Existence

Hi ICANT, Right on bro! It's about time. I'd guess that I've written more than 50 messages whose point was to get you to admit that. I sense some real progress.So, when you said that the salt flats suddently receded, that was not a correct description. There is nothing sudden about changing coordinate systems. Coordinate systems exist without regard to whether or not we choose to talk about them. In fact the coordinate systems exist regardless of whether any object is at rest in said coordinate system. They just are not all that interesting.And as you've just acknowledged changing coordinate systems does not affect the motion of the objects.So why don't you apply that same principle to the angles, speeds, and directions as they appear in different frames? When I point out that the angle of a light beam is 60 or 63+ degrees in one frame, that does not make the photon stop traveling at 90 degrees in some other frame. Stop babbling about some angle changing from 90 to 60 degrees. That ain't what happens.Now back to the question you did not answer Poppycock. I suppose I could just say, okay make a hole in the roof, but I cannot let this go.Are you suggesting that it is impossible to direct a beam to hit the sensor using a laser pen mounted on the roof of the car? That we cannot somehow weld the pen to the roof and pick some angle, possibly 26.57 from vertical, for which the photon will strike the sensor. Sorry dude, but I think we both know that there is no need to fire the beam from inside the car. That's just a stalling tactic to avoid the shoe drop that's coming.Even if we locate the laser pen on the car roof at the base of the pole, there is some angle at which we can direct the light pen at which will result in the the photon travelling to the sensor atop the pole.Consider this. If the light pen is mounted at the base of the pole, the only straight line paths to the sensor in the car frame of reference are lines essentially parallel to the four foot pole. If the photon travels in a straight line and if it hits the sensor from the point on the car I've described, the photon must travel along such a path in the car frame of reference. Period. There are no other straight line paths between the base of the pole and the sensor.But if the photon pulse is moving parallel to the vertical pole, what angle does that constitute, as measured in the reference frame of the car?Okay, make a hole in the roof at the base of the pole if you need to. It won't change anything.C'mon ICANT. You started this message doing so well. I can hear the cogs meshing...Edited by NoNukes, : change pen to sensor.

Hi NoNukes, If the laser pen is installed at a 90 angle relative to the travel of the car on the tracks will the pulse hit the detector as drawn in Message 950? Lets see if I understand what you are trying to say.

y = pen
x = sensor
| = direction pen pointed when pulse emitted.
> = direction of car traveling at 0.5 c.
                |          |         |          |
                y          y         y          y

                                     >>>>>

     x          x          x          x          x
     S          D          S          D          S  

The signal is sent when the sensor passes over the first S.
This signal causes the laser pen to release a pulse at the first y.
At this point the sensor mounted on the car just above the tracks is over the first D.

y
.
.
.
.
.
x     x  

Are you saying because the sensor mounted on the car and has moved 2 feet from the first x to the second x the pulse can not travel at a 180 relative to the position the laser pen was in when the pulse was emitted?You do realize the laser pen is directly over the second x when the sensor gets there as they are attached to the same frame.Is Newton's first law which is

quote:

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Newton's First Law states that an object will remain at rest or in uniform motion in a straight line unless acted upon by an external force.

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incorporated and operational in postulate #1 of SR?If so what external force do you apply to cause the pulse to travel at an angle? What difference does it make whether the laser pen is mounted on the frame added to the car or mounted on the ground and trigered by a sensor on the car.The pulse when emitted from the laser pen will travel in a vacuum in a straight line in which the laser pen is pointed at the moment the pulse was emitted.That means the location the sensor on the car is after it has moved 2 feet will have no effect on the pulse that was emitted from the laser pen directly above the detector on the track. The pulse will hit the detector and cause the light to flash.God Bless,

That is when the pulse is emitted. That pulse still has to travel the distance between the pen laser and the tracks. By the time the light pulse travels that distance the pen laser will be directly over the second S, will it not? If the pulse is travelling in a straight line from the pen laser in the car's frame of reference then the light pulse will strike the second S.

