The Relativity of Simultaneity

[arfa brane]

So are you saying your measurements will not factor in length contraction and time dilation, and come to the correct answer?

Are you saying you don't need measurements? Are you saying the speed of light has never been measured?

 

[Motor Daddy]

Are you saying you don't need measurements? Are you saying the speed of light has never been measured?

You don't seem to understand that the speed of light doesn't have to be measured.

Light travels at a constant speed in space. We define the meter by the length of the path that light travels in 1/299,792,458 of a second.

I DON'T NEED TO MEASURE THE SPEED OF LIGHT, IT IS DEFINED!!!

 

[arfa brane]

I DON'T NEED TO MEASURE THE SPEED OF LIGHT, IT IS DEFINED!!!

How is it defined? Who defined it, and how did they come to the conclusion that the speed is constant?

They didn't need to measure it, right? So who told them it was already defined? How long has this been known, and who was the first to know? How did they find out? Did the aliens tell them?

 

[Motor Daddy]

How is it defined? Who defined it, and how did they come to the conclusion that the speed is constant?

They didn't need to measure it, right? So who told them it was already defined? How long has this been known, and who was the first to know? How did they find out? Did the aliens tell them?

Like I previously posted in this thread.

I am going to create a new unit of measure of distance, which is called the dltios. The dltios is defined as the length of the path that light travels in vacuum in 1 second.

Therefore, the speed of light is 1 dltios/second.

Do you understand that concept?

 

[arfa brane]

I understand that Motor Diddy resorts to obfuscation and changes the topic on a regular basis, in order to avoid questions about his supposed logic.

Look, idiot, if you want to use 1 second as the basis for your new unit of distance, how do you measure it? You realise (no, you don't realise) that 1 second is measured, it is not an assumed "universal" interval of time, except here on planet earth (or, in your case, planet janet).

 

[Motor Daddy]

I understand that Motor Diddy resorts to obfuscation and changes the topic on a regular basis, in order to avoid questions about his supposed logic.

Look, idiot, if you want to use 1 second as the basis for your new unit of distance, how do you measure it? You realise (no, you don't realise) that 1 second is measured, it is not an assumed "universal" interval of time, except here on planet earth (or, in your case, planet janet).

Again you fail to grasp the concept and resort to name calling. This is my last response to you, as you can't have an adult discussion without resorting to childish tactics.

I just showed you that the unit of measure is not important, that it's the constancy of the speed of light that is used to define a unit of measure of distance.

 

[arfa brane]

I just showed you that the unit of measure is not important, that it's the constancy of the speed of light that is used to define a unit of measure of distance.

No, you didn't "show me" anything.

Units are important, actually. Very much so. And in particular, standard units of measurement.
That's the reason units are defined, so we can measure physical "things", like distance, work, power and all that useful stuff.

Your insistence that the speed of light is constant and does NOT need to be measured has a gaping hole in it, which you are either too stupid to see, or you are being deliberately obtuse to wind people up--as in: "shit, can anyone really be that dumb?".

The gaping hole is that you can't, nor can anyone, even claim that the speed of light in a vacuum is constant, without measuring it.

Your claim that you don't need to measure it is false. Someone must have measured it at some point in the history of science, or how could we have a definition otherwise?

How did you get onto this definition, was it carved in stone tablets and handed to you?

 

[quantum_wave]

Again, if light travels at a constant speed in space, from its point of origin in space, it is physically impossible for all frames to measure the speed of light to be the same in their own frame, using the standard meter and second.

Einstein has no way of determining the absolute velocity of a frame, so in order to say the speed of light is constant in all frames, he invents time dilation and length contraction, as ways to get around using the standard meter and second, so that his numbers don't lead to contradictions.

So he HAS TO assume length contraction and time dilation in order for his numbers to work.

If one uses Einstein's methods to see if the numbers match with measurements, the numbers are consistent using time dilation and length contraction. The problem is that Einstein still doesn't know the absolute velocity of the frame, relative to the constant speed of light in space.

So in my method, I don't need time dilation and length contraction, because I know the absolute velocity of the frame, and I know the speed of light is constant in space, and I know that the speed of light is measured to be different in every frame because of the absolute velocity of the frame.

For the most part, on the central issue, I think you are right to describe your postulate that way. It is true that Einstein started with two givens, the speed of light and the principle of relativity. In order to reconcile the apparent inconsistency he took the position that he could define a coordinate system that made the speed of light the same in all frames. Lorentz transformations do that.

From that coordinate system the concepts of SR time dilation and length contraction are derived and are logically sound.

