Did the universe have a beginning?

The best physical evidence we have says yes. For most of Western history the universe was assumed eternal. That changed when a Belgian priest and physicist, Georges Lemaître, showed from Einstein's own equations that the cosmos is expanding — and so was once unimaginably small, hot, and dense. Einstein reportedly told him, 'Your calculations are correct, but your physics is abominable.' Lemaître's physics proved very good indeed.

Three independent lines converge: the expansion Hubble measured in 1929; the cosmic microwave background, the relic heat found by Penzias and Wilson in 1965; and the predicted abundances of the lightest elements. None were designed to test theology, yet together they describe a cosmos with a beginning. The 2003 Borde–Guth–Vilenkin theorem strengthened the point: any universe expanding on average must have a past boundary — even inflationary and many multiverse models. Vilenkin wrote that cosmologists 'can no longer hide behind the possibility of a past-eternal universe.'

Honesty requires the limits. BGV is a classical result; the physicist Sean Carroll notes the past boundary may mark where our equations stop, not where being began, and even the theorem's co-author Alan Guth remains open to a beginningless universe. So this is powerful corroboration, not airtight proof. And note the careful wording: whatever begins to exist has a cause — not 'everything has a cause'; a being that never began is simply outside the argument's scope.

If the universe began, its cause cannot be spatial or temporal, and must be immensely powerful and uncaused — a sketch that converges with what theists mean by God, though physics alone does not reach the Father of the Nicene Creed. Hold the physics honestly and the inference humbly, and a universe with a beginning still raises the oldest question there is.