Tutorial: Relativity of simultaneity

[MacM]

As a photon itself is essentially unobservable would it not be more correct to say that "the effect of light is invariant to all observers"?

There is an important distinction in the use of the word "effect" rather than "Photon"
The thinking:
The effect of light is all that we are measuring, not the photon itself but it's effect.

This closely parallels my view where the observed invariance is not the key issue but the cause of such observation is. From my perspective they have simply drawn the wrong conclusions from the observation.

Where you say not the photon but the effect, I would say not the photon but the cause (not of the photon specifically but of the observed invariance).

 

[geistkiesel]

That's right. That's one of the postulates of SR, which I used in my example. The "c" factor in the equations for both frames is the same.

You mean don't you that the relative velocity of all frames and photons is a measured C. You mean that an object moving at .5c will measure the realtive velocity of object and photon as C . This inspite of the fact that the rest of thd universe will measure the reklative velocity as c -v, or c + V depending on the relative directions of frame and photon motion.

You are saying that there is not now and l neverwill there be a developed technology that can measure the relatrive velocity iof frame and photon to be other than C.

You are saying it is useless to ask a moving observer how much faster the photon is travelling relative to his frame velocity. He will always say C. he wont even measure. The frame must be considered at rest, that is SRT nulls out motion theoretically, before any measurements are made.
This isn't physics this is street corner three card monte. Voodoo has to be better than this..

If you insist that both photons arrive at the same time in all frames, then you have universal time. But then you throw away the invariance of the speed of light in all frames. You can't have both. The problems with universal, absolute time, are part of what led to the development of special relativity in the first place. These days, we know it doesn't exist. It is inconsistent with measurable aspects of reality.

You mean the error in analysis of physical reality led to the silliness of SRT.
I don't throw away the invariance of the speed of light, uyopu do. You make it up .
Invariance is rescued by universal time not discarded. It is SRT that discards data of motion of the frame. No, James R, it was the silliness that AE muttrered when assuming that the relative speed of frame and photon is always measured as C, when it in reality c - v or c + v. You frequently use these terms.

What measured aspects of reality are you referring to.? I mean what unambiguous measured affects are you referring.

Geistkiesel
​

 

[Quantum Quack]

Geist just to fuel the theoretical fire, Lights effects might be invariant but that doesn't mean that light has velocity to screw the figures with.

 

[geistkiesel]

James R,
An observer in the stationary embankment frame measure the round trip time of the photons to be twice d/c = t and he measures this same number 5,000 times for both photons travelling to the L and the R clocks. Or sometimes he just measures the time of flight of the photons from emission point at the LR midpoint to L and/or R and always measures t for the one way trip.

This of course is the famous gedanken we all recognize.

After 10,000 or so tests the administrators of the test now put the frame in motion wrt the embankment, which motion is unknown to the observer on the now moving frame.

The observer has never known whether he was moving or stationary. The only thing he knows is that the round trip and one way times were always the same measured value. The one way times were exactly 1/2 the roundtrip times. If the stationary observer is now placed on the frame that is actually moving wrt the embankment he will measure something other than 2t and t for the round trip the one way trip respectively, will he not?

No he wont get the same numbers on his clocks. Suddenly the observer sees a discrepancy with the 10,000 previous test results in the stationary frame.

So how does this observer rationalize the difference in the measured times?


Here is the experiment. I have kept track of the emission point of the photons which is spatially invariant. I have kept track of the moving midpoint (moving wrt the embankment) of the L and R clocks. I have kept track of the different distances the photons must travel in order to arrive at the L and R clocks on the moving frame. Here I slavishly followed the postulate of light that the speed of light is a constant 3 x 10^5 km/sec.

As pretty as the picture is, and for all the indicated detail, only the sequential vs simulataneous arrival of photons at L and R are at issue. The inset shows the t' time fopr the left and the right moving photons at different times in the test. For the right moving photon this is marked 1 and is in red. The left movng photon insert is indicated blue and number 2.

