Existence

As measured in any inertial frame of reference.An "inertial observer" would be the one doing the measuring in that inertial frame of reference.

Except that it can't be independent of the car and the motion of the car, but somehow not independent of the salt flats and the motion of planet Earth, and not independent of the motion of the Sun though the galaxy, and not independent of the motion of the galaxy through the universe, and so on.What is so special about the car's reference frame that its motion is uniquely not imparted to the photon when it is created? Well, try this:

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Suppose you are moving toward something that is moving toward you. If you measure its speed, it will seem to be moving faster than if you were not moving. Now suppose you are moving away from something that is moving toward you. If you measure its speed again, it will seem to be moving more slowly. This is the idea of "relative speed."

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Before Einstein, scientists were trying to measure the "relative speed" of light. They were doing this by measuring the speed of starlight reaching the Earth. They expected that if the Earth were moving toward a star, the light from that star should seem faster than if the Earth were moving away from that star.

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They noticed that no matter who performed the experiments, where they were performed, or what starlight they used, the measured speed of light in a vacuum was always the same.[1]

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Einstein said this happens because there is something unexpected about distance and time. He thought that as the Earth moves through space, our clocks slow down (ever so slightly). Any clock used to measure the speed of light is off by exactly the right amount to make light seem to be moving at its regular speed. Mentally constructing a "light clock" allow us to see exactly how to explain this remarkable fact.

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Also, Einstein said that as the Earth moves through space, our measuring devices change length (ever so slightly). So, any measuring device used to measure the speed of light is off by exactly the right amount to make the starlight seem to be moving at its regular speed.

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Other scientists before Einstein had written about light seeming to go the same speed no matter how it was observed. The idea that made Einstein's relativity so revolutionary is that light does not just seem to go the same speed, it is always going the same speed no matter how an observer is moving.

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http://simple.wikipedia.org/wiki/Special_relativity

It is not found verbatim in what you quoted. So what? It is a fact nevertheless. It is in fact, a statement of postulate #2.As you yourself are completely aware, there are a number of completely equivalent, variant statements of postulate #2. I'm not stuck with the version of postulate #2 that you chose to provide here. Your pretense that there is no other version, when you yourself posted and linked to another one is just like you.You can find the version of postulate #2 that describes the speed of light as measured in any inertial reference frame being "c" in any physics textbook, or on wikipedia at the link you yourself provided. As I've discussed on several occasions in this thread, Einstein himself used the fact in his paper on relativity. That statement implies that an observer at rest in an inertial frame will always measure the speed of light in a vacuum to be c. If you insist on evidence, I'll provide it. But the fact is actually rather difficult to avoid. No ICANT. The car is at rest in one frame and moving at 0.5c as measured in a different frame. Neither the car nor the photon can be at rest and moving simultaneously as measured in a single frame. That's simply not possible. Actually, you cannot. You cannot do such a thing and still perform any physics or any meaningful observations. Since postulate #2 requires that photon move in a vacuum at speed c as measured in any reference frame, all information regarding the speed of objects other than the photon would have loose their meanings making it impossible to solve a physics problem. In your proposed frame, but the ground and the car would both be moving at speed c. The information that they moving at 0.5c relative to each other could not be applied in "photon frame"Going further to apply SR, then length contraction and time dilation associated with a frame moving at speed c would be infinite, meaning that distances along the direction of motion would collapse to zero, and no time would pass. Sorry ICANT, but a photon frame just does not work.But more to the point, claiming that we have a photon frame is a mere diversion. The photon will have coordinates and a speed c in both the track frame and the car frame regardless of whether there is a photon frame. We still have to apply postulate #2 to the car and track frames regardless of whether there is a photon frame. Your only purpose for bringing up a photon frame is to avoid discussing the other frames.You can bring up photon frames if you will. Expect that my response will be something like, "... but in the car frame, the photon is moving at a right angle to the direction of motion of the tracks with speed c." You of course will ignore what I say.

Nicely said, Scientist. Succinct and to the point. Quite unlike my own verbose response!

Hi NoNukes, What unbalanced force would be applied to the pulse to cause it to miss the blackboard if the blackboard was mounted on the ground 25 feet from the track? You need to rephrase the question to ge the answer from me that you want to hear.

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So, ICANT what is the angle between the motion of the car along the tracks and the trajectory of the photon?

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The laser pen and the blackboard are at rest in the car relative to the car. So the trajectory of the photon relative to the motion of the car is 90.Now if you want the angle created between the point the pulse was emitted and the point the photon hits the blackboard due to the track moving relative to the laser pen and blackboard, I need to know the distance between the laser pen and the blackboard.You do realize we are now back to the same point we were on my cycle with the light clock. The laser pen and blackboard are at rest in the car, just as they are in the classroom.God Bless,

Hi CS, And what does an "inertial observer" have to do with light always being propagated in empty space with a definite velocity c that is independent of the state of motion of the emitting body.It says absolutely nothing about being propagated in empty space with a definite velocity c that is independent of the state of motion of the observing body.You are taking liberties with words that you do not allow me to do with Bible verses.God Bless,

The connection is that an inertial observer - any inertial observer - will observe the speed of any light in any reference frame to be c. What says nothing? Please be specific. Which words? Please be specific.

