Why does light slow down in water? 

yup! that's me-.-.-.but it's my 2nd visit-.-.

My second visit 🤠

Third visit

It's not a surprise. Nonsense is easy to forgot. Since this explanation is not just factually wrong, but also can not be quantified, nor to give a qualitive explanation of any experience, it fails to build into working cognitive pattern. How could 2 waves be superimposed if the slower one is not present near the wavefront? The origin of the badly presented theory is this: en.wikipedia.org/wiki/Ewald%E2%80%93Oseen_extinction_theorem It is similar, but there are some elementary differences: the wave emitted by the electrons has the *same* speed as the original light, this is how it can cancel the original wave at the wavefront. This is some of the explaining power of this model: the generated EM waves travels with the same c speed as the incident wave. This power is missing from Don's false explanation.

Yup

And 24 seconds

Hahaha good one!

Happy birthday

@@nikhilnegi9446 good one !

How old are you now

I was just asking myself why it bends.

Knowledgeability is like the money in your wallet. Your decisions what to buy, and when, and how, is the giant rest of the universe.

Too bad it can't be true. Light travelling through a straight tunnel would have its speed altered by filling the tunnel with microwaves. This is not the case. Also it would affect light travelling through space. Over vast distances, the small amount of radiation in the cosmos would cause light to get blurred, which does not happen.

too many easy to follow videos, they all rephrase the observation instead of answering the question

​@@governmentis-watching3303 You're wrong.Microwaves don't change the speed of light because they also travel at the speed of light, like any electromangetic wave.

It's fun seeing your comments in the videos I watch.

I know right, I figured it was the scattering explanation before I watched the video.

Uh dunno. When waves interfere, their amplitudes add up, not their speed. And afterwards the merged waves do not unmerge.

Oh c'mon, do you subscribe all the channels that I subscribe ?? Ah! Try to subscribe your own channel like I do! Got you! Wait, you can actually subscribe the Blab with the Lab and vice-versa...noooooooo! :)

@@Geo_Knows_Things the waves do not merge "physically" We perceive them as a single wave when they're superposed. Really they can be seen as any number of waves , you can look up the Fourier transform if you're interested. The universe doesn't care, as long as the electric field is following the laws, any combination of waves could exist. What matters is the overall effect of these waves. If it's the same for 1 wave or the sum of 2 different ones , then either way is fine. Once light exits the glass, the second wave is no longer generated (since it only exists inside the matter where electron are) and the "resulting" wave is the same as the starting wave. As for the speed, I have multiple answers conflicting in my head, I'm not sure yet. You said only the amplitudes are added, technically yes, but the speed and other characteristics are just a way to describe the change of amplitude. The amplitude is not constant, both in time and space, so adding the amplitudes of the 2 waves in each and every point in time and at each and every point they occupy in space will inevitably alter the perceived speed/phase/frequency of the resulting wave.

I remember that in university on a wave physics course we where taught that η1/η2==ε1/ε2. It made sense back then, but I had not a good explanation until this video.

@@jorgealzate4124 The second wave is fiction, so this video adds more confusion.

@@dreamdiction Of course, there is no second wave in the sense of a "stationary wave" but there will be a second inducted wave as long a electromagnetic wave travels through the material. Thats because the way a electromagnetic wave propagates, it induces an electric (and a magnetic) field in the propagation medium (even in the vacuum), and because in this case, the fields are moving, so they are the induced field(s), which in turn will interact with the incoming wave, and all of this results on a localized, altered wave (please physists don't kill me, I'm tryng to make myself clear, im just an engineer doing office work :'( ), then the traveling wave properties will be related to the electric permitivity of the two mediums.

@@jorgealzate4124 as an engineer you should know that mixing of waves gives you sum and difference frequency waves. However this is not the case in the medium, as by fundamental law the frequency stays the same, only the wavelength changes. Collosal error in this video.

This is what happens when you opt stem but you can't understand it 🤣🤣🤣

Exactly, he functionally didn’t explain anything

@@igorjurdana1311 because he is wrong, it doesn't work like that, the speed is the same, it is the PHASE that goes back slightly, really the speed of light is the same, it is the appearance that the phase gives that makes us believe that it is going slower

@@benjaminojeda8094 I agree ! It's exactly what I've understood after a ton of science videos....🙂

They were right and this guy is just an idiot clone mouthing 'Physics Doctrine Think why and how light is bent by a star's 'gravity' And light is neither a particle nor wave and that's why we can't have anything nice

@RogerWilco99 metals have free moving electrons that aren't attached to any particular atom. That's why they're conductive. But electrons are also what absorb light. So by having tons of free roaming electrons, it creates an impenetrable wall. Though it's worth noting that a thin enough sheet of metal actually will be transparent.

The density of glass is the reason that refractive indexes are different, as more dense materials have more atoms which also have electrons creating a new EM wave, so the net effect is a slower light beam, with the speed in the material being proportional to density

Oscillating electromagnetic fields with photons of light and electrons of matter having most of the fun (with nuclear weapons and radiation occasionally doing heir things with strong nuclear force and weak nuclear force respectively with protons and neutrons heir respective quietly up up down and down down up quark compositions, and of course spacetime itself being bent by mass creating what we like call gravity, I think I just summarized modern physics).

@@JmO-ee1bi Photons do not exist, electromagnetic radiations is waves at all frequencies.

"super cool physics wardrobe" Bwahahahahahah so true!

He doesn’t know anything he’s just standing there reading

@@rogerc23 His tribe are constantly inventing ways to pretend they are more clever than everyone else, they even invent whole subjects as a pedestal to pose upon. Relativity is a hoax and quantum mechanics is a fiction created by treating waves as if they were particles and then claiming the particles really exist. Their vanity has reduced science to a belief system, like religion.

