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joigus

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Everything posted by joigus

  1. I told you this since the very beginning there are as many "Lorentz" groups as you like just by re-defining the parameter. Studiot implied it too. Thanks for expressing what I told you and you had missed as if it were my fault. Your comments are easily the silliest I've found in these forums so far. The good thing is --apparently-- you finally understood. I can only hopel It was studiot who asked for clarification, not me. Every time you introduce an abbreviation you must clarify what you mean. That's what professionals do. It's obvious you're not one. You seem to have problems following up on the comments. Take more time to answer instead of embarrassing yourself so much. Bye. PS: Re-read the criticism. All the answers you need are there.
  2. Not Einstein, please. Not that mojo! I take it back, I take it all back! Sorry, the joker in me takes over from time to time. Identifying \( v^{2}/c^{2} \) with the classical potential, inspired in the Newtonian approximation of GR, has been thought of before. It doesn't work, as it doesn't account for all of gravity's degrees of freedom. It's also been discussed in these forums. I don't have a problem with anybody's education. Neither do I have a problem with contradicting Einstein's universe. Einstein's universe was ruled out many decades ago, so... And I've got my quotes too: Guess who said that? When one has no arguments, quoting great scientists is, I think, the rational equivalent of praying. There goes my prayer.
  3. "An upheaval will certainly come..." I was wondering when you were gonna shut down all pretence that you're doing science and start with the prophetic language. And there you go. What took you so long?
  4. joigus

    How brain work

    Hello. How question do: https://www.scienceforums.net/guidelines/
  5. For some reason I didn't see these comments yesterday. Thanks for the clarification.
  6. Etc. It's also present/important/relevant (although not enormously abundant by any means) in planetary science. Is generally considered a signature of either biology, or also interesting geology or atmospheric chemistry. Experts will tell you more or correct what I said.
  7. I couldn't agree more! It doesn't, but that doesn't mean it has a 100% consistent axiomatic formulation. In particular, it could fail at very small distances, and it might be the case that quantum theory cannot do the job of explaining away what happens at these incredibly small scales. Who knows. But so far it's done the job exceedingly well. There is a very famous quote by Feynman on the extraodinary predictive capabilities of quantum field theory.
  8. The photon is a quantum phenomenon. Spin also is. Classically (in the view previous to quantum physics) electromagnetic waves were a continuous disturbance of the vacuum. Maxwell's equations, OTOH, have resisted even the quantum revolution. Ever heard of QED? (quantum electrodynamics). The field equations one quantises are... surprise, surprise... Maxwell's equations. So everything I said holds. I appretiate your honesty. I just hope we're being helpful then. But you do understand how hard it is to get to a proper theory from a bundle of loose intuitions, right? Almost nobody does. And when you think of something interesting (a little technical thing here or there) it's almost sure somebody's thought of it already.
  9. An electron being made up of a bunch of photons (whether it be a bag or a cloud) would be inconsistent with the flux law for the electric field from Maxwell's equations. Maxwell's equations have never been found to be at odds with observation. Not for capacitors, nor for diodes, laser, inductances, magnets, firing neurons. Nothing. There would be no metals, or dielectrics... The way we understand it is: No matter how many photons you "bunch together", they would still have net charge equal to zero. Another reason is that you cannot sum a bunch of -1's and 1's and get 1/2 as a result (the electron spin). And there may be many more reasons. I'm just trying to point out what to me look like the most obvious ones.
  10. The ruler's length? Invariant under what? Rotations? It is. Lorentz transformations? It is not. General coordinate transformations? (Thereby including gravitational fields, either static or dynamic) It is not. You see. It's not as simple as something is or is not invariant. It takes a little preliminary work to even say what you mean. At least to me. Other people have the priceless ability to grasp the inner logic of fuzzy statements. Not me.
  11. No, my reason to be confused is what I said: Two observers seeing two different things see... well two different things! What's strange with that? As @Markus Hanke has made perfectly clear. GR tell you how different the different things appear to be provided you carefully specify the conditions. If they see the same thing, how come, if they are apart? @swansont said that. There are other inconsistencies or unspecified conditions: How do they synch their clocks 14 billion years ago? You didn't say or wrote a diagram. @studiot pointed it out. You're spreading all your argument with "they see", "they measure" and the like. That's not good enough, not in relativity, never mind special or general, as a good read of Einstein's original papers or a good modern relativity book --Ray D'Inverno's book is a nice example-- makes clear from the beginning. Something like this: The diagonal lines are photons going from one observer to the other, telling each other exactly where and when they "saw" something or actually "seeing" something. That's what "see" means in relativity. The non-diagonal lines are inertial observers or objects moving at v<c. By the way, how do two distant observers "see" the same photon? Because then it's just one photon we're talking about, and two distant observers somehow catch the same photon. Now it's Saturn's orbit. You seem to keep moving the goalposts. You have to state your problem clearly, and try not to change the conditions, unles it is to refine the statement of the same problem. Stating the problem clearly is part of the art of doing physics. So I'm still confused. It was many years ago that I understood there is no blame for being confused during a physics class. The real problem is being confused and not being able to tell why.
  12. Well they would agree on the speed of light, wouldn't they? They would disagree on the frequencies and wave numbers, or IOW, the number of cycles a particular physical interval contains. I'm a little confused with the initial setting of the problem, as I see no reason why Alice and Bob should agree on anything, as they see different things. But I take it that the OP is trying to reformulate the problem for just one photon. But maybe I misunderstood the whole thing, so I'll take some more time tomorrow.
  13. Here's a wild idea: https://www.google.com/search?q=applications+of+zener+diode+in+smps And take it from there.
  14. Absolutely. I reacted to your pointing this out from the very beginning. I elaborated (or tried to) a little more on that. But to no avail. The funny thing is, when I first saw this thread, I interpreted the title literally, "analogies for relativistic physics". I said to myself. "oh, that's interesting". Nothing further from the truth. Not interesting, not enlightening, not even funny at all or in any sense. --funny as in, "That's funny, this member doesn't seem to understand the principle of special relativity: It has two parts; the second one destroys his reasoning".
  15. That surely is the Laplacian operator, which is nabla dot nabla. "dot" meaning the 3D "dot". 4D nabla dot 4D nabla is called the d'Alembertian, and it's a square (at least in physics). https://en.wikipedia.org/wiki/Laplace_operator https://en.wikipedia.org/wiki/D'Alembert_operator
  16. Ok. Yes, thank you for pointing this out. The word "wave" is sometimes used very loosely, for these and other reasons. People also use the word "wave" for solitons, which are objects somewhere in between. I did go too far when I said "totally wrong". My apologies to @KJW.
  17. You were waxing philosophical, "everything is an abstraction", "it's only in our minds". So Ok, I guess in a way you're right. Ultimately, the only thing we see, the only thing we measure, is positions of measuring scales, numbers flashing in LED lights, and the like. So everything is position, colour, time, what may have you. But there's always a theoretical layer beneath that. My point was that there are concepts that seem to demand you to consider them from the theory, although they cannot be measured, directly or indirectly. Example: phase velocity of a quantum wave.
  18. I think it's probably always fair to say that theories are models in our minds. But not just any models. They are under the obligation to explain and predict the world. And that's a very stringent constriction. As to the phase velocity, the wave function, and its local phase, all indications are that there are part of a "factor" of the world we can move through using mathematics, but quite invisible for us. You seem to feel some discomfort because of this fact, that there are quantities we seem to be forced to talk about but cannot see. But that's part of physics since the inception of QM. But maybe it was always this way. We cannot directly see energy, or angular momentum. Think about it.
  19. Yes, thank you for your appreciation of this point. That's what I meant when I said, The very moment you trim down a quantum state from the idealisation of an infinite monochromatic wave to a short pulse, you are introducing infinitely many frequencies, and you need the group velocity to describe its motion. No other velocity makes any sense. In the relativistic case, it's actually superluminal, as I proved from simple relativistic-dynamical and quantum-dynamical constraints.
  20. I'm afraid we have different understandings of what "explicit" means, at least for this case. "Explicit" as in "He gave me very explicit directions on how to get there." (Taken from Oxford's dictionary). Yes, I'm sure about that. https://www.ippp.dur.ac.uk/~krauss/Lectures/QuarksLeptons/QED/GaugeInvariance_2.html Read under the heading "Local Gauge Invariance". IOW: You can re-define the local phase at will as long as you accompany such change by the corresponding gradient in the gauge field. What is "the" phase now? No wonder phase velocity is not an observable. You can concoct situations in which phase and group velocity are essentially the same. I'd venture to say that for those cases you can "measure" the phase velocity. What you're doing (secretly) is, of course, measuring the group velocity, and using the theory to deduce a value of the phase velocity consistent with it and with the choice of quantum state (or "ray") that you have obtained in that particular gauge. No. You got this totally wrong. Quantum waves are not sinusoidal. For starters, they are not real functions. They typically go like complex exponentials. No. I can write A=XY/Z, the relation be totally right, and neither A, nor X, Y or Z be measurable. In fact, what you both are saying contradicts the principles of mainstream quantum mechanics --except for free particles. If the particle is interacting, the so-called Hamiltonian has a potential energy term, and the momentum (the inverse wavelength) does not commute with it, so the principles say no, you can't measure both at the same time. They're called "incompatible." You both are confusing a component (among infinitely many) of the quantum state with the whole quantum state. More on this: https://www.mathpages.com/home/kmath210/kmath210.htm And so on, and so on, and so on...
  21. Again. How? Be explicit, please. That would contradict gauge invariance, which we know to be exact. In a nutshell, gauge invariance tells us that quantum states don't have "a" phase, meaning an unambiguous local phase. Let alone a phase velocity. The phase velocity of ripples on a pond can be measured. The phase of the wave function cannot. You can measure interference patterns. But those have nothing to do with phase velocity. You talk about frequency and wavelength as if there was just one frequency and one wavelength for matter waves. It is precisely because all "realistic" matter waves package many frequencies and wavelenths that the phase velocity is rendered all but meaningless in QM. Only the group velocity makes physical sense. I've just had a déja vu. Didn't I say something like this before? It's either right or wrong. What's sure not to be is irrelevant to the question at hand.
  22. I don't think that's what the text means. I think it's a reference to the group velocity. Whenever group velocity is different from phase velocity, we call the medium "disperssive", and that's because every monochromatic component travels at a slightly different speed. v=v(f)
  23. This sounds all very reasonable, and you do have a point. Nevertheless... We don't have a handle on the wave function itself. X-crystallography and the like is based on phase differences. Interference positions --and thereby wavelengths--... pretty much the same. No way to see the phase itself though. In fact, I'm working with some advantage here. I happen to know there is a very robust principle of physics --the gauge invariance principle-- that tells us it is impossible to know what that phase might be, as I can always gauge away any phase prescription that you take by locally re-defining the phase. So I have a pretty solid understanding of why what you claim cannot be true. Gimme any phase you like and I will "gauge it away" without breaking any known rules of quantum field theory, or classical electromagnetism, etc.
  24. The particle's velocity is the group velocity. What laboratory measurement gives you the phase velocity? Didn't I say this before? And didn't you?
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