Thursday, October 29, 2015

Wow, This Amazing Puzzle Will Reveal How Stupid You Are! (Maybe)

You know the Wason selection task. You know all about Linda the bank teller and the conjunction fallacy. You're smart. You'd never fall for those things now! You know it's not more likely that Linda is a bank teller who is active in the feminist movement than that Linda is a bank teller. You know to flip the Wason card that would break the rule rather than the one that would confirm it. Yes, of course!

Here's one I learned in junior high school, which I've never seen studied. I don't know the original source. (If you do, let me know!) Maybe it will be fresh to you. Over the years, when I've presented it orally, I've found that even people with PhDs in philosophy often struggle, though really it's very simple.

A man is looking at a picture. He says,
"Brothers and sons, I have none,
but this person's father is my father's son."
Question: Who is in the picture?

If you think you know the answer, write it down. I don't want any squirreling around about what you had really been thinking!

After you've written down your guess, click through to this post on my Underblog for the answer and discussion.

[image adapted from here]

Thursday, October 22, 2015

The Ends of Philosophy

a guest post by Regina Rini

I am sitting with a philosopher in the garden; he says again and again “I know that’s a tree”, pointing to a tree that is near us. Someone else arrives and hears this, and I tell him: “This fellow isn’t insane. We are only doing philosophy.” -Ludwig Wittgenstein, On Certainty

The word ‘end’ is usefully ambiguous in the following question: ‘What is the end of philosophy?’ This question could be asking about the goal of philosophy. What is philosophy trying to do? Or it might be asking about where philosophy ends up. What is philosophy’s final resting place? In this post I am asking – and answering – both questions at the same time.

Most philosophers will tell you that truth is their goal. They want to know the truth about Knowledge or Existence or Justice. I’m sure this is how they sincerely experience it – but I conjecture that ‘truth’ is only an instrumental goal. What these philosophers really want, I suspect, is certainty. They want to hold aspects of the world finally fixed in their minds, to make it the case that they cannot be wrong, at least about certain things. In service of this aim, they will jettison areas of inquiry about which certainty seems impossible. Hence, their category of the philosophical excludes the empirical, the accidental, and the historically contingent. What is left are the necessary truths – those that can be known to need to be true.

My conjecture fits a dominant thread in western philosophy. What was Descartes doing, after all, other than paring his thoughts back to that which could not be doubted, and then building forward only on foundations of certainty? What was positivism, but an attempt to secure certainty for philosophy by designating as ‘nonsense’ that which could not be verified? And what is the contemporary project of philosophical analysis – with its insistent investigation of proxy concepts amenable to enumerated necessary and sufficient conditions – other than a flight from uncertain actualities?

Absurdity lurks not far below certainty. We conjure thought experiments in which we have stipulated certainty about the laws of nature or human motivation, and we say that this is the real test of a philosophical concept, even as we struggle to apply that same finely sculpted concept to the unstipulated world. We carve nature at its joints, then display the bleached bones in positions they never naturally took. A protestor comes to our class from the streets of Ferguson, the smell of tear gas on her clothes, seeking guidance of which we apologetically demur; this is a seminar on ideal theory, and she is asking a non-ideal question. “We are not insane,” we say to the intruder in the garden. “We are only doing philosophy.”

This brings me to the other sense of philosophy’s ‘end’: where does philosophy end up? Where is it located in social space? At the periphery, I think, and trending further so. Contemporary American society has little interest in contemporary American philosophy. When earnest public broadcasters put together a program on the mysteries of the universe, they turn first to physicists. If they want to chat about human nature, they call neuroscientists. Plato at the Googleplex, a very successful recent book, was noted for the thesis that philosophy still matters at all. No one makes news writing that about physics.

I think that philosophy’s goal-end of certainty helps to explain its outcome-end of social irrelevance. Many people do want certainty, but philosophy is not where they will go to find it. Religion, of course, is an ancient and numerically dominant certainty-provider. But a sense of certainty can also be found in political ideology. Or, increasingly, in science. Philosophy is trying to compete in the certainty marketplace, and it is not winning.

