Will This Method Yield Absolute Synch?

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Discussion Overview

The discussion revolves around the feasibility of a method proposed to achieve absolute synchronization of clocks using a large clock's hand and two smaller clocks positioned at specific points. The conversation explores the implications of special relativity on the concept of simultaneity and the challenges posed by observers in different frames of reference.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Exploratory

Main Points Raised

  • One participant proposes a method to synchronize two clocks using a large clock's hand, suggesting that if clock B is set to half the time measured by clock A, they should be synchronized.
  • Another participant asserts that absolute simultaneity does not exist in relativity, indicating that observers in motion will not agree on the timing of events as proposed.
  • Further contributions highlight that observers may not agree on the straightness of the large clock's hand due to relativistic effects.
  • Some participants discuss the implications of the large hand's speed being constant and the potential effects of hand curvature, suggesting that slow movement or a laser beam might mitigate issues of perceived curvature.
  • There is a contention regarding whether the constant speed of the center shaft implies constant speed of the large hand, with some arguing that the shape of the shaft must also remain constant across frames.
  • One participant expresses uncertainty about the effects of special relativity on simultaneity but acknowledges that the concept may be outside the scope of the forum discussion.
  • Another participant emphasizes that any claim of absolute simultaneity must consider the agreement of all observers, which is not supported by relativity.

Areas of Agreement / Disagreement

Participants generally disagree on the possibility of achieving absolute simultaneity as proposed. While some acknowledge the challenges posed by relativity, others maintain that the method could still be valid under certain conditions. The discussion remains unresolved with multiple competing views.

Contextual Notes

Limitations include the dependence on definitions of simultaneity and the implications of relativistic effects on perceived motion and timing. The discussion does not resolve the mathematical or conceptual challenges presented.

tonto
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-simple procedure designed to absolutely synchronize clocks-

Picture the face of a very large clock with a one hand.

Let's place a small clock A at the 9 o'clk position of the
large clock, and let's place another small clock B at the
3 o'clk position.

We use clock A to time the large clock's hand for one
round trip. We then preset clock B to read half of this
time, and we let B be started by the large clock's hand
when it arrives after leaving B at its time zero.

At this point, clocks A and B should be absolutely synch'd.
 
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There is no such thing as absolute simultaneity in relativity, so no.

The specific problem with your setup is that an observer in motion with respect to the clock won't (in general) agree that it will take the same amount of time to sweep out 9-3 as it will to sweep out 3-9.
 
They also will not generally agree that the large hand is straight.
 
DaleSpam said:
They also will not generally agree that the large hand is straight.
Interesting, never thought of that... An effect of how rotation is viewed? Even if the clock is viewed "head on" (perpendicular to the direction of sight and motion)?
 
Ah thanks - not that I quite grasp the effect yet, but at least I see how it could arise.. don't say more it's a fun little puzzle:)
 
"combo reply"

I realize that special relativity does not have absolute
simultaneity, but this does not make it impossible.

In my setup, it matters not what some outside observers
may see; all that matters is the fact that the large hand's
speed must be constant because the center shaft's speed
is constant.

And any observed hand curvature would not matter as
long as there is no intrinsic curvature.

If there is intrinsic curving, then I suppose it could be
minimized by very slow hand movement.

Of maybe it could be eliminated by replacing the large
hand with a sweeping laser beam.

Just some thoughts.
 
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tonto said:
I realize that special relativity does not have absolute
simultaneity, but this does not make it impossible.
If SR is correct, then yes, it does make (or, rather, accurately describe) absolute simultaneity impossible.
 
to russ:

How?
(What -- physically -- is there about SR that makes abs. sim. not possible?)
 
The Lorentz transforms don't preserve the angle between lines, so observers in motion won't in general agree that the central axis is rotating at a constant rate (or, more precisely, will say that the rate varies as a function of angle).

As several posters have already noted, there is no absolute simultaneity in relativity. Any scheme purporting to show otherwise must be based on a misconception.
 
  • #10
tonto said:
I realize that special relativity does not have absolute simultaneity, but this does not make it impossible.
Maybe not, but it does make it outside of the scope of this forum. Thread closed.

tonto said:
In my setup, it matters not what some outside observers may see
Of course it does. "Absolute simultaneity" means that all observers agree on it. If outside observers don't agree on the simultaneity, then it isn't absolute.

tonto said:
; all that matters is the fact that the large hand's speed must be constant because the center shaft's speed is constant.
The shaft's speed being constant does not, by itself, imply that the large hand's speed is constant. That conclusion also requires the assumption that the shaft's shape remain constant in time, which is not true in all frames.

tonto said:
And any observed hand curvature would not matter as long as there is no intrinsic curvature.

If there is intrinsic curving, then I suppose it could be minimized by very slow hand movement.

Of maybe it could be eliminated by replacing the large hand with a sweeping laser beam.

Just some thoughts.
The math and the experimental evidence simply do not support any of this.
 
Last edited:

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