Doubts in special theory of relativity

[ash64449]

Hello friends,

From special theory of relativity,it is understood that if two events are simultaneous to a stationary reference frame,it is not simultaneous to a reference frame that is moving uniformly in straight direction. Is opposite possible? That is are two events are simultaneous to a reference frame that is moving uniformly simultaneous to a reference frame that is not moving?

 

[ash64449]

actually i meant the two events that are simultaneous to a reference frame which is moving uniformly simultaneous to a reference frame that is not moving?

 

[Dale]

Yes, that is possible. If two reference frames are in the standard configuration (origins coincide at t=0, all spatial axes parallel, motion along x axis) then two events separated in the x direction which are simultaneous in one frame will not be simultaneous in the other frame, but two events separated in the y or z directions which are simultaneous in one frame will be simultaneous in the other frame.

 

[Crazymechanic]

Those questions are really hard to understand but let's put it this way.
You are at point 0 now one car comes from point -1 the other from point +1, if the both cars happen to travel at the same speed they will arrive at point 0 together and you standing in point 0 will be able to say that both cars started of simultaneously.
The same goes for universe if we receive light at the same time from events that are 180 apart we can say that they both happened simultaneously.Ofcourse in universe there are forces like gravitational redshift and etc which bends light also slows it down so you have to account for that but for a simple picture I hope you got it.

Now if you are moving and not standing in the point 0 then you will see the one car approaching you faster than the other , so a reference frame that is moving will not see two events starting at the same time in opposite directions because the observer itself is moving with respect to those events.
The way you perceive events happening in relativity is bound to the position you have either a stationary or accelerating.
But stationary positions can also be traveling at different speeds if compared to one another.

 

[ash64449]

Those questions are really hard to understand but let's put it this way.
You are at point 0 now one car comes from point -1 the other from point +1, if the both cars happen to travel at the same speed they will arrive at point 0 together and you standing in point 0 will be able to say that both cars started of simultaneously.
The same goes for universe if we receive light at the same time from events that are 180 apart we can say that they both happened simultaneously.Ofcourse in universe there are forces like gravitational redshift and etc which bends light also slows it down so you have to account for that but for a simple picture I hope you got it.

Now if you are moving and not standing in the point 0 then you will see the one car approaching you faster than the other , so a reference frame that is moving will not see two events starting at the same time in opposite directions because the observer itself is moving with respect to those events.
The way you perceive events happening in relativity is bound to the position you have either a stationary or accelerating.
But stationary positions can also be traveling at different speeds if compared to one another.

so what is the answer to my quaetion?

 

[HallsofIvy]

Both DaleSpam and Crazymechanic gave you the same answer- yes, it is possible.

 

[ash64449]

Yes, that is possible. If two reference frames are in the standard configuration (origins coincide at t=0, all spatial axes parallel, motion along x axis) then two events separated in the x direction which are simultaneous in one frame will not be simultaneous in the other frame, but two events separated in the y or z directions which are simultaneous in one frame will be simultaneous in the other frame.

i mean in x-direction itself. Well,i found out that it cannot happen. Events that are simultaneous to observer who is moving should be simultaneous to observer who is stationary. It is because time dilation takes place only to observer who is moving. The reason why time dilation takes place in moving frame becuase simultaneous events in stationary reference frame were not simulatneous to to moving frame.as a result they won't agree on time of the event. But opposite is not possible because stationary observer is not moving.

 

[ash64449]

Both DaleSpam and Crazymechanic gave you the same answer- yes, it is possible.

well,i got the conclusion that it cannot happen.but one change will happen.in both frames,it will happen simultaneously but duration of the event may not be same.

 

[Vanadium 50]

Well, you're wrong.

Sorry, but there's no more polite way to say that. You asked a question, got an answer, and decided you don't like the answer. This isn't like "I hate broccoli", where any opinion is equally valid.

 

[ash64449]

Both DaleSpam and Crazymechanic gave you the same answer- yes, it is possible.

Let me explain why it can't happen.I just want reviews about it.I want you guys t help me correct my conclusions as you guys are senior members!

