This is a very old question that has been debated for many years. Therefore I will relate my experiences in this matter.
In March 1966 my uncle was killed in an automobile accident, and at the funeral I saw a young lady who just took my breath away. My first reaction was, "Oh My God, is she beautiful". After the interment she introduced herself to me and offered her condolences, I was so flabergasted by her beauty and smile that all I could think to say was "Thanks".
I saw her again at the wake, and this time I had the presence of mind to ask her for her phone number, she replied with a coy smile, that she was my step grandmothers third cousin, and that I could get the number from her. The next afternoon I called the young lady, and her father, Joe, answered the phone asking why I wanted to talk to his baby girl. I blurted that "I love her and want to marry her." Then hurriedly added "With your permission of course." He laughed and said to come over for dinner about 6:00 P.M. and to bring my grandmother.
Six months later Jackie and I were married after a two week engagement, and it lasted until her death 34 years, 8 months and 3 days later.
Later, in 2001, I was surfing the internet and stumbled upon a match making site, and saw post by a Brazilian lady living in New Hampshire. The post was pretty interesting so I answered it and we exchanged emails, then instant messenger messages, then I started calling her on the telephone.
Two months after answering her post I flew to New Hampshire on a Friday to meet her, proposed to her in the car at the airport and gave Cristina an engagement ring, which she accepted. We flew back to Kentucky on Sunday night and were married on Monday. Now I have a wife, a mother in law, one son, two stepsons, one daughter in law, and one granddaughter.
I do not know if the marriage will last, as it has only been 8 years, 10 months, 3 days, 4 hours and 12 minutes, but I guess we will give it another 20 or 30 years and then we will decide.
If you still have not determined if I believe in Love At First Sight, the answer is a resounding YES.