Why measuring one-way trip impossible?

[ghwellsjr]

See the paragraph about Romer's experiment in the wikipedia article on the One-way Speed of Light.

I have read your pointing out article from Wikipedia. From it,i understood that if we bring on the two clocks together and synchronize them and then take a clock at some speed and take it back again,we can see that the two clocks remain out of synchronization.

So the method of slow transport is used,so that clock that is moving remains synchronized.(well,there will be a slight amount of out of synchronization)

Well,based on the above facts,i have found out a way to measure the one-way speed of light!

This involves a series of experiments and some amount of calculation.

From the Wikipedia article,i found out that for example,think about two clocks together,synchronized and the amount by which clocks get un synchronized depends upon the velocity and for how much time that clock remained in that specific velocity.

We need to conduct this experiment:

We should take two identical clocks. they have to be synchronized. take for example a clock 30 meters apart and make that clock move for about 15 meters per second. now look at the amount by which the clocks were un synchronized. Now keeping the same distance,make the clock move at 30 meters per second. Now look by how much amount clocks remain un synchronized.

Conducting many times these experiment,we will find a pattern and a relationship between the amount of un synchronization and with the velocity that clock is moved.

When we have successfully completed this experiment, I will provide you friends a way we can measure one-way speed of light!

For this we need two persons and two clocks which are synchronized. make a person move for example a distance of 'c'. Now the person which has moved now knows how much or how much amount his clocks are unsynchronized. so he will reverse it and make his clock synchronized.

Now think a person has send out a light beam.he notes the time. the other person notes time when he receives the signal. when they rejoin,we will find the time interval and we know distance. so we can now measure speed. and this is off course measuring one-way speed of light.

Do you think this will work out?

No. You are making a big mistake. You are thinking that just because you can start with two synchronized clocks and slowly move one of them away and back, that the amount of de-synchronization that you can measure when they come back divided by two is a measure of the de-synchronization that the two clocks have when they are separated. The thing you are overlooking is that the two clocks are continuing to accumulate time and you cannot tell if the rates at which they accumulate time are the same when they separate. In other words, how can you tell if the clock as it moves away ticks a lot faster while it is moving, in other words, gains a lot of time, and then when it moves back it ticks a lot slower and loses most of that gain? You can't tell. You are just assuming that the motion is symmetrical and that it gains the same amount of time in both directions. So all your efforts don't prove a thing.

If you want to study this some more, read this post:

https://www.physicsforums.com/showpost.php?p=4259474&postcount=8

 

[ash64449]

i would like to ask questions to all of you.
I know that length contraction and time dilation cannot be observed. Can we observe relativity of simultaneity?

 

[ghwellsjr]

i would like to ask questions to all of you.
I know that length contraction and time dilation cannot be observed. Can we observe relativity of simultaneity?

No. It has the same issue since it is depends on the selected frame.

 

[ash64449]

No. It has the same issue since it is depends on the selected frame.

i don't know why i feel like this. But i will say. I feel that relativity of simultaneity is somewhat connected to one-way speed of light. Since we cannot define one-way speed of light,relativity of simultaneity is not observed. What do you think?

 

[ash64449]

No. It has the same issue since it is depends on the selected frame.

sorry,i didn't understand which same issue. Are you talking things about another thread which you explained why length contraction cannot be observed? Are you saying that there is some connection in that?
Sorry,if i asked previous question(RoS) here. If felt there was some connection to this thread.

 

[ghwellsjr]

No. It has the same issue since it is depends on the selected frame.

i don't know why i feel like this. But i will say. I feel that relativity of simultaneity is somewhat connected to one-way speed of light. Since we cannot define one-way speed of light,relativity of simultaneity is not observed. What do you think?

Relativity of simultaneity is connected with the one-way speed of light, because we cannot observe or measure the one-way speed of light. All we can do is define the one-way speed of light in each Inertial Reference Frame (IRF). And that definition as applied in each IRF is what leads to different coordinate times in each IRF which is what we mean by Relativity of Simultaneity.

 

[ghwellsjr]

sorry,i didn't understand which same issue. Are you talking things about another thread which you explained why length contraction cannot be observed? Are you saying that there is some connection in that?
Sorry,if i asked previous question(RoS) here. If felt there was some connection to this thread.

All coordinate dependent concepts are not observable by observers for the same reason. That includes Length Contraction, Time Dilation and Relativity of Simultaneity.

 

[ash64449]

Relativity of simultaneity is connected with the one-way speed of light, because we cannot observe or measure the one-way speed of light. All we can do is define the one-way speed of light in each Inertial Reference Frame (IRF). And that definition as applied in each IRF is what leads to different coordinate times in each IRF which is what we mean by Relativity of Simultaneity.

george, a request.
Can you elaborate or explian how one-way speed of light relates relativity of simultaneity? I haven't understood clearly..

 

[ash64449]

the thing i want to understand is how is one-way speed of light is defined in IRF and how that definition relates RoS?


