In discussing the Kalam Cosmological argument an objection is often raised against the conclusion that the universe has a cause. This is that there cannot be a cause of the universe because there were no prior instants of time before t = 0 in the initial Big Bang singularity. Similarly, for the universe to have a beginning requires there be a time before the universe existed, and since the universe includes time there is no “before” the universe, making the notion apparently incoherent.
One of the worlds leading philosophers of time and proponent of the Kalam Cosmological Argument, Dr. William Lane Craig, definitively answers this objection bellow.
For he [Grünbaum] fails to consider the obvious alternative that the cause of the Big Bang operated at t = 0, that is, simultaneously (or coincidentally) with the Big Bang. Philosophical discussions of causal directionality routinely treat simultaneous causation, the question being how to distinguish A as the cause and B as the effect when these occur together at the same time [Dummett and Flew (1954); Mackie (1966); Suchting (1968-69); Brier (1974), pp. 91-98; Brand (1979)]. Even on a mundane level, we regularly experience simultaneous causation; to borrow an example from Kant, a heavy ball’s resting on a cushion being the cause of a depression in that cushion. Indeed, some philosophers argue that all efficient causation is simultaneous, for if the causal conditions sufficient for some event E were present prior to the time t of E‘s occurrence, then E would happen prior to t; similarly if the causal conditions for E were to vanish at t after having existed at tn < t, then E would not occur at t. In any case, there seems to be no conceptual difficulty in saying that the cause of the origin of the universe acted simultaneously (or coincidentally) with the origination of the universe. We should therefore say that the cause of the origin of the universe is causally prior to the Big Bang, though not temporally prior to the Big Bang. In such a case, the cause may be said to exist spacelessly and timelessly sans the universe, but temporally subsequent to the moment of creation.
My favorite example of simultaneous causation is that of a submerged log which causes the water to be displaced. Another example is of a man who from eternity has been standing, and by sitting (the cause A) creates a lap (the effect B). In these there is no question of the causal directionality, even though the cause and effect are operative at the exact same instant.
So the so-called problem of it being impossible for the universe to have a cause is not at all insuperable. As Craig says, it is “pretty clearly a pseudo-dilemma.”
 1.) Everything that begins to exist has a cause,
2.) The universe began to exist
3.) Therefore, the universe has a cause.
 William Lane Craig, “Creation and Big Bang Cosmology.” Philosophia Naturalis 31 (1994): 217-224.
 – coincidentally in case “simultaneity” is strictly defined in terms of occurrence at the same time. Since the singularity is not an instant or moment of time, but a boundary of time, a cause producing its effect at the singularity could not be strictly said to be simultaneous with its effect. Nonetheless they both occur coincidentally (in the literal sense of the word), that is, they both occur at t = 0. Ibid., Craig, “God and Big Bang Cosmology.” Footnote 1.
 Ibid., Craig, “God and Big Bang Cosmology.”