The speed of light c is NOT a universal constant (I) | Sociology and Pure Physics | N J Wildberger

[@christophergame7977]

It is great to see Wild Egg chasing these fundamental ideas.

[@cogwheel42]

8:00 - The lineage from atomic clocks to rulers is indirect, but it's there. Measurement tools calibrated by atomic clocks are used in extreme precision machining. These are then used to produce other very high precision tools, which are eventually used to manufacture accurate versions of everyday items.

[@loicetienne7570]

The gravitational constant may also need to be reconsidered. It seems to be difficult to determine exactly: According to wikipedia, there are "recommended" values, which vary every each four years, and they are not very precise.

[@simrinsahota2398]

Thank you for your rational explanation; it's rare and refreshing to see people use logic to back up their claims!

[@peterrussell7846]

I am very excited about this idea and I am following along with great attention across on WildEgg with the series which is laying out the detail behind the approach to relativity. So while I am excited that all of this may be a breakthrough, I want to keep an open mind and in order to potentially strengthen this approach I want to lay out questions to help focus in on the essence of it. With that in mind, can I ask if you think there is a distinction between one class of issues with “speed of light” relating to the definition of c in terms of an exact distance chosen to be the one used in the definition (along with a unit of time obviously), and a second class of issues relating to what seems to be the structure of what you are laying out on WildEgg in which two way signals are assumed with no relationship to each other and in a way which means there is no real notion of the “speed” of those signals at all?

[@njwildberger]

There are several problematic issues with the speed of light, sort of piled one on top of the other. The first is with the obvious silliness in starting off with a distance unit defined in terms of "the speed of light". Then there is the overwhelming problem that if you really understand what Galileo is trying to tell us, you realize that "the speed" of anything is a meaningless phrase if we try to apply it in a universal, that is, not observer dependent, way. So any statement of physics which involves the phrase "the speed of light" is a meaningless statement if we are to accept Galileo, unless it is immediately qualified as being with respect to some particular observer, and with respect to some particular choice of units for that observer. Then another issue is that, as I lay out in the Wild Egg series on "Classical to Quantum", the essential aspect of relativity only requires some basic assumptions about signals back and forth between an observer and an event: and this signal could be light, or sound, or a myriad of other possibilities. In this way we realize that the essence of SR is quite independent of actually using light signals, it is a much more general phenomenon. The Lorentz transformations are not intrinsic to electromagnetism at all.

[@JulienBorrel]

It should be noted that the convention of the isotropy of the speed of light is very well stated in 1905 Einstein paper : …”we establish by definition that the ``time'' required by light to travel from A to B equals the ``time'' it requires to travel from B to A” Many models breaking this convention have been studied (Mansouri, Sexl).

[@njwildberger]

It is worth stressing that the quote you put around the word "time" here are also in Einstein's paper: an essential admission that he is talking about a concept which has not yet been properly defined.

[@ROForeverMan]

@@njwildberger Time is a quale in consciousness, which like all other qualia appeared for evolutionary purposes. Some consciousnesses might not have this quale, in the same way that humans don't have wings.

[@ROForeverMan]

@@njwildberger You can see my paper The Quale of Time, author Cosmin Visan.

[@tsenotanev]

i think these sociological insights are very important .. mostly for the not so obvious consequence that they convince young people that *_thinking_* is crucial for understanding a theory .. and not just doltishly internalizing something that's already been thought of enough before by the certified large heads...

[@The_Green_Man_OAP]

11:07 Also, he said you couldn't find out what _direction_ you were heading. (Let's assume he was assuming no compasses allowed)... BUT...What about _gyroscopes_ ?🤔

[@LarryRiedel]

Is it constant up to a scale factor, so every observer in every inertial reference frame will agree it's constant?

[@njwildberger]

Something in that direction holds, but one has to let go of the "speed"notion in discussing what is really going on. The real content of the statement has to do with the nature of the worldlines of light in a spacetime / timespace diagram: in a one-dimensional world, all light signals moving to the right will have parallel world lines.

[@Nah_Bohdi]

​​@@njwildberger Its called rate of induction and you dont think like a Physicist.

[@jimmyraconteur]

correct me if i'm wrong; it's been years since I read the 1905 paper, but I believe Einstein also assumes the Lorenz boost as a given as well, but does not derive it?

[@Fysiker]

I'm trying to understand your claim, so I have a clarifying question. Say we communicate with the Klingons, and we explain our definition of the meter using the cesium flips definition of a second and the distance light travels in one second. Then we ask them to measure the distance light traveled in a second in units of Bohr radii, defined using the hydrogen atom, or some other suitable choice (they will have to perhaps move a mirror back and forth until the light travels for a second). Would you contend that they do not find the same number of Bohr radii was traversed by the light in a second as compared to our measurement on another spaceship? Or is the issue you are getting at is that the communication with the Klingons is outside the scope of special relativity, or something else besides a difference in Bohr radii counted?

[@njwildberger]

What you are asking the Klingons to do is not something that we can do ourselves. Suppose we ask our own scientists to measure, by means of an explicit experiment, how many Bohr radii light has travelled in one of our (cesium defined) seconds. Do you reckon there would be any takers?

[@cogwheel42]

There's a channel, Dialect, that is trying to revive the idea of the Aether, or rather the idea that there is some fundamental reference frame that everything moves relative to. For things to work out, you merely have to allow that light can take a different amount of time going from point A to point B than from point B to point A. This is something that general relativity ASSUMES to be false (rather it asserts that the speed of light is the same in all directions), but there is no experiment in principle that can show this to be the case. The only thing that matters to causality is the _bidirectional_ speed of light. So if you're going near the speed of light to the right, it might take years for a signal to reach its destination that is also moving to the right, but then the signal bounces back nearly instantaneously. This is effectively time dilation. Now, since _forces_ are also transmitted by "particles" traveling relative to the aether, this means forces themselves take longer to reach their target. This reduces the equillibrium distance of things like atomic orbitals and such in the direction of travel, which results in a completely literal and physical length contraction. This is not however measurable, since your measurement tools are also undergoing the same contraction.

[@Fysiker]

@@njwildberger it's true that we wouldn't want to use such a unit explicitly as we take the measurement. Lining up hydrogen atoms, buckyballs, or whatever is impractical. However, I do not believe this is an issue, because we may use other units before the final conversion. We could measure our agreed upon unit (eg Bohr radius) in meters and then use metersticks (or whatever is practical) to make our light measurement. In the same way, we could use a more convenient clock than cesium for the measurement. We can't expect perfection in measurements, but we could still have measurements that agree with the Klingons' and converted to be the same units.

[@substantivalism6787]

@@cogwheel42 I feel like dialect hasn't read up enough on the philosophy of spacetime and how conventional it all is. A lot of what SR or GR has to say about the 'relativity of magnitudes' or at least the inferred changes to distances and disagreements about how long it took between two events are not really that fantastical or at least no less fantastical that we take for granted our theories which we also use to construct/test the same tools we use to test any such theory. There are things that seem to still be in stone which people such as Milik Capek and others have picked up on which survive needing neither absolute space nor the declaration of some solipsistic relativity nor the 'block spacetime'. Things such as how if two things are causally unrelated then not much can be asserted about how they connect because they have already been declared as unconnected (relativity of simultaneity). That or how while we may disagree how about the length of temporal intervals that certain sequences of causally related events happen and only in specific orders which are sustained/respected. If A causes B which causes C then no amount of speeding away. . . or towards. . . or how big the bodies near or far from it. . . will change that and in SR or GR for the most part this is respected. The thing dialect and all these Aether nuts need to pick up on is in abandoning a language that spatializes time which is common across the English language and commits us to a mathematical conception of change/identity/physicality/space/time. Course, if we did that then the mathematical physics they so strive to be a part of, just away from the Mainstream, would also come crumbling down.

[@christophergame7977]

We can get a sort of clock synchrony without reference to light by use of mechanically symmetrical separation of identically constructed atomic clocks. Symmetry is a great mathematical idea. Perhaps there is no absolute mechanical symmetry, but I think it is probably the nearest we have. We can at least explore its possibilities. The GPS does so.

[@christophergame7977]

As far as I understand, we have sharp enough clocks to measure the one-way speed of light as Galileo did? We can triangulate between mountain stations? We could take care to make the gravitational altitudes the same for each of the stations, in order to avoid gravitational effects? I have the impression that the GPS has done something like this? I have the impression that people take the recordings to show that the north-south speed of light is the same both ways, but the east-west speeds are not? Synchrony is determined in the GPS by reference to a distinguished clock lying in the earth's axis? I think that the synchrony is not necessarily of the Einstein kind? Does the gravity of the sun affect the results at different times of the year?

[@martinoconserva9718]

This is what you get when mathematicians squabble about physics.

[@njwildberger]

I would rather say that ... this is what you get when physicists don't think clearly enough about the foundations of what they are doing.

[@davidhand9721]

He was right the first time.

[@ThePallidor]

Location can only be defined as the distance of an object from every other object. Time is just a comparison of two distances traveled (the object vs. the clock hand).

