According to Romans 1:18, Unbelievers "suppress the truth in their unrighteousness". In fact, evidence of God is "clearly perceived" through everything that's made (Romans 1:20) to the point they are "without excuse" and God is infinitely just and perfect in "revealing His wrath against all unrighteousness against all men" (Romans 1:18). Whether they've heard the gospel or not, they are all "without a defense".
The fact we exist is evidence of God. The fact we are intelligible. The fact we can know. The fact there are facts. That we can know and can be known. That we can communicate and understand. These are all things we take for granted, things we presuppose as a matter of course, but only the Christian worldview can satisfactorily justify their existence. Every time someone argues against God and a truly accurate and Biblical Christian worldview, they are stealing from it to do so.
So without having to understand relativity, and the deepest parts of space, and astrophysics, or even accepting a particular view of how Creation has come to be, we don't even need to "prove" God, because God has already proven Himself.
The issue isn't ultimately whether people know God exists, but whether people will "see fit to acknowledge Him as God" (Romans 1:28). God isn't on trial. God isn't in fear of judgement. He's the judge and jury. It's us who are in fear of judgement.
We live in God's world. We breathe God's air. We think with a mind God has given us. We use knowledge made only available by God. Our reasoning is only capable because of preconditions made available by God. That's why the Psalmist says, "A fool says in his heart 'There is no God.'" (Psalm 14:1)
Our natural state is rebellion and hostility towards God, (Romans 3:10-18, Romans 8:1-9). We can't understand these things unless God intervenes. Otherwise, what is wisdom seems foolishness and what is actual foolishness seems like wisdom. (1 Corinthians 1-2)
What can you do then? The only expectation God has ever placed on you the individual: Repent of your sins and believe in Jesus Christ as your God, Lord, and Savior. If you confess this with your mouth and believe it in your heart you will be saved. (Romans 10:9)
