well, actually, we needed a new system of dating, and some guy (i forget his name) wanted to use the birth of jesus as a starting point. He traced the years of kings, etc, and came up with the date that we use today. Unfortunately, he was off a little bit (6-12 years). But anyway, just because we write the date down doesn't prove the existence of god. Many view jesus as the son of god (which, just in case you were curious, he probably never even called himself that), but that might not be the case. We do know, though, that he did exist, and during his time on earth he made an impact on many people. So really, all you can say is that we are proving that jesus is just an influential character in time.