# Still confusion in relativity of simultaneity and time dilation .

1. Apr 5, 2013

### ash64449

Still confusion in relativity of simultaneity and time dilation.....

Hello friend,

Still Something in my mind is saying that Relativity of simultaneity is the reason for time dilation even though i had some corrections in my understanding by posting various threads. Well,let me use Einstein's book Theory of Relativity to explain what i mean. I will not use any extra words or extra understandings.. Just i will explain the point by highlighting some important sentences..

Begins with chapter 8: On the Idea Of time In physics
In this paragraph that i quoted from the book,it gives the idea of time in physics.To explain this he said that clocks were kept at points A,B,C of the railway line and they are set in the manner that their pointers are simultaneously the same. From this condition,we were able to give 'time' of an event which is in immediate vicinity of event.As a result we will be able to record when every event happens. it is from this understandable that time is defined or measured with the help of events.

then by giving this idea he said that in position of their pointers are simultaneous,then these clocks are of identical construction.And again if they are of identical construction,then these clocks go at the same rate. And as the above quote used time as defined as events. so then whatever events that are simultaneous to a tick of a clock will be simultaneous to other clock,if clocks go at that same rate(from the above consideration)

This is an important line and i have got this as conclusion not from my own,i got it from the book.

Then let us go to the next chapter: The Relativity Of simultaneity
Now this paragraph says that clock go at different rates by used Relativity Of Simultaneity. In the example that is given by Einstein, Lightning was simultaneous with respect to embankment but not to train.Then Einstein immediately pointed out that Every Reference body has its own particular time and then said that there is no meaning of 'time' of event. Anyway we can understand that there is no meaning of 'time' of event from the above conclusion. But from the previous chapter we understood that time is defined by events. So the reference frames which sees events defined by same pointers of their clock go at the same rate. But in the case given in example, embankment reference frame needed only one tick of the clock to describe two events,while in train's reference frame needed two ticks of the clock to define those two events. So from the above consideration,These clocks should go at different rates!!!

But when i said this in other thread,posters said that this directly lead to Relativity Of Simultaneity. Yes,They are right. But it does lead to the clocks going at different rates too.. But i haven't said about the other chapter...

Now through Lorentz transformation,we can understand that Time goes in different rates and it shows something more. Time dilates. Well, i think we cannot get this conclusion from dealing with relativity of simultaneity itself because i don't know what would happen if time beat faster than usual when moves..

This is the reason why i said that Relativity of simultaneity is related to time dilation...
Or relativity Of simultaneity causes Time dilation. Now we know that Lorentz transformation was derived from two postulates. that predicted time dilation. Well, Relativity of simultaneity requires these two postulates.

We can understand this from the chapter on idea of time in physics, The quoted word was written in footnotes of this chapter:
Well,these words conclusion is that These clocks should go at same rate.But we already described relationship between events and time. So since relativity of simultaneity is derived from these two postulates, time dilation too is and can be derived for these two postulates.

Some General Doubts from the book:
In this quote why did he use the word "really"?

What is the meaning of these lines?

Here is the pdf of the book that i used here: http://www.marxists.org/reference/archive/einstein/works/1910s/relative/relativity.pdf

Last edited: Apr 5, 2013
2. Apr 5, 2013

### Staff: Mentor

can you edit your post using the QUOTE feature so that it is easier to see where Einstein's words end and yours begin?

Just some general advice. It is usually best to learn from more modern presentations rather than from the seminal works.

3. Apr 5, 2013

### ash64449

ok. You will have to wait sometime. Remember.i am not trying to invalidate einstein on any account. I just got conclusions like this and i want corrections in my conclusions. That is all

4. Apr 5, 2013

### Staff: Mentor

Your conclusions have already been corrected. I think that what you want is corrections in your reasoning. Unfortunately, from the above I cannot follow your reasoning. The QUOTE feature would be helpful as would making your point more concisely. If you can organize your thoughts better in the post then I could be more helpful.

5. Apr 5, 2013

### ash64449

ok. i have done the job.. Now Quotes please!!!

6. Apr 5, 2013

### Staff: Mentor

That helps, thanks!

7. Apr 5, 2013

### Staff: Mentor

OK, I looked through the Einstein quotes and found exactly one reference to the word "rate". Specifically:
This quote is a reference to the first postulate. Clocks of identical construction at rest wrt each other will tick at the same rate. I think you understand that, so I think I am just confirming what you already know.

Yes, this is correct. RoS can be derived from the two postulates and TD can also be derived from the two postulates.

I am not sure what you still feel confused about in this regards. It seems that you understand correctly, but are still bothered by something.

8. Apr 5, 2013

### ash64449

Yes. I know this.. Reference frame which is moving will tick at slower rate.

Why i am in confusion is because i from these conclusion get that Relativity Of simultaneity is the reason for Time Dilation. But if you ask me that isn't the two postulates the reason,i will agree with it too!!

9. Apr 5, 2013

### ash64449

I think simultaneous events can be simultaneous in IRF that is moving.. (not always)
ghwellsjr provided an excellent animations to show how MME is in relation with SR. But when i looked at this,i found that in this case,both the reference frame is simultaneous, but the detector of the one who is in IRF(moving) received light cone in slower rate. This is one example in which simultaneous events can be simultaneous in IRF which is moving..

Here is the link to that discussion:

10. Apr 5, 2013

### ash64449

11. Apr 6, 2013

### Staff: Mentor

How do you get that? I see no chain of logic in what you presented that indicates this.

12. Apr 6, 2013

### Staff: Mentor

Indeed, they can. We already discussed the conditions under which they can be simultaneous. Specifically, for relative motion in the x direction, the events must be separated in the y or z directions. If we have two events then the differences between the two events (in units where c=1) are given by:
$$\begin{array}{l} \Delta t' = \gamma \, (\Delta t-\Delta x \, v) \\ \Delta x' = \gamma \, (\Delta x-\Delta t \, v) \\ \Delta y' = \Delta y \\ \Delta z' = \Delta z \\ \end{array}$$

For a pair of events to be simultaneous in both frames means that $\Delta t = \Delta t' = 0$. This can only be true if $\Delta x = 0$ which implies that $\Delta y \ne 0$ or $\Delta z \ne 0$.

13. Apr 6, 2013

### 1977ub

will be *measured* to be ticking slower by someone in a different frame.

Mathematically the two principles are completely linked. If you initially observe either TD or RofS but not both, things will not add up, and you will soon realize the other is involved.

14. Apr 6, 2013

### arildno

Do remember that BOTH reference frames will be moving, relative to the other frame.
Thus, from the point of frame A, it is the clocks in B that tick slower, while from the point of frame B, it is the clocks in A that tick slower.