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Author Topic: What do you think energy is and why do you believe that?  (Read 3688 times)

Offline PmbPhy

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Re: What do you think energy is and why do you believe that?
« Reply #25 on: 21/06/2016 15:42:08 »
Quote from: garth john greiner
I believe that energy is a fundamental part of universal mechanics. The production of Energy in my opinion is a direct result of the behavior of  chemicals interacting with each other to form anything from star systems to intelligent life forms.
I feel that energy and purpose work together to deliberately form life. ( im a strong believer in the anthropic principle). The reason i feel this way about energy is i observe how my own body produces energy or indeed struggles to as the case maybe
and i spend alot of time observing nature. My answer to this question is limited to a post big bang understanding. A little look at pre-big bang energy production might be interesting ;-)
garth - This post doesn't address the question that I posed in the opening post
 

Offline dlorde

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Re: What do you think energy is and why do you believe that?
« Reply #26 on: 23/06/2016 13:04:21 »
Energy is an equivalence relation between different forms of potential for action.

I think is is a reasonable summary because energy is not 'stuff' that can be directly observed, it is a conserved attribute of the configuration of systems, indirectly observable in that configuration, and it is measured in terms of potential for action.
« Last Edit: 23/06/2016 13:16:50 by dlorde »
 

Offline PmbPhy

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Re: What do you think energy is and why do you believe that?
« Reply #27 on: 23/06/2016 16:24:03 »
Quote from: dlorde
Energy is an equivalence relation between different forms of potential for action.
That doesn't make any sense to me. An equivalence relation is a mathematical binary relation. Please see:
https://en.wikipedia.org/wiki/Equivalence_relation#Definition

and tell me how it applies to what you think energy is.

Quote from: dlorde
I think is is a reasonable summary because energy is not 'stuff' that can be directly observed, it is a conserved attribute of the configuration of systems, indirectly observable in that configuration, and it is measured in terms of potential for action.
It sounds like you mean "The capacity to do work" which is how energy is most often defined in physics texts. That definition has been shown to be wrong. In any case you've left out the defining quality of energy and that's it's property of being conserved.
 

Offline alancalverd

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Re: What do you think energy is and why do you believe that?
« Reply #28 on: 24/06/2016 00:32:16 »
Energy is a scalar parameter with dimensions ML2T-2 that is conserved in a closed system.

Why do I believe that? For the same reason that I believe a hammer is a device for hitting nails. We invent some tools to beat the universe into the shape we want, and others for describing how it works.
« Last Edit: 24/06/2016 00:41:42 by alancalverd »
 
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Offline Ethos_

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Re: What do you think energy is and why do you believe that?
« Reply #29 on: 24/06/2016 01:55:53 »
Energy is that attribute of nature that drives the evolution of our universe. And we recognize the advance of time as the unfolding of that evolution. It is conserved and can't be destroyed but it can be changed from one form to another administration evidenced by observational testing. Because matter has mass, it can be correctly said that it contains energy because mass and energy are equivalent: E=mc^2

While matter contains mass/energy, it can not be defined as concentrated energy as has been falsely stated by those who are less well informed.

Matter only contains mass/energy, it is not "Mass/Energy"
 

Offline PmbPhy

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Re: What do you think energy is and why do you believe that?
« Reply #30 on: 24/06/2016 10:54:34 »
Quote from: alancalverd
Why do I believe that? For the same reason that I believe a hammer is a device for hitting nails. We invent some tools to beat the universe into the shape we want, and others for describing how it works.
It appears that nobody understood what I was aiming at when I asked that question. I was attempting to ascertain where you learned it from, i.e. a text on thermodynamics, chemistry, journal articles, a combination of all of those, did you make it up yourself from your own genius, etc?
 

Offline alancalverd

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Re: What do you think energy is and why do you believe that?
« Reply #31 on: 25/06/2016 02:02:14 »

It appears that nobody understood what I was aiming at when I asked that question. I was attempting to ascertain where you learned it from, i.e. a text on thermodynamics, chemistry, journal articles, a combination of all of those, did you make it up yourself from your own genius, etc?

OK, it is what we were taught in school and have used ever since, because it is the definition used by every other scientist, just like engineers use the term "hammer" to denote a thing you use for bashing other things. And it turns out that every serious scientific text (as distinct from woo-woo, journalese or political mumbojumbo) uses the term energy to mean exactly the same thing. The fact that energy turns up in all sorts of forms is no problem - everything from the aural malleus of a weasel to the machine that turns a sheet of steel into a car body, is a hammer! 
 

Offline PmbPhy

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Re: What do you think energy is and why do you believe that?
« Reply #32 on: 25/06/2016 06:43:02 »
Quote from: alancalverd
OK, it is what we were taught in school and have used ever since, because it is the definition used by every other scientist, just like engineers use the term "hammer" to denote a thing you use for bashing other things. And it turns out that every serious scientific text (as distinct from woo-woo, journalese or political mumbojumbo) uses the term energy to mean exactly the same thing. The fact that energy turns up in all sorts of forms is no problem - everything from the aural malleus of a weasel to the machine that turns a sheet of steel into a car body, is a hammer!
I don't disagree with you that this is how people come to learn what energy is. However I've never seen a physics text define energy by stating that its conserved and stating its dimensions. That definition doesn't even work in all instances. For example: it doesn't work for non-conservative systems. In such systems energy is defined but not conserved. An example is a charged particle in a time varying electromagnetic field.