From your coordinate system how do you account for the fact that clocks will measure time at different rates from different frames that are in relative motion to each other.

 

[arfa brane]

Just to hammer home my point about MD's rather pointless logic:

Light travels at a constant speed in space. We define the meter by the length of the path that light travels in 1/299,792,458 of a second.

So we have that:
1. The speed of light is constant because it travels 299,792,458 metres in 1 second.
2. The speed of light is constant because the metre is defined, and is a constant, likewise the second is a defined constant.
3. The speed of light is constant because it's defined in terms of other constants.
4. The speed of light is constant because the metre is defined by the distance light travels in 1 second.
5. The speed of light is constant because the second is defined by the time it takes light to travel 299,792,458 metres, which are defined by the distance light travels in 1 second.
6. The speed of light is constant because the metre and the second are constants.
7. The speed of light is constant because the speed of light is constant.

So, if you define a distance in terms of the speed of light, and a time interval in terms of the distance light travels, you define light in terms of itself, without measuring anything.

If the speed of light in different frames of reference is different, the problem of measuring it becomes a problem of finding a frame of reference which is at absolute rest. This means, because the surface of the earth is not at rest, that the definition of the speed of light is wrong. We will not be able to determine the correct value unless we can find a frame of reference which is motionless w.r.t. everything else in the universe.

The reason we measure the speed of light to be the same in all frames, is because we don't know how to locate an absolute frame of rest. Since we measure different speeds in different frames according to their motion relative to an absolute frame of rest, we can't tell if the speed of light is, in fact, constant--it's always measured to be different in different frames.

. . .

The above (which is the guts of MD's "theory") is a pile of steaming turds, of course. We DO measure the speed of light in different frames moving relative to each other, and we always measure the same constant speed.
That's why the speed of light is defined as a constant, in terms of constant distance and time. That's reality. Reality sometimes doesn't agree with half-assed ideas.

 

[Neddy Bate]

MD only needs one single emission of a sphere of EM to deal with while you are suggesting multiple emissions and saying problems would creep in if MD was right.

I can't concede MD's whole argument on your scenario yet. I would like some more analysis that considers the points I have mentioned that differ from your scenario but you certainly are bringing up what could be a troubling scenario to MDs postulate if my hesitation is set aside.

I only need one emission, just like MD. Let's say the GPS satellite emits for only one instant and then shuts itself off. From MD's absolute frame, you should see an expanding, hollow sphere of electromagnetic radiation expanding away from the emission point, and toward the earth. But the earth can easily be moving away from the expanding sphere, because the earth is most certainly not sitting at rest in MD's absolute frame. So it should not be unreasonable to think that the signal from the GPS satellite might take an extra second or so to reach earth, compared to how long it would reach if the speed of light were constant in the earth frame.

So, when the expanding sphere finally reaches the GPS receiver on earth, the information it was carrying is about one second older than it should be for the GPS receiver to function properly. If the information that the signal was carrying happened to be the time on the satellite's clock, or the location of the satellite relative to the earth's surface, that information would be about one second late compared to what it should be if the speed of light were constant in the earth frame.

The GPS system cannot work properly if the information from the satellites does not arrive at a predictable time after it was emitted from the satellites. Yet, if MD's idea where correct, the GPS system would never have worked, at least not until the system accounted for the "absolute speed" of the earth. If that had happened, the theory of relativity would have long since been replaced with something similar to Motor Daddy's theory.

 

[quantum_wave]

I only need one emission, just like MD. Let's say the GPS satellite emits for only one instant and then shuts itself off. From MD's absolute frame, you should see an expanding, hollow sphere of electromagnetic radiation expanding away from the emission point, and toward the earth. But the earth can easily be moving away from the expanding sphere, because the earth is most certainly not sitting at rest in MD's absolute frame. So it should not be unreasonable to think that the signal from the GPS satellite might take an extra second or so to reach earth, compared to how long it would reach if the speed of light were constant in the earth frame.

So, when the expanding sphere finally reaches the GPS receiver on earth, the information it was carrying is about one second older than it should be for the GPS receiver to function properly. If the information that the signal was carrying happened to be the time on the satellite's clock, or the location of the satellite relative to the earth's surface, that information would be about one second late compared to what it should be if the speed of light were constant in the earth frame.

The GPS system cannot work properly if the information from the satellites does not arrive at a predictable time after it was emitted from the satellites. Yet, if MD's idea where correct, the GPS system would never have worked, at least not until the system accounted for the "absolute speed" of the earth. If that had happened, the theory of relativity would have long since been replaced with something similar to Motor Daddy's theory.

