[nuccy]

For the CMB we predict (or rather invent) "inflation" - a rapid expansion of the space-time to preserve uniformity of early Universe [1]. Inflation lasted for 0.00000000000000000000000000000001s but the size of the Universe increased by 10^30 times.

1. https://www.esa.int/Science_Exploration/Space_Science/Planck...

Edit: I wanted to come up with an analogy of increasing some object to the size of Earth (as it is the biggest object we can experience in real life). Though 10^30 times is so mindbogglingly large that we don't really have any sense of that small sizes at all. The object would have to be smaller than an electron by a trillion times (10^12).