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juanrga

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Everything posted by juanrga

  1. But neither Baez nor me are saying that there exists a global reference frame. We say something different.
  2. But the statement that electrons exhibit both particle-like and wave-like behaviour is the reason which many people believes that an electron is not a particle but another thing; indeed, many posters write in this forum that they believe that an electron is a wave. This same people is very confused when read that physicists and chemists consider that the electron is a particle. I completely agree with most of my colleagues and I also define the electron as a particle (I agree 100% with the IUPAC definition given above). A logical consequence is that it makes no sense to claim that a particle exhibits wave-like behaviour because all the observables are those of a particle. Of course, others may dislike this. In his book "QED : The strange theory of Light and Matter" Feynman wrote: I find delicious his joke about the days of the week. I only disagree with him on a point. Quantum electrodynamics was not the first theory that introduced a probabilistic description of particles. Sorry but you said wave and I replied to what you wrote:
  3. http://en.wikipedia....lobal_structure http://en.wikipedia....etime_structure In SR, the speed of light is only constant among inertial observers. In 1911 Einstein considered an extension of SR where the speed of light was not constant in presence of gravitational fields but finally he took a geometrical route and in 1916 he developed general relativity where the speed of light is always constant. In general relativity the speed of light is always constant, not only locally constant. c is always constant, because is a global property of the spacetimes considered in general relativity. http://curious.astro....php?number=266 http://math.ucr.edu/...d_of_light.html Yes I know that there is an old interpretation of general relativity based in an earlier misconception by Einstein that believes that the speed of light varies in the deflection of light or in the Shapiro effects but this is not true. From Baez link: Notice also that the word "local" is not even mentioned in the above link.
  4. In this same thread you can find several posters claiming that wave-particle duality means that "electrons are particles and waves", which is not right. Neither your version is still acceptable, because the wave-particle duality is always formulated within the scope of the wavefunction formulation of QM and this formulation cannot provide "classical particle-like" behaviour. In any case, I was trying to explain the difference between a system and the state of the system. I also tried to explain that a wavefunction is not a wave but a function.
  5. Interesting work, he gives an order of magnitude cH (but does not gives the value of a0) and he assumes a geometrisation principle, which is not valid for the general potentials, but interesting.
  6. I tried to explain that one can describe the behaviour of massless particles such as photons in presence of gravity, without any need to attribute to them a fictitious 'mass' (which is ill-defined and variable). Notice that I never use the term rest-mass because it is a misnomer, specially for photons because they are never at rest are you correctly point!
  7. It makes no sense to discuss something if each poster uses different terminology and definitions. Why do you think that there are international bodies devoted to define and spread a set of common terminology and definitions? To avoid confusions... This is completely wrong. The electron in the double slit experiment is always a particle. And no wave is "detected" because there is none therein. Therefore I assume that your answer to the questions is "water is never a wave" and "satellites are never ellipses". Now the key question is if you are able to differentiate between the system (water, satellite) and the motion of the system "oscillatory motion, elliptical motion", why you cannot differentiate between an electron and its motion? As you say the interference patter is obtained when the experiment is repeated with thousands of electrons. One electron does not generate an interference pattern. Why then you believe that an electron is a wave? A wave is a physical system. E.g. a wave in water is a system, an electromagnetic wave is a system. In an approximated formulation of quantum mechanics, the state of particles as electrons is given by a wavefunction. A wavefunction is not a wave, but a mathematical function. A wavefunction is not observable. A wavefunction is not the particle. A wavefunction only describes approximatedly the state of the particle. There are situations where the state of a particle is not given by a wavefunction but by a more general formalism. The wave-particle duality myth is based in the next misunderstandings: Suppose that a wavefunction always exists. Confound a wavefunction with a wave. Confound the system with one of the possible states of the system Suppose that particle is a synonym for "small-billiard-ball-following-Newtonian-laws" You ask "what is responsible for the non-parallel trajectories of the electrons that DON'T strike the surface directly behind the slits?" Sorry, but there are not trajectories in quantum mechanics. In quantum mechanics, position x and momentum p do not commute. The electron does not move classically following a trajectory as in Newtonian physics, but moves according to quantum mechanics rules, where there are not trajectories. Therefore your question makes no sense. Your question is so weird like if I was to as ask you "what is responsible for the polarization in the oxygen atoms in benzene molecule" (you would reply me that there is not oxygen atoms in that molecule!). "Are some of the electrons somehow bouncing off the edges of the slits, as was previously suggested in another thread?" The poster who said that merely wrote nonsense.
  8. I already explained why a correct computation of the speed of light using the physical spacetime of general relativity gives that the speed of light is constant, in general relativity, along any path. If you use a fictitious background spacetime then you obtain a speed that varies. A consistent computation shows that light does not bend because light is moving in a curved spacetime at constant speed. http://math.ucr.edu/...d_of_light.html Check also: Why doesn't gravity change the speed of light?
  9. juanrga

