Invisibility of the Lorentz Contraction

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Invisibility of the Lorentz Contraction

Postby DJ_Juggernaut on July 14th, 2018, 12:32 am 

Invisibility of the Lorentz Contraction
James Terrell wrote:A sphere will photograph with precisely the same circular outline whether stationary or in motion with respect to the camera. An object of less symmetry than a sphere, such as a meter stick, will appear, when in rapid motion with respect to an observer, to have undergone rotation, not contraction.

Hi all. This paper and others indicate that a sphere will look spherical whether it is moving or not. But they claim, that the sphere will appear rotated when it moves. They also say, a rod will therefore rotate instead of contracting. I disagree with the rotation bit.

I made my argument elsewhere and it is this:

Can you see a non-spherical distribution of photons due to relative velocity? I don't think so; due to relativity of simultaneity.

Take a stationary point source that emits light and keep your detector curved to register simultaneous emissions. You get spherical distribution of photons. [inverse square law] Then you move the source and take another photo. Would the two photos look the same? Would the photon distribution be the same? I think so.

Due to relativity of simultaneity, the photon distribution will remain the same whether the source moves or not. Anyone disagree? If so, why?
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Re: Invisibility of the Lorentz Contraction

Postby JMP1958 on July 14th, 2018, 1:45 am 

There will be an aberration in the direction the light from the source is measured as coming from when the source is moving relative to the observer.

This aberration can be found by the relationship:

cosAo = (cosAs -v/c)/(1-cosAs v/c)

Where Ao is the observed angle relative to the line of relative motion, and As is the angle between the line of relative motion and position of the source at the time of emission of the light.

Thus the Light leaving the source when it is abreast of the a given point of the detector will be seen as coming from an angle of ~150 degrees, rather than 90 degrees if the relative velocity between source and detector is 0.866 c.
So let's imagine that your detector is circular. Those parts of the detector that lie on the line of relative motion will see no aberration, while those parts that don't lie on that line will see various degrees of aberration. In other words, the image seen when the source has a relative motion will differ from that when there is none.
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Re: Invisibility of the Lorentz Contraction

Postby bangstrom on July 14th, 2018, 3:22 am 

DJ_Juggernaut » July 13th, 2018, 11:32 pm wrote:Invisibility of the Lorentz Contraction
James Terrell wrote:A sphere will photograph with precisely the same circular outline whether stationary or in motion with respect to the camera. An object of less symmetry than a sphere, such as a meter stick, will appear, when in rapid motion with respect to an observer, to have undergone rotation, not contraction.

Hi all. This paper and others indicate that a sphere will look spherical whether it is moving or not. But they claim, that the sphere will appear rotated when it moves. They also say, a rod will therefore rotate instead of contracting. I disagree with the rotation bit.


I don’t quite follow your explanation but, going by the cited abstract, it says, ”A sphere will photograph with precisely the same circular outline whether stationary or in motion with respect to the camera.” An object of less symmetry than a sphere, such as a meter stick, will appear, when in rapid motion with respect to an observer, to have undergone rotation, not contraction.”

It is my understanding that a sphere in relativistic motion remains circular but Lorentz contraction causes it to flatten in the direction of motion. I explained in the previous “Lorentz” thread how a Lorentz contracted train should appear normal (not contracted) to an observer or a camera so the contraction may be real but not something we can see.

If you consider a long object like a train in the dark with simultaneous flashing lights on both ends, a stationary observer and an observer in the middle of the train should both see the lights flashing simultaneously. But, if the train is moving at relativistic speeds the lights will no longer appear simultaneous to the observer. However, if the train is rotated relative to the observer, it is possible to make the lights appear simultaneous again so the train (or a sphere) appears rotated to the observer. The lights will also appear closer together as the train is rotated and even closer as the train accelerates until the train reaches c and then the two lights will appear as one and the length of the train will be zero.