Actually ICANT, we are not at the same point. I do agree that the situations are remarkable similar. But for some reason you are now admitting that the angle between the tracks and the photon trajectory in the track frame is (due to the motion of the blackboard) different from the 90 degree angle measured in the car reference frame. The line connecting the emitting point and the point at which the photon strikes the blackboard is indeed the trajectory of the photon.What's new is that you have never admitted such a thing before.
And that Mr. ICANT, was the entire point of the experiment. To demonstrate that the photon trajectory creates different angles in the two different reference frames.I'll allow you to calculate the angle, which I predict will turn out to be a very familiar number. Make the distance from the light pen to the blackboard 10 feet (or any other distance other than zero that you find convenient) and let me confirm that the the car moves at 0.5c in the track frame of reference.I did want to point out another error in your thinking about reference frames. When I say that the car is moving at 0.5c in the track frame of reference, I don't need to additionally name an object that the motion is relative to. The car is moving at 0.5c relative to any object that is at rest in the track frame of reference.Edited by NoNukes, : No reason given.Edited by NoNukes, : Redo entire postEdited by NoNukes, : Change post completelyEdited by NoNukes, : No reason given.

Your answer is absolutely correct, and yet your answer still boggles my mind.Are you suggesting that if the laser pen and blackboard were mounted on top of the car rather than inside the car, that the photon from the laser pen would miss the blackboard.Yes, I think you do believe exactly that. You must if you also believe that the sensor on top of that pole was missed in that other experiment.Please tell me that I'm wrong about you. I must be wrong...ABE:And yet, I don't see how I can be wrong. The ridiculous tube you added to the light clock, your insistence on using an open flat car in the train experiment, your attempt to distinguish between the car frame of reference and the driver's frame inside the car. Your complete inability to rationally discuss frames of reference.Man do I feel foolish...I'm arguing about special relativity with a man who thinks physics works completely differently outdoors than indoors.Tell me, ICANT,How big an opening in the car would be needed to cause photons to start missing the blackboard. Would opening a window be enough? Opening the sun roof? Opening the rear hatch?Edited by NoNukes, : Reprise..Edited by NoNukes, : Yikes

The fact that it doesn't matter where the observer is, they will always measure light as having the speed c.Even if the observer is heading right towards it at 0.5c, the light will have a measured speed of c.If we're talking about bowling balls, then if you measure one's speed while your'e flying towards it, then its going to look like its going faster than it actually is, because you're moving too.That doesn't happen with light, its always going the same speed no matter what. Do you deny that that is ture?

Hi ICANT,You seem to be making a deliberate effort to ignore the consequences of postulate #2 even while asserting the postulate. You continue to ignore that very important part of postulate #2, and then are surprised when it is pointed out to you that your understanding is wrong. That definite velocity is "c" as measured in any reference frame. If the speed of light is "c" in a reference frame, that means that the speed of light is "c" relative to an observer at rest in the reference frame.Do you know how to measure the speed of light in a reference frame. You do that by using the coordinate system and clocks in the reference frame to calculate distance traveled by light. We will find that the speed of light relative to an object at rest in the reference frame is always "c" as directly required by postulate #2.Let's demonstrate that postulate #2 as you cite it requires that the speed of light in a vacuum be "c" for any inertial observer.Once we've picked one inertial reference frame, we also know that any reference frame moving at constant speed as measured using the coordinate system of that first reference frame is also an inertial reference frame. An observer at the origin of such a reference frame will measure "c" for the speed of light.Since postulate #2 says any inertial reference frame, then we can pick any observer moving at constant velocity, since any such observer will be at rest in some inertial reference frame. Therefore, any observer moving at constant speed must measure the speed of light in a vacuum to be speed "c".It's just that simple ICANT. The phrase "as measured in any inertial reference frame" inescapably means that all observers moving at constant speed will measure the speed of light to have the same value. The two phrases are equivalent, and given your admitted inability to give meaning to the phrase "as measured in any inertial reference frame" (See Message 1028) your denials are worthless.Here's you again on postulate #2. I think the exchange above sums up all of your arguments on special and general relativity. You don't understand the subject, and your arguments don't even get to the point of attacking what GR and SR predict. All you really have are denials, appeals to quacks as authority figures who for the most part have been demonstrated to be wrong, and science that you make up on the spot.

Since ICAN'T can not seem to draw the diagram from the reference frame of the driver of the car it seems that I will have to do it for him. As before, the sensor (S) will send a signal to pen laser (P) at c. The pen laser is aimed at an angle of 90 degrees with the Salt flats. There is a detector (D) between each sensor (S). We will be using the reference frame of the driver. I will include the position everything when the pen laser emits the first photon (1), when the photon is half way to the track (2), and when the photon strikes the tracks (3).(1)

D   ----driver looking down towards track
                         P   ----pen laser is motionless
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.                   S----D----S----D    {----movement of track

(2)

D
                          P
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                   S----D----S----D  {----movement of track

(3)

D
                          P
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                S----D----S----D   <-----movement track

That's what happens from the drivers frame of reference. Can ICAN'T show where I made an error?At every point the pen laser is firing straight down from the driver's frame of reference, just as it should be since the pen laser is not moving in the driver's frame of reference. Only the tracks, sensors, and detectors are moving in the driver's frame of reference as shown in the diagram. At every moment the photons from the pen laser are directly between the driver/pen laser and the tracks. It does not travel at an angle in the driver's frame of reference.Edited by Taq, : No reason given.

How is it possible in this day and age for relativity and special relativity (already experimentally confirmed) be in question? Cant people who doubt these basic tenants of physics read? Is it some nation wide conspiracy??????? I am confounded that something as fundalmental in physics, of which has been universal and accepted as well as the corner stone in modern phyics is being treated as some sort of consipracy. If it where voodoo physics then half the shit in ER and Surgical suits would not work. Most modern telecom devices would be defunked. Every single advance in science since Einstiens papers would not be making contributions in developing scientific devices. Its one thing for some jackass to say,," Well uh,,, I dont get it." But to say..
"Well uh,, I dont get it, because it dont make no sense to me, so it must be wrong." lol...bahhhaawaahhhhhaaa!!lmao!!!Edited by 1.61803, : No reason given.

Take a look at the username. ICAN'T . . . (add sentence here).