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A magician summons a person to the material world to be their servant. Their body is not made from true atoms per se, but is some kind of force projection.

In most ways though, they act as a person and experience the laws of physics as if they were a normal flesh and blood being. This includes eating, getting sick, excreting, and so forth.

Away from the main projection though, 'matter' that was once part of the host that leaves the body in the form of carbon dioxide, skin flakes, urine or otherwise will disappear on an 'atom' by 'atom' basis without releasing much in the way of energy with a half life of two weeks.

It is widely known (or believed) that after about ten years the human body will have fully replaced every cell within it. However, I have not been able to find out how much of the material that makes up the cells remains.

How many years will it take to ensure that when the magician tires of the projection and aims to dismiss it, it can reasonably be assumed that the projection will survive with their physical and mental facilities intact?

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    $\begingroup$ How do you exactly expect a science based answer to something like "not made of atom but force projection, but still eats and pees"? $\endgroup$ – L.Dutch - Reinstate Monica Aug 6 at 11:57
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    $\begingroup$ @L.Dutch he wants to know this "t is widely known (or believed) that after about ten years the human body will have fully replaced every cell within it. However, I have not been able to find out how much of the material that makes up the cells remains." which is entirely science based. $\endgroup$ – Display name Aug 6 at 11:59
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    $\begingroup$ So a very very very very very very slow teleporter but one that in first millisecond teleport the matrix of the person. Because you have a magician then I would say "how long you want". $\endgroup$ – SZCZERZO KŁY Aug 6 at 12:44
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    $\begingroup$ @SZCZERZOKŁY or, y'know, they could just ask it here in the context of their own story and world, and get perfectly reasonable answers. As appears to have happened. $\endgroup$ – Starfish Prime Aug 6 at 12:53
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    $\begingroup$ This summoned being wouldn't happen to be named "Theseus," would he? $\endgroup$ – Mason Wheeler Aug 7 at 20:47
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Your former projection will be in for a hard time, even if they've faithfully served their summoner for decades.

Why? The calcium in bone (and more so teeth, especially the enamel) is relatively permanent -- it doesn't get replaced rapidly or frequently. This is why, for instance, Strontium 90 in nuclear fallout is such a problem -- because it replaces calcium deposited in bones and teeth, and is very difficult to remove because those deposits are relatively permanent.

At the least, when the magician dismisses the summoning, the summoned servant will lose the enamel off his teeth, and his bones will become either extremely brittle or cartilaginous (and the connective tissue that's part of a bone is far from sufficient for bone-like rigidity). It's very likely he wouldn't survive the experience; compression of the spine would heavily damage the spinal cord and result in loss of breathing even if the cartilage framework of the ribs is enough to prevent complete collapse of the chest cavity.

Also worth checking the answer by @Confoundedbybeigefish in which he points out that some cells don't get replaced as frequently as others -- or possibly at all -- and they're extremely critical to life. From comments, parts of the eye are never replaced, though it probably doesn't matter much if they're blind, if they're also dead...

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    $\begingroup$ And don't forget that cartilage... At least broken bones can repair themselves, but cartilage once injured won't even mend itself. $\endgroup$ – AlexP Aug 6 at 13:23
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    $\begingroup$ There's a potentially weird and interesting (and unpleasant) secondary effect here... anyone who has spent any time eating magical food or breathing magical air risks being severely debilitated or killed outright if the conjurer dismisses eg. the summoned cow and field of corn that have been providing your carbs and protein of late, by exactly the same mechanism as above (albeit not always so graphic and destructive). $\endgroup$ – Starfish Prime Aug 6 at 13:27
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    $\begingroup$ Hey - you've got a fantastic tool for producing boneless chicken! $\endgroup$ – Carl Witthoft Aug 6 at 17:19
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    $\begingroup$ This is incorrect. Bone remodeling occurs quite frequently. The entire skeleton is replaced on average every 10 years in an adult human (10% per year). During the first year of life, the skeleton is 100% replaced. Osteoblasts and osteoclasts are the cells involved. The calcium does tend to be recycled, but a deficit of calcium would be recognized by the thyroid gland and excess calcium would be pulled from the blood if available. The question is if the signalling processes still work with the 'magic not-atoms' of calcium. I.e. would a deficit be detected and new calcium pulled in? $\endgroup$ – stix Aug 7 at 21:46
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    $\begingroup$ @stix: Slower than that; the 10% figure I found was overall, but it's accounting for ~25% of the bone being replaced at 28% per year, and the other ~75% being replaced at 4% per year. You'd want to use the lower replacement rate number, as it doesn't help much if 25% of your bones are replaced three times over if the other 75% of your bones lose over half their mass in one fell swoop. $\endgroup$ – ShadowRanger Aug 8 at 5:51
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Even if they survived Zeiss Ikon's way, there's not a hope of surviving this:

The neurons in the brain don't get replaced over this sort of time period. It is widely understood now that new neurons can grow, but when a nerve cell dies, it is gone for good. The nerve cells in your brain today have the same molecules of DNA that they were initially created with.

