The Relativity of Simultaneity
- Thread starter Motor Daddy
- Start date
Another smart
guy on the record. I'll put you down as a "No", you do not believe that the light sphere expands spherically from the point of origin in space and traverses space potentially forever. That means, you do not think the light wave has a physical presence that is established when it is emitted and exists as long as the light wave traverses space.It doesn't really matter if anyone believes a light sphere expands forever, or if it has a physical presence in space.
What matters is measuring distances and times. Nobody knows how else to measure "light" except by comparing times and distances. It's the only physical evidence available, which is why Einstein starts with definitions of time and distance.
Actually he assumes that the definition of a distance is one that everyone understands "heuristically". So he actually starts with a good heuristic for our idea of time, using the notion of distance "traveled" to a mirror and back. He even states that doing this appears to lead to a useful definition of time in terms of the speed of light, and only has to assume that light is measured at c in all frames of reference.
This is a bigger deal than it looks at first (but I'll leave out what that is, or where to go from here, there are a lot of books, online references and forums that have this covered)
What matters is measuring distances and times. Nobody knows how else to measure "light" except by comparing times and distances. It's the only physical evidence available, which is why Einstein starts with definitions of time and distance.
Actually he assumes that the definition of a distance is one that everyone understands "heuristically". So he actually starts with a good heuristic for our idea of time, using the notion of distance "traveled" to a mirror and back. He even states that doing this appears to lead to a useful definition of time in terms of the speed of light, and only has to assume that light is measured at c in all frames of reference.
This is a bigger deal than it looks at first (but I'll leave out what that is, or where to go from here, there are a lot of books, online references and forums that have this covered)
Thank you, I've been using this text ...
http://www.bartleby.com/173/,
but like you say there are many sources out there.
I think I understand the text that covers what you are saying about the solid foundation of Einsteins SR. However, I also think that it does matter whether or not you believe that a light sphere has an ever expanding presence as it travels at c from the point of origin. It means that the calculations of light speed of a particular light sphere from the moving box are correct if you buy the scenario.
Though the ramifications are great, I don't think that anything will come of the moving box scenario anytime soon; ideas like this have been around a long time and get no traction. SR is not threatened so no one should get all upset about the fact that there is a quirky little cult out there that believes it. It only encourages the cult when people refuse to admit the obvious and resort to ridicule. Sounds familiar when I say that, lol.
Hi quantum wave,
In reality, the light sphere is composed of countless light rays moving in different directions. You identify the sphere by selecting particular points on the path of each light ray, and this selection can be done in different ways.
So while each light ray departs from it origin and progresses potentially forever, you can't unambiguously identify *the* light sphere at any time after emission - the identity of the sphere depends on the standard you use to select the points on each light ray.
Have a look at the train observer exercise I worked through with Motor Daddy so many pages ago.
From that exercise, you should be able to see that if the universe works in a particular way, then you can set up simple and consistent measurement systems that will measure the box as moving in any direction at any speed, or not moving at all, while the centre of the light sphere always stays centred on the box.
The problem is that this question implies that the light sphere is a single coherent entity that can be uniquely and unambiguously identified at any given instant.
In reality, the light sphere is composed of countless light rays moving in different directions. You identify the sphere by selecting particular points on the path of each light ray, and this selection can be done in different ways.
So while each light ray departs from it origin and progresses potentially forever, you can't unambiguously identify *the* light sphere at any time after emission - the identity of the sphere depends on the standard you use to select the points on each light ray.
Have a look at the train observer exercise I worked through with Motor Daddy so many pages ago.
From that exercise, you should be able to see that if the universe works in a particular way, then you can set up simple and consistent measurement systems that will measure the box as moving in any direction at any speed, or not moving at all, while the centre of the light sphere always stays centred on the box.
Motor Daddy:
Here is a picture of what happens in reality (i.e. the world described by Einstein) for your source in a square box:
The three diagrams on the left-hand side show successive snapshots in a reference frame in which the box moves to the right with some speed. The three diagrams on the right show the same snapshots in a reference frame in which the box is stationary.
Or, to put it another way, the left-hand diagrams show the situation in the frame of the "embankment", where the box is on a moving train. The left-hand diagrams show the same situation in the frame of the "train".
