Length contraction or Lorentz Contraction

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Discussion Overview

The discussion revolves around the concepts of Lorentz Contraction and time dilation in the context of special relativity. Participants explore how these phenomena affect measurements of distance and time for objects moving at relativistic speeds, as well as the implications of these effects on different frames of reference.

Discussion Character

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

Main Points Raised

  • One participant describes Lorentz Contraction as the phenomenon where an object appears to contract relative to its velocity from the perspective of an observer, leading to a measurement of less distance traveled.
  • Another participant asserts that the object measures a smaller distance traveled from A to B, emphasizing the symmetry of contraction between the observer and the moving object.
  • A participant expresses confusion about the relationship between time dilation and distance measurement, questioning how an object moving at high speed can experience less time while measuring a greater distance.
  • There is a discussion about the impossibility of achieving a frame of reference at the speed of light (C), with one participant suggesting that at C, everything would exist simultaneously.
  • A later reply introduces the concept of the relativity of simultaneity, noting that different observers will measure different lengths due to their varying definitions of "at the same moment."

Areas of Agreement / Disagreement

Participants exhibit some agreement on the symmetry of length contraction and time dilation, but there remains uncertainty and confusion regarding the implications of these concepts, particularly in relation to measurements from different frames of reference.

Contextual Notes

Participants highlight the importance of precise language when discussing measurements in relativity, indicating that common phrasing may overlook the complexities involved in defining length and simultaneity across different frames.

thecow99
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As I understand it, Lorentz Contraction states an object "contracts" relative to it's velocity to an observer.

So at a high velocity of speed, the meter stick (carried by the object moving relative to the observer) appears to contract (to the observer) and the observer measures less distance traveled than the object.

This seems to counter time dilation.

If the object is measuring a larger distance traveled from A to B it would seem the object would would measure an increase in observed time, not a decrease.

If object is moving at .99C and it contracts the measured distance from A to B would increase for it, which would logically say would take more time.

How am I misinterpreting this? I know the object experiences less time but a greater distance? Huh?

Cheers!
 
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The Object is measuring a smaller distance traveled from A to B. You see the object contract, the object sees you contract. It's symmetric. Always contraction of length, never dilation of length. Likewise, always dilation of time, never contraction of time.
 
Eh, my stupid brain...

The meter stick doesn't contract in it's own frame of reference. Should have guessed that!

I kind of get it now. So when time dilation occurs, the moving object experiences less space traveled because in it's frame it "time" was constant.

Wait.. is that why you can't get a frame at C? Because at C everything would exist in the same place at the same time?
 
thecow99 said:
.. is that why you can't get a frame at C? Because at C everything would exist in the same place at the same time?


Yes, I believe so. It requires an outside observer with a lower relative velocity to see light as traversing a distance.
 
To work through these questions properly, you need to consider the relativity of simultaneity as well as time dilation and length contraction. When someone says "This rod is one meter long" they're being a bit sloppy in their wording - it would be more precise to say "I found where the two ends of the rod were at the same moment, and then I measures the distance between those two points, and found them to be one meter apart".

Note that this definition does not assume that the rod is at rest relative to the person making the measurement. It also makes it clear that, because observers moving relative to each other have different definitions of "at the same moment", they will measure different lengths.
 

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