Other cells, different story, same problem: when a cell replicates its DNA by mitosis to replace old or dying cells, it unzips its DNA, and new nucleotides are synthesized to be the complimentary strand. Errors are fixed (a small percentage), then the strands are zipped up again - approximately half the atoms constituting the DNA in each daughter cell are from the original.

The mitochondrial DNA (the so-called power-houses of all cells except erythrocytes) would be similarly distributed between cells.

In conclusion:

The summoned creature’s cells would cease to function without their energy factories and the nucleus giving coherent instructions to the protein factories - probably about the same way as acute cyanide poisoning (seizures, cardiac arrest, apnea, coma and death), and probably as quick (a few seconds 'till the end).

Addendum:

A human lifetime would not be enough time for atomic replacement to occur that would enable survival. Of course, it might be possible to design a species that could withstand this treatment, but not within the scope of the question.

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    $\begingroup$ As far as I recall, mitochondria reproduce within the cells (even neurons), so would be replaced with "real" matter.. Nuclear DNA in neurons I can't say for sure. But if the neurons lose their nuclei or otherwise stop functioning, the rest doesn't matter, does it? $\endgroup$ – Zeiss Ikon Aug 6 at 13:33
  • $\begingroup$ @zeiss Correct. $\endgroup$ – SRM Aug 6 at 13:38
  • $\begingroup$ This is a very good addendum to the answer from Zeiss. This is one of those times when I wish admins could vote to merge answers so that both get the kudos and so people looking for the answer would find a complete text. $\endgroup$ – SRM Aug 6 at 13:50
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    $\begingroup$ "The neurons in the brain don't get replaced over this sort of time period" The cells themselves don't die and get replaced by new ones, but the cells replace all the molecules they're made up of with new molecules assembled from nutrients and respiration. The article here says "on the kinds of figures that are coming out now, it seems like the whole brain must get recycled about every other month." $\endgroup$ – Hypnosifl Aug 6 at 21:57
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    $\begingroup$ Ah, I see. Well, segments of DNA molecules are regularly getting replaced by copies made of new molecules due to processes like base excision repair discussed here, but I don't know how long you'd have to wait on average before every single atom of a DNA molecule in a neuron got replaced by these kinds of repair processes, maybe the average rate is slow enough that it'd be longer than a human lifespan. $\endgroup$ – Hypnosifl Aug 6 at 22:20
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I'm afraid it's even worse than the other answers say. They talk about what happens if molecules suddenly go missing, but we're talking about atoms here. You won't lose a whole DNA molecule, you'll lose some of the atoms contained in that molecule, and the remaining atoms are likely to become highly toxic free radicals. It's instant death no matter how much time has passed, because it only takes a tiny proportion of your atoms going missing for the toxicity to kill you.

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    $\begingroup$ We can make it worse. If it's been many years, some small portion of the atoms have undergone transmutation via cosmic rays. The radiation dose this low is harmless. But when the atoms are dismissed, you're also going to end up with some pieces of atoms all at once. It's worse. Radiation damage is not linear with dose. $\endgroup$ – Joshua Aug 7 at 15:55
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The answer to this depends on how whether or not your "force-body" detects that it has a problem.

Most of the answers have given cellular replacement rates and mentioned some cells don't get replaced, or that there would be problems with bones, etc...

However, this is all under normal homeostasis conditions. In most cases, there isn't a magic clock that tells your body to replace cells; your body replaces cells when it detects damage. The idea that the body completely replaces all of its cells on average every 7 years is mostly correct, but that's not due to a special clock; it's just on average how long cells last. The body doesn't replace parts that don't break down. Fast reproducing cells are in areas where they're likely to get damaged quickly and need constant replacement, slow reproducing cells are in areas where they don't get damaged. This is why your skin and digestive tract get replaced a lot; they're exposed to the outside world. Your brain isn't, so your neurons don't accumulate damage as quickly and thus don't need to be replaced.

But even cells that aren't replaced have to rebuild themselves and fix damaged parts. Entropy demands this. There are a lot of chemical reactions going on in a cell, and those reactions can damage the cellular machinery. Your neurons may not be replaced by new neurons, but the ones you have are constantly replacing and fixing their constituent parts (read: atoms and molecules).

