What physics experiment can not be explained without Feynman's paths integral? - Page 1
Forum section: electronics / general

author: RoGeorge
author_rank: Super Contributor
timestamp: February 19, 2025, 08:49:32 am
content: A new YouTube pop-science video popped into my YT subscribed channels, about Feynman's many paths or 'path-integral'.How Can Light Travel Everywhere at Once? Feynman’s Path Integral ExplainedPhysics Explainedhttps://youtu.be/ss0HABVUkeQVery nicely made, but my question is not about that video in particular. The video doesn't need to be watched in order to answer the question, if one is already familiar with the Feynman's path integral idea.My question is, why the many paths was necessary to introduce in physics, and why it got traction?I mean, what physics problem, or physics experimental results, does the path integral explains, while the classical (previous) interpretations can not?For example, I remember from high school we used to think each point of a slit as a new oscillator, and had no problem calculating wave/light interference figures on a screen.Seen along the years quite a few pop science videos and articles about the many paths interpretation. Each time I encounter the all-path-integral idea I think that (by the same logic of the all-paths-integral), I could as well think about "1+2" math addition as adding 1 and 2, together with adding as well all the other integers (which other-integers will cancel out each other), and in the end only 1 and 2 will contribute to the end result. But what would be the point of doing that?So, what physics experiment can be explained only by the Feynman's paths-integral interpretation, and not by classical wave addition? Or why was the path integral necessary? Asking as a hobby-physicist, and yes, searched online already but couldn't figure the answer.

author: woofy
author_rank: Frequent Contributor
timestamp: February 19, 2025, 09:59:30 am
content: Oh dear!I think that video is indicative of the issues in fundamental physics of the last few decades. The use of words that no-one agree the definition of, and running with it.First let me say I am a hobby physicist like you. I have no maths to back up anything I say, its all gut feeling and instinct, so take it in that light. I gain most of my "knowledge" by filtering lots of you-tube videos from popular physics lectures and talks.In this case the video talks of photons as if they are particles or little lumps of light, then to make it work give each a little clock. All he is describing is a wave with phase cancellation. The maths may well work and it does, but to then assign any reality to that is a step too far. If I have two apples and give you three of them the you will have three apples and I will have -1 apples. If you then give me two of your three apples we will each have an apple. The maths works, but to give reality to the intermediate steps is non-sense. Yet thats what happens, the maths of the many worlds interpretation of quantum physics may well work, but the the entire universe splitting with every quantum interaction, come on.

author: RoGeorge
author_rank: Super Contributor
timestamp: February 19, 2025, 12:18:02 pm
content: I see the many-world as a hypothetical speculation, as what could be vs. what it is, but anyway, the many-worlds interpretation is not mainstream physics AFAIK.Path integral, OTOH, was always shown as accepted by mainstream physics, but that is another good question.- Was the Feynman Path Integral accepted by physicists, or am I a victim of pop-science over-hyping controversial topics?- Is the Feynman path integral an established fact taught in physics schools, or is it only an interesting theory of no practical use?

author: rstofer
author_rank: Super Contributor
timestamp: February 20, 2025, 12:46:02 am
content: According to ChatGPT in reply to 'describe and define Feyman's path integral and provide examples of its application':Feynman’s path integral formulation is a fundamental framework in quantum mechanics and quantum field theory. It provides an alternative to the Schrödinger and Heisenberg formulations by expressing quantum evolution as a sum over all possible paths a particle can take between two points.The reply also includes some math that I can't seem to copy and paste.Way above my pay grade!

author: coppercone2
author_rank: Super Contributor
timestamp: February 20, 2025, 05:39:37 am
content: I thought the thin slit is a waveguide that basically is very thin so it has a giant fringe field effectI assume the slits have to have a different width when it comes to different light frequencieswhat happens if you keep making those plates the slots are in thicker?

author: Nominal Animal
author_rank: Super Contributor
timestamp: February 20, 2025, 06:04:40 am
content: Quote from: RoGeorge on February 19, 2025, 08:49:32 amPhysics does notexplain, itdescribes. And therein lies the crux!Feynman showed that the path integral formulation (which stems from Fermat's principle from 1662, and from calculus and calculus of variations that Leibnitz and Newton and others developed since late 1600s!) –– which Wiener and Dirac had applied to quantum mechanics, quantum mechanics arising classical electromagnetism theory being unable to describe (in ways matching observations) black-body radiation and photoelectric effect and others –– was a mathematically proper description of quantum mechanics, including Schrödinger equations and what Dirac had described (but not mathematically described) about the classical limit, where quantum mechanics and well-known classical models agree.At a very fundamental way, this is about a mathematical tool that has proven extraordinary good at describing physical phenomena. It helped put Diracs words into math, for example.Consider the good old double-slit experiment. Do it on individual electrons or photons, and you still get the interference pattern. However, as far as we can tell, electrons and photons seem to be elementary particles, so they cannot be "split". If we consider delocalization, the one wave function passing through both slits (which, as OP already noted one can mathematically easily represent by two new oscillators, one at each slit), what is it but describing the two paths with equal weight, interacting with each other?Just like Fermat's principle of least time and Snell's law describe the same thing –– if you write Fermat's principle for a flat static interface between two media, using calculus of variations, you end up with Snell's law ––, path integrals and calculus of variations are just tools that can be used to describe quantum wave function behaviour (and lot more besides).Consider this: How do you know that using separate oscillators, one each at a slit, is a proper/correct description of the double slit experiment? If you used path integrals to describe the entire setup, you can discretize and simplify it to two wave functions, getting the equivalent of the two separate oscillator description. (Because the slits have finite width, you do need more, say two sums or integrals, one over each slit, to get areallygood description of the results to whatever precision and fidelity you want.)In terms of quantum wave functions, it changes nothing, because it is fully compatible, even showing how at the classical limit the quantum approach produces the classical results (like Dirac discussed but did not mathematically precisely describe).

author: RoGeorge
author_rank: Super Contributor
timestamp: February 20, 2025, 08:41:31 am
content: I think I start to see my mistake: I was taking it as a physical phenomena, not as a mathematical tool.I was visualizing the particle taking all the possible routes, including the one where the photon goes to the Moon, circles it 3 times, then returns on Earth to hit the screen.If the path integral formulation is a mathematical tool, and not a physics phenomena, then this changes all. Mathematical tools don't have to have a direct translation to the physical world, so looking for a physics experiment (in which to observe evidence of my photon traveling to the dark side of the Moon while taking all the possible routes) would be irrelevant.

author: Kleinstein
author_rank: Super Contributor
timestamp: February 20, 2025, 12:40:09 pm
content: The path integrals are a mathematical method. Besides the math part it also gives some visualization for multi-particle QM. So it can help peaple to understand the QM a little better or at least look at it also from a different angle. However it does not add anything new to the physics part of quantum mechanics.

author: David Hess
author_rank: Super Contributor
timestamp: February 20, 2025, 01:50:55 pm
content: The double slit experiment comes to mind, and it also describes refraction. If you want something more readily available, the behavior of a tunnel diode or floating gate MOSFET require quantum mechanics.I always thought of it as the particle-wave taking all possible paths, including those that go back in time. We only see the result after it interferes with itself. This could be the Transactional or Time-symmetric interpretations, and fits nicely with anti-matter being time reversed normal matter, with the photon being its own anti-particle. I never liked the hubris of the observer collapse interpretation.

author: RoGeorge
author_rank: Super Contributor
timestamp: February 20, 2025, 10:35:20 pm
content: I've just finished watching one of the Feynman's lecture about light reflection and transmission. The phase difference and their adding when considering multiple paths of reflected photons (the path integral) is explained in QED Lecture 2, Reflection and Transmission.My impression after watching his lecture is that he mean it for real, that the photon takes all the possible trajectories, not just like a mathematical tool. In fact, he gives an example with a mirror placed sideways, so a physical experiment.There is a source light, a mirror, and a detector. The photons go from the source, bounce to the mirror, and they are reflected back to the detector. The phase adding of all the paths is considered, and shown how all the paths tend to cancel each other except for the straight line of direct reflection between the light source and the detector.Then he places only a small piece of mirror sideways from the direct path, and no light is detected. Here he is pointing to that piece of mirror placed sideways (so away from the straight path of direct reflection):Then he etches the mirror with alternating stripes of reflecting/not reflecting bands (thus transforming the plain mirror into a diffraction grate), and the light is detected again (if the width of the diffraction grate is just right).This experiment is shown in the part 3/7 of the lecture, starting from minute 13:10 of part 3/7, but I'll just list all the 7 parts of this lecture for the curious:Title: Richard Feynman QED Lecture 2, Reflection and Transmission : 1/7 ... part 7/7Channel: Muon Ray1/7https://youtu.be/UUAG3yDInQQ2/7https://youtu.be/Sccs-XG33EU3/7https://youtu.be/-QUj2ZRUa7c<- the printscreen is from here at about the minute 13:104/7https://youtu.be/1C7abO7LtV05/7https://youtu.be/wHRgIZseCcA6/7https://youtu.be/Rm0CuMvoyLA7/7https://youtu.be/uBt9hQGKPjUI think the experiment with the sideways mirror that is transformed into a diffraction grating was to demonstrate that the photons really travel through all the possible paths at once, and not just in a straight line.However, I did a slightly different experiment (to double check the many paths traveling) and it didn't work.I've took a laser pointer and a CD/DVD, and at first shined the laser into the mirror surface of a CD/DVD. The CD surface has stripes on it, so it's in fact a diffraction grating, not a plain mirror. And indeed, the reflected beam splits into multiple dots because of the reflection grating. So far all good.Then I've shined the laser through the middle hole of the CD, like this:Now, the reflecting grating is sideways (just like in the Feynman's example from 3/7). If it were for the photons to take all the paths, I would expect to see circles (or maybe dots) of reflected light backwards, behind the laser pointer.Well, there is no reflected ring, or dots, or any other patterned formed by the sideways mirror of the disk. All the light goes through the hole in the middle of the disk. I don't see diffraction patterns reflected back (by the mirror that encircles the laser beam).So, I'm tempted to say that no, the photons do not take all the possible paths. They only travel in a straight line.If the photons were to take all the possible paths, then many of these paths (other than the straight beam path) should have hit the CD mirror, and since the CD mirror is a diffraction grating, it should reflect some light backwards (as an interference pattern), toward the laser point. But I don't see anything like that, so the many paths assumption must have been incorrect.Or maybe I'm doing something wrong, or I might have misunderstood something. Where's the mistake?

