New video coming soon about The Principle of Least Action, Part 2! - Urgently Requesting Feedback
Added 2025-02-27 17:27:19 +0000 UTCWe've got an exciting video coming up in the next few days!
In it, we prove that light doesn't just follow a straight line, in fact -- it takes every possible path!
This has been a mind bending video to make, but also super fun.
We'd love to hear your feedback and suggestions as we wrap up this video.
Is there anything wrong? Any other questions? Anything more you'd like to see? Explanations you think don't do a good enough job or lack depth? Let us know!
Thank you so much for your help and support!
-Casper and Matthew, on behalf of Derek and the whole Ve team
Comments
Reminded me of Feynman's QED book. I think it is like Huygens said with little wavelets and the source is tiny point sources as it travels and then when it interacts with matter a new point source wave starts and the phase front is perpendicular to the propagation direction so the 'trajectory' is a continuum of pointing vector that is 3D.
meg noah
2025-03-19 21:24:51 +0000 UTCSo, I’m still trying to figure out the relationship between orbital stability and a stationary integer series of vibrational modes. For instance, in acousics, a string or a column of air will have an integral harmonic series, and will be perceived as pitched, as a result of the structure of our auditory anatomy . But a membranophone has a non-integral harmonic series , and so won’t be experienced as a pitched sound, but still does have a variety of vibrational modalities driven by increasing energy input. And they’re “quantized,” in the sense that if the membrane is driven harder, it jumps to its next possible vibrational mode. What’s special in the orbital case that demands stationary node and integer divisibility of the orbital path length to guarantee orbital stability? I think I’m missing something; can anyone help me out? Am I being too literal in my interpretation of the animation?
Paul Weiss
2025-03-02 23:09:46 +0000 UTCI see why you are excited by the concept of action. In the video at 29:30 when the laser is being “blocked” by the black surface you can see the laser spot on the surface with your eye (via the video camera); this would seem to indicate that the laser spot is not being fully absorbed (blocked) by the black surface. If you can see this spot with your eye (via the video camera), the iPhone camera would likely see it as well. Please remove the grating in this instance and see if the iPhone camera still seems the spot (which if it does would then be more obviously reflected from the black surface). Thanks for what you do.
William V. Meyer
2025-03-02 16:48:43 +0000 UTCOutstanding video. I agree with others that laser pointer portion needs more time, explanation & controls to eliminate laser scattering
Keith Arnold
2025-03-02 04:10:54 +0000 UTCDarek is on 🔥! I just like that you're adding a practical experiences & contributions from theoretical research papers! beside being a science communicator!
Mohammad Nazzal
2025-03-01 01:27:18 +0000 UTCI'll try some more versions of this! I also got this to work with the light on! So we'll include that as well, so you can see where I'm pointing the laser. If time permits, we might even try it with a more powerful laser so hopefully the effect is more pronounced. Thank you all so much for this fantastic feedback! - Casper
Veritasium
2025-02-28 13:39:27 +0000 UTCWe'll update this to make it more clear, thank you so much! - Casper
Veritasium
2025-02-28 13:36:15 +0000 UTCWe will update the wording around this - you're right. The wavefunction explores all possible paths, the particle itself does not physically go to all possible paths. Thank you! - Casper
Veritasium
2025-02-28 13:35:34 +0000 UTCYes, we'll add animations! Thank you for the suggestion - Casper
Veritasium
2025-02-28 13:34:14 +0000 UTCWatched the new vid, got some “wow” factor response, and realized that I hadn’t internalized the content of the earlier Action video. Watched that one again over a two-hour period, repeating many 20-second sequences several tens of times each. (The last calc class I took was a full 60 years ago, and analysis-based math wasn’t part of my professional life.) Watched the new vid again, and had the base of the concept of Action more firmly in my grasp. There is one concept on the section of Bohr’s work that is not intellectually obvious to me: why are standing waves a precondition of stable orbits? A non-integral division of the orbit’s length should just create a phase shift at each iteration of the wave/particle’s trajectory, shouldn’t it? I’m sure that there’s a reason for that standing-wave assertion, but it’s not established in the video, and it’s not something that I can draw on from my fading memories. Other comments made by other Patreon commenters on the inherent reflectivity of both the black mask material and of the diffraction grating seem valid to me: how do we eliminate the possibility of scattered-light reflectivity from the observed results?
