What If The Speed of Light is NOT CONSTANT?

[@haph2087]

Finally, an episode of Space Time discussing not Spacetime, but Space Time!

[@Pfhorrest]

Not "spacetime" with no space between "space" and "time", but "space time" as in "space" space "time"?

[@haph2087]

@@Pfhorrest Yep!

[@lorenzoblum868]

​@@Pfhorrest did you say spacetime or space time or spa cetime or s'pace thyme to be sure?

[@tommywendt6118]

Well we should discuss Spacetime here then?

[@space_audits]

Turns out c is variant. kzbin.info/www/bejne/gF7ZYYCKd6d6oac

[@dianagibbs3550]

5:05: I love how the cube that says space has all five letters on what should be four sides of a cube.

[@PandemoniumMeltDown]

Mages, they are mages!

[@ryanmcmenamim9871]

It's a 4d object, clearly.

[@roberttg5108]

But a cube has six sides

[@jessecail8182]

I had to rewatch that segment. I was so distracted by the 5-letter/4-side thing, I didn't hear anything Matt said.

[@Hauketal]

If speed of light doesn't change, maybe cube sides do.

[@UrgoMeister]

Love the "SPACE" cube in the graphic at 4:50. Space being 5 letters rotating on a cube with 4 faces. Neat!

[@bigboicreme]

I noticed this too

[@richardmemberhead4773]

i liked it but upon closer inspection i noticed it was skipping a frame

[@kaczan3]

That's racist.

[@oberonpanopticon]

@@kaczan3Spacist*

[@balala7567]

@@kaczan3 smh water is racist because uhh the bad guys drink it

[@SpeedbirdConcordeOne]

Matt + team. You bring astrophysics alive for me. Thank you so much for bringing us these absolute gifts.

[@DeltaV11]

I hope Matt O’Dowd wins every award for science communication and also makes a million dollars. LOVE Spacetime.

[@Whystling_Byrd]

He make think less harder.

[@CooManTunes]

You're ap itif ul s imp.

[@CooManTunes]

For uploading KZbin videos and reading a script? You'ream or on.

[@DeltaV11]

@@CooManTunes Dr. O’Dowd is a professor of physics and astronomy, with a PhD in astronomy and astrophysics, in addition to being the host and writer of Spacetime. He’s an excellent science communicator, one of the best I’ve ever seen or read. So yea. I hope he wins every award and makes a million dollars.

[@CooManTunes]

@@DeltaV11 I already said you'reap itif ul s imp and am or on. Why do you want me to emphasize it?

[@robertstevensii4018]

As Matt starts to gain traction in other spheres (referenced on Sciencephile), I hope he remains true as ever to form: Accessible but not afraid to bring out the equations.

[@xBINARYGODx]

good, because often, or perhaps always, attempting to make nearly anyone or enough people understand leads to explanations that do more to make people ignorant than they do the opposite. Michu Kaku is ultra criminal at that, but so are many of the retired scientists (etc.) who do the documentary junkets.

[@semaj_5022]

​@@xBINARYGODx One of the biggest difficulties in science communication will always lay in its actual communicability. Often times, to be accurate, it can't be accessible. If it's accessible, it's no longer accurate.

[@ickebins6948]

@@xBINARYGODx Michu is not interested in getting people into science, just in selling his books.

[@kayakMike1000]

Dr. O'dowd does not disappoint.

[@kayakMike1000]

​@@xBINARYGODxthank you! I am super happy to see you formulate the same opinion of mine! The Kaku simplifies several ideas so much, they're basically wrong!

[@kwisin1337]

Hey Matt and team, keep up the great work. It is very inspiring to have SpaceTime provide great content in a clean and professional manner. Thank you to everyone who has helped Matt along, and a BIG thank you to Matt!❤

[@PeterGaunt]

Indeed. Whoever did the 'falling smoothie' graphic has finally got me to see what I've always just kind of assumed for the past sixty-plus years. The smoothie seen from the railway platform follows a longer path than that seen by observer on the train. Ping!

[@RadicalCaveman]

@repentandbelieveinJesusChrist1 Repent of your unfounded beliefs.

[@nicksamek12]

We appreciate any time you take to respond to comments, Matt! Take whatever time you need to keep their quality so high, they won't be worth it if you let the quality drop.

[@PetraKann]

You alright nickacket13?

[@amalieemmynoether992]

I enjoy the fantastical reasons given when Matt doesn't do comment responses.

[@mudfossiluniversity]

To Matt.................I have accelerated light and crushed the fields in a venturi that created muons and electron showers and photoed using CMOS. Evidence is on my channel and I am doing a video now about your claims...I would like to engage please my Friend? I have 100% proof of my claims and all particles are dipoles (Dirac Neutrinos).

[@asianiewie9142]

oh my! Some 10 years ago I borrowed a book about VLC from the library in college where the author explained his theory and said it was rather false, but discussed its possible effects! I was captivated by this book! And now I have such a flashback to my days studying physics! What a great episode!

[@GoblinArmyInYourWalls]

I love that type of material. An understanding that "this isn't real, but what if it was"? It's basically metaphysics and it's more of a brain teaser than anything

[@Rachelebanham]

Agree that speed of light doesn't need to vary but recent work by Dragan and Ekert show that you can reproduce quantum effects by considering superluminal observers. Would love to see an episode of this show that covers this.

[@frun]

You may want to also read Gonzalez-Meistres. He explains, that quantum particle may be a collective phenomenon. It is at the origin of the speed of light.

[@Rachelebanham]

@@frun interesting. suspect that Dragan and Gonzalez-Meistres are kind of hinting at the same kind of physics.

[@frun]

@@Rachelebanham I don't remember Dragan paper well enough to say, but my own opinion is that fields resemble cantorian set and made of information.

[@frun]

@@Rachelebanham Quantum mechanics arises in the case in which you don't have enough information. It is a classical theory in disguise.