Edit: wait.. I think i know the answer! Light travels the same speed in one-way trip too! And i know people will say that light needs to travel more distance and less distance and all and there comes RoS. But doesn't light need to travel more distance same as c-v and light needs to travel less distance c+v?

 

[ghwellsjr]

george, a request.
Can you elaborate or explian how one-way speed of light relates relativity of simultaneity? I haven't understood clearly..

Did you read and study section 1 on the Definition of Simultaneity in Einstein's 1905 paper like I asked you to in another post? He explains it all very well there. Study it until it sinks in (to your brain). After it makes sense to you, go on and read the next section. OK? Read. Study. Think. Let it sink in. Read it again. Study it again. Think about it again. Over and over again until it makes perfect sense to you. It's very simple. No complicated math.

 

[bahamagreen]

Your link to Einstein's paper shows him presenting this equation:

2AB / (t'a - ta) = c

Just to be clear, that "AB" in the numerator as shown must not be strictly algebraic in that it does not mean "AxB" but must mean "absolute value of (B-A) or "absolute value of (A-B)" so that "AB" is treated as a length distance between A and B.

This is trivial, but if one pulls the equation aside to run some calculations one might miss how "AB" is meant to be assigned and erroneously multiply them together... and doing so, if either position A or B is at coordinate 0, then c=0, and otherwise, c varies with the separation between A and B because the speed of light takes on the dimension of (m^2)/s.

 

[Fredrik]

the thing i want to understand is how is one-way speed of light is defined in IRF and how that definition relates RoS?

Suppose that the light is emitted at an event A, and received at an event B. Then we want to interpret

distance between A and B
________________________________

clock display at B - clock display at A​

as a measurement of the speed of light. But this doesn't really work if the times displayed by the clocks at A and B depend on how those clocks were brought to A and B.

The above explains what sort of thing we would like to interpret as a measurement of the speed of light. But you asked about how we would define the speed of light in an IRF. The answer is similar to the above. The IRF needs to be one in which both the emitter and reciever have velocity 0. Then we can define the speed of light in that IRF as the absolute value of

x(B) - x(A)
_________

t(B) - t(A)​

where x(A) and t(A) respectively denote the position coordinate and time coordinate that the IRF assigns to the event A. So the one-way speed is always well-defined in the theory, but the IRF in which the emitter and detector are both stationary is not (always) the same in SR as in pre-relativistic classical mechanics. So the numbers t(A),x(A),t(B),x(B) depend on the theory.

 

[ash64449]

i have read first two chapters of einstein's 1905 paper. And i am a little bit surprised because i found einstein connecting RoS with that of non-synchronous of clocks of moving rods.
He said that two ends of the rods A and B have "Atime" and "Btime" but to attach a common "time" to both A and B,we need to synchronize the two clocks and it is assumed that two clocks are only synchronized if
Tb-Ta = T'a - Tb.
So we can see in the moving rod that the above cannot be maintained.so clocks in moving rod are not synchronized when viewed from stationary frame.
Because the clocks are not synchronized,events which are measured by local time(at A and B) which are spatially separated cannot be seen as simultaneous events(these two clocks are synchronized in stationary system,so above conclusion by comparing them).
Is this correct?(to george)

 

[ghwellsjr]

i have read first two chapters of einstein's 1905 paper. And i am a little bit surprised because i found einstein connecting RoS with that of non-synchronous of clocks of moving rods.
He said that two ends of the rods A and B have "Atime" and "Btime" but to attach a common "time" to both A and B,we need to synchronize the two clocks and it is assumed that two clocks are only synchronized if
Tb-Ta = T'a - Tb.

Einstein didn't say "to attach a common 'time' to both A and B,we need to synchronize the two clocks". That would be like saying "to attach a common time to both A and B, we need to set them to the same time." He saying something entirely different. He is saying that a common time to both A and B, that is, a synchronization of the two clocks has no meaning unless and until we give it meaning. We need to define what "common time" means which is the same as saying we need to define what "synchronization between two clocks" means. In other words, we give meaning to "common time" or to "synchronization between two clocks". That's why the title of his first section is Definition of Simultaneity.

So we can see in the moving rod that the above cannot be maintained.so clocks in moving rod are not synchronized when viewed from stationary frame.
Because the clocks are not synchronized,events which are measured by local time(at A and B) which are spatially separated cannot be seen as simultaneous events(these two clocks are synchronized in stationary system,so above conclusion by comparing them).
Is this correct?(to george)

I'm not sure what you are asking.

Instead of using the term "local time" which is a hangover from the LET days, you should use the terms "Proper Time" if you mean the time on an actual real clock and you should use the term "Coordinate Time" if you mean the synchronized time in an IRF. Note that for purposes of establishing what is meant by Coordinate Time, Einstein uses "imaginary" clocks but we should eventually disconnect the concept of Coordinate Time from any real clocks, just as we disconnect the concept of Coordinate Space from any real measuring rods.

With that in mind, what you should conceptualize is that a rod with clocks at each end and in which the Proper Times on the clocks have been set to the Coordinate Times of the IRF in which the rod and clocks are at rest, will not be set to the Coordinate Time of an IRF moving with respect to the first IRF.