Measuring The Relative Velocity Of Light

[ram1024]

"look for faults" does not mean "stage fake experiments to produce the results desired"

having trouble with reading comprehension?

 

[quantumdude]

"look for faults" does not mean "stage fake experiments to produce the results desired"

Then what do you mean?

having trouble with reading comprehension?

Not at all. If you examine the immediate context in which you posted your comments, you'll see that the inference I made was reasonable. I was discussing the impropriety of a skewed interpretation of experimental results to fit a worldview that one subjectively deems "rational". You jumped in with your comment about looking for faults in the experiment, with no further explanation. I just took your remark in the context of the discussion. It's not my fault if you don't say what you mean.

 

[ram1024]

i said exactly what i mean.

something is wrong with your experiments. find out what it is :P

 

[quantumdude]

i said exactly what i mean.

Might I recommend a bit more exposition then? The quick two-liners simply do not convey the information you wish to convey.

something is wrong with your experiments. find out what it is :P

Here's a perfect example.

On what basis do you say that something is wrong with an experiment, as opposed to something being wrong with a theory?

 

[ram1024]

experiments can be re-done and refined, theories are set in stone

The fact of the matter is that it only takes a single experimental counterexample to prove that a physical theory is false.

 

[quantumdude]

experiments can be re-done and refined,

Correct.

theories are set in stone

That's not a very good way to look at it. If a theory is "set in stone", then it has to be discarded in total when it is falsified. But if you take the point of view that theories can also be re-done and refined (as is the point of view of real scientists, by the way), then by keeping the good and discarding the bad, you don't have to start from scratch every time.

Anyway, you did not even come close to answering my question.


Here it is again:

On what basis do you say that something is wrong with an experiment, as opposed to something being wrong with a theory?

 

[ram1024]

when an experiment using principles proven by OTHER experiments acquires data NOT equivalent to theory. duplicate the experiment a few hundred times under multiple conditions to confirm it's not a fluke. then either that experiment and all other ones supporting it are wrong OR the theory is wrong.

the more times the experiment is tried and scrutinized the MORE correct it is.

 

[quantumdude]

when an experiment using principles proven by OTHER experiments acquires data NOT equivalent to theory. duplicate the experiment a few hundred times under multiple conditions to confirm it's not a fluke. then either that experiment and all other ones supporting it are wrong OR the theory is wrong.

This I can agree with. Now we just have to get you to see that this very thing has been done many, many times with SR.

 

[ram1024]

exactly

this is such fun

 

[reilly]

Grounded -- First, please accept my apologies for being snotty and arrogant(the physicist's disease) I misjudged your zeal and passion for understanding. (Note, however, as my dear Mother told me -- You learn more with your mouth shut than with it open)

Physics is very difficult, for two primary reasons: it requires a real facility with and understanding of a lot of advanced math; the conceptual basis is highly abstract and idealized, in E&M, QM, SR, GR, ..., and is not fully consistent. So, particularly, for the last reason, most physicists are highly pragmatic -- do the best you can with what you have, don't sweat the hard stuff unless it messes up your work. As I'm sure you know, for example, there is huge controversy about the proper interpretation of QM, but many working physicists pay little attention to the controversy. The standard ways work just fine in practice.

Everyone who teaches physics, say SR, will tell you we did not understand SR until we taught it. It takes a long time, and many exposures to SR to get it right. And, most students of SR will tell you that sometimes you have to suspend your judgement to get to a good understanding -- that's the advantage of a good teacher, he/she can suggest what to sweat now, and what to defer. All told, SR is a huge subject, of which the basic space-time kinematics, the x's and t's, comprise only a very small portion. It is the totality of SR that is so compelling.

That being said, the path to a robust understanding of SR necessarily involves lot's of math -- there's no way around that fact.

Tom's explanation of the imaginary exponential is right on. The way, typically, you build up a comfortable intuition about i, the square root of -1, is to work with it, work with it a lot. It's part of the language of physics, and is used so much because it is a powerful tool in working with waves, periodic phenomena, much of QM, and many other branches of physics and engineering.

