Speed of light for different observers

[Dale]

Well, if the light is not always moving at the same speed in respect to the source, one cannot claim that it always move with the same speed in respect to the observer.

Actually, that is exactly what one can claim, it is the whole point of the http://en.wikipedia.org/wiki/Lorentz_transform" to show that it is logically possible for something to move at c in one reference frame and also to move at c in another reference frame, despite the fact that the two reference frames are moving at some velocity v<c with respect to each other.

A pulse of light will move at c in any and all inertial reference frames including the inertial reference frame where the inertial emitter is at rest as well as any inertial reference frame where any arbitrary inertial observer is at rest. Such reference frames are related to one another via the Lorentz transform rather than via the Galilean transform, and in the Lorentz transform velocities add as follows:
s = \frac{v+u}{1+vu/c^2}
Which is equal to c if u is equal to c regardless of v.

 

[Frame Dragger]

"Faith" has nothing to do with it. You make assumptions, draw conclusions, then compare to experiment. Experiment rules!

That needs to be on T-Shirts and bumper stickers NOW. Hell, sell them from PF!

You could even have warring messages: "Experiment rules!" and then on the back "Dagon Shall Rise Again".

Wait... that last bit makes no sense at all...

 

[sisoev]

Thanks for the answers, guys.
I have one more thing to ask and tomorrow I'll post my last comment on the topic.

In my experiment you have one source and one emission with one wave length, observed with two different frequencies.
How do you intend to measure same speed for the light?

I guess some of you won't understand the question, so I'll clarify for you.

Every light source will emit light with certain wave length(λ).
The frequency will equal c/λ

When the frequency changes because of different velocity that means that the time for "passing through the wave length" has changed. The distance between the crests are the same, but they approach the observer faster or slower.
In that case we see yellow light as blue or red depending on the velocity.
Note that the light is still yellow, but we observe it as different.
That is seen on stars that approach Earth with certain speed. We see their light in the blue spectrum, but that doesn't mean that their light is blue.
By calculating their wave length without knowing the velocity we can never know their original light color. They might as well be blue stationary stars or red stars traveling with high speed, or ultraviolet stars traveling away from us.

I hope you understand my point.

Now, in my experiment we have one only wave length (color) because it is one only emission.
Having two different frequencies, we must have two different speed of the light.
But because SR does not agree with that we end up with the paradox of having two different wave lengths for one emission.

 

[Nickelodeon]

Now, in my experiment we have one only wave length (color) because it is one only emission.
Having two different frequencies, we must have two different speed of the light.
But because SR does not agree with that we end up with the paradox of having two different wave lengths for one emission.

I think that you can't pin the wave length. The wavelength and the frequency are (edit: appear to be) modified by the relative speed of the source and observer so that c stays the same. On the other hand, if the observer was accelerating either away or towards the light source then the time interval from the emission to the observation would reflect a speed greater or lesser than c.

 

[Doc Al]

In my experiment you have one source and one emission with one wave length, observed with two different frequencies.
How do you intend to measure same speed for the light?

The observed frequency shift of the light depends on the speed of the source, not the speed of the light. Your arrangement leads to multiple frequencies observed because the source is moving and some of the light is reflected from a moving mirror (which acts as a secondary source). In all cases the speed of light is the same.

Now, in my experiment we have one only wave length (color) because it is one only emission.
Having two different frequencies, we must have two different speed of the light.
But because SR does not agree with that we end up with the paradox of having two different wave lengths for one emission.

What paradox? The different frequencies observed are easily explained within SR. Again, it has nothing to do with 'different speeds of light'. You realize, of course, that the same source of light could be seen as having as many different observed frequencies are there are observers moving at different speeds with respect to the source. Why stop at two?

Here's some homework for you. Give the train some relativistic speed (say, 0.9c). And give the light source some original frequency in its own frame (600 nm, say). Why don't you predict what frequencies will be observed?

 

[dx]

Here's a spacetime diagram for your situation as I understand it, in a frame in which B is at rest:

[PLAIN]http://img11.imageshack.us/img11/1161/expnk.jpg

Now can you explain what your problem is with reference to this image? (Keep in mind the time dilation for the moving observers. That affects the frequency that they observe.)

 

[Frame Dragger]

Isn't this the precise conundrum that is the basis for SR?... that the geometry of spacetime is altered because "c" represents that limit however one chooses to think of it, or arrive at the conclusion?

I'm not trying to be sarcastic... I just want to make sure that I'm not missing more than usual. To me, this has always been where you start with the notion of Relativity.

 

[sisoev]

Here's some homework for you. Give the train some relativistic speed (say, 0.9c). And give the light source some original frequency in its own frame (600 nm, say). Why don't you predict what frequencies will be observed?

This "home work" just shows how deceived people are about wave length and wave frequency.
600 nm in the "home work" is the wave length and it never changes.
The frequency is measured in Hz and it depends on the speed of the light - how fast the wave length is observed, and that depends on the additional speed added to it by the moving source or moving observer.

When we observer different frequency, we must be able to calculate the wave length (which never changes), but that is impossible without knowing the velocity and add it to the speed of the light.
I already pointed to this in my previous comment but you chose not to comment on it.

I still have my last comment coming.

 

[sisoev]

Here's a spacetime diagram for your situation as I understand it, in a frame in which B is at rest:

[PLAIN]http://img11.imageshack.us/img11/1161/expnk.jpg

Now can you explain what your problem is with reference to this image? (Keep in mind the time dilation for the moving observers. That affects the frequency that they observe.)

I'll answer to this in my last comment.

 

[sisoev]

Isn't this the precise conundrum that is the basis for SR?... that the geometry of spacetime is altered because "c" represents that limit however one chooses to think of it, or arrive at the conclusion?

I'm not trying to be sarcastic... I just want to make sure that I'm not missing more than usual. To me, this has always been where you start with the notion of Relativity.

The geometry of space-time will be valid only if the speed of light is constant.
In this discussion it is in question and the geometry of space-time cannot be an argument.
It doesn't stand logical in the context of the experiment since one light emission is seen simultaneously with two different frequencies.
The calculation will show either different wave length (which is a paradox) or different speed of light (which will clear the paradox).

Read my above comments

 

[Doc Al]

This "home work" just shows how deceived people are about wave length and wave frequency.
600 nm in the "home work" is the wave length and it never changes.

The frequency is measured in Hz and it depends on the speed of the light - how fast the wave length is observed, and that depends on the additional speed added to it by the moving source or moving observer.

That's not even true for the classical Doppler effect for sound when the source is moving, never mind for light! When a sound source approaches, the observed frequency increases--yet the speed of the sound doesn't change.

When we observer different frequency, we must be able to calculate the wave length (which never changes), but that is impossible without knowing the velocity and add it to the speed of the light.
I already pointed to this in my previous comment but you chose not to comment on it.

You're wrong, as I've said repeatedly.

I still have my last comment coming.

Please read the sticky at the top of this forum--the one titled "IMPORTANT! Read before posting". In part, it says:

This forum is meant as a place to discuss the Theory of Relativity and is for the benefit of those who wish to learn about or expand their understanding of said theory. It is not meant as a soapbox for those who wish to argue Relativity's validity, or advertise their own personal theories.​

You don't seem to be interested in learning about relativity, just in discussing your own personal interpretation. You've had your time. This thread is done.