    What is 'mass'?

    Pmb, I note that you have modified your original post #20 after my response was posted in #21. E.g. you have deleted the term "Poincaré stress" from your post #20 after I criticized it. But your original words are still quoted in my #21. The term "Poincaré stress" is also quoted in #22 because michael also replied to you before you edited your post. I am sorry about all that. You have added more material to #20, which was not in the original post when I (or michael) replied to you. For instance now you add that a luxon is a particle that travels at v = c and that in relativity it is often useful to think of light as having mass. However a luxon is defined as a massless particle (http://en.wikipedia.org/wiki/Luxon) and, regarding light, I already gave to you a link to an introduction to general relativity where light is considered to be massless without any problem.
  10. Let me first ask the next questions: If you observe wave motion on a piece of water, do you claim that water is sometimes a substance sometimes a wave? I claim that water is never a wave. If you observe a satellite moving in an ellipse around the Earth, do you claim that it is sometimes a satellite sometimes an ellipse? I claim that satellites are never ellipses. Let us imagine by an instant that it is correct to say that a particle (electron or buckyball) moves as a wave, do you claim that the particle is sometimes a particle sometimes a wave? I claim that electron or buckyball are never a wave. Do you believe that IUPAC do not know the existence of the double slit experiment when they define the electron as a particle or the buckyball as a molecule? And the last question: Do you know what is the system observed and what is being measured and how in the double slit experiment? I recall this this because after reading your "Why does the interference pattern from a particle..." I am not sure if you know how the pattern is obtained.
  11. juanrga

    What is 'mass'?