Philosophy has a crucial weakness when it contends for certainty-seekers. Unlike religion or political ideology, it abjures the manifest certainty of a supreme authority. And unlike science, it does not trend toward disciplinary consensus. A central fact about philosophy is that philosophers have been debating the same questions for millennia, with no end in sight. Philosophy is essentially discursive, even disagreeable, in a way that makes its aim of certainty a collectively self-defeating one. Any particular philosopher may become certain about her own beliefs, but from the outside philosophy will always appear as a squabble among people asserting mutually contradictory claims with equal degrees of extreme confidence.

This shows the problem with the official justification for philosophical analysis. We say that we need to step back from messy reality in order to sharpen our concepts. We’ll just be away awhile, whetting our logical knives on some stipulated thought experiments. We’ll come back to the world, we insist, once we’ve polished our sufficient conditions. But we never come back. We argue endlessly about what we would need to make our truths necessary, and then we die and are replaced by the next generation’s assorted –ism-ists. We retire from the disorderly public square, into our shaded garden, its trees all arranged in logical space and known with certainty… and we never return.

Of course some philosophers do venture out from the garden. But for every one who does, there are a half dozen others who whisper unkindly about the impurity of the thing. Philosophy done in public rarely displays the rigor that is a precondition of necessity. There are limits to the number of fussy objections one can anticipate without hogging the speaker’s platform. And so public philosophy will never produce the certainty that many philosophers seek.

What if we took philosophy out of the certainty game? What would it mean, for philosophers to tolerate uncertainty, ambiguity, irresolution? It might mean trading the necessary for the contingent. Conceding that politics are never ideal. Acknowledging that knowers are embodied and temporal beings are located in history. None of this is absolutely alien to philosophy, but it is far from the apparent aim of many practitioners. Yet if we care about being anywhere other than the social periphery, perhaps we will have to adjust our ends.

This is my final guest post at The Splintered Mind. Thanks so much to Eric for the wonderful opportunity to speak from this platform. And thanks to everyone who has read and commented on my posts. This has been incredibly enjoyable – of that, I am certain.

image credit: 'Tree in Fog' by Matthew Paulson


Thanks so much, Gina, for your wonderful series of posts over the last several weeks!

For interested readers, here are the other five:

  • Ethics, Metaethics, and the Future of Morality (Sep. 11)
  • Philosophical Conversations (Sep. 17)
  • Microaggression and the Culture of Solidarity (Sep. 28; adapted for the L.A. Times Oct 12)
  • The Laughter of Ethicists (Oct. 6)
  • Consciousness Science and the Privileged Sample Problem (Oct. 14)
  • Monday, October 19, 2015

    Kammerer's New Anti-Nesting Principle

    Anti-nesting principles, in consciousness studies, are principles according to which one stream of consciousness cannot "nest" inside another. According to such principles, a conscious being cannot have conscious subparts -- at least under certain conditions -- even if it meets all other plausible structural criteria for being a conscious system. Probably the best-known anti-nesting principles are due to Hilary Putnam (1965, p. 434) and Giulio Tononi (2012, p. 297). Putnam's version is presented bare, and almost unmotivated, and has been criticized by Ned Block (1981, p. 74-76). Tononi's version is more clearly motivated within his "Integrated Information Theory" of consciousness, but still (I think) has significant shortcomings.

    In this forthcoming paper in Philosophia, Francois Kammerer takes another swing at an anti-nesting principle.

    Though relatively neglected, nesting issues are immensely important to consciousness studies. Intuitively or pre-theoretically, it seems very plausible that neither subparts of people nor groups of people are literally phenomenally conscious. (Unless maybe the brain as a whole is the relevant subpart.) If we want to retain this intuitive idea, then either (a.) there must be some structural feature that individuals have, which groups and subparts of individuals do not, which is plausibly necessary for consciousness, or (b.) consciousness must not nest for some other reason even in cases where human groups or subparts would have the structural features otherwise necessary for consciousness.

