321

Physics, Astronomy & Cosmology / Re: Talking about Physics

« on: 27/04/2023 01:46:34 »

Are there nonphysical units or do you just mean units?  The reason I ask is because energy has units and energy itself is not what I would call a physical thing.

Ok. Richard Feynman said nobody knows what energy is, I'm guessing that still holds. So, can you or anyone say it's not a physical thing?

In the lecture where Feynman says that, he also describes forms of energy, like heat, electricity, electromagnetic radiation etc. We know that energy has different forms and these can be converted; we know how to make heat engines that do work.

We know a lot about this thing called energy, but according to Feynman we can't say what it is, although it's ok to think of it as like a number that doesn't change.

322

Physics, Astronomy & Cosmology / Re: Talking about Physics

« on: 27/04/2023 01:36:34 »

My opinion is that physics is the business of building mathematical models of things that happen (or don't happen - see below*) in order to predict what will happen next or if we alter something.

Yes, fair enough. I would add that the models arise because Physics is also the science of measurements; it's about "how are we measuring", not so much what the thing being measured is except that "it's physical".

Try to put that into the very simple context of measuring a distance. How do we measure a distance? We use a fixed unit of . . . distance. Algebraically speaking, we tile a one dimensional space or make a pattern appear. Patterns always contain some kind of information.

323

Physics, Astronomy & Cosmology / Talking about Physics

« on: 26/04/2023 02:00:21 »

Hi. I recently had a discussion online about the subject of physics, in which I posted something about simplification, and how that seems to be where physics starts, at least. At the simple end.

A couple of examples are 1) how we can make a large, complicated object like a planet, into a less-complicated 'blob' of matter; since the mass of the planet is the important detail we don't need to know about how the matter is distributed or anything else about it. We can replace the planet with an equivalent mass, theoretically.

Then 2) there's the particle in a rectangular well, a box with infinite potential.
--In electronics you study circuits with ideal elements even though real electronic devices aren't ideal.

And at the really simple end are time and distance. The first, time, is still the subject of debate as to its conceptual existence, or actual physical existence. Distance on the other hand isn't a thing we question very much, although there are theories that suggest the universe is a hologram they are quite complicated, not easy to understand the way we understand distance innately.

If we had a simple explanation for why time and distance appear to be so different, maybe it would all be simple and easy to understand.

But usually you start at the simple end, right? I don't know, perhaps the way momentum starts with a mass and a velocity, but depending on whether you have a relativistic or a quantum context you then have a more complex physical thing. Or do you just have a more complex idea?

p.s. I was asked more than once, in the discussion I mentioned, to define what I thought "physical" means. So I said anything with physical units is physical. I also would say a distance is about as physical as you can get.
You don't erase a distance by measuring it; time on the other hand doesn't seem to work that way.
(?)

324

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

« on: 18/08/2022 22:35:22 »

You seem not to understand the word "constitute" , nor the difference between a ratio and a difference.

You seem not to understand a rational argument. How to make one, that is.

Please explain your claim, so far just a bare statement, that the difference between two masses does not constitute a fundamental physical quantity.

I want you to explain all the terms you're using. Explain what a physical quantity is, then what a fundamental physical quantity is, with examples. I want it absolutely clear and irrefutable so that the difference between two masses is excluded from the set of fundamental physical quantities.

325

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.

326

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.

327

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

328

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.

329

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?

330

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".

331

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.

332

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?

333

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?

334

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 . . ." ??

335

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.

336

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?

337

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.

338

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?

339

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?

340

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