It is shown in end that humans are living on a spaceship orbiting near saturn. But when was this ship built? There was no mention of spaceship on such a large scale being mentioned.

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    Yes there was. The ship was being built in the NASA facility that Cooper visits. There is clear mention of it when he is given the tour of the facility. – bobbyalex Nov 19 '14 at 8:45
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    Related: movies.stackexchange.com/questions/27152/… – bobbyalex Nov 19 '14 at 8:46
  • @BobbyAlexander Do you think it could have transported entire population? – coder hacker Nov 19 '14 at 13:28
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    If you are asking if it was going to transport the entire population of the world, then no. It wasn't designed to. It was designed to save the human race. You only need to have a viable subset to do that. – Pᴀᴜʟsᴛᴇʀ2 Nov 19 '14 at 14:08
  • Tejas, @Paulster2 just answered your question. – bobbyalex Nov 20 '14 at 3:45

In The Science of Interstellar by physicist Kip Thorne, chapter 31 talks about them using their new theory of quantum gravity, discovered by Murph with help from the "quantum data" transmitted by Cooper (see my answer here for details on the physics ideas involved), to temporarily decrease the Earth's gravity and launch the huge colonies off the Earth:

Early in Interstellar, when Cooper first visits the NASA facility, he is shown a giant, cylindrical enclosure being constructed to carry thousands of humans into space and house them for many generations: a space colony. And he's told there are others being constructed elsewhere.

"How does it get off Earth?" Cooper asks the Professor. "Those first gravitational anomalies changed everything," the Professor replies. "Suddenly we knew that harnessing gravity was real. So I started working on the theory—and we started building this station."


How did it get lifted into space? The key, of course, was the quantum data (in my scientist's interpretation, the quantum gravity laws) that TARS extracted from Gargantua's singularity (Chapters 26 and 28) and Cooper transmitted to Murph (Chapter 30).


Murph must have figured out how to reduce Newton's gravitational constant G inside the Earth ... In my interpretation, with Newton's G reduced inside the Earth to, say, a thousandth of its normal value for, say, an hour, rocket engines could lift the enormous colonies into space.

As a byproduct, in my interpretation the Earth's core—no longer compressed by the enormous weight of the planet above—must have sprung outward, pushing the Earth's surface upward. Gigantic earthquakes and tsunamis must have followed, wreaking havoc on Earth as the colonies soared into space, a terrible price for the Earth to pay on top of its blight-driven catastrophe. When Newton's G was restored to its normal strength, the Earth must have shrunk back to its normal size, wreaking more earthquake and tsunami havoc.

But humanity was saved. And Cooper and ninety-four-year-old Murph were reunited. Then Cooper set out in search of Amelia Brand in the far reaches of the universe.

  • It's dumb to assume all of Earth's gravity was reduced. Likely, just the gravity affecting the colony stations would be reduced. – cde Sep 28 '15 at 8:32
  • @cde - are you disagreeing that the quote by Kip Thorne indicates that in his vision of the story, the entire Earth's gravity was reduced? Or are you just saying Thorne's vision is dumb? Remember, he's a physicist--it may be that while reducing a whole planet's gravity is theoretically possible in a theory of gravity with extra dimensions, that no existing theoretical model allows for a "local" reduction of gravity a la sci-fi "antigravity" (I know that antigravity would violate Einstein's equivalence principle). – Hypnosifl Sep 28 '15 at 9:56
  • The latter. Because as we see in the movie, Coop was able to produce localized gravitational effects. Localized enough to leave a barcode pattern in dust, knock books around, and encode gravitational waves in a watch hand. And anti-gravity was not what I had in mind. Reducing the gravitational effect on a localized section of the earth would simply reduce the amount of thrust required to move that section. Why Thorne believes that G must be changed for the entire planet is the question. – cde Sep 28 '15 at 10:10
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    @cde - Those localized gravitational effects were gravitational waves, but I don't think real gravitational waves can reduce the gravitational effect in a localized region, any more than electromagnetic waves can reduce the attraction between two opposite charges in a region. And reducing the gravitational effect in a localized region should cause the same problem with the equivalence principle--if it worked, then it should work to reduce the weight of an object in a small room, but there'd be no way to get an equivalent effect if the room were accelerating in space with no gravity. – Hypnosifl Sep 28 '15 at 15:32

As @BobbyAlexander commented, the ship was being built in the NASA facility that Cooper visits. And the space station orbiting Saturn could have been a completely different ship -- it's decades (or even a century) later! Humanity on Earth did plenty of other things while Cooper was gone.

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