[@RedShiftedDollar]

This was an excellent and thought provoking video. I often like to think about a similar dilemma caused by the expansion of the universe. I believe the reason why 1+1 =2 is true is because it is ultimately a consequence of the conservation laws. Matter and energy are conserved, and if they were not, 1+1 would not equal 2. So the fact that basic arithmetic works is basically another way to say information, mass, energy, etc are conserved. This is the link that connects pure mathematics to physics. But now imagine two observers separated across the universe who begin at rest relative to each other. Their kinetic energy relative to each other is zero. But over time as the universe expands, these two individuals at rest relative to each other will develop a velocity as the universe's expansion begins to drive them away from each other. The kinetic energy that develops comes from nowhere. There is no external force applied which converts energy from another form into the energy required to drive the participants' further separation. And as a relative velocity develops, the individuals will also develop free mass. The mass of two people is more than the mass of two people after spending enough time separated by enough distance. What I interpret this to mean is that ALL mathematical truths that depend on 1+1=2, which is basically all of them, are not actually universally true. They can only be locally true at distance scales small enough to allow for us to neglect the effects of the universe's expansion. But even so, neglecting the effects means we knowingly take something which is true (expansion breaks conservation laws) and assume it is false.

[@WK-5775]

There is no need to "distribute clocks and rulers" to other inertial frames in a way that guarantees that they remain the same. As to the clocks, you seem to accept that defining the unit of time via some multiple of the oscillation period of a particular hyperfine transition of a Cs133 atom makes sense. Now it's reasonable to assume that the clingons in their space ship (inertial frame) also know these atoms (uniquely characterized as the atom made of 55 protons and 78 neutrons) and that they have observed the hyperfine transitions too. Thus they will be able to tell how many oscillation periods correspond to one quib. Therefore there is a unique conversion factor between quibs and seconds. As to the rulers, the current official definition of the metre is more a matter of convenience than of principles, since this seems to yield the highest precision among all technically practical definitions, at least a higher precision than all older definitions. I agree with you that a definition which does not rely on the speed of light would be better suited for the present discussion. So let's assume that the metre was defined as a particular multiple of the distance between two atoms in a diamond crystal, say. The clingons can use the same definition, since they know diamond crystals too. This provides a unique conversion factor between doodahs and metres. With these conversion factors it makes perfectly sense to translate "doodahs per quib" to metres per second and vice-versa. In my opinion it follows from the above that there is no substantial obstacle to the assumption that clocks and rulers identical to those used in our inertial frame are available in other inertial frames as well.

[@njwildberger]

Thanks for the interesting comment. However the discussion needs to proceed in a slow and careful pace. We should not assume that phrases like "the unit of time" make sense. For example, I am not sure that there is a prior "quantity/object/substance" called "time" for which the issue is: what units should we use for this stuff? Rather, individual observers may create particular gadgets (clocks) that give certain readings in certain situations, i.e. local times can be introduced. But how do we compare such clocks which are defined by observers far apart, and possibly moving with respect to each other? Just because our clock unit and the Klingon's clock unit say happen to be defined by the exact same number of cesium transitions, in what sense are these the "same" clock if the Klingons are moving at Warp 8 wrt us? To put it another way, suppose we have given instructions to the Klingons to build a second watch which is the "same" as ours. What experiment can we now perform where we both make a time reading to determine that indeed our clocks are the "same"? The issue with length units is similar but perhaps trickier. Yes we could attempt a crystal lattice definition of a metre (something in this direction would certainly be a big improvement on our current metre definition!) but again how do we test that the Klingons have built such a ruler honestly and accurately? And how do we know that the spacing on that diamond crystal between two neighboring atoms is "the same" once we have accelerated up to Warp 8? What does that even mean?? From a mathematical point of view, in many situations when we define an object, we like to build in an explicit notion of when two such objects are "equal". For example, a rational number is an expression of the form a/b where a and b are integers, b not equal to zero... but then we need to say when a/b is equal to c/d: and we do that by the rule that ad-bc=0. SO physicists should also think carefully about what they mean when they say that two objects far apart in "time and space" are "the same". This kind of question is in my view at the core of SR.

[@WK-5775]

When it comes to the "sameness" of two devices in different reference frames, I'd take a materialistic point of view: if they are built up from the same atoms in the same relative positions, then they are the same. (These scanning tunneling microscopes come to my mind, where people can make visible single atoms.) Since the atoms do not have any memory, it's irrelevant where or in which inertial frame such a device has been assembled. The experiments with which it can be checked whether such devices work in the same way as the original ones in our laboratory will be described in the same way, in priciple. That is, how they are built up from their parts. (Typically, a coarser description than that on the atomic level will be sufficient for practical purposes.) As to the possible relative velocity of he Klingons' space ship (in our frame of reference), I'm afraid I'm a bit old-fashioned: If I remember correctly, warp is the analog of mach, therefore I'm willing to believe everything below Warp 1.

[@AllothTian]

​​@@njwildbergerThe Klingon thought experiment is quite interesting but is it necessary? What if we built and synchronised 3 distinct atomic clocks, then put one on a plane that flies around the globe for a while? This experiment has been done and the clock on the plane consistently deviates from the stationary ones. Now you could say that this only establishes local properties of our universe and the Klingon thought experiment is still relevant at distances where we can't reasonably ship measuring apparatuses that were built in the same place, but I think it's still valuable to assume equivalence for the purpose of theorising until (if) technology allows us to experimentally verify such things at "great" distances.

[@njwildberger]

@@WK-5775 I am not sure if you intend the statement "if they are built up from the same atoms in the same relative positions, then they are the same. " to be a definition or a statement of fact.

[@njwildberger]

Keep in mind that the vast majority of the contents of the universe are in plasma state or gas state. The situation where we have somewhat hard metallic objects that seemingly maintain their shape as we are able to move them around is a very special and indeed rare situation. Would a plasmic intelligence give any credence to our definition involving the supposed sameness of hard metallic objects as we move them, and accelerate them, to far distant places?

[@melissacampbell2997]

Thank you for a very concise and thought provoking video. As ever with your videos! I recently researched the history of the metre in some detail and was faced with the circularity of trying to define a unit in terms of the speed of something that was so relative to distance in the first place. I wasn't able to formulate my difficulty with the concept properly, but it struck me how arbitrary the whole concept of defining a metre in terms of light speed was, not to mention completely impractical. Now thanks to you I have a much clearer picture. And it's not just the metre by the way, the inch was redefined in terms of the metre, so as to provide a 10 000/254 ratio, quite suddenly and seemingly randomly, possibly in a bid to reflect a soli- lunar connections between these two units, 254 being the number of sidereal months in a Metonic cycle. In terms of space and time, we should perhaps think of them as conditions of existence, that "exist" only, as Kant put it, a priori. I've recently listened to podcasts by Rupert Sheldrake in which he called into question the concept of laws of physics, as well as the constance of the speed of light. You might also be interested in Irv Bromberg's comment, a fellow Canadian I believe, on his webpage analysing the Hebrew calendar, about how the chalakim, or divisions of an hour, allow for a surprisingly simple definition of the speed of light, from ancient times. It makes you wonder, whether light moves at a constant speed or not, if ole rohmer's experiments might have been performed a very long time ago by others. www.individual.utoronto.ca/kalendis/hebrew/chelek.htm kzbin.info/www/bejne/qXeTZHmEaJyca9ksi=u_fAg6Y3zLLrz7OJ. Thank you!

[@njwildberger]

Yes, even the basic principles of definition are here blatantly disregarded: a speed is traditionally defined in terms of the ratio of a distance over a time, as we all learn in school. So it follows that we require to decide on our units of distance and time BEFORE we may meaningfully even begin to discuss speed. Then to come along hundreds of years later and decide to redefine your basic distance measurement using a prior notion of the speed of something (a photon) in the absence of even a single, clear-cut, direct, prior measurement of this speed is ... almost ridiculous. And thanks for letting us know about the inch definition. Even the Imperial unit system has then been tainted by this same circularity of reasoning. Sigh ... And thanks for the additional references.

[@bernardoxbm]

It is clear that the speed of light is not a constant, because its speed can vary depending on the medium it travels through. In air, water, and glass, for example, the speed of light differs. However, the correct statement is that the value of the speed of light in a vacuum, commonly denoted as "c", is a universal physical constant, precisely equal to 299,792,458 meters per second. This value is derived from two other fundamental constants: vacuum electric permittivity and vacuum magnetic permeability. Space is generally considered homogeneous, meaning that local physics holds true throughout the universe. While the speed of light may change when passing through different materials, its speed in a vacuum remains constant. If the value is not constant what the real number is and how to calculate it?

[@cjwilly1862]

"... space is generally considered homogeneous ...." -- but is it, in a universe where space-time is expanding, perhaps not homogeneously?

[@radiancelux]

Glad I found your channel, great nuanced discussion. 🚀

[@davidhand9721]

It isn't though.

[@christophergame7977]

It is a confusion to conflate unextended point-events with finitely extended processes. Finitely extended processes really exist and can be really identified, and we are always relating ourselves to them. I guess that perhaps you may have really read the just preceding sentence? Unextended point-events are convenient abstractions that are useful for mathematical analysis of finitely extended processes; they are real in so far as they relate to really identified finitely extended processes; Euclid, Galileo, Newton, and Einstein use them.

