# Thread: On Einstein's explanation of the invariance of c

James R, Will you be responding to me about your ship? What do you think the length of the ship is? What do you think the velocity of the ship is? Do you agree with my numbers?
Briefly, I agree with your numbers, but not in any absolute sense. The numbers you obtain using your method would be those you'd obtain standing on ANY moving object watching the spaceship go past at speed c/2. Notice how I set the problem up without specifying who was measuring the one-way light travel times? In other words, I wasn't specific about a particular reference frame. However, the numbers I constructed for the travel times of light do determine a unique relative speed for the spaceship. It is important to realise that your method of calculation does NOT give any absolute speed.

So, for this particular problem, the most you can say is that whoever did the measuring of the light travel times was moving at a relative speed of c/2 relative to the spaceship when they made the measurements. What you CANNOT conclude is that the spaceship was travelling at c/2 relative to some "absolute zero speed" reference frame.

Now, if I were to take the same light travel events and measure them in a different frame, I would measure different travel time intervals and, applying your same calculational procedure, calculate a different relative speed.

For example, suppose I measured those one-way travel times in the frame of the spaceship. In that case, I would find, experimentally, that the light travel times were the same in both directions, and I would therefore calculate that the speed of the ship was zero relative to the ship's reference frame. No surprises there.

At this point, therefore, Motor Daddy, we don't have a disagreement about mathematics (with a couple of caveats I'll mention below). What we disagree about is how the universe actually works. You imagine that you'll always measure two different travel times for any object in motion relative to your hypothetical "absolute zero speed" reference frame. But actual, real-world experiments say different. They show that Einstein's two postulates of relativity do not mandate an "absolute zero speed" reference frame. In fact, they say that the laws of physics apply equally in ALL frames of reference and that there are no preferred frames.

Now, there's no way I can convince you of the truth of Einstein's posulates by arguing about them or showing you the maths, just as there is no way you'll ever convince me of your absolute reference frame by specifying calculation methods or making assertions. The final arbiter of who is right and who is wrong is nature herself. We have to look at what real-world experiments and observations tell us. We need to see what our respective theories predict, then do the experiment, then see who was right and who was wrong.

As a matter of fact, there are literally millions of separate experiments that show that Einstein was right and you are wrong. Many of those experiments use methods that go way beyond your direct measurements of times and distances. There are relativistic effects you probably have never heard of which have been verified as accurate to tens of decimal places. But the theory that has been verified rests on just those same two postulates that apply to basic measurements.

You avoided the question when I asked you whether you believed in $E=mc^2$, for example. If you do, then you either have to believe in Einstein's spacetime (since that is where the equation comes from), or you have to produce some way of deriving the equation using your absolute picture. There's no other option, because the validity of the equation itself has been established experimental beyond all doubt.

You also avoided the question when I asked you for your explanation of why no material object has ever been measured as travelling faster than the speed of light. Einstein easily explains this observation. Can you?

To take one other example at random, your theory cannot calculate observed Doppler shifts of light correctly. Einstein's can. If the police used your theory to calibrate their radar guns, they'd get the wrong answers.

My numbers prove Einstein got it wrong!
Your numbers don't prove anything about Einstein's theory. All you have done, essentially, is to work in the ground reference frame and then imagine that that particular frame has absolutely zero velocity, without even realising that that's what you're doing.

You don't seem to have any real ability to even imagine how things translate between reference frames. You're firmly anchored to the reference frame of the ground under your feet, and when it comes down to it, you really believe that the ground is (absolutely) not moving.

In my example with the spaceship, there's in fact some other effects that I haven't even mentioned in our recent discussions. It is a theoretical and experimental fact that that time dilation and length contraction occur, for example, so the spaceship in my hypothetical scenario actually has a different length in its rest frame compared to the frame that you worked your calculations in (and that I implicitly set up the problem in). Now, you can and will deny these things along with the rest of what follows from Einstein's postulates, but as with the rest these are empirical facts, not just theoretical ones like your ones are.

When you understand the concept that light always travels in space the same distance in the same time then maybe you will start to understand why we use light to define a meter. Until then, you don't have a clue what I'm talking about.
This is a statement you are very fond of repeating. In fact, every first-year undergraduate with a week of lectures on Einstein's relativity understands that light travels in space the same distance in the same time. What those first-year students understand that you do not is that this fact is true in any reference frame. Moreover, they understand that the only way that it can be true in all reference frames is if our intuitive ideas of space and time are altered in the way that Einstein derived from his posulates.

What you mean when you make your statement is that you think there is a single preferred reference frame, and light always has the same speed in that one frame. You actually believe that it is impossible to make valid measurements in any other frame, and so it really makes no sense to even try to measure the speed of light in any other frame, let alone the speed of some other object.

You're clearly limited in the extent to which you can visualise different reference frames. Essentially, you always imagine only one frame and you're unable to mentally translate yourself into any different frame. You're always outside the train watching it go past; you don't seem to have the capacity to put yourself inside to see what happens there. And so you imagine that light travel times inside a moving train will always be different in the two directions. In actual fact, if you're inside the train, the light travel times are always the same in both directions. That's an experimental fact, not an imagined one.

Here's another example your theory can't cope with:

Suppose I'm on a train travelling along the track at 0.8c. I fire a missile (or throw a ball or whatever) at 0.5c relative to the train, in the same direction the train is moving relative to the track.

Question: how fast does somebody standing on the track see that ball moving?

Your answer will be 0.5c if you think all speeds are absolute and relative speeds are impossible or make no sense. Or, your answer will be 1.3c, because you believe that the track is an absolute frame and, more importantly, you believe in an absolute time and space that does not really exist. No other answers even begin to occur to you.
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I'm not sure whether you're familiar with the history of Einstein's theory and the questions in physics that led to its development. Have you heard of the Michelson-Morley experiment, which explicitly aimed to determine the speed of the Earth relative to your hypothetical "absolute zero speed" reference frame (at that time known as the "luminiferous aether")? It was found that the experiment always gave a result of zero, no matter what time of day it was performed, in what direction the apparatus was oriented etc. So, was the Michelson-Morley laboratory lucky enough to be the centre of the universe, absolutely stationary at all times? Or could there be some other explanation for the null results?

Why did physicists think there ought to be an "absolute zero speed" frame in the first place? Well, are you familiar with Maxwell's electromagnetic theory? It predicts a constant speed of light, irrespective of reference frame. In other words, the equations of electromagnetism (a) work in all reference frames, and (b) predict the same speed of light in every frame.

All well and good, you say, because the speed of light is a defined constant that never changes, you say. But your theory predicts mathematically that the speed of light, as determined by Maxwell's equations, should not be the same in every frame. You don't know it does that because you're probably unable to transform Maxwell's equations from one frame to another. But I can do it, and I know the answer. Worse still, your absolute-zero frame stuff doesn't even maintain the existence of travelling light waves between frames. It predicts that if you jump on a moving train, you won't see any light at all, let alone be able to measure anything with it, because your theory predicts that travelling light waves cannot exist in any reference frame except the "absolute zero speed" frame - a silly result that can be shown to be false just by you taking a quick stroll around with your eyes open so you can see stuff.

