Recently, I’ve been involved in some discussions about causality, and some of those discussions have struggled to find any resolution, which I find frustrating. I don’t think people need to agree on ideas, but my experience is that usually people can agree on how to frame and talk about those ideas.
I sometimes get the feeling people are so set on disagreeing that they don’t always engage on what the other party is saying. I never know if it’s a lack of comprehension, a lack of willingness, or (on my part) a lack of communication skill or sufficient explanation.
So here are some things I think (I hope) are uncontroversial.
I’d like to consider five different physical causal systems.
What I mean is that these systems exist as fully identifiable physical entities that work according to well understood physical principles. There are no components or behaviors in these systems we don’t understand.
Per a recent post, we can both completely define and completely describe these systems.
The first causal system is the old two tin cans and string “phones” we made as kids in a bygone era.
The system consists of two empty tin cans with lids removed. Each can has a small hole in the center of its bottom. A string is threaded through from the inside — a knot at the end keeps it anchored to the can’s bottom.
The string, which is usually very long, is stretched and held taut.
If Alice speaks into one can, her vocal chords vibrate the air which vibrates the can which vibrates the string which vibrates the other can which vibrates the air in that other can which vibrates Bob’s eardrums, and he can hear what Alice said.
Bob can speak into his can, and a reverse chain of causes happens, and Alice can hear his voice.
The system isn’t efficient — voices sound faint and “tinny” — but it does work. A voice at one end, through a chain of physical causes, is transmitted to the other end.
But the fact of a chain of physical causes isn’t the point!
I can’t stress this enough. All systems that actually do something are physical; they all have physical causal chains.
The point is what is going on in those causal chains.
In this case, what is going on is physical vibrations being transferred from vocal chord to air to can to string to other can to other air to eardrum. And at every point along the way, these vibrations directly represent the speaker’s voice.
That’s the crucial point! If Alice or Bob speak loudly, the vibrations are strong. If they speak softly, the vibrations are weak. When they speak low or high pitched the vibrations directly reflect that.
We can “see” (i.e. in some way directly sense) the system’s information (the vibrations) at any point along the way, and that information looks like the vibrations.
A technical way to put this is that the state of the system at any point in the system directly and proportionally represents the primary information content of the system.
The second causal system is similar, and I’ve discussed it in detail before — analog music recording, from musical instruments and voices to reproduced sound coming from speakers at a later time.
This system also deals with sound vibrations, but here the chain is more complex, requires external electrical power, and allows the vibrations to be stored and recalled later.
In this case the causal chain involves things like microphone diaphragms, electrical wires and components, magnetic tape and vinyl records, and (most importantly) speakers or headphones to recreate the vibrating air.
Even so, the state of the system at any point directly and proportionally represents the primary information (the music) the system is processing.
It might require an oscilloscope to see the electrical signal or an audio amplifier with a speaker to hear it, but the (electrical) vibrations of the system are the music.
With the tin can phones it’s easy to see how one part of the system physically pushes on another part of the system in order to transmit physical vibrations. Very much the same thing happens electronically — one part electronically “pushes” on the next part.
The crucial point is that the pushes directly and proportionally represent the original sound — the states of the system directly reflect primary information content.
One difference between sound recording and tin can phones involves the need for external electrical power. The latter were powered by the vibrations themselves. (Which demonstrates of the physicality of the causal chain!)
Electricity in sound recording both powers the system — that is, it enables the system to function — and at many points represents the sound — that is, it’s the signal.
At other points the signal is represented by magnetized domains on a strip of tape or by wiggles in the groove of a vinyl record. In all cases, electrical signal, magnetic signal, or wiggle signal, the original sound vibrations are clear and proportional.
The third causal system is a simple light switch circuit, such as found in most homes. This system includes the switch, the wiring, the light bulb.
Electric current plays a role here, too. In fact, it’s kind of the point of this system — electrical power to the bulb creates light for a dark room.
The chain of causality in this case is that someone flips the switch which closes a circuit which allows current to flow which heats up the filament in the bulb which emits lots of photons, and let there be light.
The primary information content, such as it is, is whether the switch is closed and current is flowing, or not. The physical state of the system, once again, clearly shows that content.
The switch has physical states, current flow is easy to detect (in fact, one needs to be careful detecting it!), and, of course, the bulb glows or not.
This system is a bit like the tin cans in that the power source is the signal, but in this case what controls the information content is whoever flips the switch.
[I’ve been saying “primary” information. The light bulb system, for example, has information about how hot the bulb gets, how much current flows, what the voltage is, etc. This is all secondary information because it is not conditional to providing light.]
The fourth causal system is a conventional car engine.
There are a lot of causal chains going on in a car engine: pistons and valves reciprocating, shafts cranking, spark plugs sparking, pumps pumping, and so on. The causality involved mechanics, electronics, fluid dynamics, and combustion.
An engine has a network of separate causal chains that connect together to generate output. For example, moving gas from the tank through the carburetor and into the piston chambers is a distinct chain. Getting spark to the spark plugs is another.
For a car the primary information is the output revolutions and torque. (Which, like the light switch, is controlled by the operator.)
And, as in the previous cases, the states of the system directly and proportionally reflect that primary information content. When the car goes fast, the engine goes fast. When the car goes slow, so does the engine. If the car labors on a hill, the engine struggles. Downshift; it recovers.
The fifth causal system is a conventional (digital) computer.
This, like sound recording, is a system that uses electrical power both to enable the system to function and to represent the information the system handles.
On the small scale, there is similarity to the light switch in that individual signals (“bits”) are either on or off. The system treats ordered groups of many such signals as comprising unique symbols (“words”) based on the on-off patterns within each group.
By combining many bits, words can have many possible patterns. At a basic level of interpretation, those patterns are interpreted as numbers in base two.
But note that at the physical level, these are just a bunch of on-off switches. The causality of the computer is the causality of the switches. What the computer knows how to do — what its system states reflect it doing — is manipulate those switches according to built in rules.
I want to stress that the computer is fully defined, and fully described, in terms of turning switches on and off. That’s its physical causality. That’s all it does.
The operations the computer can do with symbols involve moving them around, directly manipulating the bits, and doing simple math on the number the bits are interpreted to represent.
As with previous systems, we can inspect the computer states and see that information in real time. For instance, as with the light switch, we can check the voltage. And, also likewise, those states reflect the information content.
Crucially, no description or definition of the computer refers to the software being run. A computer is defined as a machine capable of running software written for it. (A computer that never runs an application is still a fully functioning computer.)
Finally, the computer has some resemblance to the car engine in having many parts and a complicated architecture. In particular, a network of separate causal chains link to implement the machine’s operation.
In all cases, these systems transfer information, and in all cases, the system states directly and proportionally represent that information.
The main point is that when we inspect that information flow at any point in the system, it always resembles itself. Loud looks loud, soft looks soft, slow looks slow, fast looks fast. If a signal has low frequency, or high frequency, this is directly observable in the signal itself.
The signal means what it appears to mean.
This has gotten long, so I’m going to leave here for now.
Hopefully, nothing here is controversial (but we shall see).
Stay physically causal, my friends!