It is commonly accepted theory that our universe came into being with the Big Bang, and grew rapidly with an inflation spurt. Since then it has expanded, and is now expanding with acceleration, so will never slow down to a Big Crunch. Our time began with the Big Bang.
My conjecture is that our universe is one of many. Each universe popped into existence, like ours, as a random event. Each has its own time. The collection of all these is a "space" that exists "everywhere" and "everywhen". There is to time as such for this space, hence no beginning.
Anthropic principle might explain why our particular universe has the laws it has. If its laws were not compatible with human life, we would not be here to observe them.
The multiple universes don't interact with each other. It's not clear whether they occupy the same "location" in this "space". Different "dimensions?" Or beyond our event horizon?
String theory still seems a stretch -- it seems made up to find a way to combine gravity and quantum mechanics, even if they don’t naturally combine. Why do they need to?
See Brian Greene's "Fabric of the Cosmos" for the bases for this thinking, though not the explicit model, and certainly not the opinion of string theory, which he is pursuing. Also see Stephen Hawkins "A Brief History of Time".Hawking page 129 (see excerpt below) says the total energy of the universe is zero — positive energy of the mass is cancelled by the negative energy of gravity. If true, this would allow a singularity to pop into existence without having to accumulate the huge energies of the hot big bang.
There are [1 with eighty zeroes after it] particles in the region of the universe that we can observe. Where did they all come from? The answer is that, in quantum theory, particles can be created out of energy in the form of particle/antiparticle pairs. But that just raises the question of where the energy came from. The answer is that the total energy of the universe is exactly zero. The matter in the universe is made out of positive energy.
However, the matter is all attracting itself by gravity. Two pieces of matter that are close to each other have less energy than the same two pieces a long way apart, because you have to expend energy to separate them against the gravitational force that is pulling them together. Thus, in a sense, the gravitational field has negative energy. In the case of a universe that is approximately uniform in space, one can show that this negative gravitational energy exactly cancels the positive energy represented by the matter. So the total energy of the universe is zero.