Is VSL the Key to Interstellar Communication and the Fate of Humanity?

AI Thread Summary
The discussion centers around the speed of light (c) and its implications for interstellar communication and the nature of spacetime. Participants debate whether c is truly constant or if it could vary due to gravitational influences, with some suggesting that all measurements of light are influenced by the conditions of spacetime. The reliability of GPS technology, which relies on the constancy of c, is highlighted as evidence for its fixed nature. Concerns are raised about how variations in c could affect fundamental physical constants and measurements, leading to questions about the implications of such changes. Ultimately, the consensus is that extensive scientific evidence supports the constancy of the speed of light, despite ongoing inquiries into its foundational role in physics.
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Any thoughts on this?
 
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you wouldn't notice?
 
Originally posted by wimms
you wouldn't notice?
You would absolutely notice if it varied.
 
Originally posted by russ_watters
You would absolutely notice if it varied.

In long frame/form How?
 
Originally posted by Mr. Robin Parsons
In long frame/form How?
I'm not sure what you are asking. Should I list all of the ways the speed of light has been measured and every implication of Relativity that depends on a fixed speed of light?
 
Originally posted by russ_watters
I'm not sure what you are asking. Should I list all of the ways the speed of light has been measured and every implication of Relativity that depends on a fixed speed of light?
Yes, I'd like to know all the way of measuring speed of light. I'm puzzled, how they measure something that is fundamental to spacetime itself, being source of both standards of time and distance. I've got impression that c is 'measured' the same always.. that leaves some options..
 
Originally posted by russ_watters
I'm not sure what you are asking. Should I list all of the ways the speed of light has been measured and every implication of Relativity that depends on a fixed speed of light?

No thanks, no need.

But, just as possiblity, it is possible that, in the near vicinity of our Sol, due to the gravitational influences of that Star, all measurements of Light end up equalling C, because the gravitational influence of the Sun, does that.

How can we have tested for that?
 
Originally posted by wimms
Yes, I'd like to know all the way of measuring speed of light. I'm puzzled, how they measure something that is fundamental to spacetime itself, being source of both standards of time and distance. I've got impression that c is 'measured' the same always.. that leaves some options..
Wimms, measurements are of course all we have to go by. Light has only recently become a standard on which to base measurements BECAUSE it is now known to be a universal constant. Not the other way around. The speed of light has been measured so many ways and under so many different conditions, not to mention the discovery that the speed of light is constant has been used for so many pracical applications, that if it were wrong, we'd know it.

The easiest way to accurately measure the speed of light is bouncing a laser off a mirror of known distance and measuring the time. The first method I believe had to do with timing the motions of Jupiter's moons. GPS depends on the constant velocity of light. If the speed wasn't constant, GPS wouldn't work.

There are more if you want more.

How can we have tested for that?
Thats easy. Its the same as the MM experiment just using the sun as the reference point instead of the earth. Any gravitational effects on the speed of light would manifest themselves through measurements at right angles to a the sun. And of course if the Sun's gravity had an effect, so would Earth's.
 
  • #10
Originally posted by russ_watters
The easiest way to accurately measure the speed of light is bouncing a laser off a mirror of known distance and measuring the time. The first method I believe had to do with timing the motions of Jupiter's moons. GPS depends on the constant velocity of light. If the speed wasn't constant, GPS wouldn't work.
How do we get 'known distance'? measure time of light travel, right, heh?
GPS depends on TIME, not c. speed of light changes when signal enters atmosphere, doesn't it? This just cancels out.

I'm worried about what else depends on velocity of light? Does size of atom depend on c? Does fields, forces depend on c? Does length of our physical meterstick depend on c? If all this does depend on c, then how on Earth can we measure c itself? It simply must appear constant...

There are more if you want more.
oh yeah, I want all of them I want to see what is the meterstick with which c is measured.
 
  • #11
Originally posted by Mattius_
Any thoughts on this?

Lots of thoughts on it. It amounts to proposing that space has a "variable index of refraction". If it were the root cause of gravity we could think of the planets as having their paths bent in space by such a diffraction.

How do we define the speed of light? One way is by using the value of electric charge.

h-bar*C/e2=137.036, so C has the value 137.036

Since electric charge is conserved and h-bar seems to be fixed this means we could measure any variation as being a change in the velocity of light.
 
  • #12
Originally posted by wimms
How do we get 'known distance'? measure time of light travel, right, heh?
No, you measure the distance through another means. Like a tape measure.
GPS depends on TIME, not c.
Yeah - the time it takes for the signal to travel the distance at C. So you still need C.
speed of light changes when signal enters atmosphere, doesn't it? This just cancels out.
GPS is far too precise to depend on cancelling errors. Also, the error would vary greatly with the azmuth of the satellite.
If all this does depend on c, then how on Earth can we measure c itself? It simply must appear constant...
I already addressed that. Reread my last post.
I want to see what is the meterstick with which c is measured.
"The" meter is a bar of platinum in a case in England (I think) with two notches on it. But its precision is limited and its accuracy changes with atmospheric conditions.

The argument here seems to be that since we don't know everything maybe there is some effect not yet observed that makes the speed of light vary. Sorry, but science doesn't work that way. Everything we know about light tells us its speed is constant. Does anyone want to present some ACTUAL EVIDENCE that it is not constant?
 
  • #13
I wonder...

how do photons jump from zero speed into c or if ther seed is only c what if something gets in the way?
 
  • #14
Originally posted by russ_watters
No, you measure the distance through another means. Like a tape measure.
What is tape measure? Platinum bar that depends on environmental conditions? What if tape length changes with variations of C? What if spacetime itself depends on C? Thats the reason why I asked what else depends on C?

Yeah - the time it takes for the signal to travel the distance at C. So you still need C. GPS is far too precise to depend on cancelling errors. Also, the error would vary greatly with the azmuth of the satellite.
You don't need C. You need locally uniform average velocity of signal. It could as well be 1/8 of C or sound, GPS would still work like a charm. And yes, GPS receivers are calculating all sorts of compensations. Of course errors cancel out, that's the point of triangulation and averaging.

I already addressed that. Reread my last post.
Not sure I got it. You simply assured me that we'd notice. I'm asking if we really would be capable of noticing, and you didn't address that imo.

"The" meter is a bar of platinum in a case in England (I think) with two notches on it. But its precision is limited and its accuracy changes with atmospheric conditions.
Exactly. Velocity of light has been found to be 'more' stable than any bar, and instead of measuring c precisely, it was dropped and 'defined' from theory, and taken as standard. Big win, but at the same time make C defined through itself. Imo, best definition of C is c=1.

The argument here seems to be that since we don't know everything maybe there is some effect not yet observed that makes the speed of light vary. Sorry, but science doesn't work that way. Everything we know about light tells us its speed is constant. Does anyone want to present some ACTUAL EVIDENCE that it is not constant?
No, argument was more like that we don't have any kind of independant from C reference to measure C. Fact that C is constant in any inertial frame, and that timeflow can differ for differing inertial frames, makes one think that length dilations compensate so that velocity of C is measured same, within the frame. Given that C isn't absolute, but only relative, its more like some sort of law of 'conservation of ratio' between spatial extent and time.
Actual evidence. I don't know. If we can't measure C then variance of C would manifest as something else. Maybe curvature of spacetime, gravity? Maybe matter?

My point is that how do we know that C is truly constant, and not that whole spacetime fabric is vibrating causing local variance of C along with spatial and temporal deformations etc?
 