[@spamwithegg]

What I find stranger are the Lorentz transformations, especially the gamma factor “1/sqr(1-v^2/c^2)”. This factor goes to infinity at v = c. The light quantum should have no expansion.

[@jiiiiiiiiiiiiiiiiiii]

Is your main concern that the Cosmological Principle might not hold? While true, my understanding is that it's a sensible hypothesis that we make until we find compelling evidence to the contrary. Similarly, we don't actually know if Galileo's principle of relativity holds true everywhere and always. It could still be disproven. But as long as all evidence seems to be fitting it, we assume that it's true. Likewise for the cosmological principle, so I don't quite get your point with the Klingons.

[@njwildberger]

No, my main concern here is that Einstein's Second Postulate is either false or meaningless.

[@ebog4841]

@njwildberger it's not a postulate- Einstein was very clear about this

[@tw5718]

What's very coincidental is that when we ignored SR (and GR), GPS failed. When we accounted for these results, we move from the schroedinger eq to the klein gordon and to the dirac, which predicts antimatters existence. At the very least, c is a local constant ( as demonstrated by michelson-morley). When c is taken to be a universal constant, we predict antimatter. When c is local ( smaller than orbital range) gps fails. Worth noting that length contraction predicts the existence of magnetism and the lorentz force.

[@njwildberger]

The essence of SR are the Lorentz transformations and Einstein's equation E=mc^2; we can all agree on their importance and applicability. However the interpretations of those equations, and the question about their underlying "meaning" is still something that we can have a lively debate about. It's not that different to the story of QM: everyone more or less agrees on the equations, but the interpretation of those equations span a wide range of possibilities.

[@davidhand9721]

Just to start, yes, it is a constant. It's been verified hundreds of times with exquisitely precise interferometers. Just because they are not using a stopwatch does not mean they aren't measuring speed. That you don't understand how is a you problem. However, the speed of light actually is not about light. It is the speed of causality. Any massless signal travels at c, including gravitational waves. It defines locality. There is no way to explain a direction dependent speed of light without breaking the first postulate. There are interferometry setups that could detect that, too, but they don't.

[@domenicobarillari2046]

You conflate "difficulty of doing" with impossibility very casually. That the speed of light is constant even in one-way measurements, for instance, is validated in the modern version of the Roemer experiment every time a message is received from a distant, fast moving probe like Voyager with atomic clock precision. Indeed, if you want to set up a nice undergraduate physics experiment, you can measure time of departure and arrival times for a photon in even in on a benchtop, with two previously synchronized atomic clocks. Most other remarks are told as if quotes from old physicists sometime contradict the findings and interpretations in modern physics, but all that I hear are red-herrings for a lay audience. For instance, there are well thought out methods (thought-experiments) for synchronizing time and space readings between space craft in motion. This would be a bit practically harder in really curved spacetimes, but there is no befuddlement that you seem to imply. Indeed, as far as absolute rulers, the standard number of oscillations of some well know atomic transition is an IDEAL way to compare sizes and times across civilizations: do you know of the gold plaque on the side of the Voyager probes? Mentioning the 21 cm line of hydrogen? What is it you are really after, critical thinking or spurious criticism?

[@njwildberger]

The "speed of light is a universal constant" statement is NOT validated every time a message is received from a probe like Voyager.

[@domenicobarillari2046]

@@njwildbergerThe motion of the Voyager probe is calculated just the dynamics involved in the Roemer experiment. Every contact with that initiating source does a displaced source experiment. Check your facts. On time arrivals of signals would not be possible, as measured by atomic clocks on earth, without this constraint.

[@chaz000006]

When you come up with a theory where the speed of light is the upper limit, of course calculations won't allow it to be met, and by extension, exceeded. Is there 'infinite' anything? Because if not, then the faster you get to the speed of light, an object would just gain a lot of mass. And could the 'ether' in part be the Earth / sun magnetic field in which light (because photons don't have mass but polarity), instantaneously falls into Earth's magnetic field lines which happen here to be a meter long? Sorry for asking dumb questions.

[@usurpvision]

I've never understood that notion, the idea that mass increases as you get closer to the speed of light. The reason it's not intuitive to me is because the less massive the primitives are, say electrons of quarks or gluons, the closer to the speed of light they appear to be moving. I can't wrap my head around the idea that if you were to further accelerate a bulk of electrons to near light-speed, that you'd be able to use some sort of measurement device (maybe a pressure sensor in a vacuum?) to determine that the "mass" of the individual electrons does in fact increase. How exactly does that work?

[@chaz000006]

@@usurpvision Yes, they say the Higgs boson is the part of the atom responsible for mass, so perhaps all these other parts of the atom technically have no mass and can go faster. But I read they've done experiments and confirmed mass is gained by objects as they get really fast, but would they gain 'infinite' mass?

[@usurpvision]

@@chaz000006 Well I'm sure we can't test anywhere near the infinite case, but do you have a link to the experimental paper so I can take a look at it?

[@santerisatama5409]

@@chaz000006 "Mass" is a unit-concept of measurement theory, not something intrinsic to nature. Same applies to particles in general, we can't prove that the particle aspect has inherent existence beyond measurment events.

[@carlosgaspar8447]

wouldn't the measurement using jupiter's moon eclipse be a one-way computation.

[@njwildberger]

That's a good question. So we should inquire: how do we know about the distance travelled? And then when we look at the actual measurement, we see that there is not really a speed measurement being done: just an indirect argument that compares time differences between two different trajectories. I will admit that this is something of a one-way computation, but perhaps not entirely. I would be interested in physicists' take on this issue.

[@carlosgaspar8447]

@@njwildberger veritasium (and others) did a recent video on the topic but just repeated the common theme of out and back measurements or the problem of synchronizing clocks.

[@zhavlan1258]

Hello from Kazakhstan. If we add NEW 50% of the Michelson-Morley experiment, then it is “possible” to prove the postulates: 1. Light is an ordered vibration of gravitational quanta. 2. Dominant gravitational fields affect the speed of light in a vacuum, its direction and frequency of oscillations. I need help co-creating an invention. The light in the device has a path of 9000 meters in a volume of 0.4/0.4/0.4 meters.

[@FergalByrne]

Norman, the Galilean relativity involves you carrying your entire apparatus around with your frame. The Einsteinian relativity is about us making measurements when the space between our apparatus is in its own frame (shared between observers). The corresponding object in your timespace affine plane is the shared pair of lines, agreed at the origin as observers pass through it.

[@draconyster]

I really enjoy hearing your perspectives on established definitions and things people take for granted in science. It would be amazing if one day you appeared on Sean Carrols Mindscape podcast, him being the other person with some great perspectives I listen usually to.

[@steffenkarl7967]

Even the balancing of charges on a metallic sphere is not instant. Does not an electron figure out where it is and what to do via photons?😊

[@dsm5d723]

Great of you to find Galileo defining inertial refence frames. I wonder if you could attempt the same thing for big G, the gravitational constant. I've heard of an experiment where two objects of the same size and weight were dropped from the same height. One had two strong opposing magnetic fields inside it, and fell slower than the other one.

[@محمدنجم-د2ط]

Doesn't the speed of light pop out naturally from Maxwell equations?

[@WildEggmathematicscourses]

No

[@josefnaus5898]

​@@WildEggmathematicscourses The derivation is easily accessible online.

[@AnimeLover-su7jh]

This discussion reminds me of Ruler introduction book to mechanics volume 1, in which he actually discuss how problematic the assumption of Newtonian mechanics about fixed frame of reference.

[@esorse]

Assume the law of non-contradiction : nothing is it's opposite, specify "not" contextually to mean either no thing equal to nothing, complement, or opposite and consequentally not delimited "category", rename it "set" * , recognize numeric syntax for a quantitative measurement system and yeah, you could avoid the contradiction from infinity and zero behaving like substitutes under multiplication, but complements under addition, by not either explicitly, or implicitly, including infinity, eliminating a discrete entity 'hedge's' value. * "The set of all sets" could be a euphemism for infinity in Russell's set theory critique : the set of all sets is a set that is not an element of itself and is not, a set that is not an element of itself.

[@RichardSouthwell]

Thanks for making these relativity videos. They seem to make physics make more sense

[@christophergame7977]

We can also measure time in a more or less universal way through atomic clocks. The GPS system does it all the time.

[@njwildberger]

The GPS system is hardly a universal system. It is based firmly on human technology, units and conventions.

[@christophergame7977]

@njwildberger Thank you for your valuable response. Yes, it has a load of very human ingredients. And, yes, it refers to the earth, a highly local factor. But it uses atomic clocks. They rely on quantum mechanics, which I say is universally available. And it uses many of them. Which I say provides the mathematical benefits of symmetry that isn't confined to Einstein synchronization. I am trying to escape the straitjacket of Einstein synchronization.

[@MrWonszBoa]

I am now watching your History of Mathematics and I like it a lot. Thank you for this!

[@dismian7]

Thank you for being willing to criticize popular science and mathematics. There are many things which seem to make no logical sense to me, yet I'm told not to question it. I think questioning things and for them to make logical sense is essential, regardless whether it's due to new insights or a change of mind. This search for understanding is in my opinion one of the most critical things for humanity to do, in order to improve in any regard. Yet, it is so often punished by popular opinion, in which people don't actually rebuke arguments, but resort to harassment or belittling. It's ok to criticize things. It's ok not to understand things and questioning it. It's ok to have a different opinion as long as it doesn't harm anyone. Hopefully people will agree on this and respect criticism and each others opinions.

