Understanding Lorentz Factor & Proper Time Invariance

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Discussion Overview

The discussion revolves around the concepts of the Lorentz factor, proper time, and their invariance in the context of special relativity. Participants explore the implications of proper time being invariant while also being dependent on relative velocity, leading to confusion and clarification about the definitions and relationships between proper time and time dilation.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • Some participants express confusion regarding the Lorentz transformation for proper time and its invariance, questioning how proper time can be invariant if it depends on relative velocity (v).
  • Others argue that proper time is defined as the time measured by a clock along its worldline and is invariant, while coordinate time is not.
  • A participant notes that the presence of v in the transformation is necessary to maintain the invariance of the expression.
  • There is a discussion about the relationship between proper time and time dilation, with some clarifying that proper time is invariant while time dilation varies between reference frames.
  • Participants discuss the distinction between proper time and time dilation, emphasizing that proper time is the length of the spacetime interval, which is frame invariant.
  • One participant seeks clarification on the representation of a worldline graph, questioning whether it is from the perspective of a moving observer or a stationary one.

Areas of Agreement / Disagreement

Participants generally agree that proper time is invariant and distinct from time dilation, but there remains some confusion and disagreement about the implications and interpretations of these concepts, particularly regarding the Lorentz transformation and the nature of reference frames.

Contextual Notes

Some statements rely on specific definitions of proper time and time dilation, which may not be universally agreed upon. The discussion also highlights the complexity of understanding these concepts within the framework of special relativity.

  • #31
vanhees71 said:
I'm always somewhat in doubt, whether Minkowski diagrams really help.
They really helped me. It was Minkowski diagrams and the concept of four-vectors that made relativity click for me.

I think different students are going to “get it” with different mental tools. So educators need to know and use all of them. Of course, it is ok to have a favorite one and it is ok for that favorite to be different from person to person
 
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  • #32
PeroK said:
...in a frame where the clock is moving it is measured to be time dilated.

Note that it's not correct to say that the proper time is dilated, because proper time is the length of the spacetime interval, which is frame invariant.

That is, perhaps, a subtle point.
imo is crucial for better understanding.
I find the part I underlined to be VERY well worded. Textbook quality imo. (only thing I can think of is including the spatial separation between measurement taken and the thing being measured. for example "is measured at a distance to be time dilated.")

I get that is very implicit as was mentioned there is relative motion. but feel it may help separate the concepts [proper / dilated time] a bit quicker for those new to them.
 
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  • #33
Dale said:
They really helped me. It was Minkowski diagrams and the concept of four-vectors that made relativity click for me.

I think different students are going to “get it” with different mental tools. So educators need to know and use all of them. Of course, it is ok to have a favorite one and it is ok for that favorite to be different from person to person
me too, though of course to a MUCH lesser understanding than you have. (you've explained lots to me years ago)
I found the simple light clock to be very helpful too, for me helped visualize / see it play out.

The Minkowski modeling gets into comparatively more abstracted presentation than the idealized clock imo, but of course is a math tool of sorts, the idealized light clock is just an imaginary thing that helps my simple mind figuratively see the "mechanics" of this "tiny bit" of spacetime physics.
 
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