What Is the True Nature of Energy?

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In summary, energy is the ability to do work and is a prerequisite for force. It can take different forms, such as gravitational potential energy, electrostatic potential energy, and kinetic energy. Energy is also the source of the gravitational field and is measured in various ways. However, the exact nature of energy is still not fully understood and is a subject of ongoing research and debate, as described by physicist Richard Feynman.
  • #71
superg33k said:
Thats exactly what equivilent means!

Let's continue, mass is energy.
Mass becomes into photons at CERN.
Photons heat water in a steam engine.
A steam engine has the ability to do work.

That is not what equivalent means in this context.

From wikipedia on E=MC^2:

The equation E = mc2 indicates that energy always exhibits mass in whatever form the energy takes.[3] Mass–energy equivalence also means that mass conservation becomes a restatement, or requirement, of the law of energy conservation, which is the first law of thermodynamics. Mass–energy equivalence does not imply that mass may be "converted" to energy, and indeed implies the opposite. Modern theory holds that neither mass nor energy may be destroyed, but only moved from one location to another. Mass and energy are both conserved separately in special relativity, and neither may be created or destroyed. In physics, mass must be differentiated from matter, a more poorly defined idea in the physical sciences. Matter, when seen as certain types of particles, can be created and destroyed (as in particle annihilation or creation), but the precursors and products of such reactions retain both the original mass and energy, each of which remains unchanged (conserved) throughout the process. Letting the m in E = mc2 stand for a quantity of "matter" (rather than mass) may lead to incorrect results, depending on which of several varying definitions of "matter" are chosen.

E = mc2 has sometimes been used as an explanation for the origin of energy in nuclear processes, but mass–energy equivalence does not explain the origin of such energies. Instead, this relationship merely indicates that the large amounts of energy released in such reactions may exhibit enough mass that the mass-loss may be measured, when the released energy (and its mass) have been removed from the system.

All forms of energy have mass, but mass is most definitely not energy.
 
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  • #72
Drakkith said:
That is not what equivalent means in this context.

From wikipedia on E=MC^2:



All forms of energy have mass, but mass is most definitely not energy.

Oh bloody hell, now I have no arguement. I thought mass wasn't conserved at CERN and in nuclear bombs. If that's the case I have to rethink this and I am unfortunately dissapointed with the lack of philisophical implications of E=mc2. Maybe I'll have to edit wikipedia...
 
  • #73
Sounds like a paradox, and actually I agree with equivalence of energy and mass, but in calculating work, mass doesn't affect the result of work calculated. For example, when you do the same work on objects with different masses they gain the same amount of kinetic energy. (Even if you calculated the gain in mass caused by the increase in kinetic energy by E=mc^2, it is still the same)

Also if you look at the kinetic energy equation E=1/2mv^2 you would conclude that how can a energy depend on energy itself?

Clearly, the Energy Equations are derived simply from W=integral F dot ds, which means they can convert freely. If the mass term doesn't affect why bother?

In addition, Energy is invented before Einstein was even born! It's because energy is defined in this manner so that Einstein can derive the E=mc^2 equation!
 
  • #74
russ_watters said:
Well, the same conceptual process exists for energy. Ever throw a ball? Somehow you learned how to get that ball to go where you wanted it to. You learned projectile motion instinctively/reflexively. Part of that is applying a force to the ball over a distance dictated by the length of your arm to accelerate it to a certain speed. A while back, someone figured that quantifying that would be useful. And then they gave it a name.

These are the simple things most people do not think about when they try to explain nature. Many posters here can not take their minds out of mathematical equations and try to explain an abstract concept from some mathematical equations. Current conventional Math can not give the type of answer OP is expecting.

When I pushed my coffee cup, it moved. But why? The cup had no reason to move. But our experience tells us it does move. Did I give the cup something that I could not see? Why didn't the cup absorb everything I gave and stood there? A concpet is thus born from observation.

OP's list goes like..
E=mc2 (there is energy in matter)
E=hf (photons, which are not matter because they have no mass, can have energy)
E=(1/2)mv2 (things that are moving have energy just because they are moving)
E=mgh (there is gravitational potential energy in a mass raised to a certain height)
E=k(q1q2)/r (there is electrostatic potential energy which will cause two like charges to repel)
E=(1/2)CV2 (a parallel-plate capacitor can store energy)

My question is why are we spending all our time, energy, money on 'Unification of Forces', in stead 'Unification of Energies' may even reveal greater mysteries of nature.
 
  • #75
Bill_K said:
Energy is defined as the source of the gravitational field.

Sorry, I know that sounds somewhat indirect, overly sophisticated, and removed from common experience. But ultimately that is in fact what energy is. Just as the answer to "what is charge": charge is the source of the electromagnetic field, so energy is anything that acts as the source of gravity. (More precisely, the source is the stress-energy tensor, and energy is the 00 component of that.) The fact that general relativity is invariant under general coordinate transformations requires that its source must be conserved. And the list of things that are commonly known as forms of energy are just those things that produce a gravitational field, and can be turned into each other.