[@familyshare3724]

We have faith that reality follows simple elegant mathematical laws. We define c and other constants as if our models are perfectly true, rather than define our models based purely on observation. Thus we conjure dark stuff and dark forces and dark constants into existence to force fit observation with our perfect models.

[@a.hardin620]

Are you going to eventually advocate for a variable speed of light theory? Is this where you are going? I’m curious what your point is. VSL theories are a tough sell: lots of physics including electromagnetism depends on/and works well with a constant light speed. So that’s a really tough road to embark on. It’s not proven impossible but VSL theories don’t look promising.

[@njwildberger]

No, I am not going to advocate for a variable speed of light theory. I do not believe that the speed of anything is meaningful in an absolute way. Similarly to say that the absolute speed of something is changing in such and such a fashion is correspondingly meaningless. We have to find more nuanced and careful language to describe what is really going on.

[@cogwheel42]

I think an even stronger statement can be made: there is no way in principle to measure the single-direction speed of light. The information about how long it took to get from source to destination has to travel back to the origin. Or rather, information has to travel from the origin to the observer, and from the origin to the destination and then to the observer. On top of that, the observers and all the apparatuses are subject to the same transformations as anything else travelling through the Aether. All these effects cancel out such that we can only ever measure the bidirectional speed of light, and it always appears the same in all directions. It then becomes a bit meaningless to question whether a cesium clock runs at the same rate on Klingon as it does on Earth. The only way to compare them is to either bring them close to each other, which immediately changes the experimental conditions, or to send information from each to a common observer, which again is subject to whatever local conditions the observer is experiencing.

[@WK-5775]

Why do you say that there's no way in principle to measure the unidirectional speed of light? If I understand it correctly, then it's exactly what they did in the 17th century. They took the "switching on and off" of Jupiter's moon Io (as Io goes through the shadow of Jupiter) as a periodical signal, and they noticed that this signal was observed on earth at times which are not as equally spaced as it was expected. The time spacing of the observed switchings was noticed to be correlated with the month in the year. They explained this phenomenon by the fact that in some month of the year, the earth is closest to Jupiter, whereas six months later it's farthest, with the diameter of the earth's orbit around the sun as the difference in distance. From the time variations of the observed switchings and this diffence of distances, they were able to compute the speed of light. That method wasn't very precise, but it gave the correct order of magnitude, and it is a unidirectional measurement. (The main lack of precision was due to an insufficient knowledge of the radius of the earth's orbit, I think.) In another post, I understand that you acknowledge the actual use of systems of high-precision clocks, positioned at fixed distances between each other and synchronized. (That's part of what people do in laboratories...) Why can't one measure the unidirectional speed of light in such a setup? Emit a light signal near one clock at some fixed time and detect it near another clock and determine (read off) the corresponding time. Once this has be done, there is no need to transmit any information at the speed of light. You can collect the observed data the next day, measure the distance between the two clocks (in your favourite length unit) in all tranquility and compute the resulting quotient.

[@cogwheel42]

Re: the 17th century experiment, this is begging the question. You have to assume that light travels the same speed in all directions in order to conclude that you're measuring the one-way speed of light. The experiment reaches the exact same conclusions if you fix the speed of light in a single inertial reference frame and allow observers to "experience" asymmetric light speed. Periodic signals coming in more or less frequently when you're moving towards or away from something is exactly what you'd expect. The problem is the measurement. The people doing the measurement will always, in principle, perceive the speed of light as the same in all direction, because it's not the speed of light: it's the speed of causality. Every bit of processing your brain does, every atomic bond length, every electromagnetic emission, radiates its influence on the universe at the speed of causality. An inertial observer can't in principle experience anything other than light seeming to travel the same speed in all directions, because the speed of causality is what _governs_ experience itself. This is true whether you accept Einstein's postulate or not. > Emit a light signal near one clock at some fixed time and detect it near another clock and determine (read off) the corresponding time. > Once this has be done, there is no need to transmit any information at the speed of light. You can collect the observed data the next day, measure the distance between the two clocks (in your favourite length unit) in all tranquility and compute the resulting quotient. The same points apply here. In order to carry out this experiment you need to synchronize the clocks which requires bringing them to the same physical location. Then you have to move them away from each other. This disrupts the experimental setup. The act of moving the clocks to different physical locations inherently changes their inertial frame, if only briefly. The distance between them creates a causal disconnection that can only be bridged by transmission of information. Assumptions we make about simultaneity break down, but more importantly, we still can't _observe_ whether the speed we're measuring is one- or two-way

[@WK-5775]

@@cogwheel42 Re: I never said that the 17th century experiment proves that light travels the same speed in all directions. I only mentioned that experiment to give an example for a one-directional measurement of the speed of light, because you asserted that that wasn't possible in principle. Indeed it "only" measured the speed of light in the direction from Jupiter to the earth. (For all nitpickers: as Jupiter wasn't standing still, it's rather the mean value of the speeds of light in all directions involved during the relevant period of time.) But guess what: other people have done similar experiments with other astronomical objects in different directions in the sky. No indication that the speed of light depends on the direction.

[@kayardin]

If Red, Green and Violet all express at different wavelengths, do they not move at different speeds? 🎉

[@hywelgriffiths5747]

No, because they have different frequencies (waves per second). Longer wavelengths have lower frequencies

[@christophergame7977]

I have an idea for a new principle to consider. The paradoxes of relativity arise when two identical clocks, initially synchronized in one and the same place and co-inertial, are separated for a substantial journey, and then brought back together in one and the same place and co-inertial. Here is my suggestion to avoid paradoxes: The course of the process should be described in terms of a single centrally placed suitably co-moving reference clock. We should not and cannot expect the separate clocks to give a coherent account of the process. For example, there is no coherent Einstein synchrony of separate clocks attached to a rotating disc. Synchronization of two clocks demands a third suitable centrally placed and co-moving reference clock. It might be said as a principle that local time is not a 'conservative' quantity. Another way of saying this is that causality rules, but must be judged in terms of a single reference clock.

[@davidhand9721]

Again, the exact value that we write as meters per second is not what makes it a constant. Nobody thinks aliens are going to use the same units or even the same number system. It is nevertheless a constant, and we will all agree on speeds as a fraction of c, and we will be able to convert from whatever units the Klingons use and get the exact numbers they do as a ratio between units.

[@johnfranklin8147]

Absolutely *no* physicist would tell you that “c” is a universal constant. Constants are things that are measurable, independent of your set of units, which means that all universal constants are *ratios* of measured things; they are dimension-less. The fine-structure constant alpha = 1/137.04 is a universal constant. The ratio of electron-mass to Planck-mass is a universal constant (although even then not a fundamental one; the fundamental constant is the Yukawa coupling constant. The speed of light is not a “constant”, and nor is Boltzmann’s constant kB - it *defines* our temperature units, not the other way round. The fact that c has the units m/s tells you one very important thing: that one of those “dimensions” has stupid human-historical units. The units mean nothing, they’re just a way for us to keep track. In this case, time could very reasonably be measured in meters; a meter happens to often be called by its stupid old human-historical name “0.3 nanoseconds” when humans put labels on clocks, but other than a naming convention there’s nothing odd about it. Lorentz invariance tells you nothing more than this: if you take a meter hypercube, ie 1 meter x 1 meter x 1 meter x 1 meter (cough 0.3 nanoseconds, cough), then if you take two observations of it from different angles (cough “relative velocity” cough), you will see the meter cube rotated. I can’t think of anything *less* surprising, when seen from that perspective. Your worry that we don’t know the “one-way speed of light”, is similarly not-fundamentally-interesting. It is no more than observing that if I take a meter stick and measure it from A to B, I get the same measurement as if I measure from B to A. So what? Perhaps you can imagine a universe where that’s not true….but it would be so alien, that you couldn’t really define the distance “between” two points at all. With the right glasses on, Special Relativity is not only simple, and not only the simplest possible, but really the only logically-consistent theory it could be!

[@christophergame7977]

Currrently, we believe that protons are relatively fixed items of existence. We can use crystals, containing organized arrays of finitely many (counted by integers) protons, to measure distance in a more or less universal way. We don't know why protons are relatively fixed items of existence. That is the unsolved problem of quantum mechanics. But it does make quantum mechanics of fundamental importance.

[@Zebinify]

Hummm, I feel like if we can accept that the atomic clock can be viewed as a measurement of time; then there is measurement of distance using speed of light; such as GPS systems, most radar and wireless communication systems; or if we are aiming fancy, femto second lasers. But I guess the difference between physics and math is that, physics will never find a "solid foundation", just as the astronomical ladder of distance; every measurement is based on another measurement. From a more real-world application side, now-a-days it takes quite a bit of sophistication to figure out that do we mean by "elevation of 0m relative to sea -level" or "the north american continent moved by 3cm last year", the position grid is somewhat calibrated to GPS and gravitational field, but move of continent also change GPS and gravitational field... so eventually there's no such thing as solid logical foundation for physics.

