I would like to know whether it is possible to, in a single game, convert all eight pawns of one colour into queens while retaining the original queen.
Presume that we are both playing chess competitively from the start of the game. Is there any circumstance where this could happen? Has it happened in the past?
Theoretically, it is possible.
In practice, it will never happen unless your opponent goes out of their way to let it happen.
It is not unheard of for "real" games to involve one player having 2 queens at the same time, and there are no rules that prohibit multiple pawns from promoting to queens (although don't forget: sometimes it is better to promote to a knight than a queen!).
Like Beofett said it is theoretically possible, but this is something you would only want to attempt while playing a weak computer for the lolz. Strong players who have a habit of playing computers from time to time, like Nakamura, may take pleasure from promoting his excess pawns to knights/bishops and proceed to checkmate the computer with them. Here is one example: http://www.chessgames.com/perl/chessgame?gid=1480850
There are two reasons why it should not happen in a game between to two human players: If your opponent allows it to happen (i.e. he is weak) you should not prolong his misery any more than necessary (which is bad etiquette). If he is aware that the situation is hopeless he should resign and not allow it to happen as well.