Electrons absorb photons when they subjected to them. They re emit it after some time

@@mubashir22ful I know that. But he said "when atom has been absorbed by a photon" which is the other way round😂

Yes you did. You missed everything. Atoms are not absorbed by photons, also this is a wave phenomenon, not a particle phenomenon.

Wayne Adams Yea I think it was kinda the joke that photons DONT usually absorb atoms.

PastafarianBEAVIS PROscience Wow that was a very scientific explanation for saying the wrong words, lets hope it really was just that...

I think it's (at least partially) because electrons have a tiny amount of mass which prevents them from moving at the speed of light. Photons don't have mass which allows them to move at the speed of light

@@myagrimm4719 great explanation

Please Bro if you find the answer to your question can you explain to me why the wave created by the electrons moves at a different speed 9:20 and also why the combined new way moves slower than the speed of light 9:43 ? Please bro I didn't find why...

They don't. The video fails to explain why that it.

​@@Khalid-Ibn-Al-Walid The combined new wave does travel at the speed of light. The thing that is sower is the group velocity, which is what we are interested in.

I think that everything is vibration: a wave in a field. WE just perceive things as particles, thus, when measured, AS a particle, we get particle-like answers. However, every physicist, and most people, understand that there isn't ANY matter. Thus, no matter to be broken down into particles.

You may have a long wait. Or just ask God, now.

The biggest misconception about light is that physicists think that photons are point objects where time and space don't exist, including Fermilab. Well truth is Photons have a volume proportional to the their wavelength. Photons definitely experience time and space as well. Einstein is wrong.

@@johnnybinghamton2117 Einstein was wrong and Johnny Binghamton is right. What a surprise... Have you written an article to back up your claims?

@@johnnybinghamton2117 here, take your Nobel 🏅

@@johnnybinghamton2117 why dont you write down equations that prove your point, and lets have observations and experiments that support your claims and equations. like Einstein did. until then, cease and desist

@@johnnybinghamton2117 If the electrons moves, that means the light looses energy and wouldn't regain speed in the same direction. I think the best explanation is that light doesn't interacts with the glass at all. The glass expands space-time, the more space, time and speed slows down, it's the relationship between space and time from relativity theory.

It's indeed fascinating, light and x-rays are both just different wavelengths of the electromagnetic spectrum. Different materials are more or less transparent to different wavelengths. So what appears opaque in one wavelength is transparent in another. When working with materials/shaders in 3D programs, IOR is also important for opaque objects as it controls their reflectiveness. There is also a distinction between dielectrics = wood, glass, plastics (strongly bound electrons) vs conductors = metals (freely flowing electrons). :)

@@SuperemeRed I felt like a genius when reading Project Hail Mary by Andy Weir and the alien left a bunch of opaque tiles except one - I realized imediatly because this fact about the EM spectrum stuck with me. Really great book. If you have not read it, I recommend it.

Thank you

If you don't have time for a 10 minute video you have issues

@@disgruntledwookie369 if you needed to watch this video to understand why light doesn't pass through other materials like it does through air, you also have issues..

Sunny shah Light always takes the shortest path...

I think it‘s because the lightwave gets influenced by the electrons. When it has passed the material, it gets faster again and changes the direction back to its original

.

This can be explained with Huygens principle of waves. It states that every point (particle if the wave is mechanical, i.e sound) touched by a wave starts propagating it by its own. Because of, you know, singular points propagating the wave, these propagate it on a sphetical way, not straight. But they end up combining to build the shape you put in the water without scattering. This is why you can see the tip of the pencil submerged under the water, not a giant yellow blob of light. *i didnt really know how to explain this part, so please search "huygens principle" on google images and use any of the first results to ilustrate my explanation. Or look for a better one while you are at it, whatever* Lets imagine you can stop time just on the moment the light of a laser is going to touch the water. Because the laser is kinda tipped, the light comes at an angle, and the light "front" is perpendicular to the ights direction, so parts of it will touch the water before others. When the light REALLY STARTS to touch the water only one of the tips of the "front" _is_ , the rest is still just hovering on the air. The particles of water touched by the tip propagate the laser light, but a big chunk of the "fronts light" emitted by the laser isnt touching the water yet. By the time another chunk of laser has touched the water and the points have started propagating it, the "sphere of light" propagated by the particles touched before is bigger. When the laser has entered the water entirely, the spheres of light propagated by the points touched first is significally bigger than the spheres of light coming from the points just touched. Then you can connect the spheres with a straight line, that shows you the new wave "front". Knowing that the "front" is perpendicular to the wave, then you can draw the new wave direction, and see *not only does it change, it is **_more vertical_* . I hope you understood this or helped you and the lurkers looking for answers to this xd.

Light must synchronize with the shape of a structure, resulting in deflecting and vectoring do to the principle of two or more elements attract called Gravity, light must randevu around elements like objects do among solar system and planets in the path, it must like so with nutrons,atoms ions etc..., because it cannot actually go through an element or it will no longer be, so until a path is merged by structure form.

Please Bro can you explain to me why the wave created by the electrons moves at a different speed 9:20 and also why the combined new way moves slower than the speed of light 9:43 ? Please bro I didn't find why...

@@Khalid-Ibn-Al-Walid it does not. The reason is in innertia due to mass of electrons which means it takes time to accelerate them and waveform to "grow". So it lags behind the original wave.

Fermilab is wrong, it doesn't work like that, the speed is the same, it is the PHASE that goes back slightly, really the speed of light is the same, it is the appearance that the phase gives that makes us believe that it is going slower@@Khalid-Ibn-Al-Walid

And slower still in Guinness!

