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What is energy

by Ghetalion
Tags: energy
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Telos
#19
Aug22-05, 11:12 PM
P: 147
And there's a State Department. Can't tell if it obeys Pauli Exclusion, though. They all look the same.
mcah5
#20
Aug23-05, 02:11 AM
P: 40
According to Feymann, energy is just a book-keeping device with the very useful property that energy is conserved. The conservation of energy comes from the fact that experiments are time symmetric (aka "things do not depend on the absolute time.)

Edit: I can't spell Feynman
Telos
#21
Aug23-05, 09:08 AM
P: 147
That's very interesting, mcah5, because for me, being a human in modern civilization, if I don't have energy, I die.

What is it that I call "energy," then, since it is more than a bookkeeping device? Is it "energy transfer?"
selfAdjoint
#22
Aug23-05, 11:11 AM
Emeritus
PF Gold
P: 8,147
Quote Quote by Telos
That's very interesting, mcah5, because for me, being a human in modern civilization, if I don't have energy, I die.

What is it that I call "energy," then, since it is more than a bookkeeping device? Is it "energy transfer?"
No; if you don't have the right chemical processes, you die. Energy, and its derivatives like free energy, are just abstractions from that. They are important to a description of what is happening, but they are part of the model, not part of the reality.
Zelos
#23
Aug23-05, 01:30 PM
P: 76
if we can define energy we can denife matter as high concentration of matter and therefor is the matter about matter solved
inha
#24
Aug23-05, 01:42 PM
P: 576
that makes no sense at all.
Telos
#25
Aug23-05, 02:03 PM
P: 147
Quote Quote by selfAdjoint
No; if you don't have the right chemical processes, you die. Energy, and its derivatives like free energy, are just abstractions from that. They are important to a description of what is happening, but they are part of the model, not part of the reality.
I understand your last statement, but your first has confused me. You seem to be saying that biochemistry is the basis for our concept of energy. Because that is from whence we abstract the notion?

How are the "right chemical processes" not also an abstraction? Why just yesterday I heard someone accuse another of having the wrong chemical processes.
mcah5
#26
Aug23-05, 08:01 PM
P: 40
Fine, if you don't like the book-keeping definition then energy is the capacity to do work =)

I think the main problem of trying to define energy is that energy is not quantized, and so we can't imagine a chewy nugget of energy. Personally, I could care less about the "real" definition of energy; problem sets are hard enough without dealing with philosophy.
Locrian
#27
Aug23-05, 08:11 PM
P: 1,737
Quote Quote by mcah5
I think the main problem of trying to define energy is that energy is not quantized,
Are you sure?
mcah5
#28
Aug23-05, 08:49 PM
P: 40
I'm pretty sure. You could argue that E=hf means energy is quantized, but f can be any value. And I'm pretty sure there is no lower bound on the frequency of light.
pmb_phy
#29
Aug23-05, 09:08 PM
P: 2,954
Quote Quote by mcah5
I'm pretty sure. You could argue that E=hf means energy is quantized, but f can be any value. And I'm pretty sure there is no lower bound on the frequency of light.
The assertion that energy is quantized is not meaningful. Before one can state that energy is quantized one must first specify what you're speaking of, i.e. energy of what??

If E = hf refers to the energy of a photon then it can't be assumed that E only comes in certain values. But if E refers to the energy state of an atom then E is quantized. In quantum mechanics there are systems which have a continuos energy spectrum and those which have a descrete energy spectrum. For example, the energy of a free particle is not quantized. The energy of a particle in a box is quantized.

Pete
pmb_phy
#30
Aug23-05, 09:11 PM
P: 2,954
Quote Quote by mcah5
Fine, if you don't like the book-keeping definition then energy is the capacity to do work =)
That holds true for potential energy and kinetic energy. So that can be taken as a definition of either. But that does not give you a definition of energy, only instances of energy. What am I talking about you ask? Suppose you ask what the definition of life is. If you give examples of life then you've not actually defined life. E.g. a human being is a life form. An ant is a life form. Yet with that knowledge I still don't know what a life form is.

Pete
Telos
#31
Aug27-05, 06:45 PM
P: 147
Once again we don't seem to have found a satisfactory answer.

Remarkably, we seem to have come to the conclusion that energy isn't real. It only exists in our models and not in reality. How strange that the entirety of physics would depend on something that isn't real? Or am I mistaken?
Enos
#32
Aug27-05, 08:55 PM
P: 193
It exist and it doesn't. That's the simplest one can put it. It exist because it takes up space. It doesn't exist because it's value is zero.

That's what I think anyway.
pmb_phy
#33
Aug27-05, 09:02 PM
P: 2,954
Quote Quote by Telos
Remarkably, we seem to have come to the conclusion that energy isn't real.
WHAT??? Where did you get that impression???

Is the number 4 real? Is height real? Is life real? Don't hold that something is not real because you've been unable to define it.

Pete
Telos
#34
Aug28-05, 11:11 AM
P: 147
Enos, that almost sounds like energy "is" space. After all, space tautologically takes up space and has an unwarpped equilibrium value we might as well call zero.

Pmb_phy, that's not what I meant. Please reread the thread.
coburg
#35
Aug30-05, 09:04 AM
P: 7
energy....something that seems to squeeze everyone's mind.....for to tell all the truth...man doesnt know too much abt out energy....we have defined energy as "energy is the ability to do work", this would be Force dotted wit distance. such that we get change in energy and if you notice its not energy itself that we are finding out...similarly in thermodynamics too...we try and calculate the change in internal energy but never rather find the total internal energy of the system.....it is thru such theards and sharing of knowledge will we be able to get in depth understanding of the world....
coburg
#36
Aug30-05, 09:21 AM
P: 7
to add to this discusion could be the fact that energy is a relative quantity.....yes...the energy possed by a system is relative to the observer.....on close thought this idea will make itself pretty clear.....wit this idea in mind...jus hypothetically thinking.....can we define as the measure of diffrence between two systems......its jus an opinion...not based on any concerte theory....nevertheless worth a thought


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