Is Energy Tangible or Just a Theoretical Concept?

[Mad_Eye]

Typically you would say that energy is a property of a system. But I don't understand your point about energy being a theoretical concept. All physics concepts are theoretical concepts, but the theory matches well with experiment so it accurately describes and predicts the behavior of nature.

Mass, for example, is a definite property of a body. I can theoretically make a machine that measure the mass of body (i mean, with nothing to do with gravity), because mass is an absolute property of the body..

but it's meaningless to say the energy of a body is some amount of jouls.. because it depends on reference frame..

i have once seen that a box of chocolate contains some amount of jouls... so what the hell is that means?!

 

[Mad_Eye]

Dalespam's post #8 is right on: it's silly to define "abstract" as anything we can't sense directly. That might mean light is "tangible", X-rays are "abstract". Or something at 98.6degrees is "abstract" because we might not feel it while all other temps are "tangible".

i have no problem to understand there things we cannot feel and there are real as things we can... my problem is different.. i think :)


i do distinguish between a few types of quantities.. for example, once again, mass. even at the atomic level, an atom or molecule, has a definite mass. the atom/molecule "knows" its mass.. it's a property of the atom..
same thing with acceleration. acceleration may be relative, but the universe it self, has its inertial system. to me, acceleration is kind of absolute or relative to the universe...

energy anyway (i think), is just an artificial calculation. if you "look" at an atom, you won't see amount of energy accumulated in it..
just like velocity.. an atom doesn't know what velocity it is moving at, because it has no meaning.. it has one velocity relative to one body, and another velocity relative to other body.. there is no absolute velocity..


so is it, like absolute ********?

 

[Mad_Eye]

Yes, use a bathroom scale. (Energy is proportional to inertia, E=mc2, though it might be more useful to know how much can be thermodynamically harnessed.)
Kinetic energy of (the centre of mass of) an isolated system (as a whole) isn't physically important, and subtracting that, even (total) kinetic energy of the individual moving parts of a system is frame invariant (not relative).

you are confusing me... I've just been told energy is relative, so how can the energy of a body can be measured if there is no absolute energy?

 

[Dale]

Mass, for example, is a definite property of a body. I can theoretically make a machine that measure the mass of body (i mean, with nothing to do with gravity), because mass is an absolute property of the body..

but it's meaningless to say the energy of a body is some amount of jouls.. because it depends on reference frame..

You have to be a little careful defining your terms here, there are different kinds of mass and different kinds of energy. Rest mass is equivalent to rest energy (E=mc²) and both are invariant (all coordinate systems agree). On the other hand, relativistic mass is similarly equivalent to total energy and both are relative (depend on the coordinate system chosen). So, to make the distinction you have made you must be specifically talking about the invariant rest mass when you say "mass" and the relative total energy when you say "energy" (that is my preferred convention, btw).

However, my point is that there is no scientific reason to classify invariant quantities as "real" and relative quantities as "not real" as both have the same scientific status. You are perfectly free to do so on any philosophical or aesthetic grounds you choose, but then the whole discussion becomes purely semantic.

you are confusing me... I've just been told energy is relative, so how can the energy of a body can be measured if there is no absolute energy?

Just because something is relative does not mean that it is not measurable. Time, distance, momentum, energy, frequency, wavelength, electric and magnetic fields, and many other things are all measurable relative quantities.

 

[Mad_Eye]

Just because something is relative does not mean that it is not measurable. Time, distance, momentum, energy, frequency, wavelength, electric and magnetic fields, and many other things are all measurable relative quantities.

so relative to what are you measure it?
and what doest it mean a box of chocolate contains X amount of jouls?

 

[Dale]

so relative to what are you measure it?

Relative to whatever coordinate system is convenient. All you have to do is specify the coordinate system you are using.

and what doest it mean a box of chocolate contains X amount of jouls?

In means that if you burn it in a bomb calorimeter you get X J of thermal energy released. This is a measure of the chemical rest energy, so it is frame invariant.

 

[SystemTheory]

This concept of absolute versus relative "energy" has me confused.

I am not a theoretical physicist, but it seems to me, zero is an imaginary number, and there is no way to measure "zero" anything.

