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I'm reading "Neutron Star" in the collection The Best of Larry Niven (on archive). Before the story there is a blurb:

This won my first Hugo Award, and a lot of mail. There are folk out there who don't stop at reading a story: they continue to do research into it. It's most flattering.

As is, Schaeffer dies. See the collection Crashlander for the fix.

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I'm not sure I understand the last sentence of the blurb in context of the actual story. At the end of the story, Schaeffer is very much alive, albeit with some injuries. I can think of a couple of possible explanations:

  • People researching the story found that Schaeffer should have died according to the physics being described, so the collection has to do additional hand-waving.
  • Schaeffer's attempt to blackmail the puppeteers implicitly gets him killed.

What is the correct explanation?

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3 Answers 3

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It is your first guess. As people like to point out, the tidal forces during Shaeffers approach to the neutron star would not be surviveable.

The closest to the center of BVS-1 that Beowulf originally plans to get is 6.5 miles or about 10,000 meters, and Beowulf is about 2.1 meters tall (really!), while the ship is about 90 meters long. Putting all this information together, the tidal force at the ends of the ship is 700 million times stronger than Earth's gravity and Beowulf's feet would be feeling a force about 16 million times stronger than earth's even when Beowulf was at the center of the ship (unless he’s curled up into a ball, which he probably should be!).

Okay, I was right, but for the wrong reason, because I confused something fans said with the reason Niven actually accepted.

I keep meeting people who have done mathematical treatments of the problem raised in the short story “Neutron Star,” from which the collection derived its title. Alas and dammit, Shaeffer can’t survive. It turns out that his ship leaves the star spinning, and keeps the spin.

Niven, Larry. Tales of Known Space (S.251-252). Spectrum Literary Agency, Inc.. Kindle-Version.

So spin was the problem, not the gravitation gradient, but Shaeffer is still dead. Niven seemed always very proud of his hard science fiction bona fides and those were only bolstered by accepting scientific criticism.

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  • Presumably, as people like to point out to him
    – Valorum
    Oct 13, 2023 at 8:54
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    If it's just his thickness, the force will still be only 1.6 million gees
    – Andrew
    Oct 13, 2023 at 15:05
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    @Andrew,well, that will reduce the thickness even further before reaching equilibrium ;-) Oct 13, 2023 at 15:32
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    Actually, the force would be acting to pull him apart, so... reduction in thickness would not happen. Unless you're using the term to refer to his viscosity.
    – tsc_chazz
    Oct 13, 2023 at 18:23
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    @JRE That probably wouldn't be enough to save him. From the equations here: physics.stackexchange.com/a/631427/123208 & data from en.wikipedia.org/wiki/Ultimate_tensile_strength the tidal force at 28 km from the centre of a 1.4 solar mass neutron star is sufficient to disrupt a 0.2 metre long rod of bone in freefall. (It's still an excellent story, though).
    – PM 2Ring
    Oct 14, 2023 at 10:16
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There is an additional problem, that Niven acknowledged in the collection Tales of Known Space: In addition to "gravity gradients", tides also exert torques on nonspherical objects such as a long slender GP-#2 hull, and hence for the overwhelming majority of initial conditions, Skydiver leaves the neutron star spinning fast enough that its bridge is still experiencing millions of gees of "spin gravity". https://en.wikipedia.org/wiki/Neutron_Star_(short_story)#Notes

An additional effect that Niven did not discuss in the novella is that Skydiver would not simply align itself with its long axis pointing towards the neutron star, but would instead oscillate like a pendulum about that line (similar to the "libration" motion of the moon), with decreasing amplitude and increasing frequency until closest approach, while the reverse would occur on the way out, until at some point its motion would transition from libration to continuous rotation for most initial conditions. https://en.wikipedia.org/wiki/Libration

https://www.physics.brocku.ca/fun/NEWT3D/PDF/PENDULUM.PDF

(Granted, IIRC Niven did mention that Skydiver's autopilot was programmed to keep its long axis aligned with the neutron star --- but a savvy pilot like Schaeffer would probably have noticed that Skydiver's ACS jets and/or reaction-wheels were behaving in an abnormally active fashion in order to maintain that alignment...)

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    Hi, welcome to the site. You could improve this answer by editing it to include quotes of the actual statements from Niven that you alluded to. Oct 14, 2023 at 0:23
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    Speaking as the guy with the accepted answer, I think this should be the accepted answer since the spin from coming out of the trajectory is the actual reason Niven gives in his "Afterthoughts" to the Tales of Known Space collection that he thinks his story has a scientific mistake (my copy is a German translation, so I cannot add a quote myself). Oct 14, 2023 at 10:03
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    I have just posted a follow-up question about the fix in Crashlander (mentioned in the quote in the above question), and if you have any knowledge or insight into that, your input would be much appreciated... scifi.stackexchange.com/questions/279877/…
    – sdenham
    Oct 14, 2023 at 15:59
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In either Fleet of Worlds or Juggler of Worlds, Niven retcon's a scene where Nessus is tasked (with a crew of humans) with retrieving the original BVS-1 exploration ship (and it's crew of "brownish stains") after their "star dive". That retcon has the ship come out spinning ferociously, and they have to use differential torque of a magnetic "tractor beam" to slow the rotation by acting on the magnetic steel of the landing equipment in the ship's tail (and by implication, not acting on the less magnetic materials of the rest of the ship, hyperdrive, etc).


Of course, like most retcons, that raises a new problem : how the (ferromagnetic) ironmongery of the ship would interact with the steep magnetic gradients around a NS. That's beyond my pay grade.

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    Hi, welcome to SF&F. This is interesting, but is it the solution that Niven referred to in The Best of Larry Niven that was described in Crashlander?
    – DavidW
    Nov 16, 2023 at 0:03

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