Rate of Passage of Time

What determines how fast we percieve the passage of time? Do flies see everything in much slower motion than we do? Does time pass faster or slower for different people? Even moment to moment time passes at different rates for me. Have you ever tried to slow down or speed up time through sheer force of will? What about long term time, not just short term time? What is a good way to measure all of this? An excellent excercise to measure an hour is to sit quietly with your eyes closed without thinking any thoughts. Learning to juggle affects the way the brain treats time. Seasoned jugglers will testify to a newly developed experience of seeing things fall in slow motion when they are knocked over.