All times are measured by clocks on the moving frame. We also have clocks on the embankment that are colocated with the clocks on the moving frame at the instant the photons arrive at L and R. These locations are determined experimentally after thousands of tests.

You have claimed that the clocks on the moving and stationary frame will measure the simultaneous arrival of photons at L and R and back at the midpoint of the postions of L and R wrt the frame.

This what you are telling us.

Here the clocks (below) are only on the stationary frame, unknown to the observer on the moving frame. The clocks are located where the L and R clocks would have been when the photons arrived uif teh clocks were attached to the movingframe. All this is determined by tests in the statioanry frame.

Do you see any differences in this scenario and the one above where the clocks are attached to the moving frame? If so what?

Geistkiesel​

 

[MacM]

Geist just to fuel the theoretical fire, Lights effects might be invariant but that doesn't mean that light has velocity to screw the figures with.

I am having trouble interreting the meaning of "Screw with the figures" in physics terms. Care to elaborate. ?

 

[Quantum Quack]

Actually MacM my post was a little off topic and unecessarilly provocative. I would have deleted it except that wouldn't change much.

The issue is simultaneousness. The decision to qyalufy light as having velocity has required us to create elaborate ways of accomodating what I believe is a myth. That being that Light travels.

The fact that 'c' is the fastest things can change at is a much better way of looking, and requires no invarifiable belief that light travels.

The issue of simultaneousness is only an issue because of this belief.

I had posted earlier a diagram that I hoped would clarify the issue of simultaneousness and relative time. In fact I have posted it a number of times. I have no idea why there has been no response as to whether or not it is a correct assessment according to SRT.

Possibly my question about simultaneousness is too hard to answer with out declaring absolute time operating in the background [NOW]

However it is not sufficient enough to claim non-simultaneousness without quantifying what that means.

In my understanding it can only mean that something occurs in the past of another object and if this is the case then it should be quantifiable.

"How far into the past are we talking about?"

Now a while ago Yuriy attempted to answer the question but before completing it he got shitty with me and the rest is history.

The hall mark of relativity is this abandoning of absolute time. But I ask what exactly do they mean by absolute time?

The standard response is to say that two events in different frames can not happen simultaneously. OK so how far into the past is the other event?

And by whos reckoning are we declaring the frames different in the first place. You guessed it...the man who declared absolute time nul and void.

If time was not declared relative there would be no need for SRT frames

Any way, the issue of simultaneity still requires clarification and evidence in the real universe to prove it's reality.

And I have no idea how non-simultaneousness can be proven, certainly simultaneousness can be proven, in fact every SRT equation implies an absolute time back ground.

 

[Quantum Quack]

Another animation to show simultaneousness of the NOW.

 

[James R]

geistkiesel:

You mean don't you that the relative velocity of all frames and photons is a measured C. You mean that an object moving at .5c will measure the realtive velocity of object and photon as C . This inspite of the fact that the rest of thd universe will measure the reklative velocity as c -v, or c + V depending on the relative directions of frame and photon motion.

The "rest of the universe" doesn't measure c-v or c+v. There's only one way to prove that, which is to actually do an experiment. Many have been done, and all show that the actual measured velocity of light is c, in all frames, and never c+v or c-v.

There's really not much more to say. Either you believe this or you don't. If you don't, go away and do some research.

 

[Sabejias]

Another animation to show simultaneousness of the NOW.

Your diagram is interesting. Indeed, the photons do arrive at B and A1 simultaneously. BUT, there is also this thing called direction of motion. The direction is essential. the light pulses are being sent perpendicular to the direction of motion of B, so they will arrive simultaneously in all frames that are moving perpdicular to that pulse. But if it were moving, say, from B to A1, the pulses would not arrive simultaneously.

 

[Sabejias]

Geist, do you believe that Earth's reference frame is the universal reference frame? That earth is at absolute rest? If so, then which of Earth's many different reference frames is it, because we go around the sun and six months later, we will be traveling the opposite direction wrt the sun.

 

[Quantum Quack]

I should have clearly stated that A and A1 frame has relative velocity of zero compared to the ship which has v = 0.8c.

