a social and progressive enterprise, possible. We can reproduce a particular observation or experiment, and follow the investigator’s explicit thinking. We can identify unappreciated factors that can influence the results observed and identify inconsistencies in logic or implications that can be tested. This becomes increasingly important when we consider how various scientific disciplines interact with one another.


  • Michael W. Klymkowsky (University of Colorado Boulder) and Melanie M. Cooper (Michigan State University) with significant contributions by Emina Begovic & some editorial assistance of Rebecca Klymkowsky.