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New poster here, so any feedback is appreciated.

In Project Hail Mary, it's stated that the Eridians don't know about radiation, and they are very susceptible to cancer because of it. However, on Earth, radiation doesn't just come from space, it comes from the ground, too.

How come the Eridians weren't exposed to ground radiation?

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I don't recall that this is specifically addressed in the novel. However, given that the book universe mostly overlaps with our own (apart from the Eridians, etc.!), we can probably make some assumptions about planetary surface environments in the book.

The main one is that the Earth may be very unusual (certainly within the solar system at least) in having deposits of radioactive substances that can literally be dug up and are active enough that relatively coarse physical effects can be observed (heat, "glow", effects on other substances and, most relevant to this question, damage to biological material) with relatively primitive technology. Whilst many other planets could have levels of radioactivity that are measurable (with modern technology) if they are not strong enough to have influenced biological life in any way then there is no specific reason why even an advanced species would have considered them - except as a scientific curiosity - even if they had observed them.

What is mentioned in the book is the extreme (relative to us) density of their atmosphere which would then completely insulate them from cosmic/space radiation.

I have no particular book source for this, but my impression is that whilst the Eridian technology was very advanced in some ways it seemed quite primitive in others and that, for example, their space technology was really kickstarted by the properties (and problem) of the Astrophage whereas the Human space technology already existed and was just enhanced to interstellar levels by the Astrophage. So it could be that they had no particular practical interest in nuclear physics so, again, would have no reason to suspect that radiation could be an issue.

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  • Thanks! Here's 25 rep for you.
    – Firedestroyer
    Commented Dec 9, 2021 at 14:01
  • @Firedestroyer - thank you! Welcome to the forum. Everyone seems very friendly so have a look round and join in if you find any questions that you know something about and can answer. In some ways I don't think my answer here was that good as it was a bit speculative and without sources from the book. I think a better example was my answer to this one: scifi.stackexchange.com/questions/250798/…
    – AdamT
    Commented Dec 9, 2021 at 14:16
  • The epa says that radioactive elements decaying into Radon and Thoron gas is the major source of background radiation exposure on Earth. So all we really need to assume is that the Eridian planet has some process which prevents this. Maybe the gases quickly move to a high altitude within the atmosphere due to its density.
    – Harabeck
    Commented Dec 9, 2021 at 16:14
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    And maybe the Eridians just never had the idea. In Anvil of Stars, Greg Bear speculated that alien civilizations normally develop technology in quite different directions, which makes contact between cultures interesting. Much earlier (1920), in This Simian World, Clarence Day conjectured how different a civilization of cat-men would be from our own. They would be fierce, haughty, poetic, he said; they would require much more individual space than humans, and city streets would be lapped clean at night.
    – Invisible Trihedron
    Commented Dec 9, 2021 at 18:34
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    Even among human cultures, it's possible to see "blind spots" in one civilization that are fully exploited by another. The Chinese invented gunpowder, but Europeans developed the idea to build cannon. The Chinese protect their health by wearing masks that many Americans reject despite being aware of germs. The early Mexicans invented the wheel and used it for toys; a working battery was constructed in Mesopotamia but electricity wasn't fully harnessed for thousands of years. The Greeks and Romans knew of many curves other than circles, but couldn't imagine that the planets moved in ellipses.
    – Invisible Trihedron
    Commented Dec 9, 2021 at 18:40

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