When you think about it that may not be that suprising as we really can only research our own area, who knows what happens in other galaxies many light years away.Regarding Newtonian physics, and Einsteins theories and quantum physics, there is a minority but growing band of scientists that are of the mind that these laws and theorems may only hold true for our galaxy,.
That is what I mean, the energy is always there just in different forms so we need to find a system that upon first using the energy can then change this energy form back into it's original form for re-use but something we don't yet understand is preventing this.That change of state may be to a form we as humans can not utilise
"Time? Is that not just a human invented measurement construct. " I think the units of time are a human unit but based upon natural phenomenon, ie movement of the moon and planets, the decay of a radioactive isotope or the resonant frequency of a crystaline substance.