The reality of energy.
in [Relativity]
|
From: BURT on 27 Feb 2010 17:59 On Feb 27, 2:36 pm, John Polasek <jpola...(a)cfl.rr.com> wrote: > On Wed, 24 Feb 2010 11:13:51 -0800 (PST), PD > > > > > > <thedraperfam...(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- Hide quoted text - > > - Show quoted text - A scale measures energy in the form of C squared mass. Mitch Raemsch
From: maxwell on 27 Feb 2010 21:05 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 > 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.htmlhttp://arxiv.org/abs/gr-qc/9701028http://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 Lagrangians lack physics. They are just 'cooked up' to give the resulting equations that were desired in the first place. This math - not physics.
From: maxwell on 27 Feb 2010 21:13 On Feb 27, 12:04 pm, PD <thedraperfam...(a)gmail.com> wrote: > On Feb 27, 1:22 pm, ben6993 <ben6...(a)hotmail.com> 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? > > That's actually an excellent point. Kinetic energy, one of the forms > of energy, is divided into stochastic and collective energy. The > collective energy is the kind of thing you would write (1/2)mv^2 for a > baseball of mass m. Stochastic energy is that which is indicated (but > not measured) by a thermometer; it is the *random* kinetic energy of > the individual molecules in the body. The former can be wholly > converted into work. The latter can only be partially converted, with > the limit set by Carnot's Theorem. > > In addition, rest energy (the energy associated with rest mass) can't > be converted into work, but the entropic definition above has nothing > to do with this. > > I don't know of any other cases, off the top of my head. Defining energy in terms of work is just the 19th century macroscopic approach to physics before the atomic basis of nature was available. It is not logical to define the parts in terms of pieces of the whole since this misses out the synergistic component of bringing parts together: this is cookery. The macro (like averages) must be defined in terms of the micro. This is why Maxwell's Equations of EM is a statistical theory and NOT a fundamental theory of physics.
From: Bill Hobba on 27 Feb 2010 22:38 On 28/02/2010 12:05 PM, maxwell wrote: > 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 >> 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.htmlhttp://arxiv.org/abs/gr-qc/9701028http://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 > > Lagrangians lack physics. They are just 'cooked up' to give the > resulting equations that were desired in the first place. This math - > not physics. Not true. The Lagrangian formalism follows directly from the axioms of QM. In that sense it is even more fundamental than the Newtonian formulation. However it is a well known fact the two are logically equivalent. See for example Chapter 2 - Zee - Quantum Field Theory in a Nutshell and Chapter 6 Morin - Introduction to Classical Mechanics. Thanks Bill
From: BURT on 27 Feb 2010 22:44
On Feb 27, 7:38 pm, Bill Hobba <bho...(a)yahoo.com> wrote: > On 28/02/2010 12:05 PM, maxwell wrote: > > > > > > > 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.... > > >> 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.htmlhttp://a.... > > >> 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 > > > Lagrangians lack physics. They are just 'cooked up' to give the > > resulting equations that were desired in the first place. This math - > > not physics. > > Not true. The Lagrangian formalism follows directly from the axioms of > QM. In that sense it is even more fundamental than the Newtonian > formulation. However it is a well known fact the two are logically > equivalent. See for example Chapter 2 - Zee - Quantum Field Theory in a > Nutshell and Chapter 6 Morin - Introduction to Classical Mechanics. > > Thanks > Bill- Hide quoted text - > > - Show quoted text - Mass is defined as infinitely dense energy. This weighs while finite density energy in bond and light wave does not. Mitch Raemsch |