What is science? It is the study of nature. Science is the study of the difference components of nature, like forces, chemicals, the structure of matter, the way that objects interact with one another, how those objects are made, and how and why they behave the way that they do.
Science is Theory
One of the criticisms of evolution is that it is just a theory.That is right, evolution is a theory. But all science, that is ALL science is theory. But there are supporting facts that make it relevant and real. Without the supporting facts, it would be a hypotheses. Which is what the critics of evolution really are trying to say, and they confuse theory with hypothesis.
Science is About Facts, A Hypothesis is About Observation
A hypothesis is not about making predictions, it is about trying to explain certain actions, certain observations. Take for example, the Michelson Morley experiment.in the late 1800's. At that time physicists were very comfortable with Newtonian physics. They could explain about 90% of all occurrences in nature. But one event was a mystery. How did light travel across space? That is, was there an underlying structure that light traveled through, much like water wavers traveled over water.
Their experiment tried to measure the speed of light and see if there was some impact on the speed by comparing the speed across different directions. They measured it by comparing the speed as it traveled north to south, east to west, north-east to south-west, up and down, and so on. If it changed it was because the light traveled on an ether. That was their hypothesis. To their surprise, the speed was constant, it never changed.
This was not a fact, it was an observation, because no one knew what it meant. How could light always travel at the same speed?
It was not until Einstein, in 1905, published his special theory of relativity, that explained how the constancy of light speed affected the force of time, that the observation about the constancyof the speed of light became a fact.
Later on, in 1917, Einstein published the general theory of relativity. One of the remarkable incidents, that is observations, was used to verify that the theory was correct. It had been know for some time that Newton's theory of gravity could not explain stars with light rays that passed near the Sun would appear to have been slightly shifted. This was a well known observation, but they could not rely of Newtonian physics for an explanation. But the General Theory of Relativity did offer an explanation. But could the observations be verified and explained by the theory?
The astro-physicist, Arthur Eddington, travelled to the Principe island near Africa to watch the solar eclipse of My 29, 1919. During the eclipse, Eddington took pictures of the stars in the region around the Sun. According to the theory of general theory, stars with light rays that passed near the Sun would appear to have been slightly shifted because their light had been curved by its gravitational field. This effect is noticeable only during eclipses, because the Sun's brightness otherwise obscures the affected stars. Eddington showed that Newtonian gravitation could be interpreted to predict half the shift predicted by Einstein. So the observation became a fact, and it supported the theory of general relativity.
Science is About Making Predictions
A hypothesis is an observation or idea but one that has no supporting facts to make it a theory. Furthermore, a hypothesis cannot be used to make predictions. A theory not only explains how certain sciences act and behave, they have a predictive element. For example, a baseball pitcher throws a baseball at a batter in a baseball game. The batter hits the ball. Sometimes it is caught, sometimes it is not. But scientists can predict certain elements about the speed of the ball before and after it is hit, where it will go, and how far the ball will travel. These predictions come from understanding the basic function of force, which is matter times acceleration.
That is not to say that a scientist will predict when the batter will strike out, when he will hit a fly ball or a ground ball or a fowl ball or a home run. These elements have variables. The speed of the ball, the direction of the pitchers ball, whether it is a curve or straight ball, the reaction of the batter, the location of the baseball bat. If all of the variables are known and the aspects of the variable are also known, then predictions can occur. But with enough details, and instruments to measure the force and direction of the ball it may eventually become possible to make such predictions. But that is the point. If there are variables that scientists cannot take into account they cannot make a prediction. Science can make predictions about the behavior of objects when the variables are known. To make a prediction there have to be facts and how those facts play out in the theory.
Science is About Verifiability
Once a theory is put into public attention, that is scientific attention, where other scientists view the theory and try to confirm it or to falsify it.
But verifying it means that the same theory is confirmed by more than one scientist, this makes it a more reliable theory because it can be replicated. If a new experiment confirms the theory, then there is another supporting fact. This explains the reason why scientists feel sure about the theory and its results. They can also add predictive features. it explains the conditions under which the theory is applied.
Science is About Falsifiability
In any science, the details which show the structure of the operation of science, there is the possibility that the explanation is wrong. Science is not about perfection, it is about explanation, and there may be events for which there is insufficient explanation about what happened. The two examples, the Michaelson-Moreley experiment, and the Eddington photographs showed that the existing theory of physics was false. The Newtonian theory of physics could not explain the speed of light behavior, nor the shifting geometry where light was concerned. So yes the Newtonian theory of physics was false...or was it?
What these experiments showed was that there are different areas that cannot be explained by the current theory, which leaves open to have another theory be created to explain. those events.
Since the bulk, say 95% of Newtonian physics, was still workable it is hard to dismiss it. What has to happen is that a new theory has to come into play to account for the areas that can't be explained by the current theory. That falsifiability leads to the sense of improvement of the theory by adjusting and showing its limitations. This falsifiability element is the reason that science grows. The observations need to become facts. To become facts, you need a theory. The theory explains the facts, and can make predictions. That is science.