Paul Weiss
2025-02-28 11:07:58 +0000 UTCi second @TTST regarding laser experiment at the end - it's not uncommon to see light bouncing off various surfaces, even with lasers, thus it's not surprising we see two reflections. also the pace there is rather fast to comprehend what's happening there. maybe a simple animation of how the interference pattern in that case works would help.
Roman Rodak
2025-02-28 11:04:00 +0000 UTC@21:45 "as the particle wave follows a path, the phase will increase" Maybe this is the wrong video to ask, but why? Are you saying that the particle exists in all places at once and the thing we call "the particle" is just a localized intense phase of that existence and therefore measuring "the particle" along a path is just sampling the phase of the wave of its existence at that point? Is there prerequisite reading to this video?
chromicacid
2025-02-28 03:53:34 +0000 UTC@20:22 "...we start a stopwatch" @21:12 "...now in these examples the stopwatch is not actually measuring time" This was unclear when the example started. Would you explain the depiction prior to the explanation that they are intended to support?
chromicacid
2025-02-28 03:51:43 +0000 UTC@15:20 "...they must take all possible paths" @17:08 "...they must still be taking all possible paths" But why? Excuse the nitpicking of words, but what physical laws compels electrons to exist in all possible paths? You said, "because this is the way the math works out", but isn't the point of this video that "because the math says so" is not the final explanation? Or is this one of those thought experiments that needs constraints? Schrodinger's Cat example was from a lecture in which he described the cat in the box as an example of caution against taking the mathematics of the quantum realm and applying them to the macro realm. Source: https://materias.df.uba.ar/f4Aa2012c2/files/2012/08/Schrod_cat.pdf THE PRESENT SITUATION IN QUANTUM MECHANICS: A TRANSLATION OF SCHRÖDINGER'S "CAT PARADOX PAPER" Section "5. Are the Variables Really Blurred? " "One can even set up quite ridiculous cases. A cat is penned up in a steel chamber..." Does this "must take all paths at once" phrase need bounds?
chromicacid
2025-02-28 03:50:58 +0000 UTC@00:17 "that everything really is going everywhere all at once" hashtag Hyperbole? I thought that the principle of least action referred to "all possible trajectories that the system could conceivably take", not necessarily everywhere at once. Source: http://www.scholarpedia.org/article/Principle_of_least_action @08:28 The sparsely labeled vertical bell curve is a bit difficult to understand. Maybe you intended to eliminate axes for artistic simplicity, but I'm used to seeing a horizontal bell curve with no vertical line only if the measurement is 0 at dead center. The video later animates that "low" is at the bottom end of the graph, suggesting that the center is not 0. If the center is not 0, then there is often a vertical line to indicate that off-center origin. @09:00 Name the graphs and the lines where they intersect with the different graphs. If I'm understanding this correctly, the graph in the upper right is the classic model indicating the energy per quantum, the graph in the upper left is the energy spectrum bell curve and indicates the number of atoms that are able to emit that energy per quantum, and the graph in the lower right is the "experimental results" and indicates the wavelength actually emitted by that energy per quantum. Is this what is being explained? @09:04 "not enough atoms have the energy to emit that wavelength" How so? The intersection line with the energy spectrum in the upper left is saying that the number of atoms with the energy to emit that wavelength has almost peaked (nearing top of the bell curve), not dropped. Am I reading this wrong? @09:10 "...the spectrum peaks, and then starts to fall" Animation out of sync? Which graph is peaking, and which is starting to fall? The white ball in the graph on the upper right has not peaked and is not falling, the horizontal intersection line with the upper left bell curve has not peaked yet, and the vertical intersection line with the lower right graph has already bottomed out at 0. @10:55 "...gives you a hint..." Audio cut? I would like to hear what this hint is @11:46 Request that your artists draw the hydrogen emission spectrum as lightsabers. Those neon bars are asking for it. @14:21 I'm having trouble with the "standing wave" animation. Is this the wrong video to ask this question? IIRC, an electron is a 3-dimensional electric field emitter with mass, but the animation shows a one-dimensional line wrapped around a circle with a fluctuating amplitude of something or other. I'm having trouble rectifying the spherical field as a one-dimensional standing wave.
