Richard Feynman said

[devrimci_kürt]

Richard Feynman said :It is important to realize that in physics today, we have no knowledge what energy is

 

what do you think?

[ajb]

I do think that the physical concept of energy is not very clear. Mathematically, it can be thought of as a variable conjugate to time.

 

Related to this is the fact that energy is the conserved charge under time translations. (Like momentum and spacial transformations).

 

Either way, these concepts are clear mathematically but no so physically.

 

The textbook on classical mechanics will say something like "the amount of work that can be performed by a force".

[swansont]

Either way, these concepts are clear mathematically but no so physically.

 

And that's physics in a nutshell. Energy is a useful quantity to help describe how systems behave. What it is is not something that physics tries to answer.

[Bob_for_short]

It has always been clear. The energy is measurable. The energy is exchangeable. The energy is a certain property of a system. There are many forms of energy. Each is well defined. Why to fool ourselves?

Edited November 1, 2009 by Bob_for_short

[dr.syntax]

It has always been clear. The energy is measurable. The energy is exchangeable. The energy is a certain property of a system. There are many forms of energy. Each is well defined. Why to fool ourselves?

 

REPLY:Hello Bob, you correct me if I am Wrong. I take this to mean you disagree with this statement attributed to Feynmann. I disagree with this statement. It seems to me we understand the nature of energy very well. ...Dr.Syntax

[gre]

can't it just be considered changes in mass?

[dr.syntax]

Richard Feynman said :It is important to realize that in physics today, we have no knowledge what energy is

 

what do you think?

 

REPLY: Do you know the source of this statement attributed to Feynman ?quote: " It is important to realize that in physics today,we have no knowledge what energy is "unquote. It seems a very extreme statement for anyone to make. And it seems to me we understand and know as much and more about energy than many other aspects of our Universe. That is why I question it`s authenticity. I hesitate and won`t say more than that. I mean no disrespect for you whatsoever. I am a bit amazed he would say this. ...Dr.Syntax

[moth]

it's from feynmans lectures here's a link to an online piece of them

http://docs.google.com/gview?a=v&q=cache:J6bghC3tpl4J:www.colorado.edu/physics/phys1110/phys1110_fa09/Feynman_energy.pdf+It+is+important+to+realize+that+in+physics+today,we+have+no+knowledge+what+energy+is&hl=en&gl=us&pid=bl&srcid=ADGEESi9De2Ux8wsHk1Ujto6gi8ZADUnqaF5w1t5bQOIuq8VPGjGCqZoeQXMHOe4H3QTzpN5iMAbj0_w2S5qPYLLD_HJHCY3EYJZ3GbAh3RpYV3y9Iz696vnbCxjxC7hQE7AWqxNCYn7&sig=AFQjCNHL_sWiMirpk4wU6LJiif8rnQCHQg

[ajb]

And that's physics in a nutshell. Energy is a useful quantity to help describe how systems behave. What it is is not something that physics tries to answer.

 

Indeed.

 

The same applies to mass, momentum, charge etc...

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It seems to me we understand the nature of energy very well. ...Dr.Syntax

 

We do understand energy well. But that is not the point. The opening question relates to defining the concept of energy physically.

 

In physics there is a "feedback loop"

 

[math]\textnormal{Physical Concept}\rightleftharpoons \textnormal{Mathematical Concept}[/math]

 

One may have some physical intuition about a concept, but that needs to be expressed mathematically. This mathematical concept then gets feed back into the physical concept.

 

Example, what is mass

 

[math]\textnormal{Mass} \rightarrow \textnormal{Physical Concept} = \textnormal{"Amount of matter"}[/math]

 

[math]\textnormal{Mass} \rightarrow \textnormal{Mathematical Concept} = \textnormal{"Positive Parameter "}[/math]

 

Feed back in

 

[math]\textnormal{Mass} \rightarrow \textnormal{Physical Concept II} = \textnormal{"inertial mass, gravitational mass " etc.}[/math]

 

The second idea of what mass is only arises when one has a mathematical model. (There may then be further refinements of concepts iteratively).

 

It is in this sense, that is we need a mathematical description that is the setting of Feynman's quote.