I hear you Ned. You probably are entirely correct and if so you are saying that this single transmission will be measured to be traveling at the same speed whether measured from the source or measured from earth which has relative motion to the source. Given all of the appropriate adjustments for SR time dilation, gravitational time dilation, possible frame dragging, etc., I can't dispute that the GPS system accuracy may very well falsify MD's postulate. However, the known adjustments required for the system to work, specific frequencies, very slight inaccuracies, unknowns as to the effect of frame dragging, the types of motion involved, and the theoretical nature of calculations like time dilation of both types etc. make me concerned that the postulate is not falsified given your efforts so far.

Give me a clean set up, maybe a granite platform, light source, etc. and emit a burst, measure its speed, and then measure its speed from another frame that is in sufficient motion relative to the source to produce meaningful results and let's talk. What is sufficient motion, it would have to be meaningful but I can't quantify it for MD.

The thing is that if the same wave front is measured from two frames that are in sufficient relative motion, you are expecting and confident that it will appear to be traveling at the same speed. MD is questioning the logic of that saying that if your are right, that would require the wave front to change speed as it expands through space depending on the frame from which it is measured. That is the simple issue.

Tell me if you can see his point or not, and confirm that your view of the effectiveness of the GPS system does in fact test the postulate with sufficient controls to falsify the claim to an independent observers satisfaction.

 

[Neddy Bate]

I hear you Ned. You probably are entirely correct and if so you are saying that this single transmission will be measured to be traveling at the same speed whether measured from the source or measured from earth which has relative motion to the source.

All I'm saying is that the signals from all of the satellites must travel at a constant speed relative to the earth, otherwise GPS would not work as designed. MD's whole argument has been that we should be able to determine the absolute speed of the earth by comparing the different travel times of light signals. The fact that GPS works demonstrates either MD is not correct, or that the earth is always at absolute rest.

Given all of the appropriate adjustments for SR time dilation, gravitational time dilation, possible frame dragging, etc., I can't dispute that the GPS system accuracy may very well falsify MD's postulate. However, the known adjustments required for the system to work, specific frequencies, very slight inaccuracies, unknowns as to the effect of frame dragging, the types of motion involved, and the theoretical nature of calculations like time dilation of both types etc. make me concerned that the postulate is not falsified given your efforts so far.

I suppose you are saying that the earth's "absolute motion" might be small enough that GPS cannot detect it. I don't think so, because even if the sun happened to be at rest in MD's absolute frame, the earth still averages 29.78 km/s relative to the sun. That is almost 0.01% of the speed of light. If the speed of light varied by 0.01% throughout the year, I think it would show up as a large inaccuracy in GPS. Any anisotropy of light speed would certainly raise some eyebrows in the physics community.

Give me a clean set up, maybe a granite platform, light source, etc. and emit a burst, measure its speed, and then measure its speed from another frame that is in sufficient motion relative to the source to produce meaningful results and let's talk. What is sufficient motion, it would have to be meaningful but I can't quantify it for MD.

You don't need a granite platform. Even MD allows for the possibility that a light source can be in motion. He claims that all light signals travel at a speed of 299,792,458 m/s relative to an absolute frame. He then reasons that one can determine one's own absolute speed by measuring how much the speed of light deviates from 299,792,458 m/s in one's own frame. For example, if a reference frame measures light to move at 299,792,457 m/s in one direction, and 299,792,459 m/s in the opposite direction, then MD calculates the absolute speed of that reference frame to be 1 m/s.

The thing is that if the same wave front is measured from two frames that are in sufficient relative motion, you are expecting and confident that it will appear to be traveling at the same speed. MD is questioning the logic of that saying that if your are right, that would require the wave front to change speed as it expands through space depending on the frame from which it is measured. That is the simple issue.

My GPS argument only demands that the speed of light must be constant relative to the earth. MD clearly argues that the speed of light can only be constant on earth if the earth is at absolute rest. So, GPS proves that either MD is wrong, or the earth is at absolute rest.

Tell me if you can see his point or not, and confirm that your view of the effectiveness of the GPS system does in fact test the postulate with sufficient controls to falsify the claim to an independent observers satisfaction.

Well, in the past, MD generally was not very interested in any explanation for how the speed of light could be constant in any reference frame other than his own absolute rest frame. Now that his own idea has been demonstrated to be incorrect, perhaps now he will ask some questions about how relativity works.

