Everything the average person has ever observed about the universe is made from a very limited number of things. Everything the average person has seen is a mix of less than 100 elements from the periodic table: all the cars, the books, the DVDs, the air conditioning, people, animals and plants, planets and moons. Basically all the energy we see is from electrons and photons (else is kinetic). All of this constitutes less than 1% of a universe that is composed of 30% dark matter and 70% dark energy. Everything you and I observe is a rounding error in the universe.
With that in mind, we are in a very limited position to say what doesn’t exist. I want to turn this fact in on the cosmological argument. It has long been the purview of theologians to assert there was nothing before the Big Bang: there was no existence. That may be true, but cosmology is currently dealing with an idea taken from quantum mechanics, namely that nothing is unstable. Nothing breaks down. Nothing can and must become 1 and -1.
The Big Bang happened. Part of the detail of that claim is that space, time, energy and matter all came into existence at this point. To claim that there was nothing before this point is to claim the knowledge that space, time, energy and matter constitute everything. Maybe. But are you really happy to defend a generic God concept on a maybe?
Knowing that I am made up of a rounding error in the universe, I don’t have to have to be able to come up with an example of something that might have existed independent of time. Everything we know is based on a less-than-1% sample of stuff that is clearly an exception (in that you can see it). How do you intend to extrapolate from that knowledge?
Some variety of physical principles or elementary physics may always have existed. Principles like String Theory are in the subset of things that can exist outside of time (not least because it would, if true, explain something about the time dimension). Maybe time is a result of the physical principle that nothing has to break down. The Cosmological Argument rest on a Nothing that simply cannot be confirmed. It is a philosophical concept that only contrived intuitions can attempt to validate. The universe has not told us such a concept is permitted. Theologians can claim that if nothing has property and can break down then it’s not really nothing, but what they might be more honest in saying is ‘it’s not the nothing I am positing’ or ‘it’s not the nothing I need for my argument to work’*. Well, I’m afraid that such a nothing is not supported by the evidence.
*(because nothing panders to what you want, nothing won’t pander to what you want.)
And it certainly isn’t a theologian’s place to tell us the limits of what can exist with one hand, and claim a God with the other.