As a kid, I remember messing around with the permittivity and permeability constants on my old Casio calculator and being gobsmacked when the speed of light jumped out at me.
@@mujtabanadeem3901 Yup, the way Big Bang shaped the Universe affected its properties. I wonder if the Big Bang had gone even slightly different, the Universe would have been completely different. Maybe an intelligent species in that universe would consider themselves "special", like we humans do. Maybe they would think God made everything for them, like we tend to do
A couple of things I'd like to see you do videos about: 1. Even pre-Einstein, physicists assumed that the speed of light was constant relative to the medium of the vacuum (the ether), just as sound in air is constant for a given set of atmospheric parameters (pressure, temperature, humidity, etc). What was really radical about special relativity was that it assumed that the speed of light was fixed not with respect to a medium but with respect to every inertial observer. This has drastically non-intuitive consequences, the simplest of which, the breakdown of simultaneity, does not require any math at all to derive. That in turn implies that faster-than-light signaling of any kind leads to reverse causality. (I.e., if events A and B have spacelike separation and A can send a superluminal signal to cause B, then in some frames A sends the signal after B occurs.) 2. The term "speed of light" is ambiguous since it can refer to the signal velocity, phase velocity, and conceivably other things, which can be numerically different. I have never seen a really good treatment of this, and it has interesting implications, for example for a sound understanding of interferometry. (Edited to fix a formatting problem and to try to improve my sloppy wording.)
The speed of light being constant for different observers is probably the most misunderstood concept in science. The first 30 seconds of this video does what 99.9% of all special relativity videos and books do. Show a moving observer in a train or on a spaceship generating a light beam and state that the speed is measured as "c" from the perspective of both the traveler and the stationary observer. It is generally stated that there is no ether and that time dilates for the traveler during this process and they all lived happily ever after. First a few facts: Light actually does travel in a medium or ether. It's called the electric field. When I turn on a flashlight, the filament in the flashlight contains atoms that once energized, promote their electrons to a higher energy and when they fall to a lower level, the energy is given off as EM radiation. What exactly is the EM radiation? It is a kink or ripple in the electron's existing electric field lines that travel in step with the electron before, during and after the generation of light. When the electron shifts to lower energy level, the surrounding field (which extends out to infinity) can't adjust to this change instantaneously. It takes time for the shift information to spread throughout the field and this shift which causes the ripple with momentary shifting of electric and magnetic fields (in phase with each other) traveling along the existing electric field at the speed of light. Ever notice why the hundreds of videos like these don't ever include the electric field of the light-producing charges while attempting convince everyone the "velocity" is the same no matter what. Read the chapter on light generation/propagation in any undergraduate physics textbook and you will see that it usually does an adequate job of describing this process with a step-by-step mechanism. Then flip ahead to the chapter on special relativity and look at all of the nice pictures of the trains and spaceships and flashlight beams and ask yourself: Where are the field lines and the waves propagating along them? Where did they go? Gee - they were here a few chapters ago. What happened? Then try on your own to make all of their claims work using the mechanism of the EM wave ripple traveling along the field lines that were in constant motion with the atoms in the flashlight the entire time. You are even welcome to throw in as much time dilation and length contraction as you like. Good luck.
@@thurston2235 My explanation based on my long description above is that the speed of light generated on a moving ship and measured by someone inside that same moving ship actually is the same value (c) as if it were measured by a stationary observer measuring light generated in that same stationary frame. I have never had any problem with that claim. But since the field lines (which act as the grid that the light travels along) are moving in unison with the moving ship, then a stationary observer would actually see the ship's light pass them at a speed different than (c). A stationary observer in front of the ship would see the light wave moving along the grid (field lines) at (c) while the grid itself is moving toward the observer at the same velocity of the ship so light in that case would be faster than light. A stationary observer behind the moving ship would see the light move along the grid (field lines) at (c) but at the same time, the grid would be getting dragged away from the observer so the result is a measured velocity less than (c).
I think this argument is circular. When we talk about e0 and mu0 being properties of free space we’re referring to a theoretical entity. It’s either a perfect vacuum, nothing, which is a physical impossibility, or it’s something which has these properties so it’s not nothing at all. I don’t know whether you’ve noticed but if you rearranged the Maxwell equation relating c, mu0 and e0 you could get something analogous to one of the versions of the equation for the speed of sound such as v = sqrt(B/rho) which is equivalent to v=sqrt(1/kappa*rho) where B is the bulk modulus of the conducting medium, kappa is its compressibility and rho is its density. In any case, the speed of sound is a function of two properties of the medium in the same way that the speed of light is a function of two properties of free space. Just as the speed of sound would vary if the density or compressibility of a medium were to change the speed of light could, in principle, change if e0 or mu0 were to change. This is where the circularity of the argument arises. You’re saying that c is constant and universal because e0 and mu0 are constant and universal but how can you know this if you can only measure c, e0 and mu0 locally? Even if you have a separate argument for the universality of c you still cannot justify the assertion that e0 and mu0 are universal except by reference to whatever proof you have for the universality of c. Therefore, the universality of e0 and mu0 cannot be said to indicate the universality of c, can it?
Science is not based on logic. It doesn't "justify" arguments in the same way. Every scientific theory has certain basic assumptions, and only applies within a certain range of perception. Many scientists believe it is possible that the vacuum properties do actually vary throughout the universe. The experimental evidence we have for the speed of light only applies to our local area, because that is the only area we have measured directly. If we receive new evidence that the speed of light isn't constant, we will have to update our theories.
I think space(time) gets completely overlooked. We're happy to describe particles from the standard model but not the 'chessboard' on which they operate.
@@skepticmoderate5790 Thanks. I think that is a good explanation of the way the science is operating. What it also shows is that the meaning of the word ‘universal’ has been weakened considerably. When something is said to be a universal constant without qualification the statement takes on a more dogmatic tone which alerts sceptical people like me (and you by your screen name).
@@wag-on Given that QFT can describe everything in terms of fields where particles are simply the solutions of equations, and often only virtual, I think you are entirely right. To a layman physicist like me, the Standard Model of particle physics looks increasingly like Ptolemy’s epicycles and I wonder whether a future physics will regard all particles as patterns and events rather than objects occurring in the substance of spacetime/the quantum vacuum/matter/aether or whatever name we settle for.
Einstein picked no assumptions from thin air. He concluded the constancy of the speed of light from experience, please read "On the electrodynamics of moving bodies", near the end of § 1. Then please also read his very next paper "Does the inertia of a body depend upon its energy-content?", where he repeats his first postulate but not his second. Instead, there is a footnote which says: The principle of the constancy of the speed of light is of course contained in Maxwell's equations". One may of course still call it an assumption since it cannot be really proven. Nothing physical can be proven in general, we just observe something that seems to always occur and then we don't believe it is a coincidence and call it a law of nature. That is called induction. The constancy of the speed of light is very well substantiated, based on facts of experience. That is the strength of Einstein, he did NOT fabricate assumptions, but based everything on experience.
Your comment is great and I don't disagree with you in general, but I want to note that your explanation of induction, that is inductive reasoning or inference, is not exactly right. Why we are taking something as an axiom (or assumption if you prefer) is irrelevant to logical inference as long as it is consistent so the difference between inductive and deductive inference is not that we choose axioms because they are observed to be probably true (although of course that is implied by the conventional definition of the word). Instead the distinction between inductive and deductive inference lies in the derivations. A deductive argument must exactly imply the conclusion (given some rules of inference but in practice these are taken for granted). An inductive argument, however, only proves that a conclusion is probably true from a set of assumptions. My point is the reason we cannot easily prove physical facts is not because they are not susceptible to deduction but rather because of a looming and fundamental gap between thoughts and ideas and the actual messy physical reality. Or to put it another way: How are we supposed to study something with exact logic if we don't actually know what it is in the first place? And so physics (and other sciences) correctly focus on observation. We cannot definitively conclude that physical things are what we say they are; we can only seem to assume we are right and validate through observation.
@@danielwimmer4698 Yes, I agree, but I just said: "that is called induction" and to me that is not an explanation of induction as such. One cannot simply turn the Modus Ponens (= "the positive way") backward. If it rains, then the roof gets wet, but if the roof gets wet, it does not necessarily rain. Ever heard of the fire brigade? But if the roof does not get wet, then it does not rain, which is the Modus Tollens (= "the negative way"). The Latin "induction" means "bringing in". For example a law of nature is brought into the logical system (or a postulate or axiom, and no, this does not define what an axiom is, it merely says induction renders an axiom, and no, this does not equate "postulate" to "axiom"). Please read Newton's Regula Philosophandi no. III in Liber Tertius "De Mundi Systemate" of his "Principia". See henk-reints.nl/astro/HR-Newton-Regulae-Philosophandi-Scholium-Generale.pdf for an accurate translation. In his original, this rule is followed by a clarification of over one page. However, he does not explicitly call this induction, but in Regula IV and in the Scholium Generale he refers to it as such. In general, an OBSERVED persistent regularity that in all experiments DOES occur and never does not, is presumed to be something universal. You no longer believe it is a fluke, but of course you never have a 100% certainty. And that is what Einstein did. He based his premises on what he referred to as "experience". Except his greatest blunder, the cosmological constant, which he picked from thin air.
As far as I know Einstein started with a Variable Speed of Light, and this makes more sense in many ways. As far as I can imagine it must work so that the local spatial metric shrinks and expands (or cell size or gap increases if using a vibrating, field cell model).. This field is the gravitational gradient and force carrier. With the variable cell size field model light must move from cell to cell in a FIXED ABSOLUTE TIME, T(ick) (+Universe Expansion)... This makes electric charge compatible with wave phase at the quantum level, no matter what the local spatial metric is.. -- As cell gap shrinks with gravity and time T(ick) to cross cells is constant, light speed absolutely locally slows with gravity, causing energy build-up due to conservation of energy, that is 'lost' in the form of acceleration of matter, but also mass and time dilation due to MORE CELLS OCCUPIED per (cyclic) quantum process, so C always measures C locally.. It's a weird one but it makes sense.
Great video, this helps so much to show where physics theory has gone wrong. The vacuum is not a thing, it is not a first order primary object, it can not have properties of itself. Is a shadow a thing? Shadows exist but they are not first order primary objects, they are second order phenomena, dependent on other first order objects (a light source and an obstruction) to exist. A shadow is a lack of light relative to other areas where light impacts, a shadow is not an independent object on its own. Space and time as well are not first order primary objects and do not have qualities on their own. Prior to the 'big bang' when all energy (and matter) were created in our universe there was no space and there was no time. If all energy and matter were removed from the universe space and time could not exist. The permeability and permissivity of 'space' as referred to in this video are not characteristics of 'space', they are aspects of electromagnetism itself, and therefore the position of an observer, moving observer, observer frame of reference in 'space' has no bearing on the observed speed of light. The great error physics has made is to objectify space as a thing, an object with qualities, when space is not a first order primary object which can not have qualities or characteristics on its own. The same is true for time. Space and time are not objects with qualities, and physics has gone in circles for more than 100 years trying to create theories where space and space - time are first order multidimensional manifolds with properties of their own, independent of energy and matter. All of these theories fail, string theory, m-brane theory every variation of them fail to account for the qualities physics attempts to assign to them. There is no experiment in the history of science which proves that in the absence of all forms of matter and energy that either space or time is an objective object with measurable quantifiable qualities.
Finally an actual explanation withouth nonsense like putting the image of Einstein with formulas floating around and just accepting that the speed of light is constant thanks !
could there be room for a "departing c1" light speed and a "arriving c2" light speed? Veritasium pointed out that you couldn't tell the difference. Then the product of c1 and c2 should be constant.
And that's all fine, but inherent in the assertion that you can't prove it, you also can't make any use of it. If you could, then you could either prove, or more importantly, disprove it.