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In summary, Motor Daddy, we have reached an impasse. No argument you can make about how you imagine light behaves can possibly convince me that it behaves in the way you imagine, because I know it doesn't behave like that from experimental results. But worse, nothing I write here can convince you that your imaginings are wrong, either, because they're all you have. I don't think you're equipped to understand much of the physical theory that led to Einstein's relativity. I doubt you have the mathematical background necessary even to understand the basic results or derivations of the theory itself. If you are aware of any of the experimental evidence, probably you have some explanations of how the expermentals are all flawed because all physicists for the past 130 years have been stupid and only you would have done the experiments correctly. But I'm guessing you're probably only aware of one or two experiments anyway, if any.

Some people try to attack Einstein's theory of special relativity by claiming that it is self-inconsistent. You're welcome to try that if you like. So far, as far as I can see you haven't made that particular claim, which is probably the most common one we see from crackpots here. You have claimed that Einstein's theory gives answers that are inconsistent with observation, but the only way you can support those claims is to point to actual experimental results that contradict the theory. Thought experiments in which measurements taken using light on a moving train, wherein the light has different travel times in each direction in the reference frame of the train won't cut the mustard. That kind of thing doesn't happen in reality; it only happens in your imagination.

To conclude, I think we've gone about as far as we can go with this, unless you can show some kind of fatal theoretical or experimental problem with Einstein's relativity, or you can show some experimental evidence for your theory.

2. You could perhaps get past this impasse by each giving a little ground.

James: you can give a little by acknowledging the issue with Einstein clock synchronization. Apologies if you have already, this is a long thread. You could also agree to employ the CMBR as a defacto "absolute reference frame”. You can gauge your motion through the universe from it. See CMBR dipole anisotropy. It isn’t something that’s "inside the box" of Lorentz-invariant local phenomena, but it is something real rather than hypothetical. If you see it as blue-shifted in one direction and red-shifted in the opposite direction, you’re headed in the blueshift direction.

MotorDaddy: you can respond by considering your clocks to be light clocks. A light clock is often a hypothetical parallel-mirror device, as per the simple inference of time dilation. A more realistic clock might be an atomic clock, but that’s essentially a light clock too. See the NIST caesium fountain clock, and note that it employs lasers and a microwave cavity along with hyperfine transitions, which are electromagnetic phenomena. Then you apply the same principle to yourself, because you’re made of electrons et cetera. Just like all material bodies. And electrons have an electromagnetic nature, just like light.

Both: when the light-clock “slows down” to half its former tick rate because you’re moving fast through the universe, you don’t notice it locally, because you’re “slowed down” too. You can however detect it if you use a pulsar for calibration. Then you can work out that it takes twice as long for the light to travel between the parallel mirrors. But look closely at what your clock is doing. It isn’t clocking up time per se, it’s “clocking up” the motion of light. You define your second using what you perceive to be the motion of light, then you use it to measure the motion of light. Hence you always measure it to be the same. It doesn’t matter whether you face forwards or backwards when doing this, because material bodies like rods and clocks are subject to the Lorentz transformation space/time skew. You measure time using the motion of light. You measure distance using the motion of light. When you move fast through the universe, your measures change, but so do you, so locally you can’t tell.

3. I should add that whilst Einstein started with the constant speed of light as a postulate in 1905, but by 1911 he'd changed his mind. Here’s a few quotes from 1911 thru 1916:

"If we call the velocity of light at the origin of co-ordinates co, then the velocity of light c at a place with the gravitation potential Φ will be given by the relation c = co(1 + Φ/c²)".

"On the other hand I am of the view that the principle of the constancy of the velocity of light can be maintained only insofar as one restricts oneself to spatio-temporal regions of constant gravitational potential"

"I arrived at the result that the velocity of light is not to be regarded as independent of the gravitational potential. Thus the principle of the constancy of the velocity of light is incompatible with the equivalence hypothesis"

"the writer of these lines is of the opinion that the theory of relativity is still in need of generalization, in the sense that the principle of the constancy of the velocity of light is to be abandoned."

Note the word “velocity” in the above. He didn't actually say velocity. He said geschwindigkeit, which translates into speed. It's clear he meant speed because c is not a vector quantity. Have a read of The Other Meaning of Special Relativity for something that's rather less black and white.

4. Originally Posted by James R

Briefly, I agree with your numbers, but not in any absolute sense. The numbers you obtain using your method would be those you'd obtain standing on ANY moving object watching the spaceship go past at speed c/2.

You have to agree with my numbers because they are absolute facts. If you don't agree with them then you must be using some wrong formula or performing your calculations wrong. Those numbers were arrived at using the very definitions of distance and time as we've defined them. They were not arrived at by using some formula from some theory using time dilation, length contraction etc.., they were arrived at using basic math that we all know to be true. There are no other objects, remember? You gave me the times you measured from within the ship. What other object are you talking about? You never mentioned another object in your thought experiment. The ship is the only object in space. I don't know why you want to refer to other objects when for one, the ship is the ONLY object, and for two, we are talking about the velocity and length of the ship as measured from within the ship. You don;t previously know the length of the ship, and you certainly don't know the velocity of the ship. You seem to believe you know the length of the ship prior to using light to measure it???

Originally Posted by James R
Notice how I set the problem up without specifying who was measuring the one-way light travel times? In other words, I wasn't specific about a particular reference frame. However, the numbers I constructed for the travel times of light do determine a unique relative speed for the spaceship. It is important to realise that your method of calculation does NOT give any absolute speed.

You are on board the ship and you measured the one-way times on the ship. You are measuring the velocity and the length of the ship from within the ship. Of course it's an absolute speed. The measurements were taken using light, and light has an absolute speed in space. Every object has an absolute speed in space. In order for any object to be in motion it must travel in space. If two objects travel together in space they will travel relative to each other, but they are still traveling in space. You can not travel unless you travel in space! If someone is riding a horse, the horse is traveling in space and the person riding is also traveling in space. The motion of each the horse and the person happen to coincide with each other for the moment, but they each are traveling in space. Do you not understand that?

Originally Posted by James R
So, for this particular problem, the most you can say is that whoever did the measuring of the light travel times was moving at a relative speed of c/2 relative to the spaceship when they made the measurements. What you CANNOT conclude is that the spaceship was travelling at c/2 relative to some "absolute zero speed" reference frame.

There was no external frame or person measuring the times. You were in the ship measuring the times. Why do you now want to say there is an external frame? You didn't say that in the experiment. Space doesn't travel, it is just volume. Infinite volume doesn't travel, it just is. We use light to define distance in that volume. What do you mean there is no absolute zero speed? Speed of what, an infinite volume?? We measure the amount of time an object takes to travel from point a to point b in the volume. We use light travel time to base our unit of measure of distance, the meter, because light speed is constant. You don't get that and probably never will.

Originally Posted by James R
Now, if I were to take the same light travel events and measure them in a different frame, I would measure different travel time intervals and, applying your same calculational procedure, calculate a different relative speed.

Relative to what?? You are using light to measure the ship's velocity and length from within the ship. There are no other objects to relate to as far as you are concerned. You seem to be stuck on wanting to know your speed in relation to another object? Why is that, because you don;t know how to determine your own speed in space? Go figure, as that was Einstein's problem, he couldn't figure out how to measure an object's velocity in space. Of course not, nobody ever did that before, and he couldn't figure it out himself. Since he couldn't know the velocity of the ship, the only way he could measure any kind of motion was to relate to another object. Great, you can talk about motion compared to another object, but that says nothing about each object's motion in space!

