That Christ will be born of a virgin was foretold by prophet Isaiah long before the birth of christ as a prophecy and as a one of the signs to identify HIM. There is nothing impossible for God whereas our science and imaginations are bound to certain limitations.
similarly, only those who have really experienced God in their lives really believe in God. and those who have personally experienced Christ in their lives do believe in HIS words that are written in the Bible. so, they do believe that Jesus is born of Virgin Mary and that he rose from his grave and that he will come again to judge the people according to their deeds.
there are people who levitate. can you scientifically prove how they are levitating by defying gravity?? can anyone scientifically demonstrate the levitation concepts??
meanwhile, what do u believe in? science or god? do u have proofs for your belief? there are thousands of theories regarding the origin of life and the existence of this universe. but, there is no theory that is completely proven scientifically nor accepted by all the other scientists. every theory has its own limitations.
and, do u believe that man has landed on the moon? there are many scientists who say that US has faked the mission. so, can you decisively prove or disprove this? itz not possible brother! only those who had really landed on the moon can believe that for real. Others can only blindly believe what the world says.