Funny - I was just reading up on this and from what I've seen, scientist are still trying to determine what actually does trigger the rut. There are varied opinions on the cause from shorter days (photoperiod), drops in temperature, moon phases etc. No one really knows. IMO it is a combination of everything. They can describe the pre rut, rut, and post rut.
I honestly don't care what triggers it but in my over 45 years experience I've found that here in PA, the last week in Oct through the first 2 weeks in Nov, the deer activity really picks up. During this period, even when deer numbers were supposedly down, I have seen as many as 7 different buck cruising the woods in a single sit in areas where you would normally see only one or two deer in a morning or evening sit. When I see things picking up, I try to stay out as much as possible as it is a magical time.
One of my most memorable hunts was during the rut. Although I didn't get a shot that day I had 6 buck chasing 4 different doe all around my stand. It was the craziest and coolest thing I ever watched in my life in the woods.