author: Georgy.Moshkin
author_rank: Frequent Contributor
timestamp: February 21, 2025, 03:36:18 am
content: Probably because the scale is important too. Imagine CD which is 10 meters in diameter with a 1 m hole. In this context slits become irrelevant, because the hole is too big.I think that it's nearly impossible to make experiment similar to yours work, because the closer trajectory to straight line is, the more "inphase" trajectories are there. If we put a bunch of wires through the CD hole, the number of wires is limited by their diameters. But the trajectories can overlap. In some sense, it's infinity against infinity. I think that number of nearly straight trajectories is the same as number of random trajectories. Therefore, no matter what and how close you place near the laser beam, if there is a tiny hole that provides a shorter path, it will be "used" by the beam.Thanks for bringing this topic. The strangeness of this principle leads to another question: is it possible to create a large structure that provides higher probability than a straight line. While total speculation, it's interesting to think that such structure placed at any distance (on the Moon) can steal a laser beam and "teleport" the laser dot to the Moon's surface just because the "phase" probabilities was higher than for a straight line.

author: Analog Kid
author_rank: Super Contributor
timestamp: February 21, 2025, 03:45:02 am
content: All this stuff is waaaaaay over my head.Just one dumb question, though:Don't photons actually travel in straight paths? I thought they did. Why wouldn't they?If they don't, then wouldn't "all possible paths" for a photon be an infinitely large set of paths?

author: woofy
author_rank: Frequent Contributor
timestamp: February 21, 2025, 09:38:30 am
content: Quote from: RoGeorge on February 20, 2025, 10:35:20 pmThat was my point, the maths works and is a useful tool but don't trust it to describe reality.People do think of photons as particles or little lumps of light, they are not. Neither are the fermions, electrons etc. They are all waves in their respective quantum fields. Those fields are smooth, not quantised and the waves can take ANY amplitude. Imagine throwing food pellets to ducks on a lake. The pellets create waves that propagate in all directions and the ducks paddling adds to it.. At any point, the surface is a complex jittering as waves of different amplitudes pass through. That is how I see the electro-magnetic field, and all the others as well. What we observe as a photon is the interaction of the EM field with another field, say the electron field and we see it as a photon in the MK1 eyeball. The same for all fields, electron, up quark, etc. They are all smoothly varying waves in their own fields. What is quantised are the interactions between quantum fields. The interaction between the EM field and any other IS quantised. If the EM and electron fields interacted we would observe the electron move up in energy. The EM field would be depleted by that amount.Of course its not as simple as that, but its a reasonable starting point.Take what I say with the caveat in the previous post above.

author: Nominal Animal
author_rank: Super Contributor
timestamp: February 21, 2025, 11:01:08 am
content: Quote from: Analog Kid on February 21, 2025, 03:45:02 amThe simplest answer is to replace "straight" with "geodesic", and then say "yes". This is because when light refracts or is reflected, the geodesic represents the "shortest path", and Fermat's principle applies in optics.The complex answer is they don't, and both "travel" and "straight" would need to be well defined first anyway, since we are talking about a wave function that extends to infinity, and often has more than one peak. Although the wave function amplitude squared indicates the probability density, we're not talking about statistics or uncertainty. As the double slit experiment done on individual electrons and photons still shows the interference pattern, we can only interpret the result as the individual electron or photon somehow passing throughbothslits at the same time. Does your definition of "straight" allow that? See, human language makes all this even harder.Quote from: Analog Kid on February 21, 2025, 03:45:02 amYes, indeed.All this comes back to the classical limit as explained by Dirac: among the infinity of paths, almost all cancel out by destructive interference. This has a centuries-old basis incalculus of variations, and in how one can approximate the value of a difficult integral by only looking at the parts where its magnitude is large, the definition of "large" setting the precision in that approximation. There are entire families of calculus tools based on that. (Feynman showed using path integrals that at the limit where Planck constant tends towards zero, you get the expected classical forms for basically all simple cases.)

author: EPAIII
author_rank: Super Contributor
timestamp: February 21, 2025, 01:15:26 pm
content: I have a BS degree in physics so I am no where near Feynman but I would offer this in answer to some of the suggested and "performed" experiments. You are neglecting two ideas. First there is the conservation of matter-energy. I say this because the energy (matter-energy because they are equivalent) of that laser beam or string of particles or even of a single particle is a constant. The total energy to be found at the "target" (for lack of a better word) end of the beam will be the same as that generated at the source. That may be a simplistic way of saying it, but it is pretty much true.And second, the Feynman proposition does not just attempt to explain the intensity of one "target" point. It attempts to explain the intensity of all possible "target" points, throughout ALL of space-time.Some of these "points" and I am talking about a four dimensional point in space-time (remember that space and time are the same thing) will be more favored with a higher percentage of this energy (actually matter-energy) than others and the ratios, the differences between any two, can be very large.One practical consequence of this is that, just because your experimental apparatus does not detect any matter-energy at a given point, does not mean that there is none there. It only means that the amount of matter-energy is too small for your limited apparatus to detect.I would offer one more, disconnected thought; "The science is NEVER settled." I don't care who says it is; I don't care how much alphabet soup he/she has after her/his name, if anyone says that, then that person just does NOT understand the nature of science. Science is a NEVER ENDING succession of observation, development of theories, experimentation, and discovery of the INEVITABLE ERRORS in that latest theory or some earlier one. And then the process repeats,ad infinitum.There is NO SETTLED SCIENCE! EVER! NO EXCEPTIONS, EVER! And if you think otherwise, you are a fool. Feynman's theories are just that, theories. Theories, not laws of nature. And the same thing goes for every thing that every other scientist says, ever has said, and ever will say. They are attempting to predict what happens, what will happen in reality. They are not defining reality: in that they are totally helpless. It is reality that defines their failures, not the other way around.

author: David Hess
author_rank: Super Contributor
timestamp: February 21, 2025, 03:41:13 pm
content: Quote from: Analog Kid on February 21, 2025, 03:45:02 amThe answer is no, which is what the double slit experiment demonstrates.With a single slit, only the photons which enter the slit proceed to the target, like one would expect. When the slit is narrow, the photons refract through it like a wave would, spreading out on the other side, demonstrating that they act as both particles and waves. So far so good.When we add a second slit besides the first, the blast of photons go through both slits and because of the refraction they spread out from both slits, and then interfere with each other at the target producing an interference pattern. Also so far so good.But what happens if we send just one photon through two side by side slits? We might expect the photon to go through one or the other slit, or get blocked. If it goes through one slit, then it should refract as usual and hit the target somewhere producing a normal distribution, but this is not what happens. Somehow the photon goes through *both* slits and interferes with itself, landing on the target with a distribution showing the interference pattern. So it *did* take all possible paths to the target, even though there was only one photon.This can be extended with an angled piece of glass to explain diffraction. When the photon enters the glass it slows down, and bends, and then speeds up and bends again when it exits. The amount of bending yields the minimum time to the target. In the quantum version, the photon takes *every* path through the glass to the target, and all of the paths except for the minimum time path cancel out, yielding the same result and what we observe.

author: Analog Kid
author_rank: Super Contributor
timestamp: February 22, 2025, 12:30:27 am
content: OK, let's bring this back to reality, or at least observable reality:In ordinary optics, such as a projector, after passing through a condenser, light rays appear to travel in straight lines toward the screen. Most of the light cast off from the light source reaches the screen. We don't see light taking random paths outside of the beam concentrated on the screen.So how does that square with what's being described here? Does light (particles, waves, whatever) travel in straight lines or not?Regarding the term "geodesic" introduced below, I can appreciate that light paths may be influenced by forces such as gravity, so by "straight" let's say "a straight line except for certain influences", okay?I'm sorry to sound like a Philistine (or worse, "anti-science"), but I must say that these abstruse, esoteric discussions leave me cold. Not only because this whole field seems to have little practical application; that shouldn't be a reason not to investigate something, but except for curiosity it limits the import or relevance of the discussion. It's just that the whole thing seems like trying to determine how many angels dance on the head of a pin. Is this stuff really know-able? And besides, how much of what is accepted today in quantum physics will be overthrown in the future by other theories? (Hasn't string theory and its dozens of dimensions kind of been quietly pushed aside?)

