What Science Does
Although science does not deal with the latter type of questions directly, it can be helpful in clarifying them. Namely, it explains what things are, so that we know more about them as we ask what their meaning or purpose or value is. For example, you may wonder whether it would be ethical to go back in time and help your parents become rich so you could have a more comfortable childhood that you did. Science would have no direct answer to your question, but it could inform you that, to the best of our knowledge, time travel is impossible, so you would never actually face this moral dilemma. Knowing this might lead you to focus your ethical inquiries on situations you are more likely to encounter. In this sense, the scientific method can help guide our questions even when it cannot provide answers.
Theory and Experiment
Scientific method involves an interplay of theoretical ideas and empirical observations. ("Empirical" means "from experience".) We observe the phenomena around us (and within us); this way we learn facts. But to interpret the facts we must understand relationships among them. Theoretical ideas - hypotheses and theories - explain those relationships. In turn, new observations and facts can be compared to predictions from hypotheses and theories, and so test their validity. Science is a process of continued updating of our knowledge, checking our existing explanations against new evidence, and improving or revising those explanations that fail to account for the new facts. Scientists have more confidence in theories that have withstood the test of many new facts, but no theory is immune to questioning and rejection if it becomes inconsistent with evidence. In other words, scientists do not "believe" in the results of science
Theoretical ideas in science are usually divided into three broad classes: hypotheses, theories, and laws. A hypothesis is usually a relatively simple statement about a fairly narrow set of phenomena. Of course, to be a scientific statement, it must have some clear and testable implications. An example is the hypothesis of dominant and recessive genes in genetics: if the dominant gene is inherited from one parent, and a recessive one from the other, the characteristic (phenotype) carried by the dominant gene will develop, but the recessive one can be passed on to the next generation and will show up when it is not combined with a dominant gene. This hypothesis was verified by Gregor Mendel's (1822-1884) famous experiment with peas.
A theory is generally a more complex set of statements that explains a broader set of phenomena. Genetics is based on a theory of inheritance of physical characteristics through genes - strings of DNA that carry information. Theories often develop from hypotheses. Modern theory of genetics was developed in the early 20th century, expanding on Mendel's ideas, and later enriched with understanding of the chemistry of DNA. A virtually inexhaustible variety of predictions can be derived from this theory, so it is tested every day in thousands of experiments in laboratories around the world. Most such experiments are done to develop new techniques to fight disease or improve food, rather than with the explicit idea of testing the well-established theory. Nevertheless, if any of them produced an outcome inconsistent with the theory, scientists would have to get busy improving and revising the theory. Many scientific breakthroughs in history resulted from a surprising observation in an experiment that had a practical purpose other than directly testing a theory.
In order to be testable, all hypotheses and theories must lead to predictions. Predictions are not necessarily statements about the future. They can be about oil deposits in the ground, about the diet of tyrannosaurus rex, or about the early Universe - all of which are about the past. The nature of a prediction is that it says something about observations that have not been made yet, or at least were not taken into account when constructing the hypothesis or theory from which the prediction is derived. It is new information (output) coming from the theory, so it must not be part of the input that gave rise to the theory in the first place.
A scientific law is a special type of prediction. It is a concise statement - a mathematical formula or a general rule - that can be applied as a prediction to a large number of situations. Newton's Second Law of Motion, F = ma, predicts what acceleration an object will achieve in every possible situation, as long as we know the object's mass and the force(s) acting on it. Mendel's law of inheritance, in its simplest form, says that mixing with a single trait will result in a 3:1 ratio of dominant to recessive phenotypes.
Due to a different use of words like "law" and "theory" in everyday life, many people are confused about their meaning in science. We are used to thinking of laws as something that must not be violated, and theories more-or-less as guesses, such as where a lost sock might be.
This might mislead you to think of a scientific theory as something less respectable than a scientific law. That would be completely incorrect; in fact, a scientific law is a statement derived from a theory. It is thus subordinated to a theory, not superior to it.
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