The earth was about to be doomed
As the Earth was about to be doomed because of an Environmental Catastrophe Cooper , who used to be an astronaut, discovered co-ordinates for a secret government facility working on saving humanity.
The government wants to scout for other planets fit for life
The government wanted to sent a team , including Cooper, to scout for planets that are fit for human life. They sent 13 people earlier , who landed on different planets, and were still getting signals from three of them without being able to reach them directly.
Cooper and team went after those 3 humans
Cooper and his team were sent after the 3 humans NASA believes they are still living.
The team plans to use a wormhole to save time
The Team planned to use a wormhole built by an unknown civilization to save traveling time. Passing through the wormhole would save years of traditional space travelling.
The wormhole was built by future humans
As the events unfolded it turned out the the future civilization referred to as ‘they’ were just ordinary humans who survived until the future and managed to master time , space and the 5th dimension. In short, future humans were trying to save humans from the past throughout the movie.
Professor brand was working on Plan A
Professor Brand was working on an Equation that if solved will allow humans to master 5th dimensional physics and make them able to transport all surviving humans using a specially built ship that utilizes those new discoveries. This was called Plan A.
Plan B was about saving the human Race
Plan B wasn’t about saving all living humans but rather sending some human Embryos under supervision to any planet that is fit for human life to prevent the human race from being extinct. (See Alien Covenant Movie Explained)
Why 23 years passed when the team returned to orbit
Because time passes in a different way on one of the planets the team visited 23 passed years before the team returned back. one hour on that planet was roughly 10 years of ordinary earth time.
Cooper got pulled inside a Tesseract
Cooper sacrificed himself during the journey to save others but instead of dying he landed inside a Tesseract, which is a place , similar to a control room, built by the future humans to help past humans control the 5th dimension in order to survive.
Cooper used the Tesseract to send information to earth
Cooper used the Tesseract , which was designed to bypass time and space, to send information that could save humanity to his daughter. In other words, one of the future humans who were helping current humans survive was Cooper communicating from the Tesseract. (See Oblivion (2013) Movie Explained)
The ghost pushing the books was Cooper
When Cooper was still living with his daughter Murph , before travelling to space, she used to believe that the house was haunted by Ghosts who push books off the shelf. The one pushing the books was the future version of Cooper using the Tesseract.
Cooper was sending Morse code to his room
When Murph opened the window accidentally the dust lied on the floor in a regular form representing symbols similar to Morse Code. Again that was Cooper using the 5th dimension technology built by future humans to communicate with Murph.
Cooper was the ghost
The ghost doing all the strange stuff since the beginning of the movie was just Cooper sending messages to earth through the Tesseract.
The coordinates Cooper found were sent by him
The coordinates Cooper found in the beginning of the movie were sent by him and not a ghost. Cooper of the future was sending the coordinates to Cooper of the past (himself) to discover NASA’s secret facility and save the earth.
The information Cooper sent helped save humanity
The information Cooper passed to his daughter helped save humanity as it will allowed them to execute plan A.
Interstellar (2014) Movie Explained
Interstellar movie review & film summary (2014) | Let’s talk about the plot of ‘Interstellar’