author: dietert1
author_rank: Super Contributor
timestamp: February 22, 2025, 02:04:11 am
content: As a former high energy physicist i'd recommend reading about Feynman diagrams and their relationship to quantum mechanics and the mathematics involved, e.g.https://physics.stackexchange.com/questions/114399/the-path-integral-and-feynman-diagrams.Feynman diagrams are the standard method to describe processes in high energy physics. High energy physics is a field of research where particle accelerators are used to create and collide particle beams of particle energy high enough to form new particles, for example weak interaction bosons or the Higgs boson. The methods proposed by Feynman are considered the "correct" way to describe those interactions and predict their properties.Regards, Dieter

author: Nominal Animal
author_rank: Super Contributor
timestamp: February 22, 2025, 05:20:09 am
content: Apologies to those who hate my wall–of–text answers in advance.Quote from: Analog Kid on February 22, 2025, 12:30:27 amWrong question. The correct question is, "How good an approximation is it to treat light as if it travels in straight lines?"The answer is, in optics and elsewhere, ittypicallymodels observable reality to within measurement precision. There are situations like the one at a time double slit experiment, high energy photons, high beam density photons, and so on, where it breaks down.The model all this resulted in is calledquantum electrodynamics(Wikipedia article). The link itself points to how Feynman described the probability amplitudes without complex numbers, and currently is illustrated with a nice little animation that should help you understand. Only a few of the infinite number of possible paths are shown, though.But wait: those paths shown all show straight paths for the photons!? Yes. The cases where a photon changes direction from its geodesic ("straight line" for most intents and purposes) are due to interactions with other fields/particles; these can even bevirtual particles(which really just represent the underlying quantum fields). Simply put, even in a vacuum flask chilled to near absolute zero floating about in intergalactic space far from anything else, a single photon can change direction. It's just quite rare, and can usually be ignored because of its rarity.So... it's more like straight lines between interactions with other stuff? Yeah, that's what QED describes. Instead of individual possible paths, the photon is described using a quantum wavefunction, whose amplitude squared corresponds to the probability of that photon being detected there if interacted with somehow.A very similar thing happens with electrons bound to an atom nucleus. They do not whizz around the nucleus, they'redelocalizedaround the nucleus. We call it an "electron cloud", but technically it's just single electrons being smeared over a volume of space. They do have a quantum mechanical property that is basically equivalent to the angular momentum if it did. Because of this delocalization, we useelectron densityto describe the likelihood of poking it somehow and discovering the electron there. If we treat the atom nucleus as a single point of charge, even combining with the electrons bound closest to the nucleus so we only worry about the few outermost electrons, and treat these electrons as smeared over the atom according to their orbital, angular momentum, and spin, we get anab initio(from scratch) model of matter. Even though such simulations only model the electrons in their relaxed states –– so no photon emission and such ––, those models uncannily accurately describe molecules and how matter behaves. (The wavefunctions are hard work to calculate even for computers, so we have a practical complexity limit somwhere in the order of thousands of electrons, depending on the amount of hardware you can use. And the models must be periodic, currently. If we simplify those interactions into theirclassical potentialmodels, which is what I like to work with, we can model millions to even billions of atoms, without periodic boundaries; but some elements are easier to model, some harder. For example, copper and iron are easy metals, but chromium hard, because of the magnetic component in the interactions. Water molecules scare the bejesus out of simulator people, because they happen to be quite complex and their interactions reach a fair distance.)Does it mean that photons actually do take all possible paths? No, I don't think so. Even if it does, all the infinitely many weird ones always cancel out. Essentially,quantum electrodynamicstells us what happens when light and matter interact, and between such interactions the wave function travels/moves/evolves –– no,propagates–– "unchanged" at the speed of light, along a geodesic. When in a medium such as glass, the interactions are what slows the speed down to about 2/3 of that in vacuum.Quote from: Analog Kid on February 22, 2025, 12:30:27 amBah! It is exactly the reason I love physics: it is developed by questioning every single facet of it. Even in my own field, molecular dynamics simulations, the very first question one must always ask after getting results is "does this make any sense?"In my opinion, your questions are exactly what anyone studying physics (or any other natural science) should be asking, all the time. I do.(Note that in my answers, I do not strive for exact accuracy like I would when communicating with other people working on this stuff. My intent/hope is to use language that steers readers' understanding towards useful paths, so that they can build on top. I always hated the way I was taught one thing in high school, then in university shown that that was just an approximation and here's what we really think is the correct model. So, I'm trying to steer your understanding and intuition, rather than give precisely mathematically correct answers. Unless I include the math in the answer.)Quote from: Analog Kid on February 22, 2025, 12:30:27 amOh no, quite the opposite. It was only these more complicated models that we could explain photoelectric effect, and can model at the atomic level what kind of structures and materials can make for better solar panels, for example. Or anything involving laser light: it's not just monochromatic, but all the photons are in the same phase. Or quantum entanglement, which is already used in order to detect intrusion/external observation of optical information traffic.In many cases the complex equations can be simplified to a simpler model that only applies in a certain situation. This is exactly the case withSnell's lawin optics, describing how light refracts, even though we discovered the simpler model before the underlying one. That does not mean the underlying model is useless, because a lot of the interesting stuff happens at the "edges".If we didn't have these models, we wouldn't have laser LEDs, OLEDs, maybe even FETs, LCDs, or TFTs.Quote from: Analog Kid on February 22, 2025, 12:30:27 amWhat we don't know is whether the form of math we use to describe these phenomena is related to how reality does it. What we do know, is that the models do predict what happens in the corresponding real world phenomena, and that gives us tools to build more useful technologies.Quote from: Analog Kid on February 22, 2025, 12:30:27 amThat is a fallacy, untrue. When Einstein proposed special relativity, Newton's laws of motion weren't overthrown per se:the two agreewhen velocities, masses, and energies are low enough. It is only when you get close to light speed in velocity, high masses, or very high energy densities, that we find that Newton's laws do not correctly match observations, but special relativity does.The often used example of that is the precession of Mercury's perihelion. The difference between special relativity and Newton's laws of motion is just one tenth of a degreeper century. It's tiny, but it was measurable already back in1859; and it matches special relativity.Old findings cannot be thrown out. We still use Newton's laws of motion even in atomic simulations, because they are less work than applying special relativity, but within the numerical precision we have,the two produce the same results.Similarly, new theories do not invalidate the old ones in the domain they apply. They onlyextend, and give more precision. Within the domain previously known, theymustagree to within the previous precision, or something is wrong.I play a lot with 2D and 3D representations, including atom and molecular system visualization. (The underlying problem is how to generate the correct intuitive understanding, controlling the subconscious facets of the understanding of the image. Using photorealistic gleaming marbles for atoms looks nice, but it gives the impression that they have a definite outer boundary, which they don't! Even their shape varies a bit depending on other charges nearby. I've found that eliminating unnecessary information is most powerful, so I like to use cartoon-likecel shadingtechniques instead. One of my forever projects is a way to use existing 3D rendering engines to produce the color information, but overlaid with vector curves on top, for maximal image quality at minimal file/image size.)If I don't have transparency or different optical media, I don't need to apply even Snell's law (which, again, is equivalent to Fermat's principle with clearly delineated uniform optical media): pure basic vector algebra suffices. The more precisely I want to model, the more detailed a model I need to use. If you wanted to model how different materials interact with light, producing all the effects we see in real life, you need to either apply (parts of) QED, or empirically model the effects of QED.

author: Andy Chee
author_rank: Super Contributor
timestamp: February 22, 2025, 05:40:59 am
content: Quote from: Analog Kid on February 22, 2025, 12:30:27 amIt has important practical application in semiconductor manufacturing, particularly if you want to shrink your transistor sizes down (which incidentally, China still struggles with).But yes, the emergence of interference patterns, even when sending particles slowly and one at a time, seems to defy logic!

author: RoGeorge
author_rank: Super Contributor
timestamp: February 22, 2025, 02:03:52 pm
content: Quote from: Nominal Animal on February 22, 2025, 05:20:09 amIt's funny because that animation, while not wrong, it is very, very misleading. That's what Feynman explains in that lecture 2 reflection and refraction video.Misleading because, first of all, the scale. Those few arrows leave the impression of a relatively small phase shift. Did yesterday a for-loop with python, to estimate some numerical quantities. When considering something of the size of the CD and a laser pointer, that phasor arrow doesn't turn a few times, but rather millions of times.Another thing, it needs coherent light, all the photons (at the source) have to be in phase for that animated diagram to work. So, either you have a laser that sprays in phase photons in all directions equally (then it works), or you say one photon (alone) takes all the possible paths at once, which sounds very bamboozling to me.The only way I could negotiate that (single photon on all paths at once) would be if the EM wave responsible for that photon (so not the photon itself, but the wave that produces/carries the photon - the photon is a squared always positive quantity, the wave is with either + or -), so if the EM wave of a single photon is in fact a ripple sphere (just like the ripple circle on the surface of the water in a lake, but in 3D). Such an EM wave sphere would explain how it is possible to take "all the possible paths at once". Not the photon, but the EM wave (with + and -) takes all the paths at once, because the wave it's that enlarging sphere. That will also explain interference, double slit and all the rest in a classical way, as we do it for waves.But if I think it like that, I don't know how to think about the direction of light, and how to put back all the energy of that ripple sphere into a single point on the sphere (the photon).I'm aware that thousands other people tried already all the possible explanations, but I still can not just admit it takes all the possible paths at once. Most probably there is some other missing aspects, something not known yet, and that is why it doesn't make any sense.

author: RoGeorge
author_rank: Super Contributor
timestamp: February 23, 2025, 05:57:16 am
content: I want to simulate numerically the outcome of my green laser pointer and a CD (or other reflecting surface), maybe some other arrangements with obstacles, too, not only a direct reflection.In the animation showing how to add phasors from Wikipedia(and in the recorded QED lecture 2 video, too), I see only the straight paths were considered, more precisely only the intersection area enclosed between the source/detector and the edges of the mirror (no matter the reflection angle). I'm not sure which paths to consider for a more complicated arrangement than just a flat mirror.What does "all possible paths" means (assuming homogeneous medium and no other photon interactions with the air)? Do I consider crazy trajectories (for example curved, or "around the corner" paths)?For example, if I have an opaque object (a partial obturation) between the source and the mirror, which paths do I need to consider when adding the phase/amplitude at the detector point?

