The adjective “physical” is often tossed around as a term by which to distinguish or classify phenomena, or to describe some general aspect of things. As such, “physical” would useful for purposes of metaphysics. Does it succeed at that purpose? Can one articulate that meaning?
One digression-worthy example of this use of the word occurs in Rolf Landauer's series of articles where he stated and argued that “information is physical”. He initially drew this conclusion in a 1961 paper on the basis “that devices exhibiting logical irreversibility are essential to computing. Logical irreversibility, we believe, in turn implies physical irreversibility, and the latter is accompanied by dissipative effects.” His reasoning is made more explicit (and slightly revised) in his 1996 paper, where he begins:
More succinct restatements his equivalence of logical and physical irreversibility (e.g., erasure of a bit of information increases thermodynamic entropy) have become known as Landauer's Principle. While the principle has been widely accepted in the past 40 years, numerous scientists have energetically criticized associating information entropy and thermodynamic entropy, which entails an exorcism of Maxwell's Demon (e.g., Morowitz 1986; Norton 2005 and 2011; Earman and Norton 1999; and Shenker 2005). A study published last year by Lopez-Suarez et al. provides experimental evidence indicating that Landauer's Principle is in error:
An article at phys.org ends with the comment “Though Landauer famously said 'information is physical,' it turns out that information is not so physical after all.” Surely that means one can hold out hope that information will turn out to be at least slightly physical.
Oddly I have come across few, if any, discussions that have made a big deal about what seems to me an important point: the fact that the phenomena of heat generation which premises Landauer's conclusion that “information is physical” is actually the product of computation or processing by a device, rather than some intrinsic characteristic of the quantity information. Information isn't a necessary element in Landauer's scenario.
In any case, the topic of this thread concerns what “physical” means. Does Landauer's assertion that “information is physical” contradict Norbert Wierner's statement in Cybernetics, “Information is information, not matter or energy”?
Of course, it depends on what is meant by “physical”. Perusing dictionaries, one finds that some definitions bespeak a contradiction in defining "physical" in terms of matter and energy:
the definition of physical
Definition of PHYSICAL
Physical definition and meaning | Collins English Dictionary
On the other hand, all dictionaries also include a definition in which “physical” is just the adjectival form of “physics,” meaning “of or relating to physics.” Undeniably information relates to physics (though this is not what Landauer meant by “information is physical.”)
But to say that something is “of or relates to physics” is acutely uninformative of the intrinsic nature of the thing. Physics is a broad field of inquiry, without strict boundaries for what might “relate to” it, and the popular ideas and theories of physics change radically over time. Going by a keyword hits among the physics papers at arXiv.org, one can conclude that muskrats and maple syrup do not relate to physics and therefore are not physical according to such definition. Giraffes do relate to physics, but not the animal. Infinite sets and all algebraic structures I could think of relate to physics, thus meeting this definition of physical.
Obviously “physical” is not a scientific term. Neither physics nor any other scientific discipline defines the adjective or utilizes it to classify phenomena. There is no method for testing a hypothesis about whether something is “physical” or not. It's interesting that many people who declare their allegiance to science have an attachment for this adjective.
One might think that an intelligible concept of “physical” would be found in the scholarly expositions of the metaphysical thesis of physicalism. But one would be woefully wrong. In the Encyclopedia of Philosophy article on physicalism, Professor Macdonald addresses the issue upfront and immediately wades into the problem of Hempel's Dilemma:
She quickly dismisses this predicament by merely asserting that “nevertheless what is physical is all and only what a completed physics countenances.” In other words, no one can possibly know what the adjective “physical” refers to at any given point in time. Moreover, the very idea of “a completed physics” is of questionable coherence, as there are no criteria for determining when “physics” will cease to enjoy further discoveries or ideas.
In the SEP article, Professor Stoljar exhibits the same sort of faint bravery when he eventually confesses that “Without any understanding of what the physical is, we can have no serious understanding of what physicalism is.” Then he proceeds to state two definitions of “physical property” that provide no understanding of what “the physical” is, both of which are blatantly circular (e.g., “A property is physical iff: it . . . is the sort of property required by a complete account of the intrinsic nature of paradigmatic physical objects . . .”), which he acknowledges to be circular and assures us it is not problematic. It's vacuous. Nevertheless, under this definition one could never claim that consciousness is a “physical property”. Consciousness is obviously not “the sort of property required by a complete account of the intrinsic nature of paradigmatic physical objects”.
So what does “physical” really mean? Give your definition.
Does the adjective serve any productive purpose in the context of metaphysics, that is, as descriptive of some intrinsic or general characteristic of phenomena?
One digression-worthy example of this use of the word occurs in Rolf Landauer's series of articles where he stated and argued that “information is physical”. He initially drew this conclusion in a 1961 paper on the basis “that devices exhibiting logical irreversibility are essential to computing. Logical irreversibility, we believe, in turn implies physical irreversibility, and the latter is accompanied by dissipative effects.” His reasoning is made more explicit (and slightly revised) in his 1996 paper, where he begins:
1. Information is physical
Information is not a disembodied abstract entity; it is always tied to a physical representation. It is represented by engraving on a stone tablet, a spin, a charge, a hole in a punched card, a mark on paper, or some other equivalent. This ties the handling of information to all the possibilities and restrictions of our real physical word, its laws of physics and its storehouse of available parts.
Information is not a disembodied abstract entity; it is always tied to a physical representation. It is represented by engraving on a stone tablet, a spin, a charge, a hole in a punched card, a mark on paper, or some other equivalent. This ties the handling of information to all the possibilities and restrictions of our real physical word, its laws of physics and its storehouse of available parts.
