The reality of energy.
in [Relativity]
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From: BURT on 27 Feb 2010 15:53 On Feb 27, 12:33 pm, "Androcles" <Headmas...(a)Hogwarts.physics_u> wrote: > "ben6993" <ben6...(a)hotmail.com> wrote in message > > news:8568dbb7-ba06-4b3e-a352-25a90f8560c7(a)q15g2000yqj.googlegroups.com... > > > "Energy" is the ability to do work, an ability that is possessed by > > organized portions of matter. > > I have noticed a definition in wiki which seems to imply that energy > is more complicated than the definition above: > "The thermodynamic entropy S, often simply called the entropy in the > context of thermodynamics, can provide a measure of the amount of > energy in a physical system that cannot be used to do work." (http:// > en.wikipedia.org/wiki/Introduction_to_entropy) > > If energy is the ability to do work, but at the same time entropy > implies that some portion of energy is not available to do work, then > how do we re-define that portion of the energy in a system not > available to do work? Is there a more complex definition of energy? > ================================================ > You haven't defined work. Lifting x gallons of water a height of > y feet from a mine is "useful work" for an engine, but if that engine > burns coal to raise steam to do the work and then the heat is simply > lost to atmosphere, that portion of energy the coal had which didn't > do useful work is still called energy. > Entropy says you can't make 100% of the coal's energy lift water, > some will always be lost as heat. This leads to silly arguments about > "closed systems" which don't exist, fools devising perpetual > motion machines, and misunderstood definitions of entropy. > Entropy is a theoretical physicist's lame attempt to face practical > reality and place his own stamp on it. Mass is infinitely dense energy. FInite density energy does not weigh. Finite density energy is light and bond. Mitch Raemsch
From: Bill Hobba on 27 Feb 2010 16:13 On 28/02/2010 5:22 AM, ben6993 wrote: > >> "Energy" is the ability to do work, an ability that is possessed by >> organized portions of matter. > > I have noticed a definition in wiki which seems to imply that energy > is more complicated than the definition above: > "The thermodynamic entropy S, often simply called the entropy in the > context of thermodynamics, can provide a measure of the amount of > energy in a physical system that cannot be used to do work." (http:// > en.wikipedia.org/wiki/Introduction_to_entropy) > > If energy is the ability to do work, but at the same time entropy > implies that some portion of energy is not available to do work, then > how do we re-define that portion of the energy in a system not > available to do work? Is there a more complex definition of energy? > Indeed there is. The modern definition is based on one of the most beautiful and useful theorems in all physics (and indeed in math IMHO - but I am biased towards mathematical physics) - Noethers Theorem: http://en.wikipedia.org/wiki/Noether%27s_theorem http://www.mathpages.com/home/kmath564/kmath564.htm http://www.physics.ucla.edu/~cwp/articles/noether.asg/noether.html Energy, by definition, is the quantity associated with the time symmetry of a system. Under this definition it is automatically conserved. It is also seen that energy conservation is basically a tautological consequence of that time symmetry - in systems that don't have it (eg accelerated systems) then it may not be conserved. It also sheds light on one of the great issues of GR - you cant in general define energy in it. It sheds light on it but issues still remain (you basically cant define it completely and unambiguously in a way all physicists will accept): http://scope.joemirando.net/faqs/Relativity/GR/energy_gr.html http://arxiv.org/abs/gr-qc/9701028 http://philsci-archive.pitt.edu/archive/00000821/00/TorrettiB&B.pdf If you want to discuss a genuine problem with energy then its problems in GR is certainly on the table. E=MC2 and all that sort of stuff follows quite beautifully from this definition - in fact its almost pulled out of thin air from the only reasonable Lagrangian you can cook up for a free particle. It is so beautiful Zwiebach in his book on string theory devotes a whole chapter to it (chapter 5) - and he is not the only one. But energy in GR is still an issue. Thanks Bill
From: BURT on 27 Feb 2010 16:22 On Feb 27, 1:13 pm, Bill Hobba <bho...(a)yahoo.com> wrote: > On 28/02/2010 5:22 AM, ben6993 wrote: > > > > > > > > >> "Energy" is the ability to do work, an ability that is possessed by > >> organized portions of matter. > > > I have noticed a definition in wiki which seems to imply that energy > > is more complicated than the definition above: > > "The thermodynamic entropy S, often simply called the entropy in the > > context of thermodynamics, can provide a measure of the amount of > > energy in a physical system that cannot be used to do work." (http:// > > en.wikipedia.org/wiki/Introduction_to_entropy) > > > If energy is the ability to do work, but at the same time entropy > > implies that some portion of energy is not available to do work, then > > how do we re-define that portion of the energy in a system not > > available to do work? Is there a more complex definition of energy? > > Indeed there is. The modern definition is based on one of the most > beautiful and useful theorems in all physics (and indeed in math IMHO - > but I am biased towards mathematical physics) - Noethers Theorem:http://en.wikipedia.org/wiki/Noether%27s_theoremhttp://www.mathpages.com/home/kmath564/kmath564.htmhttp://www.physics.ucla.edu/~cwp/articles/noether.asg/noether.html > > Energy, by definition, is the quantity associated with the time symmetry There is no double arrow for time therefore time symmetry does not apply. Mitch Raemsch
