The Relativity of Simultaneity

[Neddy Bate]

Which again, would be impossible for the lights to reach the end of the train simultaneously from a single source at the midpoint of the train.

Say the train observer flashed a light from the midpoint when A and B on the train lined up with A and B on the embankment. It is simply impossible for the light to reach the front and back of the train simultaneously. That's like saying it takes the same time for light to reach you from a lamp post if you run towards it when light is emitted, and when you run away from it when light is emitted. It's simply impossible for light to travel the same distance in both scenarios.

It's not impossible. Imagine you are the embankment observer, and when you look at the train clocks, you see that they are set in such a way that the clock at the rear of the train is ahead of the clock at the front of the train.

1. You see the light from the center of the train reach the rear train-clock first, but that train-clock is set ahead, so it recorded a longer travel time for the light, compared to what you would say is true.

2. You see the light from the center of the train reach the front train-clock later, but that train-clock is set behind, so it recorded a shorter travel time for the light, compared to what you would say is true.

3. The travel times for both light signals are measured to be the same according to the train clocks. Thus, the train observer says they reached the ends of the train simultaneously.

4. Meanwhile, you were on the embankment, and you said that the light signals did not reach the ends of the train at the same time. "Relativity of Simultaneity"!

 

[Motor Daddy]

It's not impossible. Imagine you are the embankment observer, and when you look at the train clocks, you see that they are set in such a way that the clock at the rear of the train is ahead of the clock at the front of the train.

1. You see the light from the center of the train reach the rear train-clock first, but that train-clock is set ahead, so it recorded a longer travel time for the light, compared to what you would say is true.

2. You see the light from the center of the train reach the front train-clock later, but that train-clock is set behind, so it recorded a shorter travel time for the light, compared to what you would say is true.

3. The travel times for both light signals are measured to be the same according to the train clocks. Thus, the train observer says they reached the ends of the train simultaneously.

4. Meanwhile, you were on the embankment, and you said that the light signals did not reach the ends of the train at the same time. "Relativity of Simultaneity"!

It's not about what you see while it is happening, that is an illusion!! How many times do I have to say it? It is an illusion.

The measurements are accurate, regardless of what someone at a distance perceive them to be. When the results are in, and when the measurements have been completed, there is nothing to look at. The clocks have stopped. You are only looking at measurements of distance and time, as they occurred in the past.

The historical record of the universe is not up for debate. It is not a matter of debate how much distance an object actually traveled in a specific amount of time. It is a fact that an object traveled 10 meters in 10 seconds, and it is recorded in the historical records. ALL records of the past must match.

 

[Neddy Bate]

It's not about what you see while it is happening, that is an illusion!! How many times do I have to say it? It is an illusion.

The measurements are accurate, regardless of what someone at a distance perceive them to be. When the results are in, and when the measurements have been completed, there is nothing to look at. The clocks have stopped. You are only looking at measurements of distance and time, as they occurred in the past.

The historical record of the universe is not up for debate. It is not a matter of debate how much distance an object actually traveled in a specific amount of time. It is a fact that an object traveled 10 meters in 10 seconds, and it is recorded in the historical records. ALL records of the past must match.

They do match. Read my post again. You are the embankment observer and you see how the train's clocks are out of synch. The travel times recorded in the train's history books are taken from the train's own clocks.

 

[Neddy Bate]

Do you actually believe that crap? Neddy Bate, You sound like an intelligent person. Why do you believe that garbage? You may as well be saying the clocks are different because a pink fairy is in between the embankment and the train, and she is waving her magic wand, and throwing magic dust in the air, which causes one to have massive illusions about space and time.

What a load of garbage!!!

Who cares what illusions appear to be, we are talking about measuring distance and time in the universe!! Illusions are for magic shows! Measurements are not magic.

It doesn't matter what I believe. I'm just telling you what relativity says would happen.

 

[Motor Daddy]

They do match. Read my post again. You are the embankment observer and you see how the train's clocks are out of synch. The travel times recorded in the train's history books are taken from the train's own clocks.

There is ONE history book, not more. An observer is in no position to "see" anything as it actually happens. The observer is looking at distortions of distance and time, because he is seeing a smear of different distances and not only that, he only "sees" the past. He can not see the present. He can't "be the object" in motion, so he has a distorted view. Any observer a distance away is having an illusion. It never really happened that way.

Look out at the sky tonight. look at all those stars and moon. Guess what? It was never that way in reality! You are having an illusion because you are seeing a smear of light from all different distances, which are all from different times. It was never that way in reality!