Not at all....at least it wouldn't _feel_ fast if, as in the animation, no accelerations occur on the body: you don't _feel_ speed; you _feel_ acceleration; What it would do is it would *look* fast. That is because of visual specific differences between prior experiences of traveling slower looked different in specific ways than the current higher velocity travel. :D
Some points that should be discussed: the values of vacuum permittivity and vacuum permeability are dependent on the units chosen. In fact, Coulomb's law is an expression of proportionality, it doesn't give absolute numbers, the chosen system of units does. Even the units of permittivity and permeability change when you use different systems (CGS, SI, etc). So as to the question, "why do the vacuum permittivity and permeability have the values they have?" The answer is, units, partly. The important aspect of these quantities is their values *relative to one-another*, and relative to physical space. That's the key point to highlight in a discussion like this, which you sort of tried to do. Next thing: the "speed of light" is ill-defined here. The speed of light could rather be called the speed of electromagnetic propagation in a vacuum. When you say "the speed of light changes in different materials", there's two very important footnotes: (1) the 'speed of light' is actually the *phase velocity* of an electromagnetic wave in a given material; and (2) this is a *macroscopic* phenomenon, meaning we're simplifying highly complicated systems in terms of behavior on average. Microscopic electromagnetism has a single, fixed 'speed of light'. Lastly, the speed of light being constant. This really is fascinating. To reiterate a common example, imagine two people watching ripples in a pool, but the people are moving at different speeds; the ripples in the pool will appear to move at different speeds to the different observers. Now repeat the experiment, but instead of ripples in a pool, you're looking at ripples in the electromagnetic field. An identical scenario, with a wave front and multiple observers at different speeds. But now, both observers see the ripples at the *same speed*. The important difference between the propagation of the waves in these examples, is the relationship between the physical space and the wave phenomenon. In water waves, the waves exist *in* the physical space of the observers. In electromagnetic waves, the properties of the physical space don't factor in directly, and the video points out correctly that the vacuum permittivity and permeability are the only deciding factors- their relationship to the units of time and distance are the deciding factors in the phenomenon. It's really amazing.
As far as I know Einstein started with a Variable Speed of Light, and this makes more sense in many ways. As far as I can imagine it must work so that the local spatial metric shrinks and expands (or cell size or gap increases if using a vibrating, field cell model).. This field is the gravitational gradient and force carrier. With the variable cell size field model light must move from cell to cell in a FIXED ABSOLUTE TIME, T(ick) (+Universe Expansion)... This makes electric charge compatible with wave phase at the quantum level, no matter what the local spatial metric is.. -- As cell gap shrinks with gravity and time T(ick) to cross cells is constant, light speed absolutely locally slows with gravity, causing energy build-up due to conservation of energy, that is 'lost' in the form of acceleration of matter, but also mass and time dilation due to MORE CELLS OCCUPIED per (cyclic) quantum process, so C always measures C locally.. It's a weird one but it makes sense.
Nice video and presentation. A mechanical elites was asked what vacuum means. In his reply - vacuum is empty of matter. An electrical engineer was given the same question - he replies, vacuum is empty of matter but Aether. Aether is a fluid that has no physical but electrical property, with a permittivity, Aether measuring 8.8541817128*10-12 Farad per meter. Therefore Aether is a component necessary to enable (e field) and (displacement charge q) launch into the vacuum for light to propagate. - See also e0, u0 in Maxwell’s equations. Furthermore, Aether, is a fluid, always attaches to matter, size from subatomic particles to atoms to molecules to ions to solid to liquid to gas and to plasma. When gas, liquid, solid moves Aether drag along with it, locally, and also drag with the MMX’s apparatus. On the other hand, from a macrocosm scale, Aether as a fluid continues to drag remotely at a mean velocity dominated by mean distance and mean mass of bodies in the vicinity. With that we can rewrite SR and GR.
Einstein recognized he based part his "Relativity works" also in Maxwell EM formulas... also in several other previous theories... from Newton to Boltzman... to Planck... etc... This constant (for now!) has to do basically on interaction of properties of EM wave and the medium where is traveling... very simplistically the wave frequency the medium allow the EM wave to progress... number of cycles for unit of time... Parth did a great job explaining it mathemathically... but we sure need 'better words' to explain this to people who 'love+hate maths' (like me)
Question: How was charge and magnetic permeability isolated, experimentally? How is it that permeability constants units fit with their derivation of c? I would assume that Eo and Mo would have been tuned to equal c in that way, and not the other way around. Is the clue that c is the speed of causality not so much that Eo and Mo solve to a pretty equation, but more so that they needed a constant (if actually derived from c) for the charge and magnetic force equations?
There's a lot of history on both the measurement of the electric and magentic forces and the speed of light. But specific to your question, you're likely interested in the Coulomb torsion balance experiment. It demonstrated the inverse square law and the charge dependance for the force between charges. However, the constant in the derived equation was determines as the "Coulomb constant" that just happens to equal 1/(4*pi*e0), but the permittivity wasn't specifically separated out by Coloumb in the 18th century (to my knowledge). A similar experiment is possible for the magnetic force, and I've seen setups to do it, but am not familiar with the history of that one. There were many experiments on the speed of light as well, some fairly good ones based on astronomical observations that predate Coulomb, but I don't think the connection between c0, u0, and e0 were brought together until the 19th century. It's certainly made by Maxwell, but I'd guess that specific connection was proposed prior to his contributions (though I don't know). The three constants can be (and were) independently determined, but they are not independent. Knowing 2 is sufficient to describe the third (light is an electromagnetic wave, so the relationship makes sense). It's interesting to note the progression: e0 is related to electric charge, u0 to charge velocity (creating a magnetic field), and c0 charge accleration (creating an electromagnetic field/wave). Or more simply: stationary charge interaction-> moving charge interaction-> accelerating charge interaction.
To answer your question, No Eo and Mo were not force fitted to equate to c neither were they derived from c, historically speaking the laws for force between the charges (i.e Coulomb's Law - Published in 1785) and the force between two wires carrying current (i.e Biot-Sarvart Law - Published in 1820) existed before we knew light was an EM wave. And the units of Eo and Mo appearing in the equation had their units according to the equations so for example for Coulomb's law we have F = (1/4*pi*Eo)(q1*q2/r^2), here F is measured in Newton (N), q1&q2 measured in Coulombs (C) and r measured in meters (m) and 4,pi,1 are just numbers they have no units. so Eo gets the unit of (C^2/N*m^2). Similarly you have units for Mo as (N*t^2/C^2). This was purely a result of these laws and had nothing to do with light whatsoever (I mean it has to do with light Physicist hadn't figured that out yet). Parallelly, wave theory of light was gaining popularity (Physicist still didn't know it was an EM wave but they were definitely sure it is some kind of wave (As opposed to what Newton had suggested in the 1700s (Corpuscles model of light which reigned supreme until the 1800s)) due to a guy named Thomas Yong's famous experiment (Double Slit Experiment - 1801). Now Physicist were curious to figure out the speed of this propagating wave (i.e speed of light which has fascinated humans since the dawn of civilization and was a dream of the likes of Galileo, Ibn Haytham and Newton). Now Hippolyte Fizeau measured the speed of light (3*10^8 m/s - in1848) by purely experimental method still not knowing they were EM waves. Now in 1865 Maxwell published his famous Maxwell's equations and then he showed that a mathematical consequence of his equations (No force fitting but an absolute rigorous mathematical derivation) are that EM waves can propagate in free space at a speed given by [1/√(Eo*Mo)]. Also, earlier in 1854 and in 1860 Weber and Foucault (respectively in those years) has experimentally shown that the value of [1/√(Eo*Mo)] was equal to that of the speed of light calculated by Fizeau in 1848 but didn't understand what it meant. Now finally with Maxwell theoretically deriving the same result and them experimentally observing them painted a beautiful and complete picture. Finally Hertz in 1888 produced a Radio wave (a type of EM wave) in lab and measured its speed which agreed Maxwell's theory. Thus visible light and other EM waves became one family known as EM waves and their speed was that of light. This later set deep implications which were then finally understood in a much deeper sense via Theory of Relativity. So in a nutshell the laws of force for charge and currents were already discovered prior to Maxwell's work with no knowledge of their deep relationship to light. But when Maxwell derived the relationship mathematically with full rigor and also various experimental confirmation started emerging the real picture came forward and a new much further deeper questioned crept out. HOPE YOU GOT SOMEWHAT OF AN SATISFACTORY ANSWER.
The values of e0 and u0 are only depending on your unit system, the same is true for c. If you measure in a different system, the values will change, but the equation c = 1/sqrt(e0*u0) will still be true. That equation is universal and can also be explained by looking at the propagation of EM waves like light. The way how the electric and magnetic fields of the wave create each other is also connected to e0 and u0 (by the maxwell equations), and the resulting speed of the propagating wave is c. So those variables were not chosen to fit the equation with c. Instead e0 and u0 as well as c result from the same phenomenon: the interaction of magnetic and electric fields. But I have to admit: The fact that the coulomb equation has the same factor e0 as one of the maxwell equations seems kind of random to me.
"On the First Electromagnetic Measurement of the Velocity of Light" by Wilhelm Weber and Rudolf Kohlrausch and "A History of the Theories of Aether and Electricity" by British mathematician Sir Edmund Taylor Whittaker are good places to start. The various experiments that measured the supposed velocity of light directly are either incorrectly interpreted or not very compelling. But you should come to your own conclusions. What I do know is that a lot of us like to parrot our textbook knowledge without considering if that knowledge is accurate. All the peer-review rewarding in the world cannot make the illogical logical. Or make the undemonstrable demonstrable.
Wonderful video as always! Just a quick question: I heard on pbs spacetime that we actually have a false vacuum, as in there is still a baseline 'vacuum' energy. If we were in a true vacuum, would the speed of light be affected?
About 20 years ago I interviewed N. David Mermin for my Senior Thesis in Philosophy of Physics. He wrote the paper Relativity Without Light, proving that the speed of light is constant starting with some more basic assumptions. I wanted to make sure I wasn't misusing his paper in my philosophy context.
I did thought about this while studying special relativity.Though left this part. Nice that u made a video about it. The thing that light propagation has to do something with the very space its propagating makes a really good intuition. Really liked the video😊👍
If one tried to measure c by means of the force between two charges and that between two conducting line segments, he would have to measure the distance between the charges and between the line segments. These are not constants. Rather they depend on the relative motion between the observer and the charges and lines. The analysis offered applies only to an observer fixed with respect to the charges and the line segment.
I remember my teacher of electromagnetic waves course solved the Maxwell's equations using quite a lot of assumptions and he arrived to a wave equation with the speed of light as the speed of propagation. However, in general, the wave equation describes any wave propagating through any medium, such as waves in a water pond and tells nothing about the speed of the wave measured by different observers.
The reason why we know the speed of light from a static or moving source doe not add is because it is measured. Since the famous experiment by Michelson and Morley it has been neasured with increased precision...
Imo, the Michelson and Morely experiment is invalid. It's like claiming that a car isn't moving because you don't measure any wind inside the cabin. Plus, the interferometer experiment has since been repeated and gotten different results in recent years. I'm referring of course to the supposed detection of gravitational waves. You can't have it both ways. "Empty space" is either acting on light, or it's not.
My history of science may be a bit off, but I don’t think it was known at the time that Maxwell’s equations were describing light waves, but only that they described propagating electromagnetic disturbances. Later it was realized, after the values were plugged in, that this was close to the experimental value for c, and that thus, light was a propagating electromagnetic disturbance.
@@ahgflyguy «With the publication of "A Dynamical Theory of the Electromagnetic Field" in 1865, Maxwell demonstrated that electric and magnetic fields travel through space as waves moving at the speed of light. He proposed that light is an undulation in the same medium that is the cause of electric and magnetic phenomena.»
@@AdrianBoyko so you’re saying that in the initial publication of the theory, that Maxwell knew that the electromagnetic wave his theory predicted was the light of everyday experience? Or was this a later publication?
@@ahgflyguy «Towards the end of 1861 while working on part III of his paper On Physical Lines of Force, Maxwell travelled from Scotland to London and looked up Weber and Kohlrausch's results. He converted them into a format which was compatible with his own writings, and in doing so he established the connection to the speed of light and concluded that light is a form of electromagnetic radiation.» So, Maxwell made the claim that light is EM waves 5 years before publishing his equations in their final form.
