If you didn't have a holy book, how could you present evidence that any god exists?

Logic proves that God exists. Relativity and cause adn effect. Every thing has a cause Example you were caused at your conception by your mother, if you keep going back you will find as far back as has been recorded. That being stated every thing has a cause but where did the first cause come from-there is your answer in the uncased cause there is no other possible explanation for existence. I can state this 'FACT' because if anyone could of debunked God's exist I guarantee it would of been already done!