What are Plan A and Plan B in Interstellar?

In the movie Interstellar, Plan A and Plan B are two distinct strategies devised by Professor Brand to ensure the survival of humanity as Earth faces imminent environmental disaster.

Plan A

• Objective: Plan A aims to develop a gravitational propulsion theory that would allow spacecraft to carry people off Earth into another galaxy. This involves Cooper transmitting quantum data back to Earth from a black hole to help solve the gravity equation necessary for mass evacuation12.
• Challenges: However, it is later revealed that Plan A was never feasible. Dr. Brand admits that solving the gravity equation required entering a black hole, which was not possible with current technology12.

Plan B

• Objective: Plan B is a backup plan to establish a human colony on a distant planet using fertilized eggs. This plan involves the crew finding a habitable planet and starting a new society there, effectively abandoning those left on Earth12.
• Reality: It is revealed that Plan B was actually the primary intention all along, as Plan A was deemed unfeasible from the start2.

In essence, Plan A was a theoretical solution to save everyone on Earth, while Plan B was a practical approach to ensure the survival of humanity by establishing a new colony elsewhere.