# Thread: c = k

1. Hi,
what is the evidence that the speed of light is constant?

2. ### Related Discussions:

3. Originally Posted by whizkid
what is the evidence that the speed of light is constant?
Do you mean constant for all observers, or constant over time ?

4. Originally Posted by Markus Hanke
Do you mean constant for all observers, or constant over time ?
Are they different proofs? I mean verifiable evidence, no math.
I mean: that it is always the same in the same medium: 3x10^10 c/s in vacuum.

If you know any other proof, you are welcome!
Thanks

5. Originally Posted by whizkid
Are they different proofs? I mean physical verifiable evidence, not math or theories.I mean that it is always the same in the same medium: 3x10^10 c/s in vacuum.
If you know any other proof, you are welcome!
Thanks
Well, I think in this case the question should be phrased the other way around - is there any evidence that the speed of light is not constant for all observers ?
Fact is quite simply that no experiment or observation ever conducted yielded any derivation whatsoever from c for the speed of light in vacuum, independent of the state of motion of the observer. That is not surprising either, because that speed ( and its constancy ) is a direct result of the basic laws of electrodynamics, which also underlie everything from computers to microwaves to telescopes to light bulbs. So really, the best evidence I can offer you is the fact that all of these things work as they do, and that in 150 years of extensive experimentation no derivation from c in the vacuum speed of light has ever been detected; not to mention of course all the modern tests of relativity ( see the sticky in the physics section ), which further support those results.

As for the other question, whether there is any evidence that the speed of light is not constant - the answer is no, there isn't.

6. If I got it right it's only theoretical, there is no way to prove it in practice. I suppose it's the same for c being the limit of speed.

7. Originally Posted by whizkid
If I got it right it's only theoretical...
Which, of course, in science means it is as close to a "fact" as you get. But you seem to have missed the evidence.

there is no way to prove it in practice
There is no way to prove anything much (outside of mathematics).

8. Originally Posted by Strange

There is no way to prove anything much (outside of mathematics).
can we prove that c= 3*10^10 c/s? can we prove that g is 9.8 m/s^2? can we prove that red light has wavelength 700 nm? can we prove that EMR is influenced by g ,? can we prove that momentum is conserved?etc

9. Originally Posted by whizkid
If I got it right it's only theoretical, there is no way to prove it in practice. I suppose it's the same for c being the limit of speed.
Well, it is a little more than just theoretical in that no experiment has ever yielded anything else than exactly c for the vacuum light speed, and neither have we observed anything ever going at more than c. There is simply no reason to suspect anything different, neither theoretically nor in terms of empirical observations.

10. Originally Posted by whizkid
can we prove that g is 9.8 m/s?
Actually it is 9.8 m/s^2. This is an empirically measurable quantity. Just like the speed of light.

11. It's never been proven false.

Science is much better at proving things false than proving them true.

You only need one single instance of something being shown to be incorrect to prove it false, whereas you'd need an infinity of instances of it being correct to "prove" it true.

12. Thank you!, I thought there might be a way to prove that.

13. Originally Posted by whizkid
can we prove that g is 9.8 m/s? can we prove that red light has wavelength 700 nm? can we prove that EMR is influenced by g ,?etc
No. You can measure g to whatever accuracy you want (but always limited accuracy). You can measure it at different places and times (and get slightly different values). But you can't "prove" it has a given value. Ditto the others.

You can measure the speed of light and find it is always the same (independent of your velocity, the velocity of the source, the day of the week and what you had for lunch.) You can then formulate a theory based on that well-supported fact and test the theory. Interestingly: the theory appears to work and no evidence can be found to contradict it.

It certainly appears that there is overwhelming evidence that the speed of light is always constant.

The case for it not being constant is: .... (yep, that's about it).

14. Originally Posted by whizkid
Thank you!
No problem

15. Originally Posted by whizkid
Hi,
what is the evidence that the speed of light is constant?
Light speed constancy is an axiom, as such it cannot be proven.
Several of us already pointed out that , one experiment contradicting the axiom is sufficient to disprove the axiom. Here is a partial list of the experiments aimed at disproving the axiom. To date, the axiom stands.

16. Originally Posted by xyzt
Originally Posted by whizkid
Hi,
what is the evidence that the speed of light is constant?
Light speed constancy is an axiom, as such it cannot be proven.
Several of us already pointed out that , one experiment contradicting the axiom is sufficient to disprove the axiom. Here is a partial list of the experiments aimed at disproving the axiom. To date, the axiom stands.
Thanks,
probably I gave the impression that I need a proof, actually I think it is obvious as nothing can influence c except the medium as it is obvious that matter is not ubiquitous. I thought it easier to prove, at least rationally.
Likewise it would not matter if it was proven that it can vary or it is not the limit.

17. Originally Posted by xyzt
Light speed constancy is an axiom
The constant speed of light is also a direct result of Maxwell's equations; these in turn can be mathematically show to be invariant under arbitrary Lorentz boosts, hence the speed of light must be constant for all observers. This, of course, relies on the assumption that Maxwell's equations are a valid description of electrodynamics...

18. Originally Posted by whizkid
Hi,
what is the evidence that the speed of light is constant?
Turning to the experimental evidence, it seems, slightly to my surprise, that nobody so far has mentioned the Michelson-Morley experiment. This demonstrated there was no light-propagating medium, movement relative to which would cause the measured speed to vary like any "normal" type of wave.

The Wiki entry on the speed of light gives some idea of how this led to concepts of physics in which the speed of light was an absolute constant, thus setting up the environment of ideas for Einstein to bring it all together: Speed of light - Wikipedia, the free encyclopedia

Since the formulation of the Special Theory of Relativity, it has been put to the test in several different ways, all of which have vindicated the theory. As this theory is axiomatically based on the idea that the speed of light is constant, it would have failed if this assumption were not correct, would it not?

19. Originally Posted by exchemist
Originally Posted by whizkid
Hi,
what is the evidence that the speed of light is constant?
Turning to the experimental evidence, it seems, slightly to my surprise, that nobody so far has mentioned the Michelson-Morley experiment. This demonstrated there was no light-propagating medium, movement relative to which would cause the measured speed to vary like any "normal" type of wave.
The reason is that MMX can be (and was) explained by the ballistic/emission theory (Ritz). So, MMX is not a valid disproof of the emission theory. The experiments I cited , are.

