The accepted answer is always listed first.
After that, answers are sorted by the number of votes, then by when the answer was created (oldest-to-newest).
This can cause "jumping" when an older answer is voted up to have the same number of votes as a younger answer. For example:
Answer 2 is listed above answer 1 because it has more votes.
+--------+-------+---------+
| Answer | Votes | Created |
+--------+-------+---------+
| 2 | 2 | 00:01 |
+--------+-------+---------+
| 1 | 1 | 00:00 |
+--------+-------+---------+
Answer 1 receives a vote, and appears to jump over answer 2 because, even though they now have the same vote count, answer 1 is older.
+--------+-------+---------+
| Answer | Votes | Created |
+--------+-------+---------+
| 1 | 2 | 00:00 |
+--------+-------+---------+
| 2 | 2 | 00:01 |
+--------+-------+---------+
