"We don't know" doesn't imply "Anything is possible".
If you roll a pair of standard dice behind a screen, and ask me what the total is, it would be unjustified for me to claim to know. The most likely result is seven; but it could be anything from two to twelve.
So my honest answer is "I don't know".
Now, if you were to say "My holy book says that two dice rolled behind a screen always sum to fifteen", I am completely justified in saying that your holy book is wrong. And I can do so while still declaring that I don't know what the right answer is.
I don't know if, nor how, the universe began. But I know it wasn't caused by a god, for the same reason that I know two standard, six-sided dice, don't add up to fifteen, even though I don't know what they do add up to.