If you are serious about physics, you need to hit the books, and do the homework. Resnick and Halliday is a good place to start. And, absolutely necessary, learn calculus. Then you will understand that the x and t in the exponential are not x2-x1, t2-t1. That exponential gives you the compex value of the wave amplitude at x at time t.

Once a professor, always a professor.
Regards and good luck

Reilly Atkinson

 

[geistkiesel]

Grounded -- First, please accept my apologies for being snotty and arrogant(the physicist's disease) I misjudged your zeal and passion for understanding. (Note, however, as my dear Mother told me -- You learn more with your mouth shut than with it open)

Physics is very difficult, for two primary reasons: it requires a real facility with and understanding of a lot of advanced math; the conceptual basis is highly abstract and idealized, in E&M, QM, SR, GR, ..., and is not fully consistent. So, particularly, for the last reason, most physicists are highly pragmatic -- do the best you can with what you have, don't sweat the hard stuff unless it messes up your work. As I'm sure you know, for example, there is huge controversy about the proper interpretation of QM, but many working physicists pay little attention to the controversy. The standard ways work just fine in practice.

Everyone who teaches physics, say SR, will tell you we did not understand SR until we taught it. It takes a long time, and many exposures to SR to get it right. And, most students of SR will tell you that sometimes you have to suspend your judgement to get to a good understanding -- that's the advantage of a good teacher, he/she can suggest what to sweat now, and what to defer. All told, SR is a huge subject, of which the basic space-time kinematics, the x's and t's, comprise only a very small portion. It is the totality of SR that is so compelling.

That being said, the path to a robust understanding of SR necessarily involves lot's of math -- there's no way around that fact.

Tom's explanation of the imaginary exponential is right on. The way, typically, you build up a comfortable intuition about i, the square root of -1, is to work with it, work with it a lot. It's part of the language of physics, and is used so much because it is a powerful tool in working with waves, periodic phenomena, much of QM, and many other branches of physics and engineering.

If you are serious about physics, you need to hit the books, and do the homework. Resnick and Halliday is a good place to start. And, absolutely necessary, learn calculus. Then you will understand that the x and t in the exponential are not x2-x1, t2-t1. That exponential gives you the compex value of the wave amplitude at x at time t.

Once a professor, always a professor.
Regards and good luck

Reilly Atkinson

Really, Reilly, how dare you, but you recovered nicely. perhaps ou can elucidate us on the following:

All moving frame values are non-primed with the exception of M’, the consistent location of the observer O in the moving frame.

At no time is there an inference that M’ was at the midpoint of the A and B photons emitted in the stationary frame.

To demonstrate the following:

Einstein’s moving train calculation indicating when the oncoming B photon is detected at t1 the A photon was located at a position consistent with –t1. Said in other words, as t1 is determined from t0 which locates M’ at t0, the A and B were equidistant to M’(t0) when t = t1.

Proof:
A moving observer located at M’ on a moving frame passes through the midpoint M of photon sources located at A and B in the stationary frame just as A and B emit photons. M’ is moving along a line connecting A and B, toward B.

At this instant the moving source t = t0. Later the moving observer detects the photon from B at t1, and later the photon from A at t2. The observer has measured her velocity wrt the stationary frame as v. Determine the position of the A photon at tx in terms of t0, t1, t2, and v when the B photon was detected at t1.

The photon from A must reach the position of M’ when t = t2. Therefore, the distance traveled by the A photon during Δt = t2 – t1, is Δtc. This is equal to the distance cΔt = vΔt + vt1 + vtx . Now we rearrange somewhat to arrive at, vtx = vΔt – cΔt + –vt1. Now as vΔt - cΔt is just -vtx - vt1

vtx = -vtx - vt1 – vt1

2tx = -2t1

tx = -t1

Therefore, in the moving frame the photon from A and the photon from B were equidistant from M’(t0) at t1.

 

[geistkiesel]

But we can see that he isn't transcending anything. He is making choices that lead to the physics of the 19th century, and we know that those choices are wrong.

Tom, excuse me if I've asked this before, but show me Grounded's math in 19th Century physics, AND that 19th century physics is passe because it is so old.

 

[reilly]

geistkiesel -- I really can't figure out what's going on in your scenario. A diagram or two would be very helpful.

