Some light quantum mechanics (with minutephysics)




  • Really sad to see an aweful 3Blue1Brown video like this. Too much bullshits from munitephysics that does not touch the essense. Unless this is a sub-brand you are working on, stop working with minutephysics. He can only dilute your brand.

  • Thanks! Great video… Feynman's QED is an excellent book that addresses this and other quantum analysis of photons [Edit:- @ 0:45 Feynman lectures! Thanks again!!!] ✌🏾👌🏾

  • Great video. In case of photons there are two kind of waves involved: solutions of Maxwell equations and solutions of Schrödinger equation, the first describe photons macroscopic behaviour and the second photons microscopic behavior.

  • Saying "Energy in the horizontal direction" is sloppy, energy is a scalar quatity. Maybe "Energy from the horizontal component of the electric field vector" is better?

  • Saying that a photon is a discrete wave packet seems contradictory according to this very video since a photon is merely an electromagnetic wave in the lowest energy state. This wave could be an infinite plane wave in the minimal energy state, yet the 'quantum' in quantum mechanics is often explained via spatial discreteness rather than energy discreteness.

  • Whose brilliant idea was it to alternate slides with a black background with slides with white background? This makes it painful to watch in low light. Otherwise it appears to be satisfactory.

  • Oh, I thought that multiverse thing explains everything. Now I see that it doesn't. Or is there an explanation of this in multiverse framework? Look: I believed that when a 45° photon passes through 0° filter, then it passes with 50% chance, because in 50% of sub universes it is 0 polarized and in other sub universes it is 90° polarized. But this logic fails to explain 100% of chance to pass through 45° filter: with that explanation the chance would be 50% instead of 100%.

  • I am kinda understand some things. But not everything…
    Anyways, I want to know what happens to the blocked Photons?
    Where does their energy go?
    This could be a stupid question, so sorry but I am that bright…..

  • You say about light polarization on 6:32 is this representation of a bunch of photons, or it could be accepted for one photon as well? I mean, Would single photon change polarization from time to time?

  • U could of just draw a wave graph like as lines instead of all the moving arrows to help people understand at the start but obviously I would never argue with u lol good video:D

  • 18:03 is not more discrete numbers but more that light is elector magnetic wave by using Pythagorean theorem every component of x^2-(iy)^2=1 (100%) 85% is carried as electric field witch human eye can see and 15% as magnetic field. Absorption filter is very bad term. Absorption of light by opaque material called Beer – Lambert law coincidentally uses also exponential function , Beer – Lambert law shows absorption of light by defects inside opaque material this absorption is not reversible is lost as heat inside material (entropy), polarization materials light "absorption" is reversible.

  • I am so mad at you guys – this video literally says all of the things I was yelling at the screen as I watched the video on the other channel, that each filter was changing the polarization of the light and modifying its ability to go through the next filter, etc.. The other video was infuriatingly full of feigned naivety, apparently. -_- At least I feel vindicated after you confirmed my whole understanding in this video.

  • Why don't you two use the phrase "wave packet"? It seems perfectly natural to me to think of a particle governed by wave equations when you realize that the particle isn't a discrete object but an object-like "packet" in a field, and "wave packet" denotes this pretty nicely IMO.

  • perhaps the answer to the funky polarization problem is that the electric and magnetic fields are omnipresent; that nothing is passing through the glasses in a linear sense, only disturbances in the already present fields are occurring, so it wouldn’t be too difficult to imagine those funky effects when you stop thinking about light as traveling linearly, as if it has mass; or interacts with the Higgs field. Right? Slightly right? 22.5 percent right? Hmphf!

  • What happens if a photon with higher energy say an integer multiple like 2 or 3, thus having atleast one component along either the horizontal or vertical direction with energy greater than 1 quanta, is made to pass through a polarized filter?

  • I wish more of the discussion here explained what's actually going on with the polarizing filter. At a chemical level, the filter is absorbing and emitting the energy carried by the wave. Photons being reimited is what happens when electrons quickly jump between energy states, and that simply follows the classical mechanics of electric fields being wiggled. An electron moved, and thus its associated electric field also moved, propagating at the speed of light. If you think about light only as this electromagnetic wave, the behavior of polarizing filters makes much more sense. Simplifying back down to a simple, classical oscillation, the electric field imparts energy either enough to bounce the electrons up an orbital or not. That is, they either push each atom to a stable state momentarily or not. If an atom does go up an energy level, it releases the energy again when just enough loss occurs to cause it to drop back down to its stable state, causing a new electric field wave to propagate. Going back to the classical vector components, if the atoms are bonded in such a way that energy along one dimension is distributed among the larger structure and energy in the other dimension causes the atoms to violently increase (and subsequently decrease) their energies, the reasoning behind the quantum behavior becomes very clear. Either an atom reached a high enough level to violently wiggle an electron and thus cause a new wave of electric field changes to be propagated, or it didn't. Some energy of a polarized wave is absorbed because electrons can freely travel in that direction instead of jumping orbitals, and other energy is emitted again because the energy states of the atoms changed. Thus only a certain number of these electron jumps, and their associated photon emissions, will happen.

    It's only a useful abstraction to say that observation has an effect on a photon's state. What we really mean by observation is interception. The only way to observe something is for its energy to affect us in some way. For that to happen, thanks to conservation of energy, something has to change about it. That's pretty normal from the classical physicist's mindset. If the only way to measure the speed of a billiards ball was to measure the energy it imparted to another ball, we wouldn't say that the ball spookily knows we looked at its energy, but rather that our measurement of the ball's energy required us to absorb some of its energy and therefore change its course from what it would have experienced had we not interfered.

    In the same way, 100% of the energy of an electric field is deposited into a filter. That filter's electrons can move freely between atoms in one dimension but must jump orbitals in other dimensions or simply absorb the energy. Those atoms which absorb enough energy to emit the energy again by wiggling their electrons violently as they bounce between stable orbits and therefore generate new field waves emit those waves only in the orientation that is perpendicular to the free moving path. These are brand new photons. They're not the same ones that came in. Only some of the energy will be radiated again, but all that energy will be in the direction of the new energy jumps of the atoms in the filter. These new waves don't care about the state of the waves behind them, and thus the light can travel between filters without any hidden variable determining which filters they'll pass through and which they won't. The quantum nature here is merely whether enough energy was imparted in the right direction to cause an electron to climb to its next state or not.

    And it's worth noting that these energy states of atoms states too are regulated by continuous differential equations that converge on a few points. Either an electron has enough energy to be shot into its next orbital or it slides back down to where it started. It's almost analogous to shooting a ball up a ramp with notches in it. It isn't that the portions of the ramp without notches somehow don't exist, but rather that the ball can't stop there, and we just can't detect it in motion.

    Quantum is often taught as vastly different from classical, but it really is just abstracting the sinks and nodes of differential equations into distinct states because they are the useful bits. It's like characterizing a roller coaster only by its local minima. It's a useful representation when all you care about is in which spots the car ends up depending on how much velocity is applied to it. Quantum abstraction is useful, but it's important to understand it as just that- abstraction- and not some abnormal discontinuity with the rest of the universe. The tricky thing is that because our ability to observe really small amounts of energy moving around also requires us to significantly change its course, much is simply immeasurable.

    Anyway, off my soapbox I go. What do you think about this way of looking at quantum?

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