I was looking for such a video and u know Iwished if u would make it. And there it is. I think tbat is the deep connenction between a teacher and a student that promted u to do that video. Well done keep it up!
There is sort of a chicken-and-egg problem with attributing the speed of light to Maxwell's equations. Namely: how are we supposed to know a kinematic quantity (the speed of light) from electrodynamic properties? Originally Maxwell's equations was not expressed with a SI unit system with vacuum permeability or permittivity, and cgs units defined quantities such as charge, electric, and magnetic fields based on assuming vacuum permeability and permittivity were unitless. This was a choice made to relate the constants of Maxwell's equations to electrostatic and magnetostatic measurements so that quantities like the ampere for which the coulomb was based on could be made from magnetostatic measurements (now the coulomb is defined by elementary charges as of 2019). This can be seen by examining the Lorentz force in SI units and Gaussian units, because if one assumes that permittivity and permeability are unitless, magnetic fields and the Lorentz force due to the magnetic fields both have the speed of light in their derivations. The inference comes in with Maxwell's inclusion of the displacement field in Ampere's law which includes the speed of light as a constant. It's not clear to me or many exactly why Maxwell took this leap: aapt.scitation.org/doi/abs/10.1119/1.15263?journalCode=ajp So to some degree the "why" is that it worked and a wave was measured that matched that of the speed of light obtained by other means (for example the Fizeau-Foucault experiment).
Goodness gracious, I recently thought about the topic of why the speed of light is changing in other substances. Of course, it's happening cause of N, just like N of water is 1.33 as I remember. However, where is the N actually coming from was a riddle for me, but now I see, it is just N = √ε*μ , and how incredible it is that we can now magnetic properties of water , kerosene and others , knowing just their μ . Thanks a lot for such a great video 🙂
Quantum dipoles are what make up empty space. Empty space alone doesn't do anything. Fluctuations that come into existence and then annihilate do though. These fluctuations according to quantum physicist are made of particle pairs like electron positron pairs with magnetic fields and frequencies of their own and they quickly polarize with other particles traveling through them before they annihilate. This interacts with photons and other particles and puts Vanderwaals Torque on them. So you could say that light speed is not a fundamental constant but a secondary or tertiary result of the permittivity and permeability of space, caused by the interaction with quantum fields and the Vanderwaals Torque they exert on everything. Empty space does not contain time either and has no dimensions and cannot warp, bend, dilate or contract. However, space filled with quantum dipoles, which are real particle pairs with frequency, magnetic fields and spin have time and dimensions. So it's the quantum fields that give everything clock rates and mass, and evidently produce gravity. More mass, more torque. Just a thought.
I get that epsilon nought and mu nought dictate the speed of electromagnetic radiation. This is an amazing and awe inspiring insight into the nature of the cosmos and is indisputable. I also get that the frequency of the electric field source dictates the frequency and hence wavelength ("color") of the radiation; and that once initiated the E & M field interaction is self sustaining and the wave will propagate through space indefinitely. What I don't get is why 'c' is still 'c' to an observer who is moving parallel at 'near c' speed; all the "baseball thrown from the moving train' analogies are simply inadequate - the baseball never gets near any 'limiting speed' (such as the sound barrier for baseballs in air) and so the analogies are useless. If the source is moving close to 'c' how can the emitted radiation travel away from it at 'c' given that epsilon nought & mu nought dictate the speed of electromagnetic radiation? It seems we use the two constants of nature to calculate (and limit) "light speed" but then ignore those same constants if the source happens to be moving at 'near c' speed! Why did Einstein need to make this bizarre proposition anyway? And the particle accelerator "proofs" are unconvincing.
If standard model explains photoelectric effect as a boson-fermion interaction in which the mediator is photon, which is mediator for electromagnetic force, then what explains the threshold frequency?? Hope u understood my question
the electromagnetic field in this case is quantized (That's also what standard model teaches us. The electromagnetic fields due to photon being a mediator are not given by MAXWELL'S EQUATION (which only worked for the classical scenario) but rather by QUANTUM ELECTRODYNAMICS (QED)). So that makes the energy quantized as well of those fields and that's what gives rise to the THRESHHOLD FREQUENCY. Einstein kind off explained the same effect without knowing QED instead he just postulated that Photon's can have such a nature (With good mathematical justifications tho). HOPE THIS ANSWERS :)
@Parth G 2:25 ɛ₀ reduces force between charges in a vacuum. Is this because of polarisation of the quantum foam that appears in a vacuum? In a capacitor, ɛ is related to how much the electron clouds can get displaced from the positive nuclei in the dielectric eg in a high permittivity material eg plastic, the electron clouds get displaced a lot. This *polarisation* creates a 2nd electric field that opposes the electric field between the capacitor plates. So is something like this happening in the vacuum?
Hi Parth, my question is about the depiction of an EM wave. You show it, as everyone does, as two sin waves at (pi/2) radians between them. They both cross zero at the same time. When I interpret Maxwells's equations, I think the curl of the E field depends on the rate of change of the B field. That rate of change of B is greatest when it crosses zero, so E should be maximum at that time. But plenty of smart people show E as zero at that time. What am I missing?
Parth, can i ask you something, lets say i shoot a photon in one direction, and then i use semireflective lenses and stuff to shoot another photon so they travel together. But i invert the phases, so as to have destructive interference from now on. Where does the energy goes? Do both photons disappear? Since i cant detect them after they interact...
Destructive interference is not an annihilation of energy. Even a single photon will give you interference pattern when you try to let it interfere with a -180 degree phased photon. So what you will observe is a central dark spot where's there is high destructive interference but then nearby concentric circles of light fading. So all that happened is that your energy dispersed from a central bright region to a outer faded region and central prominent dark region. Total energy is still conserved.
Please help me to understand. If light travels slower through a medium (e.g. air or water), why doesn't this also effect the passage of time, speed that information can travel or causation? In other words, why wouldn't time pass slower for me at the bottom of a pool relative to floating on my raft at the surface if light is slowed my the medium (water)?
The simple answer is that what light does in a medium is irrelevant. There are plenty of substances through which light cannot travel - a brick, a tree, a wall, most solid things in fact. That doesn't affect the fundamental laws of physics inside a brick.
@@RAFAELSILVA-by6dy Thank you. I think I got it. As you said, light IT SELF is irrelevant-it just so happens to travel the universal speed limit because it can. EVENTS, however, can never occur faster then light speed. Light itself has nothing to do with it, it's the SPEED 3x10^5 km/s that can not be surpassed.
Time is quantised in a vacuum - it cannot be zero - therefore any velocity has a limit. At a small scale, QM (which is not a theory, it has no explanation) time is not quantised and can be zero - so velocity can be infinite, and events can be instantaneous. So there is a time paradox, hence relativity and QM cannot be reconciled. One or both are wrong. There is something missing.
So I never actually thought about this but from this I assume the speed of light _in a medium_ is also constant for all observers and more interestingly, it is also independent from the movement of the medium itself, is that correct?
I don't think so...if this were the case particles causing cherenkov radiation in water for example could break causality. I'm not sure but I think that maxwell's equations in linear media implicitly assume the reference frame of the medium. Hence the speed that pops out is with respect to that medium (like with any other wave equation), as opposed to being constant for all observers like in the vacuum.
The biggest clue that the speed of is constant is that light from distant starts reaches us as a clear image. All of the colors reach us at the same time. The stars aren't smeared across the sky. The radio and xray bursts align with the positions of the rest of the spectrum.
I really like the way this guy explains this stuff. Thank you 👍 Just one question, Is it okay to think of the permittivity of free space of an electric field as being sort of like a voltage drop of voltage when current is flowing through a wire? So , in other words , does free space obsorb 8.85^-12 farads of electric field per meter? Kind of like a copper wire having a bit of unavoidable resistance of current flow , thus producing a slight voltage drop.?
You should say the speed of light is causally constant in all frames of reference ,In 4d dimensional space its not constant velocity. If you use Greens function for at static charge with the correct limits you have opposite charge in imaginary space. This describes a Wormhole-in-a-wormhole (Hopf Fibration).The speed of light in causality is a fractional derivative of sin wave.(Phasal shift)A static charge is a mono-pole magnet..Guido Wugi youtube has good visuals of these typologies.
Good explanation. Thank you. One question: the permittivity and permeability being constant in the vacuum definitely indicate speed of light also constant. However this equation doesn't address the interaction between two frame of references, right ? In the vacuum the speed is constant, but if a stationary person measure the speed of a spaceship headlight will this equation be sufficient to explain the constant nature of light ?
Depends what you mean by sufficient. If you trust Maxwell's theory of electromagnetism, then yes. But, of course, even Maxwell himself didn't trust it that much. Einstein was the one who eventually dared to say: all right then, let's assume Maxwell's equation are totally correct. That led to the theory of special relativity.
Lights/EM waves rate of induction is Magnetism's rate of creation. Both transverse waves of Dielectric energy and Magnetism are needed to merge into the nodes, that EM waves/Light propagate on. Light/EM waves are modalities of Magnetism and Dielectric energy. Magnetism gives Magnitude to the Universe. You can have Magnetism without Electricity. You can not have Electricity without Magnetism/Dielectric voidence field and Dielectric energy.
Because they supply a medium that allows for the propagation of light and the photons from distant galaxies reach us and our telescopes. In other words, the combination of the vacuum's permittivity and permeability is just another name for the electromagnetic field, which, if light is to reach us from distant galaxies, must be "in between" us. It'd be better to say the EM field saturates the whole universe and is omnipresent.
@@SophiasIchor You can say that but you cannot be sure of that, the speed of propagation might be consistent within a galaxy but different galaxies may have different speeds and that may account for intrinsic redshifts. Very young and dense galaxies may appear to be further away than they are if we rely on doppler alone.
Yes I am sure of that. The EM field exists everywhere, all-the-time, omnipresently. The speed of light is the speed of light (did you not just watch the video?) Redshift is caused by dark energy's expansion of the "vacuum's" spatial configuration. But that doesn't effect the speed of light, which, stays the same for all inertial observers: the speed of light never changes, it is invariant, and "we know what the vacuum permittivity and permeability is in other galaxies or between them" because of that fact.
@@whig01 dude, you didn't ask or claim that. You asked how we know what the vacuum's permittivity and permeability are in other areas of the universe. And we know what they are because they're used to calculate the speed of light, and being that that is a physical constant so too are the vacuum's permittivity and permeability parameters. You're right though, about my not knowing about cosmological distances, but Idgaf about the error ratio of cosmological distances. Regardless, you're original question has been answered.
Only in the same reference frame. Constant: occurring continuously over a period of time, or belongs to a situation that does not change. We already know different mediums alters that passage through space. AE meant it vibrates more or less in different mediums. Plus, QM already stated the emf is not continuous but discreet. Both states light has a time dilation effect to it. You as the observer is not objective. You are subjective. Can't see those other universes! Not tuned for it.
The problem I see is that it does not predict the speed of light but does so for the speed of causality or so is claimed. This seems like an issue to me as it's only the case in respect to electromagnetic forces so I fail to see how this appropriately shows the speed of causality. When we look at the other boson dues to tge fact tge have mass the forces they carry should be manipulated by its own form of relativity. Is any one capable of showing me the error of my thinking here please and by all means be as complex as need be.
@Part G Great vid but in some sense incomplete though, or shortcut, one can say. MAXWELL himself believed in a super-substance called the luminiferous aether ε₀ and μ₀ are properties of. This means that the speed of light _with respect to the aether_ were already constant. What (old, pre-LORENTZian) aether theory is missing is the good old GALILEI principle of relativity which tells us that the fundamental relationships between physical quantities (this is what _natural laws_ actually are) are independent on what coordinate system we're using to calculate, including the rest frames of those observers. In other words, natural laws are _invariant_ under any coordinate transformation. *GALILEI meets MAXWELL* Since MAXWELL's equation are natural laws, the should meet GALILEI's principle of relativity, and since the speed is purely derived from them, so should it as well. This is what's actually new about Special Relativity.
Hey Parth, can you explain this, a group of mathematicians has shown that at critical moments, a symmetry called rotational invariance is a universal property across many physical systems.
