Time represented internally as seconds since the (platform-dependent) epoch
t = Time.now.to_i # => 1184036194 seconds since epoch
Time.at(t) # => seconds since epoch to Time object
t = Time.now.to_f # => 1184036322.90872: includes 908720 microseconds
Time.at(0) # => Wed Dec 31 16:00:00 -0800 1969: epoch in local time