Relativity of Simultaneity

mangaroosh

thanks gh, I'll have a look at Einstein's paper and try to base my questions on Einstein's paper.


Just one quick question though, to see if I am even in the ball park with understanding this: am I at least [some way] right in thinking that if all clocks ticked at the same rate then absolute simultaneity would prevail; but because clocks tick at different rates RoS prevails?

DaleSpam

No, I explicitly showed that to be incorrect above, and I have stated it clearly multiple times.

DaleSpam

This interpretation is incorrect. dt'/dt=1 so all of the clocks run at the same rate.

If the transform is linear (I.e. Both frames are inertial) then the transform in general includes a spatial term. It may be that the coefficient is zero, but that is an additional assumption.

Naty1

in some sense, it makes no sense. But this may offer a way to begin to think about it:

A simple minded thought experiment: picture an x,y plot....as two particles move around there in different paths, they experience different rates of x and y distances covered,,,right? we don't normally think much about that......each would observe the
other moving differenty through space [distance] than themselves....

now consider a plot of time versus,say, x distance: observe two particles moving differently.... say straight lines with different slopes as an example....one moves faster thru time and another faster thru distance [space]. We observe the particles and each observe's the other moving differently through time and the x direction than themselves....all the
observations are 'correct' but they are also 'different'.

mangaroosh

Hi Dalespam, are you referring to another thread, because I only saw your response on the first page of this one and had a few questions about it?

I'm sorry, I don't really understand what dt'/dt=1; I am familiar with the notation from high school maths but I'm not sure how to interpret it in this context.


Where I am not clear is why there is absolute simultaneity according to Lorentzian relativity but RoS according to Einsteinian. Do both not use the same transformations?

DaleSpam

I explicitly showed it to be incorrect here:
http://www.physicsforums.com/showpos...22&postcount=2

And I stated it clearly here:
http://www.physicsforums.com/showpos...5&postcount=57
http://www.physicsforums.com/showpos...9&postcount=59
http://www.physicsforums.com/showpos...7&postcount=11

It means that the ratio of the time in one frame to the time in the other frame is 1, i.e. time is not dilated.

mangaroosh

I appreciate you taking the time to reply DaleSpam, but it was the comments in "the constancy of c" thread lead to me starting this thread, to try and get a better understanding. You posted a few responses in the first page of this thread, the first being post #2; I replied to that explaining that I didn't fully understand the logic as represented by the maths; your subsequent reply was an expansion on that point (post #11); to which I posted some questions in reply. From there the discussion of my reply to your post was continued with George and Harry, where I outlined my rationale; your next reply was post #36 where you said that you had explicitly addressed the issue in a previous post (in the thread) and has stated it countless times. As mentioned, however, there were subsequent questions to that clarification which lead to the conversation with George and Harry.

I do appreciate your taking the time to entertain my questions, and I'm sure you're probably addressing countless other [perhaps equally naiive] questions, so it will hopefully reduce any frustration you might be feeling by highlighting why I still haven't got my head around the issue, despite your generous attempts to clarify it.


Thanks for the clarification.

My trouble with "getting it" lies in the difference, or lack thereof, between Einsteinian relativity and Lorentzian relativity; do I understand correctly that there is essentially no difference between the mathematics of both interpretations?

If so, the trouble I have is understanding how one interpretation includes RoS while the other includes absolute simultaneity. George suggested that it is down to the different assumptions about the propagation of light, but I don't see how that would lead to RoS without some intermediary step(s).

If my understanding is correct, and the mathematics is the same for both theories, then I'm not sure a mathematical explanation will address the issue; I would imagine it has to be more of a theoretical consideration of what the maths represents.

James_Harford

Hello Mangaroosh,

May I suggest yet another way of answering your two questions about Relativity of Simultaneity [RoS]? You might find it simpler to understand, and I am confident that DaleSpam, Ghwellsir, and other posters who have been answering your questions so tirelessly will vouch for its correctness:

Your OP question is,

And your latest post question is (with [SR] & [LET] inserted for clarity):

Fortunately in this case, both questions can be addressed without Lorentz transforms, clocks or rulers. The price of using this approach is that we cannot quantify RoS, but we can demonstrate its existence.

Relativity of Simultaneity means simply that two events, separated by a distance from one another, and simultaneous according to one competent observer are not (generally) simultaneous according to another moving relative to the first at some constant speed.

The simultaneity of two events can be established using a shuttered lamp on a track between two distant mirrors positioned on the track to reflect any light pulses from the lamp back to it and yourself, the observer. The mirrors need not be at rest and may move independently at arbitrary speeds along the track. Suppose that you are very quick with the shutter and send an extremely brief pulse of light towards both mirrors. If the reflected pulses from both mirrors happen to return simultaneously, what can you legitimately infer? Since by Einstein's postulate, light moves at one speed only, you know these two things:
1. the mirrors were equidistant from the lamp at the time of the reflection, and
2. the two reflections occurred simultaneously.

Now suppose that a second observer happens to be moving along the track just as you send your light pulse from the lamp. Will he agree that the reflections were simultaneous? No. By the time the two reflected pulses meet at your lamp, observer #2 has moved some distance along the track, and correctly notes that the two pulses did not "return" simultaneously to his "here", and for that reason, by Einstein's postulate he must infer that the two reflections did not occur simultaneously.

