The burn mark problem

[Pete]

Let me help you. You are wrong.

I see you're open to learning. Good on you.

In accordance with definition the two clocks synchronize if

tB - tA = t'A - tB

We assume that this definition of synchronism is free from contradictions, and possible for any number of points; and that the following relations are universally valid:--
http://www.fourmilab.ch/etexts/einstein/specrel/www/

Can you explain why "free from contradictions" is not absolute?

I said "SR does not claim that the light path is absolute, and this is not a physical contradiction."
Where does SR claim that the light path is absolute? How is this extract supposed to show that I was wrong?

I don't know exactly what Einstein meant by that particular phrase in that context. I would have said that it means exactly the same as the following two points, but it seems to have been meant as a separate assumption.

I do know that the synch procedure is frame dependent, not absolute. If two clocks are synchronized in one frame of reference, they will not be synchronized in others.

In logic, that means a logical truth.

A logical truth, as I understand it, is a logically valid conditional argument, such as "If Max is a crow and all crows are white, then Max is white."

Well, that could make sense in this case. The definition of synchronism does appear to be free of internal contradiction.

 

[James R]

One more thing, Jack_: you STILL didn't answer the following question:

What are the two axes on your diagram above?

Pete has already asked you this question several times, and I have now asked you twice.

If you can't answer this, I guess we'll have to assume either (a) your diagram above only has one axis (the x axis), or (b) your diagram is meaningless.

 

[Pete]

Yes, it does. So does it with the diagram I offered. Necessarily, this imples a sequence of drawings. I can imagine that sequence, can you?

So, your diagram is a snapshot of space at a single moment in time?
Do you understand that a Minkowski diagram shows the entire sequence on a single graph, that it shows space on one axis and time on the other?

Wrong, this spacetime diagram is for the weak minded and leaves off the diverging light emission points.

The diverging light emission locations are plain to see - they are the lines labelled O and O'.
In the rest frame of O, the light emission location is at x=0.
In the rest frame of O', the light emission location is at x'=0.

Like this:

Guess what. You have not handled the geometry of my diagram. Why? You cannot. If so, do it. I want to see it.

Perhaps if you clarified whether the vertical axis is t or y?

Does the laser stop at x, or does it continue burning a path indefintely
This does not matter for the problem.

Of course it matters. In your burn path problem, the burn path grows with the laser. How can you tell how long it is if you don't know when it stops?
How do you expect anyone to address your scenario if you don't say what your scenario is?


Anyway, enjoy your break, and try to relax. We'll chat more when you return.

 

[Jack_]

Jack_:



You gave a link to the text yourself. All you have to do is read what Einstein says. For example:



It is quite clear that M and M' are points or locations or positions in space, not entire reference frames.



I am claiming that it is only possible for the coordinates of ONE point in two relatively-moving frames to coincide at any one instant of time.

I am not claiming it is impossible for two objects to occupy the same location in space.



He co-located the origins O and O' of two coordinate systems (an unprimed one and a primed one) at one particular instant of time. Note that O and O', like M and M', are two points in space that coincide at one particular instant. At that instant, NONE of the other coordinates in the O and O' frames coincide (i.e. have the same numeric value at the same location in space).



That's an empty assertion from you. Please don't descend to personal insults. If you can show that I am wrong, great. If not, insulting me won't help you.



You link me to Einstein's entire first paper introducing special relativity. I have read it and am very familiar with its arguments. Which part in particular are you disputing?

good, all this above is your education that frames points can be co-located.

You questioned me on this and now you understand.

 

[Jack_]

Please draw me a spacetime diagram that shows the diverging light emission points. For clarity, please include the space and time coordinates of each of those points on your diagram.

Then we can compare to Pete's diagrams above and see where the difference lies.

Ok?

You cannot. That is their weakness. I thought you knew all this stuff.

 

[Jack_]

I see you're open to learning. Good on you.


I said "SR does not claim that the light path is absolute, and this is not a physical contradiction."
Where does SR claim that the light path is absolute? How is this extract supposed to show that I was wrong?