Does the constant really have to do with light? Or is it just the speed at which energy moves through a vacuum? For example, gravity waves should also move at C. Neutrinos too. Does that mean a gravity wave is also an oscillation of electric and magnetic waves? If gravity and light travel at the same speed what's the correlation?
Gravitational waves doesn’t exist, it’s an human contrivance, a fallacy since the physicists don’t understand space and light! Light doesn’t exist nor do gravity as an force. Gravity is dielectric acceleration towards counterspace. Reed my post for more info 😊
@@klassemyra Sorry, I can't explain the difference between a phenomenon caused by massive bodies interacting in space and a fluid dynamics effect that you can see on the oceans to someone who doesn't have the vocabulary to understand any of the words and too much mental noise and nonsense to understand the concepts. I'd normally recommend that you try googling the terms but I don't see how that would help you either. ¯\_(ツ)_/¯
And no, that gravitational waves travel at lightspeed does not mean that they are an electromagnetic oscillation at all. If that were true we'd be flying around on antigravity cars by now. Gravitational effects working at light speed implies that if gravity is a force then its (as yet undiscovered) force carrier, the graviton, is massless and if gravity is not a force and is an emergent feature of spacetime (or some deeper reality) then it's simply limited to the speed of causality. We used to insist that neutrinos traveled at lightspeed but we used to think that they were massless. They're very, very light but not massless so they may be moving very close to lightspeed but not quite as fast.
Shared, subscribed. SPIRAL cosmological redshift hypothesis and model based on light speed limit of 'c' standard light speed the universe attained mature size and density by 4/365(5781) a fraction of history, = to 4 days, with a radius of 2B+/- LY., and the entire universe approximates the visible universe, so over 150 T times a more reasonable cosmological model (than the competing SCM-LCDM where the entire universes is assumed at over 200x the visible universe), just for starters based on size, density and a straight line entropy factor. ..
in optics we have been learning that speed of light slows down in medium .so we don't have same speed of light..what about its frequency and wavelength ?? and speed of light is same for all observer, and fundamental ? in this case how it is even possible? Parth G will you please elaborate this..
It's because the light that hits the medium excites it's atoms and they also emit their own light and all the waves interfere with each other and the resulting wave looks like it's travelling slower than 'c'. But if u consider actual photons they're still travelling at 'c'.
@@rajat4712 how light knows it has to travel in specific direction,,when electron comes in lower energy level ,,it can emit photon in any direction,,when light comes out from a medium it is aligned in single path..
They don’t ever meet. Electricity is not a force, just an hybrid of dielectricity and magnetism. The meeting of a circular magnetic field and the radiell dielectric gives rise to electricity.
Can u please discuss about Fraunhofer and Fresnel diffraction with diagram (like u discussed about formation of wavefront in your old video) something like comparison . 🙏
Hey Parth, nice video! My question is that have we do some further research to find why the permeability and the permittivity have those specific values or did we just treat it as a fundamental truth about our reality?
I believe we're supposed to take it as fundamental truth about our universe. Its not like those values are dependent on some other variables and also very slight changes in their values won't have huge consequences ... I think. Same can be said for G being 6.674×10−11 m3/kgs2. That's just how our universe is.
They are both 'fiddle factors' measured experimentally to allow the maths to make sense of the physics based upon our current definition of the basic units of measurement. One could redefine things so as to set them both equal to 1 but that would upset people at the Gas stations big time :-)
@@vassun4891 meh. There's always a reason. It is dependent on other variables. Slight changes would have quite big consequences because computers are sensitive to variations in voltage
@@alphalunamare Like Parth G says they are measures of how much electromagnetism can permeate things. i.e. actual measures of things that exist outside in the universe whether we are "fiddling" or not. They are not just like eg 3.28 is the constant we need to change feet to metres. That constant is arbitrary
@@alwaysdisputin9930 I am not sure that you got my point. What I am saying is that if we change our units of measurement we can arrive at a situation whereby both constants are equal to 1 and hence the speed of light = 1 in those new units etc.
Nice explanation.. Please I would like to make more videos related to Special and General Theory of Relativity.. Please I would be appreciate it... Thank you😊
So... if we find a way to alter E or M then we can modify the local speed of light.. They may be constants at the moment, but in the future they might not be....
If space is somehow quantized and light is actually propagating through these quantized space "particles" ( - for a lack of better term), it makes all the sense why speed of light would not depend on the speed of inertial object from which it originates. Cause speed of light is not really a speed, as in it is not really measured against time, since time makes no sense for photons.
There are other frames of reference apart from the photon's frame of reference. In other people's frame of reference it is a speed. Why would quantised space make any difference?
Because in a quantized space a quantized packet of energy can only enter into an exit out of a quantized space in descrete packets. The energy transfer process is quantized itself, and can only occur at a certain rate, that the Universe has defined. So from the photons point of view it can only travel through these quantized spaces at a given rate.
Those were the clues, but where's the evidence? Since all equations are simplifications (by necessity), we can be quite certain that they don't tell the full story. When we talk about magnetic fields in wires, and that equal currents attract, I wonder whether that's still true for free electrons in empty space? Think of a cathode ray tube. If you have two rays of electrons, will they attract or repel?
But there is a nother explanation… That light is an ”coaxial circuit”, an longitudinal field (pulse) pertubation of compression and rarefaction of dielectricity that gives rise to alternating magnetic and electric fields. The dielectric discharge creates two volyms, one of magnetism and one of electricity. This takes time, and is what we messure as the speed of light but it’s an rate of induction (of the medium against it self), or one can also say the hysteresis of this fields rate of disturbance from counterspace (which is the field, the medium). Light is not an particle, nor is it a wave, (a wave is what something does, not what something is). Light in this sense has no speed, and is not an emission, light doesn’t even travel. Light doesn’t travel in an field (medium), it is the field it self. This is why they could not find the ether. The experiment was wrong because they did not understand light and what light is. The ether (quantum field) is counterspace and can therefore not be measured in our cartesian space, nor be detected, but it’s still everywere! This also explain the so called spooky action at a distance. Light ultimately doesn’t exist as something physical, not more then a magnetic field does. It’s first when light interacts with matter that it makes it self known through it’s attributes, for example lumination.
@@Ni999 Just because you're not smart enough to understand doesn’t mean it's nonsense. Its logical & sensible and this solves a lot of today's problems in physics, for example, that light is supposed to be a duality. Light is a field perturbation.
Well here you're babbling about light being caused by a dielectric discharge and elsewhere you're babbling that gravity is a dielectric acceleration. I have to admit that you are right - I'm not smart enough to translate the word salad from your faith and make sense of it in the real world where words mean things.
Can anyone explain the result of Michelson Morley experiment ....i am not understand it....that experiment proves that ether does not exist ....and light does not need any medium to propogate ...but how experiment tells that light in independent of inertial frame of reference ......
So wait a minute... I am very confused! We all know that nobody has actually measured the *one way* speed of light correct? We only know and have measured the *2 way* speed of light. Which is (exactly) K = 599,584,916 m/s. To do this we have shined a laser through a mirror, the laser bounced back and we got this number... The reason why we can't measure the one way speed of light, is because of Einstein's relativity... Einstein himself new that, and he thought that since we don't (or might never know the answer) it actually doesn't matter how fast the laser is going towards the mirror VS how fast is coming from the mirror, as long as when added together they yield "K" as the answer... So for simplicity Einstein said, that he will treat the speed of light as being c = K/2 which is c =299,792,458 m/s. But that speed we have not actually measured experimentally... And it could be that we will NEVER be able to measure it, because of the limitations imposed by relativity... So how does that work with c = 1/sqr(εμ) ? That gives us a definite number for the speed of light? So we know what the one way speed is, we just can't measure it?
A question might rise here, is the speed of transverse travelling waves in a string independant of observer's POV since it depends on tension force and the linear mass of the string? same for sound waves too?
NONE of this precludes the possibility that the permittivity and/or the permeability of vacuum varies with reference frame. CERTAINLY, the permittivity and the permeability of materials DO vary with reference frame as experiments on flowing liquids demonstrate.
So, if you have two charges submerged in some fluid, and the fluid has a very fast laminar flow, do you expect this to change the electric force between them?
@@drdca8263 It doesn't have to move that fast. Matter has a lot of charge; the + and - just cancels. In a static field, the + and - experience opposite forces that get canceled by electron-nucleus moving off center. But when the matter (or charge) is moving, the electron-nucleus offset is also changing. Since they both have mass (and inertia), they don't find the equilibrium offset until later... and that offset has then changed again. Not only is the force different in magnitude, it might even have a different direction.
@@byronwatkins2565 That seems like an experiment or demonstration that probably wouldn’t be that hard to pull off, and which seems like it would be interesting to see, *especially* if it reverses the direction of the force. Would have to be careful to separate out the forces arising from just the flow of the fluid pushing up against the instruments independent of the electric charge I guess? If the number changes as you say it would, that would seem to imply that the refractive index of a fluid would also change when it is moving? I haven’t noticed such a phenomenon, but “I haven’t noticed” doesn’t say much, as I often fail to notice things.
@@drdca8263 It has been done. It does NOT reverse the force direction; it merely rotates it a little if the flow is perpendicular to the field. The hard part is maintaining electrostatic charges and measuring the small force. Separate stands easily isolate the moving medium from the forces. The square root makes the index of refraction less sensitive, but a small bi-refringence has been observed. (Index perpendicular to motion is slightly different than parallel to motion.) They cannot swear that this is not due to strain, however.
The universe is not flat. It might appear like it is locally but on larger scales the speed of light changes since the measures of time and distance change relative to where we are.
Maxwell's equations of electromagnetism give one speed for light energy in a vacuum. That applies for any observer in his Inertial Reference Frame (IRF) and only in his IRF where there is no acceleration and no gravitational field. He has no way of determining his velocity and he will always obtain 'c' for his IRF. It is not a license to conclude that it is also true for that observer viewing another IRF. There is no experimental confirmation for that. There is only Einstein's assumption and declaration of that in his second postulate in the Special Theory of Relativity which leads to the error of time dilation.
Maxwell : speed of light is constant I guess
Einstein : And I took that personally!
Lol!
As a kid, I remember messing around with the permittivity and permeability constants on my old Casio calculator and being gobsmacked when the speed of light jumped out at me.
Did this influence the subject you studied later?
@@andik70 It certainly made me realise that things were connected in surprising ways.
@@Jehannum2000 they sure are!
@@andik70 you asked a nice question
@@mujtabanadeem3901 Yup, the way Big Bang shaped the Universe affected its properties. I wonder if the Big Bang had gone even slightly different, the Universe would have been completely different. Maybe an intelligent species in that universe would consider themselves "special", like we humans do. Maybe they would think God made everything for them, like we tend to do
A couple of things I'd like to see you do videos about:
1. Even pre-Einstein, physicists assumed that the speed of light was constant relative to the medium of the vacuum (the ether), just as sound in air is constant for a given set of atmospheric parameters (pressure, temperature, humidity, etc). What was really radical about special relativity was that it assumed that the speed of light was fixed not with respect to a medium but with respect to every inertial observer. This has drastically non-intuitive consequences, the simplest of which, the breakdown of simultaneity, does not require any math at all to derive. That in turn implies that faster-than-light signaling of any kind leads to reverse causality. (I.e., if events A and B have spacelike separation and A can send a superluminal signal to cause B, then in some frames A sends the signal after B occurs.)
2. The term "speed of light" is ambiguous since it can refer to the signal velocity, phase velocity, and conceivably other things, which can be numerically different. I have never seen a really good treatment of this, and it has interesting implications, for example for a sound understanding of interferometry.
(Edited to fix a formatting problem and to try to improve my sloppy wording.)
Exactly!
because of your first point, i think "speed of causality" is a nice name for it. then the "c" makes sense as well
The speed of light being constant for different observers is probably the most misunderstood concept in science. The first 30 seconds of this video does what 99.9% of all special relativity videos and books do. Show a moving observer in a train or on a spaceship generating a light beam and state that the speed is measured as "c" from the perspective of both the traveler and the stationary observer. It is generally stated that there is no ether and that time dilates for the traveler during this process and they all lived happily ever after.
