In Interstellar, the crew of the Endurance experience extreme time dilation (7 years to an hour) on Miller's planet, due to its proximity to a black hole. However, they only feel 130% of Earth's gravity when on the planet. How does a gravitational field powerful enough to create that kind of time dilation not also manifest as a huge physical force?

  • @HorusKol No. I read that question and it doesn't answer mine. – Bluefire Feb 4 '16 at 21:25
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    @Bluefire Can you specify how it doesn't? What details in specific are you looking for which aren't in the other post? Thanks. – Möoz Feb 4 '16 at 21:45
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    These answers are turning into a physics discussion rather than a science fiction discussion... – Chrismas007 Feb 4 '16 at 21:47
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    Has Physics tackled any of these types of questions?... they have one... and a tag... perhaps they'd like more? – Catija Feb 4 '16 at 21:50
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    @Chrismas007 - Since the question is about the explanation in-universe, and the in-universe laws of gravity were intended to work the same as the real-world laws, it shouldn't be an issue that the answers refer to how things should work according to real-world gravitational laws, see the accepted answer to a question about the policy on "science in science fiction" type questions here. – Hypnosifl Feb 4 '16 at 21:52

If an object is in free fall around a gravitating body, it feels no locally-measurable gravitational effects from that body aside from tidal forces (time dilation is not locally measurable, it can only be defined relative to distant clocks), and tidal forces are not significant on a human body near the event horizon of such a large black hole (see my answer here about tidal forces near a supermassive black hole). And any orbiting object is in free fall--for example, this is why a shuttle astronaut in low Earth orbit feels weightless even though the orbit is fractionally not much farther from the center of the planet than the surface is (see this page for a brief discussion, and I tried to explain the concept of feeling weightless in this answer on the physics stack exchange...it may also be worth noting that in Einstein's theory of general relativity the local equivalence between being in free fall and moving inertially in the absence of any gravity is formalized into the "equivalence principle", there's a good article on this here). So, a person on Miller's planet shouldn't feel any gravity from the black hole, though they are not in free fall relative to Miller's planet itself so they do feel gravity from the planet.


You're confusing the physics here. The operational concern for the surface gravity is the mass of the planet itself. The operational concern for the time dilation is the mass of the black hole. The huge physical force in play for the black hole would be the character of the orbit of the planet around the black hole - probably a very short orbital period.

  • Yes, but you'd still feel the gravitational force of the black hole on Miller's planet, right? We feel the gravitational force of the Sun on Earth, we just don't notice it. If the Sun had enough gravity to contract time from 7 years to one hour, that force would be a lot greater. – Bluefire Feb 4 '16 at 21:27
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    Yes, but because of the inverse square law, it's an infinitesimal fraction of the pull from the planet. – Chris B. Behrens Feb 4 '16 at 21:28
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    It would depend on the rotation of the planet - when the side you were on was facing Gargantua, it would pull you up; when it faced away, it would pull you down. But yeah. – Chris B. Behrens Feb 4 '16 at 21:30
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    @CBredlow - How do you figure you'd feel gravity from Gargantua? I don't think you would at all, just like you don't feel gravity from Earth when you're in orbit around the Earth, see my answer to the question. – Hypnosifl Feb 4 '16 at 21:32
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    @Bluefire - while on the planet you are in orbit around the black hole. If you remove the planet from this scenario, you would still be in orbit around the black hole - you are in its gravitational field, but since you are in orbit you would feel like you're in freefall. Think about things in Earth orbit - if they weren't moving fast enough to orbit, they would fall to Earth (ie, "feel" Earth's gravity) - but they are in orbit, so are in Earth's gravity, but don't feel it. – HorusKol Feb 4 '16 at 21:52

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