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After the (in)famous eruption of Mt. Vesuvius, Pompeii was buried under ash. In 1860, an archaeologist digging down found cavities where a body had been, and injected plaster.

I understand that that the bodies would decompose, but all of the matter should still be there, right? Conservation of matter, right? How can there be a hollow space where the body was?

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closed as off-topic by Jon Custer, JMac, Bill N, stafusa, ZeroTheHero May 12 at 19:56

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If this question can be reworded to fit the rules in the help center, please edit the question.

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    $\begingroup$ About 60% of the human body is water. $\endgroup$ – Samuel Weir May 4 at 2:41
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    $\begingroup$ I'm voting to close this question as off-topic because it isn't about physics. Earth Science might be better. $\endgroup$ – Jon Custer May 6 at 12:51
  • $\begingroup$ I'm voting to close and upvoting. :) $\endgroup$ – stafusa May 9 at 21:03
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This is really more about archaeology, biology, and/or chemistry than physics. Of course mass-energy is conserved. That's not the issue.

Compacted lava ash is porous. Liquids and maybe even microbes can squeeze through it.

Except for bones, everything in a human body is biodegradable and/or liquid. And bones can dissolve too, given enough time.

In other words, the body shaped spaces in Pompeii were not mysterious voids of vanished mass. They were filled with leftover gases, some bone fragments and maybe dessicated tissue, after the rest of the victim's decomposed mass drained and evaporated away.

Ok, that's probably close to the right answer. I'm not a Pompeii expert. An archaeologist or forensic MD would be able to explain it better.

In general, when any topic doesn't make sense, a curious person should ask "what knowledge am I missing about this subject area?" many times before considering "what if the laws of physics are wrong?"

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    $\begingroup$ One of my favorite mentors summarized the sentiment in your final paragraph by saying, "nothing resembles a new effect quite so much as a mistake." $\endgroup$ – rob May 4 at 21:18
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    $\begingroup$ I very much sympathize with your final paragraph as a general principle, but my reading of the OP is that it is intended to ask "what am I missing?" $\endgroup$ – WillO May 4 at 22:28
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The bodies didn't go anywhere. The ash cast of the bodies still contain the bones of the victims. The pyroclastic flows scorched the the lungs of the bodies and seriously burned the bodies.

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