But I do suggest you go to any text that discusses basic SR space-time definitions and (idealized) measurements, take pencil and paper and work through, step-by-step, the arguments. Then you will be in a position to answer your own question. If not, you will have far more specific questions to ask about SR. Einstein's book Relativity is elegant and insightful, the more recent Basic Relativity by Richard Mould goes into the basic SR space time structure in enormous detail -- requires only high school algebra at that stage.

Regards,
Reilly Atkinson

 

[geistkiesel]

geistkiesel -- I really can't figure out what's going on in your scenario. A diagram or two would be very helpful.

But I do suggest you go to any text that discusses basic SR space-time definitions and (idealized) measurements, take pencil and paper and work through, step-by-step, the arguments. Then you will be in a position to answer your own question. If not, you will have far more specific questions to ask about SR. Einstein's book Relativity is elegant and insightful, the more recent Basic Relativity by Richard Mould goes into the basic SR space time structure in enormous detail -- requires only high school algebra at that stage.

Regards,
Reilly Atkinson

Reilly, I truly am grateful for your suggestions but I am a confessed SR heretic, and I am not going to indulge myself in learning something that I am working to get rid of, capice? I do not buy inro the SR story and am especially motivated since Sir Grounded came upon the scene. We should all feel rather grateful that Sir Grounded selected this forum to have his views aired. I do see a lot of denial in respoding posts, do you agree Reilly? Rather than urge Sir Grounded along with suggestions and clues, it seems the SR bushwahackers have come put of theri hiding places and are attempting a full scale assault on the citidel. Echoes, Reilly, a chorus of echoes, some on harmony some off key, but all are echoes, of SR I see.

Here is the experimental arrangement, I bet it looks familiar, doesn't it Reilly? "relativity" pages 25-27 you mean? My favorite science book of all time. Check it out.
---> motion

A________________M______|_______|______B
                 M'(t0) M'(t1)  M'(t2)

M is the midpoint of photon emitters at A and B. M'(t0) is the observer location on the moving frame that coincides with M in the stationary frame just as the photons were emitted simultaneously at A and B.
Later the Oberver detects the B photon at M'(t1) and then the photon from A at M'(t2). This is the Einstein train experiment that has been passing through the threads lately. And t'' ithe signals from A and B at the midpoint of A and B (for a long train).

IF SR predicts that the photons were not emitted simultaneously in the moving frame describe the location of the A photon when the B photon was detected at M'(t1) in terms of t's and v, the velocity known by the observer wrt to the stationary frame.

Simple high school algebra Reilly, you shouldn't have any problem, especially as I have already done the math.

Thank you for your help.

 

[geistkiesel]

Grounded -- First, please accept my apologies for being snotty and arrogant(the physicist's disease) I misjudged your zeal and passion for understanding. (Note, however, as my dear Mother told me -- You learn more with your mouth shut than with it open)

Physics is very difficult, for two primary reasons: it requires a real facility with and understanding of a lot of advanced math; the conceptual basis is highly abstract and idealized, in E&M, QM, SR, GR, ..., and is not fully consistent. So, particularly, for the last reason, most physicists are highly pragmatic -- do the best you can with what you have, don't sweat the hard stuff unless it messes up your work. As I'm sure you know, for example, there is huge controversy about the proper interpretation of QM, but many working physicists pay little attention to the controversy. The standard ways work just fine in practice.

Everyone who teaches physics, say SR, will tell you we did not understand SR until we taught it. It takes a long time, and many exposures to SR to get it right. And, most students of SR will tell you that sometimes you have to suspend your judgement to get to a good understanding -- that's the advantage of a good teacher, he/she can suggest what to sweat now, and what to defer. All told, SR is a huge subject, of which the basic space-time kinematics, the x's and t's, comprise only a very small portion. It is the totality of SR that is so compelling.

That being said, the path to a robust understanding of SR necessarily involves lot's of math -- there's no way around that fact.

Tom's explanation of the imaginary exponential is right on. The way, typically, you build up a comfortable intuition about i, the square root of -1, is to work with it, work with it a lot. It's part of the language of physics, and is used so much because it is a powerful tool in working with waves, periodic phenomena, much of QM, and many other branches of physics and engineering.

