Why is "Expires" 1981?

Question

My CRON Job returned an error that CRON job did not work. In that this was there:

Set-Cookie: PHPSESSID=2t2drultihqci4em15nbfmeb63; path=/
Expires: Thu, 19 Nov 1981 08:52:00 GMT
Cache-Control: no-store, no-cache, must-revalidate, post-check=0, pre-check=0
Pragma: no-cache
Content-type: text/html

I am wondering why is Expires set to "1981". What is the significance?

Answer 1

It's an attempt to disable caching.

The date is the birthday of the developer Sascha Schumann who added the code.

From session.c:

Authors: Sascha Schumann <[email protected]> 
         Andrei Zmievski <[email protected]> 

// ...

CACHE_LIMITER_FUNC(private)
{
    ADD_HEADER("Expires: Thu, 19 Nov 1981 08:52:00 GMT");
    CACHE_LIMITER(private_no_expire)(TSRMLS_C);
}