“Time is stored internally as the number of seconds with fraction since the Epoch, January 1, 1970 00:00 UTC.”

 >>require 'time'
 >>Time.parse("January 1, 1970 00:00 UTC").to_i
 => 0

As expected, but nice to verify.

For the reverse, be sure to use Time.at rather than Time.new

>> Time.at(0).to_i
=> 0
>> Time.new(0).to_i
=> -62167201200