What Does "Physical" Really Mean?

[Polymath257]

General Relativity describes the geometrical relationships between a 4-dimensional manifold called "spacetime" and an energy-momentum tensor. Does the fact that the geometry of spacetime is relative to such factors make spacetime "physical"? What is your definition of "physical" again?

Yes, it does mean space and time are physical. Space and time interact with the components of the energy-momentum tensor, which are, not surprisingly, energy, momentum, and stress. All of those are pysical, so space and time are physical.

Again, to be physical means you interact with something previously known to be physical. It's an inductive definition.

 

[Nous]

Yes, it does mean space and time are physical. Space and time interact with the components of the energy-momentum tensor, which are, not surprisingly, energy, momentum, and stress. All of those are pysical, so space and time are physical.

Again, to be physical means you interact with something previously known to be physical. It's an inductive definition.

Yes, that's all very consistent about the manifold.

 

[Polymath257]

It would be unbelieveable to people in the 18th century to learn that the concept of and issues about "matter" have become really unimportant to physics these days. It's easy to imagine the concept of "matter" being dispensed with in the future.

Matter is a concept that is still useful for the atomic level and above (and, at times, for nuclear physics). Everything that was previously considered to be matter is now considered to be physical, but some additional things (like photons and other bosons) are also considered to be physical.

Define "physical state".

Why? It only leads to semantic games that don't serve to enlighten the topic. vaguely, a physical state is the collection of physical properties of a physical system. Such properties at least include mass, energy, momentum, angular momentum, spin, charge, relative velocity, etc. Essentially, anything physics needs to describe the behavior of the system.

 

[Polymath257]

Yes, that's all very consistent about the manifold.

The manifold is our mathematical model. Don't con model with the reality.

 

[Nous]

The manifold is our mathematical model. Don't con model with the reality.

In what ways are the manifold and the reality distinguished?

 

[Polymath257]

In what ways are the manifold and the reality distinguished?

How do you distinguish a finger pointing to the moon and the moon?

 

[Nous]

How do you distinguish a finger pointing to the moon and the moon?

Yes, grasshopper, but I'm not clear on how that analogy helps to identify the supposed distinguishing traits of the manifold and the reality. If the GR manifold is inadequate in describing the reality, then you need to point out how, as it is you who is warning against conflating the two.

BTW, did you see my questions to you in #38?

 

[siti]

I've never heard anyone speaking of God as without characterization until she is completed. I've lived a very sheltered life.

Ah! I see - that's the problem - you are interpreting "incomplete" or "evolving" as "without" - so much for precise definition of terms. Black and white thinking in a grey-shaded world. And if you've never heard of anyone speaking of an evolving God that can, and does, acquire characteristics over time - well - you have now. But its only really a restatement of pantheism in view of what we now understand about the evolving cosmos and pantheism is certainly not a new idea.

 

[Nous]

Ah! I see - that's the problem - you are interpreting "incomplete" or "evolving" as "without"

Only because the encyclopedia articles failed to articulate any definition whatsoever of the adjective "physical" except what "a completed physics" will be about.

 

[Polymath257]

Yes, grasshopper, but I'm not clear on how that analogy helps to identify the supposed distinguishing traits of the manifold and the reality. If the GR manifold is inadequate in describing the reality, then you need to point out how, as it is you who is warning against conflating the two.

BTW, did you see my questions to you in #38?

See #39

 

[Nous]

Once again, this depends on specific definitions. Using the information=physical state definition, the information would have existed prior to creatures able to interpret it. Using the definition in terms of apprehension, it would not have.

Obviously those are two contradictory concepts of "information". Both concepts can't be true.

Further, to say that information is nothing more than "the physical state," and that information does not itself cause that state or that state's further effects, it makes information an unnecessary redundancy. Is that correct? We don't need the concept of information; it's just an needless complication?

Here is the basic question: does it make sense to say something exists that does not interact with anything physical? I would say no.

From what possible evidence would one deduce that nothing exists that doesn't interact with something "physical"? The proposition that nothing exists that doesn't interact with stuff that is "physical"--which you defined as stuff which interacts with stuff that is "physical"--is question-begging. It's that problem of circular definitions again. Physicalism just never gets beyond traveling on the hamster wheel.

 

[siti]

Only because the encyclopedia articles failed to articulate any definition whatsoever of the adjective "physical" except what "a completed physics" will be about.

But that doesn't mean that we cannot define some things as unquestionably physical does it - you even did so yourself with your 'empirical' and 'sense datum' thing. Anything that has mass/energy is unquestionably physical and there is absolutely no reason to anticipate that this will change. But if we are talking about 'information' we are not sure - the current definition is not precise enough to make the distinction - if it IS physical then certainly "a completed physics" will be able to explain it and it can then be brought into the physical 'fold' along with things that have mass/energy and things from which we can acquire a 'sense datum' etc. - if it turns out that it is NOT physical then "a completed physics" could not - even in principle - explain it and we will have to look elsewhere.