[@Rachelebanham]

@@frun hmmm I don't agree with this last statement. I think the fact non-locality is fundamental (i.e. no local hidden variables) is deeply non-classical. Furthermore, there are plenty of experiments that show that the quantum nature of reality whilst potentially having a partially subjective characteristic, is not just because you don't have enough information.

[@viewsandrates]

"Thank you!! Omg." - Me, after looking for something to watch forever but then Space Time uploads.

[@lyrimetacurl0]

One of the moments of space time.

[@AdrianBoyko]

You want to watch something forever? 😳

[@SortaFresh]

Literally me lol

[@eSKAone-]

Yea dude, streching my brain like that feels always healthy 💟

[@sirdiealot53]

Yep the same old social media apps are getting so boring. Even KZbin is becoming a wasteland of crap. Wonder if writers strike has to do with it

[@CaptainCuttlefish74]

With regards to the speed of photons varying with energy, there's actually a very interesting sci-fi series that uses that as one of its physical properties. It's the Orthogonal Trilogy, by Greg Egan. An interesting consequence of that is that stars don't appear pointlike. They instead look like rainbow trails across the sky, tracing their paths over time, with the red end corresponding to the oldest visible position, and the violet end the newest. That's actually one of the *less* weird things about it.

[@swancrunch]

Amazing series, and incredible author. Loved his take on determinism in third book)

[@someonerandom704]

I'm not a fan of that guy. I got half way through Dichronauts and just didn't like it. The alternate light physics in the book is fascinating, but I didn't like the characters or dialogue. I was already spending a lot of effort trying to understand its physics, and the fact that the plot and characters were extremely dry just took away all motivation to finish the book.

[@andrewfleenor7459]

Yeah, you read Egan for the science, not the characters. :D That said, having read Orthgonal but only read about Dichronauts, I believe Dichronauts is an even higher level of bonkers, and the characters in Orthogonal do have *some* stuff going on, so if anyone feels like giving Egan a second chance, that would be a decent place. You're still reading it for the physics first, though.

[@mattwecrazy3236]

You are a busy man! I think we appreciate ANY comments you actually have time to respond to, especially with such high quality answers!

[@stephanieparker1250]

What I love about this channel is that about half way through the videos, I become completely lost. 😂 I like that because the videos always challenge me. 👍

[@bigboicreme]

Same 😂

[@192mait]

you guys are my favorite youtube space channel. i bet i talk for the most of people, who are silent about their appreciation for your work- much love to you all who make these vids

[@odysseus9672]

Fun fact: you can treat the expansion of space as being a changing of the speed of light. In fact, in co-moving coordinates (a coordinate system that doesn't expand with space-time) that's exactly what it is. The FLRW metric is diag(-c^2, a(t)^2), where a(t) is the scale factor (it's defined to be 1 today, and smaller in the past). So in this coordinate system the distance a photon can travel is c / a(t). In this picture light gradually slows down, and eventually stops. We normally don't use this picture, though, instead saying that physical distances are expanding and c is constant. To keep alpha constant, you'd have to have other constants changing, too, and since c^2 = 1/(epsilon_0 * mu_0), epsilon_0 would naturally, also, change with time in such a way that keeps alpha constant.

[@DrDeuteron]

But how does that work with quantum mechanics? The Bohr radius is a Compton wavelength divide by alpha, and if you mess with epsilon and c, you mess with alpha, but if you do it in away that cancels, you mess with mu….does that mess with spin orbit…which then affects fine structure? Kinda circular, but not quite. And idk what happens to nuclear structure….that’s just a mess.

[@ChevisPreston]

@@DrDeuteron​​⁠​⁠​⁠​⁠​​⁠ [Not to be confused with tired light, which has to do with energies.] But yes, as the universe “expands” the causal horizon contracts, and if light does benchmark causality it would appear no different to us as the universe expanding from light bleeding velocity and eventually “stopping”, as it approaches our causal horizon. Just another example of theoretical horizons bending your brain. The argument is, either the speed of light is invariable and the universe is expanding, or the speed of light is variable, and over time it diminishes. We’re fairly confident that it is the former, due to our best research into the fine structure. So our understanding of elementary particles/QM remains intact, but from an OBSERVER, a photon they emitted will, at their causal horizon, appear to slow, and eventually appear to pause with the causal horizon. Despite appearances, the photon continues to travel at c, but will be so horribly redshifted due to the expansion that it’s near undetectable. From our frame of reference as inertial observers, the speed of the photon slows down, which is the same as invariable c with cosmic expansion. Eventually it “stops,” because our cosmic horizon recedes, but it is functionally identical to c being variable. Again, our best observations show that it doesn’t actually slow, and is constant, but as inertial observers it’s virtually indistinguishable from slowing light. VSL actually has some merit as a theory, and an alternative to cosmic inflation altogether, but because of the difficulty to test, and the inflationary model’s success with our current physical understanding and observations, there hasn’t been too much of an urgency to overthrow all of QM and redefine our models with variable light.

[@manuelcheta]

Did anyone notice that the word SPACE ends up written, letter by letter, on the vertical faces of a cube? That cube has 4 faces, but then in the video it shows rotating and having 5 letters of S-P-A-C-E showing up. Clever stuff :D At 05:04 minutes.

[@Platanov]

I noticed! I feel smart.

[@Bik3N3rd]

Yes. And it did somewhat annoy me. :D

[@PandemoniumMeltDown]

Damn, I just commented that.

[@KieranLeCam]

Tesseract!

[@thezipcreator]

@@KieranLeCam a tesseract rotating like this would look very strange to us, and nothing like this

[@Nathan-vt1jz]

Thanks Matt and team for addressing this topic! I brought it up due to things I’d heard from other sources. I wasn’t convinced, but also couldn’t make a good argument against the position as a non-physicist. You all do a great job!

