outhouse
Atheistically
Something had to have
Again we don't know is the best answer.
Things don't just explode or expand, especially when the thing expanding is nothing.
A singularity can be defined as "we don't know".
My personal belief is a super massive black hole expanded after feeding to much, maybe tow collided. Its imaginative at best. We dont know.
Nothing should be here if the universe or evolution has no cause
Non sequitur
We know evolution is a product of this earths and the environment we are all part of "nature"
The universe again "we don't know" but what we do know for a fact, is that the universe is full of singularities so they seem to be a typical part of nature.