author: RoGeorge
author_rank: Super Contributor
timestamp: February 23, 2025, 08:57:51 am
content: Meanwhile I've read the QED Wikipedia page, and realized the whole idea is not at all about what I thought it is.The path integral is about paths in Feynman diagrams, is it? And about how virtual interactions between photons and electrons can happen in those diagrams in all the possible ways. All the possible interactions in space, in time, and in the way the photon is absorbed and or emitted. And these are allprobabilityamplitudes (not wave amplitudes of an electron, or a photon).And these probabilities of possible combinations and outcomes only virtually happen in all the possible ways "at once". Time is one of the axis in Feynman diagrams, so the words "happens at once" are very misleading. We just consider all the possibilities, including the crazy one going backwards in time. I didn't notice the arrow of time being mentioned, so I guess in Feynman diagrams there is no direction of time.Overall, these "all possible paths" we add up in the Feynman path integral, are trajectory paths inspace-time, not normal trajectories in space-only, as the trajectories one used to study in classical mechanic. Or at least that's my understanding for now.And all these infinite combinations of possible space-time trajectories when they split in more and more possible interactions, the space-time path "explodes" in complexity. But they have the funny property that, the more complicated the combinations, the less they contribute to the final result, so in practice one can calculate a good enough outcome considering only a few of those infinite paths/combinations/interactions shown in a space-time Feynman diagram.And the end result is a probability, so when instantiated in a physical experiment, it will happen in only one way out of all those infinite possibilities. And when repeated again, it will happen in some other way from that set of possible outcomes.TL;DRThe path integral does not refer to classical trajectory of a photon through space, as we know from optics, but to the paths found in a Feynman diagrams.Those diagrams are space-time diagrams. The Y axis in Feynman diagrams is time, X axis is space (which I guess is a distance). And the particles can travel just as well either in space or in time, either forward or backward in time.That example of how to graphically add phasors, while not wrong, was very misleading to me. It made me assume the Feynman path integral formulation was about the classical trajectory of a photon in space.Also misleading is he was talking aboutamplitude-probability, while I was taking that aswave-amplitudeof the photon. Then, another misleading overlap of concepts is between the square of theamplitude-probabilitywhich is proportional with the chances of finding the particle there, and the square of thewave-amplitude, which is proportional with the energy of a particle.That is, of course, if I'm not still in a totally misunderstanding of the idea, and still not realizing I'm still wrong.

author: EPAIII
author_rank: Super Contributor
timestamp: February 24, 2025, 07:27:02 am
content: https://quoteinvestigator.com/2018/12/25/universe/

author: Nominal Animal
author_rank: Super Contributor
timestamp: February 24, 2025, 09:53:04 am
content: Quote from: RoGeorge on February 23, 2025, 08:57:51 amWell, no. It is a commonly used tool in QED and quantum field theories. Other than that, I think you're on the right track.To repeat, the path integral is a mathematical tool to describe "all possible paths". Its value, or "result", is a description of the related quantum amplitude.Feynman diagrams describe the key contributions in a qualitative manner, ignoring the exact quantities and math needed to describe it.Quote from: RoGeorge on February 23, 2025, 08:57:51 amWell, no, not exactly. It depends on the interaction, you see.For example, when electrons are bound to an atom nucleus, they do not interact with each other like point charges: they interact like their charge is spread all over, according to the (squared) amplitude of the wave function. It is the entire wave functions that interact, not two points that have random location (according to their probability distributions) in space. (This is particularly important in simulating matter. In QM/ab initio simulations, each electron is spread over the entire simulated volume (repeating in all directions); in classical models, we use the atom to represent the electrons bound to it.) In this sense, the quantum wave function is a real description of the particle/wave/field. Other interactions can result in events like the electron being kicked out from the atom and flying off in some specific direction: then, we can point to "where" the interaction occurred, so those interactions localize the electron in a specific small region, with the (squared) amplitude of the wave function describeing the probability distribution for where that region ("point") is/was.We cannot measure the wave function directly, not even in theory, because all the interactions we know of are like that. This is also what the uncertainty principle and entanglement are all about: all interactions are between wave functions. If the wave functions are similar, their "overlap" –– not just in space, but also in all quantum properties, like photon energy = wavelength, electron spin, and so on –– is large, and the end result is entanglement, where the two are still very much fuzzy-quantumy-wavey, but determining the properties of one also determines the properties of the other, because otherwise the past interaction between the two would be inconsistent with reality. When the "overlap" is small, the interaction constrains one or both in properties. Uncertainty principle also means that for complementary properties like position and momentum, the more constrained one property is, the more uncertain/unconstrained the complementary one is, because these interactions themselves are quantized.Thus, the quantum wave function is not just a funny way to describe probability densities. It is a model that describes observable interactions precisely. I don't think of them as waves at all myself, just as descriptions of quantum properties that themselves cannot be directly measured.Those measurements are just normal interactions, and when the interactions constrain the properties, the observable values we see will have the same statistical distribution as the (squared) wave function amplitude. I guess "fuzzy blob with familiar-sounding properties" is the closest description.I suspect you will soon encounter the concept of "wave function collapse" and the related observer-related issues already mentioned in this thread. To me, they are attempts at trying to reconcile the human intuitive understanding of the macro-scale world with quantum scale descriptions. Interactions do not need to precisely specify the properties of the interaction exactly, they can just limit the properties of the interacting quanta to a subset. (This is all entanglement is, too.) "Wave function collapse" occurs when interactions cause those properties to be "exactly" defined. I don't think it is an useful way to look at interactions, and personally prefer to think that even quantum properties are similarly "fuzzy" and end up more constrained by further interactions. They can also get more fuzzy by interactions where the other has less constrained properties, so in my view, "collapse" is similar to thinking that sliding down a hill with a sled is somehow permanent and catastrophic. Exactly how reality does it, I have no idea: physics describes, it does not explain.Quote from: RoGeorge on February 23, 2025, 08:57:51 amOuch. No, quantum wave functions havesomeproperties that are analogous to measurable waves, but they do not describe measurable waves, and should not be thought of as describing measurable waves or vibration. Just like a bound electron having angular momentum doesn't mean it orbits the nucleus like a planet orbits a star.The main reason "wave function" name is used, I believe, is that the mathematical tools for solving these heavily relies on the complex exponential function, \$e^{i \, z} = \cos z + i \sin z\$, that we intuitively associate with oscillation. However, when \$z\$ is complex itself, \$z = z_\text{re} + i \, z_\text{im}\$, \$z_\text{re}, z_\text{im} \in \mathbb{R}\$, \$e^{i\,z} = e^{-z_\text{re}} \cos z_\text{im} + i \, e^{-z_\text{re}} \sin z_\text{im}\$, so again, I think the math actually describes a whole class of phenomena (diffusion, for example!) and is therefore useful in a wide range of stuff, but we humans intuitively associate those with natural wave motion and oscillation we observe everywhere in macro-scale. Yet, wave motion and oscillation are just a small subset of that entire class of phenomena. Pity we do not have a better human-language name for that superclass.This, that "wave function" is just a label and does not necessarily involve any kind of "wavering" or "oscillation" we're familiar with, is thefirst thingI usually explain to anyone I'm trying to tutor. It is also exactly why I try to post intuitive descriptions with corner-cutting, instead of exactly correct details, because getting the intuitive part right from the get go saves time and frustrations, and the exact details can be built on top.

author: RoGeorge
author_rank: Super Contributor
timestamp: February 24, 2025, 10:09:18 am
content: Quote from: EPAIII on February 24, 2025, 07:27:02 am("Reality is not only stranger than we suppose, but stranger than we can suppose.")The Universe is strange, indeed, but everything is strange at first.I mean, we (as humans) interpret our observation and all the experiences we have by classifying them according with previous experiences. Out of these previous experiences we have distilled certain categories/notions/ideas/definitions and other abstractions. Our life can be sen as a data stream, data stream we keep classifying and sorting it out by marching with previous abstractions already formed from previous experiences.Everything that can not be classified according with our inner concept tokens, is perceived as "mind blowing". Then we create new tokens for that "mind blowing" thing, then it is no longer mind blowing because we now have a category in our mind that matches with the "mind blowing" thing.Of course, each individual has a slightly different set of tokens/concepts already formed, each mind has its own set according to its former past (learning) experiences. So what might look "crazy" to one mind, might look "normal" to another.The funny aspect about how a mind works, is that a mind can be trained with dead-wrong ideas, either intentionally or not. Once a mind is boxed/gaslighted/filled with untrue token-concepts, that mind won't register the true meaning of facts and events and experiences it encounters, and will keep misclassifying everything according to the wrong tokens it has.That is why I always want to double check for myself even the most established theories, preferably by physical experiments. To make sure I didn't got it wrong in the first place, then to make sure the new tokens/ideas will fit with the ones I already have in my mind. I know it is not always possible to double check, but I'll never give up trying.

author: Nominal Animal
author_rank: Super Contributor
timestamp: February 24, 2025, 10:52:46 am
content: Quote from: RoGeorge on February 24, 2025, 10:09:18 amIt's even worse than that, actually. Un-learning is harder than learning. And even if you have the concepts in your mind and patterns in your thinking, just by forcing you to repeat others out loud will cause you to shift your concepts and patterns towards that speech. It is the underlying reason why I abhor forced speech, and want to allow free speech even when it offends and is crass and vulgar: new ideas and viewpoints, even if erroneous, and not being boxed in to any pattern are worth that much to me.(As I understand it, being forced tolistenhas a much lesser effect compared to being forced tospeakor write out loud.)I also love questioning, the act of asking questions, and looking at the answers to rationally qualify and examine them, often looking at the fragile spots where the underlying assumptions (that may or may not be true, and humans are often not consciously aware of them) show through. Often, the question itself is incorrect, because of those assumptions or previous conclusions, and one has to ask counter-questions to find out the truth of the problem at hand.(It turns out that I'm not well suited to Q&A sites like StackExchange, exactly because I'm not interested in just offering an answer: I want to include the context and the reasoning behind the question and answer, and that requires discussion. I'm not at all suited for "just the answer, please".)