[@borsty2000]

Please correct me if I'm wrong, but in the comparison at 4:30, it is stated that time slows down when the speed of light is also slowed down. So far, so good. In the lower example, it is said that time slows down when distance increases. And that's where I disagree. The speed in Example 3 is the same as in 1 (blue dot), but time passes as slowly as in Example 2 (red clock). When the distance is extended, but the speed remains constant, time does not slow down, only the light takes longer. The representation of the "clocks" is not clocks but rather counters, which increment each time the light has overcome the distance between the mirrors.

[@BisexualPlagueDoctor]

I will label my answer in the middle of this. Please be aware I am not professionally educated on the topic and my explanation may be incorrect, however my understanding I believe should be sufficient. Scroll to where you see [answer] if you don't want to read this all. Time is not a physical thing, time is just a dimension. All dimensions are truely and absolutely constant coordinates from every perspective, and this is also true for time. The speed of light is merely the rate at which dimensions of space can change through the linear path of time. Since this is true, and assuming a reduction in light speed is a reduction of all adjacent rates, this would mean that *relative to another object* the time would slow down from a reduction in time spent at any given point. Now the question for distance is genuinely a good point, but from any conceivable method of measuring transfer of information over time, double the distance would be identical to half the speed of light. Since the rate of change of space-time is what massless particles and waves must be, this would mean that the time it takes light to get anywhere is exactly proportional to the change of time, one again relative to an object This is fundamentally what time dilation is, as when you accelerate, the 'drag' of space-time with time dilation is also a contraction of space, as, in the terms I understand, every point in space has a true point in time and this information can only be relayed to each infinite surrounding point at the rate which forces can propagate throughout, and *[answer]* since light is the only fundamental field with which has a physical and massless, it is also the only one we can very easily use to record the change of time and space. This is also why extremely high energy or gravity have the same effect as speed, as both stretch space, which is in essence the difference between half speed and double distance as you have asked. Truly, time at any given point is invariable, but this information is transferred incredibly slowly on a cosmic scale and fundamentally whatever observed is what is true until this can be circumnavigated by somehow changing the relationship between points in space, such as making a wormhole or warpdrive.

[@j4crip755]

As mentioned in this episode "The speed of light is just the unit conversion factor between our arbitrary choice of spatial and temporal units" and I think it creates a good link to an interesting subject for a next video: the Einstein and E. A. Milne discussion of what concept is more fundamental: "distance" or "time". On one side you have those "rigid bodies" with the need of two observers while on the other hand you have "two times at the same place" and just one observer. I'm with Milne on this one.

[@AverageAlien]

I'm guessing they're equally fundamental

[@kingofflames738]

What I got from this is that the speed of "light", or causality, is the universe's framerate

[@MarshmallowRadiation]

This just in: God forgot to multiply by Time.deltaTime 😂

[@dcquence]

I would put it more as that the speed of light is limited by the universe's frame rate, aka the speed of causality.

[@RSxRS3]

So wouldn't 1 Planck length cube be a single pixel of the universe ??

[@MarshmallowRadiation]

​@@RSxRS3Can't be a cube, because it's greater than 1 planck length from corner to corner. It's more like a sphere, but spheres can't tesselate so you have to define each sphere independently, which means they overlap, but any sub-Planck distances get rounded up, so it's more like an infinite continuum of overlapping Planck spheres in an infinite superposition of every possible Planck sphere, but all that is physically meaningless anyway, and the more you try to understand it the more you can feel the ghost of Richard Feynman looming over your shoulder, eyes glowing red, tempting you to "shut up and calculate"

[@Lund.J]

The speed of light depends on the medium, that is the undulating ("waving") substance i.e. "light-ether" (in space). "Electron orbital is light-ether, that is chrystallized around the nucleus". Electron is a vortex of heat. Quantum leap of electron is based on its nature: Vortex of heat can "jump" through the etheric realm and manifest "non-locally": this "manifestation" releases a photon. Quantum leap can be very distant (unprobable but possible) and immediate. Also two or more distant vortexes of heat can interfere (like waves do) with each others immediately, non-locally, through etheric realm. Both of these cases are related to quantum phenomena of the electron.

[@vangough7031]

Who's gonna stop me if I break the speed limit? The Causality police? I'd like to see them try...

[@Space_Police]

We will stop you 🚔

[@smergthedargon8974]

To me, it's always seemed like if you slowed down causality, nothing would actually change. If you double the time everything takes to happen, then everything is going to still be perceived at the same rate 'cause now brains, computers, whatever in that space take twice as long to think. Edit: I can't tell whether the absolute incomprehensibility of these replies is because I'm stupid or they're insane.

[@mikithekynd]

This makes me think whether the universe expands, or slows down...

[@maeton-gaming]

well you're not wrong, C is incorrectly named the speed of light due to the cult of quanta making everything about, well, quantization. Instead, you could more accurate refer to it as the maximum rate of disturbance, or hysterisis, or the maximum rate a medium can experience a perturbation through it (wavefront).

[@smergthedargon8974]

@@maeton-gaming "cult of quanta" 🤨yeah ok schizo

[@purplenanite]

that's the reason behind the giant disclaimer that matt put in front (the "is the speed of light invariant" section) normally you would be right, but we assume that there is a disconnect between space and time and see where that takes us.

[@schakiarligonde1736]

What if you made causality happen faster

[@jpt3640]

I enjoy questioning the seemingly unquestionable. Great work!

[@christiannersinger7529]

I think the speed of light is the speed at which the medium of space and the medium of time can interact with each other, in order to increase the speed of light you have to further increase the "overlapping" of space and time, the problem with that is altering your space (the physical space you occupy) alters your time (the temporal space you occupy), and it appears to be inversely related, the more matter you have the less time affects you (faster you travel the more relative mass you have but the slower time moves for you), you could theoretically increase both (therefore allowing ftl travel) by overlapping time and space, creating what we call a worm hole

[@bradysmith4405]

What if we could increase the limit of causality by somehow altering the factor or space time that limits it? (And we really don’t know exactly what that is yet) This would mean locally you aren’t traveling ftl (the speed of light would be increased) but outside of the altered highway you’ve created you would be.

