A short while back I posted my amateur position on the issues of reduction and emergence in physics.
I shared it with Chlesea Haramia, a philosopher that works on problems of ethics in astrobiology, and she and Thomas Metcalf kindly responded with a lengthy discussion. I’m really appreciative of the time they have taken to “translate” my post into proper terminology of philosophy and give professional feedback.
So, if you’re interested in a professional take on the ideas I raised in my prior post, please read on!
Reduction, emergence, and the limits of physics
Thomas Metcalf and Chelsea Haramia
Jason Wright presents a thoughtful and interesting discussion of his views on emergence and reduction. In academic philosophy, these terms and concepts are both widely used and the subjects of vigorous debate. In this short note, we want to outline how philosophers think of reduction and emergence and in which ways these concepts can illuminate some topics Jason mentions.
Reduction vs. emergence, weak and strong
Put simply, those who believe in emergence (rather than reduction) maintain that the big (holistic) stuff is as real as the small (basic) stuff. Minds and waves of bathwater, then, are as real as electrons and molecules. It makes sense to have scientific theories that talk about tornadoes, mammals, colors, planets, phobias, and so on, instead of merely having theories that talk about the atoms and fields that compose those things.
Emergent phenomena (e.g. planets) are distinct from their basic components or substrates (e.g. atoms of silicon and iron), but there are different ways of describing this distinctness. We’ll look at two: strong and weak.
One way is to maintain that, while complex combinations of the small stuff cause and fully determine the nature of the big stuff, the big stuff is not “realized in” the small stuff: it comes from the small stuff but it’s not ultimately the same stuff as the small stuff. Some of this emergent stuff, in fact, might not even be physical at all, or might not interact with the physical world at all. This “strong emergence,” then, is normally taken to be incompatible with what philosophers call “physicalism,” i.e., the thesis that everything is ultimately physical. Strong emergence occurs when the emergent phenomenon is of a fundamentally different type of stuff than is the stuff it emerges from.
A different way to posit emergence is to take the view Jason favors. Emergent properties are still fully physical, but they’re realized at different scales and often require different academic disciplines, approaches, and analyses for their study. These disciplines study entities and phenomena that are just as real as what the quantum physicist or neuroscientist studies, but we might still need to understand the small stuff to properly identify and fully understand the big stuff. Despite this emergence’s compatibility with a fully physical world, we may call it “weak emergence.” What separates this weak emergence from reductionism is that the emergent (big) stuff is still real in itself (and useful to talk about and include in scientific theories), and crucially, can often be realized in very different sets of small stuff. For example, perhaps there could be silicon-based, rather than carbon-based animals. We would still properly call them “animals,” but “animal” wouldn’t be reducible to “carbon-based (among other things)” because there could be animals that aren’t carbon-based at all. Being an animal would emerge from (among other things) being carbon-based, but it could also emerge from (among other things) being silicon-based. In contrast, perhaps only H2O would ever really be “water.” Something that looked and acted just like water at the macroscale, but wasn’t made of H2O, wouldn’t really be water. If so, then water wouldn’t just emerge from H2O; it would reduce to H2O. (The example of “water” vs. “H2O” is ubiquitous in philosophy; you can read more here and here.)
One of the virtues of Jason’s view is that it provides a coherent avenue of response for anyone who finds that, often, those who attempt to make appeals to emergence have not actually posited anything beyond the purely physical realm. Some emergent accounts are congenial to reductive accounts, and these accounts may all manifest in a fully deterministic, measurable, physical world. The compatibility of Jason’s “weak physical emergence” and reductionism is a useful way of responding to certain claims of emergence—a way of demonstrating that many purported appeals to emergence are actually perfectly compatible with strong physicalism.
Again, these concepts and terms are commonly debated in philosophy, so for much more discussion on the topic, we invite you to visit this link.
The case for strong physical emergence
As you can see from the linked entry just above, there may be reason to quibble a bit with Jason’s (and our) definitions of both “weak emergence” and “strong emergence.” Nonetheless, when addressing issues of strong emergence, we’re happy to help ourselves to Jason’s terminology: that “strong physical emergence” refers to a phenomenon that is truly, fundamentally real, and emerges from some set of physical causes, but is not itself realized in any set of physical objects. For example, consciousness might arise from neurons, but not be identical to any set of neurons, and it might have fundamental properties that neurons don’t have.
What might those properties be like? Well, the four most-commonly discussed are consciousness, intentionality, perspective, and unity. Consider these four pairs of premises (you can imagine how the rest of each argument would go):
The Argument from Consciousness
C1. At-least-some minds have conscious experiences.
C2. No atoms have conscious experiences.
The Argument from Intentionality
I1. At-least-some beliefs are about things.
I2. No atoms are about things.
The Argument from Perspective
P1. At-least-some experiences necessarily have first-person, subjective perspectives inherently attached to them.