I don't know exactly what Einstein meant by that particular phrase in that context. I would have said that it means exactly the same as the following two points, but it seems to have been meant as a separate assumption.

I do know that the synch procedure is frame dependent, not absolute. If two clocks are synchronized in one frame of reference, they will not be synchronized in others.


A logical truth, as I understand it, is a logically valid conditional argument, such as "If Max is a crow and all crows are white, then Max is white."

Well, that could make sense in this case. The definition of synchronism does appear to be free of internal contradiction.

OK, since you refute my interpretation of his clear logic, give yours.

 

[Jack_]

One more thing, Jack_: you STILL didn't answer the following question:

What are the two axes on your diagram above?

Pete has already asked you this question several times, and I have now asked you twice.

If you can't answer this, I guess we'll have to assume either (a) your diagram above only has one axis (the x axis), or (b) your diagram is meaningless.

LOL, my diagram is that of LT.

Have you not seen this?

If you think it is meaningless, then you claim LT is meaningless.

Hence, you will need to prove my diagram is illogical with one of your own for LT and prove mine is false.

Don't forget, you said you understand LT better than I do.

Can't wait.

 

[Pete]

LOL, my diagram is that of LT.

Jack, this makes no sense.
A Lorentz transform is a transformation of spacetime coordinates between reference frames. It is not a diagram.

Please, this is a simple question - what is the vertical axis on your diagram?

 

[James R]

Jack_:

I'm beginning to wonder whether Pete and I have lost you in this conversation. You seem not to understand our explanations, and it looks a lot like you've given up trying to follow the conversation.

good, all this above is your education that frames points can be co-located.

You questioned me on this and now you understand.

So you and I now agree that 2 points in two different frames can be co-located at one particular time, but in that case no other points in the frame are co-located at that time. Good.

You cannot [draw a spacetime diagram showing the diverging light emission points]. That is their weakness. I thought you knew all this stuff.

I didn't know about this flaw in spacetime diagrams. Please explain it to me.

My understanding is that any spacetime event can be located as a point on a spacetime graph. However, you are claiming that this is not possible for what you call "diverging light emission points".

Does this mean that diverging light emission points are not events in spacetime? Or does it mean you don't know how to specify the spacetime coordinates of diverging light emission points? Or what?

Please explain your point in detail. Or, alternatively, explain why spacetime diagrams are incapable of properly representing spacetime events.

LOL, my diagram is that of LT.

...

Hence, you will need to prove my diagram is illogical with one of your own for LT and prove mine is false.

What are the axes on a diagram of the LT?

 

[Pete]

Sorry, I didn't finish an earlier response. Try again:

Wrong, this spacetime diagram is for the weak minded and leaves off the diverging light emission points.

The diverging light emission locations are plain to see - they are the lines labelled O and O'.
The light emission location according to O is at x=0 (the black line).
The light emission location according to O' is at x'=0 (the red line):

 

[James R]

Pete:

I think Jack deserves more respect than our long-term antirelativity cranks - he seems to be coming from firmer grounding, and may be interested in learning something.

What do you think now?

 

[Pete]

I plead the fifth!

 

[James R]

Jack_:

One more thing. Notice from Pete's diagram in post #110, that the points x=0 and x'=0 are co-located only at time t=t'=0 and at no other time, confirming what I taught you above.

 

[Pincho Paxton]

I imagine light moves like a fuse, and matter moves like a snake. If you check the frame of light it is identical to its start frame. If you check the frame of the snake it is in a number of lengths, but ends up stretched back out again. When cars collide you can see the snake frames combined in the dents in the bonnet. The problem with the snake movement is that it does not coincide with the end point. It could be any length until it stretches back out again, and it could stretch back out beyond the end point, it can't time its final stretch perfectly to a point without slowing down first which alters the maths. In space however, the snake can remain elongated, and still continue its trajectory from inertia.

If you can figure out what I am talking about, then it applies to your maths. Unfortunately, I can only work in the physics.

