Paul contends in Romans 1:18-22 that, although God is invisible, his works are a visible proof of his actions and existence. Everyone realizes, in their heart, that there is a God; but many try to suppress this knowledge even from themselves.
Apologetics
Physics Says You Shouldn’t Exist
The creation is singing and dancing the praises of its Maker so clearly and so loudly, that Paul says everyone is “without excuse” when they ignore what is “clearly perceived” (Romans 1:20). The fine-tuning of this massive, marvelous, intricate universe we live in is just one of many ways that the creation is declaring the existence and glory of its Creator. Yet the effort to suppress the truth (Romans 1:18) continues in every generation, in a variety of ways.