[alancalverd]

Beware of falling into the trap of thinking that a photon is a "thing". It is a model that describes the interaction of electromagnetic energy with material entities. Pointless books have been written, and careers ruined, over whether light "is" a wave or a particle: it is a phenomenon that is best described by two different mathematical models depending on which of its properties you are interested in.

Is a man the embodiment of a creative and beautiful soul, or 70 kg of water and a few bones?  Depends on whether you are dealing with a live musician or a dead one.

"Complete" surprise is rare. A lot of particles were hypothesised because of an apparent breach of the usual conservation rules, and then discovered when we have worked out where to look.   

[Zer0]

Given that such "new" quantum effects have appeared unexpectedly, what does that do to any quantum philosophy?
The philosophical problem might be connected to how the theories we have, don't tell us all that much in terms of what to expect. Unlike Newtonian mechanics which generally does.

Maybe the Theories propose the idea that We should accept Probabilities, not similar to expecting the unexpected.

[varsigma (OP)]

"Complete" surprise is rare. A lot of particles were hypothesised because of an apparent breach of the usual conservation rules, and then discovered when we have worked out where to look.   

Ok. I'd say that the Higgs boson and the top quark qualify as discoveries that at least had an expectation of being detected.
But another example: the fractional quantum Hall effect, was not hypothesised although it was detected.

And there are plenty of other examples of quantum effects, that have been detected experimentally but were not expected.
So that could explain to some extent why philosophers struggle with, you know, ontology or objective reality.
How are they dealing with a nonlocal universe? Even understanding what that means has to be a problem for a lot of people. I admit I'm probably one of those.

[alancalverd]

So that could explain to some extent why philosophers struggle with, you know, ontology or objective reality.

Philosophers invent things to struggle with, because they don't have meaningful lives.

In my world people have real problems and I get paid to understand and solve them with physics, chemistry, maths, brute force and duct tape. Very satisfying.

On reflection, radioactivity was indeed a complete surprise, along with the discovery of life in deep ocean vents, Earth's cyclic climate, and a whole lot of stuff that hadn't been seen until someone looked out of curiosity rather than necessity. In that context, the exploration of the moon and Mars hasn't provided much bang for your buck - so far.

[varsigma (OP)]

In my world people have real problems and I get paid to understand and solve them with physics, chemistry, maths, brute force and duct tape. Very satisfying.

I would agree that hands on is more interesting than sitting around wondering what everything is, erm, is.

I personally find it frustrating when people don't seem to be able to question their own understanding or even admit they don't, nor does anyone else really, know that much about it after all.

Sure there is all that mathematics and a bunch of concepts, there are things that can go into bottles, and things that can't, but is that it? I shudder when I consider the possibility.

This other "discussion" (another forum) about what the word physical means, as opposed to what a physical thing "is", has  problem right off the bat. The universe is full of information, and we as observers decide what it means. Information isn't "encoded" with any meaning (at all).

Assume (ignore any objections here) that Hydrogen is a form of information. To us as observers the existence of this information leads us to theorise that it means stars, in the future. Hydrogen "by itself" tells us no such thing.

How useful is the "put it in a bottle" approach? What is a bottle, first of all?
Is it an entity, then what are its attributes? Is it an attribute because it's a particular shape, the material it's made of is the entity?

Then what does "in the bottle" mean? The material the bottle is made of is "in" the bottle a priori, and material has mass so mass is "in" the bottle. Now you struggle with what the mass of this bottle means, or with the difference between what the bottle is made of and what you can put in the ah, interior, whether this or that is an entity or an attribute--the bottle "has" mass, so it's an attribute of this thing you're calling a bottle.

What a headache.

[geordief]

What a headache

Or what fun.
Plus ,what is to say that those abstruse considerations may not give rise to practical outcomes  eventually?

What of Einstein's proposal that spacetime was curved? How practical  must that have seemed to anyone else at the time?