That is Lorentz contraction but the rotation is not visible because the rotation is in 4-D spacetime rather than in 3-D and the contraction is not visible because the light related time delays between front and back restore the image of the train to its previous length. As the article says, “Observers photographing the meter stick simultaneously from the same position will obtain precisely the same picture, except for a change in scale given by the Doppler shift ratio, irrespective of their velocity relative to the meter stick. Even if methods of measuring distance, such as stereoscopic photography, are used, the Lorentz contraction will not be visible, although correction for the finite velocity of light will reveal it to be present.
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Re: Invisibility of the Lorentz Contraction

Postby DJ_Juggernaut on July 14th, 2018, 6:52 am 

JMP1958 » July 14th, 2018, 1:45 am wrote:There will be an aberration in the direction the light from the source is measured as coming from when the source is moving relative to the observer.

Aberration angle is the tilting of the telescope, and depends on the observer's velocity. Take a laser for example. You are at rest with the laser. It emits a short burst of light at 90 degrees. You don't tilt your telescope, relative to the horizontal. Now you move to the left and repeat the experiment, the telescope needs to be titled to the left based on your velocity. The burst of light still reaches you at 90 degrees, but you need to tilt your telescope. In both instances, the image is the same.

You can extend this to an entire sphere of light, as well. No? That the emissions follow the inverse square law distribution, in both the frames? In other words, the sphere looks the same in both photos.
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Re: Invisibility of the Lorentz Contraction

Postby DJ_Juggernaut on July 14th, 2018, 7:18 am 

bangstrom » July 14th, 2018, 3:22 am wrote:That is Lorentz contraction but the rotation is not visible because the rotation is in 4-D spacetime rather than in 3-D

Ah, okay.
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Re: Invisibility of the Lorentz Contraction

Postby DJ_Juggernaut on July 14th, 2018, 9:40 am 

bangstrom » July 14th, 2018, 3:22 am wrote:It is my understanding that a sphere in relativistic motion remains circular but Lorentz contraction causes it to flatten in the direction of motion.

My interest in the sphere is with regard to how we see it if there is a relative velocity between the sphere and an observer. If length contraction cannot be seen, perhaps one can't see relativistic beaming either. That is, a sphere of light with all its light bunching in the direction of its motion. My contention is, that the distribution of photons will be evenly spread out across the sphere (inverse square law) regardless of relative velocity.

Think of a sphere of light as a set of lasers emitting light in a circular fashion. Each of these lasers will have its own telescope to capture light. Then pick one telescope and extend this reasoning to all telescope and you will have applied this logic to a sphere of light.

Pick a 90 degree ray of light stationary to an observer (telescope). The telescope is vertical and doesn't need tilting. Light is captured by an observer. Move the telescope (observer). It needs to be titled by an angle v/c. Light still reaches the telescope at 90 degrees, it is the telescope that is tilted. Hence in both instances, the image is the same. Applying this to all telescopes, you will get the inverse square law distribution of photons, regardless of the relative motion. That means, in both instances, the image is the same.

I have not included length contraction here. But you could, at high speeds. And simultaneity applies. But the basic premise is the same. The images produced will not be different. With simultaneity, into play, there is just a delay in capturing light. Does this make sense?
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Re: Invisibility of the Lorentz Contraction

Postby JMP1958 on July 14th, 2018, 11:55 am 

DJ_Juggernaut » July 14th, 2018, 6:40 am wrote:
bangstrom » July 14th, 2018, 3:22 am wrote:It is my understanding that a sphere in relativistic motion remains circular but Lorentz contraction causes it to flatten in the direction of motion.

My interest in the sphere is with regard to how we see it if there is a relative velocity between the sphere and an observer. If length contraction cannot be seen, perhaps one can't see relativistic beaming either. That is, a sphere of light with all its light bunching in the direction of its motion. My contention is, that the distribution of photons will be evenly spread out across the sphere (inverse square law) regardless of relative velocity.

Think of a sphere of light as a set of lasers emitting light in a circular fashion. Each of these lasers will have its own telescope to capture light. Then pick one telescope and extend this reasoning to all telescope and you will have applied this logic to a sphere of light.

Pick a 90 degree ray of light stationary to an observer (telescope). The telescope is vertical and doesn't need tilting. Light is captured by an observer. Move the telescope (observer). It needs to be titled by an angle v/c. Light still reaches the telescope at 90 degrees, it is the telescope that is tilted. Hence in both instances, the image is the same. Applying this to all telescopes, you will get the inverse square law distribution of photons, regardless of the relative motion. That means, in both instances, the image is the same.