Originally Posted by James R
For example, suppose I measured those one-way travel times in the frame of the spaceship. In that case, I would find, experimentally, that the light travel times were the same in both directions, and I would therefore calculate that the speed of the ship was zero relative to the ship's reference frame. No surprises there.

NO! No you wouldn't find the times were the same. You are basing your incorrect assumptions on the fact that Einstein thinks the length of the plane is the round trip time divided by two, which gets the length wrong. You are basing your incorrect assumption on the fact that the ship has a velocity in space, and you have no way of knowing that velocity. Einstein doesn't know the velocity of the ship, period!!! Since he doesn't know the velocity of the ship he CAN"T know the length of the ship. His problems snowball from there.

Originally Posted by James R
At this point, therefore, Motor Daddy, we don't have a disagreement about mathematics (with a couple of caveats I'll mention below). What we disagree about is how the universe actually works. You imagine that you'll always measure two different travel times for any object in motion relative to your hypothetical "absolute zero speed" reference frame. But actual, real-world experiments say different. They show that Einstein's two postulates of relativity do not mandate an "absolute zero speed" reference frame. In fact, they say that the laws of physics apply equally in ALL frames of reference and that there are no preferred frames.

I have a disagreement about Einstein's mathematics, as I've pointed out. What you mean is that you can't possibly disagree with mine, because they are as sound as sound gets. They are basic simple math using the very definitions of distance and time as we have defined them. These numbers simply can't be refuted. They simply can not. It is impossible!! However, I refute Einstein's numbers on a daily basis using my dead accurate numbers.

Originally Posted by James R
Now, there's no way I can convince you of the truth of Einstein's posulates by arguing about them or showing you the maths, just as there is no way you'll ever convince me of your absolute reference frame by specifying calculation methods or making assertions. The final arbiter of who is right and who is wrong is nature herself. We have to look at what real-world experiments and observations tell us. We need to see what our respective theories predict, then do the experiment, then see who was right and who was wrong.

You dare not show me Einstein's numbers, as I already know you get the length wrong, and he doesn't know the velocity of the ship. Basically he has no numbers, he RELIES on measuring motion in relation to another object's motion, of which he also doesn't know the velocity and length of. His method is laughable.

Originally Posted by James R
As a matter of fact, there are literally millions of separate experiments that show that Einstein was right and you are wrong. Many of those experiments use methods that go way beyond your direct measurements of times and distances. There are relativistic effects you probably have never heard of which have been verified as accurate to tens of decimal places. But the theory that has been verified rests on just those same two postulates that apply to basic measurements.
Those experiments use his method to arrive at a result, of which is consistent with his method using his math. Hence forth, since I can find the velocity of the ship and actual length of the ship from withing the ship using one-way times, I can call his numbers crap! Show me the experiments involving one-way times that prove his theory correct. Show me one of the million experiments that uses one-way times using my sync method. Just one.

Originally Posted by James R
You avoided the question when I asked you whether you believed in $E=mc^2$, for example. If you do, then you either have to believe in Einstein's spacetime (since that is where the equation comes from), or you have to produce some way of deriving the equation using your absolute picture. There's no other option, because the validity of the equation itself has been established experimental beyond all doubt.
C^2 is an acceleration. It is 186,000 meters per second per second. We are talking about velocity, which isn't squared, it is 186,000 miles per second. Two different animals.

Originally Posted by James R
You also avoided the question when I asked you for your explanation of why no material object has ever been measured as travelling faster than the speed of light. Einstein easily explains this observation. Can you?
His method can't measure a speed faster than light so how would he know? We measure motion relative to light. I'm not saying an object of mass could ever travel faster than light, but there may come a time when we need to measure a velocity greater than the speed of light, and Einstein's method will fall flat on its face trying to do so, mine doesn't. His sync method is absurd! It is inconsistent with the very nature of time and simultaneity. ALL motion takes time to occur. He disregards the time it takes light to travel from one clock to the other. That is crazy talk. By the very definition, light takes time to travel. You can;t say light left one clock at 12:00:00 and arrived at the other clock a distance apart and arrived there at 12:00:00. That means light travels instantaneously. Change takes time to occur! Nothing travels instantly, no matter how fast it travels or how short of a distance it travels.

Originally Posted by James R
To take one other example at random, your theory cannot calculate observed Doppler shifts of light correctly. Einstein's can. If the police used your theory to calibrate their radar guns, they'd get the wrong answers.
My theory is the very nature of Doppler. The very nature of a source emitting light and the light traveling away from the point in space it was emitted, and then the source could also have its own motion, traveling away form the point in space it was when it emitted the light. That means the source is closer to one side of the light sphere than the other side of the light sphere. You can measure the velocity of the source in space by knowing the light travel times, as I've clearly shown. The sources velocity is relative to light. The sources velocity is the motion of the source in space!

Originally Posted by James R
Your numbers don't prove anything about Einstein's theory. All you have done, essentially, is to work in the ground reference frame and then imagine that that particular frame has absolutely zero velocity, without even realising that that's what you're doing.
There is no ground in your example. You simply don;t understand what is being measured and how it is being measured. I am measuring the ship's velocity and length in space against light travel time. That tells me how far the ship traveled in space. It has NOTHING to do with a ground with a zero reference frame. Of course if a ground was measured to be at a zero velocity it would show equal times. Would you expect anything different from a zero velocity frame?

Originally Posted by James R
You don't seem to have any real ability to even imagine how things translate between reference frames. You're firmly anchored to the reference frame of the ground under your feet, and when it comes down to it, you really believe that the ground is (absolutely) not moving.
Again, I am taking about a frame's velocity and length in space. I told you the numbers and you agreed with them, even though you have no way of knowing the velocity and length using Einstein's methods. I make no mention of "ground" or any other frame for that matter. You are the one that keeps bringing up other frames. Of course my numbers are consistent will all objects motion in space, because my method measures length and velocity in space, not against another object. That other object will also have its own numbers in space, and the two sets of numbers will be consistent with one another. That is a rock solid fact!

Originally Posted by James R
In my example with the spaceship, there's in fact some other effects that I haven't even mentioned in our recent discussions. It is a theoretical and experimental fact that that time dilation and length contraction occur, for example, so the spaceship in my hypothetical scenario actually has a different length in its rest frame compared to the frame that you worked your calculations in (and that I implicitly set up the problem in). Now, you can and will deny these things along with the rest of what follows from Einstein's postulates, but as with the rest these are empirical facts, not just theoretical ones like your ones are.
The ship is at rest. What frame do you speak of? The ship is inertial, the velocity is not changing. The ship is not accelerating. What frame do you speak of that the ship's length is different? There is only a ship in space, and I told you the numbers. Maybe you can't accept the truth?

Originally Posted by James R
This is a statement you are very fond of repeating. In fact, every first-year undergraduate with a week of lectures on Einstein's relativity understands that light travels in space the same distance in the same time. What those first-year students understand that you do not is that this fact is true in any reference frame. Moreover, they understand that the only way that it can be true in all reference frames is if our intuitive ideas of space and time are altered in the way that Einstein derived from his posulates.
Einstein can't tell you the length of the ship because he doesn't know the velocity of the ship. I repeat that over and over and you seem to blow it off as just something I keep repeating. If you tell me there is two piles of apples, one pile has 4 apples and the other pile has 6 apples, then conclude there is 11 apples, and go on to give 11 people an apple each, you story is flawed at the beginning, as there are only 10 apples. I keep telling you there are only 10 apples, but you blow it off like some insignificant trivia, and then continue speaking about 11 apples. Stop right there! There is only 10 apples, and I will continue to tell you there is only 10 apples until you finally realize that you r story is meaningless talking about 11 apples. THERE IS ONLY 10 APPLES!!!

