The big bang theory not only doesn’t fit with a lot of cosmological evidence; it also creates just as much mystery as it attempts to solve.
What came before it? Why did it happen?
To my mind, it makes a lot more sense if there was no beginning; rather if everything was going round and round in cycles, in perfect symmetry with itself. Such a symmetry must have many dimensions / degrees of freedom, some or many of which still remain unfathomable to us. That is to say, we are still yet to discover the opposite (or opposites) of some (or many) things.
It’s interesting to imagine the scale of this overall symmetry as being enormous. String theorists aim to put a number (or numbers) on it, guided by the mathematics of high-dimensionality manifolds. Perhaps it will always prove to be larger though. Whatever the scale, I find it hard to imagine that things wouldn’t go further than “CPT”. I imagine CPT symmetry being violated by particles made of anti-energy, contravening the arrow of time, but… we don’t even know of anti-energy yet.
Within this kind of symmetrical, cyclic thinking, if we ask the question “how did it all begin?” we’re actually asking a question that doesn’t make sense. Nor does the question “how does it end?”. Neither ever happened nor ever will.
We already understand that, if we “zoom out” enough spatially, the universe appears completely isotropic and homogenous.
So, if we zoom out far enough temporally, surely it follows that everything will be homogenous and isotropic in terms of time. That is to say, the past will be the same as the future. In other words, the universe is cycling, over and over — a loop of itself, with no end nor beginning.
Somehow the distribution of entropy from matter degrees of freedom to gravitational degrees of freedom must have some counterpart cancelling it out, or there must be some mechanism through which it could go into reverse or come back full circle…