author: dietert1
author_rank: Super Contributor
timestamp: February 25, 2025, 02:42:25 am
content: The progress of experimental physics is mind blowing indeed, largely enabled by progress in technology, especially in the area of electronics.When i was working at DESY in Hamburg in the 80s, our detection system was a multimillion $ machine with about 10000 detection channels equipped with ADCs and TDCs to digitize incoming signals. It had a complex trigger system to filter and record interesting events on magnetic tape. I remember building some NIM modules in order to implement a single track trigger meant for new particle search. For preprocessing it used kind of a microprocessor built from about 500 TTL chips. It would run at 20 MHz and we were glad when we could mod one of them to run at 27 MHz. At the time the system included a PDP11 computer for monitoring and data recording and a VAX computer for offline data analysis.That whole system would appear completely ridiculous in comparison to modern equipment. The top quark we expected to detect was only found much later.Regards, Dieter

author: Nominal Animal
author_rank: Super Contributor
timestamp: February 25, 2025, 06:21:55 am
content: Quote from: dietert1 on February 25, 2025, 02:42:25 amThe numerical data flow from CERN experiments is absolutely staggering for sure. I spent a couple of years a decade or two ago maintaining some computing clusters that shared in some of the processing work.I remember seeing a high-speed pulse counter card in a 80386 PC in maybe 1989 or 1990 when I was still in high school, connected to a particle detector/counter of some kind connected to an ion beam accelerator. The idea is simple: the card detects very brief pulses and counts them using a simple very fast counter, and the PC reads the counter value at sufficiently small intervals to account for overflow (during periods known to be "idle", i.e. between ion pulses). I don't think it even had pulse interval counting. I felt that was bloody amazing back then.Nowadays, high-speed USB (480 Mbit/s) makes thingseasy. Off the shelf developer boards like $30 Teensy 4.1 can easily sustain 200+ Mbit/s in one direction indefinitely, i.e. 21-29 Mbytes/second, to or from a Linux host using just the standard USB Serial protocol, and it runs at 600 MHz. Not to mention gigabit/2.5G/5G/10G Ethernet, and the ubiquitous optical networking hardware.It's not just research, however. For example, the detector technology developed for particle physics research directly lead to solid-state X-ray imaging with much reduced radiation dosages. Dental x-ray machines, for example, are much better and safer now, purely thanks to particle physics research side effects.Bridging the mathematical descriptions and physics tools to human intuitive understanding ishard, and I definitely appreciate the efforts those physicists that are good at it, like Feynman was. We need more of them. I still struggle with many aspects of QED, and was never happy with the related courses I took at uni.

author: m k
author_rank: Super Contributor
timestamp: February 25, 2025, 02:12:00 pm
content: A photon has a "clock" that creates what we call a frequency.That seems to be fundamental.A photon has has also a polarization.Don't know how fundamental that is.Interacting material has also a "clock" and polarization.Those all together creates the effect.There seems to be also photon and photon interaction.Don't know how real that is.https://en.wikipedia.org/wiki/Two-photon_physicsIntuition says that it's a by product.(photon is all space and no time)For the double slit thing, the fun part is that photon is quanta.So you can only measure it going through one slit, but that measured photon has also nothing to do with the interference.

author: Nominal Animal
author_rank: Super Contributor
timestamp: July 30, 2025, 01:50:31 pm
content: Quote from: Nominal Animal on February 24, 2025, 09:53:04 amA recent paper (Vitaly Fedoseev, Hanzhen Lin (林翰桢), Yu-Kun Lu, Yoo Kyung Lee, Jiahao Lyu, and Wolfgang Ketterle:Coherent and Incoherent Light Scattering by Single-Atom Wave Packets,https://doi.org/10.1103/zwhd-1k2t;MIT News article) proves this quantum theoretical description, by controlling the states of the atoms that act as the "slits" in a simplified quantum-scale double slit experiment, and thus the intensity of the interference pattern.In short, it shows that when simplified to the bare quantum essentials, interaction between the photons and the "slits" controls the intensity of the interference pattern, as one would intuit using the entanglement description/approach I outlined above. It's not like every photon either shows an interference pattern or not; it too varies. Very minor interaction causes only slight entanglement, with most of the photon properties (including location) "wavelike", yielding high-intensity interference pattern. When interactions strenghten, localizing the photon to one particular "slit", the interference pattern intensity drops. When the interactions are such that each photon is localized to a specific slit, there is no interference pattern.Put simply, when quanta interact, the result is not a single event, but a probability distribution of possible events. Further interactions further limit that distribution. Measurement occurs when a property is limited to a "single value" due to those interactions.For the wave-particle duality, this means that it is not either-or, but a point within a triangle having "wave", "particle", and "neither/undetermined" in the vertices.It is no surprise that we've developed concepts like "quantum collapse".

author: RoGeorge
author_rank: Super Contributor
timestamp: July 30, 2025, 03:23:06 pm
content: Can't find the paper to read what they did. The abstract contains the words "Gedanken experiment"?QuoteTo me, that means an imaginary experiment. Did they use any physical setup, and made physical measurements on it, or they just thought and reason about an imaginary experiment?

author: John Coloccia
author_rank: Super Contributor
timestamp: July 31, 2025, 04:13:17 am
content: There is no real wave-particle duality. That's a very ancient view, from like the early 1900s, when the situation was really very confused, and experiments lagged behind.We always measure particles. That's all. And they ALWAYS behave like point particles. Never wavelike when you actually force the issue. So they're particles.The theories you use to calculate expected outcomes have non-physical mathematical objects in them that are wavelike, along with a bunch of other non-physical mathematical constructs (spinors, abstract spaces, etc).The whole wonder of the thing is WHY do you need to use this abstract math to explain the behavior, and more to the point how does mother nature do it? It's all very unsatisfying.But there is no duality. It's particles. The mathematics that describe it have wavelike things. But the math isn't the thing, anymore than a complex number is an AC current.

author: woofy
author_rank: Frequent Contributor
timestamp: July 31, 2025, 09:06:18 am
content: Quote from: John Coloccia on July 31, 2025, 04:13:17 amI'm not seeing that at all.How do you explain the dual slit experiment which demonstrates the wavelike nature of light, or shining a UV light on a zinc plate and discharging a gold leaf electroscope while a red light of any intensity cannot. That's particle like behaviour.It sounds a bit like you are describing Bohmian Mechanics (pilot wave theory), which is not an interpretation of quantum mechanics I would go along with.

author: Nominal Animal
author_rank: Super Contributor
timestamp: July 31, 2025, 10:01:53 am
content: Quote from: RoGeorge on July 30, 2025, 03:23:06 pmThey did a physical experiment, where two cold atoms acted as the slit, with very low-intensity laser providing the individual photons, and the interference pattern observed parallel to the laser beam. That is, instead of having a barrier with two slits, they used two single atoms to scatter the photons, observing the intensity pattern of the scattered photons.Thus, it is not exactly the same as the double-slit experiment, but is analogous to it; this is the idealized/most simplified version of the double-slit experiment using individual quanta for the "slits" too. Essentially, each photon and the two "slit atoms" are the only three quanta interacting here, the minimum amount possible.Because the photons have a specific wavelength, the experimenters could control the interaction between the photons and the "slit atoms" by changing the excitation state of the two atoms.Quote from: John Coloccia on July 31, 2025, 04:13:17 amWhat do you mean by "particle"? In physics, it is a generic term used for smalllocalized objects.As an example, consider an electron bound to an atom, molecule, or crystal lattice. The electron is not a point orbiting around the nucleus, it is delocalized, with probability distribution in the non-excited state corresponding to the electron orbital models, even though electrons being leptons are considered to be basically point-like ("smaller" than 10⁻²² m). That probability distribution corresponds to the charge distribution. When two such atoms/molecules/particles interact at long distances (say one nanometer or longer distances), it is only the electrons in the outermost orbitals that interact; and they interact according to their charge distribution, and definitely not as if two particles were whizzing around their nuclei.When we talk about two such particles colliding at say room temperature (not hot enough for collisions to ionize, to kick out any of the bound electrons), the two probability density distributions do not even overlap: the particles' interactions are basically electrostatic. Approximation models like Lennard–Jones potential describe this, and because they reproduce well-known physical phenomena (like triple point, where gaseous, liquid, and solid phases are in dynamic equilibrium), are practically useful and thus usefully (even if only approximately) model physical reality.Put more specifically, interactions vary from very weak that do not e.g. localize the interacting quanta much –– the above long-range molecular interactions being one example; even given the specific trajectories of the two molecules before and after there are actually many possible "collision" trajectories between the two, because the trajectories are curved and does not have a specific point of "contact" at all –– to very strong that do localize particles very strongly. However, the weaker the interaction, the less information conveyed (and the weaker the entanglement of properties), so formeasurements, we prefer the stronger ones: they provide more information.(Another similar "wave-like" interaction is surface plasmons in nanocrystals, andquantum dots(or semiconductor nanocrystals) in general.)The entire idea of treating measurements (both single measurements, and sets of measurements) as probability distributions in the measured variable thus links to entanglement. Particle properties like location are "easy" to measure with small measurement error bounds (tight probability distribution), so we normally repeat the measurement many many times to build a picture of the total probability distribution –– and in that sense, John Coloccia is correct: we measure particles; but only because that is much much easier, not because everything is a particle. However, it is still possible to measure "wave-like properties" as well, by setting up the interaction or process to be measured with weak interactions. To more easily record the results of such interactions, we do tend to use methods like the photoelectric effect (image sensors for example), so one could say "we measure weak/non-particle-like interactions indirectly, and tend to measure particles", but that is just convenience.The best example of measuring wavelike phenomena directly and not as particles, in my opinion, isholography. Specifically, if you cut a holographic plate in two, you don't get different halves of the holographic image, but two copies of the original image, just with less detail in each compared to the original whole.

author: John Coloccia
author_rank: Super Contributor
timestamp: July 31, 2025, 11:14:56 am
content: Quote from: woofy on July 31, 2025, 09:06:18 amNothing Bohmian about it. Just the opposite, in fact. Don't confuse the mathematics of the thing with the thing.I don't explain the dual slit, andneither does anyone else. I calculate where the particle is likely to end up. The ONLY thing I actually know is my measurement, which is the detector goes off. And whenever the detector goes off, you always measure a particle...not a wave, not a part of a wave. It's either there or it's not. It's very un-wavelike.