[dr.syntax]

it's from feynmans lectures here's a link to an online piece of them

http://docs.google.com/gview?a=v&q=cache:J6bghC3tpl4J:www.colorado.edu/physics/phys1110/phys1110_fa09/Feynman_energy.pdf+It+is+important+to+realize+that+in+physics+today,we+have+no+knowledge+what+energy+is&hl=en&gl=us&pid=bl&srcid=ADGEESi9De2Ux8wsHk1Ujto6gi8ZADUnqaF5w1t5bQOIuq8VPGjGCqZoeQXMHOe4H3QTzpN5iMAbj0_w2S5qPYLLD_HJHCY3EYJZ3GbAh3RpYV3y9Iz696vnbCxjxC7hQE7AWqxNCYn7&sig=AFQjCNHL_sWiMirpk4wU6LJiif8rnQCHQg

 

REPLY: Thank you moth,there it was and the context it was given in. I still don`t know what to make of it other than he said a lot of things,much of which there is a public record of. I do not consider it one of his best, far from it. That is my opinion. I can surely remember a very many things I have said and would rather I had not said them. For me just about every day. Thank you for digging up that piece. I very much appreciate it. ...Dr.Syntax

[foodchain]

Richard Feynman said :It is important to realize that in physics today, we have no knowledge what energy is

 

what do you think?

 

So why is physics considered a natural science if in reality all you can of it is that it produces abstractions of reality in the form of mathematical models. Before people knew of math or what not I am sure frostbite was still occurring in the world, why do we call it physics and not just applied math?

 

I understand its all ultimately human thought, but with evolution for instance in the biological sciences is that just a model or some paradigm? Not trying to produce some one up on the empirical scale here, but is that not some point in physics when you can say its actually objectively grasping something.

 

*On a side note I always looked at energy as the capability for some amount of change really. I mean this may not be even close to scientific, but if nothing in the universe could change in any form then you could have no concept like energy as no observations could take place or nothing could happen really, you could have no form of motion or really I don't think anything would exist.

 

This brings me to my far out hypothesis that the physical universe is simply just a perpetual thermodynamic evolution of sorts in its current state going from thermodynamic laws. I think that's why mathematically we get a sense of multiple universes because that possibility exists. Heck the existence of life could be just that, who is to say. Yet I guess such proves that math is far more scientific and proper to employ in a scientific sense of things. I guess this idea of mine is why I am so interested in quantum decoherence really.

[dr.syntax]

Indeed.

 

The same applies to mass, momentum, charge etc...

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We do understand energy well. But that is not the point. The opening question relates to defining the concept of energy physically.

 

In physics there is a "feedback loop"

 

[math]\textnormal{Physical Concept}\rightleftharpoons \textnormal{Mathematical Concept}[/math]

 

One may have some physical intuition about a concept, but that needs to be expressed mathematically. This mathematical concept then gets feed back into the physical concept.

 

Example, what is mass

 

[math]\textnormal{Mass} \rightarrow \textnormal{Physical Concept} = \textnormal{"Amount of matter"}[/math]

 

[math]\textnormal{Mass} \rightarrow \textnormal{Mathematical Concept} = \textnormal{"Positive Parameter "}[/math]

 

Feed back in

 

[math]\textnormal{Mass} \rightarrow \textnormal{Physical Concept II} = \textnormal{"inertial mass, gravitational mass " etc.}[/math]

 

The second idea of what mass is only arises when one has a mathematical model. (There may then be further refinements of concepts iteratively).

 

It is in this sense, that is we need a mathematical description that is the setting of Feynman's quote.

 

REPLY: Frankly, I have a very hard time understanding things in what seems to me such an abstract manner. I want to be real clear about this: I see this as the lack of this ability on my part, my mind lacks this ability to comprehend things on this level. I know with absolute certainty, Richard Feynman was a far more intelligent person than I am . ...Dr.Syntax

[ajb]

So why is physics considered a natural science if in reality all you can of it is that it produces abstractions of reality in the form of mathematical models.

 

...and then use them to make predictions that can be tested or engineer technology.

 

There is some kind of interplay between the "mathematical world" and the "physical world". Like my "feed back loop". You need to "map" between these worlds via predictions of the models and observation/experiment.

 

 

*On a side note I always looked at energy as the capability for some amount of change really.

 

That is a good way to think of it. It is the "capacity of something to make things change". Like a "Doing property"or something.

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REPLY: Frankly, I have a very hard time understanding things in what seems to me such an abstract manner. I want to be real clear about this: I see this as the lack of this ability on my part, my mind lacks this ability to comprehend things on this level. I know with absolute certainty, Richard Feynman was a far more intelligent person than I am . ...Dr.Syntax

 

I think that the distinction between physical concepts and mathematical constructs in not emphasised enough in typical physics textbooks. It can be subtle.

 

You need to present physical ideas in a mathematical framework.

 

It is not something I have thought too deeply about, but it is clear that the original physical idea needs to be cast in a mathematical language. This may then lead to a refinement of the idea or even lead to new physical ideas.

[Severian]

I would say energy is the conserved quantity associated with the invariance of physics under time translations.

 

Or more technically, it is the time-like component of the Noether current associated with space-time translations.

[Bob_for_short]

What is also important that it is additive in particles or other "species" involved in interaction. So its conservation means a clear thing: what is taken from one particle is given to another.