361

Physics, Astronomy & Cosmology / Re: How are physical units defined?

« on: 18/08/2022 05:50:53 »

The difference between the masses of the earth and the moon, or indeed any two bodies, does not constitute a fundamental physical quantity,

So you say.

I say it does constitute something more fundamental than physical units, in this case units of mass. The mass difference is physically significant and it does contain information. I don't understand why that means it is or isn't a physical quantity; I don't understand the significance of the rest of your post.

I say that difference is more fundamental and you say the distance between two points is fundamental. Why aren't the two points more fundamental?

Mass is defined without introducing a second object or point.

A point is defined without introducing a second point, but you need a second point to define a distance. You need a second distinct mass to define a mass difference likewise.

Like I said, difference is more fundamental than a choice of units.

362

Physics, Astronomy & Cosmology / Re: How are physical units defined?

« on: 17/08/2022 00:49:50 »

There are two unsupported claims there.
Were you expecting us to "just believe you"?

There are two unsupported claims? Surely the masses of the earth and moon being different isn't an unsupported claim?
Or perhaps I could weigh their masses and make sure, but how?

Is the other unsupported claim that the difference is useful information?
In physics, there are indeed things that you should 'just believe'. For instance, you should believe that distances exist and can be measured. That's actually what most people do believe, so physics teachers usually skip the definition of distance and measuring distance.

363

Physics, Astronomy & Cosmology / Re: How are physical units defined?

« on: 16/08/2022 21:54:59 »

Mass is mass. No difference between anything.

?? Not sure what that means; the mass of the earth and the mass of the moon are both masses. And yet, there's a difference between them; if I subtract one from the other, that's the difference, and it might be negative.

It might be the case that this difference has no physical significance (except that isn't true); it might be that the information the difference has in it, amounts to nothing useful. Except it does

364

Physics, Astronomy & Cosmology / Re: How are physical units defined?

« on: 16/08/2022 00:20:44 »

I think the more fundamental thing isn't actually any physical units, but rather difference.

A distance "lies between" two different points; a voltage "exists between" two different amounts of charge.

Without fundamental differences, measurement isn't that well-defined, I would say.

365

Physics, Astronomy & Cosmology / Re: How are physical units defined?

« on: 07/08/2022 05:19:02 »

My best attempt at explaining what distance is, is that it turns out to be a kind of information.
Or at least it does when we introduce a unit of distance and use it to measure another distance.

So it's like an alphabet with one character if you choose units that evenly divide a physical distance--the information per se is then literally the length of a string. Is information physically real or just conceptual? Can I really think of a real distance in metres as having entropy?

366

Physics, Astronomy & Cosmology / Re: How are physical units defined?

« on: 04/08/2022 22:28:12 »

Just checking I'm on the same page as most people, when I try to define physical stuff like distance.

Or rather, why I assume distances exist and that measuring them isn't a problem with any special difficulty. Distance, area and volume are such a part of our experience that we don't ask, usually, about why distances, or why spaces, exist.
Beyond measurement and theory, there is philosophy. I guess the philosophy of distance isn't interesting.
I remember though, an interesting question about time in an electronics lecture; why is time a real number (of seconds) in formulas and equations? The answer given was pretty much "it just is".

367

Physics, Astronomy & Cosmology / Re: How are physical units defined?

« on: 03/08/2022 23:57:36 »

Ok. So it looks like the uncertainty problem has come up. I suppose it's a rule of thumb that any measurement is uncertain.

And I've realised that the problem of 'fundamental' units is more or less resolved (depending on I also guess a realist or positivist stance) by the constant speed of light.  So the metre and second are defined in terms of this constant plus a constant frequency of light. Nonetheless the measurement problem doesn't go away--in wave mechanics there is always a classical uncertainty when measuring frequencies or counting wavefronts. (It's in Modern Physics by Kenneth Krane too)

So if, axiomatically, the speed of light is constant in  a vacuum, then there is a finite number of wavefronts in a unit distance, passing a fixed point, in a unit time. Uncertainty has to apply to this 'fixed' point, though.

368

Physics, Astronomy & Cosmology / Re: How are physical units defined?

« on: 02/08/2022 01:56:42 »

I'll add that there are also definitions of more abstract kinds of 'distance'; one obvious one is the distance between two primes in number theory.

Another kind is the distance of a path through a graph in graph theory, or the distance between two permutations of a permutation group in group theory. An affine distance is encountered sometimes in lectures on black holes and the like, but what is an affine distance? In any manifold distance is given by a metric; the surface of our planet qualifies as a manifold because it can be given coordinates, because it has distances 'built in' between different locations. It's just a fact of nature that planets have a finite volume and a finite surface, so finite distances are just a kind of trivial subset.

