Another Relativity Question........

Sorry, I read it wrong. I was thinking that C was the stationary clock. So, if A and C are accelerated in such a way that they are always traveling with the same speed relative to B, then they will always be synchronized as determined by frame B. This does not mean that A and C will agree that their clocks are synchronized with each other.

Tom

 

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Tom2,

So are you saying that the clocks are truly synchronized, but the fact that clocks A an C don't see themselves as being synchronized is actually the result of an illusion?

Before you answer the question, remember that the all three clocks can have only one reading each. If the second hand of a clock is on the two second mark, it is on that same location in all frames of reference. Einstein speaks of time dilation and length contraction, but none of his formulas would imply that the physical second hand of the clock is in different locations dependent on your frame of reference. Therefore, this fact would imply that there is an absolute frame of reference, and that, at least part of the theory of relativity is flawed.

Tom

 

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Hi Tom,

"Before you answer the question, remember that the all three clocks can have only one reading each. If the second hand of a clock is on the two second mark, it is on that same location in all frames of reference."

Eventually it will, yes. But you are forgetting that simultanity is no longer preserved when going from one observer to the other: for one frame of reference, the second hand can be on the second mark, while for another frame of reference, it is not (yet) at that moment.

Bye!

Crisp

 

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Crisp,

As I explained on another thread, the fact that one observer sees the second hand on the second mark, while the other does not yet, is not the result of relativity. It is the result of the light taking longer to reach the second observer. In other words, the observer that is farthur away "percieves" a greater delay than the closer observer. If you take this delay into consideration, you will find that the second hand is on the two second mark in all frames of reference at the same time.

Tom

 

James R,

I'm sorry, James. It's just that it's so hard for me to understand things that are illogical.

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Tom

 

Stop: What is "truly synchronized"? Synchronization in one frame does not imply synchronization in any other frame.

No, there is no illusion, unless you want to consider all points of view an illusion.

If the event of the second hand reaching the two second mark occurs in one frame, then yes, it occurs in every frame. However, there is no guarantee that it happens simultaneously in every frame. That is the thing you are missing.

 

Prosoothus

Before you answer the question, remember that the all three clocks can have only one reading each. If the second hand of a clock is on the two second mark, it is on that same location in all frames of reference.

You are inferring the speed of light is instantaneous. If a star goes supernova in a galaxy 10 million light years away, will we on Earth observe the event the instant it occurs? Will an observer who is halfway between us and the galaxy (5 million light years) view the event the instant it occurs?

 

Ok here we go again, lets try and sort this one out ... Well actually I am also making it more complicated, so you can see why it works.

The story so far... We have three frames A, B, C. From B's point of view A nd C accelerate away. And then accelerate back.

From B's view point, they do this identically with the directions reversed. From B's point of view they both return with their clocks time dilated by identical amounts (maybe see below). I.e slower than B's time.

Now A and C's point of view. In this experiment they are the same except for the direction so lets pick one say A. From A's point of view it is accelarted away from B. Can we say that B accelerated away from A ? No only in A's reference is the driver pushed into the back of the seat. I.e A is accelerated not B. A and C are not inertial frames of reference. An inertial frame of reference is S/R shorthand for an unaccelerated frame.

Ok so how about adding a fourth object D. Now this is traveling at .45c away from B, in the direction A will be accelerated.

Assume from D's point of view. B's clock is running slower than D's. From D's point of view while A is traveling along with B it is at the same slower rate as B. When A accelerates away from B, from D's point of view you might argue it is decelerating. If decelerating then A's clock stops being slowed, i.e speeds up. If we keep going it then it accelearates away from D and rejoins B. Sound like D should return with a time more than B'S ?

The reason this does not work is the key question is A acelerating D's point of view or accelerating from B's point of view ? Popular views on S/R say both, causes confusion, and is wrong. To show why consider we have two clocks on D and B based on vibrations of hydrogen. Now we have both send signals to each other 1 second long. Both frames will agree that one of the two is longer than the other. One of the two will have a slower clock.

To explain this consdier how the situation might arise. B and D are traveling together and their clocks agree. Now change it so they are moving apart at .45c. If D is accelarated relative to B, D's clock slows down. If B is accelerated relative to D B's clock slows down.

So to return to D's point of view. We have two scenarios. If we measure B's time from D's point of view we might find time is slower on D so when A starts out it is acclerated and time slows for A and all is as it was from B's point of view.

Ok take the opposite view Time is faster on D. When A returns it will have a clock that appears to have run faster. To solve this we need to return to B's point of view. Because in this situation, we can show that B has already been accelerated. So from B's point of view when A gets up to speed and moves away it is DEcelerating, and the clock on A will speed up. While C is accelearting and will slow down.

