Before the the beginning of time...
May be a fraction of second prior to the beginning of time or a trillion years prior to the first tick of the universal clock..
Doesn't matter since there was no time[at that time].It will not be right to say that it certainly happened in the past.The direction of the arrow of time we are using for our psychological flow of time was not there.For the purpose of narration we may call it past.
There was no observable or effective universe. It had zero volume means no space or empty field.Its mass was infinite.It had no form for the lack of volume.
And big bang happened.
HOW AND WHY? Even God will not know but, of course, out of his own will and decision to stay away. Anything happening prior to that most spectacular and magnificient event of this universe,can't be the part of our story as it was undoubtedly a break point even if we disagree to accept it as a starting point.Therefore the reason and process of big bang falls out of the territory of our universe,the effective and observable one.There was no light, not even darkness.
THERE WAS ABSOLUTELY NOTHING EXCEPT THAT UNOBSERVABLE MASS OF ZERO OR NEAR ZERO VOLUME, IF THERE CAN BE SOMETHING BETWEEN OBSERVABLE AND UNOBSERVABLE.
The infinite mass released or to be precise got converted into infinite energy. THe birth of this universe 00.00.00 the univesal clock time.This was the birth of time and the birth of space.Not as twins but as one entity having more than one attributes.Like Ram, his life and his age...
The expansion began with the speed of time or we can say the time or the speed of time is nothing but the speed of expansion of our universe and that is in turn the space.
It took thousands of years of active research for human mind to conclude that time and space are inseperable. They are in fact two ATTRIBUTES OF ONE AND THE SAME entitity now known as space-time ,in scientific parlance.The software of human brain,particularly in its scientific pursuits ,is essentially analytical.It can't ,therefore,understand something that is absolute and never changing. But it has an amazing sense to understand what it understands not.Hence, the view stated above.
SPACE-TIME is not something really existing independently .Not an entity in itself but an attribute of mass- energy,the real stuff this universe is made of.The inter convertibility of mass and enegy, proves them to be again one and the same thing it when comes to the core. That confirms the fact that the manifested or the effective universe including the mankind, the most complex part of it ,is a varying configuration of waves of energy.The particle as the smallest unit of mass is also the manifestaion of wave and so the whole universe.Energy can therfore be taken as the ultimate contituent of the universe.Or we can find name for it tentatively the mest-- mass, energy, space and time being its four attributes or dimensions.This simply arrived conclusion may take volumes of pages and years of nerve breaking time to be proven right.It is evidently messing up with so many established laws of physics.It has already kept the author intrigued and the same time fascinated for a good part of his life.
Theoritical physics today seems standing very close to the threshold to witness the grand finale with the opening key in the hand-- the much debated grand unified theorey. The lock may open never !