Uncial asked:
I have a question about Craig Skinner’s recent reply to a question about teleportation. I noticed repeated use of the idea of an exact molecular copy of my body.
Thinking about how this might work, it occurred to me that (a) there are so many different velocities going on simultaneously, wouldn’t it cause problems with a half, a third, a quarter, an eighth etc motion being recorded? (b) if on the other hand the time slice is so small as to include them all, the result would surely be a motionless image? (c) but if this is true, how can the copy restart the motion without some information on the direction of every molecule? (d) how could the copy be alive?
It seems to me that at the instant of taking the scan, a lot of information needed to make another living body is just not there. Or am I missing something?
Answer by Craig Skinner
No, you’re not missing something. Contrariwise, you’ve put your finger on something important. In these thought experiments, we talk glibly about scanning/ reconstruction with little thought as to whether it could ever actually be done. It may be that the idea is no more workable than the 19th century fiction of sewing together body parts and animating the whole thing with bolts of electricity.
Consider first how a human is naturally made.
It requires:
* information specifying the form
* assembly of matter into the specified form
Information: this is coded in the DNA sequence (genome) of the starting cell (fertilized egg, zygote). It is transcribed into a similar RNA sequence which is then translated by ribosomes into amino acids (translation from Nucleotidian into Aminoacidean) which join up to make proteins. These proteins provide cell structure and function (enzymes).
Assembly: this happens by growth/ development. The original cell repeatedly divides producing different cell lines expressing different bits of the genome, helped along by environmental cues, positional information, chemical gradients and cell-to-cell signals.
In our scan-and-build fantasy, instead of growing a human from an existing living cell, we seek to capture the information as a database obtained by scanning a living adult human and then assemble a duplicate by some nanotech tour-de-force whereby we build the human, molecule by molecule, using the database information.
Let’s consider each of the two steps.
Information: as your question suggests, no scan could capture the exact location/ momentum of all moving parts (the uncertainty principle disallows this for even one electron). But this wouldn’t be necessary. After all I continuously exchange molecules with the environment so that my exact molecular constitution changes second by second whilst I remain me. So, there is redundancy in the information, which gives us some leeway. However, what would be necessary is exact information for every one of my trillions of cells as to structure of DNA, RNA, ribosomes, proteins including enzymes, chemical messengers, neurotransmitters, cell surface markers and chaperone molecules. Otherwise cells couldn’t function, either in themselves, or cooperatively as a living organism. I doubt this could ever be done. But let’s say it could so that we can consider step two.
Assembly: we have the software (the scan database in our computer). We have the matter to build the hardware (wetware) in vats of the necessary chemicals. But the software and the chemicals are inert. How can we make them interact so as to assemble a human form. If we had some fancy nanotechnology capable of picking up the right molecules and placing them one by one from the soles of the feet upwards say, what would stop them falling in a heap long before a body was made. And, as you suggest, since the database is a static snapshot, how could the right motion be imparted to the molecules of the new body so that we end up with a living breathing human rather than a corpse.
I suspect the only way to make a human is to start with the form in potential i.e. a zygote, or maybe another suitable human cell, and, by growth/ development, in-form dumb matter to make the form actual i.e. a human being. Aristotle said all this a long time ago (but then messed it up by suggesting some lifeforms arise spontaneously from decaying matter, an erroneous notion that persisted into the 19th century).
Ask a Philosopher 
As far as I know, Emil du Bois-Reymond was the first to suggest this form of exact personal duplication in a discussion of a similar thought experiment by Leibniz:
“Imagine all the atoms of which Caesar consisted at any given moment, say, as he stood at the Rubicon, to be brought together by mechanical artistry, each in its own place and possessed of its own velocity in its proper direction. In our view Caesar would then be restored mentally as well as bodily. This artificial Caesar would have the same sensations, ambitions, and ideas as his prototype on the Rubicon, and would share the same memories, inherited and acquired abilities, and so forth. Suppose several artificial figures of the same model to be simultaneously formed out of a like number of other atoms of carbon, hydrogen, etc. What would be the difference between the new Caesar and his duplicate, beyond the differences in the places where they were formed? But the mind imagined by Leibniz, after fashioning the new Caesar and his many Sosiae, could never understand how the atoms he had arranged and set into motion could lead to consciousness.”
—“Über die Grenzen des Naturerkennens. In der zweiten allgemeinen Sitzung der 45. Versammlung Deutscher Naturforscher und Ärzte zu Leipzig am 14. August 1872 gehaltener Vortrag,” in Reden von Emil du Bois-Reymond, ed. Estelle du Bois-Reymond, 2nd edn., 2 vols. (Leipzig: Veit, 1912), 1: 441-473, on 462-463.
Most likely du Bois-Reymond was alluding to Heinrich von Kleist’s version of Amphitryon (1807), in which the hapless Sosia is tricked and thrashed by his divine Doppelgänger Mercury. He may also have been alluding to Vico’s discussion of the play in an essay on truth and consciousness. Giambattista Vico, “On the Ancient Wisdom of the Italians Taken from the Origins of the Latin Language,” Selected Writings, tr. Leon Pompa (Cambridge; New York: Cambridge University, 1982), 49-78, 56-59. Gustav Theodor Fechner discussed a similar Doppelgänger in Elemente der Psychophysik, 2 (Leipzig: Breitkopf and Hartel, 1860), 2: 536-537, cited in Anne Harrington, Medicine, Mind, and the Double Brain: A Study in Nineteenth-Century Thought (Princeton: Princeton University, 1987), 123-124. The theme of duplicate people was picked up later by Stansław Lem in “Solaris.”
Thanks for that. I had vaguely heard of the thought experiment about Caesar’s atoms, but now I know it originates with Leibniz and du Bois-Reymond. Despite being a physician, I hadn’t heard of the latter, although I see he was one of the fathers of electrophysiology, as well as doctor and philosopher. The 1872 reference you give is available to read from The Online Books Page, so that I could see the original text about “der neue Caesar und seine Doppelgänger”