Nothing is impossible.
That statement can be interpreted two different ways.
The first interpretation is that it means that anything is possible, nothing is quite out of reach.
The second is that it is impossible to achieve "nothing." No matter how hard you, or even the universe tries, something will exist.
I think that the second interpretation is most correct, even though it is the less obvious one. We can observe things, and we are conscious, therefore we know that something exists. It doesn't matter if the universe is a simulation or a giant power generator or just a random blob of wibbly-wobbly timey-wimey stuff, we know that something exists. Therefore, nothing doesn't exist. So nothing is impossible. If nothing is impossible now, then nothing has always been impossible because nothing stretches out across everything. So if there was something a trillion years ago but there is nothing now, then there is still something that has existed. With that philosophy, there has always been something in the multiverse, but there has never been nothing, nor will there ever be.
Therefore, the universe had to come into existence because otherwise there would be nothing. That's a little paradoxical and redundant but that's just the way it seems to be when we come to these kinds of questions. At the beginning of time there was a singularity, that's a zero-dimensional point with all the energy of the universe contained in it. Therefore, the concentration of energy was {total energy of the universe}/0. We all know that there are no rules when we divide by zero. So maybe that's how anything can happen, because there are infinite possibilities when we divide by zero, and when the singularity picks one, like the roll of an infinity-sided die, a new universe is born.
All that thought is making my head spin, I think I'll go do something else now.