is rand() in php really random?

random.php

<?php

function countValueInArray($value, $array) {
	$count = 0;
	for ($i=0; $i < count($array); $i++) { 
		if($value == $array[$i]) {
			$count++;
		}
	}
	return $count;
}

$numbers = array();

for ($i=0; $i < 100; $i++) { 
	$numbers[$i] = rand(0, 100);
}

$duplicates = array();
for ($x=0; $x < count($numbers); $x++) { 
	$number = countValueInArray($numbers[$x], $numbers);

	if ($number > 1) {
		array_push($duplicates, $numbers[$x]);
	}
}

$duplicatesList = array_values(array_unique($duplicates));

echo "number of duplicates: ".count($duplicatesList);
echo "<br>these are: <br>";

print_r($duplicatesList);

 ?>

I wanted to find out if the rand()-function is really random.
This script creates 100 random numbers in the range between 0 and 100. After that it counts if a number appears more than once in the array.
The result is a count of the duplicate numbers as the list of them.