Need help understanding time dilation

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Discussion Overview

The discussion revolves around the concept of time dilation in the context of special relativity, specifically addressing how different observers perceive the passage of time for moving clocks compared to their own local clocks. Participants explore the implications of proper time and the effects of relative motion on time measurement.

Discussion Character

  • Exploratory, Conceptual clarification, Debate/contested

Main Points Raised

  • Some participants express confusion about how a moving clock can measure a longer time period when compared to a local clock, questioning the concept of proper time.
  • One participant clarifies that proper time is measured by the clock at rest relative to the events being timed, suggesting that the moving clock measures proper time between its own events.
  • A scenario is presented where an Earth observer measures one hour on their clock and questions how much time would have elapsed on a spaceship clock, leading to the assertion that less than one hour would have elapsed on the spaceship clock according to the Earth observer.
  • Another participant prompts consideration of how the observer on the rapidly moving spaceship would perceive the elapsed time on Earth, introducing a perspective shift regarding relative motion.

Areas of Agreement / Disagreement

Participants generally agree on the principle that moving clocks run slow from the perspective of a stationary observer, but there is ongoing confusion and debate regarding the implications of proper time and how different observers perceive time intervals.

Contextual Notes

There are unresolved questions regarding the definitions of proper time and the conditions under which time dilation is observed, as well as the implications of relative motion on time perception.

Who May Find This Useful

This discussion may be useful for individuals interested in understanding the nuances of time dilation, special relativity, and the perspectives of different observers in relativistic scenarios.

annms
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I keep reading that an observer will find the clock moving relative to him to be slower than his own local clock. But isn't his own local clock measuring proper time, which should be a shorter time period than the moving clock? How can the slower (moving) clock measure a longer time period? Isn't that a contradiction? I'm so confused please help.
 
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annms said:
I keep reading that an observer will find the clock moving relative to him to be slower than his own local clock.
Right.
But isn't his own local clock measuring proper time, which should be a shorter time period than the moving clock?
Proper time between what events?
How can the slower (moving) clock measure a longer time period?
A slower clock measures less time between events, of course.

If the 'events' are the ticks of the moving clock, then it is the moving clock that measures the proper time between them. Not you! (Your clocks measure proper time between events that occur at your location.)

Say you are observing a rocket speeding by. The rocket has a clock that is set to flash a burst of light every time a minute passes. You, using your own Earth clocks, would say that the time between flashes was greater than one minute and thus you would describe the moving clock on the rocket as running slow. Since the flashes take place at the location of the moving clock, that clock measures the proper time between them.
 
Last edited:
Thanks. I think I'm getting it a little better.

This was what really confused me: Let's say a spaceship is traveling at a speed near c relative to earth. If one hour has elapsed according to an Earth observer's clock, how much will have elapsed in the spaceship's clock according to the Earth observer? (ie. greater than one hour or less than one hour?) And why?
 
annms said:
If one hour has elapsed according to an Earth observer's clock, how much will have elapsed in the spaceship's clock according to the Earth observer? (ie. greater than one hour or less than one hour?)
The Earth observer would say that during the one hour on earth, less than an hour would have elapsed on the spaceship clock.
And why?
Moving clocks run slowly.
 
Annms:

What do you think the rapidly moving spaceship observer will say about the elapsed time he observes on earth??

Hint: who is moving rapidly now??
 

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