This is a phrase that has appeared since Greek times, by thinkers like Parmenides; however, its most famous use has been by Shakespeare in King Lear. In Shakespeare's case, we are dealing less with cosmological facts than a useful human part of wisdom; if you don't put effort into obtaining something, you cannot expect it to actually happen.
Yet in the previous instance, ex nihilo nihil fit, it is implied that things cannot be created from nothing and that, as a matter of fact, they cannot simply disappear. Some of it is actually proven by modern science. Energy cannot be destroyed or cannot simply disappear into thin air; it is rather transformed. Although it is a far cry from claiming immortality or proving the existence of an immortal soul, it is still a means of solace that something will indeed persevere (it remains to be seen what that something is, while the scientific notion of energy seems rather vague and general).
What about going back to the beginning of things? How was the universe created? Or has it always existed from time immemorial? In fact, to my knowledge, the question of whether the universe is finite or infinite still remains open.
If it is finite, then we are dealing with a “closed” system. And since the universe is constantly expanding then, according to the second law of thermodynamics, it is getting more and more compressed. At some point in the far future - we're talking many many years from now - the universe would eventually collapse into itself and become a great ball of fire.
If the universe is infinite, then it would be an “open” system. That would still mean that the universe would reach its end, but in a different manner. Now as it expands in open unlimited space, the universe would cool down and in a far future we will be turned into ice crystals.
So far the picture is bleak, and I am sorry to start with such observations on the dawn of a new, perhaps promising year. It would appear we come from nothing and disappear into nothing.
But there seems to be more. As the universe is and has always been expanding, that means that it can be reduced to a single point when it all started, a beginning of some sort. That is when scientists become hazy. They claim it all goes back to the “Big Bang,” which apparently was a silent explosion.
I am not denying the validity of this belief, nor would I would be in the position to criticize it anyhow. But I would like to return to where I started, to the beginning of my post, namely that nothing comes from nothing. Sure, it can have been a total fluke, and we have collectively drawn nature's winning lottery ticket, and, as a result, we have come into existence.
But what if there was a starting point and actually something or somebody may have created something out of nothing? Would that prove Parmenides right? Can there be a so-called Creator or a creating substance after all?
That would mean, in true "King Lear" fashion, we need to put on our thinking caps and through effort find satisfying answers to these eternal riddles and tell dear Cordelia in the meantime: Nothing will come of nothing: speak again.