P2. No sets of atoms necessarily have first-person, subjective perspectives inherently attached to them.
The Argument from Unity
U1. At-least-some minds are unified: they are not made of individual parts.
U2. All sets of atoms are disunified: they are made of individual parts.
All these arguments would then conclude that minds, or beliefs, or experiences aren’t ultimately just sets of atoms.
We don’t pretend that these arguments are all decisive; many philosophers would reject them, and most philosophers believe that the mind is ultimately physical. And there are important arguments against dualism about the mind, i.e., the thesis that the mind and the brain are two different objects, which might imply that the mind is non-physical. If we think there are two fundamental categories of stuff—say, physical and non-physical—then we have to explain how these fundamentally different things could possibly interact with each other. At least as far back as the philosopher Elisabeth of Bohemia (1618–1680), skeptics about dualistic views of reality have offered this challenge. (You can read more here.) But you can see how someone might argue, based on the alleged intrinsic properties of mental states, for the strong emergence of minds.
One more thing for now: There are lots of other arguments that the mind isn’t a physical object. We’re not going to get into such arguments much here, but you can read about them if you want.
Against strong emergence
Now we can consider Jason’s argument against strong emergence. It’s based on a good point. We have reason to believe that consciousness and intentionality at-least-weakly-emerge from neurons, since as far as we know, destruction of neurons harms or destroys consciousness and intentionality. If you cut off the current to the broadcast antenna, you lose most of the photons. But that’s all compatible with weak emergence and even with reduction. The interesting question for us is whether causation goes in the other direction. Is there any reason to believe that some extra thing—beyond our neurons and the corresponding current and neurotransmitters—has any causal influence on anything physical? Can my beliefs cause me to do things without my neurons’ causing me to do things? If so, then this would begin to look like what Jason calls “strong physical emergence.”
Well, let’s take a minute to identify an alternative view: epiphenomenalism. Strictly speaking, strong emergence of minds can occur without those minds’ having any causal influence on the physical world. Maybe minds are just extra things, floating out there, passengers along for the ride that never put their hands on the steering wheel. This mind could still be an example of strong emergence; it could still have intrinsic properties (such as, arguably, consciousness) that atoms don’t have. In correspondence, Jason gave the apt analogy of a child’s holding a disconnected video-game controller and watching the video-game feed on a screen, falsely believing that they’re the one controlling the video game. (You can read more about epiphenomenalism here.)
Maybe we think epiphenomenalism is implausible. Maybe we think, for example, that consciousness would have no reason to evolve if it didn’t have some influence on our bodies. Let’s set epiphenomenalism aside for now and go back to Jason’s argument: in essence, that we haven’t found any good candidates for strong emergence yet. We haven’t, for example, found neurons that just kind of fire for no reason at all. If we did, then maybe some strongly emergent beliefs or desires would be the cause of that firing. Similarly, we haven’t found any good evidence of a “life force” or anima that determines whether an animal is alive or dead. So that’s a good point. Maybe if we haven’t found any evidence of something, then by Occam’s Razor, we should dismiss it until we acquire such evidence. (One of us has criticized a version of Occam’s Razor in print, however.)
Potential examples of strong emergence?
Of course, Jason grants that we may have already found something that seems indeterministic in that way, i.e., that seems to result without a sufficient antecedent cause. If I measure an electron’s spin about some axis and then measure its spin about an orthogonal axis, then perhaps the second measurement’s result can’t be explained by anything intrinsic to the electron. This might even make room for something like indeterministic free will, if somehow there were some event or force that could influence the probabilities of our making certain decisions, while still leaving room for other possible decisions. This is a very interesting case and possibly one of the best routes for arguing for indeterministic free will. (Of course, this only really works if we believe in an indeterministic physical story.) If the actual free-will decisions are non-physical events, or if the tie between microscopic particles and free-will decisions is merely a law of nature (such that God, say, could have changed that relationship, by rewriting the laws of nature), then this looks like strong emergence. The free-will decisions are of a fundamentally different type of entity than are the neurological events.
Let’s go back to the question of neurons, then. Does the fact that we haven’t found any firing-for-no-reason neurons suggest that there are no “extra,” strongly emergent beliefs and experiences out there (beyond our neurons) causing our neurons to fire? Let’s grant the empirical premise: maybe we really haven’t found any such neurons. But as far as we know, no one has fully traced the entire process of stimulus-response in a way that rules out any extra influences. At the present moment, we have some fancy devices that allow us to scan brains in gross terms: we can see where blood is flowing, or where there’s lots of chemical activity, for example. But that’s a far cry from (say) getting everything reduced down to something like an observable chain of falling dominoes from external stimulus to neuronal firings to external response. But suppose we did reach that point. Even then, as noted, that wouldn’t rule out strong emergence. For one thing, as noted, the strongly emerging events might be epiphenomenal: they are caused by the physical realm, but don’t cause anything in the physical realm.