If you are serious about physics, you need to hit the books, and do the homework. Resnick and Halliday is a good place to start. And, absolutely necessary, learn calculus. Then you will understand that the x and t in the exponential are not x2-x1, t2-t1. That exponential gives you the compex value of the wave amplitude at x at time t.

Once a professor, always a professor.
Regards and good luck

Reilly Atkinson

Reilly, I don't know if you have read all of the posts Grounded has made in this thread, but a cursory examination will show you that he making a most robust effort to teach you something, but your instincts seem to be to throw the dust of whatever subtle discouragement you have to the man. Condescending, superior intelligence, education and wit you know the attitue, don't you?. When you understand what he is saying, meaning you have to read it of course, you can understand his tenacity he has built into the model he his presenting.

Again, Reilly. he is teaching you something. Physics isn't so difficult, but useless phyiscs is very difficult, don't you agree?.

 

[geistkiesel]

Might I recommend a bit more exposition then? The quick two-liners simply do not convey the information you wish to convey.



Here's a perfect example.

On what basis do you say that something is wrong with an experiment, as opposed to something being wrong with a theory?

Tom, Grounded showed by example the necessity of including the observers relative velocity less a mistake be made in the measurement of the length of the cars (wave length of light). The SR system creates a mistake in measuremment and needed to create SR to explain the error. How many times can you echo "the vast amount of experimental results" describing your collective error? The experiments that prove time dilation, contraction of matter, loss of simultaneity?

How long can you keep it up before the echo wears thin? Tom, lifting the weight of SR will be a relief, a huge relief.

They're are errors Tom, great big huge errors.

 

[geistkiesel]

What about your own faith, Geistkiesel? It must be pretty strong for you to continue to have your unwavering belief in the incorrectness of Special Relativity.

I mean, if I had a strong conviction against learning something, I would resign myself to the fact that I don't know that thing.

But here you are, steadfastly refusing to learn Special Relativity, refusing to hear evidence confirming it, and you are able to stick to your conviction that it cannot possibly be anywhere close to valid!


Wait, I'm wrong, you're not so much sticking to your convictions; you never face any scrutiny because you denounce anyone who would scrutinize you as being in a "state of blind obedient sleep-walking darkness".

You still have your blind faith, but you don't have the confidence in your faith, so you need to belittle those who might erode your faith in order to maintain it.


You liken learning SR to putting a finger in a fire. Why? Putting your finger in a fire can cause physical pain and injury; are you suggesting that you will suffer mental pain and injury if you tried to learn SR? Are you really that afraid you might be wrong?

Here is where I question your sophistication. I said I woudn't put my finger in the fire just to see how hot it was. Did you really read that as a suggestion that I would suffer mental pain and injurty learning SR?. You know what, you are absolutely correct. But you misjudge faith and conviction and are unable to distuinguish them from sheer boredom. There are millions of subject matter in the world available to me for perusal. I reject most of those subjects from scrutiny. SR happens to be one of them. All theories are temporary, SR is falling to the floor.


Why do you steer the conversation around to faith and pain and conviction? I thought you were posing as an SR theorist, here I see petty propagandist. Luring me around by your trained and practiced metaphors.

"The enemies of truth. Convictions are more dangerous enemies of truth than lies"

 

[russ_watters]

Why do you steer the conversation around to faith and pain and conviction?

Simple: your position defies rational explanation. Indeed, you actively repel any attempt at rational discussion. You ignore evidence and you ignore math. These discussions are not scientific because you refuse to be scientific in your approach to the problem.

 

[Hurkyl]

Why do you steer the conversation around to faith and pain and conviction?

If you didn't want your opinions and beliefs questioned directly, then you shouldn't state them in a discussion forum.

I've yet to understand why people who state (or imply) such things feel they should be immune from scrutiny.

 

[wespe]

An interferometer can be calibrated using a light source with a known wavelength. As long as the distance between the observer and the source are not changing, this will work. Since light travels 186,000 miles per second, the wavelength equals the amount of distance traveled, traveling at 186,000 miles per second, in the amount of time it takes the light to complete one cycle. If the distance between the observer and the source are decreasing, then the wavelength equals the amount of distance traveled, traveling at the sum of “186,000 miles per second” added to “the speed at which the distance between the source and the observer is decreasing”, in the amount of time it takes the light to complete one cycle. If we measure the wavelength in this fashion, we will not measure a change.