    In "If Materialism Is True, the United States Is Probably Conscious", I argue that human groups do have all the structural features that materialists normally regard as characteristic of conscious systems. A materialist who accepts that claim but wishes nonetheless to deny that groups of people are literally phenomenally conscious might then be attracted to an anti-nesting principle.

    Kammerer's principle is a bit complex. Here it is in his own words:

    "Given a whole W that instantiates the functional property P, such that W’s instantiation of P is normally sufficient for W to instantiate the conscious mental state S, W does not instantiate S if W has at least one subpart that plays a role in its functional organization which fulfills at the same time the two following conditions:

  • (A) The performing of this role by the subpart requires (given the nature of this functional role and our theory of consciousness) that this subpart has conscious mental states (beliefs, emotions, hopes, experiences, desires, etc.) that represent W (what it is, what it does, what it should do). That is to say, this subpart has a functional property Q, Q being a sufficient condition for the subpart having the conscious mental state R (where R is a mental state representing W).
  • (B) If such a functional role (i.e., a functional role of such a kind that it requires that the subpart performing it has conscious mental states representing W) was not performed by at least one of the subparts of W, W would no longer have the property P (or any other functional property sufficient for the having of S). In other words: if no subpart of W had R, then W would no longer have S."
  • Short, somewhat simplified version: If the reason a larger entity acts like it’s conscious is that it contains smaller entities within it who have conscious representations of that larger entity, then that larger entity is not in fact conscious. (I hope that's fair, and not too simple to capture Kammerer's main idea.)

    Though Kammerer's anti-nesting principle avoids some of the (apparent) problems with Putnam's and Tononi's principles, and is perhaps the best-developed anti-nesting principle to date, I'm not convinced that we should embrace it.

    I'm working on a formal reply (which I'll probably post a link to later), but my main thoughts are three:

    First, Kammerer's principle doesn't appear to fulfill the intended(?) role of excluding group-level consciousness among actually existing humans, since it excludes group consciousness in only a limited range of cases.

    Second, Kammerer's principle appears to make the existence of consciousness at the group level depend oddly on factors on the individual-person level that might have no influence on group-level functioning (such as whether an individual's thinking of herself as part of the group is emotionally motivating to her, which might vary with her mood even while her participation in the group remains the same, creating "dancing qualia" cases).

    Third, it appears to be unmotivated by a general theory that would explain why satisfying or failing to satisfy (A) or (B) would be crucial to the absence or presence of group-level consciousness.

    None of these three points would be news to Kammerer, so to make them stick would require more development than I'm going to give them today. But before doing that, I thought I solicit reactions from others -- either to the general issue of anti-nesting principles or to Kammerer's specific principle.

    Update Jan. 26, 2016:

    I have now drafted a more formal reply essay here.


    Related posts:

    Martian Rabbit Superorganisms, Yeah! (May 4, 2012)

    Tononi's Exclusion Postulate Would Make Consciousness (Nearly) Irrelevant (Jul 16, 2014)

    The Copernican Sweets of Not Looking Too Closely Inside an Alien's Head (Mar 14, 2014)

    Why [X] Should Think the United States Is Conscious (X = Dennett, Dretske, Humphrey) (Winter 2012).

    [image source]

    Wednesday, October 14, 2015

    Consciousness Science and the Privileged Sample Problem

    a guest post by Regina Rini

    There is, undeniably, such a thing as a science of consciousness. People use brain scanners and clever experimental techniques to figure out the neural processes correlated with conscious experience. I don’t wish to challenge the value of this research. However, I think there is something odd about consciousness as a scientific subject, something I’ll call the privileged sample problem. If I’m right, then consciousness is importantly unlike anything else science claims to study.