I have not included length contraction here. But you could, at high speeds. And simultaneity applies. But the basic premise is the same. The images produced will not be different. With simultaneity, into play, there is just a delay in capturing light. Does this make sense?


But the extra angle at which you need the telescope changes depending on the direction of the objects you are looking at. Imagine you are making a map of the sky. You point the telescope so that you see a star in it. Note the angle that the telescope is pointed, and then use that to mark a point on a globe. If you were stationary with respect to the stars then you get a certain pattern on the globe. However, what if you are moving at some respectable fraction of the speed of light relative to them? for stars that are in the same direction from you as the relative motion, You need to add no correction for aberration. But as you point at stars in other directions, the correction for aberration increase. Now if you create a map of the star positions on your globe based on the direction you have to point the telescope in order to see a given star, you will produce a different map.

Or you can just use a wide angle lens that captures a single image of the sky all at once. The image formed will depend on the angle at which the light hits the lens as seen by the lens. You will get a different recorded image when you are moving at a high velocity with respect to the stars than if you were stationary.

Or let's consider another scenario. You have two light sources spaced one light sec apart along a line at a right angle to the line of motion and so that as they pass by you at a right angle to the line of motion, they are in a straight line pointed away from you. (in this same position, if viewed while stationary to you, you would see one light source directly behind the other.)

Now assume that they are moving with respect to you. Light leaving the sources at that moment they are at a right angle from you relative to the motion will appear aberrated and will appear to come from some other angle than 90 degrees. This angle will be the same for both sources.

However, the light from the two sources emitted at that moment will not reach you at the same time. one of the sources is 1 light sec further away and thus its light from that moment won't arrive until 1 sec after the light from the nearer light.

This also means that light from the further light arriving at your eye/instrument at the same moment as the light from the nearer light, had to have left that light earlier and thus when it was not at a position of being at a right angle from you, And you will not see this light as coming from the same direction as that of the nearer light. You will not see it right behind the other light, but offset to the side.
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Re: Invisibility of the Lorentz Contraction

Postby DJ_Juggernaut on July 14th, 2018, 1:24 pm 

JMP1958 » July 14th, 2018, 11:55 am wrote:Or you can just use a wide angle lens that captures a single image of the sky all at once. The image formed will depend on the angle at which the light hits the lens as seen by the lens.

That's not what I am talking about. I am talking about an expanding sphere of light. I used lasers to model a sphere of light; and of course, telescopes, since aberration is involved. What did you make of it?
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Re: Invisibility of the Lorentz Contraction

Postby bangstrom on July 14th, 2018, 2:52 pm 

DJ_Juggernaut » July 14th, 2018, 8:40 am wrote:
My interest in the sphere is with regard to how we see it if there is a relative velocity between the sphere and an observer. If length contraction cannot be seen, perhaps one can't see relativistic beaming either. That is, a sphere of light with all its light bunching in the direction of its motion. My contention is, that the distribution of photons will be evenly spread out across the sphere (inverse square law) regardless of relative velocity.


I may be missing something here but light coming from a 90 degree angle relative to a stationary observer would not be visible to an observer moving at relativistic speed. It is like someone running in the rain. The rain may strike them from straight above when they are standing still but it will strike them from the front when they are in motion.

With a sphere of light, the light doesn’t bunch to the front of an observer but, since the observer is moving into sphere of light, they will be capturing more light from the forward direction than from behind making it appear that light from their side is coming from the forward direction. The effect is often displayed in Si-Fi movies where the stars appear to be bunching to the front of the vehicle as the spaceship reaches warp speed. Their view of the stars is warped in the forward direction.

If an observer is moving at relativistic speed and they pass by a cube shaped object, they will be able to “run into” light that was emitted from the back side of the object making it appear that the object has been rotated.
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Re: Invisibility of the Lorentz Contraction

Postby DJ_Juggernaut on July 15th, 2018, 1:00 am 

bangstrom wrote:I may be missing something here but light coming from a 90 degree angle relative to a stationary observer would not be visible to an observer moving at relativistic speed.

No, it won't miss the observer. The observer needs to tilt his telescope by an angle v/c.