[varsigma (OP)]

Or what fun.
Plus ,what is to say that those abstruse considerations may not give rise to practical outcomes  eventually?

Abstruse considerations being the "can it go in a bottle" rule?
I haven't been able to see any advantage in doing this. As I stated, what does a bottle already have in it? What does "in" mean?

This attempt to apply a somewhat ill-defined "model" to the physical world I think fails because, for one, it's anthropocentric. It assumes that anything physical is something humans can see and feel.
I think one question that upsets this model is "is an atom a bottle, what does it contain?"

Further, I think any arbitrary distinction at the macroscopic level (it goes in a bottle or it doesn't) is going to have to leave a lot of physics in some kind of twilight zone. We already know that computing with classical information is a completely different physical context than computing with quantum information (i.e. entanglement between particles).

You can't put entanglement in a bottle; therefore . . . ??

[varsigma (OP)]

I'd like to canvas some responses, about the subject of energy and how this is understood.

I've been having a back and forth with someone about this topic, which centres around something Richard Feynman said in one of his lectures. This was that "in physics today, it's important to understand that nobody knows what energy is".

It's important to note that Feynman distinguishes between knowing what a thing is, and understanding it. We certainly do understand how to "use" energy. We build machines (heat engines) that cycle this thing called energy. We understand energy well enough that we can convert it from one form to another. So, it's interesting that we can do all that with a thing we have no knowledge of, in terms of "what" it is.

To my way of thinking, energy could well be an anthropic invention, a very useful one. It can be seen as a kind of physical boundary, or limit. It is undeniably a very useful and fruitful idea. But does it "really exist"?

Does it matter? What does "really exist" mean, anyway (one for the philosophers, perhaps)?
One more detail: Feynman says that energy is a conserved numerical quantity. What's your opinion of that? Do you think he's saying energy is just a number?
If he is, is he contradicting his "nobody knows" proposition?
Is energy a physical thing, or a numerical quantity, and are those two things different?

Oops, I just realised the answer is, nobody knows.

[Eternal Student]

Hi.

I'd like to canvas some responses, about the subject of energy and how this is understood.

   There was a fairly recent (end of 2022) discussion in this thread:
https://www.thenakedscientists.com/forum/index.php?topic=85721.0

I don't suppose anyone would mind discussing it again but there's already quite a bit of information and opinion in that thread.   It's recent enough that many of the regulars will remember a little about it.

@alancalverd said this:

In simple terms, there isn't a simple explanation or even a simple definition.  Energy is one of the quantities that is conserved in classical physics, and very few adults have any idea what that means.

@Bogie_smiles said this:

In the simplest terms, I have always understood energy as the ability to do work.

@paul cotter  said this:

To return to the original question, I propose the following: energy is the capacity to do work with the limitation that in the case of thermal energy some or all( worst case ) will  not be able to do useful work.

@Eternal Student  (me) said stuff that took a lot of space and I'll just try to summarise here:
    1.   School level definitions don't really do it (Energy) any justice.
    2.   Energy is that which appears in Noether's theorem and as such it can only be identified as a conserved quantity in systems with time translation symmetry.  For example, in our expanding universe, there isn't a conserved quantity you can call energy.   (To condense that severely:  What most people think of as Energy is not conserved).

- - - - - -

One more detail: Feynman says that energy is a conserved numerical quantity. What's your opinion of that? Do you think he's saying energy is just a number?

    Yes, that is pretty much the gist of what he was saying in that lecture.
    There were some other lectures discussing symmetries and conservation laws but they are more specialised.  He discusses symmetry and conservation laws mainly in the context of Quantum Mechanics:
You see, therefore, the relation between the conservation laws and the symmetry of the world. Symmetry with respect to displacements in time implies the conservation of energy;...

[Taken from Feynman 17-3  between eq. 17.24 and 17.25.  https://www.feynmanlectures.caltech.edu/III_17.html ]   

    In the time of those lectures the relationship was mainly used just in Quantum mechanics but that particular relationship is much more general and not just limited to QM.