    To see the problem, imagine this: you are one of the world’s pre-eminent neuroscientists. You know as much about the cutting-edge science of consciousness as anyone else. Unfortunately, you are in a car crash and suffer serious head injury. For several weeks you are in a coma, but gradually you emerge into consciousness again. Unfortunately, you quickly realize that you have no control over any part of your body. You are an extreme victim of locked-in syndrome: though you are conscious and aware of your surroundings, you cannot move or speak or indicate your awareness to the outside world. (Unlike Jean-Dominique Bauby, the author of The Diving Bell and the Butterfly, you can’t even control your eyelids, so you can’t communicate by blinking.) As far as anyone else can tell, you are just as you were in coma: lying there in bed, eyes open and unfixed, unable to respond to anyone.

    As it happens, your neuroscientist colleagues have been keeping vigil at your bedside. They are always arguing with each other, and of course they want to know whether you are conscious. Eventually they arrange to have your brain scanned, using the most sophisticated existing techniques for consciousness-detection. But the tests come back negative! And here’s the important part: when they gather around your bedside to discuss the data, you listen. You understand the science just as well as they do, and you realize that, given the data they have and the best existing scientific theory of consciousness, you agree that they are right to conclude that you are not conscious. If you were out there with them and had the same data, you’d think so too. But because you are in here, in your own mind, you know they are wrong. You are conscious. And so now you know that the best existing scientific theory of consciousness is wrong.

    In this story, you are in a position to refute the best existing science based upon a single sample of the phenomenon being studied. This is not a normal feature of science. Science is inductive. Normally, if we discover a single sample which seems to defy our best scientific theory, we first check to see if we have made a mistake in measuring the sample. If we rule that out, we start looking for other samples that replicate the finding. If we can’t find any others – that is, if all other samples remain consistent with the best existing theory – then we will very likely conclude that the single inconsistent sample is a fluke. Our observation about the sample has gone wrong in some way, even if we can’t figure out exactly how it has gone wrong. What we will not do is overturn the best existing theory simply because it fails to cohere with a single sample.

    But things are different when it comes to consciousness. Your own conscious experience is, for you, a privileged sample. It is reasonable for you to conclude that the best existing theory is false if the best existing theory predicts that you are not conscious. It doesn’t matter whether the best existing theory continues to correctly predict all other cases you know about - your own case is special. This is nothing other than Descartes’ famous point: your own consciousness is the last thing you can doubt. You are right to doubt anything else, including the best existing scientific theory, before you doubt that you are conscious.

    Of course, your case is not special for anyone else. This is the other puzzling features of a privileged sample. You and only you have a certain type of access to this sample. Your grounds for employing it to refute the best existing theory are not publicly confirmable. Public confirmation is a cardinal feature of science, yet the science of consciousness is (in principle) constrained by observations that are not publicly confirmable. There exist possible observations that reasonably refute the best existing scientific theory on the basis of a single sample that is not available to public confirmation. That is the privileged sample problem.

    What does the privileged sample problem imply about the nature of consciousness? Well, it doesn’t obviously imply anything radical about the ontology of the conscious mind. We can still be fully-committed physicalists even if we accept that there is something odd about the science of consciousness. But I think it does imply that we should be suspicious of any attempt to treat consciousness as a target of physicalist reduction. Really all I am doing here is find another way to express a point made by Thomas Nagel a long time ago: we have subjective and objective ways of thinking about our own minds, and one cannot be reduced to the other. We should not try to entirely replace conscious-subjectivity talk with physicalist-science talk, because the privileged sample problem shows that the science of consciousness is not a science like any other.

    I got the idea for the privileged sample problem while formulating a question at the ‘Measuring Borderline States of Consciousness’ conference at NYU. Thanks in particular to Adrian Owen and Tim Bayne, whose fascinating talks on detecting consciousness provoked my question.

    image credit: 'Sub Conscious' by Gregg Jaden

    Tuesday, October 13, 2015

    "1% Skepticism" in Nous; "Experimental Evidence for the Existence of an External World" in JAPA

    About a week ago, two of my forthcoming essays appeared.

