Why do cats have whiskers?

Question: Why do cats have whiskers?

Observation: All cats have whiskers.

Hypothesis #1
May be whiskers are cats' form of mustache - since we are to assume that every creature evolved from one parent life organism then such similarity may have stayed during the course evolution. This implies that whiskers have no particular use for cats.

Hypothesis #2
May be whiskers are like ant antennae. They assist in cats' olfactory sensing.

Fact
Whiskers are properly known as Vibrissae.
They don't only appear in the "mustache-area" or in the snout or muzzle of car (and most mammals) but also above the eyes (like eyebrows, but not really since cats don't have eyebrows).
Cat whiskers are especially sensitive. They use it to navigate through space - especially useful in judging if it will fit itself through a narrow opening. A cat's whiskers are usually as wide as its body, making space measurements more effective.