Getting time difference between two times in PHP

$val1 = '2014-03-18 10:34:09.939';$val2 = '2014-03-18 10:34:09.940';
$datetime1 = new DateTime($val1);$datetime2 = new DateTime($val2);
echo "

"

;var_dump($datetime1->diff($datetime2));

if($datetime1 > $datetime2)
  echo "1 is bigger";
else
  echo "2 is bigger";

?>