Mission of Gravity Q1: Do you like Hard Sci-Fi?


Mission of Gravity is a classic hard sci-fi novel. Generally speaking, the science is real and researched and calculated. (I recall seeing a later edition of the book fixed some of the gravity figures.) Notably, this planet was imagined from a real-world discovery: a (later found to be incorrect) wobble of a star, 61 Cygni: What would a planet with a mass of 16 Jupiters look like? And thus, the world of Mesklin.

So, do you like hard scifi? What does that mean to you? What else have you read that meets this definition?


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    edited April 2019

    I think of myself as someone who likes hard science fiction, but I'm not entirely sure. When it comes to Mission of Gravity, I did like the fact that the whole book isn't about plot or character- it's about physics! It's a change...but it's going to be quite a while before I'll want to read something like that again.

    Other authors writing books meeting the hard science fiction definition...

    (*) Much of Asimov's output (though I'd argue not all, even in science fiction) is hard SF. And Asimov was a fascination throughout my teens. I need to look back as a 40 something to see if there's anything there for me these days. Arthur C. Clarke's work is also hard SF, but I've not read nearly as much of him as I have Asimov.

    (*) Alistair Reynolds. Reynolds _can_ be extremely good, and he's one of the few authors who takes the speed of light seriously (even Asimov and Clements casually allow FTL travel when it suits).

    (*) Charles Stross. Most of his output apart from the Laundry novels and the Merchant Princes is hard science fiction. And I like some Charles Stross stuff, though not all.

    (*) Andy Weir's two books, The Martian and Artemis, are undeniably hard science fiction.

    (*) Oh, also Kim Stanley Robinson's Mars trilogy is another exemplar of the genre.

    (*) And finally we should count previous book club picks Spin and The Forever War as hard SF. Sure, Spin in particular has an odd set-up, but it's not really any more extreme than that in Mission of Gravity when it comes down to it.

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    In general I enjoy hard sf, though this book really felt like it was written by an engineer As a thought exercise about solving a matter of physics, and I find that a little dull. There was very little human condition here, unlike most of the other authors Paul listed.
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    Generally yes, but the problem with hard sf is that it encourages you to check it out, so you'd better be right. I went down something of a rabbit hole about gravity on the surface of oblate spheroids, and think that Clement vastly overstated the ratio of gravity at the poles vs equator. His figures vary from 3g at the equator to well over 600 at the poles - a ratio of over 200. Now, the calculation is non-trivial, and involves either numerical approximation or some fearful integrals, but the chart at this page https://physics.stackexchange.com/questions/144914/distribution-of-gravitational-force-on-a-non-rotating-oblate-spheroid
    shows that even for a very oblate object, the ratio is only about 1/0.8 = 1.25. Basically, although the pole is closer to the centre, there is less mass between you and that centre. You can argue for some centrifugal effect from the rotation, but not, I think, anywhere near as much as he says.

    There are indeed some fascinating effects on an extreme body, such as the gravitational pull not being perpendicular to the surface (see eg
    figure 3a) but I don't think such an extreme gravity profile is one of them.

    But my main disappointment about the book was not the calculations (I can suspend disbelief with that quite easily), but with the fact that we never really seemed to get to know the Mesklins, and in particular Mesklin women and children (I am, of course, assuming that both exist).

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    Another curiosity I found out - about Earth, but it would apply to pretty much any planet - is that rivers near the equator flow uphill. This is an effect of the component of net gravity due to rotation, meaning that the surfaces of equal gravity don't quite do what you think. THe source of the Mississippi is slightly closer to the Earth's centre than the outflow into the sea. Indeed, sea level at the Equator is 21.36 KM higher than at the poles. There is a nice study of "what would Earth's oceans look like if the Earth were to stop rotating" at

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    I love hard SF. The game I am currently designing is very much hard SF. I also love other flavors of SF just as much.

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