 

[Jack_]

One more thing, Jack_: you STILL didn't answer the following question:

What are the two axes on your diagram above?

Pete has already asked you this question several times, and I have now asked you twice.

If you can't answer this, I guess we'll have to assume either (a) your diagram above only has one axis (the x axis), or (b) your diagram is meaningless.

Sorry, I was not trying to evade the question.

I have made a decent picture, I think. It will show the exact experiment.

I am not able to upload it though.

http://www.freeimagehosting.net/uploads/f56141ffa5.gif

 

[Jack_]

Jack_:

One more thing. Notice from Pete's diagram in post #110, that the points x=0 and x'=0 are co-located only at time t=t'=0 and at no other time, confirming what I taught you above.

LOLOLOLOL

Thanks for the lesson.

Oh, where is it after that?

 

[Jack_]

Jack, this makes no sense.
A Lorentz transform is a transformation of spacetime coordinates between reference frames. It is not a diagram.

Please, this is a simple question - what is the vertical axis on your diagram?

Now, Pete, LT must have a geometry.

You know that right?

 

[Jack_]

Jack_:

I'm beginning to wonder whether Pete and I have lost you in this conversation. You seem not to understand our explanations, and it looks a lot like you've given up trying to follow the conversation.

I like your sense of humor.

So you and I now agree that 2 points in two different frames can be co-located at one particular time, but in that case no other points in the frame are co-located at that time. Good.

Looks like I will have to teach you more.
Let a moving rod have rest length dλ.

Let a stationary frame of a rod of length d.

The endpoints of the two rods can be co-located from the view of the stationary frame.

I didn't know about this flaw in spacetime diagrams. Please explain it to me.

My understanding is that any spacetime event can be located as a point on a spacetime graph. However, you are claiming that this is not possible for what you call "diverging light emission points".

Does this mean that diverging light emission points are not events in spacetime? Or does it mean you don't know how to specify the spacetime coordinates of diverging light emission points? Or what?

Please explain your point in detail. Or, alternatively, explain why spacetime diagrams are incapable of properly representing spacetime events.

Sure, wordline diagrams co-locate the origins of the frames. That is false in reality.

When light move d, the frame origins diverge (v/c)d.

Hence, word line diagrams do not contains this physical fact.

Anyway, once you study the picture I posted, you will gain more understanding.

 

[Jack_]

I imagine light moves like a fuse, and matter moves like a snake. If you check the frame of light it is identical to its start frame. If you check the frame of the snake it is in a number of lengths, but ends up stretched back out again. When cars collide you can see the snake frames combined in the dents in the bonnet. The problem with the snake movement is that it does not coincide with the end point. It could be any length until it stretches back out again, and it could stretch back out beyond the end point, it can't time its final stretch perfectly to a point without slowing down first which alters the maths. In space however, the snake can remain elongated, and still continue its trajectory from inertia.

If you can figure out what I am talking about, then it applies to your maths. Unfortunately, I can only work in the physics.

If you check the frame of light it is identical to its start frame.

You imply light has its own frame. If that is what you are saying, then I agree and a SR frame cannot possible know what that light frame is.

Hence, the light path is not logically decidable.

 

[Pete]

Sorry, I was not trying to evade the question.

I have made a decent picture, I think. It will show the exact experiment.

I am not able to upload it though.

http://www.freeimagehosting.net/uploads/f56141ffa5.gif

Thanks for that, Jack, I appreciate your patience. Working through communication barriers is difficult.
You can link to images using tags, like this:
[img] (image url here)

OK, so we have two snapshots, one at time t=zero, and one at time t=d/c.
Great!

Now, work with me for a second while I make sure that I properly understand what you mean.

• It looks like O is moving to the left toward the burn mark, while O' is stationary.
  Is that right, or should O and O' be swapped around?
• In the second snapshot, there are two green lines.
  Are they light beams?
  Does that mean there are there two light sources, one carried by O and one carried by O'?

Thanks again, Pete.