First a few facts:
Light actually does travel in a medium or ether. It's called the electric field. When I turn on a flashlight, the filament in the flashlight contains atoms that once energized, promote their electrons to a higher energy and when they fall to a lower level, the energy is given off as EM radiation.
What exactly is the EM radiation? It is a kink or ripple in the electron's existing electric field lines that travel in step with the electron before, during and after the generation of light. When the electron shifts to lower energy level, the surrounding field (which extends out to infinity) can't adjust to this change instantaneously. It takes time for the shift information to spread throughout the field and this shift which causes the ripple with momentary shifting of electric and magnetic fields (in phase with each other) traveling along the existing electric field at the speed of light.
Ever notice why the hundreds of videos like these don't ever include the electric field of the light-producing charges while attempting convince everyone the "velocity" is the same no matter what.
Read the chapter on light generation/propagation in any undergraduate physics textbook and you will see that it usually does an adequate job of describing this process with a step-by-step mechanism. Then flip ahead to the chapter on special relativity and look at all of the nice pictures of the trains and spaceships and flashlight beams and ask yourself: Where are the field lines and the waves propagating along them? Where did they go? Gee - they were here a few chapters ago. What happened? Then try on your own to make all of their claims work using the mechanism of the EM wave ripple traveling along the field lines that were in constant motion with the atoms in the flashlight the entire time. You are even welcome to throw in as much time dilation and length contraction as you like. Good luck.
@@chriskennedy2846 How would you explain it further then?
@@thurston2235 My explanation based on my long description above is that the speed of light generated on a moving ship and measured by someone inside that same moving ship actually is the same value (c) as if it were measured by a stationary observer measuring light generated in that same stationary frame. I have never had any problem with that claim.
But since the field lines (which act as the grid that the light travels along) are moving in unison with the moving ship, then a stationary observer would actually see the ship's light pass them at a speed different than (c). A stationary observer in front of the ship would see the light wave moving along the grid (field lines) at (c) while the grid itself is moving toward the observer at the same velocity of the ship so light in that case would be faster than light. A stationary observer behind the moving ship would see the light move along the grid (field lines) at (c) but at the same time, the grid would be getting dragged away from the observer so the result is a measured velocity less than (c).
I think this argument is circular. When we talk about e0 and mu0 being properties of free space we’re referring to a theoretical entity. It’s either a perfect vacuum, nothing, which is a physical impossibility, or it’s something which has these properties so it’s not nothing at all.
I don’t know whether you’ve noticed but if you rearranged the Maxwell equation relating c, mu0 and e0 you could get something analogous to one of the versions of the equation for the speed of sound such as v = sqrt(B/rho) which is equivalent to v=sqrt(1/kappa*rho) where B is the bulk modulus of the conducting medium, kappa is its compressibility and rho is its density. In any case, the speed of sound is a function of two properties of the medium in the same way that the speed of light is a function of two properties of free space.
Just as the speed of sound would vary if the density or compressibility of a medium were to change the speed of light could, in principle, change if e0 or mu0 were to change. This is where the circularity of the argument arises. You’re saying that c is constant and universal because e0 and mu0 are constant and universal but how can you know this if you can only measure c, e0 and mu0 locally? Even if you have a separate argument for the universality of c you still cannot justify the assertion that e0 and mu0 are universal except by reference to whatever proof you have for the universality of c. Therefore, the universality of e0 and mu0 cannot be said to indicate the universality of c, can it?
Science is not based on logic. It doesn't "justify" arguments in the same way. Every scientific theory has certain basic assumptions, and only applies within a certain range of perception. Many scientists believe it is possible that the vacuum properties do actually vary throughout the universe. The experimental evidence we have for the speed of light only applies to our local area, because that is the only area we have measured directly. If we receive new evidence that the speed of light isn't constant, we will have to update our theories.
I think space(time) gets completely overlooked. We're happy to describe particles from the standard model but not the 'chessboard' on which they operate.
@@skepticmoderate5790 Thanks. I think that is a good explanation of the way the science is operating. What it also shows is that the meaning of the word ‘universal’ has been weakened considerably. When something is said to be a universal constant without qualification the statement takes on a more dogmatic tone which alerts sceptical people like me (and you by your screen name).
@@wag-on Given that QFT can describe everything in terms of fields where particles are simply the solutions of equations, and often only virtual, I think you are entirely right. To a layman physicist like me, the Standard Model of particle physics looks increasingly like Ptolemy’s epicycles and I wonder whether a future physics will regard all particles as patterns and events rather than objects occurring in the substance of spacetime/the quantum vacuum/matter/aether or whatever name we settle for.
Einstein picked no assumptions from thin air. He concluded the constancy of the speed of light from experience, please read "On the electrodynamics of moving bodies", near the end of § 1. Then please also read his very next paper "Does the inertia of a body depend upon its energy-content?", where he repeats his first postulate but not his second. Instead, there is a footnote which says: The principle of the constancy of the speed of light is of course contained in Maxwell's equations". One may of course still call it an assumption since it cannot be really proven. Nothing physical can be proven in general, we just observe something that seems to always occur and then we don't believe it is a coincidence and call it a law of nature. That is called induction. The constancy of the speed of light is very well substantiated, based on facts of experience. That is the strength of Einstein, he did NOT fabricate assumptions, but based everything on experience.
Wow someone actually cited a source on an internet comment...
Your comment is great and I don't disagree with you in general, but I want to note that your explanation of induction, that is inductive reasoning or inference, is not exactly right. Why we are taking something as an axiom (or assumption if you prefer) is irrelevant to logical inference as long as it is consistent so the difference between inductive and deductive inference is not that we choose axioms because they are observed to be probably true (although of course that is implied by the conventional definition of the word). Instead the distinction between inductive and deductive inference lies in the derivations. A deductive argument must exactly imply the conclusion (given some rules of inference but in practice these are taken for granted). An inductive argument, however, only proves that a conclusion is probably true from a set of assumptions. My point is the reason we cannot easily prove physical facts is not because they are not susceptible to deduction but rather because of a looming and fundamental gap between thoughts and ideas and the actual messy physical reality. Or to put it another way: How are we supposed to study something with exact logic if we don't actually know what it is in the first place? And so physics (and other sciences) correctly focus on observation. We cannot definitively conclude that physical things are what we say they are; we can only seem to assume we are right and validate through observation.
This is pretty much what Parth said in the video.
@@danielwimmer4698 Yes, I agree, but I just said: "that is called induction" and to me that is not an explanation of induction as such. One cannot simply turn the Modus Ponens (= "the positive way") backward. If it rains, then the roof gets wet, but if the roof gets wet, it does not necessarily rain. Ever heard of the fire brigade? But if the roof does not get wet, then it does not rain, which is the Modus Tollens (= "the negative way").
The Latin "induction" means "bringing in". For example a law of nature is brought into the logical system (or a postulate or axiom, and no, this does not define what an axiom is, it merely says induction renders an axiom, and no, this does not equate "postulate" to "axiom").
Please read Newton's Regula Philosophandi no. III in Liber Tertius "De Mundi Systemate" of his "Principia". See henk-reints.nl/astro/HR-Newton-Regulae-Philosophandi-Scholium-Generale.pdf for an accurate translation. In his original, this rule is followed by a clarification of over one page. However, he does not explicitly call this induction, but in Regula IV and in the Scholium Generale he refers to it as such. In general, an OBSERVED persistent regularity that in all experiments DOES occur and never does not, is presumed to be something universal. You no longer believe it is a fluke, but of course you never have a 100% certainty.
And that is what Einstein did. He based his premises on what he referred to as "experience". Except his greatest blunder, the cosmological constant, which he picked from thin air.
As far as I know Einstein started with a Variable Speed of Light, and this makes more sense in many ways. As far as I can imagine it must work so that the local spatial metric shrinks and expands (or cell size or gap increases if using a vibrating, field cell model).. This field is the gravitational gradient and force carrier. With the variable cell size field model light must move from cell to cell in a FIXED ABSOLUTE TIME, T(ick) (+Universe Expansion)... This makes electric charge compatible with wave phase at the quantum level, no matter what the local spatial metric is..
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As cell gap shrinks with gravity and time T(ick) to cross cells is constant, light speed absolutely locally slows with gravity, causing energy build-up due to conservation of energy, that is 'lost' in the form of acceleration of matter, but also mass and time dilation due to MORE CELLS OCCUPIED per (cyclic) quantum process, so C always measures C locally.. It's a weird one but it makes sense.
the cradle of relativity
Great video, this helps so much to show where physics theory has gone wrong. The vacuum is not a thing, it is not a first order primary object, it can not have properties of itself. Is a shadow a thing? Shadows exist but they are not first order primary objects, they are second order phenomena, dependent on other first order objects (a light source and an obstruction) to exist. A shadow is a lack of light relative to other areas where light impacts, a shadow is not an independent object on its own. Space and time as well are not first order primary objects and do not have qualities on their own. Prior to the 'big bang' when all energy (and matter) were created in our universe there was no space and there was no time. If all energy and matter were removed from the universe space and time could not exist. The permeability and permissivity of 'space' as referred to in this video are not characteristics of 'space', they are aspects of electromagnetism itself, and therefore the position of an observer, moving observer, observer frame of reference in 'space' has no bearing on the observed speed of light. The great error physics has made is to objectify space as a thing, an object with qualities, when space is not a first order primary object which can not have qualities or characteristics on its own. The same is true for time. Space and time are not objects with qualities, and physics has gone in circles for more than 100 years trying to create theories where space and space - time are first order multidimensional manifolds with properties of their own, independent of energy and matter. All of these theories fail, string theory, m-brane theory every variation of them fail to account for the qualities physics attempts to assign to them. There is no experiment in the history of science which proves that in the absence of all forms of matter and energy that either space or time is an objective object with measurable quantifiable qualities.
Finally an actual explanation withouth nonsense like putting the image of Einstein with formulas floating around and just accepting that the speed of light is constant thanks !
could there be room for a "departing c1" light speed and a "arriving c2" light speed? Veritasium pointed out that you couldn't tell the difference. Then the product of c1 and c2 should be constant.
And that's all fine, but inherent in the assertion that you can't prove it, you also can't make any use of it. If you could, then you could either prove, or more importantly, disprove it.
I came for Parth's voice but stayed for the physics lesson. Lol
Physics 😊, he's the King. His voice is a gift God was bound to give. 😂🤣😹LOL
0:40 : Must feel like the speed of light to go at 360 km/h (100 m/s) in this little van…
Not at all....at least it wouldn't _feel_ fast if, as in the animation, no accelerations occur on the body: you don't _feel_ speed; you _feel_ acceleration; What it would do is it would *look* fast. That is because of visual specific differences between prior experiences of traveling slower looked different in specific ways than the current higher velocity travel. :D
Some points that should be discussed: the values of vacuum permittivity and vacuum permeability are dependent on the units chosen. In fact, Coulomb's law is an expression of proportionality, it doesn't give absolute numbers, the chosen system of units does. Even the units of permittivity and permeability change when you use different systems (CGS, SI, etc). So as to the question, "why do the vacuum permittivity and permeability have the values they have?" The answer is, units, partly. The important aspect of these quantities is their values *relative to one-another*, and relative to physical space. That's the key point to highlight in a discussion like this, which you sort of tried to do.
Next thing: the "speed of light" is ill-defined here. The speed of light could rather be called the speed of electromagnetic propagation in a vacuum. When you say "the speed of light changes in different materials", there's two very important footnotes: (1) the 'speed of light' is actually the *phase velocity* of an electromagnetic wave in a given material; and (2) this is a *macroscopic* phenomenon, meaning we're simplifying highly complicated systems in terms of behavior on average. Microscopic electromagnetism has a single, fixed 'speed of light'.
