What is the Kalam cosmological argument?

The Kalam is a short, disciplined argument with two premises. Premise 1: whatever begins to exist has a cause. Premise 2: the universe began to exist. Conclusion: therefore, the universe has a cause. Notice the first premise carefully - it does not say 'everything has a cause' (which would invite the retort 'then what caused God?'). It says whatever begins to exist. A thing that never began needs no cause.

Premise 1 rests on a deep intuition: out of nothing, nothing comes. (The quantum-vacuum objection fails because the vacuum is a real physical thing with structure and energy, not the 'nothing' - no space, no fields - that the premise means.) Premise 2 is defended two independent ways: philosophically, that an actually infinite past cannot be traversed to reach today; and scientifically, that cosmology traces the universe to a finite beginning, reinforced by the Borde-Guth-Vilenkin theorem, which shows that any on-average expanding universe must have a past boundary. That science is powerful corroboration, not airtight proof - a point careful proponents like William Lane Craig readily grant.

If the argument works, we learn a great deal about the cause from the premises alone: since it made all space, time, and matter, it must be spaceless, timeless, immaterial, uncaused, and enormously powerful - and plausibly a personal mind, since only a free agent explains how a timeless cause produces an effect with a beginning.

Be clear about scope: on its own, Kalam reaches a transcendent cause, not yet the Triune God of the Nicene Creed. That is not a flaw; it is honesty. It is one strand in a cumulative case - alongside fine-tuning, morality, and the resurrection - that opens the door to a Creator.