{"id":1810,"date":"2016-03-01T14:04:46","date_gmt":"2016-03-01T14:04:46","guid":{"rendered":"http:\/\/www.brainpreservation.org\/?p=1810"},"modified":"2016-03-01T14:04:46","modified_gmt":"2016-03-01T14:04:46","slug":"scott-aaronson-on-the-relevance-of-quantum-mechanics-to-brain-preservation-uploading-and-identity","status":"publish","type":"post","link":"https:\/\/www.brainpreservation.org\/zh\/scott-aaronson-on-the-relevance-of-quantum-mechanics-to-brain-preservation-uploading-and-identity\/","title":{"rendered":"Scott Aaronson \u8c08\u5230\u91cf\u5b50\u529b\u5b66\u4e0e\u8111\u90e8\u4fdd\u5b58\u3001\u4e0a\u4f20\u548c\u8eab\u4efd\u8bc6\u522b\u7684\u76f8\u5173\u6027"},"content":{"rendered":"

Biography<\/strong>: Scott Aaronson is\u00a0an Associate Professor of\u00a0Electrical Engineering and Computer Science<\/a>\u00a0at\u00a0MIT<\/a>. His research interests center around the capabilities and limits of quantum computers, and computational complexity theory more generally. He also has written about consciousness and personal identity and the relevance of quantum mechanics to these issues.<\/p>\n

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Michael Cerullo:<\/strong> Thanks for taking the time to talk with me. Given the recent advances in brain preservation, questions of personal identity are moving from merely academic to extremely practical questions. I want to focus on your ideas related to the relevance of quantum mechanics to consciousness and personal identity which are found in your paper \u201cGhost in the Quantum Turing Machine\u201d (<\/em>http:\/\/arxiv.org\/abs\/1306.0159<\/em><\/a>), your blog \u201cCould a Quantum Computer Have Subjective Experience?\u201d (<\/em>http:\/\/www.scottaaronson.com\/blog\/?p=1951<\/em><\/a>), and your book \u201cQuantum Computing since Democritus\u201d (<\/em>http:\/\/www.scottaaronson.com\/democritus\/)<\/em><\/a>.<\/em><\/p>\n

Before we get to your own speculations in this field I want to review some of the prior work of Roger Penrose and Stuart Hameroff (<\/em>http:\/\/www.quantumconsciousness.org\/content\/hameroff-penrose-review-orch-or-theory<\/em><\/a>). Let me try to summarize some of the criticism of their work (including some of your own critiques of their theory). Penrose and Hameroff abandon conventional wisdom in neuroscience (i.e. that neurons are the essential computational element in the brain) and instead posit that the microtubules (which conventional neuroscience tell us are involved in nucleic and cell division, organization of intracellular structure, and intracellular transport, as well as ciliary and flagellar motility) are an essential part of the computational structure of the brain. Specifically, they claim the microtubules are quantum computers that grant a person the ability to perform non-computable computations (and Penrose claims these kinds of computations are necessary for things like mathematical understanding). The main critiques of their theory are: it relies on future results in quantum gravity that don\u2019t exist; there is no empirical evidence that microtubules are relevant to the function of the brain; work in quantum decoherence also makes it extremely unlikely that the brain is a quatum computer; even if a brain could somehow compute non-computable functions it isn\u2019t clear what this has to do with consciousness.\u00a0 Would you say these are fair criticisms of their theory and are there any other criticisms you see as relevant?\u00a0<\/em><\/p>\n

Scott Aaronson: \u00a0<\/strong>Yes, I think all four of those are fair criticisms!\u00a0 I could add a fifth criticism: Penrose\u2019s case for the brain having non-computational abilities relies on an appeal to G\u00f6del\u2019s Incompleteness Theorem, to the idea that no machine working within a fixed formal system can prove the system\u2019s consistency, whereas a human can \u201cjust see\u201d that it\u2019s consistent.\u00a0 But like most mathematicians and computer scientists, I don\u2019t agree with that argument, because I think a machine could<\/em> show all the same external behavior as a human who \u201csees\u201d a formal system\u2019s consistency.\u00a0 So then, the argument devolves into one about indescribable inner experiences, of \u201cjust seeing\u201d (for example) that set theory is consistent. \u00a0But if we wanted to rest the case on indescribable inner experiences, then why not forget about G\u00f6del\u2019s Theorem, and just talk about less abstruse things like the experience of falling in love or tasting strawberries or whatever?<\/p>\n

