juanrga

In an early post I introduced the quote (bold from mine): You continue citing Am. J. Phys. papers, which are educational papers for basic level stuff, they are not serious contemporary theoretical sources. The Tomonura et al. paper reports a beautiful experiment that proves that electrons are quantum particles (as everyone knows). From Ballentine's Quantum Mechanics a Modern development page 4: A rigorous quantum mechanical and statistical analysis of Tomonura diffraction experiment does not support the duality interpretation. Where is the mistake? It was emphasized before, but I will repeat once more. Tomonura et al. use the term "particle" to mean little localized point or Newtonian particle. They need to appeal to an imagined duality (with waves) to explain the experiment, because an electron is not a Newtonian particle. If you look to the figures they represent the electron as a little black sphere with a little wave superposed!!! Moreover, the article makes very misleading claims as the one that you quote: "a single electron passes through the slits as a wave". There are three misconceptions of QM in this small quote!!! Quantum mechanics does not say that the electron was a little localized point (a Newtonian particle); when the quantum character of the electron is taken into account, there is no need to appeal to a hypothetical duality. As emphasized before, and by several people, there is no duality in quantum mechanics. In the first place, QFT is not the more advanced formulation of Quantum Mechanics. In the second place, you again cite an educational paper: The Physics Teacher does not belong to serious contemporary theoretical sources. In the third place, nowhere in that paper the author develops or applies any QFT, but he only takes the idea of field quanta in a pictorial way. In the fourth place, this paper is one of the most misleading papers about quantum physics that I read in a long time. This paper even contradicts itself!!! Maybe you do not, but others in this thread argued just that. Bohr's complementary principle, where he postulated the existence of complementary aspects of reality which would be revealed to us when "the account of all evidence must be expressed in classical terms" is plain wrong, as Steven Weinberg emphasized in Physics Today November 2005, page 31 [*]: And Weinberg explains why Bohr was wrong. I do not need to repeat again but it is rooted in Bohr's artificial split of universe into quantum and classical 'spheres of existence'. [*] Notice that it is "Physics Today", not "Physics 100 Years Ago". Our understanding of quantum physics has advanced a lot of since Bohr.

Yes we can 'make' one photon and next study its properties/behavior No idea what do you mean by "minimum unit". Photon mass is zero, as said above.

This is one of reasons which I am attracted by the idea. If you cannot localize the particles in the SM it is difficult that you can concentrate on the 'spacetime' between them. But in any case, as said above, the SM (more correctly the underlying QFT framework) does not study the properties of the spacetime, except by its basic metric and topological properties [*]. [*] There are some attempts to do QFT in more general spacetimes, but are plagued with technical/conceptual difficulties.

In the Standard Model (SM) it is made of nothing, because it is not a material system. There are speculative theories where spacetime is made of something, the "something" depends of the theory. Yes it is a prior 'structure', a kind of 'background', in the SM. However, some relational models beyond the SM claim that spacetime cannot exist without particles and I am attracted by such ideas. The situation in the SM is much more complex than that. Any attempt to measure the localization in spacetime of a relativistic particle is blocked by spontaneous generation of virtual pairs. This is part of the reason for which (as I mentioned in the thread about duality) solutions to Dirac and Klein-Gordon equation cannot be interpreted as wavefunctions.

The standard model consists of 12 matter particles plus 4 force particles. Add the Higgs boson recently announced [*]. In a 4D spacetime. If you mean that each member of a kind is distinguishable from members of another kind, the response is "Yes". We sort particles by their properties And in practice we also assembly-disassembly composite bodies into particles. Precisely this knowledge illustrates the hierarchical structure of matter with a decomposition of one methane molecule into quarks plus electrons taking into consideration intermediate levels (atomic, nuclear, nucleon). See above Evidently spacetime is different from the particles in the above table, but I am not sure what you mean by "clear boundary round each particle". [*] The other particles are discovered, the Higgs boson has only been found. This is a technical terminology related to statistical uncertainties.

If you zoom the image can read in the back "Made in China"

We do not do that. The Bohr/Heisenberg old formulation of quantum mechanics left out the observer and have been criticized precisely by that! For instance Steven Weinberg writes in Physics Today, November 2005, page 31: All this familiar story is true, but it leaves out an irony. Bohr's version of quantum mechanics was deeply flawed, but not for the reason Einstein thought. The Copenhagen interpretation describes what happens when an observer makes a measurement, but the observer and the act of measurement are themselves treated classically. This is surely wrong: Physicists and their apparatus must be governed by the same quantum mechanical rules that govern everything else in the universe. But these rules are expressed in terms of a wave function (or, more precisely, a state vector) that evolves in a perfectly deterministic way. So where do the probabilistic rules of the Copenhagen interpretation come from? Considerable progress has been made in recent years toward the resolution of the problem, which I cannot go into here. It is enough to say that neither Bohr nor Einstein had focused on the real problem with quantum mechanics. The Copenhagen rules clearly work, so they have to be accepted. But this leaves the task of explaining them by applying the deterministic equation for the evolution of the wave function, the Schrödinger equation, to observers and their apparatus.

