The Scientific Revolution

Before the 15th Century scientists developed their theories based upon the ideas of the Greeks and Romans or upon Christian doctrine.
The ancient Greeks and Christianity taught that Earth was the center of the Universe and that the sun revolved around the earth. The development of the Scientific method changed this methodology.
After 1500, instead of accepting what was taught scientists began to test methods for their validity and the origin of the current doctrine was born which is thus; assume to know nothing and merely state that something is what it appears to be based upon the data that is given. As time moves on theories are tested in different circumstances and conditions; improved upon and tested to see if they remain true. This was quite possibly the greatest revolution in all of modern science. " Science is best defined as a careful, disciplined, logical search for knowledge about any and all aspects of the universe, obtained by examination of the best available evidence and always subject to correction and improvement upon discovery of better evidence. What's left is magic. And it doesn't work. " -- James Randi
Now science is built upon theories that can instantaneously be proven or disproven throughout the ages as time wears on rather than being accepted as pure fact, but based upon data available at any given time.
a theory is a conceptual framework that explains existing observations and predicts new ones
A hypothesis is a theory that hasn't been proven, but guessed.
An example of changing what is accepted as true can be seen in the legend of Italian Galileo who disproved Aristotles theory that heavier objects would drop at greater speed. It is said that he dropped stones of different weights to the ground from atop the Leaning Tower of Pisa. He proved that objects of different weights fell at the same speed.
In Science it is now accepted that when an old theory cannot explain new observations than a new one must be conceived. There is often a blurry line between fact and speculation as time wears on and Man catapults himself with higher knowledge.
The line must be drawn when one accepts this statement; "When a theory is said to be ``true'' it means that it agrees with all known experimental evidence"
The same truths have always been since the begginning of time, but we gather more of them as time continues in its never ending trek.
Ocham's Razor
Ockham's Razor simply means to keep it simple when two or more theories conflict with each other based upon different assumptions. They may both be valid in some respects, but to test which one is to be used by the the one that yields the most accurate data.