Originally Posted by James R
What you mean when you make your statement is that you think there is a single preferred reference frame, and light always has the same speed in that one frame. You actually believe that it is impossible to make valid measurements in any other frame, and so it really makes no sense to even try to measure the speed of light in any other frame, let alone the speed of some other object.
1. You are wasting your time measuring the speed of light.
2. Light travels in space. Space doesn't move. Light travel time defines distance in space.
3. I can measure any frame you like, and I will tell you the exact numbers. You on the other hand have no way of knowing a frames velocity or even its length.

Originally Posted by James R
You're clearly limited in the extent to which you can visualise different reference frames. Essentially, you always imagine only one frame and you're unable to mentally translate yourself into any different frame. You're always outside the train watching it go past; you don't seem to have the capacity to put yourself inside to see what happens there. And so you imagine that light travel times inside a moving train will always be different in the two directions. In actual fact, if you're inside the train, the light travel times are always the same in both directions. That's an experimental fact, not an imagined one.
Wrong. Using Einstein's sync method is mistake number 1. Assuming light takes no time to travel from one clock to the other clock is mistake number 2. Measuring round trip time and dividing by two is mistake number 3. Three mistakes that all those experiments are based on.

You say I can't visualize different frames? That's funny. I can tell you the speed of any object in the universe, and you can't tell me even one of the speeds. The only thing you can say about motion is that the car in front of you going down the highway in the same direction as you is either traveling the same speed as you, or is traveling a different speed. You don't know your speed so you certainly don't know his! As a matter of fact, you can't even say for sure how far the car is apart from you, as you have no clue of his length or your length! You live in Einstein's fantasy world, where nobody know the real length or velocity of an object in space!

Originally Posted by James R
Here's another example your theory can't cope with:

Suppose I'm on a train travelling along the track at 0.8c. I fire a missile (or throw a ball or whatever) at 0.5c relative to the train, in the same direction the train is moving relative to the track.

Question: how fast does somebody standing on the track see that ball moving?

Your answer will be 0.5c if you think all speeds are absolute and relative speeds are impossible or make no sense. Or, your answer will be 1.3c, because you believe that the track is an absolute frame and, more importantly, you believe in an absolute time and space that does not really exist. No other answers even begin to occur to you.
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There you go again, basing all your assumptions on a zero velocity track, and then go on to try and prove there is no zero velocity. Don't you see what you are doing?? I've repeatedly told you your problem, and yet you persist on doing the same thing over and over and over!

Originally Posted by James R
I'm not sure whether you're familiar with the history of Einstein's theory and the questions in physics that led to its development. Have you heard of the Michelson-Morley experiment, which explicitly aimed to determine the speed of the Earth relative to your hypothetical "absolute zero speed" reference frame (at that time known as the "luminiferous aether")? It was found that the experiment always gave a result of zero, no matter what time of day it was performed, in what direction the apparatus was oriented etc. So, was the Michelson-Morley laboratory lucky enough to be the centre of the universe, absolutely stationary at all times? Or could there be some other explanation for the null results?
Until you show me an experiment that used one-way times and sync'd clocks my way, I can not acknowledge any type of validity in your results. You get the lengths wrong. You don't know the velocities, and you use round trip times and divide by two. You continually measure the speed of light when it is already defined. Stop telling me there are 11 apples!

Originally Posted by James R
Why did physicists think there ought to be an "absolute zero speed" frame in the first place? Well, are you familiar with Maxwell's electromagnetic theory? It predicts a constant speed of light, irrespective of reference frame. In other words, the equations of electromagnetism (a) work in all reference frames, and (b) predict the same speed of light in every frame.

Light travels in space. Space doesn't have motion, objects in space have motion. Period!

Originally Posted by James R
All well and good, you say, because the speed of light is a defined constant that never changes, you say. But your theory predicts mathematically that the speed of light, as determined by Maxwell's equations, should not be the same in every frame. You don't know it does that because you're probably unable to transform Maxwell's equations from one frame to another. But I can do it, and I know the answer. Worse still, your absolute-zero frame stuff doesn't even maintain the existence of travelling light waves between frames. It predicts that if you jump on a moving train, you won't see any light at all, let alone be able to measure anything with it, because your theory predicts that travelling light waves cannot exist in any reference frame except the "absolute zero speed" frame - a silly result that can be shown to be false just by you taking a quick stroll around with your eyes open so you can see stuff.

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I already told you repeatedly how light travels in space and we use light to define distance. You don't understand that concept, otherwise you would not make the statements you do. I am the one that tells you how fast the train, or plane, or ship is traveling in space, relative to space. I am the one that tells you how to measure length using light. You can not tell the same. Show me one example such as your ship that you tell me the velocity of the ship and the length of the ship using light travel. Just give me one example, with no reference to any other object. YOU CAN'T DO IT!!! You can't because you don't know how to properly measure velocity and length using light. Einstein didn't know how, hence neither do you.

Originally Posted by James R
In summary, Motor Daddy, we have reached an impasse. No argument you can make about how you imagine light behaves can possibly convince me that it behaves in the way you imagine, because I know it doesn't behave like that from experimental results.

You only know that Einstein's methods are consistent. But what you don't understand is that they are consistently wrong, and I've shown why. I don;t expect you to believe me, as it is so deeply embedded in your brain that Einstein is right, that even the remote possibility of him being wrong is out of the question to you. You've been brainwashed into thinking as he did, in his imaginary world of objects only traveling in relation to the other. Great they do that, but in order to be in motion in the first place they must each have their own velocity. That is indisputable. An object's motion doesn't depend on another object's motion. The object has its own motion in space. We measure that motion with light, as light travel defines distance in space.

Originally Posted by James R
But worse, nothing I write here can convince you that your imaginings are wrong, either, because they're all you have. I don't think you're equipped to understand much of the physical theory that led to Einstein's relativity. I doubt you have the mathematical background necessary even to understand the basic results or derivations of the theory itself. If you are aware of any of the experimental evidence, probably you have some explanations of how the expermentals are all flawed because all physicists for the past 130 years have been stupid and only you would have done the experiments correctly. But I'm guessing you're probably only aware of one or two experiments anyway, if any.

I don't care if his theory stood for 10,000 years, wrong is wrong, and time doesn't make things right. Nothing I say here will convince you, as you have it so deeply embedded in your brain that he is correct, that the thought of being wrong is unimaginable to you. You prove it to yourself. Show me one thought experiment that shows me you can determine the velocity or length of an object without relating to another object. Show me, and I will be on my merry way. If your numbers are correct, I will gladly admit I am wrong and be out of your life. I'm willing to do that if you can accurately measure an object's velocity and length. I KNOW you can't do that, as I know your methods and I know why you can't do that.

Originally Posted by James R
Some people try to attack Einstein's theory of special relativity by claiming that it is self-inconsistent. You're welcome to try that if you like. So far, as far as I can see you haven't made that particular claim, which is probably the most common one we see from crackpots here. You have claimed that Einstein's theory gives answers that are inconsistent with observation, but the only way you can support those claims is to point to actual experimental results that contradict the theory. Thought experiments in which measurements taken using light on a moving train, wherein the light has different travel times in each direction in the reference frame of the train won't cut the mustard. That kind of thing doesn't happen in reality; it only happens in your imagination.

