Arguably the biggest question is cosmology is where the Big Bang came from. We can extrapolate back from our observations of the universe and draw some high confidence conclusions. Since the universe is expanding, if we rewind time then the universe would contract as we go back in time until – it must have been a single point, an original singularity. The moment this point expanded rapidly into the universe was the Big Bang, but where did all the matter and energy that make up the universe come from to begin with? To make matters more confusing, the Big Bang also created space-time, so any reference to things happening at or before the Big Bang is tricky.

We can actually do experiments to test our ideas about the very early universe (less than a second after the Big Bang) by reproducing these high energies in particle accelerators. But at some point the energies exceed anything we can produce, and we are in the realm of purely theoretical physics. The question of where the singularity that became the Big Bang came from fits into this category.

There is no shortage of hypotheses about where the universe came from. One question is whether or not the universe could have come from literally nothing. This is a deep question that would take a book-length discussion to explore fully. My very basic understanding is that there are essentially two camps. The first states that something cannot come from nothing, and therefore there always had to be something, even if it was only a quantum fluctuation similar to what exists in “empty” space within our universe. Even the emptiest of space still contains a quantum “foam” of energy with particles briefly coming into existence and then annihilating each other. Maybe the entire universe is a giant quantum fluctuation in some grander quantum foam.

The other approach is to argue that the universe can come from nothing, but we perhaps need to reconsider what “nothing” means. Perhaps the laws of reality (the metaverse, whatever) simply do not allow for a state that we would understand as completely nothing. We think of nothing as simply the absence of stuff, of matter and energy, but perhaps it’s more complicated than that. It may simply be impossible for there to be truly nothing in that simplistic sense. This, of course, deals with the ultimate nature of reality, where physics borders metaphysics.

Added to all this is the notion of time. It is very difficult for us to get out of our linear concept of time, or to imagine a situation in which time does not exist. What would that even mean? Further, some physicists postulate that the Big Bang was not a singular event but part of some infinite cycle. The initial idea was that the universe might ultimately slow its expansion, then contract and come together again in a Big Crunch, then explode again in another Big Bang, on and on for infinity. But we now have evidence that the universe is accelerating its expansion – no Big Crunch.

Instead the universe will continue to expand until all the stars burn out and all the black holes evaporate away. This is called the heat death of the universe – it will become a very large, cold, and empty universe, without any usable energy. The end.  Or is it? Roger Penrose speculates that perhaps a heat death universe could also recycle into a Big Bang (what he calls conformal cyclic cosmology). This sounds very counter-intuitive, because it is. His idea started with a mathematical similarity (math is always a good place to start – see Relativity). There are some similarities between the math used to describe the Big Bang and the math used to describe the heat death of the universe. This may be nothing, just a coincidence or a mathematical curiosity, but Penrose speculated – what if it isn’t?

What if the maximally expanded and cold universe mathematically approaches the identical state as the singularity that resulted in the Big Bang? Again, our human minds limited by the frame of the Earth cannot wrap around this concept, but we can crunch the numbers. At some point the heat death universe becomes a singularity, and then starts another cycle of the universe. If you want to really blow your mind, some physicists even speculate that this would be the same universe. Not another version of the same matter and energy, but the actual same universe in space and time. Essentially the end of the universe and the beginning of the universe are the same moment in time, the universe loops back in on itself in one giant self-contained temporal cycle.

The universe would then be temporally finite but unbound (Stephen Hawking discussed this in his book, A Brief History of Time). The best analogy is a ring, we just keeping going around the ring forever, but there is no true beginning or end. In this concept there is no beginning or end, there is no before, there is just a bound infinite loop. This solves the “something from nothing” problem, because the universe did not come from anything, it just always was. This still leaves us with the deeper question – why is there something instead of nothing, but that may not be a useful line of inquiry.

At this level of theoretical physics I don’t think there are any perfect analogies, only sideways glimpses of shadows. But there is math, which is the only way to truly understand things. We may also be reaching the limits of experimental physics, and if we can’t test our ideas they will remain forever speculative. These may be questions that will take thousands or millions of years to unravel, rather than the few centuries we have been working at it.