See this gif below. (Just picture a tilted telescope, it's missing in the gif)
https://en.wikipedia.org/wiki/Aberration_of_light#/media/File:Aberrationlighttimebeaming.gif
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Re: Invisibility of the Lorentz Contraction

Postby DJ_Juggernaut on July 15th, 2018, 1:07 am 

bangstrom wrote:The rain may strike them from straight above when they are standing still but it will strike them from the front when they are in motion.

Even when in motion, the rain falls at 90 degrees. You just tilt your umbrella because you are moving.

You could see this effect with a droplet of water and a test tube. Keep the test tube vertical, drop a droplet of water. It lands vertically and won't touch the sides of the tube. Now repeat, by moving the test tube when the droplet falls. You have to tilt the test tube or else it will hit the sides of the tube. This is the same with a light particle. In both instances, the droplet is the same and it drops from the same location and at the same angle.

This animation is good:
https://plus.google.com/photos/photo/11 ... 7120977010
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Re: Invisibility of the Lorentz Contraction

Postby bangstrom on July 15th, 2018, 1:40 am 

I understand what you are saying but light that is emitted at right angles to the target will miss the target unless it is emitted before it is at right angles and the light will strike the observer from a forward angle making the object appear to be forward of its true position when the light arrives. I suspect we are saying the same thing.
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Re: Invisibility of the Lorentz Contraction

Postby DJ_Juggernaut on July 15th, 2018, 1:49 am 

bangstrom » July 15th, 2018, 1:40 am wrote:I suspect we are saying the same thing.

I think so too. So, what do you think of the laser set up and moving telescopes? Shouldn't the photon angles or photon distribution be the same upon reception, despite relative velocity?
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Re: Invisibility of the Lorentz Contraction

Postby bangstrom on July 15th, 2018, 2:58 am 

DJ_Juggernaut » July 13th, 2018, 11:32 pm wrote:
Can you see a non-spherical distribution of photons due to relative velocity? I don't think so; due to relativity of simultaneity.

I think the picture of non-spherical distribution is correct but it looks like a diagram of the Doppler effect rather than Lorentz contraction.

Lorentz contraction would rotate and flatten the shape of the stars appearing to the side of a moving observer but the contraction part of the change would not be visible. If the laser setup is similar, it would also be distorted by the Doppler effect.
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Postby DJ_Juggernaut on July 15th, 2018, 7:08 am 

bangstrom wrote:
DJ_Juggernaut » July 13th, 2018, 11:32 pm wrote:
Can you see a non-spherical distribution of photons due to relative velocity? I don't think so; due to relativity of simultaneity.

I think the picture of non-spherical distribution is correct but it looks like a diagram of the Doppler effect rather than Lorentz contraction.

I did not notice that the picture was referring to a celestial sphere. It's the wrong picture. It's of incoming light. My interest is in an expanding sphere of light, and how it will land on a detector, for eg.

You can pick any three telescopes in the laser setup. Picking the 90 degree laser and its two adjacent lasers is enough to detect this. If the spacing between these three telescopes is uniform, then I take it to mean, the sphere of light expanded identically regardless of relative motion. Would you agree?

We already know the spacing will be identical due to simultaneity. I set up the scenario such. Even if we're going to ignore telescopes for the moment.
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Re: Invisibility of the Lorentz Contraction

Postby DJ_Juggernaut on July 15th, 2018, 8:38 am 

I made a crude graphic of the laser setup.
https://ibb.co/dY99HT

PS. All that matters is the incoming angle of the photon and telescope's velocity. If we agree that a 90 degree photon arrives at 90 degrees, whether you are moving or not, then we can say, the sphere of light expands the same whether you are moving or not. The incoming angle of photon gives you the tilting angle of the telescope if you're moving.
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Re: Invisibility of the Lorentz Contraction

Postby bangstrom on July 15th, 2018, 2:46 pm 

The sphere of light should expand the same whether the detectors are moving or not but it appears to me that the photons will miss all three detectors if the detectors move out of the paths of the incoming photons.
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Re:

Postby JMP1958 on July 15th, 2018, 3:50 pm 

DJ_Juggernaut » July 15th, 2018, 4:08 am wrote:
bangstrom wrote:
DJ_Juggernaut » July 13th, 2018, 11:32 pm wrote:
Can you see a non-spherical distribution of photons due to relative velocity? I don't think so; due to relativity of simultaneity.

