Why we cant measure the speed of light

originally posted by: ManFromEurope
Please don't let this sink into "is Ether real or not" (regarding some none-scalar values of the speed of light, of running "against" the ether or "with" the ether).

This was closed in the beginning of the 19th century.

Light speed can be measured. Light and its very well known speed is (a) the SI-basis of the meter and (b) is used in highest resolution in many, many applications like lidar etc.

This thread should be closed, as there cannot come any new knowledge from this.

Actually this topic does have certain parallels with the aether, and is somewhat related. We never actually proved that the "Lorentz aether" didn't exist, but the properties of such an aether made it indistinguishable from relativity in experiments. So, the addition of the Lorentz aether seemed like an unnecessary complication to the simpler model by Einstein, at least most scientists agree that Einstein's model is simpler. Nobody has proven it's more correct than the Lorentz aether theory, since both predict the same experimental results.

I don't think anybody will figure out a one-way measure of the speed of light soon; it's been pursued for a long time, though some day a clever person might figure out a way to do it. Like the assumption that the aether is an unnecessary complication is probably a good assumption, the assumption that the speed of light is isotropic is also probably a good assumption, and I don't think anybody here is trying to say it's not.

If there's an importance to this topic, it's not necessarily figuring out a better measurement of the speed of light, though that would be nice, but I think one point this topic should make is a rebuttal to those who invoke the straw man argument that "scientists think they know so much, or think they know everything". What this topic shows me is how ignorant such a statement is, that science doesn't necessarily take for granted even some trivial assumptions, and that scientists are willing to admit that they've never measured the one way speed of light and they haven't proven the speed is the same in all directions (without making some assumptions).

So rather than thinking of this thread as some kind of an attack on science as apparently you may see it, I see the topic actually supporting science by showing that scientists are willing to admit their ignorance and that scientists search for rigorous experimental validations of their models. Most of them do anyway, though some branches of science don't have enough experimental focus, like string theory.

a reply to: Arbitrageur

Thanks for your comment.

I put that video up to simply show there was an alternative to what he said in his OP.

Apart from that. I don't think the actual speed of light, (correct or not) is the issue with this thread.

For me. I was trying to show that whatever the speed. It is the same in all observed directions. As in the Mobius reply, isotropic.

a reply to: Arbitrageur

People seem to think i disagree with the speed of light being the same in all directions i do not. What i was simply trying to show people is we have never verifird the speed of light in any single direction. I got caught in this by another professor who was arguing for an aether. And I was forced to admit that yes the speed of light could vary dependent on direction. So he invalidated my argument of there was no aether detected.

What this shows is its possible and we would have no way to tell the difference if light is not the same in aall directions. Mind you this is just an argument for now he won next time hopefully i will. We will have more of these if people re interested its all part of the game.

IF we assume, for a moment, that it's possible for the speed of light to differ depending on direction of travel, I'm curious to know what you might theorize as factors that could cause this to happen.

I have been thinking about what could possibly influence light to travel at different speeds depending on which way it's traveling, and the only idea I had that made any sense to me was the possibility that Hubble's Constant isn't really "constant", and there could be areas/pockets at the periphery of the universe where expansion is occurring at different rates. If the very fabric of the universe is moving at different rates depending on which way we look, then it'd be reasonable to assume that light traveling to/from that area might move slower or faster relative to other regions of the universe.

Other than that ... and assuming that in our thought experiment, we normalize influencing forces like gravity of nearby celestial bodies, and we expect that the very firmament of the universe is more or less consistent in every direction... what could possibly make light travel at a different speed depending on which way it's traveling?

a reply to: SleeperHasAwakened

Actually, there is a discrepancy in Hubble's constant we have to different answers. but this would effect the speed of light only the distance it travels.

Now how could light have different speeds one would be if time is involved. Did you know on earth that if we synchronize a clock and send it north south east and west it will lose different amounts of time? Sounds strange but north-south will be the same but east-west will not match. Your clock can actually gain time by heading west. Going east it will lose time. This is known as the sagnet effect. If I take a Sagnac interferometer basically looped a laser around a circle the idea was to test Earth's rotation. Now sending light in either direction will be the same until we add a gyroscope to stop angular momentum then our light beam would travel one direction faster. Much like our clocks do on our spinning globe.

en.wikipedia.org...