  • #15


Originally posted by ddr
how do photons jump from zero speed into c or if ther seed is only c what if something gets in the way?
If something gets in the way then it gets absorbed or reflected as usual. As far as the acceleration goes, photons have no mass.
What is tape measure? Platinum bar that depends on environmental conditions? What if tape length changes with variations of C? What if spacetime itself depends on C? Thats the reason why I asked what else depends on C?
Again, all of the relevant effects are quite well understood.
You don't need C. You need locally uniform average velocity of signal.
Certainly. But since satellites use radio waves, GPS uses C. Please remember that all of the satellites move independently and the Earth rotates. The relativistic effects of these motions *IS* considered when using GPS.
Of course errors cancel out, that's the point of triangulation and averaging.
I ugre you to read more about how GPS works. For that matter, read a little bit about the concept of "precision" ie significant digits in ANY calculation. Errors do NOT cancel out, they build up. You learned that in 8th grade science class (if you are an American). Remember the pictures of a target with groupings of arrows illustrating the difference between precision and accuracy? Same unit.
Not sure I got it. You simply assured me that we'd notice. I'm asking if we really would be capable of noticing, and you didn't address that imo.
What are you looking for? I gave examples of situations where we would notice. Thats all I can really do for you. If you choose not to believe it, that's up to you.
Imo, best definition of C is c=1.
Sure. But of course that only works if C really is constant. I guess I'll have to repeat it: this isn't an assumption used for convenience, its observed data. C is constant.
Given that C isn't absolute, but only relative, its more like some sort of law of 'conservation of ratio' between spatial extent and time.
Given based on WHAT? You haven't given a shred of evidence that C isn't constant.
No, argument was more like that we don't have any kind of independant from C reference to measure C.
Which is exactly the point: there isn't any reference frame independent of C. Its constant in all frames. Are you suggesting we've never measured C in another reference frame? Again, I'll have to invoke GPS.
My point is that how do we know that C is truly constant, and not that whole spacetime fabric is vibrating causing local variance of C along with spatial and temporal deformations etc?
We know that C is constant because we measure it and it is always constant. There is no simpler way to explain it than that. If you won't accept that fact, there really isn't any way for me to help you understand the implications of that fact.
 
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  • #16


Originally posted by russ_watters
Again, all of the relevant effects are quite well understood.
Really? I didn't know that. And that was salt of my this question. I haven't seen anyone describing what would it imply if C would change, fundamental as it is, and how would it be perceived. And not just change of C alone, but together with all that depends on it together with it.
Can you explain to me or point to, what would be implications of it changing? What would change together with C, especially that which we'd have to use as 'meterstick' to measure C itself.

I ugre you to read more about how GPS works. For that matter, read a little bit about the concept of "precision" ie significant digits in ANY calculation. Errors do NOT cancel out, they build up.
Here we are. You called errors what I called variance of C due to entering atmosphere. I said this variance cancels out because same change in C occurs for signals from any satellite. I also implied they account for different distances C has to travel in atmosphere depending on azimuth. I was not talking about last digit precision errors. But they are canceled by averaging process.

What are you looking for? I gave examples of situations where we would notice. Thats all I can really do for you. If you choose not to believe it, that's up to you.
Russ, I'm not arguing that we measure C as constant, so its not issue of me believing. We can notice variance of C IF we have something given, like spatial extent that is independant from C, or time measure. But do we have that? For eg. if C would speedup, then time to moon should decrease. But if together with speedup of C, timeflow would slow down, then our clock measure of time would be same. In effect, we can't measure change in time to moon, it would produce same time as with constant C. You say we would notice variance of C, but seems to me you assume that there exists space independant from C. Does it? Afaik whole sense of spacetime is that its intimately relating space with time through C.

Suppose C was 1billion times faster. Then objects 1B lyrs away would seem like 1 lyr away, and completely other stuff would appear 1b lyrs away. Does it matter what the actual C is? Nope, only relation between space and time is what matters. If C would change, our perception of world would change. How? Can we explain something if we suppose that C can change without us being able to directly measure that?

Given based on WHAT? You haven't given a shred of evidence that C isn't constant.
I'm not in position to give evidence. I ask questions. C is same within any inertial frame. C is same between any inertial frames. What is it? Perception of reality or alice in wonderland?

Which is exactly the point: there isn't any reference frame independent of C. Its constant in all frames. Are you suggesting we've never measured C in another reference frame?
No. My point is that together with change in C our whole reference frame would change. If that includes timeflow, we have very hard time in detecting changes in C.

We know that C is constant because we measure it and it is always constant.
I know that Russ. I'm asking myself, WHY is C constant in all inertial frames or interframe comms? 'Its just so' is only one answer. That its fundamental limit due to Planck length per Planck time is another, but here I suggest that perhaps its so because we wouldn't have any reference frame to notice changes in C, and being restricted to measure C in measures of frame that depends on C itself, what else can we detect?
 
  • #17


Originally posted by wimms
Really? I didn't know that. And that was salt of my this question. I haven't seen anyone describing what would it imply if C would change, fundamental as it is, and how would it be perceived. And not just change of C alone, but together with all that depends on it together with it.
Can you explain to me or point to, what would be implications of it changing? What would change together with C, especially that which we'd have to use as 'meterstick' to measure C itself.
Special Relativity is the theory that explains why the speed of light is constant. General Relativity is an extension of Special Relativity to explain gravity. If the speed of light were found to be varialbe, then both theories would be proven wrong and all of their implications (which are vast) would be called into question. Besides just the nature of light, that's all we know about time and gravity as well. We'd need to find another explanation for why the rate of the passage of time is variable for example. Gravitational lensing. Gravitational red shift. The "light barrier": (if the speed of light changes, would this "barrier" change too? Matter/energy relationship. The behavior of particle accelerators.

Thats a major chunk of physics that depends on our explanation of the MM experiment.

This is starting to get big. Have you read any books on this? "A Brief History of Time" would be a good start. I can't give you a 150 page book in one post.
You called errors what I called variance of C due to entering atmosphere. I said this variance cancels out because same change in C occurs for signals from any satellite.
Actually, YOU brought up errors in GPS. And C DOES change (on average) when it passes through the atmosphere as it does when passing through any medium. But the effect of that is different for each satellite because the signal passes through different parts/amounts of the atmosphere. Thats yet another part of the calculations done in GPS recievers. Since its a known effect taken into account in calculations, its not an error and its certainly not offsetting errors.
We can notice variance of C IF we have something given, like spatial extent that is independant from C, or time measure.
You mean step outside of the universe? Not really an option, is it? And not really relevant either.
You say we would notice variance of C, but seems to me you assume that there exists space independant from C. Does it? Afaik whole sense of spacetime is that its intimately relating space with time through C.
Are you saying that you can't measure the speed of a car while inside the car? Why not? Also, relativity talks about different reference frames, not different universes. According to classical mechanics, measuring the speed of anything including light in different reference frames will not necessarily produce the same result. So all you need to do to prove that is to measure the speed of light in different reference frames. And we have.

After relativity explained why, and tecnology provided the means, it became possible to measure TIME in different reference frames. Lo and behold, the rate of the passage of time was found to vary exactly as relativity predicts.
Suppose C was 1billion times faster. Then objects 1B lyrs away would seem like 1 lyr away, and completely other stuff would appear 1b lyrs away. Does it matter what the actual C is? Nope, only relation between space and time is what matters.
Except of course this would affect GRAVITY among other things.
I'm not in position to give evidence. I ask questions. C is same within any inertial frame. C is same between any inertial frames. What is it? Perception of reality or alice in wonderland?
Then you shouldn't use the word "given." And questions on reality are philosophical, not scientific.
I know that Russ. I'm asking myself, WHY is C constant in all inertial frames or interframe comms? 'Its just so' is only one answer. That its fundamental limit due to Planck length per Planck time is another, but here I suggest that perhaps its so because we wouldn't have any reference frame to notice changes in C, and being restricted to measure C in measures of frame that depends on C itself, what else can we detect?
Again, "why" is a philosophical question. For the purpose of explaining HOW it works, "why" really doesn't matter. Science doesn't answer why. I submit to you that the question is irrelevant for understanding how it works. The universe is the way it is and this is the only universe that's relevant to us. How things would work in another universe doesn't really matter.

And what you are describing is a chicken vs egg scenario. Is the universe the way it is because we are here to see it or are we here to see it because that's the way it is? Thats the "anthropic principle" (there are two version) and its philosophical, but also discussed in "A Brief History of Time."
 
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  • #18
My point is that how do we know that C is truly constant, and not that whole spacetime fabric is vibrating causing local variance of C along with spatial and temporal deformations etc?

That's when we apply Occham's Razor. If the whole of spacetime is conspiring to make any variation in c unmeasurable, then we can get no wrong answers by presuming c does not vary in our theories.


Special Relativity is the theory that explains why the speed of light is constant.

Just to be picky, it was Maxwell's electrodynamics that explained "why" the speed of light is constant; Special Relativity just dealt with the consequences of that constancy.
 
