Relativity of Simultaneity

mangaroosh

Thanks Agerhall, I am familiat with the thought experiment alright, and it is essentially the same one that James posted, I think.

What phenomena occur that means the speed of light is c "in any inertial frame"? We would, ordinarily, expect the moving observer to measure a different speed of light - why is this not the case?

harrylin

Then, evidently, you did not understand it. As Dalespam suggests, you can simply re-post the reformulation of your question without including a link to a crank(?) site.

Agerhell

If you first assume that the speed of light is c in relation to the guy standing on the platform. The guy on the platform would classically expect that it takes longer time for the light from the guy on the train to reach the back and front wall and bounce back towards the guy on the train than if the train had not been moving. You can do the math, it is simple.

However, in Special Relativity the Time Dilation formula kicks in and it so happens that if the guy on the platform would expect it to take a factor k longer for the light to reach the back and front wall and get back to the guy on the train again, then the time for the guy on the train slows down with the same factor k so he thinks the two way speed of light has the same value, c, no matter what the velocity of the train relative to the ground is...

In this way the "two-way speed of light is the same in all inertial frames".

I belive this is how it is always explained...

harrylin

The way you describe it, you probably mean the ceiling and the floor. Else you should add length contraction to the mix...
And to top it off (in view of the topic!), one usually makes the one-way speed equal to the two-way speed by means of the Poincare-Einstein synchronization procedure.

James_Harford

Your OP question:

And your latest question about LET:

are answered in my earlier post. I guess I missed that you have a third question:

May I suggest that we work on them one at a time? Bouncing back and forth between all of them and adding time dilation and lorentz contractions and LET makes all of this a rather poisonous mix of unrelated factors. Please go back to my earlier post and note that it fully answers your first two questions, as stated. The only valid questions about that post are
1. Is it a correct analysis?
2. Do you understand it?

If you do not, then, I would not go on to the third question until you do.
If you do, then you have just the third question.

That question, unlike the others, is about the ratio of a time and a space measurement, and this unavoidably requires some level of understanding of the Lorentz transforms themselves, which is bad news for you. Give up the notion that time dilations and Lorentz space contractions are sufficient. You will fail. You need a complete coordinate transformation, because only that gives exactly the differences in how the various observers make these measurements.

I would recommend that you start playing around with pencil and paper with various XT coordinate systems, and see if you can find (by trial and error) two coordinate systems in which the path of a photon (a slanted line) has the same speed. Whether you succeed or not, the exercise will get you past a psychological obstacle and improve your chances of grasping what your friends here are telling you.

I doubt it.

- Regards

Naty1

yes. Galileo would have EXPECTED to measure a different speed, but if he had the proper apparatus, would have been dumbfounded when he actually observed the fixed speed of light! And probably so would have Newton.

Dalespam:
YES!!! YES!!!! .....I was just about to post similar when I realized there is this last page.

Harford: again, YES!!!! Let's get the proper theory explained, then it
will become clear why older theories were inadequate.


The HISTORY section here explains why such confusion reigned before Einstein....nobody had Einstein's physical insights.....

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

mangaroosh

Does this not just verify the point of the OP that RoS is just a consequence of Lorentz contractions, and isn't necessarily a separate, third aspect of Einsteinian relativity?

mangaroosh

Apologies DS, I tend to treat each conversation individually and try not to take it for granted that every poster reads every post, so I tend to restate certain points for the purpose of the conversation. A number of the times I have restated the point, however, has either been in somewhat different context or for the purpose of reformulating for clarity.

I would argue, though, that the times I have restated it it hasn't necessarily been superfluous to the two-way conversation. I can understand how it might be frustrating to read the same point repeated, particularly when you are under the impression that you have already answered it, but, as mentioned, I had subsequent questions which were taken up by someone else; this lead me to repeat and/or reformulate the point for the purpose of that discussion.


The purpose of this thread isn't necessarily to discuss Lorentzian relativity, I think it is sufficient to discuss it in the competing theories thread; the purpose of bringing up Lorentzian relativity here, was solely to juxtapose it with Einsteinian relativity for the purpose of clarification; namely that it appears that the same transformations can result in both absolute simultaneity and RoS. The question that is begged from that is, what is the difference between the two; why RoS under one interpretation, but absolute relativity in the other?