[@konradswart4069]

Every time I see Norman Wildberger 'produce' something, I have the feeling that he _never_ goes to the bottom of things! I have followed him for decades. Especially in his analyses of problems surrounding infinity. I have tried to communicate with him about it, and have, inspired by his questions, found answers to his conundrums about infinity, but although I got some really good responses of others who wrote my comments, I _never_ got satisfactory responses _from him!_ Some praises about my cleverness. But that is not what I am after. I rather have _a real dialogue_ with him! To me, the issues he raises are interesting. But _his solutions_ are never _so_ clear-cut that they actually _solve_ the problems he raises. And I have the same misgivings about this video. For example, I wonder whether Norman Wildberger is aware of the fact, that _all physical constants that have units of measurrement_ are not absolute magnitudes, and they _all_ depend on what we choose to measure them with, and that _therefore_ the numerical values those constants have _are irrelevant!?_ In other words: all constants are parts of laws of nature expressed as differential equations, and having a particular dimensionality (= units of measurement.) They are just manifestations of the particular instruments we use to measure them, and the units these instruments incorporate. But this is not true for _all_ constants we find in nature. When some constant of nature is independent of the particular measure instruments and the units they either implicitly or explicitly represent, it is _a real constant_ representing _a really existing phenomenon!_ And _only_ if this is the case, they are physically relevant! The question therefore is not whether the speed of light is a universal _constant!_ It is _not_ because the particular numerical value it gets depends on what units of measurements are chosen. The same applies to many other magnitudes, like charge, mass, electric permittivity in a vacuum, magnetic permeability in a vacuum etc... But something like the electrical force between two charged objects divided by their gravitational attraction results in a dimensionless quantity, which therefore _is_ relevant for physics, and needs an explanation. Or something as simple as the number of spatial dimensions. Although the extend of spatial dimensions can only be measured by measuring rods or something similar, the _number of spatial dimensions_ is dimensionless, and therefore is a real problem to explain. Realizing this, the question then becomes: what _regularities_ do we observe with our measurements? The constants in the differential equations expressing laws of nature _with_ units of measurement have no physical significance. But _dimensionless constants_, which for this reason are _independent of_ units of measurement _have_ physical significance. That is why many theoretical physicists put all such constants like the speed of light, Planck's constant and others just to be equal to 1, only to 'translate them back' to the ordinary constants when measurements are needed to either corroborate or refute their theories. And when we _then_ look at the speed of light, the numerical value depends indeed on the way it is measured, but _this fact has no physical meaning!_ The particular constant depends on the units of measurements we choose. But _the experimental outcome_ of the Michelson - Morley experiment, and Galileo's statement of fish in a hull of a boat etc is still, that the speed of light _is the same_ for different observers _if_ they use the same units of measurement! Therefore, if we understand the statement: 'the speed of light is a universal constant' as saying: 'the speed of light is a universal magnitude; i.e. the same for all observers, irrespective of the way they measure it, or whenever they use the same units of measurement,' then _we have found something we must be able to explain!_ We then have found _a real puzzle, a real question!_ Looking at the speed of light like this, then it is _an undeniable fact_ that the speed of light _is indeed the same for all observers!_ Meaning, if any observer obtains a certain value of some measurement of the speed of light according to his units of measurement, he can convert it to another by just converting the numerical values of their rulers and compasses to that of used by others. There is a deeper problem here. One I have never seen addressed by anybody else. And that is the simple question: _how can it be that such a phenomenon like the Galilean Relativity exist?_ _What tells the Galilean Principle us about space and time itself?_ That is a question that is simply _disregarded_ by all physicists as far as I know. All just _begin with the Galilean Principle of Relativity!_ But _the real question_ is: how are we to _understand_ the Galilean Principle of Relativity in its most universal form? I have devoted myself about 20 years, and _I have found the answer to this question!_ In fact, I claim that I can _derive_ the Galilean Principle of Relativity (which is also Einstein's Principle of Relativity) _from first principles!_ And, remarkably, when I did this, not only the Lorentz transformations 'pop out' as an absolutely necessary consequence, but even the 3 + 1 space-time pattern, _including_ the universal nature of the speed of light, _and_ the fact that space itself is, of necessity, 3 dimensional! I claim that the 3 space dimensions + 1 time dimension _is the only way_ wherein such a thing like the Galilean Principle of Relativity can exist! It tells even something _much deeper_ about how existence can be in the first place!

[@jiiiiiiiiiiiiiiiiiii]

Well, then please publish a blog post, or even better, a paper, with that derivation. A claim in a KZbin comment is rather meaningless.

[@konradswart4069]

@@jiiiiiiiiiiiiiiiiiii You are very right. _Working on it!_

[@njwildberger]

Hi Konrad, If I don't always respond, don't take it personally -- I am pretty busy. You can make it easier by focusing on one issue / question at a time. When faced with a long comment or reply, I am usually perplexed in deciding on what to respond to.

[@konradswart4069]

​@@njwildberger ​ Thanks for your response, Norman. Well, let us consider then just one issue. The issue of understanding infinity. My central idea is that Cantor had it wrong. You cannot consider an infinite set as something complete. Infinity cannot be defined constructively. That is, you cannot understand the concept of infinity as an end result of some process that is imagined to have been completed, resulting in a structure that is infinite. Allowing this to happen leads to contradictions. However, This does _not_ mean, that we cannot _understand_ the concept of infinity! You undoubtedly know Cantor's argument, so I shall not repeat it. What I want to show is an example that is in contradiction of his own notion of a completed infinity. Suppose I make a list of real numbers between 0 and 1, which I claim to contain _all_ real numbers. For simplicity I use a binary representation. I construct this list in the following way. I begin with 0.0 0.I Then I continue this list in the following way 0.00 0.01 0.10 0.11 I continue this list in the following way: 0.000 0.001 0.010 0.011 0.100 0.101 0.110 0.111 I continue this list then in the following way: 0.0000 0.0001 0.0010 0.0011 0.0100 0.0101 0.0110 0.0111 0.1000 0.1001 0.1010 0.1011 0.1100 0.1101 0.1110 0.1111 I now _imagine_ that I have _completed_ this list, up to and including Infinity, as Cantor suggests. As you can see, I basically go through all _finite_ numbers, and in each step I add double the number of numbers I have added in the previous step., Now, I can imagine to apply Cantor's diagonalization argument at the 'last part of this infinite list'. Cantor asserts that that number is not in this 'list at infinity'. But, according to this construction, that 'last list' _must contain_ every real number between 0 and 1 and therefore _is in this list!_ So, we have a contradiction here. I have 'constructed' a number that is both _in_ a complete list _and not_ in that list. The only way out of this contradiction is changing _the meaning of_ infinity. I define 'infinity' simply as 'not finite'. And that is an _eliminative_ definition! Understanding _does not only consist of construction!_ Understanding can also be based on _elimination!_ The set of all positive integers, for example, is said to be infinite. Infinite means: _not finite!_ Infinity can not be understood in terms of a construction. However, infinity _can_ be understood in terms of an elimination, which is _a totally different form of understanding!_ Understanding this _resolves_ the conflict between the formalist approach to mathematics of Hilbert and the constructivist approach to mathematics of Brouwer. Both were talking about two different, but complementary, even dual forms of understanding. Understanding as elimination gives a new understanding of what axiomatic systems are. Axioms _are not_ descriptions of structures that exist in the mind. No, they are _criteria_ that certain constructions must satisfy. Therefore, axiomatic systems, at their deepest level, describe what systems _are not!_ This distinction is important. To apply it to the idea in this video, for example. What Einstein did, was taking the Galilean Principle of Relativity _as a criterion of elimination!_ He stated that _any theory of physics must satisfy the Galilean Principle of Relativity!_ The Maxwell equations _do not describe what electromagnetics is!_ No, they describe _what electromagnetic phenomena are not!_ This, in fact, applies to _all_ laws of physics. All laws of physics are written in the form of mathematical equations containing a time variable _in the numerator!_ Newton's basic law of mechanics *F* = d*p*/dt is a case in point. This is a law of nature. But we cannot derive _anything_ from this law alone that tells us something _positive_ about reality. Only _adding initial conditions_ to this differential equation, and adding those in a concrete experiment, leads to a differential equation that can have a particular solution. But if we abstain from adding initial conditions. What then, does this equation *F* = d*p*/dt say? Only one thing. It tells us what we must _reject_ as a description of reality. For example, according to this equation, it is impossible that an object disappears at one point and at the same time appears at another point in space. It tells us that teleportation is impossible! It violates Newton's law of mechanics. Such a 'process' would be inviolation of the law of conservation of momentum, which is one of the consequences of Newton's equation. In other words, the laws of physics, _without_ their initial conditions, tell us _what is impossible!_ And, and _that_ is my point, _as such they can be understood!_ Understood _not in the form of some mental construction,_ but in the form of _elimination!_ An intuitionist is somebody who is not aware of this perspective of elimination as a second form of understanding. In fact, I have _never_ seen a book about either physics or mathematics that shows some awareness of this crucial distinction. The result is _a lot of confusion!_ _Understanding_ this issue, causes more carefulness about what we understand and what we don't understand. We can understand in terms of construction, and that is maybe 'the best'. But if you believe that any understanding based on elimination is not understanding at all, you are blind to this second form of understanding. And _that_ is basically my critique on many things you assert! Let me apply this elimination thinking on the speed of light. From the Galilean Principle as extended by Einstein, applied to Maxwell's equations follows, that there is nothing to eliminate the possibility of an electromagnetic phenomenon that sustains itself in existence and having a definite speed c with respect to any observer. That is one of the consequences of Maxwell's equations. Maxwell extended the equations to make them logically consistent, by adding a term. Then he eliminated charge and current, leading to simpler differential equations. He solved them and from this he constructed a possible wave which 'upholds itself in existence' in the following way. A _constantly changing_ electric field causes _a constant magnetic field!_ A constantly _changing_ magnetic field causes _a constant elecrit field!_ Therefore, _a sinusoidal changing electric field causes a sinusoidal changing magnetic field which causes a sinusoilda changing electric field ..._ In other words, _a phenomenon that upholds itself in existence by becoming its own cause and effect!_ Moreover, this phenomenon _has a definite speed!_ And, since Einstein generalized the Galilean Principle of Relativity to be applicable _to all phenomena of nature,_ the speed of light _had to be independent of the speed of the observer!_ Therefore, the constancy of the speed of light _is a consequence of the generalized Galilean Principle of Relativity!_ It _must be_ constant with respect to any observer. Any theory that _rejects_ this, is in violation with the Galilean Principle of Relativity. This means, that even in general relativity, the speed of light _must be constant_ when the force of gravity is eliminated. This was Einstein's own argument! According to his own statements about special relativity, he _wasn't aware_ of the Michelson-Morley experiment. He just argued strict according to the laws of physics and by using the Galilean Principle of Relativity. However, realize that both Maxwell's equations _and_ the Galilean Principle of relativity are _exclusion principles!_ They tell us what theories _to eliminate_ to be acceptable as constructive theories of physics. Therefore, I can safely conclude that Einstein _did not understand special relativity as a construction!_ This is because Einstein used _a postulational, that is, axiomatic approach to both special and general relativity!_ And axioms _do not tell us what reality is!_ No, axioms tell us _what criteria construction must have to be called the special name given to the axiomatic system! The group axioms, for example, _do not tell us what groups are!_ No, they tell us _what to reject if we want to call something a group!_ The same applies to rings, Hilbert spaces, Euclid's axioms etc... They are all statements of exclusion or elimination. That is what _mathematical rigor means!_ Pure mathematics is about seeing _what not to consider, and therefore to see the scope of theories!_ The whole 'circus' around Quantum Mechanics is also the result of _misunderstanding_ what our present theories of quantum mechanics really are. They are also _postulational!_ Therefore, our books about quantum mechanics tell us what theories about quantum mechanics _to reject!_ And it turns out that we can formulate several _constructive_ theories of quantum mechanics, none of which violating the postulates of quantum mechanics. Like the Copenhagen approach, Everett's many world theories and what have you! Richard Feynman, for example, didn't understand this. He asserted: 'I can safely say that nobody understands quantum mechanics'. Well, _he was wrong!_ Physicists _do understand_ quantum mechanics. But _not_ as a construction, but as _an elimination!_ They understand _what theories to reject when somebody proposes a new theory, a new interpretation of quantum mechanics!_ This is what 'calculate and shut up' is about. Well, for the time being, I stop here. I hope I have given you something to ponder about!

