• A tentative explanation or idea about how things work
• A hypothesis guides you in further work to get a better answer

Example of a hypothesis: "The moon is made of cheese" (note: this is the kind of hypothesis my wife would come up with). How could we test this hypothesis?

• Construct a rocket to go to the moon and return with samples
• Make a cheese pizza substituting the moon samples for the cheese
• Ask people (e.g. graduate students. No, wait, they aren't real people…) to eat the pizza and see if they can tell any difference from pizza made with real cheese^TM (from Wisconsin)
• Most likely conclusion: Hey, this pizza tastes like dirt

New hypothesis (altered to include additional information from above experiment): The moon is not made of cheese, but is made of dirt, sort of like the Earth

• A theory is an explanation of the general principles of certain phenomena with considerable facts to support it
• A theory remains valid only if every new piece of information supports it
• If a single piece of available information does not support a theory, then the theory (as proposed) is disproved

• An indisputable truth

Example:

• It is a fact that on June 30, 1908 in Tunguska, Siberia, an explosion equivalent to about 15 million tons of TNT occurred.
• It is a theory that this explosion was due to a natural, extra-terrestrial phenomenon and not to an activity associated with man.
• One hypothesis is that a comet collided with the Earth (a competing hypothesis is that a small black hole collided with the Earth)