It is clear that the two events in two relative v frames are simultaneous.

 

[Neddy Bate]

Another animation to show simultaneousness of the NOW.

First we will stipulate that your animation is true for the reference frame in which lamp A and point A1 are at rest. In this frame, the arrival of the light at point A1 and ship B are simultaneous.

Let us now consider the reference frame in which ship B is at rest (the reference frame of people aboard the ship). In this frame, it is the lamp A and point A1 that appear to be moving relative to the ship at 0.8c. Therefore, the pulse of light would be a vector that started when the lamp was some distance 'above' the position shown in the animation. The vector velocity of the light pulse must be c even though it is a resultant of the forward propagation, p, toward the ship, and the velocity of the lamp, 0.8c:

c^2 = 0.8c^2 + p^2
c^2 - 0.8c^2 = p^2
sqrt (c^2 - 0.8c^2) = p
0.6c = p

Therefore, the light takes longer to reach ship B, in this frame of reference.

Note: there are clarification posts here, and here.

 

[Quantum Quack]

This is what I wish to have clarified. According to SRT what exactly does it mean to have a loss of simultaneousness.

Neddy, in your example I wouldn't call it a loss of simultaneousness at teh depth that JamesR is suggesting. It is true that teh light will not reach their repective destinations simultaneously as in my example, but this is simply due to a change in length for the light to travel.

Does this mean that the "NOW"s of our events are somehow different?

I am awaiting JamesRs response to the question of simultaneous as posed by this diagram:

The thing that sticks out for me is that a light event can only happen at a point of zero time duration between the past and future.
SRT as described atthis forum seems to suggest that that NOW event can somehow happen at different moments in another frames timeline.

That a light event aboard a ship at v= 0.8c happens somewhere in the past of a light event aboard a ship at relative v= 0

The second diagram:

Shows that a light event at reflector A1 and the ship occur in the same NOW.
If the ship had a transparent hull, would the light in side the ship somehow exist in the past of the light sent by "A" or would both photons exists in the same NOW.

If the ships NOW is not in the same NOw as "A" then where is it? How far into teh past or future....etc....If the ships NOW was in the past then the light sent from A would not be seen by the observer in the ship as the observer also can only see the NOW [remembering that a light event can only occur in between the past and the future]

 

[Quantum Quack]

If I place two clocks togther and their tick rate ratio was 1 : 0.6 would that show a lack of simultaneousness?

Certainly the second markers are not simultaneous but is that any indication of actual loss of time simultaneousness or are they just measuring the same second duration differently.

Or more precisely are we confusing relative duration with relative NOW's?

 

[MacM]

If I place two clocks togther and their tick rate ratio was 1 : 0.6 would that show a lack of simultaneousness?

Certainly the second markers are not simultaneous but is that any indication of actual loss of time simultaneousness or are they just measuring the same second duration differently.

Or more precisely are we confusing relative duration with relative NOW's?

You seem to be suggesting my view. That is we should refer to "Clock Dilation" and not "Time Dilation".

That is external energy inputs to the clock causes it's process to change hence marking the time interval at a different frequency but with no actual change in time perse.

It is simular to the affect of the batteries getting low in my timex.

 

[Quantum Quack]

You seem to be suggesting my view. That is we should refer to "Clock Dilation" and not "Time Dilation".

That is external energy inputs to the clock causes it's process to change hence marking the time interval at a different frequency but with no actual change in time perse.

It is simular to the affect of the batteries getting low in my timex.

MacM, I have also been suggesting the same for some time.

I was thinking the other night if we compare boiling water with cold water. Is boiling water somehow existing in a different time zone or dimension to the cold water?

The rate of movement has increased and so therefore a greater distance is travelled ina gven moment of time thus time has slowed.... but so what? This is common pheno, and not some special time dimensional shifting that SRT seems to suggest.

The tick rate of am atomic clock slows down becassue it's atomic rate is slowing as it gains velocity......this doesn't mean that time is slowing it just simply means that the atomic rate is slowing.......that is the contention any way.....
So how does this imply a loss of simultaneousness, what ever that simultaneousness means any way?

