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Everything posted by juanrga

  1. My personal definition (although peer-reviewed): Science is the enterprise dealing with (i) the description, analysis, and synthesis of parts of the observable universe and their transformations, following systematic methods, (ii) the recording and organization of the acquired accumulative knowledge into testable formalisms and methods, and (iii) the dissemination of this knowledge.
  2. For a closed system and reversible process TdS=dQ. Adiabatic process means dQ=0. Therefore dS = 0
  3. You grossly misinterpret me, misquote me, and ignore what I have said and repeated.
  4. At contrary, an unambiguous definition of what is the system is needed to answer if the system is open or closed. By a question of pure logic you cannot specify a "system process" without first saying what the "system" is. You claim now that the system process was "adding another block by pushing it across", but adding to what? Across what? To a ill-defined system which you did not even can say if was a single crystal or two? Does this system include the "aura" that Michael123456 attributes to it? Just after reading your ill-defined examples I wrote: You continue being imprecise. Is "half full barrel" the same than "The barrel"? "The barrel + fluid"? "The Barrel + fluid + air"?... See (*) (*) Is doing statement about sources that you "have not seen" your idea of "critical examination"? Conservation of total energy is not an assumption but a law. It is untrue that statistical mechanics is based in your assumptions. In any case this has nothing to see with this thread. Open a new thread if you want discuss that kind of stuff. This again? The internal energy of what? Of a system which you have not still defined?
  5. It was initially believed that the difference between the observed gravitational lensing and the gravitational lensing predicted by GR could be due to a hypothetical missing mass, which was named dark matter. However, this hypothetical mass has never been found where it was supposed to exist once. Today, observed gravitational lensing can be explained by theories such as MOND, TeVeS, and others without any appeal to a hypothetical dark matter.
  6. You can add energy to a closed system. You cannot add energy to an isolated system. See the references cited. E.g. Ref. [1]. This attempt to read inside my mind is fascinating, but that was not what happened. My post, which you are replying, contains the exact quote and it was: You assume that "therefoe" was a typo but "into" was not. I never was able to move a crystal block into another crystal block . If you know how to do it, please explain me how. Moreover I interpret "onto the right" as "onto the right". I will draw again the diagram where the system is denoted by the X and the moving block ("onto the right") by the upper B B --> B BX --> BX You can draw an alternative diagram, if you disagree with this. I could not rebate such scientific arguments as "should be said, that the system has an "aura" around it". I have not still studied the thermodynamic of systems with "auras" and my textbooks have not such chapter
  7. Evidently if you can add mass to a system the system is open. But this was not your example: The system is, your own words, the "solitary right hand block" (aka the X) and if you put another block B above it B --> B BX --> BX you have not added mass to the system (aka the original block X). About the barrels, you completely ignored that I wrote. The proof that dU=dQ+dW is not valid for open system is trivial (just consider an open system with zero work, zero heat, add or remove mass and measure its internal energy). Many textbooks emphasize that dU=dQ+dW is valid for closed but not for open systems (I have cited a textbook that does). You ignore what is being said to you and insist on applying a closed-system law to an open system Your "the internal energy increases by exactly the heat content of the added liquid" is plain wrong. The Gibbs 'paradox' is a well-known misapplication of the thermodynamic formalism. Any decent reference explains why there is not paradox. Moreover, this has nothing to see with this thread. Maybe you could open a new thread for discussing that.