    "1% Skepticism":

    A 1% skeptic is someone who has about a 99% credence in non-skeptical realism and about a 1% credence that some radically skeptical scenario obtains. The first half of this essay defends the epistemic rationality of 1% skepticism, endorsing modest versions of dream skepticism, simulation skepticism, cosmological skepticism, and wildcard skepticism. The second half of the essay explores the practical behavioral consequences of 1% skepticism.

    Official version in Nous.
    Free manuscript version from my academic homepage.

    "Experimental Evidence for the Existence of an External World" (with Alan T. Moore):

    In this essay I attempt to refute radical solipsism by means of a series of empirical experiments. In the first experiment, I exhibit unreliable judgment about the primeness or divisibility of four-digit numbers, in contrast to a seeming Excel program. In the second experiment, I exhibit an imperfect memory for arbitrary-seeming three-digit number and letter combinations, in contrast to my seeming collaborator with seemingly hidden notes. In the third experiment, I seem to suffer repeated defeats at chess. In all three experiments, the most straightforward interpretation of the experiential evidence is that something exists in the universe that is superior in the relevant respects – theoretical reasoning (about primes), memorial retention (for digits and letters), or practical reasoning (at chess) – to my own solipsistically-conceived self.

    Official version in JAPA.
    Free manuscript version from my academic homepage.

    Both essays began life as posts on The Splintered Mind, the Experimental Philosophy Blog and NewAPPS. Many thanks to those who read and commented!

    By the way, the little picture of me in the upper right corner of this blog is cropped from a photo from the "External World" paper. Why do I look so contemplative? Because Alan is proving to me that the external world exists by beating me in speed chess!

    (photo credit: Gerardo Sanchez)

    Monday, October 12, 2015

    The Los Angeles Times

    ... has been publishing philosophers' op-eds recently -- a couple by me (here and here), and this past week Harry Frankfurt on why inequality isn't immoral and an adaptation of Regina Rini's Splintered Mind guest post on microaggression.

    The new op-ed editor Juliet Lapidos is behind this trend. Encourage Juliet by sharing the LA Times philosophy links widely and by sending the LA Times your best op-ed queries. It would be terrific if this trend could stick and we could have another major U.S. newspaper that regularly publishes philosophers!

    Thursday, October 08, 2015

    If Memories and Personality Make You "You", Here's How You Could Transfer into Another Body (Maybe)

    ... with no high technology required!

    Step 1: Write extensive memoirs, and have servants constantly follow you around, recording every detail of your life, in painting, story, and song.

    Step 2: Drink some hemlock to kill your present body.

    Step 3A: Have your servants find a newborn baby. Your servants will be experts in hypnosis, in the induction of "false" memories, and in psychological training. They will induce in the child, as she grows, memories from your past -- not false memories, but veridical, accurate memories! Memories at least as accurate and complete as other people's normal memories of three or ten years ago. With proper suggestion, the growing child will experience the memories from the first-person perspective and think of them as her own.

    Step 3B (simultaneous with 3A): Surround the child with institutions designed to convince her -- I mean you -- that she/you really is just the continuation of you in a new body. She will look on all of her induced memories as memories of the old days from her previous body. She will share your name, "remember" your friends and attitudes as her own, be personally proud of your past accomplishments and personally embarrassed by your past failures, identify with your old goals, projects, debts, and obligations. With some luck and good psychological training, the child will grow into an adult who shares the values and attitudes of your old self -- perhaps about as much as normal people retain their values and attitudes over the course of a decade or two.

    If she and all of society then say that she really is the re-embodiment of you -- that is, a continuation of the same person over time (only in a new body), as much as your 40-year-old self is normally thought to be a continuation of your 20-year-old self -- would she and all her society be factually, philosophically, metaphysically mistaken? If she isn't really a metaphysically legitimate continuer of you, why not? What would be missing, exactly?

    You might say they aren't real memories, because they're the memories of a different person -- but to say that is just to beg the question, assuming the falsity of the very view in dispute.

