Exploding and Imploding

Turn your solution into a function named humanized_list(). You should
be able to pass the $physicists_array as the only argument, and your
function will return the result.
Update your code to list the physicists by first name, in alphabetical
order.

Create a second argument to make alphabetical sorting optional.

Default alphabetical sorting to false. If no args are passed, no
sorting takes place.