Confused about the logic of a Special Relativity problem

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Discussion Overview

The discussion revolves around the concepts of time dilation and Lorentz contraction in the context of the twin paradox in special relativity. Participants explore the implications of relativistic speeds on the perception of time and events as experienced by two twins, one of whom travels to Alpha Centauri and back.

Discussion Character

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

Main Points Raised

  • One participant expresses confusion about the implications of light travel time on the perception of events, particularly regarding when the Earthbound twin sees the traveling twin turn around and how this relates to their actual positions.
  • Another participant clarifies that the traveling twin is never ahead of the light and emphasizes the importance of distinguishing between what is seen by an observer and what is happening in terms of coordinate time.
  • There is a discussion about the Doppler effect and how it influences the perception of events, with one participant questioning how the traveling twin's actions would appear to the Earthbound twin.
  • One participant explains a non-relativistic example of the Doppler effect using a stationary clock, illustrating how the perceived timing of events changes as the clock moves towards the observer.
  • Another participant acknowledges the relationship between the Doppler effect and time dilation, noting that while the moving clock ticks slower, the perceived rate of events can appear faster due to the motion of the source.
  • There is a further exploration of the implications of light travel time and how it affects the perceived timing of events, with participants questioning the relationship between the traveling twin's position and the light emitted from her at various points during her journey.

Areas of Agreement / Disagreement

Participants express differing views on the implications of light travel time and the Doppler effect, indicating that multiple competing interpretations exist regarding the perception of time and events in the context of special relativity. The discussion remains unresolved, with participants seeking clarification on various points.

Contextual Notes

Participants highlight the complexity of understanding the relationship between light travel time, the Doppler effect, and time dilation, indicating that assumptions about simultaneity and the perception of events may not be straightforward.

  • #61
jartsa said:
I see. When I'm trying to reverse a distant clock, by a sharp acceleration of myself, the clock starts to resist further reversing at some time. Or rather: the more a clock is reversed, the more it resist reversing. Thank you guys. It's clear now.

When I'm trying to reverse a distant clock, the clock tends to become a nearby clock, nearby clocks behave less weird than distant clocks.

That's how it works. It's the length contraction phenomenon. Very simple actually.
 
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  • #62
jartsa said:
When I'm trying to reverse a distant clock, the clock tends to become a nearby clock, nearby clocks behave less weird than distant clocks.

You don't reverse distant clocks. You don't even change distant clocks. You change reference frames, but you'll never be in a reference frame that observes or even sees clocks running backwards.
 
  • #63
Mister T said:
You don't reverse distant clocks. You don't even change distant clocks. You change reference frames, but you'll never be in a reference frame that observes or even sees clocks running backwards.
Maybe if I use scare quotes the error is not so severe.

So I'm looking at Earth that is 1000 ly away, I'm seeing year 3000 going on, and it is now year 4000 on Earth according to me. Then I accelerate to speed 0.99999999 c away from the earth. Now I'm seeing year 3000 going on, and it is now year 3000 on Earth according to me. As I'm seeing Earth without much delay, the Earth must be near.

The Earth "moved closer" and "reversed" as I accelerated.
 
  • #64
jartsa said:
Maybe if I use scare quotes the error is not so severe.

So I'm looking at Earth that is 1000 ly away, I'm seeing year 3000 going on, and it is now year 4000 on Earth according to me. Then I accelerate to speed 0.99999999 c away from the earth. Now I'm seeing year 3000 going on, and it is now year 3000 on Earth according to me. As I'm seeing Earth without much delay, the Earth must be near.

The Earth "moved closer" and "reversed" as I accelerated.

No that is not what happens. And you aren't paying attention to what was said in #53 and #57 of this thread.
 
  • #65
Nugatory said:
No that is not what happens. And you aren't paying attention to what was said in #53 and #57 of this thread.

It's not the same scenario as before, I curbed the "reversing".

How much can I tilt the line of simultaneity? Almost 45 degrees. As the wordline of light is tilted 45 degrees, the light that an observer is seeing left the light source about now, according to the observer, when observer's line of simultaneity is almost parallel to the wordline of light.
 
  • #66
Without going into all the detail, the explanation of what's happening during this "experiment" is badly worded. In fact it's just wrong. Comparing "times" is misleading because there is no shared moment, so shared now! Only when they are together do they share the same time and the same location, apart from that their times and locations are only truly comparable by reference to a combined space-time.
 
  • #67
Hey don't give up, most people even the experts only understand this particular "experiment" on a very superficial level. The explanation provided by your expert is misleading and in fact downright incorrect. Comparing the times between the two individuals is not possible, there is no shares moment, no shares now! Making time like comparisons is without reference to space is impossible. Only by reference to full space time coordinates is a comparison possible, and. It is neither a true time comparison nor a true space comparison but rather a blend of both.
 

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