20. Originally Posted by xyzt
Originally Posted by exchemist
Originally Posted by whizkid
Hi,
what is the evidence that the speed of light is constant?
Turning to the experimental evidence, it seems, slightly to my surprise, that nobody so far has mentioned the Michelson-Morley experiment. This demonstrated there was no light-propagating medium, movement relative to which would cause the measured speed to vary like any "normal" type of wave.
The reason is that MMX can be (and was) explained by the ballistic/emission theory (Ritz). So, MMX is not a valid disproof of the emission theory. The experiments I cited , are.
Yes indeed, fair enough.

21. The Principle of Invariant Light Speed – "... light is always propagated in empty space with a definite velocity [speed] c which is independent of the state of motion of the emitting body."
Can someone tell me why the motion of the emitting or the receiving body should influence the speed of propagation of light?

22. Originally Posted by whizkid
The Principle of Invariant Light Speed – "... light is always propagated in empty space with a definite velocity [speed] c which is independent of the state of motion of the emitting body."
Can someone tell me why the motion of the emitting or the receiving body should influence the speed of propagation of light?
Do you mean why it shouldn't? [Edit after exchemist: doh, I see what you mean now.]

Either way, that is just the way the geometry of space-time works. Or, it is because things like Maxwell's equations are independent of the state of relative motion.

23. Originally Posted by whizkid
The Principle of Invariant Light Speed – "... light is always propagated in empty space with a definite velocity [speed] c which is independent of the state of motion of the emitting body."
Can someone tell me why the motion of the emitting or the receiving body should influence the speed of propagation of light?
If light were made of classical particles, you would expect a source of light to be like a gun with a defined muzzle velocity. If you are in a train at 100mph and fire a bullet in the direction you've come from, it will travel at 100mph less, relative to an observer by the track, than it would if the train were stationary.

On the other hand if light were made of classical waves, you would expect the speed of the waves to be independent of the source of the disturbance, but dependent instead on the speed of motion of the detector through the medium propagating the waves. The latter is what the Michelson Morley experiment showed could not be the case.

Light is observed to be neither.

24. Originally Posted by exchemist
On the other hand if light were made of classical waves, you would expect the speed of the waves to be independent of the source of the disturbance, but dependent instead on the speed of motion of the detector through the medium propagating the waves. The latter is what the Michelson Morley experiment showed could not be the case. .
Light is a wave and is independent of the emitter and of the receiver. MMX showed there is no other medium : the medium is the vacuum.
Two photons travelling in opposite direction appear to travel at 2 * c , but are each still travelling at c: the speeds just do not sum up. Whatever an observer perceives is only his problem. The more so if the receiver is matter travelling at relatively slow speed.

25. Originally Posted by whizkid
Originally Posted by exchemist
On the other hand if light were made of classical waves, you would expect the speed of the waves to be independent of the source of the disturbance, but dependent instead on the speed of motion of the detector through the medium propagating the waves. The latter is what the Michelson Morley experiment showed could not be the case. .
Light is a wave and is independent of the emitter and of the receiver. MMX showed there is no other medium : the medium is the vacuum.
Two photons travelling in opposite direction appear to travel at 2 * c , but are each still travelling at c: the speeds just do not sum up. Whatever an observer perceives is only his problem. The more so if the receiver is matter travelling at relatively slow speed.
Quite so. Light is also made of particles, however.

26. Originally Posted by exchemist

Quite so.
What is the problem , then, what is the need of transforms?

27. Originally Posted by whizkid
What is the problem , then?
There is no problem. It is just that some people insist there is. ("Einstein must be wrong because ... because ... it doesn't make sense!!")

28. Sorry, I was not quoting Einstein or SR, I was saying we do not need transforms as that makes sense without any extra theory

29. Originally Posted by whizkid
Sorry, I was not quoting Einstein or SR, I was saying we do not need transforms as that makes sense without any extra theory
I'm confused now. What do you mean by "not needing transforms"? And what makes sense? Without which extra theory?

30. I mean lorenz and SR transforms, if it is obvious that c is invariant. Who says it is not?

31. Originally Posted by whizkid
I mean lorenz and SR transforms, if it is obvious that c is invariant
You need Lorentz transforms to relate measurements between inertial frames; it doesn't really apply to light at all, since a photon is not a valid frame of reference.

32. Originally Posted by whizkid
Originally Posted by exchemist

Quite so.
What is the problem , then, what is the need of transforms?
I confess you've lost me now. I suspect we're all in violent agreement but don't quite realise it.

33. We both agree that c is invariant, but you seem to believe it because SR says so,
I believe it because it is obvious without SR or anyone saying it.
I am asking why you think SR is necessary in order to believe it and who does not agree with both of us and what are their arguments.

34. Originally Posted by whizkid
We both agree that c is invariant, but you seem to believe it because SR says so,
I believe it because it is obvious without SR or anyone saying it.
I am asking why you think SR is necessary in order to believe it and who does not agree with both of us and what are their arguments.
Not sure whom you are replying to here, but surely it's the other way round: SR explains the consequences of c being invariant, not the necessity for it to be so.

35. Originally Posted by whizkid
I believe it because it is obvious without SR or anyone saying it.
Science has been a very effective means of demonstrating that the obvious is wrong. What is obvious today was not obvious yesterday. What is not obvious today becomes obvious once we deepen or broaden our knowledge. You seem to wish to base your acceptance of 'facts' upon personal credulity. That is sad when it is present in a creationist, it is dangerous when it is present in someone apparently favouring science.

36. Originally Posted by whizkid
We both agree that c is invariant, but you seem to believe it because SR says so,
I believe it because it is obvious without SR or anyone saying it.
As exchemist says, SR is derived from the axiom of light speed being invariant; specifically from Maxwell's equations.

So it isn't true because of SR. But SR does provide experimental confirmation of the "obvious" (I share John Galt's distrust of the word "obvious").

I am asking why you think SR is necessary in order to believe it and who does not agree with both of us and what are their arguments.
As for what others believe and why: just browse the pseudoscience or trash sections of any science forum.