Photons are not objects, they don't have rest mass, and are not subject to this law.The detector cannot move relative to the car because its attached to it.But yes, the thought you're having of the light moving at an angle should help. Since its an angle, its going to have to travel a longer distance than a perpindicular line.Now, Velocity is distance over time. Since the distance is longer, and the velocity must remain constant, then the time component has to become larger. That is time-dilation.Edited by Catholic Scientist, : No reason given.

Hi Taq, Do you ever read anything posted?Are do you just put your fingers in motion and allow them to type anything without first putting your brain into gear?The experiment is set up with the car traveling over the Salt Lake Flats at 0.5 c relative to the Salt Lake Flats.There is a pole mounted on top of the car at a 90 angle relative to the travel of the car. On top of that pole is exactly 4 feet from the exterior surface of the roof of the car. The detector extends 9 inches towards the rear of the car.The laser pen is mounted through the roof of the car flush with exterior of the roof at a 90 angle relative to the travel of the car.The laser pen is not mounted at an angle other than 90 relative to the travel of the car.Now according to Newton the pulse will travel in a vacuum in a straight line at a constant c unless an external force is applied.This law of Newton is a part of postulate #1. Yes. Yes the pulse will travel in a straight line relative to the pole.The problem is the pole is moving as it is attached to the car that is traveling at 0.5 c relative to the emitted pulse. So the pulse will travel in a straight line path from the point it was emitted which will be 2 feet from the pole when the pulse reaches the 4 foot height the detector is from the roof of the car.Therefore the pulse will miss the detector. But the pulse is not traveling parallel to the vertical pole, because the pole is moving at 0.5 c horozontal relative to the vertical motion of the pulse. The laser pen has been mounted through and flush with the exterior of the roof of the car since Message 827.God Bless,

So that's your hypothesis. Now when you actually test it and you find that the puls *IS* hitting the detector, how are you going to explain your results?You gonna have to use time dilation.

Hi ICANTI really appreciate the effort you've but in to dissect my post. The post was long, but I can tell you've thoroughly considered my remarks. Let me help you over some rough spots. I'm not committing to anything like that. Tell me what reference frame you are measuring the angle in and I will answer your question. But that detail does not matter for the purpose of this discussion. It is certainly possible to direct a photon along the paths you describe. Let's just say that you have done so. I'm not saying anything at all about the direction of the pen. For the purpose of this discussion it is unnecessary for me to do so, and I'm trying to stick to what common ground there is between us. Right now I agree that you can have light beams that are vertical in the track reference frame. It is not important to me for now how they got there. I've been clear that both the direction of the light pulse and the direction of the laser pen are different in different frames. So it's pointless to ask me a question about the direction of the pulse without specifying a reference frame. Right now I'm discussing things in the reference frame in which the car and sensor are stationary. Other than being noncommital on the direction of the light pen, I'm taking the drawing in this current post of yours as accurate. It's pointless, but amusing for you to lecture me on Newton or any other aspect of classical mechanics. F = ma does not apply to photons because photons have no mass. What force does Newtonian mechanics predict is required to accelerate a massless particle such as a photon? Newton's law of inertial and F=ma make absolutely no prediction whatsoever regarding the force needed to change the direction of photons or any other massless particle.More importantly, I have never claimed that the photon changes direction. What has changed is the reference frame in which the photon's direction is being measured.What force is required to change the speed of a car from 0.5c in one reference frame to zero in a different reference frame? The correct answer to that question is, "Are you daft, dude?" Those circumstances exist simultaneously. No force required. True, but not relevant and not contrary to any position I've taken. It does not matter one iota why the photon got released. What is important is that the photon was released at the first point y. The coordinates of point y are 4 feet high and directly over the sensor at the time of release. Since the sensor is the zero point for both the X and Y axis, the coordinate of the photon relative to the senor is (0 feet horizontal, +4 feet vertical). I certainly do. But we are talking about the coordinates of the photon and not the location of the laser pen. At the first point X, the photon happens to be at the laser pen. It does not stay there.Is the photon at the laser pen at the point in time where the laser pen is over the second X, or is the photon at 'D' as you yourself have stated? Well the photon is at D, not X and not S, so let's stick with what's relevant. At the point in time where the photon reaches D, zero feet high, the photon is two feet behind the sensor which is then at the second X. At least that's what you've stated. Photon Coordinates (-2 feet horizontally, height 0 feet)You haven't provide a single argument that the coordinates of the starting and ending point for the photon in the car reference frame are not as I have given them. And for good reason. I have correctly calculated the coordinates in the car/sensor based reference frame. Other than ignoring SR, there is no error.