[@The_Green_Man_OAP]

I'm sure John Chappell Natural Philosophy (on YT) would love to have you on as a guest speaker‼️ 😁

[@robertjmakowski4047]

space-time means that neither length per se, nor time per se, are invariants of motion. accordingly, a special relativistic "event" was redefined in terms of a space-time vector, whose 4-vector length is invariant under inertial motion. The theory never asserts anything about the construction of clocks or rulers, but GPS measurements of location are ubiquitous and all dependent on general relativistic concepts and C. Einstein's special relativity was transitively the consequence of Michelson-Morley. Michelson-Morley was an experiment for an existence proof of the ether, not a measurement of C per se. nor was Michelson-Morley conducted at relativistic speeds, though event Galileo knew C was finite and measurable. Michelson-Morley wanted to find which of the 2 competing theories of ether were correct, as they calculated there would be a interferometric difference based on motion of the light emitter. they found none. Physicists are not "over confident" on definitions of time or length. Since Einstein adopted Michelson-Morley's results as a "postulate", many many experiments of many concepts of special relativity have been tested experimentally. the statistics of all of these results is where the "confidence" comes from. finally, Einstein was a student of Minkowski, who in turn collaborated with Einstein using Einstein's postulates. (Of course, Einstein's 1st postulate is adopted from Galileo.) Minkowski then showed Maxwell's equations were Lorentz invariant. Galileo had none of that; Galileo in fact assumed time and length per se were independent of each other, which is not correct.

[@njwildberger]

I would argue that the adoption of the current (since 1983) definition of a metre based on a prior assumption about the "speed of light" is very much indication of an over-confidence amongst physicists.

[@mathewsamuel1386]

Well, the only way to avoid having the speed of light as a universal constant is to bring back the ether theory. But not only is that more complicating, the Michelson-Morley experiment put an end to the ether theory.

[@njwildberger]

That is not the only way. To admit to having been in error does not commit oneself to any particular further direction.

[@santerisatama5409]

Well, stuff-like ether seems currently like a no-go, but vacuum is also a hugely problematic metaphysical presupposition. Wave and/or field "ether" seem interesting possibilities, or more generally ether of measuring-going-on. Measuring is a temporal process and part of the system, not external to the system.

[@ebog4841]

Almost every serious physicist is aware of this

[@njwildberger]

Could you provide some evidence for this claim?

[@ebog4841]

​@@njwildberger ​ Yes, Einstein himself wrote in "On the Electrodynamics of Moving Bodies" that it's impossible to define a one-way speed of light, so we choose to define c as the round-trip distance. He wrote that the isotropy of c "... is neither a supposition, nor a hypothesis about the physical nature of light, but a stipulation that I can make of my own free will to arrive at a definition of simultaneity." It's a matter of convention! There's still much to experiment on, there's even models of EM that break Lorentz symmetry in various ways. Everything you said is correct, I've just never seen a serious physicist who doesn't know about it, is all. Relativity is pretty WILD hehe

[@jacobwise7008]

Veritasium and PBS spacetime have made some really good videos about the "one way speed of light" too. I particularly liked Veritasium's because of how well he presented the subject.

[@WildEggmathematicscourses]

@@jacobwise7008 It’s funny how this distinction between “one-way” and “two-way” speed only ever gets mentioned in the context of light.

[@lukemolyneaux9711]

Yep, this makes sense, I plan to use it the next time I get pulled over for a speeding ticket

[@esorse]

Given that infinity is the logical opposite of finite * , couldn't you argue that any sequence of terms indexed by numbers ** , must have a bounded greatest lower bound and least upper bound - including the trivial empty sequence - , delimiting it's measurement by integral? * Wouldn't your space be static by compensating for it's contents, liberating any efficatious coordinate system? ** Contradiction acts like a permit for anything imaginable, leaving valid argument, where the conclusion is entailed by the premises, logically impossible from it's opposite being as plausible and since any Minkowski spacetime coordinate is a complex number ^ , where negative is the logical opposite of positive, reasonable argument in these circumstances makes about as much sense as showing up to your local beach fully equipped with gun - big wave surfboard - underarm for the swell of the century on last night's dream's grounds. ^ z = a + b.i for " . " multiplied by and a, b real numbers from negative to positive infinity exclusive, including any rational number that can be written as a non-zero denominator whole number (0, 1, 2, .. ) fraction and any irrational number that can't, with a possibly infinite non-recurring sequence of digits after the decimal point : any real number is a complex number with zero imaginary, " i " equal to the square root of negative one, geometrically implying it is the length of the side of a square with area of negative one, part.

[@njwildberger]

Sorry, but in what sense if infinity the "logical opposite" of finite?

[@peterjansen7929]

Thank you for another very interesting video, laying down sound principles with unsound sound and commenting on shaky science in front of a shaking camera. I know that this does not touch the main point of your argument, but it is perhaps worth remembering, that the world ether was postulated on the basis of light being a transverse wave, which is itself at best an assumption. Most of us here will know graphic representations of ''rays' of light, with vectors drawn at right angles to them, REPRESENTING electric and magnetic fields. For some curious reason, light is then treated as if it WERE such a representation, ignoring that the lenght of each drawn vector merely represents the strenght of the field in the 'POINT' of the 'ray' from which it is drawn, that while the vector has a direction, there is nothing actually moving sideways in that direction. So, in my view, the most one can say is that electromagnetic waves are ASSOCIATED with phenomena that can have effects perpendicular to the direction of the light itself, but not that the light 'wave' is in itself a transverse wave.

[@peterjansen7929]

On further reflection, it is also curious that the transverse nature of the wave is generally stressed in relation to the ether postulate, considering that a longitudinal wave would probably have led to the same assumption sooner or later.