    You might say that personal identity requires strict continuity of body, which she doesn't have with you. But that's to move away from psychological criteria for personal identity, which many people find attractive in hypothetical upload cases, brain transplant cases, and teleporter cases.

    This is the topic of my latest science fiction story, "The Dauphin's Metaphysics", now out in the latest issue of Unlikely Story.

    Related Posts:
  • A Somewhat Impractical Plan for Immortality (Apr. 22, 2013)
  • The Mnemonists (Apr. 22, 2013)
  • Tuesday, October 06, 2015

    The Laughter of Ethicists

    A guest post by Regina Rini

    You are loitering by the railyard when you see an out-of-control trolley hurtling toward five innocent orphans who’ve been lashed to the track by a mustachioed villain. There is a switch nearby, which would activate an enormous fan and disrupt the air above you. There is a very fat man hang-gliding over the tracks. Since (like most ethicists) you are an expert in the aerodynamics of obesity, you know that the fan would force him to swoop down right into the path of the trolley; the collision would save the five orphans, though the very fat hang-glider would die.

    There is another option. You happen to be carrying one of those t-shirt cannons they use to fire souvenir t-shirts into the stands at sporting events. And the tracks are right next to a nursey for babies born without developed brains, who will surely die within hours in any case. Since (like most ethicists) you are an expert in infant ballistics, you know that you could use the t-shirt cannon to fire ten anencephalic infants at the trolley, and that would be just enough to derail it, saving the orphans, though killing the projectile babies.

    What should you do? Do nothing and let the five orphans die? Flip the switch and blow the very fat hang-glider into the trolley? Or use the t-shirt cannon to fire the ten anencephalic infants at the trolley?

    Actually, don’t answer that. My story is only a parody, though it is not far off from many stories you will find in professional philosophy journals. Moral philosophers have a penchant for inventing goofy thought experiments in which numerous people are oddly imperiled. These stories have a purpose: they are meant to isolate and test some purported moral principle. The absurd details are often unnecessary, though they keep the writing from becoming dull. But we might ask: should we really be amusing ourselves with ethics?

    One possible worry is that amusingly absurd thought experiments can make our moral intuitions less reliable. Some have thought that the frequent use of unrealistic scenarios might make for bad philosophy. Others might point out that being put in a humorous mood changes how people react to moral dilemmas. But I will leave that sort of objection to the side. My question is this: is there something morally inappropriate about constructing amusing moral dilemmas?

    It’s important to keep in mind that these scenarios are often intended to provide simplified models of very troubling moral issues: killing in war, abortion, euthanasia. Even when justified, killing is killing, and it would obviously never be appropriate to laugh at a person wracked by guilt over a justifiable homicide. If our thought experiments are meant to inform reflective moral deliberation, or to model the features of real-world moral dilemma, then should we really be so irreverent toward our ultimate subject matter? The worry is that our practice of constructing funny thought experiments has caused us to become desensitized to the real human suffering we claim to be studying.

    One response to this worry is that we are simply engaged in gallows humors. Emergency room physicians talk about this phenomenon often. When you are confronted with pain and death every day, and when inevitably people will die in your care, some levity may be necessary to keep yourself functioning. Physicians make jokes about their patients, sometimes even about their patients’ suffering, and perhaps this is just a psychological necessity (though extreme instances give pause to even the most hardened medics [WARNING: this link may be triggering to victims of sexual assault]).

    But this can’t be the right justification for moral philosophers. We don’t actually watch people suffer and die right in front of us, and certainly not under our care. Our professional experience of dying is a pale imitation of what physicians experience.

    However, there may be something to the parallel with medical gallows humor. What moral philosophers are intimately familiar with is the absurdity of human life and choice. It is absurd, the existentialists will remind us, that we imbue so much meaning in the lives and the deaths of tiny beings dangling from a vast chain of eternal galactic causation. Yet we do, of course, see our lives as meaningful – and so it is absurd that our meaningful lives can be ended by things that do not matter. People are killed by trolleys. People die hang-gliding. Human pain and mortality are not produced exclusively by wrenching sacrificial choice. Sometimes a three-cent bolt comes loose, sometimes the insulation peels off the wires, sometimes a pebble is in just the wrong place on the bike path – and then a meaningful human life ends with no meaning at all.