Are you still there, Grounded?

I see no reason to for any calibration, but apart from that, I don't think an interferometer can be calibrated in such a way that it will always measure the "true" wavelength (the wavelength in the emitter's frame). You can't even calculate the "true" wavelength by just knowing the measured relative frequency (and the speed of light, which is constant), you also have to know the relative speed [between you and the light source]. You can calibrate [at a certain relative speed], but then it will not work [when the relative speed changes]. You must constantly "calibrate" it by feeding it with the value of relative speed, then what kind of calibration is that? What do you think?

editing to add:
Am I misunderstanding? You are saying that a "true" wavelength exists independent of the relative speed. Then you should be able to measure it without taking relative speed into account. Therefore your calibration must not involve relative speed. Right? Also, the "traveled distance" is the result of relative speed. Actually, according to yourself, you aren't going anywhere. It is the other object that travels. Without relative speed, there is no meaning to traveled distance.

 

[grounded]

Whether you are using Galilean relativity or SR, the equation is the same.

I can calculate the relative velocity between a light pulse and myself by measuring the following:

Event 1: Pulse Emitted
x₁=Location of emitter on x-axis at time t₁.
t₁=Time of emission.

Event 2: Pulse Detected
x₂=Location of detector on x-axis at time t₂.
t₂=Time of detection.

The speed of the pulse relative to me is then:

v=(x₂-x₁)/(t₂-t₁).

For light, this will always come out to be c. And as you can see, that result is not "built in" to the way we calculate relative speed. It is a simple, undeniable experimental fact.

Tom, you say it is not "built in", but consider the following;

Can you calculate the relative velocity between a moving car and yourself by measuring the following?

Event 1: Car Accelerated (Assume instantaneous acceleration to 60 Miles Per Hour)
x₁=Location of car on x-axis at time t₁.
t₁=Time of acceleration.

Event 2: Car Detected
x₂=Location of car on x-axis at time t₂.
t₂=Time of detection.

The speed of the car relative to you is then:

v=(x₂-x₁)/(t₂-t₁).

Can you alter the relative speed of the car while using this formula?
If not, then how is this formula the very definition of relative speed?

 

[grounded]

Are you still there, Grounded?

I see no reason to for any calibration, but apart from that, I don't think an interferometer can be calibrated in such a way that it will always measure the "true" wavelength (the wavelength in the emitter's frame). You can't even calculate the "true" wavelength by just knowing the measured relative frequency (and the speed of light, which is constant), you also have to know the relative speed [between you and the light source].

I agree...partly.

The relative speed IS the distance the observer travels towards (or away from) the source in one second, which IS the same thing as the change in distance between the observer and the source per second.

This is why I say we must include the distance the observer has traveled relative to the source in order to accurately measure the wavelength.

The speed of light is calculated to be constant because we use an incorrectly measured wavelength.

You can calibrate [at a certain relative speed], but then it will not work [when the relative speed changes]. You must constantly "calibrate" it by feeding it with the value of relative speed.

If the change in distance between the observer and the source is not at a constant velocity, then yes, it must be constantly calibrated.

 

[wespe]

This is why I say we must include the distance the observer has traveled relative to the source in order to accurately measure the wavelength.

The speed of light is calculated to be constant because we use an incorrectly measured wavelength.

OK, suppose I claim the following:

"There exists a true frequency and we are measuring it wrong. Because we must include relative speed [or, the distance the observer has traveled relative to the source] in order to accurately measure the frequency. We must calibrate our equipments constantly according to the relative speed."

Do you see? If you do such a correction on wavelength, you must also do it for frequency. And with both wavelength and frequency "corrected", you get constant c when you multiply them. That's what I meant by "mixing frames" in an earlier post.

 

[grounded]

Am I misunderstanding? You are saying that a "true" wavelength exists independent of the relative speed. Then you should be able to measure it without taking relative speed into account.

I am saying that if you account for the change in distance between the observer and the source, you can always measure the true wavelength.