Now the other possibility there is a medium for the light that it uses to travel an aether if you will. It is almost impossible to detect. Basically, this means that while physics should remain the same in non-accelerated experiments, light would not follow the same rules because it is travelling in the universal "aether frame". So motion would have an effect on our speeds.

There are a couple of strange possibilities such as we are existing in a black hole but this would be the major 2.

originally posted by: dragonridr
a reply to: Arbitrageur

People seem to think i disagree with the speed of light being the same in all directions i do not.

Right. I didn't take your thread that way, but some people might have misinterpreted it that way.

originally posted by: SleeperHasAwakened
I have been thinking about what could possibly influence light to travel at different speeds depending on which way it's traveling, and the only idea I had that made any sense to me was the possibility that Hubble's Constant isn't really "constant"

We know the Hubble constant isn't constant, your link even says so, but I don't think it's particularly relevant to the one-way speed of light measuremnt issue:

the Hubble parameter H [displaystyle H] H, which the Hubble constant is the current value of, varies with time, so the term constant is sometimes thought of as somewhat of a misnomer.

It's not necessarily constant in space either. It doesn't even apply within a few parsecs of Earth (let's call those cosmologically "short" distances", and at cosmologically "long" distances the linear relationship may also not apply, depending on what model is used for interpretation, also discussed in your link.

Other than that ... and assuming that in our thought experiment, we normalize influencing forces like gravity of nearby celestial bodies, and we expect that the very firmament of the universe is more or less consistent in every direction... what could possibly make light travel at a different speed depending on which way it's traveling?

As I alluded to earlier and as Dragonridr explained in his post immediately prior to yours, this can come up in discussions about aether which was widely thought to exist up until around 1920-ish and Lorentz continued to defend his version of the aether until his death in 1928.

originally posted by: dragonridr
a reply to: Arbitrageur
I got caught in this by another professor who was arguing for an aether. And I was forced to admit that yes the speed of light could vary dependent on direction. So he invalidated my argument of there was no aether detected.

a reply to: SleeperHasAwakened
So aether is one possible answer to your question "what could possibly make light travel at a different speed", to which we should probably add the word "appear" as in "appear to travel at a different speed", which apparent speed might depend on the observer's motion in the aether.

Let me start by saying most relativity deniers are nuts. This is confirmed by a relativity denier who posts here from time to time, physicist Delbert Larson, who isn't nuts, but he admits most relativity deniers are nuts. He has valid questions and rightly says that the Lorentz aether theory has never been proven "wrong", because it makes exactly the same predictions as relativity so every experiment that supports relativity so far also supports the Lorentz aether theory.
Hopefully the scientist Dragonridr debated with is also not a nut. There are some respectable scientists with valid questions which do lead to valid debates.

Again the main reason Lorentz aether theory was dropped isn't because it was ever proven false, it wasn't ever proven false. It was dropped because of the application of Occam's razor preferred relativity, and that's why relativity is the generally accepted model.

Attached is a paper trying to support the aether model, and I can't say it's right about everything, but it does try to make the point that if the aether exists then it's possible the speed of light may not appear isotopic (not the same in all directions):

The Relative Motion of the Earth and the Ether Detected

It is important to note that Lorentz, acknowledged as the pre-eminent theoretical physicist at the beginning of the 20th century, defended the concept of the ether right up to his death in 1928.

That's true and I think most physicists who have looked into this would admit Lorentz has never actually been proven wrong, then they might explain why they prefer relativity because of Occam's razor, which is a useful tool, but it's not definitive or rigorous in excluding the idea of Lorentz.

