When confronted with a demand that the universe have a cause, infidels have usually pointed out that God was not much of an explanation. This is true enough, but not really a positive argument. After mechanistic explanation became popular, infidels liked to restrict causality to the chain of causes in an eternal material universe, pointing out that no supernatural cause was then necessary. Plausible, but still rather defensive. Today's skeptic can do better. In all likelihood, the universe is uncaused. It is random. It just is.

Asking about a time before the beginning of our spherical spacetime is like asking what lies north of the North Pole. There is no such thing.

To talk intelligibly about modern physics, we have to admit the possibility of uncaused events.

Quantum mechanics is so counter-intuitive, physicists have never been able to come up with a comfortable picture of how it works.

Quantum events have a way of just happening, without any cause, as when a radioactive atom decays at a random time. Even the quantum vacuum is not an inert void, but is boiling with quantum fluctuations. In our macroscopic world, we are used to energy conservation, but in the quantum realm this holds only on average. Energy fluctuations out of nothing create short-lived particle-antiparticle pairs, which is why the vacuum is not emptiness but a sea of transient particles. An uncaused beginning, even out of nothing, for spacetime is no great leap of the imagination.

In the popular imagination, the Big Bang is a great explosion; at one time there was nothing, then matter erupted into previously empty space. However, the Big Bang is the beginning of spacetime itself, not an event in time.

Physicists use 'God' as a metaphor more often than other scientists-- especially in popular writing, but in the technical literature as well. Of course, this is just a metaphor for order at the heart of confusion. A rational or aesthetic pattern underlying reality is far from a theistic God.