  • #19


Originally posted by russ_watters
Special Relativity is the theory that explains why the speed of light is constant.
Fundamental postulate 'explains'?

General Relativity is an extension of Special Relativity to explain gravity. If the speed of light were found to be varialbe, then both theories would be proven wrong and all of their implications (which are vast) would be called into question. Besides just the nature of light, that's all we know about time and gravity as well. We'd need to find another explanation for why the rate of the passage of time is variable for example.
We need to find that out anyway. Why you think we'd need to throw all out of window? Who said that C can change 'freely' and independant from anything else?

This is starting to get big. Have you read any books on this? "A Brief History of Time" would be a good start. I can't give you a 150 page book in one post.
I have read books. But nowhere have I seen coherent approach to what would change in C imply to all of the physics. Only bits here and there, but no complete picture. I wonder if we even can have such picture before we have complete understanding of all underlying fundamentals.

Actually, YOU brought up errors in GPS. And C DOES change (on average) when it passes through the atmosphere as it does when passing through any medium. But the effect of that is different for each satellite because the signal passes through different parts/amounts of the atmosphere. Thats yet another part of the calculations done in GPS recievers.
sigh. Please reread posts. I was talking about C variance due to entering atm and that it cancels out for usable satellites. I didn't call that errors. There is no way to account for fluctuations in atm due to weather, and these are canceled out by averaging samples over time.

You mean step outside of the universe? Not really an option, is it? And not really relevant either.
Are you chasing ghosts? That was precisely my point! We can't step outside, thus all we can measure is relations between what we observe. And if C underlies all of what we observe, we have hard time to measure its variance. And why isn't this relevant?

Are you saying that you can't measure the speed of a car while inside the car? Why not?
Are you saying that speed of car affects space around it, gravity, timeflow, physical processes to same extent as C does? IF together with car speedup exactly proportional time speedup occured, what speed change could you measure from inside a car?

After relativity explained why, and tecnology provided the means, it became possible to measure TIME in different reference frames.
Is that end of story? Have we reached the 'finish'? As I've understood, relativity put things into correlation so we can compute, not explained 'why'.

Except of course this would affect GRAVITY among other things.
Of course. It would affect everything. And if it would affect everything in such a way that all would change proportionally, how would we go for detecting such C change? And if we can't detect it directly, doesn't it make you wonder that it might manifest itself as something else, eg GRAVITY? I'm asking, I'm curious how we'd observe it manifesting itself.

Then you shouldn't use the word "given."
Whats wrong with word 'given'? Do you attribute some special meaning to 'given' that I as nonenglish person don't get? For me, what SR says is given.

Again, "why" is a philosophical question. For the purpose of explaining HOW it works, "why" really doesn't matter. Science doesn't answer why. I submit to you that the question is irrelevant for understanding how it works.
nah. "Why" is the driving question. Without it, science has no purpose and no function. "How" is substitute until we get to the "why". Question is relevant, because to answer it we'd need to have deeper insight into how things work.

And what you are describing is a chicken vs egg scenario.
Noo. I'm not asking the question in that sense. I'm inquiring what fixes C to appear constant in any inertial frame? Is there possibly a reason for that to seek? And so I ask, would we notice change in C at all if it affected all that we can observe? Or would we notice only indirect effects of that, like time variance or gravity, or matter?


Originally posted by Hurkyl
That's when we apply Occham's Razor. If the whole of spacetime is conspiring to make any variation in c unmeasurable, then we can get no wrong answers by presuming c does not vary in our theories.
I'm not arguing this. There is tiny detail though, our theories say that C appears constant for any frame by any measurements. This is different than saying that it IS constant. This difference leaves some room to ponder what would be indirect evidence if C changed in such a way that our direct measurements wouldn't detect it.

Just to be picky, it was Maxwell's electrodynamics that explained "why" the speed of light is constant; Special Relativity just dealt with the consequences of that constancy.
"The fact that the speed of light is a constant in nature is DUE ONLY TO THE FACT THAT FREE SPACE HAPPENS TO HAVE A SPECIFIC PERMEABILITY & PERMITTIVITY. We do not know why this is. Maxwell's equations do not know why this is. The only thing that Maxwell's equations say is: "given this fact that the permeability and permittivity seem to be constant, the speed of light will be constant too." In regions where the permeability and permittivity is NOT constant, the speed of light is also not constant (such as in layered dielectric materials in modern fiber-optic cables). I assure you that the Maxwell equations can very happily accommodate a light-speed that is not constant!"

Thats not my claims. Do you agree with this?

"Maxwell equation for c implies that, assuming the permittivity and permeability of the vacuum are the same when evaluated at rest with respect to any inertial frame of reference, in accord with the classical principle of relativity, and assuming Maxwell's equations are strictly valid in all inertial frames of reference, then it follows that the speed of light must be independent of the frame of reference."

What is source of permittivity and permeability constants? Fact: matter changes permittivity and permeability. Q: is matter a manifestation of change in permittivity and permeability? If possible, then isn't gravity fieldlike change in permittivity and permeability?
 
  • #20


Originally posted by wimms
Whats wrong with word 'given'? Do you attribute some special meaning to 'given' that I as nonenglish person don't get? For me, what SR says is given.
The word "given" is followed by an accepted fact. If what follows is not an accepted fact, then the word "given" doesn't apply. Yeah, its an English thing.

Leemme give this one last try with three important points to take from this thread:

1. The expierment you want done has already been done, or at the very least covered by other experiments. Now I'm sure you can nitpick forever about tiny differences between what was done and what you want done, but it doesn't matter because:

2. As Hurkyl so eloquently put it, if the laws of the universe are "conspiring against us" to make it unobservable, then there is no possible experiment that will ever be able to show a VSL even if it exists. But that doesn't matter because:

3. If the effect can never be observed and it doesn't change how the laws of the universe work, you can (and should) ignore it.
 
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  • #21


Originally posted by russ_watters
1. The expierment you want done has already been done, or at the very least covered by other experiments.
Hello, when did I say anything about experiment? Are you confusing me with someone? I'm asking what would be implications of C changing? And is there a possibility that we wouldn't detect changes in C by direct measurements but instead as some other phenomena?

2. As Hurkyl so eloquently put it, if the laws of the universe are "conspiring against us" to make it unobservable, then there is no possible experiment that will ever be able to show a VSL even if it exists.
Strings. 10+ dimensions. what the heck are they doing then? Why are they wondering about 10+ dimensions if "universe is conspiring against us"? Go bash them out of waters.
If not, then why not ask 'what if' questions with other ideas?

3. If the effect can never be observed and it doesn't change how the laws of the universe work, you can (and should) ignore it.
Who says it can never be observed? What I meant is that it might prove difficult to detect by straightforward means, what macroscopic measurements are. Let me think of one effect that doesn't change how the laws of the universe work: uniform motion. Let's ignore it? If not light and "windows", you'd do this?

My very question IS how would it change the laws of universe? Do YOU know? Or are you just 'ignoring' questions? Somehow, without me ever giving reason, you started to defend SR as if I was refuting it.

You asked what's the evidence that C changes. There's plenty, it changes in presence of matter, in BEC. Does TIME flow differently there? Vacuum isn't exactly empty, its full of EM and G fields. Does this change C? There are changes in C, but they are called something else. And I still don't understand why its 'stupid' to seek for reasons why C appears constant in any frame, instead of just endlessly repeating conclusions derivered from fundamental postulate.
 