Best Wishes.

[varsigma (OP)]

Yes, that is pretty much the gist of what he was saying in that lecture.
    There were some other lectures discussing symmetries and conservation laws but they are more specialised.  He discusses symmetry and conservation laws mainly in the context of Quantum Mechanics:
You see, therefore, the relation between the conservation laws and the symmetry of the world. Symmetry with respect to displacements in time implies the conservation of energy;...

I think you need to be careful about the phrase "numerical quantity" that Feynman uses. My opinion of it is that he's reminding everyone he also used an analogy of counting up 'abstract' children's toy blocks.

Numerical quantity I think should properly belong in the theoretical ballpark because it either means a measured quantity of say, matter, or it means an abstract quantity that has physical units.
It can't be that nobody knows what energy is, but we know it's a number, because . . . we then know what it is.

[Eternal Student]

Hi.

I think you need to be careful about the phrase "numerical quantity" that Feynman uses. My opinion of it is that he's reminding everyone he also used an analogy of counting up 'abstract' children's toy blocks.

   You are free to make of Feynman's lectures what you please, however there are some conventional understandings of what was said and intended.   Feynman wasn't really using language or addressing his lectures to an audience of philosophers, he was aiming at scientists and that particular lecture was an early one for the students (in their progress through undergraduate studies).  So he was aiming to break some misconceptions from school and provide a good introduction to undergraduate level physics.
   
    Given the audience, it's fair to say that Feynman was attempting to communicate something different when he said "Energy is a numerical quantity".   He meant that it is a quantity AND ALSO it has numerical properties.

     Most people would assume the natural division was between numerical quantities and non-numerical quantities.    Even the word "quantities" is an issue since in the English language one tends to think of something you can count and number.   Overlooking that, a numerical quantity is one where a number is assigned to it.  A non-numerical quantity is something that doesn't meaningfully behave like a number.
   How many people are in this room?   How long is this string (in inches)?    Those are numerical quantities.
   What is the name of this person?   What is the colour of this t-shirt?   Those are non-numerical quantities.

Numerical quantities follow all the properties you expect of things that are numerical.   For example you can order them,  4 (people in this room) is more than  2 (people in this room).      You can also multiply and add them meaningfully,   a room with 4 people in really does have  2 times the number of people as a room with 2 people in it.   Similarly you can add the people from two rooms together and you will get a number of people that is the sum.

At best, non-numerical quantities can be ordered but they do not have all the properties of numbers.  Quite often you can't even order them.    Example:    "Pink" is not more than "Blue", there is no natural order relation on non-numerical data like colours.    If you assessed peoples size as "Small", "Medium" or "Large"  then that data actually is partially ordered but it still lacks all the other properties of numbers,   for example  you cannot add small people together and end up creating a medium person.   Meanwhile, if you had actually measured the mass of the person, then that would be a numerical quantity.

What Feynman was saying is that Energy has the properties you expect of a numerical quantity rather than being some qualitative or descriptive data only.   So, it's not as if at the start of an experiment all we can say is that the total energy was "medium" and at the end of the experiment the amount of energy was also "medium".   Energy isn't just any old sort of descriptive quantity, it is a numerical quantity.   So you can meaningfully add two energies together   AND  write a conservation law as a conventional mathematical expression:   
    The numerical sum of all energies at the start  =   the numerical sum of all energies at the end.

It can't be that nobody knows what energy is, but we know it's a number, because . . . we then know what it is.

    It is commonly understood that what Feynman was saying is that all you (his students) should accept about energy is just it is a numerical quantity which seems to be conserved (does not change with time) in all experiments and observations.  Just don't make any further assumptions about it - because you can't.
   As discussed in an earlier post,  Feynman did have more to say about energy in some later lectures.  So these are not the last or final word from him but I am confining my attention to the spirit and meaning of just this lecture.
 