In response, one may reasonably be suspicious of a view that arguably inherently rules out the possibility that we could empirically verify its truth. But of course it’s possible for an empirically unverifiable theory to be true, and the position “We should only believe in empirically verifiable claims” is infamously potentially self-defeating. In any case, there’s substantial current debate about whether there is a detectable role for (say) quantum-mechanical decoherence in brain events. (See here for more information.)
We also want to discuss a very interesting example Jason gives: a hypothetical behavior of gravity, dark energy, or some other force. The idea, in brief, would be of a force or field (call it “Force X”) that seems to manifest, say at large scales, and in proportion or otherwise in relation to familiar, “light” matter, but can’t be explained by any of the microphysical-scale events or objects. Force X might influence the light matter around us, but we can’t find any individual particle that constitutes or mediates this force.
This might be evidence that Force X was strongly emergent. After all, Force X might seem to be related to the presence of light matter, but not composed of light matter nor of anything else we can specifically detect. If it was composed of some fundamentally different type of stuff, and not realized in the familiar particles of the Standard Model, then this would look like strong emergence. And this would, in turn, push us toward having to discuss the very deep question of what it means for something to be physical or a part of physics. (You can read more here.) If we never discover any candidate particle to be the matter or mediator of Force X, do we have to conclude that physics itself is a fundamentally incomplete description of reality? Or, perhaps by induction, are we entitled to conclude that Force X is realized in, and mediated by, physical particles that are simply undetectable to us? What if they’re apparently forever undetectable—may we really say that those particles are still part of physics, or still part of physical reality?
These are obviously difficult issues that we can’t solve here. But we mention them to give you an idea of how philosophers think about these issues and to potentially generate further discussion. And we’d like to thank Jason for a simulating post and for the opportunity to present our thoughts here.
Semi-technical appendix: Varieties of reduction and emergence
Okay, for those of you who have followed so far and want to know, in more explicit terms, how to tell the differences between reduction, weak emergence, strong emergence, and complete independence, here we go.
First, it helps to understand the difference between “physical” and “metaphysical” possibility. Something is physically possible when it’s compatible with the laws of physics, whatever they are. For example, to accelerate to half the speed of light, or to undergo an exothermic reaction. Something is metaphysically possible when it could happen, whatever the laws of physics happen to be. For example, to accelerate to twice the speed of light, or to know the exact position and velocity of a particle. (If an omnipotent God exists, then she can create whatever is metaphysically possible, even if it’s not physically possible—after all, she can change the laws of physics.) Of course, some things aren’t even metaphysically possible. Arguably, it’s metaphysically impossible for the number eight to be prime, and metaphysically impossible for something to exist and not exist at the same time. (By the way, there are far more than two varieties of possibility; see here for a much longer discussion.)
Now that we’ve got an idea of those two varieties of possibility, we can think about a procedure for distinguishing emergence, reduction, and so on. (We don’t intend this to be 100% correct and foolproof, but instead, to give a generally useful procedure.)
Take two events, phenomena, or objects. Let’s call them “Micro” and “Macro” since typically, emergent phenomena are on the larger scale than are the phenomena they’re alleged to emerge from. Now suppose we want to know whether Macro is reducible to Micro, or emerges from Micro in some way, or is independent of Micro. We can begin by asking some sets of questions in order.
- Is it physically and metaphysically possible for Macro to exist alone in the universe? If “yes,” then Macro is independent of (i.e. non-emergent-from and non-reducible-to) Micro. If “no,” then proceed.
- (a) Does Macro have inherent properties or powers that Micro doesn’t have? (b) Is Macro non-physical while Micro is physical, or is Macro otherwise a fundamentally different type of entity than Micro is? (c) Does Micro produce Macro by physical or psycho-physical law (or law of nature) but not by metaphysical necessity? If the answer to all of these is “yes,” then Macro strongly emerges from Micro. If not, then proceed.
- (a) Is Macro equally real as Micro? (b) Is it possible for true theories to mention Macro explicitly? (c) Could Macro be realized in many different sets of objects instead of Micro as well? (d) Does Macro produce Micro by metaphysical necessity? If the answer to all of these is “yes,” then Macro weakly emerges from Micro. If not, then proceed.
- Does Macro exist? If “no,” then Macro is just a myth. If “yes,” then Macro is reducible to Micro, or we’re at some borderline case.
What about those borderline cases? There are a few possibilities left unaddressed by this procedure, in which in ##2–3 some but not all of the (a)–(c) or (a)–(d) criteria are satisfied. In those cases, we’re probably dealing with some borderline case between strong and weak emergence or between weak emergence and reduction. For more, check out this article.