The question of God’s existence is essentially philosophical or theological. God is metaphysical or beyond the physical realm in which science and empiricism operates within their parameters. It’s not subject to scientific investigation: God cannot be measured, observed, or tested for hypothesis or validated even by experience in an empirical method because He is not audible, visible, nor tangible but spirit. We can no more measure God for experimental reasons that measure foot of love or pound of justice. God will not submit to our laboratory conditions.
The question of God’s existence may be verified in an ontological scheme of thinking: where did we acquire this knowledge since apes don’t build chapels? How can we conceive of God if He doesn’t exist? God has put the knowledge of eternity and basic awareness of Him in us; that’s why every culture throughout history has had its gods and religions. God has made it plain to us (cf. Romans 1:19-21) so that we are without excuse.
Seeing God as the First Cause or unmoved mover or uncaused cause is a cosmological rationale. Nothing happens by itself but all events are caused: what caused the big bang, for instance—Christians believe the best explanation is God because He is omnipotent. The law of cause and effect has been very handy in deducing God’s existence. Everything that begins to exist, has a cause; the universe began to exist and must be caused—nothing can create or cause itself. God needs no cause because He is eternal without beginning and is the Creator, not the creature or creation.
In other words, there are many ways to prove or argue for God’s existence including the teleological one in which things have purpose and intelligence or harmony. Purpose, design, plans, and beauty don’t just happen. Design implies a Designer for example. Purpose a Purposer. Intelligence demands an Ultimate Mind. The order of creation must be “Thinker, thought, thing.” Things don’t think on their own initiative but demand a Thinker who designed them so. Soli Deo Gloria!