  8. Quantum electrodynamics is a quantum field theory and quantum field theory does not use wave-functions. You grossly misinterpret me, misquote me, ignore what I have said and repeated... For instance, I wrote that Nikolic emphasizes that "wave-particle duality" is a myth [*]. In no other part of the post that you quoted I used the word "myth". But you now pretend that I said that "wave mechanics in quantum mechanics is a myth", when in the post that you quoted I wrote: "The wave-function approach is still given in introductory courses to QM, which only deal with simplest problems". If you cannot read my posts and/or understand what I am really saying, maybe you would stop from reading them. [*] Indeed the corresponding section of his paper is titled "Wave-particle duality as a myth" )
  9. You wrote "consider the solitary right hand block as the system". It is evident that the system (the right hand block) is closed. Now, if you change the definition of system in arbitrary ways and at any time that you want, then it is not a surprise that you get into troubles . If you read my previous message you would find my response to your other questions. You pretended others to say properties of systems which you did not even defined . This is weird. I think that I already said to you two or three times (another poster emphasized the same here) that the law dU = dQ + dW is valid for closed systems but not for open systems. I will not repeat more.
  10. I wrote "As any textbook in thermodynamics..." I could not disagree more! It is not true that thermodynamics covers systems outside the scope of statistical mechanics (statistical thermodynamics). No trick here! Before starting the study of some system you would first define what your system is. You ask questions about a system without first saying what is the system is. The barrel? The barrel + fluid? The Barrel + fluid + air? The Barrel + fluid + air + the added extra fluid? The Barrel + fluid + air + the refrigerator? The Barrel + fluid + the added miscible fluid? Any other? Closed. I assume that by "absolute zero" you really mean [math]T \rightarrow 0K[/math]. Perfect crystal and 0+K would imply no friction, no compressibility, no external gravity effects... I assume that all the blocks are at thermal equilibrium and that there is not electric or magnetic effects. The only reliable source of energy become from electrostatic effects, but would average close to zero due to total neutrality of the crystals. Therefore the change in U would be zero.
  11. Nothing of this is related to what I have really said.
  12. I fail to see from where you got this. It cannot be a misunderstanding about the symbols and formalism used, because the article cited in the OP says in words (I add bold face for emphasis): Moreover, I already explained that the article uses standard stuff (see [1]). As any textbook in thermodynamics explains the state of thermodynamic equilibrium is a dynamic one. The 'net' or 'macroscopic' variation of energy is zero, but there are 'microscopic' variations of energy due to molecular fluctuations. As a consequence the energy of a finite system at equilibrium with a heat bath is not constant due to fluctuations. Textbooks in statistical mechanics explain how to compute those variations in the energy using the canonical ensemble. As you correctly notice thermodynamic equilibrium is given by [math]dE=0[/math], this is not the same than [math]d\tilde{E}=0[/math] Precisely, I am preparing another article, this is about stochastic variables and fluctuations and explains the difference between quantities and the usual averaged quantities used in thermodynamics and other disciplines.
  13. Particle physics is based in QM, but does not use the old wave formulation of QM. Modern and advanced treatises on QM do not use the old wave-function approach. The wave-function approach is still given in introductory courses to QM, which only deal with simplest problems; whereas more advanced treatises on QM deal with the old wave-function approach only in the chapter dealing with the history of QM. The old wave-function approach is not abandoned by aesthetic or philosophical reasons. It happens that quantum particles cannot be always described by wavefunctions. People who only takes an introductory course in QM seems the believe the contrary. I already cited three or four standard books in QM and QFT giving the details of all that I am saying here. Consider the textbook by Cohen. The volume 1 starts with a historical introduction that deals with older experiments, the old wave-function approach, the old duality concept, and all that. But then in chapter II, which is a kind of interlude for the rest of the material in the volume, adds [bold emphasis is from mine]: As I already emphasized, more than one time, a particle cannot be a wave or behave as a wave. First, this wave-particle-duality-nonsense (Nickolic names it "myth") is traced to an old confusion between the quantum system under study (aka the particle) with its mechanical state in the wave-function formulation (aka the wavefunction). Second there are experimental situations where the state of a particle is not given by a wavefunction. Or said in another equivalent form: there experimental situations where the observables of a particle cannot be described using wavefunctions. Some examples of systems whose quantum state is not given by a wavefunction include: A single isolated stable particle when one takes into account spin (see quote above). A Klein-Gordon particle (see Ryder's). An electron in a multi-electronic atom. Due to electron-electron correlation (see previous posts from mine). An unstable particle. Unstable states are not describable by wavefunctions (see the Adv. Chem. Phys. paper por details) Etc. Finally I want emphasize that I do not find a "too much controversy". Some aspects of QM are still under debate by the experts, but others are not. It happens that QM is a technical and complex subject and some authors are more prone to error that others. I do not know what you mean by "How is charge defined under QFT?" Charge is not defined, but is one fundamental physical quantity, which is measured in the lab. E.g. the charge of an electron is e and its value is given in tables of constants.
