Maybe I should ask how anything's particularity could arise after its beginning.
I already described that (but admittedly in very simplistic terms). Approximately 10
⁻⁴³ seconds
after its beginning, when quantum gravity effects would have begun to dominate, matter and antimatter started annihilating each other in a blaze of gamma radiation. A tiny surplus of matter was left behind, about one extra baryon for every billion matter-antimatter pairs. As the universe expanded and cooled, quarks combined into protons and neutrons, which later fused into light nuclei (nucleosynthesis), producing mostly hydrogen and helium. Matter eventually came to dominate the gravitational dynamics—when the energy density of matter surpassed that of radiation—allowing tiny primordial density fluctuations to start collapsing under gravity, matter that would come to shape the universe's large-scale structure (i.e., the kind of "particularity" that eventually became the galaxies, stars, and planets that fill the universe today), all according to the fundamental laws of physics.
As you noted, "Whatever happens is caused to happen by what came before it"—a trajectory from quarks to planets.
... except for first cause, before which nothing existed.
Well, that's the question. Can the first cause be the singularity out of which sprang the Big Bang and our universe? I don't think so, personally, because that singularity would be ontologically
contingent, not necessary, and would therefore require an explanation. That explanation would be the candidate for the first cause—namely, God, who is
necessary being.
"As is obvious," or "as is assumed by any good scientific pursuit." Can you show me otherwise? Does science actually assume that any fact springs into being on its own?
Based on countless observations, science assumes that facts spring into being according to the fundamental laws of physics, and not randomly but deterministically (at least on the macroscopic scale). That assumption is one of the essential drivers of scientific investigation. The evolutionary history of nature, for example, is a voluminous testimony to that trajectory—if individuals and populations are "facts" (and I would say they are).
Of course, this raises interesting questions, like whether the fundamental laws of physics are ontologically prior to the reality they govern. Now that is one serious can of worms.
What is the contingent fact in my statement?
The universe.
There can be only one first cause. More than one implies pre-existing principle(s).
You misunderstood. Let me try to be more clear: The idea that a first cause must be willed is fueled by "a hidden presupposition, that
any first cause is necessarily personal." Again, an assumption by definition is not a conclusion drawn either from logic or observation.
By that, are you referring to the fact that they are looking for the origin of matter itself, as produced by the BB or as what came before the BB?
Both. We have pushed back to the origin of matter itself, but to go even further back—into the Planck epoch—requires a new model of physics, something like a quantum theory of gravity (e.g., loop quantum gravity). We're not there yet, and that doesn't mean we never will be.
(So, the word "the" was a typo—it should have said "the very origin of matter itself." You had already started your response when I edited that typo.)
All I ever hear—which, granted, isn't much—has to do with figuring out what the BB is, [which is] not quite the same thing as to assume that something caused it.
However, before we can figure out what caused a thing, we first need to somewhat understand what the thing is. So, that is an appropriate line of inquiry.
Well, I'm sorry, but I don't think anyone will find that unified theory if they assume causation by mere chance. They will only find conjecture.
Chance is not a necessary or even requisite component. For example, a loop quantum gravity theory has a more natural fit with deterministic or realist interpretations of quantum theory—which see the universe as fundamentally determined rather than random—such as de Broglie–Bohm (pilot wave theory), or even the relational quantum mechanics of Carlo Rovelli himself, one of the founders of LQG.