What is a theory and how does it relate to the universe?

[rudransh verma]

I was reading brief history of time by hawking and there I stuck on this line “A theory is a model of universe or a restricted part of it and a set of rules that relate quantities in the model to observations we make.” What is it saying? Please elaborate. What are rules and quantities ? Also “You can disprove a theory by finding even a single observation that disagree with the predictions of the theory.” What is this prediction ?

 

[hutchphd]

Think of Newton's theory of gravitation. Now explain it to me in Hawking's terms: restrictions ,quantities, observations.

 

[jbriggs444]

I was reading brief history of time by hawking and there I stuck on this line “A theory is a model of universe or a restricted part of it and a set of rules that relate quantities in the model to observations we make.” What is it saying? Please elaborate. What are rules and quantities ? Also “You can disprove a theory by finding even a single observation that disagree with the predictions of the theory.” What is this prediction ?

The label we put on something is not very important. Whether we call it Newton's Theory of Gravity, Newton's Law of Gravity or the Newtonian model of Gravity doesn't matter. It's still $F=\frac{Gm_1m_2}{r^2}$ and $F=ma$ regardless.

This theory of gravity predicts that in the absence of other effects all objects fall at the same rate. So one prediction of the theory is that if we set up a bell jar with a vacuum and if we arrange to drop a feather and a lead ball in the jar at the same time, they should hit the bottom at the same time. If we perform this experiment and observe that the two do not land at the same time, that would contradict the theory of gravity.

Of course, one would want to look carefully for confounding factors before accepting an experimental result which is so starkly in conflict with this particular theory. See this Wiki article (the OPERA faster-than-light neutrinos) for a real-life experiment in which confounding factors existed.

 

[fresh_42]

I was reading brief history of time by hawking and there I stuck on this line “A theory is a model of universe or a restricted part of it and a set of rules that relate quantities in the model to observations we make.” What is it saying? Please elaborate. What are rules and quantities ? Also “You can disprove a theory by finding even a single observation that disagree with the predictions of the theory.” What is this prediction ?

An observation is a measurement of a quantity.
Rules are mathematical equations with those quantities as variables, e.g. their behavior with respect to the quantity time.
All rules (equations) which contain a certain given set of observations (measurement and variables) build a theory.

If we define theory top-down, and not bottom-up what I just did, then we consider a part of the universe, collect all related quantities, measure them (or try to), and find equations among them (or try to).

In the end, we have a mathematical framework, that describes the part of the universe we started with as a model. The translation process between observations and equations is an interpretation of that model.

Theory is primarily only a word. I attempted to describe it by its normal use. A philosopher would write a book about what I just put in a few lines. I would add that Sir Charles Popper did, however, I do not really want to recommend that book.