I previously blogged my answer to Martin Heidegger's deep question, "Why is there something rather than nothing?"
I just wrote it up for a friend. It says basically the same thing the earlier post does, but in a more accessible form.
What's not a good answer
First, I like to say what is not a good answer. For instance, it's not a good answer to talk about quantum fluctuations creating matter out of empty space. That may or may not follow from the rules of quantum mechanics, but those rules are a "something" too. Why do they exist? So to my mind, that doesn't really answer the question.
The full flavor of the question
Heidegger's question is deeper than that. What it asks to explain is not why is there matter, or why there is quantum mechanics, but why is there anything at all. Why does the world have any structure whatsoever?
My insight was that the question still assumes one little thing: that it's one or the other, either/or, obeying the law of the excluded middle. Which I know sounds like simple common sense, but consider this: any evidence it could possibly be based on is a something too, and so is the law of the excluded middle. Even antinomy, the law of non-contradiction, is a something about which we can ask why it exists.
So take a deep intellectual breath and imagine for a moment that it could be both ways. Imagine that you can see both a world of nothingness and a normal world. Doesn't matter how. If you like, you can imagine some sort of blend of a something-world and a nothing-world, or a split-screen of both worlds, or perhaps you gaze alternately on one world and the other, or teleport between them.
What would the nothingness look like? Seems like nothingness wouldn't make much of an impression. It wouldn't even mark its absence by the passage of time or an empty reach of space. It hasn't got time and space or anything else. It hasn't got its half of the split-screen you may have imagined. It hasn't even got a you in it to do the perceiving. Seems to me nothingness makes absolutely zero impression of any kind.
Now add up the impressions of both worlds. You get all the impressions from the normal world of somethings, plus zero. So you see just the normal world.
So that's my anthrophic, multiple-worlds answer to Heidegger's question. Even if you start with no assumption of something-ness, you end up seeing a world of somethings, a world with some propositions about it that aren't both true and false or neither. QED.
T's to cross and i's to dot
There are some philosophical t's to cross and i's to dot, but AFAICT they cross and dot easily. (Like, are there otherwise ways to aggregate the impressions of two worlds that give a different result? No, by definition aggregating X with nothing gives X.)