Dave Dewhurst it never reappear after a Guinness

@@JohnnyMotel99 Aye, and this is where we get the phrase "blind drunk"...because all the light we need to see by is absorbed by the booze. See how everything makes sense on the internet?

I'd figure in Ireland it was because the light was depressed it wasn't passing through whiskey.

But in Ireland, thirst is not quenched by water....

Please can you explain to me why the wave created by the electrons moves at a different speed 9:20 and also why the combined new way moves slower than the speed of light 9:43 ? Please I didn't find why...

@@Khalid-Ibn-Al-Walid The wave created by the atoms isn't actually going anywhere. It is an electrical vibration. Light is also an electrical vibration. There is a diagram of the combined wave at 7:05. You can see that the top wave is actually considered to be stationary. Anyway, that is the best I can explain. I became an engineer because I knew I wasn't smart enough to be a scientist.

@@JaimeWarlock I saw the video many times again and focused on the 7:05 as you said and I think I finally got it ! Thank you very much bro ! ( Btw me to I want to be engineer, in IT, I like physics but I find IT to be way more accessible and practical 👍)

And why does the new, slower wave does not generate a new wave, slowing down the light even more?

My guess. Because the speed of the electrons and the resultant wave is dependant upon the medium that they are part of. They are simply being agitated by the light.

i think because, unlike photons, electrons have mass.

My guess is that the wave generated is in opposition to the incident wave (moving in the other direction or even at other various angles) and the overall combination is impeding the initial wave.

@@pahom2 Thinking about it as 2 separate waves that you add together, is a human idea. What actually goes on is a complicated ripple in a pool called the electric field.

hahaha tell me how they measure the lifetime of a muon at rest? If they don't know the lifetime of a muon at rest, how do they know the life of the muon is extended by moving at velocity?

Please can you explain to me why the wave created by the electrons moves at a different speed 9:20 and also why the combined new way moves slower than the speed of light 9:43 ? Please I didn't find why...

The speed of light is not constant; bye, bye, Einstein.

@@melvynobrien6193 Einstein said the speed of light is constant in a vacuum, which it is, and is also reinforced by the explanation in this video.

Please can you explain to me why the wave created by the electrons moves at a different speed 9:20 and also why the combined new way moves slower than the speed of light 9:43 ? Please I didn't find why...

Please can you explain to me why the wave created by the electrons moves at a different speed 9:20 and also why the combined new way moves slower than the speed of light 9:43 ? Please I didn't find why...

@@Khalid-Ibn-Al-Walid Good question, but I don't think they went into an extreme depth in this video. For your second question, it's kind of simple. The "oscillated" field created by the electron is slower, so that would slow down the original light temporarily, until it speeds up again after passing through the object.

@@thechannelofknowledge5145 Thank you very much for answering ! But please why The oscillated field created by the electron would slow down the original light ? I can understand that if the field created by the electron is slower then it's light will reach us slower (the light of the electron) and it can also modify the structure of the original wave, but why would it slow the original wave ?

@@Khalid-Ibn-Al-Walid Sorry if I do not give a good or correct explanation, but I think that the field created by the electron isn't exactly light. I believe they said it is an electric field. If it was an electromagnetic field instead, the original light wouldn't slow down, as photons don't interact with each other. Anyways, the electric field would start slamming into the photons, causing them to slow down. Since photons are restless, they would speed up again after passing through the container. Since I do not have a correct answer for this, it's more of what I think that why the light slows down.

His name is Don Lincoln, Fermilab is the name of the lab he works in.

@@Vagabond-Cosmique yeshh

I'm no physicist, but here goes: 1. I think the question here is 'why does light refract through a medium?' (you should watch a video on this - very simple) 2. No. Firstly, I think you mean 'superimpose' rather than 'cancel' as for two waves to cancel it implies that the wave height has become zero. It was stated in the video that when two waves of different speeds superimpose, the resulting superimposed waves net velocity is 'slower', as for why this is exactly, I'm not sure, but it would imply that it does not ever become 'faster'. The speed of light is calculated by [wavelength * frequency], take it from there... maybe... 3. The light will either interact with the electrons of the atoms or it won't. This interaction will only slow light, not change its direction (refer to 1. 'refraction'). 4. It isn't blocked, but reflected, some light will get through. A solid material reflects the wavelengths of light that give it it's colour, e.g. a red brick absorbs all wavelengths of light, except for red wavelengths, which it reflects to your eyes. 5. Electrons act as particles, but they also act as waves (wave-particle duality). The light is interacting with the electrons electromagnetic field, which extends past what can be thought of as the physical electron itself. Hope this at least helped you onto the right path towards getting fuller answers to your questions. Never stop asking questions :)

2. ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-uh-e4UFwzqE.html

@@fadair 1. No, I meant why does light change its direction according to his theory. 2. Okay 3. U gave the answer to this question in 4 4. Why is it reflected and why can't the light pass through the object if they are both made of atoms, e.g. if coal and diamond are made of the same element then why does light get reflected from coal and get refracted in a diamond block. 5. Okay Another question popped up in my mind: How does quantum particles form a colour?

@@samerator4233 Here's a little common sense intuition, You can not see any object in the universe without light either reflecting off of it, or refracting through it. And, you can not tell if light exists or not without the presence of objects, because in order to see light, you need it to hit objects, without which, you can't see light.

Sunny shah That definitely helped me answer any of my questions and I definitely did not know that -_-

It not that “a certain incidence angle is unable to cause the secondary electric fields”, it is quite the opposite. The secondary electric field is still there in both cases it just might combine to give a different transmitted forward velocity or combine and give a reflected reverse velocity at the interface depending on the different medium/vacuum and angle. So, the answer is same idea from wave theory introduced in this video of wave superposition, but not only can they combine to have different speeds, but the combination can also be in the reverse direction to the primary wave depending on conditions. BTW great video and great question :)

@@aaronhoney2217 Any correlation to Lenz's Law?

