Maybe all of the mysteries of particle theory can be solved by invoking the same mantra: if the universe were any other way, we could not live in it. - Lawrence M. Krauss

The Universe must be flat. Why? Well, there is two reasons. There's the one I normally say, which is: it's the only mathematically beautiful universe. Which is true, but there's another reason I don't usually... talk about but I'll talk about here. It turns out that in a flat universe the total energy of the universe is precisely zero because gravity can have negative energy. So the negative energy of gravity balances out the positive energy of matter. What's so beautiful about a universe with total energy zero? Well, only such a universe can begin from nothing, and that is remarkable because the laws of physics allow a universe to begin from nothing. You don't need a Deity. You have nothing: zero total energy, and quantum fluctuations can produce a universe. So, if the Universe isn't flat we're worried, because then you've got energy at... the very beginning of Time.

But what we've discovered is that, in fact... the total energy of the universe could be zero, which is a first clue that maybe it could come from nothing. ...In physics, ...once you include gravity, there's positive energy and negative energy, and our universe appears as if its total energy could be precisely zero, which is the first hint that maybe it could come from nothing. That, and the great discovery... that namely empty space, you take a region of space, get rid of all the particles and all the radiation ...so there's nothing there. That empty space weighs something, and we don't understand why.

At the heart of quantum mechanics is a rule that sometimes governs politicians or CEOs - as long as no one is watching, anything goes.