From: glird on 27 Feb 2010 17:06 On Feb 27, 1:36 pm, PD <thedraperfam...(a)gmail.com> wrote: > On Feb 27, 11:32 am, glird <gl...(a)aol.com> wrote: > > On Feb 27, 10:34 am, PD wrote: > > > On Feb 26, 7:54 pm, glird <gl...(a)aol.com> wrote: > > > > On Feb 23, 4:48 pm, Occidental wrote: >< Discussion in physics refer to energy as if it were as fundamental a part of the universe as space, time and matter. In Newtonian mechanics, energy is a useful mathematical abstraction, but not a directly measurable part of any dynamical system. Presumably this is also true in Relativity, despite mass/energy equivalence. > gl: >>>> Before replying to this message I glanced through the previous nine replies. As I expected, none of them defined "energy". Having long ago noticed that unless a key word is defined nobody understands what other people mean when they use it, I defined it thus: "Energy" is the ability to do work, > > pd: >>> The above is a common definition, yes. > >>>> an ability that is possessed by organized portions of matter. > > >>> Not just by matter. > >> Other than matter, what do YOU think >> can have that ability? > > A system containing light, and light alone, also > exhibits energy. No matter present. Other than in the theories of physicists, there is no such system. gl: BTW, here is the definition of energy taken from my latest book, The Universe. (The portion in parentheses was in a different font because it followed the first appearance of the defined word.) The rest of the quoted bit is relevant here, but isn't part of the definition. ("Energy" is the capacity to do work, and is equal to mass times acceleration. > > The first clause is correct, the second is wrong. Thank you for pointing that out to me, PD! It followed the following discussion: "Classical Physics has the two equations, F = ma and e = Fd, from which we get e = Fd = ma x d = m x cm/sec2 x cm = m(cm2/sec2). Since cm2/sec2 = v2, that gives us e = mv2; which becomes e = mc2 at the relativistic upper limit of velocity. "Because the units of mass and weight were identical, however, F = ma and e = mc2 are mistakenly thought to say that matter and energy are interconvertible." I corrected the silly error in the second clause of the next sentence as follows, "('Energy' is the capacity to do work, and is equal to mass times the distance moved" and then continued, "Matter, not space, possesses this capacity.)" The next comment by PD referred to my erroneous clause that energy "is equal to mass times acceleration". > That's force, not energy. Two completely different > things. His first clause in sentence one is correct. As shown below, his second sentence is bullshit. pd: <You'll notice below you also note the distinction by the units. Energy has units 1 gcm²/sec², but mass times acceleration has different units, 1 gcm/sec². To understand the key difference, as well as the connection between the two (work), please see any introductory physics text. I didn't read further, presuming that the rest followed from this mistake. > If he didn't read further than my erroneous clause, how did he know what I wrote "below" AFTER the next bit which he snipped out? >><Since the only thing that can change the state of motion of a mass is a net pressure, energy is a net pressure, thus is a force. >> Didn't like that, eh,PD? Is THAT why you deliberately snipped it out? >>< Accordingly, rather than being a basic item or a form of matter, energy is a dimension. Its unit of measure is an erg, which is defined as a force of one dyne exerted for a distance of one centimeter; i.e. 1 gcm²/sec² = m_wv² in which m_w denotes the weight of a given mass rather than the quantity of matter in it. > So, PD, whachoogonnasay about THAT? >> For those who might be interested, here is some more from The Universe: "Complementarity says, Sometimes light is a particle and sometimes it is a wave, therefore both aspects are needed to fully explain light. The converse of that is, Sometimes light cannot be a particle and sometimes it cannot be a wave, therefore it is neither. "It is here that the semantics and concepts of present Physics broke down and the adequate existing equations became uninterpretable. That isn't because the laws of nature don't apply at the very small quantum level; it is because the laws of Quantum Physics deal with particles, with masses, with single inertial or accelerating units or with statistical probabilities based on the actions of myriad such separate individuals. "When we consider the actions taking place in a continuous field, actions that have no particles as part of what is happening and weight does not exist, the laws and even the logic of what particles might do no longer apply. {'Stop at a red light' does not apply to aircraft.} aircraft.