Which is better: to achieve Nirvana, or become a Boddhissatva?

Of course, Jastrow's comment is exaggerated at best; theologians hardly predicted the Big Bang. If our universe turns out to be closed, hence with an end, this does not mean apocalyptic visions of the end of the world were on target. And even if a beginning for the universe is a successful prediction of one version of theism, this is still not that impressive. After all, even a stopped clock is right twice a day. The Big Bang becomes strong support for God only with an argument showing that such a beginning requires a Creator.

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.

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.

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.

Creation out of absolute nothing is a metaphysical quagmire for theists anyway, since nothing must at least have the potentiality for becoming something. Since theists are stuck with potentiality, it might as well be something like a quantum vacuum.

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