    The moral philosopher is responsible for being reflectively aware of the ultimate limits of human life. We do not face concrete instances of death and suffering as physicians must, but we do confront the abstract reality of human limitation, with its inevitable implication of our own personal vulnerability. Perhaps this is a professional hazard of moral philosophy; we are not in a business that allows us to simply look away from unpleasant ultimate realities. Perhaps all philosophers must find some way to sublimate their necessary awareness of life’s fragility. Some bury it under anodyne logical formalism. Others lean into the absurd, mocking death’s dominion over their thought experiment characters – and so, over themselves. Perhaps the laughter of ethicists is not irreverence, but the unyielding desire to find human joy even in the contemplation of human misery.

    Thanks to Tyler Doggett and William Ruddick for helping me think through how to express this idea.

    image credit: 'Tracks' by Clint Losee

    Thursday, October 01, 2015

    Against the "Still Here" Reply to the Boltzmann Brains Problem

    I find the Boltzmann Brain skeptical scenario interesting. I've discussed it in past posts, as well as in this paper, which I'll be presenting in Chapel Hill on Saturday.

    A Boltzmann Brain, or "freak observer" is a hypothetical self-aware entity that arises from a low-likelihood fluctuation in a disorganized system. Suddenly, from a chaos of gasses, say, 10^27 atoms just happen to converge in exactly the right way to form a human brain thinking to itself, "I wonder if I'm a Boltzmann Brain". Extremely unlikely. But, on many physical theories, not entirely impossible. Given infinite time, perhaps inevitable! Some cosmological theories seem to imply that Boltzmann Brains vastly outnumber ordinary observers.

    This invites the question, might I be a Boltzmann brain?

    The idea started getting attention in the physics community in the late 2000s. One early response, which seems to me superficially appealing but not to withstand scrutiny, is what I'll call the Still Here response. Here's how J. Richard Gott III put it in 2008:

    How do I know that I am an ordinary observer, rather than just a BB [Boltzmann Brain] with the same experiences up to now? Here is how: I will wait 10 seconds and see if I am still here. 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 ... Yes I am still here. If I were a random BB with all the perceptions I had had up to the point where I said "I will wait 10 seconds and see if I am still here," which the Copernican Principle would require -- as I should not be special among those BB's -- then I would not be answering that next question or lasting those 10 extra seconds.

    There's also a version of the Still Here response in Max Tegmark's influential 2014 book:

    Before you get too worried about the ontological status of your body, here's a simple test you can do to determine whether you're a Boltzmann brain. Pause. Introspect. Examine your memories. In the Boltzmann-brain scenario, it's indeed more likely that any particular memories that you have are false rather than real. However, for every set of false memories that could pass as having been real, very similar sets of memories with a few random crazy bits tossed in (say, you remembering Beethoven's Fifth Symphony sounding like pure static) are vastly more likely, because there are vastly more disembodied brains with such memories. This is because there are vastly more ways of getting things almost right than of getting them exactly right. Which means that if you really are a Boltzmann brain who at first thinks you're not, then when you start jogging your memory, you should discover more and more utter absurdities. And after that you'll feel your reality dissolving, as your constituent particles drift back into the cold and almost empty space from which they came.

    In other words, if you're still reading this, you're not a Boltzmann brain (p. 307-308)

    I see two problems with the Still Here response.