37. Originally Posted by whizkid
I believe it because it is obvious without SR or anyone saying it.
Hm, it is obvious only in a certain formulation of Maxwell's equations ( in fact, it is trivial there ); in all other formulations it requires some maths to prove. In any case, SR helps us understand the consequences of c being invariant for all observers, not the root cause.

38. Originally Posted by John Galt
Science has been a very effective means of demonstrating that the obvious is wrong. You seem to wish to base your acceptance of 'facts' upon personal credulity. That is sad when it is present in a creationist, it is dangerous when it is present in someone apparently favouring science.
If you say that I am not ubiquitous, I accept it and wouldn't dream of saying you are basing that on personal credulity. If someone says he is he should prove it. Should someone write a book full with math trying to prove I am not, I wouldn't bother to read it , as he is trying to prove with math what cannot be proven by math. Likewise if someone says that light-speed can be influenced should show when and how, else it remains an unlikely conjecture. Moreover, as you said, science cannot prove anything: one day we might find out that light is not invariant and no absolute limit. Do we agree on that or is that dangerous?

We all agree in principle that light cannot be influenced by emitter or receiver and that observer is irrelevant, independently of what Maxwell or Lorenz or Einstein may say.
I wish to know what consequences are there that need SR or other to be explained.

39. I couldn't make any sense of most of that post I'm afraid ... but

Originally Posted by whizkid
I wish to know what consequences are there that need SR or other to be explained.
I suppose time dilation and length contraction are the obvious, initial answers. And then, of course, extending the theory led to GR and an explanation of gravity.

40. Originally Posted by Strange
I suppose time dilation and length contraction are the obvious.
Are you able to explain briefly why they are obvious and linked-together consequences?

41. Originally Posted by whizkid
Originally Posted by Strange
I suppose time dilation and length contraction are the obvious.
Are you able to explain briefly why they are obvious and linked-together consequences?
(I don't mean they are obvious consequences, in fact they are quite counter-intuitive - and a good example why things that seem "obvious" may not be.)

I guess you need to get an introductory text book on special relativity. Someone else might be able to recommend something.

42. Originally Posted by whizkid
Are you able to explain briefly why they are obvious and linked-together consequences?
The dimensions of the value for the speed of light are m/s - in order for the numerical value of c to be the same for all observers, regardless of their state of relative motion, necessarily means that the relations of measurements of space and time in uniformely moving frames must be functions of relative velocity ( or else speeds would linearly add, and c couldn't be constant ); if you do the maths you find that these are precisely the Lorentz transformations. In other words - to ensure that c is constant for all inertial observers, regardless of their state of relative motion, space-time must be everywhere locally Minkowskian, i.e. have an underlying symmetry group of SO(1,3). Note that this is not necessarily true globally, but always locally.

43. Originally Posted by Strange

I guess you need to get an introductory text book on special relativity. Someone else might be able to recommend something.
Special Relativity, by W. Pauli

44. Originally Posted by Markus Hanke
The dimensions of the value for the speed of light are m/s - in order for the numerical value of c to be the same for all observers, regardless of their state of relative motion, necessarily means that the relations of measurements of space and time in uniformely moving frames must be functions of relative velocity ( or else speeds would linearly add, and c couldn't be constant ); if you do the maths you find that these are precisely the Lorentz transformations. In other words - to ensure that c is constant for all inertial observers, regardless of their state of relative motion, space-time must be everywhere locally Minkowskian, i.e. have an underlying symmetry group of SO(1,3). Note that this is not necessarily true globally, but always locally.
Thanks , Markus , for your effort. What I do not understand is why c should be equal for all observers, as we agreed that what an observer perceive is only his problem. Even in ordinary motion what we perceive is and must be different in certain circumstances.

45. Originally Posted by whizkid
Originally Posted by Markus Hanke
The dimensions of the value for the speed of light are m/s - in order for the numerical value of c to be the same for all observers, regardless of their state of relative motion, necessarily means that the relations of measurements of space and time in uniformely moving frames must be functions of relative velocity ( or else speeds would linearly add, and c couldn't be constant ); if you do the maths you find that these are precisely the Lorentz transformations. In other words - to ensure that c is constant for all inertial observers, regardless of their state of relative motion, space-time must be everywhere locally Minkowskian, i.e. have an underlying symmetry group of SO(1,3). Note that this is not necessarily true globally, but always locally.
Thanks , Markus , for your effort. What I do not understand is why c should be equal for all observers, as we agreed that what an observer perceive is only his problem. Even in ordinary motion what we perceive is and must be different in certain circumstances.
...because there are certain quantities that are frame invariant. c is one of these invariants, the interval ds is another one, the wave vector, k is another one. At this point, you should really try to enroll in a class.

46. Originally Posted by whizkid
Originally Posted by Strange
I suppose time dilation and length contraction are the obvious.
Are you able to explain briefly why they are obvious and linked-together consequences?
I'll give you one qualitative example. We find the lifetime of some unstable particles coming down to Earth as cosmic rays, (or products of them, I forget which exactly and it doesn't matter) is longer than it is in a particle physics lab, due to the fact that their incoming speed is a significant fraction of the speed of light.

Imagine such a particle descending vertically, close to Mt Everest, and imagine we note when it passes the top and then when it hits the ground. We see the probability of decay being less than we would expect for a particle travelling this distance. If we were travelling with the particle, we would see the same thing. But you can get this result in 2 ways. The way we see it, the height of the mountain appears normal and so it is time that is passing more slowly for the particle than for us. But from the particle' s perspective, time passes normally and it is the height of the mountain which has shrunk, making it less likely that decay will occur between the height of the top and the ground.

This illustrates that time dilation and Lorentz contraction of distance are corollaries of each other.

47. Originally Posted by whizkid
Thanks , Markus , for your effort. What I do not understand is why c should be equal for all observers, as we agreed that what an observer perceive is only his problem. Even in ordinary motion what we perceive is and must be different in certain circumstances.
I am not quite sure what you mean by this. Take an arbitrary inertial reference frame, a space-ship, an asteroid, anything at all - now imagine some observer A, who is at rest with respect to that reference frame. He measures the speed of light as exactly c. Now imagine another observer B, who moves at, say, c/2 with respect to that reference frame - he also measures the speed of light to be exactly c. And so on. That is what it means when we say that c is the same for all observers - it is the same regardless of their states of relative motion. To put it differently - in Minkowsky space-time, relativistic speeds do not add linearly.

