It has been said that scientists have proof without certainty and philosophers have certainty without proof. While that is a clever way to think of the two areas of knowledge it is also pretty close to how science differs from other areas of truth-seeking.
Scientists cannot explore the entire universe or travel through time looking for swans or anything else. Instead, science must be satisfied with statements like, "So far, all swans known to 18th century scientists are white".
New data can change the world and our view of it.

We find it convenient to say things are "true" when in fact they are only ideas that have not (yet) been proven false. Scientists fall into the habit of saying things are "true" when what we mean to say is, "The current data support the idea that this is true, but we might be wrong."

Until recently many biologists would have thought these ideas were "true".

1. "The Sun is the source of energy for all life on Earth".
   We now know that some ecosystems (in the deep oceans and underground) do quite well without the Sun.
2. "Mitochondria are inherited from the mother's line."
   While true most of the time it is not true of all species, all of the time.
3. "Mammals cannot be cloned".
   Well, "Hello Dolly!"

You should not go away with the impression that science is some kind of wishy-washy search for truth which it cannot achieve. Instead you should understand that science has its limits. Good scientists know the limits of scientific truth. They know that a statement (hypothesis) that cannot be disproven is not scientific and therefore not within the domain of the scientific method. They also know that new data, often using new instruments and methods, might disprove a popular hypothesis.

The power of the scientific method lies in "disproof" - falsifiability.
Rutherford used the data collected from X-rays passing through materials to disprove Bohr's hypothesis that atoms are single spheres of matter.
Kepler used careful observations of the planets' motion to disprove that they move in a circle around the sun. They move in an ellipse, not a circle
Galelio used a variety of experiments to disprove that heavy objects fall faster than lighter ones.
There are many other famous "disproofs" in science including some in the biological sciences and you will learn some of them in this module.

When presented with an idea, a hypothesis, ask yourself, "Can this be disproven? Is it faslifiable?"
You will find that experiments and observations do not prove anything to be the truth. The best they can do is support an idea.

When a hypothesis has stood the test of falsifiablity, often many times and in many ways, it takes on the status of a theory. Theories grow from successful hypotheses and usually encompass a grand unifying idea that cements together many observations, experiments and thoughts into a succinct description or process.

To learn how all this relates to evolution click here to continue.