Schrödinger's Cat: A History of Quantum Physics - Page 1
Forum section: electronics / general

author: joeqsmith
author_rank: Super Contributor
timestamp: June 28, 2025, 03:12:10 pm
content: I like the history guy's channel. He recently released a video on quantum physics.

author: TimFox
author_rank: Super Contributor
timestamp: June 28, 2025, 04:02:25 pm
content: My problem with the traditional statement of Schrödinger’s Cat:In the physics of the radioactive decay that triggers the poison, there is no difference between having the cat in a Lucite (transparent) box or a Bakelite (opaque) box.Putting the victim in an opaque box is throwing away (or ignoring) physically valid information, as opposed to the unknowable quantum details of the radioactive nucleus before it decays.

author: SiliconWizard
author_rank: Super Contributor
timestamp: June 28, 2025, 04:33:13 pm
content: Quote from: TimFox on June 28, 2025, 04:02:25 pmI also don't see what this would bring to the table to make it opaque. But I still haven't come to terms with the whole observer thing in quantum mechanics, so bear with me. The whole idea of an external observer being able to influence the reality experienced by someone or something else is a bit troublesome.

author: SteveThackery
author_rank: Super Contributor
timestamp: June 28, 2025, 04:35:50 pm
content: Quote from: TimFox on June 28, 2025, 04:02:25 pmFirstly, it's only a metaphor; but more importantly, Schrodinger actually used the story to demonstrate how absurd and counter-intuitive quantum mechanics is. In reality, quantum superposition only applies to particles, not cats.

author: TimFox
author_rank: Super Contributor
timestamp: June 28, 2025, 04:49:12 pm
content: A better thought experiment (that also works in practice) is the double-slit experiment (which route was taken?), and the Stern-Gerlach experiment (for polarization). I refer the interested reader to the huge literature on these topics.

author: SteveThackery
author_rank: Super Contributor
timestamp: June 28, 2025, 05:05:19 pm
content: Quote from: SiliconWizard on June 28, 2025, 04:33:13 pmI think everyone - including quantum physicists - are in the same boat.My view fundamentally changed when I had the following explained to me:Physics basically stopped "making sense" around the turn of the 20th century.In 1905, Special Relativity became the first development in physics that just didn't, and doesn't, make sense intuitively. The idea that time runs at different speeds (NOT clocks! -time itself) is completely contrary to all common sense and observed reality. Same with objects becoming more massive as they go faster. Where does the extra mass come from? And where does it go? And why do they changelength, of all things? Plus it leads to any number of paradoxes that simply cannot be resolved in a way that makes sense.The only thing you can do with Special Relativity is simply accept it. Do the calculations, take the measurements, and yes, they come out as SR predicts. But there is no escaping the fact that it goes against "common sense".The next big one that doesn't "make sense" is General Relativity, with the strange phenomenon that time runs slower at the top of a mountain than at the bottom. And then, in the 1920s, quantum physics put the topping on the cake: now,nophysics makes sense!The lesson is this:nowhere does it say that physics has to "make sense". It is what it is. All we can do is test the predictions and confirm that yes, the predictions come out right.That is what physicists have been doing for the past 120 years. Accepting it, accepting that it goes against common sense, but using it anyway. And unfortunately for us, it means that numerous well-intentioned people create metaphors and thought experiments with the aim of "explaining" relativity, or quantum superposition, or quantum entanglement. None of which really help!

author: Analog Kid
author_rank: Super Contributor
timestamp: June 28, 2025, 05:20:46 pm
content: One of my many problems with quantum physics is that it doesn't seem to applyat allto readily observable, ordinary everyday phenomena here on Planet Earth, like all the stuff which can still be explained by simple Newtonian physics: gravity, mass, acceleration, all that "classical" mechanical stuff.It seems to me to be an excessively abstruse explanation of "other-worldly" phenomena, like near-light-speed travel, which most of us Earthlings will never come close to experiencing in our lifetime here on the planetary surface. It seems to apply only to a few edge or corner cases. It's almost as if those pointy-headed scientists who deal in this realm are kind of goosing or trolling the rest of with their fantastic tales of what happens (they think) when someone is on a rocket ship traveling near the speed of light: "Oooh, aah, look what happens to your clocks and your rulers!".So excuse me if I just ignore the whole shebang altogether.

author: ejeffrey
author_rank: Super Contributor
timestamp: June 28, 2025, 05:27:14 pm
content: Quote from: SteveThackery on June 28, 2025, 04:35:50 pmYet every time someone sets a bound on "you wouldn't be able to observe superposition on that scale" they have been wrong. Obviously we are still a long way from cats but we are up to showing diffraction of molecules with thousands of atoms and superposition of quantized vibrational states of mechanical resonators weighing micrograms which is closer to a cat than an atom.Schrodinger intended the thought experiment as a reductio ad absurdum, but so far no evidence suggests anything but technical limits to the ability to perform it in real life.