I think the picture of non-spherical distribution is correct but it looks like a diagram of the Doppler effect rather than Lorentz contraction.

I did not notice that the picture was referring to a celestial sphere. It's the wrong picture. It's of incoming light. My interest is in an expanding sphere of light, and how it will land on a detector, for eg.

You can pick any three telescopes in the laser setup. Picking the 90 degree laser and its two adjacent lasers is enough to detect this. If the spacing between these three telescopes is uniform, then I take it to mean, the sphere of light expanded identically regardless of relative motion. Would you agree?

We already know the spacing will be identical due to simultaneity. I set up the scenario such. Even if we're going to ignore telescopes for the moment.


Consider a semicircular detector ( the blue arc), and a pulse of light emitted from the midpoint.
for a situation where the light source is stationary to the detector, All points on the detector will sense the light as having come from a single point as shown by the white lines which all intersect at that single point like this:
aberration1.gif


However if the source is moving with respect to the detector at the time of the emission, then the lines representing the direction from which the light is coming from for different points of the detector would look like this (diagram assumes a relative velocity of 0.5c):
aberration2.gif

The lines do not all intersect at the same point.

Thus if you had telescopes mounted at each of the points shown on the arc, then if the source was stationary with respect to the telescopes, you would point them all towards the center of the circle of the arc to see the flash.
However, if the source was moving with respect to the telescopes, then to see the flash, none of them would point at the center of the circle, nor would they be pointing at the same point.
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Re: Invisibility of the Lorentz Contraction

Postby bangstrom on July 15th, 2018, 6:15 pm 

The emission from a single flash should look like the diagram on top whether the source is in motion or not. The motion of the source does not add or subtract from the direction of light.
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Re: Invisibility of the Lorentz Contraction

Postby JMP1958 on July 15th, 2018, 8:07 pm 

bangstrom » July 15th, 2018, 3:15 pm wrote:The emission from a single flash should look like the diagram on top whether the source is in motion or not. The motion of the source does not add or subtract from the direction of light.


Yes it does. It's called aberration.
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Re: Invisibility of the Lorentz Contraction

Postby DJ_Juggernaut on July 15th, 2018, 10:39 pm 

bangstrom » July 15th, 2018, 6:15 pm wrote:The emission from a single flash should look like the diagram on top whether the source is in motion or not. The motion of the source does not add or subtract from the direction of light.

I agree. I just modified JMP's graphic with dotted lines so we can distinguish between true photon paths and the tilting angle of telescopes.
https://ibb.co/kCCpKJ
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Tilting angle of telescopes

Postby DJ_Juggernaut on July 15th, 2018, 10:47 pm 

bangstrom » July 15th, 2018, 2:46 pm wrote:The sphere of light should expand the same whether the detectors are moving or not

I agree.

bangstrom wrote: but it appears to me that the photons will miss all three detectors if the detectors move out of the paths of the incoming photons.

Yes, if you're not in the path of an incoming photon you will miss it. You have to synchronize your telescope to match a photon's arrival time.
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Tilting angle of telescopes

Postby DJ_Juggernaut on July 15th, 2018, 10:51 pm 

JMP1958 » July 15th, 2018, 3:50 pm wrote:However, if the source was moving with respect to the telescopes, then to see the flash, none of them would point at the center of the circle, nor would they be pointing at the same point.

I agree, though in my set up, it's the telescopes that are moving. I would also show the tilting angle of telescopes in dotted lines. So we don't confuse them with true paths. See here: https://ibb.co/kCCpKJ
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Re: Invisibility of the Lorentz Contraction

Postby bangstrom on July 15th, 2018, 11:52 pm 

JMP1958 » July 15th, 2018, 7:07 pm wrote:
bangstrom » July 15th, 2018, 3:15 pm wrote:The emission from a single flash should look like the diagram on top whether the source is in motion or not. The motion of the source does not add or subtract from the direction of light.


Yes it does. It's called aberration.


If I am following the last diagram correctly, you have multiple telescopes circling a single flash of light all at the same speed. If that is correct, the angle of tilt for each telescopes should be the same and it should make no difference if the light source is moving or not.
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Re: Invisibility of the Lorentz Contraction

Postby DJ_Juggernaut on July 16th, 2018, 1:40 am 

JMP1958 » July 15th, 2018, 8:07 pm wrote:
bangstrom » July 15th, 2018, 3:15 pm wrote:The emission from a single flash should look like the diagram on top whether the source is in motion or not. The motion of the source does not add or subtract from the direction of light.

