The rule could be anything, as funny or as serious as you want. The universe will progress in a similar way that it has up until this point, unless your changed rule prevented it from doing so.
Some examples might be:
- The invention of currency is not allowed.
- Iron is slightly less stable.
- The Ancient Greeks are able to cultivate Silphium, which does not go extinct now.
I guess that would mean we can travel faster between planets. Communication would be much faster also.
Unless this gets me faster internet, I’m not interested
Good news! Internet would be technically faster.
Time would be faster also so you wouldn’t be able to tell it but compared to us your internet would be faster
Yay!
Aw!