Michael Cerullo: <\/strong>Your own work in this field attempts to show the relevance of quantum mechanics to consciousness without requiring us to abandon what we know from neuroscience. You also state that the motivation for some of your speculations is to avoid the seeming paradoxes (e.g. Boltzmann’s brains, copies, degrees of identity, multiple copies etc.) that would occur if personal identity could be copied as easy as any other type of information. Can you expand on this?<\/em><\/p>\n

Scott Aaronson:\u00a0<\/strong>To my mind, one of the central things that any account of consciousness needs to do, is to explain where your consciousness \u201cis\u201d in space, which physical objects are the locus of it.\u00a0 I mean, not just in ordinary life (where presumably we can all agree that your consciousness resides in your brain, and especially in your cerebral cortex\u2014though which parts<\/em> of your cerebral cortex?), but in all sorts of hypothetical situations that we can devise.\u00a0 What if we made a backup copy of all the information in your brain and ran it on a server somewhere?\u00a0 Knowing that, should you then expect there\u2019s a 50% chance that \u201cyou\u2019re\u201d the backup copy?\u00a0 Or are you and your backup copy somehow tethered together as a single consciousness, no matter how far apart in space you might be?\u00a0 Or are you tethered together for a while, but then become untethered when your experiences start to diverge?\u00a0 Does it matter if your backup copy is actually \u201crun,\u201d and what counts as running it?\u00a0 Would a simulation on pen and paper (a huge amount<\/em> of pen and paper, but no matter) suffice?\u00a0 What if the simulation of you was encrypted, and the only decryption key was stored in some other galaxy?\u00a0 Or, if the universe is infinite, should you assume that \u201cyour\u201d consciousness is spread across infinitely many physical entities, namely all the brains physically indistinguishable from yours\u2014including \u201cBoltzmann brains\u201d that arise purely by chance fluctuations?<\/p>\n

It\u2019s very easy to get disoriented, to feel a sense of vertigo, thinking about all these science-fiction puzzles.\u00a0 But before we tie ourselves in knots, perhaps one response is to step back and think hard about which of these scenarios are actually possible<\/em>, according to the laws of physics as we currently understand them.\u00a0 For example, could<\/em> you actually copy all the functionally-relevant information in a human brain, convert it to digital form, without an invasive scan that would kill the brain in the process?\u00a0 Well, the answer to that question hinges on how much information about a brain you think is \u201cfunctionally relevant.\u201d\u00a0 If you believe the brain has a \u201cclean digital abstraction layer\u201d containing all the information relevant to consciousness\u2014say, the neurons, their wiring diagram, the approximate synapse strengths, a few other things\u2014and that that layer \u201cnotices\u201d the underlying molecular layer at most as a thermal noise source, then presumably the answer is yes<\/em>, a sufficiently advanced civilization could upload your consciousness to a computer and thereafter make as many copies of it as it wanted.\u00a0 If, on the other hand, you believe that microscopic details of your brain\u2014e.g., the exact quantum state of some sodium-ion channel, which might later get amplified to macroscopic scale and influence whether a neuron fires, etc.\u2014are an important part of your personal identity, then the rules of quantum mechanics would generally rule out making a sufficiently precise copy of those details, so that some of these science-fiction scenarios couldn\u2019t even get off the ground.\u00a0 So, I don\u2019t have answers, but those are the sorts of questions that I\u2019ve tried to draw attention to, because I think progress on them might actually be possible.<\/p>\n