Yes it does. It's called aberration.

Aberration angle is simply the tilting angle of a telescope. It depends on the velocity of the "telescope". There is a distinction between the velocity of a source vs. the velocity of a telescope. In my laser setup, the telescopes move. Not the source. The graphic you made depicts moving telescopes and hence the need for aberration angles. That is, the tilting angle of a telescope. If a telescope isn't moving. There is no aberration meaning there is no need for the tilting of a telescope.

I edited your graphic depicting aberration angles in dotted lines: https://ibb.co/kCCpKJ
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Re: Invisibility of the Lorentz Contraction

Postby bangstrom on July 16th, 2018, 3:44 am 

For clarification, I understand the need for the aberration angle and the distinction between the velocity of the source versus the velocity of the telescopes. The telescopes are all moving but in which direction? Their direction is circular I presume.

Also, I don’t know who did the graphic but it wasn’t I.

My claim is that, with moving telescopes and a single flash at the center, it makes no difference if the flash at the center came from a moving source or a stationary source and the aberration angle for all the telescopes should be identical.They should not all merge at a point within the expanding circle of light.
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Re: Invisibility of the Lorentz Contraction

Postby DJ_Juggernaut on July 16th, 2018, 4:35 am 

bangstrom » July 16th, 2018, 3:44 am wrote:For clarification, I understand the need for the aberration angle and the distinction between the velocity of the source versus the velocity of the telescopes.

Okay. I was addressing JMP.

The telescopes are moving in a straight line to the right. Not in a circle. The graphic below shows this.
https://ibb.co/dY99HT

bangstrom wrote:My claim is that, with moving telescopes and a single flash at the center, it makes no difference if the flash at the center came from a moving source or a stationary source and the aberration angle for all the telescopes should be identical. They should not all merge at a point within the expanding circle of light.

I think you misunderstood my setup. The ring of telescopes moves to the right. JMPs graphic is correct, but he says, the source is moving relative to stationary telescopes. My setup involves, moving telescopes, and a stationary source.
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Aberration is the tilting of a telescope

Postby DJ_Juggernaut on July 16th, 2018, 5:40 am 

Hi all.

This graphic shows a ring of three telescopes moving to the right in a straight line. The tilting angle ϕ of the telescopes is shown in dotted lines. The true path of photons is shown in bold lines and is given by the angle θ.

If θ = 90 degrees, the tilting angle ϕ is given by tan(ϕ) = v/c.
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Re: Invisibility of the Lorentz Contraction

Postby bangstrom on July 16th, 2018, 4:11 pm 

DJ_Juggernaut » July 16th, 2018, 3:35 am wrote:
The telescopes are moving in a straight line to the right. Not in a circle. The graphic below shows this.
https://ibb.co/dY99HT


I considered that possibility because that is the way it is shown in the figure but the outgoing light paths in the other figures were all straight lines and drawn from the perspective of a stationary source at the center. The incoming light paths to the telescopes should all be strongly curved if drawn from the perspective of the telescopes and this would change the aberration angles.

And this graphic is unrealistic because it shows the light source at the center of the circle of the telescopes but, by the time the light reaches the telescopes, the origin of the light source has been passed by and it is no longer at the center. The circle of light and its center do not move with the circle of telescopes.

Lorentz contraction should make the circle of telescopes appear ovoid from the perspective of the light source and the expanding circle of light should appear ovoid from the perspective of the telescopes but this in not depicted in any of the figures. The figures appear to be an over simplification of a complex problem which makes it difficult to draw any conclusion from them.

.
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Three locations

Postby DJ_Juggernaut on July 16th, 2018, 10:55 pm 

bangstrom,

JMPs graphic is correct. His interpretation is incorrect. There are three positions to consider here:

Laser location 0
Laser location 1
Laser location 2

He conflates, laser location 1 with laser location 0. That's the source of his (and possibly your) confusion. This graphic highlighting these three locations should help fix the confusion. Let me know if it worked for you.
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