[@christiannersinger7529]

@@bradysmith4405 My theory is we can use an "antimatter" generator to create a bubble around solid matter separating the spacetime of the vessel from the spacetime of the rest of the universe, then we can theoretically roll the spacetime hamster wheel wherever we want as fast as we want

[@ronsirman6867]

The density of the matrix the photon travels through effects it's speed. A photon created in the middle of a star takes 1 million years to reach the stars surface. A photon traveling through water is slower than through air. Interstellar space light speed would be at its fastest due to the density of space.

[@christiannersinger7529]

@@ronsirman6867 that's what I said 😅 but yes, it does appear that light moving through space is the fastest light can move, sure overlapping space with space "creates" more space but the space isn't what I'm talking about, because the overlapping also creates a "negative" space between the overlap, this negative space would have, theoretically, a negative friction coefficient, friction less than 0 means your being accelerated by friction to a point of stability, instead of friction stopping you at a point of stability, that negative space is called a wormhole This is all theoretical, and not "legit" science, so it's not something we can really prove, our technology is way too primitive for that, which is why I proposed my "antimatter bubble" theory as an alternative, we're much closer to that than the physical manipulation of space that we'd need to be able to do to make useable wormholes

[@ronsirman6867]

@@christiannersinger7529 could you imagine the power needed to warp space time in such a manor. There has to be physics that is currently unknown to us

[@jeremytipton6076]

It's good to occasionally question the uttermost foundations. Especially when facing an impasse.

[@murraymadness4674]

The belief in dark matter and dark energy only to keep GR intact shows how far scientists will go to not reject current beliefs

[@froyocrew]

General relativity is fundamentally flawed, but I suppose a few more billion dollars and particle accelerators need to be built before we accept that

[@shadowdragon3521]

Alexander Unzicker has written on the theory of Variable Speed of Light in his book _Einstein's Lost Key_ and he explains many things about the theory on his KZbin channel. It's an interesting topic for those who want to take a deeper dive.

[@ArgumentumAdHominem]

Would be really nice if Matt could comment on the claims of Mr Unziker. Their statements seem fundamentally incompatible to me

[@goldwhitedragon]

Done 30 years ago by Christopher Langan and his CTMU. Everyone's starting to plagiarize him.

[@jorje58965]

@@goldwhitedragon can you give me a summary before I dive into it?

[@goldwhitedragon]

@@jorje58965 reality is a mind. We are part of its unfolding and growth.

[@ddarkjared]

I would like to add to the super fluid discussion. You can apply "normal forces" to the super fluid. The super fluid just has a very low/ zero drag coefficient. Trying to stir the fluid with a tooth pick wouldn't work, but with a large surface would work just fine.

[@ambition112]

0:13: 🔬 The speed of light in a vacuum is constant for all observers, according to the theory of relativity. 3:19: 🔬 The concept of variable speed of light suggests that changing the speed of light could affect the relationship between space and time on a quantum scale. 6:45: 🌌 The idea of a variable speed of light could potentially explain the homogeneity of the early universe and the apparent acceleration of galaxies. 9:56: 🔬 The theory of variable speed of light (VSL) suggests that the speed of light may have changed over cosmological distances and times. 13:09: 🔬 Exploring the possibility of changing the speed of light in a dense medium like water and its implications on the universe. 16:25: 🔬 The spoon imparts energy to the fluid, creating a flow and rotation of the vortex in a superfluid. 19:31: 🌌 There are electromagnetic signatures that can distinguish non-black hole cases from aliens, and the effects of a supernova on Earth can be global. Recap by Tammy AI

[@zacharywong483]

Brilliant script and explanations! Fantastic video, as always!

[@uss_04]

As a kid I always wondered this. Same as gravity or whatever we think of as “constants”

[@Rome101yoav]

Ah, why would we just assume gravity is always constant? It'd be true if the universe was flat, but it's apparently not completely flat.

[@BioShock55Airsoft]

@@Rome101yoavG changes? With what?

[@felicityc]

@@Rome101yoav If it wasn't constant the life cycles of stars would not be so exceedingly consistent.

[@smlanka4u]

Relative time depends on mass, and speed changes mass.Therefore, relative time is an illusion.

[@xBINARYGODx]

@@smlanka4u just enough knowledge to get it rather wrong

[@ritemolawbks8012]

That still doesn't explain how Matt O'Dowd stopped aging after 28. He used to be older than Derek Muller. The United Nations and international community need to intervene and shut down CERN, LIGO, SETI, and all the particle accelerators before it's too late.

[@Rubrickety]

I believe the speed of light has remained constant since the universe began, but if it should decide to change in the future, we should be fully supportive of its decision.

[@kenbrunet6120]

Or his or her or their decision.

[@masonnasty3293]

Idk, I think that SoL dude is just trying to move passed this problem as fast as it wants.

[@JoeBtfzplk]

How many psychologists does it take to change the speed of light? Only one, but the speed or light really has to want to change.

[@flowerpt]

Perhaps the speed of light is inversely proportional to the current size of the universe. Hyperinflationary period - very fast; heat-death days - very slow Maybe below a certain universal-constant threshold you get an instability that causes a new Penrose epoch.

[@PlasmaHH]

The problem I think is that people cannot grasp a concept of "speed of causality" that is not tied to the everyday concept of speed. I always like to explain it in terms of conways game of life. Imagine the underlying mechanism of the universe to be something like a cellular automata. Now every "tick" of it, adjacent cells can interact. While we can speed up or slow down from the outside of such a simulation, from the inside, there is no notion of how fast a "tick" is, as everything is happening as those tickes, every perception and measurement too. Any spacetime warping and thus time dilatation inside there could be described as the amounts of ticks for something to be relative different to each other. In that way time is kinda an emergent property of the distance of cells.

