Comments by "Lepi Doptera" (@lepidoptera9337) on "Why is quantum mechanics weird? The bomb experiment" video.

  1. It is not a logical game because logic only applies to classical objects, whereas what we are tracking here is energy. Energy does not follow the laws of logic, which happens to be a commutative algebra. Energy in quantum mechanics is subject to the rules of non-commutative algebras (the commutators between linear operators can be non-zero, i.e. non-commutive). What quantum mysticism like this does is to expose the casual viewer to a very naive understanding (or, better, non-understanding) of the theory, which causes unnecessary confusion. That mechanics is somehow non-commutative has already been known since the early 19th century, when the Hamilton formalism was developed. The classical equivalents of these commutators (Lie-brackets) are already showing signs of these internal mathematical structures in the theory.
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  2. You got it. The theory is, indeed, about the flow of energy between systems. "Wave function collapse" is simply a very, very poor choice of words for the irreversible transfer of one quantum of energy from the original, isolated quantum system to the measurement system. Energy never had paths, not even in quantum mechanics. It doesn't have "location", either. The potential energy in a spring is not somehow concentrated in the center of mass of the spring. The kinetic energy of an object is not in the object. It's a function of the relative motion of the object to a rest system. A quantum is, indeed, simply the amount of energy that two systems are exchanging. It's not a particle, it's not an object. It's just work that system A performs on system B.
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  3.  @skhi7658  IMHO it's the way we teach introductory quantum mechanics. I was completely lost after my own QM 101 class. I understood the math, of course, that's easy enough, but I had no idea what it actually meant. I didn't develop a working intuition until after I got into experimental high energy physics, had to read the CERN detector design documents and began to work on actual detector hardware. After that it became clear very quickly that all we are ever measuring are energy, momentum, angular momentum and charge. It was really that "hands on" experimental work that clarified the concepts for me. The textbooks, however, are usually being written by theorists and are staying close to the original "particle" language from the early days, which, unfortunately, is misleading. So, yeah, we have a century's worth of quantum mechanics textbooks that should be rewritten... same math but emphasizing that we are looking at energy that is distributed in a quantum field.
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  4.  @skhi7658  I agree. Here is the thing, though: I can not compete with Sean Carrol and Michio Kaku... I don't have the hair and the kind of face that people want to see. Neither am I willing to lie to people to make things "more interesting". That means nobody is ever going to listen to my technically correct explanation that are about as interesting as watching paint dry.
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  5. ​ @SteveKelly1  The particle language goes back to Einstein's 1905 paper on the photoelectric effect. In that paper he gives a congenial explanation for the macroscopic photoelectric data in terms of the quantization of the electromagnetic field. But at the same time he commits his actual biggest blunder. After having identified quanta of energy, he immediately concludes in a single sentence that these quanta have to have location properties like Newtonian corpuscles. That conclusion isn't backed up by any observational detail of the photoelectric effect. It doesn't match the well known definition of energy as a system property. It's also completely unnecessary for the remainder of the paper. It's a completely unforced slip of Einstein's mind. Unfortunately other authors after Einstein have picked up this mistake and they kept building on it (to this day). What physicists mean by "a particle" is actually a quantum of energy, momentum, angular momentum and charge. Neither of these properties refers to a "small, localized object". They are all system properties. The theory does not describe particles. It describes changes in the energy of systems. You can find this clearly expressed in Heisenberg's matrix mechanics paper where initial and final energy was used as index into the matrices. That's the correct interpretation except that it's not just energy but the quad of energy/momentum/angular momentum and charges. Why these? Because these are the only locally conserved quantities in nature. Everything else changes, but these quantities get transferred from system to system. We have language for property exchanges. Energy FLOWS. It does NOT take a path. The entire concept of path makes no sense because systems are random subdivisions of nature. They don't even have to be some continuous regions of spacetime. Even in classical mechanics the energy of a spring is not localized, for instance. It's in the entire spring. The kinetic energy of an extended object is not in the center of mass of that object, either. We never had this illusion that energy etc. has to be focused in some tiny region of spacetime. That is purely an invention (and not a good one) of non-relativistic quantum mechanics. In quantum field theory it's even worse. the only well defined states are the plane waves of the (interaction) free theory. Everything else is a jumbled mess without any known physical interpretation. Whatever happens in the interaction volume can only be described with classical quantities if we look at it from infinitely far away. In other words: the closer we look, the blurrier nature gets. It doesn't get more "point-like". So, no, not only do particles not travel along paths, there simply are no particles. There are initial and final system states and they are characterized by changes in energy, momentum, angular momentum and charge. That is a fundamentally different (and 100% correct) way of looking at the world.
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  6. That's the definition of the authors. A more rational person would have called this "Quantum mechanical cardboard insertion tester" because all it does is to determine if a piece of cardboard has been inserted into one of the paths of the interferometer. In technical terms the authors are comparing two different experiments with each other. In one experiment the light path is open, in the other one it is blocked. Technically that is neither classical physics nor quantum mechanics. Imagine you did this in classical mechanics e.g. by looking at the motion of a block on an inclined plane... and you calculate the problem once with an inclined plane and once without. Without the inclined plane the block simply drops down straight. Would you find that particularly interesting or strange? If not, then why is this scenario any different? We are simply comparing apples and oranges here. I think the authors were mostly confused by their own attempt to look smart.
