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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?

Bluefire
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  • @HorusKol No. I read that question and it doesn't answer mine. – Bluefire Feb 04 '16 at 21:25
  • Yes it does: "the black hole caused the extreme time dilation they suffered while traveling there and on the surface (of Miller's planet)" – HorusKol Feb 04 '16 at 21:44
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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 04 '16 at 21:45
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    These answers are turning into a physics discussion rather than a science fiction discussion... – Chrismas007 Feb 04 '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 04 '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 04 '16 at 21:52
  • @Mooz - The other question is asking about whether the time dilation was caused by Miller's planet or the black hole, it doesn't ask about any effects of gravity other than time dilation. This question is specifically about the gravitational force felt by people on Miller's planet, for example how heavy they feel, what they would weigh if they stood on a scale, etc. You can't "feel" time dilation! So I don't think this is a duplicate at all, I'm voting to reopen. – Hypnosifl Feb 04 '16 at 22:03
  • Related: How could they survive and move that easily on Miller's planet if the gravity field is so powerful? – TARS Feb 10 '17 at 00:45

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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.

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Hypnosifl
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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.

Chris B. Behrens
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  • 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 04 '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 04 '16 at 21:28
  • @Chris Just as the gravitational force deteriorates, so does the time dilation factor. – Bluefire Feb 04 '16 at 21:30
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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 04 '16 at 21:30
  • @CBredlow That's only if you were on the side facing the black hole, which they're not on, since they beelined to the planet from the Endurance, which was outside of the black hole's "range". – Bluefire Feb 04 '16 at 21:31
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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 04 '16 at 21:32
  • @Hypnosifl - you wouldn't "feel" it, but it would be there. – Chris B. Behrens Feb 04 '16 at 21:34
  • @Chris B. Behrens - The spacetime curvature in the region would still reflect the presence of the black hole--is that what you mean or do you mean something else by "it would be there"? In any case, you responded "yes" to Bluefire's question "you'd still feel the gravitational force of the black hole on Miller's planet, right?", so I thought that could be potentially misleading since if they were on a separate orbit around the black hole (not on Miller's planet) they would feel totally weightless. – Hypnosifl Feb 04 '16 at 21:39
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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 04 '16 at 21:52
  • @Hypnosifl - yeah, I suppose I should have said "you would EXPERIENCE the force", not "feel". – Chris B. Behrens Feb 04 '16 at 22:43