If you don't accept relativity (or merely question it), you can try to apply an absolute space model which is discussed in that paper as a generalized Galilean Transformation (GGT):

In the framework of the GGT light propagates isotropically at a speed c in a preferred or absolute reference frame. In such an absolute frame, consistent with classical velocity composition, the one-way speed of light relative to an observer changes according to the observer's motion relative to the preferred reference frame. Thus as observed by Hawking, " It was expected that light would travel at a fixed speed through the ether but if you were travelling through the ether in the same direction as the light, its speed would appear lower, and if you were travelling in the opposite direction of the light, its speed would appear higher"9'P6'. This anticipated light speed change in the GGT characterizes ether drift and is the basis of the Michelson - Morley, Kennedy-Thorndike and many other ether - drift detection experiments. This is completely different from special relativity in which the light speed invariance postulate requires that no such light speed changes be detectable by a moving observer. In addition, FLL contractions (1.1) and (1.2) occur as a result of movement relative to the preferred frame and true measurements are those made in frames fixed relative to the preferred frame.
These contractions alter the normal Galilean transformations that relate the coordinates of the preferred reference frame to coordinates in any other inertial frame, which now become (1.3). Our objective is to investigate the possibility of
detecting movement relative to this preferred frame i.e. ether drift, from a moving platform.

Until someone can devise an experiment which can distinguish the Lorentz aether theory or similar theories from relativity, I think relativity will continue to be the preferred model. I don't buy all the arguments in that paper by Stephan Gift, but he is right about some things like the Lorentz aether model never really being proven wrong, and I think most physicists will admit that.

originally posted by: dragonridr

Now the other possibility there is a medium for the light that it uses to travel an aether if you will. It is almost impossible to detect. Basically, this means that while physics should remain the same in non-accelerated experiments, light would not follow the same rules because it is travelling in the universal "aether frame". So motion would have an effect on our speeds.

Yes, that is the concept I was aiming to describe; the notion of an "aether frame" (nice term). In an expansionary universe, if all distant points are moving away from on another with accelerating velocity, then eventually that expansion process should hit a point where even the speed of light won't be fast enough to traverse the increasing distance between two points, say Earth and a very distant galaxy. If there are practically infinite "aether frames", and they are moving at different speeds relative to one another (and speeding up as they move), then in my thinking that would be a reasonable explanation for how light would travel at different speeds in different directions, depending on what "aether frames" it traverses.

originally posted by: Arbitrageur
We know the Hubble constant isn't constant, your link even says so, but I don't think it's particularly relevant to the one-way speed of light measuremnt issue:

True, Hubble's law and the expansionary model is not going to help measure C in a s single direction. It was just something I had thought about in my musings as a way for C to be exceeded, if the actual points in spacetime end up (eventually) moving apart at a velocity exceeding the speed of light, the accerlating dispersal of "aether frames" as dragonridr termed them.

a reply to: Arbitrageur

... Most of them do anyway, though some branches of science don't have enough experimental focus, like string theory.

Thank you! I've been saying this for quite a while now.

Sometimes I view quantum physics discussions as this bucket where folks throw stuff when they can't figure out how to prove Einstein wrong. "Welp, Einstein wins again, so we'll just play the 'we're right' card because...quantum physics. You know, that fantastical place where time moves backwards, and 1+1=9, white is really black, cats lay with dogs and everything is possible. "

originally posted by: SleeperHasAwakened
True, Hubble's law and the expansionary model is not going to help measure C in a s single direction. It was just something I had thought about in my musings as a way for C to be exceeded, if the actual points in spacetime end up (eventually) moving apart at a velocity exceeding the speed of light, the accerlating dispersal of "aether frames" as dragonridr termed them.

You read dragonridr's post differently than me, when he said 'the universal "aether frame" ', that sounded singular to me, then you started talking about frames plural and who knows how the aether would fit into the accelerating expansion of the universe, since we don't seem to be able to detect any aether properties if there is such a thing as aether? Einstein tried to call the spacetime of general relativity (GR) a "new aether" with different properties than the luminiferous aether scientists previously believed in, but his term didn't stick and we now call it "space-time", but it does allow us to see apparently faster than light speed of light (which may surprise some people), though you have to be specific about the context, like this example is (by the way this source has some interesting insights on the speed of light so more than just this excerpt is probably relevant to this thread):

Is The Speed of Light Everywhere the Same?

