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The quantum theory of fields

di Steven Weinberg

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2011,091,121 (5)Nessuno
Available for the first time in paperback, The Quantum Theory of Fields is a self-contained, comprehensive, and up-to-date introduction to quantum field theory from Nobel Laureate Steven Weinberg. The first volume introduces the foundations of quantum field theory, the second volume examines modern applications, and finally the third volume presents supersymmetry, an area of theoretical physics likely to be at the centre of progress in the physics of elementary particles and gravitation. The development is fresh and logical throughout, with each step carefully motivated by what has gone before. The presentation of modern mathematical methods is throughout interwoven with accounts of applications in both elementary particle and condensed matter physics. The three volumes contain much original material, and are peppered with examples and insights drawn from the author's experience as a leader of elementary particle research. Exercises are included at the end of each chapter.… (altro)
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Let me get this out of way first. Here is the bottom line: most of the Real Reality will be forever hidden from our eyes and minds. We perceive in the minutest fraction of the electromagnetic spectrum. Our brains are three pound marvels. Very smart but ultimately limited. Think of Gödel's Incompleteness Theorem. Our physics will always be incomplete which is good news. That means we will always have room to struggle with our limitations. We are humans, not God. Only God (whatever It is) can know All. We will have to settle for what we can tease out from the phenomena. Kant was right. The noumena is denied to us. All we have is the phenomena. We cannot get to rock bottom. We are 15 orders of magnitude removed from Planck Length. We have not got the money or the wits to get more than a few more orders of magnitude toward The Ultimate Smallness. And I believe QFT is not the answer as well, but Weinberg's take on it it's still marvellous after all these years.

Was there any physics explained to people (professional or layman) beyond the 5 (mostly wrong) sentences about quantum mechanics that are focused in every pop science book? It is almost purely philosophical beyond that. In the end those books should belong to the science podcast category. I don't think current pop science books treat enough science for that. It's all just about "sexy-sounding topics". What do people take away from those books, in terms of "learning about science"? Very little. Why not explain more genuine science. I'm interested in quantum field theory, general relativity, cosmology in general. Just to make clear that I'm not against theoretical perspective for the point that I want to make: I think the pop science books should be heavier on explaining the applications of physical theories, how physics has solved certain problems. Teach people stuff, physics has very practical use. Not go on in a circlejerk about how mysterious it all is.

I think the work people like Einstein, Maxwell, Dirac, Heisenberg, Pauli, Fermi, Weinberg, the list is very long, such as those could pull the physics right out of the math and make either predictions that can be measured or better yet people used the principles to make things like AM/FM radio , transistors , more recently GPS from good old Al, the list is almost endless. But some theoretical work seems very difficult to solidify. Maybe a 1927 style Solvay conference is needed to help the general audience understand where the focus is going on QM, QFT, Quantum Gravity, Cosmology, particle physics, the hunt for dark matter, etc. Lot's of great work is being done right now in condensed matter physics that may bring great practical applications but the money spent of the LHC thus far seems to be a dud. Other than the technology that went into it is remarkable but nothing remarkable came out yet. This has to be deeply worrying for particle physicists. Except for the Higgs, the LHC has failed to discover any new physics despite there being so many unsolved puzzles. Will anyone risk pouring billions into a replacement for the LHC if nothing turns up in the coming couple of years?

The current topics in physics are a good example of woowoo. It looks like exactly the kind of thing you would be producing when you want to appeal to people that reject "establishment physics", because they find it "hard to understand" or "overly complicated" (in terms of math) or think that "physics has made a wrong turn at some point in the 20th century, the universe can't be 'that complicated'" and search for ways to avoid modern physics (quantum theory and general relativity + standard model cosmology) and their mathematical complexity by .. well inventing alternative theories that attempt to make a step back towards "easy to understand" classical mechanics. But modern physics is here to stay. Make friends with it. The problem is that almost no content on hard research and physics remains. Like this, it's a sad story of decline. I still give it a chance from time to time but I don't have hope left that it will ever deliver a good standard again (Alok Jha days). I don't think anyone who's seriously/professionally involved in science can enjoy this anymore. That is why people have - for a decade or so now - been working on trying to design laser-pumped accelerators that could reach supra-LHC energy densities in point-like particles at a metaphorical tabletop scale. Of course, no-one has built one yet, but they're at the cusp of coming up with priceable designs.