} "It isn't that human logic is inadequate or that the laws of particles do not apply in the realm of the very small. It's just that a relatively homogeneous continuum acts differently than groups of particles. (If a particle entered our etheric field it would obey the laws of particles.) Human logic does not break down. Indeed, our equations, a stylized form of symbolic logic, have already provided the answers. "To understand those answers, however, we need to escape the Promethean confines of formalized systems of logic in which, by Godel's accepted theorem and Einstein's characterizations, truth and reason are irrelevant." For any of you who enjoy my words, here's what The Universe said next: "The concept that a movable, compressible, fluid material medium fills all places and spaces in the known universe is not part of present theory. Neither, therefore, is the concept that this substance is permeated by a basic expansive pressure exerted by itself against itself. Neither is the concept that condensation of basic continuous material can accommodate what would otherwise be a pressure- disequilibrium. For the moment, then, these concepts may be considered basic postulates of the theories to be presented in Book Two [and in this one]. "There IS a space filling medium. It IS capable of motion and resilience. It exerts an expansive pressure in all directions. It is but a small step from there to the recognition that this very same material substance is what is formed into the atoms and molecules of gross matter. To take that step, however, a vast conceptual chasm had to be crossed." Lest anyone feels left out of this loop, here's what came next: "Look around you. Look at a glass, a metal one-piece wrench, or any other one-piece object. I am now going to ask you to do something that will do violence to every instinct of a trained scientist:- Recognize that it is indeed one piece! "Of course there are very-fine-grained density gradients all through the unit, and you can't see them overtly. But if you look closely enough, you can see them too (with a little help from some instruments). An object isn't a collection of separate particles moving randomly within a confined space. It is one big particle with no empty places inside it. Think of it as exactly what it looks like, all the way through. It is no different than it looks." PD would disagree, of course. So would the rest of the scientific community. Knowing that, here's what The Universe said next: "Note. Today's theorists would say that anyone who made this claim either was uneducated or insane. {In a lunatic asylum a sane man is abnormal!} A later generation that understands the structure of the physical world will know that a material continuum fills space. It will know that we are made of highly organized, patterned portions of this one universal material. It will know that light and energy are functions of the structure of this substance. "Imagine what would happen to a modern scientist who materialized in a public park, at such a time, and proudly announced that matter is made of a void, that light is a vibration of nothing, that his feet and the ground supporting them are made of disembodied particles as far apart, on a smaller scale, as the stars in the sky. Where do you think he would end up if he insisted that everything we see in the park isn't really there?" Oops.. lucky you! I just came upon something in the next paragraph that caused me to wonder what the connection between it and my "flower" might be. It was this: "the strong coupling of the Yukawa field to its source is extremely important; its strength, 2pg2/hc, is of the order of magnitude of ten (in contrast with the Sommerfeld constant 2pe2/hc = 1/137 in electrodynamics)." Noting that 1/137 is the Fine Structure constant, which is part of the Flower for Einstein:; h = 2pirmc', in which c' = c x Fs; i will go play with this stuff on my Texas Instrument hand calculator. So good bye, now. glird
From: John Polasek on 27 Feb 2010 17:36
On Wed, 24 Feb 2010 11:13:51 -0800 (PST), PD <thedraperfamily(a)gmail.com> wrote: >On Feb 23, 3:48�pm, Occidental <Occiden...(a)comcast.net> wrote: >> Discussion in physics refer to energy as if it were as fundamental a >> part of the universe as space, time and matter. > >It is a measurable property of systems which seems to have an >extraordinarily consistent rule that applies to it, making it of >fundamental interest in science. I'm not sure what you mean by "a >fundamental part of the universe". > >> In Newtonian >> mechanics, energy is a useful mathematical abstraction, but not a >> directly measurable part of any dynamical system. > >What on earth ever gave you that idea? > >> Presumably this is >> also true in Relativity, despite mass/energy equivalence. Energy beams >> are a staple of science fiction, but (ISTM) they are impossible since >> particle or waves are needed to transmit energy. > >I assume you mean waves in a material medium, and again I ask, >whatever gave you that idea? > >Secondly, if energy is a mathematical abstraction and not a measurable >part of a system, then what is it that is being transmitted by >particles or waves in material media? Formulas? Numbers? > >Third, we can confirm experimentally that energy is being transmitted >in certain circumstances. You have a statement, which you are alleging >is universally true, that the observation of energy transfer >*necessarily* implies the presence of material particles or a material >medium. This statement should be taken as something with testable >consequences, whereby we could *independently* confirm the presences >of these particles or this medium by some signal other than the >transmission of the energy. What are those testable consequences, and >do those match up with the experimental data at hand? If not, then you >have an untestable statement, and untestable statements are purely >USELESS in science. > >> Ie a pure energy beam >> could not exist. In order to back up the statement that energy is measurable, please name an instrument that measures energy. There is none. Where energy has a specific value, it exists only as a scalar product of two other quantities. A watt-hour meter has a wheel that turns as the scalar product of a voltage coil and a current coil and thus integrates power over time. John Polasek |