Michael Cerullo:<\/strong> Before I get into your thoughts on freebits and the arrow of time, I want to discuss the relevance of the quantum no-cloning theorem to identity. To remind our readers, the no-cloning theorem states that it is impossible to make an exact copy of any quantum state . In quantum computing the relevance of the no-cloning theorem is obvious: error correction based on copying quantum qubits is impossible. Now let\u2019s jump to the macroscopic scale. Information is copied with high fidelity all the time at the nanoscale level: nature does this every time DNA is copied during cell division and we do this whenever we copy files on a computer or burn pits onto a blue ray disk. The information in these systems can be completely described at the classical level, and of course this brings up the issues of the quantum measurement problem and how the classical world develops from the quantum world (which no one really understands). Neuroscience seems to tell us that identity (i.e. memory and personality) is encoded in the connections and strength of neural synapses which can be completely modeled with classical physics. Given this it would seem personal identity can be wholly described within classical physics and is more like the information in a blue-ray than a qubit, and thus the no-cloning isn’t relevant at this scale.\u00a0 Can you tell me why you disagree and how the no-cloning may be relevant to the brain, consciousness, or identity?<\/em><\/p>\n

Scott Aaronson:\u00a0<\/strong>As I said, I don\u2019t know.\u00a0 On the one hand, I find Penrose and Hameroff\u2019s speculations about quantum gravity effects in microtubules to be totally implausible.\u00a0 But on the other hand, even the most hardheaded neuroscientist is going to model action potentials in neurons using the Hodgkin-Huxley equations, which treat neural firings as partly stochastic events\u2014i.e., events that are influenced by molecular details that are treated as outside neuroscience\u2019s scope.\u00a0 And it\u2019s not even particularly controversial to say that this creates a causal path for quantum indeterminism to get chaotically amplified, and eventually influence (say) the course of a human decision.\u00a0 The question, of course, is whether any of that matters<\/em>.\u00a0 In my way of thinking, the question becomes: could an external observer, using far-future technology, decompose everything in your brain into (a) a \u201cdigital, classical layer\u201d that can be scanned and copied, and (b) a \u201cthermal noise layer\u201d that can\u2019t<\/em> be copied, but that can safely be ignored with no effect on your personal identity?\u00a0 So, I dunno: is it obvious to you that the answer is yes?<\/p>\n

Michael Cerullo: <\/strong>Now I want to discuss some of your thoughts about complexity, the arrow of time and freebits and their relation to identity. Rather than try to summarize your arguments for freebits and the arrow of time, I will refer our readers to your very readable paper \u201cThe Ghost in the Quantum Turing Machine\u201d and one of your blogs where you discuss these issues (<\/em>http:\/\/www.scottaaronson.com\/blog\/?p=1951<\/em><\/a>). \u00a0One of the limitations with computationalism is that no one quite understands what exactly it means to implement a computation. Many people agree there is something wrong with saying that a look up table that could pass a Turing test is conscious, even if this look up table is implemented in the real world. I share this intuition and you also mention your doubts about this possibility. \u00a0In your book \u201cQuantum Computing since Democritus\u201d you discuss this question and how it may be related to questions of computational complexity. To implement the Turing test look up table would be a problem with NP complexity. Hence having a look up table that could pass a Turing test doesn\u2019t really you help you make a program that can pass the Turing test in the real world. I can\u2019t help but be reminded of the Borges\u2019 Library of Babel here. Having the Library of Babel doesn\u2019t really give you any information since it would be easier to create it than search for it. Is this a fair summary of your current views?\u00a0 Any thoughts on how complexity and the arrow of time may be related to the question of implementing a computation?<\/em><\/p>\n

Scott Aaronson:\u00a0<\/strong>Well, the lookup table is sort of the extreme version of some of the thought experiments that we discussed earlier.\u00a0 If anything that passes a Turing Test is conscious, then what about a huge table that just stores your replies in every five-minute conversation I could possibly have with you?\u00a0 Would it even matter if anyone consulted<\/em> the table, or could it just sit there, silently bringing about your consciousness?\u00a0 (And for that matter, why does the lookup table even need to be physically built<\/em>?\u00a0 Why isn\u2019t its abstract existence, as a function mapping inputs to outputs, enough to bring about your consciousness?\u00a0 That\u2019s a slippery slope that Max Tegmark, for example, with his \u201cMathematical Universe Hypothesis,\u201d is happy to ride all the way to the bottom!)<\/p>\n