Lastly, the speed of light being constant. This really is fascinating. To reiterate a common example, imagine two people watching ripples in a pool, but the people are moving at different speeds; the ripples in the pool will appear to move at different speeds to the different observers. Now repeat the experiment, but instead of ripples in a pool, you're looking at ripples in the electromagnetic field. An identical scenario, with a wave front and multiple observers at different speeds. But now, both observers see the ripples at the *same speed*. The important difference between the propagation of the waves in these examples, is the relationship between the physical space and the wave phenomenon. In water waves, the waves exist *in* the physical space of the observers. In electromagnetic waves, the properties of the physical space don't factor in directly, and the video points out correctly that the vacuum permittivity and permeability are the only deciding factors- their relationship to the units of time and distance are the deciding factors in the phenomenon. It's really amazing.
As far as I know Einstein started with a Variable Speed of Light, and this makes more sense in many ways. As far as I can imagine it must work so that the local spatial metric shrinks and expands (or cell size or gap increases if using a vibrating, field cell model).. This field is the gravitational gradient and force carrier. With the variable cell size field model light must move from cell to cell in a FIXED ABSOLUTE TIME, T(ick) (+Universe Expansion)... This makes electric charge compatible with wave phase at the quantum level, no matter what the local spatial metric is..
--
As cell gap shrinks with gravity and time T(ick) to cross cells is constant, light speed absolutely locally slows with gravity, causing energy build-up due to conservation of energy, that is 'lost' in the form of acceleration of matter, but also mass and time dilation due to MORE CELLS OCCUPIED per (cyclic) quantum process, so C always measures C locally.. It's a weird one but it makes sense.
Nice video and presentation.
A mechanical elites was asked what vacuum means. In his reply - vacuum is empty of matter.
An electrical engineer was given the same question - he replies, vacuum is empty of matter but Aether.
Aether is a fluid that has no physical but electrical property, with a permittivity, Aether measuring 8.8541817128*10-12 Farad per meter.
Therefore Aether is a component necessary to enable (e field) and (displacement charge q) launch into the vacuum for light to propagate. - See also e0, u0 in Maxwell’s equations.
Furthermore, Aether, is a fluid, always attaches to matter, size from subatomic particles to atoms to molecules to ions to solid to liquid to gas and to plasma. When gas, liquid, solid moves Aether drag along with it, locally, and also drag with the MMX’s apparatus.
On the other hand, from a macrocosm scale, Aether as a fluid continues to drag remotely at a mean velocity dominated by mean distance and mean mass of bodies in the vicinity.
With that we can rewrite SR and GR.
Einstein recognized he based part his "Relativity works" also in Maxwell EM formulas...
also in several other previous theories... from Newton to Boltzman... to Planck... etc...
This constant (for now!) has to do basically on interaction of properties of EM wave and the medium where is traveling...
very simplistically the wave frequency the medium allow the EM wave to progress... number of cycles for unit of time...
Parth did a great job explaining it mathemathically... but we sure need 'better words' to explain this to people who 'love+hate maths' (like me)
Question: How was charge and magnetic permeability isolated, experimentally? How is it that permeability constants units fit with their derivation of c? I would assume that Eo and Mo would have been tuned to equal c in that way, and not the other way around. Is the clue that c is the speed of causality not so much that Eo and Mo solve to a pretty equation, but more so that they needed a constant (if actually derived from c) for the charge and magnetic force equations?
Interesting!
There's a lot of history on both the measurement of the electric and magentic forces and the speed of light. But specific to your question, you're likely interested in the Coulomb torsion balance experiment. It demonstrated the inverse square law and the charge dependance for the force between charges. However, the constant in the derived equation was determines as the "Coulomb constant" that just happens to equal 1/(4*pi*e0), but the permittivity wasn't specifically separated out by Coloumb in the 18th century (to my knowledge). A similar experiment is possible for the magnetic force, and I've seen setups to do it, but am not familiar with the history of that one. There were many experiments on the speed of light as well, some fairly good ones based on astronomical observations that predate Coulomb, but I don't think the connection between c0, u0, and e0 were brought together until the 19th century. It's certainly made by Maxwell, but I'd guess that specific connection was proposed prior to his contributions (though I don't know).
The three constants can be (and were) independently determined, but they are not independent. Knowing 2 is sufficient to describe the third (light is an electromagnetic wave, so the relationship makes sense). It's interesting to note the progression: e0 is related to electric charge, u0 to charge velocity (creating a magnetic field), and c0 charge accleration (creating an electromagnetic field/wave). Or more simply: stationary charge interaction-> moving charge interaction-> accelerating charge interaction.
To answer your question, No Eo and Mo were not force fitted to equate to c neither were they derived from c, historically speaking the laws for force between the charges (i.e Coulomb's Law - Published in 1785) and the force between two wires carrying current (i.e Biot-Sarvart Law - Published in 1820) existed before we knew light was an EM wave. And the units of Eo and Mo appearing in the equation had their units according to the equations so for example for Coulomb's law we have F = (1/4*pi*Eo)(q1*q2/r^2), here F is measured in Newton (N), q1&q2 measured in Coulombs (C) and r measured in meters (m) and 4,pi,1 are just numbers they have no units. so Eo gets the unit of (C^2/N*m^2). Similarly you have units for Mo as (N*t^2/C^2). This was purely a result of these laws and had nothing to do with light whatsoever (I mean it has to do with light Physicist hadn't figured that out yet).
Parallelly, wave theory of light was gaining popularity (Physicist still didn't know it was an EM wave but they were definitely sure it is some kind of wave (As opposed to what Newton had suggested in the 1700s (Corpuscles model of light which reigned supreme until the 1800s)) due to a guy named Thomas Yong's famous experiment (Double Slit Experiment - 1801). Now Physicist were curious to figure out the speed of this propagating wave (i.e speed of light which has fascinated humans since the dawn of civilization and was a dream of the likes of Galileo, Ibn Haytham and Newton). Now Hippolyte Fizeau measured the speed of light (3*10^8 m/s - in1848) by purely experimental method still not knowing they were EM waves.
Now in 1865 Maxwell published his famous Maxwell's equations and then he showed that a mathematical consequence of his equations (No force fitting but an absolute rigorous mathematical derivation) are that EM waves can propagate in free space at a speed given by [1/√(Eo*Mo)]. Also, earlier in 1854 and in 1860 Weber and Foucault (respectively in those years) has experimentally shown that the value of [1/√(Eo*Mo)] was equal to that of the speed of light calculated by Fizeau in 1848 but didn't understand what it meant.
Now finally with Maxwell theoretically deriving the same result and them experimentally observing them painted a beautiful and complete picture. Finally Hertz in 1888 produced a Radio wave (a type of EM wave) in lab and measured its speed which agreed Maxwell's theory. Thus visible light and other EM waves became one family known as EM waves and their speed was that of light. This later set deep implications which were then finally understood in a much deeper sense via Theory of Relativity.
So in a nutshell the laws of force for charge and currents were already discovered prior to Maxwell's work with no knowledge of their deep relationship to light. But when Maxwell derived the relationship mathematically with full rigor and also various experimental confirmation started emerging the real picture came forward and a new much further deeper questioned crept out.
HOPE YOU GOT SOMEWHAT OF AN SATISFACTORY ANSWER.
The values of e0 and u0 are only depending on your unit system, the same is true for c. If you measure in a different system, the values will change, but the equation c = 1/sqrt(e0*u0) will still be true. That equation is universal and can also be explained by looking at the propagation of EM waves like light. The way how the electric and magnetic fields of the wave create each other is also connected to e0 and u0 (by the maxwell equations), and the resulting speed of the propagating wave is c.
So those variables were not chosen to fit the equation with c. Instead e0 and u0 as well as c result from the same phenomenon: the interaction of magnetic and electric fields.
But I have to admit: The fact that the coulomb equation has the same factor e0 as one of the maxwell equations seems kind of random to me.
"On the First Electromagnetic Measurement of the Velocity of Light" by Wilhelm Weber and Rudolf Kohlrausch
and "A History of the Theories of Aether and Electricity" by British mathematician Sir Edmund Taylor Whittaker are good places to start.
The various experiments that measured the supposed velocity of light directly are either incorrectly interpreted or not very compelling. But you should come to your own conclusions. What I do know is that a lot of us like to parrot our textbook knowledge without considering if that knowledge is accurate. All the peer-review rewarding in the world cannot make the illogical logical. Or make the undemonstrable demonstrable.
Wonderful video as always! Just a quick question: I heard on pbs spacetime that we actually have a false vacuum, as in there is still a baseline 'vacuum' energy. If we were in a true vacuum, would the speed of light be affected?
A very concise explanation.
About 20 years ago I interviewed N. David Mermin for my Senior Thesis in Philosophy of Physics. He wrote the paper Relativity Without Light, proving that the speed of light is constant starting with some more basic assumptions. I wanted to make sure I wasn't misusing his paper in my philosophy context.
First of your videos I've seen, and I liked it!
Thumbs Up'd & Subscribe'd
I did thought about this while studying special relativity.Though left this part.
Nice that u made a video about it.
The thing that light propagation has to do something with the very space its propagating makes a really good intuition.
Really liked the video😊👍
Request parth g to make a video on oscillation
If one tried to measure c by means of the force between two charges and that between two conducting line segments, he would have to measure the distance between the charges and between the line segments. These are not constants. Rather they depend on the relative motion between the observer and the charges and lines. The analysis offered applies only to an observer fixed with respect to the charges and the line segment.
I remember my teacher of electromagnetic waves course solved the Maxwell's equations using quite a lot of assumptions and he arrived to a wave equation with the speed of light as the speed of propagation. However, in general, the wave equation describes any wave propagating through any medium, such as waves in a water pond and tells nothing about the speed of the wave measured by different observers.
Very eloquently put
The reason why we know the speed of light from a static or moving source doe not add is because it is measured. Since the famous experiment by Michelson and Morley it has been neasured with increased precision...
Imo, the Michelson and Morely experiment is invalid. It's like claiming that a car isn't moving because you don't measure any wind inside the cabin. Plus, the interferometer experiment has since been repeated and gotten different results in recent years. I'm referring of course to the supposed detection of gravitational waves. You can't have it both ways. "Empty space" is either acting on light, or it's not.
Thanks dude! Your videos are always super informative and super interesting and you make concepts really clear. Never stop! :) :)
Hi, thanks for the video. Also please make a video on Riemann Hypothesis.
Great explanation, thank you
Why two same charges always repels and two opposite charges always attracts? Sir , please tell me.
So the biggest “clue” that the speed of light is constant was that the theory of light (Maxwell’s Equations) says it is, in no uncertain terms?
Wut?
My history of science may be a bit off, but I don’t think it was known at the time that Maxwell’s equations were describing light waves, but only that they described propagating electromagnetic disturbances. Later it was realized, after the values were plugged in, that this was close to the experimental value for c, and that thus, light was a propagating electromagnetic disturbance.
@@ahgflyguy «With the publication of "A Dynamical Theory of the Electromagnetic Field" in 1865, Maxwell demonstrated that electric and magnetic fields travel through space as waves moving at the speed of light. He proposed that light is an undulation in the same medium that is the cause of electric and magnetic phenomena.»
@@AdrianBoyko so you’re saying that in the initial publication of the theory, that Maxwell knew that the electromagnetic wave his theory predicted was the light of everyday experience? Or was this a later publication?
@@ahgflyguy «Towards the end of 1861 while working on part III of his paper On Physical Lines of Force, Maxwell travelled from Scotland to London and looked up Weber and Kohlrausch's results. He converted them into a format which was compatible with his own writings, and in doing so he established the connection to the speed of light and concluded that light is a form of electromagnetic radiation.»
So, Maxwell made the claim that light is EM waves 5 years before publishing his equations in their final form.
I was looking for such a video and u know Iwished if u would make it. And there it is. I think tbat is the deep connenction between a teacher and a student that promted u to do that video. Well done keep it up!
dude that last song is so good. bass tabs pls??
So can light be stopped from moving? Why does it have to move at all? How can light be remained in the same spot?