Best Wishes.

[varsigma (OP)]

You are free to make of Feynman's lectures what you please, however there are some conventional understandings of what was said and intended.

I've noticed that plenty of people seem to be able to make what they please of what Feynman said in that lecture. For instance, they maintain doggedly that Feynman means energy is a concept. That's what it is in any theory, but what about the physics?

Feynman wasn't really using language or addressing his lectures to an audience of philosophers, he was aiming at scientists and that particular lecture was an early one for the students (in their progress through undergraduate studies).  So he was aiming to break some misconceptions from school and provide a good introduction to undergraduate level physics.

Yep. I think he was trying to uncover the big secret about physics; theories don't really tell you what physical things are, mathematics is about relations between sets of numbers. I can't see that therefore taking away the idea that he says "energy is a number", when he actually says "energy is a conserved numerical quantity", follows at all.

If we don't know what energy "really" is, and if mathematics doesn't tell us beyond it being conserved (numerically), that's as far as it goes. What about experiments and measurements?

What is a measurement "really"?

Given the audience, it's fair to say that Feynman was attempting to communicate something different when he said "Energy is a numerical quantity".   He meant that it is a quantity AND ALSO it has numerical properties.

Yes. I would caution though, that that conclusion needs to stay in the theoretical domain. Recall that properties are things that entities have, except so far we have that energy is numerical. Numbers are entities because they have properties or attributes, right? Numbers most certainly don't have a physical existence, all they have is a value.
Perhaps that's why some people like to believe they know what energy is--it's a  number. Except that isn't what Feynman actually said.

So, measurement. A physical quantity is measured directly or indirectly and mapped to a numerical quantity so we can do some math. I maintain that the only physical quantity that can be measured directly, is distance. Believe it or not, I've been trying to have a discussion with someone who is convinced that distance, because you can measure it, is a concept. Although the out here is, space is real.

Yeah, doesn't work for me.

[Eternal Student]

Hi.

I've noticed that plenty of people seem to be able to make what they please of what Feynman said in that lecture.

    Yes, that's what people will do when they read a document that is about 3 pages (or listen to lecture of about 1 hour),  they will summarise and/or condense it.   Different words are bound to be used by them.
    If you read that lecture I don't think there is a compact sentence that is held up high as the perfect definition.   There isn't a single sentence that you should try to utilize as a self-contained definition of energy.   He takes an entire lecture to make his point and provide examples.  He is frequently telling you what energy isn't instead of attempting to tell you what it definitely is.   Overall, a scientist should have some appreciation of what energy is and isn't by the end of that lecture.
   Split the lecture into thirds:
1st section:   Smash pre-conceived ideas.  Illustrate that all we know is that energy is some abstract numerical quantity.
2nd section:   Provide some examples.   Illustrate that what we have understood is enough to do a lot.
3rd section:    Explain that it is even more complicated than this lecture suggested and even more things are going on.

   Example phrases from the 3rd section:  There are many other forms of energy, and of course we cannot describe them in any more detail just now.  ;     independence of time has to do with the conservation of energy*   ;  we should note that available energy is another matter?.... The laws which govern how much energy is available are called the laws of thermodynamics and involve a concept called entropy 
   
* - In a previous post I've already taken some extracts out of his discussion of conservation laws and time translation invariance.   I haven't taken extracts from lectures on thermodynamics or many other things but they are there.

I think he was trying to uncover the big secret about physics;

   OK, sure.   I wasn't looking that deeply.  On the face of it, he was just presenting a lecture to educate his students.   So trying to introduce them to some of the big ideas in physics or uncover the big secrets etc. is precisely what he was trying to do.   Although, in the wider sense, his own motivation for studying and teaching physics may very well have been trying to discover some of the fundamental questions he has himself (why are we here?, what is the nature of our world? etc.)

I can't see that therefore taking away the idea that he says "energy is a number", when he actually says "energy is a conserved numerical quantity", follows at all.

