# Time Dilation and Neutron Stars **URL:** \ **Category:** Factual Questions\ **Created:** [April 25, 2021, 7:42pm UTC](https://boards.straightdope.com/t/time-dilation-and-neutron-stars/940748 "2021-04-25T19:42:39Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![FelixF](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/felixf/32/7703_2.png) [@FelixF](https://boards.straightdope.com/u/FelixF)\ **Post date:** [April 25, 2021, 7:42pm UTC](https://boards.straightdope.com/t/time-dilation-and-neutron-stars/940748/1 "2021-04-25T19:42:39Z")
I recently read on recommendation a SciFi novel about life evolving on a neutron star or its crust. One thing that puzzled me was the assertion the neutron star life was living roughly a million times faster than some human astronauts who visited the wandering star (but orbit hundreds of Km above to avoid the extreme gravitational tides or something like that). However, I think I understand that the extreme gravity of the neutron star - 67 billion Gs I think in the story - should have extreme effects on relative flow of time. While reading this bothered me as the novel was otherwise trying to be super hard scifi. Question: what would be the time effects between normal G and 67 billion Gs (if this question is properly formulated, maybe not)? ---
**Author:** ![TheGunIsMightierThanThePen](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/thegunismightierthanthepen/32/2981_2.png) [@TheGunIsMightierThanThePen](https://boards.straightdope.com/u/TheGunIsMightierThanThePen)\ **Post date:** [April 25, 2021, 8:09pm UTC](https://boards.straightdope.com/t/time-dilation-and-neutron-stars/940748/2 "2021-04-25T20:09:14Z")
I entered some numbers into this [online calculator](https://www.engineersedge.com/calculators/gravitational_time_dilation_15003.htm), using 2.8 x 1030 kg as a typical neutron star mass, 10 km as a typical neutron star radius, and having the astronauts orbit 1000 km from the neutron star (I left the other parameters unchanged). The calculator spat out a time dilation factor of ~0.2341 for an object on the surface of the neutron star, meaning for every year that passes for the astronauts, an object on the surface would only age ~0.8103 years. I also found a [StackExchange post](https://astronomy.stackexchange.com/a/10739) that claims the theoretical maximum possible time dilation factor for a neutron star is ~2.29. So it looks like the novel’s assertion that neutron star life is living “a million times faster” is outrageous bunk. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [April 25, 2021, 8:17pm UTC](https://boards.straightdope.com/t/time-dilation-and-neutron-stars/940748/3 "2021-04-25T20:17:32Z")
I think, if it’s the story I’m thinking of, it’s not time dilation, but that the physiology of the neutron star creatures is so different that they live much faster than we do. ---
**Author:** ![crowmanyclouds](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crowmanyclouds/32/19884_2.png) [@crowmanyclouds](https://boards.straightdope.com/u/crowmanyclouds)\ **Post date:** [April 25, 2021, 8:20pm UTC](https://boards.straightdope.com/t/time-dilation-and-neutron-stars/940748/4 "2021-04-25T20:20:36Z")
Robert L. Forward’s _Dragon’s Egg_? > **[Dragon's Egg](https://en.wikipedia.org/wiki/Dragon%27s_Egg)** > > Pages for logged out editors learn more > > > Dragon's Egg is a 1980 hard science fiction novel by American writer Robert L. Forward. In the story, Dragon's Egg is a neutron star with a surface gravity 67 billion times that of Earth, and inhabited by cheela, intelligent creatures the size of a sesame seed who live, think and develop a million times faster than humans. Most of the novel, from May to June 2050, chronicles the cheela civilization beginning with its discovery of agriculture to ... ---
**Author:** ![Riemann](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/riemann/32/3133_2.png) [@Riemann](https://boards.straightdope.com/u/Riemann)\ **Post date:** [April 25, 2021, 8:24pm UTC](https://boards.straightdope.com/t/time-dilation-and-neutron-stars/940748/5 "2021-04-25T20:24:07Z")
Nothing to do with time dilation. The factor of a million in processes there is because “chemical” reactions are mediated by the strong nuclear force rather than EM. ---
**Author:** ![FelixF](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/felixf/32/7703_2.png) [@FelixF](https://boards.straightdope.com/u/FelixF)\ **Post date:** [April 25, 2021, 8:26pm UTC](https://boards.straightdope.com/t/time-dilation-and-neutron-stars/940748/6 "2021-04-25T20:26:03Z")
Yes, but what I was trying to get at was the sense that one would counter-balance the other. ---
**Author:** ![FelixF](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/felixf/32/7703_2.png) [@FelixF](https://boards.straightdope.com/u/FelixF)\ **Post date:** [April 25, 2021, 8:26pm UTC](https://boards.straightdope.com/t/time-dilation-and-neutron-stars/940748/7 "2021-04-25T20:26:55Z")
I know, I guess I did not express the question well - the sense I had was the time dilation effect was being ignored. ---