I did read in "The End of Certainty" (by Prigogine) but he gives no further info/references. I found this link to a book with some more info: http://books.google.com/books?id=SoZhv5feNQ4C&pg=PA189&lpg=PA189&dq=zero+energy+cosmology+Pascual+Jordan&source=bl&ots=-aKjH1GlQd&sig=9j6EqG3C02uwTnHJMQjG0J7w9rM&hl=es&sa=X&ei=FVT9T6HVN4jS0QWq9emEBw&ved=0CFkQ6AEwAw

You are using an old concept of mass mrel. Currently photon is a massless particle m = 0 http://en.wikipedia.org/wiki/Photon#Physical_properties

Personally I have considered the original definition of duality, which postulated that quantum particles are both particles and waves (two or three posters used this), and the posterior definition, which postulates that quantum particles exhibit both wave and particle properties (at least one poster used this).

I believed that the quote from Quantum Mechanics, A Modern Development, explaining why the early idea of a duality of particle and wave properties was an historical accident would suffice, but I was being too naive and once again you retort to 'ancient' misguided ideas such as DeBroglie "matter waves". In my previous post, which you quote verbatim, I also tried to explain how we also use wave packets and wave vectors in classical mechanics. Indeed the state of a classical particle in classical mechanics can be represented using wave packets. But those wave packets are mathematical functions that represent the state of the classical particle, are not physical waves. Equations such as ∆t ∆ω ≈ 1 , with ∆ω being the range of frequencies of the packet, can be also found in textbooks dealing with classical mechanics. That v in the classical wave packet is, indeed, equal to the velocity of the classical particle, but this is not anything mysterious. It merely reflects the obvious fact of that the state of the particle is parametrized by properties of the particle. How could not depend on the particle velocity [math](p/m)[/math] if the Hamiltonian of the particle depends on it [math]H=m/2 (p/m)^2[/math] and the equation of motion depends on the Hamiltonian? The introduction of a wave packet for the representation of some states of a classical particle does not introduce a wave-particle duality in classical mechanics. Believing that the wave packet is a physical wave is a mistake, believing that the wave packet represents a wave moving in ordinary space is a mistake. Believing that the equality between the group velocity of the wave packet and the velocity of the classical particle implies that a classical object can be described as a particle or as a wave is a complete misunderstanding of classical mechanics. Now substitute "classical" by "quantum" in the above discussion about wave packets and you are gone. I only want to emphasize that there are lots of myths/misconceptions regarding quantum mechanics, duality is only one of them.

Because such expressions do not imply that there is a wave therein, neither that the electron (a particle) behaves like a wave. Consider the length [math]\lambda = \frac{h}{|p|} = \frac{2\pi}{|k|}[/math] with the vector [math]k[/math] being the momentum of the particle in 'units' of hbar: [math]p = \hbar k[/math]. The vector [math]k[/math] allows for a simplification of many QM formulae involving [math](i/\hbar)[/math] factors. For instance, instead writting [math]\exp(ipx/\hbar)[/math] you write [math]\exp(ikx)[/math]. There is no mystery here. Using [math]k[/math] instead of [math]p[/math] does not introduce a duality. Although by historical reasons [#] [math]k[/math] is often named the wavevector, in modern literature it is named the vector [math]k[/math] (the term "wave" is dropped, which is a good idea). Taking of the inverse of [math]|k|[/math] does not introduce a duality neither does multiplying by [math]2\pi[/math] For a free particle, under the approximations outlined in previous posts from mine, the quantum state is given by a function [math]\psi(x) \propto \exp(ikx)[/math]. This is not a wave (a physical system), but a function. The use of [math]\psi(x)[/math] does not introduce a duality in the formalism (the electron is always a particle and behaves as a particle), although by historical reasons [$] it is still named the wavefunction. We can explain the same quantum behavior using formulations of QM that do not rely on [math]\psi(x)[/math]. I use one of that formulations in my research work. In fact, in more advanced and general formalisms of QM the wavefunction [math]\psi(x)[/math] is superseded by the state vector [math]|\Psi\rangle[/math] (note that the term "wave" is dropped, which is again a good idea). Evidently, associating this state vector [math]|\Psi\rangle[/math] to a particle does not introduce a vector-particle duality. Trying to believe that [math]\psi(x)[/math] or [math]\lambda[/math] are representative of a fundamental wave-particle duality is a gross misunderstanding of QM because the state of a quantum particle is not given by [math]\psi(x)[/math] in the general case. Moreover, [math]\lambda[/math] is only defined when momentum is well-defined for a particle, which is far from the general case. In the general case, [math]\lambda[/math] is not even defined for a particle. Moreover, you can find similar expressions on classical mechanics. Advanced textbooks in classical dynamics show how the state of a classical particle can be also formally expanded in terms of planewaves [math]exp(ikx)[/math], with k being the classical wavevector associated to the classical particle. Of course attributing a classical wavevector k to a classical particle does not mean that there is a wave-particle duality in classical mechanics. This formulation of classical mechanics in terms of wavevectors is very useful in the study of collisions of classical particles, but particles continue being particles and behave as particles. It is worth to mention that the own wikipedia page on duality cited before contains a comment from L. Ballentine, Quantum Mechanics, A Modern Development, p. 4, explaining why wave-particle duality is a misnomer (although I prefer the term myth; bold face from mine): [#] Wavelength was first introduced by DeBroglie, but he believed on the existence of a real wave, which is nowhere. His subsequent work/interpretation was shown to be wrong (De Broglie-Bohm theory) although the original name/term "wavelength" remained, causing confusion up to today. [$] Again during the development of QM, DeBroglie, Schrödinger, and others believed on the existence of a real wave. The original name "wavefunction" remained with us, although any textbook in QM remarks that [math]\psi(x)[/math] is a non-observable function, not a real wave.