I understand how to measure an object's velocity in space using light. You don't. I understand the proper way to measure length in space, you don't. You only imagine that an object's motion is only relative to another object's motion. You fail to grasp even the most simple concept that object's are in motion in space. An object's motion does not depend on another object's motion. We use light to measure motion. You fail to grasp the concept that a source could emit light, and the source could also travel in the time the light is traveling. You fail to grasp the concept that the source's motion doesn't change the light's motion. The light sphere will continue to grow, and the radius will be measured from the point in space that the light was emitted. If the source remains at a zero velocity the source will be at the center of the sphere. If the source has a velocity the source will be closer to one edge of the outer sphere than the other edge. Light travels independently of objects. You don't understand that, as is evident by your statements.

Originally Posted by James R
To conclude, I think we've gone about as far as we can go with this, unless you can show some kind of fatal theoretical or experimental problem with Einstein's relativity, or you can show some experimental evidence for your theory.
I've showed MANY FATAL flaws in Einstein's methods, yet you fail to acknowledge them. You fail to show me how you determine the motion of an object in space, relative to space. You fail to acknowledge Einstein's methods are flawed from the start. What more can I do? You can lead a horse to water but you can't make him drink!

As I predicted, we've made no progress with your latest post, and I don't think any progress is likely from this point on. You will keep making the same assertions and you will keep asserting that I don't understand what you're saying. I understand just fine; I just know you're wrong.

You have to agree with my numbers because they are absolute facts. If you don't agree with them then you must be using some wrong formula or performing your calculations wrong. Those numbers were arrived at using the very definitions of distance and time as we've defined them. They were not arrived at by using some formula from some theory using time dilation, length contraction etc.., they were arrived at using basic math that we all know to be true. There are no other objects, remember? You gave me the times you measured from within the ship.
No. I explicitly constucted numbers that would be measured by somebody outside the ship. I just didn't tell you I'd done that. Also, I fudged things a little by omitting the correct length contraction and time dilation effects. In other words, what I did was to present you with a hypothetical problem in a Newtonian universe, which you were quite comfortable in solving. Since you assume that a time is a time is a time, no matter which reference frame you measure it is, it didn't even occur to you that the times I gave you might not be measured inside the spaceship.

What other object are you talking about? You never mentioned another object in your thought experiment. The ship is the only object in space. I don't know why you want to refer to other objects when for one, the ship is the ONLY object, and for two, we are talking about the velocity and length of the ship as measured from within the ship.
It's not just about objects. Relativity is primarily about reference frames, not objects. It is about events in spacetime. A length consists of two spacetime events. A time interval consists of two spacetime events. Objects just help us to specify which particular events we're talking about in spacetime.

You are on board the ship and you measured the one-way times on the ship.
In reality, the one-way times will always be the same in both directions when measured on the ship. Galileo appreciated this fact back in the 17th century. The one-way times can only be different if you measure them in some frame that watches the ship flying past.

The measurements were taken using light, and light has an absolute speed in space. Every object has an absolute speed in space. In order for any object to be in motion it must travel in space. If two objects travel together in space they will travel relative to each other, but they are still traveling in space. You can not travel unless you travel in space!
You're stuck in etherland, where you believe that "space" is like a substance. Space isn't a substance and it has no speed (or, if you prefer, it has whatever speed you want it to have). There's no such thing as the speed of a spaceship or a horse or a person relative to "space", because "space" is a nothing, not a substance.

There was no external frame or person measuring the times. You were in the ship measuring the times. Why do you now want to say there is an external frame? You didn't say that in the experiment.
If you read back, you'll notice I didn't say anything about who did the measuring or where they were. All I said was some times were measured. If you weren't stuck in your "only one real reference frame exists" mindset, you would have asked me those questions, but for you every measurement happens in the "absolute" reference frame.

Space doesn't travel, it is just volume. Infinite volume doesn't travel, it just is. We use light to define distance in that volume. What do you mean there is no absolute zero speed? Speed of what, an infinite volume?? We measure the amount of time an object takes to travel from point a to point b in the volume. We use light travel time to base our unit of measure of distance, the meter, because light speed is constant. You don't get that and probably never will.
Your point of view is strange and inconsistent. On the one hand, you claim to accept Einstein's speed-of-light postulate. That's what you say, although you can't bring yourself to actually say the words "I agree with Einstein on this point." But on the other hand, everything you do suggests that you only really believe that light has a particular speed relative to just ONE reference frame - that of "space", which you view as a substance relative to which all motion must be measured.

You seem to be stuck on wanting to know your speed in relation to another object? Why is that, because you don;t know how to determine your own speed in space?
Actually, what I'm "stuck on" is in insisting that a reference frame be specified for all measurements. There is no absolute "speed in space". There's only relative speed - speed relative to this reference frame or the other reference frame.

Go figure, as that was Einstein's problem, he couldn't figure out how to measure an object's velocity in space.
Einstein, like me, was perfectly well aware of how an absolute universe would look. Like me, he deliberately rejected that view as being inconsistent with experimental fact. He was then forced by the evidence to construct a new theory wherein there was no absolute speed. The resulting theory is tremendously counter-intuitive, to the extent that many like yourself react against it instinctively. But nature decides; you do not.

For example, suppose I measured those one-way travel times in the frame of the spaceship. In that case, I would find, experimentally, that the light travel times were the same in both directions, and I would therefore calculate that the speed of the ship was zero relative to the ship's reference frame. No surprises there.
NO! No you wouldn't find the times were the same.
Here's the crux of where we differ. You assert one thing; I assert something very different. The only way to tell the difference is to do the experiment. And so we're stuck.

What I do know, however, is that even if this precise experiment has not been done (and I'm not certain it hasn't been), then countless other experiments still put the result of this one beyond any doubt.

You are basing your incorrect assumptions on the fact that Einstein thinks the length of the plane is the round trip time divided by two, which gets the length wrong. You are basing your incorrect assumption on the fact that the ship has a velocity in space, and you have no way of knowing that velocity. Einstein doesn't know the velocity of the ship, period!!! Since he doesn't know the velocity of the ship he CAN"T know the length of the ship. His problems snowball from there.
Einstein can measure the velocity of the ship relative to any frame you care to name. There is no absolute reference frame, so there is no "the velocity of the ship" in the sense you mean. You can bluster all you want about that, but it's the truth.

I have a disagreement about Einstein's mathematics, as I've pointed out. What you mean is that you can't possibly disagree with mine, because they are as sound as sound gets. They are basic simple math using the very definitions of distance and time as we have defined them. These numbers simply can't be refuted. They simply can not. It is impossible!! However, I refute Einstein's numbers on a daily basis using my dead accurate numbers.
Your version of "refuting Einstein's numbers" is to claim, without any proof whatsoever, that the one-way travel times inside the spaceship will be different when measured inside the ship. They will not. Ever.

You dare not show me Einstein's numbers, as I already know you get the length wrong, and he doesn't know the velocity of the ship.
You're not getting it. There is no "the velocity of the ship". There's only velocity relative to a frame of reference. I can show you Einstein's numbers, but what would be the point? You say he gets the length wrong. I say he gets it right. One of you must be wrong and I know where I'm putting my money (and why).