[@christophergame7977]

Wild Egg says that Einstein's second postulate is that the speed of light is the same in every inertial frame in which it is measured. Sometines, indeed often, it is said that one doesn't need to measure it: it is so by definition. Sometimes, indeed often, it is said that the one-way speed of light cannot be measured. Sad to say, a fully inertial frame, free of gravity, isn't conveniently available. I think that modern atomic clocks are now available, and more accurate and precise than they were in Einstein's day. I think Einstein's synchronization has a crippling effect on mathematical physical thinking in this area. Clock synchronization should be done through symmetrical motion that separates identically constructed clocks, sometimes adjusted for altitude. No light signalling for synchronization, please. Don't postulate or arbitrarily define the speed of light. Use crystals to define local distance, and atomic clocks to define local time, and just measure the local speed of light. This has been done. The result is that it isn't the same in every direction. Rather than armchair speculation, we should conduct empirical investigations of light speed, until we establish the simple local facts. When know the local facts, then we can venture into facts for the nearby world. Then investigate facts about the less nearby world. Don't go for broke from the beginning. Work gradually or step by step.

[@jiiiiiiiiiiiiiiiiiii]

Please consider improving your audio. Besides background noises, there is a weird kind of reverb going on in your recording, and it sounds like some sort of lossy-compression artifacts. I find it quite distracting and hard to listen to.

[@njwildberger]

Yes, I am sorry about that. Hopefully the scintillating content compensated somewhat! :)

[@steffenkarl7967]

Meaning that being reflected in a mirror it is not the same photon coming back out

[@santerisatama5409]

What if we consider Stern-Brocot (SB) type constructs holistic perspectives to measure-theory (1/0 does not properly exist in field arithmetics, but is a necessary generator of SB-construct), and tentatively assume that SB-metric holds at least in a Galilean reference frame? SB-denominators can be considered clocks and SB-fractions frequencies. Each mediant is between its parents, but from this it doesn't follow that every mediant is located strictly half-way in the interval between it's parents. There are many ways to proceed to think of SB-type structure as a metric or a relation of metrics. We could start from 2-sided structure, where Left-side 1/0 and Right-side 1/0 represent propagating wave fronts from the same sound-like or light-like event. The denominator element can be formed by defining that 1/0+1/0=0/1, and from that we get the 2-sided generator row 1/0 0/1 1/0 and can proceed concatenating mediants the usual way, either tree-style or row-by-row style preserving the ancestors on each row: 1/0 1/0 1/0 0/1 1/0 1/0 1/1 0/1 1/1 0/1 1/0 2/1 1/1 1/2 0/1 1/2 1/1 2/1 0/1 Empirically, computing more measurement resolution is a temporal process, not an instantaneous event. Sociology of physics has a huge problem with the common methodological and/or ontological metaphysical assumption of instantly infinite measurement resolution. Based on the discussions I've had, physicists are generally not very familiar with the SB-type constructs. The 2-sided SB-construct could offer perhaps a novel perspective to measure theory, where denominators express continuous intervals and SB-fractions are not "points" on the number line but mereological parts. Is there a natural way to interprete 2-sided SB-construct as a commensurable measure theory of wave mechanics? Food for thought.

[@ebog4841]

@njwildberger One could make a living and a killing from studying the sociology of comments like this^ LOL (seriously, dear Professor. the COMMENTS on KZbin science vids are ABSOLUTELY OFF THE RAILS LMAO)

[@santerisatama5409]

@@ebog4841Off the rails, you say? :D I'd say that the reflective domain (search Louis H. Kauffman for the concept of reflective domains) in question is very much on the rails of a Gaussian gauge measurement theory. ;)

[@wesbaumguardner8829]

There is no such thing as an "inertial reference frame" as defined by Einstein. Every single hypothetical reference frame in this universe is undergoing numerous and varying accelerations at all times due to gravitation. This is simply proven by dropping a physical object at any location here on earth and watching it accelerate towards the earth. Even if you were in outer space, the object would be falling towards the strongest gravitational field, whichever direction that is, even if it is at a much, much slower rate of acceleration. Of course, the entire space ship and everything in it would be undergoing the same acceleration and so a person on the space ship would not even acknowledge this acceleration. Light is also affected by gravity the same exact way any physical object is according to the Pound Rebka and Pound Snider experiments. Thus, it is rather difficult to even use light to determine gravitational acceleration.

[@WK-5775]

An "inertial reference frame" is a concept of Special Relativity, which is the framework for the description of a world without gravity. As gravity is everywhere in the real world, you're right with the claim that inertial reference frames do not exist. However, they are a good idealisation for the description of phenomena where gravity is neglectably small, as for instance in elementary particle physics.

[@wesbaumguardner8829]

@@WK-5775 "However, they are a good idealisation for the description of phenomena where gravity is neglectably small, as for instance in elementary particle physics." Gravity acts on everything equally. You cannot claim that it does not act on an atom, because it does. You are basically using erroneous assumptions (special relativity) to back up other erroneous assumptions (quantum physics). In reality, nothing that exists escapes gravity, including light or any other form of energy. These people are so wrong they do not even fathom how wrong they are.

[@camerontorrance1992]

If I remember correctly there is a general result from differential geometry that says you can find a local inertial frame. Sure you can't necessarily find a global inertial frame, given we are working with curved manifolds it is probably too much even to ask for a global chart.

[@wesbaumguardner8829]

@@WK-5775 "n "inertial reference frame" is a concept of Special Relativity, which is the framework for the description of a world without gravity." Which means it is abject nonsense. This whole ideology is crap. Crap, stacked upon crap, is crap squared. That is where we are.

[@ebog4841]

@@camerontorrance1992 how insane is the user "wesbaumguardner8829" you are replying to? Youre trying to explain basic things to the man but he's spouting off about how SR is "abject nonsense" because he seems to not actually know how gravity or frames of refence actually work LMAO KZbin comment section FTW , as usual. Insane.

[@GrahamMilkdrop]

I'm not an academic, nor am I particularly gifted in any particular discipline. There are lots of things I don't understand. What I do understand however, is that the scientific world is largely just as dogmatic as any cult or religion! Thank you for holding the establishment to account and standing up to the tyranny of social conditioning! My faith in human nature has been starving for lack of nourishment in recent times!

[@MisterrLi]

Comparing Einsteinian relativity with Galilean relativity is not problematic, as long as you keep speed differences small. I fail to see a criticism here that is threatening to Einstein's theory, at least so far. For this to happen, you would have to come up with an experiment that results differently compared to what Einstein's theory tells us, such an experiment could also be a theoretical one. The problem is that Einstein's theory has been confirmed consistently in experiments and practical use, so to crack it, you would have to in principle find a better theory (super hard). What Einstein did was to add laws to Galilean relativity so that there is now a max relative speed, something that neither Galileo nor Newton recognized.

[@Anonimus-96]

I thank God for the opoortunity to see and listen to you ! Thank you very much,Sir!

[@RosaLichtenstein01]

Excellent as usual, but it would have been even better had it not been recorded when someone (off camera) seems to have been trying to build a boat or a car in the same room. The ambient noise was very distracting.

[@TimJSwan]

I agree. It is only closer to being a constant than a time variable. It is also a variable but may only be measurable as different in a wider context.

[@steffenkarl7967]

The results about an ever faster and faster expanding universe from the turn of the millennium have just been confirmed again. Candles we can observe agree. Something is up 😊

[@santerisatama5409]

Can we tell from our perspective whether universe is expanding, or are we computing more resolution faster?

[@chuckjones9159]

For many years I defended modern physics and cosmology. Eventually though I started to see cracks and began to look for alternate explanations, my own and others. Now it seems more likely that we have missed something early on. At this point I no longer accept that cosmological redshift is definitively caused by recessional effects, that dark energy exists in its common interpretation etc. I think we need a complete overhaul.

[@lindsayweir4931]

this makes 0 sense. the other ship can have their own atomic clock and their own way of measuring the speed of light just like we do, we don't have to supply it to them. it's equivalent up to a scaling constant with which they define their units which is unimportant mathematically and easily converted. if we shared a radio transmission after the measurement sharing the results they would agree so long as we know the conversion from our units to theirs. is the point of this 20 minute long video that you can't convert between units without knowing the conversion factor? or am i missing something

[@ThePallidor]

This guy explains the problem more clearly in my opinion: kzbin.info/www/bejne/jamueWB8osiFr6ssi=aEs6ZTriNOqDy_OP

[@thomasfuhrmann]

Why shouldn't we accept the fact that we can not convert and see what follows from it? There's no way to prove that we can do it anyway.

[@lindsayweir4931]

@@thomasfuhrmann LOL

[@thomasfuhrmann]

@@lindsayweir4931 ok! That's an argument.

[@lindsayweir4931]

@@thomasfuhrmann there's no way to prove that we can convert a number from one set of units to another? i don't know what to say to that

[@christopherellis2663]

I knew it! There is too much hubris in the sciences 😢

[@ebog4841]

LMAO, no. well... maybe. But mostly no. Depends what you mean by "hubris" and how it is applied... What are these comments... Almost every Prof Wildberger vid is like this... ... Was that the point of making this video? To wait for a kid like "christopherellis2663" to say this and give it a heart? PROF PLS You WILD New South Welshman! There's a constant "C" in sociology, too- it stands for Crazy , and all have isotropically infinite of it lol A sea of C's , these comments be!