There is sort of a chicken-and-egg problem with attributing the speed of light to Maxwell's equations. Namely: how are we supposed to know a kinematic quantity (the speed of light) from electrodynamic properties? Originally Maxwell's equations was not expressed with a SI unit system with vacuum permeability or permittivity, and cgs units defined quantities such as charge, electric, and magnetic fields based on assuming vacuum permeability and permittivity were unitless. This was a choice made to relate the constants of Maxwell's equations to electrostatic and magnetostatic measurements so that quantities like the ampere for which the coulomb was based on could be made from magnetostatic measurements (now the coulomb is defined by elementary charges as of 2019). This can be seen by examining the Lorentz force in SI units and Gaussian units, because if one assumes that permittivity and permeability are unitless, magnetic fields and the Lorentz force due to the magnetic fields both have the speed of light in their derivations. The inference comes in with Maxwell's inclusion of the displacement field in Ampere's law which includes the speed of light as a constant. It's not clear to me or many exactly why Maxwell took this leap:
aapt.scitation.org/doi/abs/10.1119/1.15263?journalCode=ajp
So to some degree the "why" is that it worked and a wave was measured that matched that of the speed of light obtained by other means (for example the Fizeau-Foucault experiment).
Hi Parth, I'm wondering who first measured µ0 and ε0? are they experimentally determined ?
Excellent!
Goodness gracious, I recently thought about the topic of why the speed of light is changing in other substances. Of course, it's happening cause of N, just like N of water is 1.33 as I remember. However, where is the N actually coming from was a riddle for me, but now I see, it is just N = √ε*μ , and how incredible it is that we can now magnetic properties of water , kerosene and others , knowing just their μ . Thanks a lot for such a great video 🙂
Quantum dipoles are what make up empty space. Empty space alone doesn't do anything. Fluctuations that come into existence and then annihilate do though. These fluctuations according to quantum physicist are made of particle pairs like electron positron pairs with magnetic fields and frequencies of their own and they quickly polarize with other particles traveling through them before they annihilate. This interacts with photons and other particles and puts Vanderwaals Torque on them. So you could say that light speed is not a fundamental constant but a secondary or tertiary result of the permittivity and permeability of space, caused by the interaction with quantum fields and the Vanderwaals Torque they exert on everything. Empty space does not contain time either and has no dimensions and cannot warp, bend, dilate or contract. However, space filled with quantum dipoles, which are real particle pairs with frequency, magnetic fields and spin have time and dimensions. So it's the quantum fields that give everything clock rates and mass, and evidently produce gravity. More mass, more torque. Just a thought.
I get that epsilon nought and mu nought dictate the speed of electromagnetic radiation. This is an amazing and awe inspiring insight into the nature of the cosmos and is indisputable.
I also get that the frequency of the electric field source dictates the frequency and hence wavelength ("color") of the radiation; and that once initiated the E & M field interaction is self sustaining and the wave will propagate through space indefinitely.
What I don't get is why 'c' is still 'c' to an observer who is moving parallel at 'near c' speed; all the "baseball thrown from the moving train' analogies are simply inadequate - the baseball never gets near any 'limiting speed' (such as the sound barrier for baseballs in air) and so the analogies are useless.
If the source is moving close to 'c' how can the emitted radiation travel away from it at 'c' given that epsilon nought & mu nought dictate the speed of electromagnetic radiation?
It seems we use the two constants of nature to calculate (and limit) "light speed" but then ignore those same constants if the source happens to be moving at 'near c' speed!
Why did Einstein need to make this bizarre proposition anyway?
And the particle accelerator "proofs" are unconvincing.
Thank you for a good explanation of this important subject.
Really liked the video,it is awesome ♥
If standard model explains photoelectric effect as a boson-fermion interaction in which the mediator is photon, which is mediator for electromagnetic force, then what explains the threshold frequency?? Hope u understood my question
the electromagnetic field in this case is quantized (That's also what standard model teaches us. The electromagnetic fields due to photon being a mediator are not given by MAXWELL'S EQUATION (which only worked for the classical scenario) but rather by QUANTUM ELECTRODYNAMICS (QED)). So that makes the energy quantized as well of those fields and that's what gives rise to the THRESHHOLD FREQUENCY.
Einstein kind off explained the same effect without knowing QED instead he just postulated that Photon's can have such a nature (With good mathematical justifications tho).
HOPE THIS ANSWERS :)
@Parth G 2:25 ɛ₀ reduces force between charges in a vacuum. Is this because of polarisation of the quantum foam that appears in a vacuum?
In a capacitor, ɛ is related to how much the electron clouds can get displaced from the positive nuclei in the dielectric eg in a high permittivity material eg plastic, the electron clouds get displaced a lot. This *polarisation* creates a 2nd electric field that opposes the electric field between the capacitor plates. So is something like this happening in the vacuum?
Hi Parth, my question is about the depiction of an EM wave. You show it, as everyone does, as two sin waves at (pi/2) radians between them. They both cross zero at the same time. When I interpret Maxwells's equations, I think the curl of the E field depends on the rate of change of the B field. That rate of change of B is greatest when it crosses zero, so E should be maximum at that time. But plenty of smart people show E as zero at that time. What am I missing?
Parth, can i ask you something, lets say i shoot a photon in one direction, and then i use semireflective lenses and stuff to shoot another photon so they travel together. But i invert the phases, so as to have destructive interference from now on. Where does the energy goes? Do both photons disappear? Since i cant detect them after they interact...
Light as a wave a good idea except it interect with particles?
Destructive interference is not an annihilation of energy. Even a single photon will give you interference pattern when you try to let it interfere with a -180 degree phased photon. So what you will observe is a central dark spot where's there is high destructive interference but then nearby concentric circles of light fading.
So all that happened is that your energy dispersed from a central bright region to a outer faded region and central prominent dark region.
Total energy is still conserved.
Short, sharp and sweet
Please help me to understand.
If light travels slower through a medium (e.g. air or water), why doesn't this also effect the passage of time, speed that information can travel or causation?
In other words, why wouldn't time pass slower for me at the bottom of a pool relative to floating on my raft at the surface if light is slowed my the medium (water)?
The simple answer is that what light does in a medium is irrelevant. There are plenty of substances through which light cannot travel - a brick, a tree, a wall, most solid things in fact. That doesn't affect the fundamental laws of physics inside a brick.
@@RAFAELSILVA-by6dy Thank you. I think I got it. As you said, light IT SELF is irrelevant-it just so happens to travel the universal speed limit because it can.
EVENTS, however, can never occur faster then light speed. Light itself has nothing to do with it, it's the SPEED 3x10^5 km/s that can not be surpassed.
Very good explanation!
Can you make a video on scalar waves ?
Is there any proof that epsilon nought and mu nought are constant?
Time is quantised in a vacuum - it cannot be zero - therefore any velocity has a limit. At a small scale, QM (which is not a theory, it has no explanation) time is not quantised and can be zero - so velocity can be infinite, and events can be instantaneous. So there is a time paradox, hence relativity and QM cannot be reconciled. One or both are wrong. There is something missing.
So the beam of light from the moving source, no matter the speed of that source would not gain on the beam from the stationary source?
That's correct. The speed of light is independent of the motion of the source.
So I never actually thought about this but from this I assume the speed of light _in a medium_ is also constant for all observers and more interestingly, it is also independent from the movement of the medium itself, is that correct?
I don't think so...if this were the case particles causing cherenkov radiation in water for example could break causality. I'm not sure but I think that maxwell's equations in linear media implicitly assume the reference frame of the medium. Hence the speed that pops out is with respect to that medium (like with any other wave equation), as opposed to being constant for all observers like in the vacuum.
The biggest clue that the speed of is constant is that light from distant starts reaches us as a clear image. All of the colors reach us at the same time. The stars aren't smeared across the sky. The radio and xray bursts align with the positions of the rest of the spectrum.
I really like the way this guy explains this stuff.
Thank you 👍
Just one question,
Is it okay to think of the permittivity of free space of an electric field as being sort of like a voltage drop of voltage when current is flowing through a wire?
So , in other words , does free space obsorb 8.85^-12 farads of electric field per meter?
Kind of like a copper wire having a bit of unavoidable resistance of current flow , thus producing a slight voltage drop.?
You should say the speed of light is causally constant in all frames of reference ,In 4d dimensional space its not constant velocity. If you use Greens function for at static charge with the correct limits you have opposite charge in imaginary space. This describes a Wormhole-in-a-wormhole (Hopf Fibration).The speed of light in causality is a fractional derivative of sin wave.(Phasal shift)A static charge is a mono-pole magnet..Guido Wugi youtube has good visuals of these typologies.
Good explanation. Thank you.
One question: the permittivity and permeability being constant in the vacuum definitely indicate speed of light also constant. However this equation doesn't address the interaction between two frame of references, right ? In the vacuum the speed is constant, but if a stationary person measure the speed of a spaceship headlight will this equation be sufficient to explain the constant nature of light ?
Depends what you mean by sufficient. If you trust Maxwell's theory of electromagnetism, then yes. But, of course, even Maxwell himself didn't trust it that much. Einstein was the one who eventually dared to say: all right then, let's assume Maxwell's equation are totally correct. That led to the theory of special relativity.
Lights/EM waves rate of induction is Magnetism's rate of creation. Both transverse waves of Dielectric energy and Magnetism are needed to merge into the nodes, that EM waves/Light propagate on. Light/EM waves are modalities of Magnetism and Dielectric energy. Magnetism gives Magnitude to the Universe. You can have Magnetism without Electricity. You can not have Electricity without Magnetism/Dielectric voidence field and Dielectric energy.
How do we know what the vacuum permittivity and permeability is in other galaxies or between them?
Because they supply a medium that allows for the propagation of light and the photons from distant galaxies reach us and our telescopes. In other words, the combination of the vacuum's permittivity and permeability is just another name for the electromagnetic field, which, if light is to reach us from distant galaxies, must be "in between" us. It'd be better to say the EM field saturates the whole universe and is omnipresent.
@@SophiasIchor You can say that but you cannot be sure of that, the speed of propagation might be consistent within a galaxy but different galaxies may have different speeds and that may account for intrinsic redshifts. Very young and dense galaxies may appear to be further away than they are if we rely on doppler alone.
Yes I am sure of that. The EM field exists everywhere, all-the-time, omnipresently. The speed of light is the speed of light (did you not just watch the video?) Redshift is caused by dark energy's expansion of the "vacuum's" spatial configuration. But that doesn't effect the speed of light, which, stays the same for all inertial observers: the speed of light never changes, it is invariant, and "we know what the vacuum permittivity and permeability is in other galaxies or between them" because of that fact.
@@SophiasIchor You're basically just reciting dicta. You don't know that quasars are much closer than they appear.
@@whig01 dude, you didn't ask or claim that. You asked how we know what the vacuum's permittivity and permeability are in other areas of the universe. And we know what they are because they're used to calculate the speed of light, and being that that is a physical constant so too are the vacuum's permittivity and permeability parameters. You're right though, about my not knowing about cosmological distances, but Idgaf about the error ratio of cosmological distances. Regardless, you're original question has been answered.
Only in the same reference frame. Constant: occurring continuously over a period of time, or belongs to a situation that does not change. We already know different mediums alters that passage through space. AE meant it vibrates more or less in different mediums. Plus, QM already stated the emf is not continuous but discreet. Both states light has a time dilation effect to it. You as the observer is not objective. You are subjective. Can't see those other universes! Not tuned for it.
Pls make a video on feynman infinite path integrals
2:23
What is gravity behaves the same way
The problem I see is that it does not predict the speed of light but does so for the speed of causality or so is claimed. This seems like an issue to me as it's only the case in respect to electromagnetic forces so I fail to see how this appropriately shows the speed of causality. When we look at the other boson dues to tge fact tge have mass the forces they carry should be manipulated by its own form of relativity. Is any one capable of showing me the error of my thinking here please and by all means be as complex as need be.
@Part G
Great vid but in some sense incomplete though, or shortcut, one can say. MAXWELL himself believed in a super-substance called the luminiferous aether ε₀ and μ₀ are properties of. This means that the speed of light _with respect to the aether_ were already constant.
What (old, pre-LORENTZian) aether theory is missing is the good old GALILEI principle of relativity which tells us that the fundamental relationships between physical quantities (this is what _natural laws_ actually are) are independent on what coordinate system we're using to calculate, including the rest frames of those observers. In other words, natural laws are _invariant_ under any coordinate transformation.
