 Many researchers believe that the fine-tuning of the universe’s laws, constants, and boundary conditions for life calls for inferring the existence of a divine designer (see  Section 3)  or a multiverse—a vast collection of universes with differing laws, constants, and boundary conditions (see  Section 4).  The inference to a divine designer or a multiverse typically rests on the idea that, in view of the required fine-tuning, life-friendly conditions are in some sense highly improbable if there is only one, un-designed, universe. It is controversial, however, whether this idea can coherently be fleshed out in terms of any philosophical account of probability.