More succinct restatements his equivalence of logical and physical irreversibility (e.g., erasure of a bit of information increases thermodynamic entropy) have become known as Landauer's Principle. While the principle has been widely accepted in the past 40 years, numerous scientists have energetically criticized associating information entropy and thermodynamic entropy, which entails an exorcism of Maxwell's Demon (e.g., Morowitz 1986; Norton 2005 and 2011; Earman and Norton 1999; and Shenker 2005). A study published last year by Lopez-Suarez et al. provides experimental evidence indicating that Landauer's Principle is in error:
The claimed linkage[11] between logical and physical irreversibility has animated a long debate[12]. Although recent studies[13] have contributed to clarify this aspect from a purely theoretical point of view, it remains widely controversial and is still missing experimental verification. Our experiment rules out the presence of a finite ‘minimum dissipated heat’ due to logical irreversibility, an argument often invoked when the reduction of input–output information is considered. We stress here that our experiment does not question the so-called Landauer-reset interpretation, where a net decrease of physical entropy requires a minimum energy expenditure[10,14]. What we have here is a logically irreversible computation, that is a generic process where a decrease in the amount of information between the output and the input is realized with an arbitrarily small energy dissipation; this shows that logical reversibility and physical reversibility have to be treated on independent bases[12].
An article at phys.org ends with the comment “Though Landauer famously said 'information is physical,' it turns out that information is not so physical after all.” Surely that means one can hold out hope that information will turn out to be at least slightly physical.
Oddly I have come across few, if any, discussions that have made a big deal about what seems to me an important point: the fact that the phenomena of heat generation which premises Landauer's conclusion that “information is physical” is actually the product of computation or processing by a device, rather than some intrinsic characteristic of the quantity information. Information isn't a necessary element in Landauer's scenario.
In any case, the topic of this thread concerns what “physical” means. Does Landauer's assertion that “information is physical” contradict Norbert Wierner's statement in Cybernetics, “Information is information, not matter or energy”?
Of course, it depends on what is meant by “physical”. Perusing dictionaries, one finds that some definitions bespeak a contradiction in defining "physical" in terms of matter and energy:
the definition of physical
2. of or relating to that which is material:
the physical universe; the physical sciences.
3. noting or pertaining to the properties of matter and energy other than those peculiar to living matter.
the physical universe; the physical sciences.
3. noting or pertaining to the properties of matter and energy other than those peculiar to living matter.
Definition of PHYSICAL
2 a :having material existence: perceptible especially through the senses and subject to the laws of nature
“everything physical is measurable by weight, motion, and resistance” —Thomas De Quincey
b: of or relating to material things
“everything physical is measurable by weight, motion, and resistance” —Thomas De Quincey
b: of or relating to material things
Physical definition and meaning | Collins English Dictionary
1. of nature and all matter; natural; material
On the other hand, all dictionaries also include a definition in which “physical” is just the adjectival form of “physics,” meaning “of or relating to physics.” Undeniably information relates to physics (though this is not what Landauer meant by “information is physical.”)
But to say that something is “of or relates to physics” is acutely uninformative of the intrinsic nature of the thing. Physics is a broad field of inquiry, without strict boundaries for what might “relate to” it, and the popular ideas and theories of physics change radically over time. Going by a keyword hits among the physics papers at arXiv.org, one can conclude that muskrats and maple syrup do not relate to physics and therefore are not physical according to such definition. Giraffes do relate to physics, but not the animal. Infinite sets and all algebraic structures I could think of relate to physics, thus meeting this definition of physical.
Obviously “physical” is not a scientific term. Neither physics nor any other scientific discipline defines the adjective or utilizes it to classify phenomena. There is no method for testing a hypothesis about whether something is “physical” or not. It's interesting that many people who declare their allegiance to science have an attachment for this adjective.
One might think that an intelligible concept of “physical” would be found in the scholarly expositions of the metaphysical thesis of physicalism. But one would be woefully wrong. In the Encyclopedia of Philosophy article on physicalism, Professor Macdonald addresses the issue upfront and immediately wades into the problem of Hempel's Dilemma:
Any formulation of physicalism raises the question, What is meant by "physical"? It is difficult to formulate a conception of the physical that is neither too strong, making physicalism obviously false, nor too weak, making physicalism trivially true. For example, what is physical may be simply identified through the language of physics. However, a problem arises over the conception of physics appealed to. Current physics seems too narrow because future extensions of physics would not count as physical; but the idea of a completed physics is too indeterminate because there is no clear idea of what that physics might include.
She quickly dismisses this predicament by merely asserting that “nevertheless what is physical is all and only what a completed physics countenances.” In other words, no one can possibly know what the adjective “physical” refers to at any given point in time. Moreover, the very idea of “a completed physics” is of questionable coherence, as there are no criteria for determining when “physics” will cease to enjoy further discoveries or ideas.
In the SEP article, Professor Stoljar exhibits the same sort of faint bravery when he eventually confesses that “Without any understanding of what the physical is, we can have no serious understanding of what physicalism is.” Then he proceeds to state two definitions of “physical property” that provide no understanding of what “the physical” is, both of which are blatantly circular (e.g., “A property is physical iff: it . . . is the sort of property required by a complete account of the intrinsic nature of paradigmatic physical objects . . .”), which he acknowledges to be circular and assures us it is not problematic. It's vacuous. Nevertheless, under this definition one could never claim that consciousness is a “physical property”. Consciousness is obviously not “the sort of property required by a complete account of the intrinsic nature of paradigmatic physical objects”.
So what does “physical” really mean? Give your definition.
Does the adjective serve any productive purpose in the context of metaphysics, that is, as descriptive of some intrinsic or general characteristic of phenomena?