[@jolkert]

im a programmer, and as soon as i heard him mention the "speed of causality" i immediately thought "so its kinda like the tickrate of the universe". feel kinda vindicated to not be the only one making this connection

[@ryoriotwow]

The only real constant in this universe is Matt having a cold.

[@charliekim2939]

Next talk I wish to hear is "What if the Wavelength of Light gets longer with Age?" Although I left physics half a century ago, the question still bugs me. Thank you for your interesting talks.

[@danc.5509]

I like your question. If the sun is white light at noonday, then orange to red light at sunrise or sunset, is the earth's atmosphere lengthening the wavelength of light? Also, white light is comprised of different colours of light. It makes sense that high frequency ultra violet light is seen as new light, that may decay to longer wavelengths such as red.

[@GiuseppeSan]

I believe this is called "tired light" and has basically been ruled out as it's not consistent with the surface brightness of distant galaxies.

[@vhawk1951kl]

Merely out of idle curiosity, I wonder why anyone might suppose light to have a peed; it is not exactly as if one's experience of illumination is one of anything moving, so it seems a little queer to imagine that light moves at all. If I go into an otherwise unlit room and light a candle it does not appear to me that it takes a noticeable amount of time for me to see what I see- I do not get any impression of anything moving, so why might anyone suppose light to move or have a speed? I can't quite understand why the little patent clerk got it into his head that whatever he means by energy was a number of units of something having to do with its mass multiplied by what he imagined the speed of light might be. If it had les energy would that affect the so-called " speed of light? If so, by what mechanism might reducing the mas of, say, a brick slow down what is imagined or assumed to be " the speed of light? By what mechanism are the two connected? It's a queer sort of idea from a queer sort of chap to suppose that there is anything that might connect energy mass and the speed of light, white mice or kangaroos for that matter; it's a very queer idea that the energy of something might have something to do with the speed of something else that has absolutely*Nothing to do with it. it is rather like saying that the energy of a brick has something to do with how long it takes Fred to get from his front door to his car; for the life of me I can think of no rational or sensible reason why the energy or mas of something might have anything to do with something else wholly unconnected with it. I is not as if I an ancient duffer suppose the mas or energy of a car that passes me on the street has anything to with how long it takes me to remember where I left my spectacles, which would be like my supposing the weight of any of my wives is contingent on how long it takes me to realise that rather than marrying any one of them it might be cheaper for me to find a disagreeable woman and give her a house.

[@danc.5509]

@@vhawk1951kl perhaps that's what studying things is all about. We are all different and so we know our perceptions also differ. Finding the truth about things gives meaning to some persons on why people have their differences, and consequential disagreements. To view through a prism that sunlight can be separated into a rainbow of colours piques the imagination of some to go on to further query how the prism can bend the sunlight into separating. To discover that this separation of sunlight was due to different colours of light having different frequencies has always surprised me. It's still an X-Files dream that the truth is out there. More often the truth lies within. One intuitively knows lightspeed, if such a thing exists, is incomprehensible. Anyhow, lightspeed and houses for disagreeable women are first world problems. Many in the third world are often abandoned in the dark

[@vhawk1951kl]

@@danc.5509 I'm not sure that whatever you mean by " studying things" is " all about " anything, but it depends on what you are studying and why. If you are studying great white sharks, I rather suppose that the idea is to avoid studying them from inside. If you mean force-feeding reluctant young beings with information, that is "all about" the stronger and larger bullying the smaller and weaker. Al sorts of monkey business can shelter under the umbrella "study", but ideally study should be active rather than what takes place in those monstrosities that are called schools, where the victim is require passively to wallow and regurgitate what is forced down his throat on pain of a beating if he does not, and get 100% in a test or get a thrashing does tend to encourage young beings to memorise what they are being forced to commit to memory and pain is undoubtedly a powerful incentive to that end, rather as hunger is a powerful incentive to engage in honourable sweat work

[@AltNomad]

Hi Spacetime, are transcripts of your episodes available somewhere? Thank you for making such amazing free educational content!

[@HatsuneSquidward]

It's hard to find but KZbin provides auto generated transcripts. On mobile it appears below the description after you expand it. But a quick Google search could help you find it on whatever platform you use

[@Zeraevous]

One of the community members a while back cataloged, tagged, and transcribed a bunch of episodes. They linked it and gave a shout-out a while back. I'll see if I can dig it up

[@AltNomad]

For anyone looking for the real answer they have their scripts available if you are a Patreon subscriber

[@HatsuneSquidward]

@@AltNomad so did you know that already or...?

[@AltNomad]

@@HatsuneSquidward No, I was genuinely curious. I don't normally check out patreon and there wasn't an indication in the video description that it would be there so I figured I'd ask. Jenny's comment about throwing money at them made me think maybe it was on their patreon since some shows do that and yup, there it is

[@andrewbodor4891]

The medium through which EM waves travel permits only one maximum and minimum speed for EM waves. If it appears that the EM wave goes at a slower speed it is because the medium is to “blame”. Light travels inside quantum fields or threads that have standing waves stretching through them. These standing waves contain a certain energy(wavelength, frequency and amplitude). Gravity bunches up (compresses) the standing waves into one with higher amplitude and sorter wavelength. The EM wave rides piggy back on the standing wave and has to travel a greater distance to get around large bodies of mater, appearing to slow down. Greater distance, same speed means more time to get past matter or out of gravity wells.

[@MrMoose1347]

The field not medium

[@ivvy1221]

I appreciate this awesome content, and I hope that comfort is coming, hero. You're all so awesome. Thank you!