The LET interpretation predicts exactly the same phenomena, but differs from SR only in that it insists that light depends upon a hypothetical medium, or aether, Therefore the method of "simultaneous arrival" for determining simultaneity is valid only for an observer who is motionless in the aether, and there is only one "true" definition of simultaneity -- that of the motionless observer. Einstein's great insight was that the aether hypothesis was completely superfluous.

- Regards

harrylin

Hi I answered that in post #28 and also, indirectly, in post #31. RoS corresponds to the "local time" concept as interpreted by Poincare but Einstein interpreted it differently. Did you study the references? Is there something unclear about it?

harrylin

Apparently you missed my post here, in which I explained this in detail and with a lot of precision:
http://physicsforums.com/showpost.ph...3&postcount=54

Harald

PhilDSP

It would probably be fair and correct to say that the mathematics going into and coming out of the Lorentz Transformation and their usage is very different comparing Einstein-Minkowski and Lorentz-Poincare relativity. While the Lorentz Transformation itself is obviously common. For the most part, Lorentz worked with vectors, differential equations and their initial and boundary conditions. Einstein and Minkowski built a platform where those things were abstracted away in which tensors and 4-vectors are preferred.

Agerhell

http://en.wikipedia.org/wiki/Relativity_of_simultaneity

From wikipedia:

Is this helpful? According to SR the speed of light on earth is not c in relation to the gravitational field of the earth but relative to "any inertial frame". Thus the observer on the platform sees the front- and the backside of the wagon lit up at different times but the guy on the train will think that the front and the backside of the train are lit up simultanesously, because the light coming back from the rear and the front end of the wagon walls will hit him simultaneously.

I think this type of thought experiments are always what is meant when someone talks about "relativity of simultaneity", but I might be wrong...

mangaroosh

Hi James, thanks a million for taking the time to reply.

I hope I'm using the right phraseology here when I say that, under Galilean transformations we would expect the moving observer to measure a different speed of light to the pulse operator, but under Lorentz transformations this isn't the case; is that accurate?

Lorentzian relativity maintains absolute simultaneity, while Einsteinian relativity incorporates RoS. I don't think we're too concerned with Lorentzian relativity in this particular instance, what we're looking for, or rather, what I'm trying to understand, is what phenomena must occur in order for the speed of light to remain constant for all observers, regardless of their motion realtive to the source of the light; which appears to be the reason given, why RoS prevails. That was essentially the point made by George, so I presume he would agree with your statement to a similar effect.


One thing he might disagree on is that Lorentzian relativity necessarily includes the superfluous concept of an aether.

mangaroosh

Hi Harry, the conversation with DaleSpam is in reference to mathematical transformations, while your reply in post #28 was with respect to clocks; unfortunately I don't have the nous to make the connection between the two, so I find it more beneficial to engage with the point that is raised and see where it goes.

I had a quick glance at the reference in post #31, but statement immediately following the link was something you had mentioned before, with respect to detecting absolute simultaneity (or the time on a distant clock) and which I had addressed in #18; so that affected my judgement of the necessity to go through it in detail. Is there a specific part that I can jump to that would address the issue?

Just reading back over the exchange I realise that I didn't address reply in #20 directly. I tried reformulating the question, which lead to your reply in #28, which appears to just be a reformulation of the same reply that was questioned previously.

Post #20:The issue being raised appears to be the idea of detecting absolute simultaneity; but that isn't necessarily an issue that needs to be addressed. We don't need to figure out how to synchronise clocks to say that if all clocks remained synchronised then there would be absolute simultaneity; it's somewhat of a tautology. If any clock falls out of sync, and the change isn't due to mechanical processes, then RoS prevails; if the change is down to mechanical processes then absolute simultaneity prevails - that is assuming that a clock measures time, because if a clock doesn't measure time, then we have no way of measuring time, and it wouldn't necessarily be something that could be dealt with in physics - as someone mentioned in another thread on here a while ago, pertaining to the MMX.


This is #28, which, as mentioned, appears to just reformulate the issue of detecting absolute simultaneity.

mangaroosh

I didn't miss it, my reply was deleted because I used an invalid reference; although I didn't intend for it to be a reference per se, rather as a means of explaining a point that was made more eloquently than I could have done.

I'll PM you the reply, but I'd prefer to continue the discussion in an open thread. Perhaps if I PM you, you might be able to paraphrase the quote in your reply, for the posterity of the thread - that is if you deem it worthy of reply, of course.

DaleSpam

That is fine. If you don't understand then ask new questions that will help me get at your root concern. But if you merely repeat the same incorrect claim that I answered already then all I can do is as I did above and refer back to my previous answers.

You are correct, I was travelling for about two weeks with reduced time and access. However, I did find it frustrating to come back and find you repeating the same mistake that I already addressed weeks ago.

I don't think that anything productive will come from a discussion of Lorentzian relativity. It is a defunct interpretation which asserts the reality of undetectable entities. All of the confusion with LET comes from the simple fact that the aether is undetectable, so in LET you continually have to make careful distinctions between measurements and what is happening in (undetectable) reality. It is a rabbit hole not worth going down.

DaleSpam

Try the reply without the invalid reference. Btw, I saw the reference, and if that is the kind of material that you are trying to learn relativity by reading then it is no wonder that you are confused.