Any fluctuation would require existing time to take place. And that according me needs to be understood first.
One possible way (and personally my favorite way) to think about the birth of the universe is:
- Empty Space (please note, not spacetime) may have always existed. The stage analogy of Newtonian Space
- Energy may have always existed encoded in quantum fields. These quantum fields may perhaps be in such an equilibrium that nothing effectively happens or changes
And because of this state, whether time exists or not does not mean anything because effective change is zero and hence effective time is also zero.
- Nothing evolves
- No difference between “before” & “after”, and
- Time has no operational meaning
Now Quantum Fields are the playground of possibilities, where lot is happening but as established already above nothing is changing, because of being in equilibrium.
In some random case of tunneling effect or symmetry breaking this equilibrium may break.
Breaking of this equilibrium causes the change to begin. This transition itself may be what gives rise to effective time and hence Spacetime (the ‘actor - not a stage’ analogy of Einstein’s spacetime).
Hence forth the story of Big Bang continues..