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  7.  @filosofiadetalhista  Where am I attacking you? You are trivially wrong on a number of things and I am merely pointing that out. I would suggest that you leave your hurt ego at home. It has no use in science. There is no such thing as wave function collapse. A wave function is an abstract description of a quantum mechanical ensemble (i.e. a hypothetical infinite repetition of the same experiment). Just like a probability distribution a construction that depends on an average over an infinite number of hypothetical events isn't being changed by a single actual event. Copenhagen doesn't talk about collapse anywhere. It talks about the reversible dynamics of a completely isolated unitary ensemble of one system (as described by the Schroedinger equation) and the irreversible energy exchange between the first and an ADDITIONAL second system that performs "the measurement" (that's the function of the Born Rule). The entire "collapse" language is simply nonsense that you have picked up on the internet. It is, as far as I know, not even defined in textbooks. One system IS NOT EQUAL to two systems, hence there is a need for a second formula. Reversible dynamics IS NOT EQUAL to irreversible dynamics, hence there is, again, a need for a second formula. That's why the Born rule has to exist in one form or another. From a logical perspective all of this is crystal clear. What is not obvious is why our education system does such a poor job explaining these otherwise trivial facts almost 120 years after they were first properly identified. There is an incredible amount of confusion and very little clarity about the ontological connection between reality and the theory going on, both at the layman and the professional level. That confusion has to stop. With regards to your second point... the wave function approach does not lead to ultra-precise physics. It's a remnant of the initial non-relativistic phase of quantum mechanics. It explains some trivial systems (particle in a box, hydrogen atom) with reasonable precision and completely falls apart on pretty much everything else (it's almost useless on scattering problems like in high energy physics). One can not do quantum field theory with normalized wave functions and we don't. Reality IS NOT like the non-relativistic Schroedinger equation suggests. It just happens that the step up in mathematical difficulty between the non-relativistic case that has ontological problems and the relativistic field theory case that doesn't have them is enormous. It's far too much for most students to absorb. It also doesn't buy the practitioner anything to learn a theory that has very little predictive power at low energies where effective potential theories suffice and are much, much easier to use (like in solid state physics).
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  8.  @kaushalsuvarna5156  It tells us absolutely nothing because light doesn't take classical paths. Classical paths are an approximation. Even in classical wave theory it's the replacement of (almost straight) wave fronts by their local geometric normals that we call rays. That's a good approximation for plane waves in the free wave propagation problem. It breaks down as soon as we have interaction with surfaces that are changing rapidly at the spatial scale of the wavelength. Then we have to use the full wave theory. In quantum mechanics the validity of these approximations breaks down even further because we are never looking at just one particular system. We are always looking at all possible physical variations of the system (that's called "the quantum mechanical ensemble"). The point I was trying to make is that there is a solid mathematical reason behind all of this "weirdness", but at the end of the day it all breaks down to having to give up the wrong mental models. The world is NOT made of material objects that are flying around on Newtonian trajectories. It is made of energy flow between systems. That energy flow obeys different rules than Newtonian objects (which don't exist except as approximations) would.
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  9. Why don't you tell us your "theory"? :-)
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  10. Congrats. You are one in thousands who actually understands what is really going in.
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  11.  @titusfx  You are correct. It is not different. The problem with these examples is that some semi-smart physicist inserts a complicated Rube-Goldberg device into a simple problem. The analysis is just as trivial as you said. Whether a bomb explodes or not is a CLASSICAL event. No amount of QM intermediary mechanism can make this into a linear superposition of an |exploded> + |non-exploded> bomb. Such a thing does not exist. The device can also not guarantee that the bomb never explodes in the test because it is not interaction-free. What can guarantee that the bomb never explodes is a bit of black tape over its photosensor. That's 100% safe and effective. It's also 100% classical. :-)
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  12. What is weird is that an endless number of authors have been trying to find "paths" for a quantity that doesn't have one. Photons are small amounts of energy. They are system properties. System properties never had any location or any path. They belong either to one system or the other. Quantum mechanics doesn't change anything about that.
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  13.  @skhi7658  Yeah, I actually got interested in the cosmological equivalent of the "mapmaker's problem". Unfortunately a search through dozens of math textbooks on differential geometry eventually turned up a bunch of theorems that showed that one needs at least six dimensions to have a "correct" embedding of a flat metric and ten for more complex cases. At that point I kind of gave up on ever understanding the true geometry of reality... my eyes don't work so well in six and ten dimensions... There are more misleading analogies like that. The "virtual particle" explanation for quantum mechanical uncertainty is completely wrong and all the "vacuum fluctuation" language that laymen are being sold is just plain nonsensical. If the vacuum was "fluctuating", then it would be glowing brightly and one could not possible see all the way to the beginning of the big bang. I have no idea why otherwise highly capable theorists keep pushing these false analogies that would fail undergrad students in oral exams.
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  14. No. The absence of a detection simply means that the energy remained in the free field.
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  15. You can openly say that there is nothing weird about the bomb detector because there is absolutely nothing weird about it. If it could actually prevent the bomb from exploding despite being probed, then it would be weird, but it can't do that.
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  16. Neither do the guys who came up with this hypothetical experiment that doesn't work like that in reality. :-) In all honesty, It's just a Rube Goldberg version of the double slit with one slit covered up and slightly improved detection odds.
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  17.  @Langkowski  Photons don't have paths. That's one of the grand misunderstandings of quantum mechanics. Quanta are small amounts of energy. Energy doesn't have a location and it doesn't have a path. It's not a classical object with center of mass coordinates. Even in classical mechanics energy is a system property. It "flows" from one system to another, which reflects local energy conservation as an accounting principle, but it was never meant to pretend that energy can be localized below the system level.
