Set a cookie to never expire

Looking at the [php documentation on setting a cookie][1] I see that I can set an expiration date for the cookie. You can set the cookie to expire at the end of the browser session or at some time in the future but I do not see a way to set the cookie to never expire. Is this even possible and how is this accomplished? [1]: http://php.net/manual/en/function.setcookie.php