According to me time can be simply explained as a series of all events happening in between the preferred two main events which explain the rate at which the time ticks. For example,i will make two ticks of a clock as the two main events.We can find that all the clocks which can make the two main events simultaneous go at the same rate. Now in between those two events,many events are taking place.some events are simultaneous.some events take place after that. So in between two main events,there are finite number of events that describe the time itself.So according to me time can be traced as events. And when events also have duration.(in this take this as according to stationary observer)

So since i have given definition of time,let me bring out Einstein's thought experiment. All of you guys must have heard,so no need to explain it. In this experiment, Events that were simultaneous to the observer who is at rest was not simultaneous to the observer in the train. Based on this,i can say that clocks of observer at rest and observer in motion do not go at the same rate. let me bring two ticks of clock as main events. Events happening to stationary observer happens to observer who is moving. And also a particular duration of time is explained by not a single event,that duration of time is explained by many events also. That many events is what we call as simultaneous events. now these events are not simultaneous to observer who is moving.i.e:events which explained same duration of time explained different duration in the observer who is moving.Since events that take place in stationary observer do take place in all observers irrespective of their motion(as they are not traveling at the speed of light), Two ticks which are main events that describe same rate are delayed in the case of moving observer.That is why observer moving time slows down.

Did you get my point up to here? Then i will explain the other part.

 

[ash64449]

Both DaleSpam and Crazymechanic gave you the same answer- yes, it is possible.

Well, you're wrong.

Sorry, but there's no more polite way to say that. You asked a question, got an answer, and decided you don't like the answer. This isn't like "I hate broccoli", where any opinion is equally valid.

Sorry friend,I didn't get the answer. I get conflicting answer. I posted this discussion as i didn't get the answer.Suddenly an answer came to me that it cannot happen.But here the posters said that it can happen.So don't i have the right to know what i was wrong in my conclusion?

 

[jambaugh]

ash64449, there is one point in the formation of your question I would address. You speak of "stationary frame" vs "moving frame". The "relativity" part of SR is that the observer in each frame sees himself as stationary and the other as moving. Note that there is Einstein's special relativity and its precursor, Galillean relativity which SR asymptotically approaches for low velocities relative to c and thus our experience based intuition tends toward assuming.

[edit] My point here being that even in Galillean relativity you have no special "stationary frame" but motion is relative. (It's just that the transformation group is different.)

I bring this up because formulating the question the way you do can introduce implicit assumptions (guided by your Galilean intuition) which are contrary to the facts in SR. You have to first understand Gallilean relativity, then unlearn those parts of it which differ in SR then work through some examples like the Twin "Paradox" doing the numbers so to speak. It takes a while to retrain your intuition. Remember that drawing a space-time diagram on paper, while a very useful tool, is embedding a non-euclidean geometry onto euclidean paper. You can't just "rotate" the paper but have to redraw different versions of a diagram for different obsever frames.

 

[ash64449]

ash64449, there is one point in the formation of your question I would address. You speak of "stationary frame" vs "moving frame". The "relativity" part of SR is that the observer in each frame sees himself as stationary and the other as moving. Note that there is Einstein's special relativity and its precursor, Galillean relativity which SR asymptotically approaches for low velocities relative to c and thus our experience based intuition tends toward assuming.

[edit] My point here being that even in Galillean relativity you have no special "stationary frame" but motion is relative. (It's just that the transformation group is different.)

yes.i know this friend.I am sure you know the famous Einstein's Thought Experiment:
I know what you said above."The "relativity" part of SR is that the observer in each frame sees himself as stationary and the other as moving"

I based on this one itself. Let me tell the problem in Galileo's theory of relativity.(though it had some points same as to SR,there is one problem. it is because of this problem that Einsteins lead to the creation of his famous thought experiment!)

the problem; According to both SR and Galileo's theory of relativity, the meaning of rest and uniform motion has no meaning. Everything is relative. It is because an object in rest would be in motion relative to something else.As a result we cannot say one is moving uniformly or he is at rest. You cannot identify your motion as you consider yourself as rest even though you are moving uniformly. But in actual sense he is moving. But he thinks that he is at rest. So it becomes a fact that one cannot identify who is moving who is not. But when we compare with the light,We can understand that we are moving! This is contradicting.. Is this the thing you were trying to explain?
OR are you telling that Maxwell's theory appear to contradict Galileo's theory of relativity?