Did you read the name of the person you are responding to? Wrong. We are using the driver's frame of reference. In this experiment, the car is stationary and the salt lake flats are moving 0.5 c relative to the car. Um, dude, Newton was wrong. We are using Einstein's equations, not Newton's. The discussion we are having deals with the end points of this straight line, and where they are relative to each other in a given frame of reference. I think we all agree that light moves in a straight line. What you keep getting wrong is the endpoints of those straight lines. The pole is stationary with respect to the pen laser. It is the salt lake flats that are moving relative to the pen laser.Edited by Taq, : No reason given.

No, this is incorrect. The pole is not moving at all in the reference frame of the car. Thus, in the reference frame of the car the pulse will strike the detector. No, this is incorrect. If the pulse were traveling at .5 c relative to the car or the car .5 c relative to the pulse, then an observer in the car would observe that the speed of light was .5 c.But we know what speed of light the observer in the car has to observe: c. Therefore we know that the pulse is moving at c relative to the car. Completely wrong. The pulse's path of travel in the reference frame of both the car and both the salt flats is straight, and it intersects with the detector in both reference frames. When it intersects with the detector in each reference frame - that's what's different, and that's the result of time dilation/ Everyone is agreed on this, ICANT, and no one has ever been able to exploit your "light doesn't take on velocity" position to construct a universal intrinsic velocity detector. Why do you suppose that is the case?

Hi Taq, Yes. Yes. The pulse does not travel in a straight line from the laser pen.So no the pulse will not strike the second S.The pulse is not traveling verticle relative to the position of the pen.The pulse is traveling verticle relative to the position the pulse was emitted at Y.At the moment the pulse is emitted from the laser pen at Y which is mounted at a 90 angle to the motion of the car the pulse is in a vacuum with nothing to exert force on it to change it's direction.Since it was emitted at the point it was directly over the detector aimed at the detector the pulse will hit the detector and cause the light to flash.For the pulse to somehow change its direction and hit the S as you claim there would have to be external force placed upon the pulse to change it's straight line journey to the detector.What do you propose to exert that force.In the modified light clock on my cycle where the pulse is in a vacuum tube the tube exerts external force on the pulse as it travels between the mirrors and forces the pulse in the direction the cycle is traveling.But in the open vacuum there is nothing to force the pulse to not travel at 180 relative to the laser pen which is mounted at a 90 angle to the travel of the car.God Bless,

Why not? Why not? The pen laser is pointed straight down. Why doesn't the light pulse travel straight down? In the car's frame of reference, the car is not moving. Please adjust your math accordingly. The tracks, sensors, and detectors are moving in the car's frame of reference. It was emitted at a target moving 0.5 c relative to the motionless car. Are you saying that there is some sort of aether that causes the light to be drug along by the moving sensors and detectors? That is the most ludicrous thing I have ever heard. Tubes do not exert force on photons.