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  18. Time has a direction because time is that which clocks measure. A clock is simply a system with a local energy source that slowly and steadily releases that energy towards infinity. Why does a clock only run one way? Because there is more volume out at "infinity" than there is near the clock and energy has a tendency to spread out. So what "time" is, is just the precise measurement of the tendency of energy to take in as much space as possible. Now, why does energy spread out? Well, it doesn't always spread out. In a system in thermodynamic equilibrium energy doesn't spread out and such a system is static. It doesn't even make sense to define time for such a system. So what is missing from this puzzle? A microscopic understanding of "volume". We don't know what causes spacetime to be geometric on our scale and we don't know if it stays geometric on all scales. The microscopic explanation for both time and energy are therefor at the scale where geometry emerges from "something else". It is this "something else" that we are really missing.
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  19. That's just as good as shining a light on it directly. Or... you could do the right thing and disarm it by taping over the bomb's photo sensor.
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  20. There are no particles in quantum mechanics. There are only quanta of energy. We are trying to teach this in high school, but most people aren't listening. So what is a quantum? It's the amount of energy that gets absorbed by the detector. Without that absorption process there simply is no quantum. This paper is part deception (the definition of a bomb implies that an active one is an absorber, but an inactive one is transparent), part quantum mysticism (quanta are endpoints, they don't have paths) and part interesting (it gives a simple example for weak measurement ). I would take the last part and forget about the first two.
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  21. A measurement in physics is an irreversible energy transfer. You weren't paying attention in undergrad physics. It's usually defined that way in thermodynamics/statistical mechanic courses when thermal noise is being discussed. Admittedly, my professor may not have spent more than fifteen minutes and one or two classroom exercise problems on it, but why would he have? It's the most trivial piece of physics there is. If you can't figure this out on your own, then science is not a good match for you. Superposition is a CONSTRUCTED mathematical property of the theory. It follows trivially from the requirements that members of the quantum mechanical ensemble are statistically independent. That's also something you should have been able to figure out on your own even if nobody ever told you about it. Where else would perfect linearity come from in nature???? It has to be a mathematical rather than a physical property.
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  22. In that case it simply didn't get probed.
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  23. No.
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  24.  @toymaker3474  Einstein did that? The cookie is on the way.
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  25. That sounded like gibberish.
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  26. Because of the strange way they define a dud... as basically transparent. No such duds exist in the real world, of course. The simple fact is that these folks were too smart for their own good. They tried to manufacture a quantum mechanical system out of a classical one with a slightly weird definition. IMHO it doesn't work because the system doesn't ever become quantum mechanical (no system does in which Planck's constant doesn't show up somewhere). The bomb explodes whenever it absorbs field energy and it doesn't when it doesn't. That's no different from a match (which lights when you rub on it or it doesn't when you don't) or a piece of black cardboard that is either inserted in the light path or it isn't. The fact that it's a bomb is simply show. It has absolutely no physical significance. We can build as much interferometer around such a classical absorptive system as we want, it never becomes the equivalent of a quantum mechanical system like an atom, which can not only absorb field energy by undergoing an optical absorption event but then also give that field energy back by a symmetrical emission event. That is the true physical difference between the bomb scenario and an actual quantum mechanical object like an atom.
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  27. Interference is not a physical effect. It's the absence of a physical effect (there is no self-interaction in linear systems). Photons do, of course, not take paths. Only the averages of many photons do.
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  28.  @Langkowski  Light isn't "made" of photons. That's a false semi-classical mental model that tries to apply the principles of classical atomism to a purely quantum mechanical system. Photons are quanta of energy. They only "exist" as irreversible energy exchanges between the source and the electromagnetic field in emission and the electromagnetic field and an absorber in absorption processes. There are, however, no photons in the free em field. The theory does not pretend that there are, either.
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  29. A force is that which accelerates a mass in an inertial system. That's the definition of force. A quantum of energy is the same thing as energy, usually just a lot smaller. You are right, there is nothing weird about either.
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  30. Ah, so you are the guy who wins the lottery every weekend. ;-)
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  31.  @MaryAnnNytowl  So you don't' know what the term "dark energy" means. OK. More physics DK at work. :-)
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  32. Photons simply don't exist on paths. They are work that the source performs on the electromagnetic field and work that the electromagnetic field performs at the detector. That performed work is simply electromagnetic field energy as long as it's not being removed from the field... but energy does not have a location or a path. It is simply a system property of the field.
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  33. Bohmian mechanics has to introduce yet another physically undetectable concept without predicting anything new. Don't do it.
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  34. Yes, that did sound dumb.
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  35. One can make one. Imagine a bomb with a battery. When it's on, the battery operates an electromagnetic lever that exposes the photosensor to the outside world. Without battery the photosensor retracts into the bomb. Now... is that how one would build a bomb? No, of course not. It's just another layer of Rube-Goldberg thinking that the authors of this experiment had to build in to get to something that they considered an "interesting" result. There is, of course, nothing interesting about it. The bomb is a completely classical detector. It has no quantum state itself, so whatever quantum system we build around it, it's not going to change how it works. At most we are ever going to measure the behavior of the quantum system (in this case the mirrors) themselves.
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  36. Why? Spinning something without knowing its orientation before the spin creates something with unknown orientation. So your spinning operation went from "unknown" to "unknown", which is no physical change at all. You are basically still believing in the existence of an actual, objective state before the measurement and nature keeps saying "Nope, I don't care. If you don't know, then I don't know.". Some people call that "realism", but in reality it's actually a blindness to the facts.