 

[ash64449]

ash64449, there is one point in the formation of your question I would address. You speak of "stationary frame" vs "moving frame". The "relativity" part of SR is that the observer in each frame sees himself as stationary and the other as moving. Note that there is Einstein's special relativity and its precursor, Galillean relativity which SR asymptotically approaches for low velocities relative to c and thus our experience based intuition tends toward assuming.

[edit] My point here being that even in Galillean relativity you have no special "stationary frame" but motion is relative. (It's just that the transformation group is different.)

I bring this up because formulating the question the way you do can introduce implicit assumptions (guided by your Galilean intuition) which are contrary to the facts in SR. You have to first understand Gallilean relativity, then unlearn those parts of it which differ in SR then work through some examples like the Twin "Paradox" doing the numbers so to speak. It takes a while to retrain your intuition. Remember that drawing a space-time diagram on paper, while a very useful tool, is embedding a non-euclidean geometry onto euclidean paper. You can't just "rotate" the paper but have to redraw different versions of a diagram for different obsever frames.

Sorry,Not moving frame, train moving relative to observer who is stationary.

 

[Dale]

i mean in x-direction itself. Well,i found out that it cannot happen.

Restricting yourself to the x-direction only then two distinct events which are simultaneous to one will not be simultaneous to the other.

Events that are simultaneous to observer who is moving should be simultaneous to observer who is stationary.

No.

It is because time dilation takes place only to observer who is moving. The reason why time dilation takes place in moving frame becuase simultaneous events in stationary reference frame were not simulatneous to to moving frame.as a result they won't agree on time of the event. But opposite is not possible because stationary observer is not moving.

Irrelevant. Time dilation is not the cause of the relativity of simultaneity.

 

[ash64449]

Time dilation is not the cause of the relativity of simultaneity.

Who said? i said Relativity of simultaneity is the reason for time dilation.i.e events are not simultaneous to moving train relative to observer stationary. And events are simultaneous to observer who is stationary. That is the reason why time dilation takes place.. Read the comment #10 And tell what was i wrong in that comment.

 

[ash64449]

.

Irrelevant. Time dilation is not the cause of the relativity of simultaneity.

Then what causes Time dilation?

 

[Dale]

i said Relativity of simultaneity is the reason for time dilation.

This is also false. The two postulates are the cause of time dilation, length contraction, and relativity of simultaneity. The effects do not cause each other.

 

[Dale]

For example,i will make two ticks of a clock as the two main events.We can find that all the clocks which can make the two main events simultaneous go at the same rate.

Two ticks of a single clock cannot be simultaneous in any reference frame. They are timelike separated. Only spacelike events can be simultaneous in any frame.

So in between two main events,there are finite number of events that describe the time itself.

No, there are an infinite number of events between any two events.

And when events also have duration.

Events do not have duration. They are instantaneous. I.e. they are "points" in spacetime.

Events that were simultaneous to the observer who is at rest was not simultaneous to the observer in the train. Based on this,i can say that clocks of observer at rest and observer in motion do not go at the same rate.

No. The relativity of simultaneity does not cause time dilation. They are both caused by the two postulates.

Since events that take place in stationary observer do take place in all observers irrespective of their motion(as they are not traveling at the speed of light), Two ticks which are main events that describe same rate are delayed in the case of moving observer.That is why observer moving time slows down.

Again, no, for the same reason as above.

 

[ash64449]

Two ticks of a single clock cannot be simultaneous in any reference frame. They are timelike separated. Only spacelike events can be simultaneous in any frame.

Read my comments carefully,i said two clocks whose pointers are simultaneous are simultaneous

No, there are an infinite number of events between any two events.

May be i was wrong on that sense

Events do not have duration. They are instantaneous. I.e. they are "points" in spacetime.

May be i was wrong on this count also

No. The relativity of simultaneity does not cause time dilation. They are both caused by the two postulates.