Show me the experiments involving one-way times that prove his theory correct. Show me one of the million experiments that uses one-way times using my sync method. Just one.
I'm sorry, Motor Daddy, but I really can't be bothered doing the necessary research on your behalf. It is possible that your one-way times experiment has been done; I'm really not sure. What I do know is that it's not necessary to do that particular experiment, because Einstein's relativity is confirmed beyond doubt by millions of other experiments. If you experiment worked as you say it should, then half of modern physics would collapse in a heap. And yet, every day, it works just fine.

C^2 is an acceleration. It is 186,000 meters per second per second. We are talking about velocity, which isn't squared, it is 186,000 miles per second. Two different animals.
See, this is an example of why I doubt your capacity to discuss this topic with any real understanding.

c^2 is not an acceleration. It is the square of a velocity. For example, if we measure the speed of light in metres per second, then c^2 has units of square metres per second squared. Accelerations, on the other hand, have units of metres per second squared.

This is a basic error that not even a first-year undergraduate would make.

I'm sure you have no idea where the c^2 comes from in $E=mc^2$, or even why it has to be squared. And I note you avoided the question about whether you believe that equation is correct or not. And if you think it is unrelated to your light-travel-time problem, you're quite wrong.

I'm not saying an object of mass could ever travel faster than light, but there may come a time when we need to measure a velocity greater than the speed of light, and Einstein's method will fall flat on its face trying to do so, mine doesn't. His sync method is absurd! It is inconsistent with the very nature of time and simultaneity. ALL motion takes time to occur. He disregards the time it takes light to travel from one clock to the other. That is crazy talk. By the very definition, light takes time to travel. You can;t say light left one clock at 12:00:00 and arrived at the other clock a distance apart and arrived there at 12:00:00. That means light travels instantaneously. Change takes time to occur! Nothing travels instantly, no matter how fast it travels or how short of a distance it travels.
You appear to have a misunderstanding of Einstein's synchronisation method here. I'm not sure what it is, but I assure you that Einstein never "disregards the time it takes light to travel".

My guess is that you've confused the times that events occur in spacetime with the time that light from those events reaches some other object, but there's no way to know for sure without further explanation from you.

My theory is the very nature of Doppler. The very nature of a source emitting light and the light traveling away from the point in space it was emitted, and then the source could also have its own motion, traveling away form the point in space it was when it emitted the light. That means the source is closer to one side of the light sphere than the other side of the light sphere. You can measure the velocity of the source in space by knowing the light travel times, as I've clearly shown. The sources velocity is relative to light. The sources velocity is the motion of the source in space!
Please give me your formula for the Doppler shift of light. i.e. Suppose light is emitted at frequency f from a source moving at velocity v (make that an absolute velocity if you need to). If the source is approaching the receiver, what frequency f' does the receiver measure for the light? Please give a formula for f' in terms of f, v and c. We'll compare your formula to Einstein's.

The ship is at rest. What frame do you speak of? The ship is inertial, the velocity is not changing. The ship is not accelerating. What frame do you speak of that the ship's length is different? There is only a ship in space, and I told you the numbers. Maybe you can't accept the truth?
I'm talking of the frame in which the light travel times were as I specified. That is NOT the rest frame of the spaceship, because in the rest frame of the spaceship the light travel times will always be equal. (Yes, yes, deny it again. It doesn't advance the argument.) Length contraction doesn't require acceleration, by the way. Special relativity is always concerned with frames moving at constant relative velocity.

Einstein can't tell you the length of the ship because he doesn't know the velocity of the ship.
Sure he can. In any given frame, he only needs to send a one-way pulse of light from one end of the ship to the other and time how long it takes. Then use x=ct. Where he disagrees with you is that the time it takes will vary depending on which reference frame the measurement is made in, whereas you assume a single universal time frame.

1. You are wasting your time measuring the speed of light.
Earlier in the thread, I told you part of the history of the definition of the metre. Prior to 1960ish (I forget the exact year), the metre was defined as about 1/10000th of the distance from the North pole to the equator. Its definition was NOT based on the travel time of light.

Do you think it was a waste of time to measure the speed of light prior to 1960? And what happened in 1960 to make it suddenly a waste of time?

2. Light travels in space. Space doesn't move. Light travel time defines distance in space.
"Space" isn't a thing that is stationary. It isn't a thing at all. Thinking of it as a thing is a mistake.

3. I can measure any frame you like, and I will tell you the exact numbers.
No. You can't even do the correct numbers inside the spaceship. You assert that the travel times will be different when measured inside the ship; that is false.

Wrong. Using Einstein's sync method is mistake number 1. Assuming light takes no time to travel from one clock to the other clock is mistake number 2. Measuring round trip time and dividing by two is mistake number 3. Three mistakes that all those experiments are based on.
As to (1), it's not clear to me that you understand "Einstein's sync method" at this point. As to (2), that would be wrong if it was an assumption that Einstein made, but he never made that assumption, so this is a misconception on your part. As to (3), whether it is right or wrong really depends on exactly what you're trying to work out in the end.

You say I can't visualize different frames? That's funny. I can tell you the speed of any object in the universe, and you can't tell me even one of the speeds.
You can tell me the speed relative to an imagined absolute frame using imagined travel times. I have given you a step-by-step procedure for working out the relative speed of any object in any given reference frame, which is the most anyone can do.

Until you show me an experiment that used one-way times and sync'd clocks my way, I can not acknowledge any type of validity in your results. You get the lengths wrong. You don't know the velocities, and you use round trip times and divide by two. You continually measure the speed of light when it is already defined.
So we're at an impasse, like I said. You're certainly unwilling and probably unable to properly consider the mountains of evidence that prove Einstein's theory. And you're unwilling to even entertain the possibility that the outcomes you assume for your thought experiments might be wrong. In short, your mind is closed, and I don't see any possibility of it opening any time soon.

Why did physicists think there ought to be an "absolute zero speed" frame in the first place? Well, are you familiar with Maxwell's electromagnetic theory? It predicts a constant speed of light, irrespective of reference frame. In other words, the equations of electromagnetism (a) work in all reference frames, and (b) predict the same speed of light in every frame.
Light travels in space. Space doesn't have motion, objects in space have motion. Period!
That's inconsistent with Maxwell's equations, which predict the same speed of light in all reference frames.

You only know that Einstein's methods are consistent.
Do you agree they are consistent?

What do you mean by "consistent"? They give correct physical answers that we can use to work out other things? Or that we never notice the problems because all of physics is inconsistent in the same way as Einstein? Or what?

But what you don't understand is that they are consistently wrong, and I've shown why. I don;t expect you to believe me, as it is so deeply embedded in your brain that Einstein is right, that even the remote possibility of him being wrong is out of the question to you. You've been brainwashed into thinking as he did, in his imaginary world of objects only traveling in relation to the other.
Well, those people who supposedly brainwashed me sure did a fine job of it. Einstein's theory is utterly counter-intuitive. If I was coming up with a theory from scratch, knowing next to nothing about physics, I think I'd probably invent a theory similar to the one you've got. It's in accordance with everyday observation, as far as I can tell without using complicated equipment. It makes intuitive sense. I don't need to understand anything about reference frames to apply it. I don't have to do any complicated algebra or calculus. It is attractive because it has absolute time and absolute space, which might make me feel comfortable and cosy. Unfortunately, it's also wrong. And I know why.

