Brute Fact or Coincidence
The Explanation
One possible response to fine-tuning is that there is nothing further to explain. The universe has a particular set of physical properties, and those properties happen to permit observers like us.
Not every unusual or improbable event requires a special explanation. Any particular outcome can appear remarkable after it has occurred. From this perspective, the life-permitting character of our universe may simply be a fact about reality that has no deeper cause available to us.
Supporting Evidence
This explanation has the advantage of simplicity. It does not require additional universes, an undiscovered physical mechanism, or an intelligent cause.
It also reminds us that describing a condition as unusual is not enough by itself to prove that the condition was deliberately selected.
Limitations
The principal limitation is that calling something a brute fact does not explain why it has the particular properties observed.
If many apparently independent requirements must work together before complex structures are possible, some investigators argue that simply accepting the entire combination as coincidence leaves an important question unanswered.
Questions That Remain
At what point, if ever, does a collection of life-permitting conditions reasonably call for an explanation beyond the statement that this is simply how the universe happens to be?
Intelligent Design Response
Intelligent Design proponents generally argue that coincidence becomes less satisfying as the number and coordination of relevant conditions increase. The design argument therefore depends upon the cumulative pattern rather than merely upon finding one unusual physical number.