I don't "believe" in QFT as I stated above, but Quantum Mechanics confused me for years before I learned QFT. It was Weinberg’s QFT book that opened my eyes. I’m amazed that learned physicists still don’t know quantum field theory. It's possible to "explain" the major phenomena of quantum physics with QFT instead of quantum mechanics. Fields are actually just generalizations of equations describing individual particles, that allow for particle creation and annihilation and other interesting, and necessary properties. Recall that the quantum of a field is a particle. In fact Weinberg is substituting one mindbogging concept 1. (probability waves - not by definition existing but ruling the world) with another mindbogging concept 2. (field - unobservable by definition - they collapse if something tries to observe them = they vanish in the whole space in one single moment everywhere without trace). Now there lies buried the dog = why no seriuos physicist can accept 2 better 1. Because: 1. The probability can vanish (collapse) because it doesnt exist. 2. Quantum fields can not because they exist. Now you choose for yourself how do you feel more confortable: 1. something vanishes as it doesnt exist - Copenhagen interpretation. 2. something vanishes as it exists - Weinberg's interpretation (Weinberg is not alone in this: Frank Wilczek, Art Hobson, and Julian Schwinger; they believe QFT is the only theory that offers a picture of reality that is understandable and makes sense. For a brief time in the early 60's, QFT went out of favour with many west coast physicists because of its apparent inability to deal with the strong force. At that point there was interest in using the S Matrix and early string formulations to describe these interactions. However, it was soon seen that QCD (another quantum field theory) actually described the strong interactions very precisely and is a component of the Standard model. If the concept closely matches observation, it's a good model. That doesn't mean the model is reality. Reality is the elusive holy grail which we can only approach - and I doubt that we'll know if we ever reach it. Particle physics (where we don't know what a particle is) and QFT (where we don't know what a field is) are two models. Both work reasonably well (in that their predictions are good). Is one "correct" - in terms of the way the world is actually created? No one knows! I can create a concept (model of the world) in which gravity is caused by 21 angels pushing matter together. Ridiculous? You can only say that once you see my mathematics! If my mathematics (based on the angel concept) predicts everything from quantum gravity fluctuations to gravitational lensing to black holes, then my concept is a good one! May not be "reality", but it works. And that's what physics is all about. Concepts are easy to develop. Not so easy is the mathematics to test how well those concepts conform to the real world.

Regardless of what I think about QFT, Weinberg's three volumes are an epic scale, rigorous saga, well written, as all of Weinberg is, and are a good place to go if you really want to know why "something is as it is, is as it must be, both formally and physically". Weinberg does a masterful job at attempting connecting QFT with reality on every single page and not becoming mired in formalism. ( )
  antao | Dec 7, 2020 |
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Available for the first time in paperback, The Quantum Theory of Fields is a self-contained, comprehensive, and up-to-date introduction to quantum field theory from Nobel Laureate Steven Weinberg. The first volume introduces the foundations of quantum field theory, the second volume examines modern applications, and finally the third volume presents supersymmetry, an area of theoretical physics likely to be at the centre of progress in the physics of elementary particles and gravitation. The development is fresh and logical throughout, with each step carefully motivated by what has gone before. The presentation of modern mathematical methods is throughout interwoven with accounts of applications in both elementary particle and condensed matter physics. The three volumes contain much original material, and are peppered with examples and insights drawn from the author's experience as a leader of elementary particle research. Exercises are included at the end of each chapter.

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