Written by Phillip Berrie
I am writing this in direct response to the poor treatment of gravity I saw recently in a published science fiction novel. Hopefully this article and later ones might prevent such similar treatment in the future.
For Christmas I was given a bookstore voucher and so I recently treated myself to a copy of Dan Simmon's 'Hyperion' (and no this is not a book review). The book has since redeemed itself many times over, but I almost didn't get past the first chapter when I baulked at how he handled the gravity onboard a kilometre long spaceship. The description given was that the gravity on board this ship was provided by gravitational singularities embedded in one end of the ship. These singularities supposedly generated a one-sixth standard gravity throughout the vessel.
I'm afraid it doesn't work that way.
On Earth, the direction we fondly refer to as 'down' is where unsupported things go when they are released. The Earth is so large that there is rarely any difference of opinion as to this direction in normal day-to-day activities. However, a little thought should reveal that this is not the case when the scale of the gravitational attractor is reduced to something far less than a kilometre in size as the following diagram should emphasise to the level of absurdity.
Simmons attempts to get round this problem by saying there are a number of singularities in the ship and whereas a suitable arrangement of these gravitational point sources might fix his problem with 'down' they compound the other errors in his gravitational 'technology'.
As the following high school level equation indicates;
Gravitation is a force whose strength varies in an inverse square relationship with the distance it acts over (r, standing for radius). This means the gravitational effect of one of Simmons' singularities at a thousand metres will be one-millionth the effect at 1 metre. There cannot be a common one-sixth standard gravity along his one kilometre long ship using gravitational point sources; the gravitational effect will vary drastically along its length.
Note: A kilometre of height difference on the surface of the Earth obviously does not have the same massive difference in gravitational effect. There are a number of reasons for this, but the main one is that there is little difference in the result in the above equation between 6,371 kilometres and 6,372 kilometres.
He also fails to take into account the reactive force of the sub-light drives of his ship. The drive thrust that is not cancelled out by the gravity of the singularities will give the ship an acceleration in the direction of its flight. This thrust on the superstructure of the ship will act very much like a uniform gravitational effect over its whole length and more than overpower the effect of the singularities at the front of the ship. However, this is only really works when the drives are on and interesting things happen when the ship begins to manoeuvre.
To give Simmons some credit, this book was first published in 1989. Back then, singularities were cutting-edge, high-energy Physics and something we know a lot more about today. However, even that realisation does not help understand why Simmons made these mistakes because, he assumes his readers know what a gravitational singularity is, and if one does know about them then his 'technology' looks very suspect, indeed.
So, as a writer, what should you take away from this?
Dealing with leading edge science and technology is likely to date your text very fast unless you're lucky enough to get it right. I suspect the trick is being suitably vague and try not to make the story hinge about one specific speculation that might be proven wrong in the near future.
Also, gravity is a real downer, if you'll excuse the pun. If you are going to set your stories outside the gravity well of a friendly planet. Gravity, the lack of it, or the replacement of it, is something that you must always keep in mind if you want to portray the environment correctly.
Next article I am going to look at some of the more realistic ways of giving your characters gravity.
References:
To find out more about Dan Simmons and his works
More on Newton's Theory of Gravitational Force
http://en.wikipedia.org/wiki/Gravitational_force
The Mean radius for the Earth taken from
http://en.wikipedia.org/wiki/Earth_radius
N.B. Please note that I although I use the Wikipedia (and WikiMedia Commons) a lot for references, this is for expediency and the familiarity of my readers. Anyone interested in further studies should make use of the references where available and understand that the Wikipedia is a co-operative project contributable to by anyone and must always be looked at in that light.
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