I thought you got half of the retirement///401 automatically when you got the divorce

It looks like you thought wrong. The judge doesn't know about the retirement if you don't tell him or her. And the administrator of the retirement plan doesn't know about the divorce unless the QDRO (https://en.wikipedia.org/wiki/QDRO) specifies what is to be done about it.

Did you have an attorney?

What, if anything, does the divorce decree say about the retirement?

More details, and a question, would be helpful too. I.e.: what do you want to know?

Also, no, you don't automatically get half.

Say, for example, the spouse who is to retire was working at a company for forty years. Let's say that at the end of that forty years, the couple was married for one week and then divorced. The other spouse would not "automatically" be entitled to half.

In a divorce everything is negiotiable. In general it's true that each spouse is considered to "get" 1/2 of the value of retirement plans (like 401(k)'s) that accrued during the term of the marriage. But of course the parties may agree to swap an interest in one asset for another - for example giving up rights to a spouse's 401(k) in order to get full ownership of the house.