Actually because of those two postulates,Simultaneous events are not simultaneous as a result Time dilation can be explained.

Again, no, for the same reason as above.

Same as the above i told

 

[Dale]

Read my comments carefully,i said two clocks whose pointers are simultaneous are simultaneous

No. You need to WRITE your comments carefully. You said "two ticks of a clock". That means one clock. Don't blame others for not reading your mind, I can only read what you write. If you meant two clocks then you should have said two clocks.

Simultaneous events are not simultaneous as a result Time dilation can be explained.

Simply false. If you believe that this point is correct then you must provide a mainstream scientific reference which supports it. Do not repeat this incorrect point without providing a valid reference.

 

[ash64449]

Two ticks of a single clock cannot be simultaneous in any reference frame. They are timelike separated. Only spacelike events can be simultaneous in any frame.

No, there are an infinite number of events between any two events.

Events do not have duration. They are instantaneous. I.e. they are "points" in spacetime.

No. The relativity of simultaneity does not cause time dilation. They are both caused by the two postulates.

Again, no, for the same reason as above.

You mean the two postulates Principle Of Relativity and Constancy Of speed of light right?

If that is the case,I am surely correct and i have read the book written by einstein itself used Relativity of simultaneity to show that there is no meaning of 'time' of an event. As a result he said that different observers time go at different rates. that is why.. And how this conclusion came? Those two postulates. if you think i am wrong,then derive in the other way. Difference in opinion of simultaneity is not the consequence of time dilation. It is the reason for time dilation.

 

[Dale]

You mean the two postulates Principle Of Relativity and Constancy Of speed of light right?

Yes.

Difference in opinion of simultaneity is not the consequence of time dilation. It is the reason for time dilation.

No, the relativity of simultaneity is neither a consequence of time dilation nor the reason for time dilation.

Both time dilation and relativity of simultaneity are derived from the two postulates. They are NOT derived from each other. If you believe otherwise then please provide a reference which derives one from the other without invoking the postulates.

 

[ash64449]

No. You need to WRITE your comments carefully. You said "two ticks of a clock". That means one clock. Don't blame others for not reading your mind, I can only read what you write. If you meant two clocks then you should have said two clocks.

"For example,i will make two ticks of a clock as the two main events.We can find that all the clocks which can make the two main events simultaneous go at the same rate."
This is what i said.. See i said Two ticks as two main events.
then look what i said. All the clocks which make the two main events(Two ticks) as simultaneous go at the same rate.


Simply false. If you believe that this point is correct then you must provide a mainstream scientific reference which supports it. Do not repeat this incorrect point without providing a valid reference.[/QUOTE]
So you want scientific reference.If the above said is wrong,Then Einstein is wrong. Because Einstein himself used this Thought experiment to prove that Time go at different rates depending on who moves.

A train is moving.In the middle,there is an observer(inside the train). Two lightning strikes at the extreme parts of the train.An observer at outside sees this two lightning as simultaneous. Now Einstein asked the question.Will the events be simultaneous to observer in the train?

So let us consider,When two lightning strike as it happened according to observer outside,as train is moving forward,The observer in the middle is hastening towards the light from the lightning and away from the light from the lightning in the backwards. as a result,he should come to the conclusion that lightning stuck at the front first and then at the back. So simultaneous events in one frame of reference is not simultaneous in reference to the other. So there is no 'time' of the event. As a result both the observer have time going at the same rate loses meaning.

 

[Dale]

So you want scientific reference.If the above said is wrong,Then Einstein is wrong. Because Einstein himself used this Thought experiment to prove that Time go at different rates depending on who moves.

Einstein used the two postulates to derive relativity of simultaneity and time dilation. He did not use relativity of simultaneity to derive time dilation nor vice versa.

 

[Nugatory]

Because Einstein himself used this Thought experiment to prove that Time go at different rates depending on who moves...

A train is moving.In the middle,there is an observer(inside the train). Two lightning strikes at the extreme parts of the train.An observer at outside sees this two lightning as simultaneous. Now Einstein asked the question.Will the events be simultaneous to observer in the train?