  • #22
Originally posted by wimms
Hello, when did I say anything about experiment? Are you confusing me with someone?
Apologies. Wisp/wimms - simlilar names, similar threads.
And is there a possibility that we wouldn't detect changes in C by direct measurements but instead as some other phenomena?
repost: Special Relativity is the theory that explains why the speed of light is constant. General Relativity is an extension of Special Relativity to explain gravity. If the speed of light were found to be varialbe, then both theories would be proven wrong and all of their implications (which are vast) would be called into question. Besides just the nature of light, that's all we know about time and gravity as well. We'd need to find another explanation for why the rate of the passage of time is variable for example. Gravitational lensing. Gravitational red shift. The "light barrier": (if the speed of light changes, would this "barrier" change too? Matter/energy relationship. The behavior of particle accelerators.

your response:
Fundamental postulate 'explains'?
Maybe I shouldn't have ignored this. Relativity isn't a postulate, its a theory and all of its implications are theories. You're still looking at the issue backwards - relativity depends on the speed of light being constant, not the other way around. Maybe this is the key.
We need to find that out anyway [re: variable time].
No, Einstein already found that out. Or rather he PREDICTED it and later experiments verified it (at the time, clocks weren't accurate enough to detect it).
Why you think we'd need to throw all out of window?
Time dilation results directly from a constant C. If C were found to not be constant, time dilation would have to have another cause.
I have read books. But nowhere have I seen coherent approach to what would change in C imply to all of the physics. Only bits here and there, but no complete picture. I wonder if we even can have such picture before we have complete understanding of all underlying fundamentals.
Relativity is the underlying fundamental and its implications are the big picture.
Who says it can never be observed?
You certainly implied it:
My point is that how do we know that C is truly constant, and not that whole spacetime fabric is vibrating causing local variance of C along with spatial and temporal deformations etc?
My very question IS how would it change the laws of universe? Do YOU know? Or are you just 'ignoring' questions? Somehow, without me ever giving reason, you started to defend SR as if I was refuting it.
The answer to your question is now and always has been SR. You ARE trying to refute it whether you know it or not.
Strings. 10+ dimensions. what the heck are they doing then? Why are they wondering about 10+ dimensions if "universe is conspiring against us"? Go bash them out of waters.
String theory is an attempt to unify Relativity and QM. It does not change my point #2. Or rather, point 2 does not change string theory.
You asked what's the evidence that C changes. There's plenty, it changes in presence of matter, in BEC. Does TIME flow differently there? Vacuum isn't exactly empty, its full of EM and G fields. Does this change C? There are changes in C, but they are called something else. And I still don't understand why its 'stupid' to seek for reasons why C appears constant in any frame, instead of just endlessly repeating conclusions derivered from fundamental postulate.
Fundamental postulate thing addressed above: this isn't one. But maybe we're getting somewhere now: you're now saying there IS evidence that C is not constant. Could you be more specific? Specifically changes in C that "are called something else." You're saying we have observed C to not be constant? Are you talking about refraction? Clarify.

It certainly appears to me that you have a point to your questions. But you are trying very hard to not argue it. Make your point. If it has some validity, we will accept it. If it doesn't we well tell you why and YOU must accept it. But running from a discussion of your point won't help you prove it.
 
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  • #23
VSL book

Just finished reading Faster Than The Speed of Light by Joao Magueijo ISBN 0-434-00948-2 (if you're curious).

The book outlines the theory that c is a constant now but has not always been a constant. Can't say honestly that I followed it all, but as speculation goes the idea has possibilities.

Proposed as an alternative theory to inflation whereby the the early hotter universe produced light waves that traveled at a greater velocity. C./C was the term used.

If anyone has seen this and has an opinion I'd love to hear it. Me, I'm just a sucker for a good tale.

Later,
 
  • #24
Originally posted by russ_watters
Maybe I shouldn't have ignored this. Relativity isn't a postulate, its a theory and all of its implications are theories. You're still looking at the issue backwards - relativity depends on the speed of light being constant, not the other way around. Maybe this is the key.
Right. If you see I'm off, please don't ignore. Let me get this straight: fundamental postulate of SR is that speed of C is constant (relative to any frame, not some absolute space), and from this and other assumptions it works out a theory that is in amazing correlation to observable. That makes this model very viable in that it explains 'how' things relate. So we basically go ahead and assume that C IS constant. From there, we bend space fabric and timeflow that SR initially assumes to have independant existence. Our point of reference becomes C, not space, not time.
Fundamental result of SR is that time and space can vary and DO vary. And we know that they vary in such a way that C remains constant for any frame.

Assumption that C is constant was smart and resulted in consistent theory. But now that inter-relations between variables are known, it becomes irrelevant which 'ingredient' is considered primary. Equations make indgredients equal. Given any of ingredients, we can derive correctly others. Constancy of C becomes historical assumption. Now to put things into perspective of what is anterior and what is posterior, or what makes what, we make 'physical interpretations'. Based on initial postulate, we rely on C being constant, and all else being variable. And I ask what if we don't restrict C to being constant, but take a look at how other 'ingredients' must behave to gain same sort kind of evidence we observe.

No, Einstein already found that out. Or rather he PREDICTED it and later experiments verified it (at the time, clocks weren't accurate enough to detect it).
Exactly. He 'modeled' how to predict it. He didn't explain 'WHY' it happens, or even mechanism of 'HOW' it happens. Thats left to be found.

Time dilation results directly from a constant C. If C were found to not be constant, time dilation would have to have another cause.
All-or-nothing. Is world black&white? Maybe time dilation that goes in pair with space dilation always results in same velocity C for observer?

(Who says it can never be observed?)
You certainly implied it:
No. I implied that we can't observe it NOW because we have no theory that predicts that and offers means to detect it. My stress was on word 'never'.

The answer to your question is now and always has been SR. You ARE trying to refute it whether you know it or not.
SR is NOT and answer. In QM they even question existence of space that SR takes for granted. Nature of time is mystery. I'm not trying to refute SR. SR is in the end a bunch of equations that interconnects space, time and motion of energy. At best you might say I'm wondering if SR could be expanded or perhaps rephrased from different ground.

String theory is an attempt to unify Relativity and QM. It does not change my point #2. Or rather, point 2 does not change string theory.
Whats the point of #2 then?

Fundamental postulate thing addressed above: this isn't one. But maybe we're getting somewhere now: you're now saying there IS evidence that C is not constant. Could you be more specific? Specifically changes in C that "are called something else." You're saying we have observed C to not be constant? Are you talking about refraction? Clarify.
I'm about permittivity and permeability. I quoted for Hurkyl claims about Maxwell equations that underlie constancy of C. Could you comment? Obviously in presence of matter things change. One can explain it with other theories and debunk me, but just consider, if its not matter that 'resists' C in matter, but infact that matter IS manifestation of changes in C. c2[mu]0ε0 = 1

It certainly appears to me that you have a point to your questions. But you are trying very hard to not argue it. Make your point. If it has some validity, we will accept it. If it doesn't we well tell you why and YOU must accept it. But running from a discussion of your point won't help you prove it.
My point is to get things into perspective for myself.
Conceptual idea of SR is among others that 'measurement of absolute velocity is impossible'. That leaves only relative velocity, or velocity relative to our current frame of reference, c included. Now that we know time can vary, it seems to me that velocity of C measured depends on time rate of our measurement frame. On what would time rate depend no ideas, or what is meaning of distance, but their relations are such that to yield a constant C.
This makes me sincerely wonder if we'd really be able to detect changes in C. Changes in C could be detectable only indirectly, perhaps as difference in momentum between inertial frames, or gravity.
 
  • #25


Originally posted by SamBuckler
Just finished reading Faster Than The Speed of Light by Joao Magueijo ISBN 0-434-00948-2 (if you're curious)...
Thats a different issue, but an interesting theory nonetheless.

fundamental postulate of SR is that speed of C is constant...So we basically go ahead and assume that C IS constant.
You keep using those words. I don't know where you are getting them and I don't know how else to say it: The fact that C is constant in all reference frames is IMPERICAL DATA. Its not a postulate, assumption, stipulation, or other baseline position made for mathematical convenience. You're still looking at Relativity backwards.
He 'modeled' how to predict it. He didn't explain 'WHY' it happens, or even mechanism of 'HOW' it happens.
"Why?" is a philosophical/religious question. But Einstein most certainly did explain "HOW?" it happens. "HOW?" is the mathematical derivation itself. And the question of whether a mathematical model is a real extension of a physical reality is an interesting one, but it is also largely philosophical. As far as scientists are concerned, if it makes an accurate prediction, its a real extension of physical reality.