Nearly all textbooks define energy as the ability/capacity to do work. Two notable exceptions are Feynman and Glashow, two well-known Nobel Laureates. The explain that energy can't be defined and give the reasons why. They then explain what it is. If that's confusing to some members then note that defining and explaining are not the same thing. In math the term set is an undefined term. Its explained by giving examples of it and rely on our common sense to understand it.

Recall what Feynman wrote in his lectures on energy
Quote
It is important to realize that in physics today, we have no knowledge of what energy is. We do not have a picture that energy comes in little blobs of a definite amount. It is not that way. However, there are formulas for calculating some numerical quantity, and we add it all together it gives 28 -  always the same number. It is an abstract thing in that it does not tell us the mechanism or the reasons for the various formulas.

Let's
 

Offline agyejy

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Re: What do you think energy is and why do you believe that?
« Reply #33 on: 25/06/2016 08:25:12 »
For example: it doesn't work for non-conservative systems. In such systems energy is defined but not conserved. An example is a charged particle in a time varying electromagnetic field.

Any non-conservative system can be made into a conservative system by an extension of the boundaries of said system. Since all systems are defined relatively arbitrarily by some human that is studying some process or another such redefinitions of the boundaries are always possible. In short as far as we have been able to observe energy is always conserved humans just sometimes draw arbitrary boundaries or forget to account for certain types of energy. For example, a system of a charged particle in a time varying electromagnetic field is conservative if you consider the source of the time varying field and any radiation the charged particle might emit (assuming there is nothing for it to collide with but if there is you just include that too).

Too bad you're apparently ignoring me for no real reason I can discern besides the fact that I didn't agree with you on something.
 

Offline alancalverd

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Re: What do you think energy is and why do you believe that?
« Reply #34 on: 25/06/2016 08:43:44 »
If you want to play linguistics, you could start by claiming that momentum isn't defined - or even mass, for that matter. But we physicists try to build useful mathematical models of the universe rather than muck about with Aristotelian definitions, so if ∑mv turns out to be conserved, we give it a name because it is useful.

Ultimately all scientific definitions tend towards "that which...." because science begins with observation.  You could define hydrogen as "any number of atoms each of which consists of a single electron and a single proton" but some brilliant philosopher will point out that you haven't defined a proton, so chemists define hydrogen as "the element which..." and for most purposes it turns out that adding one or two neutrons doesn't alter its chemical characteristics, so it's a good definition - and applicable to all other elements too.

Your nonconservative system is excluded from the definition I gave because it is not a closed system. Friction is a nonconservative force but in a closed system the kinetic energy of your car is entirely converted by brake friction into heat energy. If the energy of a closed (i.e. complete) system were not conserved, we couldn't calculate the temperature rise of the brake disc (or re-entry module), which is kinda important when you want to build a machine that can stop without melting. You might argue that the definition now becomes circular as I've effectively defined a closed system as one in which energy is conserved, but it isn't because we can in principle measure every element of that parameter.   
 

Offline Thebox

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Re: What do you think energy is and why do you believe that?
« Reply #35 on: 25/06/2016 11:26:45 »
If you want to play linguistics, you could start by claiming that momentum isn't defined - or even mass, for that matter. But we physicists try to build useful mathematical models of the universe rather than muck about with Aristotelian definitions, so if ∑mv turns out to be conserved, we give it a name because it is useful.

Ultimately all scientific definitions tend towards "that which...." because science begins with observation.  You could define hydrogen as "any number of atoms each of which consists of a single electron and a single proton" but some brilliant philosopher will point out that you haven't defined a proton, so chemists define hydrogen as "the element which..." and for most purposes it turns out that adding one or two neutrons doesn't alter its chemical characteristics, so it's a good definition - and applicable to all other elements too.

Your nonconservative system is excluded from the definition I gave because it is not a closed system. Friction is a nonconservative force but in a closed system the kinetic energy of your car is entirely converted by brake friction into heat energy. If the energy of a closed (i.e. complete) system were not conserved, we couldn't calculate the temperature rise of the brake disc (or re-entry module), which is kinda important when you want to build a machine that can stop without melting. You might argue that the definition now becomes circular as I've effectively defined a closed system as one in which energy is conserved, but it isn't because we can in principle measure every element of that parameter.

Sorry this may be a little off topic but I have a question and will not reply to the answer. 


Is ''light'' passing through space a conserved ''system''?
 

Offline dlorde

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Re: What do you think energy is and why do you believe that?
« Reply #36 on: 25/06/2016 19:20:26 »
... tell me how it applies to what you think energy is.
When I said 'equivalence relation', I meant it allows us to compare or relate different forms of energy using a common measure. Double-entendre...
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It sounds like you mean "The capacity to do work".
Action isn't work  ;)
Quote
Quote from: dlorde
... energy is not 'stuff' that can be directly observed, it is a conserved attribute of the configuration of systems
In any case you've left out the defining quality of energy and that's it's property of being conserved.
I think you haven't read what I posted carefully enough (I've bolded the relevant part) :)
 

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Re: What do you think energy is and why do you believe that?
« Reply #36 on: 25/06/2016 19:20:26 »

 

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