Change relative date to actual date.

I'm searching for a way to change the display of dates from relative (today,yesterday, etc.) to real dates. I need it mostly for the activity tab but if it can be changed easily, application wide, it would be even better.
I've tried to modify 'views/activities/index.html.erb' but it didn't work. I've also tried to modify the 'format_activity_date' function with no luck either.

Can anyone point me in the right direction?