Also, mechanisms are unnecessary here and are somewhat linked to the "why?". What is the mechanism by which C stays constant? Dunno - maybe a later theory will answer that. Maybe its just something God decided. Either way, it doesn't change the fact that C is constant and it doesn't change the theories that use the fact that C is constant.
Maybe time dilation that goes in pair with space dilation always results in same velocity C for observer?
I'm going to have to invoke Occam's razor again. It makes more sense to conclude from observing through imperical data that shows C is a constant and T is a variable, that C is a constant and T is a varible. You're going back to 'the universe is conspiring against us' position again.
I implied that we can't observe it NOW because we have no theory that predicts that and offers means to detect it.
You have it almost exactly backwards. You don't need a theory to know how to observe something. And generally, before you can have a theory, you need the data. You're putting the cart before the horse. Example: The MM experiment confused the hell out of M&M, but it was data and they accepted it. It was years later that a theory was constructed that adequately explained their data. The exception is theories that are built on other theories.
At best you might say I'm wondering if SR could be expanded or perhaps rephrased from different ground.
Discarding the theory completely can hardly be called "rephras[ing]" it. It can of course be expanded - and that's not even close to the same as what you are proposing. Example: Newton vs Einstein's gravity.
Whats the point of #2 then?
String theory is an example of expansion - but it doesn't change the fundamental principles of relativity. It does not claim VSL. Just like the above, you're confusing expanding on a theory with discarding it completely. There is a huge difference.
Obviously in presence of matter things change. One can explain it with other theories and debunk me [re: evidence that C isn't constant]
Sounds like you already know that scientists have a different explanation from what you prefer.
I quoted for Hurkyl claims about Maxwell equations that underlie constancy of C. Could you comment?
Sure. Those quotes display a lack of understanding of the mechanism behind refraction. Or to be nice, the variability of C is a mathematical convenience, used in refraction calculations, which leads to a very common misunderstanding of the mechanism behind refraction. I'd bet my last paycheck that quote came from a site who'se purpose is to try to refute relativity.
 
  • #26


Originally posted by russ_watters
You keep using those words. I don't know where you are getting them and I don't know how else to say it: The fact that C is constant in all reference frames is IMPERICAL DATA. Its not a postulate, assumption, stipulation, or other baseline position made for mathematical convenience. You're still looking at Relativity backwards.
bs. constant C is very first sentence of SR. its literally postulate. That the ideas to create SR came from empirical data is irrelevant. And value for c isn't even part of SR. And that it matches empirical data is the only reason its accepted.
I don't really understand what you argue here.

"Why?" is a philosophical/religious question. But Einstein most certainly did explain "HOW?" it happens. "HOW?" is the mathematical derivation itself. And the question of whether a mathematical model is a real extension of a physical reality is an interesting one, but it is also largely philosophical. As far as scientists are concerned, if it makes an accurate prediction, its a real extension of physical reality.
Are you saying that all scientists as positivists? I see two-sided razor here, on one side this is nice way to be open for unexpected ideas, but on other hand this is nice way to close you eyes on possibilities.
Mathematical derivation itself may contain components that cancel out in certain conditions. You say these components do not exist. I'm not saying they do, I'm asking if the possibility exists that they might.

Also, mechanisms are unnecessary here and are somewhat linked to the "why?". What is the mechanism by which C stays constant? Dunno - maybe a later theory will answer that. Maybe its just something God decided. Either way, it doesn't change the fact that C is constant and it doesn't change the theories that use the fact that C is constant.
Exactly about this I am talking. Is there a possible mechanism due which we observe C always as constant.
Any theory that will answer that must explain why we observe C as a constant.

I'm going to have to invoke Occam's razor again. It makes more sense to conclude from observing through imperical data that shows C is a constant and T is a variable, that C is a constant and T is a varible. You're going back to 'the universe is conspiring against us' position again.
I'm not about conspiring. I'm about possiblity that variations cancel out for us. 10 spatial dimensions that no one can ever detect is consipiring. Go apply your razor on strings.

You have it almost exactly backwards. You don't need a theory to know how to observe something. And generally, before you can have a theory, you need the data. You're putting the cart before the horse. Example: The MM experiment confused the hell out of M&M, but it was data and they accepted it. It was years later that a theory was constructed that adequately explained their data. The exception is theories that are built on other theories.
bs again. Whole criteria for being theory is requirement to offer predictions that can falsify theory. I've never heard of empirical data about strings. Have you?

Discarding the theory completely can hardly be called "rephras[ing]" it. It can of course be expanded - and that's not even close to the same as what you are proposing. Example: Newton vs Einstein's gravity.
Whats the bloody matter with you? What makes you say I'm discarding it? I've never said C is observable as VSL. I repeat: I'm ASKING if variations of C could manifest itself as some other phenomena.

Can't you really understand what I'm asking? C isn't dimensionless. It is ratio of distance and time. To keep the ratio constant while having variable time implies variance of meaning of distance. And that the measurement we make is dictated by time of frame we are in. If we accept that time flow can vary, then we must accept that meaning of distance must vary accordingly, else we couldn't observe constant C locally. Now, if we don't have absolute time, and we don't have absolute distance, then why should there exist absolute C? Obviously, we observe one. Still, imo, question is valid. How would we observe world around us, if speed limit of U varied?

String theory is an example of expansion - but it doesn't change the fundamental principles of relativity. It does not claim VSL. Just like the above, you're confusing expanding on a theory with discarding it completely. There is a huge difference.
Er, what does fundamental principles of relativity has to do with precise value of C in specific point of universe?

Sounds like you already know that scientists have a different explanation from what you prefer.
I don't prefer anything. I'm inquiring of possibility. If I'll need to compute, I'll use methods that scientists have accepted. This doesn't forbid me from inquiring unconventional ideas. AND this doesn't forbid you from explaining why they'd be ruled out.

Sure. Those quotes display a lack of understanding of the mechanism behind refraction. Or to be nice, the variability of C is a mathematical convenience, used in refraction calculations, which leads to a very common misunderstanding of the mechanism behind refraction. I'd bet my last paycheck that quote came from a site who'se purpose is to try to refute relativity.
Could you please explain in simple way, what do you mean? Are you saying that c is same inside water, air, fiber?
You'd loose your check, but it isn't serious science site either.
 
  • #27


Originally posted by wimms
bs. constant C is very first sentence of SR. its literally postulate. That the ideas to create SR came from empirical data is irrelevant... And that it matches empirical data is the only reason its accepted.
I just looked it up. You're right. I stand corrected. It is a postulate. However, the fact that it is based on imperical evidence is to me very important. You say its the "only reason its accepted" and that's fine. Its a damn good reason.
You say these components do not exist. I'm not saying they do, I'm asking if the possibility exists that they might.
Certainly possibilities exist. Possibilites ALWAYS exist. But without any evidence to support the existence, "possibility" isn't enough to build a new theory or challenge an existing one.
. Is there a possible mechanism due which we observe C always as constant. Any theory that will answer that must explain why we observe C as a constant.
Thats your point, not mine, so you tell me. I'm sticking to the obvious answer: we observe C to be constant becaus C is constant.
Whole criteria for being theory is requirement to offer predictions that can falsify theory. I've never heard of empirical data about strings.
I know significantly less about string theory than I do about relativity. But this discusion is about relativity and relativity *IS* falsifiable.
Whats the bloody matter with you? What makes you say I'm discarding it? I've never said C is observable as VSL. I repeat: I'm ASKING if variations of C could manifest itself as some other phenomena.
The implications of the "yes" answer (if verified) that you appear to desire are that relativity and other major theories would need to be discarded. Its a loaded question. The answer is of course yes because of the word "could." Could I grow wings and fly? Yes, but its not likely.
then we must accept that meaning of distance must vary accordingly
...and it does.
Are you saying that c is same inside water, air, fiber?
YES. The principle of refraction is dependent on AVERAGE speed through a medium. The mechanism is that when light hits an atom, it gets absorbed and re-emitted. The delay associated with this causes a change in the APPARENT speed of light through that medium. When moving from one atom to another inside a medium (and anywhere else for that matter), light is traveling through a vacuum and travels at C.
 
  • #28
Russ,
You are doing an execellent job defending the correct positon, but as a ME it is clear that you have not been exposed to a full blown course in E&M.

Einstein's postulate of a constant c was NOT based on empirical evidence! Gads, people, at least make a minimum effort to study a bit of History of Science before you start talking! (Russ, this is not meant for you, but please listen!, or should I say read!)