author: nctnico
author_rank: Super Contributor
timestamp: June 28, 2025, 05:30:50 pm
content: Quote from: Analog Kid on June 28, 2025, 05:20:46 pmIt is kind of like the various transistor models. You start out with the Hfe model and later on you'll learn it is completely wrong and inadequate. And this cycle repeats a couple of times once you advance in electronics engineeringStill, there certainly is a place for quantum physics and relativity theory. One of the fields I'm involved in is long distance time transfer. When using long links, the relativistic effect of the earth's rotational speed starts to play a role on the signals going back & forth causing a time offset. So that needs to be compensated.

author: Analog Kid
author_rank: Super Contributor
timestamp: June 28, 2025, 05:55:46 pm
content: Quote from: nctnico on June 28, 2025, 05:30:50 pmWell, of course there is a place: like they say, it ain't chopped liver.My thesis is that the more advanced quantum physics and relativity theory become, the more irrelevant they become to 99.98% of Earthlings.I would hazard a guess that about that proportion of Earthlings doesn't understand this stuffat all. Nor do they care.I don't understand it myself. And that bothers me less and less as I age. I feel I can just safely ignore it and get on with my life.

author: SteveThackery
author_rank: Super Contributor
timestamp: June 28, 2025, 05:59:39 pm
content: Quote from: Analog Kid on June 28, 2025, 05:55:46 pmRelevant only unknowingly: the clocks on the GPS satellites are adjusted for both special and general relativity.As I say, nobody really understands it, they just use it because it works.

author: TimFox
author_rank: Super Contributor
timestamp: June 28, 2025, 06:06:04 pm
content: Quote from: Analog Kid on June 28, 2025, 05:20:46 pmOne of the wingnut engineers at work, who took his science politically, therefore did not believe in evolution nor quantum mechanics.I told him that he would have to stop using solid-state electronics, which requires quantum mechanics to deal with the solid-state electronic structure of semiconductors, etc., at room temperature and atmospheric pressure at measly volts applied to the devices.How would you understand a “band-gap reference” circuit classically?Vacuum-tube operation is almost describable with non-quantum classical thermodynamics, but not relevant to the ordinary phenomena we use in cell phones.

author: djsb
author_rank: Super Contributor
timestamp: June 28, 2025, 06:15:45 pm
content: I'm still rereading Nick Herberts Quantum reality book. It's hard work but maybe worth persevering with. I read a book recently on quantum computers, and it seems to be relevant to how they operate. It also seems that understanding the quantum realm could help us to solve how photosynthesis works, for example.I still find Mr Shrodinger and cats in general a complete mystery.

author: SiliconWizard
author_rank: Super Contributor
timestamp: June 28, 2025, 06:16:11 pm
content: Quote from: TimFox on June 28, 2025, 04:49:12 pmSchrödinger's Cat is actually a rather interesting thought experiment in that it tries to address the point: "oh, but quantum mechanics only applies to particles". In this case, sure, it applies to particles, but what if said particles can have a (deadly, in this case) effect on a much larger object - a living being, in this case?In that regard, it's much deeper than the double-slit experiment. The latter is not only easily reproducible, but also somewhat easier to grasp.The former opens a can of worms.

author: TimFox
author_rank: Super Contributor
timestamp: June 28, 2025, 06:16:58 pm
content: Anything chemical (photosynthesis or other reactions) is governed by quantum mechanics.

author: TimFox
author_rank: Super Contributor
timestamp: June 28, 2025, 06:18:55 pm
content: Quote from: SiliconWizard on June 28, 2025, 06:16:11 pmYes, quantum physics can kill.However, there is a fundamental difference between the “hidden” things that are not observable and things that are knowable but ignored by the experimenter. Lucite vs. Bakelite in my example.

author: Nominal Animal
author_rank: Super Contributor
timestamp: June 28, 2025, 06:52:40 pm
content: One of the missing pieces in quantum physics is the conundrum that is entanglement and often called "wavefunction collapse". Many-world models can be classified as the latter.If the Schrödinger's cat box was completely opaque to all information transfer, then the state of the cat would be entangled with that of the decaying atom.So-called "wavefunction collapse" occurs when that entangled state is resolved, by interacting with other matter or fields in a way that is only compatible with one possible result state. Even a simple observation is such an interaction.The reason we do not see human-scale items behaving in the same manner as atom-scale particles, is that large systems of particles have so many interactions of so many different types, that any entanglement "collapses" before QM behaviour oddities can be observed. It is not just simple particles, however. Bose-Einstein condensates of 10,000,000 atoms have been created. These are cryogenically cooled clumps of particles that behave as a single particle, according to quantum mechanics.The funny thing about quantum physics is that because it is a model that offers very useful predictions, others can apply those predictions without understanding anything of the quantum physics; in the human scale, the applications often exist in a relatively "calm and smooth parameter space", where simple rules of thumb can be applied to approximate the results of the proper model. This is very similar to why we do not need to teach Newtonian mechanics to athletes throwing, kicking, or hitting balls or pucks around: their brains can automatically do the necessary approximations and guide their limbs, so they can concentrate on the strategy and actions needed, and do not need to consciously think about the mechanics and kinematics occurring, integrating particle paths from observed samples, and so on.An excellent example issurface plasmons. Put simply, when you form small ordered clumps of atoms of the same or compatible types,nanocrystals, their optical properties like color is determined solely by the clump size, because the outermost atoms' outermost electrons form a "common" delocalized electron or electrons across its entire surface. The exact atoms used are basically irrelevant. If you use a vacuum oven, you can grow such nanocrystals easily using very low pressure hot gas on an industrial scale, and their size is very tightly controlled by the duration and temperature is the gas bath. So much so, that for the smallest crystals, the size is controlled to within a couple of atoms, with very little variance across huge batches of such nanocrystals. These (and other related QM stuff) are at the core of current LED technologies and many specific-color fluorescent dyes used on e.g. the thin film display technology you are most likely using to read this very text right now. (E-ink/e-paper is different, and in many ways simpler tech.) (I am familiar with this, because it is a very useful atomic simulation scenario. On one hand, it is very simple and immediately real-world applicable and thus very useful as an exercise. On the other hand, it also points out the issues in simulation implementation details like the temperature control mechanism (in practice in such chambers via black-body radiation), with certain simulated temperature controls causing the famous spinning ice cube scenario, yielding utterly unrealistic results.)