But a topological distance can be nontrivial, right?

369

Physics, Astronomy & Cosmology / How are physical units defined?

« on: 02/08/2022 00:32:22 »

I've been having a stoush with someone recently, about a simple enough thing which is, how physical units are defined.

It seems that, at first we don't bother defining distance, other than in terms of a unit thereof. That is, we just assume that distances are somehow axiomatic. This is clearly not the case when we define units of time; currently defined accurately in terms of a single, 'central' frequency, and the constant speed of light.

But physics doesn't stop and ask, "what really is a unit of distance", or "what is a unit of time", etc. Physics just assumes that units can be defined in terms of each other--speed, in terms of time and distance e.g.--and doesn't bother with the philosophy.

Distance "is what it is"; you measure some and just get on with it. In fact humans measure distances all the time, walking or driving is a 'measurement' of distance; when you move any part of your body it 'moves through' a distance and this constitutes a measurement (of distance). Accurate measurements aren't a rule as such, but are assumed to be a requirement if a theory is being supported by experiments.

Or, why don't we have definitions of time and distance, etc, in other more fundamental terms?

370

Physics, Astronomy & Cosmology / Re: What is charge?

« on: 06/06/2022 22:26:28 »

I think this kind of question, and the answers, point to something Feynman said about energy--nobody understands what it is.

But you can't help but notice that, after saying this, he goes on to say quite a lot about energy and work, which suggests that whether anybody knows what it "really" is, we get to use it anyway.

What he actually says is: "it's important to understand that in physics today, nobody understands what energy is", then he more or less adds "but it doesn't matter . . ."

But if you take his warning to heart, then you should be wary of someone saying they do understand what energy is.
In the same lecture, Feynman says energy is just a number. How can he know that? I'm still processing it, and he said it a while ago. Isn't he "just" saying it's a way to think about what it is, since "nobody knows what a number is . . ." ??

371

Physics, Astronomy & Cosmology / Re: Is mass a number?

« on: 30/05/2022 03:00:09 »

That is the principle of realism, and the only way it can be true is if one accepts superluminal causality. Physics isn't so classical as you'd like it to be.

Well, sorry, but that doesn't say much about whether observers are needed so that "reality" exists.

It doesn't say much either, about measuring a real distance, or a real interval of time. These are both fundamental physical quantities, I challenge anyone to devise an experiment which doesn't measure both of these in some direct way.

Usually you don't need to learn about time or distance when you study physics, you assume, like everyone else, that they can be measured and that's sufficient.

372

Physics, Astronomy & Cosmology / Re: Is mass a number?

« on: 30/05/2022 01:18:27 »

The person getting challenged is you- because you keep saying things that are wrong.

What things am I saying that are wrong? Please explain.
I haven't said mass is a number; I haven't said mass is a concept. I haven't said charge and spin are concepts. I haven't said a field is a concept. That's what someone else is saying.

I'm not saying it. So what am I saying that's wrong?

373

Physics, Astronomy & Cosmology / Re: Is mass a number?

« on: 29/05/2022 22:34:38 »

This thinking, at what used to be a science site but is now I don't know what exactly, is extended to the electron like this:

Electrons are real particles, but their mass is a concept, invented by humans. The electron's charge is a concept and so is the spin.

Yeah, really.

There's a thing called realism, in physics, which asserts that a real universe exists whether or not observers exist, who then construct theories to explain their observations. I don't need to look at the moon to make it exist.

But I don't know how a theory that says it's all conceptual, actually fits in there. I don't think it does, because an experiment involves measurements; ultimately wouldn't that mean you have to define distances as conceptual--a metre of distance is also a concept? It seems a bit woolly.

Nobody else is challenging this person at this site; I've given up.

374

Physics, Astronomy & Cosmology / Re: Is mass a number?

« on: 09/05/2022 19:56:43 »

Thanks  for the replies.

The "mass is a number" argument is ongoing.

I don't know how to argue against it. My understanding of what it is is that it's physical and all matter "has" mass.
If it was just a number why do we give it units of kg? Why is 1 kg a number? What does the "mass is a number" principle tell us about physics?
Why bother trying to argue its validity or usefulness, or prove it isn't true?

This is the latest version of this person's thinking:

Objects have inertia because they are made out of matter, not because they "have mass". Mass is a property that quantifies inertia, but it doesn't cause inertia. How could a concept cause something physical?

Nah . . . that just isn't right is it? It seems this person is confused about what physical means. I should just give up trying to understand them, right?

375

Physics, Astronomy & Cosmology / Is mass a number?

« on: 29/04/2022 10:00:40 »

This idea is being promoted at another site. I can't make much sense of it.

But I'm wondering if it's true does that mean there's a proof? Isn't it relatively straightforward to prove a number exists?

