According to Wikipedia, Love at first sight is an emotional condition whereby a person feels romantic attraction for a stranger on the first encounter with the stranger. The term may be used to refer to a mere sexual attraction or crush, but it usually refers to actually falling in love with someone literally the very first time one sees him or her, along with the deep desire to have an intimate relationship with that person. The stranger may or may not be aware that the other person has any such notion, and may not even be aware of the other person's presence (such as in a crowded place). Sometimes two people experience this phenomenon towards each other at the same time, usually when their eyes meet.
I've read somewhere that Scientists study our brain activity and say that it’s quiet possible but there are many who really don't believe that it exist, and some people claim that it happened to them.
Psychologists say that love at first sight depends on our psychological state at the moment. In some case we won’t even notice those charming eyes in another they can make a lasting impression. Also they say that it takes about 30 seconds to fall in love or precisely speaking to estimate whether the person is worth to fall in love with. By the way psychologists claim that men fall in love first.
In my own opinion, I don't believe in Love At First Sight but I do believe in attraction at first sight which eventually lead to falling in love to that same person when time pass by..