48. Originally Posted by Markus Hanke
Take an arbitrary inertial reference frame, a space-ship, an asteroid, anything at all - now imagine some observer A, who is at rest with respect to that reference frame. He measures the speed of light as exactly c. Now imagine another observer B, who moves at, say, c/2 with respect to that reference frame - he also measures the speed of light to be exactly c. And so on. That is what it means when we say that c is the same for all observers - it is the same regardless of their states of relative motion. To put it differently - in Minkowsky space-time, relativistic speeds do not add linearly.
I know what is meant by that, Markus, If you forget about SR for a minute, can you explain clearly why you do not allow for observers to perceive different results? What is the conceptual or practical problem. If a train speedds at 100 km/h along a motorway each motorist will perceive different result, now why if the trains speeds at c the situation should change? Why force everybody to get same result?
Do you follow me?
Thanks.

49. Originally Posted by xyzt
, the interval ds is another one, the wave vector, k is another one. At this point, you should really try to enroll in a class.
Can you tell me what are they and what should I search to learn more about it.?

50. Originally Posted by whizkid
Originally Posted by Markus Hanke
Take an arbitrary inertial reference frame, a space-ship, an asteroid, anything at all - now imagine some observer A, who is at rest with respect to that reference frame. He measures the speed of light as exactly c. Now imagine another observer B, who moves at, say, c/2 with respect to that reference frame - he also measures the speed of light to be exactly c. And so on. That is what it means when we say that c is the same for all observers - it is the same regardless of their states of relative motion. To put it differently - in Minkowsky space-time, relativistic speeds do not add linearly.
I know what is meant by that, Markus, If you forget about SR for a minute, can you explain clearly why you do not allow for observers to perceive different results? What is the conceptual or practical problem. If a train speedds at 100 km/h along a motorway each motorist will perceive different result, now why if the trains speeds at c the situation should change? Why force everybody to get same result?
Do you follow me?
Thanks.
But this wouldn't happen, because the train is not made of light. It's only light that has the same speed to all observers, regardless of their relative motion. And nobody is forcing anything - it is simply what we seem to observe, experimentally.

So, having that (unpleasantly counterintuitive) experimental result before us, it is nature that forces us to make sense of it. Which is what SR is all about. And, since SR's predictions have been amply confirmed by experiment, we are confident we are on the right track with it.

51. Originally Posted by whizkid
Why force everybody to get same result?
It is more that this is (a) an apparent consequence of Maxwell's equations and (b) an experimentally observed result.

Based on that (actually just (a)) Einstein worked out the consequences and came up with SR. Which has since been extensively tested.

No one is forced to get the same results, they can't help it.

52. The invariance of the speed of light in vacuum is a consequence of the invariance of Maxwell's equations with respect to Lorentz transformations. More generally, the homogenous wave equation:

is invariant to Lorentz transformations just as the equation:

is invariant to rotations.

53. Originally Posted by exchemist
light that has the same speed to all observers, regardless of their relative motion..
I thought we ascertained that the speed of the receiver does not influence the speed of light,(at most it might influence its frequency).
Don't you think that MMX was a rather naive experiment as expected to detect the motion in the solar orbit, while the earth is moving 100 faster in another direction.
Light coming from the Sun is perceived at c because all the motions of the earth do not influence its speed, how could they? if light is coming from the opposite direction there might be an increase in frequency a shift (like in Doppler) that would add up to the gravitational shift, but how can we detect it, how can we know the original frequency to establish that?
Why cannot it be like that?

54. Originally Posted by whizkid
Don't you think that MMX was a rather naive experiment as expected to detect the motion in the solar orbit, while the earth is moving 100 faster in another direction.
I thought it was mainly intended to detect changes due to the rotation of the Earth as well as its movement round the sun. And there have been many other, equivalent, experiments since then that show that the speed of light appears to be constant (see post #14).

Why cannot it be like that?
Because theory and experiment show that it isn't. Why? Who knows. Maybe God made it that way. <shrug>

55. Originally Posted by whizkid
If you forget about SR for a minute, can you explain clearly why you do not allow for observers to perceive different results?
My answer to this would be because the speed of light is a function of vacuum permittivity and permeability ( note : no reference to SR at this stage ). Since all observers "see" the same vacuum with the same properties, regardless of how fast they go relative to some reference point, they must thus detect the same speed of light :

Taking this as a starting point, SR then provides of model of what consequences this constancy of c has.

Note that this is just a reformulation of my earlier statement that Maxwell's laws are invariant under general Lorentz boosts.

56. Originally Posted by whizkid
Originally Posted by exchemist
light that has the same speed to all observers, regardless of their relative motion..
I thought we ascertained that the speed of the receiver does not influence the speed of light,(at most it might influence its frequency).
Don't you think that MMX was a rather naive experiment as expected to detect the motion in the solar orbit, while the earth is moving 100 faster in another direction.
Light coming from the Sun is perceived at c because all the motions of the earth do not influence its speed, how could they? if light is coming from the opposite direction there might be an increase in frequency a shift (like in Doppler) that would add up to the gravitational shift, but how can we detect it, how can we know the original frequency to establish that?
Why cannot it be like that?
No I don't think the Michelson-Morley experiment was naive and neither do historians of science. It is regarded as one of the more significant experiments done in physics, leading, as it did, to a lot of thought about what was really going on with light, the formulation of the Lorentz contraction and Poincaré's elaborations on its significance, all of which paved the way for Einstein. The apparatus was set up to be easily capable of detecting speed changes of the order that would result if the Earth were moving through a luminiferous aether. Whether or not the whole solar system, including the Earth, might itself be moving through this aether at another speed would not affect the differences in speed that the experiment was designed to detect.

I'm having trouble following the rest of your post. Can you restate more clearly what your point is?

57. I meant that MMX was flawed as it assumed that something(luminiferous or not) can push light: if we assume that nothing can influence in any way light, it could prove nothing even if it existed. On the other hand, if it did exist and could indeed push-pull light, they would get a result only if they pointed their instrument to a different direction.