Light travels faster near the ceiling than near the floor. But where you are, you always measure it to travel at c; no matter where you place yourself, the mechanism that runs the clock you're using to measure the light's speed will speed up or slow down precisely in step with what the light is doing. If you're fixed to the ceiling, you measure light that is right next to you to travel at c. And if you're fixed to the floor, you measure light that is right next to you to travel at c. But if you are on the floor, you maintain that light travels faster than c near the ceiling. And if you're on the ceiling, you maintain that light travels slower than c near the floor.

By the same token, your head ages faster than your feet because clocks run faster near the ceiling.

Also due to the properties inferred by general relativity, we can see light from galaxies that are and always have been traveling away from us faster than the speed of light, which would be impossible without the space-time properties inferred by GR.

originally posted by: Flyingclaydisk
Sometimes I view quantum physics discussions as this bucket where folks throw stuff when they can't figure out how to prove Einstein wrong. "Welp, Einstein wins again, so we'll just play the 'we're right' card because...quantum physics. You know, that fantastical place where time moves backwards, and 1+1=9, white is really black, cats lay with dogs and everything is possible. "

Quantum mechanics does seen strange to us, but there are tons of experiments testing quantum mechanics and also lots of experiments testing relativity, so I can't complain about those branches of science lacking experiments. The science in both those fields is fairly rigorous in terms of models to predict experimental results, and experiments which match the predictions of the models. That's how science should be, so I'm not sure why you're complaining about quantum mechanics if that's what you're doing. If I have any complaints, it's not about what scientists do with QM, but there are a lot of charlatans out there telling people what they want to hear and claiming QM has some magical properties, because "nobody understands quantum mechanics" so they can claim it can do magic and who can deny it if nobody understands it? But that charlatanism is pretty far removed from the actual science, there's a rational wiki about that problem. The models are very accurate in making predictions and don't allow for invoking magic as some sources would have us believe:

Quantum woo

If a sentence has the word "quantum" in it, and if it is coming out of a non-physicist's mouth, you can almost be certain that there's a huge quantum of BS being dumped on your head.
—Physicist Devashish Singh, quoting a colleague
...
The reason for quantum woo is the almost mystical status of quantum mechanics in the collective imagination: almost nobody knows what it actually is, but it's definitely extremely hard science about very awesome stuff.

...all it takes to make something appear to be based on Hard Science™ is spouting a little bit of vague technobabble about quantum stuff.
The logical process runs something like this:

I want magic to exist.
I don't understand quantum.
Therefore, quantum could mean magic exists.

So the hard science of QM done by scientists is very good. What's very bad is what ends up getting communicated to the public by science writers who don't understand the science and the seemingly endless stream of charlatans who also don't understand quantum science but make all sorts of unsupportable claims about it. The average person who hasn't spent years studying quantum mechanics probably has little chance of sorting out fact from fiction among all that noise, unless they make it a point to check multiple university sources and read multiple scientific papers on a topic, though the papers may be too technical for the average person to understand.

In contrast to the multitude of experiments confirming our models of quantum mechanics, predictions made by string theory are sparse and a number of predictions that string theorists made about what the LHC should detect failed to materialize. So far string theory seems to be either untestable in its current form, or, to the extent that it's been tested in experiment, the experiments failed to confirm the string theory predictions. My signature on string theory looks like a cartoon, but it's not that far removed from the reality of how little string theory has really accomplished that can be experimentally verified.

a reply to: dragonridr

TextPeople seem to think i disagree with the speed of light being the same in all directions i do not.

You did say similar in replies to me. But, as you still argued for the concept of the OP. It was fair to argue against it.

A problem for me is. How do you measure an instant?

I don't think c is the difference between half and instant.

Instant is an infinitely small point.

The best example i think i can use here. Although not related to the OP is.

How long does it take a person to die?

At one point. They are alive. At another point they're not.

I don't see how the point can be measured.

Maybe not the beat example. I admit.

