In Anathem, I recall that the alien spacecraft was partitioned in such a way that the various incompatible variants of matter from the different worldlines was kept separated. I think this even included a description about liquid water being stored in different repositories.

However, the people from the different variants of Arbre/Earth were able to interact to some extent. Since they all were perspiring, how did they maintain the purity of their water supply? Humidity in the air would easily have mixed and, once mixed, been hard to filter & separate.

This may be less true with other breathable gasses as well.


Hydrogen and Oxygen are either identical or quite similar across Narratives, and bodies are shown to be adaptable with variant Oxygen, so it's highly likely that people could handle H2O from another Narrative with a little exposure.

"Do they have water? Oxygen?"

"Their hydrogen is identical to ours. Their oxygen is similar enough to give them water. We don't know whether we could breathe it. Carbon seems to be a little different. The metals and so on show greater divergence."

And we later learn that, yes, the oxygen is compatible:

She shrugged. "Hemoglobin is a classy molecule. Finely tuned to what it does - take oxygen from the lungs and get it to every cell in the body. If you give it oxygen that is only a little bit different from what it's used to, well, it still works - just not as well. It's like being at high altitude. You get short of breath, woozy, can't think straight."


"...but wait a second, Jules can get along just fine on Arbre air."

"You acclimatize. Your body responds by generating more red blood cells. After a week or two, you can handle it..."

As for other gases, the comment about Carbon and the metals might suggest that gases are more similar across Narratives than solid elements, but there's no data to support or disprove that theory.

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