"Brainwashing" is a process by which you ultimately accept things on the basis of somebody's authority. I don't believe relativity is correct because Einstein was a towering figure in physics, Motor Daddy. If Einstein hadn't invented (special) relativity, somebody else surely would have. I believe relativity is correct because everything else I know about physics tells me it is correct. Attractive as Newtonian physics is, it is wrong. Well, right up to a point, to give Isaac due credit.

I don't care if his theory stood for 10,000 years, wrong is wrong, and time doesn't make things right. Nothing I say here will convince you, as you have it so deeply embedded in your brain that he is correct, that the thought of being wrong is unimaginable to you.
I've been imagining how it could be wrong through the entire course of this thread. And I reject your ideas for good reason, not because I can't understand them or conceive of your worldview. On the other hand, I'm not convinced you either understand or are open to Einstein's ideas.

You prove it to yourself. Show me one thought experiment that shows me you can determine the velocity or length of an object without relating to another object.
You're not getting it. You fall at the first hurdle, by assuming that every object has "a length" and "a velocity" in the absolute sense. Such things don't actually exist.

I understand how to measure an object's velocity in space using light.
Not really. Your essential method is fine. The problem comes where you imagine what the result of your time measurements will be in different reference frames. But I'm sure you're not going to admit that you're making assumptions about how the world is. You assume you're right. You need no real-world evidence.

I've showed MANY FATAL flaws in Einstein's methods, yet you fail to acknowledge them.
I've responded to three of these supposedly "fatal flaws" earlier in this post. They are not as "fatal" as you think; in fact not fatal at all.

6. James R, I'm not going to respond to all that you've typed, as I'll just be repeating myself.

To show me you know the velocity and length of an object in space, without referring to another object of which you also don't know the velocity or length, please give me the length and velocity of a ship that has a round trip light travel time of 2 seconds. That's all you need, just the round trip time, correct?

7. Originally Posted by MD
without referring to another object of which you also don't know the velocity or length
Impossible. You will need to refer to a ruler which has zero velocity in the ship's frame, or to something with a constant velocity, such as light.

If you use a clock, it has a constant velocity AND frequency, just like light can have (e.g. laser light). That's what the phrase "light clocks and rigid rods" is about.

Your reference to the Doppler effect appears to avoid any use of the word "frequency", why is that? Don't you know what it is?

James R, I'm not going to respond to all that you've typed, as I'll just be repeating myself.
Fair enough. I hope you read it, though.

To show me you know the velocity and length of an object in space, without referring to another object of which you also don't know the velocity or length, please give me the length and velocity of a ship that has a round trip light travel time of 2 seconds. That's all you need, just the round trip time, correct?
Is the travel time measured in the frame of the object to be measured? If so, then the length of the object is 1 light-second. And yes, in that case the round-trip time is sufficient to determine the length. The velocity of the object in its own rest frame is, of course, zero.

If the travel time was not measured in that frame, then you'll need to tell me what frame it was measured in. That's equivalent to telling me the velocity of the object with respect to the frame used to measure the time, of course.

A measurement without a specified frame of reference is meaningless.

Alternatively, if I'm allowed to put a metre ruler (which I define to be a ruler with rest length 1 metre) on the object to be measured, then I could just measure the length directly (in whichever frame). That would still not tell me "the velocity" of the object, since we still need to know which reference frame you want the velocity to be relative to. Absolute velocities, as I have said, do not exist.

9. Originally Posted by James R

Is the travel time measured in the frame of the object to be measured?
Yes. Your one way times from your ship were too, but that's neither here nor there now. Let's work on this example now.

Originally Posted by James R
If so, then the length of the object is 1 light-second. And yes, in that case the round-trip time is sufficient to determine the length. The velocity of the object in its own rest frame is, of course, zero.
Of course it's zero, how could the ship ever have a velocity other than zero? Your ship never has motion in the universe. As a matter of fact, if I asked 50 other ships what their length and velocity was, and they used Einstein's methods, as you have, and their round trip times were all 2 seconds, they would also tell me they were 1 light second in length and had a zero velocity. Isn't it amazing that 51 ships in the universe all have a zero velocity? Just ask them, they'll tell ya!

Originally Posted by James R
If the travel time was not measured in that frame, then you'll need to tell me what frame it was measured in. That's equivalent to telling me the velocity of the object with respect to the frame used to measure the time, of course.

A measurement without a specified frame of reference is meaningless.
The time was measured from within your ship using clocks and light. Now, did you ever consider that IF the ship had a velocity, that the round trip time would be worthless? Do you acknowledge that round trip time would not detect a velocity? You do think the object COULD be in motion in the universe, don't you? I mean, you believe in motion, don't you? Is it possible that your ship could be in motion?

Originally Posted by James R
Alternatively, if I'm allowed to put a metre ruler (which I define to be a ruler with rest length 1 metre) on the object to be measured, then I could just measure the length directly (in whichever frame). That would still not tell me "the velocity" of the object, since we still need to know which reference frame you want the velocity to be relative to. Absolute velocities, as I have said, do not exist.
In your ship, you have no need for a meter stick. Your meter stick is exactly 1⁄299,792,458 the length of the ship. That's strange, because the meter is defined in terms of light travel time, and yet you define it to be a portion of the length of your ship.

You say, you define a meter ruler to be a ruler with rest length 1 meter? That is a very odd definition of a meter. If you don't know the definition of a meter, how do you know how long a meter is?

10. James R: In addtion to having a better grasp of SR than I, you also have more patience. I am amazed at the amount of words you have posted in this thread.

Does anyone here remember GenX? I think that was his ID.

Like Motor Daddy, he disputed General Relativity. One of his arguments related to apparent FTL motion of stars, which appears to be observational evidence of objects moving faster than c.

I wonder what Motor Daddy & GenX would think about some of the counterintuitive weirdness of Quantum Theory.

11. Originally Posted by Motor Daddy
Do you acknowledge that round trip time would not detect a velocity? You do think the object COULD be in motion in the universe, don't you? I mean, you believe in motion, don't you? Is it possible that your ship could be in motion?
Breaking news: that's exactly what Einstein's theory says. You can't tell the ship's velocity from inside the ship, so its velocity is unknown. The "external" velocity isn't just an unknown, it's unknowable.

However, an external observer, say on the earth (or anywhere else, of course, except inside the same ship), can determine a velocity for the ship (not "the" velocity) relative to their frame of reference. That's because all velocities are relative.

And before you remind us all that the metre is defined (by a bureau of standards, consisting of ordinary human beings, not aliens) in terms of the speed of light, it was initially defined in terms of the dimensions of the earth--as James R stated, as a fraction of the distance from the equator to the north pole. Presumably that distance is the same as from the equator to the south pole. It was also defined in terms of the length and period of a pendulum. There is nothing meaningless about measuring the speed of light either. In fact, this is a common 1st year or even high school experiment, and the world has not stopped turning.

12. Originally Posted by Dinosaur
James R: In addtion to having a better grasp of SR than I, you also have more patience. I am amazed at the amount of words you have posted in this thread.

Does anyone here remember GenX? I think that was his ID.

Like Motor Daddy, he disputed General Relativity. One of his arguments related to apparent FTL motion of stars, which appears to be observational evidence of objects moving faster than c.

I wonder what Motor Daddy & GenX would think about some of the counterintuitive weirdness of Quantum Theory.
I believe James R. is a closet SR disbeliever, and is astonished that I am the first person known to man to ever have determined the absolute velocity of an object in space, without reference to any other external object. Who wouldn't be fascinated? This is history in the making!