From my original post:

Traveling towards the train will increase the number of boxcars that are passed and it will increase the relative speed between the observer and the train, but it will not change the length of the boxcars. If the observer plotted the number of boxcars that passed in one minute on a four-inch line, and then did the same thing after increasing speed towards the train, the second experiment would have more marks on the four-inch line and they would be closer together. This does not mean the length of the boxcars have gotten shorter, it means that the four-inch line represents a greater distance while traveling towards the source than it does when not moving relative to the source.

 

[jcsd]

I am saying that if you account for the change in distance between the observer and the source, you can always measure the true wavelength.

From my original post:

But the problem is the light is not atatched to the refernce frame of the source, what happens when the source is accelarting? what happens when the source is unknown?

 

[grounded]

OK, suppose I claim the following:

"There exists a true frequency and we are measuring it wrong. Because we must include relative speed [or, the distance the observer has traveled relative to the source] in order to accurately measure the frequency. We must calibrate our equipments constantly according to the relative speed."

Do you see? If you do such a correction on wavelength, you must also do it for frequency. And with both wavelength and frequency "corrected", you get constant c when you multiply them. That's what I meant by "mixing frames" in an earlier post.

Current measurments of frequency already include the distance the observer has traveled relative to the source. The change in distance between the source and the observer in one second, divided by the true wavelength, equals the change in frequency.

We include the distance the observer has traveled relative to the source when measuring frequency, but we do not include it when measuring wavelength, which is why the relative speed can never change.

The frequency wrt the observer equals the number of cycles that pass by the observer due to the velocity of the light, added to the number of cycles passed caused by the observers speed towards the source.

Like you said, what we do to one, we must do to the other.

 

[wespe]

Current measurments of frequency already include the distance the observer has traveled relative to the source. The change in distance between the source and the observer in one second, divided by the true wavelength, equals the change in frequency.

We include the distance the observer has traveled relative to the source when measuring frequency, but we do not include it when measuring wavelength, which is why the relative speed can never change.

The frequency wrt the observer equals the number of cycles that pass by the observer due to the velocity of the light, added to the number of cycles passed caused by the observers speed towards the source.

Like you said, what we do to one, we must do to the other.

OK

Let's say, according to light source: the frequency is 300,000 Hz and wavelength is 1 km.

Due to some relative speed..
The observer measures: frequency is 600,000 Hz, wavelength is 0,5 km
The observer calculates: relative speed = relative frequency x relative wavelength = 300,000 km/sec
The observer can also directly measure relative speed like I described in an earlier post. This measurement verifies the calculated relative speed: 300,000 km/sec

According yo you: true wavelength is 1 km, but true frequency is still 600,000 Hz
So observer must calculate: relative speed = 600,000 km/sec
This result does not match the directly measured relative speed. What do you say about that?

 

[grounded]

But the problem is the light is not atatched to the refernce frame of the source, what happens when the source is accelarting? what happens when the source is unknown?

To say the source is traveling towards the observer at a faster rate, is the same thing as saying the observer is traveling towards the source at a faster rate, assuming the observer was already traveling towards the source.

Like Tom has said, it is not the speed of the observer or the speed of the source that is important, it is the amount of change in distance between the source and the observer in one second that matters.

We can use a spectrometer and a spectrograph to analyze and discover what the source is made of and what its true wavelength is. The amount of shift in the spectrum will tell you the relative speed. This shift is caused by not changing the scale.

 

[jcsd]

To say the source is traveling towards the observer is the same thing as saying the observer is traveling towards the source at a faster rate, assuming the observer was already traveling towards the source.

Like Tom has said, it is not the speed of the observer or the speed of the source that is important, it is the amount of change in distance between the source and the observer in one second that matters.

We can use a spectrometer and a spectrograph to analyze and discover what the source is made of and what its true wavelength is. The amount of shift in the spectrum will tell you the relative speed. This shift is caused by not changing the scale.

No it is not because accelartion is npot relative in the same way asvelcotiy is relative you can't transform an accelarated frame into an inertail frame in special relatvity.

 

[grounded]

What do you say about that?

I say I am extremely interested in learning about a real world experiment such as you described, minus the spaceship. Remember, it must be done while in motion relative to the source. A link describing the details of the experiment would be appreciated.