   OK.  Although you asked about it in post #107, so you got a reply.

Do you think he's saying energy is just a number?

    There is at least one sentence where he does DIRECTLY talk about energy with the word "number":
...it is just a strange fact that we can calculate some number and when we finish watching nature go through her tricks and calculate the number again, it is the same...     
    However, I am not advocating that you take just that sentence as a definition,  the whole point is that you can't, you need the whole lecture (and more).   However, if you did "take away" the idea that energy is a number then that's OK and you're not wrong (although it is only a small portion of what is in the lecture). 

If we don't know what energy "really" is, and if mathematics doesn't tell us beyond it being conserved (numerically), that's as far as it goes.

    As discussed previously.  Feynman is not the only source of information about what energy is or isn't.   However, just confining our attention to this one lecture,  yes,  that is pretty much what he was saying here.  Well done.

Numbers are entities because they have properties or attributes, right? Numbers most certainly don't have a physical existence, all they have is a value.

   I'm not sure I can discuss the nature of numbers in a small amount of space and this post has already taken too much time (to write or to read).

Best Wishes.

[varsigma (OP)]

Overall, a scientist should have some appreciation of what energy is and isn't by the end of that lecture.
   Split the lecture into thirds:
1st section:   Smash pre-conceived ideas.  Illustrate that all we know is that energy is some abstract numerical quantity.

I think it goes further, in that all physical quantities are abstract numerical quantities.
Mathematics doesn't say much about what measurements are. On the other hand operator algebras with a momentum operator do appear to.

And I think physicists like Seth Loyd or Lenny Susskind would agree that there is definitely a connection between information and energy.

[Zer0]

& maybe that connection is
" Matter " .

But of course, what is Matter?

(Doesn't Really Matter)

[alancalverd]

Energy is a conserved quantity in newtonian mechanics, but interchangeable with mass (another newtonian conserved quantity)  in relativistic mechanics. Nothing more, nothing less.

School curricula tend to be written by educationalists, not teachers, and therefore serve only to confuse the student and put him off "difficult" subjects like physics. Fact is that physics is really dead easy because it is about what happens (dynamics) or doesn't happen (statics) - stuff you see in everyday life.  Quite unlike history (deciding which account of stuff you never experienced is less unreliable) languages (the grunts made by apes who look like us but live somewhere else) literature (many books of bad English written about a few lines of good English) or religion (you'd be prosecuted for selling any other product that doesn't work).

[alancalverd]

At best, non-numerical quantities can be ordered but they do not have all the properties of numbers. 

Friendly grumble:

I'd reserve quantity for something that can be associated with a numerical value, and quality for a property that can't. Keeps life simple and explicit.

You could of course analyse the spectrum of a pink dawn, but whilst your numbers would mean something to a blind physicist (even to the extent of estimating the sun altitude and the nature of atmospheric dust)  "pink" wouldn't convey anything of value.

[alancalverd]

What is a bottle, first of all?

A bottle is something we make (or imagine) to contain something else. It is a member of the set of containers, which includes boxes, cages, and finite bounded universes.

[Eternal Student]

Hi.

Friendly grumble:  I'd reserve quantity for something that can be associated with a numerical value

    Agreed and it was agreed originally.

Even the word "quantities" is an issue since in the English language one tends to think of something you can count and number.   Overlooking that....

    Since Feynamn said ".... Energy is a numerical quantity...",  it was much more natural just to change one word in that and have   numerical quantities    vs.     non-numerical quantities     rather than changing everything and talking about      numerical data   vs.    non-numerical data.

Best Wishes.

[alancalverd]

One should never be afraid to disagree with Feynman - there is no better way to learn than to argue with a master, and he always enjoyed a tussle! The published "Lectures" are a committee document compiled from audio tapes, may well contain a few infelicities, and I think predate the usefully rigid ISO definitions of entity, quantity and unit.