  14. This is why I was reluctant to cite that paper, although it correctly points that wave-particle duality has only historical interest and is not used in any modern and rigorous presentation of QM, it contains ideas that are simply plain wrong. In #87 I wrote about this paper: The idea of that particles are waves is plain wrong. That is the reason which particle physics is not named "wave physics". And this is also why an electron is considered an "elementary particle" and not an "elementary wave". Standard textbooks in QM and QFT as Weinberg, Cohen, Mandl and Shaw... explain why it is not true that a particle was associated to a wavefunction. Weinberg emphasizes that what we measure in the lab are particles. If my memory does not fail, yourself quoted part of a textbook emphasizing that solutions to Klein-Gordon equation are not wavefunctions! I apologize for citing that paper when swansont asked. Although it seems that it settled out that duality is an outdated concept it has generated other doubts .
  15. I did mean that dQ and dW are given by functions of dU, dV, dN when the state is given by (U,V,N). E.g., for the thermometer cited above, the important variable is its internal energy U and heat is given by dQ=dU. I have not said such thing neither wrote such equations. See also my reply to Cap'n Refsmmat. I already explained before in this same thread that both heat and work are represented by inexact differentials, δQ and δW, in classical thermodynamics, due to limitations of the classical formulation. Modern thermodynamics works with an extended thermodynamics space beyond the classical formulation, abandons inexact differentials, and uses well-defined dQ and dW. As I already emphasized before the classical law dU = δQ + δW is an approximation to the more modern and general law dE = dQ + dW See the textbook "Modern thermodynamics" by Prigogine and Kondepudi, cited before, for the details.
  16. The problem with the OP is that he is asking for details of an obsolete model which is not even valid as approximation. You can obtain the Schrödinger formulation of QM as approximation to a more general formulation. Indeed, there are atoms which are well-described by the Schrödinger equation, whereas others are not. But you cannot obtain what the OP has in mind as an approximation to QM, because the 'planetary model' of the atom is non-physical. None atom of the periodic table can be described by the 'planetary model'. Sorry, but the concept of electron orbits does not exist neither in the theory of QM nor in the lab! Adequate answers to the OP are given in the responses from #2 to #5 including the mine. http://www.springerlink.com/content/71rp68556843238n/?MUD=MP The abstract is here http://www.springerlink.com/content/71RP68556843238N/primary I agree with many of what he says but disagree on other aspects. E.g. I agree on that duality is a myth, but disagree with his Bohmian approach to waves. Some of his claims are shown incorrect in standard textbooks (Weinberg, Cohen...). I think that this is a good reference for people who already knows QM, otherwise it can be a confusing reference. Therefore use it at your own risk
  17. Mechanisms that stop gravitational collapse are given in the literature associated to those objects. Regarding the one that I am familiar (see my previous post), gravitational collapse is stopped by the pressure exerted by the own graviton field associated to ANY star.
