# How to explain Einstein's Special theory of Relativity.

by Lochlan.H
Tags: explanation, relativity
P: 52
 Quote by tensor33 The time equation of SR is LT. the lorentz transforms are a set of equations for transforming from one reference frame to another. They are a part of SR.
If you think LT is part of SR, that's fine. Now, we have two "time dilation" equations.

As I know, SR can be used for two systems with constant relative speed; however, in case of constant relative velocity SR should be correct as well. I mean, in cases of constant relative velocity, should I use LT or SR? Do you have website where I can find the answer of it? Thanks.
 P: 784 There is a lot in SR. The Lorentz Transformations were a set of coordinate transformations that Lorentz first developed with regards to electromagnetism. It was Einstein who first used them to describe space itself, and the time dilation and length contraction equations come directly from the lorentz transformations. You keep saying that LT and SR are seemingly two distinct things, which is completely wrong. The Lorentz Transformations are a part of SR. To ask whether to use Special Relativity or the Lorentz Transformations is like to ask whether to use Newtonian Mechanics or Newton's Second Law; the question doesn't make sense.
P: 52
 Quote by John Huang If you think LT is part of SR, that's fine. Now, we have two "time dilation" equations. As I know, SR can be used for two systems with constant relative speed; however, in case of constant relative velocity SR should be correct as well. I mean, in cases of constant relative velocity, should I use LT or SR? Do you have website where I can find the answer of it? Thanks.
I'm not quite sure I understand your question. When you say "Should I use LT or SR?", it makes no sense. It is my understanding that LT is a part of LR. There is no need to choose between the two.
Maybe if you gave me an example of what you consider to be an equation of SR and an equation of LT I would better understand your question.
PF Gold
P: 4,087
 Quote by John Huang Thanks for the comment. I know that Einstein also supported LT and he claimed that he proved LT by 2 postulates. Actually I also know that after Einstein introduced his SR in the section 3 of his 6/30/1905 paper, he extended SR from "constant relative velocity" to "constant relative speed" in the section 4 right away. Even with the new expansion, I think SR should continue its support to the situation of "constant relative velocity".
The changing of the term 'velocity' and 'speed' makes no operational difference. Speed is defined as s = √(vx2+vy2+vz2) where the v terms are the magnitudes of the x,y and z velocities. It is always possible to rotate the coordinates so only one component is non-zero in these coords.

What difference do you think it makes ?
Mentor
P: 17,543
 Quote by John Huang Thanks for the comment. I know that Einstein also supported LT and he claimed that he proved LT by 2 postulates. Actually I also know that after Einstein introduced his SR in the section 3 of his 6/30/1905 paper
In that section he clearly derived the LT from his two postulates. Therefore, the LT is part of SR, and has been from the beginning of SR.

 Quote by John Huang he extended SR from "constant relative velocity" to "constant relative speed" in the section 4 right away.
In section four he derives the time dilation equation from the LT with the additional restriction that the other clock is "at rest relative to the moving system, to be located at the origin". I.e. That is the only time that derived formula applies.

 Quote by John Huang So, could you explain why in the situation that {the observed event happened at a location other than O'} we should use LT, not SR?
Can you explain in playing football why you should use your leg, not your foot?

 Quote by John Huang I think the main purpose of SR is to introduce the time dilation equation. However, if you could show me what else SR has provided to people, I will appreciate and study it.
Please re read the 1905 paper. Clearly he includes more than just the time dilation equation. So for you to make this statement is absurd. Furthermore, going beyond Einstein, SR now includes also Minkowski's spacetime, and even pseudo-Riemannian geometry on flat manifolds.
Mentor
P: 17,543
 Quote by John Huang If you think LT is part of SR, that's fine. Now, we have two "time dilation" equations.
No, you have the LT which simplifies to the time dilation equation under specific circumstances. When the circumstances match then you can use the simplified equation or the LT equally since they agree. When the circumstances don't match then you cannot use the simplified equation since it doesnt apply.
 P: 52 That is the best answer I have received so far. Thanks. Do you mean, only when x'=0 we can use SR, otherwise, we should apply LT?
P: 52
 Quote by Mentz114 The changing of the term 'velocity' and 'speed' makes no operational difference. Speed is defined as s = √(vx2+vy2+vz2) where the v terms are the magnitudes of the x,y and z velocities. It is always possible to rotate the coordinates so only one component is non-zero in these coords. What difference do you think it makes ?
With constant velocity, LT works for inertial systems only; with constant speed, SR can expand to circling or any kind of constant speed situation.
P: 52
 Quote by Vorde You keep saying that LT and SR are seemingly two distinct things, which is completely wrong. The Lorentz Transformations are a part of SR. To ask whether to use Special Relativity or the Lorentz Transformations is like to ask whether to use Newtonian Mechanics or Newton's Second Law; the question doesn't make sense.
According to # 42, my understanding is that SR is part of LT. What do you think?
P: 52
 Quote by tensor33 I'm not quite sure I understand your question. When you say "Should I use LT or SR?", it makes no sense. It is my understanding that LT is a part of LR. There is no need to choose between the two. Maybe if you gave me an example of what you consider to be an equation of SR and an equation of LT I would better understand your question.
For example, if we focus on the events happen at the origin point of the stationary system, the point O, then we will have x=0. If LT is part of SR, then, both of the time equations in LT and SR should apply and under this situation, the time equations are inverse. Which one should apply?
Mentor
P: 41,579
 Quote by John Huang According to # 42, my understanding is that SR is part of LT. What do you think?
Realize that in common usage SR means "Special Relativity". The LT is part of SR, of course.