All of this bodily restructuring is controlled through complex chemical signalling mechanisms. Cells detect whether or not they're damaged, and attempt repairs. If the cell is too damaged to repair itself, it decides to die, allowing itself to be replaced by a new cell. These are the processes of catabolism (breaking down) and anabolism (building up), and they occur in every part of the body without exception. Even your bones are constantly being broken down by osteoclasts and rebuilt by osteoblasts in response to signalling from the thyroid and parathyroid.

Now, the question is whether or not your cells can detect that the "force-atoms" aren't real and need to be replaced. This is actually where things can get very interesting from a story point of view.

If your force-atoms don't behave exactly like real atoms, there is a chance they won't break down at all, in which case your force-body will not be subject to the chemical stresses that drive homeostasis in the first place. Cells won't age and won't break down, and your force-person will be immortal. They also won't replace any atoms and will only rely on food/water for energy. At best you have a person full of ATP and not much else, maybe some real water.

Assuming your force-atoms are subject to the same kind of entropy and uncertainty as real atoms, we could reasonably expect that your force-person will replace itself at the same rate as a fully physical person. In this case, your force-body will very slowly replace parts of itself, but never a complete whole. This is because the parts that normally won't break down won't break down, and so will remain mostly composed of force-atoms. But, it is conceivable that on a long enough timescale, all of the atoms would be replaced. Unfortunately, this timescale is likely longer than an average human lifespan.

However, as I mentioned before, homeostasis is actively regulated. The body understands what's broken and what needs replacing, and will do whatever it must to maintain that balance. If your body detects that the force atoms aren't real, and thus "damage," it can ramp itself up and replace them rather rapidly. Cells will see their force atoms as not real and seek to replace them. Some cells will be replaced entirely, etc... Even neurons would eventually repair themselves in this case by replacing their machinery. This is essentially how wound healing works.

There is a problem with this though: a cell that has sustained irreparable damage will commit suicide through apoptosis, and a cell detecting that all of its atoms are completely fake may decide it is too damaged to repair.

In this case, your force-person dies a rather slow and painful death over several weeks in a manner that would resemble radiation poisoning. Not a fun way to go.

The key here, if you want your force person to completely replace their atoms, is to ensure that the cells detect damage that is repairable and attempt to do so, with them having a preference for real atoms and molecules over force-atoms. In this case, your force-person would replace themselves rather quickly, probably in less than a year, if they were well fed with a highly nutritious diet. Their force-bodies would also suffer from an insatiable hunger at all times as the body desperately signaled to increase nutrient intake in order to repair itself.

As an aside, there are also some deeper questions you'll want to think about. A human being isn't just all of the cells that make that human up, but rather a collection of human cells and commensal flora and fauna: a bacteriome. In fact, numbers-wise you are made up more of your bacteria than your actual human cells. These bacteria can't survive without you, nor you without them. They live in your gut and process certain foods into vitamins for you, they live on your skin and keep you protected from pathogens, they're even involved in determining your weight. They are you, and also aren't you. Is the bacteriome also made up of force-atoms, or are they real living bacteria?

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  • $\begingroup$ The bacteria would be also projections to begin with, yes. $\endgroup$ – Piomicron Aug 8 at 16:50
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While our cells die and new are created in their place we do not just excrete them - they are reused, especially molecules that are scarce as it would be highly inefficient to just throw them away.

After a cell dies, it allows itself to be caught and digested by a macrophage in its lysosome (a kind of acidic cell stomach). https://www.sciencedirect.com/science/article/pii/S0092867410001297

I dont have no idea what is the probability the digested cell parts are excreted but it does not make much of a sense to remove the DNA nucleotides that are recycled from body. And as Mike Scott said in his answer, the damages that would occur in DNA would be catastrophic.

So it seems unlikely even an almost complete replacement would occur over during a persons lifetime...

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Survival is impossible.

Yes, the body turns over the atoms in it, at different rates for different parts of the body. The problem is that this is not a first-in-first-out process.

Calcium has been singled out in other answers, lets look a bit more carefully. Suppose it has 100% turnover in 10 years. Does that mean all the original calcium is gone? No, it is a random process. You actually will have about half of the original calcium present. In 100 years you'll still have about .1%.

However, calcium isn't the biggest problem. Rather, the weak point is DNA. The turnover is very low and it's very sensitive to damage. You can temporarily survive this damage as the DNA isn't used directly, but you can't make new cells. We already have a partial model of what happens in this case: Look at what happens with a lethal radiation dose.

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