Therefore when we assign a number value to a measured quantity, we always assign some state of existence a "zero" value, when in fact, the exact amount of the quantity in the universe is indeterminable.

Perhaps a reference frame is invariant, and apparently the amount of chemical energy is the same when we burn two samples of a similar mass and material regardless of the numbers and units assigned. However, in no way am I convinced that a number assigned to a measurement is in anyway an absolute quantity, because there is a choice in which number to assign to the quantity.

The laws of physics should predict the same differences in energy during a process when we account for reference frame and unit transformations, so what is absolute in this process besides the methods applied by observers being consistently defined and applied?

 

[A.T.]

zero is an imaginary number

Is 0^2 negative?

and there is no way to measure "zero" anything.

Why?

The laws of physics should predict the same differences in energy during a process when we account for reference frame and unit transformations,

A process like acceleration might not even take place in some frames. Energy conservation is valid within a frame not between frames.

 

[SystemTheory]

Zero is a memory process. If I say "there are zero elephants in the room," you must first imagine one elephant to understand the quantity "zero elephants." Elephants exist but zero elephants exists as an imaginary number, not as zero elephants! Can you measure zero without a positive definition attached to the idea of zero?

Here are the definitions of SI base units.

http://physics.nist.gov/Pubs/SP811/appenA.html

The numbers assigned to measured physical quantities under these definitions are different than if one applies British Engineering units, so the numbers are relative.

Someone mention's Planck's constant above. A google search shows the number for this constant is a variable depending on which system of units is applied. If the numbers vary then what is meant by "absolute" measurement?

 

[A.T.]

zero elephants exists as an imaginary number

Please learn what an imaginary number is:
http://en.wikipedia.org/wiki/Imaginary_number
Zero is not one.

I guess you mean that zero is more abstract than natural numbers:
http://en.wikipedia.org/wiki/Natural_number

Can you measure zero without a positive definition attached to the idea of zero?

You are confusing natural counting with measuring real number values:
http://en.wikipedia.org/wiki/Real_number

 

[Dale]

This concept of absolute versus relative "energy" has me confused.

I am not a theoretical physicist, but it seems to me, zero is an imaginary number, and there is no way to measure "zero" anything.

Sure you can. Obviously you can only measure any number (including zero) to within the precision of your measuring device, but within that limit you can easily measure zero. Also, as A.T. mentioned 0 is a real number.

Perhaps a reference frame is invariant, and apparently the amount of chemical energy is the same when we burn two samples of a similar mass and material regardless of the numbers and units assigned. However, in no way am I convinced that a number assigned to a measurement is in anyway an absolute quantity, because there is a choice in which number to assign to the quantity.

The laws of physics should predict the same differences in energy during a process when we account for reference frame and unit transformations, so what is absolute in this process besides the methods applied by observers being consistently defined and applied?

I can't parse this at all. If you think it is important and would like an answer then could you please rephrase it?

 

[SystemTheory]

Yes, I confused the appropriate terms used for conventional number theory. Still, calling zero or negative numbers "real" does not imply anything other than a conventional name.

I think my points are valid just the same.

 

[Dale]

Yes, I confused the appropriate terms used for conventional number theory. Still, calling zero or negative numbers "real" does not imply anything other than a conventional name.

I think my points are valid just the same.

They might be, but I can't understand them enough to tell. The "conventional names" and "appropriate terms" are important because they aid communication. Please try to use them correctly to get your point across.

 

[SystemTheory]

DaleSpam,

"A number without a unit is meaningless," my old professor used to say. When I measure zero of some quantity, I do so with respect to a positive definition of that quantity, and I assume something positive is absent in the problem.

An example is NASA failure due to confusing MKS units and British Engineering units in the Mars climate orbirter. The project burned up because the programmers specified numbers in one system and the thrust engineers assumed the other system, so the thrust was wrong.

If the procedure to assign numbers and units is via a relative convention, that can be altered by intention or accident, then how does one "measure" energy in an absolute sense if the numbers assigned are relative to many socially agreed upon arbitrary definitions?

I think that states my question properly. The symbolic equations are the same, but the numbers we assign can never come up with some absolute scale of energy, as far as I can fathom at this point.