Hi crash, How do you place the pulse in the frame of the car?The pulse has it's own coordinate system. It has distance from the laser diode and distance from the pole and distance from the detector.So the car is traveling relative to that coordinate system at 0.5 c. The pulse is traveling at c in a straight line relative to the position of the laser pen at the point the laser pen was activated and the pulse was emitted, which is at a 90 angle relative to the motion of the car.So the statement the car is traveling at 0.5 c relative to the point the pulse was emitted at is true. And if you want to say the point the pulse was emitted at is traveling at 0.5 c relative to the car that is also true. Maybe I did not make that clear. If you disagree explain why. To be correct you would have to say the observer will observe the pulse moving at c at a 90 angle relative to the motion of the car. I was talking about the car with the laser pen mounted on a frame on the rear and you are talking about the one with the laser pen in the roof with the pole on top. So I will make you a diagram.

D = detector
P = pulse emitted
| = direction pen pointed when pulse emitted.
> = direction of car traveling at 0.5 c.

     D          D          D

                  ^ 4 feet
                     direction of car travel  >>>>>

     ^          ^ direction pulse emitted
     P  > 2'    P
     |          | 

The laser pen is located below the P in the position it is in when the pulse is released.So the pulse is released from the pen at the first P in the direction the pen is pointed.
You say the pulse will travel in a straight line but will hit the second detector rather that the one directly above the point the pulse is emitted.What causes the pulse to change it's straight line direction so it hits the second detector instead of the one directly above the point the pulse is emitted?God Bless,

Hi ICANT,I think you meant to direct your remarks towards me and not Taq. Looks like I changed things a bit, didn't I. And further, I announced that I was doing so as well, didn't I? In response to which you insisted that an potential angle of 26+ degrees was required.From Message 961Any doubt now that I announced changing the angle and that you at least considered the idea and told me that I had to install the laser pen in a certain way. It is not necessary to install the laser pen in quite that way, and there is nothing wrong with modifying a thought experiment as long as you make the modification clear.Do we react this way when you modify thought experiments?Now go apologize to Taq.Given that your remaining remarks apply to the unmodified thought experiment, I'll ignore them. I think we are covering the same ground in your modified salt flats experiment anyway. Hey, how did those modifications sneak in there???

By measuring its position over time in a coordinate system whose origin moves with the car.I can place anything in any frame of reference at any time, but an object's inertial reference frame is the one in which it is not accelerating (has constant velocity, frequently constant zero velocity, i.e. is at rest.) A frame of reference is a frame, a coordinate system, for reference, i.e. a convenient or simplifying way to describe where an object is at different points in time. No, that is incorrect. The car has velocity .5 c in only one coordinate system - the reference frame of the salt flats. Relative to the emitter+detector system, the car has zero velocity. Relative to the car, the pulse can have only one velocity - c. The speed of light is the same for all observers, remember? The point in what coordinate system? Remember we're talking about multiple frames of reference, and your continued effort to obfuscate which frame of reference you're speaking from is the source of your confusion. When you become appropriately diligent about making explicit the frame of reference from which you're operating when you make statements about this "point" or that, you'll see that we have been correct all along. I have explained why. It's a matter of verified fact that the speed of light is the same for all observers regardless of their velocity, so the observer in the car can only observe pulses of light travel at c. They can never go any slower than that in a vacuum. That's what I did say the observer in the car would observe. The observer on the salt flats, however, because he is in a different reference frame and therefore in a different coordinate system, observes the path of the pulse at a shallower angle than 90° to the motion of the car. It doesn't matter where the emitter is located on the car. Light pulses leaving it will only travel at c. It doesn't matter how fast the car is going or the direction in which the emitter is located; observers in any reference frame will observe that light leaves the emitter at the speed of c. Nothing. The light pulse never leaves its straight line direction, so it hits the detector directly above where it is pointed. How many times do we have to explain that?

Inertial frames are not containers. They are a set of coordinates relative to an observer. I highly doubt that, given the fact that length contraction and time dilation at c is infinite.However, the driver does have his/her own coordinate system, and that is the one we are using. In this coordinate system, the pen laser and car are not moving, but the tracks, sensors, and detectors are. Which observer are you talking about? Your diagram is wrong. For the driver, the car and pen laser are stationary. The tracks, sensors, and detector are moving.Edited by Taq, : No reason given.