God did not create the Universe or the Earth or the human race, and we have no reason to think that He (or She/It?) exists at all.

I should argue that God did not create the Universe, so there is no reason to think that God exists. First, I try to use logic and not science in my reasoning.

Although it is difficult to prove a negative, it is not impossible. According to the philosopher Immanuel Kant, there are two types of statements: analytic statements and synthetic statements. Analytical statements are true by definition. Or definitions themselves. Synthetic statements are only incidentally true. Only synthetic negative statements cannot be proven. Negative analytical statements can be proven.

An example of such a synthetic statement is Russell's teapot. The mathematician, Bertrand Russel, claimed that if there was a teapot floating somewhere in the solar system, we might never find it, but we wouldn't be able to prove its non-existence either.

The existence or non-existence of this teapot has no practical meaning. A universe (or solar system) in which this teapot exists would be indistinguishable from one in which this teapot does not exist.

Russell used this thought experiment to illustrate that even if we treat God's existence as a synthetic statement that cannot be disproven, then if we never end up proving it either, then the existence of God is no more likely than the non-existence of it.

In the same way, despite the fact that we cannot find a floating teapot anywhere, the existence of this teapot is not more likely because we cannot prove that it does not exist.

However, what if we treat the statement that God does not exist as an analytical statement. An example of an analytical negative statement is, for example, the statement that "there are no married bachelors". Of course, we haven't searched the entire Universe, but that doesn't mean there's a chance we'll ever find a married bachelor.

The reason I wrote this down is that if God is supposedly a disembodied mind that doesn't exist in space and time, then I don't understand what his existence would mean, and I can prove the statement that he doesn't exist as an analytical negative statement. There are no disembodied minds by definition, since a mind as such cannot exist without a brain. Consciousness and thought are both creations of the brain. What would it even mean for a conscious brain capable of thinking to exist without a physical brain?

Besides (assuming that a disembodied brain could exist, which is not true) what would it mean for this God to exist outside of space and time? If God supposedly created time and space, obviously he must exist outside of them, as those who believe in creation often say. However, if God existed outside of time and space, when and where did he exist?

Believers often say that an independent, therefore self-sufficient, necessary being must exist. Actually, I agree, since I am not convinced that it is possible for absolutely nothing as a state to exist. However, I see no reason why the Universe could not be this first necessary "being". The universe doesn't need a cause. 

Since there was never a state when the Universe did not exist, the existence of the Universe did not mean a change. For this reason, the existence of the Universe does not require a root cause, due to the lack of change. There is no point where a God could be smuggled in, because even if a multiverse exists, there has never been a state where this multiverse did not exist. Where does God fit in?

God is not necessary to explain the existence of the Universe, and even if we tried to explain the existence of the Universe using God, I do not see that we could do so successfully, since an omnipotent disembodied mind that does not exist in space and time does not fit into the story anywhere, as the first independent, self-sufficient necessary being.