Now, some people point out that such a lookup table would require size that grows exponentially in the length of the conversation\u2014so in particular, it would very<\/em> quickly exceed the storage capacity of the observable universe.\u00a0 And some of them might go even further, and conjecture that any simulation of you that didn\u2019t<\/em> suffer such an exponential explosion would need to have memories, internal representations of concepts, etc. that might of course differ in detail from the way your brain organizes things, but would still be \u201cvaguely brain-like\u201d\u2014and that would therefore<\/em>, in their view, bring about consciousness for the same organizational reasons why your brain brings about consciousness (reasons that wouldn\u2019t apply to the lookup table).<\/p>\n

I still haven\u2019t figured out what I think about that position, but I do find it fascinating\u2014not only because of how it brings one of my favorite subjects (polynomial versus exponential complexity) into the discussion of consciousness, but also because of how it answers a philosophical thought experiment (would the giant lookup table be conscious, or not?) by questioning the experiment\u2019s premises<\/em>, by asking whether the lookup table, or anything like it, could exist in our universe.\u00a0 In that respect, it\u2019s analogous to what I tried to do in my \u201cGhost in the Quantum Turing Machine\u201d essay: namely, to take crazy philosophical thought experiments (in my case, involving perfect copies of you), but then ask different questions about them than the ones you\u2019re \u201csupposed\u201d to ask\u2014questions about whether our best current theories of physics, cosmology, computer science, and so forth predict the experiments can be done or not.<\/p>\n

Michael Cerullo: <\/strong>How about freebits? Do you think they have any relationship to implementing a computation?<\/em><\/p>\n

Scott Aaronson:\u00a0<\/strong>\u201cFreebits\u201d are just a label for whatever it is that you believe in, if you think the answer to my earlier question about copyability is \u201cno\u201d: that is, if you think that, even with arbitrarily advanced technology, it won\u2019t be possible to scan your brain accurately enough to make copies that are probabilistically indistinguishable from the original.\u00a0 Freebits are bits about the physical state of your brain (and ultimately, about your behavior) that the copying procedure would necessarily miss.<\/p>\n

To make myself clear: unlike in Penrose and Hameroff\u2019s model, freebits are not \u201coracles\u201d that let you solve uncomputable problems, or do anything else that defies a conventional physical understanding of the brain.\u00a0 So for example, even if I didn\u2019t know any of the freebits relevant to you, I see no reason at all why I couldn\u2019t build a second brain that was extremely similar to yours, that not only passed the Turing Test but fooled a lot of people into thinking it was you, that behaved similarly to you in most situations.\u00a0 But by hypothesis, the copy wouldn\u2019t behave like you in all<\/em> situations, and the differences could serve as a sort of empirical certificate that your consciousness hadn\u2019t been cleaved into two, or transferred from one physical substrate to another, or anything like that.\u00a0 A second consciousness might or might not have been brought into being.\u00a0 But at any rate, the \u201coriginal\u201d you would be inextricably bound up with microscopic, unclonable details of your brain state that aren\u2019t magical, don\u2019t give you any computational superpowers or anything like that, but are part of how we localize which physical entity we\u2019re talking about when we talk about \u201cyou.\u201d<\/p>\n

Michael Cerullo: <\/strong>In your paper \u201cThe Ghost in the Quantum Turing Machine\u201d you discuss how freebits may help to solve the problem of free will by preventing any perfect prediction of human behavior. In this paper you seem to be suggesting that free will is necessary for consciousness and therefore for any conception of personal identity. Can you expand on this?<\/em><\/p>\n

Scott Aaronson:\u00a0<\/strong>Look, I have no idea whether free will in the sense that interests me (that is, the sense of in-principle unpredictability) is necessary for consciousness.\u00a0 The one thing I\u2019m confident about is that, if it\u2019s not<\/em> necessary, then any account of consciousness will have to solve all sorts of thorny conceptual problems that it could otherwise avoid.\u00a0 For in that case, one and the same intelligent being\u2014that is, a being that responds to all possible stimuli in the same way\u2014could be copied promiscuously all over the universe and transferred to countless physical substrates: not only to digital electronics but to pen-and-paper, even giant lookup tables, etc.\u00a0 And we\u2019d then have to confront questions about which of those copies \u201cis you,\u201d what you should do if someone asks you to place a bet about \u201cwhich one you are,\u201d and so on.\u00a0 Any algorithm that took as input a description of the entire universe, and tried to locate the \u201cyou\u201d parts of it, would then have to be much more complicated!<\/p>\n