author: John Coloccia
author_rank: Super Contributor
timestamp: July 31, 2025, 11:43:14 am
content: Quote from: Nominal Animal on July 31, 2025, 10:01:53 amYou're describing scattering. When you do a scattering experiment, you don't measure the individual electrons, unless you knock one out or create one in the process. In those cases, the measurement is always a particle, not a wave.By "particle" I mean the thing that you actually measure, which is all the information that's knowable.Quote from: Nominal Animal on July 31, 2025, 10:01:53 amUltimately, any such experiment would require detecting a particle and it's properties.Quote from: Nominal Animal on July 31, 2025, 10:01:53 amBut you aren't measuring the wavelike properties. You are measuring the individual photons that arrive at your eye, or your detector.The wavelike nature exists in the mathematical formalism. No one has ever observed it, and whenever you try you ONLY ever see the particle. The particle has wavelike behavior, which is described by the formalism. But the formalism isn't the thing.This is sorta like the old Einstein-Bohr arguments. The only way it's moved forward all this time is:1) take the equations seriously2) stop fretting over "how can that possibly be??"3) you know what you measure...everything else is unknowable and at best, a wild guess. At worst, misleading and unhelpful.So like even the idea that light travels in straight lines is unhelpful. Or the idea that it "travels" at all. You setup an experiment, and your detector goes off or it doesn't. It's sometimes useful to imagine that light went from the source, to the mirror, bounced off and ended up in your detector, but this is just visualization and is not part of the formalism. The formalism is "tell me how likely it is my detector goes off."

author: Nominal Animal
author_rank: Super Contributor
timestamp: July 31, 2025, 06:45:30 pm
content: Quote from: John Coloccia on July 31, 2025, 11:43:14 amNo, I'm not. The charge distributions of two delocalized point charges interact according to precisely their charge distributions, not as if two point charges randomly jump around according to their probability distribution; even a simple simulation shows these two produce very different results in specific test cases.In other words, my point is that you actuallycanmeasure the effect an individual electron or photon has, even with weak interactions that do not cause the electron or photon to be precisely localized.Quote from: John Coloccia on July 31, 2025, 11:43:14 amI was taught to call thosemeasurablesinstead, or perhapsquantized properties. Definitely not "particles".Human language is the biggest barrier here. I often point out that I am not trying to be text-book exact here (online), but instead try to convey an useful intuitive model anyone can build on. This is because most interesting discussions and ideas nowadays tend to cross knowledge domains, andintuitioncan generate such, as long as the intuitive model or understanding is suitable.Just memorizing our best current physical models and the mathematical tools to manipulate them tends to not generate anythingneworinterestingin my experience, so I'm not interested in repeating those verbatim. And, there are excellent reference books and lecture notes on all physics subjects, much better than I could ever write, so my focus is in trying to help with the intuitive understanding.A very important distinction fromparticleisquantum(whose plural isquanta). For example, I do not like to treat photons as particles (with a preciselocation), but as a quantum ("wave packet") with specific momentum (\$p = h / \lambda\$), energy (\$E = \frac{h c}{\lambda}\$), wavelength (\$\lambda\$) and frequency (\$f = c / \lambda\$), and trajectory.I don't care about is precise location at any specific time, only its trajectory and energy (or wavelength or frequency or momentum) involved.Consider the rod cells in the human eye. In optimal conditions, the cell is capable of sensing an individual photon. These photons are not very tightly localized, as it is arborbed by the chromophore "dot" attached to the photoreceptor protein. The photon is not spatially tightly localized; we only know it hit the chromophore, but not where it hit that chromophore. (Surface plasmons in nanocrystals absorbing a photon occurs in a very similar manner. The outer electrons in the nanocrystal arecoherent, and the absorption is such that the photon is not localized better than the entire surface of the nanocrystal, because of the coherence.) I just don't think you can call a photon quantum delocalized over several atoms a "particle" anymore.Quote from: Nominal Animal on July 31, 2025, 10:01:53 amIf we go by the standard physics definition, whereparticleis alocalized object, then no.It suffices that the property being measured gets quantized.For human vision, it means that one or more photons with suitable energy hits a chromophore often enough to activate the photoreceptor protein. The chromophore is a large molecule, but the absorption event is such that the photon cannot be localized any tighter than "it hit the chromophore somewhere". However, the energy that photon has will be rather precisely quantized by the process that converts the energy of the photon to the chemical activation energy of the protein itself. Thus, it is the energy, and not location, that gets quantized here. If you try to model this process as if a point-like photon impacts one of the point-like electrons on the outer "surface" of the chromophore molecule, you'll get results that do not match biophysics experiments with these cells.Quote from: John Coloccia on July 31, 2025, 11:43:14 amThe mathematical model is the physical description, not the human understanding. If you want synergistic cross-discipline results, the math alone is not sufficient: you need a suitable human understanding that can make the leaps the math does not even hint at.In my opinion, "just use the formula, and don't try to think what or how", directs humans towards rote memorizing and repeating without any insight or understanding, and is therefore useless.Feel free to disagree, but do note that this is written for laypeople and non-physicists/non-mathematicians, intended to build a better intuitive understanding that supports the concepts needed to apply the physical models and math, not repeat verbatim what every physicist learns in Modern Physics 101.

author: John Coloccia
author_rank: Super Contributor
timestamp: July 31, 2025, 09:47:15 pm
content: Quote from: Nominal Animal on July 31, 2025, 06:45:30 pmBut this is the point. They "interact" in the mathematical formalism (they "bump" into each other and do something...that's scattering). But we never "see" the interaction. What we see is what we can measure (you call themmeasureables...American physicists call themobservables, just fyi), and what we measure is always, ultimately, a particle.I think we've generally done a disservice to lay people by both making it more magical than it is, while at the same hiding the the real beauty and wonder of the whole thing. It's not that there's a thing that's sometimes a particle and sometimes a wave.It's a completely new object. It's always a particle, and that's all we can ever actually ever see, but it's dynamics can described by completely abstract, mathematical waves. It's not so much that it changes back and forth, which is kind of like voodoo, but once you get past the voodoo then you can sort of start to understand at least some of the simpler experiments.It's more like "how can this practically featureless, incredibly simple particle have such rich behavior?" If I tell you the mass, charge and spin of the electron, I've literally told you everything I possibly can about it (ok, there's one more thing, but it's just a different kind of charge). THAT's the mind blowing part. How does mother nature do it?? It seems impossible. How can it know it's supposed to show up HERE?And this is why Einstein wanted so much for there to be hidden variables. Bohm even concocted such a thing, and it's so philosophically ugly that even he didn't like it.

author: John Coloccia
author_rank: Super Contributor
timestamp: July 31, 2025, 10:14:26 pm
content: Imagining what you can not measure/directly observe is a useful visualization if you don't take it too seriously. Like, it's useful to imagine waves, sometimes, and it's useful to imagine that light actually travels through space in a nice, continuous way. Like, it leaves the light bulb there, travels through space, and hits a receptor in my eye. That's not unreasonable. But it's also like intellectual shackles, and without getting into it, raises additional questions. In a loose sense, it rhymes with the need for renormalization and the tension between the standard model and relativity.If you take the visualization it too seriously, you'll never ask questions like, "Could we exist in a simulation, i.e. just calculations in some computer, spitting out observables consistent with physics?" Not DO we, but COULD we. And this is a really interesting question, because then you ask things like:- what is calculable?- what ISN'T calculable?- what would such a computer look like?And these questions give you real insights.And oddly enough, some other interpretations and insights make the idea of the wavefunction THE fundamental thing that exists, and it's the measurement that's the illusion, in a sense.

author: RoGeorge
author_rank: Super Contributor
timestamp: August 01, 2025, 06:42:01 am
content: Quote from: John Coloccia on July 31, 2025, 10:14:26 pmI don't follow. Insights about what?

author: John Coloccia
author_rank: Super Contributor
timestamp: August 01, 2025, 07:48:55 am
content: Quote from: RoGeorge on August 01, 2025, 06:42:01 amAbout physics. As an example, Deutsch wrote a paper in 85 (I can probably find a link) that talks about some of these question, and makes an argument for why Many Worlds should be taken seriously. Incidentally, he would probably also have a strong negative view of wave-particle duality, since it kind of spoils Many Worlds and is not necessary.

