There's nothing special about humans or Earth -- that's the Copernican principle in a nutshell, proposed by Renaissance astronomer Nicolaus Copernicus in the 16th century. The most obvious application of the idea relates to the old geocentric cosmological model, which placed Earth at the center of the universe and which the famed astronomer boldly challenged, saying that Earth is not in any specially favored position. Today, the theory is pretty widely accepted by most scientists.
There are, however, some who point out that the Copernican principle has never truly been proven. Physicists Robert Caldwell and Albert Stebbins attempted to prove the principle by observing the cosmic microwave background (CMB). They looked for deviations in the CMB that might be caused by a void, or non-Copernican structure. Basically, they compared the experiment to looking at the universe in a mirror: If we saw our universe in the mirror, it would mean we were in a privileged spot; if not, though, the Copernican principle would hold true [source: Zyga].
The Copernican principle also comes into play in one version of astronomer Brandon Carter's anthropic principle. The anthropic principle, which includes the idea that coincidences are part of the universe's structure, may draw on the idea that there's nothing privileged about humanity or Earth, and since our universe supports life, then all universes must be able to support life. In other words, humans might presume that since we're here in this universe, this is the most probable of all universes. No evidence exists for this specific theory, though [source: Berger].
The Copernican principle also has practical applications -- some scientists use it when forming statistics, and some even believe that it can be used to determine how long the human species will last on Earth [source: Gott].
How do exoplanets get their names?
Answered by Dr. Gerard van Belle
How did Newton's discovery of gravity advance astronomy?
Answered by Discovery Channel
How do creationists explain geologic time?
Answered by Science Channel