I've just finished the original Ringworld, but I'm slightly confused by the ending. Specifically, Louis Wu explains how

he guessed that the Fist-of-God mountain was created by an external impact.

Louis explains to Speaker

"How did I know? I’ve been telling you that. Didn’t I mention the landscape? … That was the clincher. All the peaks of foundation material showing through the rock, and the fall of civilization only fifteen hundred years old! It was because those two asteroid punctures had fouled up the wind patterns. Do you realize that most of the traveling we did was between those two punctures?"

What does he mean by this? How did he work it out?

(No spoilers from other books in the series, please, as I haven't read them yet. This book was apparently meant to be a standalone novel, so direct reference to this should suffice.)

Also, related,

are the two punctures he refers to the Fist-of-God and the smaller puncture that created the vertical hurricane? Wouldn't the latter cause all the air to leak out of the Ringworld?

3 Answers 3


There is ample evidence that the Ringworld is very old (millions of years); the evidence includes, for example, the level of divergence of the humanoids populating the Ringworld from Earthly humanity. However, there is also evidence of decay that cannot have been going on for nearly that long. Louis cites two specific elements of the decay that seem to be relatively recent:

All the peaks of foundation material showing through the rock...

Along their voyage, the characters observe a number of locations where the underlying scrith that makes up the backbone of the Ringworld has been exposed by erosion. Louis knows enough about erosive geology to recognize the the erosion patterns he sees are relatively recent. If they had been proceeding at their present pace for the entire lifetime of the Ringworld, then most of the soil would have been gone from the entire structure.

... and the fall of civilization only fifteen hundred years old!

There had been an advanced civilization of the Ringworld, but it had collapsed—and quite recently. They know that because a fair amount of technology (where it possessed an autonomous power source) is intact and functioning. Again, it would be very peculiar if the Ringworld had been functioning for millions of years, but it just coincidentally happened to have had a major disaster, leading to the collapse of an advanced civilization, only thousands of years ago.

These things suggest that something relatively recent (only thousands of years ago) upset the ecological balance on the part of the Ringworld the characters were exploring. Louis concludes that it was probably the presence of the two holes in the scrith (which might have been caused by a single event with multiple impacts) are responsible for the disturbance.

The fact is that a substantial amount of air is indeed leaking out of at least one of the holes (the one with the eye storm above it). That is producing the racing winds that have started wearing the soil off the surface of the scrith. The amounts of atmosphere loss involved could not be sustained indefinitely. Over the lifetime of the Ringworld, the losses would be ecologically catastrophic; this is another piece of evidence that the damage is relatively recent. However, one of the key points about the Ringworld is how vast it is; the effects of the lost air are not going to be felt for a long time.

Regarding Fist-Of-God Mountain, my recollection is actually that it is so large that there is not significant air loss through the hole in its center. Remember that at the edges of the Ringworld, the air is only held in place by tall walls. The impact mountain is, I believe, actually taller than the side walls, so air losses up its slopes are minimal.

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    Regarding its height: At one point, when Louis is thinking through his mental reconstruction of how Fist-of-God must be a hollow cone created by a fairly recent impact of a huge rock coming straight up from "beneath" the Ringworld, where the automated defenses couldn't blast it first, he thinks: The natives could be thankful that the Ring floor had deformed as much as it did. The hole was easily big enough to let all the air out of the Ringworld; but it was a thousand miles too high . . .
    – Lorendiac
    Apr 22, 2018 at 2:07
  • Great answer (+1). One point from the quote that I still don't understand is "Do you realize that most of the traveling we did was between those two punctures?" I felt that this was key, but I didn't understand it. Regarding air losses, it's hard to envisage the time scales, but Teela was supposedly marooned in order to protect form the core explosion in 20,000 years time. I would have thought that the air leak would be a major issue over that scale. (As you suggest, the Fist-of-God mountain's peak is above the atmosphere, so it's not a problem for air losses.)
    – Sparhawk
    Apr 22, 2018 at 2:32
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    @Sparhawk The subject of "how to seal punctures in the Ring floor" is examined in detail in some of the sequels to the original Ringworld novel. I won't be specific, because I don't want to give spoilers for those books, but it's quite possible that Teela's luck, at the end of Ringworld, was muttering to itself: "The 'eye storm puncture' will be sealed shut long before loss of air becomes a serious threat -- so I'm going to concentrate on other large-scale problems, instead!"
    – Lorendiac
    Apr 22, 2018 at 2:52
  • @Lorendiac Ah okay, got it. Thank you for the answer and also for not answering too much! (I'll still wait for the response to the first part of my comment.)
    – Sparhawk
    Apr 22, 2018 at 3:30
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    @DavidTonhofer Given the spontaneous work people did showing the Ringworld was unstable, I'm actually a little sad that nobody has worked out the erosive wind pattern effects in detail.
    – Buzz
    Apr 22, 2018 at 21:23

The key piece of information was the view from the map room the expedition discovered. The room displayed tapes from telescopes that offered an aerial view of the ringworld in the past. Fist-of-God mountain was not on the tapes, so the huge mountain must have appeared long after the ringworld was constructed and populated. There are no plate tectonics on the ringworld, which left no other explanation for the jagged caldera than some kind of impact.


The previous answers cover most of the questions @Sparhawk asked, but I'll elaborate on this:

"Do you realize that most of the traveling we did was between those two punctures?"

This is simply Louis responding again to the massive scale of Ringworld. They've traveled a distance sufficient to circumnavigate a normal world - not much by space standards but a truly remarkable distance on/near a surface - yet they haven't surveyed the full scope of the Ring - they've just traveled in the vicinity of two features (the punctures) that would seem to be very near neighbors on a map of the Ring. As happened other times in the story, the scale of the Ring has made an impression on Louis and he's trying to share his amazement.

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