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Physics LibreTexts

1.1: The Scientific Method

Since the time of the ancient Greeks, people who study the natural world have developed a system for establishing knowledge, called the scientific method. The scientific method requires, as a minimum, the following: terminology that is precisely defined, measurements that are quantitative and repeatable, and assertions that are backed up by evidence.

Flowchart of the steps in the Scientific Method. Click here for original source URL.

There are several essential steps in the scientific method. The first step is gathering evidence, usually in the form of observations or data. The evidence might be physical, such as rocks brought back from the Moon, or it might be readings from instruments, such as measures of light focused by a telescope. Statements made with no evidence to support them are called speculation; they might be true or they might not. Without supporting evidence, there is no way to prove or disprove them. In some scientific fields, like chemistry andphysics and biology, evidence often comes from experiments in a laboratory. In astronomy, where many objects are very remote, most of the evidence comes in the form of light and other types of electromagnetic radiation.

The second essential step in the scientific method is analysis of the data, which usually involves a process of pattern recognition. For example, astronomers might analyze the nightly positions of a planet in the sky and recognize regularity in the motion, or they might find a similarity in the chemical composition of stars in different parts of our galaxy. A complication in the search for patterns in data is the fact that data are never perfect; observations are always finite in number and they have errors or uncertainties attached. The idea of searching for patterns in nature is at the heart of science. Discoveries start with a playful and curious mind at work.

The third step is the development of an explanation for the results of the analysis. Such an explanation is called a hypothesis. Often it is called a "working hypothesis" to emphasize that it is only a tentative proposal. An essential aspect of a scientific hypothesis is that it must be testable. That is, there must be some further observation or experiment that is capable of affirming or disproving the hypothesis. Scientists propose different hypotheses. The wrong ones are weeded out by such experiments. There is always more than one possible explanation for any set of data, which is one of the reasons scientists argue so much! The last element of the scientific method is therefore the critical evaluation of hypotheses through testing.

Often, an idea that starts out as one researcher’s working hypothesis survives many tests and becomes widely accepted. A hypothesis that has been tested repeatedly and successfully is usually called a theory, indicating that it is stronger than a mere working hypothesis. The term theory is usually preserved for a hypothesis that covers a wide range of phenomena. For example, you might hypothesize that people who watch a lot of television are overweight. You might have evidence to support your hypothesis, but this insight will never have the weight of a theory. Why? Because many people who watch a lot of television are not overweight and there are many reasons that a person might be overweight. A theory should be broad in scope and application. An example of a modern robust theory is Einstein's theory of relativity.

The scientific method can never guarantee truth, but it can be used to draw conclusions with a much higher degree of reliability than other systems of knowledge. Stronger evidence yields more reliable conclusions. This statement is not an idle boast, but a conclusion based on a long history of scientific advances. The scientific method is more reliable in part because of the pains taken to gather evidence.


Scientist-Astronaut Harrison H. Schmitt is photographed standing next to a huge, split boulder during the third Apollo 17 extravehicular activity (EVA-3) at the?Taurus?Littrow?landing site on the Moon. Schmitt is the Apollo 17 lunar module pilot. This picture was taken by Astronaut?Eugene A. Cernan, commander. Click here for original source URL.