    First as quantum theory shows a photon is not a localizable particle. The classical trajectories studied in relativity correspond to a kind of average position and speed of that collection of photons that we name "light signal". Second, the Heisenberg Uncertainty Relation is a fundamental property of non-relativistic QM; it is not something that you can use or ignore at your own choice. Rohrlich's classic text is a rather good source (although outdated in some parts) and he agrees 100% with what I said of course. I know very well that Poincaré stresses are, but it seems that you do not know that the Poincaré speculative model of the electron is inconsistent and was abandoned about 100 years ago.
  12. In the other thread alluded by the OP, about 30 references to general dictionaries, scientific encyclopedias, textbooks and academic websites, including the CERN website and similar international research centres were given. All the references state that the electron is a particle. A Wikipedia talk page was also added in the other thread. In that page several Wikipedians stated that wave-particle duality is a misnomer and that "wave-particle duality" is not used in modern treatises on quantum mechanics. In this thread I have given a link to the official definition of electron promoted by chemists. The IUPAC defines the electron as a particle, because this definition is perfectly compatible with the quantum states of a particle being given by atomic orbitals. I am aware that most if not all of the popular physics literature is plain wrong and surely you can find many popular presentations of quantum mechanics that still allude to a supposed wave-particle duality, which does not exist. Being a real scientist I am not obligated to repeat those errors, even if are relatively common. I think this sums things up quite well. You can call everything a particle if you redefine what you mean by particle and adopt the position of "by particle we mean quantum particle". As with many issues, it's a matter of defining your terms. However, it's a bit tiresome to leverage this into a matter of equivocation. Scientists calling electrons particles is an issue, in part, of convenience. I think most scientists understand what is implied by quantum particle, i.e. that it means you can have effects like interference and diffraction, which are wavelike properties. The term particle was never defined by "small-billiard-ball-following-Newtonian-laws". The electron was also considered a particle in Maxwell electrodynamics, where Newtonian laws are not valid in general. If you redefine particle to mean "small-billiard-ball-following-Newtonian-laws" then you will have to invent new terms for all those experimental situations where electrons do not behave as "small-billiard-ball-following-Newtonian-laws". Then you will be forced to invent new terms such as "wave-particle duality". The term "quantum particle" is redundant. That is the reason which IUPAC defines electron simply as a "particle" not as "quantum particle". An electron can behave as "classical particle" described by the laws of Maxwell electrodynamics in some situations. I also find a mistake to talk about "wavelike properties". This non-rigorous terminology is at the source of many misconceptions about quantum mechanics. Those "interference and diffraction effects" are not the interference and diffraction effects of a real wave as described by electromagnetic theory, but have a completely different physical interpretation. Recall that the wavefunction is not a real wave but a mathematical function.
  13. His computation does not even use general relativity! He assumes a flat background spacetime, which is not the physical spacetime of general relativity. Baez is right. The speed of light in general relativity is a constant. The shapiro time delay is perfectly compatible with the speed of light being a constant in general relativity. You are confused about modern physics because you rely on historical sources of about 1911 (even before general relativity was formulated!). It is possible to compute the speed of light in general relativity and check that it is a constant that equals c.
  14. In general relativity, photons are considered massless particles. Photons are affected by gravity is because gravity curves spacetime and photons (or more correctly light signals if you want emphasize that general relativity is not a quantum theory) travel in a curved spacetime as any other object does, was massive or not. Search "massless" in this introduction to general relativity and you will find the geodesics for light signals. And if you search the term again you will find the equation of motion for a massless particle in a Schwarzschild spacetime. This equation and the rest of the discussion therein explains why light cannot explain black holes (see also figure 2).
  15. As you know chemists define the electron as a particle. For instance the IUPAC officially defines an electron as: I remark this because some people here pretends again that only particle physicists consider the electron a particle, which is just untrue. Electrons are always particles. They are particles in atoms, in big accelerators, in solids conductors, in electrolytes, in stars, in living cells... The above definition of electron by the IUPAC is valid for any branch of chemistry, from electroweak quantum chemistry to astrochemistry and cosmochemistry, passing by any other branch: biochemistry, chemistry of solid state, nuclear chemistry, incorganic chemistry, analytic chemistry, organic chemistry, chemical thermodynamics, molecular spectroscopy, electrochemistry... Now your questions. Atomic orbitals are not standing waves, but stationary wavefunctions. A wave (e.g. an electromagnetic wave) is a physical system a wavefunction is a mathematical function. As emphasized in any quantum chemistry textbook, wavefunctions are merely mathematical functions that describe the quantum state of a particle or system under certain approximations. In fact, any decent textbook in quantum chemistry explains that atomic orbitals are only approximations when one ignores electron-electron correlation, spin, and other corrections. If you want study the quantum state of an electron in a given molecule immersed in a fluid, you cannot use a wavefunction ψ. Wavefunctions ψ describe the quantum state of the particle only in some special cases. However |ψ|2 never describe the state, but the amplitude of probability associated to the reduction of the wavefunction during a measurement. If you are measuring the position of an electron and ψ=ψ(r,θ,φ) is an atomic orbital that describe the state of the particle before the measurement, then |ψ|2 gives the probability that you will find the particle in position (r,θ,φ) when measuring. There is no need to modify the observations that you report. They are 100% compatible with the electron being a quantum particle. That is the reason which IUPAC defines the electron as a particle. Recall that "particle" is not a synonym for small-billiard-ball-following-Newtonian-laws. Only two comments about the observations. First, electrons in the atom do not "exist as standing waves" they exists as particles and its quantum state can be approximated by a wavefunction (at least as a first crude approximation). Second, it is not true that "electrons are never in a single point location". When the electron is in state ψ which is an eigenstate of the position operator, the electron has a position. Yes, the so-named wave-particle duality is an outdated viewpoint very similar to the phlogiston theory. Phlogiston theory is today a historical curiosity and forgotten by physicists/chemists. Any modern and rigorous textbook in quantum physics or quantum chemistry discusses wave-particle duality only in the introductory chapter about the history of the subject and then immediately avoids duality when presents the subject in rigorous and complete form.
  16. juanrga

    What is 'mass'?