 

[Neddy Bate]

There is ONE history book, not more. An observer is in no position to "see" anything as it actually happens. The observer is looking at distortions of distance and time, because he is seeing a smear of different distances and not only that, he only "sees" the past. He can not see the present. He can't "be the object" in motion, so he has a distorted view. Any observer a distance away is having an illusion. It never really happened that way.

Look out at the sky tonight. look at all those stars and moon. Guess what? It was never that way in reality! You are having an illusion because you are seeing a smear of light from all different distances, which are all from different times. It was never that way in reality!

The embankment observer finds the train-clocks at the ends of train to be out of synch with each other. This has nothing to do with any kind of visual illusion. They are out of synch for real, just like if you were to set your wristwatch 5 minutes ahead of my wristwatch.

 

[Motor Daddy]

The embankment observer finds the train-clocks at the ends of train to be out of synch with each other. This has nothing to do with any kind of visual illusion. They are out of synch for real, just like if you were to set your wristwatch 5 minutes ahead of my wristwatch.

They are not out of sync. According to the definition of the meter and the speed of light, and velocity, they match perfectly. What grounds does he have to say they are out of sync? Does he refute the velocity of the train? Does he refute the speed of light or the definition of a meter??

 

[Neddy Bate]

They are not out of sync. According to the definition of the meter and the speed of light, and velocity, they match perfectly. What grounds does he have to say they are out of sync? Does he refute the velocity of the train? Does he refute the speed of light or the definition of a meter??

Relativity says that the train observer finds the speed of light to be 299792458 m/s relative to the train. That is why the train observer can use the standard definition of the meter without having to account for his "absolute velocity".

Relativity also says that the embankment observer also finds the speed of light to be 299792458 m/s relative to the embankment. Thus, the embankment observer can also use the standard definition of the meter without having to account for his "absolute velocity".

But in order for both of the above things to be true, some ideas have to be discarded. One of those ideas is the notion of "absolute simultaneity". The clocks at rest in any one reference frame can only be synched according to one reference frame.

 

[arfa brane]

Light moves in space at c. Objects have relative velocities to the light. If light is at each end of a train, and an observer midway between the lights, the light from each source will travel different distances to reach the midpoint observer if the train has a velocity.

Motor Daddy hasn't figured out what's wrong with this argument.
He does seem to think that light itself can be used as an absolute frame of reference.

 

[Pete]

If he has no way of syncing clocks then he has no way to measure velocity, which means he has no way to measure length using light travel time. So I suggest that he stops making assumptions about one's motion. If he wants to make statements about distance and time, according to the proper definition of the speed of light and the meter, then he needs to conform to the standards. If he wants to make his own standards, fine, but he has no business pretending those standards are correct according to the definition of the meter.

He doesn't pretend that.
He knows that the train-standard is a distinct standard.
Do you see that it is a useful standard?

If he wants to make false statements about when lightening strikes occurred and the simultaneity of the strikes, yes, he should assume whatever make believe BS he wants to, and he can be happy in his own little imagination.

He doesn't want to make false statements. But what choice does he have?

His microwave will work, and his radios will work, but his dictionary will be different, so that won't work. His dictionary is BS, and he doesn't even know it. See, I told you ignorance is bliss!

So it's only a semantic difference then?

...another idea for the sync of clocks.

Place a light transmitter and a receiver a distance apart from each other on a table, inline with the train from front to rear, roughly an arm's length apart from each other. Make a steel wheel that is a circle, roughly an arms length in diameter. Place steel tabs sticking out 180 degrees apart from each other on the wheel. Install a bearing in the center of the steel circle. Find the center of the distance between the transmitter and receiver on the table. Mount the wheel on a shaft at the center in such a fashion that when the wheel rotates, the tabs come in contact with the actuator on the transmitter and receiver. Rotate the wheel so the tabs are almost touching the actuators. Calibrate each actuator so that when the wheel is spun the tabs contact the two actuators simultaneously.

Now spin the wheel. As soon as the tabs make contact, the transmitter sends a light pulse to the receiver, and at the same time the receiver starts a clock. So when the light arrives at the receiver the clock is stopped and the elapsed time is shown.

Now repeat the test in the opposite direction.

Mind you, the distance between the transmitter and receiver is still unknown, but the two one-way times are known.

Use the equation L=(2cTt)/(T+t) to find the distance between the transmitter and receiver.

Use the equation v=(ct-L)/t to find the velocity of the train.

No sticks required.

... and no suspicions, illusions, assumptions of convenience, or pretending involved! Just straight up measurements of distance and time!