 

[Dale]

OK, I think I understand your objection. Let me try out this example and see if I am getting the point. Let's use the famous E=mc² formula to calculate the invariant energy released from the annihilation of an electron and a positron in their mutual rest frame.

The rest mass of an electron or positron is 9.1E-31 kg and c is 3.0E8 m/s so the energy released is (2 9.1E-31 kg) (3.0E8 m/s)² = 1.6E-13 J. All reference frames agree that 1.6E-13 J was released.

The rest mass of an electron or positron is 511 keV/c² and c is c so the energy released is (2 511 keV/c²) (c²) = 1.02 MeV. All reference frames agree that 1.02 MeV was released.

Is your concern: how can all reference frames absolutely agree that 1.6E-13 J was released if they can also all absolutely agree that 1.02 MeV was released? If so the answer is that 1.6E-13 J = 1.02 MeV, they are the same thing.

 

[SystemTheory]

DaleSpam,

I appreciate your concrete example and effort to address my question.

Look at it again. Doesn't your example demonstrate my original closing comment where an observer applies a law of physics, describes standard units of measure, and then considers the net change in energy during a process to be equivalent in two relative unit systems?

The laws of physics should predict the same differences in energy during a process when we account for reference frame and unit transformations, so what is absolute in this process besides the methods applied by observers being consistently defined and applied?

I know the change in energy is the same for this particular process when measured, but in what sense does measuring the energy of a process give us an absolute reference point?

 

[Dale]

Look at it again. Doesn't your example demonstrate my original closing comment where an observer applies a law of physics, describes standard units of measure, and then considers the net change in energy during a process to be equivalent in two relative unit systems?

Yes, the change in energy is equivalent in both J and eV.

I know the change in energy is the same for this particular process when measured, but in what sense does measuring the energy of a process give us an absolute reference point?

In the sense that all coordinate systems (reference frames) will agree on this value. Btw, I prefer the term "invariant" to "absolute" because it is more clear.

 

[mikelepore]

Physical properties are not abstractions. What are abstract are the way that we refer to them, representing them by making vocal sounds, or marks with ink on paper going from left to right, etc. The things to which the symbols refer exist objectively. The forms of expression are creations of the mind. This distinction is confused by those who say that the physical properties are abstractions.

 

[SystemTheory]

DaleSpam,

I appreciate the extra effort. I must investigate the nature of invariant reference frames to improve my understanding.

It is still my understanding that the Conservation Laws only allow us to measure and specify that the change in energy during an interaction, measured in both the system and surroundings, equals zero. This is accomplished by assigning energy states in any relative manner consistent with good measurement procedures, and there is no absolute energy value involved in the process.

If I live in a universe that is a vast sea of energy in perpetual motion (transferring power continuously) ... where in the heck am I going to discover "the one and only zero energy" reference point?

To imagine zero energy I must picture non-existence!

 

[A.T.]

Physical properties are not abstractions.

I think you just misunderstand what 'abstraction' means in that context. It just means a generalization of a concept, so it is applicable to a broader set of observed phenomena.

What are abstract are the way that we refer to them, representing them by making vocal sounds, or marks with ink on paper going from left to right, etc.

No, the vocal sounds and marks with ink on paper are not abstractions, but 'real' objects. They are just used to communicate abstract ideas.

This distinction is confused by those who say that the physical properties are abstractions.

I think that you confuse 'real' objects and their abstract properties. Let me give you an example:

Mathematical abstraction:

A heap of 5 apples: The apples are 'real', but the number 5 is just a human idea, and the amount of entities is an abstract property of the heap of apples. It is called abstract, because it is not only applicable to this heap of apples, but all kinds of collections of all kinds of objects.

Physical abstraction:

A heap of variably sized sticks: The sticks are 'real', but their length is an abstract property of a stick. It is called abstract, because it is not only applicable to a certain stick, but to other sticks and many different objects.

 

[Dale]

where in the heck am I going to discover "the one and only zero energy" reference point?

You can set your zero energy wherever is convenient for most forms of energy. I think you are confusing invariance under gauge transformations with invariance under coordinate transformations.