chromicacid
2025-02-28 03:48:07 +0000 UTCThe demo with the laser, black paper, and diffraction grating is very compelling. It happened very quickly and there were no arrows pointing out the exciting effect, so maybe consider improving that somehow. Nice tutorial! Thank you. I'll share widely when released.
TTST
2025-02-28 01:25:04 +0000 UTCI also had a hard time understanding what was going on with the laser pointer - it looked to me like it was just pointing at the black paper and reflecting off it.
Fran
2025-02-28 00:33:45 +0000 UTCSo if energy & matter are just waves, and humans are obviously matter, does that make death simply a wave dissipating? A return to the lowest possible state of action? Is bringing a child into the world the interaction of two unique waves experiencing positive wave interference?
Kimberly Green
2025-02-27 23:15:02 +0000 UTCI would also like to see the laser tip being coverred by a bit of a tube, as the front lens of a laser does scatter some of the red light, which is why you can see the front of a laser from the sides. It acts like a very dim non coherent light source. Then you see reflections, extremely dim, as you're using a reflective diffraction grating. where the peaks are scattering light, rather than a flat grill grating, or at least that's what I took away from that section.l
FatalXception
2025-02-27 22:52:11 +0000 UTCI agree with Charles, my view was that the camera picked up the reflection of the laser off of the black paper which is not a surprise as it would take very special black paper not to reflect some of the laser output even at 3 milliwatt. Having said that maybe I didn't understand what was happening. The Diffraction Grating was more impressive but here I am curious if the Diffraction Grating is actually non reflective and if the results might again be a reflection.
Kat Seibert
2025-02-27 21:35:46 +0000 UTCAgreed. a rotatable clamp so that the producer can rotate the laser (on) while the light is on and then repeat with the light off?
Poker Chen
2025-02-27 20:44:30 +0000 UTCPrior to this, I've read the explanation of light travelling in all directions in the graphical novel style biography of Feynmann. I feel instinctively that the book version was more clear than this video presentation from 20:00, even though it's almost identical. Perhaps this is just some sort of anchoring bias. For the laser demonstration at 30:00, I think you need a morr sensitive camera to catch the Bragg peaks, as they are not visible on my screen. Or, can the inset image and main image be swapped and their brightness adjusted? The third phase and third path clock is slightly visible at 21:20, which seems like a placeholder.
Poker Chen
2025-02-27 20:37:07 +0000 UTCme too
Donald J Arndt
2025-02-27 20:27:36 +0000 UTCAs usual it's very well done and the Feyman anecdote (which I'd never heard before) makes the point extraordinarily well. I think the intricacies of the math presented math may be lost on a lot of folks though.
Rich Murphy
2025-02-27 19:01:31 +0000 UTCThis video very well done and does make a lot of sense. But it is way above my level. In the part where the red laser pointer is being demonstrated, about 29:20, it seems to me that the laser is just pointing to the black paper over the other side of the mirror, and that the laser pointer is a small device that fits inside his hand and we cannot see what direction it is pointing. Further, you have a device to hold the light steady and another to hold the phone/camera steady, yet no device to hold the laser steady. If you could either draw lines showing the laser direction or re-do this experiment to show clearly what direction it is pointing it would help to show that the laser is doing what he says.
Charles S. Cook
2025-02-27 18:47:10 +0000 UTC