**Author:** ![Riemann](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/riemann/32/3133_2.png) [@Riemann](https://boards.straightdope.com/u/Riemann)\ **Post date:** [April 25, 2021, 8:34pm UTC](https://boards.straightdope.com/t/time-dilation-and-neutron-stars/940748/8 "2021-04-25T20:34:57Z")
What do you think is being wrongly ignored exactly? Time dilation is not significant relative to the factor of a million in the speed of the chemical processes that dictate the rate at which events proceed for the Cheela. ---
**Author:** ![Jackknifed\_Juggernaut](https://avatars.discourse-cdn.com/v4/letter/j/9de053/32.png) [@Jackknifed\_Juggernaut](https://boards.straightdope.com/u/Jackknifed_Juggernaut)\ **Post date:** [April 27, 2021, 12:38am UTC](https://boards.straightdope.com/t/time-dilation-and-neutron-stars/940748/9 "2021-04-27T00:38:50Z")
In the movie _Interstellar_, I remember that the team of astronauts drop onto a planet with very strong gravity. IIRC it was the one with the huge tidal wave. When they return to the ship, they see that one astronaut who stayed on the ship aged significantly. So is this bad science, since a neutron star would presumably have considerably more gravity than any planet? ---
**Author:** ![Babale](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/babale/32/15666_2.png) [@Babale](https://boards.straightdope.com/u/Babale)\ **Post date:** [April 27, 2021, 12:47am UTC](https://boards.straightdope.com/t/time-dilation-and-neutron-stars/940748/10 "2021-04-27T00:47:58Z")
The time dilation wasn’t due to the planet’s gravity IIRC it was due to the gravity of the supermassive black hole it was in orbit around. IANAPhysicist but if I’m remembering right the numbers for interstellar work out, but they had to give their black hole an extremely rapid spin to get the desired time dilation (as spinning black holes have different properties than nonspinning ones) ---
**Author:** ![wolfpup](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/wolfpup/32/10618_2.png) [@wolfpup](https://boards.straightdope.com/u/wolfpup)\ **Post date:** [April 27, 2021, 12:57am UTC](https://boards.straightdope.com/t/time-dilation-and-neutron-stars/940748/11 "2021-04-27T00:57:23Z")
> [@Riemann](#): > > Nothing to do with time dilation. The factor of a million in processes there is because “chemical” reactions are mediated by the strong nuclear force rather than EM. I love “hard” science fiction. Arthur C. Clarke had a number of such stories, an old classic example being _Technical Error_, in which a technician in the core of a huge generator is suddenly subject to enormous electromagnetic forces with … unpredictable results. But the idea of life on a neutron star seems to be beyond far-fetched. Not even atoms can exist on a neutron star, let alone molecules. So the possibility of the kinds of complex structures necessary for life being formed from a homogenous mass of neutrons and a few stray unassociated electrons and protons seems rather silly. ---
**Author:** ![Jackknifed\_Juggernaut](https://avatars.discourse-cdn.com/v4/letter/j/9de053/32.png) [@Jackknifed\_Juggernaut](https://boards.straightdope.com/u/Jackknifed_Juggernaut)\ **Post date:** [April 27, 2021, 12:59am UTC](https://boards.straightdope.com/t/time-dilation-and-neutron-stars/940748/12 "2021-04-27T00:59:52Z")
> [@Babale](#): > > it was due to the gravity of the supermassive black hole it was in orbit around. Totally forgot about the SMBH. Thanks, I almost never watch movies twice, but I need to watch that one again. ---
**Author:** ![CookingWithGas](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cookingwithgas/32/485_2.png) [@CookingWithGas](https://boards.straightdope.com/u/CookingWithGas)\ **Post date:** [April 27, 2021, 1:47am UTC](https://boards.straightdope.com/t/time-dilation-and-neutron-stars/940748/13 "2021-04-27T01:47:21Z")
> [@Babale](#): > > The time dilation wasn’t due to the planet’s gravity IIRC it was due to the gravity of the supermassive black hole it was in orbit around. I saw Interstellar but it’s been a while. There is nothing magical about a black hole. If you were in orbit around a black hole, it wouldn’t be a different experience than orbiting a large body of the same mass. I don’t know anything orbital mechanics but I’m guessing that if they could establish a stable orbit around a black hole they couldn’t have been close enough for significant time dilation, any more than what the astronauts on the Space Shuttle experience. ---
**Author:** ![Babale](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/babale/32/15666_2.png) [@Babale](https://boards.straightdope.com/u/Babale)\ **Post date:** [April 27, 2021, 1:48am UTC](https://boards.straightdope.com/t/time-dilation-and-neutron-stars/940748/14 "2021-04-27T01:48:44Z")
> [@CookingWithGas](#): > > I don’t know anything orbital mechanics but I’m guessing that if they could establish a stable orbit around a black hole they couldn’t have been close enough for significant time dilation, any more than what the astronauts on the Space Shuttle experience. And IIRC that is why they gave the black hole a ludicrously high spin. I’ll see if I can dig up the article I’d previously read about it. ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [April 27, 2021, 1:56am UTC](https://boards.straightdope.com/t/time-dilation-and-neutron-stars/940748/15 "2021-04-27T01:56:50Z")
