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  Physics (Greek, ‘about nature’) is humankind\'s attempt at understanding the laws of nature. It is our quest to find the physical laws which underpin the workings of the universe. As such, it is concerned only with the truth. A theory is correct if it successfully explains observations, and wrong if it does not.

The principle of experiment is crucial to physics. Two assumptions must be made when performing experiments. The first is that the world is not a figment of the experimenter\'s imagination. This is not as trivial as it sounds: there is no proof that can be offered to the reader which will prove beyond doubt that the world exists outside of his or her mind! But if we assume that the world exists, we may begin to formulate theories about the nature of that existence.

The second assumption is that the laws of Nature do not change from day to day. A simple example is that of gravity. We know that if we let an object fall, it will drop to the ground. We believe that this will happen because it has always happened before: that if an experiment gives a certain result on one day, it will give the same result under the same conditions for all time. As with the first assumption, we do not know that this holds true; but physics would not get very far without it, and it seems to have been true for all of the history of humankind.

A physical theory is formulated as follows: experiments are performed which give results. These results seem to obey certain laws, for example, for the law of gravity, we may say that the further an object falls, the harder it hits the ground. Then, using the laws that were formulated from the results of the experiment, we may go on to predict the results of other experiments for which the same laws are relevant. It is important to realize that theories contain inherent limitations; they only claim to be true within a range of conditions.

Never at any point do we assume that these ‘laws’ or theories are anything more than models of the environment, and at any point, if an experiment gives results that contradict the predictions of a particular law, that law is considered to be invalid. A theory is only valid within its limitations; Newton\'s law of gravitation is only valid for relatively low gravity, and general relativity must be used for very massive objects like neutron stars and black holes.

Each theory enhances our understanding of the universe. The breakdown of a theory indicates that the universe is more complicated than was previously assumed, and that a more subtle theory must be formulated to take its place.

Theory and experiment proceed hand-in-hand; as technical knowledge improves the sensitivity of experiments, theory must keep up with the results and continue to predict further experiments. JJ

See also philosophy of science; science; scientific method.



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