Or is there a way to prove mass isn't a number? Or do you just accept mass occupies a volume, the same volume some matter is in and forget about proving it?

376

Physics, Astronomy & Cosmology / Re: Science and information theory

« on: 17/04/2022 19:35:08 »

It might be the case that understanding the nature of information-as-patterning could lead to insights into the nature of the workings of the human, or any animal brains. A paper I've been reading says this:

Abstract
This article reviews the preliminary results of an analysis of the brain that may supplement our
current understanding of its structure and function, even if by falsification. This analysis seems to
reveal that the information in a system of the brain can be quantified to an appreciable degree of
objective precision, that many qualitative properties of the information content of a system of the
brain can be inferred by observing matter and energy, and that many general features of the
brain’s anatomy and architecture illustrate simple information-energy relationships. It is possible
that the brain provides a unique window into the relationship between matter, energy, and
physical information.

--https://www.biorxiv.org/content/biorxiv/early/2016/07/06/060467.full.pdf

377

Physics, Astronomy & Cosmology / Re: Science and information theory

« on: 10/04/2022 10:15:18 »

I think just as a reality check, I should define my version of information.

It's a pattern, however that gets defined, in matter. Really information entropy is only given that name because of a formula that looks superficially like the one for thermodynamic entropy.

Information and its entropy is just a structure, an arrangement of particles of matter, then we decide which ones are interesting or useful. I might be going a bit far with the superficial thing, but what information is, still seems to be an open question, so that's my best answer. Patterns in nature are what motivates us to create them ourselves, type of thing; but it's all just structure of some kind that matter allows.

Shannon "only" showed that the information content is proportional to the expectation of "seeing" it. So if you arrive home and the TV is missing, that has more entropy than if it's still where you expect it to be. You see a different pattern than what you expected.

378

Physics, Astronomy & Cosmology / Re: Science and information theory

« on: 06/04/2022 20:21:01 »

Information can be rather abstract, as can its counterpart Entropy.

I'm interested in Landauer's principle. I've studied information theory and Shannon entropy (I have a double major in math and CS)

Recently I spotted some updates--new research--that claims to refute the principle in the low-dissipation regime, that is, information was erased by resetting a memory and the heat generated was well below Landauer's limit.
Right next to this new result was an article that confirmed Landauer's limit in a quantum memory.

So now I'm asking myself, did Maxwell's demon really get "exorcised" by Charles Bennett? Is there something more fundamental about information and its erasure or loss, that everyone is overlooking? I guess the jury is still out; Hawking's paradox also has a lot of open questions; it's all theoretical I realise, actual measurements to confirm certain theoretical ideas about the nature of black hole entropy, will have to wait for some pretty clever devices to appear.

Than again, what does QM predict, about the nature of quantum information? If we knew that, why are there so many discoveries that QM hasn't predicted? For example the quantum Hall effect, certain quasiparticles that have only recently been observed, or even how small a physical object needs to be to exhibit quantum behaviour such as superposition of states? These are things that only experiments and research with new materials can answer, it seems. But why is that?

379

Physics, Astronomy & Cosmology / Science and information theory

« on: 04/04/2022 19:40:39 »

I've recently been trying to have a discussion about the relevance of information, and what exactly is information, at another site.
It didn't really get anywhere and I found myself up against some rather fixed views. Science is meant to be about enquiry, I thought. So why are so many people not willing to examine their own beliefs and ideas, why is there so much fear about examining the possibiity that you don't "really" understand something and might need to adjust those beliefs?

But to the topic: I mentioned Landauer's principle, what it says and tried to examine whether it does pertain to erasure of information.

Well, one person who is a moderator tried to convince me that information isn't physical, so erasing it doesn't make any sense. He also appeared to believe that thoughts aren't physical, although strangely, the process of thinking, or conceiving is physical. I think that's really confused and not particularly enlightening.

So is information physical? Does the question come down to is information a pattern and can a pattern be non-physical? Moreover, is Landauer's principle true? I know it's generally accepted as true, but is that because computers are also heat engines, or are they?

Or take a look at the science of astronomy: is it just an information-gathering disciplne? how is the information gathered physically; what do humans do with this information?
How does the theory that information is not physical, fit into it?

Another question I have is, can information be characterised without the notion of a sender, a receiver, and a communications channel for transmission of signals?

380

Plant Sciences, Zoology & Evolution / Re: If whales have such huge brains, why are they not doing intelligent things?

« on: 18/03/2022 07:11:43 »

Humans can communicate with each other more intelligently than they can communicate with whales; this applies the other way as well (!)

That of course says absolutely nothing about which species is "more" intelligent. And how can we tell if human intelligence is more of anything than whale intelligence? it's one of those questions that needs a context.