Why are these two NSString pointers the same?

When I alloc and init two NSString variables and compare their pointers, they are the same. Here's a snippet that shows this:

NSString *s1 = [[NSString alloc] initWithString:@"hello world"];
NSString *s2 = [[NSString alloc] initWithString:@"hello world"];

if (s1 == s2) {
    NSLog(@"==");
}else {
    NSLog(@"!=");
}

Why are s1 and s2 the same?