author: Nominal Animal
author_rank: Super Contributor
timestamp: June 28, 2025, 07:08:11 pm
content: Quote from: TimFox on June 28, 2025, 06:16:58 pmVery true.This is exactly why there is very little to no difference between quantum chemistry, quantum biology or biophysics, and material physics at the atomic/quantum scale.Whatever difference there is, is a difference in what is currently a hot research topic in each field, and these vary more in time than between these subjects.The compulsory automotive analog is mechanics specializing in ordinary passenger cars or trucks, or specific brands/makes/models, or ICE vs. electric. They all share the same kind of wheels/tires, shock absorbers, et cetera.

author: ejeffrey
author_rank: Super Contributor
timestamp: June 28, 2025, 07:14:27 pm
content: Quote from: Analog Kid on June 28, 2025, 05:20:46 pmYou can see quantum interference with a strand of hair and a lightbulb.Because optical diffraction is quantum interference, and quantum mechanics is just wave mechanics. Yes, we figured out optical wave theory before the rest of quantum theory, but it's all the same thing.Most people don't need to know or care why they see diffraction patterns at all, but it's equally true that most people don't need to know how gravity works -- like people need to know that stuff falls down, but they don't need to know the acceleration depends on the mass of the earth, or that the same force keeps the earth and moon in their orbits. People don't even really need to know inertia and acceleration. Aristotelian mechanics is good enough for most people's daily lives. But that's a pointless statement.

author: TimFox
author_rank: Super Contributor
timestamp: June 28, 2025, 07:19:02 pm
content: Newton and his contemporaries replaced Aristotelian “impetus” with Cartesian “momentum”, but the disproven concept lives on in the popular imagination.

author: armandine2
author_rank: Frequent Contributor
timestamp: June 28, 2025, 10:30:52 pm
content: ...I'd rather watch hair dry

author: vad
author_rank: Frequent Contributor
timestamp: June 28, 2025, 10:37:58 pm
content: Quote from: ejeffrey on June 28, 2025, 07:14:27 pmUnless you are using a special kind of lightbulb that emits single photons, and by “seeing” you mean detecting them with single-photon detectors, this statement is misleading. Quantum interference occurs when a single photon travels all possible paths, and those paths interfere with each other. You can’t observe that effect with just a hair and a regular lightbulb.Quote from: ejeffrey on June 28, 2025, 07:14:27 pmSure, to the same degree as classical mechanics is a limiting case of quantum mechanics. In theory, you could write a wavefunction for the ~10^52 particles making up Earth and solve Schrodinger’s equation to predict its orbit around the Sun. But that doesn’t make Kepler’s laws quantum mechanics, they are classical laws that theoretically can be derived from quantum mechanics under appropriate limits.PS. Try immersing the lightbulb and the hair in water. The diffraction pattern will change due to the reduced speed of light in water / shorter wavelength. Classical optics explains this easily. Have fun explaining it using QED.

author: TimFox
author_rank: Super Contributor
timestamp: June 28, 2025, 10:56:06 pm
content: Of course, in order to see the optical diffraction pattern, you need to run many, many photons through the apparatus to generate a visible pattern.A single photon will generate only a single event at the detector or film.One of my University professors, Dr. U Fano, liked to demonstrate how to calculate macroscopic effects as expectation values of quantum-mechanical processes.

author: Nominal Animal
author_rank: Super Contributor
timestamp: June 29, 2025, 07:34:59 pm
content: It's exactly those, combined with measurement devices having their own uncertainty (that is, yielding a results according to a specific probability distribution even when the exact same physical quantity is being measured) that helped me truly understand statistics principles, like when to use mean or median, what confidence intervals/error bars actually indicate and how to properly calculate and present them, and so on. Very useful!I was never much good atabstractmathematics without any practical implementation. I just need a problem set to apply it to, to really understand and learn it.