You seem to be using "SR" to mean the time dilation formula, which is a special case of the LT (as has been explained). Your non-standard use of "SR" is creating some confusion.
Mentor
P: 41,579
 Quote by John Huang For example, if we focus on the events happen at the origin point of the stationary system, the point O, then we will have x=0. If LT is part of SR, then, both of the time equations in LT and SR should apply and under this situation, the time equations are inverse. Which one should apply?
If you want to convert measurements from one frame to another you can always use the LT. In certain cases the simplified 'time dilation' formula can be applied.

In this example, since the events in question all take place at x = 0, you can convert the time between them (Δt) to the moving frame (Δt') using the time dilation formula: Δt' = γΔt. But that's just an application of the LT.

Mentor
P: 17,543
 Quote by John Huang Do you mean, only when x'=0 we can use SR, otherwise, we should apply LT?
No, I mean what I said. The LT is part of SR. The time dilation formula (which is part of the LT) only applies when x'=0.

You continue to identify SR with only the time dilation formula. That is simply WRONG.
Mentor
P: 17,543
 Quote by John Huang According to # 42, my understanding is that SR is part of LT. What do you think?
No, you have this backwards. The LT is part of SR.

I think there is some language barrier. Perhaps this will help:
$SR \supset LT \supset time \; dilation$
$SR \neq time \; dilation$
P: 52
 Quote by Doc Al If you want to convert measurements from one frame to another you can always use the LT. In certain cases the simplified 'time dilation' formula can be applied. In this example, since the events in question all take place at x = 0, you can convert the time between them (Δt) to the moving frame (Δt') using the time dilation formula: Δt' = γΔt. But that's just an application of the LT. What's your point?
My point is a logical issue.

In above example, two systems have constant relative velocity so that the speed of time in the moving system t' and the speed of time in the stationary system t should be decided once we select the point O as the stationary point, and the O' as the moving point. Under this SPECIFIC arrangement, when we talk about a period of time for ONE SPECIFIC EVENT then we should have ONLY ONE event period Δt as recorded in the stationary system and ONLY ONE event period Δt' as recorded in the moving system.

Now, what SR claims is Δt' = Δt/γ and what LT claims is Δt' = γΔt for the ABOVE example. Logically speaking, this should not happen UNLESS γ=1, isn't it? How do you explain this logical issue?

If you like the event to stay in the moving system, then you may let x'=1.
P: 52
 Quote by John Huang Now, what SR claims is Δt' = Δt/γ and what LT claims is Δt' = γΔt for the ABOVE example. Logically speaking, this should not happen UNLESS γ=1, isn't it? How do you explain this logical issue?
I don't know where you got this idea. In SR Δt' = γΔt not Δt/γ. It is the same for LT. That is where your confusion lies.
 P: 784 You are wrong with these equations. In both LT and SR (it seems stupid as I previously mentioned to distinguish between the two like that but I'll cave for argument's sake), ##\Delta t'=\Delta t \gamma##. You may be confusing the time dilation equation with the length contraction equation, which is ##\Delta L'= \frac{\Delta L}{\gamma}##
Mentor
P: 41,579
 Quote by John Huang Now, what SR claims is Δt' = Δt/γ and what LT claims is Δt' = γΔt for the ABOVE example. Logically speaking, this should not happen UNLESS γ=1, isn't it? How do you explain this logical issue?
The simple explanation is that you do not understand how and when to apply the time dilation formula. (And please stop saying "SR claims...".)

Events that happen at x = 0 can be treated similar to a clock at that point that is stationary in the unprimed frame. From the primed frame, that clock is moving and obeys the 'time dilation' formula (which is derived from the LT). You'll get Δt' = γΔt no matter how you slice it.

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