[@janetcox4873]

I learned in junior high that speed equals rate times distance --- Einstein calling 'speed' a constant and claiming time and space are 'relative' was always woo-woo freaky talk to me.. What Einstein isn't saying is that light is not matter and it appears when electrical variables of magnetism and energy are married and disappears when magnetism and energy are no longer combined in the right conditions to make light. [Go a layer deeper and you get to the conclusion that the ether/air around us is filled with magnetism and energy, and *that* is what Einstein was promoted to lie about -- Einstein's hair was outrageous to support his outrageous idea that air is empty and the ether doesn't exist. If the nice folks teaching in the academies want to keep their jobs, they won't contradict the hair or the riduculously wrong conclusions of Einstein. Since when does a guy who MAKES UP VARIABLES to make equations work get academics to respect him ?!] Light doesn't 'travel' at all. I like your sense that people modern academics are acting more like babysitters than explorers or discoverers. I could not agree more. [The fact that 'quantum' is a measure of possibilities rather than any material matter or issue, even, hasn't made the mainstream yet. It should. 'Quantum' is a way to estimate sheeeeeet we don't know and believe we can't know, but (we believe) we can estimate the range of 'relevant' possibilities. More babysitting, in a way, imo.]

[@nvjt101]

Hi Professor, i guess you should team up with Unzicker Real Physics. He's the same man like you trying to get away with the existing dogmas of Physics

[@brendawilliams8062]

Everyone that seeks the flower of life knows what yt channel knows the deck of cards.

[@MichaelLesterClockwork]

We have measured the speed of light precisely in a bunch of different directions (using a bunch of different methods) and found it the same (thus ignoring Earth's motion through the universe because frame of reference). And we have measured one-way speed of light. So we don't need to go down the rest of your rabbit hole, because your assumption about 2-way measurements is false. And then you are ignoring time frames of reference, which is important for time dilation and how it all interacts. And then pretending we cannot define frames of reference outside ourselves.

[@MichaelLesterClockwork]

And for our frame of reference, the definition of a metre is valid. And can be compared to other frames of reference by accounting for effects of relativity. Heck, we use all of this for accurate time keeping on satellites (relative to us). And to do sub-millimetre positioning of points on Earth using all of this wrapped in with other mathematical systems. Which wouldn't be possible if what you say (based on a flawed initial assumption) was true.

[@njwildberger]

Please let us know where we can find the details of these one-way measurements of the speed of light.

[@2550205]

As expressed by you to have been expressed by Galileo who would have been working on a way to understand what had not been two or too or et tu brutus well communicated to three people by the pyramid builders who had understood that A line is a straight line by any definition of straight witch which but not twitch or filch moves in on and is the plane when made subject to the ultimate ruler i.e. X...:.. meanwhile back at the mean which defines the line from a point needed to define the ark the arch the arc which is not the covenant that a line is and is the covenant that the arc represents as any arc any Where wolfs not necessary as the #Geometer knows by observing the roundness of things such as drops of water or G #'s and the other things floating in the black magnetic ethθWΘater which by all ob serve able observations works the way water works and when the plug is pulled on the basin of baseless nonsense that made sense to the crowd not mingling mind wise with the wizened mind of the day turned books out as the funding was pumped in to the bubble of belief that all of the ...:..with the obvious exception of the Wildberger occasionally seen in the wild things they said on the internet in 1905 were true because those things made their way to the internet rather than to the circular file where the postulates belong while masquerading as rules written on old underwear turned into the papier that only a papier mache ideee can fester together in the aftermassacre of some other Stein hoisting human happened to be conjuring up at the identical moment in the system where you take a 360 degree circle divide it at the 15 degree marks and you've got yourself a system that is going to be right 24 hours a day 24 days a month 24 times a year and everything else in between that is some newly "discovered" iteration of 2^x X 3^y where x an y are the bits what make up the 2 and the 3 up to the point where the circle of () is joined at 1 the metric system {designed and observed by the builders of pointy buildings} is the system for measuring the volume of curved surfaces in weight real relative to the floating point of a drop of water at the edge of the at most sphere of influenza influence which begins at the sun and ends at the moon where the rest of the influences influenzing the fluence of this sphere with a 4000 mile long radius defining the 24000 mile wide arc which is not a line as the first postulate which now demonstrates itself to be ΘΣ rule of law and the line drawn in/on some sand of time which for the clingons might look like here butt meanwhile back on or around Uranus where a day is something other than a night here and a dingelberry is something other than the Staten Island ferry Geometry rules the day and those who come to see the straight which the arc does not represent know where the edge is relative to where the edge looks like it is which from any angle defined using the straight line system of 2^2 X 3^1 finding the answer is not a problem more than it is the final solution still sought by those actually looking And you my friend are the one whoooo preaches today from the mount of the internet where as a sea filled with blind sheep the fluffy curved surface disguises the arc seconds defining a G# as much as green when one puts the compass to the test at the edge of seventeen or a ruler which ever is at hand speak on my friend this stuff can not be erased by any burning of the library of Alexandria type attempt at keeping the clueless as clueless as cluelessness permits the clueless to be kept chained to the wall in front of the wall with the shadows dancing in the distance

[@JungleJargon]

I have an exciting old theory that is now an observation. There is no need to modify gravity. Less gravity accelerates time and inflates distance both of which accelerate causation making everything happen faster including lightspeed while maintaining the speed of light 186,000 miles per second. The concept is so simple at least for mechanically minded people. If you change the size of a cubit, you will change the size of the house that you build with it. If instead of driving 60 kilometers an hour you drive 60 miles an hour, you will increase your speed because you increased the distance that you traveled in an hour. Then if you change from 60 miles an hour to 60 miles in half an hour, you increased your speed again because you traveled 60 miles in a faster time. General relativity is no longer a theory, it is an observation. Distance expands with less gravity and time speeds up with less gravity effectively making everything faster including light without breaking the speed of light.

[@konradswart4069]

This what you say here, is one of the first ideas Einstein had. He thought about the consequences of a variable speed of light, and understood gravity, and spacetime in this way in his original paper. He abandoned this approach though, because he realized that whether you say that the speed of light is variable, letting space and time be constant, or whether you define the speed of light as being constant, but spacetime is warping, are basically equivalent statements. There is a man on KZbin, (unzicker physics) who has devoted a lot of time to this idea, and lots of videos. kzbin.info/www/bejne/paWTo4ppo9Z1m6s

[@JungleJargon]

@@konradswart4069 I don’t know but I don’t think anyone is talking about both the changing measures of time AND distance.

[@christopherellis2663]

The terms am & pm tell the time relative to the sun crossing the meridian, something that varies daily. It's a perfectly valid and accurate measurement, but only for that particular meridian. The same might hold for other things

[@ADVscout]

most every mathematician who has worked in the past 200 some odd years is wrong, but I am right! oh but also every physicist in the past 100 years is wrong! But I am right! And every Sociologist is wrong!! But I am right! and so on It seems a little sad to have dedicated the past 20 years of your life to declare yourself as the only person with a brain

[@njwildberger]

Relax, it’s not as bad as all that

[@arnoldsygo4673]

I don’t agree with everything he said, especially when he got philosophical about space. However, it’s not impossible for one person to know something that nobody else knows. It is generally accepted that everybody was wrong about relativity in 1905 except Einstein.

[@dadsonworldwide3238]

Im happy to see so many required angles coming at this from every avenue possible because its gonna take that to wake up 80 years of subtly miss guided revisionism taught and used for 50 year olds. How would one locate a 1 minute expanded plank length of space to draw a maze of time around mass displacement of space by product of gravity manifolds anyways ? Lol Job security allocating symbols of data in a library as big as the solar system even in a qauntom computer lol probably why greek didnt map atomized world around them. But as a tool of generalization to order & categorize with a grain of salt makes value but clearly its way less critical extreme state and potential lattus to define & label than every plank length bit of cosmos lol

[@davidrandell2224]

Light is a cluster of expanding electrons. All EMR also manifestations of expanding electrons. SR wrong due to reference frame mixing and bad math.GR follows as incorrect. Gravity is simple Galilean relative motion. The earth is approaching- expanding at 16.14 feet per second per second constant acceleration- the released object (apple). “G” calculated from first principles- the hydrogen atom- in 2002. No energy, charge, photons, waves, spin, fields, potential, quantum,quarks, space, time, space-time: I.e. ALL Standard Theory/Model was replaced by Expansion Theory. “The Final Theory: Rethinking Our Scientific Legacy “, Mark McCutcheon for proper physics including the CAUSE of gravity, electricity, magnetism, light and well..... everything.

[@davidhand9721]

You're really having a lot of conceptual difficulty with relative speeds. I've already explained how this works. Not having a fixed coordinate system is what SR is all about. Stop fighting it.

[@simrinsahota2398]

then your SR is not based in reality. Physics is the science of understanding reality. Reality is objective, not relative. If I have a piece of cake or not, that is a fact of reality. Changing your viewpoint or 'coordinate system' will not change that fact. You can not reach a logical conclusion through illogical means. Hence, you can not make a valid measurement if you are changing the means of making that measurement.