Of all the arguments for the existence of God, the cosmological argument is one of them. How else to describe it, really?
The bare essence is this: everything is caused, therefore there must be a first cause.
The obvious objection: what caused the first cause?
they reply, the first cause is causeless. The Kalām variant
is a way of rephrasing the original premises such that this retort is already couched within them--a rhetorical tiger waiting to pounce.
But hang on: we assert that all things belong to the set of things which do have causes. Then we reverse and assert the existence of a set of things which do not have causes. And we further assert that spacetime and mass-energy must belong in set 1 and not set 2, and that Vishnu or whoever definitely goes in set 2 and not set 1. On what basis?
Now it's normal to think of things and events having causes. You are reading this blog because you clicked a link. I wrote it because I find the argument annoying. You were born because countless millions of years of evolution programmed your parents to love babies and enjoy making them, and so on. But the ordinary, everyday events and objects with which we interact are merely arrangements of much smaller parts: molecules, which in turn are made of atoms, which in turn are made of parts smaller still, which are interchangeable with energy, and so on. So yes, stuff rearranges itself in patterns which derive from previous patterns, but stuff and space remain.
In fact, in the only examples we have wherein stuff and space come into being, they do so from nothing. Space is expanding: the space between the galaxies is growing. Stuff pops into being all the time in the form of virtual particle/antiparticle pairs: provided the positive and negative energy of the particle pairs cancel each other out, there is no violation of the laws of physics.
So if the universe had zero net energy--if the positive mass and energy were canceled by gravity or other forces, let's say--then there's no particular reason to suppose that it cannot causelessly pop into being like any other net-zero fluctuation.
Aha! the apologist might interject, in both cases the space and the stuff arose within already-extant spacetime! They wouldn't arise from absolute Nothing! But this is a testable hypothesis: let them find some absolute Nothing, and through a series of rigorous tests determine what, if anything, arises from it, and I shall of course revise my position accordingly.
Nothing--"real" nothing, absolute nothing--is inconceivable. When I try to picture it, I picture a dark empty space, which, as Einstein showed, is something. It is meaningless to speak of its properties, just as it is meaningless to speak of causality "before" time--or, for that matter, to view quantum mechanics in terms of causality as opposed to probability. The more modest "nothing" of the physicists, however, can get us everything we need to start up a universe quite nicely. The disembodied First Cause is essentially moot.