Quantum Theory

To unlock this achievement you must complete scene 6 on hard. If you are using the easy method for beating the game on hard, you are going to want to exit to the title menu at the beginning of the boss battle with the Gargantua. Continue from here on hard, simply defeat the Gargantua and the scene is over.

For more information on how to unlock the “Professional Exterminator” achievement at the same time, please see its respective solution.

I hope this solution helped! Leave a comment letting me know if there is any room for improvement! Thanks.