A theoretical physicist who wrote the Interstellar book released alongside Christopher Nolan's film has explained what really happens in the ending, as many of us still don't get it.
Kip Thorne, a Nobel Prize winning theoretical physicist and an executive producer of Interstellar, also worked as a scientific consultant on the film.
The sci-fi is centred around former NASA pilot Cooper (Matthew McConaughey) who embarks on a mission to find a new habitable planet.
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Cooper and a team of astronauts then head on a journey through a wormhole near Saturn in search of life-supporting worlds.
Interstellar ending explained
At the end of the film, Cooper sacrifices himself by detaching his spacecraft and falling into a black hole so the other astronauts could continue towards the planet.
Inside the black hole, he enters a tesseract where he communicates with his daughter Murph (Jessica Chastain) across time.
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"Okay, so when he gets inside the black hole, he is scooped up by a spacecraft that was built by this advanced civilisation that provided the wormhole to him and to humanity," Thorne told Neil deGrasse Tyson on the StarTalk Plus podcast last year (3 December).
"And it's called the tesseract, and it's a four dimensional cube or spatial dimension, and that's why, in there you saw, I guess, the past and future all kind of related, very higher dimensional."
In the end, Cooper is rescued and wakes up on a space station called Cooper Station, named after Murph.
Christopher Nolan's request for Interstellar's ending
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Thorne, 85, said that Nolan wanted to bring Cooper back to Earth by a different route than the wormhole 'faster than the speed of light'. But the scientist said this wasn't possible, and that the only way it would work is if 'he goes inside the black hole'.
"He gets deposited on the three dimensional surface of a four dimensional sphere. And this four dimensional sphere is a spacecraft that can go into the higher dimension, and it goes out of the black hole, not through the horizon," he explained.
"It can't do that [it goes] up through the fourth space dimension, or what's called the fifth dimension in the movie this time is the fourth dimension, and goes back to Earth.
"And the distance back to the Earth is less than the distance between the Earth and the Sun, even though it's 10 billion light years inside of our universe, up in the bulk, it's a very short distance. And so we can get back.
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"He gets back very quickly, riding on the surfaces four dimensional sphere."
Thorne said that the director was on board but wanted 'to use a four dimensional cube instead of a four dimensional sphere'.
"That's a tesseract, and so that's what happens." Thorne said.
He went on to say that the scene of Cooper 'flailing around' is actually him 'being carried by the tesseract back to Earth' before the tesseract is 'docked' in Murph's bedroom - finally answering the question of who Murph's 'ghost' was.
He added: "You don't know that's what's happening until you read my book.
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"That's an agreement between Chris and me. That's the only way anyone's going to know."
Topics: Space, Film, Matthew McConaughey
Anish Vij