*GALILEI meets MAXWELL*
Since MAXWELL's equation are natural laws, the should meet GALILEI's principle of relativity, and since the speed is purely derived from them, so should it as well. This is what's actually new about Special Relativity.
Hey Parth, can you explain this, a group of mathematicians has shown that at critical moments, a symmetry called rotational invariance is a universal property across many physical systems.
Thank you. This is super helpful
Does the constant really have to do with light? Or is it just the speed at which energy moves through a vacuum? For example, gravity waves should also move at C. Neutrinos too. Does that mean a gravity wave is also an oscillation of electric and magnetic waves? If gravity and light travel at the same speed what's the correlation?
Gravitational waves doesn’t exist, it’s an human contrivance, a fallacy since the physicists don’t understand space and light! Light doesn’t exist nor do gravity as an force. Gravity is dielectric acceleration towards counterspace. Reed my post for more info 😊
Gravitational waves do travel at lightspeed. Gravity waves are a completely different phenomenon.
@@Ni999 so what are the difference between gravitational waves and a gravity wave?
@@klassemyra Sorry, I can't explain the difference between a phenomenon caused by massive bodies interacting in space and a fluid dynamics effect that you can see on the oceans to someone who doesn't have the vocabulary to understand any of the words and too much mental noise and nonsense to understand the concepts. I'd normally recommend that you try googling the terms but I don't see how that would help you either. ¯\_(ツ)_/¯
And no, that gravitational waves travel at lightspeed does not mean that they are an electromagnetic oscillation at all. If that were true we'd be flying around on antigravity cars by now. Gravitational effects working at light speed implies that if gravity is a force then its (as yet undiscovered) force carrier, the graviton, is massless and if gravity is not a force and is an emergent feature of spacetime (or some deeper reality) then it's simply limited to the speed of causality. We used to insist that neutrinos traveled at lightspeed but we used to think that they were massless. They're very, very light but not massless so they may be moving very close to lightspeed but not quite as fast.
Shared, subscribed. SPIRAL cosmological redshift hypothesis and model based on light speed limit of 'c' standard light speed the universe attained mature size and density by 4/365(5781) a fraction of history, = to 4 days, with a radius of 2B+/- LY., and the entire universe approximates the visible universe, so over 150 T times a more reasonable cosmological model (than the competing SCM-LCDM where the entire universes is assumed at over 200x the visible universe), just for starters based on size, density and a straight line entropy factor.
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in optics we have been learning that speed of light slows down in medium .so we don't have same speed of light..what about its frequency and wavelength ?? and speed of light is same for all observer, and fundamental ? in this case how it is even possible? Parth G will you please elaborate this..
It's because the light that hits the medium excites it's atoms and they also emit their own light and all the waves interfere with each other and the resulting wave looks like it's travelling slower than 'c'. But if u consider actual photons they're still travelling at 'c'.
Obviously frequency and wavelength change ..hence The Rainbow :-)
It is same for all observer but not same in all medium. Frequency remain constant (except space expansion) and Wavelength decreses.
@@kirkhamandy But it does change, at least to the view of an inertial observer? Hence I see a Rainbow :-)
@@rajat4712 how light knows it has to travel in specific direction,,when electron comes in lower energy level ,,it can emit photon in any direction,,when light comes out from a medium it is aligned in single path..
What happens at the intersection where Electric and magnetic wave meet ?
They don’t ever meet. Electricity is not a force, just an hybrid of dielectricity and magnetism. The meeting of a circular magnetic field and the radiell dielectric gives rise to electricity.
Can u please discuss about Fraunhofer and Fresnel diffraction with diagram (like u discussed about formation of wavefront in your old video) something like comparison . 🙏
grazie !
But what happens to mu and epsilon when space expands?
What's a flash light?
Was the speed of light the same near the big bang?
This clue also makes an assumptions about the constancy of mu_nought and epsilon_nought.
Hey Parth, nice video!
My question is that have we do some further research to find why the permeability and the permittivity have those specific values or did we just treat it as a fundamental truth about our reality?
I believe we're supposed to take it as fundamental truth about our universe. Its not like those values are dependent on some other variables and also very slight changes in their values won't have huge consequences ... I think. Same can be said for G being 6.674×10−11 m3/kgs2. That's just how our universe is.
They are both 'fiddle factors' measured experimentally to allow the maths to make sense of the physics based upon our current definition of the basic units of measurement. One could redefine things so as to set them both equal to 1 but that would upset people at the Gas stations big time :-)
@@vassun4891 meh. There's always a reason. It is dependent on other variables. Slight changes would have quite big consequences because computers are sensitive to variations in voltage
@@alphalunamare Like Parth G says they are measures of how much electromagnetism can permeate things. i.e. actual measures of things that exist outside in the universe whether we are "fiddling" or not. They are not just like eg 3.28 is the constant we need to change feet to metres. That constant is arbitrary
@@alwaysdisputin9930 I am not sure that you got my point. What I am saying is that if we change our units of measurement we can arrive at a situation whereby both constants are equal to 1 and hence the speed of light = 1 in those new units etc.
Awesome content, great job...
speed of light video should be sponsored by M&Ms
Why the square root?
Nobody proved yet that epsilon_null and mu_null are observer independent constants!
Whats the speed of light inside a blackhole ?
299,792,458 Hz/dpt - time and one space axis are exchanged inside a black hole.
Nice explanation.. Please I would like to make more videos related to Special and General Theory of Relativity.. Please I would be appreciate it...
Thank you😊
So... if we find a way to alter E or M then we can modify the local speed of light.. They may be constants at the moment, but in the future they might not be....
This raised a head scratcher for me. I the medium changes, would the relativity we know, still apply? (E.g., light going through water.)
If I remember right, each atom delays the phase of the EM wave/of the light for a tiny bit. But between atoms, it always travels at light speed.
Please could you make a video about special and general relativity next
If space is somehow quantized and light is actually propagating through these quantized space "particles" ( - for a lack of better term), it makes all the sense why speed of light would not depend on the speed of inertial object from which it originates. Cause speed of light is not really a speed, as in it is not really measured against time, since time makes no sense for photons.
There are other frames of reference apart from the photon's frame of reference. In other people's frame of reference it is a speed. Why would quantised space make any difference?
Because in a quantized space a quantized packet of energy can only enter into an exit out of a quantized space in descrete packets. The energy transfer process is quantized itself, and can only occur at a certain rate, that the Universe has defined. So from the photons point of view it can only travel through these quantized spaces at a given rate.
Those were the clues, but where's the evidence? Since all equations are simplifications (by necessity), we can be quite certain that they don't tell the full story.
When we talk about magnetic fields in wires, and that equal currents attract, I wonder whether that's still true for free electrons in empty space? Think of a cathode ray tube. If you have two rays of electrons, will they attract or repel?
But there is a nother explanation…
That light is an ”coaxial circuit”, an longitudinal field (pulse) pertubation of compression and rarefaction of dielectricity that gives rise to alternating magnetic and electric fields.
The dielectric discharge creates two volyms, one of magnetism and one of electricity. This takes time, and is what we messure as the speed of light but it’s an rate of induction (of the medium against it self), or one can also say the hysteresis of this fields rate of disturbance from counterspace (which is the field, the medium).
Light is not an particle, nor is it a wave, (a wave is what something does, not what something is). Light in this sense has no speed, and is not an emission, light doesn’t even travel.
Light doesn’t travel in an field (medium), it is the field it self. This is why they could not find the ether. The experiment was wrong because they did not understand light and what light is. The ether (quantum field) is counterspace and can therefore not be measured in our cartesian space, nor be detected, but it’s still everywere! This also explain the so called spooky action at a distance.
Light ultimately doesn’t exist as something physical, not more then a magnetic field does. It’s first when light interacts with matter that it makes it self known through it’s attributes, for example lumination.
Your quackadoodle nonsense spammed all over this comment section is just noise.
@@Ni999 Just because you're not smart enough to understand doesn’t mean it's nonsense. Its logical & sensible and this solves a lot of today's problems in physics, for example, that light is supposed to be a duality. Light is a field perturbation.
Well here you're babbling about light being caused by a dielectric discharge and elsewhere you're babbling that gravity is a dielectric acceleration. I have to admit that you are right - I'm not smart enough to translate the word salad from your faith and make sense of it in the real world where words mean things.
Can anyone explain the result of Michelson Morley experiment ....i am not understand it....that experiment proves that ether does not exist ....and light does not need any medium to propogate ...but how experiment tells that light in independent of inertial frame of reference ......
So wait a minute... I am very confused!
We all know that nobody has actually measured the *one way* speed of light correct? We only know and have measured the *2 way* speed of light. Which is (exactly) K = 599,584,916 m/s.
To do this we have shined a laser through a mirror, the laser bounced back and we got this number... The reason why we can't measure the one way speed of light, is because of Einstein's relativity... Einstein himself new that, and he thought that since we don't (or might never know the answer) it actually doesn't matter how fast the laser is going towards the mirror VS how fast is coming from the mirror, as long as when added together they yield "K" as the answer...
So for simplicity Einstein said, that he will treat the speed of light as being c = K/2 which is c =299,792,458 m/s. But that speed we have not actually measured experimentally... And it could be that we will NEVER be able to measure it, because of the limitations imposed by relativity...
So how does that work with c = 1/sqr(εμ) ?
That gives us a definite number for the speed of light?
So we know what the one way speed is, we just can't measure it?
Thank you very much sir
A question might rise here, is the speed of transverse travelling waves in a string independant of observer's POV since it depends on tension force and the linear mass of the string? same for sound waves too?
Maybe if the voyager exit the medium sorrouding the solar system , and into the interstellar medium , light maybe detected moving faster there.
NONE of this precludes the possibility that the permittivity and/or the permeability of vacuum varies with reference frame. CERTAINLY, the permittivity and the permeability of materials DO vary with reference frame as experiments on flowing liquids demonstrate.
So, if you have two charges submerged in some fluid, and the fluid has a very fast laminar flow, do you expect this to change the electric force between them?
@@drdca8263 It doesn't have to move that fast. Matter has a lot of charge; the + and - just cancels. In a static field, the + and - experience opposite forces that get canceled by electron-nucleus moving off center. But when the matter (or charge) is moving, the electron-nucleus offset is also changing. Since they both have mass (and inertia), they don't find the equilibrium offset until later... and that offset has then changed again. Not only is the force different in magnitude, it might even have a different direction.
@@byronwatkins2565 That seems like an experiment or demonstration that probably wouldn’t be that hard to pull off, and which seems like it would be interesting to see, *especially* if it reverses the direction of the force.
Would have to be careful to separate out the forces arising from just the flow of the fluid pushing up against the instruments independent of the electric charge I guess?
If the number changes as you say it would, that would seem to imply that the refractive index of a fluid would also change when it is moving? I haven’t noticed such a phenomenon, but “I haven’t noticed” doesn’t say much, as I often fail to notice things.
@@drdca8263 It has been done. It does NOT reverse the force direction; it merely rotates it a little if the flow is perpendicular to the field. The hard part is maintaining electrostatic charges and measuring the small force. Separate stands easily isolate the moving medium from the forces. The square root makes the index of refraction less sensitive, but a small bi-refringence has been observed. (Index perpendicular to motion is slightly different than parallel to motion.) They cannot swear that this is not due to strain, however.
@@byronwatkins2565 very cool! Thank you
The universe is not flat. It might appear like it is locally but on larger scales the speed of light changes since the measures of time and distance change relative to where we are.
Maxwell's equations of electromagnetism give one speed for light energy in a vacuum. That applies for any observer in his Inertial Reference Frame (IRF) and only in his IRF where there is no acceleration and no gravitational field. He has no way of determining his velocity and he will always obtain 'c' for his IRF. It is not a license to conclude that it is also true for that observer viewing another IRF. There is no experimental confirmation for that. There is only Einstein's assumption and declaration of that in his second postulate in the Special Theory of Relativity which leads to the error of time dilation.
Is it your position that we've never measured time dilation?
Make a video on oscillation
Love your hair! thanks for the video
The speed of light is constant for a particular medium.