I did not need to put the variable in the URL,
the reason I could not use the $current_user
variable is because it didn't exist in "detailview.php"
which is where the link ends up.
I used:
echo "<pre>";
print_r($GLOBALS);
echo "</pre>";
to view all globals, there I found the authenticated_user_id
Knowing I could use this I was able to access the global from my file without the URL:
$current_user = $_SESSION["authenticated_user_id"];
I would like to thank STT LCU
for his advice, as he was the only one who helped me through this problem, which took me a full week in total.