If I have any complaints, it's not about what scientists do with QM, but there are a lot of charlatans out there telling people what they want to hear and claiming QM has some magical properties, because "nobody understands quantum mechanics" so they can claim it can do magic and who can deny it if nobody understands it? But that charlatanism is pretty far removed from the actual science, there's a rational wiki about that problem. The models are very accurate in making predictions and don't allow for invoking magic as some sources would have us believe:

So then we agree, right???

But it's only after the fact, when they say "Uh-OH" and then try some actual experiments to prove their theories. The first go is just, 'well because...quantum physics'.

Candidly, I have a lot less confidence in "scientists" today, because I think many of them go looking for a solution in need of a problem. I'm sure you differ, but that's my take.

Best, anyway!

LOL!!!!

originally posted by: Flyingclaydisk
So then we agree, right???

But it's only after the fact, when they say "Uh-OH" and then try some actual experiments to prove their theories. The first go is just, 'well because...quantum physics'.

It would help if you had specific examples of what you're talking about. There are, always have been and always will be a handful of fringe scientists, so if you're talking about some fringe stuff yes there are a few fringe scientists.

But if you're talking about the mainstream science of quantum mechanics which has a huge body of experimental evidence consistent with quantum mechanics models, I can see no reason why you would cite that as being anything like the lack of evidence of string theory I lamented in my earlier post which you quoted. If mainstream science has a problem with quantum mechanics, it's not a lack of experiments verifying the model, it's a problem with trying to interpret what the experiments and models are trying to tell us about nature. The scientists are quite candid in admitting they have different ideas about that but nobody has figured out a way yet to confirm which interpretation of quantum mechanics is the right one. They may have a preferred idea, but without experimental evidence to back it up they can't claim it's the right one. For an example of this, you can click my signature and watch the video in the OP by physicist Sean Carroll explaining that problem.

He has his own preferred interpretation of QM, but he admits he can't prove it's right so he argues where physicists need progress is figuring out which interpretation is correct, whether it's the interpretation he prefers, or some other interpretation, there are many possibilities.

So the problem with understanding QM seems to me a bit like the problem understanding gravity, where we can describe exactly how nature behaves in great detail, and how much slower the speed of light travels at the floor as seen by a ceiling observer, which experiments confirm, but I don't think we understand exactly WHY gravity does what it does. Exactly why does mass warp space-time the way it does? I don't think we really understand that at any deep level. Similarly, we have some accurate descriptions of QM behavior, but as with gravity we are lacking a deeper understanding than the statement that "experiments are consistent with our models".

a reply to: Arbitrageur


Im going to go out in a limb and say string theory is wrong and has become the Frankenstein of science. Just keep adding new parts all the time while you claim its alive.

a reply to: dragonridr
If a model can be tested, you can test it and use the test results to analyze if the model is right or wrong.

But worse than being wrong, is a model that can't even be tested, because it's not really a clear model which makes clear quantitative predictions. The biggest criticism scientists offer for such a model is "Not even wrong" and physicist Peter Woit has had a blog about string theory by that name for years, he also published a book on the subject too. He would tell you it's "not even wrong".

Not Even Wrong
On November 13, 2020, he made a post there about researchers of the black hole information paradox:
"researchers cut the tether to string theory altogether." from an article in quantamagazine.

At least we can measure the two-way speed of light with some accuracy, even if we can't effectively measure the one way speed of light yet. It's interesting to see string theory abandoned on the black hole research because it wasn't getting them anywhere; they don't seem to be able to measure anything about string theory.

a reply to: Arbitrageur

String theory is a dead end the problem is many have spent there lives trying to make it work. And worse are now trying to add ehatever they need to to keep it relevant.

People like Michio Kaku have invested so much time they are not willing to admit they chased the white rabbit.

originally posted by: Vroomfondel
What always fascinated me about light isn't just how fast it is, its that photons have mass yet still travel at the speed of light - something nothing with mass is supposed to do. Light also moves in wave form like ripples on water. Only fluid mass can do that.