@@dizzydinonysius This connects to Lenz’s law which relates to Faraday's law of induction by giving the direction of the induced electromotive force . Maxwell's classical electrodynamics is the theory for classical electromagnetic wave most commonly used in Heaviside’s form of vector calculus containing four equations. (Which most people learn. Do a google image search of to see Maxwell's equations). Two of the four equations are for electrostatics (1. Gauss' equation) and magnetostatics (2. Gauss' equation for magnetism) the other two are relate to electromagnetic dynamics , 3. Maxwell-Faraday equation (contain Lenz Law) and 4. Maxell-Ampere equation. The last two form a coupled equation to give the wave equation and contains the speed of light. Applying all equations to reflection and refraction problems give the wave theory explained in this video.

@@aaronhoney2217 Thanks

@@aaronhoney2217 But who uses 'wave theory' to explain the propagation of EM energy these days? Do they not teach quantum physics any more these days? PS For a modern approach read the well known Richard Feynman. Yes, I know he is dead and he got some things wrong but he is much, much better than this dinosaur.

Yeah, the induced electric field inside the medium causes some energy loss. This is transformed into heat, which is simply the jiggling of atoms (the same jiggling that generates the second electric wave to begin with). The exit wave will have the same frequency, but a slighty smaller amplitude, thus a drop in intensity.

@@KingIsulgard that’s not how energy in photons works. Higher energy means higher frequency / shorter wavelengths. You can’t apply the concept of “amplitude” to light waves. (Don’t take my word for this, look it up.) So this also has me scratching my head: how can light lose energy but still maintain the same frequency? And why would the frequency influence the speed of light? If that were true then light would travel at different speed according to its frequency. But it doesn’t, C is constant for all frequencies. Light is massless so if it’s not losing energy through it’s frequency then it’s not losing any energy at all. I’ve just started investigating this specific topic but my theory so far is that the interactions of the electromagnetic waves in light and matter causes some warping in space-time similar to gravity in general relativity, which causes time to dilate.

@@Yogarine Light speed is the same for all frequencies in vacuum. Matter slows down light of different colors in different amounts, hence rainbows (and dismay among optical fiber engineers). The light doesn't lose energy due to the slowness (and the description in the video is a bit superficial, not even talking about quantum mechanics). Absorption and hence energy transfer to the medium happens by losing photon, not by changing their frequency.

@@Yogarine you can't use "amplitude" for _photons_, NOT light _waves_. The amplitude is an indispensable part of describing a wave. The energy delivered by the wave per second will be proportional to its frequency and the square of its amplitude. In case of a light wave, this amplitude is simply the "size" of oscillations in the electromagnetic field - the larger the wave, and the more it wiggles, the more the energy carried by it. More mathematically, an EM wave can be written as E = E0 • sin(ωt). The amplitude of this EM wave is E0 - the maximum height of the wave. Frequencies manifest themselves to our senses as colours, so if you change the energy of a light wave by altering the frequency, you'll see it changing colour. But you could also change the amount of energy delivered by increasing or decreasing the size of the oscillations, while keeping the frequency constant, in the electromagnetic field. That simply amounts to seeing a brighter or dimmer light of the same colour. Here's a nice explanation from a freshman physics textbook to help you out. Follow through the maths to completely understand what's going on here. (In case you feel tempted to "debunk" me before going through this, here's the first line from the learning objectives of the chapter: "Express the time-averaged energy density of electromagnetic waves in terms of their electric and magnetic field *amplitudes*") openstax.org/books/university-physics-volume-2/pages/16-3-energy-carried-by-electromagnetic-waves

Light itself doesn't change. Its wave superimposes upon the generated electric field of the electron. The energy of the superimposition is the energy of the light minus the energy of the generation of the electric field (the work required to jiggle the electron). Thus when the light exits the medium the superimposition ceases and light is free to be the Universe's speed limiter once again. Physics is essentially the study of how light interacts with matter and how matter interacts with itself. Light and matter are fundamentally separate entities so when we speak of light "changing" within a medium, we are really describing *the interaction* between light and matter. Once you factor in gravity fields generated in spacetime, the interactions become more than a little wonky...

Please can you explain to me why the wave created by the electrons moves at a different speed 9:20 and also why the combined new way moves slower than the speed of light 9:43 ? Please I didn't find why...

You can observe a similar effect with sound waves. If you've ever heard someone tune a guitar by tuning an open string to the one next to it (by pressing it to a fret), you'll hear the difference in frequency between the two strings as a slow, undulating frequency, which corresponds to the difference in frequency between the two strings. The person tuning the guitar will be looking to reduce this effect to zero, which means the two strings are at the same frequency.

Feynman's lecture (Volume I, Chapter 31) is better.

Please can you explain to me why the wave created by the electrons moves at a different speed 9:20 and also why the combined new way moves slower than the speed of light 9:43 ? Please I didn't find why...

@@carmelo665 Please can you explain to me why the wave created by the electrons moves at a different speed 9:20 and also why the combined new way moves slower than the speed of light 9:43 ? Please I didn't find why...

@@Khalid-Ibn-Al-Walid In short, the interactions of light with atoms (absorptions and re-emissions of photons) cause a net phase shift and the apparent speed of light as c/n. The speed of light in the "vacuum" within the glass remains constant. In Feynman's words, “It is approximately true that light or any electrical wave does appear to travel at the speed c/n through a material whose index of refraction is n, but the fields are still produced by the motions of all the charges - including the charges moving in the material - and with these basic contributions of the field traveling at the ultimate velocity c (Feynman et al., 1963, p. 31-1).