I meant that relative motion toward or away from the direction of the photon might result eventually only in a chance in frequency , as it happens with sound.

Now, suppose we have an instrument like the one in MMX that instead of light shoots elastic balls onto a screen. Iif we operate it on the ground or on a plane flying at 3000km/h , do you expect the balls to come back at the same instant from each side or not?

58. Originally Posted by whizkid
I meant that MMX was flawed as it assumed that something(luminiferous or not) can push light
More accurately, it was based on the hypothesis (I do wish people wouldn't use the word "assumption") that the aether was the medium for light. If we were moving through this medium, we would detect different speeds of light in different directions (realtive to our motion through the aether).

On the other hand, if it did exist and could indeed push-pull light, they would get a result only if they pointed their instrument to a different direction.
They did point the instrument in different directions. It was designed to rotate and, you might be surprised to know, the Earth rotates.

59. Originally Posted by whizkid

Now, suppose we have an instrument like the one in MMX that instead of light shoots elastic balls onto a screen. Iif we operate it on the ground or on a plane flying at 3000km/h , do you expect the balls to come back at the same instant from each side or not?
MMX executed with sound, with ping-pong balls, with tennis balls, gives the same exact result as the original MMX with light. The proof is not trivial, you need to know a LOT of relativity to be able to follow the calculations. This explains why, the Ritz (ballistic) theory is consistent with MMX (though it contradicts SR).

60. Originally Posted by whizkid
I meant that MMX was flawed as it assumed that something(luminiferous or not) can push light: if we assume that nothing can influence in any way light, it could prove nothing even if it existed. On the other hand, if it did exist and could indeed push-pull light, they would get a result only if they pointed their instrument to a different direction.

I meant that relative motion toward or away from the direction of the photon might result eventually only in a chance in frequency , as it happens with sound.

Now, suppose we have an instrument like the one in MMX that instead of light shoots elastic balls onto a screen. Iif we operate it on the ground or on a plane flying at 3000km/h , do you expect the balls to come back at the same instant from each side or not?
You seem to be talking nonsense now. To say that if you assume nothing can influence light, then the M-M experiment would be incapable of giving a result that showed there was an aether, is manifest rubbish. The assumptions one makes don't affect physical reality, you know (!). But in any case, the experiment was set up expressly to determine whether it was correct to assume there was an aether, or that there was not. Which it succeeded in doing.

Also, your notion that the aether would "push" or "pull" light suggests you have no idea how waves are transmitted through a medium. For example, your last para talks in terms of particles, while the M-M experiment was expressly designed to settle an issue about the transmission of light waves. You seem to have missed the whole point of the experiment.

61. Originally Posted by xyzt
MMX executed with sound, with ping-pong balls, with tennis balls, gives the same exact result as the original MMX with light. The proof is not trivial, you need to know a LOT of relativity to be able to follow the calculations. This explains why, the Ritz (ballistic) theory is consistent with MMX (though it contradicts SR).
Could you explain what you mean? If understand correctly you are saying that balls on a plane would rebound back in the same istant, same as light.
Then you are saying we need relativity to explain that?

62. Originally Posted by exchemist
The assumptions one makes don't affect physical reality, you know (!).
Also, your notion that the aether would "push" or "pull" light suggests you have no idea
your last para talks in terms of particles, while the M-M experiment was expressly designed to settle an issue about the transmission of light waves.
Of course my terminology is not precise, I hope you could excuse it and try to get the gist of my propositions:
push-pull means influence or even bear light and its speed; you surely know the meaning of (wiki: luminiferous ether, meaning light-bearing),

Mine was not an assumption, I thought you all agreed with the conclusions in post #23.
You agreed that whatever the perception of the observer, ( be it that c is invariant or not), is irrelevant: only his problem.
Light is a wave: is immaterial, is pure EMR and its medium is the vacuum. , be it empty space or space occupied by (water or glass or other) matter where speed may be only slowed down.
Nothing can bear light. If eher exists cannot carry/push/pull light. Speeds of emitter, receiver or observer do not affect its speed, nor add up.
Please correct what is wrong

63. Originally Posted by whizkid
Originally Posted by exchemist
The assumptions one makes don't affect physical reality, you know (!).
Also, your notion that the aether would "push" or "pull" light suggests you have no idea
your last para talks in terms of particles, while the M-M experiment was expressly designed to settle an issue about the transmission of light waves.
Of course my terminology is not precise, I hope you could excuse it and try to get the gist of my propositions:
push-pull means influence or even bear light and its speed; you surely know the meaning of (wiki: luminiferous ether, meaning light-bearing),

Mine was not an assumption, I thought you all agreed with the conclusions in post #23.
You agreed that whatever the perception of the observer, ( be it that c is invariant or not), is irrelevant: only his problem.
Light is a wave: is immaterial, is pure EMR and its medium is the vacuum. , be it empty space or space occupied by (water or glass or other) matter where speed may be only slowed down.
Nothing can bear light. If eher exists cannot carry/push/pull light. Speeds of emitter, receiver or observer do not affect its speed, nor add up.
Please correct what is wrong
This is hopeless. "Push-pull" is not, by any stretch of the imagination, equivalent to "influence".

The rest of what you have written is, likewise, too garbled to respond to. All I can do with it is guess, iteratively, what you may possibly mean. I have neither the time nor the interest to do that. If you can't communicate with more precision, further correspondence is going to be pointless. Up to you.

64. Originally Posted by whizkid
Speeds of emitter, receiver or observer do not affect its speed, nor add up.
Please correct what is wrong
The Michelson-Morley experiment attempted to measure the velocity of the observer relative to the ether. This is analogous to sound waves propagating through the air. The speed of sound relative to the air is constant (though dependent on the physical properties of the air, but this is beside the point). Consider an observer who is stationary relative to the air measuring the speed of sound from an emitter that is also stationary relative to the air. Take this to be our reference for comparison. Now consider three scenarios:

(1): Stationary observer, moving emitter.
(2): Moving observer, stationary emitter.
(3): Both observer and emitter are moving, but at the same velocity (stationary relative to each other).