> [@wolfpup](#): > > So the possibility of the kinds of complex structures necessary for life being formed from a homogenous mass of neutrons and a few stray unassociated electrons and protons seems rather silly. I agree on the silliness, but the surface of a neutron star will have quite a few protons, not just a scattering. In fact, the crust of a neutron star should be made of “normal” matter. Well, not strictly normal, but of normal nuclei in a sea of electrons. As you go deeper, the atomic numbers and weights of the nuclei increase, with increasing number of neutrons in them as well as free neutrons that the pressure prevents the decay of. Similarly, a lot of the heavy nuclei would quickly decay in our environment, but be stable in that environment. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [April 27, 2021, 2:14am UTC](https://boards.straightdope.com/t/time-dilation-and-neutron-stars/940748/16 "2021-04-27T02:14:55Z")
The strong force is far more complicated than electromagnetism. If electromagnetism-based life is plausible, then strong-force-based-life is even more so. Heck, it might even be possible to get “living glueballs”, life composed entirely of strong-carrier-particles, without even needing protons and neutrons (a trick which has no equivalent for electromagnetism). ---
**Author:** ![Dr.Strangelove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr.strangelove/32/6613_2.png) [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)\ **Post date:** [April 27, 2021, 2:30am UTC](https://boards.straightdope.com/t/time-dilation-and-neutron-stars/940748/17 "2021-04-27T02:30:01Z")
Plus our neutron star creatures can eat [nuclear pasta](https://en.wikipedia.org/wiki/Nuclear_pasta). ---
**Author:** ![MikeS](https://avatars.discourse-cdn.com/v4/letter/m/919ad9/32.png) [@MikeS](https://boards.straightdope.com/u/MikeS)\ **Post date:** [April 27, 2021, 12:09pm UTC](https://boards.straightdope.com/t/time-dilation-and-neutron-stars/940748/18 "2021-04-27T12:09:00Z")
It’s true that if the Sun was replaced today by a black hole of the same mass, the Earth would go on orbiting merrily in its path without being affected. But that’s only because we’re relatively far away from the Sun. In Newtonian gravity (pre-Einstein), the only limit on how closely you can orbit an object is the physical size of the object itself (i.e., don’t run into the thing.) If “point masses” existed, you could whip around them 1 mm away so long as you were going fast enough. At least, that’s what Newton thought. In Einstein’s GR, though, if you try to orbit a non-spinning compact object very closely, it turns out that there is distance called the [ISCO (innermost stable circular orbit)](https://en.wikipedia.org/wiki/Innermost_stable_circular_orbit). This orbital distance works out to be 3 times the size of the black hole itself. IIRC you end up with a time-dilation factor of √2 for a planet in such an orbit (though don’t quote me on that.) This wouldn’t be large enough to give you a time-dilation factor like that shown on the water planet in _Interstellar_. However, if you have a rotating black hole, it turns out that you can orbit it stably at a much closer radius—arbitrarily close to the event horizon, in fact. This in turn allows you to get arbitrarily large time dilation, though you have to get the black hole spinning stupidly fast to get the magnitude of the time dilation as large was shown in _Interstellar_. ---
**Author:** ![running\_coach](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/running_coach/32/15836_2.png) [@running\_coach](https://boards.straightdope.com/u/running_coach)\ **Post date:** [April 27, 2021, 12:16pm UTC](https://boards.straightdope.com/t/time-dilation-and-neutron-stars/940748/19 "2021-04-27T12:16:13Z")
> [@Babale](#): > > And IIRC that is why they gave the black hole a ludicrously high spin. I’ll see if I can dig up the article I’d previously read about it. - It’s not a black hole. It’s an ultra-dense Spaceball. ---
**Author:** ![CookingWithGas](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cookingwithgas/32/485_2.png) [@CookingWithGas](https://boards.straightdope.com/u/CookingWithGas)\ **Post date:** [April 27, 2021, 12:39pm UTC](https://boards.straightdope.com/t/time-dilation-and-neutron-stars/940748/20 "2021-04-27T12:39:29Z")
> [@MikeS](#): > > However, if you have a rotating black hole, it turns out that you can orbit it stably at a much closer radius I’m afraid to ask, because I may not understand the answer–but why does spinning matter for how close you can orbit it? [Next page](https://boards.straightdope.com/t/time-dilation-and-neutron-stars/940748.md?page=2)