The first thing to notice is that the box is square on the right and rectangular on the left. This is due to length contraction. In the train's frame, the box is at rest so it is square/cubical. In the embankment frame, the box is moving and so relativity tells us that it contracts in the direction of motion.
Also note that in the left-hand diagrams the box moves to the right, because the embankment sees the train moving to the right. In the right-hand diagrams, the box does not move, because a person on the train does not see the box move.
The next thing to notice is the round dot marked on each diagram. That is the location at which light was emitted, which doesn't change in each frame.
Next thing: the three diagrams show the light wave spreading out. The wavefront is circular/spherical in BOTH frames, due to Einstein's speed-of-light postulate. Note in particular that in the Motor-Daddy universe the wavefront would NOT be circular in the train frame, since the speed of light travels at different speeds in different directions in the Motor Daddy universe.
The top two diagrams shows the wavefront a short time after emission.
The middle diagram on the left shows the wave hitting the "back" wall of the box in the embankment frame.
The two bottom diagrams shows the situation when the wave hits the "front" wall of the box. Notice that in the train frame the wave also hits the back wall at this time.
The middle diagram on the right shows a time in the train frame where the light wave has not yet reached either wall of the box.
Next thing to note: in the train frame, the light wave hit both the front and back of the train simultaneously (as shown in the bottom-right diagram). In the embankment frame, the walls were hit at two different times - first the back wall (middle-left diagram), then the front wall (bottom-left diagram).
It is important to remember that two different clocks are being used on the right and on the left. The diagrams on the left use the embankment clocks; the diagrams on the right use clocks on the train.
Here is a picture of what happens in reality (i.e. the world described by Einstein) for your source in a square box:
The three diagrams on the left-hand side show successive snapshots in a reference frame in which the box moves to the right with some speed. The three diagrams on the right show the same snapshots in a reference frame in which the box is stationary.
Or, to put it another way, the left-hand diagrams show the situation in the frame of the "embankment", where the box is on a moving train. The left-hand diagrams show the same situation in the frame of the "train".
The first thing to notice is that the box is square on the right and rectangular on the left. This is due to length contraction. In the train's frame, the box is at rest so it is square/cubical. In the embankment frame, the box is moving and so relativity tells us that it contracts in the direction of motion.
Also note that in the left-hand diagrams the box moves to the right, because the embankment sees the train moving to the right. In the right-hand diagrams, the box does not move, because a person on the train does not see the box move.
The next thing to notice is the round dot marked on each diagram. That is the location at which light was emitted, which doesn't change in each frame.
Next thing: the three diagrams show the light wave spreading out. The wavefront is circular/spherical in BOTH frames, due to Einstein's speed-of-light postulate. Note in particular that in the Motor-Daddy universe the wavefront would NOT be circular in the train frame, since the speed of light travels at different speeds in different directions in the Motor Daddy universe.
The top two diagrams shows the wavefront a short time after emission.
The middle diagram on the left shows the wave hitting the "back" wall of the box in the embankment frame.
The two bottom diagrams shows the situation when the wave hits the "front" wall of the box. Notice that in the train frame the wave also hits the back wall at this time.
The middle diagram on the right shows a time in the train frame where the light wave has not yet reached either wall of the box.
Next thing to note: in the train frame, the light wave hit both the front and back of the train simultaneously (as shown in the bottom-right diagram). In the embankment frame, the walls were hit at two different times - first the back wall (middle-left diagram), then the front wall (bottom-left diagram).
It is important to remember that two different clocks are being used on the right and on the left. The diagrams on the left use the embankment clocks; the diagrams on the right use clocks on the train.
Motor Daddy
Valued Senior Member
Still waiting on your coordinates, James. What are the coordinates of the y receiver at .65 seconds?
Motor Daddy
Valued Senior Member
Pete, you should be studying! Are you now returning to the thread?
Motor Daddy
Valued Senior Member
Maybe you can help James and tell him what the coordinates of the y receiver are at t=.65 seconds? You do have coordinates at time t=0 and t=.65 for the y receiver, correct?
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Very true about the light sphere being composed of multiple rays. When they are considered in-phase they are talked about as curved plane waves. When light passes through a pin hole smaller than the wave length it comes out spherical and in-phase. I am pretty sure there are characteristics of light we don't understand. Anywhere across the curved light plane there is a ray reaching the observer from the point of origin. As the sphere spreads out there are more and more points on the surface in theory and yet each one is a ray. Curious, much science in the field to be considered.