@@carmelo665 Thank you very much for this answer ! But Why does it cause a shift in the wave ? I agree that it does modify the wave, but why it does Reduce it's size ?

i think this has to do with the frame of reference as light must always travel at a constant speed therefore it takes a longer path inside the material with higher refraction index and shorter path in air so it must change direction

@@Nightspyz1 The path inside water (or glass or whatever) doesn't matter. Light bends at the transition between different medium and only returns to the same direction if the surface of both transitions (air->glass, glass-air) are parallel. And Yes, that's not explained in the video even if both effects are connected.

@Cornelius Corcoran Perhaps a way to think of it is that as the light is coming in at an angle, the "inside" (left side of the red line in the video) of the light ray slows down before the "outside" as it enters the glass first. As the light maintains it's own speed and the slow down is just due to wave addition, on the way out of the glass where the light wave is no longer interacting with the electrons in the glass, the reverse is true with the left side of the light moving faster compared to the right, bending it back. Therefore, the light has the same velocity (speed and direction) when in the vacuum again (it helps having parallel sides on either side of the glass in the example to make that true). Refractive index and Snell's Law is key to all of this regarding determination of angles. I hope that's right / helpful as it's just my personal understanding!

@@a.k.1902 I think thats a common misconception. What about single photons? Do they have something like "inside" and "outside"? What about light traveling through caesium gas with refraction index < 1and phase velocity > c? PS: Feynman's path integrals may give an consistent answer to light bending. Feynman says a singe photon takes each possible path (it may even fly around the moon to reach a screen 2m in front of the light source ;). But... almost all possible paths interfere with each other in a destructive way so the resultant probability along a straight line usually becomes almost 100%. However, because of different phase velocity inside glass (and other materials) the interference and thus the probability distribution also changes according the incident angle -- the phase shift on the inner side happens earlier than on the outer side. The exact same principle is used by holograms on bank bills or many other today's uses. Holograms are partially covered mirrors which changes the probability distribution of reflected light to form a 3D effect.

Light approaching at an angle has a kind of angular velocity relative the surface. As it slows its angular velocity is kept but not its forward velocity. Why that happens is even more complex.

That still is complicated terminology. I’d say the best explanation is mass. Electrons have mass and so its electron field go slower than the speed of light in comparison to a photon. The photon’s speed averages out with the speed of the electron, making a slower overall speed than the one the photon began with and once it is out of range of the electron field by the matter, the speed it will return to.

It is.

Oh yeah good point; I wonder if that happens

It's easier when they use the formulae - in speech & writing it's hard to distinguish "THE Speed of Light", ("C", the constant defined as the speed of light in a vacuum), and "the speed of light" - (the speed of that light right there going through that prism right now.) "The speed of light, C, does not change, but the speed of the light in the prism moving at "C divided by the refraction index" is moving slower.

Note that the refracted path through the glass is shorter than the straight line of the original light direction. The travel time of the slower light through the shorter path in the glass is exactly the same as the time of travel that would be at the speed of light c through the straight path.

@@ozachar Don't the outer portions of a convex lens cause the light to bend toward the thicker center, taking a path that goes through more glass? (Not an optics guy, that's why it's a question, not a statement of fact)

@@muninrob I still don’t get why the « slowed » wave will change its direction by an angle depending on the material itself… what have I missed in this otherwise very clear explanation of the light wave deceleration ?

But frequency is not speed, so the electrons in the glass vibrate at the same f but do not propagate with the dange v

Exactly my thought Rohan!!! I don’t agree with the explanation in this video (just yet)!

Thats the video wrong axioma, I think. Interference dont change the speed of the beam.

Was that an explanation? - I'm not sure

it may have something to do with electrons having some form of natural frequency in the way they can be moved by the electric wave of the passing light... similar to pendulum or spring natural frequency ....

I can tell you this much: the electrons are part of the atom and the chemical state of the atom as well as the number of electrons determine the degree of interaction. The spatial range is definitely on the scale of 'touching'. Touching in any case is electrostatic interaction. If you think about a wave passing one atom... do you think it is possible to measure a change in the time tavelled for a photon for a single such event? Don's explanation (with reference to refractive indeces) is clearly meant to describe light passing through continuous matter.

Think about how the coupling of coils in a transformer varies with the core material. Now consider that at wavelengths like those of light, it wouldn't particularly be electric conduction electrons that would provide the coupling (as in the transformer), but electrons held in various degrees of tightness according to their energy state.

This is why I hated math and loved physics. Many teachers fail to include real world applications and just teach the calculations and formulae. In my opinion it should be standard to at least name the top applications for any mathematical method you are about to teach to give students a chance to connect it with the real world.

@@boooster101 But then you have to consider which applications would be of interest to the student. This is why I think even algebra (let alone trig) shouldn't be as widely taught as it is. Sure, it has applications in life -- but to whom? And which? And that goes for lots of other school subjects that wind up a waste of time for most people.

May I put my two cents in as a holder of a BA in mathematics who has read a first-year college textbook in physics? First off, keep in mind that physicists are the only group of people in the world who don't know that the Big Bang theory is stupid. (Just kidding; they know it's stupid, but they need a placeholder for the expansion of Space.) Secondly, your question appears to relate to quantum theory as contrasted with classical theory. As Dr. Lincoln said, physicists believe that Light sometimes acts as a wave and sometimes as a particle. That's my input, which might not even be worth two cents, but read the third paragraph of the Wikipedia article "Electromagnetic field". Have a glass of water and two aspirins nearby.