Strictly speaking, this thought experiments leads directly to relativity of simultaneity, not different rates of time (aka time dilation). But this entire argument is a bit sterile, because Einstein used a number of different thought experiments and a number of different paths from the postulates to the Lorentz transforms from which the mutually dependent concepts of RoS, time dilation, and length contraction flow - there's no one "right" way of explaining and understanding this stuff.

 

[Philip Wood]

I respectfully suggest that the original poster try to re-formulate the original question without using the terms 'stationary observer', 'stationary frame', 'moving observer', 'moving frame'.

 

[ash64449]

Strictly speaking, this thought experiments leads directly to relativity of simultaneity, not different rates of time (aka time dilation). But this entire argument is a bit sterile, because Einstein used a number of different thought experiments and a number of different paths from the postulates to the Lorentz transforms from which the mutually dependent concepts of RoS, time dilation, and length contraction flow - there's no one "right" way of explaining and understanding this stuff.

i will quote the exact words said by einstein in his book:

events which are simultaneous with reference to the embankment are not simultaneous with respect to the train,and vice versa.every reference body has its own particular time;unless we are told the reference-body to which statement of time refers,there is no meaning in th statement of the time of an event.

Einstein wrote this after stating the thought experiment. Look how he said..

 

[ash64449]

Strictly speaking, this thought experiments leads directly to relativity of simultaneity, not different rates of time (aka time dilation). But this entire argument is a bit sterile, because Einstein used a number of different thought experiments and a number of different paths from the postulates to the Lorentz transforms from which the mutually dependent concepts of RoS, time dilation, and length contraction flow - there's no one "right" way of explaining and understanding this stuff.

if this is not the way to explain time dilation,since you said einstein used many thought experiment,tell me a thought experiment that shows time dilation.

 

[Dale]

i will quote the exact words said by einstein in his book

Note how Einstein's quote directly contradicts your earlier claim that:

Events that are simultaneous to observer who is moving should be simultaneous to observer who is stationary.

Specifically, Einstein said "events which are simultaneous with reference to the embankment are not simultaneous with respect to the train, and vice versa". (emphasis added). The "and vice versa" specifically rejects your earlier statement which is also incompatible with the first postulate.

 

[Nugatory]

if this is not the way to explain time dilation,since you said einstein used many thought experiment,tell me a thought experiment that shows time dilation.

That experiment demonstrates relativity of simultaneity not time dilation. It's easy enough to construct thought experiments that do demonstrate time dilation though; look for something that explains the relative doppler effect in a coordinate-independent way.

When you have a chance, dig up a copy of Einstein's 1905 paper "On the electrodynamics of moving bodies". It will give you a more systematic and formal development of this stuff while still retaining the historical flavor of Einstein's explanations.

Also, you might try Philip Wood's excellent advice:

I respectfully suggest that the original poster try to re-formulate the original question without using the terms 'stationary observer', 'stationary frame', 'moving observer', 'moving frame'.

 

[ash64449]

Note how Einstein's quote directly contradicts your earlier claim that:

Specifically, Einstein said "events which are simultaneous with reference to the embankment are not simultaneous with respect to the train, and vice versa". (emphasis added). The "and vice versa" specifically rejects your earlier statement which is also incompatible with the first postulate.

Ok. DaleSpam. I agree with you. In order to understand Time Dilation,i will take a copy of Einstein's 1905 paper. Thank You!

 

[DrewD]

So it becomes a fact that one cannot identify who is moving who is not. But when we compare with the light,We can understand that we are moving! This is contradicting.. Is this the thing you were trying to explain?
OR are you telling that Maxwell's theory appear to contradict Galileo's theory of relativity?

I know this wasn't your main point and I'm not sure exactly what you are saying here, but (at least for the sake of others that might read this for info) it should be emphasized that Maxwell's theory does contradict Galilean Relativity and when we compare our motion with light, we cannot discern whether or not we are moving. Uniform motion can only be defined after choosing a reference which may be chosen arbitrarily. I found this paragraph a little confusing; perhaps I misunderstood what you meant.