  18. I understand your wise point. Thank you for sharing it. Please, let me state the mine. When being a student, I was tired of being said, "sorry what they said you, the past course, was not true". My didactic approach is different. I agree on that you must adapt your teaching level to the student level. But I do not think that one would be teaching stuff which is simply untrue [*]. Particularly, I find no reason for the outdated concept of duality and I am not the first who propose that it would be eliminated from textbooks. Duality is not really needed for explaining anything even at the basic level of the Schrödinger formulation, and of course it makes no sense in more advanced formulations of QM, not even as approximation. Why then introduce it in the first place? A wiki-editor noted the analogy of the wave-particle duality with the concept of relativistic mass. Relativistic masses play no role in fundamental physics, but they are used in very old textbooks of the 60s and in some recent introductory textbooks. My experience is that relativistic mass only adds confusion to students. There is a fierce debate with some physicists claiming for the elimination of this concept from textbooks and other claiming the contrary. Regarding the wave-particle duality concept the author of the FOP paper that I alluded in a previous post writes: I agree with all of this, although I strongly disagree with many what he says in the same work about waves and particles and other QM stuff. Moreover, you assume that the student will take a more advanced course in future. But in my experience, most students take some introductory course in some discipline, never take a more advanced course and then believe that the stuff that was said to them would be taken as Divine Truth. Precisely, what I did when posted here was to correct to another poster who apparently believes that what he says is always true. Maybe my didactical approach is unrealistic or completely wrong. But I wait that it can be at least useful for those students who as myself hate the "sorry what they said you..." [*] I am not objecting to stuff which can be valid as approximation. E.g. Newtonian gravity can be taught today because it is an approximation to a more general theory of gravity and can be used to explain/predict phenomena. Number Pi can be approximated as 3.1416. Neither I am objecting to stuff said in chapters dealing with the history of the subject.
  19. I do not know why you say this. The definition of closed system that I gave is the standard one (check reference [1]) and it is perfectly compatible with equilibrium and with thermodynamic scale. I do not know what do you mean here. In thermodynamics, both heat and work are functions of variables on the thermodynamic space of the system (U,V,N...). For an isolated system both dQ and dW are zero.
  20. As explained before in this thread (Wiki-editors post similar thoughts in the talk page linked) duality is still used in introductory, historical, and non-rigorous treatments. E.g. Weinberg cites both duality and wave mechanics in the chapter 1 "Historical introduction" of the first volume of his textbook on QFT. But then in the chapter 2 "Relativistic Quantum Mechanics" he never mentions or use wave mechanics neither duality. Cohen in the first volume of his QM, discuss wave-functions and duality in the introductory chapter. Then in posterior chapters dealing with the serious stuff warns readers that not all quantum systems can be described by wavefunctions and then go to the generalized formalism. The Chapter 6 of Volume 1 of the Handbook on molecular physics and quantum chemistry gives an introduction to wave-particle duality. Then write: There exists a well-known article published in FOP that devotes an entire section to explain why wave-particle duality is a myth and would be abandoned. The problem is that some of his arguments are wrong and other would only confound to some people here and for this reason I have not cited it. The verified theories are not wrong when further experiments are done. They already were verified. That is the reason which classical physics continue being used today and works so well (for the kind of systems to which it apply) as 300 years ago. Relativity contains the classical stuff as a particular case.
  21. I think that I addressed your points. The physicists cited "were not developing Gibbs canonical equation" because the Gibbs equation has nothing to see with the definition of open, closed and isolated systems. My complain was, in essence, that these authors confounded a flow term with a production term and then did the misguided claim about conservation. I have not criticized "DH for using different notation". About 1) and 2). An isolated system is defined as [math]d_eE= 0[/math] and, using conservation of total energy [math]d_iE= 0[/math], the balance law gives [math]dE= 0[/math] or in words "total energy E is constant". A closed system is defined as [math]d_eE \neq 0[/math] and, using conservation of total energy [math]d_iE= 0[/math], the balance law gives [math]dE \neq 0[/math]. Moreover, the generalized first law of thermo for a closed system is [math]dE =dQ + dW[/math]. For a thermometer at rest and in absence of external fields effects [math]dE=dU[/math] and [math]dW=0[/math], which gives [math]dU=dQ[/math] Or in words "internal energy U of thermometer is not constant and varies with the heat". Of course, [math]dU=dQ[/math] continues being cited in textbooks as a statement the law of conservation of energy. About 3) I already explained to you that [math]dU= dQ + dW[/math] is not valid for open systems. Therefore your argument which relies on applying [math]dU= dQ + dW[/math] to an open system, is not valid.