Electrons motion can have different frequencies depending on the electric potential binding them. When bound to a single nucleus (a Hydrogen atom), they produce a certain set of frequencies, probably what you were thinking of. However, when bound to a crystal lattice, such as inside a piece of glass, the potential is more complex, and allows the electrons to take on a continuous range of frequencies. It's a rough explanation but I hope it helps

I am far from satisfied as he was again telling a half story and trying to evade the real problem. People tend to play the wave-particle duality whenever it's convenient to them, without giving any accurate (though there's an extremely rough one) criteria when to use which. If you want to explain everything with wave, just keep consistent by viewing every glass quark as a de Broglie wave... Or alternative let's put it this way: try explain what happens when a single photon EM wave shoots into the glass from vacuum.

@@avivschwarz8513 Media like water and glass are not crystal lattices, yet they show a rainbow pattern of refraction. And yes, in metal-like lattices there is "merging" of electron energy levels into bands. But that's not universal either.

@@albat6538 I'm curious; why do you think the rainbow is a continuous (smooth) spectrum of colors? Surely quantum theorists have shown that only certain EM frequencies have the requisite energy amounts to produce a photon (?) of light. Forgive me if I'm showing my ignorance.

The speed of light is different for different wavelengths of light. Nutrinos pass through without slowing down.

@@MrElvis1971 Just to be clear, on your first sentence, that only applies in a medium. All wavelengths of light travel at the same speed, of C, in a vacuum.

@Hagakure42 yes, in a vacuum all EM radiation travels at the speed limit C. Not sure if a particular wavelength of light experiences time in a medium as C is still unchanged, it's just light isn't travelling at C.

No u don't know why because he doesn't explain it

Please Bro can you explain to me why the wave created by the electrons moves at a different speed 9:20 and also why the combined new way moves slower than the speed of light 9:43 ? Please bro I didn't find why...

There are crystals that can slow down light enough to trap it

It is pretty good. Its important to not take stuff like this for granted when there is soooooo much junk out there.

Please can you explain to me why the wave created by the electrons moves at a different speed 9:20 and also why the combined new way moves slower than the speed of light 9:43 ? Please I didn't find why...

it's because electrons and photons have fundamentally different speeds. this is because the electrons interact with the highs field, which pervases all of space so the space between atoms still has the higgs field. photons don't interact with the higgs field and this is seen because electrons constantly and randomly change their spin direction (indicating an interaction with the higgs boson, the constituent of the higgs field) while photons have one consistent spin direction which means it is not interacting with the higgs field.

@@leemaina8170 Perhaps Higgs mechanism could be used to explain why electrons don’t vibrate at speed of light, but this has nothing to do with EM wave that their vibration produces, which always will propagate at the speed of light. Think of a simple radio antenna as an example. Thus, there should be no difference between speed of external light wave, and internal EM wave produced by particle vibration in the same medium. Rather, I would point out two problems I have with that cool animation @7:10: First, frequency of resultant wave in glass seems changed while wavelength is same as before, which is quite the opposite from every physics book (wavelength should decrease with speed). Second, using Maxwell’s equations, Dr. Lincoln explains in “Why light bends in glass” that bend is caused by a fact that resultant electric field decreases in glass, while animation here shows that it oscillates and can actually increase at times.

I think that's a mistake, both EM waves move at c, but their superposition at < c

Electrons have mass, they can not move at speed of light. Because they move, they generate electrical field opposite.

I have the same question. If somebody could explain it, i would appreciate it very much.

Write a paper on it.

To answer your first question, it is because different frequencies of light have waves that have...well... different frequencies. since the velocities of the wave from light and the electric field are "added" together, different frequencies of light would yield different final speeds of the wave.

@@leemaina8170 This is the same preposterous claim made by fermilab. There is not only no math to support this, but the Fourier transform is the best piece of math to refute it. It is an illusion to be caught up in an apparent identity that sin (a+b) is the same as sin (a) + sin (b). The first form is definitely a sine wave but the second form is what you actually get when you add two sine waves of frequencies/wavelengths a & b together and that is not a simple sine wave with a single frequency. The deception is an attempt to equate the two equations. Not only does the math refute this but a glass prism or diffraction grating will also split apart the frequencies which were never combined in the first place. Interaction with electrons at the atomic level can absorb some of the energy and release it as light at a lower energy level/frequency. My assertion is that the speed of light through matter is a function of both the energy level of the light and the mass of the material it is traveling through. Light travels slower through higher density glass and the speed difference is exaggerated based on the energy level (frequency) of the light waves. Lens makers use this trick with compound lenses to reduce or eliminate chromatic aberration. This kind of infers Einstein's curvature or warping of space at the atomic level. But I left physics a long time ago and those equations are not on the tip of my tongue. Can somebody else write that paper?

If he did all that the video would be at least an hour long.

His brain is entangled with yours

Spooky action at a distance. 😃

@@azelectrical9093 google more stuff, i want more episodes

illuminati confirmed

because google is recording your information so it gives you more "tailored" results whenever you search in a google sphere website or a website that bought your information from google.

yes, people are doing that with metamaterials! they can even make materials that "break the rules" about direction of the light bending

@@nmarbletoe8210 thanks for the explanation.

Please can you explain to me why the wave created by the electrons moves at a different speed 9:20 and also why the combined new way moves slower than the speed of light 9:43 ? Please I didn't find why...