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  37. There is nothing to explain. Collapse doesn't exist. It's a myth, very much like cow tipping. If you don't believe me, try to tip a cow and then go and try to observe a collapse. ;-)
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  38. Interference is a linear phenomenon. It's the absence of interaction, so even "multiple photons" don't interact with each other. The lowest order physical interaction in these systems would cause photons with sum and difference frequencies to appear, i.e. it would change the spectral composition of light. A non-linear field with self-interaction automatically scatters its excitations all over the place, i.e. even a fairly monochromatic source will create higher harmonics and low frequency (near DC) excitations and over a long distance the source will appear washed out as if it had gone trough a fog.
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  39. Superposition is the description of what we don't know about a system. In quantum mechanics the "don't know space" can be enormous. In certain cases that can be used to calculate things. Don't let the proofs that quantum algorithms are equivalent to classical algorithms fool you. They only prove that one can always find a quantum algorithm that calculates the same results as a classical algorithm but with uncertainty. It's not a proof that an efficient quantum algorithm exists. My best bet is that there will be a few amazingly efficient quantum algorithms that will give us new insights into the mathematical nature of certain problems (like factoring and prime numbers). In general, however, most problems that only have inefficient classical algorithms will probably turn out to have no more efficient (or far less efficient) quantum algorithms. Just my two cents.
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  40. In what function? As a critic of physics DK or as a demonstration of physics DK? He seems to have done a good job about both sides of that problem. His probabilistic interpretations of quantum mechanics are complete bullshit, of course. Probabilistic theories can not be time-reversal invariant and QM is, both in theory and in the closest possible physical form of phase-conjugation experiments. We can show that quantum systems remember their past as long as they are not being subjected to a measurement. The only irreversible aspects of quantum mechanics are preparation and measurement, which means that the only "mysteries" are what preparation and measurement mean. Quantum field theory gives a perfectly natural explanation for both: it's the local interaction of waves coming from and going to infinity. In other words, what gives structure to quantum mechanics is the same thing that causes "time" to exist: the fact that there is way more "out there" than there is "over here". Every physicist who has ever done atomic physics and high energy physics experiments should know this intuitively. There is simply no mystery here, there are only people who don't know enough about physics.
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  41. You aren't missing anything. This is physics bullshit pure. If you think about it rationally then it becomes obvious that each bomb behaves like a classical object: bombs explode whenever they absorb energy (photons are electromagnetic field energy, nothing more, nothing less). No amount of fog and mirrors can convert that classical behavior into quantum mechanics. Moreover, mirrors and beam splitters alone don't make for quantum mechanical experiments (neither do slits). None of these experiments introduces Planck's constant anywhere. It might therefor be zero, it's original value or 137 trillion... the theory wouldn't predict any change in the behavior of the experiment. Why? Because we never leave the realm of classical electromagnetism except at the detector... and those basically just detect quanta with a frequency that is proportional to the classical intensity of the light. Whenever somebody tells you that "there is exactly one photon in the apparatus", that's metaphysical bullshit. It's an untestable assumption. A photon is an irreversible energy transfer. There are no photons without that irreversible event, at all. How much energy was in total in the apparatus can not be known without actually measuring it. All that can be known is how much energy was taken out of the field.
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  42.  @blahdiblah2169  What do you mean by "no actual theory"? That is total bullshit, Love. Quantum mechanics does exactly the same thing as every other theory does in physics: it tells you how physical systems exchange energy, momentum, angular momentum and other locally observed quantities. You simply don't know how it does that. :-)
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  43.  @MaryAnnNytowl  Why do I have to write a paper about things that were already understood in the 1930s? My point is that you are 90 years behind in science. :-)
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  44.  @blahdiblah2169  It was never "shut up and calculate". For me it was always "I don't understand QM101 at all, so let's go to the library and see if we can't find something that makes sense". It took me several weeks of more or less random digging in old journals and textbooks, but then I found Feynman's 1948 paper on the path integral formulation of the Schroedinger equation and then the lights went on. From there I began dabbling in quantum field theory and it took me years (I suck at theory) to understand why the QFT guys don't give a frell about measurement operators. And then I did a PhD in experimental high energy physics and there you notice very quickly that what your detectors are measuring are always energy and momentum. You aren't measuring some random linear operator over a general Hilbert space. It's not math but the most concrete physics in the world. It's the relativistic miniature version of collisions between massive objects that you have seen in high school physics, except that there are no massive objects, but the formulas for kinetic energy and momentum exchanges are still valid. And then I read some more about it and I found Mott's paper from 1929 that explains why plane waves with high momenta automatically form particle tracks in detectors and another set of lights went on. And at that point you can completely abandon the QM 101 nonsense about particles. There are no particles. There are only quanta and quanta are energy and momentum and angular momentum exchanges between fields. And once you know all of that, then you can go back and re-read the old papers of Heisenberg and others from the 1920s and you will find that you were never asked to shut up and calculate. It's all in those old papers, already. The entire physics intuition that you needed to make it successfully in QM101 was already there. What had simply happened in my case is that the guy who read QM101 to us (literally... he didn't give a frell) was not a high energy physicist, he didn't care about foundations of quantum mechanics, he had never built a relativistic detector, he had never read a thing about path integrals, he had never read Heisenberg's papers, either. He knew the formalism from abstract modern textbooks that didn't mention any of that and that was enough for him to do his job in solid state physics. He was the last guy on Earth who should have been teaching QM 101. That is not a problem with quantum mechanics. That is a problem with how we teach quantum mechanics to undergrads. And that, my friends, is exactly the state of quantum mechanics "teaching" on the internet. You are getting a completely mutilated version of a non-relativistic approximation of quantum field theory (which is the only real physical theory that is self consistent) presented by people who don't know that what they are showing you is not the real deal. They simply don't know what they don't know. That is physics DK. And now you have to decide if you want to download Mott's 1929 paper and Heisenberg's 1927 papers (or thereabouts) and read a good textbook or two on QFT and go through Feynman's derivation of the path integral for the Schroedinger equation (one of the most beautiful theory papers in all of physics IMHO) or if you want to pretend that you know it all when you don't know anything, whatsoever. Take care.