[@EVILJAMARR]

Right when ChatGPT was released, I asked it what the implications of a variable C constant would be. It had a remarkably well "thought out" response that included all the hits you'd expect and are listed in this video. Wild times to be a large language model!

[@maeton-gaming]

You think that's surprising? I fed it tesla's dynamic aether model and it confirmed that its likely that C is the maximum hysteris of the universe. this validates the need for a universal medium (faradays dielectric field)

[@pacotaco1246]

im so glad im a large language model

[@EVILJAMARR]

@@jennyanydots2389 "thought out" is in quotes, because it doesn't think. It doesn't even look up information when crafting a response, it merely shows us what a competent response should look like, not what it is. Fine distinction to make, missed by most.

[@darcycrews]

it uses existing information, it didn’t come up with that on its own just scraped information that a human put out there

[@EVILJAMARR]

@@darcycrews agreed, isn’t this what I said? If not, this is what I meant but you say it much clearer 😅

[@LilRedDog]

The speed of light is defiantly constant: (I, almost, fixed that typo but I, actually, think it is better.) Constantly questioned, constantly researched and a consistent carrot some people hope will win them a Nobel prize.

[@imaginaryuniverse632]

Hope springs eternal for those who thirst 👍

[@randomnobody660]

I heard some time ago that more specifically we've tested the round trip time in any direction to be constant. Do we actually know whether the speed of light is actually the same in reverse yet?

[@jamesmoss5221]

That gosh darned defiant speed of light!

[@bevanodonohue2873]

kzbin.info/www/bejne/gF7ZYYCKd6d6oac I'd like to see you discuss that under this video.

[@coolninjabroguy]

Great videos. I like how in science even oversights are respected, don't you? Then something else is discovered.

[@AppNasty]

That 4 sided cube rotating the 5 letter word SPACE....broke my brain.

[@ChaoticNeutralMatt]

"Can't have varied much." I wish you'd expanded on this a touch more. I'll see what I can find though. Thanks for the video.

[@Graycy808]

As usual I understood about one third of the information... that said, I still love every minute of these uploads and hope to understand more soon! Thanks Matt and crew! Great content as usual!

[@space_audits]

It was meant to overload you and make you repeat the following: c is invariant for all observers. This way you can know nothing about the subject but still adhere to the beliefs. kzbin.info/www/bejne/eKibk2yPi5V4hqM

[@physicsunderstander4958]

​@@space_audits the speed of light is provably invariant for all observers. You can do the math yourself and check it if you want to, nothing is stopping you. Or do you have a better explanation?

[@wcsxwcsx]

Indeed, it's fundamental that we could never notice if the vacuum speed of light changed since everything else would change along with it.

[@MorphSenior]

Three Body Problem homies know that the speed of light used to be infinite during the universe's Edenic era, but the expanse of the black domains has continually lowered it.

[@mythicdawn9574]

I think it's one more thing that shows Liu Cixin actually wrote his books while knowing what was still going on in the research in physics. There are many "physicists problems" that are either explained by aliens, or that humans / aliens have to face in one way or another. This is certainly the most important books in Science Fiction written these last 20 years, I hope Liu Cixin becomes known as one of the pillars of the genre because he very much deserves it.

[@fanciestsauce677]

Ave, True to Trisolaris

[@Greenmachine305]

Given that there is no such thing as a constant, invariable perfect vacuum, it follows that there is no constant speed of light. We can all agree that the universe is a perpetually changing environment of energy. Personally, I find comfort in minute variables. I gather that many people who think about these things would prefer if there were a constant. I see this as an emotional weakness. Causality is the key. Do lets keep questioning space time.

[@siquod]

That at 1:06 is NOT a Lorentz transform, but a Galilei transform. What a pity.

[@cmelonwheels]

Great episode! Gotta say though, I'm really hoping for an episode on the one-way speed of light! (Or is there already one that I missed?)

[@garypalmer997]

Actually, there is a video on that. It's not a PBS one, but it talks about it. m.kzbin.info/www/bejne/poXRZ3itncdlbc0&pp=ygUcU3BlZWQgb2YgbGlnaCBpb25lIGRpcmVjdGlvbg%3D%3D

[@DenisLoubet]

The Veritasium treatment: kzbin.info/www/bejne/poXRZ3itncdlbc0

[@emuevalrandomised9129]

Thank you! This is a question I've been pondering but could never get any concrete answer and the equations and their implications are insanely complicated.

[@alfadog67]

I second this, Matt. Thank you!

[@osmosisjones4912]

The speed of light is basically the speed of time if you move at the speed of time with destination moving towards you you should move at infinite speed relative to destination. . Unless their stuff that slows it down

[@gheckolock81]

This helped me to understand cosmic inflation for the first time! Coming at it from the point of view of why a simpler/more intuitive theory cannot fully explain our observations worked for me.

[@aR3mYs]

6:00 that diamond moment

[@sephrinx4958]

I've often pondered this. What of the speed of light differs entirely based on many variables, and it's only localized to our perception and/or region of space.

[@HatsuneSquidward]

Wouldnt that be detectable in comparing our observations of different distant galaxies and other structures

[@colt45caliber]

Try multiverse theory. The runners of the simulations might experiment with entirely different laws of physics.

[@maeton-gaming]

the speed of light is the maximum rate of induction in the local enviroment or medium. So you are correct in a way, it can remain the variable 'C' but it should correctly be refered to as the maximum rate of CHANGE in a medium or universal medium.

[@WokeandProud]

It isn't otherwise the entire universe would look different.

[@stefansauvageonwhat-a-twis1369]

@@colt45caliber Multiverse theory doesnt say anything about simulations or changing the laws of physics afaik

[@rohanshah7960]

The animation at 11:53 looks pretty cool. I can only wonder how many hours must've been poured by the designer into making it.