Consider what it means in this context for the light to lose energy. It means the wave behind the material has a lower amplitude than in front of it. The wave behind the material is the sum of the original wave and the response wave. If these are in phase the result will have _higher_ amplitude. Which would mean we extracted energy from the material. If these are in some way out of phase we can keep the overall amplitude and energy the same. And since the electrons in the material just move up and down, no net work has been done. The electron is accelerated by the E-field potential, gains energy, and falls back down, giving the energy back. (You can get into more detail because there is a static potential from the proton and a moving potential from the wave). If they are out of phase such that the amplitude is _lower_ then we have deposited energy in the material. Light has been absorbed and the material heats up. We call a material "transparent" when it does not (significantly) absorb the light we are working with.

Alen Gabric yes and the atoms would only emit at frequencies allowed by their electron orbitals... and btw what you are describing does exist, it’s called fluorescence :)

you wanna look at a huge orange blob that moves and/or a ball with blue dots in shells?

what do you mean inhabiting? as in going so fast that it looks like rings instead of balls ?

It would be difficult to draw an orbital shell that stretches across the universe. Let's just agree that all drawings are stylized.

It's ironic that you are using the word "orbitals" while trying to get away from the solar system model. (yes I'm aware that orbital is the technical term)

It isn't even like the Solar system - nuclei aren't even in the foci of electrons' orbits!

isnt it destructive interference ?? im confused

There is wrong in him ,all em wave travel in same speed ,when he saying about the electron hear it carefuly

@@umermukthar4959 If what you said was true, then it would be impossible to light to have an effective velocity in a material medium which was slower than light. Then, electromagnetic waves induced by electrons when they're moving translationally because of light's electromagnetic fields's influence in them can't have the same velocity as light ones. They need to be instead slower than light ones.

Moving electron generate EM (light) waves. Al moving charges emit EM waves.

@@wayneyadams if so, the EM waves from electron should have the same speed as light, so why the combined wave is slower? Also, why the wave from the electron cannot leave the material? So confusing.

​ people93 I don't know the effect distance of an electron but the reason for slowing when interacting with the electron's magnetic field is clearly shown (the sum of 2 sine waves out of phase). The TER will speed up between electron effects but then be affected by another electron which slows it again so the photon wave is not travelling at a consistent slower speed but is accelerating & decelerating as it approaches electrons and distances itself from them. The reduced speed is the =average= through the material. This is why it slows more i a liquid and solid (molecules packed tight) than in a gas (e.g. air) with molecules and their electrons much sparser and even faster in a vacuum (minimal molecules and their electrons). I deduced all this from the speed variation and interacting magnetic sine wave explanation, never read it anywhere so you best search & check that.

@@grindupBaker the sum of sine waves in the same speed, even if out of phase, should not slow down the resulting wave, only change other parameters as wavelength or amplitude

The frequency can remain the same but if the wavelength changes the equation will change for wave velocity, V=wavelengthxfrequency

This is a very interesting point and let me try to answer: color is not a wavelength but a frequency. Frequency of a foton is proportional to the energy of this foton so every detector (any device or just a human eye) will see the same photon, even if its wavelength will be different because of properties of the medium. Every kind of detector (like eye) is sensitive to the ENERGY of a photon. But a very interesting outcome comes along: the interference pattern of a certain laser beam should look different in the air and in the water (diffraction grating used remains the same). I'm so keen to see this... I'm gonna make this experiment actually

this video has taken many shortcuts in explaining the relations between the two systems and how it affects them. to better understand this, we need to talk about d'alembert's equation and its dispersion formula and how it describes a wave. so d'alembert's equation is used to link together the spatial and temporal variation of a wave. and from this equation comes the dispersion relation that links together the frequency, wavelength and celerity of a wave. to access to this equation, we use maxwell relations to describe this phenomenon. when we consider those relations in the void, we get the relation: c² = w²/k² where k is the angular wavenumber and w its angular frequency. (just google it, ain’t that hard to understand) thus we can see here that the celerity is proportional to its angular frequency. however, as explained in the video, when light enter a medium, there are charges that can be influenced by the electric field, especially electrons that are 2000 times lighter than their counterparts protons. thus, when light comes in this medium, we assume that only electrons are affected by the electric field. we then apply newton's second law to those electrons to find a relation between an electron's speed and the electric current (we also neglect the magnetic field of the light as the electron is relativistic thus the force from the electric field is much greater than the magnetic one see lorentz law to better understand this ) and then by generalizing this equation to all electrons in the medium, we can get an induced current from the electric field of the light. ( the current is j = n * v with n the volumic density of charges and v the celerity of electrons) then when we put this back to maxwell ampere local equation, we introduce a new component: the induced current which thus gives us a new dispersion equation: c² = (w² - wp²) / k² with wp the plasma oscillation and thus we can see that from the value of wp, we'll get a different value of the celerity of the wave. thus we can say without a doubt that they are wrong in their explanation as it is not the combination from the electric current of the electrons and the wave that makes it slower but the induced current inside the medium that modifies the dispersion relation thus modifying its speed. or in simpler words, it's the movement of electrons that changes the frequency and celerity of the light, but not the combination of the two electric current. (also on a side note, trying to represent the electric current of a dipole using a sine wave.. funny thing you did there 😅) and finally, as for the reason why the light has a different angle, well you can easily explain this using two waves parallel to each other crossing the medium in phase with each other. as they have the same wave plane, you can easily come to the relation between the refracted angle and the incident angle using some basic geometry. i recommend you to see the demonstration of descartes second law if you want to better understand what i'm talking about.

He captures my whole attention span. What charisma, personality and articulation! In my opinion this particular speaker is a "physicist at 💙. He exudes the affection he feels towards such a venerable and indescribable science. Thank you. Ana Abreu.

