Ok, so from the point of view of modern cosmology, we can postulate a beginning without the need for a creator [in a nutshell, although our best theory of gravity cannot give a successful description of the universe when it was of atomic dimensions, quantum physics predicts that the universe could in principle have arisen out of nothing, see posts below].
It is interesting to turn the problem around, and look at it from the point of religion. The most famous arguments concerning the origin of the universe were first put by St Thomas of Aquinas
His main arguments were basically
1. Everything observable has a cause outside itself, therefore the universe must have a cause outside itself – by a process of regression this can only be God.
2. The natural world is much too complicated not to have been designed by deity.
it is often pointed out that the problem with the first argument is that it is not entirely self-consistent – it assumes God does not have a cause. Also, it is not clear that God should be omnipotent etc
The second argument seems to me to be a perfectly valid and powerful argument for a 10th century philosopher. It is not so valid for modern philosophers. For example, Darwin’s theory of evolution provides a powerful explanation of how complex organisms arise from simple origins – certainly not by chance, but by a process of natural selection (the theory is of course backed up by extensive fossil evidence). In modern cosmology, a similar argument applies – much of the apparent fine-tuning is not independent, but deeply inter-related (see below).
The complexity argument for the existence of God has become very popular recently, especially in the US – this is the famous Intelligent Design (ID) argument (see the Answers in Genesis website) . it seems to me that the argument has progressed v little beyond the Aquinas argument: except that St Thomas did not know what we know now, whether it is evidence from the fossil record of mammals, or evidence from the sub-atomic world of particle physics.
This raises a tricky point for religion. Since the time of Galileo, the Church has learnt that religion should provide an explanation for our existence that does not contradict known facts – otherwise it becomes enforced dogma, not personal faith (blind faith rather than faith). As science progresses, this task does not become easier, but more difficult…Richard Dawkins has a good discussion on this in chapter 4 of his recent book ‘The God Delusion’