[@pXnTilde]

probably just a shader on a stock model tbh

[@whoknowsthefuture]

Well, as I remember from the secondary school, the trajectory of the cup should be parabolic...😮

[@Zdman2001]

I love these types of videos. More entertaining when get to you think outside of the box. But, you also get to double down on knowing the fundamentals.

[@somethingelse2740]

Editors, Love how you put the 5 letter word SPACE onto a 4 sided rotating cube. Well done.

[@ArmaniDurham-j6g]

Brilliant script and explanations! Fantastic video, as always!. Finally, an episode of Space Time discussing not Spacetime, but Space Time!.

[@HeisenbergFam]

Bro's casually in space asking questions mankind desperately needs answers for

[@MegaManki]

I have had similar ideas and my current hypothesis for a possible variable speed of light is that it is actually constant, and that spacetime itself is emergent from the rate of interactions between particles/fields. Basically, the more two particles interact on average, the closer they can be interpreted to be. So because the early universe was high-energy and low-entropy, interactions were aplenty and thus all the particles seemed geometrically close, which means that light had to travel shorter distances. But as the universe cooled down, interactions decreased and the effective spacetime inflated. And now that the universe is basically isotropic, the scale of spacetime has plateaued macroscopically due to higher entropy.

[@mikemondano3624]

Clearly, physics isn't for everyone.

[@MegaManki]

@@mikemondano3624 ???

[@Nathan-vt1jz]

@@mikemondano3624apparently so is being polite and decent. Notice how in the video Matt didn’t disparage those he disagreed and also had the maturity to re-examine old theories vs. new based on the evidence. This guy is trying to make sense of the evidence the best he can and discussed it politely on a relevant video.

[@Nathan-vt1jz]

@@MegaMankihe’s just being a sarcastic jerk. I don’t think you’re correct, but I also think it’s great you’re engaging the concepts honestly.

[@MegaManki]

@@Nathan-vt1jz I know I’m very likely not correct, it’s just an interesting hypothetical. There actually are ideas by people smarter than me that gravity (and hence spacetime) might be entropic in nature. I’m a physics PhD student in quantum gravity so I should know. Also not a guy :P

[@NASASpaceNewsagency]

Thanks for this interesting video. The idea is super cool, it is part of a more general hypothesis that the physical constants might vary over time and space. For example, some scientists have suggested that the gravitational constant or the fine-structure constant might also change. Recently, a researcher named Rajendra Gupta has used this hypothesis to claim that our universe is 27 billion years old, not 13.7 billion and that the cosmological constant is not constant at all. His model is based on two old ideas: that the speed of light decreases as photons travel (tired light theory) and that the coupling constants evolve with time (Dirac’s hypothesis). However, this model can solve some problems in cosmology, but also has some problems and critics. What do you think? Do you agree or disagree with him? I’m curious to know your thoughts. 😊

[@brianmcdaniels8249]

Jon Evans, Little Jimmy from Nepal, and others, solved it all. Top to bottom. If a model doesn't put together everything, it is wrong. Every force from bottom to top is the same, just different names at different strengths. There is only one field. The Higgs Field.

[@ryanbriggs3391]

The Fine Structure Constant at 11:00 is a poor argument as h*c -has- remained constant. Since both are multiplied in the denominator it also fails to address the possibility of a historical increase in h.

[@kemboidickson284]

This is mind bending. Good one!

[@drakkondarkspell]

So the question is if the speed of light has changed, does that mean the devs upgraded the server hardware?

[@zebulonstevens305]

No it means the program is becoming more complex but the hardware isn't changing so we're getting lag.

[@hadensnodgrass3472]

Can you go over the 26.7 billion year universe vs. the previously thought 13.7 billion year old universe. I don't really understand it and would love a deep dive on it. 😁

[@physicsunderstander4958]

The 26.7 billion year figure is sort of nonsense. The whole thing came from a single paper that was trying to force an old hypothesis to fit new observational data. The paper itself basically said "If our entire understanding of redshift is wrong then the universe is twice as old as we think it is." The problem is that there's absolutely no evidence that our understanding of redshifting is even slightly wrong. It's just another case of a pop science news source misunderstanding a paper and exaggerating the conclusion to get clicks. No serious physicists think that this paper is proof that the universe is 26.7 billion years old, it's just an interesting little paper that describes what basically amounts to a thought experiment.

[@1dgram]

Rajendra Gupta's theory is based on a reimagining of the causes of redshift and his measurement only takes into account supernovæ. There are a variety of ways to measure the age of the universe, so Gupta should try harder.

[@1dgram]

@@Stompcurb There are a variety of ways to measure the age of the universe and the measurements agree. NASA's WMAP spacecraft used observations of the cosmic microwave background radiation to come to 13.772 billion years old, plus or minus about 59 million years. The Planck Collaboration estimated the age of the universe to be 13.813 billion years plus or minus 38 million years. This matches what is seen by studying the the oldest stars in globular clusters, supernovae, and calculations based off the Hubble constant (Hubble's law). Both Earth and the universe are much older than 5783 years old - if you want to believe that fine, but not all those 5783 "years" were of the same length then.

[@garethdean6382]

Currently a bunch of people are making clickbait claiming that new evidence OVERTURNS EVERYTHING WE THOUGHT WE KNEW! Their evidence doesn't really stack up and I'd wait a few years before giving it much thought.

[@wyatta7442]

Just get the FNAF fan base to start studying the universe, they'll figure it out in no time 😂

[@llahneb10]

Best science content on KZbin, hands down

[@nonono.yesyesyes]

I had to rewatch that pretty prism simulation several times. That was really good.

[@NeoShameMan]

But what if gravity was a spatial dimension and we were only living on a slice of it? That is, if light going through a gravity well is like a ants moving through a bump on the ground?

