Stephen Hawking in his book The Grand Design acknowledges:

Our universe and its laws appear to have a design that both is tailor-made to support us and, if we are to exist, leaves little room for alteration. That is not easily explained and raises the natural question of why it is that way.

Anthropic Principle

One common response to the fine-tuning problem is the anthropic principle, which states that we shouldn’t be surprised to find ourselves in a universe that allows for our existence since we wouldn’t be around to observe a universe that wasn’t conducive to our existence.

Philosopher John Leslie counters this with the following analogy, retold by Dr. Francis Collins (former head of the Human Genome Project and the National Institutes of Health): 

In this parable, an individual faces a firing squad, and fifty expert marksmen aim their rifles to carry out the deed. The order is given, the shots ring out, and yet somehow all the bullets miss and the condemned individual walks away unscathed.

How could such a remarkable event be explained? Leslie suggests that there are two possible alternatives ... In the first place, there may have been thousands of executions being carried out in that same day, and even the best marksman will occasionally miss. So the odds just happen to be in favor of this one individual, and all fifty of the marksmen fail to hit the target. The other option is that something more directed is going on, and the apparent poor aim of the fifty experts was actually intentional. Which seems more plausible? (Collins, p. 77)

While the anthropic principle points out that there is a limited range of outcomes that can be observed in a universe that has the characteristics to support intelligent life, it is an unsatisfying answer to how our fine-tuned universe came to be despite the infinitesimal odds. If something unlikely happens, whether it’s 50 marksmen all missing their target or the far more improbable existence of our universe, it’s reasonable to look for a reason why. 

Multiverse Theory

Stephen Hawking proposed one solution: Our universe is just one among a potentially infinite number of universes, each with different physical constants. While this multiverse theory could explain the existence of our universe, it suffers from a lack of evidence. Sir Penrose, the aforementioned Nobel laureate who collaborated extensively with Hawking, said the following about Hawking’s use of the multiverse theory and the related M-Theory in The Grand Design:

It’s overused, and this is a place where it is overused. It’s an excuse for not having a good theory.

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The book is a bit misleading. It gives you this impression of a theory that is going to explain everything; it’s nothing of the sort. It’s not even a theory.

Shortly before he passed away, Hawking acknowledged the following in his 2018 paper A Smooth Exit from Eternal Inflation?:

We are not down to a single, unique universe, but our findings imply a significant reduction of the multiverse, to a much smaller range of possible universes.

Referring to this paper, British author and professor Philip Goff wrote in the Guardian:

The problem is that the less variety there is among the universes, the less capable the multiverse hypothesis is of explaining fine-tuning. If there is a huge amount of variation in the laws across the multiverse, it is not so surprising that one of the universes would happen to have fine-tuned laws. But if all of the universes have exactly the same laws—as in Hawking and Hertog’s proposal—the problem returns, as we now need an explanation of why the single set of laws that govern the entire multiverse is fine-tuned. 

…

There is still hope for a scientific account of fine-tuning. However, by ruling out one of the two scientifically credible options for doing this, Hawking and Hertog have slightly strengthened the alternative explanation in terms of God. It is ironic that the atheist Hawking should, in his final contribution to the science, make God’s existence less improbable.

The Universe Is Like a Garden

So we live in a universe that has a beginning and is fine-tuned for life.

But Richard Dawkins protests in The God Delusion:

Isn’t it enough to see that a garden is beautiful without having to believe that there are fairies at the bottom of it too?

Oxford mathematician Dr. John Lennox responds,

But when he sees the beauty of a garden, does Dawkins really believe that there is no gardener?... I find it incomprehensible and rather sad that he presents us with such an obviously false set of alternatives: the garden on its own, or the garden plus fairies. Real gardens do not produce themselves: they have gardeners and owners. Similarly with the universe: it did not generate itself. It has a creator—and an owner. (Lennox 2011, p. 230)