The idea is that as improbable as a universe so exquisitely calibrated as ours is - a universe in which life can thrive - if there are an infinity of different universes then one that's life-permitting just has to exist and we happen to be in it.
In short, for many scientists the chief motivation for promoting the multiverse idea is the desire to escape having to acknowledge that an intelligent mind has engineered the universe.
As Stanford physicist Leonard Susskind put it,
If...the [multiverse] turns out to be inconsistent - maybe for mathematical reasons or because it disagrees with observation, [then] we will be in a very awkward position. Without any explanation of nature's fine-tunings we will be hard pressed to answer the [intelligent Design] critics.University of London physicist Bernard Carr observed that,
To the hard-line physicist the Multiverse may not be entirely respectable, but it is at least preferable to invoking a Creator. Indeed, [many] physicists are attracted to the multiverse precisely because it seems to dispense with God as the explanation of cosmic design.But as philosopher of science Stephen Meyer explains in his excellent new book Return of the God Hypothesis, the multiverse doesn't really help the naturalistic scientist escape the cosmic designer because, among other reasons, whatever is producing that endless parade of universes must itself be exquisitely fine-tuned.
Brierly is the host of the weekly British radio show Unbelievable which is available on podcast. Each week Justin brings together believers and unbelievers to talk about some issue related to matters of faith. The discussions are almost always pleasant, informative, and Justin does an excellent job moderating them. They're usually what such conversations should be like, but too often aren't.
If you'd like to sign up for the podcast or browse the archives of past shows which have featured discussions on almost every topic related to religious belief you can go to the Unbelievable website here. Meanwhile, here's another short video that does a fine job of explaining cosmic fine-tuning: