MigL 1638 Posted March 25, 2020 Share Posted March 25, 2020 33 minutes ago, Alex Caledin said: no one tried to find out how exactly Nature was finding that least action way to move things I don't know if that's true. Symmetry considerations support least action. "A well known example is furnished by the theory of the pure (sourceless) electromagnetic field. One may infer its action from the requirements of gauge symmetry, time reversal symmetry and Lorentz invariance. From that action one infers the energy momentum tensor (by the well known recipes for the canonical or symmetric one). Then by requiring that the tensor’s divergence vanish (energy–momentum conservation) one ob-tains a set of equations which, for generic values of the Faraday tensor, imply that the latter’s divergence must vanish[2]. Thus the Gauss and Ampere laws emerge from energy–momentum conservation, itself a consequence of the symmetry of the action under spacetime translations. The magnetic Gauss and Faraday laws are automatic consequences of the use of the electromagnetic 4-potential as basic field variable. Thus, in the mentioned example, the symmetries plus energy–momentum conservation lead to the field equations without any appeal being made to the LAP." https://www.sciencedirect.com/science/article/pii/S0550321315000267 Link to post Share on other sites

Alex Caledin 2 Posted March 25, 2020 Share Posted March 25, 2020 35 minutes ago, dimreepr said: How far back are you going? - to 1962! Niels Bohr and Feynman said all the real necessary things about QM. Link to post Share on other sites

joigus 507 Posted May 14, 2020 Share Posted May 14, 2020 (edited) This is just my two cents, for whatever it's worth. You can live a long, healthy, and fulfilling life without ever thinking about the 'weirdness' at all. Even become a very valuable person in the scientific community. Further go on to win a Nobel Prize and have a university named after you. But, if you are a compulsive thinker, if you can't make peace with yourself until you've made as much sense of it all as it's humanly possible (in other words, you are a 'theorist,' you should ask for something more. Send your papers and accept the peer-review system. Above all, if your ideas meet the criteria of acceptability and make it to the laboratory (that's something you must always ask yourself: Can this be brought to the laboratory?), it's still OK if you make some room for the possibility that there's an error in the interpretation of the experimental results, because it could still be right in some sense. But in the end, if your idea is rejected by Nature (and I don't mean the publisher,) and you're going against all odds to save it, then it's probably wrong, no matter how beautiful or plausible it looks in your mind, and it belongs in the rubbish can. Why must we, or anyone at all, keep thinking about the QM rationale? IMO, because there is the possibility of understanding a little bit further. Theoretical physics (that's my perspective) is about mapping the world with mathematical tools. So in that sense it's like the geometer looking at geometry from the other end. As a geometer, you depart from a differential manifold (fancy name for an n-dimensional surface, with dashes of more sophistication) and study its properties. As a theoretical physicist, you're compelled to look at the world rather more like the cartographer: You are given the landscape at different scales and from different vantage points, and you (and others like you) must try and figure out what the underlying 'space of variables' is. If you squarely deny yourself the possibility of understanding deeper and further, you're probably looking at the world from a vintage point rather than a vantage point. Edited May 14, 2020 by joigus choice of word 1 Link to post Share on other sites

Alex Caledin 2 Posted May 14, 2020 Share Posted May 14, 2020 (edited) Ah yes those high theorists ambitions are ever so powerful over them - but what really matters is the worldview of the people who use QM to understand practical things like chemical and semiconductor behavior - they need Feynman's clearness of describing things in the Feynman Lectures: "this is just how Nature really is" (=Nature is just giving you the actual events). Edited May 14, 2020 by Alex Caledin language Link to post Share on other sites

joigus 507 Posted May 14, 2020 Share Posted May 14, 2020 31 minutes ago, Alex Caledin said: they need Feynman's clearness of describing things in the Feynman Lectures: Don't try to frame Feynman. He was deceptively clear. As to what really matters, I can't wait to hear your arguments. No, really, I can't wait. Link to post Share on other sites

GaryV 0 Posted May 15, 2020 Share Posted May 15, 2020 The real problem is that we cannot see things that small, therefore, we cannot view exactly what is happening on the test we can run. That is why the equations are probabilistic. We can count up the amounts of each type of result and compare them to the predicted probability. That is also why classical viewpoints are not comparable. Classical equations predict the motions of individual objects and QM just gives a probability of many outcomes. In spite of this, I believe we can understand it. However, without the ability to test and witness the act of an individual quantum particle, no one will believe the theory. I wonder if someone can build a simulation based on such a theory and run multiple sims to test the probabilities based on it? If this is possible, I think there is a way to explain QM by linking String Theory's many spacial dimensions, the idea of a fluidic space, and idea that such particles are actually both a wave and a particle. However, I have not yet talked to, read about, or heard quotes from someone else who claims to be able to visualize the universe in more than three spacial dimensions. Link to post Share on other sites

Mordred 1372 Posted May 15, 2020 Share Posted May 15, 2020 (edited) UpString theory doesn't entail more than three spatial dimensions. One of the most common misunderstandings of physics terminology is the word dimension. It literally means an independent variable, or other mathematical object. In relativity you have the three spatial dimensions x,y,z. Then variable time each of these mathematical objects can change value without affecting the other. The same occurs in String theory. Step one is to take a point particle and describe that point particle in one dimension (a string). Step two you will need a dimensional value to describe tension of that string as well as its length. [math]T=1/2\pi\alpha[/math] The steps continue into how the manifolds or worksheet is defined to describe the particles action. Then you need mappings etc of the different manifolds to get to the Calibaou space etc. However the meaning of dimension still remains the same. You will often see the descriptive extremely small space etc for certain states being described however these can often be parameter space or other mathematical spaces such as configuration space. What makes the nature of QM probability seems weird but it really boils down to having a theory that can predict all possible outcomes. When your dealing with waveforms and doing a Fourier transformation you will have uncertainties. Here is a visual image. Take a rope and wave the rope up and down so you get a sinusoidal wave through the 50 foot length. Now ask yourself the following question. What is the waveforms position ? You cannot answer that with certainty. You can be certain on its wavelength. Now take the same rope and shake it once to get a single amplitude. Now you are more certain of the position but you lose certainty on the wavelength. The probability goes beyond simply not being able to measure the small. The example above shows the need for probability even on a macro object. However in the quantum regime it gets more complicated. You have the uncertainty principle which the above loosely describes. The quantum harmonic oscillator which gets involved in multiparticle interactions. Then you also have the probability of which particle state ie spin of electron ie entanglement along with the correlation functions. Superposition of a wavefunction prior to measurement to determined states upon measurement. When you start examining the math and the usefulness of the probability functions QM isn't nearly that weird after all. One just has to recognize their is inherent uncertainties and recognize that the probability functions account for those. Edited May 15, 2020 by Mordred Link to post Share on other sites

Schmelzer 15 Posted May 31, 2020 Share Posted May 31, 2020 The most common sense compatible interpretation is IMHO Caticha's entropic dynamics Caticha, A. (2011). Entropic Dynamics, Time and Quantum Theory, J. Phys. A44:225303, arxiv:1005.2357 There is a configuration space trajectory \(q(t)\in Q\) and there are some other, unspecified variables y. I prefer to use as these variables simply the same configuration space, but of the external world. Then, we have incomplete information about it if we know only how the state was prepared, thus, we know some probability distribution \(\rho(q,y)\). Then we define for each \(q\in Q\) the resulting probability \(\rho(q) = \int \rho(q,y)dy\) and the entropy \(S(q) = -\int \ln \rho(q,y) \rho(q,y)dy\). Then we have for \(\rho(q)\) a diffusion (Brownian motion) with parameter \(\hbar\) combined with a movement toward higher entropy, and a generalization of the Hamilton-Jacobi equation for the entropy. This pair of equations gives, if one combines \(\rho(q)\) and \(S(q)\) into some artificial complex function with the phase \(\ln \rho - S\) (modulo signs and so on) this gives the Schrödinger equation for that complex function. This nice accident allows us to use the full power of the mathematics of quantum theory, but is otherwise of no fundamental importance. Just a happy accident. Link to post Share on other sites

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