He was asking me about something that I never said. His exact words: One time more. I have not made such claims. I have never said that those expressions are wrong! And the correct answer is that the expression does not represent wave-particle duality.

I have edited and eliminated a superfluous "his". He directly asked me to explain "why" I think that those expressions are wrong. Since I have never made such one claim about those expressions, I do not need to answer him. Now you are claiming that (i) those expressions are representative of the waveparticle duality, and that if there is not wave-particle duality then those (ii) expressions are, "ipso facto", wrong, but both are your claims, not mine.

You report the mathematical mistake when he 'obtains' his fourth equation, but his mathematical and physical errors start even before as noticed in this thread. You do not know what you are saying, [math]\frac{d \hat{p}}{d t} = \hat{F}[/math] is a known quantum mechanical equation.

No, science is not a branch of philosophy. The definition is well-known, studied in textbooks and was also given here by me. Once again, move your philosophical ruminations and your links to the philosophical journal "Humanamente" to the correct subforum http://www.sciencefo...101-philosophy/

I am not quoting you. You are blatantly confounding me with another poster, because I never did such claim. Both you and Aethelwul write that a single particle is a wave. Both of you are plain wrong.

No. Experimental physics does not claim that a particle is a wave. You do not understand anything of what is being discussed here. you confound my with Aethelwul. You and Aethelwul are saying that the wave-particle duality states that a single particle is a wave. Both of you are plain wrong. We are not discussing philosophy of science, but physics. Post your thoughts about philosophy in the corresponding forum. The links given are not all from CERN. Of course, none of them is using your personal definition of particle, but they are using the standard definition. You continue rejecting overwhelm scientists consensus about the physical nature of the world. Post your personal views in the speculations forum and stop from abusing this thread. Any scientist knows that the world is made of particles: electrons, photons, quarks...

In that paragraph he merely reproduces the misconceptions that have the people who has never studied QM. Continue reading from where you stop (the bold face is in the original): In fact, your previous question to me was: And the article that you read says at the end, in its conclusions, (bold face from mine): Before continuing, just explains me how you can interpret the above physicist's phrase "So in QM, there is no such thing as a wave-particle duality!" as contradicting my claim that "there is no wave particle duality in QM".

By the technical reasons that I outlined before. As this physicist writes:

That is the point! When you are not expert in a concrete topic you are obligated to resort to 'indirect' measures such as author reputation, citations index, and similar ones. But those measures are only a 'statistical' tool. They say you the probability of that an individual paper was more or less right/adequate, but are not a substitute for expert analysis. When you are an expert you can evaluate the works by yourself.

The product of the collision of two photons depends of the situation. For instance two photons can annihilate to give a pair electron positron, as you notice [math]\gamma + \gamma \rightarrow e^{-} + e^{+}[/math] but to higher energies two photons can collide and scatter [math]\gamma + \gamma \rightarrow \gamma + \gamma[/math] Here you have a basic tutorial on two-photon physics http://www.hep.ucl.ac.uk/opal/gammagamma/gg-tutorial.html

http://www.amazon.com/Six-Easy-Pieces-Essentials-Brilliant/dp/0465023924 Good weekend also for you!

I do not need to convince the scientific community of something that is well-known: http://www.particlep...-particles.html http://public.web.ce...rdModel-en.html http://www.fnal.gov/...deof/index.html http://www.pbs.org/w...elegant_09.html And so on and so on. The properties [#] of those particles are also well-known and listed in tables such as the table 15.2 of the same physics textbook that you cited in the past. [#] Your term "attributes" must be adequate for the philosophers.