None of that is exactly right. Electrons have no rest mass. They have energy, but are not energy, so energy-mass equivalency isn't applicable. And as for only liquids bing subject to wave propagation, I would suggest you find a copy somewhere of the translation of Federov's treatise on the propagation of waves in crystals and other anisotropic solids.

a reply to: blackcrowe


Well time is relative or so Einstien told us anyway. But lets look at light to light no time passes from its creation to when it hits something. Meaning even light from a distant galaxy billions and billions of lightyears away is instantanous to our photon that made the journey. Its that time thing you were talking about from the photons reference frame it traveled instantly to us and no time passes for it. The advantage to travelling at the speed of light time stops. As we learned from special relativity this is a perfectly valid reference frame.


So you never have a true time on anything it depends on where you observe it from.

a reply to: F4guy

Your right however we still dont know if light has mass. What we do know is if it does it to small for us to detect. But this is one of those catch 22s unless we prove it does have mass then we can never be 100 percent sure it doesnt.

originally posted by: dragonridr
a reply to: F4guy

Your right however we still dont know if light has mass. What we do know is if it does it to small for us to detect. But this is one of those catch 22s unless we prove it does have mass then we can never be 100 percent sure it doesnt.

I can't believe you said "Your right" and then say "we still dont know if light has mass", he said electrons, not photons which comprise light. You have to know electrons have mass, right? F4 was right about waves in solids, but he completely botched his "correction". I'm 99% sure you know better, so I'm surprised you didn't catch it.

originally posted by: F4guy

originally posted by: Vroomfondel
What always fascinated me about light isn't just how fast it is, its that photons have mass yet still travel at the speed of light - something nothing with mass is supposed to do. Light also moves in wave form like ripples on water. Only fluid mass can do that.

None of that is exactly right. Electrons have no rest mass. They have energy, but are not energy, so energy-mass equivalency isn't applicable. And as for only liquids bing subject to wave propagation, I would suggest you find a copy somewhere of the translation of Federov's treatise on the propagation of waves in crystals and other anisotropic solids.

You got the part right about waves traveling in solids, but your supposed "correction" of what Vroomfondel said is also wrong, neither of you got it right.

Electrons definitely have mass. I don't call it "rest mass" because according to Einstein there is no other kind of mass. The particle data group in 2018 put the mass at 0.5109989461±0.0000000031 MeV. By convention they drop the "divided by c-squared" which is implied in the stated mass. Also notice they just call it "mass", not "rest mass".

I know some textbooks taught the concept called "relativistic mass", but it's gradually being dropped from textbooks as more scientists are realizing that's not correct. Einstein himself thought relativistic mass was a flawed concept and he tried to discourage its use, maybe his advice is finally sinking in.

If you meant to say "photons" where you said "electrons", you would be part right and still part wrong. Part right because we teach beginning physics students that photons have no mass, but as dragonridr said, what we teach more accurately to more advanced students is that if photons have mass, so far it has been too small to measure. The particle data group data on mass of the photon doesn't say it's zero, it puts an upper limit on the mass, which is fairly close to zero.

For the energy of an electron, you can't normally use E=mc² since they are usually moving. Instead you have to use the more complicated formula which is in my thread explaining why E=mc² is wrong for moving particles which have momentum.

The more accurate formula for energy has a mass component and a momentum component. About 5 posts from the bottom of the first page is Einstein's explanation of why there is only one kind of mass, and he refers to the momentum formula which I give in the opening post, which has mass, and momentum.

They have energy, but are not energy, so energy-mass equivalency isn't applicable.

If you meant to say photons instead of electrons...

Electromagnetic radiation is energy. A photon is a quantum of electromagnetic radiation.
For photons, since we've never measured the mass, their energy comes from their momentum, as a function of their frequency.

a reply to: Arbitrageur

I believe that was me thinking what he must meant to say instead of reading what he wrote. oh well only human. I will add i hate the term rest mass as well because everything in the universe is in motion. Weak equivalence principle states that rest mass and inertial mass are equivalent. So there is no need to even discuss rest mass anymore unless we are discussing newtonian physics,