In 1867 Clerk Maxwell expressed his set of equations in the form of the traveling wave equation. The velocity of the traveling wave, call it v, was expressed as v2= ε0μ0. When he computed the value of this quanity, The two contants, one geometric the other long known experimentally, the result was equal to the then current experimental value for the speed of light. This was the first solid bit of evidence that light was electomagnetic in nature.

This was a shocking discovery, primarly because it equated the speed of light to fundamental constants of the universe, the speed of light was a fundamental CONSTANT! This discovery created a rift in Physics which lasted until Einstein Published his Theory of Special Relativity.

Can you please make an effort to put a bit of historic perspective on this problem. Pretty much for the last half of the 19th century the world of Physics was forced to live with a c a fundamental constant. This did not fit into Newtonian Physics and many were not happy. To make matters worse, Michelson and Morley did an experiment which, rather then showing Maxwell to be wrong, VERIFIED the fact. The problem was called Maxwells Cundrum and many were simply waiting for Maxwell to find his error.

What it comes down to, is that for the last 150 yrs, mankind has known that the the speed of light is a fundamental constant. In the last 150 yrs the best minds known to man have been developing science and technoloy to degrees never dreamed possible. One of the keys to this sucess has been the understanding we have of ElectroMagnetism. This basic understanding started with Maxwell and a constant c. If you wish to change then simply turn off your computer because it does not, and cannot work without a constant c.

With this understanding you must understand why the main body of Phyiscs pretty much distains the chriping of the crackpots who doubt the constancy of c. It has withstood a centruy and a half of intense scrunity and it will continue to stand as a fundatmental constant.

My advise to the naysayers is to make an effort to understand the current state of knowledge, without the benifit of the current knowledge you are wasting your time, my time and everyones time who reads your posts.

With all that said I recently was looking at a book called VSL, varible speed light, where this reputable physicist is proposing a higher speed of light theory to explain the early expansion of the universe. Note that this would mean that the fundatment constants of the universe may be chaning with time. Very slowly of course, so we may not be able to detect it. I would not argue against such a theory but I will certianly argue against anyone who claims that the speed of light is different traveling to the left then to the right.
 
  • #29
Originally posted by russ_watters
However, the fact that it is based on imperical evidence is to me very important. You say its the "only reason its accepted" and that's fine. Its a damn good reason.
Sure it is. Thats why its called theory not fancy idea. But notice how things went, first they measured c by approx means. People assumed ether existed and c depends on it (LET). Then Maxwell equations predicted that c is constant, and offered way to calculate c precisely. By then there were questions about invariance of c. Then MM made their experiment, and bummer. Then came SR to turn over the world.
Imo its no less important to notice that constant and limit of c was predicted before it was even possible to measure precisely. So it went in this order: predicted as possibility, then included into consistent theory, then confirmed with endless faultless demonstration.

Certainly possibilities exist. Possibilites ALWAYS exist. But without any evidence to support the existence, "possibility" isn't enough to build a new theory or challenge an existing one.
Thats interesting, because in other thread you went quite far to show that possibilities do NOT always exist. I'm not challeging existing SR. As to "possibility", if it exists to build a theory that explains "more" than existing ones, then this is "enough" to go for it. This is not to say that I offer some new theory, but to merely justify 'what if' thinking as an excercise.

Thats your point, not mine, so you tell me. I'm sticking to the obvious answer: we observe C to be constant becaus C is constant.
Russ, don't challenge me to offer consistent theory, you realize well that I'm not equipped to do that in form you'd ever accept as truth. I AM sticking with same answer as you if it comes to betting your last check.
But you still don't realize what I'm about. There is a difference between what we observe and what IS. Your positivist approach is nice, but it limits imagination. Let's for sake of argument say that what SR postulate really says, is that C will always be measured same in any equivalent inertial frame. This puts any potential variance of C outside SR if it is ever possible. Simply because inertial frames with different C are NOT equivalent. Laws of nature would be different. And this means manifestation of something else.
See, within realm of SR, variance of C isn't even meaningful question. But that doesn't mean that question itself is necessarily meaningless.

We can say from SR that inertial frames are equivalent only if C measures the same. See, we can compare frames only if we know how to convert them to equivalent form. And that implies time dilation, length dilation, energy. Thats the math of SR. It holds, and within domain of SR its bulletproof, even if C 'really' varied, over long time or over short time.

There are more assumptions under SR or any theory. For eg. assumption that all inertial frames ARE equivalent, that laws of nature are same in any. Its all nice and I'm not refuting these assumptions either. But with any of them you could play 'what if' and wonder if we'd be even capable of noticing if that wasn't strictly true from some imaginary absolute frame. Our whole construction of observable reality depends on what we consider comparable. My only point is, that we possibly wouldn't be able to detect fluctuations of such kind, simply because we consist of the very fluctuations that also offer us frame of reference. Frames with different timeflow are NOT equal until we transform them so that we can compare them with same clock rates. Distances are NOT equal until we transform frames to common measures.

The implications of the "yes" answer (if verified) that you appear to desire are that relativity and other major theories would need to be discarded. Its a loaded question.
NO. I do not agree that implications are what you think. Any theory has "Domain of Applicability". For SR, one of its components is postulate of const C, for variable C it simply wouldn't be applicable. This doesn't mean SR is wrong, it only means that variations of C are outside scope of SR. Its a loaded questions yes, but not in the sense you wish to imply.

Lets for a second consider what variance of C means. To even consider such thing, we need to imagine being separate from universe. But same happens when you imagine time dilation. To say it occurs we are forced to imagine timeflow here and timeflow there. But unless we imagine some absolute external frame, even such distinction isn't necessarily valid. Yet we do that. Same for distances and space. Somehow we imagine that there is some independant space inside which all frames are. But the very meaning of spatial distances depends on frames timeflow.

It occurred to me, that perhaps you assume like Integral that I'm arguing C differing based on direction? Or that I propose FTL possibility or smth? No, what I'm trying to understand, is what is our reference ruler by which we could possibly detect variance of C, if any change in it causes change in laws, making frames not comparable. I'm thinking that we DON'T have such ruler. Any time we detect difference in frames, we observe it in some way that requires us to transform it to our reference measures. And that such difference would manifsest itself not as change in C, but perhaps as relativistic v of a frame, or somthing.

re: then we must accept that meaning of distance must vary accordingly
...and it does.
Exactly. And this means that rulers change. Now question is: what are we measuring, and with what rulers, if rulers themselves aren't absolute? The only answer is that relationship between the rulers is constant C. And that too with restriction to equivalent frames.

Look, by corollary from SR itself, if we have inertial frame, and right next to it another that happens to have different timeflow, then this difference transforms into space and velocity between them! Mere change of time relative to nearby frames is effectively equivalent to motion. Slowdown of time in spacepoint relative to surroundings is equivalent to contraction, increase of mass and latency for photon traversal if viewed from 'outside'. For observer 'inside', opposite is observed, expansion of the frame, and speedup of photon that leaves into surroundings.

YES. The principle of refraction is dependent on AVERAGE speed through a medium. The mechanism is that when light hits an atom, it gets absorbed and re-emitted. The delay associated with this causes a change in the APPARENT speed of light through that medium. When moving from one atom to another inside a medium (and anywhere else for that matter), light is traveling through a vacuum and travels at C.
Really? Where can I find a source to back this up? Anything I've seen claims c itself differs in medium.
Absorbtion of photon is energy dependent. Would photon with low enough energy get ever absorbed? Refraction angle can't be explained by particle behaviour. Either can't explain why light ray maintains direction of line or can't explain why it bends. Also, matter is sparse enough for photon pass it without ever hitting any atom. This means impulss sent to a medium must be measured to travel through it at anywhere between C in vacuum and its slowest pass though the medium. If that were true it'd have devastating impact on communucation signals.
 
  • #30
Originally posted by Integral
With this understanding you must understand why the main body of Phyiscs pretty much distains the chriping of the crackpots who doubt the constancy of c. It has withstood a centruy and a half of intense scrunity and it will continue to stand as a fundamental constant.
Right. C is observed constant. Length and time varies. The very dimensions of velocity.

