Science Fiction & Fantasy Asked on April 14, 2021
In the short story Neutron Star by Larry Niven, the main character Beowulf Shaeffer’s face is sunburned somehow when his ship – built from a General Products starship hull – passes very fast and very close to a neutron star. These hulls were said to only allow visible light (and gravity) to penetrate (edit: at least that’s how I remember it). I think there is something about blueshifting needed to explain the sunburn, but if so, is the light shifted after it passes through the window? How is the physics behind the sunburn described?
edit: I should clarify that I’m interested primarily in the explanation given in the story itself. If there is any further elaboration in other stories within the series, that would be also interesting.
The first mention of light being able to penetrate a GP hull says this.
Nothing, but nothing, can get through a General Products Hull. No kind of electromagnetic energy except visible light.
A little later there is a small, but significant, expansion.
No such force could penetrate a General Products hull. Neither could heat, except in special bands of radiated light, bands visible to at least one of the puppeteers' alien customers.
It's not stated explicitly, but this would mean that if one of the puppeteers' clients can see beyond violet that ultraviolet would be allowed to go through a GP hull.
Then at several points in the story mention is made of starlight turning to blue.
Were the stars turning blue?
The stars were fiercely blue, [...]
Then at the end Beowulf states he "got a bad sunburn from exposure to starlight". Normally for a bad sunburn you need high-intensity UV but Beowulf is an albino.
To be honest, I think Niven made a mistake because Beowulf, as a spaceship pilot, takes "tannin pills" to counteract his albinism.
(Edit: I used the paperback version of 'Crashlander' as the source.)
Correct answer by user45485 on April 14, 2021
According to larryniven.net, General Products hulls are transparent to visible light and UV rays.
Answered by Ginasius on April 14, 2021
According to the actual story itself, as it originally appeared in If, October 1966, it was just visible light. You can read the whole story at the Internet Archive. The following quotation is from pages 11-12:
"Two humans named Peter Laskin and Sonya Laskin wished to use the ship. They intended to come within one mile of the surface in a hyperbolic orbit. At some point during their trip, an unknown force apparently reached through the hull to do this to the landing shocks. The unknown force also seems to have killed the pilots."
"But that's impossible. Isn't it?"
"You see the point. Come with me." The puppeteer trotted toward the bow.
I saw the point, all right. Nothing, but nothing can get through a General Products hull. No kind of electromagnetic energy except visible light. No kind of matter, from the smallest subatomic particle to the fastest meteor. That's what the company's advertisements claim, and the guarantee backs them up. I've never doubted it, and I've never heard of a General Products hull being damaged by a weapon or by anything else.
P.S. The clarification pointed out in Hans's answer, that "visible" does not necessarily mean "visible to Earthmen", can be found on p. 16, column 2 of the original magazine publication.
Answered by user14111 on April 14, 2021
If you came within -one mile- of a neutron star (and survived), I would imagine that gravitational lensing of the ambient starlight would produce a very high intensity light beam in your immediate vicinity. Sunburn? Oh, yeah!
Answered by PMar on April 14, 2021
Although I haven't read the book, I'll bring my solid state physics training to bear on this question. When the intensity of the EM field -- even in the visible spectrum -- is high enough, there will be some nonlinear interactions between the field and the light is passing through. One consequence of this nonlinearity is that it becomes possible for two lower energy photons to be converted into one higher energy photon, with the crystal acting as a medium to help conserve linear momentum and total energy. The early versions of green laser pointers worked on this very principle where two IR photons interacted with a nonlinear "frequency-doubling" crystal to get green photons out.
Answered by Appolonius27 on April 14, 2021
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