Is there a limit on real inertial frames?

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    Frames Inertial Limit
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Discussion Overview

The discussion revolves around the nature of inertial frames in the context of relativistic physics, particularly focusing on the implications of time dilation and acceleration as objects approach the speed of light. Participants explore the effects of these phenomena on observers and the observed, questioning the reality of relativistic effects and the limits of acceleration.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • One participant questions whether it is impossible for an observer to see an object accelerating to the speed of light and discusses the implications of time dilation on perceived motion.
  • Another participant asserts that the inability of a rocket to reach the speed of light is not solely due to time dilation, suggesting that an observer on the rocket could experience constant acceleration without measuring the outside universe moving at light speed.
  • Several participants emphasize that relativistic effects such as length contraction and time dilation are "real" phenomena, though the interpretation of what is "real" is debated.
  • There is a discussion about the reference frame of moving objects and the significance of frame dependence in measuring spatial and temporal separations between events.

Areas of Agreement / Disagreement

Participants express differing views on the nature of relativistic effects and their implications. While some agree on the reality of these effects, others question the meaning of "real" and the reference frames involved. The discussion remains unresolved regarding the interpretation of these concepts.

Contextual Notes

Participants highlight the dependence of relativistic effects on the chosen inertial reference frame and the implications of acceleration on the perception of time and motion. There are unresolved nuances regarding the definitions and interpretations of "real" effects in relativity.

TimGooding
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Hi guys,

I initially posted this here ...

https://www.physicsforums.com/showthread.php?p=1871724#post1871724

... but I see by the forum rules I should have posted it independently.

First of all, am I correct in understanding that a) it is impossible for an observer to observe anything accelerating to c? b) all the equations concerning this are relativistic except c) acceleration which does have a real affect of slowing the "clock" on any accelerated object?

If any of this is wrong, please correct me.

The problem for me is this: regardless of how an observer sees a moving object, even if the apparently relative speeds approaching c, the observed is still experiencing time normally. As the observed object appears to approach c the relative time is slowing.

But this is just relative; it is not a real effect. The object being observed still is experiencing normal time (processes) passing even if they are observed to be almost stopping or stopped by an outside observer.

To explain my question let me paint a theoretical picture. A rocket is observed passing at just below c (relatively speaking). The hand of the pilot is poised to accelerate but because of time dilation, it is practically frozen (moving so slowly that the observer would die before any movement could be detected).

If the pilot's and rocket's process were somehow maintaining their normal rate to an observer (as things would appear if they were in the same inertial frame) as the rocket's speed was relatively approaching c, the rocket's acceleration would be exponentially increasing.

But that is exactly what is happening from the point of view of the pilot. From her point of view, it takes two seconds to move the throttle fully forward, even the the observer dies, along with several of his suns, before he can experience any of it.

So, my question is: what has happened to this pilot relative to the first observer (other than the observer and his universe dies before the hand reaches the throttle) once she has moved the throttle fully forward and the rocket accelerated away?

Is my question clear?
 
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The fact that the rocket can't reach c is not solely due to time dilation, in fact an observer on board the rocket could be accelerating at a constant rate (constant G-force as felt on board the rocket) forever according to her own clock and still never see measure the outside universe to be moving at c in the rocket's inertial rest frame at any given moment (equations concerning a rocket accelerating at a constant rate can be found on the http://math.ucr.edu/home/baez/physics/Relativity/SR/rocket.html .
 
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relativistic effects are 'real'. objects that are moving really are length contracted, time dilated, and really do experience loss of simultaneity.
 
granpa said:
relativistic effects are 'real'. objects that are moving really are length contracted, time dilated, and really do experience loss of simultaneity.

You say "objects that are moving really are length contracted, time dilated, and really do experience loss of simultaneity". What are they "moving" relative to?
 
TimGooding said:
You say "objects that are moving really are length contracted, time dilated, and really do experience loss of simultaneity". What are they "moving" relative to?

A particular inertial reference frame. And I think one has to take care with what is meant by "real."

These things are "real" in the sense that given a pair of events, the spatial and temporal separations between the events are frame dependent. A moving watch, however, doesn't notice anything special happening to the way it keeps time, i.e., it doesn't notice any physical change in itself.
 
Okay, thanks everyone. I got it.
 

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