Identify this gedankenexperiment…

…and tell us what other famous term owes its origins to this experiment.

Part cracks: Kal, Ps, p vs np, udupendra, Vijay Shankar, Raghuvansh, Mo, Neeraj and Abhishek

Full cracks: sne, Dibyo, shrik, nisha’s thambi, username, duriel, priyananda

Har har I made a joke!

Kal, Ps, p vs np, sne, Dibyo, shrik, udupendra, nisha’s thambi, Vijay Shankar, username, Raghuvansh, duriel, Mo, priyananda, Neeraj and Abhishek