13. Originally Posted by arfa brane
Breaking news: that's exactly what Einstein's theory says. You can't tell the ship's velocity from inside the ship, so its velocity is unknown. The "external" velocity isn't just an unknown, it's unknowable.

However, an external observer, say on the earth (or anywhere else, of course, except inside the same ship), can determine a velocity for the ship (not "the" velocity) relative to their frame of reference. That's because all velocities are relative.
Breaking news: I have shown multiple times in this thread that I can determine the velocity of a ship from inside the ship! Einstein was wrong again!

14. I believe James R. is a closet SR disbeliever, and is astonished that I am the first person known to man to ever have determined the absolute velocity of an object in space, without reference to any other external object.
I would say he, like most people who have done actual physics, is even more astonished at your inability to understand what light 'really' is.
Breaking news: I have shown multiple times in this thread that I can determine the velocity of a ship from inside the ship! Einstein was wrong again!
Only in your tiny little brain, my son.

Originally Posted by James R
If so, then the length of the object is 1 light-second. And yes, in that case the round-trip time is sufficient to determine the length. The velocity of the object in its own rest frame is, of course, zero.
Of course it's zero, how could the ship ever have a velocity other than zero? Your ship never has motion in the universe. As a matter of fact, if I asked 50 other ships what their length and velocity was, and they used Einstein's methods, as you have, and their round trip times were all 2 seconds, they would also tell me they were 1 light second in length and had a zero velocity. Isn't it amazing that 51 ships in the universe all have a zero velocity? Just ask them, they'll tell ya!
See the words in bold above? They are important. They actually mean something. I'm beginning to think you don't really have much of an idea of what a reference frame is.

When you say a spaceship has a velocity, you're not working in the frame of the ship. You're viewing it from outside, as it flies past you. If you're sitting in the ship, it isn't moving relative to you. You're in its rest frame, and as far as you're concerned it has zero velocity. And yes, that's true of your other 50 ships for the people in them too.

The time was measured from within your ship using clocks and light.
Then the one-way travel times will always be equal, and my answers are correct.

Now, did you ever consider that IF the ship had a velocity, that the round trip time would be worthless?
Yes. I considered this when I set the problem for you earlier in the thread. But those times weren't measured in the rest frame; they could not have been.

You do think the object COULD be in motion in the universe, don't you? I mean, you believe in motion, don't you? Is it possible that your ship could be in motion?
Sure, but it can't be in motion in its own rest frame. Obviously.

In your ship, you have no need for a meter stick. Your meter stick is exactly 1⁄299,792,458 the length of the ship. That's strange, because the meter is defined in terms of light travel time, and yet you define it to be a portion of the length of your ship.
No. I define a metre stick to be the distance light travels in 1/299792458 seconds - in any frame. Because the speed of light is the same in all frames (completely counter-intuitively, I might add).

You say, you define a meter ruler to be a ruler with rest length 1 meter? That is a very odd definition of a meter. If you don't know the definition of a meter, how do you know how long a meter is?
When I say it has a rest length of 1 metre, I need to measure that. For example, use light.

16. Originally Posted by James R

See the words in bold above? They are important. They actually mean something. I'm beginning to think you don't really have much of an idea of what a reference frame is.
I know exactly what a reference frame is, and I know what "at rest" means (not accelerating).

Originally Posted by James R
When you say a spaceship has a velocity, you're not working in the frame of the ship.
I am measuring the velocity of the ship in space. The ship has its own velocity in space, which is not relative to any other object. I am determining the velocity of the ship in space using light, which also travels in space with its own velocity. You don't seem to get that an object can be in motion in space. Do you not understand that an object can traverse space? Why do you insist on saying an object can't be in motion in space? I can measure the motion of an object in space, using light. The ship has a velocity in space just as light has a velocity in space.

Originally Posted by James R
You're viewing it from outside, as it flies past you. If you're sitting in the ship, it isn't moving relative to you. You're in its rest frame, and as far as you're concerned it has zero velocity. And yes, that's true of your other 50 ships for the people in them too.
No I'm not viewing it from outside. I am not measuring my velocity compared to the ship, I am measuring the ship's velocity in space from inside the ship using light. Do you not understand what I am saying?

Originally Posted by James R
Then the one-way travel times will always be equal, and my answers are correct.
Your answers are only correct if the ship is not moving in space, which means it has a zero velocity.

Originally Posted by James R
Yes. I considered this when I set the problem for you earlier in the thread. But those times weren't measured in the rest frame; they could not have been.
Yes they were measured from within the ship. All my numbers add up in and outside the ship, compared to every frame in the universe. Light measures distance in space. I use light to measure distance, hence, all my numbers add up with all objects in space.

Originally Posted by James R
Sure, but it can't be in motion in its own rest frame. Obviously.
You want to try and say an object has a zero velocity if there is nothing to measure it against. I am telling you that I can measure the velocity of the ship in space, which means I can tell you the distance the ship traversed "empty space" in a given amount of time. Space has distance, and the ship can travel a distance in space in x amount of time, no other object or frame required to measure the distance or time. Do you understand that volume has distance, and objects can travel in a volume?

Originally Posted by James R
No. I define a metre stick to be the distance light travels in 1/299792458 seconds - in any frame. Because the speed of light is the same in all frames (completely counter-intuitively, I might add).
The speed of light is in fact the same in all frames. The part you fail to realize is that objects also have speed, and the object's speed changes the amount of time the light takes to travel from point a to point b on the ship. Do you not understand that the ship's velocity changes the distance light has to travel from one end of the ship to the other? The ship could be 1 meter in length, and it could take light .5 seconds to travel from end to end of the ship, because the ship has a velocity in space too!

Originally Posted by James R
When I say it has a rest length of 1 metre, I need to measure that. For example, use light.
But first you must know if the meter stick is in motion in space. You nee3d to know if the meter stick has a velocity in space, as a velocity changes the amount of time it takes light to traverse the stick.

17. Originally Posted by Farsight
You could also agree to employ the CMBR as a defacto "absolute reference frame”. You can gauge your motion through the universe from it. See CMBR dipole anisotropy. It isn’t something that’s "inside the box" of Lorentz-invariant local phenomena, but it is something real rather than hypothetical. If you see it as blue-shifted in one direction and red-shifted in the opposite direction, you’re headed in the blueshift direction.
The CMB rest frame is different for each point in space-time. Two people at different places who each make themselves move in such a way as to view the CMB as having no Doppler shift will find they are moving relative to one another.

18. James R.

As Neddy Bate previously mentioned, the formula for my theory of finding the absolute velocity and distance between clocks is:

v = (cT - ct) / (T + t)
d = T(c - v)
where:
v is the absolute speed along the line between the clocks
d is the distance between the clocks
T is the greater time
t is the lesser time

There is no time dilation or length contraction involved.

You measure one-way light travel times and find the absolute velocity of the ship.

19. I quote:

Surely this thread has run its course.

20. Originally Posted by Motor Daddy
James R.

As Neddy Bate previously mentioned, the formula for my theory of finding the absolute velocity and distance between clocks is:

v = (cT - ct) / (T + t)
d = T(c - v)
where:
v is the absolute speed along the line between the clocks
d is the distance between the clocks
T is the greater time
t is the lesser time
Just for the record, I contributed those equations because I thought they applied to Motor Daddy's fictional universe. I realize that the real universe does not work that way. Sorry Motor Daddy!