    First, we can reset the clock. While after ten seconds I could ask the question "am I a Boltzmann Brain who has already lasted ten seconds?", that question is not the sharpest form of the skeptical worry. A sharper question would be this, "Am I a Boltzmann Brain who came into existence just now with a false memory of having counted out ten seconds?" In other words, there seems to be nothing that prevents the Boltzmann Brain skeptic from restarting the clock at will. Similarly, a Boltzmann Brain might come into existence thinking that it had just finished introspecting its memories Tegmark-style, having found them coherent. That's the possibility that the Boltzmann Brain skeptic will be worried about, after having completed (or seeming to have completed) Tegmark's test. The Still Here response begs the question, or argues in a circle, by assuming that we can have veridical memories of implementing such tests over the course of tens of seconds; but it is exactly the veridicality of such memories, even over short durations, that the Boltzmann Brain hypothesis calls into doubt.

    Second, this response ignores the base rate of Boltzmann Brains. It's widely assumed that if there are Boltzmann Brains, they might be vastly more numerous than normally embodied observers. For example, a universe might produce a finite number of normal observers and then settle into an infinitely enduring high entropy state that gives rise, at extremely long intervals, to an infinite number of Boltzmann Brains. Since infinitude is hard to deal with, let's hypothesize a cosmos with a googolplex (10^(10^100)) of Boltzmann Brains for every normal observer. Given some sort of indifference principle, the Boltzmann Brain argument goes, I should initially assign a 1-in-a-googolplex chance to being a normal observer instead of a Boltzmann Brain. Not good. But now, what are the odds that a Boltzmann Brain can hold it together for ten seconds without lapsing into incoherence? Tiny! Let's assume one in a googol (10^100). The exact number doesn't matter. Setting aside worries about resetting the clock, let's assume that I now find that I have indeed endured coherently for ten seconds. What should be my new odds that I am a Boltzmann brain? Much lower than 1-in-a-googolplex. Yay! Only about a googolth of a googolplex! Let's see, how much is that? Instead of a ten followed by a googol of zeroes, it's only ten followed by a googol-minus-100 zeros. So... still virtual certainty that I am a Boltzmann Brain.

    So how should we respond to the Boltzmann Brain hypothesis, then? Sean Carroll has a two-pronged answer that I think makes a lot of sense.

    First, one can consider whether physical theories can be independently justified which imply a low ratio of Boltzmann Brains to normal observers. Boddy, Carroll, and Pollack 2015 offer such a theory. If it turns out that the best physical theories imply that there are zero or very few Boltzmann Brains, then we lose some of our grounds for worry.

    Second, one can point to the cognitive instability of the Boltzmann Brain hypothesis (Carroll 2010, p. 223, drawing on earlier work by David Albert). Here's how I'd put it: To the extent I think it likely that I am a Boltzmann Brain, I think it likely that evidence I have in favor of that hypothesis is delusional -- which should undercut my credence in that evidence and thus my credence in the hypothesis itself. If I think it 99% likely that I'm a Boltzmann Brain, for example, then I should think it 99% likely that my evidence in favor of the Boltzmann Brain hypothesis is in fact bogus evidence -- false memories, not reflecting real evidence from the world outside -- and that should in turn reduce my credence in the Boltzmann Brain hypothesis.

    An interesting feature of Carroll's responses, which distinguishes them from the Still Here response, is this: Carroll's responses appear to be compatible with still assigning a small but non-trivial subjective probability to being a Boltzmann Brain. Maybe the best cosmological theory turns out not to allow for (many) Boltzmann Brains. But we shouldn't have 100% confidence in any such theory -- certainly not at this point in the history of cosmological science -- and if there are still some contender cosmologies that allow for many Boltzmann Brains, we (you? I?) might want to assign a small probability to being a Boltzmann Brain, in view the acknowledged possibility that the cosmos might, though unlikely, have a non-trivial ratio of Boltzmann Brains to normal observers. And although a greater than 50% credence in the Boltzmann Brain hypothesis seems cognitively unstable in Carroll's sense, it's not clear that, say, an approximately 0.1% credence in the Boltzmann Brain hypothesis would be similarly unstable, since in that case one still might have quite a high degree of confidence in the physical theories that lead one to speculate about the small-but-not-minuscule possibility of being a Boltzmann Brain.

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