For (1), the observer measures the speed of sound to be the same, but the sound is Doppler-shifted in frequency. For (2), the observer measures a different speed of sound, and the sound is Doppler-shifted in frequency. For (3), the observer measures a different speed of sound, but the sound is not Doppler-shifted in frequency. Thus, it is the speed of the observer, not the speed of the emitter that is crucial. The Michelson-Morley experiment was designed to ensure that under reasonable assumptions about the ether, the speed of the observer relative to the ether could not be the same throughout the duration of the experiment due to the motion of the earth. Therefore, at some point during the experiment, the speed of the observer relative to the ether in one direction had to differ from the speed of the observer relative to the ether in the perpendicular direction, and thus the speed of light relative to observer ought to differ in the two directions. The negative result indicated that the speed of light is independent of the motion of the observer, contrary to the propagation of light through a medium.

One further point: the speed of light was measured by interferometry, which depends on the wavelength of the light. In the case of (3) above, the speed changes, but the frequency does not change, thus resulting in a change in the wavelength, and it is this change that was being measured.

65. Originally Posted by whizkid
Originally Posted by John Galt
Science has been a very effective means of demonstrating that the obvious is wrong. You seem to wish to base your acceptance of 'facts' upon personal credulity. That is sad when it is present in a creationist, it is dangerous when it is present in someone apparently favouring science.
If you say that I am not ubiquitous, I accept it and wouldn't dream of saying you are basing that on personal credulity. If someone says he is he should prove it. Should someone write a book full with math trying to prove I am not, I wouldn't bother to read it , as he is trying to prove with math what cannot be proven by math. Likewise if someone says that light-speed can be influenced should show when and how, else it remains an unlikely conjecture. Moreover, as you said, science cannot prove anything: one day we might find out that light is not invariant and no absolute limit. Do we agree on that or is that dangerous?

We all agree in principle that light cannot be influenced by emitter or receiver and that observer is irrelevant, independently of what Maxwell or Lorenz or Einstein may say.
I wish to know what consequences are there that need SR or other to be explained.
I have absolutely no idea what this means. In short, its meaning is not obvious to me, just as it is not obvious to me why the speed of light should be invariant. Again, you appear to be arriving at beliefs based upon what seems to you to be obvious. That is not science.

66. Originally Posted by whizkid
Mine was not an assumption, I thought you all agreed with the conclusions in post #23.
In general, yes.

But then you go and say:

You agreed that whatever the perception of the observer, ( be it that c is invariant or not), is irrelevant: only his problem.
Another observer's measurements are obviously not irrelevant. We need to be able to calculate the effects described by SR for a huge range of applications. From the basics like explaining magnetic fields, to the practical like GPS or particle accelerators, to the less obvious like quantum physics.

I'm really not sure what your point is. You seem to accept that the the speed of light is independent of the state of motion of the observer, and the conclusion that this means many other things are observer dependent and yet you are arguing against ... well, something. But I have no idea what.

67. Originally Posted by whizkid
Originally Posted by xyzt
MMX executed with sound, with ping-pong balls, with tennis balls, gives the same exact result as the original MMX with light. The proof is not trivial, you need to know a LOT of relativity to be able to follow the calculations. This explains why, the Ritz (ballistic) theory is consistent with MMX (though it contradicts SR).
Could you explain what you mean? If understand correctly you are saying that balls on a plane would rebound back in the same istant, same as light.
Then you are saying we need relativity to explain that?
What I am saying is that I answered your question. The fact that you don't understand the answer means that you need to take the introductory class that I was suggesting earlier for you. MMX executed with ANY other object (like sound, tennis balls, ping-pong balls, billiard balls, roller bearing balls) produces the same NULL result as MMX done with light. And yes, you need to know SR in order to understand the explanation. Suffice to say that if you are an observer inside the plane carrying the MMX interferometer you would notice the balls, sound, etc, bouncing perfectly vertically between the mirrors. Therefore, by the principle of relativity, any other observer, in motion wrt. the plane would notice the objects bouncing between the mirrors (albeit at an aberation angle). The balls will leave and return to the starting point simultaneously in all frames, resulting into a null result.

68. Originally Posted by whizkid
Please correct what is wrong
I think it would be good if you could briefly explain just what your point/question/contention really is, because I have pretty much lost you now. You appear to accept the constancy of c, and you have been given several explanations as to why that is so, and what the consequences are.

So where's the issue ?

69. Originally Posted by Markus Hanke
So where's the issue ?
Originally Posted by xyzt
MMX executed with sound, with ping-pong balls, with tennis balls, gives the same exact result as the original MMX with light. The proof is not trivial, you need to know a LOT of relativity to be able to follow the calculations.
And yes, you need to know SR in order to understand the explanation..
Thanks, Markus, for your patience,
I am muddled as I thought that SR applies only to light an not to pimg pong balls. If it is really so, I must reconsider my questions.

70. Originally Posted by whizkid
Originally Posted by Markus Hanke
So where's the issue ?
Originally Posted by xyzt
MMX executed with sound, with ping-pong balls, with tennis balls, gives the same exact result as the original MMX with light. The proof is not trivial, you need to know a LOT of relativity to be able to follow the calculations.
And yes, you need to know SR in order to understand the explanation..
Thanks, Markus, for your patience,
I am muddled as I thought that SR applies only to light an not to pimg pong balls. If it is really so, I must reconsider my questions.
The principle of relativity applies equally to ALL experiments.

71. Originally Posted by whizkid
Thanks, Markus, for your patience,
I am muddled as I thought that SR applies only to light an not to pimg pong balls. If it is really so, I must reconsider my questions.
Yes, as xyzt states, the principles of SR apply to all situations which can be formulated against a flat space-time background. This includes both ping pong balls and light, so long as there is no gravity involved. SR is fundamentally incompatible with the notion of gravity.

72. Originally Posted by Markus Hanke
Originally Posted by whizkid
Thanks, Markus, for your patience,
I am muddled as I thought that SR applies only to light an not to pimg pong balls. If it is really so, I must reconsider my questions.
Yes, as xyzt states, the principles of SR apply to all situations which can be formulated against a flat space-time background. This includes both ping pong balls and light, so long as there is no gravity involved. SR is fundamentally incompatible with the notion of gravity.
Hence the continuing search for a "theory of everything".

73. Originally Posted by Markus Hanke
the principles of SR apply to all situations This includes both ping pong balls and light, so long as there is no gravity involved. SR is fundamentally incompatible with the notion of gravity.
Why that? what has gravity got to do with the invariance of c?