author: RoGeorge
author_rank: Super Contributor
timestamp: August 01, 2025, 10:04:12 am
content: If you mean this Deutsch:https://en.wikipedia.org/wiki/David_Deutsch, then no, I've tried looking at his stance in the past, and ended up dismissing almost everything he claims. Or maybe he's only really bad at communicating, and I couldn't understand what all that was about.Those ideas doesn't make any sense. And even if it were to make sense, they are not disprovable, can not be tested, and with no practical applications, so to me that's no different than discussing how many angels can dance on the top of a pinhead.As for your question regarding simulation, (by the way you put it, you seem interested about the possibility of living in a simulation - but I might have misread that). Yes you could be "calculated". You do exist, don't you? The objective reality can "calculate" you. So, yes, you could be in a simulation, but most likely you are not in a simulation, but a part of the physical world, and the Universe "calculate" everything in it, including "calculating" you and I.This reminds me about the "brain in a vat" idea. If you were to be just a brain floating in a vat, and be fed with (fake) datastreams simulating what you know as "physical world", then you wouldn't know. And you wouldn't be able to prove or disprove anything about that, simply because for you (the brain in a vat), the "physical world" IS that fake simulated data stream.There are two very distinctive "realities".- there is an objective reality: the physical Universe, with all that is out there, whether you know about all those out there or not- then there is the inner reality: an internal representation of the objective reality. The inner reality is only a draft model. Can never be a complete representation, that would mean to be the universe itself. So we all have to make the best out of this draft model. Not only that the inner reality is incomplete, but sometimes can be simply wrong (e.g. heliocentrism).The objective reality is the same for everybody, yet the inner representation of that usually differs (more or less) from one individual to another.With this demarcation between the objective reality and its internal representation inside each one's head, those questions are no longer puzzling.- what is calculable?- what ISN'T calculable?Any reducible phenomena could be calculable, as long as you know it. The physical world is an analog computer, if you want to see it that way (from the perspective of information technology). There is structure and predictability in the physical world.So, from the perspective of the objective reality (of the Universe itself) everything is calculable. Saying this because the laws of physics seem consistent to me. From your perspective, a brain, you'll have to have the knowledge (the model) first, then you'll have to have enough computing power to run that model.As about what isn't calculable, from your perspective, anything you don't understand (don't have a model) is not calculable.Even more, anything that will require too much time, or too much computing power may be not calculable for you, even when you already have the model.From the perspective of the objective reality (if you were the Universe itself), then anything is calculable.Again, saying this because the laws of physics seem consistent. All the clues around make me think an objective reality do exist out there, independent of what I think about it. So yes, since the Universe do exist and it's consistent, then it must be calculable.(If so, next question would be if there is any randomness at all in the Universe, or if random things only appear to be random to us, because they are very very complicated and hard to predict? - That's a very old question, and nobody knows for sure, I'm inclined to dismiss randomness).- what would such a computer look like?Can be a wet brain, a digital computer, a toy model. Can be anything, depending on the needed level of details. The ultimate computer to simulate the Universe is the Universe itself.The only complete calculation of the objective reality is the physical world itself. Parts of it can be modeled by anything you can envision, anything that can run your model. So, the computer can be pretty much any form and shape, but the simulation results will be limited anyway, limited by how accurate is your model, and limited by the computing resolution of your device. A toy boat is such an example of a computer to compute a real boat. Or you can simulate the floating of the boat in Python, or in a video game. Doesn't matter, anything goes.Again, you can not simulate the real thing. You can only run a model of it. And that model isnotthe real thing, it is what you *think* it is. And no matter how close your model would be with the real thing, the model will always be incomplete, unless you are the Universe itself.

author: John Coloccia
author_rank: Super Contributor
timestamp: August 01, 2025, 10:29:59 am
content: Yes, you misread the point of considering the simulation.You really should read his 85 paper on computation, and forget about Wikipedia if you have a real interest in this.

author: m k
author_rank: Super Contributor
timestamp: August 01, 2025, 01:25:07 pm
content: Deutsch videos thought me once how to calculate with observables, qubit was also present.From me that knowledge is long gone now, but maybe it was more difficult than I remember since Deutsch himself was also slipping here and there, or maybe his thoughts just went so much ahead.

author: Nominal Animal
author_rank: Super Contributor
timestamp: August 01, 2025, 02:28:49 pm
content: Asthis recent Nature article outlines, not even physicists agree on what is the best/most proper/most effective/most useful human description or analog for the underlying models defined using mathematical expressions.Quote from: John Coloccia on July 31, 2025, 09:47:15 pmTrue: we usually cannot directly observe/measure the actual interactions, and almost always have to use indirect measurements. (And yes,observablesis even more common, although it has connotations to quantum mechanics and wave functions that can cause premature jumps in intuitive associations for learners.)Quote from: John Coloccia on July 31, 2025, 09:47:15 pmI disagree, because "particle" implies specific location, and there are many practical cases where the location is not well determined at all. I do like "quanta" or even "packets" better, but only because it seems to me the word "particle" implies small size and a specific location. Again, language issue.Quote from: John Coloccia on July 31, 2025, 09:47:15 pmWe are in absolute agreement on this.There is no magic, just different behaviour than what the human brain has evolved to deal with. No magic at all. Our existing mathematical models reproduce basically all phenomena we've been able to measure. I am only discussing what kind of interpretations are useful for non-physicists and learners, especially for later building exact knowledge and understanding upon, and to raise awareness of how useful such intuitive models are for cross-discipline innovations –– which of course are to be examined and probed and tested, including mathematically, to see whether they are useful for not."Quanta" are not sometimes a particle and sometimes a wave; it is just that their behaviour is such that past physicistschose"wave-particle duality" as one of those analogs used to build intuitive understanding. It is not even an approximation, it is a human analog for intuitive understanding only.I suppose I object to "everything we measure is a particle" mostly because the word "particle" has specific connotations that I believe can lead a learner/non-physicist astray. To them, a particle is like say a dust particle: a point-like object. Quanta, for example photons, are not really point-like, being able to form interference patterns with itself, and so on. Most of our measurement devices can be described as operating on particles, but again, especially with photons, at the atomic scales, the interactions (like photon-phonon interactions, when a photon is absorbed by the coherent outermost electrons in an atomic lattice) just aren't point-like.I do find my objection funny/ironic, because my own specialization is classical atomic and molecular simulations and specifically simulator development (computational materials physics); where everything (atoms) are definitely point-like particles, and Newtonian mechanics suffice. However, in ab-initio/quantum simulations (DFT), atom nuclei and innermost electrons are described as point charges, with electrons described using electron density, with forces due toelectrostatic potentialonly. While conceptually simpler, it is mathematically much more work, but is precise enough to describe the unexcited states of basically all molecules we've been able to measure the structure of. If a competent programmer decided to shift into ab-initio simulator development, going into it with "everything we can measure is particles", they'd have a horrible time understanding the underlying idea in such simulations.Quote from: John Coloccia on July 31, 2025, 09:47:15 pmThe aboveparts are my modifications, to reflect my own point. I did it thus to show that we're not arguing opposite sides, just approaching the underlying issue from different directions: how to bridge the gap between the mathematical models and layman understanding, to build a solid basis for further learning and understanding.Every single physicist interested in helping others learn about this stuff has tangled with this. It is why there are so many different analogies, and why even well-known physicists disagree on which ones are useful. It's not like this is precisely defined stuff like the math is; this is fuzzy, squishy, vaguely defined and varying in time human language stuff.

author: RoGeorge
author_rank: Super Contributor
timestamp: August 01, 2025, 04:05:58 pm
content: To me, with physics as a hobby and not as a profession, a particle means a small part, as in the real life (I've read particle is the Latin diminutive form of the word "part", as in "a small component"). A particle implies localization, and also implies being small, but not necessarily indivisible.By contrast to a particle, a quanta to me implies being indivisible. You can not cut/break/chop a quanta in smaller parts. Usually a quanta is also very small in size, but not necessarily. Thinking here, for example, about the photon corresponding to LW radio, or maybe even longer EM wavelengths. I picture such a LW photon as a fuzzy blob, not well localized and rather large, like a space with fog/mist/haze in it (and for some reason, my mind pictures that fog denser in the middle, and fading out towards the margins, though there are no well defined borders).

author: John Coloccia
author_rank: Super Contributor
timestamp: August 01, 2025, 04:38:30 pm
content: It's a technical term. The quanta of the field is basically an electron, for example. But as it's understood in QFT, it's really more a collection of properties, I suppose, that kind of stick together. Loosely speaking.But it's the electron for practical purposes of what we're taking about.

author: vad
author_rank: Frequent Contributor
timestamp: August 01, 2025, 06:41:14 pm
content: To my humble opinion, the term quantum has a broader meaning than particle (specifically - an elementary particle). A quantum refers to the smallest indivisible unit of a physical quantity that can be measured and exchanged.An electron, for example, is a quantum excitation of the Dirac field, and it is also an elementary particle.A hole in a semiconductor is a quantum of an absence of an electron in a valence band. This absence behaves like a positively charged particle with quantized properties, such as charge, mass, momentum. The hole is not an elementary particle though.A phonon is a quantum of lattice vibration in a crystal, and it has its energy and momentum. Phonon is not an elementary particle.

author: vad
author_rank: Frequent Contributor
timestamp: August 01, 2025, 06:54:23 pm
content: Also in my humble opinion, the simulation hypothesis (a hypothesis that our Universe is an artificial simulation run by some advanced intelligence) is not a scientific theory but a variation of intelligent design.

author: iMo
author_rank: Super Contributor
timestamp: August 01, 2025, 07:46:31 pm
content: Quote from: vad on August 01, 2025, 06:41:14 pmI wonder why today's physics still considers "particles". Which "properties of a particle" cannot be described by some theories of "fields"?PS: when there will be no "particles" the Feynman's idea on "integrating over the entire Universe" will work for everything (as the fields exist throughout entire space)..

author: John Coloccia
author_rank: Super Contributor
timestamp: August 01, 2025, 11:52:35 pm
content: Quote from: Nominal Animal on August 01, 2025, 02:28:49 pmI'm not trying to hide your quote. Just cutting it off there so my post doesn't take up 2 pages. I could talk about this stuff forever. I was doing a double major physics/comp sci in college. Dropped the physics before I graduated because the stupid chem labs were taking up all of my time, and I really had to choose one. LOL. But I've kept up, best I can.It never occurred to me that we were arguing. I really enjoy talking with other people about this stuff, and it's extremely rare I get to do it with anyone.Yes, you're right. The most successful framework we have is QFT. But I use the word "particle" because talking about QFT, trying to explain field excitations, etc., isn't going to mean anything to most, and I really don't think it changes the basic ideas. Ultimately, something makes a detector go off.I think we're in quite an exciting time at the moment, even though it looks just really boring. I mean, the standard model, more or less, is complete. In a sense it's mathematically complete. But we're still in a shambles. A different shambles than the 30s, 40s, 50s, and 60s, but a shambles nonetheless. We can compute more precisely...and that's really nice.But the fundamental incompatibility between gravity and the standard model is at least as stubborn as it's ever been.-Penrose is all in with wave-particle duality, thinks quantum gravity is BS. What we need is gravitational quantum physics, and BTW gravitational energy causes the (real) wavefunction collapse into (also real) particles (quanta....same thing)-t'Hooft thinks quantum physics is complete BS (and I suppose relativity too). What we need is cellular automatons (which is similar to Wolfram, I think...except Wolfram won't give any details? I dunno)-Susskind et. al, as I understand it, think space-time is emergent from entanglement-Carrol/Deutsch et. al. like many worlds (which also says wave-particle duality is garbage...just one gigantic wavefunction is real)-I think someone is still working on string theory? Feels like the Compact Flourescent Lamp of physics. I have to admit I don't understand ANYTHING about this, at any level other than the most fluff pop-sci level. I read a couple of Brian Greene's books.It's really exciting right now. It feels like either gravity (i.e. space-time) or quantum physics is an emergent property of the other. Or maybe they're both emergent properties of something else.This is why I'm really interested in ideas like what is calculable. The holographic principle is amazing too. It's almost trivial, but who expected that? Not that I think we're living in a simulation, or a hologram, or whatever. There's so much complex structure there, but nothing in either theory is complex, so where does it come from?It's like imagining that planets are pushed around by gods, according to their whims, and the weather, and the position of other gods in the sky, etc. And the reality is that they follow a really simple inverse square law. That's what this all feels like to me.