I think the forces all are energy and they explain it in as much as they can, but as to what energy is discretely we can only imply it by terms such as kinetic, gravitational, potential etc, by its action rather than by what it actually is per se. It is something it is akin and the same or as equivalent as matter, but as to what fundamentally is, well that's the big question, and it requires a big answer. I personally don't think we have that answer as yet, that however is just an opinion.
 
  • #76
Neandethal00 said:
These are the simple things most people do not think about when they try to explain nature. Many posters here can not take their minds out of mathematical equations and try to explain an abstract concept from some mathematical equations. Current conventional Math can not give the type of answer OP is expecting.

Maths is not reality, reality is I quite agree. Sadly though some people think maths = reality, this creates no end of problems. Maths is an approximation of reality, it is not the underlying reality no matter what Euclid says maths is an invention not a discovery.

When I pushed my coffee cup, it moved. But why? The cup had no reason to move. But our experience tells us it does move. Did I give the cup something that I could not see? Why didn't the cup absorb everything I gave and stood there? A concpet is thus born from observation.

Because it just didn't it behoves us to explain why it would move given x not ask why it moved, we might as well say God done it otherwise. Experiment tells us things will move with enough force, so we shouldn't question the fundamentals, we should just explain them. It's all we can do. If not we are just indulging in philosophy or worse religion.

I quite agree all we have really in science is observation. If we cannot agree on that then we have a position to move on.

OP's list goes like..My question is why are we spending all our time, energy, money on 'Unification of Forces', in stead 'Unification of Energies' may even reveal greater mysteries of nature.

Probably because unification of forces and energy are the same question with slightly different terms.
 
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  • #77
Energy is not something you can touch or feel. It is actually something people have made up to understand movement of things better. But as I understand is Energy something which can make thing move which tells us that it is an another word for work.
 
  • #78
Am I correct when I say energy and potential energy are different things? Energy is a characteristic of the object, like mass energy or kinetic energy, where potential energy is a characteristic of position in space, like being near to a charged particle an charge carrying photon in the objects vicinity might will give it energy. Energy is what it has, potential energy is what it will get?
 
  • #79
Energy is the sum total of a force applied across a distance. Potential energy is the recognition that a force exists and if it is allowed to act across a distance, then the calculation of force times distance can be made. The sum total of that calculation becomes what we call energy. The question, at the most fundamental level is: What is force? We do not know what force is because, we do not know any cause. We only have empirical evidence of effects.

James
 
  • #80
Drakkith said:
That is not what equivalent means in this context.

From wikipedia on E=MC^2:

All forms of energy have mass, but mass is most definitely not energy.

Yes indeed; and funny enough, one of the most careful and accurate descriptions can be found in Einstein's 1905 paper on that equation:

"The mass of a body is a measure of its energy-content"
- http://www.fourmilab.ch/etexts/einstein/E_mc2/www/
 
  • #81
Mass is a measure of its energy.
Temperature is a measure of average molecular kinetic energy.
Thermodynamic entropy is a measure of disorder or unusable energy.
Each explanation that 'this is a measure of that' is incomplete. The question, right from the beginning, is: What is this?

So, what is energy? What is mass? What is temperature? What is thermodynamic entropy? Or, returning to the real first question, what is this? 'This' is something that remains unexplained.

James
 
  • #82
ugur0072 said:
Energy is not something you can touch or feel.

Do you not feel infrared energy?
 
  • #83
"Do you not feel infrared energy?"

What is energy?

James
 
  • #84
JaredJames said:
Do you not feel infrared energy?

No, you do not "feel energy". Not directly! Your nerves and brain respond to temperature, i.e., a raising of the average velocity of the molecules in your skin (or whatever sensor you use).

This is not just semantics. There are some forms of energy change that can be indirectly sensed like this. But what about gravitational potential energy? Can you "feel" that? No. In general, no one can ever feel energy directly because, as I posted a day ago, energy is not a concrete reality, it is an abstraction. Only changes in energy are important in physics.

The velocity of molecules is, however, concrete, so any energy change associated with molecular motion or similar observables, will sometimes appear as if it can be "felt". But you have to keep a clear mind and not be tempted to tell your students or your kids that what they are feeling is raw energy. They aint'!

The heat being felt is not energy. What you are feeling is a secondary effect of a change in energy of a system, in this case, the statistical raising of the average velocity of molecules. Physicists use the concept of energy to keep track of where this motion came from and where it dissipates, but that's all.

Least you misunderstand me, I would argue that energy is none the less a reality for it's being an abstract concept. Indeed, for me, I think of energy as a primary concept in physics, it drives almost everything. It's a unifying concept for describing almost everything. So it is REAL in that sense. But it is a pure abstraction nevertheless, like money.
 
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  • #85
Koss,

"I would argue that energy is none the less a reality for it's being an abstract concept. Indeed, for me, I think of energy as a primary concept in physics, it drives almost everything. It's a unifying concept for describing almost everything. So it is REAL in that sense. But it is a pure abstraction nevertheless, like money. "

Energy is like money? I read the earlier messages. Money is real. It can be held. It can be contained and tested for its physical effects. It is physical effects that concerns physics. Do we know what energy is or do we not know what it is? Likenesses, meaning analogies, do not count.