My advise to the naysayers is to make an effort to understand the current state of knowledge,
I do make my sincere effort. Its damn frustrating to see that every thinking attempts of nonauthorty is bashed to a crackpot category. Yes, I'm not able to express myself as clear as you'd wish. I Can't express more clearly than I've already have: I DO respect SR. Thats why I'm ASKING, not making statements.

During this thread, I've came across something that perhaps better and with more authority talks about similar things: Double SR.
http://arxiv.org/abs/gr-qc/0012051

or even better, overview of VSL stuff by Joao Magueijo:
http://arxiv.org/abs/astro-ph/0305457
 
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  • #31
Refraction angle can't be explained by particle behaviour.

A photon is a quantum particle, not a classical particle.
 
  • #32
Originally posted by Integral
Russ,
You are doing an execellent job defending the correct positon, but as a ME it is clear that you have not been exposed to a full blown course in E&M.
Heh, yeah or the history of physics. Thanks though.

It was always my understanding that until MM, it was believed that light traveled on the "ether" and therefore would vary. They were of that belief, weren't they? I thought they were surpised at the result of their experiment.

I did not however know the magnitude of the "rift" in the physics community at the time. The short history lesson often looks very different from the long one.

Really? Where can I find a source to back this up? re: refraction
Anywhwere you care to look, wimms. Any book or site that explains the mechanism and not just the usage of refraction. Start with google.
 
  • #33
Originally posted by russ_watters
Anywhwere you care to look, wimms. Any book or site that explains the mechanism and not just the usage of refraction. Start with google.
Obviously, as I said, I did. Everywhere I look, they say c is lower in medium.

Actually, what confuses me is notion of absorption and reemitting with delay. This seems to imply pointparticles. But medium is complex sum of fields where there is no clear borders between particles and vacuum. Even if we say that retardation of light in such fields is only apparent slowdown of c, this doesn't say anything about reason vacuum itself has specific permittivity/permeability. Seems like saying that vacuum has anthropic reasons, and everything else gets lower speed due to complex tensions between the fields of particles.
 
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  • #34
Originally posted by wimms
Obviously, as I said, I did. Everywhere I look, they say c is lower in medium.
[?] [?] There is another thread on this board about it. You've posted in it. But could you post some links that you looked at that confirm your belief? I suspect the sites are all high school physics type sites that only talk about refraction in a Newtonian sense.

Like I said, google (type in "light refraction mechanism"). This is the first link:

When the wave impinges upon a particle of matter, the energy is absorbed and sets electrons within the atoms into vibrational motion. If the frequency of the electromagnetic wave does not match the resonant frequency of vibration of the electron, then the energy is reemitted in the form of an electromagnetic wave. This new electromagnetic wave has the same frequency as the original wave and it too will travel at a speed of c through the empty space between atoms. The newly emitted light wave continues to move through the interatomic space until it impinges upon a neighboring particle. The energy is absorbed by this new particle and sets the electrons of its atoms into vibration motion. And once more, if there is no match between the frequency of the electromagnetic wave and the resonant frequency of the electron, the energy is reemitted in the form of a new electromagnetic wave. The cycle of absorption and reemission continues as the energy is transported from particle to particle through the bulk of a medium. Every photon (bundle of electromagnetic energy) travels between the interatomic void at a speed of c; yet time delay involve in the process of being absorbed and reemitted by the atoms of the matter lowers the net speed of transport from one end of the medium to the other. Subsequently, the net speed of an electromagnetic wave in any medium is somewhat less than its speed in a vacuum - c (3 x 108 m/s).
http://www.glenbrook.k12.il.us/gbssci/phys/Class/refrn/u14l1d.html

I guess this explains your problem with Relativity - you think the baseline assumption is wrong. It isn't.
Even if we say that retardation of light in such fields is only apparent slowdown of c, this doesn't say anything about reason vacuum itself has specific permittivity/permeability
Looks like another "why" question to me. But I'm not sure I'd use the same concepts in a vacuum that you'd apply to a medium. A vacuum isn't a medium per se.
 
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  • #35
well i was actually referring to a book by joao magueijo titled 'faster than the speed of light'... it is an actual theory with substantial reasoning.
 
  • #36
Originally posted by russ_watters
But could you post some links that you looked at that confirm your belief? I suspect the sites are all high school physics type sites that only talk about refraction in a Newtonian sense.
Well, of course I have seen such descriptions as you offer, but mostly in what I saw as school physics simplified texts.

http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/ltrans.html#c3
http://hyperphysics.phy-astr.gsu.edu/hbase/electric/elefie.html#c3

http://www.ldolphin.org/setterfield/vacuum.html

Like I said, google (type in "light refraction mechanism").
Yeah, and I find simplified explanations, like marching soldiers analogy in chapter before one you quoted.

I guess this explains your problem with Relativity - you think the baseline assumption is wrong. It isn't.
No. This C in matter issue isn't even related to my questions about R.
Again. how many times have I say that I have no problems with R and that I DO NOT think baseline assumption is WRONG. As Hurkyl and you have put it, if we can't observe it, then we need not be concerned with it.
Again, I raise a question, that perhaps the baseline assumption is right because we have no means to detect variance in C, as we have no other better reference for measures!
Would we notice change in standard of 1 meter, if ALL spatial distances changed in accord? No. SR predicts length dilation that observer in given frame would not notice. Thus, observer in inertial frame has different standards of measure without ability to notice that. All it can do is to compare his standards to standards in other frame, by applying SR transforms.
C, as a fundamental unit in existence is so deeply into any phenomena that any of its change would cause whole phenomena to get redefined.
I'm seeking to understand IF we could possibly detect change in C, accounting for all of the implications, or would all of the implications cause so coherent change in our frame that our observational means would be unable to notice. If possible, then what kind of phenomena would we notice when we compare our frame with other inertial frames?

Looks like another "why" question to me. But I'm not sure I'd use the same concepts in a vacuum that you'd apply to a medium. A vacuum isn't a medium per se.
I'm not sure why you see it as 'why' question. It is a point of analogy. Vacuum has fundamental constants that define c without presence of any matter. Light is EM, thus has to do with fields. Are you saying that space between matter particles is empty of EM fields? Are you saying that atoms take up specific volume with sharp boundaries separated by pure vacuum? That there is some specific distance between atoms instead of some probability waves?
As I understand, inside matter there are complex EM fields that interact with each other and photons, causing continuum-like changes in refraction and thus C. Maybe this is wrong, but I didn't make this up.
 
  • #37
Originally posted by wimms
Yeah, and I find simplified explanations, like marching soldiers analogy in chapter before one you quoted.
...which clearly don't say anything at all about the mechanism of refraction.
Maybe this is wrong...
Yes.

There really isn't anything else to say here. Either you choose to accept accepted physics or you don't. Its up to you.
 
  • #38
Originally posted by russ_watters
There really isn't anything else to say here. Either you choose to accept accepted physics or you don't. Its up to you.
What kind of answer is that?
I asked questions, and you answer with .. this? Is it that you have no idea yourself, and the only thing you can do is to accuse in crackpotery, again?? Damn, this is so arrogant.
And it isn't even relevant to the main discussion, for which you can't also answer anything sensible other than crack-crack-crack as if every single blody question about SR means attack on it. Can't you really never get out of the box and explain to a layman why would we necessarily in any case notice change in C?
 
  • #39
Originally posted by wimms
What kind of answer is that? I asked questions, and you answer with .. this?
Its the only way out of this cycle. We HAVE given you answers, you just refuse to accept them. There isn't anything more I can do for you.
 
  • #40
Russ, you haven't given answers to my questions. You accused me in hell knows what, and have kept repeating what I already know.
You say I refuse to accept answers, that's bs. I accept perfectly all that you explain. You just don't. Perhaps you don't even understand the question. And that's because you keep accusing me in herecy. You don't seem to even understand what is meant by VSL. Its not additive v, but relativistic C, value of which varies on whatever, but not addition of motion v. More like in the book of VSL, but on very small scale and very short time. Best answer so far was Hurkyl's, that we don't bother with it. Yes I'm not happy because I want to understand what impact it would have if speed of light changed, very globally or very locally.

This question remains unclear to me, and its sad that you can't do me a favour explaining to me. You obviously imply that you could.
 
