The birth of the universe resembles not an explosion, but a traffic jam. At first, a tiny fraction of a second after the Big Bang, space expanded sluggishly, like cars stuck in gridlock. Then came a sharp surge — accelerated expansion, which cosmologists call inflation. This contrasting transition explains an ancient mystery: why there are no large spots in the snapshot of the universe's microwave 'echo.' The slow phase acted like a filter, preventing large energy fluctuations from growing. Only fine ripples remained — the very quantum jolts from which galaxies later emerged. Remarkably, without such a jam, the familiar cosmos might never have formed: all matter would have collapsed into giant black holes or remained a diffuse fog. The new model, consistent with Planck satellite data, was developed by Alan Guth and others. Yet back in the 1940s this 'echo' was predicted by George Gamow, and in 1965 it was serendipitously detected by Arno Penzias and Robert Wilson.
A delay in the first minuscule fraction of a second shaped the cosmos: without this 'cosmic traffic jam,' stars might never have ignited at all.