Just an enthusiastic amateur who’s done a lot of reading. If you’re interested in hearing a more informed version of the pro-cryonics argument (and seeing some of the data) I recommend the following links:
You might be interested in Aaronson’s proposed theory for why it might be physically impossible to copy a human brain. He outlined it in “The Ghost in the Quantum Turing Machine”: http://arxiv.org/abs/1306.0159
In that essay he discusses a falsifiable theory of the brain that, if true, would mean brain states are un-copyable. So Yudkowsky’s counter-argument may be a little too strong: it is indeed consistent with modern physics for brain simulation to be impossible.
Yudkowsky’s counter-argument is a counter-argument to a straw man, since I don’t think anybody ever argued in modern times that personal identity is linked to a specific set of individual atoms. Everybody knows that atoms in the brain are constantly replaced.
If I understand correctly, long lived and highly metabolically active cells like neurons still replace most, if not all, of their atoms during their lifetime, since metabolism and environmental radiation cause chemical damage which needs to be repaired in order to keep the cell functional.
There’s actually been some cool studies on DNA extracted from brain tissue from people born before the first nuclear tests...
DNA is turned over for the most part during DNA replication. Neurons are terminally differentiated and do not divide, and thus their DNA is more or less frozen in place even as other molecules turn over (barring small repair events). People born before the first nuclear tests have neurons bearing a different carbon isotope ratio in their DNA than people born afterwards, and this was used in a study to determine the rate over a human lifetime of new neurogenesis versus nerve cells that stick with you for your whole life. Turns out most neurons stick around but in particular regions like your hippocampus there is a good deal of turnover of cells, with only about two thirds of the DNA there with you from birth:
The claim isn’t that the cells are constantly replaced, but that the atoms are; see e.g. this blog post as an example of the claim being made. [EDITED to add:] More specifically, an example where the claim is made and “new cells” and “new atoms” are explicitly distinguished.
and there are some pro and contra comments in there about atoms and molecules of the nerve cells.
Probably I need a lot more reading on this subject , txs for the guidance.
Just an enthusiastic amateur who’s done a lot of reading. If you’re interested in hearing a more informed version of the pro-cryonics argument (and seeing some of the data) I recommend the following links:
On ischemic damage and the no-reflow phenomenon: http://www.benbest.com/cryonics/ischemia.html
Alcor’s research on how much data is preserved by their methods: http://www.alcor.org/Library/html/braincryopreservation1.html http://www.alcor.org/Library/html/newtechnology.html http://www.alcor.org/Library/html/CryopreservationAndFracturing.html
Yudkowsky’s counter-argument to the philosophical issue of copies vs. “really you”: http://lesswrong.com/lw/r9/quantum_mechanics_and_personal_identity/
You might be interested in Aaronson’s proposed theory for why it might be physically impossible to copy a human brain. He outlined it in “The Ghost in the Quantum Turing Machine”: http://arxiv.org/abs/1306.0159
In that essay he discusses a falsifiable theory of the brain that, if true, would mean brain states are un-copyable. So Yudkowsky’s counter-argument may be a little too strong: it is indeed consistent with modern physics for brain simulation to be impossible.
Yudkowsky’s counter-argument is a counter-argument to a straw man, since I don’t think anybody ever argued in modern times that personal identity is linked to a specific set of individual atoms. Everybody knows that atoms in the brain are constantly replaced.
I don’t know if this is true.
http://askanaturalist.com/do-we-replace-our-cells-every-7-or-10-years/ http://rebrn.com/re/theseus-body-is-there-any-part-of-a-human-that-is-cellularly-or-873979/ http://www.theguardian.com/science/neurophilosophy/2012/feb/23/brain-new-cells-adult-neurogenesis All 3 links suggest the opposite.
Can You provide a source for this claim?
BR
If I understand correctly, long lived and highly metabolically active cells like neurons still replace most, if not all, of their atoms during their lifetime, since metabolism and environmental radiation cause chemical damage which needs to be repaired in order to keep the cell functional.
There’s actually been some cool studies on DNA extracted from brain tissue from people born before the first nuclear tests...
DNA is turned over for the most part during DNA replication. Neurons are terminally differentiated and do not divide, and thus their DNA is more or less frozen in place even as other molecules turn over (barring small repair events). People born before the first nuclear tests have neurons bearing a different carbon isotope ratio in their DNA than people born afterwards, and this was used in a study to determine the rate over a human lifetime of new neurogenesis versus nerve cells that stick with you for your whole life. Turns out most neurons stick around but in particular regions like your hippocampus there is a good deal of turnover of cells, with only about two thirds of the DNA there with you from birth:
http://www.physicscentral.com/explore/action/images/Neuron-by-age.jpg
The turnover of DNA molecules doesn’t really make any difference, just something fun that lets you track cells incidentally.
Nice information!
The claim isn’t that the cells are constantly replaced, but that the atoms are; see e.g. this blog post as an example of the claim being made. [EDITED to add:] More specifically, an example where the claim is made and “new cells” and “new atoms” are explicitly distinguished.
I have found this reddit discussion:
https://www.reddit.com/r/askscience/comments/1q16hw/im_32_is_there_a_single_cell_or_even_molecule/
and there are some pro and contra comments in there about atoms and molecules of the nerve cells. Probably I need a lot more reading on this subject , txs for the guidance.
BR