[@Riskninjaz]

Good call. I also wonder if light from BB is from a higher dimension and microwave background is based on some light slippage from the BB when some light was allowed to traverse into our dimension and as a consequence the laws of physics obey Lorentz invariance. But perhaps this is not true in the next dimension. Similar to gravity. So move to higher dimension, travel, then come back to this dimension.

[@ravenmad9225]

If we ever find a 5th dimension and measure the speed of dark,we still won't know what to do with the information. Spacetime.

[@NeoShameMan]

@@ravenmad9225 the point is that gravity is a spatial dimension, nothing else to find. It makes gravity well makes more sense not just as a metaphor.

[@kittenisageek]

EDIT: Re-wrote to be a bit more concise: Prior to 2019, the meter, which is used to measure the speed of light, was defined using the distance from the equator to the north pole. It was changed to instead be defined by the speed of light. So, since 2019, the meter is defined by the speed of light, the speed of light is defined by the meter and the second, and the second is defined by the meter and the speed of light. All three are circularly defined and treated as constants. If any one of them changes, no one will ever know....

[@Real_MisterSir]

This is not true. The meter was originally in 1791 defined as a derivative of the distance from Equator to the North Pole, but was changed in 1799 it was redefined and in the 60's the meter became based on the Krypton-86 wavelength. It was in 1983 that the meter became defined by the distance light travels in a vacuum. In 2019 the definition was simply updated with a rewording, but the measurement is still the same and has been since 1983. We haven't used the Equator-North Pole definition for over 60 years.

[@kittenisageek]

@@Real_MisterSir Thank you for clarifying the history of the meter. That doesn't change the fact that the meter, the second, and the speed of light are all defined by aspects of each other making them all linked.

[@Real_MisterSir]

@@kittenisageek I'm not disputing that part, only clarifying that the statement about when the Equator-to-Pole standard was misrepresented, as it was not used pre 2019, but rather pre 1960.

[@darrenc8776]

What if we had the balls to just say we haven't a clue what's really happening.

[@theobrayford4004]

That is my favourite of your shirts to date. By far.

[@justletmepostthis276]

@4:28. You don't have to increase the distance between the Mirrors to slow the clock. A wave (Up and down) can hold more data in the line in the same space. IMO.

[@artificercreator]

Thank you for exploring the idea! Ya awesome!

[@dansmith5901]

Matt is putting on such a great show!!

[@LionidasL10]

Thanks for your great videos Matt and team.

[@joshuaburke9516]

Glad I watched the homework before this video. It really helped. Please keep doing that!

[@fuzzblightyear145]

that's the beauty of science. You can come up with an idea, and then go about testing it to see if its good or not

[@JohnRandomness105]

3:05 SI defines the second in terms of Cs-133's ground-state hyperfine transition radiation. The meter is defined in terms of the speed of light and the second. The 2018 redefinition defines constants rather than units. A variable speed of light becomes a variable meter length. SI is going to have to work hard if, by unlikely chance, the speed of light is variable. 4:10 Several possibilities give several results. If the Coulomb force constant remains unchanged when the speed of light changes, the dominant interaction in atomic and molecular physics remains unchanged. The speed of light change is unambiguously measurable in that case. (The second might change, though, since the cesium radiation depends on the magnetic force as well as the electric force.)

[@jahosaphat]

Thank you PBS. Thank you Matt.

[@amaree9732]

I used to have a car that traveled at the speed of light, but I was afraid to drive it at night. I wasn't sure if the headlights would work.

[@null-0x]

This channel is so addictive!

[@tac0cat14]

I was real curious about this concept while working on some research for school. Reworked what SR would be… and quickly put it to rest, figured that wasn’t the right approach.

[@Michael75579]

The video touched on this in the bit about the fine structure constant, but there are more earth-bound ways to do the same thing. For example, the Oklo natural nuclear reactor. The equations which govern the behaviour include c, so we can tell that c is essentially unchanged in the last 2 billion years by examining the remains.

[@jamesmckenzie4572]

I understand that it's difficult, but I do appreciate you, and others, going to the effort to make this information understandable to 'lay' persons such as myself.

[@chiphill4856]

Thumbnails like this just give kooks the courage to speak their mind.

[@9000ft]

Love this channel, love Physics.

[@nicodesmidt4034]

The subject is hard enough by itself, no annoying cricket music needed thank you

[@hawaiianrobot]

great videos Dr Matt!

[@michaelperrone3867]

If the fundamental forces all unify, then particles are a limit case of photons and they too would be affected by vacuum refractive index - but from the perspective of someone made of particles, it would look like spacetime curvature. Setting C=1 discourages people from looking at it this way. 00:06:05 Frame dragging doesn't disprove variable index models if you consider the vacuum to be anisotropic - which it is in the case of vacuum birefringence. Gravitational waves can be waves of refractive index - so I don't see how that isn't possible, especially because squeezed vacuum states have wave equation solutions.

[@iangrosan]

11:01 Big problem using fine structure to calculate speed of light. Plank's constant (and also permittivity) has units of meters, which means it's dimensionally fixed to the speed of light. Any variations on c would be absorbed by h (and ε₀) to produce the same result. If your language presumes speed of light, which it does in meters, there's nothing inside your language that can explain speed of light.

[@erikefse01]

Great video. Using alternative theories to vulgarize several concepts from general relativity. Very smart ;)

[@sergiogiacomosammartano7623]

Nice episode :)

[@Articulate99]

Always interesting, thank you.

[@EliasMheart]

4:55 Wow. I love that the cube of space has seven sides :D Not sure if mistake or intended, but fun either way 😊

[@tim40gabby25]

.. at least seven sides.. more like 15, given that the choice of 5-side wraparound is arbitrary :)

[@jo_crespo11235]

Great video, keep the hard work

[@gumball1216]

“Time is what clocks measure” -Albert Einstein I love the idea of that quote without context.

[@gh8447]

5:00 Watching the four vertical sides of a cube spell a five letter word is trippy.