    juan never backed up his claim. That's just poor form. Without him being clear I'd wager that he's thinking that I was forgetting the momentum due to the the electrons field. If so then he is sorely misinformed. Let m = the proper mass of an electron. Let m0 = bare mass of the electron, dm = electromagnetic mass of electrons field. Then m = m0 + dm. The proper mass of an electron has the mass contribution of the electrons field built right into it. That's pretty well established. You substitution m --> m = m0 + dm changes nothing because is m --> m. Your momentum p=m gamma v is not the momentum of an electron in an electromagnetic field because its momentum receives a correction due to interaction with the field. Neither your p is the momentum of Mercury planet near the Sun because its momentum p receives a corrections due to deviation of spacetime from flatness. You mixed what I said about a massless particle such as the photon with what I said about a massive particle such as the electron. Moreover, you are mixing the modern concept of mass (which I like) with the old concept of "relativistic mass" (used by the poster whom I replied). This "relativistic mass" (which I dislike) is what others call "inertial mass". The term "relativistic mass" has acquired a bad fame among most academics and is virtually not used in research. Not even close to reality. In the other thread, I started posting that there are different definitions of matter. Next, I added that one of those definitions is accepted by the immense majority of physicists and chemists and can be found in many textbooks. I gave a link to astrophysics page (it is in the other thread) that agrees. I gave a link to CERN page that agrees and I gave a link to an introductory textbook on general relativity by a cosmologist that agrees (see the link above). At least three posters more used the same definition of matter that myself when replied to you and none is (I am rather sure) a particle physicist... The definiton of mass that I use is standard among physicists, chemists, biologists, engineers... The m in the above book in general relativity is the same m that I use. This is the same m that one finds in thousands of books from thermodynamics to quantum field theory.
  17. Their suggestion about photons is not considered by the immense majority of physicists and chemists, because their approach to understanding matter is based in a classical coarse-grained approach, instead of the modern fine-grained approach which has generated the above SM table with the three generations of matter.
  18. No. I have just said the contrary. In general relativity, the speed of light is also constant for non-inertial frames. We do not agree because I am saying the contrary than you: the speed of light is always constant in general relativity. The link by Baez says the same that I am saying:
  19. Different authors advance/suggest different interpretations using different theories. Some authors think that non-newtonian effects are due to changes in inertia other think that the effects are due to changes in the gravitational interaction. If my memory does not fail Milgrom likes the inertia explanation, but I like the other. There are many theories. Some of the theories are AQUAL, PCG, TeVeS...
  20. First. In the above quote Baez is writing about inertial frames. This is related to what I said about observers not conected by Lorentzian transformations. Second, in another part of the same link Baez confirms what I said regarding the constancy of the speed of light :
  21. Sorry, but a reply is needed here. In my last response to PMB which you moved to the other thread (search post #11 in the other thread that you created), I wrote explicitly that I would not reply more about the definition of mass. Therefore I was not going to answer what PMB wrote after my last post (see #12 in the other thread) about mass. Neither I am going to reply now, where PMB continues writing about the definition of mass in #18... just after your note. It was unneeded to cite me in your note. In #3 I explained to you that there are different definitions of matter, but that the standard definition of matter considers that photons are not matter. I gave you a link to an astrophysics page explaining the differences between matter and radiation. This division into matter plus radiation is standard in both physics and chemistry and can be found in many textbooks. Another presentation of the standard definition of matter is given in the CERN website http://public.web.ce...rdmodel-en.html where it is again stated that photons are not matter particles. There are several good reasons for which photons are not considered matter. See the above link.
  22. I repeat For an open system entropy can increase, decrease, or remain constant.
  23. juanrga

    What is 'mass'?

    No Pete. This thread main topic is if photons are or are not matter as the OP asked. At least three posters including myself explained that photons are not usually considered matter. I added that our definition of matter agrees with the usual in the Standard Model where photons are not considered matter. I added a link to CERN website explaining why photons are not considered matter after you asked me explicitly in #20 if I could prove my statements. Pete, you are who is pulling this thread off-topic with several large posts about the definition of mass. I will not discuss more with you about mass neither about general relativity here (This is a thread under the Quantum Theory subforum!). I only want to add that modern textbooks in general relativity define the four momentum as [math]P^\mu = m U^\mu[/math] and that this m is the same m used by particle physicists. No other concept of mass is needed in general relativity. Indeed, general relativists and cosmologists agree on that photons are massless m=0. I recommend you start with A No-Nonsense Introduction to General Relativity.
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