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Why I think that SR might be wrong?


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#35 modest

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Posted 26 December 2008 - 05:21 PM

I was just skimming threads and clicked on that, and the animated .gif seems quite wrong, someone should probably fix it. I mean this:

File:Relativity of Simultaneity Animation.gif - Wikipedia, the free encyclopedia

If you perform a lorentz transformation to a spacetime where you have marked some events, those events would move along (with the grid). Also in each inertial frame the animation (erroneously) displays the simultaneity plane of "v=0". Doh!


It needs another axis. The one marked ct should be maked ct' while another axis (ct) should be added that never moves. It'd then be more apparent that we're looking at a second, transformed frame from our world line which never accelerated. I think that's what it's trying to show.

~modest

#36 arkain101

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Posted 27 December 2008 - 12:28 AM

Okay, with this tool (these animations) we should be able to clear everything up.

What I did is take this train concept:

Posted Image
The train-and-platform experiment from the reference frame of an observer onboard the train


Posted Image
Reference frame of an observer standing on the platform (length contraction not depicted)


Then I made an animation and blew things up in scale. I did this so that each ship could look as though they are hardly moving relative to each other. They are separated by such a large distance that they appear slow ( in the minds eye ). And also, so that on the illustration, they could remain in position. As you can see the blue lines represent the path of the light in order to reach the other ship and how it increases with time.


Scenario:

Two ships that are One light second in length. Moving in space relative to each other and we say:
-Neither ship underwent acceleration, they were found in space
-A person is located in the center of each ship.
-Each person begins the experiment by turning on light a light switch located at the center of the ship.
-This light switch sends a light signal to each end of the ship.
-On its path it passes through a series of evenly spaced devices that turn on a very bright light located at each device.
-Each blue circle represents the blue lights.
-The perspective is (birds eye view) however, it represents the data and/or results that the person in ship A records. (it should be the same results for each ship).



Experiment and Animation #1:
This animation shows the lights turning on towards the front and rear of the ship in a synchronized fashion (relative to person A inside ship A) after the person turns on the switch at t=0

http://hypography.co...=1&d=1230358517



Experiment and Animation #2:
This animation shows the lights turning on towards the front and rear of the ship NOT in a synchronized fashion (relative to ship A observing ship :evil: after the person turns on the switch at t=0

http://hypography.co...=1&d=1230358517



The light moves exactly 3 faster one way than the other. Ignoring some of my distances let's explain and calculate.

If I am correct:

relative velocity = 1/3 of C
distance between A and B = (later determined)
(.25 light seconds = 75,000,000meters)

Attached Thumbnails

  • delay.gif
  • nodelay.gif


#37 AnssiH

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Posted 27 December 2008 - 02:49 AM

It needs another axis. The one marked ct should be maked ct' while another axis (ct) should be added that never moves. It'd then be more apparent that we're looking at a second, transformed frame from our world line which never accelerated. I think that's what it's trying to show.


I think so too. So if I'm interpreting the pic and your reply correctly, then the events should move along when the transformation is performed (otherwise they are not the same events anymore in the transformed pic), and simultaneity plane should be displayed as straight horizontal line always; as it is it implies the simultaneity of the first frame is considered somehow special.

At least I can't figure out any valid interpretation for the first animation. The latter animation that I linked to is correct though. The events move with the Lorentz transformation, obviously; the transformation is for moving the events around, that's what relativity of simultaneity means.

I don't know if it's possible to send a message to the author of that picture. Just link him to my previous post or something.

-Anssi

#38 modest

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Posted 28 December 2008 - 02:39 AM

I think so too. So if I'm interpreting the pic and your reply correctly, then the events should move along when the transformation is performed (otherwise they are not the same events anymore in the transformed pic), and simultaneity plane should be displayed as straight horizontal line always; as it is it implies the simultaneity of the first frame is considered somehow special.


No, if the events moved along with the grid then there would be no relativity of simultaneity. I think what’s throwing you off is that the animation only shows one coordinate chart rather than two. It's usually shown more like this:

Posted Image

which comes from this website and offers this explanation:

Every point represents the location of a possible event in space and time (called a “world-point”), and superimposing a second reference frame makes it possible to give such coordinates in either reference frame. From the coordinates for any event in the first reference frame, we can simply read off the coordinates for the same event in the moving reference frame, and vice versa. In the case of event E, for example, the coordinates in the first frame are (2,1), and in Minkowski's diagram, they are (1.3,0.3). All possible reference frames can be represented in this way, each with a different tilt to its time-axis representing its velocity relative to the first.


The events are moving as the animation changes the velocity of the transformed reference frame. It just doesn't look like they're moving because it's the coordinate chart that's being moved on the screen rather than the event's dots.

Posted Image
-source

But, notice event A is sometimes above the X axis and sometimes below. As the velocity of the transformed frame changes, the location of the event changes in that coordinate system.

At least I can't figure out any valid interpretation for the first animation. The latter animation that I linked to is correct though. The events move with the Lorentz transformation, obviously; the transformation is for moving the events around, that's what relativity of simultaneity means.


The latter animation is showing the same thing.

Posted Image
-source

It's just showing it from the perspective of the transformed frame. Its coordinate system never changes relative to itself. As it changes velocity, it's the location of events inside its coordinate system that change.

I don't know if it's possible to send a message to the author of that picture. Just link him to my previous post or something.


If you have a wikipedia account then you can leave the animation's author a message here:

User talk:Acdx - Wikipedia, the free encyclopedia

Or, you can discuss the image on the relativity of simultaneity discussion page:

Talk:Relativity of simultaneity - Wikipedia, the free encyclopedia

~modest

#39 AnssiH

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Posted 28 December 2008 - 04:12 AM

Oh I see what you are saying. I was indeed interpreting the picture and your reply wrong.

What was throwing me off was that the text description on the pic seemed to imply a transformation from one frame to another as oppose to displaying different frames inside a static frame. Probably got that implication because I'm used to think of the transformation that way in my head (as what happens when you move from one frame to another).

Actually don't think now that it is critical to change the picture in wikipedia, albeit I do think it gives a clearer picture of the idea (and the symmetry of it) when the transformation is performed the way it was in the latter picture.

-Anssi