He just described the Ewald-Oseen extinction theorem totally wrong. en.m.wikipedia.org/wiki/Ewald%E2%80%93Oseen_extinction_theorem You can find the falsification explicitely: "...each of these waves travels at the speed of light in vacuum, not at the (slower) speed of light in glass." The explanation of Don Lincoln is just plain wrong, both in physics and math. "recombination" of 2 waves travelling at different speeds is just a stupid, impossible idea. If the slower one is just not there yet (in a specific point where "the light" has already arrived), then how could it be added to the faster one?

@@PafiTheOne lmao, that guy has a PhD, there's a reason he works at Fermilab not you

@@rajdeepbhandari8969 It seems science is a religion for you. Do you undertand anything I wrote? If not, then please learn first! Your claim is a fallacy: en.m.wikipedia.org/wiki/Argument_from_authority However your claim is not even an argument, only bullshit, because you also failed to state your relevant opinion. en.m.wikipedia.org/wiki/File:Graham%27s_Hierarchy_of_Disagreement.svg Your response is an ad hominem attack, while my comment was a falsification of a central statement of this video.

@@wolfie54321 That theorem is just an alternative mathematic description of wave propagation. It is compatible with Hygens principle, and that recognize particles, that's why it is preferred (sometimes) in describing wave propagation in substances. But applying Maxwell's equations with the measured (or calculated) average electrical properties of materials is simpler. Both are correct in normal case. But at very high freq neither of them are accurate (in materials).

It still doesn't make sense to me

@@MrSpock-sm3dd There are 2 crucial bits: 1. 8:03 - 8:21 - the oscilating photons induce the oscilation of electrons. The oscilation naturally have the same frequency, but different phase and the amplitude. 2. A sum of sinusoids at the same frequency is another sinusoid at that frequency - always true. The proofs of that are a bit complicated, so You can just remember that's how it is. What changes is phase and amplitude. An animated illustration of that is 7:06 - 7:30. The original wave (2) moves at the speed of c, while the induced wave (1) is almost stationary (at least here, I don't know how is it in phisical body e.g. glass). The resulting wave (3) is the weighted sum of (1) or (2), weights being amplitudes. The larger the amplitude of (1) the more (3) resembles it, so also the slower it moves. That's how I understand it on a basic level, although I wouldn't be surprised if there are some holes. If anyone would like to correct me or add something, please do.

@@MCMaterac Where I get lost is the assertion that the amplitude being changed somehow affects the speed. I don't think that's a property we observe in other waves, to include light. And there's no explanation in the video as to how we arrive at that conclusion.

@@That_Montage_Nerd You're right, that's a wrong assumption. I've just made a javascript simulation. If the 2 amplitudes are equal, it looks just like in this video and in relation to wave1 the resulting wave3 moves half as fast as wave2. However at other amplitude ratios the resulting wave moves on average at the same speed as the input wave that has higher amplitude, with additional left-right oscilations repeating each time wave2 has amplitude higher than wave1, the wave3 propagates on average as fast as wave2, accellerating and decellerating each period on repeat. So yeah... the video (and my answer) doesn't seem to explain the matter well.

@@MCMaterac Bro are you Indian?

In my opinion bcz, the electric field of light repulse electrons in atoms which creates countering wave which ultimately slows down the light

@@kaushalvyas1142 Yeah, he could have been a bit more thorough there. From what he said it sounds like those waves actually combine, but we could also see it is as kind of interference/resistance process whereby the light wave cannot travel unimpaired because it passes through the electron wave. In any case, I am wondering whether those waves are related to gravity effects. Seems there is still a lot of mystery about the origin and nature of those EM-waves, and since matter is atoms, with electrons, you always have EM effects in matter. This leads into matter being condensed energy. There still seems to be that hard wall in front of an understanding of the 'effects beyond', the driver(s) of the observed phenomena. (Basically: Why does stuff happen at all? Why do things move?) The big scientific challenge is to not get stuck in a rut, to not ever-more solidify our belief of what we know. It helps to apply mental exercises like: _What the guy explained there could be producing tears of laughter for an average human 500 years from now._

That depends on perspective. An hour is a long time to a child to a gamer that can literally feel like 10 mins.8 hours is the determining factor for bacteria and the like to grow. A billion years for life to exist only mere seconds needed to wipe it out completely. Also Light could be considered a supreme ultra thin material as its a result of a energy process and will be part of the resource consumption. Radiation, soot, dangerous particles, gases, heat, electric and magnetic forces a lot of things lay in Light. Sorta like how we equate red markings on insects to mean extremely dangerous thou it's not always the case due to mimicry

That's a very good question. It seems clear that the "interaction propagation speed" at the boundary cannot exceed the speed of light, thus there must be some period and some distance, however minute (a layer) in which the light wave slows, decelerates in a sense. Imagine a planar layer of one-atom thick glass (know glass is not an element and I use the word atom very loosely). Then a layer of vacuum several glass atoms thick then another single atom thick layer of glass with a repeated sandwich of any thickness. Could light defract in that? It might seem like the distance the light deflects to an offset parallel path would be tiny, on the order of an atomic "diameter", but in fact it may be zero??? For example, would a one atom thick sheet of glass defract a beam of light any differently than a one atom thick layer of water? Would the speed of light in a "near vacuum" be identical to that of a vacuum until there is some threshold density of atoms that can interact to form a refracting wave? Regardless of whether it would be measurable, could a single atom/molecule in a vacuum slow light?

Which in this case are both corresponding to the waves :D - Brilliant.

@@Kombivar, and both give you perspective on "Time". 😉

The electrons themselves will oscillate at the same frequency as the light, but the resulting electric field that interferes with the light wave will not be

@@johnsMITHhhhhh88 Could you elaborate? I'd think the frequency of the produced field would correspond exactly to the frequency of the oscillation of the charge