  22. The problem with Popper is that he was not aware that scientific theories are not universally applicable but have associated a field of applicability. When you verify a theory for a given kind of systems you are certifying that the theory is valid under those circumstances. When you find a system which cannot be described by the theory, this does not invalidate the theory but limits the scope of the theory to the previously verified systems. In fact, when you develop a new theory, you must check that the new theory contains to the previous theory as a particular case. E.g., Newtonian theory is not wrong and this is the reason which astronomers continue using it today (for the kind of systems within its scope) for explaining observations and for doing new predictions. I recall a recent issue in some journal with scientists criticizing the views of Popper and other philosophers about science, but I cannot find it now. One editor wrote the term obsolete, a second editor partially agreed with him, and a third confirmed the main argument of the first: modern formulations of QM do not use duality. Moreover, I also stated that I agree on that duality is obsolete and gave both technical reasons and references. The same Wikipedia explains that their 'peer-review' And a look to their archived 'peer-review' reveals that several editors noticed their disagreement with parts of the article, which still remain in the current version. So what?
  23. It is not a terminology issue, DH is clearly confused about this topic and rejected the well-known equation [math]d_i E = 0[/math] because he was completely unfamiliar with the modern thermodynamic literature that I am using. As stated before E denotes total energy. Total energy is always conserved [math]d_i E = 0[/math]. Internal energy is not always conserved. In fact, textbooks cited here by me explain how to compute the production of internal energy [math]d_i U[/math] for different processes where internal energy is not conserved. The general thermodynamic expression for closed systems is [math]dE = dQ + dW[/math]. The common expression that DH used [math]d U = \delta Q + \delta W[/math] is an approximation which only applies to closed systems at rest, in absence of external fields, and under certain additional approximations. As I already explained conservation of energy [math]d_i E = 0[/math] would not confused with constancy of energy [math]d E = 0[/math]. This same confusion is the reason for the which the physicists cited in the OP made, in his book, the silly claim that the number of particles N in a closed system are conserved. They confounded constancy of N [math]d N = 0[/math] for a closed system with the law of conservation of N [math]d_i N = 0[/math]. For a thermometer at rest, in absence of external fields and with zero work, the internal energy is conserved because [math]d_i U = 0[/math]. An alternative statement is [math]dU = dQ[/math] which unsurprisingly is named the law of conservation of (internal) energy. The second equation is a direct consequence of the first. The law [math]dU = dQ + dW[/math] is only valid for closed systems. It is not valid for open systems.
  24. That is not a correct approach to scientific theories. A scientific theory is something which has been experimentally confirmed [*], therefore it cannot be wrong. [*] Yes I know that currently some physicists and cosmologists abuse of the term and name "theories" to certain pseudo-philosophical speculations and hypothesis.
  25. Then you will find disturbing that the own Wiki-editors use terms as obsolete to refer to the article that you linked. When I said that your link was obsolete, I did mean that its scientific content was obsolete. This fact is not changed by a Wiki-bot who automatically fixed a typo in a French word. You can open a Word document, write some scientific nonsense, then use the automatic spell-checker, and the resulting doc (now without typos) will continue to be scientific nonsense. About your three questions. I will repeat the quote from the Talk page of the article that you linked, because it explains the situation very well. It explains why about 1930 physicists lacked the adequate concepts and invented new words as duality. How those new words have now only historical interest, and how serious modern resources do not even mention duality. The quote also gives a beautiful analogy with the obsolete concept of relativistic mass. It was invented in the early years, when relativistic theory was in its infancy, but it is not used in serious and modern resources.
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