According to the Heisenberg uncertainty principle, the energy and duration of a quantum fluctuation are related by the inequation
∆E ∆t ≥ ħ /2
where ħ is Planck's constant divided by 2π. It follows that an energetically neutral quantum fluctuation must persist forever, even though all the quantum fluctuations we have ever observed persist for only a very short time. Therefore the universe can be created from quantum fluctuations, provided that it is energetically neutral