Introduction 
"Our universe could have popped into existence 13.7 billion years ago without any divine help whatsoever, because with the laws of physics, you can get universes". The purpose of this statement is not to attack the existence of God. If we're after the ultimate origin of everything, invoking the laws of physics doesn't quite do the trick, because the question, then, is: "Why are there laws of physics?". The process leads to a never-ending chain that always leaves you short of the ultimate answer. So, I'm not going to talk to you about how quantum fluctuations could have created our universe. For now, let's just talk about how they work in our Universe.
Quantum Field Theory
According to Quantum Field Theory, every elementary particle in our universe is a ripple (a wave of smallest possible intensity) in a corresponding elementary quantum field. A "x" particle is a ripple in a "x" field. A photon is a ripple in the electric field, an up quark is a ripple in the up quark field and so on. And if there are no particles around? Even in what we consider empty space, the fields are still there, sitting quietly in empty space, much as there's still air in the room even if there's no sound. But here's the thing: those fields are never entirely quiet. It's a consequence of the famous "uncertainty principle" of Heisenberg.
What Causes Quantum Fluctuations?
Since the quantum effects are probabilistic and not deterministic, a quantum fluctuation has no "cause". So, not everything needs a cause in our Universe (this is not necessarily valid for the Big Bang, we don't know what was there before it). But anyway, quantum fluctuations occur due to uncertainty. Uncertainty in the position, is also linked to uncertainty in the momentum (the speed), while uncertainty in time, is linked to uncertainty in energy. This is the source of quantum fluctuations. In other words, quantum mechanics is purely random and randomness always entails fluctuations.
Energy of Quantum Fluctuations
Note that,
- The energy of the fluctuations of boson fields (the fields for the photon, the gluons, the W, the Z and the Higgs) is positive.
- The energy of the fluctuations of fermion fields (the fields for the electron, muon, tau, neutrinos and quarks) is negative.
When we add up the energy from all the fields, the total energy is zero. But if we do this calculation using only the Standard Model we'll see it doesn't work. There are ways too many fermions and there should be a huge negative energy in empty space. A solution comes from a theory called "supersymmetry", that seems forces nature to add exactly the right particles, so we get this cancellation automatically!
Information About Our Universe
But even though it is possible that there is a special cancellation between the boson fields of nature and the fermion fields of nature, it appears that such a cancellation could only occur by accident, and in only a very tiny fraction of quantum field theories, or of quantum theories of any type (including string theory and loop quantum gravity). Thus, only a tiny fraction of imaginable universes would even vaguely resemble our own (or at least, the part of our own that we can observe with our eyes and telescopes). In this sense, the universe we live in appears to be highly non-generic and non-typical one. But is it true, or are we only missing pieces of knowledge?
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