Here is the full list of all 24 The Past Within achievements. It takes around 2-3 hours to unlock all of the achievements on Windows.
The Future - Chapter 1 - Five
The Past - Chapter 2 - Ten
The Past - Chapter 1 - Six
The Past - Chapter 1 - Four
The Future - Chapter 2 - Eleven
The Future - Chapter 2 - Twelve
The Future - Chapter 1 - Six
The Future - Chapter 1 - Four
The Future - Chapter 1 - Two
The Future - Chapter 1 - One
The Past - Chapter 2 - Eleven
The Past - Chapter 2 - Nine
The Future - Chapter 2 - Eight
The Future - Chapter 2 - Ten
The Future - Chapter 2 - Seven
The Future - Chapter 1 - Three
The Future - Chapter 2 - Nine
The Past - Chapter 2 - Twelve
The Past - Chapter 2 - Eight
The Past - Chapter 2 - Seven
The Past - Chapter 1 - Three
The Past - Chapter 1 - Two
The Past - Chapter 1 - One
The Past - Chapter 1 - Five