Science is often seen as indecipherable, as is the process to obtain that knowledge. Scientific knowledge is based on observations made during experimentation and testing. This structure for obtaining knowledge is known as the scientific method, a logical stepwise progression through questioning, making an educated guess as to the answer to that question, testing whether that is true, and then proceeding based on the results to start over again at questioning. This process has been used for over three millennia, with references made to the basic steps of the process in ancient Egyptian medical papyri, the earliest of which is known as the Edwin Smith papyrus.
The empirical method
Falsification (also known as refutability) occurs, and is important at, the educated guess (hypothesis) and experimentation step. What is testable? Only suppositions or hypotheses that can be proven to be false, otherwise no definitive answer can be obtained and the knowledge base cannot be added to. And this provides an accurate model for understanding the progression of scientific knowledge; scientific principles advance by eliminating what is not true.
All new theories are developed by falsifying the previous theory. This is how science builds upon itself. If theories were not falsifiable, there would be a million forgotten and wrong natural laws based on assumption and misinterpretation. Falsification carries weight in the progress of all sciences from astrophysics to medicine to genetics. The scientific method using falsifiable hypotheses has pinpointed gene function, carved out the nuances of relativity, developed Koch's postulates and germ theory, opened the doors to vaccination and public health, and rebuilt the phylogenic tree based on fossil evidence.
Progress in science
To measure the progress of scientific knowledge, chart the ebb and flow of theories, observing which theories were held in esteem at which time. From the idea of atoms being molecules floating through the air to the electron density model of atomic structure; from the culling of small animals to quell plague to finally understanding the role of fleas in the absence of those animals; from superstition about disease propagation to germ theory, each advance was because the previous was found to be false and new observations were made that added to the knowledge.
As time has gone on, scientific research has kept itself in check by falsification, and science constantly reshapes what is known based on new understanding of how the world works. There have been deviations from this, for instance, eugenics and Lysenkoism, which marred the scientific process and establishment, but they were eventually overtaken by the scientific method and falsification because it advances science on a solid foundation, offering an accurate model of the progression of scientific knowledge.