Lengths and times relative to S' and S

  • Context: Graduate 
  • Thread starter Thread starter arbol
  • Start date Start date
  • Tags Tags
    Relative
Click For Summary
SUMMARY

This discussion presents a detailed examination of the relationship between lengths and times in two coordinate systems, S and S', where S' moves with velocity v along the x-axis of S. The analysis defines key variables such as t', t, T, and their respective relationships, particularly focusing on the propagation of light rays in both systems. The conclusion emphasizes that the lengths of the paths taken by light emitted from both systems are equal, leading to the equation T2 = 2*t'1, while also addressing potential contradictions with special relativity.

PREREQUISITES
  • Understanding of special relativity principles
  • Familiarity with coordinate transformations
  • Knowledge of light propagation and speed of light (c)
  • Basic grasp of inertial reference frames
NEXT STEPS
  • Study Lorentz transformations in special relativity
  • Explore the implications of simultaneity in different reference frames
  • Investigate the concept of time dilation and length contraction
  • Learn about the Einstein's theory of relativity and its mathematical formulations
USEFUL FOR

Physicists, students of relativity, and anyone interested in the mathematical foundations of motion and light in different inertial frames.

arbol
Messages
50
Reaction score
0
I propose a new look at lenghts and times relative to S' and S (at least new to me).

Let S' be an x'-coordinate system. Let the x'-axis of S' coincide with the x-axis of an x-coordinate system S, and let S' move along the x-axis of S with velocity v in the direction of increasing x.

Let t' = the time, with respect to S', a ray of light emitted by S' takes to move along the x'-axis of S'.

Let t = the time, with respect to S, a ray of light emitted by S takes to move along the x-axis of S.

Let T = the time, with respect to S, the ray of light emitted by S' takes to move along the x'-axis of S'.

At t' = 0s, the ray of light emitted by S' is located at x' = 0m.

At t' = t'1, the ray of light emitted by S' is located at x' = c*t'1.

At t' = 2*t'1, the ray of light emitted by S' is located at x' = 0m.

At t = 0s, (1) the ray of light emitted by S is located at x = 0m, (2) the origin of S' is located at x = 0m, and (3) t' = t.

At t = t1, (1) the ray of light emitted by S is located at x = c*t1, (2) the origin of S' is located at x = v*t1, and (3) t' = t.

At = t = 2*t1, (1) the ray of light emitted by S is located at x = 0m, (2) the origin of S' is located at x = 2*v*t1, and (3) t' = t.

At T = 0s, the ray of light emitted by S' is located at x = 0m.

At T = T1, the ray of light emitted by S' is located at x = c*T1 = v*t1 + c*t'1 = c*t'1 + v*t'1 = t'1*(c + v).

Note: t1 = t'1. It is given that the length of the path of the ray of light emitted by S' is equal to the length of the path of the ray of light emitted by S.

At T = T2, the ray of light emitted by S' is located at x = 2*v*t1.

T1 = t'1(c + v)/c.

c*(T2 - T1) = |2*v*t1 - (c*t'1 + v*t'1)| = c*t'1 + v*t'1 - 2*v*t'1 = c*t'1 - v*t'1 = t'1*(c - v).

T2 - T1 = t'1*(c - v)/c.

Note: T1 is not equal to T2 - T1, but this inequality does not mean that the clock located at x = 0m and the one located at x = c*T1 are not synchronous. The clock that marks the time T = 0s is located at x = 0m, the one that marks the time T = T1 is located at x = c*T1, and the one that marks the time T = T2 is located at x = 2*v*t'1 (or x = v*T2).

T = T1 + (T2 - T1) = T2 = 2*t'1.
 
Physics news on Phys.org
arbol said:
Let the x'-axis of S' coincide with the x-axis of an x-coordinate system S, and let S' move along the x-axis of S with velocity v in the direction of increasing x.
I haven't read the whole thing, but you're already contradicting special relativity here. If S and S' are inertial frames, the x' axis would intersect the x-axis with slope v (when the units are such that c=1).

You also need to explain what you're trying to do more carefully. I'm having a hard time following your argument.
 
Fredrik said:
I haven't read the whole thing, but you're already contradicting special relativity here. If S and S' are inertial frames, the x' axis would intersect the x-axis with slope v (when the units are such that c=1).

You also need to explain what you're trying to do more carefully. I'm having a hard time following your argument.

Yes. I am even having difficulties following what I am writing. I hope this reply is easier to read.

Let S' be an x'-coordinate system. Let the x'-axis of S' coincide with the x-axis of an x-coordinate system S, and let S' move along the x-axis of S with velocity v in the direction of increasing x, and let the origin of S' coincide with the origin of S at t = t' = 0s.

Let a ray of light emitted by the moving system S' depart from x' = 0m at the time t' = 0s towards x' = x'1 and reach x' = x'1 at the time t' = t'1, and let it be reflected at x' = x'1 back to x' = 0m, and reach x' = 0m at the time t' = t'2.

With respect to the moving system S', the length of the path of the ray of light emited by S' is

2*x'1.

t'2 = 2*x'1/c.

Let a ray of light emitted by the stationary system S depart from x = 0m at the time t = 0s towards x = x1 and reach x = x1 at the time t = t1, and let it be reflected at x = x1 back to x = 0m, and reach x = 0m at the time t = t2.

With respect to the stationary system S, the length of the path of the ray of light emited by S is

2*x1.

t2 = 2*x1/c.

It is given in this thread that x = x'1.

With respect to the stationary system S, the length of the path of the ray of light emitted by the moving system S' is

x'1 + v*t'1 + (x'1 - v*t'1) = 2*x'1 = 2*x1.

Thus, with respect to the stationary system S, the ray of light emitted by the moving system S' takes the time t2 = t'2 to move from x' = 0m to x' = x'1 and back to x' = 0m.
 
x'1 + v*t'1 + (x'1 - v*t'1) = 2*x'1 = 2*x1.
Yes, as long as x'=x and t'=t, x'=x and t'=t. That's fact.
 

Similar threads

  • · Replies 9 ·
Replies
9
Views
1K
  • · Replies 32 ·
2
Replies
32
Views
3K
  • · Replies 25 ·
Replies
25
Views
2K
  • · Replies 143 ·
5
Replies
143
Views
9K
  • · Replies 25 ·
Replies
25
Views
1K
  • · Replies 10 ·
Replies
10
Views
2K
  • · Replies 12 ·
Replies
12
Views
3K
  • · Replies 31 ·
2
Replies
31
Views
3K
  • · Replies 20 ·
Replies
20
Views
2K
  • · Replies 48 ·
2
Replies
48
Views
5K