How can I make such a definitive statement? It is because, unlike some deist god who doesn’t intervene in the universe and whose existence or non-existence would therefore be entirely untestable, the Christian god is pretty clearly defined.

Since you write 'God’ with a capital G, I assume you are thinking of the Christian god? If so, I am absolutely certain it does not exist.

How can I make such a definitive statement? It is because, unlike some deist god who doesn’t intervene in the universe and whose existence or non-existence would therefore be entirely untestable, the Christian god is pretty clearly defined.

It is all-powerful
It is all-loving
It is all-knowing
It is all-just
It is the source of absolute morality
It created our universe and everything in it, including everything that lives
It is omni-present
It longs to be known and for us to believe in it
It answers prayers
It occasionally performs miracles
It heals
It was incarnated by means of a virgin
It died and was resurrected 3 days later
In so doing, it absolved us of all guilt for our 'sins’, provided we believe it has
It will judge us all, and those who pass muster (i.e. who believe that their sins have been forgiven through the death and resurrection of Jesus) will spend eternity in heaven and those who don’t (i.e. who don’t believe …) will spend eternity in hell.

And probably more besides. This gives us a lot of claims that are testable, by empirical experiment and by logic. If such a god existed, it should be possible to demonstrate the fact, because there is plenty here to work with. But the fact is, such a god fails at every turn.

Prayers demonstrably do not get answered more than we would expect through sheer chance.

Faith healing demonstrably does not work more than we would expect through sheer chance and placebo effect.

Alleged miracles are always totally lacking in reliable evidence.

Even theologians have acknowledged that this god cannot be all-knowing AND all-powerful AND all-loving because otherwise there simply could not be so much suffering in the world.

Evidence shows that living forms were not created but evolved; any suggestion that God drove the process of evolution would again immediately categorically contradict the characteristics of omnipotence and omnibenevolence, since evolution proceeds through the application of cruelty (remember: evolution is a statement of reality, not of desirability).

It cannot both long to be known and be all powerful and all knowing and yet STILL remain hidden to us
It cannot be just and yet consign any living being to eternal hell (no one – LITERALLY no one) has ever been so bad as to make that a just and commensurate punishment; and a punishment that isn’t proportionate to the crime is by definition unjust).

For the same reason it cannot be all-loving.

It cannot be all-just and believe in the idea that guilt can be transferred to someone else. This is not justice, it is obscenity. As Christopher Hitchens has pointed out so eloquently, I can, if I am very generous, take your punishment on your behalf, but I can never assume your responsibility for the crime. To do so would be to undermine the very basis of morality, which assumes that we are responsible for our own actions.

Morality has been shown to be a) not absolute and b) not to be remotely dependent on any deity but to have evolved and been shaped through entirely natural processes.

And so I could go on. The Christian God is logically impossible. I cannot say with absolute confidence that there is nothing out there that we might conceivably call a god (though there is not the slightest evidence for one and therefore I don’t believe in one); but even if there were, it could not POSSIBLY be the Christian one. The Christian one is impossible, by its own definition.