Doesn't work, MD. The wheel is moving, so it's length contracted. Different parts of the wheel are moving at different rates, so the length contraction varies around its radius.
The complete analysis is tricky, but very interesting.
In this mathematical world of length contraction, the spinning wheel must undergo some physical stress - either the spokes of the wheel have to be physically compressed, or the circumference of the wheel has to be physically stretched, or both.


There's a question you haven't addressed yet: how can you tell if your preferred mathematical world matches the real world?

 

[arfa brane]

I can see another problem with MD's universe. He has claimed repeatedly that the absolute velocity of a single frame of reference can be determined with reference to light.

Motor Daddy appears to be unable to see that his claims of absolute velocity being measurable, viz:

The point is that you can see what an absolute velocity is in that example.

When you have two sources separated by a distance, and the sources emit light simultaneously, where the lights spheres meet in the middle is the midpoint. It doesn't matter what the sources do after they emit light, the lights will meet at the original midpoint in space. If an object was at that midpoint when the lights were emitted, and the object is not struck by the lights simultaneously, then the object had an absolute velocity. It's not even debatable!

Does not answer the original question I asked, about absolute velocity for a single frame, which he also claims is:

If a light source in space emits light, one second later the light sphere will have a radius of ~299,792,458 meters. If the source moved during that one second, the source will not be at the center of the sphere. The distance from the center of the sphere to the point the source is at one second is the distance the source traveled in one second.

It has nothing to do with another object.

If the absolute velocity has nothing to do with another object, why introduce two sources of light, and a third object at the point the light spheres meet?

 

[AlexG]

The major problem with MD's universe is that it contradicts over 100 years of experiment and observation, and so does not correspond to reality.

He never acknowledges that though.

 

[James R]

Motor Daddy:

f Einstein's speed-of-light postulate is correct, then a source at the centre of the train will be at the centre of the sphere at all times in the train frame, since the speed of light in that frame is 299792458 m/s in both directions, and in the train frame the source never moves at all.

That simply can't be, James, because if you say the light from the center of the train impacts the ends of the train in the same amount of time, then you are also saying that lights emitted from the ends of the train simultaneously will reach the midpoint of the train simultaneously. But it is clearly stated in Einstein's chapter 9 that the lights impacted the train observer at different times.

I don't have Einstein's chapter 9 at hand, so it's difficult to comment on this. I have no way of checking whether the scenario Einstein was dealing with there is the same as the one we have been discussing.

But you've left out a very important part of Einstein's analysis. You haven't specified which reference frame Einstein was talking about - the train frame or the embankment frame.

Clearly, if the observer is standing in the middle of the train (i.e. on the train, moving with it) and lights are emitted from the two ends, then the ONLY way the light from both ends can reach the observer simultaneously in the train's frame is if the light was emitted at the two ends simultaneously. If the emissions were not simultaneous, neither would the flashes reach the observer in the centre at the same time.

In the embankment frame, light from the two ends can reach the observer on the train simultaneously ONLY if it was emitted non-simultaneously from the two ends, since in this frame it has different distances to travel in each direction.

Conclusion: the light might well have been emitted simultaneously in the train frame, but in that case it was not emitted simultaneously in the embankment frame. And I'm guessing that's what Einstein was telling you in chapter 9.

The rest of your reply bases its assumptions on Einstein's incorrect 2nd postulate.

You haven't shown it is incorrect.

I note you have still produced no real-world evidence to show that your postulate is correct and Einstein is wrong? Do you ever plan to present evidence?

I'll say it again, James, the situation is not reversible. The train observer can't justify the train being at rest and the embankment being in motion, because each observer was at the midpoint between A and B when the lightening struck A and B simultaneously. The embankment observer was impacted by the lights simultaneously and the train observer was impacted by the lights at different times. In order to reverse the situation, the train observer would have to be able to say that it was himself that was impacted by the lights simultaneously, and that the embankment observer had the lights hit him at different times.

What you describe is impossible, even in Einstein's world, so you've mixed something up.

If two photons of light enter an observer's eye simultaneously in one frame, they enter the observer's eye simultaneously in every frame. Simultaneity can never be lost for events that occur at the same location. Simultaneity is only ever relative for spatially-separated events.

Note that the emissions of the lights from the ends of the train happen at different locations - the two ends of the train, which are spatially separated. The seeing of the light happens at one spatial location - the location of the guy standing in the centre of the train.

The lights impacting the embankment observer simultaneously proves the embankment was at an absolute zero velocity.

Lights impacting the embankment observer simultaneously only tells you that in the embankment frame there were equal distances between the sources of those lights and the observer (and that the embankment observer did not move relative to those sources). In other words, it tells you that the velocity of the observer was zero in the embankment frame. It says nothing about any velocity of the embankment frame itself.