The idea that radiation of a wavelength that is not quite within the current conventional approximations of 'red' to be considered unquestionably red does not mean that there are, in fact, no unquestionably red things at all, does it?

 

[Nous]

But that doesn't mean that we cannot define some things as unquestionably physical does it - you even did so yourself with your 'empirical' and 'sense datum' thing. Anything that has mass/energy is unquestionably physical and there is absolutely no reason to anticipate that this will change. But if we are talking about 'information' we are not sure - the current definition is not precise enough to make the distinction - if it IS physical then certainly "a completed physics" will be able to explain it and it can then be brought into the physical 'fold' along with things that have mass/energy and things from which we can acquire a 'sense datum' etc. - if it turns out that it is NOT physical then "a completed physics" could not - even in principle - explain it and we will have to look elsewhere.

That sounds all very sensible, but I am not convinced that there will not be more revolutions in physics, ones more radical than the relativity and QM revolutions, so that one day physicists and everyone else agree that "nothing is physical".

Moreover, I am even less convinced that it is coherent to anticipate a time when physicists (et al.) will say, "Physics is complete. There will be no more discoveries. There will be no new ideas about the world."

The idea that radiation of a wavelength that is not quite within the current conventional approximations of 'red' to be considered unquestionably red does not mean that there are, in fact, no unquestionably red things at all, does it?

Well, I don't know. I thought we could fairly well determine what is within the range of 625-740 nm.

 

[blü 2]

So this doesn't mean that the images and other features of things that are imagined do not exist, but they are merely non-physical.

The concept of a unicorn is a physical set of relations between neurons in the brain; and the drawing of a unicorn is physical as to drawing and paper; but the thing conceived / drawn has no counterpart in reality. It's imaginary.

The concept (physical) of 'a chair' is an abstraction. It too has no counterpart in reality. The concept of 'this chair' is the concept of a real thing, since it has a real counterpart (is physical).

Thinking about the case law that premises a court decision, and how that case law justifies that decision but not another seemingly closely related proposition is quite different than and distinguishable from thinking about the topic of this thread (what does 'physical' mean?).

Is it? Both involve thinking about and reasoning about various concepts in relation to each other. Many of those concepts are abstractions or generalizations, and many of them are concepts of things with physical existence (people, facts) and real states of affairs (also physical ─ though come to think of it, in law many of them have to be reconstructed from often inconsistent evidence, so perhaps they're better regarded as fairly-well-founded hypotheses).

Is there any evidence that one can distinguish those topics by examining what's happening in another person's brain?

As far as I'm aware, not so far. We can, as I recall, determine in real time from a brain scan MRI what area of the brain the subject is employing ─ doing sums, consulting memory, editing and censoring, and quite a few more ─ and following a famous experiment since improved on, we can determine when the nonconscious brain makes a decision, and when the conscious brain becomes aware of that decision, up to ten seconds later ─ but as far as I'm aware we can't determine the particulars, like, What decision? or What sum? or Legal or medical or general knowledge problem?

The one from information theory.

That, at least in Shannon's original papers, refers to strings of 0s and 1s, encoding letters, pictures, tables and so on.

But I don't see how that would account for Wheeler's statement; so he may well have been using some further refinement of Shannon's ideas. But in fine, I don't know enough to attempt a useful comment.

However, I still see no significant distinction between 'information' (in physics) and 'data'. Though I may doubt that this is what Wheeler was doing, on various occasions of reading about such matters I've thought the distinction is an emotional one, trying to invest data with super-powers.

 

[Polymath257]

Obviously those are two contradictory concepts of "information". Both concepts can't be true.

Yes, they are different concepts. Both can legitimately be called 'information', but if you are doing technical work it might be a good idea to distinguish them. Sort of like how 'sound' can be used both for the physical pressure wave and the perception a person has. Different concepts, same word.

As for being 'true': definitions are neither true nor false. They are useful or not.

Further, to say that information is nothing more than "the physical state," and that information does not itself cause that state or that state's further effects, it makes information an unnecessary redundancy. Is that correct? We don't need the concept of information; it's just an needless complication?

More like a *useful* complication. So, for example, we don't *need* the concept of temperature. The concept reduces to the average kinetic energy of molecules. But it is still a *useful* property to have and to discuss. Information is the same way: it is reducible to the physical properties, but it is *convenient* to separate it out as a property for discussion.

