December 25 is celebrated worldwide as Christmas. Doc Brown demonstrated the time circuits by setting the time to this date in the year 0000 if one wanted to witness the birth of Jesus Christ. However, there is no year "0" between 1 B.C. and 1 A.D., nor is there proof that Jesus was born on December 25, although the anniversary of his birth is celebrated annually on that day.
Behind the scenes
- Bob Gale has stated in the DVD commentary that it was an example of a joke that nobody else laughed at -- the idea that a scientist that specialized in time travel experiments for the past 30 years would punch in a nonexistent year "DEC 25 0000" to witness the birth of Christ.
- The animated series included a special Christmas episode, "Dickens of a Christmas", where the family celebrated the holiday in 1845 London.