Michael Cerullo: <\/strong>In neurology, there are examples of syndromes where people seem to believe they have no free will or that they have control over actions that they clearly do not. Doesn\u2019t this suggest that free will is simply one more qualia, the qualia of feeling like we (whatever \u201cwe\u201d is, if you take something like Baars\u2019 Theater of Consciousness approach for example, it doesn\u2019t have to involve a homunculus) have control of our actions?\u00a0 <\/em><\/p>\n

Scott Aaronson:\u00a0<\/strong>To my way of thinking, free will is special because it\u2019s bound up with the predictability of your actions\u2014and in particular, with the question of whether it\u2019s possible to create a second entity that behaves indistinguishably from you, and which an empiricist like me would therefore have to say is<\/em> you, is a second copy or instantiation of you that inhabits the same world.\u00a0 I like that framing precisely because it\u2019s not<\/em> about your subjective feeling of freedom or lack of freedom: rather, we\u2019re asking an actual, bona fide question about the physical universe that could turn out one way or the other.<\/p>\n

You know, when I wrote an 85-page essay about these issues, I tried as hard as I could not once<\/em> to rely on introspection or \u201cwhat it feels like\u201d to make a choice, because that strikes me as just an obvious nonstarter.\u00a0 I mean, introspection can\u2019t even tell us vastly simpler, more uncontroversial things about how our minds work, like how our visual systems pick out triangles and squares, stuff like that.\u00a0 And given all the moral, philosophical, and theological issues with which free will is entangled, it seems obvious that people could \u201cfeel like\u201d they had free will (or say that they felt that way, or convince themselves they did) even if they didn\u2019t, and vice versa.<\/p>\n

By contrast, I want a notion of \u201cfree will\u201d that\u2019s clear and well-defined enough that someday, in principle, we could tell people that they had no free will even if they felt sure they had it, or conversely, tell them they had it even if they felt sure they didn\u2019t.\u00a0 And focusing on the in-principle predictability of our actions seems to me like a huge step in that direction.<\/p>\n

Michael Cerullo:<\/strong> Thanks for taking time to talk with me, I look forward to reading more of your work on these issues. <\/em><\/p>","protected":false},"excerpt":{"rendered":"

Biography: Scott Aaronson is\u00a0an Associate Professor of\u00a0Electrical Engineering and Computer Science\u00a0at\u00a0MIT. His research interests center around the capabilities and limits of quantum computers, and computational complexity theory more generally. He also has written about consciousness and personal identity and the relevance of quantum mechanics to these issues.   Michael Cerullo: Thanks for taking the time […]<\/p>\n","protected":false},"author":13,"featured_media":1814,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"coauthors":[32],"class_list":["post-1810","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-brain-preservation"],"_links":{"self":[{"href":"https:\/\/www.brainpreservation.org\/zh\/wp-json\/wp\/v2\/posts\/1810","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.brainpreservation.org\/zh\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.brainpreservation.org\/zh\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.brainpreservation.org\/zh\/wp-json\/wp\/v2\/users\/13"}],"replies":[{"embeddable":true,"href":"https:\/\/www.brainpreservation.org\/zh\/wp-json\/wp\/v2\/comments?post=1810"}],"version-history":[{"count":1,"href":"https:\/\/www.brainpreservation.org\/zh\/wp-json\/wp\/v2\/posts\/1810\/revisions"}],"predecessor-version":[{"id":1812,"href":"https:\/\/www.brainpreservation.org\/zh\/wp-json\/wp\/v2\/posts\/1810\/revisions\/1812"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.brainpreservation.org\/zh\/wp-json\/wp\/v2\/media\/1814"}],"wp:attachment":[{"href":"https:\/\/www.brainpreservation.org\/zh\/wp-json\/wp\/v2\/media?parent=1810"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.brainpreservation.org\/zh\/wp-json\/wp\/v2\/categories?post=1810"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.brainpreservation.org\/zh\/wp-json\/wp\/v2\/tags?post=1810"},{"taxonomy":"author","embeddable":true,"href":"https:\/\/www.brainpreservation.org\/zh\/wp-json\/wp\/v2\/coauthors?post=1810"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}