 

[Motor Daddy]

Relativity says that the train observer finds the speed of light to be 299792458 m/s relative to the train. That is why the train observer can use the standard definition of the meter without having to account for his "absolute velocity".

Relativity also says that the embankment observer also finds the speed of light to be 299792458 m/s relative to the embankment. Thus, the embankment observer can also use the standard definition of the meter without having to account for his "absolute velocity".

But in order for both of the above things to be true, some ideas have to be discarded. One of those ideas is the notion of "absolute simultaneity". The clocks at rest in any one reference frame can only be synched according to one reference frame.

If there were observers at A and B on the train, and A and B on the embankment, when the points on the train were aligned with the points on the embankment, would their watches agree that it is exactly 12:00:00?

There is no duration to the term 12:00:00, it is a point in time. There is no motion that occurs at the point in time 12:00:00. There is no relative velocity from 12:00:00 to 12:00:00 because there is no duration of time. It is a point in time.

In order for the train observer and the embankment observer to be at the same location at the same point in time (12:00:00) their watches must read the exact same thing.

Do you agree?

 

[Motor Daddy]

Motor Daddy hasn't figured out what's wrong with this argument.
He does seem to think that light itself can be used as an absolute frame of reference.

I don't just think that, I've mathematically proved that.

Light travels in space.
Objects travel in space.
The meter is defined by light travel time.
An object travels a distance measured in meters.
The object travels relative to light, because light travel time defines the meter.
The meter is inseparable from a specific light travel time.

That is how I am able to calculate the absolute velocity of a train, from within the train, not using the tracks as a reference. Therefore, since I KNOW the absolute velocity of the train, and I know the relative velocity between the train and the tracks, I also know the absolute velocity of the tracks. My mathematical world is in complete synchronization and every observer agrees with all others, and Einstein's falls apart. He never has two observers agree on anything. What does that tell you??

 

[Motor Daddy]

The major problem with MD's universe is that it contradicts over 100 years of experiment and observation, and so does not correspond to reality.

He never acknowledges that though.

Experiments performed and calculated properly according to my universe are not in contradiction. What is in contradiction is my method compared to the previous methods of calculating those experiments. My way has never been known before, so nobody has ever used the method to calculate any experiments.

Maybe you don't understand. I've done what Einstein said was impossible, I've calculated the velocity of a train from WITHIN the train, with no respect to the tracks, or any other external frame or object. Do you understand the significance of that???

 

[AlexG]

Maybe you don't understand. I've done what Einstein said was impossible, I've calculated the velocity of a train from WITHIN the train, with no respect to the tracks, or any other external frame or object. Do you understand the significance of that???

Except you haven't. You assume an absolute frame of reference, which doesn't exist.

All you've done is get it wrong, as the last hundred years has shown.

 

[Motor Daddy]

Except you haven't. You assume an absolute frame of reference, which doesn't exist.

All you've done is get it wrong, as the last hundred years has shown.

I don't assume anything, I measure the time light travels from point A to point B, and use the definition of the meter to calculate the length and velocity.

You on the other hand, have no idea of what the motion of the train is, so you resort to pretending it's motionless. You keep living in your pretend world, dude. Ignorance is bliss!

 

[Pete]

You ignoring me now, MD?

 

[origin]

Experiments performed and calculated properly according to my universe are not in contradiction. What is in contradiction is my method compared to the previous methods of calculating those experiments. My way has never been known before, so nobody has ever used the method to calculate any experiments.

Nothing needs to be calculated. Your whole premise is based on the assumption that the speed of light changes relative to the observer. All you have to do is to present some evidence (measurements) that the relative speed of light varies with the observers speed. Untill you can do that your analysis is pure and simply based an idea in your head and not reality. A result based on a faulty premise is crap. Show a mesurement where c varies with the speed of the oserver. If you can't then your premise is wrong, your analysis is wrong and your results are wrong.

Maybe you don't understand. I've done what Einstein said was impossible, I've calculated the velocity of a train from WITHIN the train, with no respect to the tracks, or any other external frame or object. Do you understand the significance of that???

There is absolutely no significance what so ever. You have in essence said, "if we ignore that the speed of light is always measured as c regardless of the inertial frame then I can get a nonstandard result". Gee really! If I ignore that gravity is an attractive force then people can jump into outer space. I can even calculate their velocity based on how strong there legs are - amazing huh?

You don't present evidence because you know that there isn't any, whcih means you are simply screwing around and trolling.