Love at first sight is something that a lot of people claim they've experienced; when they see someone they like, and automatically assume that they're in love because they feel attractive feelings toward that person. But what makes this happen?
Love is a complicated brain process, but the functions that occur when you see someone you like can be instantaneous at times. The brain triggers chemicals like dopamine, oxytocin, and other chemicals that it uses to help you determine whether or not something is fit for you.
Research has suggested that various parts of the brain can start pumping these chemicals as quickly as .2 seconds after laying eyes on someone. With that being said, you've probably already made your decision before the first date on whether or not you want to spend any time with that person.