 

[quantum_wave]

My GPS argument only demands that the speed of light must be constant relative to the earth. MD clearly argues that the speed of light can only be constant on earth if the earth is at absolute rest. So, GPS proves that either MD is wrong, or the earth is at absolute rest.

When I questioned him about his view he conveyed his postulate by saying, and I paraphrase, that if the same wave front is measured from two frames that are in sufficient relative motion, current theory says that you are expecting and confident that it will appear to be traveling at the same speed. MD is questioning the logic of that saying that if your are right, that would require the wave front to change speed as it expands through space depending on the frame from which it is measured. That is the simple issue.

Well, maybe not simple after all the debate. One, you have to be able to assume a single wave front expanding spherically from a point in space. Two, you have to be able to contemplate the speed of that wave front being measured by an observer who is in relative motion to the source of the light. Unless that wave front has some way to adjust its speed through space it will be measured to be traveling at c plus or minus the velocity of the relative frame according to the postulate.

That is the extent of what I interpret from what MD said to me. Other claims he has made that modify that postulate could certainly change the nature of the discussion. However, he seems to stand by how he explained it to me according to his statement that he thought I understand his intention.

 

[origin]

When I questioned him about his view he conveyed his postulate by saying, and I paraphrase, that if the same wave front is measured from two frames that are in sufficient relative motion, current theory says that you are expecting and confident that it will appear to be traveling at the same speed.

I am typing this very slowly in hopes that it will sink in this time. It is not theory it is actual measurement. The speed of light in a vacuum is always measured at the same speed regardless of the inertial frame.

MD is questioning the logic of that saying that if your are right, that would require the wave front to change speed as it expands through space depending on the frame from which it is measured.

Or we could use the special relativity (You know that robust theory that has been shown to be correct for 100 years) and realize that time and length contraction come into play. The wave front (speed of light) never changes speed in a vacuum.

 

[Motor Daddy]

All I'm saying is that the signals from all of the satellites must travel at a constant speed relative to the earth, otherwise GPS would not work as designed. MD's whole argument has been that we should be able to determine the absolute speed of the earth by comparing the different travel times of light signals. The fact that GPS works demonstrates either MD is not correct, or that the earth is always at absolute rest.

I never said I could calculate the absolute velocity of the Earth. I said that in Einstein's train example, the embankment MUST be at an absolute zero velocity in order for the lights to have been emitted simultaneously at A and B, and the lights strike the midpoint observer simultaneously. There is no other choice, the embankment MUST be at an absolute zero velocity. If you think that is impossible to be on Earth and have an absolute zero velocity, take it up with Einstein, he made the example, I didn't!!

My GPS argument only demands that the speed of light must be constant relative to the earth. MD clearly argues that the speed of light can only be constant on earth if the earth is at absolute rest. So, GPS proves that either MD is wrong, or the earth is at absolute rest.

Do you understand what it means to say the speed of light is constant in vacuum?

What you are saying when you say I'm wrong is that if there was a box in space within a box in space, the inner box traveling inside the outer box, that light will be measured to be the same speed in each box. That is simply impossible!!! You don't even realize what you are saying when you say light is always measured to be c in every frame.

Well, in the past, MD generally was not very interested in any explanation for how the speed of light could be constant in any reference frame other than his own absolute rest frame. Now that his own idea has been demonstrated to be incorrect, perhaps now he will ask some questions about how relativity works.

You haven't demonstrated anything other than your lack of understanding of the concept of the constant speed of light. I can prove that light can not be measured to be c in a box in space, regardless of where in the box you measure it. Maybe you forgot? I'll get the quote.

 

[Motor Daddy]

I am typing this very slowly in hopes that it will sink in this time. It is not theory it is actual measurement. The speed of light in a vacuum is always measured at the same speed regardless of the inertial frame.

Again, nobody disputes the speed of light is constant. You seem to have a problem understanding the difference between the speed of light, and the speed of the frame. Go figure, Einstein never understood it either.

 

[Neddy Bate]

When I questioned him about his view he conveyed his postulate by saying, and I paraphrase, that if the same wave front is measured from two frames that are in sufficient relative motion, current theory says that you are expecting and confident that it will appear to be traveling at the same speed. MD is questioning the logic of that saying that if your are right, that would require the wave front to change speed as it expands through space depending on the frame from which it is measured. That is the simple issue.

