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VSL Varying Speed Of Light

  1. Aug 4, 2003 #1
    Any thoughts on this?
  2. jcsd
  3. Aug 6, 2003 #2


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    It doesn't.
  4. Aug 6, 2003 #3
    you wouldn't notice?
  5. Aug 6, 2003 #4


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    You would absolutely notice if it varied.
  6. Aug 6, 2003 #5
    In long frame/form How?
  7. Aug 6, 2003 #6


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    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?
  8. Aug 7, 2003 #7
    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..
  9. Aug 7, 2003 #8
    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?
  10. Aug 7, 2003 #9


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    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.

    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.
  11. Aug 7, 2003 #10
    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...

    oh yeah, I want all of them I want to see what is the meterstick with which c is measured.
  12. Aug 7, 2003 #11
    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.
  13. Aug 7, 2003 #12


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    No, you measure the distance through another means. Like a tape measure.
    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.
    I already addressed that. Reread my last post.
    "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 arguement 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?
  14. Aug 8, 2003 #13


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    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?
  15. Aug 8, 2003 #14
    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?

    You don't need C. You need locally uniform average velocity of signal. It could aswell 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, thats the point of triangulation and averaging.

    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.

    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.

    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 truely constant, and not that whole spacetime fabric is vibrating causing local variance of C along with spatial and temporal deformations etc?
  16. Aug 8, 2003 #15


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    Re: I wonder...

    If something gets in the way then it gets absorbed or reflected as usual. As far as the acceleration goes, photons have no mass.
    Again, all of the relevant effects are quite well understood.
    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.
    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.
    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, thats up to you.
    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 based on WHAT? You haven't given a shred of evidence that C isn't constant.
    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.
    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.
    Last edited: Aug 8, 2003
  17. Aug 9, 2003 #16
    Re: Re: I wonder...

    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.

    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.

    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?

    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?

    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.

    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?
  18. Aug 9, 2003 #17


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    Re: Re: Re: I wonder...

    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, thats 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.
    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.
    You mean step outside of the universe? Not really an option, is it? And not really relevant either.
    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.
    Except of course this would affect GRAVITY among other things.
    Then you shouldn't use the word "given." And questions on reality are philosophical, not scientific.
    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 unverse thats 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 thats the way it is? Thats the "anthropic principle" (there are two version) and its philosophical, but also discussed in "A Brief History of Time."
    Last edited: Aug 9, 2003
  19. Aug 9, 2003 #18


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    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.

    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.
  20. Aug 11, 2003 #19
    Re: Re: Re: Re: I wonder...

    Fundamental postulate 'explains'???

    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?

    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.

    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 cancelled out by averaging samples over time.

    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 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?

    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'.

    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.

    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.

    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.

    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?

    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.

    "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?
  21. Aug 11, 2003 #20


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    Re: Re: Re: Re: Re: I wonder...

    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.
    Last edited: Aug 11, 2003
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