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  45. It is not in higher spatial dimensions. Angular momentum and multi-quanta states are represented by ever larger matrices. Unitary dynamics in the linear spaces of these matrices are similar to rotations in higher dimensions (except that "coordinates" are complex numbers and not real numbers).
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  46. Where does quantum mechanics say that? On the internet? On the internet the Earth is flat, too.
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  47.  @thememaster7  Well, you are welcome to give me a citation of a book about quantum mechanics in the library that says that. :-)
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  48.  @thememaster7  I accept internet sources of library books as an answer. :-)
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  49.  @thememaster7  All you said was "Beam me up, Scotty!". :-)
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  50. You can never tell whether it's either without taking a chance of exploding it. The whole setup simply confuses you without the most obvious piece of analysis: this kind of bomb is a perfectly classical system and never stops behaving like one.
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  51. Photons don't take any paths at all. Photons are the amounts of energy that gets absorbed by a detector at the end of the experiment. That energy doesn't have a path. Energy never had a path, not even in classical physics. It's a system property. It always "belongs" to the whole system. We tried to teach you that in classical mechanics in high school... but you (like all other students) weren't paying any attention.
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  52. Why are you thinking such absurd thought?
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  53.  @neillibertine3044  There simply are no particles in quantum mechanics. There is nothing to discuss about that. Quanta are amounts of energy. They are not "objects" but system properties. If you are personally offended by that, then you have to think some more about quantum mechanics on your own time. I can't do that for you. I can only tell you what QM is and is not and it is not a theory of particles. It is a theory of energy transfers.
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  54.  @neillibertine3044  What are the most general systems that we know about? Fields. If we want a fundamental theory, then we have to study fields. Unfortunately it turns out that fields are very hard to study, both experimentally and theoretically. That's why we don't start physics with fields but with systems with discrete "components" like "chunks of matter". For instance, the most important of all solvable classical particle systems, the Kepler problem, is handled by abstracting a gravitational field and the matter fields away. We decide that we don't care about the nature of matter and assign a classical kinetic energy to chunks of it and we decide that we don't care about the details of gravitation and we describe it in a simplified way as a potential energy term (that depends on the distance of the centers of mass of our chunks). We are then solving the equations that transform kinetic energy in potential energy and vice versa (while obeying global momentum and angular momentum conservation). The critical term that describes which particular system we are analyzing (Kepler problem, harmonic oscillator, pendulum etc.) is therefor the potential energy term. It is here that we can realize that potential energy does not belong to any particular constituent of the system but to the system as a whole. No matter how many parts (chunks of matter, springs etc.) the system has, there is always one potential energy term that describes all of it. You are correct that this is not how we are teaching classical mechanics in high school. We are, however, teaching exactly this in the first theory classes in university by introducing the Lagrange and Hamilton formalisms. Then, a semester later, or so, we are teaching students how to "quantize" these classical systems by using the Schroedinger formalism, which replaces the kinetic energy term with a Laplacian and the potential energy term with a multiplicative linear operator. If you happen to take classes on electrodynamics (the most simple of fundamental physical field theories), then you can later learn in your graduate level QED class how one goes from the Hamiltonian of the electromagnetic field to the quantized field equations by inserting it into a path integral. That, like the Schroedinger equation, is a quantization procedure. It is, however, a much, much more complicated one with sheer endless mathematical consequences that are still not fully understood, yet. In any case, the big picture is that we never work with "chunks of matter" in these theoretical descriptions. We are always working on the level of system energy.
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  55.  @neillibertine3044  "first thing first, if an atom is in higher energy state how it come to so." Usually by absorbing a photon, i.e. from the electromagnetic field. That is already a simplifying description because "an atom" is actually an electromagnetically bound system. The atom/em field distinction is already a system boundary made by physicists, it's not one made by nature. So when you say "extra energy from outside", then you are already using the system language that I was talking about. That atoms are "particles" are semi-classical approximations that you were taught to believe in in school because it is extremely difficult (and in most cases also unnecessary) to describe atoms with quantum field theory. The only difference between us is that I know when I am dealing with an approximation of that kind and you are glossing over it. "Field theory, field whether scalar like temperature or vector like electric, dont exist without particles." Why does an electromagnetic field not exist without particles? The classical field description is through either a four vector with a scalar electric field potential and a three vector for the magnetic vector potential. You can expand that to a four-by-four tensor for the electric and magnetic field components, if you like. Once you quantize that you won't get particles, either. What you will get are field quanta, which are energy/momentum/angular momentum (spin) values. There will never be "an object" jumping out of a quantized em field. Experimentally that is fully supported by something as trivial as solar panels. They absorb electromagnetic field energy at 1e15Hz and convert it into a different form of electromagnetic field energy at near 0Hz. No particles needed. "About kepler description, there is no conservation of angular momentum for elliptical orbit, so keplers description is faulty." You really need to go back to your physics books for that one. It's completely false.
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  56.  @neillibertine3044  There are no particles. :-) I would suggest you clean up your physics act first by learning that all central potentials are angular momentum conserving.