OK, well maybe you have a slightly different take on MD's argument. I don't think MD would have any problem with the idea that the speed of light would be measured to change when comparing different frames. For example, he says that the speed of light is 299,792 km/s in the absolute rest frame only. Thus, in a reference frame that has an absolute speed of 1,000 km/s, he says that the speed of light would be measured to be 298,792 km/s in one direction, and 301,792 km/s in the other direction.

On the other hand, it seems that you, quantum_wave, are concerned that if the speed of light could somehow be 299,792 km/s in all reference frames, that the wave front would have to change speed? Perhaps reading too much MD has got you all confused?

Well, maybe not simple after all the debate. One, you have to be able to assume a single wave front expanding spherically from a point in space. Two, you have to be able to contemplate the speed of that wave front being measured by an observer who is in relative motion to the source of the light. Unless that wave front has some way to adjust its speed through space it will be measured to be traveling at c plus or minus the velocity of the relative frame according to the postulate.

Yes, according to MD's postulate, the speed would be measured to be different.

That is the extent of what I interpret from what MD said to me. Other claims he has made that modify that postulate could certainly change the nature of the discussion. However, he seems to stand by how he explained it to me according to his statement that he thought I understand his intention.

Oh, okay, I think I see what you mean now. You are saying that, in order for Einstein's light postulate to hold true, the speed would have to change from c+v (for example) to c. That is true enough, and it can be explained. Relativity employs these three means to achieve that end:

1. time dilation
2. length contraction
3. relativity of simultaneity

You can derive all of these things from Einstein's two postulates.

 

[James R]

Do you understand what it means to say the speed of light is constant in vacuum?

What you are saying when you say I'm wrong is that if there was a box in space within a box in space, the inner box traveling inside the outer box, that light will be measured to be the same speed in each box. That is simply impossible!!!

Your gut feelings and wishful thinking and fantasy universes are neither here nor there. These things, despite being "impossible" according to you, are actually how the universe works when you go test it.

 

[Motor Daddy]

According to the following, tell me which direction you measure the speed of light to be c, Neddy Bate.

I have a partial equation that finds the velocity of x, and the time to the receiver at x, if the y time is known, and the y and z component velocities are zero, which goes like this:


v(x)=sqrt(t(y)^2-l(y)^2)/t(y)
t(x)=l(x)/(c-v(x))




Using the same cube with sides of length 1 light second, and a source at the center of the cube with receivers in the center of the x,y, and z walls, given a y and z time of .65 seconds, I know the x component velocity and the x component time to receiver.



x time= 1.384930 seconds
y time= .65 seconds
z time= .65 seconds

x component velocity = 0.638971 c
y component velocity = 0 c
z component velocity = 0 c

The location of the y receiver at .65 seconds is (0.41533, .5, 0)

x= .65(.63897c)=.41533
y= .5


(0.41533, 0.5, 0)
d = sqrt(0.41533^2 + 0.5^2 )
d = sqrt(0.1724990089 + 0.25)
d = sqrt(0.4224990089)
d = 0.65 light seconds



Does that look right for a zero y and z component velocity?

BTW...look what v=(ct-l)/t says the x component velocity is:

v(x)=(1.384930-.5)/1.384930

v(x)=.63897 c

 

[Neddy Bate]

I never said I could calculate the absolute velocity of the Earth.

You had said that you could calculate the absolute speed of a box from inside the box. You would take light measurements in various directions, and then you would calculate the absolute speed of the box. Well, the earth is just like a box, so you should be able to calculate it's absolute speed, shouldn't you? In fact, the GPS system has done all the work for you. It measures the speed of light to be constant, in all directions, relative to earth. This either proves you are wrong, or it proves the earth is at absolute rest. Take your pick!

Do you understand what it means to say the speed of light is constant in vacuum?

I understand what it really means, and I also understand what you think it means.

What you are saying when you say I'm wrong is that if there was a box in space within a box in space, the inner box traveling inside the outer box, that light will be measured to be the same speed in each box. That is simply impossible!!! You don't even realize what you are saying when you say light is always measured to be c in every frame.

Yes, that is what I am saying, the speed of light in the inner box would be c, and the speed of light in the outer box would also be c. It is not impossible. it has to do with:

1. Time dilation
2. length contraction
3. Relativity of simultaneity

Of course if you refuse to consider those things, then you will continue to say it is "simply impossible".

You haven't demonstrated anything other than your lack of understanding of the concept of the constant speed of light. I can prove that light can not be measured to be c in a box in space, regardless of where in the box you measure it.

I have demonstrated that GPS can only function properly if the speed of light is constant relative to the earth. The GPS does function properly. Therefore, according to you, that means the earth is at absolute rest, right?