If we have a distance ratio of 1:0.6 how does this suggest non-simultaneousness?
I personally believe that the issue of non-simultaneousness is a way of diverting solid arguement on SRT.

The tck rates may be relative but this does not necessarilly extend to mean that the NOW is also.

 

[Neddy Bate]

Neddy, in your example I wouldn't call it a loss of simultaneousness at teh depth that JamesR is suggesting. It is true that teh light will not reach their repective destinations simultaneously as in my example, but this is simply due to a change in length for the light to travel.

I should clarify my post. The c vector was not necessarily meant to represent the path that the light took, although that is an interesting interpretation in a way. It was supposed to be a geometric representation of the velocity vector of the light ray.

Think of it as a laser pointer, and consider that the light could not have been emitted at the angle shown in my diagram. The light would have traversed horizontally at p=0.6c and the ships movement provided the rest of the velocity so that the resultant vector=c.

The apparent 0.6c propagation rate represents the time dilation apparent in the A-A1 frame as viewed from the B frame.

Does this mean that the "NOW"s of our events are somehow different?

That is the question indeed. Please let me know when you find out, because it is a mystery to me as well. There are celestial bodies that have been in relative motion for as long as the solar system has existed, and yet as far as I know, no one disagrees as to where any of them are in terms of space-time. I would have no problem throwing the concept of reciprocal time dilation out the window if I had a better theory that still kept the speed of light at c in all inertial reference frames (which I've never tested myself, but assume is true).

 

[Neddy Bate]

The apparent 0.6c propagation rate represents the time dilation apparent in the A-A1 frame as viewed from the B frame.

I just realized that the light would also appear to propagate from A to A1 at 0.6c and now we have simultanaety back. (This surprises me, but it is quite a relief.) Unfortunately, we still have time dilation, but as long as there is simultanaety perpendicular to the axis of motion, I think I can work around that. Whew, I feel better now.

 

[Quantum Quack]

say we take the diagram and extend it's use to include a round trip at 0.8c by the ship. The clocks of A1 and B are started simultaneously and stopped simultaneously using the same method.

the record will show that:
Ship B will accumulate 6 seconds for every 10 seconds that A accumulates.

a ratio of 1 : 0.6

The mere mention of a ratio indicates simultaneousness or absolute time does it not?

The same process can be used for length or distance......

It is true that the two frames combined are also relative to other unknown frames but the same logic applies..... you can stack as many time ratios as you like the NOW stays absolute.
The thinking:
What this means is that for light to be invariant the NOW must also be invariant to all observers.

 

[James R]

QQ:

I was thinking the other night if we compare boiling water with cold water. Is boiling water somehow existing in a different time zone or dimension to the cold water?

The rate of movement has increased and so therefore a greater distance is travelled ina gven moment of time thus time has slowed

How do you go from "rate of movement has increased" to "thus time has slowed"?

Seems completely illogical to me.

The tick rate of am atomic clock slows down becassue it's atomic rate is slowing as it gains velocity.

What do you mean by "atomic rate", exactly? And why would it slow down in the way you say? And why do different atoms all seem to slow by the same amount? And why does the slowing appear to be frame-dependent?

So how does this imply a loss of simultaneousness, what ever that simultaneousness means any way?

Simultaneous means occurring at the same time. There's no special meaning to the term "simultaneous".

If you're interested in the relativity of simultaneity, please see the thread I started on that very topic.

If we have a distance ratio of 1:0.6 how does this suggest non-simultaneousness?

I don't know. Why don't you tell us?

I personally believe that the issue of non-simultaneousness is a way of diverting solid arguement on SRT.

The relativity of simultaneity is a derived consequence of the postulates of special relativity, which hardly makes it a way of avoiding "solid argument". It isn't introduced ad hoc. It's a consequence of the theory.

If you want to discuss it, please see my thread titled "Tutorial: Relativity of simultaneity"

The tck rates may be relative but this does not necessarilly extend to mean that the NOW is also.

What is "the NOW"?