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  57. @UC35cKjwzdRtI-PHvy7ZFViA Everything emerges from quantum fields. Energy is the same property of quantum fields as always. I don't know why this seems strange to you. "Quantum field" only means that these fields behave in a certain (and extremely well tested) way. There is no magic to it, except that you didn't read enough books about these things, yet, and you have not done enough experiments with them, either, to feel emotionally secure about your knowledge about them. Philosophy is bullshit. I won't even go there.
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  58.  @neillibertine3044  What, exactly, are you crying about, right now? That you are still a kid and I am a guy who has been doing physics his entire adult life? Goodness. If you can find me an experiment that shows particles, then go and find one. I am happy to learn something from you that I have never seen before. :-)
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  59.  @neillibertine3044  So you can't find an experiment that shows particles. That settles it, then. I win. :-)
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  60.  @neillibertine3044  And there it is... still no experiment. I win.
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  61.  @neillibertine3044  And there it is, still no experiment. Only a lot of self-pity, right now. Boring.
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  62.  @neillibertine3044  So where is the experiment that shows that there are particles? Stop feeling sorry for yourself and show me that experiment.
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  63.  @neillibertine3044  So particles are droplets of water? OK. :-) And atoms and molecules are not further divisible? OK. :-)
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  64.  @neillibertine3044  I don't have to demonstrate anything. In science we only talk about things that can be proven to exist physically. If you want to start a particle religion, that's up to you, but please don't expect me to take your new creed seriously.
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  65.  @neillibertine3044  No, that's not what a "particle" is. You clearly don't even know basic definitions. :-)
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  66.  @neillibertine3044  It's not "my" definition of particle. It's THE definition of particle. Look, my friend, physics is precise about its choice of words. It's a bit like the law that way. If you can't wrap your mind around that, then maybe you would be more comfortable in a field that requires creative writing\speaking skills? How about work in advertising, real estate sales or motivational speaking?
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  67.  @neillibertine3044  Look, it's not my problem that you don't have physics books, either. The definition of particle is explained in the first few sentences in the first paragraph of "Mechanics: Volume 1 (Course of Theoretical Physics S)" by by Landau and Lifshitz. Enjoy. And while you are at it, please read the entire book. It will teach you what classical mechanics really looks like.
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  68.  @neillibertine3044  Photons are neither localized nor do they have mass. Electrons are not localized. :-)
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  69.  @neillibertine3044  How do you get a dark and a bright stripe from a single dot? What magic is that? :-)
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  70.  @neillibertine3044  There are photons outside quantum theory now? Where? :-) And since when have photons wavelengths? Since you didn't pay attention in science class? :-) In general, you should presume less and learn more. That way you would know more and look less uneducated. Just my two cents.
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  71.  @neillibertine3044  Why are you asking me? You are the world class physicist here. :-)
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  72. ​ @neillibertine3044  Let's hope for you that your sarcasm is as strong as mine. :-)
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  73. ​ @neillibertine3044  You don't even have a sense of humor? Oh, boy.
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  74.  @neillibertine3044  Whatever happened to those experiments that demonstrate particles? Did you forget about those, already? I didn't. :-)
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  75.  @neillibertine3044  See, you still got nothing. :-)
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  76.  @neillibertine3044  See, you still got nothing. :-)
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  77.  @neillibertine3044  See, you still got nothing. :-)
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  78. So can a classical experiment. You shine light on the bomb and it doesn't go off, then it was a dud.
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  79. Your first sentence is wrong, already. There are no "particles" in quantum theory, at all. There are quanta (which are energy values) and system states. There are ensembles and single copies of a system. None of that has anything to do with particles. Those only enter when somebody who doesn't understand quantum mechanics teaches it the wrong way.
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  80.  @neillibertine3044  Matter is an emergent phenomenon of quantum fields. Protons and neutrons are bound states of quarks and gluons. Nuclei are bound states of protons and neutrons, atoms are bound states of nuclei and electrons, molecules are bound states of atoms and so on. Where quanta come in is during system changes. Nature doesn't know about systems. Nature is all one entity. Systems are definitions by physicists. We know that these artificial entities interact by exchanging globally preserved physical properties like energy, momentum, angular momentum, electric charge etc.. "A quantum" is an irreversible exchange of one or several of these properties. For thermodynamic reasons energy always has to change (that follows from the third law that does not allow zero temperature, which basically leads to a minimal thermal background energy density condition). So if any detectable change in a physical system should occur, there has to be an irreversible energy exchange. That is what we call "preparation" (aka "source") and "observation" (aka "detector"). As you can see, quantum mechanics is therefor a systems theory. It describes how physical systems interact with each other using measurable (classical) physical quantities. No particles required at any time. Classical mechanics is also a system theory, by the way, you were just never taught to understand it that way. If you had been taught properly, then the "emotional" transition to quantum mechanics would have been trivial.
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  81. Unitarity, i.e. the property that all emitted quanta are also detected, is an assumption of the theory. In reality all of this is marred by what experimentalists call "quantum efficiency". We can, at most, detect 80-90 of photons with our quantum detectors and we generally do not even count how many quanta our sources are emitting. 10% or more are always lost, even in the best of experiments, and then there is thermal noise in addition, which causes "false positives". All of that has to be dealt with at the experimental level when we are performing the systematic error calculations. The theory is not describing any of that.
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  82.  @erinm9445  You certainly won the internet binge drinking competition with that one. ;-)
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  83. There is no wave function in an individual experiment. A wave function is a property of an ensemble.
