What's the best way if I'm modifying a scenario to slow down science? I don't want to just set the minimum time for a research advance to 10 turns or something, as that just equalizes everyone's research. What I'd like to do is something like slowing down everyone's research by 50% - - so that the fast researcher takes 8 turns for an advance and a slow researcher takes 20 turns, that kind of thing. Thanks in advance.

Try to change the tech rate from the world sizes menu

or go in and change the costs for all the techs

or move communications trading to a later tech. I recomend Navigation.

while your at it move map trading to a later tech too.