In honor of Takaaki Kajita and Arthur B. McDonald, winners of this year's Nobel Prize for Physics :
There is no such thing as scientific truth. Today we say E=MC2. Tomorrow we may say E=MC2 plus a little. Albert Einstein said that God does not play dice with the universe. Emerson said that the dice of God are always loaded. Maybe that is the same thing.
Science deals with three kinds of knowledge: theories, hypotheses, and observations. Theories are guesses. Hypotheses are guesses that can be tested (in other words, a guess that allows you to predict some behavior that can then be observed). Testing involves making repeatable observations under controlled conditions.
Notice that there is nothing about truth in any of those definitions. An observation is considered factual if you believe the scientist and instruments making it. A hypothesis is considered factual as long you believe the observations supporting it.
For example, the current hypothesis regarding sub-atomic structure (called the Standard Model) predicts an elementary particle called a neutrino. According to this hypothesis, neutrinos are so prevalent throughout the universe that 100 trillion of the particles pass through a human body every second. (I always wonder where they're going and why I wasn't invited.) Neutrinos are difficult to observe because they have no electric charge and very little mass.
Now scientifically, I can use this hypothesis to make a prediction: neutrinos do not pass through the body; instead, they are trapped by fat cells, accounting for weight gain in adults after age 30. My next book, The Neutrino Diet, will explain how to get rid of those pesky over-thirty neutrinos. Here's a hint: immerse yourself for a year in an 800,000 gallon tank of cleaning fluid in an abandoned gold mine...