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  84. Single photons do not show interference. It takes a large number of them to see interference patterns. Interference is a pretty bad terminology to begin with. Interference happens in linear systems in which parts of the system do not interact with each other, at all, i.e. interference is the absence of all physical effects, not a physical effect itself. More properly it would be called "non-interference". It is amazing how few people understand this fact intuitively.
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  85.  @neillibertine3044  Like I said, a single photon does not produce a measurement that even shows interference. In an interference experiment we need, at least, two measurements. On dark stripe, one bright stripe, for instance. That's a non-reducible number (and it will give very poor statistics). None of this has anything to do with interaction. Again, it's the total absence of interaction that causes this. In quantum field theoretical terms, if you want to have a self-interacting theory, then you have to have, at least, a phy^4 term (phy^2 is just the energy of a linear field). Light, at least at optical frequencies, is completely without self-interaction. The lowest order photon-photon scattering process is a four-photon gamma_1 + gamma_2 -> gamma_3 + gamma_4 process, which is suppressed by some 50 orders of magnitude for ordinary photon densities in optical light sources if I remember correctly. It's a very hard experimental challenge to make free-electron gamma sources and femto-second laser sources that can actually produce these non-linear interaction between photons without the use of electrons or other charged particles.
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  86.  @A.Raybould  I still don't see it. There is a 50% chance that a live bomb goes off, one way or another.
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  87.  @eljcd  The dud bomb in this case is basically a bomb that's not in the light path. Of course a bomb that does not receive a signal does not go off. That's a completely classical result.
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  88.  @A.Raybould  I am not seeing non-classical behavior by the bomb. It goes off every time a photon is detected by a live bomb. It does not go off when a photon is not being detected by a defective bomb. What is strange about that?
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  89.  @A.Raybould  We can make a bomb that has an electrically operated lever arm with the photodetector on it. When the battery in the bomb works, the detector is in the light path. When the battery is empty, then the arm drops down by gravity or using a spring. That way "the detector" is completely transparent when the bomb is "off". Of course the detector is classical, the level arm is classical, the trigger is classical and the explosive is classical, i.e. even this Rube-Goldberg bomb is an entirely classical system. Every time it is hit by light and is on it explodes. No amount of quantum magic around it will ever change something about that. You are correct that without this mechanical lever the bomb's detector would always absorb photons and then the entire experiment would be completely ridiculous.
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  90.  @A.Raybould  A photon is an irreversible energy transfer between the quantum field and an external system. That process is classical. What is not classical is the energy propagation within the field itself, but then, there are no photons in there, to begin with.
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  91.  @A.Raybould  I am simply giving you a detailed model of how to build such a quirky detector and why it is entirely classical. It is, at no time, in a quantum superposition.
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  92.  @A.Raybould  Quantum mechanics doesn't tell us anything about paths. In order to measure a path we would have to make at least two consecutive measurements on the same physical object. That is not possible with quanta. As soon as we measure a quantum it is gone. More precisely, the quantum only "exists" during the measurement. Before it is field energy and thereafter it is thermalized energy in the "detector" system. I am a physicist. As a matter of principle I don't "imagine" things that can not be measured. That procedure, I am afraid, belongs into religion, philosophy and creative writing. What I am saying is that none of these parlor trick experiments teach you anything substantial about quantum mechanics. The realization that quanta are, in some sense, monads of energy, does.
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  93.  @A.Raybould  I know that the video talks about paths. What I am telling you is that videos that talk about paths of quanta are confusing you about what quantum mechanics is. Yes. If the bomb goes off, then the energy was deposited in the bomb's detector. If it doesn't, then it has to be deposited either in A or B. What did you learn here? How to make a Rube-Goldberg machine to demonstrate energy conservation? How to attract more people to a physics video by talking about a bomb instead of detectors A, B and C?
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  94.  @Something-tx6cl  If quantum mechanics is weird to you, then you didn't study it enough.
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  95.  @Something-tx6cl  Feynman made a pretty lame physics joke about superposition that 100% of humorless laymen don't pick up on. Yes, my DK is so bad that it earned me a PhD in physics from a major university, kid. I must have been really bad at physics. ;-)
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  96.  @Something-tx6cl  What about a joke do you not understand? And what is so hard to understand about quantum mechanics? It's the theory of quantized energy, momentum and angular momentum transfers. Guess what classical mechanics is? It's the theory of un-quantized energy, momentum and angular momentum transfers. Anybody who pays close attention in high school physics will, eventually, notice that it is not about "stuff". Classical mechanics is exclusively about the change of conserved properties of "stuff". CM has absolutely nothing to say about "stuff" itself. And if you are paying close attention to the structure of quantum mechanics, then you will notice the exact same phenomenon. Why is this? Well, because there is no "stuff". There is only a geometric and relative entity called "the physical vacuum" that is capable of exchanging these physical properties with itself. Everything else, including all "matter" and "radiation" (i.e. "stuff") is a secondary emergent effect of these exchanges. Easy.
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  97. I must have missed the news that Einstein's theory of general relativity failed a precision test. ;-)
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  98. No, it's not possible. It just seems that way. :-)
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  99.  @alexojideagu  None of the examples given are interaction free. They all have detectors. "The lack of a detection" is not a detection. You still need an actual detection somewhere else to determine that there has been a lack of a detection in front of it. These are all just Rube-Goldberg machines that are meant to confuse you (and their authors) about the actual physics. If you want to learn something about a quantum system, then you have to change a state somewhere and that change of state is inevitably linked to an irreversible energy transfer.
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  100. A live bomb is an absorber. A dud is transparent.
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  101. A correlation is not physical causation and you can never learn about it faster than at the speed of light.