From what possible evidence would one deduce that nothing exists that doesn't interact with something "physical"? The proposition that nothing exists that doesn't interact with stuff that is "physical"--which you defined as stuff which interacts with stuff that is "physical"--is question-begging. It's that problem of circular definitions again. Physicalism just never gets beyond traveling on the hamster wheel.

OK, so how do *you* define the concept of 'exists'? I gave a definition. I argued for that definition (by pointing out it is meaningless to talk about the existence of anything that doens't interact). So I find it to be a useful concept. Now, if you have a different definition of the term 'exists', then we can discuss whether that definition is useful and how the two definitions differ.

 

[shunyadragon]

The question is what does "physical" mean.

The definitions you provided are adequate for "what does "physical" mean."

 

[Polymath257]

But I don't see how that would account for Wheeler's statement; so he may well have been using some further refinement of Shannon's ideas. But in fine, I don't know enough to attempt a useful comment.

However, I still see no significant distinction between 'information' (in physics) and 'data'. Though I may doubt that this is what Wheeler was doing, on various occasions of reading about such matters I've thought the distinction is an emotional one, trying to invest data with super-powers.

One of the things that Wheeler was emphasizing was that physical things are defined by how they interact. So, an electron is something that interacts via the electromagnetic force with a certain strength (charge), interacts with the gravitational force with a certain strength (mass), doesn't interact via the strong force, and interacts with other leptons via the weak force. The specifics of those interactions (the information, in Wheeler's portrayal) are what define specific physical entities. The types and strengths of the interactions are the information about the thing which then defines that thing.

 

[siti]

That sounds all very sensible, but I am not convinced that there will not be more revolutions in physics, ones more radical than the relativity and QM revolutions, so that one day physicists and everyone else agree that "nothing is physical".

...or that everything is? Of course there might very well be many more revolutions in our understanding but how does that invalidate physicalism? By your definition of physical things - i.e. 'things from which we can acquire a sense datum' - isn't physicalism simply defining the limits of what we will ever (even in principle) be able to discover empirically? We might be like the drunk searching under the lamppost for the keys that he knows he may have dropped elsewhere - but how will we ever find the secrets of the universe if they truly lie hidden in the darkness beyond the scope of the empirically observable?

Moreover, I am even less convinced that it is coherent to anticipate a time when physicists (et al.) will say, "Physics is complete. There will be no more discoveries. There will be no new ideas about the world."

Who is even suggesting that?

Well, I don't know. I thought we could fairly well determine what is within the range of 625-740 nm.

You can, but try looking at the emission line spectrum of neon and tell me that the lines immediately either side of precisely 625nm are unquestionably 'red' or unquestionably 'orange'.

 

[Nous]

The concept of a unicorn is a physical set of relations between neurons in the brain

Cite that evidence.

Thinking about the case law that premises a court decision, and how that case law justifies that decision but not another seemingly closely related proposition is quite different than and distinguishable from thinking about the topic of this thread (what does 'physical' mean?).

Is it?

Dramatically different, even though logic is used in both cases. For instance, a 2010 opinion by the Third Circuit, In re Application of the U.S. for an Order Directing a Provider of Electronic Communication Service to Disclose Records to the Government, which the Supreme Court might or might not lend its attention to this term, stands for the proposition that the Stored Communications Act, 18 USC § 2703, does not require courts to issue orders to disclose cell site location information to the government upon application even if the government provides (quoting the statute) "specific and articulable facts showing that there are reasonable grounds to believe that the contents of a wire or electronic communication, or the records or other information sought, are relevant and material to an ongoing criminal investigation." This is a unique opinion on the meaning of § 2703, and it was a unique holding in denying the government the information it sought in those circumstances. Those are quite different facts and issue than any facts and issues relevant to the topic of this thread, and the facts are obviously utilized in different ways.

That, at least in Shannon's original papers, refers to strings of 0s and 1s, encoding letters, pictures, tables and so on.

But I don't see how that would account for Wheeler's statement; so he may well have been using some further refinement of Shannon's ideas. But in fine, I don't know enough to attempt a useful comment.

I don't either at the moment. Wheeler obviously inferred something that Shannon never did.

 

[blü 2]

One of the things that Wheeler was emphasizing was that physical things are defined by how they interact. So, an electron is something that interacts via the electromagnetic force with a certain strength (charge), interacts with the gravitational force with a certain strength (mass), doesn't interact via the strong force, and interacts with other leptons via the weak force. The specifics of those interactions (the information, in Wheeler's portrayal) are what define specific physical entities. The types and strengths of the interactions are the information about the thing which then defines that thing.

Ah! Thank you. Very interesting.

Do those particular pieces of information differ from data, would you say? Or, are they 'information' because 'information' in physics only applies to specific categories of data?