- so, the balls do not return at the same instant just because the distance and speed is the same?
- what happens if a planet is rotating with speed close to c, it shrinks in which direction
- suppose a planet has speed close to c in direction +x , id shrinks to half its length in direction +x, now suppose a train on the surface has speed close to c in direction -x, what happens, does it shrink to half in direction -x and becomes a quarter of its original length, or what?

74. Originally Posted by Daecon
Hence the continuing search for a "theory of everything".
Actually, incorporating gravity simply means going from Special Relativity ( SR ) to General Relativity ( GR ). A "theory of everything" would be the unification of all fundamental forces - which is indeed an ongoing effort.

75. Originally Posted by whizkid
Originally Posted by Markus Hanke
the principles of SR apply to all situations This includes both ping pong balls and light, so long as there is no gravity involved. SR is fundamentally incompatible with the notion of gravity.
Why that? what has gravity got to do with the invariance of c?

- so, the balls do not return at the same instant just because the distance and speed is the same?
- what happens if a planet is rotating with speed close to c, it shrinks in which direction
- suppose a planet has speed close to c in direction +x , id shrinks to half its length in direction +x, now suppose a train on the surface has speed close to c in direction -x, what happens, does it shrink to half in direction -x and becomes a quarter of its original length, or what?
I can no longer tell if these are intended to be serious questions or just part of an "SR must be wrong because it doesn't make sense to me" rant. But...

what has gravity got to do with the invariance of c?
Nothing. Except that they are explained by the same theory: they are both a consequence of the geometry of space-time.

- what happens if a planet is rotating with speed close to c, it shrinks in which direction
My understanding is that, because this involves acceleration (i.e. you are not talking about an inertial frame of reference) you would need to use general relativity to understand this (and I suspect it is non-trivial).

- suppose a planet has speed close to c in direction +x , id shrinks to half its length in direction +x, now suppose a train on the surface has speed close to c in direction -x, what happens, does it shrink to half in direction -x and becomes a quarter of its original length, or what?
As above but also: what frame of reference are you measuring the speed of the train in? And velocities do not add linearly in relativity so you would need to use the velocity addition formula to answer this (and, as you haven't given any values, we can't do that for you).

76. Originally Posted by whizkid
Why that? what has gravity got to do with the invariance of c?
What I meant to point out is simply that SR as a whole relies on a flat space-time ( Minkowski space-time ); if space-time is not flat, i.e. if gravity is present, we need to use the full formalism of GR. The speed of light remains invariant locally, though.

what happens if a planet is rotating with speed close to c, it shrinks in which direction
Apart from this being physically impossible - it would be the planet's circumference that shrinks in this instance.

- suppose a planet has speed close to c in direction +x , id shrinks to half its length in direction +x, now suppose a train on the surface has speed close to c in direction -x, what happens, does it shrink to half in direction -x and becomes a quarter of its original length, or what?
It is unclear to me what you are asking here; from the point of view of an outside observer the planet is no longer spherical, and the velocities of planet and train are opposite in direction. What the observer sees then is a length contraction in accordance to the relative speed of the train, but since the track is not straight, this isn't very easy to calculate because it will involve the apparent geometry of the track on the flattened sphere as well as the viewing angle of the observer. The result will be a length contraction which is time dependent; this isn't an easy scenario.

77. Originally Posted by Markus Hanke
Apart from this being physically impossible - it would be the planet's circumference that shrinks in this instance.

It is unclear to me what you are asking here; from the point of view of an outside observer the planet is no longer spherical, and the velocities of planet and train are opposite in direction. What the observer sees then is a length contraction in accordance to the relative speed of the train.
I have some more stupid questions for you:
-How can the circonference shrink, as every circunference shrinks more than the circumference below?
- why not a smaller sphere?
- is it the observer tha sees it smaller or is it really smaller? an atom of hydrogen there has same circumference as the atom on earth?
- suppose the train as same but opposite speed so that it stands still to an obsever , does it shrinks or not?

78. Originally Posted by whizkid
-How can the circonference shrink, as every circunference shrinks more than the circumference below?
- why not a smaller sphere?
Because length contraction happens only in the direction of motion, which in this case is not along the radial coordinate.

is it the observer tha sees it smaller or is it really smaller?
The question is meaningless - all measurements made by any observer are equally valid, but only in that particular observer's frame of reference. So, for an outside observer looking at the planet, the circumference is really smaller than that of some non-rotating reference planet.

suppose the train as same but opposite speed so that it stands still to an obsever , does it shrinks or not?
If the relative speed between train and observer is zero, then no length contraction of the train is observed.

79. Originally Posted by whizkid
-How can the circonference shrink, as every circunference shrinks more than the circumference below?
You can't make sense of this in the context of special relativity. This was one of the things that led Einstein to understand the nature of space time curvature. This is a related problem: Ehrenfest paradox - Wikipedia, the free encyclopedia

an atom of hydrogen there has same circumference as the atom on earth?
It depends who measures it.

80. If the speed of light was constant, would that mean there is only a finite amount of particles travelling at the speed of light?

81. Originally Posted by The Huntsman
If the speed of light was constant, would that mean there is only a finite amount of particles travelling at the speed of light?
Only particles without any rest mass ( i.e. photons and gluons ) travel at exactly the speed of light, always.

82. Originally Posted by Markus Hanke

The question is meaningless - all measurements made by any observer are equally valid, but only in that particular observer's frame of reference. So, for an outside observer looking at the planet, the circumference is really smaller than that of some non-rotating reference planet.
Are you saying thta an atom of oxigen has not same radius anywhere in the universe?

83. Originally Posted by Markus Hanke
Originally Posted by The Huntsman
If the speed of light was constant, would that mean there is only a finite amount of particles travelling at the speed of light?
Only particles without any rest mass ( i.e. photons and gluons ) travel at exactly the speed of light, always.
Where do they get the infinite amount of energy they need to do this?

84. Originally Posted by The Huntsman
Where do they get the infinite amount of energy they need to do this?
They don't need "infinite energy" because they don't have a rest mass.