I could go on and give a description of C from D's point of view. The point is that S/R works consistantly when looked at from an inertial frame of reference. If your point of view has two or more different velocities compared to something else at different measuring times you need to be sure the frame ypou are calculating from is not the one being accelerated.

If I describe, the alternate situation of A,B and C and have B accelerate away from A to .45c and C away from A to .90c. I have described a different stituation. In this one B and C experience acceleration, in the previous experiment A and C experieince acceleration. And the results of these two different experiments are different.

Bright sparks that are following the above will be asking. How does an object know it is accelerating or has been accelerated ? Doesn't that mean there is a kind of zero frame that we can measure acceleration against ? The answer is yes. But note there is no zero speed, only a kind of zero acceleration. To make matters worse the zero acceleration is local, if separated by time or distance, observers may not agree on the zero of acceleration. (mind bending ain't it?).

The full answer to the accelaration zero requires G/R and the concept of space/time and curvature so go study G/R ! To give a hint: The accelaration is (kind of) against the space/time curve defined by gravity.

 

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Prosoothus...
Now i am really lost.
Are you saying that the time shouldn't change?

I take back the statement I said about it resyncronizing when returning to the starting point. A and C should read a slower time than B.
I think. Explain...?

Sorry for getting in your "over my head" discussion... but I don't understand what you mean Crisp?

"Before you answer the question, remember that the all three clocks can have only one reading each. If the second hand of a clock is on the two second mark, it is on that same location in all frames of reference."

Are you saying that no two clocks can have the same time if they are in different locations? I am so lost...

 

JimmyJames,

I can explain to you what I really think, but my explanation differs from that of relativists. Here is what I think:

1) Clocks A and C will be almost synchronized, and both will be slower than the stationairy clock B.

2) The slight variance between clocks A and C will be the directly proportional to the absolute speed of clock B.

3) Clocks A and C will always be synchronized(minus the variance), at all times. Clock A will never be slower than C, or vice versa. If they ever where, it would be recorded by the clocks.

4)Clocks A and C will not be slower because time slows down, they will be slower because the speed of the electromagnetic radiation, that the clock is made of, changes based on the clocks speed.

The secret to making sense of all this is to seperate illusion from reality. Relativity tries to teach you that illusion is reality: That if the observer perceives something, it must be true. If you've ever been to a magic show, you know that this is not the case

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Tom

 

Q,

No, I am saying that just because two observers see an event occuring at different times doesn't mean that the event actually occured at different times.

In the case you described, both observers are wrong. They are both observing an illusion based on the fact that the speed of light is finite. The only observer that wouldn't witness this delay-illusion is an observer that is right next to the supernova.

Tom

 

Prosoothus

No, I am saying that just because two observers see an event occuring at different times doesn't mean that the event actually occured at different times.

That is correct. The observers, in whatever reference frame they may view, will always see a delay due to the finite speed of light and the distance and velocity of the observers to the event.

In the case you described, both observers are wrong. They are both observing an illusion based on the fact that the speed of light is finite.

What is your definition of "illusion?" (An erroneous perception of reality.) That is not the case. The view of the observer is a delayed view of the event and is not erroneous in any way. The observer on Earth will view the same event as the observer 5 million light years closer to the event. The only difference is that they will view the event at different times due to the finite speed of light. This is not an illusion.

The only observer that wouldn't witness this delay-illusion is an observer that is right next to the supernova.

Incorrect. Although this observer is right next to the supernova, he too will witness a delay in the time between the occurrence of the event and his viewing of the event, under exactly the same conditions as any other observer, based on the finite speed of light and his distance and velocity to the event.

Of course, this observer's view of the supernova may be the last thing he ever sees.

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Q,

The observer is not seeing reality, he is seeing a reality that existed 5 million years ago. Even though there is no spacial illusion, there is a time illusion.

If you wan't to get picky about it, I agree that the observer next to the star experiences a delay as well.

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Tom

 

prosoothus

The observer is not seeing reality, he is seeing a reality that existed 5 million years ago.

Good, we agree he is viewing a reality and not an illusion. If an amount of matter blown off by the supernova were to travel towards the observer and the observer was struck by the matter, would this be an illusion or a reality ? What would be the difference between this amount of matter striking the observer and the photons emitted by the supernova striking the observer ?

Even though there is no spacial illusion, there is a time illusion.

Not an illusion, just a delay, a similar delay the blown off matter would undergo traveling towards the observer.

If you wan't to get picky about it, I agree that the observer next to the star experiences a delay as well.

We gotta make sure our facts are straight, right ?

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