Please forgive the repetition there, I'm using it solely to emphasise that the question hasn't been addressed just yet.


I'm not sure the specific example of the transform you gave fully addresses the question, because the question is more general. It might be the case that length contraction and time dilation do not lead every single event to be relatively simultaneous, but if time dilation and/or length contraction never occurred at all, anywhere, would RoS still prevail?



It's not so much that I'm confused, rather I haven't made the logical connection yet as to how RoS is separate, stand-alone aspect of Einsteinian relativity and not just a consequence of Lorentzian contractions.

It's probably also worth pointing out that I don't try to learn relativity from sources such as the one posted; I learn relativity largely from discussions with people on sites like this, from the references they post and from my own searches; however, I tend not to simply accept as gospel what I am told, and try to subject such things to critical inquiry, which usually serves the purpose of developing a better understaning; on that basis I will consider alternative viewpoints as long as they stand up to reason, and of course experiment.

The "reference" posted seems to make quite a reasonable point about the propagation of light, which I haven't seen considered elsewhere. Unfortunately I'm not in a position to subject it to the level of critical reasoning required so I can only present it as it is and see if there are arguments against it. However, as it strikes me as being quite reasonable, and conforms to [more reliable] information I have encountered previously, I would lean more towards accepting it (without accepting it fully).

Incidentally, I posted the reply without the reference in the other thread.

mangaroosh

Hi James, if possible I'd like to change the first question; I didn't formulate it in reply to yourself, but did in reply to Agerhall.

Your explanation was based on the second postulate, the constancy of c in every reference frame, regardless of the motion relative to the source. The question that arises from that is, what phenomena have to occur to allow for this possibility? Ordinarily, with the addition of velocities we would expect the moving observer to measure a different speed of light; what phenomena occur that leads to him measuring the speed of light to be the same as the other observer?

mangaroosh

DS, just wondering if you would agree with what George said was accurate, that Lorentzian relativity had been divested of all the trappings except for the absolute rest frame?

mangaroosh

Thanks Phil.

The points being raised appear to pertain to the Lorentz transformation; does it make sense then to ask why the transformation under one interpretation has RoS while under the other interpretation has absolute simultaneity?

mangaroosh

I could be completely wrong Harry, but based on your posts and the fact that you mentioned you prefer to base your understanding on Einstein's original German paper I would guess that either English or German is your native language - of course you could be form a bilungual family. But if one of them isn't your native language, then you presumably have experience in learning a foreign language. If so, I'm sure you will have noticed that there is usually a disconnect between how much a person can understand and how much they can express themselves, such that it is possible to understand something without necessarily being able to express it [adequately] in your own words. The inability to express it in your own words wouldn't necessarily mean that you haven't understood something that has been said.

The post has been re-posted without the link. As to whether or not the site is a "crank" site, I prefer to examine the content and judge it on that basis.

DaleSpam

I specifically addressed that in the math above. In one transform I showed there can be no length contraction nor time dilation at all, anywhere, and there is still RoS.

The opposite claim is that the RoS is a consequence of length contraction and time dilation, and I disproved that claim also by providing a transform that had length contraction and time dilation, but no RoS.

Both claims have been disproven by counter-example. I don't know why you persist in them.

DaleSpam

He and I disagree about LET, but it is such a useless topic that I do not intend to dispute it, neither with him nor with you.

mangaroosh

I have a few questions relating to that, so if it is possible to proceed from here I might be able to get my head around it.

Were the transformations you gave for just one event EDIT: between two reference frames?

Would the same transformations be used in Lorentzian relativity and not include RoS in any of them?

In the example of the transform where there was no RoS, would we conclude that absolute simultaneity prevails, right across the universe, under the Einsteinian interpretation?

DaleSpam

They were for all events.

Those transforms are not the Lorentz transform, so it is not used in LET.

Again, those transforms are not the Lorentz transform, so it is not used by SR.

mangaroosh

sorry, you've thrown me with the last 2 comments; I thought we were talking about Lorentz transformations under Einsteinian relativity.

EDIT: that might be where the confusion is arising from.