I think you are saying "no" to the question, right?
Hi MD. I'm thinking of working on the graphics today and thought we could start with a picture of the light box itself. I think of it as an open cube framework. I guess the dimensions are that the cube is one light second per edge. There are receptors centered on each of the six sides, and right in the middle of the light cube there is a light source fixed in the center of the box.
When activated, a light burst is emitted from the source and a point in space is established. The point in space where the emission took place remains as our fixed reference point and the box itself has rectilinear motion away from the point of emission. We will be able to quantify the motion of the box relative to the fixed point in space from the data we receive at the receptors on the sides of the box.
We are considering the light burst to be of a spherical nature so that as it expands outward from the point of emission at c (the invariant speed of light) in all directions from a point of emission it becomes an in-phase spherical curved plane wave front.
So do you already have a picture of this light box? I guess I could sketch it out using MS Paint otherwise, though I don't have my staff with me. I'm at the Maple Pavilion on the salt marsh on Upper Tampa Bay Park, among the pines and Saw Palmettos and looking down at the fiddler crabs, lol. Quite a quiet place of solitude on Fridays and I come out here often. It is like a picnic.
When activated, a light burst is emitted from the source and a point in space is established. The point in space where the emission took place remains as our fixed reference point and the box itself has rectilinear motion away from the point of emission. We will be able to quantify the motion of the box relative to the fixed point in space from the data we receive at the receptors on the sides of the box.
We are considering the light burst to be of a spherical nature so that as it expands outward from the point of emission at c (the invariant speed of light) in all directions from a point of emission it becomes an in-phase spherical curved plane wave front.
So do you already have a picture of this light box? I guess I could sketch it out using MS Paint otherwise, though I don't have my staff with me. I'm at the Maple Pavilion on the salt marsh on Upper Tampa Bay Park, among the pines and Saw Palmettos and looking down at the fiddler crabs, lol. Quite a quiet place of solitude on Fridays and I come out here often. It is like a picnic
.Motor Daddy
Valued Senior Member
Hi MD. I'm thinking of working on the graphics today and thought we could start with a picture of the light box itself. I think of it as an open cube framework. I guess the dimensions are that the cube is one light second per edge. There are receptors centered on each of the six sides, and right in the middle of the light cube there is a light source fixed in the center of the box.
When activated, a light burst is emitted from the source and a point in space is established. The point in space where the emission took place remains as our fixed reference point and the box itself has rectilinear motion away from the point of emission. We will be able to quantify the motion of the box relative to the fixed point in space from the data we receive at the receptors on the sides of the box.
We are considering the light burst to be of a spherical nature so that as it expands outward from the point of emission at c (the invariant speed of light) in all directions from a point of emission it becomes an in-phase spherical curved plane wave front.
So do you already have a picture of this light box? I guess I could sketch it out using MS Paint otherwise, though I don't have my staff with me. I'm at the Maple Pavilion on the salt marsh on Upper Tampa Bay Park, among the pines and Saw Palmettos and looking down at the fiddler crabs, lol. Quite a quiet place of solitude on Fridays and I come out here often. It is like a picnic
Yes I do as a matter of fact.
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Oh excellent.
Here is how I view the box itself:
Here is how I view the box itself:
Motor Daddy
Valued Senior Member
Oh excellent.
Here is how I view the box itself:
That is how I envision it too!!!
Do you want to explain what you mean by T= 1.384930 in frame 3? Give me all the details about it for the record.
Motor Daddy
Valued Senior Member
Sure. The light sphere has a radius of 299,792,458*1.384930=415,191,568.85794 meters 1.384930 seconds after being emitted at coordinates (0,0,0). The x receiver received the light at coordinates (1.384930,0,0) at t=1.384930. Light traveled at c, as usual.
But, in the cube frame, it took light 1.384930 seconds to travel the distance of .5 light seconds along the x axis from the source to the receiver. That means light is measured to be .5/1.384930=.361c along the x axis from the source to the receiver in the cube frame.
So you can clearly see from the pic, it would be impossible for light to reach the x receiver in .5 seconds, due to the cube's absolute velocity, and hence, it would be impossible to measure the speed of light to be c from the source to the x receiver in the cube frame.
Thanks, that is what I thought.
Can I be an honorary member of the Light Box Cult?