  • #41
Wimms, the thing is is that the speed of light in a vacuum just does not vary. It stays at c. Even if it varies, our measuring equipment would vary with it, and like Hurkyl(...I think) said, then we'd implement Occums razor and simply state that for all intents and purposes, c does not change, because even if it did, we wouldn't have any way to tell.
 
  • #42
Originally posted by cytokinesis
Wimms, the thing is is that the speed of light in a vacuum just does not vary. It stays at c. Even if it varies, our measuring equipment would vary with it, and like Hurkyl(...I think) said, then we'd implement Occums razor and simply state that for all intents and purposes, c does not change, because even if it did, we wouldn't have any way to tell.
Thats pretty much my point, BUT, if you go further, and suppose that C varies in some 'area' of universe and not other, then, there must be detectable difference between the areas. What would it be? Suppose 2 extremes, 10 billion lightyears apart, and few hundred Planck lengths apart. What should we observe and detect?
 
  • #43
I don't see how that'd either be possible, or really matter to us for our purposes, because in our corner of the universe the speed of light does not vary, so to speculate about it's variance is pointless for our purposes.
 
  • #44
It has point. Change in C around our reference frame would cause us to perceive that other area differently. For eg, we could detect change in spatial distances, curvature of space. Maybe relative motion.

As to being pointless if unobservable, then there is just a thread about gravity waves, gravity field being defined as that which couples to spacetime. So they are searching for ways to detect gravity waves, or variance in something that very much defines all our measures, our very shape and dimensions. This reminds a 2D creatures on surface of a paper sheet trying hard to detect vibrations of the sheet by 2D measurements. Sure they won't succeed, but if they suspect existence of 3rd dimension, is their attempts pointless?
 
  • #45
Originally posted by Hurkyl:
That's when we apply Occham's Razor. If the whole of spacetime is conspiring to make any variation in c unmeasurable, then we can get no wrong answers by presuming c does not vary in our theories.

This is by my understanding an improper use of Ockham's razor.

If we believe in the constancy of c in all inertial frames, then this believe is in fact not the easiest way in the advice of Ockham, that we should avoid unnecessary assumptions.

1. It is a definite consequence of the relativistic phenomena 'contraction' and 'dilation' that the measurement of the velocity of an object, having speed c, from a different frame of reference will yield the same result, even though the velocity is different in relation to the other frame. - It is a quite simple application of the Lorentz transformation to prove this.

2. The (so called 'geometrized') relativity theory of Einstein is not at all the simplest way to understand relativity. There are many persons who have studied physics, who have difficulties to understand the 4-dim. frame, where time and space are interrelated to each other in the given way. On the other hand, if it is assumed that there is a constant velocity c in exactly one reference frame (as stated by Lorentz/Poincare), the theory is simple enough so that most college students will be able to understand it.

3. At a different meaning of this point: the velocity of light is reduced in a gravitational field. So it is not constant everywhere. This is a very important fact because it is (according to Roman Sexl) the reason for the gravitational acceleration.

4. As we do not understand the reason why the velocity of light is constant, we do not know what may happen in other areas of the universe. But we know that we do not really understand the spatial development of the universe. So, something in our present physical understanding must definitely be wrong. This may also be the believe in the constancy of c in relation to the location within the universe. So also from this consideration we have to be open for a variable value of c.

And, apart from this: Professor Guenter Nimtz, Cologne, has made an experiment during which a signal was transmitted with a velocity greater than c. I have seen the experiment by my own eyes and it was a true superluminal transmission of information.
 
  • #46
VSL comes in a couple of different flavors, so to speak. There are some of us who accept variance if the vacuum state is altered. Generally of those in this camp some of us see only quantum effects and non-locality as generating a real change in C, in which case classical information transfer is always regular C limited and only Quantum information can transfer FTL. However, quantum information gives rise to classical information and may offer methods of varying the classical information faster also.

There are also members of the VSL camp that believe that C has altered over time in this Cosmos so that early own we may detect differences in the value of C as far as studying the information on space-time structure we gain from astronomy sources. Generally those of the accelerated expansion camp have held to C slowing down over time which makes them VSL and in light of the recent evidence from the MAP project the accelerated expansion issue seems rather upheld so some version of a variable C is at play.

Generally Smolin and some of the members of his own group are within the VSL camp and do hold to one aspect of this or another.

As for predictions in general, depending upon who's VSL model you follow the predictions can range simular to those found in standard inflationary models to some odd quantum scale effects where the cutoff on ultra-violet may be higher than standard theory has presupposed. There is also some speculation on the IR cutoff issue though those have never been as codified as the UV type.

The issue with certain experiments showing faster times by tunneling fits more within the quantum information camp. If you go back to the original wording of Einstein's paper in German it basically says that the speed of light is constant in the vacuum which GR tends to put some strong qualifications on what exactly that vacuum state is. In any case where the medium is altered either by natural effects or by artificial ones you are not dealing with a direct violation of relativity at all even if the speed of information transfer is higher or lower. Particles entering our atmosphere have long been known to travel faster in the atmosphere than photons do. Einstein in his time knew of this effect. Read SR. It only implies Lorentz invariance of the general type within the vacuum state.

The standard difference between those of us who follow VSL principles of the quantum informational type and regular VSL approaches is most of us tend to hold to Lorentz Invariance in ever modified vacuum state. That does not eliminate differences when you compare one vacuum state to another. In that case there will always be a difference in velocity. But when you alter the vacuum state then you can't directly compare the two.

Your's
Doctor Paul Karl Hoiland
A VSL Researcher who a bit back
was mentioned in connection with
Smolin in New Scientists.
 
  • #47
It is true that the subject about Alpha varying is not a settled one. However, the vacuum state during inflation is not the same vacuum state after inflation, nor is our present vacuum state the same as during the early part of the Big Bang itself. Also adding in some version of exotic energy also alters the vacuum state somewhat. Its the how that is more or less in debate.

Dr. Andrew Strominger of Harvard pointed out that Einstein himself modified relativity in 1915, when he brought gravity into the picture with his general theory of relativity. Special relativity, as the 1905 theory became known, is only strictly valid in flat space without gravity, Dr. Strominger said.

He added, "It is natural to think that Einstein's relativity will in some sense be violated by small corrections, just as Newton's theory of gravity has small corrections." These corrections did not make Newton wrong, he said, they just meant his theory was not always perfectly applicable. Likewise, relativity may give way to a more complete and accurate theory.

How relativity could break down, if it does, depends on how physics might act at the quantum gravity scale. Basically, until that question is more or less answered the debate of this will still stand and the idea that light is not as constant as once thought will remain a possibility.

Most who support VSL, not all though, general believe relativity is correct under normal conditions. Some of us also believe that even when C alters it still remains Invariant within that specific frame. Some of these perfered reference frame ideas that have showed up in LANl and elsewhere have a ring of Newtonian ideas and tends to make some of us suspecious. I don't personally have a problem with the ZPF as a background, or even the few articles that have discussed the CMB as such. But when one tries invoking some version of an absolute space and time frame back into the equation then you run into the older Aether like frame.
 
  • #48
The fundamental problem is that we do not have any idea which physical phenomenon causes the speed of light to have a specific value.

Also the relativity of Einstein merely uses this fact without understanding or explaining it. So we cannot do anything then to wait for a measurement which shows a deviation. Anything theoretical will most probably be guesswork.

Apart from this we should not forget that Einstein's relativity is a (so called) geometrized theory. Geometrization can be done with every physical theory. In most cases it provides an elegant mathematical presentation. But it does not tell about the physics behind it. The same is true for Einstein's relativity. Einstein has never explained why our physical world has relativity.
 
  • #49
To what extent does a clear, well-accepted observation that alpha (the fine-structure constant) has varied, in cosmological time, require that c has also changed over cosmological time?

How theory-dependent is such an alpha-c connection?
 
  • #50
Actually VSL ideas do not always involve a change in Alpha. But if Alpha did change we would have a variance of C. The assumption based on some of those observations was that Alpha must have varied to get those results. This lead to the further assumption that if Alpha changed then C must have changed. But some models of VSL have C vary even though Alpha never changes. One such model has a varying scalar coupling where the vacuum's energy density has varied over time. One article on that, though I do not have the exact link this moment was done by Smolin and Magueijo.
 

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