 

[Fredrik]

In order to understand Time Dilation,i will take a copy of Einstein's 1905 paper. Thank You!

That's certainly better than nothing, but I don't know why everyone chooses to study the original papers instead of modern presentations. A presentation based on spacetime diagrams is far easier in my opinion, and they hadn't even been invented in 1905.

My favorite intro to SR is the one in the first few chapters in the GR book by Schutz. Link. The one by Taylor & Wheeler is the one that gets the most recommendations, so it's probably very good too. It's also recommended by Schutz, in the following words:

There are many good introductions to SR, but a avery readable one which has guided our own treatment and is far more detailed is Taylor & Wheeler (1966).​

 

[ash64449]

That experiment demonstrates relativity of simultaneity not time dilation. It's easy enough to construct thought experiments that do demonstrate time dilation though; look for something that explains the relative doppler effect in a coordinate-independent way.

When you have a chance, dig up a copy of Einstein's 1905 paper "On the electrodynamics of moving bodies". It will give you a more systematic and formal development of this stuff while still retaining the historical flavor of Einstein's explanations.

Also, you might try Philip Wood's excellent advice:

I find no difference in what Einstein said in my book and in On the electrodynamics of moving bodies. Let me copy-paste the exact words and what i mean by it also,as a result you can help me correct. I agree that i was making wrong assumption on the exact question i asked. Let me see whether i understood or not why Time dilation takes place.

On the electrodynamics of moving bodies

Actual Print of Einstein's 1905 paper

"We have to take into
account that all our judgments in which time plays a part are always judgments
of simultaneous events"

Here Einstein said that we should consider Time as playing the part of simultaneous events.
Example(From Einstein's 1905 paper): “That train arrives here at 7
o’clock,” I mean something like this: “The pointing of the small hand of my
watch to 7 and the arrival of the train are simultaneous events.”
"We assume that this definition of synchronism is free from contradictions,
and possible for any number of points; and that the following relations are
universally valid:—
1. If the clock at B synchronizes with the clock at A, the clock at A synchronizes with the clock at B.
2. If the clock at A synchronizes with the clock at B and also with the clock
at C, the clocks at B and C also synchronize with each other"

By this he means that If the clocks satisfy this simultaneous considerations,then these clocks go at the same rate.(my words)

These words of Einstein is from the chapter Definition of Simultaneity.
Let me go to the second chapter On the Relativity of Lengths and Times.

Words of Einstein:

The following reflexions are based on the principle of relativity and on the
principle of the constancy of the velocity of light. These two principles we define
as follows:—
1. The laws by which the states of physical systems undergo change are not
affected, whether these changes of state be referred to the one or the other of
two systems of co-ordinates in uniform translatory motion.
2. Any ray of light moves in the “stationary” system of co-ordinates with
the determined velocity c, whether the ray be emitted by a stationary or by a
moving body
. Hence
velocity = light path/
time interval.

Two postulates. Note what he said:"where time interval is to be taken in the sense of the definition in § 1."

Time should be taken by the definition of simultaneous considerations.

note this chapter explain why two clocks are not synchronous.i.e it shows clocks on stationary observer and clocks of moving observer relative to stationary system do not go at the same rate.
His words:
We imagine further that with each clock there is a moving observer, and
that these observers apply to both clocks the criterion established in § 1 for the
synchronization of two clocks. Let a ray of light depart from A at the time4
tA,let it be reflected at B at the time tB, and reach A again at the time t
0
A. Taking
into consideration the principle of the constancy of the velocity of light we find
that
tB − tA =
rAB/
c − v
and t
0
A − tB =
rAB/
c + v
where rAB denotes the length of the moving rod—measured in the stationary
system. Observers moving with the moving rod would thus find that the two
clocks were not synchronous, while observers in the stationary system would
declare the clocks to be synchronous.
So we see that we cannot attach any absolute signification to the concept of
simultaneity, but that two events which, viewed from a system of co-ordinates,
are simultaneous, can no longer be looked upon as simultaneous events when
envisaged from a system which is in motion relatively to that system.

See this he used simultaneous consideration to Two clocks don't go at the same rate.(You know what i mean)