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  102.  @hannes7695  No offense, but you sound like a hard physical realist. You seem to believe that a quantum state is an actual physical property in the sense of a classical state. So if two of these properties are correlated by a global symmetry, they have to be causally linked. If the ball is turned around here, then the entangled ball at the other end of the universe has to turn as well. That is exactly what nature tells us does not happen. I hope I misunderstand your comment.
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  103. You are obviously not good at thinking. Don't do it! Go with "feeling", instead.
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  104. Photons don't go on any paths. That's just very, very poor teaching of quantum mechanics.
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  105. Yes. There are no detectors like that. A normal photodetector is always absorbing. The easiest way to build something like that is a magnetically powered level arm with the photodetector on it. When the power supply of the bomb is on, then the photodetector is in the light path, when the power is off, then it drops down or is pulled to the side by a spring. But then, what did you really build here? A slightly more complicated double slit experiment with a mechanical shutter in front of one slit. Detectors a and b would simply sit in the central maximum and the first minimum. That's it. There is no magic here, just a silly but ultimately trivial variation of a known system.
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  106. There is our physics genius, again, who knows nothing about physics. :-)
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  107. Quantum mechanics doesn't talk about things. It talks about energy. Energy only exists if you put it in there. Of course sometimes it doesn't... because you never put it in there to begin with.
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  108. Of course. She caters to physics armchair coaches like yourself. If she would only address those with real education in the subject, then she would get like three hits a week and two would be from me. ;-)
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  109. Next up: earth is flat and pocket perpetual motion machines.
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  110. One can easily build a bomb like that. It's a simple lever that removes the photodetector from the light path when the bomb is not active. It's a somewhat quirky idea. A simple photodetector is, of course, always absorbing, whether it actually triggers something or not. Having said that, the analysis is what really fails. This bomb detector is no better at finding a bomb than anything conventional and a real bomb "test" would not test the bomb, at all. One would simply put some black tape on the bomb's photodetector to make it insensitive to light. The problem with all of these "experiments" in quantum mechanics is that they don't teach us anything about quantum mechanics, at all.
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  111. Photons don't have paths. That concept only exists in your failed mental model of photons as particles. In reality photons are quanta of energy and energy never had a path, not even in classical mechanics.
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  112.  @nitchipa2  What do I not understand? Physics? I am a physics PhD. Are you also a physics PhD? ;-)
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  113. You are clearly living in a different universe, then.
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  114. The measured state is not the physical state of the quantum system. It's the classical state the measurement apparatus is in after interaction with the quantum system. People tend to confuse one for the other. That's why superposition seems so weird... nature simply doesn't care about our measurement systems because before the interaction it doesn't even know about them.
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  115. Interference is simply another name for the linear behavior of light. It's always there, even if one shapes gaussian wave fronts.
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  116.  @neillibertine3044  I think you need to read up on the behavior of classical electromagnetic waves in addition.
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  117.  @neillibertine3044  Yeah, good luck with that.
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  118. I have never seen an electron take any path. Neither have you. You are very good at imagining that it must have taken a path, though. :-)
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  119. Photons don't have paths. That's just a common amateur mistake that is being reinforced by plenty of poorly worded and outright false videos on the internet.
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  120.  @nottieru  Yes, people have been talking about paths since 1905, when Einstein made his actual biggest blunder. But talking about something that nobody has ever seen is not physics. It's religion.
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  121.  @nottieru  Electromagnetic waves are made from many quanta. I can measure them over and over again. I can only measure one quantum once. That's the definition of quantum. The physical difference is not rocket science. It's the same as the "Sesame Street" lesson about the difference between "One cookie and many cookies" with Ernie and cookie monster. It's on YouTube. :-)
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  122.  @nottieru  Why? So that I get seven hits by trolls who claim it's all god's work? Who gives a frell? Not this guy. :-)
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  123.  @nottieru  Well, try "Jesus has been dead since 35 AD!" on them. :-)
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  124. Only on the internet. You can't get any hits any other way.
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  125. The bombs are perfectly classical. You can replace them with a simple piece of black cardboard.
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  126.  @bulhakov  The bomb is either functional (carboard in) or not (cardboard out). The "inventors" of this Rube Goldberg non-QM Gedankenexperiment aren't as smart as they think they are. You are basically just testing if one arm of the interferometer is blocked or not. It's not fundamentally different from the double slit and that's not even a quantum experiment (and neither is this).
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  127. Because the authors of this paper defined it that way. If you want to know how to implement this: a working bomb is a black piece of cardboard. A defective bomb is no cardboard. The proper name for this experiment is therefor "Quantum mechanical cardboard insertion tester". :-)
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  128.  @SteveKelly1  None of them understand quantum mechanics. In Sabine's case you can find the proof for that in her own papers. She talks nonsense about it even in her science publications. The wider problem is how we teach quantum mechanics at the university level. All of our introductions to it are non-relativistic but in reality quantum mechanics is a deeply relativistic phenomenon.
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  129.  @jdthood  Dude, I don't care that you don't understand physics, either. That you weren't paying attention in science class was a problem between you, your parents and your teachers in high school. It's all over. You failed and you keep failing and that's that. I can't change that. ;-)
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  130. That "weirdness" has very little to do with entanglement, though. We are simply not used to what happens when symmetries are applied to states which are capable of linear superposition. In other words... humans can't think "matrix". That's all it is.
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  131. I have never seen a broken detector that didn't absorb photons. They look exactly the same, whether they are on or off, brand new working or fried and dead. I think the theoretical physicists need to spend a bit more time in the lab before they come up with theoretical experiments that don't exist like that in nature.
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