James
 
  • #86
James A. Putnam said:
Energy is like money? I read the earlier messages. Money is real. It can be held. It can be contained and tested for its physical effects. It is physical effects that concerns physics. Do we know what energy is or do we not know what it is? Likenesses, meaning analogies, do not count.

For the record, money doesn't exist.

If you read a British note, it says "I promise to pay the bearer on demand the sum of...". In other words, it's basically an IOU. Interesting discussion if you're interested: http://www.consumeractiongroup.co.u...?110424-I-promise-to-pay-the-bearer..-oh-yeah

I'm certainly intrigued by the question now regarding energy, going to do a bit of further reading I think. There must be an answer. PF can't be the first place to ask and attempt to answer it.
 
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  • #87
There is no satisfactory answer to: What is energy? Everytime the questions approach why we are here? What is our cause? There is no answer in physics. That is because physics is the study of patterns in changes of velocity and, for theoretical physics, the invention of substitutes for cause.

James
 
  • #88
James A. Putnam said:
There is no satisfactory answer to: What is energy?
Yes, there is a perfectly satisfactory answer to the question, which has been given several times in this thread: energy is the capacity to do work. That is it. Nothing mysterious nor circular nor confusing nor ambiguous. It is straight-forward and clear.

You and the other people in this thread who insist on trying to shroud it in some mystical obscurity are completely unnecessarily injecting confusion. I don't understand y'all's motivation for doing that.
 
  • #89
DaleSpan,

I see you have a strong position. I do not shruod anything. I remove shrouds. I remove mysticism. Scientists have no more right to institute mystical, obscure, answers than does anyone else. I press for: What is energy? Or, what is anything? I press for admissions that we do not know cause. Do you know cause?

James
 
  • #90
James A. Putnam said:
DaleSpan,

I see you have a strong position. I do not shruod anything. I remove shrouds. I remove mysticism. Scientists have no more right to institute mystical, obscure, answers than does anyone else. I press for: What is energy? Or, what is anything? I press for admissions that we do not know cause. Do you know cause?

James

Energy isn't defined in some mystical or obscure way. That's what you don't understand. Energy is specifically defined in science. Would you ask that we get rid of our definition in favor of something more mystical or philosophical like you are proposing?
 
  • #91
Dale Spam, sorry for misstyping your identify.

Drakkith,

I think I understand. Energy is the sum total of force times distance. I propose only that we leave it at that. I may be mistaken, perhaps you know what energy is beyond this definition?

James
 
  • #92
James A. Putnam said:
Dale Spam, sorry for misstyping your identify.

Drakkith,

I think I understand. Energy is the sum total of force times distance. I propose only that we leave it at that. I may be mistaken, perhaps you know what energy is beyond this definition?

James

I've already given my views multiple times above.
 
  • #93
James A. Putnam said:
What is energy?
How many times do I have to repeat this: energy is the capacity to do work. And work, in turn, is clearly defined in terms of experimentally measurable values. Crystal clear and unambiguous.
 
  • #94
I haven't seen any answers above that explained what energy is.

James
 
  • #95
James A. Putnam said:
I haven't seen any answers above that explained what energy is.
If you haven't seen it then perhaps the font was too small

Energy is the capacity to do work.

Hopefully you could see it that time. :rolleyes:
 
  • #96
Dale Spam,

"How many times do I have to repeat this: energy is the capacity to do work. And work, in turn, is clearly defined in terms of experimentally measurable values. Crystal clear and unambiguous."

You do not have to repeat it. What is capacity if it is not cause? Experimentally measurable values tell us about effects. Your crystal clear is no answer to: What is energy? Unless you are saying that it is a given?

James
 
  • #97
I ask for an answer and you respond with gigantic fonts. How about a crystal clear answer?

James
 
  • #98
James A. Putnam said:
I haven't seen any answers above that explained what energy is.

James

Yes you have. You just don't agree with them.

I ask for an answer and you respond with gigantic fonts. How about a crystal clear answer?

We've given you one. You are trying to get a philosophical answer which we cannot give you.
 
  • #99
I do agree with 'energy is force times distance'. What else is it that I should agree with?

James
 
  • #100
James A. Putnam said:
I do agree with 'energy is force times distance'. What else is it that I should agree with?

James

I don't think that is correct. I believe you are describing work, not energy.
 
  • #101
No I am describing energy.

James
 
  • #102
James A. Putnam said:
No I am describing energy.

James

From wikipedia:

Since work is defined as a force acting through a distance (a length of space), energy is always equivalent to the ability to exert pulls or pushes against the basic forces of nature, along a path of a certain length.

Work is force x distance, energy is not.
 
  • #103
Work is force times distance that results in useful something or other. Energy is force times distance whether or not it is useful to us.

James
 
  • #104
James A. Putnam said:
Work is force times distance that results in useful something or other. Energy is force times distance whether or not it is useful to us.

James

I don't think that's true. Got a reference?
 
  • #105
You don't think that is true? Do yo
 

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