How does use of the word theory differ in science and in daily life?

Answer 1

In science, a theory is a testable or falsifiable proposition. A scientific theory can never by proven, only disproven.

A thoery is an idea that is developed to a state where you can make a prediction that can be tested. Relevant tests are carried out and it is assumed that there were no errors in the tests (else you do the tests again). The outcome of the tests can be the opposite of what was predicted so the theory is falsified. The theory may need a few tweaks which only apply in some "extreme conditions" or it may require a complete rethink. One example of the first is Newtonian physics and Relativity in the macro world (Newtonian physics is not "true" but it is accurate enough for most purposes); an example of the second is the geocentric view of the Universe - falsified by Copenicus and, later, Galileo.

The other possible outcome is that the experimental result is as predicted. This does not prove the theory (unfortunately) - it only adds support to it. Iif you want more about falsification and proving read Karl Popper).

There is a third possible outcome - that the experiment did not go either way. But that could simply mean that the experiment needs to be refined.

One difference between theory in science and daily life is illustrated by the Newtonian v Relative theory. For most daily life applications Newtonian physics works perfectly well but for some daily life applications, eg STANAVs, a more refined theory is required.

But more generally, most people use the term "theory" to mean belief. These beliefs are not developed to a stage where testable predictions are made.