85. Originally Posted by whizkid
Are you saying thta an atom of oxigen has not same radius anywhere in the universe?
The atom's radius that is being measured depends on the observer - if the atom and observer are at rest relative to each other, the radius will be approximately 60 pico meters, but if they are moving at relativistic speeds relative to each other, than the radius will be length contracted along the direction of motion ( not in any other direction ), turning the atom into an oblate sphere.

This is, in fact, the basic working principle behind the Relativistic Heavy Ion Collider ( RHIC ) - see here :

RHIC | Physics of the Relativistic Heavy Ion Collider

Where do they get the infinite amount of energy they need to do this?
They don't need any energy to do this, because massless particles cannot be accelerated or decelerated - they always move at exactly the speed of light, they cannot do anything else.

86. what would the effect on what we believe now if science found a way of proppeling something faster than the speed of light. like if we somehopw harnesed "dark energy"if there is such a thng, and it turns out that that actually can travel faster than light itself.
As a total self proclaimed idiot, am i right in thinking that the bigger the force the more likely it is to be faster and more powerful for example, if you had a "thing" a "force" of some sort,unknown to us that covered the entire univers, it wrapped a fabric around the whole cosmos and this is like a outer layer, which scientists say is expanding, well if any movement or event happened on the fabric, if this happened and could be felt, around the whole fabric, instantly, then you would have something that was defanatly faster than light.
Because of how small earth is, i think that the bigger something is the less we can think we understand it. at the moment we are a tiny atom on the living room carpet thinking we know whats going on in the attic space

87. Originally Posted by graemedon
what would the effect on what we believe now if science found a way of proppeling something faster than the speed of light.
A few years ago some researchers thought they had found neutrinos travelling faster than light. Although most people pointed out why this couldn't possibly be correct (it wasn't) a few scientists produced possible explanations (and ways to test them).

I imagine the same thing would happen.

88. I thought it was proven through experiment.

Photoelectric effect, diode threshold voltage paired with wave theory anyway, and analysis of the frequency and wavelengths of EM waves in vacuums.

89. What are you on about? The photoelectric effect shows light behaves as particles i.e. is quantised what has that got to do with c? What have diodes got to do with c?

90. The speed of light is pretty well constant. Anyone know about photoelectric effects at 0 kelvin. Or entropy regarding photoelectric on materials at 0 kelvin? Light moving electrons in materialsis cooler than, argueing over the speed of light constant. Its still 3^6.

91. Originally Posted by Magic Pixel
Its still 3^6.
Whut?

92. Originally Posted by Magic Pixel
The speed of light is pretty well constant. Anyone know about photoelectric effects at 0 kelvin. Or entropy regarding photoelectric on materials at 0 kelvin? Light moving electrons in materialsis cooler than, argueing over the speed of light constant. Its still 3^6.
Please stop posting your stupidity and nonsense in the hard science forums. Stick to pseudo and trash where your ignorance belongs.

93. Photoelectric effect should support the speed of light as being constant, since it can be used in quantum electrodynamics, and in conjunction with equations that express the energy of a photon in terms of the characteristics of it's corresponding wave, including it's speed.

Diodes make use of threshold frequencies that can also be used to determine the speed of the wave in a known medium.

94. The photoelectric effect does not contradict c being constant (how could it) but it does not depend on c being constant either so it is not a relevant example. The diodes example I admit is something I don't know a lot about (hence my question) but from what you say this is at best only indirect evidence and probably just clouding the issue when there is better evidnce out there.

95. Originally Posted by Subliminal
Diodes make use of threshold frequencies that can also be used to determine the speed of the wave in a known medium.
I don't recognise this description of diode function. It is more due to the fact there is a larger potential barrier for charge carriers in one direction than the other. I'm not sure where frequency comes into it. Can you explain...

96. LEDS which emit low energy photons a low energy LED, requiring low threshold (bolded to accentuate relation to E=hf) voltage, combined with equation eV=hc/lambda. You could make use of potential dividers in the form of LDRs connected in series along with the LEDs of different threshold voltages to further emphasize the different energies of light. Small changes in the frequency will have immediate effects showing that there is no room for (notable) fluctuations in c.

97. What are you on about? The two equations you have given are the same just using f=c/"lambda", (and for some reason replacing E with the unit eV). What you are saying is that if f changes c/lambda changes, so what?

If you are not measuring lambda as well as f this does not prove c is constant1, it proves when you change the frequency of light either lambda or c or both change.

1. (it is, but it does not follow from what you have presented).

98. Originally Posted by PhDemon
What are you on about? The two equations you have given are the same just using f=c/"lambda", (and for some reason replacing E with the unit eV). What you are saying is that if f changes c/lambda changes, so what?

If you are not measuring lambda as well as f this does not prove c is constant1, it proves when you change the frequency of light either lambda or c or both change.

1. (it is, but it does not follow from what you have presented).
I didn't choose to replace E with eV, that is the accepted equation for this particular case.

If c is to remain constant then a change in "f" or lambda must be offset by a change in the other, thus low energy light emitting diodes emit light of a longer wavelength then high then high energy light emitting diodes. Planks constant can be shown to be constant in the same way.

99. Nonsense, eV is just a unit of energy.

"If c is to remain constant..." you are proposing this effect as evidence the speed of light is constant, you cannot therefore assume c is constantin your interpretation of the experiment. That is the logical fallacy of circular reasoning.

What you are essentially saying is if we assume the speed of light is constant in interpreting this experiment, this experiment shows the speed of light is constant...

(c is actually constant, I'm just trying to show your reasoning is flawed and this experiment does not show c is constanyt. The equations you have shown just depend on c=f/lambda being true.

100. Originally Posted by PhDemon
Nonsense, eV is just a unit of energy.

"If c is to remain constant..." you are proposing this effect as evidence the speed of light is constant, you cannot therefore assume c is constantin your interpretation of the experiment. That is the logical fallacy of circular reasoning.
It's not being used here as a unit, just as "c" is not. I'm not, it's "e" * "V".

101. As I said eV is a UNIT of energy, do you know what a unit is? It means electron volt -- a unit I use almost every day equal to 1.6 x 10-19 J.

Electronvolt - Wikipedia, the free encyclopedia

The fact you have such a poor understanding of your own argument and the equations you have presented leads me to think I'm wasting my time here...

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