author: Nominal Animal
author_rank: Super Contributor
timestamp: August 02, 2025, 12:24:36 pm
content: Quote from: John Coloccia on August 01, 2025, 11:52:35 pm"Arguing" only in the sense of positing different views, in my opinion; no negative emotions involved at least on my part!I too like to talk about this stuff over a nice beverage just for fun. I often also play the part ofadvocatus diaboli, describing various fringe and foil-hat theories, just to pull out deeper thoughts than the easiest surface chit-chat. For example, one would be surprised to find how many physicists like to read about unexplained phenomena, UFOs et cetera, even though almost none will voluntarily talk about them! Fear of being socially labeled and ostracized by the "proper scientific community" is extremely strong.Quote from: John Coloccia on August 01, 2025, 11:52:35 pmMy goal is exactly the same.Let me tell you a background story. In high school, my chemistry teacher claimed that electronsorbitthe nucleus as point-like objects. Just a year later, in my first year at university, in the Introduction to Modern Physics (101) course, I realized how wrong that was. It was a lot of effort getting rid of all the related misconceptions and associations until I could actuallyintuitivelyunderstand the concepts ofdelocalized electronandelectron orbitals. Sure, I could do the math just fine, but it all only "clicked together" when I started developing simulation software, and read all sorts of papers on different approximations on atomic interactions and their physical basis models, years later.(It wasn't the teacher's fault: she was young, competent and had the degrees in the subject – and was an accomplished researcher in chemistry the last time I checked –, but just followed the lesson plans and chosen chemistry books too precisely. It was a highly-regarded high school, and we were knowledgeable students enough to immediately suspect the definition; also had had differential calculus and statistics just the period before, so I do believe we were ready to treat the model as an approximation only, with the note that it is an approximation only, with the actual exact models being the realm of quantum physics. I believe they chose the assertive approach to avoid risking the teacher's authority/believability, which I admit can be an issue with teenagers.)I've seen the similar happen again and again in computing. Power users and developers specializing in a single OS or environment develop intuitive understanding and associations about that environment, without ever realizing they are specific to that environment or OS and not universal at all; through hard work and experience, definitely making them more efficient within that environment or OS. However, when they switch, many of those turn out to be incorrect (in the new environment or OS), causing untold grife and unhappiness. It isdoubly hardto then learn the new environment or OS, because you have to first pinpoint, understand, andun-learnthose intuitive associations, before you can learn new ones. For many, it is too much, so they become extremely dissatisfied with anything dissimilar to their original OS or environment. I've seen this most often with Microsoft Windows, but that is just because it is the only environment that has basically the same assumptions it has had for the last two or three decades; all others have changed significantly – Mac OS has switched underlying architectures twice, Unix in general has always had quirks and differences between variants, and Linux has always more or less followed GNU and POSIX making it relatively portable across hardware architectures.Quote from: John Coloccia on August 01, 2025, 11:52:35 pmThere is similarity to computing, too. Programming languages haven't reallyevolvedin the last two or three decades, definitely not the way they did in the two or three decades prior that. We just have much more powerful computing hardware. There are singular new things like parallel and distributed computing, but the language interfaces for those haven't evolved with the hardware. Simply put, transport someone from the 1970s to today, and they'd be amazed with the hardware, but could really quickly pick up the changes in the programming languages. In my opinion (without any research to back it up, just anecdotal evidence and personal experience), it is all because we've stuck with incorrect analogs and intuitive understanding: we've hobbled ourselves. And, because our tool (software especially) development has targetedease for nontechnical users, next generations are unlikely to have any better understanding than we do.I'm not good or intelligent enough to develop my own programming language or do physics research that could break that cycle, so instead, I've decided to focus on making tiny incremental steps instead. For physics, the intuitive descriptions that support the mathematical models is one. For computing, changing the basic libraries, especially the C standard library, to something much better suited for our current OSes and hardware. I'll leave the Big Stuff for people with more brainpower and skill than I have.Besides, I'm often wrong myself.Quote from: John Coloccia on August 01, 2025, 11:52:35 pmExactly. The related models have been developed separately, and to unify them, you need cross-domain expertise; and that is rare.I do claim one roadblock is the incompatible mental models and intuition in those two domains, too. One only needs to talk to cosmologists and QM/particle physicists to see the differences. I fear that those who deliberately study both cannot meld the two, and just develop a skill to compartmentalize, much the same way security specialists develop a separate "attacker mentality" they keep in tight leash to understand how others might attack a secure system. We humans have evolved to do stuff that way, with each individual having different social roles at the same time, so all that comes to us naturally.Quote from: John Coloccia on August 01, 2025, 11:52:35 pmHeh... I do consider it mathematics only myself, at least until it can actually predict something we could not predict before, and do the experiments/measurements to verify.Quote from: John Coloccia on August 01, 2025, 11:52:35 pmYes; magical thinking is the real danger, and is the easier to fall into the further the models get from the intuitive everyday phenomena we've evolved to deal with.Un-useful intuitive models/understanding is only a step away from magical thinking, which explains why there is no agreement on which are useful and which are not.

author: Nominal Animal
author_rank: Super Contributor
timestamp: August 02, 2025, 12:29:06 pm
content: Quote from: iMo on August 01, 2025, 07:46:31 pmFields have no good analogs for us humans, which means the risk of treating it all as abstract math is very high, with no chance of cross-discipline innovations.Our models are so good and the discipline focuses so very narrow that cross-discipline innovations are the key for forward leaps.Think of annealing: without those (relatively rare) random jumps, you're stuck to a local optimum; with those random jumps (distance and probability controlled by temperature, both in the physical process and the computational analog processes), you've got a decent chance of finding the global optimum.

author: John Coloccia
author_rank: Super Contributor
timestamp: August 02, 2025, 03:48:49 pm
content: Quote from: Nominal Animal on August 02, 2025, 12:24:36 pmActually, I think someone who's only ever used Fortran would have a really hard time understanding modern C#. But for people that were a bit more adventurous, all the building blocks were in place VERY early on for imperative programming languages. Fortran introduced the concept, Lisp introduced lambdas (in the 50s, I think), and simula introduced OOP in the 60s. That's pretty much the whole ball of wax.But honestly, computers just haven't changed that much either. They're a lot faster, have complicated subsystems, etc, but conceptually they move sequentially from instruction to instruction. So if you're going to have an imperative language to program that thing, there's only so many ways you can describe (or try to hide) going from step to step.The declarative languages are more interesting, and really have evolved pretty considerably....and are also not always Turing-complete:SQL - turing complete with extensionsHTML - NOT turing completeProlog - turing completeyacc - not turing completeLaTex - turing completeI picked those 5 because they are so different from any imperative language, but they're also completely different from themselves. Which is often the case across declarative languages.Quote from: Nominal Animal on August 02, 2025, 12:24:36 pmI'm betting that one, or both, are fundamentally flawed. My gut, based on absolutely nothing concrete, is that space-time is an emergent feature of something we've yet to discover in the standard model. And when space-time goes away, so does all the trouble it causes. It's like you're sitting in the park, and it's a beautiful day, and everything is just perfect. And then a big, loud, smelly garbage truck shows up and starts emptying all the bins for the next 20 minutes. Yes, it's absolutely necessary, and we can't do without it. Space-time is like the smelly garbage truck. It's sooooo out of place.Maybe it's the other way around. Or maybe they're both smelly garbage trucks. It may take until someone makes an observation or invents an experiment that can probe the incompatibility. I'm not sure anyone even has an idea how to do this. You'd love to be able to look inside of a black hole. Maybe we'll find a source for micro black holes, and the radiation coming off tells us something? I don't think this will get resolved until we figure out how to concentrate enough energy into a tiny little spot so that we can actually probe gravity/space-time at energies where things might get interesting.That both theories are so incredibly successful that we're running our of ways to probe them, and that they stand up perfectly, is a testament to the brilliance and hard work of so many physicists and experimenters.

author: RoGeorge
author_rank: Super Contributor
timestamp: August 03, 2025, 09:21:07 am
content: Quote from: John Coloccia on August 01, 2025, 10:29:59 amIs this the paper?https://www.daviddeutsch.org.uk/wp-content/deutsch85.pdfAsking because somewhere inside that, there is a mention of another paper of his also from 85:Quote

author: John Coloccia
author_rank: Super Contributor
timestamp: August 03, 2025, 11:40:58 am
content: Yes, that is the one.

author: John Coloccia
author_rank: Super Contributor
timestamp: August 03, 2025, 02:03:42 pm
content: Quote from: Nominal Animal on August 02, 2025, 12:24:36 pmSo I did a bit of research, and I was wrong about it sort of dying out. And again, I'll readily admit that I do not at all understand it any deeper than pop-sci fluff, but apparently string theory is alive and well, and progress is being made.